Despite the emergence of high level drug resistance in HIV-infected patients on stable antiretroviral therapy, plasma HIV RNA levels generally remain below the pretherapy viral load "set-point". The virologic and immunologic determinants of this lower steady state level of viremia have not been defined. Preliminary data indicate that: 1) drug resistant variants have reduced replicative capacity and pathogenic potential; 2) drug resistant viremia is associated with reduced T cell activation and turnover compared to wild-type viremia; and 3) patients with low level drug resistant viremia often have HIV-specific CD4 cells that are absent in patients with higher levels of viremia. This study will investigate whether the emergence of a poorly fit, drug resistant variant results in the generation of an effective HIV-specific CD4 cell response and if this response contributes to the establishment of a lower steady state level of viremia.
Participants in this study will be followed for 2 years or until antiretroviral therapy is modified or discontinued. Study visits will occur every 2 months, for a total of 14 visits. Study visits will include a patient interview and blood tests to measure the breadth and magnitude of the HIV-specific CD4 and CD8 cell responses as a function of viral load, viral replicative capacity, drug resistance phenotype, T cell turnover, and thymic function.