CD8 T cells can play both a protective and pathogenic role in inflammation and autoimmune development. Recent studies have highlighted the ability of CD8 T cells to function as T follicular helper (Tfh) cells in the germinal center in the context of infection. However, whether this phenomenon occurs in autoimmunity and contributes to autoimmune pathogenesis is largely unexplored. In this study, we show that CD8 T cells acquire a CD4 Tfh profile in the absence of functional regulatory T cells in both the IL-2-deficient and scurfy mouse models. Depletion of CD8 T cells mitigates autoimmune pathogenesis in IL-2-deficient mice. CD8 T cells express the B cell follicle-localizing chemokine receptor CXCR5, a principal Tfh transcription factor Bcl6, and the Tfh effector cytokine IL-21. CD8 T cells localize to the B cell follicle, express B cell costimulatory proteins, and promote B cell differentiation and Ab isotype class switching. These data reveal a novel contribution of autoreactive CD8 T cells to autoimmune disease, in part, through CD4 follicular-like differentiation and functionality.

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CXCR5+CD8 T cells have attracted significant interest within multiple areas of immunology, cancer, and infection. This is in part due to their apparent dual functionality. These cells perform as cytotoxic cells in a variety of infection states including LCMV, HBV, HIV and SIV. However, CXCR5+CD8 T cells also associate with B cells in peripheral organs and function to stimulate B cell proliferation, antibody/B cell receptor class-switch, and antibody production. CXCR5+CD8 T cells are similar to CXCR5+CD4 T follicular helpers in their genetic make-up, B cell interactions, and functionality despite possessing elevated programmed cell death 1 and cytotoxic proteins. Within cancer CXCR5+CD8 T cells have risen as potential prognostic markers for overall survival and are functionally cytotoxic within tumor microenvironments. In inflammatory disease and autoimmunity, CXCR5+CD8 T cells are implicated in disease progression. During viral infection and cancer, CXCR5 expression on CD8 T cells generally is indicative of progenitor memory stem-like exhausted cells, which are more responsive to immune checkpoint blockade therapy. The use of immune checkpoint inhibitors to overcome immune exhaustion in cancer, and subsequent consequence of immune adverse events, highlights the dual nature of the cellular immune response. This review will detail the functionality of CXCR5+CD8 T cells in cancer and autoimmunity with potential repercussions during immune checkpoint blockade therapy discussed.

IL-2Rα is required to generate the high affinity receptor for IL-2, a cytokine important in immune proliferation, activation, and regulation. Mice deficient in IL-2Rα (IL-2Rα-KO) develop systemic autoimmune disease and die from severe anemia between 18-80 days of age. These mice develop kinetically differing autoimmune disease, with approximately a quarter dying by 21 days of age and half dying after 30 days. This research aims to define immune parameters that distinguish cohorts of mice that develop early- and late-stage autoimmune disease in the IL-2Rα-KO genetic background. To investigate these differences, we evaluated complete blood counts (CBC), antibody binding of RBCs, T cell numbers and activation, and hematopoietic progenitor changes, to assess the extent of peripheral autoimmune hemolytic anemia and bone marrow failure. Early onset disease correlated with anti-RBC antibodies and lower hematocrit on day 19. We also found that predicted late stage-disease IL-2Rα-KO mice have higher numbers of developing memory CD4 and CD8 T cells and reduced AIHA at early ages. The expansion of CD8 T cells seen in IL-2R -KO mice is driven by unimpaired IL-2 signaling which correlated with increased IL-2RP expression. Using a simple CBC we were able to predict disease kinetics to explore mechanisms underlying early and late disease.