Functionally inert HIV-specific cytotoxic T lymphocytes do not play a major role in chronically infected adults and children

The highly sensitive quantitation of virus-specific CD8(+) T cells using ma jor histocompatibility complex-peptide tetramer assays has revealed higher levels of cytotoxic T lymphocytes (CTLs) in acute and chronic virus infecti ons than were recognized previously. However, studies in lymphocytic chorio meningitis virus infection have shown that tetramer assays may include meas urement of a substantial number of tetramer-binding cells that are function ally inert. Such phenotypically silent CTLs, which lack cytolytic function and do not produce interferon (IFN)-gamma, have been hypothesized to explai n the persistence of virus in the face of a quantitatively large immune res ponse, particularly when CD4 help is impaired. In this study, we examined t he role of functionally inert CTLs in chronic HIV infection. Subjects studi ed included children and adults (n = 42) whose viral loads ranged from < 50 to > 100,000 RNA copies/ml plasma. Tetramer assays were compared with thre e functional assays: enzyme-linked immuno-spot (Elispot), intracellular cyt okine staining, and precursor frequency (limiting dilution assay [LDA]) cyt otoxicity assays. Strong positive associations were observed between cell n umbers derived by the Elispot and the tetramer assay (r = 0.90). An even st ronger association between tetramer-derived numbers and intracellular cytok ine staining for IFN-gamma was present (r = 0.97). The majority (median 76% ) of tetramer-binding cells were consistently detectable via intracellular IFN-gamma cytokine staining. Furthermore, modifications to the LDA, using a low input cell. number into each well, enabled LDAs to reach equivalence w ith the other methods of CTL enumeration. These data together show that fun ctionally inert CTLs do not play a significant role in chronic pediatric or adult HIV infection.