Effector CD8⁺ T cell IFN-γ production and cytotoxicity are enhanced by mild hyperthermia

Abstract

Purpose: Clinical trials combining hyperthermia with radiation and/or chemotherapy for cancer treatment have resulted in improved overall survival and control of local recurrences. The contribution of thermally enhanced anti-immune function in these effects is of considerable interest, but not understood; studies on the fundamental effects of elevated temperature on immune effector cells are needed. The goal of this study is to investigate the potential of mild hyperthermia to impact tumour antigen-specific (Ag) effector CD8⁺ T cell functions.

Method: Pmel-1 Ag-specific CD8⁺ T cells were exposed to mild hyperthermia and tested for changes in IFN-γ production and cytotoxicity. Additionally, overall plasma membrane organisation and the phosphorylation of signalling proteins were also investigated following heat treatment.

Results: Exposing effector Pmel-1-specific CD8⁺ T cells to mild hyperthermia (39.5°C) resulted in significantly enhanced Ag-specific IFN-γ production and tumour target cell killing compared to that seen using lower temperatures (33° and 37°C). Further, inhibition of protein synthesis during hyperthermia did not reduce subsequent Ag-induced IFN-γ production by CD8⁺ T cells. Correlated with these effects, we observed a distinct clustering of GM1⁺ lipid microdomains at the plasma membrane and enhanced phosphorylation of LAT and PKCθ which may be related to an observed enhancement of Ag-specific effector CD8⁺ T cell IFN-γ gene transcription following mild hyperthermia. However, mitogen-mediated production of IFN-γ, which bypasses T cell receptor activation with antigen, was not enhanced.

Conclusions: Antigen-dependent effector T cell activity is enhanced following mild hyperthermia. These effects could potentially occur in patients being treated with thermal therapies. These data also provide support for the use of thermal therapy as an adjuvant for immunotherapies to improve CD8⁺ effector cell function.

• cytotoxicity
• fever
• hyperthermia
• interferon-γ
• T lymphocytes

Acknowledgements

We thank members of the Department of Flow and Image Cytometry Core Facility as well as the Roswell Park Cancer Institute Animal Resource Facility. We also thank Jeanne Prendergast for her assistance in the lab and Bonnie Hylander for her help in reviewing this manuscript.

Declaration of interest: This work was supported by grants NIH R01 CA135368-01A1, R01 CA071599-11, 2 T32 CA085183 Immunology Department Training Grant, and the Roswell Park Cancer Institute Core grant CA16056. The authors alone are responsible for the content and writing of the paper.