Immune-based therapies and preventive technologies pipeline

1 July 2010. Related: Pipeline report, HIV prevention and transmission, Basic science and immunology, Vaccines and microbicides.

Richard Jefferys

Unlike the other pipelines discussed in this report, there are no approved immune-based therapies or biomedical preventive technologies for HIV— aside from antiretroviral therapy itself—(see 2010 Pipeline Summary) to offer a guidepost for product developers. For those attempting to navigate this uncharted terrain, 2009 proved to be another year of vertiginous ups and downs.

In the realm of biomedical prevention, a microbicide candidate (PRO2000 gel) that came within a whisker of showing statistically significant protection in a phase IIb study (Abdool Karim 2009) failed to show any efficacy in a larger, definitive phase III trial (Chisembele 2010). PRO2000 gel was essentially the last in a class of broad-spectrum microbicide candidates and the focus has now shifted to products with more potent and specific anti-HIV effects (after the first edition of this report went to press, encouraging results from a trial of the first antiretroviral-based microbicide were announced – see later in this chapter).

Meanwhile, a huge HIV vaccine trial that took place in Thailand involving two ancient candidates (ALVAC and AIDSVAX) surprised everyone by showing a meager (31.2%) but just about statistically significant degree of protection (Rerks-Ngarm 2009). Despite the size of the trial, however, there were relatively few HIV infection endpoints and the confidence intervals—a statistical measure of the uncertainty associated with a result—were vast, raising the specter that the findings may be as illusory as those of the phase IIb PRO2000 gel trial. Nevertheless, after the paucity of good news in HIV vaccine research, and despite the possibility of a statistical fluke, the Thai trial results have been widely hailed as historic. Plans are now afoot to try and reproduce and improve upon them with similar regimens.

Results from the first efficacy trials of pre-exposure prophylaxis (PrEP) are due to become available later this year, after this report is printed. The antiretrovirals being studied for PrEP are tenofovir and the combination of tenofovir and emtricitabine in a single pill (Truvada). Several other agents are under consideration but, unsurprisingly, PrEP research is currently in a holding pattern awaiting the crucial first efficacy data. Several small studies are evaluating the safety and acceptability of intermittent rather than continuous PrEP, but as yet no efficacy studies are planned.

As in previous years, there remains an imbalance between the need for novel immune-based and gene therapies for HIV and the limited number of candidates trickling sluggishly through the pipeline. Similar to HIV vaccines, the immune-based therapy (IBT) pipeline is prone to tortuous plumbing; even apparently promising candidates often seem to circle back to earlier phase trials rather than progress onward. An example is IL-7, which is widely viewed as the lead CD4 T-cell-boosting candidate: after showing promising results in two phase I trials reported in 2007 (Levy 2007; Sereti 2007), this cytokine therapy was modified to ease its dosing schedule and only recently re-entered phase I testing in its new form. Over the same time period, data have accumulated demonstrating that poor CD4 T-cell reconstitution is a significant risk factor for illness and death in the antiretroviral therapy (ART) era (Marin 2009; Tan 2008; Tuboi 2010). Concern about the overlap between the immunological effects of HIV and aging—particularly depletion of a subset of T cells called naive cells—has renewed interest in boosting the function of the thymus, but there is a striking lack of therapies with any demonstrated potential. IL-7 may have some effect, but appears to preferentially stimulate naive T-cell division rather than enhancing thymic production (Fry 2005). The one approach proven to increase thymus function in people, human growth hormone, is associated with a counterproductive panoply of side effects (Napolitano 2008; Smith 2010).

Beyond general immune-boosting, achievement of a “functional cure”—defined as an absence of detectable HIV replication in the absence of any ongoing treatment—is an ambitious goal of some IBTs and gene therapies. Once almost unimaginable, this possibility has been pushed back into the spotlight by the case of an individual who appears to have been cured of HIV infection after receiving a stem cell transplant while undergoing treatment for a life-threatening cancer (Hütter 2009). The German doctor who performed the transplant, Gero Hütter smartly sought out a donor with the mutation that abrogates expression of CCR5 (the major HIV coreceptor) on cells. The result was that the individual’s immune system was repopulated with cells highly resistant to HIV infection. More than three years after the procedure, despite a slow and complicated recovery from the cancer and its treatment, the individual remains off ART and lacks any detectable HIV in blood or tissues. The case is being viewed as a “proof of concept” that a cure for HIV is possible, providing a welcome impetus for research efforts in this area.

Table 1. HIV Vaccines Pipeline 2010

The HIV vaccine field has been deluged by disappointment over the years, but September 2009 saw the first sliver of encouragement emerge from Thailand. A huge 16,402-person efficacy trial of two candidates widely viewed as en route to the scrap heap, ALVAC and AIDSVAX, reported evidence of 31.2% efficacy in protecting against HIV infection, a result that just scraped across the boundary of statistical significance. In raw numbers, this represented 51 infections among the 8,192 people randomised to receive the vaccines and 74 infections among the 8,198 placebo recipients (5 participants were excluded from these analyses after being found to have been HIV infected at baseline). However, it is important to note that the statistical robustness of a trial result derives not just from the total sample size but is crucially dependent on the number of endpoints that occur, which in this case was very few relative to the overall number of participants. The upshot is that the confidence intervals around the 31.2% reduction in risk of HIV infection are extremely wide, ranging from 1.1% to 52.1%. In statistical terms, the confidence interval represents the range of possible outcomes if the experiment were to be repeated. From a glass-half-full perspective, it may be considered encouraging that the efficacy of the vaccines might have been as high as 52.1%. But given the poor track record of the candidates involved, the glass-half-empty view inevitably must consider that a large swathe of the numerical territory between 1.1% and 52.1% is indistinguishable from the efficacy of the vaccines being zero.

Beyond the borderline nature of the findings, there was some controversy at the time of the initial announcement by the trial’s sponsors—the U.S. Military HIV Research Program, the Thai Ministry of Health and the U.S. National Institutes of Allergy and Infectious Diseases (NIAID). Rumors abounded that the statistically significant result was undermined by other unreported analyses. The publication of the data in the New England Journal of Medicine a few weeks later set these concerns to rest, as the issue turned out to be related to the strictest “intent-to-treat” (ITT) approach, under which the five individuals found to be HIV infected at baseline had to be included. Using this method the result no longer reached statistically significance, but given that exclusion of people who were infected prior to receipt of any vaccine is both logical and standard in these trials there was no reason for this to be controversial. The fact that so few infection endpoints could affect significance in this way does, however, highlight the statistical fragility of the main result (which is described as the “modified ITT” analysis).

But even if the Thai trial had produced a statistical trend toward efficacy rather than achieving significance, it would have been important for the vaccine field to follow up, and this is indeed what is occurring. Data from participants will be mined in the hope of revealing vaccine-induced immune responses associated with reduced risk of acquiring HIV, known as correlates of immunity. While discovering correlates would be a huge advance, the marginal efficacy and limited numbers of samples may stymie the effort. Currently, the main theories point to some type of antibody-mediated effect, either relating to binding antibodies or antibody-dependent cellular cytotoxicity (ADCC) wherein nonneutralizing antibody responses promote killing of virus-infected cells. The reasoning behind these theories is partly based on evidence of a short-term protective effect in the trial; after the first year, infection rates in the vaccine and placebo groups were very similar, and this observation tracks with binding antibody responses, which peaked in magnitude after the last vaccine booster at six months and declined precipitously thereafter (Michael 2010). Evidence of ADCC was observed in the majority of recipients of the vaccine regimen in earlier trials (Karnasuta 2005). Less likely candidates for immune correlates include HIV-specific CD4 T-cell responses, detected in around 50–90% of vaccinees (as measured by lymphoproliferation to p24 or gp120 antigens) and HIV-specific CD8 T-cell responses that, while detected in around 20% of recipients in prior studies (Nitayaphan 2004), were essentially undetectable in the analyses reported in the New England Journal of Medicine paper (Rerks-Ngarm 2009). The lack of CD8 T cell responses is consistent with the failure of vaccination to measurably affect post-infection viral load among the trial participants who became infected.

The Thai trial follow-up

The main stakeholders in HIV vaccine research have outlined a variety of plans for new studies informed by the Thai trial outcome. Future research needs to address and try and disentangle several interrelated issues:

The Population

The vast majority of the Thai study population were heterosexuals at very low risk for HIV infection, and the entry criteria limited the age range of participants to between 18 and 30. This contrasts with prior trials, which have focused on higher-risk gay men and intravenous drug users as well as recruiting from a broader age range. The extent to which the study population may have affected the Thai trial outcome is unclear, and needs to be addressed. Additional population-specific factors potentially relevant to efforts to replicate or build upon the results elsewhere include circulating HIV strains, routes of HIV exposure, other prevalent sexually transmitted diseases, and co-infections (such as tuberculosis, helminths, and hepatitis B & C).

The Vaccine Constructs

Contrary to a number of erroneous media stories published when the results were first announced, Sanofi Pasteur’s ALVAC vector was not previously tested for efficacy. The vector is made of a bird virus that is harmless to humans called canarypox, and it is not known if there might be unique aspects of this virus that could contribute to immune protection against HIV. ALVAC was not previously regarded as very promising because it only provokes weak immune responses to the HIV antigens it contains. Now it will be necessary to study whether similar poxvirus vectors that appear better at inducing immune responses (such as MVA and NYVAC) have superior or inferior protective efficacy compared to ALVAC. According to a letter sent to collaborators on April 23, 2010, Sanofi Pasteur is in the process of producing additional doses of ALVAC for research purposes. New supplies of vCP1521 are expected to become available in the fall.

The vaccine used as a booster in the Thai trial, AIDSVAX, consists of two recombinant HIV Env proteins from clades B and CRF01_AE and had previously failed to show any efficacy when tested alone in two large trials involving high-risk gay men and intravenous drug users (Flynn 2005; Pitisuttithum 2006). It is impossible to know what role, if any, AIDSVAX played in the trial outcome because there was no comparison with ALVAC alone. One principal investigator, Nelson Michael, has spoken of the need to “deconvolute” the contribution of the two constructs. A planned US-based phase III trial that would have compared ALVAC alone to ALVAC+AIDSVAX did not take place because a prespecified level of immunogenicity was not achieved in phase II (Russell 2007). The company that manufactured AIDSVAX, VaxGen, no longer exists and the rights are held by a non-profit organization called Global Solutions to Infectious Diseases (GSID). Currently planned studies are using existing lots of AIDSVAX and GSID is not being funded to produce additional supplies, at least as yet.

The HIV Vaccine Trials Network (HVTN) has developed a proposal for “sequential adaptive design phase IIb trials” that are intended for the higher-incidence setting of South Africa. The population would be high-risk heterosexual people, with each trial enrolling 1,500 per arm. Based on an annual HIV infection rate of 4%, the HVTN calculates that a nonworking vaccine could be identified and discarded within 20 months, and by 24 months an efficacy signal would be detectable. Around 50 HIV infection endpoints would be enough to know if a vaccine wasn’t working, while 80 would be sufficient to show evidence of efficacy (a 40% or greater reduction in risk of infection). A variety of DNA, poxvirus vector, and protein prime-boost combinations are under consideration for these trials, including DNA+NYVAC+gp120, NYVAC+NYVAC+gp120 and ALVAC+ALVAC+gp120. The exact types of inserts and envelope boosts are still under discussion.

The U.S. Military HIV Research Program (USMHRP) is looking to shed more light on the Thai trial results by conducting new, detailed phase I immunogenicity studies of the vaccine regimen, particularly focusing on mucosal immune responses. Another plan is to boost a small subset of the original trial participants (~100) with another dose of ALVAC or AIDSVAX, or a combination of the two. The USMHRP also has additional candidates waiting in the wings, including a DNA prime MVA boost approach (Earl 2009; Gudmundsdotter 2009).

The Collaboration for AIDS Vaccine Discovery (CAVD), supported by the Bill and Melinda Gates Foundation, is developing a clade C DNA prime/NYVAC boost regimen that has shown immunogenicity in early phase trials (Harari 2008; McCormack 2008). A replication-competent version of the NYVAC vector is also under consideration (vectors currently being studied cannot replicate in humans). The current plan is for an efficacy trial to be conducted in Africa starting in 2013 or 2014.

A DNA prime/adenovirus serotype 5 (Ad5) boost approach developed by the Vaccine Research Center (VRC) at NIAID is being evaluated in an ongoing phase IIb trial designated HVTN 505. The main goal is to assess the effect of the vaccines on viral load levels among recipients who become infected. The Thai trial results provoked some discussion as to whether the size of HVTN 505 should be increased in order to find out if the vaccines could reduce risk of acquiring HIV infection, but this has not occurred. The DNA/Ad5 combination has demonstrated the ability to induce HIV-specific CD4 and CD8 T-cell responses, along with binding (but mostly nonneutralizing) antibodies (Koup 2010). However, whatever the outcome of HTVTN 505, Ad5 vectors will not be developed further due to evidence suggesting they may increase risk of HIV infection among people with preexisting antibody responses against adenovirus serotype 5 (which many people have been exposed to in its natural form, as it is a common cause of bad colds) (Buchbinder 2008). To try and circumvent this problem, the VRC is developing vectors based on adenovirus serotypes that are far less common in nature, Ad26 and Ad28.

Overall, the major repercussion of the Thai trial results has been the re-prioritization of prevention of HIV infection as the major goal for vaccines. This is a significant shift from the previous focus on slowing post-infection disease progression using candidates that only induce T-cell responses against HIV.

The antibody revival

HIV’s mutating, sugar-clustered outer envelope presents a daunting obstacle to antibody-mediated neutralization. Up until last year, only a few rare antibodies capable of broadly neutralizing a diverse array of primary HIV isolates had been identified. These antibodies were cloned from HIV-infected people and, while they are unable to retard disease progression in the setting of chronic infection, it is hoped they could protect an uninfected person if similar antibodies could be induced by vaccination. Reverse engineering a vaccine from an antibody is not easy, however, and only limited progress has been reported to date (Walker 2010). The year 2009 saw notable advances in this area with the discovery of several new broadly neutralizing antibodies (Corti 2010; Walker 2009; Wu 2010). These newer antibodies are far more potent than prior candidates, meaning they exert their inhibitory effect at lower concentrations. While efforts are ongoing to uncover their precise targets on HIV (Kwong 2010; Pejchal 2010), many stakeholders in vaccine research are considering conducting a trial in which a combination of the antibodies would be passively infused in order to test their efficacy at preventing HIV infection.

The International AIDS Vaccine Initiative (IAVI) is planning a phase I trial using adeno-associated virus (AAV) in a manner more akin to gene therapy than traditional vaccination: the AAV vector will encode a gene that persistently manufactures neutralizing antibodies after injection, an approach that has shown promise in macaques challenged with simian immunodeficiency virus (SIV) (Johnson 2009).

Vaccine approaches in human trials

The majority of HIV vaccine candidates in trials represent variations on the prime-boost theme, in which one vaccine is used to initiate immune responses to HIV antigens and a second boosts the responses to higher levels. The goal is to create “memory” immune responses specifically targeting HIV, including CD4 T cells (also called helper cells), CD8 T cells (known as killer T cells due to their primary role of killing infected cells) and B cells that act as factories for the production of antibodies. Exactly which components of HIV represent the best targets for immune responses remains uncertain, so many different possibilities are being studied. Although it has been argued that the viral envelope makes a poor target for immune responses (Kiepiela 2007), the Thai trial results have been interpreted as a strong counterargument, and most vaccines in trials include an envelope antigen or antigens.

A key issue identified after the failure of Merck’s HIV vaccine candidate is the need to improve the breadth of immune responses. T cells and B cells specifically recognise fragments of viral proteins called epitopes, and HIV contains hundreds of potential epitope targets. However, recipients of the Merck vaccine showed CD8 T cell responses against only three epitopes on average (McElrath 2008). To try and address this problem, researchers have developed a new type of antigen called a mosaic which has improved the breadth of epitope targeting in macaque studies (Barouch 2010). Vaccines containing mosaic HIV antigens are expected to enter human studies soon.

ALVAC

Prior to the results of the Thai trial, a plethora of different versions of the ALVAC canarypox vector had been studied in phase I and II trials involving well over a thousand volunteers. The construct used in Thailand, vCP1521, contains the gene encoding the gp120 protein from a virus code named 92TH023 isolated from a Thai individual in Bangkok in the early 1990s. The virus was originally designated as belonging to subtype E, but it has since been recognised that this subtype is largely a circulating recombinant form now known by the name CRF01_AE. The vCP1521 vector also contains a portion of the gp41 protein from the first HIV ever isolated, LAI, which belongs to subtype B. The other two antigens encoded by the ALVAC vector are Gag and protease, also derived from LAI.

Adenovirus Vectors

Controversy persists regarding evidence that Merck’s Ad5 HIV vaccine candidate enhanced susceptibility to HIV infection among study participants with preexisting antibodies against Ad5. A series of analyses conducted by Susan Buchbinder and colleagues considering the impact of multiple variables on the infection rate was unable to rule out an independent contribution of Ad5 vaccination, but the enhancement effect was almost exclusively seen in circumcised men with antibodies against Ad5, whose main risk factor for acquiring HIV infection was insertive anal sex (Robertson 2008). One hypothesis put forward to explain the results was that the vaccine activated Ad5-specific CD4 T cells in a way that provided more targets for HIV infection. Two studies subsequently argued against this possibility by showing that Ad5-specific CD4 T-cell levels—as measured by cytokine production—were not linked to baseline Ad5 antibody status (Hutnick 2009; O’Brien 2009). But a UK-based group has since reported that Ad5-specific CD4 T-cell responses measured by their ability to proliferate do correlate with Ad5 antibody levels, and these CD4 T cells become more susceptible to HIV after stimulation and display markers associated with homing to mucosal tissues (Benlahrech 2009). These researchers argue that there is a link between the extent of prior exposure to natural Ad5 infection and the likelihood of generating mucosal-homing Ad5-specific CD4 T cells in response to Ad5 vaccination. New data has revealed that natural adenovirus infection can be remarkably persistent, with 75% of a small sample of HIV-positive Peruvian men who have sex with men showing detectable virus DNA in rectal swabs (Curlin 2010). More studies are needed to address this concern, which may also apply to other adenovirus vectors because adenovirus-specific CD4 T-cell responses cross-react with multiple different serotypes. A number of alternate adenovirus serotype HIV vaccines are in trials, including Ad26, Ad35, and Ad5HVR48 (the latter uses a backbone of Ad5 but the major antibody target, the hexon protein, is from the rarer Ad48 serotype).

Modified Vaccinia Virus Ankara Strain

The Modified Vaccinia Virus Ankara strain (MVA) is an attenuated, nonpathogenic derivative of the cowpox virus. The Karolinska Institute and the USMHRP are advancing a DNA/MVA prime-boost approach into phase II studies. Published studies indicate the approach induces HIV-specific CD4 and CD8 T-cell responses in the majority of volunteers (Aboud 2010; Sandstr 2008). A similar DNA/MVA approach developed by a company called GeoVax is in a phase IIa immunogenicity trial under the aegis of the HVTN.

Vaccinia-based Vectors

NYVAC is a highly attenuated derivative of the Copenhagen strain of vaccinia virus being studied as an HIV vaccine vector by the CAVD. The vector is being manufactured by Sanofi Pasteur. Judith Hurwitz at St. Jude Children’s Hospital in Memphis, Tennessee, is employing a vaccinia vector as part of an experimental HIV vaccine regimen that delivers a cocktail of 23 different viral envelope proteins (Sealy 2009).

DNA Vaccines

DNA vaccines represent one of the simplest approaches to vaccination. They consist of DNA sequences encoding protein antigens and typically contain little in the way of extraneous components. Despite encouraging initial results in mice, DNA vaccines have proven poorly immunogenic in people. One promising approach for improving the immune response to DNA vaccines is called electroporation, which involves using a special wand to deliver a brief electrical charge to the muscle into eiwhich the vaccine is being injected. The electricity opens transient pores in local cell membranes, allowing the DNA easier access to the cell’s nucleus, where it produces vaccine-encoded antigens. Electroporation also attracts inflammatory cells—including antigen-presenting dendritic cells—to the immunization site. Preliminary results from a phase I trial conducted by the Aaron Diamond AIDS Research Center, the International AIDS Vaccine Initiative, and Ichor Medical Systems suggest that the approach may be able to improve the magnitude, breadth and rate of response to DNA immunization (Vasan 2009).

MYM-V101

One of relatively few vaccines not following the DNA or vector model is a candidate developed by the Swiss company Mymetics. The approach involves components from the HIV envelope encased in a mimic of the viral membrane called a “virosome.” The intent is not the induction of traditional neutralizing antibodies, but rather antibodies that can inhibit the transport of HIV across mucosal surfaces. In a study presented at CROI last year, the vaccine completely protected monkeys from a hybrid SIV/HIV virus called SHIV162p3 (which, unlike prior simian-human immunodeficiency viruses, includes the envelope from an R5-using primary HIV isolate) (Bomsel 2009). Mymetics is now working with animal model expert Chris Miller at the University of California–San Diego to establish whether these results can be independently confirmed. Phase I human trials are also underway.

DCVax-001

Dendritic cells are responsible for initiating immune responses and have been dubbed “nature’s adjuvant” by immunologist Ralph Steinman. Steinman’s own laboratory has recently entered the vaccine development arena with a phase 1 trial of a vaccine that specifically targets dendritic cells via a receptor called DEC-205 (Nchinda 2010). The prototype under study only encodes the HIV-1 Gag p24 protein, but additional inserts are planned if the approach shows promising immunogenicity.

Pre-exposure prophylaxis

Pre-exposure prophylaxis (PrEP) is the prophylactic use of antiretroviral drugs to prevent HIV infection. Currently two drugs are being evaluated in phase II and III studies as PrEP: the nucleotide reverse transcriptase inhibitor tenofovir (Viread) and a combination pill called Truvada, which contains tenofovir and the nucleoside reverse transcriptase inhibitor emtrictabine (Emtriva).

The U.S. Centers for Disease Control and Prevention (CDC) is sponsoring two ongoing PrEP efficacy trials: a study among 2,400 injection drug users in Thailand is evaluating tenofovir alone, while a study in Botswana is looking at Truvada in a population of 2,000 heterosexual men and women. Results from these trials are anticipated later in 2010. An NIH-sponsored efficacy trial of Truvada as PrEP in high-risk gay men in Brazil, Ecuador, Peru, South Africa, Thailand, and the United States—which underwent a long period of community consultation, planning, and preparation—is now well underway, with interim results possibly also becoming available before the end of 2010.

More recently initiated trials include a comparison of tenofovir to Truvada as PrEP in 3,900 serodiscordant couples, being conducted by the University of Washington in Kenya and Uganda. The Microbicide Trial Network’s VOICE study is enrolling 4,200 African women and will compare three strategies: oral PrEP, using tenofovir or Truvada, versus a tenofovir-containing vaginal microbicide gel. Family Health International has launched a trial of Truvada as PrEP in 3,900 women at sites in Kenya, Malawi, South Africa, and Tanzania. Finally, a smaller pilot study looking at the acceptability and feasibility of PrEP among men who have sex with men aged 18–22 is taking place in Chicago under the sponsorship of the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

Table 2. PrEP and Microbicides Pipeline 2010

Microbicides

Microbicides are substances that aim to prevent HIV infection via application to the vagina or rectum prior to sex. As mentioned in the introduction (and covered in last year’s Pipeline Report), a presentation by Salim Abdool Karim at the 2009 Conference of Retroviruses and Opportunistic Infections (CROI) generated a great deal of excitement because it suggested that PRO2000 gel might have been mildly efficacious at preventing HIV infection in a trial among high-risk South African women (Abdool Karim 2009). In a comparison with a control group that received no gel, PRO2000 appeared to reduce risk by 33% with a p-value of 0.06 (the standard threshold for significance is 0.05). A CROI audience member noted that a comparison between the PRO2000 gel group and a combination of two control groups in the trial (one that received no gel and another that received a placebo gel) would push the result into significance. To his credit, Abdool Karim explicitly resisted this illegitimate statistical maneuver because combining the control groups was not part of the prespecified plan.

Abdool Karim’s caution proved prescient when the results of a far larger phase III efficacy trial of PRO2000 gel (which enrolled close to 10,000 women) were announced at the end of 2009. HIV infection rates were essentially identical between placebo and active gel recipients (Chisembele 2010). While disappointing, the outcome has reinforced a shift in microbicide research toward antiretroviral-based products. Efficacy results from an important first test of this approach—a phase IIb study of a gel form of the reverse transcriptase inhibitor tenofovir (Viread) called CAPRISA 004—were published in the journal Science on July 19, 2010 (Karim 2010) and presented at the International AIDS Conference in Vienna the following day. In an extremely encouraging development for the microbicide field, recipients of tenofovir gel showed a 39% reduction in risk of HIV acquisition that was highly statistically significant (p=0.017). In raw numbers, there were 38 infections out of a total of 445 tenofovir gel recipients and 60 among the 444 placebo recipients. An analysis of genital tract tenofovir levels, presented in Vienna by Angela Kashuba but not yet published, found significant associations between the amount of drug present and risk of HIV infection, bolstering the case that the observed protective efficacy was real (Kashuba 2010). However, there are limitations: the study was relatively small and the 95% confidence interval was wide, ranging from 6-60% protection. Plans are now afoot to rapidly try and confirm the findings. There is also a large ongoing trial sponsored by the Microbicides Trial Network called the VOICE study which includes an arm in which women are receiving tenofovir gel. The 2011 edition of the TAG pipeline report will include a more detailed and extensive discussion of the CAPRISA 004 findings and follow-up planning.

A number of other antiretroviral microbicides are advancing in human trials. The reverse transcriptase inhibitor UC-781, originally developed by Uniroyal Chemical and Biosyn, is in a phase I trial sponsored by CONRAD (Schwartz 2008). UC-781 is also being explored for potential rectal use, with encouraging results from a phase I trial published recently (Ventuneac 2010).

The International Partnership for Microbicides (IPM) is developing a nonnucleoside reverse transcriptase inhibitor, dapirivine gel (licensed from Tibotec and formerly known as TMC120), that is currently in phase I/II trials. The IPM has pioneered studies of novel delivery methods, and results indicate that dapirivine can be safely delivered via a matrix intravaginal ring (Nel 2009).

The push toward long-acting delivery methods for microbicides reflects longstanding concerns about the usability and efficacy of topically applied candidates. Adherence to the use of coitally dependent products has been reported to be an issue in some trials (Skoler-Karpoff 2008), and even if adherence is optimal there is evidence that the physical act of sex may affect the genital-tract distribution of a topical microbicide and thereby reduce its ability to inhibit HIV infection (Keller 2010).

Immune-based therapies

The designation immune-based therapy encompasses a broad range of approaches that aim to produce health benefits by affecting the function of the immune system. IBTs can be subdivided into candidates that seek to improve immune function and/or clinical health overall (e.g., cytokines like IL-7 and anti-inflammatory approaches), those that try to enhance the immune response to HIV itself (e.g., therapeutic vaccines), and gene therapies that alter the makeup of the immune system in ways intended to ameliorate the harmful effects of HIV (or perhaps even shut down the virus completely).

Suppression of viral replication by ART is associated with a huge reduction in risk of illness and death, closing the life expectancy gap between HIV-positive people and their HIV-negative counterparts (Antiretroviral Therapy Cohort Collaboration 2008, 2009; Lohse 2007; van Sighem 2010). However, in most studies, a gap still exists. Furthermore, poor CD4 recovery despite viral load control and persistently elevated levels of immune activation and inflammation on ART are associated with an increased risk of morbidity and mortality (Kuller 2008; Rodger 2009). These findings suggest that IBTs capable of enhancing immune reconstitution and/or reducing residual immune activation and inflammation could provide significant health benefits to a subset of people with HIV on ART. Unfortunately however, there remains a dearth of candidates in the pipeline.

An interrelated concern is the association between HIV infection and immune senescence, which is characterised by the accumulation of dysfunctional memory T-cell populations in the CD4 and the CD8 T-cell pools—particularly the latter. These dysfunctional cells are stubbornly resistant to apoptosis (cell death), produce large amounts of proinflammatory cytokines and are characterised by lack of cell surface expression of the costimulatory molecule CD28 and elevated expression of a senescence marker, CD57 (Effros 2005). A similar phenomenon is seen in the elderly in the absence of HIV infection; in this setting, elevated levels of senescent CD8 T cells designate an “immune risk phenotype” that is associated with frailty, ill health, and earlier mortality (Larbi 2008). A number of recent studies suggest that people with HIV may face similar issues at a younger age due to an acceleration of immune senescence (Desai 2010). Researchers such as Rita Effros from the University of California–Los Angeles are working on strategies aiming to reverse senescence and/or eliminate senescent cells, but they are as yet only at the preclinical stages of development (Fauce 2008). Another important immunological consequence of both aging and HIV infection is the decline in thymus function and resultant diminution of naive T cells (Schacker 2010) and, as stated in the introduction, researchers continue to look for approaches that may halt or reverse this process.

Table 3. Therapeutic Vaccines Pipeline 2010

Table 4. Cytokine, Immunomodulator, and Gene Therapy Pipeline 2010

Therapeutic Vaccines

A bewildering array of therapeutic vaccine candidates continues to undergo testing. The large body of evidence suggesting that HIV-specific CD4 and CD8 cells play a key role in individuals who control viral replication in the absence of ART has prompted this research. (Hersperger 2010; Saag 2010). For the most part, the hope is that therapeutic vaccines may be able to induce the maturation of new HIV-specific T-cell responses while viral load is suppressed by ART, and these responses may be better equipped to battle HIV when ART is subsequently interrupted. Results from a phase IIb treatment interruption trial of Vacc-4x, a peptide-based therapeutic vaccine developed by Bionor Immuno, are anticipated before the end of 2010.

Another strategy being employed is the immunization of HIV-positive people prior to any significant CD4 T-cell decline, with the aim of delaying the need for ART. Two new studies of peptide-based therapeutic vaccines, HIV-v and AFO-18, are taking this tack. At the 2010 International AIDS Conference, results from a 60-person randomised controlled study of this type were reported, showing that a DNA vaccine manufactured by FIT Biotech lowered viral load by around half a log after two years of follow up. A small but statistically significant increase in CD4 T cell counts was also reported (Vardas 2010).

One possibility receiving little attention is that therapeutic vaccination might reduce HIV-induced inflammation by bolstering virus-specific T cell responses. This may seem counterintuitive, but decreased immune activation was been reported many years ago in a trial of Jonas Salk’s now discontinued whole-killed therapeutic HIV vaccine (Fernandez-Cruz 2002).

Anti-inflammatory Approaches

The associations between inflammatory markers and adverse clinical events have bolstered the rationale for studying approaches that might reduce immune activation in people with HIV infection. The malaria drug chloroquine phosphate is being studied for both direct anti-HIV and anti-inflammatory effects. Aspirin and pentoxifylline are also being studied in combination with ART, but not to assess their impact on HIV progression; instead, the outcome measures being looked at are markers of cardiovascular disease risk. Encouraging results from the phase I trial of pentoxifylline have been published (Gupta 2010), leading to the opening of a larger phase II study.

Mesalamine

Mesalamine is an oral anti-inflammatory drug that acts particularly on the cells of the gut (Iacucci 2010), and the U.S. Food and Drug Administration has approved it for the treatment of ulcerative colitis, proctitis, and proctosigmoiditis. Researchers at the University of California–San Francisco are conducting a small study to ascertain if mesalamine can reduce inflammation levels in HIV-positive people on ART. The study is motivated by evidence that leakage of normally friendly gut bacteria into systemic circulation (microbial translocation) contributes to immune activation in HIV infection (Brenchley 2006) and is associated with poor immune reconstitution on ART (Marchetti 2008).

Cell Infusion and Gene Therapies

Several phase I and II studies of gene therapies are ongoing. The broad goal of these approaches is to enable CD4 T cells to resist HIV infection. Results from the phase II trial of Johnson & Johnson’s OZ-1 anti-Tat gene therapy were published in 2009; the product failed to meet the primary endpoint of significantly reducing viral load during an ART interruption but several exploratory analysis suggested that there may have been a mild antiviral effect (Mitsuyasu 2009).

Carl June’s research group has launched a novel study in which CD4 T cells are sampled and manipulated in the laboratory so that they can no longer express the CCR5 coreceptor. This is achieved using a zinc finger nuclease technology developed and manufactured by Sangamo Biosciences. The zinc finger nucleases act like biological scissors and snip out the CCR5 gene from the CD4 T cells’ DNA. The CCR5-negative CD4 T cells are then expanded and reinfused into the individual. Interest in this approach has been piqued by the case of the apparently cured individual cited in the introduction (Hütter 2009). June gave an update on the status of the trial at a Keystone HIV pathogenesis meeting in January 2010: the research is proceeding slowly due to careful safety evaluations and so far only one person has been infused. No concerns have arisen and preliminary evidence suggests that the CCR5-negative CD4 T cells are persisting and expanding slightly in vivo, representing 2.1% of peripheral blood CD4 cells at 140 days of follow up (June 2010). June’s research group is also evaluating a different gene therapy that modifies CD8 T cells ex vivo, equipping them with a T cell receptor (TCR) that is particularly adept at recognizing HIV-infected cells (Varela-Rohena 2008). The souped-up CD8 T cells are then expanded and re-infused back into the individual. The ultimate goal is to combine the CD4 and CD8 T cell gene therapy approaches in order to bolster the ability of both subsets to deal with HIV.

Just prior to this report going to press, researcher John Rossi published results from a phase I trial of a combined gene therapy approach in HIV-infected individuals undergoing hematopoietic stem cell (HSC) transplantation for AIDS-related lymphoma (DiGiusto 2010). Genes encoding three different anti-HIV RNA molecules were introduced into a subset of transplanted HSCs in four individuals, and long-term persistence in multiple cell lineages was demonstrated, albeit at very low levels. Although no therapeutic effect could be demonstrated, the study has been hailed as proof that the concept is feasible.

A similar protocol is being employed by researchers developing M87o, a gene therapy that encodes an HIV entry inhibitor similar to the drug Fuzeon (van Lunzen 2007). A phase I trial is being performed in individuals with AIDS-related lymphoma who require stem cell transplantation, and the M87o gene is added to a subset of the stem cells prior to the procedure.

IL-7

IL-7 is a cytokine that plays a key role in T-cell development and naive and memory T-cell proliferation and survival. Results from two phase I trials of IL-7 in people with HIV reported substantial increases in CD4 and CD8 T-cell counts even at the lowest dose studied (Levy 2007; Sereti 2007). The drug was well tolerated. These results suggest that IL-7 may be an excellent candidate for studies in people with inadequate immune reconstitution despite ART. A new glycosylated form of IL-7 that allows less frequent dosing is now in phase I trials. The manufacturer is a French company called Cytheris.

Maraviroc

Maraviroc is an approved antiretroviral drug (marketed under the name Selzentry) that works by blocking the interaction between HIV and the chemokine receptor CCR5. Five clinical trials are evaluating whether adding maraviroc can increase CD4 T-cell counts in people on ART with poor CD4 T-cell recovery despite prolonged viral load suppression. Researchers from the U.S.-based AIDS Clinical Trials Group recently presented results of a study addressing this question and, while receipt of maraviroc was associated with declines in immune activation markers, there was no significant CD4 T-cell increase compared to standard ART (Wilkin 2010).

TXA127

TXA127 is one of the very few IBTs being studied in individuals with poor CD4 T-cell reconstitution despite viral load suppression by ART. The other name for the drug is angiotensin 1-7 and it has been shown to stimulate bone marrow production of hematopoietic progenitor cells in animal models (Heringer-Walther 2009). These progenitor cells give rise to multiple lineages of immune cells, including CD4 T cells, hence the rationale for study in HIV. A small phase I/II trial has reported a reduction in the incidence of low blood cells after chemotherapy for breast cancer (Rodgers 2006).

Conclusion

The Thai results have boosted flagging hopes for HIV vaccine research, but it will be some time before it is known whether they can be repeated in other settings. The apparent success of the trial has shone on a spotlight on the shortsightedness of the design which, as the investigators have acknowledged, made the relative contributions of the two components impossible to disentangle. TAG drew attention to this obvious issue when the trial first began (Jefferys 2004). From a policy perspective this is problematic: on the one hand the urgent need for an HIV vaccine is emphasised to the public to promote support for research funding, while on the other investigators unabashedly propose repeating a huge, lengthy trial in order to “deconvolute” the results. In the future, trials must be designed in a way that precludes the contribution of the individual vaccine components becoming convoluted in the first place. The PreP and microbicide fields are united in anticipation of imminent efficacy trial results. The findings from these trials will be crucial in determining the next steps in these research areas. Immune-based therapies continue to appeal on paper while struggling in the real world. But renewed attention to the importance of translational (bench-to-bedside) research and some encouraging signs from the cancer field offer hope that breakthroughs are possible. Ultimately, it is to be hoped that the reinvigorated research effort into curing HIV infection, along with a successful sterilizing vaccine, will render these pipelines moot.

References

Abdool Karim SS, Coletti A, Richardson B, et al. Safety and effectiveness of vaginal microbicides BufferGel and 0.5% PRO 2000/5 Gel for the prevention of HIV infection in women: Results of the HPTN 035 trial. (Paper 48LB.) Paper presented at the Sixteenth Conference on Retroviruses and Opportunistic Infections, Montreal, 8–11 February 2009.

Aboud S, Nilsson C, Karl* K, et al. Strong HIV-specific CD4+ and CD8+ T lymphocyte proliferative responses in healthy individuals immunised with a HIV-1 DNA vaccine and boosted with HIV-1 recombinant Modified Vaccinia virus Ankara (MVA). Clin Vaccine Immunol. 2010 May 12. doi:10.1128/CVI.00008-10 [Epub ahead of print]

Antiretroviral Therapy Cohort Collaboration. Life expectancy of individuals on combination antiretroviral therapy in high-income countries: a collaborative analysis of 14 cohort studies. Lancet. 2008;372(9635):293–99.

Antiretroviral Therapy Cohort Collaboration. Mortality of HIV-infected patients starting potent antiretroviral therapy: comparison with the general population in nine industrialised countries. Int J Epidemiol. 2009;38(6):1624–33. Epub 2009 Oct 9.

Barouch DH, O’Brien KL, Simmons NL, et al. Mosaic HIV-1 vaccines expand the breadth and depth of cellular immune responses in rhesus monkeys. Nat Med. 2010;16(3):319–23. Epub 2010 Feb 21.

Benlahrech A, Harris J, Meiser A, et al. Adenovirus vector vaccination induces expansion of memory CD4 T cells with a mucosal homing phenotype that are readily susceptible to HIV-1. Proc Natl Acad Sci U S A. 2009;106(47):19940–45. Epub 2009 Nov 16.

Brenchley JM, Price DA, Schacker TW, et al. Microbial translocation is a cause of systemic immune activation in chronic HIV infection. Nat Med. 2006;12(12):1365–71. Epub 2006 Nov 19.

Bomsel M, Drillet A-S, Roger M-G, et al. Virosome-Gp41 vaccination triggers mucosal defense mechanisms that highly protects female macaques from repeated intravaginal low-dose challenges with simian HIV162P3. (Paper #520.) Paper presented at the Sixteenth Conference on Retroviruses and Opportunistic Infections, Montreal, 8-11 February 2009.

Buchbinder SP, Mehrotra DV, Duerr A, et al. Efficacy assessment of a cell-mediated immunity HIV-1 vaccine (the Step Study): a double-blind, randomised, placebo-controlled, test-of-concept trial. Lancet. 2008;372(9653):1881–93. Epub 2008 Nov 13.

Chakupurakal G, Onion D, Cobbold M, Mautner V, Moss PA. Adenovirus vector-specific T cells demonstrate a unique memory phenotype with high proliferative potential and coexpression of CCR5 and integrin alpha4beta7. AIDS. 2010;24(2):205–10.

Chisembele M, Crook A, Gafos M, et al. PRO2000 vaginal gel is ineffective in preventing HIV infection: Results of the MDP301 phase III microbicide trial. (Paper # 87LB.) Paper presented at the Seventeenth Conference on Retroviruses and Opportunistic Infections, San Francisco, 16–19 February 2010.

Corti D, Langedijk JP, Hinz A, et al. Analysis of memory B cell responses and isolation of novel monoclonal antibodies with neutralizing breadth from HIV-1-infected individuals. PLoS One. 2010;5(1):e8805.

Curlin ME, Huang M-L, Lu X, Celum CL, Sanchez J, et al. 2010 Frequent Detection of Human Adenovirus from the Lower Gastrointestinal Tract in Men Who Have Sex with Men. PLoS ONE 5(6): e11321.

Desai S, Landay A. Early immune senescence in HIV disease. Curr HIV/AIDS Rep. 201;7(1):4–10.

DiGiusto DL, Krishnan A, Li L, et al. RNA-based gene therapy for HIV with lentiviral vector-modified CD34(+) cells in patients undergoing transplantation for AIDS-related lymphoma. Sci Transl Med. 2010;2(36):36ra43.

Earl PL, Cotter C, Moss B, et al. Design and evaluation of multi-gene, multi-clade HIV-1 MVA vaccines. Vaccine. 2009;27(42):5885–95. Epub 2009 Aug 3.

Effros RB, Dagarag M, Spaulding C, Man J. The role of CD8+ T-cell replicative senescence in human aging. Immunol Rev. 2005;205(1):147–57.

Fauce SR, Jamieson BD, Chin AC, et al. Telomerase-based pharmacologic enhancement of antiviral function of human CD8+ T lymphocytes. J Immunol. 2008;181(10):7400–7406.

Fernandez-Cruz E, Navarro J, Abad ML et al. Augmentation of HIV-1-specific memory subsets of T lymphocytes and decrease of immune activation in HIV-1+ individuals treated with a therapeutic vaccine plus antiretrovirals: Impact on viral load. (Paper 318-W.) Paper presented at the Ninth Conference on Retroviruses and Opportunistic Infections, Seattle, 24–28 February 2002.

Flynn NM, Forthal DN, Harro CD, Judson FN, Mayer KH, Para MF; rgp120 HIV Vaccine Study Group. Placebo-controlled phase 3 trial of a recombinant glycoprotein 120 vaccine to prevent HIV-1 infection. J Infect Dis. 2005;191(5):654–65. Epub 2005 Jan 27.

Fry TJ, Mackall CL. The many faces of IL-7: from lymphopoiesis to peripheral T cell maintenance. J Immunol. 2005;174(11):6571–76.

Gudmundsdotter L, Nilsson C, Brave A, et al. Recombinant Modified Vaccinia Ankara (MVA) effectively boosts DNA-primed HIV-specific immune responses in humans despite pre-existing vaccinia immunity. Vaccine. 2009;27(33):4468–74. Epub 2009 May 29.

Gupta SK, Johnson RM, Mather KJ, Clauss M, Rehman J, Saha C, Desta Z, Dubé P. Anti-inflammatory treatment with pentoxifylline improves HIV-related endothelial dysfunction: a pilot study. AIDS. 2010;24(9):1377–1380.

Harari A, Bart PA, Stör W, et al. An HIV-1 clade C DNA prime, NYVAC boost vaccine regimen induces reliable, polyfunctional, and long-lasting T cell responses. J Exp Med. 2008;205(1):63–77. Epub 2008 Jan 14.

Heringer-Walther S, Eckert K, et al. Angiotensin-(1-7) stimulates hematopoietic progenitor cells in vitro and in vivo. Haematologica. 2009;94(6):857–60. Epub 2009 Apr 18.

Hersperger AR, Pereyra F, Nason M, Det al. Perforin expression directly ex vivo by HIV-specific CD8 T-cells is a correlate of HIV elite control. PLoS Pathog. 2010;6(5):e1000917.

Hutnick NA, Carnathan DG, Dubey SA, et al. Baseline Ad5 serostatus does not predict Ad5 HIV vaccine-induced expansion of adenovirus-specific CD4+ T cells. Nat Med. 2009;15(8):876–88. Epub 2009 Jul 20.

Hütter G, Nowak D, Mossner M, et al. Long-term control of HIV by CCR5 Delta32/Delta32 stem-cell transplantation. N Engl J Med. 2009;360(7):692–8.

Iacucci M, de Silva S, Ghosh S. Mesalazine in inflammatory bowel disease: a trendy topic once again? Can J Gastroenterol. 2010;24(2):127–33.

Jefferys R, Harrington M. Outstanding questions on HIV vaccine trial. Science. 2004;305(5681):180; author reply, 180.

Johnson PR, Schnepp BC, Zhang J, Connell MJ, Greene SM, Yuste E, Desrosiers RC, Clark KR. Vector-mediated gene transfer engenders long-lived neutralizing activity and protection against SIV infection in monkeys. Nat Med. 2009;15(8):901–906. Epub 2009 May 17.

June CH. Exploring the potential of gene modified CD4 T cells to target the HIV-1 reservoir. Paper presented at Keystone HIV Biology and Pathogenesis (A6), Sante Fe, 12–17 January 2010.

Karim QA, Karim SS, Frohlich JA, et al. Effectiveness and Safety of Tenofovir Gel, an Antiretroviral Microbicide, for the Prevention of HIV Infection in Women. Science. 2010 Jul 19. [Epub ahead of print]

Kashuba AD, Abdool Karim SS, Kraft E et al. Do systemic and genital tract tenofovir concentrations predict HIV seroconversion in the CAPRISA 004 tenofovir gel trial? Abstract#TUSS0503, XVIII International AIDS Conference, Vienna, July 18-23, 2010.

Karnasuta C, Paris RM, Cox JH, et al. Antibody-dependent cell-mediated cytotoxic responses in participants enrolled in a phase I/II ALVAC-HIV/AIDSVAX B/E prime-boost HIV-1 vaccine trial in Thailand. Vaccine. 2005;23(19):2522–29.

Keller MJ, Mesquita PM, Torres NM, et al. Postcoital bioavailability and antiviral activity of 0.5% PRO 2000 gel: implications for future microbicide clinical trials. PLoS One. 2010;5(1):e8781.

Kibuuka H, Kimutai R, Maboko L, et al. A phase 1/2 study of a multiclade HIV-1 DNA plasmid prime and recombinant adenovirus serotype 5 boost vaccine in HIV-uninfected East Africans (RV 172). J Infect Dis. 2010;201(4):600–607.

Koup RA, Roederer M, Lamoreaux L, et al. Priming immunization with DNA augments immunogenicity of recombinant adenoviral vectors for both HIV-1 specific antibody and T-cell responses. PLoS One. 2010;5(2):e9015.

Kuller LH, Tracy R, Belloso W, et al. Inflammatory and coagulation biomarkers and mortality in patients with HIV infection. PLoS Med. 2008 Oct 21;5(10):e203.

Kwong PD. Antibody VRC01: To be or not to be like CD4. (Paper 011.) Paper presented at Keystone HIV Vaccines (X5), Banff, Alberta, Canada, 21–26 March 2010

Larbi A, Franceschi C, Mazzatti D, Solana R, Wikby A, Pawelec G. Aging of the immune system as a prognostic factor for human longevity. Physiology (Bethesda). 2008;23:64-74.

Levy Y, Lacabaratz C, Weiss L, et al. Enhanced T cell recovery in HIV-1-infected adults through IL-7 treatment. J Clin Invest. 2009;119(4):997–1007. Epub 2009 Mar 16.

Lohse N, Hansen AB, Pedersen G, Kronborg G, Gerstoft J, Vaeth M, Obel N. Survival of persons with and without HIV infection in Denmark, 1995-2005. Ann Intern Med. 2007;146(2):87–95.

Marchetti G, Bellistro* M, Borghi E, et al. Microbial translocation is associated with sustained failure in CD4+ T-cell reconstitution in HIV-infected patients on long-term highly active antiretroviral therapy. AIDS. 2008;22(15):2035–8.

Marin B, Thiébaut R, Bucher HC, et al. Non-AIDS-defining deaths and immunodeficiency in the era of combination antiretroviral therapy. AIDS. 2009;23(13):1743–53.

McCormack S, Stuior W, Barber T, et al. EV02: a phase I trial to compare the safety and immunogenicity of HIV DNA-C prime-NYVAC-C boost to NYVAC-C alone. Vaccine. 2008;26(25):3162–74. Epub 2008 May 6.

McElrath MJ, De Rosa SC, Moodie Z, et al. HIV-1 vaccine-induced immunity in the test-of-concept Step Study: a case-cohort analysis. Lancet. 2008;372(9653):1894–905. Epub 2008 Nov 13.

Michael N. RV 144 Update: Vaccination with ALVAC and AIDSVAX to Prevent HIV-1 Infection in Thai Adults. (Paper 74.) Paper presented at the Seventeenth Conference on Retroviruses and Opportunistic Infections, San Francisco,16–19 February 2010.

Mitsuyasu RT, Merigan TC, Carr A, et al. Phase 2 gene therapy trial of an anti-HIV ribozyme in autologous CD34+ cells. Nat Med. 2009;15(3):285–92. Epub 2009 Feb 15.

Napolitano LA, Schmidt D, Gotway MB, et al. Growth hormone enhances thymic function in HIV-1-infected adults. J Clin Invest. 2008;118(3):1085–98.

Nchinda G, Amadu D, Trumpfheller C, Mizenina O, Uberla K, Steinman RM. Dendritic cell targeted HIV gag protein vaccine provides help to a DNA vaccine including mobilization of protective CD8+ T cells. Proc Natl Acad Sci U S A. 2010;107(9):4281–86. Epub 2010 Feb 16.

Nel A, Smythe S, Young K, Malcolm K, McCoy C, Rosenberg Z, Romano J. Safety and pharmacokinetics of dapivirine delivery from matrix and reservoir intravaginal rings to HIV-negative women. J Acquir Immune Defic Syndr. 2009;51(4):416–23.

Nitayaphan S, Pitisuttithum P, Karnasuta C, et al. Safety and immunogenicity of an HIV subtype B and E prime-boost vaccine combination in HIV-negative Thai adults. J Infect Dis. 2004;190(4):702–706. Epub 2004 Jul 20.

O’Brien KL, Liu J, King SL, Sun YH, et al. Adenovirus-specific immunity after immunization with an Ad5 HIV-1 vaccine candidate in humans. Nat Med. 2009;15(8):873–75. Epub 2009 Jul 20.

Pejchal R, Walker LM, Stanfield RL, et al. Structure and function of broadly reactive antibody PG16 reveal an H3 subdomain that mediates potent neutralization of HIV-1. Proc Natl Acad Sci U S A. 2010;107(25):11483–88. Epub 2010 Jun 2.

Pitisuttithum P, Gilbert P, Gurwith M, et al. Randomised, double-blind, placebo-controlled efficacy trial of a bivalent recombinant glycoprotein 120 HIV-1 vaccine among injection drug users in Bangkok, Thailand. J Infect Dis. 2006;194(12):1661–71. Epub 2006 Nov 3.

Rerks-Ngarm S, Pitisuttithum P, Nitayaphan S, et al. Vaccination with ALVAC and AIDSVAX to prevent HIV-1 infection in Thailand. N Engl J Med. 2009;361(23):2209–20. Epub 2009 Oct 20.

Robertson M, Mehrotra D, Fitzgerald D, et al. Efficacy results from the STEP study (Merck V520 Protocol 023/HVTN 502): A phase II test-of-concept trial of the MRKAd5 HIV-1 Gag/Pol/Nef trivalent vaccine. (Paper # 88LB.) Paper presented at the Fifteenth Conference on Retroviruses & Opportunistic Infections, Boston, 3–6 February 2008.

Rodger AJ, Fox Z, Lundgren JD, et al. Activation and coagulation biomarkers are independent predictors of the development of opportunistic disease in patients with HIV infection. J Infect Dis. 2009;200(6):973–83.

Rodgers KE, Oliver J, diZerega GS. Phase I/II dose escalation study of angiotensin 1-7 [A(1-7)] administered before and after chemotherapy in patients with newly diagnosed breast cancer. Cancer Chemother Pharmacol. 2006;57(5):559–68. Epub 2005 Aug 12.

Russell ND, Graham BS, Keefer MC, et al.Phase 2 study of an HIV-1 canarypox vaccine (vCP1452) alone and in combination with rgp120: negative results fail to trigger a phase 3 correlates trial. J Acquir Immune Defic Syndr. 2007;44(2):203–12.

Saag M, Deeks SG. How Do HIV Elite Controllers Do What They Do? Clin Infect Dis. 2010;51(2):239–41.

Sandstrøm, Nilsson C, Hejdeman B, et al. Broad immunogenicity of a multigene, multiclade HIV-1 DNA vaccine boosted with heterologous HIV-1 recombinant modified vaccinia virus Ankara. J Infect Dis. 2008;198(10):1482–90.

Schacker TW, Bosch RJ, Bennett K, et al. Measurement of naive CD4 cells reliably predicts potential for immune reconstitution in HIV. J Acquir Immune Defic Syndr. 2010;54(1):59–62.

Schwartz JL, Kovalevsky G, Lai JJ, Ballagh SA, McCormick T, Douville K, Mauck CK, Callahan MM. A randomised six-day safety study of an antiretroviral microbicide candidate UC781, a non-nucleoside reverse transcriptase inhibitor. Sex Transm Dis. 2008;35(4):414–9.

Sealy R, Slobod KS, Flynn P, et al. Preclinical and clinical development of a multi-envelope, DNA-virus-protein (D-V-P) HIV-1 vaccine. Int Rev Immunol. 2009;28(1):49–68.

Sereti I, Dunham RM, Spritzler J, et al. IL-7 administration drives T cell-cycle entry and expansion in HIV-1 infection. Blood. 2009;113(25):6304–14. Epub 2009 Apr 20.

Skoler-Karpoff S, Ramjee G, Ahmed K, et al. Efficacy of Carraguard for prevention of HIV infection in women in South Africa: a randomised, double-blind, placebo-controlled trial. Lancet. 2008;372(9654):1977–87.

Smith K, Zheng L, Bosch R, et al. Treatment with recombinant growth hormone is associated with modest improvement in CD4 lymphocyte reconstitution in HIV-infected persons on antiretroviral therapy: results of ACTG A5174. AIDS Res Hum Retroviruses. 2010;26(4):425–32.

Strategies for Management of Antiretroviral Therapy (SMART) Study Group, El-Sadr WM, Lundgren JD, et al. CD4+ count-guided interruption of antiretroviral treatment. N Engl J Med. 2006;355(22):2283–96.

Tan R, Westfall AO, Willig JH, Mugavero MJ, Saag MS, Kaslow RA, Kempf MC. Clinical outcome of HIV-infected antiretroviral-naive patients with discordant immunologic and virologic responses to highly active antiretroviral therapy. J Acquir Immune Defic Syndr. 2008;47(5):553–8.

Tuboi SH, Pacheco AG, Harrison LH, et al. Mortality associated with discordant responses to antiretroviral therapy in resource-constrained settings. J Acquir Immune Defic Syndr. 2010;53(1):70–77.

van Lunzen J, Glaunsinger T, Stahmer I, et al. Transfer of autologous gene-modified T cells in HIV-infected patients with advanced immunodeficiency and drug-resistant virus. Mol Ther. 2007;15(5):1024–33. Epub 2007 Mar 13.

van Sighem AI, Gras LA, Reiss P, Brinkman K, de Wolf F; ATHENA national observational cohort study. Life expectancy of recently diagnosed asymptomatic HIV-infected patients approaches that of uninfected individuals. AIDS. 2010;24(10):1527–35.

Vardas E, Stanescu I, Valtavaara M, et al. Indicators of therapeutic vaccine effect using GTU-MultiHIV B clade DNA in treatment-naive subtype C HIV-1 infected subjects. Abstract#MOPDB102, XVIII International AIDS Conference, Vienna, July 18-23, 2010.

Varela-Rohena A, Molloy PE, Dunn SM, et al. Control of HIV-1 immune escape by CD8 T cells expressing enhanced T-cell receptor. Nat Med. 2008;14(12):1390–5. Epub 2008 Nov 9.

Vasan S, Hurley A, Schlesinger SJ, et al. OA05-01. In vivo electroporation enhances the immunogenicity of ADVAX, a DNA-based HIV-1 vaccine candidate, in healthy volunteers Retrovirology 2009;6(suppl 3):O31.

Ventuneac A, Carballo-Di*ez A, McGowan I, et al. Acceptability of UC781 gel as a rectal microbicide among HIV-uninfected women and men. AIDS Behav. 2010;14(3):618–28. Epub 2009 Sep 11.

Walker LM, Phogat SK, Chan-Hui PY, et al. Broad and potent neutralizing antibodies from an African donor reveal a new HIV-1 vaccine target. Science. 2009;326(5950):285–89. Epub 2009 Sep 3.

Walker LM, Burton DR. Rational antibody-based HIV-1 vaccine design: current approaches and future directions. Curr Opin Immunol. 2010;22(3):358–66. Epub 2010 Mar 17.

Wilkin T, Lalama C, Tenorio A, et al. Maraviroc intensification for suboptimal CD4+ cell response despite sustained virologic suppression: ACTG 5256. (Paper 285.) Paper presented at the Seventeenth Conference on Retroviruses and Opportunistic Infections, San Francisco, 16–19 February 2010.

Wu X, Yang ZY, Li Y et al. Novel broadly neutralizing antibodies isolated using an epitope-specific resurfaced HIV-1 envelope probe that targets the CD4-binding site. (Paper 442.) Paper presented at Keystone HIV Vaccines (X5), Banff, Alberta, Canada, 21–26 March 2010.