A study, published in the Journal of Virology, showed that the body's defenses against the virus are random rather than genetically determined.

The researchers followed the cases of male twins who were infected shortly after their 1983 births in Los Angeles by blood transfusions administered from the same donor at the same time. Infected with the same strain of the virus, the twins continue to live in the Los Angeles area and grew up exposed to the same environmental forces.

Yet their T-cell receptors ( TCR ) reacted differently in each twin, showing that the body's defense response was random--and unpredictable.
TCRs play an important role in the immune system by binding viruses and other antigens to receptors on their surface, killing the invader. HIV escapes this action by changing shape so that it does not fit into those receptors.

" These boys are as similar as two humans can be, yet we see differences in how they fight the virus," said Paul Krogstad, one of the researchers. " That's one more thing that makes it difficult to develop a vaccine for everyone."

When a virus invades a body, the cellular immune response targets small parts of proteins in the virus. This targeting mechanism itself is genetically determined. ". The virus tries to escape that immune response by mutating and changing shape.

The twins' targeting of the HIV was remarkably similar 17 years after infection yet their overall TCR characteristics were highly divergent. The finding, demonstrates that the interaction between their immune systems and the virus was random and unpredictable--indicating that a "one size fits all" vaccine may not be possible.

" If the goal is to develop a vaccine, our findings suggest this may not be so straightforward," said Otto Yang, at UCLA, and the study's lead researcher.

According to the UCLA researchers, the results of this study have broader implications, and could apply to other viruses such as cytomegalovirus ( CMV ), a herpes virus that causes opportunistic infections in immunosuppressed individuals, and hepatitis C, the latter being similar to HIV in both its changeable and chronic nature.

Source: University of California - Los Angeles, 2005


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