Therapeutic intervention with antiretroviral therapy (ART) enables the modulation of HIV virus load and hence provides a unique opportunity to study the consequences of varying antigen load on the phenotype of virus-specific CD8+ T lymphocytes in a persistent human viral infection. The recent advent of tetrameric peptide / HLA class I complexes has enabled the direct phenotypic characterization of antigen-specific T cell populations ex vivo. Here, we use this technology to examine directly ex vivo the consequences of therapeutic manipulation of HIV virus load on the phenotype of HIV-specific CTL. Our observations using samples from 3 patients show that: (1) distinct sequential activation patterns of CD8+ T cells are associated with increasing virus load; (2) T cell receptor (TCR) down-regulation without apoptosis represents an early event during the generation of a T cell response in a natural infection and precedes the emergence of two distinct antigen-specific CD8+ T cell populations which differ in TCR and CD8 expression levels. Clear differences in surface Annexin V staining were observed between these populations. The observation that CTL activation, demonstrated by TCR and CD8 down-regulation, in response to rising levels of virus load, co-segregates with apoptosis only during later stages of the response indicates that antigen-associated cell death is restricted to distinct subpopulations of CTL.
European Journal of Immunology (2001) Volume 31 Issue 4, Pages 1115 - 1121 [doi:10.1002/1521-4141(200104)31:41115::AID-IMMU11153.0.CO;2-9]