Results from HSV-2 acyclovir studies
Nathan Geffen, TAC
Acyclovir studies at IAS 2009
Connie Celum, the principal investigator on the HPTN 039 trial, together with Jai Lingappa, the medical director, and other members of the Partners in Prevention HSV-HIV Transmission Team presented findings at IAS2009 on a counterpart trial to HPTN 039. This study, in HIV serodiscordant couples, looked at whether suppressing HSV-2 in people dually infected with HSV-2 and HIV infections could reduce HIV transmissions to their HIV-negative partners. 
HPTN 039 was a double-blind placebo controlled trial of standard doses of acyclovir for HSV-2 suppression (400 mg twice daily) to prevent HIV acquisition among over 3200 African women and MSM in Peru and the United States who were HIV-negative and HSV-2 positive. HTPN 039 found that acyclovir suppression did not reduce HIV incidence compared to placebo. Results were reported at CROI2008 and subsequently in the Lancet. 
Celum presented the main results of this new double-blind placebo controlled trial, conducted at 14 sites in sub-Saharan Africa, including South Africa, Kenya, Zambia, Botswana, Tanzania, Rwanda and Uganda.
Of 6544 heterosexual HIV discordant couples screened, 3408 were enrolled. The inclusion criteria for the coinfected partner included a CD4 cell count >250/mm3. The other partner could be either HSV-2 positive or negative, but had to be HIV-negative. HIV-positive participants could not be eligible for ART at trial entry according to their country guidelines.
The HIV-positive partners were randomised to receive either 400mg acyclovir twice-daily or placebo twice-daily. Couples were followed for a maximum of 24 months. Participants were provided with ART if they became eligible for it according to country guidelines.
The primary endpoint was HIV infection in the HIV-negative partners. The secondary endpoints included plasma and genital HIV viral load in the HIV-positive partners, and HIV disease progression. The trial was set up so that if 88 linked HIV transmissions (i.e. the virus transmitted from the enrolled partner to the seroconverting partner was determined by molecular sequencing to be linked) were observed, the trial would have high statistical power (90%) to see a 50% reduction in HIV transmissions in the acyclovir arm.
Baseline characteristics of the group included:
- 67% of HIV-positive partners were female;
- 65% of volunteers were <35 years old;
- average partnership duration was five years;
- 90% were cohabiting;
- a median of five sex acts were reported in the month prior to baseline measurements:
- 29% reported unprotected sex;
- 22% of the HIV-positive partners reported genital ulcer disease (GUD) in the prior three months;
- 4% of HIV-positive and 7% of HIV-negative partners reported outside partners respectively;
- median CD4 count was 460 cells/mm3 and median plasma HIV viral load was 4.2 log.
Monthly follow-up visits included medication provision, pill count and adherence support and individual and couple HIV risk reduction counselling. Every three months, HIV-positive partners were examined for GUD and plasma viral load and HIV-negative partners were tested for HIV and given risk reduction counselling. CD4 cell counts were taken every six months.
Retention was high. At 24 months, 92% of HIV-positive and 84% of HIV-negative participants were still in follow-up. Adherence measured by pill count was also high: 88% of all bottles were dispensed and 97% of dispensed bottle doses were taken.
No significant differences in incidence
There were 136 seroconversions at a rate of 2.8/100py (95% CI: 2.3-3.3), one after an incorrect drug kit was dispensed. Of the remaining 135, 68 occurred on the acyclovir arm and 67 on the placebo arm (HR: 0.92; 95%CI 0.60-1.41; p=0.70).
In a modified intention to treat analysis, 43 transmissions were linked by viral sequencing technology to partners on the acyclovir arm and 47 were linked to partners on the placebo arm. However, two in the acyclovir arm and four in the placebo arm were excluded from analysis because the study drug was withheld during pregnancy. Here too, there were no significant differences between the two arms. The sequencing methodology for this study was explained in a late breaker poster from Mary Campbell. 
Benefits of acyclovir
There were fewer GUD events in the acyclovir arm (217 vs 550; RR: 0.39; 95% CI: 0.32-0.48; p<0.001). HSV-2-positive GUD as determined by DNA PCR was also lower in the acyclovir arm (92 vs 336; RR: 0.27; 95%CI 0.2-0.36; p<0.001).
The acyclovir arm also had a 0.25 log reduction in plasma viral load (95%CI: 0.22-0.29).
A novel component of this study was evaluation of herpes suppression on HIV disease progression, an important secondary endpoint of the Partners in Prevention trial. In a separate analysis presented by Jairam Lingappa, 3,381 of the HIV-positive participants were followed up until a composite endpoint of first of CD4 cell count <200 cells/mm3, ART initiation, or death from non-trauma causes. 
In the acyclovir arm, 284 participants reached this endpoint versus 325 in the placebo arm (HR 0.83; 95%CI: 0.71-0.90; p=0.03). Similar reductions were found for each component of the composite endpoint analysed separately. However, Lingappas team further calculated that for every 43 people treated with the trial dose of acyclovir for a year, only one person would be prevented from attaining the composite endpoint. (We have previously reported findings demonstrating acyclovir and its pro-drug, valacyclovirs effect on HIV plasma RNA levels, in the October 2006 and July/August 2008 issues of HIV Treatment Bulletin, but this is the first report documenting impact of herpes suppression on HIV disease progression.)
Among participants with CD4 counts >350 cells/mm3 at enrollment, acyclovir delayed the time to CD4 < 350 cells/mm3 (HR 0.81; 95%CI 0.71-0.93; p=0.002). Here, 20 people would need to be treated to prevent one person from progressing to a CD4 count < 350 cells/mm3.
Acyclovir effect on genital viral load
A late breaker poster by Jared Baeten et al presented the results of a substudy that examined genital HIV RNA concentrations as a surrogate marker for HIV infectivity. 
Endocervical and semen samples were collected from 2,521 (1,805 women and 716 men) of 3,408 HIV-positive participants. For 1,797 of these, plasma was concurrently taken. For the remainder a plasma viral load within six months was available. Since the genital samples were taken only once during the study, the genital viral load was analysed as a time-independent variable.
HIV was detected in 60% of endocervical swab samples and 57% of semen samples. The median endocervical HIV concentration was 3.2 log (IQR 2.08-3.87) overall. Genital HIV-1 concentrations were significantly lower among those randomised to acyclovir (median 2.98 vs 3.29 for endocervical swabs; p<0.001 and 2.38 vs 2.76 for semen; p=0.008). The key finding of the study was that genital HIV concentrations were higher among HIV transmitting couples, where transmission was genetically linked to the partner (3.44 vs 2.49 log copies/mL for semen, p<0.001 and 3.91 vs 3.18 log copies/swab for endocervical swabs, p<0.001). Each log increase in genital HIV-1 RNA concentration was associated with 1.85-fold increased odds of HIV transmission for semen (p<0.001) and 2.03-fold increased odds of transmission for endocervical swabs (p<0.001). The study found no significant difference in genital HIV concentration for participants whose partners acquired HIV from outside sexual partners versus those who did not transmit HIV.
However, despite a 73% reduction in GUD and 0.25 log decline in plasma HIV levels and an approximately 0.3 log decline in genital HIV levels, acyclovir conferred no reduction in HIV transmission. The authors interpret the overall results of the trial to indicate that the plasma and genital tract HIV viral load reduction from herpes suppression with standard doses of acyclovir is too small to confer a protective effect against HIV transmission.
Future acyclovir trials
Nevertheless, given the promising effect of acyclovir on HIV viral load, Steve Reynolds described an ongoing double-blind placebo controlled trial in Rakai, Uganda. 
The purpose of the trial is to evaluate the effect of suppressive HSV-2 therapy among HIV-1/HSV-2 co-infected individuals on progression to AIDS, defined as CD4 count < 250 cells/mm3 or WHO stage IV disease. Volunteers with CD4 counts between 300 and 400 cells/mm3, not on ART, without WHO III/IV symptoms and no history of opportunistic infections, other than mucocutaneous Kaposi Sarcoma, candida or treated TB were eligible for inclusion. Enrollment was completed in November 2008. The trial assumes that 40% of individuals in the placebo arm will progress to CD4 counts <250 cells/mm3 or AIDS over 24 months and is powered to detect at least a 20% reduction in HIV disease progression in the intervention arm.
These studies show that a standard dose of acyclovir for HSV-2 suppression does not reduce HIV transmission. These are disappointing findings for an HIV prevention strategy that is already available.
A mechanism for the lack of protection has been suggested by Laurence Corey and colleagues in a recent paper in Nature Medicine. 
By analysing regular skin biopsies taken during acute lesions and over 20 weeks follow-up, they indentified a massive localised infiltration of CD4 and CD8 cells, thereby increasing the targets for HIV infection. Eight weeks after lesions healed, these levels were still 8-fold higher (655 and 618 cells/mm2 of skin, respectively, compared to 68 and 55 cells/mm2 in unaffected skin samples).
This paper is reported in detail in the Basic Science section of this issue of HTB. 
It has been conventional wisdom that wider availability of acyclovir for patients with genital herpes outbreaks would reduce HIV transmissions. We now know this is incorrect, at least with the doses of acyclovir (400 mg twice daily) used in these trials. However, efforts to make acyclovir widely accessible should continue because herpes is a debilitating, unpleasant disease which acyclovir effectively treats and because HSV-2 in widely prevalent in both HIV-negative and HIV-positive people. One of the barriers to its accessibility remains its high price in many developing countries.
Despite the negative findings, this trial and its substudies have set a high standard for the testing of future HIV prevention interventions. Furthermore, modeling studies using the data from this trial provide a potential threshold of HIV plasma viral load reduction in HIV-infected persons that will be needed to impact HIV transmission.
We now need to know whether a therapeutic dose of acyclovir could delay the time until initiation of HIV treatment, and whether this would be cost effective. The trial in Rakai described by Steve Reynolds using 400 mg twice-daily dose will provide complimentary information to the Partners in Prevention trial.
Studies with higher doses of valacyclovir will evaluate whether greater reduction in plasma HIV levels is feasible compared to acyclovir 400 mg twice daily. However, this research could be overtaken by new developments in ART management, if guidelines recommend earlier treatment.
Unless othewise stated, all references are to the Programme and Abstracts of 5th IAS Conference on HIV Pathogenesis, Treatment and Prevention, 19-22 July 2009, Cape Town.
- Celum C et al. Twice-daily acyclovir to reduce HIV-1 transmission from HIV-1 / HSV-2 co-infected persons within HIV-1 serodiscordant couples: a randomized, double-blind, placebo-controlled trial. 5th IAS 2009, Cape Town. Oral abstract WELBC101.
- Celum C et al. Effect of aciclovir on HIV-1 acquisition in herpes simplex virus 2 seropositive women and men who have sex with men: a randomised, double-blind, placebo-controlled trial. Lancet, 21 June 2008. 371(9630):2109-19.
- Campbell M et al. Determination of transmission linkage in the Partners in Prevention Study. 5th IAS 2009, Cape Town. Poster abstract LBPEC07.
- Lingappa JR et al. Daily acyclovir delays HIV-1 disease progression among HIV-1/HSV-2 dually-infected persons: a randomised trial. 5th IAS 2009, Cape Town. Oral abstract WELBC102.
- Baeten J et al. Genital HIV-1 RNA concentrations and heterosexual HIV-1 transmission risk. 5th IAS 2009, Cape Town. Poster abstract LBPEA07.
- Reynolds SJ. HSV-2 Suppression Trial, Rakai, Uganda. Partners in Prevention presentation reported with permission.
- Zhu J et al. Persistence of HIV-1 receptorpositive cells after HSV-2 reactivation is a potential mechanism for increased HIV-1 acquisition. Nature Medicine. Published online: 2 August 2009 | doi:10.1038/nm.2006.
- Jefferys R. Immune surveillance below the radar: study offers explanation for acyclovirs failure to reduce HIV risk. HTB September/November 2009. Vol 10, No 4. (Vol 2, No 3 of HTB South).