Study Explains Why Thai HIV Vaccine May Have Worked:
Antibodies helped, hindered vaccine
by Healthy Living News
Scientists have found that those who developed a protective antibody after taking an experimental HIV vaccine were less likely to become infected with the virus. The researchers also discovered another antibody that may have blocked the effectiveness of the vaccine. The discoveries provide important new clues on how an effective HIV vaccine could work.
The research was published in the New England Journal of Medicine (NEJM). The study looked at participants from the now famous RV144 vaccine study that took place in Thailand. That 2009 study used the first experimental HIV vaccine to ever provide some protection against the virus. The vaccine reduced the risk of contracting HIV by 31%.
Discovering and then reproducing effective HIV immunity in humans has been the holy grail of HIV research. In the NEJM study, the researchers sought to find which specific immune responses made the Thai vaccine work. The researchers analyzed HIV antibody responses of some for whom the vaccine provided protection from HIV infection and for others for whom it did not. Those in the study with Immunoglobulin G, or IgG antibodies, targeting a specific protein on the virus’s outer coat had a lower rate of HIV infection. However, those with the highest blood levels of an Immunoglobulin A, or IgA HIV binding antibody, were not protected by the vaccine. The researchers think the IgA antibodies may be interfering with the effective IgG antibodies.
“These studies reinforce and extend the results seen in the RV144 trial and provide new insights that may lead to a better and longer lasting HIV vaccine,” noted Col. Jerome Kim of the U.S. Military HIV Research Program and senior author of the study.
The RV144 study involved more than 16,000 adults in Thailand who were given a ALVAC and AIDSVAX B/E combo vaccine. Last September, new data was presented showing that the vaccine provides its highest level of protection in the first 6-12 months. That raised the possibility that the vaccine may require booster shots to prolong the limited protection it offers. If those booster shots can sustain or increase HIV immunity that would be a significant accomplishment. To that end, two booster shot studies will soon examine their effectiveness.
However, because HIV is a diverse and variable target, even booster shots may have their limitations. A vaccine that may work to some extent in Thailand may not work as well where other HIV types and viral strains predominate. With HIV being a moving target, the virus could also mutate so that the Thai vaccine may not work at all, similar to what happens with the flu virus every year. Large clinical studies of the vaccine are being planned for other parts of the world.
Despite the challenges ahead, researchers may have discovered what could be a significant chink in HIV’s armor. It could be the breakthrough that could lead to an effective preventative vaccine as well even a therapeutic vaccine for treating HIV infection.