Promising strategy to help vaccines outsmart HIV

Researchers have discovered a promising delivery method to help make an HIV vaccine effective prior to and even after the infection.
The new finding at Oregon Health & Science University highlights an ingenious method to ensure the body effectively reacts when infected with the highly evasive HIV virus that causes AIDS.
Researchers have been utilising this unique approach to develop its own HIV vaccine candidate, which has so far shown promising results in animal studies.
"A major challenge in developing an effective HIV vaccine is figuring out how to target this evasive virus," said Dr Louis Picker, associate director of the OHSU Vaccine and Gene Therapy Institute.

CD8+ "cytotoxic" T cells are an important component of the immune system and are particularly important for pathogens, like HIV, that easily evade antibodies.
They serve as sentries within the body that detect and destroy virus-infected cells, accomplishing this function by recognising short viral peptides on the surface of infected cells.

T-cells are designed to be quite frugal in the number of different viral peptides they recognise, typically responding to just a handful of such peptides. This is a problem for control of HIV, which is able to change its peptides and thus escape T cells responses that do not target the relatively few functionally critical peptides that can't change without debilitating the virus.

In the vast majority of HIV infections, the few viral peptides recognised by T cells are not the vulnerable ones, and the virus escapes.
Therefore, the strategy that Picker and his colleagues adopted was to try to develop a vaccine to increase the number of viral peptides that T cells would recognise, reasoning that increasing this "recognition breadth" would allow T cells to more effectively respond to HIV.
Researchers found that cytomegalovirus or CMV, a common virus already carried by a large percentage of the population, may hold the key.
Their studies in the non-human primate model of HIV, called Simian immunodeficiency virus (SIV), found that a modified version of CMV engineered to express SIV proteins generates SIV-specific T cells that recognise three-fold as many SIV peptides as T cell generated by conventional vaccines and SIV itself.

These responses were entirely different from conventional responses, such that even viruses that had previously escaped natural responses would still be vulnerable.
Picker and his colleagues believe an HIV vaccine equipped with a modified CMV vector might be able to both prevent infection (prophylactic vaccine) and effectively battle the virus even if applied post-infection in individuals with infections suppressed by anti-retroviral therapy.
The study was published in the journal Science.