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When a viral infection cannot be eradicated and becomes chronic, the immune system gets exhausted. Human studies have shown that lymphocytes that are exhausted by chronic HIV infection display greater numbers of a receptor called programmed death 1 (PD-1). In an in vitro study, researchers found that an antibody that blocked the ability of PD-1 to activate its suicidal signals allowed lymphocytes to fight HIV more effectively (JW Gen Med Oct 10 2006).
Nine monkeys were treated with partially humanized PD-1 antibodies at 10 weeks or at 90 weeks after they were infected with simian immunodeficiency virus (SIV; a cousin of HIV). Five SIV-infected control monkeys were treated with an antibody against another receptor. The active treatment greatl…