IL-15 induces unspecific effector functions in human peptide-specific CD8+ T-cell cultures

Circulating rotavirus-specific T cells have a poor functional profile

Frequencies of circulating T cells producing IFN-γ, TNF-α, and IL-2, and percentages of T cells proliferating after stimulation with rotavirus (RV), tetanus toxoid, and influenza were evaluated in PBMC derived from healthy adults and children. In addition, the potential anergic state of RV-specific T cells was analyzed by stimulation of PBMC with RV antigen in the presence of three anergy inhibitors (rIL-2, rIL-12, or DGKα-i). The quality and magnitude of RV-T cell responses were significantly lower than those of tetanus toxoid and influenza antigens. RV-CD4 T cell response was enriched in monofunctional IFN-γ(+) cells, while influenza-CD4 and tetanus toxoid-CD4 T cell responses were enriched in multifunctional T cells. Moreover, rIL-2--unlike rIL-12 or DGKα-i--increased the frequencies of RV-CD4 TNF-α(+), CD4 IFN-γ(+), and CD8 IFN-γ(+) cells. Thus, circulating RV-T cells seem to have a relatively poor functional profile that may be partially reversed in vitro by the addition of rIL-2.

Functional profile of human influenza virus-specific cytotoxic T lymphocyte activity is influenced by interleukin-2 concentration and epitope specificity

The ability of influenza A virus-specific cytotoxic T lymphocytes (CTL) to degranulate and produce cytokines upon antigenic restimulation was studied in four HLA-A*0101 and HLA-A*0201 positive subjects. Peripheral blood mononuclear cells of these subjects were stimulated with influenza A virus in the presence of high or low interleukin (IL)-2 concentrations. CD8(+) T cell populations specific for the HLA-A*0101 restricted epitope NP(44-52) and the HLA-A*0201 restricted epitope M1(58-66) were identified by positive staining with tetramers of peptide major histocompatibility complexes (MHC) (NP-Tm and M1-Tm, respectively). Within these populations, the proportion of cells mobilizing CD107a, or expressing interferon (IFN)-gamma and tumour necrosis factor-(TNF)-alpha upon short-term peptide restimulation was determined by flow cytometry. Independent of IL-2 concentrations, large subject-dependent differences in the mobilization of CD107a and expression of IFN-gamma and TNF-alpha by both NP- and M1-specific T cells were observed. In two of the four subjects, the functional profile of NP-Tm(+) and M1-Tm(+) cells differed considerably. Overall, no difference in the proportion of NP-Tm(+) or M1-Tm(+) cells expressing CD107a was observed. The proportion of M1-Tm(+) cells that produced IFN-gamma (P < 0.05) was larger than for NP-Tm(+) cells, independent of IL-2 concentration. When cultured under IL-2(hi) concentrations higher TNF-alpha expression was also observed in M1-Tm(+) cells (P < 0.05). The IL-2 concentration during expansion of virus-specific cells had a profound effect on the functionality of both M1-Tm(+) and NP-Tm(+) cells.

CD56+-T-cell responses to bacterial superantigens and immune recognition of attenuated vaccines

Natural killer T (NKT) cells, coexpressing natural killer (NK) and T-cell receptors (TCR), are associated with immunity to viruses, tumors, and parasites. A well-characterized subclass of these NKT cells expresses biased TCR and recognizes glycolipids such as alpha-galactoceramide, which is found naturally only in marine sponges and presented by the cell surface glycoprotein CD1d. However, a larger number of T cells present in human blood coexpress the NK marker CD56 and unbiased TCR and do not appear to require CD1 for antigen presentation. Observing high frequencies of CD4 and CD8 coreceptor expression in human CD56+ T cells, we examined the potential role of major histocompatibility complex (MHC) class II molecules in the activation of these cells. Activation of mononuclear cells with bacterial superantigens presented by MHC class II molecules resulted in increased frequency of CD56+ T cells. Primarily, CD4+ cells within the CD56+-T-cell population responded to the bacterial superantigens, and cytokine expression profiles were Th1-like. Further, increased levels of T cells expressing CD56 were observed in mononuclear cell cultures responding to a Staphylococcus aureus vaccine or tetanus toxoid. Collectively, our data suggest that a significant number of CD56+ T cells recognize pathogen-associated ligands in association with MHC class II molecules.

Role of NKG2D signaling in the cytotoxicity of activated and expanded CD8+ T cells

Activating and expanding T cells using T-cell receptor (TCR) cross-linking antibodies and interleukin 2 (IL-2) results in potent cytotoxic effector cells capable of recognizing a broad range of malignant cell targets, including autologous leukemic cells. The mechanism of target cell recognition has previously been unknown. Recent studies show that ligation of NKG2D on natural killer (NK) cells directly induces cytotoxicity, whereas on T cells it costimulates TCR signaling. Here we demonstrate that NKG2D expression is up-regulated upon activation and expansion of human CD8+ T cells. Antibody blocking, redirected cytolysis, and small interfering RNA (siRNA) studies using purified CD8+ T cells demonstrate that cytotoxicity against malignant target cells occurs through NKG2D-mediated recognition and signaling and not through the TCR. Activated and expanded CD8+ T cells develop cytotoxicity after 10 to 14 days of culture, coincident with the expression of the adapter protein DAP10. T cells activated and expanded in low (30 U/mL) and high (300 U/mL) concentrations of IL-2 both up-regulated NKG2D expression equally, but only cells cultured in high-dose IL-2 expressed DAP10 and were cytotoxic. Collectively these results establish that NKG2D triggering accounts for the majority of major histocompatibility complex (MHC)-unrestricted cytotoxicity of activated and expanded CD8+ T cells, likely through DAP10-mediated signaling.