Abstract 3865: A translational immuno-oncology platform to model T cell activation and Tex recovery in the tumor microenvironment
Authors: Nunan Robert , Gill Hannah , Aylott Ilona , Yap Michelle , Iannitti Tommaso , Harvey Louise , Jenkinson Rhiannon 
Published: September 2020

Abstract
The tumor microenvironment (TME) is a complex network, consisting of malignant tumor cells, stromal and immune cells, blood vessels, extracellular matrix and soluble factors. The immune system plays an important role in combating tumor growth, and multiple studies associate immune infiltrate with beneficial outcome. Various tractable immuno-oncology targets have been identified that influence the behavior of immune cells in the TME. These include Cytotoxic CD8+ T cells; which can directly kill tumour cells and produce pro-inflammatory cytokines such as IFNγ. However, CD8+ T cell activity and survival can be suppressed by the TME and chronic exposure leads to the generation of exhausted T cells (Tex) which have a lowered proliferative capacity and diminished capacity for pro-inflammatory cytokine production. Conversely, a regulatory subset of CD4+ T cells (Tregs) act to skew the TME towards immunosuppression. Here we describe human and murine models to assess both relative T cell subset activation and whether T cell exhaustion can be broken. Screening assays using T cell stimulants such as SEB or IL-2 can be utilised to select candidate therapeutics based on functional target engagement. SEB stimulation of PBMC reveals a robust additive effect on T cell activation by established and emerging checkpoint inhibitors. Use of more complicated flow based readouts allows the discrimination of immune subset responses. IL-2, a key lymphocyte activator, drives pSTAT5 expression with differing potency in PBMC subsets (regulatory T cells, conventional CD4 cells, CD8 T cells, NKT cells and NK cells). The ability to target specific subset activation could expand anti-tumour responses. Persistent antigenic stimulation, such as chronic exposure to the TME (MHC I restricted peptides), can lead to a CD8 Tex cell phenotype. Tex cell generation and reversal can be modelled using CEFT peptide pool and monitored via the expression of markers such as LAG-3, TIM-3, TOX and IFNγ. We show here that CD8 Tex cells respond positively to PD-1 blockade treatment, as seen by a restoration in cellular proliferation and increased IFNγ production. Therapeutic candidates identified through in vitro lead optimization can be assessed for their ability to activate T cells via a murine pharmacodynamic (PD) model. Transgenic OT-I CD8 T cells expressing TCR recognising OVA peptide (SIINFEKL) were transferred into syngeneic mice with SIINFEKL challenge in the presence of test therapeutic. Flow cytometry was used to determine OT-I T cell proliferation, activation and cytokine release. As seen in vitro, OT-I cell activation was increased by CPI treatment. We show here the powerful combination of using sophisticated in vitro and in vivo models to determine the effect of therapeutic intervention in an immuno-oncology context.
Citation Format: Robert Nunan, Hannah Gill, Ilona Aylott, Michelle Yap, Tommaso Iannitti, Louise Harvey, Rhiannon Jenkinson. A translational immuno-oncology platform to model T cell activation and Tex recovery in the tumor microenvironment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3865.