Examination of CD8+ T cell function in humans using MHC class I tetramers: similar cytotoxicity but variable proliferation and cytokine production among different clonal CD8+ T cells specific to a single viral epitope

Role of effector cell-derived IL-4, IL-5, and perforin in early and late stages of type 2 CD8 effector cell-mediated tumor rejection

Type 2 CD8 T cells (Tc2) secrete IL-4 and IL-5 and display perforin-dependent cytolysis in vitro. Using an OVA-transfected B16-melanoma model, we show that tumor-reactive Tc2 effector cells accumulated at the tumor site and induced tumor regression that enhanced survival in mice with pulmonary tumors. Transfer of perforin-deficient Tc2 cells generated from perforin gene knockout mice showed no differences in therapeutic efficiency when compared with wild-type Tc2 cells. In contrast, Tc2 cells derived from select cytokine gene-deficient mice showed that therapeutic effects were dependent on effector cell-derived IL-4 and IL-5 that led to a local elevation in lung-derived chemoattractants and accumulation of activated host-derived CD8/CD44(high), CD4/CD44(high), and OVA-specific tetramer-positive CD8 cells in vivo. Host-derived T and non-T immune cells increased in the lung over time and correlated with an elevated production of type 1-related chemokines. Conversely, donor Tc2 cell numbers markedly diminished at later times, suggesting that prolonged therapeutic responses were due to host-derived mechanisms. Moreover, type 1 host responses were detectable with increased levels of IFN-gamma production by lung-derived CD4 and CD8 T cells from surviving Tc2-treated mice. Transfer of Tc2 cells into IFN-gamma-deficient tumor-bearing mice was markedly less effective then into wild-type mice, suggesting that host-derived IFN-gamma-dependent mechanisms play a role in Tc2-mediated antitumor responses.

Uncoupling p70(s6) kinase activation and proliferation: rapamycin-resistant proliferation of human CD8(+) T lymphocytes

Rapamycin is a fungal macrolide that inhibits the proliferation of T cells. Studies in both animals and humans have found that rapamycin significantly reduces graft rejection. However, though CD8(+) T cells are involved in graft infiltration and rejection, little is known regarding the effects of rapamycin on CD8(+) human T cell responses. In this study, we examined the mechanism of rapamycin-induced inhibition of Ag-driven activation of CD8(+) T cells. Surprisingly, a heterogeneous proliferative response in the presence of rapamycin was observed among different Ag-specific CD8(+) T cell clones; this was also observed in CD8(+) peripheral blood T cells activated with TCR cross-linking ex vivo. Inhibition of T cell proliferation by rapamycin was controlled by both the strength of signal delivered through the Ag receptor as well as the specific costimulatory signals received by the T cell. Rapamycin-resistant proliferation occurred despite inhibition of p70(s6) kinase activity. Moreover, rapamycin-resistant proliferation of the CD8(+) T cell clones was blocked by anti-IL-2 Abs, suggesting that while some of the parallel pathways triggered by IL-2R signaling are sensitive to the effects of rapamycin, others account for the Ag-driven rapamycin resistance. These data provide a new framework for examining the specific mechanism of action of rapamycin in human disease.