Selective CD4 + T cell deletion after specific activation in HIV‐infected individuals; protection by anti‐CD28 monoclonal antibodies

AIDS is characterized by a progressive decline in the number of CD4 + T cells. This is preceded by an early selective defect in the proliferation of these cells to recall antigens [1–3], pokeweed mitogen (PWM) [4–6] and to superantigens (SAg) [4,7]. In contrast, the proliferative response to phytohaemagglutinin (PHA) remains intact [1,2,5]. We and others have shown that the proliferative defect in response to some stimuli was in fact due to the induction of cell death [4,7]. The activation‐induced cell death mechanism that explains the proliferative defects observed in vitro might also account for the progressive in vivo deletion of CD4 + T cells. Indeed, studies performed on different models of primates have shown that induction of cell death in CD4 + T cells was detected only when T cells were isolated from animals infected with a type of retrovirus that induces an AIDS‐like disease [8]. This correlation prompted us to analyse further the mechanism of HIV‐induced activation cell death to determine the specificity and rate of induction of cell death. T cells from HIV‐infected individuals were activated with superantigens and the Vβ T cell receptor (TCR) expression analysed. Data presented here show that cell death is restricted to activated CD4 + T cells, and does not affect bystander cells. More importantly, addition of anti‐CD28 MoAb specifically inhibited the induction of apoptosis, raising possibilities for therapy.