Intratumoral Convergence of the TCR Repertoires of Effector and Foxp3+ CD4+ T cells

Michal Kuczma,Grzegorz A Rempala,Magdalena Kopij,Cong-Yi Wang,Iwona Pawlikowska,Piotr Kraj

doi:10.1371/journal.pone.0013623

Abstract

The presence of Foxp3+ regulatory CD4+ T cells in tumor lesions is considered one of the major causes of ineffective immune response in cancer. It is not clear whether intratumoral Treg cells represent Treg cells pre-existing in healthy mice, or arise from tumor-specific effector CD4+ T cells and thus representing adaptive Treg cells. The generation of Treg population in tumors could be further complicated by recent evidence showing that both in humans and mice the peripheral population of Treg cells is heterogenous and consists of subsets which may differentially respond to tumor-derived antigens. We have studied Treg cells in cancer in experimental mice that express naturally selected, polyclonal repertoire of CD4+ T cells and which preserve the heterogeneity of the Treg population. The majority of Treg cells present in healthy mice maintained a stable suppressor phenotype, expressed high level of Foxp3 and an exclusive set of TCRs not used by naive CD4+ T cells. A small Treg subset, utilized TCRs shared with effector T cells and expressed a lower level of Foxp3. We show that response to tumor-derived antigens induced efficient clonal recruitment and expansion of antigen-specific effector and Treg cells. However, the population of Treg cells in tumors was dominated by cells expressing TCRs shared with effector CD4+ T cells. In contrast, Treg cells expressing an exclusive set of TCRs, that dominate in healthy mice, accounted for only a small fraction of all Treg cells in tumor lesions. Our results suggest that the Treg repertoire in tumors is generated by conversion of effector CD4+ T cells or expansion of a minor subset of Treg cells. In conclusion, successful cancer immunotherapy may depend on the ability to block upregulation of Foxp3 in effector CD4+ T cells and/or selectively inhibiting the expansion of a minor Treg subset.

Highlights

The observation that tumor antigen-specific B and T cells are activated in the course of tumor growth led to the presumption that augmenting the immune system function will lead to the eradication of tumor cells [1]
Immunotherapy protocols used so far have had only a limited success what was attributed to poor recruitment of antigen specific T cells into tumor lesions, inadequate stimulation by antigens derived from tumor cells causing T cell anergy instead of T cell activation and, in particular, to the presence of regulatory T cells (Treg) expressing a transcription factor Foxp3 [2,3,4]
Emerging data suggest that the population of Foxp3+ Treg cells is heterogeneous in humans and mice in terms of its origin and functional properties [19,20,24,26]

Summary

Introduction

The observation that tumor antigen-specific B and T cells are activated in the course of tumor growth led to the presumption that augmenting the immune system function will lead to the eradication of tumor cells [1]. Immunotherapy protocols used so far have had only a limited success what was attributed to poor recruitment of antigen specific T cells into tumor lesions, inadequate stimulation by antigens derived from tumor cells causing T cell anergy instead of T cell activation and, in particular, to the presence of regulatory T cells (Treg) expressing a transcription factor Foxp3 [2,3,4]. Despite their importance for cancer immunity, the origin of Treg cells in tumors remains little known. Removal or inactivation of Treg cells led to enhanced antitumor immune response and better efficacy of cancer vaccines [12,13,14,15]

Methods

Results

Conclusion