The phenotype of virus-specific cells during chronic HIV infection (Chr-tet⁺ cells). Chr-tet⁺ were identified by labeling with MHC class I tetramers loaded with HIV peptides. (A) CD27/CD28 phenotypes in Chr-tet⁺ T_EM. Each dot represents a different donor. (B-D) Dot plots of individual donors showing that CD27/CD28 phenotypes: (B-C) do not correlate with the frequency of tet⁺ cells recognizing each epitope, epitope specificity, or MHC class I alleles associated with good or poor prognosis in HIV infection; and (D) do not reflect a tendency of the donor to generate a particular cell type, as the phenotypes of Chr-tet⁺ cells differ from the phenotypes of T_EM tet⁻ cells in the same subject. We also verified that these phenotypes did not depend on the viral load, the time from onset of symptoms, or disease progression. Notably, CD8 cells from the same donor recognizing different HIV epitopes could exhibit different population distributions (data not shown). These phenotypes were not all evaluated in the same experiment, so markers defining quadrants vary. In each experiment, markers defining quadrants were established based on isotype control staining of the sample concerned.