Secondary iTreg generation has a major impact on tumor-infiltrating Treg in cancer patients
Maria Xydia1,2*, Eliana Ruggiero3,4, Svetlana Mastitskaya4 , Maria Pritsch3 , Manfred Schmidt3,4, Christof von Kalle3,4 and Philipp Beckhove1,2 1RCI Regensburg Centre for Interventional Immunology, 2University of Regensburg, 3German Cancer Research Centre (DKFZ), 4National Centre for Tumor Diseases, 5Heidelberg University Hospital, Germany *Corresponding Author
CD4+ regulatory T cells (Treg) are detrimental for cancer-immunity, as they hinder tumor-specific effector T cells (Teff) from tumor eradication. Increased Treg numbers in various cancer types correlate with poor patient prognosis. In animal models Treg enrichment may result from the expansion of thymic natural Treg but also from the conversion of conventional T cells (Tconv) into induced Treg (iTreg) under tumor-suppressive conditions. However, little is known about tumor-specific iTreg generation in humans and its impact on the TCR repertoire of peripheral Treg. Therefore, we compared the TCRβ pool of total Treg and tumor-reactive Teff or total Tconv in peripheral blood of breast cancer patients or healthy individuals, as negative control, to identify overlapping TCRs, representing iTreg. In addition, using high-throughput single-cell transcriptome sequencing combined with TCRαβ characterization we analyze the functional profile of individual Treg/Tconv clones to elucidate their role in anti-tumor immunity in humans. No major TCR overlap was observed between circulating Treg and tumor-reactive Teff or total Tconv in patients and healthy individuals. Nevertheless, within the tumor Treg and Tconv shared dominant highly-expanded clones, representing 10-65% of the tumor-infiltrating Treg pool but with no effect in the blood. Taken together, our data suggest that intratumoral secondary Treg conversion from dominant Tconv clones may have a major impact on the tumor-infiltrating but not on the circulating Treg population.