Apoptosis of epitope-specific antiretroviral cytotoxic T lymphocytes via fas ligand-fas interactions

C57BL/6 (B6; H-2(b)) mice are capable of mounting a vigorous AKR/Gross Murine Leukemia Virus (MuLV)-speciflc cytotoxic T lymphocyte (CTL) response to AKR/Gross MuLVs whereas AKR.H-2(b) congenic mice, although carrying the responder H-2b major histocompatibility haplotype, are specifically nonresponsive. Furthermore, when viable AKR.H-2(b) spleen cells are cocultured with primed responder B6 antiviral precursor CTLs, the AKR.H-2(b) cells function as "veto" cells that actively mediate the inhibition by apoptosis of B6 antiviral CTL generation in a contact-dependent, MHC-restricted, and veto cell Fas ligand (FasL)/responder T cell Fas-dependent manner. In the present study we show that antigen-specific, antiviral CTLs that survive apoptotic inhibition by AKR.H-2(b) veto cells display a less activated cell surface phenotype, and are less able to bind specific MHC-peptide tetramers, including on a per-T cell receptor (TcR) basis. In addition, surviving antiviral CTLs also appeared to be functionally deficient, based on both their reduced ability to lyse specific target cells and to produce interferon (IFN)-gamma. Carboxyfluorescein diacetate succinimidyl ester staining confirmed that AKR/Gross MuLV-specific CTLs proliferated less extensively when AKR.H-2(b) veto cells were included in cocultures. AKR/Gross MuLV-specific effector CTLs as well as memory CTLs were each efficiently targeted for inhibition by AKR.H-2(b) veto cells. Attempts to enhance the quality of the priming by multiple in vivo immunizations did not alter the capacity of the AKR.H-2(b) cells to inhibit the antiviral CTL response. These results further characterize the nature of the interaction between veto cells and antiviral CTLs, and underscore the efficiency of veto cell-mediated inhibition of the CTL response.