July 30, 2020

Could HIV vaccines be reducing their own effectiveness by stimulating too much help? According to scientists at Yerkes National Primate Research Center (YNPRC), this could be the case.

In a recent paper that considered information from four studies on macaques immunized against SIV (HIV’s relative) or the hybrid SHIV virus, the researchers concluded a certain type of immune system cell known for helping may actually represent a weak spot in the body’s defenses.

HIV targets and replicates inside helper T cells, which aid in the body’s antiviral immune response. The problem comes when vaccination generates too many of a particular type of helper immune cell, Th1 cells.

We can think of Th1 cells as the well-intentioned first responders to a zombie attack. These cells travel to mucosal tissues, such as the rectum, cervix and vagina, where HIV/SIV first enters the body in the majority of infections. Th1 cells combat the virus initially, but then they get taken over.

What’s needed instead are Tfh cells, which remain in the lymph nodes and aid the immune system in creating antibodies. 

“We’re not saying Th1 cells are bad,” noted Rama Rao Amara, PhD, YNPRC and Emory Vaccine Center researcher, and co-director of Emory’s Consortium for Innovative AIDS Research in Nonhuman Primates. “But if you have too many, they take away from effective vaccine protection.”

“It’s a matter of stimulating just the right amount of immune help for a strong immune response, but not so much that it increases susceptibility to the virus,” added Eric Hunter, PhD, co-author and co-director with Amara of the AIDS research consortium, and an Emory Vaccine Center researcher. 

This could possibly be achieved using adjuvants, which are vaccine components that enhance the immune response. Amara noted the need for the effects of adjuvants to be explored in future research, and he further stated scientists studying candidate HIV vaccines in humans should examine whether these vaccines create too many Th1 target cells. This information could help immunologists design vaccines that provide more reliable protection against HIV.

Researchers across the NPRC network continue to explore new treatments for HIV/AIDS every day. You can keep up with the latest breakthroughs here.