Regulatory T cell-mediated immunosuppression orchestrated by cancer: towards an immuno-genomic paradigm for precision medicine

Abstract

Accumulating evidence indicates that aberrant signalling stemming from genetic abnormalities in cancer cells has a fundamental role in their evasion of antitumour immunity. Immune escape mechanisms include enhanced expression of immunosuppressive molecules, such as immune-checkpoint proteins, and the accumulation of immunosuppressive cells, including regulatory T (Treg) cells, in the tumour microenvironment. Therefore, Treg cells are key targets for cancer immunotherapy. Given that therapies targeting molecules predominantly expressed by Treg cells, such as CD25 or GITR, have thus far had limited antitumour efficacy, elucidating how certain characteristics of cancer, particularly genetic abnormalities, influence Treg cells is necessary to develop novel immunotherapeutic strategies. Hence, Treg cell-targeted strategies based on the particular characteristics of cancer in each patient, such as the combination of immune-checkpoint inhibitors with molecularly targeted agents that disrupt the immunosuppressive networks mediating Treg cell recruitment and/or activation, could become a new paradigm of cancer therapy. In this Review, we discuss new insights on the mechanisms by which cancers generate immunosuppressive networks that attenuate antitumour immunity and how these networks confer resistance to cancer immunotherapy, with a focus on Treg cells. These insights lead us to propose the concept of ‘immuno-genomic precision medicine’ based on specific characteristics of cancer, especially genetic profiles, that correlate with particular mechanisms of tumour immune escape and might, therefore, inform the optimal choice of immunotherapy for individual patients. Increasing evidence indicates that signalling networks activated downstream of oncogenic alterations contribute fundamentally to cancer immune evasion, including by promoting the accumulation of regulatory T (Treg) cells and other immunosuppressive cells in the tumour microenvironment (TME). Herein, the authors discuss the mechanisms via which cancers engage Treg cells to evade antitumour immunity, as well as the characteristics of Treg cells in the TME and their roles in resistance to immune-checkpoint inhibitors. Considering these aspects, they propose the concept of ‘immuno-genomic cancer evolution’ for tumorigenesis and the related paradigm of ‘immuno-genomic precision medicine’, postulating that the specific characteristics of cancer, especially genetic profiles that correlate with particular immunosuppressive networks in the TME, are likely to inform individualized strategies for combining molecularly targeted agents with immunotherapies.