Pivotal roles of CD8+ T cells restricted by MHC class I-like molecules in autoimmune diseases

MHC class Ib-restricted CD8+ T cells possess strong tumoricidal activities

The importance of classical CD8+ T cells in tumor eradication is well acknowledged. However, the anti-tumor activity of MHC (major histocompatibility complex) Ib-restricted CD8+ T (Ib-CD8+ T) cells remains obscure. Here, we show that CX3CR1-expressing Ib-CD8+ T cells (Ib-restricted CD8+ T cells) highly express cytotoxic factors, austerely resist exhaustion, and effectively eliminate various tumors. These Ib-CD8+ T cells can be primed by MHC Ia (MHC class Ia molecules) expressed on various cell types for optimal activation in a Tbet-dependent manner. Importantly, MHC Ia does not allogeneically activate Ib-CD8+ T cells, rather, sensitizes these cells for T cell receptor activation. Such effects were observed when MHC Ia+ cells were administered to tumor-bearing Kb-/-Db-/-mice. A similar population of tumoricidal CX3CR1+CD8+ T cells was identified in wild-type mice and melanoma patients. Adoptive transfer of Ib-CD8+ T cells to wild-type mice inhibited tumor progression without damaging normal tissues. Taken together, we demonstrate that MHC class Ia can prime Ib-CD8+ T cells for robust tumoricidal activities.

CD8(+) T activation attenuates CD4(+) T proliferation through dendritic cells modification

Emerging evidence has suggested that CD8(+) T had modulatory function on CD4(+) T mediated autoimmune and inflammatory diseases. However, the underlying mechanisms remain unclear. In this study, we found that CD8(+) T activation inhibited OVA(323-339) antigen specific CD4(+) T cells proliferation in vitro and in vivo. Further investigation demonstrated that this immunosuppression largely depended on the soluble factor from activated CD8(+) T to modify the phenotype and functions of DCs. Moreover, not only the inhibitors for IDO or iNOS, but also IFN-γ neutralization markedly reversed this immunosuppression on OVA(323-339) antigen specific CD4(+) T cells proliferation. Interestingly, CD8(+) T cells absence aggravated the pathological damage in lung in OVA-induced asthma model, but alleviated by CD8(+) T transfer and activation. Thus, these findings suggested that activated CD8(+) T population exerted feedback regulation in DCs modification, and then attenuated CD4(+) T mediated immune response.

Requirements for eomesodermin and promyelocytic leukemia zinc finger in the development of innate-like CD8+ T cells

Conventional and nonconventional T cell development occur in the thymus. Nonconventional thymocytes that bear characteristics typically associated with innate immune cells are termed innate-like lymphocytes (ILLs). Mice harboring a tyrosine to phenylalanine mutation in the adaptor protein Src homology 2 domain-containing leukocyte protein of 76 kDa at residue 145 (Y145F mice) develop an expanded population of CD8(+)CD122(+)CD44(+) ILLs, typified by expression of the T-box transcription factor eomesodermin. Y145F mice also have an expanded population of γδ T cells that produce copious amounts of IL-4 via a mechanism that is dependent on the BTB-ZF transcription factor promyelocytic leukemia zinc finger. Using mice with T cell-specific deletion of Eomes, we demonstrate that this transcription factor is required for CD8(+) ILL development in Y145F as well as wild-type mice. Moreover, we show that promyelocytic leukemia zinc finger and IL-4 are also required for the generation of this ILL population. Taken together, these data shed light on the cell-intrinsic and cell-extrinsic factors that drive CD8(+) ILL differentiation.

Polyclonal MHC Ib-restricted CD8+ T cells undergo homeostatic expansion in the absence of conventional MHC-restricted T cells

Naive T cells have the capacity to expand in a lymphopenic environment in a process called homeostatic expansion, where they gain a memory-like phenotype. Homeostatic expansion is dependent on competition for a number of factors, including growth factors and interactions with their selecting self-MHC molecules. In contrast to conventional T cells, it is unclear whether class Ib-restricted CD8+ T cells have a capacity to undergo homeostatic expansion. In this study, we demonstrate that polyclonal MHC Ib-restricted CD8+ T cells can undergo homeostatic expansion and that their peripheral expansion is suppressed by conventional MHC-restricted T cells. The acute depletion of CD4+ T cells in MHC class Ia-deficient Kb-/-Db-/- mice led to the substantial expansion of class Ib-restricted CD8+ T cells. Adoptive transfer of class Ib-restricted CD8+ T cells to congenic lymphopenic recipients revealed their ability to undergo homeostatic expansion in a MHC Ib-dependent manner. To further study the homeostatic expansion of MHC Ib-restricted T cells in the absence of all conventional MHC-restricted T cells, we generated mice that express only MHC Ib molecules by crossing H-2Kb-/-Db-/- with CIITA-/- mice. CD8+ T cells in these mice exhibit all of the hallmarks of naive T cells actively undergoing homeostatic expansion with constitutive memory-like surface and functional phenotype. These findings provide direct evidence that MHC Ib-restricted CD8+ T cells have the capacity to undergo homeostatic expansion. Their peripheral expansion is suppressed under normal conditions by a numerical excess of conventional MHC class Ia- and class II-restricted T cells.