Immune response
to HIV can differ among twins

Researchers at the University of California, Los Angeles's AIDS Institute report that they've discovered that each person's immune system responds to HIV in different ways--even the immune systems of identical twins. Writing in the December 5 edition of the Journal of Virology, the scientists said their findings show 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 factors. Yet T-cell receptors (TCRs) 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 to the receptors on the surfaces of viruses and then 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 researcher and UCLA professor of pediatrics Paul Krogstad in a press release. "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, and the twins' targeting of HIV was remarkably similar, even 17 years after infection. But their overall TCR characteristics were highly divergent. This 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, associate professor of infectious diseases at the David Geffen School of Medicine at UCLA, and the study's lead researcher, in a press release.

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