Lymphocyte subsets as surrogate markers in antiretroviral therapy

Efficacy of antiretroviral treatment is evaluated usually according to reduction of serious events (e.g. opportunistic infections while on therapy) and improvement of survival time. In stages of asymptomatic disease treatment trials have to cover very long time periods to fulfil these requirements. In asymptomatic stages, when viremia is commonly absent, monitoring the host's immune response is an indirect means of measuring antiviral efficacy. CD4+ lymphocyte counts are generally accepted as surrogate in all major trials. The subsets of the CD8+ compartment reflect early and late activation and cytotoxic immune response. CD38+, CD57, CD8+ HLA/DR+ subsets reflect the host's vigorous cellular immune response even in early stages. These subsets are candidate surrogate markers in early and late stages of HIV infection. On the other hand, CD3+ CD4- CD8-, CD19/20 (B lymphocytes) and CD16+ (natural killer cells) do not exhibit any properties of candidate surrogate markers. Established and experimental cellular surrogate markers are discussed including own data and a review of the literature.