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Many autoimmune diseases are characterized by the production of autoantibodies. The current view is that CD4+ T follicular helper (Tfh) cells are the main subset regulating autoreactive B cells. Here we report a CXCR5+PD1+ Tfh subset of CD8+ T cells whose development and function are negatively modulated by Stat5. These CD8+ Tfh cells regulate the germinal center B cell response and control autoantibody production, as deficiency of Stat5 in CD8 T cells leads to an increase of CD8+ Tfh cells, resulting in the breakdown of B cell tolerance and concomitant autoantibody production. CD8+ Tfh cells share similar gene signatures with CD4+ Tfh, and require CD40L/CD40 and TCR/MHCI interactions to deliver help to B cells. Our study thus highlights the diversity of follicular T cell subsets that contribute to the breakdown of B-cell tolerance. B cell response and antibody production are generally facilitated by CD4+ follicular helper (Tfh) cells. Here the authors identify a subset of CXCR5+PD1+CD8+ Tfh cells that is normally suppressed by STAT5 signaling, so that STAT5 deficiency in mice increases the number of these CD8+ Tfh cells and induces concomitant production of autoantibodies. [ABSTRACT FROM AUTHOR]