HIV bNAbs prevent intravenous exposure to SHIV in macaques as PrEP
Simon Collins, HIV i-Base
Positive results from an animal study using a combination of two HIV broadly neutralising monoclonal antibodies (bNAbs) showed protection against intravenous (IV) exposure to SHIV. 
This study is significant because the risk of IV transmission are significantly higher than the highest risks from sexual exposure. Also, because registration PrEP studies have only focused on sexual exposure, leaving little data for people whose risk comes from injecting drug use.
The study, from David Garber and colleagues is published on 5 May 2021 ahead of print in the journal AIDS.
This was a small study with five cytologous macaques treated with a single subcutaneous injection of each bNAbs (10-1074 and 3BNC117) with two untreated animals as controls.
All animals were then exposed intravenously to SHIV each week until viral load was detected.
Animals receiving the bNAbs took a median of 5 viral challenges before becoming infected. This compared to both controls who becomes infected after a single challenge.
PK levels of the bNAbs correlated with infection, with median plasma level of 10-1074 at SHIV breakthrough was 1.1 μg mL−1 (range: 0.6 to 1.6 μg mL−1), by which time levels of 3BNC117 were undetectable.
The study concluded that protection was primarily due to 10-1074 and that the results suggest the potential for a long-acting formulation to work as PrEP for people who inject drugs.
These antibodies were developed by researchers at Rockefeller University in New York and were recently acquired by Gilead. They are now available in long-acting formulations that potentially allow for six-monthly dosing.
These results are important because efficacy of other PrEP drugs in animal studies was closely correlated with human results.
These results were first presented at CROI in 2019, together with results showing protection from penile exposure. 
This dual combination is also being studies in the UK RIO study for their potential to maintain undetectable viral load during a treatment interruption. 
Simon Collins is a community representative on the RIO study.
- Garber DA et al. Broadly neutralizing antibody-mediated protection of macaques against repeated intravenous exposures to simian-human immunodeficiency virus. AIDS, ahead of print. doi: 10.1097/QAD.0000000000002934. (5 May 2021).
- Collins S. bNAb research at CROI 2019: vaccine, prevention, treatment and cure… HTB (30 April 2019).
- RIO Study.
This report was first published on 16 May 2021.