Impaired T cell proliferation by ex vivo BET-inhibition impedes adoptive immunotherapy in a murine melanoma model

ABSTRACT

Activation of naïve CD8⁺ T cells stimulates proliferation and differentiation into cytotoxic T-lymphocytes (CTLs). Adoptive T Cell Therapy (ACT) involves multiple rounds of ex vivo activation to generate enough CTLs for reinfusion into patients, but this drives differentiation into terminal effector T cells. Less differentiated CTL populations, such as stem cell memory T cells, are more ideal candidates for ACT because of increased self-renewal and persistent properties. Ex vivo targeting of T cell differentiation with epigenetic modifiers is a potential strategy to improve cytotoxic T-lymphocyte (CTL) generation for ACT. We established a pipeline to assess the effects of epigenetic modifiers on CD8⁺ T cell proliferation, differentiation, and efficacy in a preclinical melanoma model. Single treatment with epigenetic modifiers inhibited T cell proliferation in vitro, producing CD44^hiCD62L^hi effector-like T cells rather than a stem cell memory T cell phenotype. Most epigenetic modifying agents had no significant effect on ACT efficacy with the notable exception of the bromodomain and extraterminal (BET)-inhibitor JQ1 which was associated with a decrease in efficacy compared to unmodified T cells. These findings reveal the complexity of epigenetic targeting of T cell differentiation, highlighting the need to precisely define the epigenetic targeting strategies to improve CTL generation for ACT.

KEYWORDS:

• Cancer immunotherapy
• adoptive cell therapy
• T cell differentiation
• melanoma
• cytotoxic T lymphocytes
• BET inhibition

Acknowledgments

The authors thank the Telethon Kids Institute Bioresources team for their excellent animal care and the Telethon Kids Flow Cytometry Facility for assistance in sorting experiments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by a project grant and Fellowship from the Children’s Leukaemia and Cancer Research Foundation, Western Australia (to MNC). JC was supported by a Cancer Council Western Australia Suzanne Cavanagh Early Career Investigator Award, and a US Department of Defense Peer Reviewed Cancer Program Cancer Horizon Award. JW was supported by fellowships from the NHMRC and Cancer Council WA.