CHENNAI: Researchers at Yerkes National Primate Research Center at Emory University, Atlanta, US, have shown that it is possible to restore immunity in lab macaques infected with the Simian Immunodeficiency Virus (SIV), providing hope of evolving similar mechanisms for HIV infection in humans.
In a paper that was published in Nature journal on December 10, Vijayakumar Velu et al showed that using an antibody to block a protein “programmed death 1” (PD1) — which dulls immune responses — results in rejuvenating the CD 8 T cells or killer cells, thereby restoring immunity and reducing the viral load.
Rama Rao Amara, one of the authors, speaking to The Hindu, said, “What PD1, present on the infected cell, does is to bind itself on to the killer cell and send it a negative signal, hypnotising the killer cell to believe it is a friend. The killer cell is fooled into not functioning and immunity is compromised.”
The team, including co-first author Kehmia Titanji, working on the HIV-like disease in macaques, sent the antibody in to latch itself onto the PD1.
This antibody blocked PD1’s interaction with the killer cell, thereby allowing the killer cell to function normally, demolishing the infected cells. The nine monkeys that were treated developed none of the characteristic symptoms up to eight months. The five animals that formed the control group, however, developed symptoms within four-five months, demonstrating the normal course of the disease. “In an infected monkey, we have shown that it is possible to convert non-functional killer cells to functional cells. And what is better, there is a substantial multiplication of these cells,” Dr. Amara says. “What we have seen in the monkey – it is too good to be true.”
The findings have great value in HIV, where the immune system is compromised by the virus, Dr. Amara says. It could well be the first step towards developing a therapeutic vaccine for HIV infections. The trial, funded by the National Institutes of Health, has also resolved safety issues concerning the use of the antibody – the animals have been given four doses over 10 days.
The team will take up a follow-up trial of 2-3 months of treatment to examine safety issues further. He adds that a similar procedure is being adopted by scientists researching cancer and Hepatitis C in humans and was being tolerated well. “We strongly feel that combining the treatment with anti-retrovirals and/or therapeutic vaccination could help improve outcomes,” Dr. Velu said in a telecon from Atlanta.