A new experimental HIV vaccine has been shown to be effective in pre-clinical trials performed in non-human primates. The current findings were developed as part of a nearly 30-year effort by researchers at Scripps Research and reported in the journal Immunity.
The strategy the researchers have been working on aims to identify the rare, vulnerable areas on HIV and teach the immune system to make antibodies to target those areas. They identified the virus’s outer envelop protein trimer as a target for production of neutralizing antibodies. In a previous experiment, they were able to show that animal models injected with neutralizing antibodies produced in the lab developed resistance to HIV.
Next, they aimed to get animals to make neutralizing antibodies themselves by exposing their immune system to the envelope protein trimer. However, this trimer is unstable and falls apart when isolated. It wasn’t until 2013, when scientists engineered a more stable trimer, called SOSIP, that the team was able to move forward with their vaccine design.
In the current study, the SOSIP-containing vaccine was tested in two groups of rhesus macaques. Six of the macaques had previously been identified as generating low neutralizing antibody titers, while six were identified as high-titer generators of neutralizing antibody. Twelve unimmunized primates were used as the control group.
The primates were then exposed to a simian form of HIV, called SHIV, that contains the same envelope trimer as the human virus. Both the low and high-titer groups could produce sufficient levels of neutralizing antibodies to prevent infection. However, the titers were shown to drop off over time as the primates were continuously exposed to the virus.
In future studies, the researchers plan to focus on methods for keeping titers high over time. They also note that this study indicates that neutralizing antibodies, but not other aspects of the immune system were key to stopping the virus.