The T-cell receptor repertoire of tumor-infiltrating regulatory T lymphocytes is skewed towards public sequences Short title: T-cell repertoire of tumor-infiltrating Treg Authors

184 words Figure/ table count: 7 figures / tables Reference count: 40 Disclosure of potential conflicts of interest: The authors have no conflicting interests. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. ABSTRACT The accumulation of CD4 + T regulatory cells (Treg) in tumor tissue is a widely described phenomenon in mouse models and in human cancer patients. Understanding the mechanisms by which Treg migrate and accumulate in tumors is important because they strongly influence the potential efficacy of many immunotherapies. In this study, we used immunoscope technology to analyze the T-cell receptor (TCR) repertoire of tumor-infiltrating T cells in non-TCR transgenic mice. Both tumor-infiltrating Tregs and T effector cells (Teff) displayed sequence profiles in the CDR3 region which were characteristic of biased repertoires seen during clonal cell expansions, implying that strong T-cell responses have occurred within the tumor tissue. By comparing the TCR sequences of tumor-infiltrating Tregs, we obtained evidence of the presence of so-called public TCR sequences that are common to many individuals yet were tumor-specific in nature. Such comparisons also suggested that the Treg-Teff conversion process is not an active process at the tumor site or tumor-draining lymph nodes. Our findings strongly suggest that Treg infiltration of tumor tissue is followed by marked proliferation of a few dominant T cell clones in the tumor. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.