628 IL-2 augments immTAC-dependent T cell activation and tumour cell killing

Background Immune mobilising TCRs against cancer (ImmTAC) are a novel class of soluble bispecifics which bind both CD3 on T cells and specific peptide/MHC antigen on tumour cells.1 Four ImmTAC molecules are currently in clinical trials, one of these being tebentafusp which targets a gp100-derived HLA-A*02:01 peptide. Tebentafusp has demonstrated monotherapy activity in cutaneous and uveal melanoma.2 3 Here, we explored approaches to enhance ImmTAC-mediated T cell activation and anti-tumour activity. We hypothesised that the cytokine IL-2, which is approved for treatment of cutaneous melanoma and renal cell cancer, might augment ImmTAC-mediated T cell responses.4 Methods Tumour cell killing was determined by IncuCyte assay. Cell lines, healthy donor PBMC, tumour cell populations and cytokines including IL-2 (Proleukin, Novartis) were sourced commercially. ImmTAC molecules recognising peptides from either gp100 or the tumour antigen PRAME5 were used for in vitro assays. Surface marker expression was determined by flow cytometry. Results Clinically relevant IL-2 levels (60 to 600U/ml) improved both the speed (maximum killing after ~15 hours following 60 U/ml IL-2 pre-treatment versus ~30 hours without IL-2) and potency (mean EC50 13.6pM with IL-2 versus 81.2pM in absence of supplementation) of antigen-specific ImmTAC-dependent tumour killing in vitro by either PBMC or purified T cell populations. Addition of IL-2 was sufficient to improve killing responses when either T cell numbers or target peptide:HLA levels were limiting, and IL-2-cultured TILs exhibited ImmTAC-dependent killing. Dose-dependent cytokine enhancement of ImmTAC-mediated killing response was also consistent with increased surface CD3 and CD69 expression on T cell populations. Notably, weak PBMC donor populations with minimal intrinsic killing activity could be induced to provide robust ImmTAC-dependent tumour cell killing responses by physiological IL-2 treatment. Conclusions These results suggest that the anti-tumour activity of ImmTAC molecules could be enhanced by combination treatment with the cytokine IL-2. Ethics Approval The study was approved by the South Central - Oxford A Research Ethics Committee (UK), REC reference 13/SC/0226 References Lowe, et al. Cancer Treat Rev 2019. Vol.77, p35–432. Middleton, et al. ( 2019) J. Clin. Oncol. 37, no. 15_suppl (May 20, 2019). Shoustari, et al. SITC poster 2019, J. Immunother Cancer 2019;7. Tang and Harding Cytokine: X 2019 Moureau, et al. ( 2020) AACR poster