This news article states that combining two ineffective HIV vaccines made a vaccine that cut the risk of HIV infection by 30%. This was a longitudinal study done over three years in Thailand with about 16,000 participants. It would make sense that combining multiple vaccines would increase protection because it would most likely be able to protect against more strains of HIV. Also the vaccine was comprised of HIV strains found predominately in Thailand and thus it is unclear and probably unlikely that the vaccine would work in other countries where those specific HIV strains are not circulating.

http://www.aidsbeacon.com/news/2009/09/12/discovery-of-antibodies-may-lead-to-hiv-vaccine

This news article states that scientists believe they have discovered two antibodies that are broadly neutralizing antibodies, which would target the epitopes of HIV and make the HIV receptors unable to attach to the cells they target for infection. If these turn out to actually be effective, this would be one of the biggest breakthroughs for an HIV vaccine. Before, one of the largest obstacles in creating an HIV vaccine was that scientists could not figure out how to elicit a neutralizing antibody response that effectively stopped HIV from attaching to receptors.

This article titled, “HIV Vaccine Research: The Way Forward,” states that the actual biology of HIV is one of the biggest reasons why a vaccine has not been developed. Also, there are scientific limitations meaning that scientists will need to think “outside of the box” and come up with new techniques and technology in order to find the key to an HIV vaccine. The review points out  the key immune responses that a vaccine would have to elicit in order for it to effectively prevent someone from contracting HIV. The vaccine would have to elicit a strong enough response of both antibodies and T cells and theses cells would have to be able to recognize  and fight off an extremely wide range of HIV strains. This has yet to be accomplished and producing a neutralizing antibody response has been one of the biggest HIV vaccine obstacles. Thus, some researchers are considering a T cell vaccine that would “reduce viral replication after infection” meaning that an HIV positive person would have a slower progression time to AIDS. Also, a vaccine like this would reduce the transmission rate between the person vaccinated and all of his/her partners because the viral load would be much lower. (However, I believe I have heard that a vaccine cannot be created on the sole criterion that it will reduce transmission rates while not giving the vaccinated person any benefits). Since scientists have come up against so many biological obstacles, this has forced them to consider other possibly beneficial vaccine ideas that are more feasible, yet wouldn’t confer complete resistance to HIV infection.
The review mentions the failure of different clinical trials for what seemed to be some of the most promising HIV vaccine candidates. It mentions the STEP trial that failed and was actually prematurely stopped when the researchers thought that the people receiving the vaccine were becoming more susceptible to HIV infection. The researchers thought that this had to do with the fact that the vaccine was built using the backbone of an adenovirus. They thought that the people in the trial who had previously been exposed to this virus were having stronger T cell responses and thus their T cells were more susceptible to HIV infection. However, after a couple of years of analysis, the researchers have concluded that this was not the reason, thus leaving the failed vaccine still a mystery. (http://www.nature.com/news/2009/090720/full/news.2009.707.html).
However, one of the main points of the review is that research for an HIV vaccine should not be halted or reduced because this is the only way that new breakthroughs can be made. This is encouraging because it is easy to find many other articles that say money is being wasted on research and development for an HIV vaccine because a vaccine is not possible. There are even scientists that say money is being squandered in pursuit of an HIV vaccine and that funding would be better off going somewhere else.

Reference:

Fauci S., Anthony et al. “HIV Vaccine Research: THe Way Forward.” Science. 321 (2008): 530-532.