Microbes in Rectum Could be Key in Experimental HIV Vaccines

Researchers aimed to understand whether microbes living in the rectum and vagina, sites of HIV transmission, interacted with experimental HIV vaccines similar to the HVTN 111 vaccine currently in early stage clinical trials in humans.

Microbes living in the rectum could make a difference in the effectiveness of experimental HIV vaccines, according to researchers at the University of California, Davis. The findings were published in the journal mSphere.

Evidence from studies with other vaccines suggests that Lactobacillus supplements can boost production of antibodies, while treatment with antibiotics can hamper beneficial immune responses.

Researchers wanted to know whether microbes living in the rectum and vagina, sites of HIV transmission, interacted with experimental HIV vaccines similar to the HVTN 111 vaccine currently in early stage clinical trials in humans.

HVTN 111 includes 2 doses of HIV DNA snippets and a final boost with an HIV protein, all given through the skin. A vaccine that produces antibodies at the mucosal membranes where infection takes place is thought to be important in preventing HIV infection.

The common gut bacteria Lactobacillus and Clostridia did not change with vaccination, but the amounts of these microbes in the rectum did correlate with the immune response. High levels of either Lactobacillus or Clostridia were associated with more antibodies to the HIV proteins gp120 and gp140. Prevotella bacteria showed the opposite pattern. High level of Prevotella were correlated with weaker immune responses.

According to the study authors, it’s not clear what the mechanism could be for some bacteria to boost local immune responses in a specific site of the body. However, targeting these bacteria could be important to get the best possible performance out of vaccines that do not induce a particularly strong immune response, as in the case with HIV.

The microbiome could also be an important but overlooked factor to consider when evaluating vaccines.

Reference

  • Rectal Mirobes Influence Effectiveness of HIV Vaccine [press release]. UC Davis website. Published December 13, 2019. https://www.ucdavis.edu/news/rectal-microbes-influence-effectiveness-hiv-vaccine. Accessed January 3, 2020.