CD8+ T cell exhaustion as a result of prolonged antigenic stimulation in the tumour microenvironment is thought to be a major mechanism by which tumours can escape immune surveillance. T cell exhaustion is characterised by co-expression of checkpoint inhibitor molecules such as PD-1, LAG-3 and TIM-3; reduced proliferative capacity; and diminished production of pro-inflammatory cytokines such as IL-2, IFN-γ and TNF-α and treatment with checkpoint inhibitor blockade such as Nivolumab (anti-PD-1) have shown great promise in the treatment of a subset of individuals and tumour types. However, resistance to these approaches is prevalent and there is a need to identify novel targets to provide alternative options for the rescue of T cell exhaustion and cancer treatment for use alone or potentially in combination with checkpoint inhibitor modulation. One such target is IKZF3, a transcription factor that is increased in murine models of T cell exhaustion and reduces IL-2 expression. Previously we presented an in vitro human T cell exhaustion assay whereby in vitro stimulated T cells phenotypically and functionally recapitulate the exhausted T cells found within the tumour microenvironment and now we demonstrate that exhaustion can be partially rescued by treatment with the IKZF3 small molecule inhibitor, Lenalidomide, alone and in combination with checkpoint inhibitor blockade. The use of small molecule inhibitors offers new avenues for reversing T cell exhaustion in cases of checkpoint inhibitor resistance and this platform delivers a robust assay allowing for assessment of small molecules or checkpoint inhibitors both individually and in combination. Citation Format: Joanne Hay, Francis Acklam, Darryl Turner, Mark Barbour, Preeti Singh, Courtney Grant, Hayley Gooding, Rhoanne McPherson, Justyna Rzepecka. Demonstrating restoration of T cell function in exhausted T cells with IKZF3 small molecule inhibitor, Lenalidomide [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5586.

BackgroundThe ability to reverse exhaustion in CD8+ T cells holds great promise for therapeutic intervention in oncology. Indeed, treatment with therapeutics targeted at checkpoint inhibitors, such as Nivolumab (anti-PD-1), have shown great promise in the treatment of a subset of individuals and tumour types. However, pre-clinical success does not always translate to success in clinical trials and resistance to these approaches is prevalent. As such, there is a pressing need to develop novel approaches that target alternative pathways for use alone or potentially in combination with checkpoint inhibitor modulation. A secondary need is the requirement for advanced assays that accurately recapitulate the pathways and cell phenotypes prevalent in the tumour environment.MethodsHere we describe the characteristics of an in vitro human T cell exhaustion assay whereby in vitro stimulated T cells phenotypically and functionally recapitulate the exhausted T cells found within the tumour microenvironment. We also demonstrate the effect of checkpoint blockade as well as small molecule inhibition of a novel target on the exhausted T cell phenotype.ResultsIn this assay, exhaustion can be partially but not fully reversed by treatment with anti-PD-1 alone. In addition, we demonstrate the effect of a small molecule inhibitor targeting IKZF3, a transcription factor shown to be upregulated in T cell exhaustion, on reversing T cell exhaustion alone and in combination with checkpoint inhibitor blockade.ConclusionsThese assays and approaches enable investigation into the ability of compounds to influence reversal of T cell exhaustion where anti-PD-1 treatment does not fully reverse the exhausted phenotype and offers the ability to test combination therapy approaches.AcknowledgementsThis work was aided by the valuable input and insight of Professor Stephen Anderton.Ethics ApprovalThe study obtained ethics approval from West Midlands – Black Country Research Ethics Committee under IRAS project ID 270936. All donors gave informed consent before taking part.

The induction of CD8+ T cell exhaustion, driven by the tumor microenvironment, is thought to be a major mechanism by which tumors can escape immune surveillance and are able to persist and progress. T cell exhaustion is typically characterized by the expression of co-inhibitory markers such as PD-1, LAG-3 and TIM-3 and a reduced capacity for pro-inflammatory cytokine production. Whilst treatment with therapeutics targeted at checkpoint inhibitors, such as Nivolumab (anti-PD-1), have shown great promise in the treatment of a subset of individuals and tumor types, resistance to these approaches is prevalent. As such, novel approaches are required in order to provide alternative options for the rescue of T cell exhaustion and cancer treatment. Here we describe the characteristics of an in vitro human T cell exhaustion assay whereby in vitro stimulated T cells phenotypically and functionally recapitulate the exhausted T cells found within the tumor microenvironment and where exhaustion can be partially rescued by treatment with anti-PD-1. Furthermore, we demonstrate the effect of treatment with an inhibitor of a novel target identified in exhausted T cells on T cell function; both through analysis of pro-inflammatory cytokine production and the ability to kill tumor cells. These assays and approaches enable investigation into the ability of compounds to influence reversal of T cell exhaustion where anti-PD-1 treatment does not fully reverse the exhausted phenotype and offers the ability to test combination therapy approaches. Citation Format: Rhoanne McPherson, Francis Acklam, Joanne Hay, Mark Barbour, Courtney Grant, Preeti Singh, Adriana Gambardella, Justyna Rzepecka, Stephen Anderton, Hayley Gooding. Implications of Targeting Novel Pathways in Exhausted T Cells for Immuno-Oncology Therapeutic Intervention [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB158.