Tim-3 identifies exhausted follicular helper T cells in breast cancer patients

Breast cancer is the most common cancer diagnosed in women worldwide. Although a series of treatment options have improved the overall 5-year survival rate to 90%, individual responses still vary from patient to patient. New evidence suggested that the infiltration of CXCL13-expressing CD4+ follicular helper cells (Tfh) in breast tumor predicted better survival. Here, we examined the regulation of Tfh function in breast cancer patients in depth. We found that the frequencies of circulating Tfh cells were not altered in breast cancer patients compared to healthy controls. However, the expression of PD-1 and Tim-3 in Tfh cells was significantly elevated in breast cancer patients. Interestingly, we observed a preferential upregulation of PD-1 in Tim-3+ Tfh cells compared to Tim-3− Tfh cells. Coexpression of PD-1 and Tim-3 is typically a hallmark of functional exhaustion in chronic virus infections and tumor. To examine whether Tim-3+ identifies exhausted Tfh cells, we stimulated Tfh cells with anti-CD3/CD28, and found that Tim-3+ T cells expressed reduced frequencies of chemokine CXCL13 and cytokine interleukin 21 (IL-21), and contained fewer proliferating cells, than Tim-3− Tfh cells. Compared to those cocultured with Tim-3− Tfh cells, naive B cells cocultured with Tim-3+ Tfh cells resulted in significantly less IgM, IgG and IgA production after 12 day incubation, demonstrating a reduction in Tim-3+ Tfh-mediated B cell help. Moreover, the frequencies of Tim-3+ Tfh cells in resected breast tumor were further upregulated than autologous blood, suggesting a participation of Tim-3+ Tfh cells in tumor physiology. Overall, the data presented here provided new insight in the regulation of Tfh cells in breast cancer patients.