ESTRO 2023 - Abstract Book

S201

Saturday 13 May

ESTRO 2023

Purpose or Objective Early clinical trials have provided evidence for RT-induced systemic effects in conjunction with α PD-1 or IL-2 in metastatic patients, but strong abscopal responses are clinically rare. Dual combinations of α PD-1 with more effective and less toxic IL-2 derivatives, e.g., CD122-directed pegylated IL-2, are also currently under investigation. Whether a combination of RT, α PD-1, and CD122-directed IL-2/anti-IL-2 complexes (IL-2c) can increase abscopal effects against established non-irradiated tumors is unknown. Also, in-depth analyses of the differentiation of tumor-specific CD8+ T cells have not yet been reported for α PD-1/IL-2c in combination with RT. We investigated how adding IL-2c to hRT/ α PD-1 affects tumor-specific CD8+ T cell differentiation in mouse tumor models and the potential of this triple combination to enhance the abscopal effect compared to the respective dual treatments. Materials and Methods Mice bearing bilateral tumors were treated with two fractions of 8 Gy (C51 colon carcinoma model) or 12 Gy (B16 melanoma model); α PD1 was given weekly; IL-2c was given for five consecutive days. CD8 T cell-depleting and CXCR3-blocking antibodies were used to determine if the therapeutic effects depend on CD8+ and CXCR3+ T cells. Differentiation stages of tumor-specific CD8+ T cells in tumor-draining lymph nodes, spleen, blood, and tumors were determined by flow cytometry using MHC-I tetramers and various antibodies. Results The abscopal effect was significantly stronger in triple-treated mice compared to mice treated with RT/ α PD-1 (C51 model: P< 0.01; B16 model: P< 0.05), RT/IL-2c (C51 model: P< 0.01; B16 model: P< 0.001) or α PD-1/IL-2c (C51 model: P< 0.0001, B16 model: P< 0.01). Moreover, triple therapy improved survival and resulted in complete cures of 3/12 mice in the C51 model and 2/12 mice in the B16 model. These anti-tumor effects were associated with dramatic expansion of tumor-specific CD8+ T cells. Undifferentiated stem-like and effector-like but not terminally differentiated exhausted cells particularly strongly increased. Moreover, IL-2c induced CXCR3 expression on tumor-specific CD8+ T cells. Both CD8+ (C51 model: P< 0.0001; B16 model: P< 0.01) and CXCR3+ (C51 model: P< 0.0001) T cells were crucial for the RT-induced abscopal effect upon RT/ α PD-1/IL-2c treatment. Conclusion RT/ α PD-1/IL-2c triple treatment resulted in superior local and systemic expansion of tumor-specific CD8+ T cells with stem- and effector-like phenotypes. Also, IL-2c strongly increased CXCR3+ CD8+ T cells that were associated with pronounced abscopal responses in models with an established metastasis resistant to α PD-1/IL-2c and only transiently responding to RT/ α PD-1 or RT/IL-2c. Therefore, such triple combinations appear promising for clinical evaluation in metastatic patients. Purpose or Objective Preclinical data have shown modulation of the tumour immune microenvironment by ATRi and radiation, through enhanced DNA damage leading to an interferon response triggered by cytoplasmic nucleic acid. We analysed clinical trial samples to determine whether there is evidence for this in humans. Materials and Methods Patients were treated within the PATRIOT study, a non-randomised phase 1 study of ATRi with ceralasertib and palliative radiotherapy, or ceralasertib alone. Radiation dose was 30 Gy in 15 fractions. In combination with radiotherapy, patients were treated with 80 mg BD ceralasertib (the RP2D in combination), or 160 mg BD as monotherapy (the RP2D monotherapy dose). Peripheral blood was taken at various time points and circulating immune cells analysed by flow cytometry. Plasma cytokines were analysed using multiplex bead-based flow. Two patients had tumour biopsies before treatment and prior to the second fraction of radiation, differential gene expression between these samples was analysed by RNAseq. Results There was a significant increase in the proportion of activated CD8 T-cells (CD69+. CD95+), NK (CD95+, TIM-3+), and unconventional T-cells (CD69+, TIM-3+) in peripheral blood with combination treatment. With ATRi alone, a trend towards increased NK activation was seen. Both monotherapy and combination therapy resulted in modulation of plasma cytokine levels, with an increase in CCL2 and a decrease in CCL5 noted in monotherapy, and an increase in CXCL10 with combination therapy. Paired tumour biopsy analysis found significant differential gene expression in multiple immune-related pathways in both innate and adaptive immunity after combination treatment and cell-type deconvolution inferred an expansion of natural killer cells and macrophages after combination treatment. The number of differentially expressed genes was higher in patients receiving combination therapy than in those receiving ceralasertib alone. Conclusion We have found evidence that there is marked modulation of the tumour immune microenvironment by the combination of ATRi and radiotherapy. This is reflected in circulating immune cells. The changes that we observe are similar to those previously noted in preclinical models and support further investigation of combinations of DNA damage response inhibitors, radiation and immune-targeted therapies. OC-0265 Dynamics of T-cell-driven immune responses to radiotherapy in a model of head and neck cancer C.M.L. Chan Wah Hak 1 , H. Baldock 2 , E. Appleton 3 , J. Hassan 4 , M. Pedersen 3 , M. Ono 4 , K.J. Harrington 3 , A. Melcher 1 1 The Institute of Cancer Research, Translational Immunotherapy Team, London, United Kingdom; 2 The Institute of Cancer Research, Biological Services Unit, London, United Kingdom; 3 The Institute of Cancer Research, Targeted Therapy Team, London, United Kingdom; 4 Imperial College London, Faculty of Natural Sciences, Department of Life Sciences, London, United Kingdom Purpose or Objective Combination treatment immunotherapy (IO) and radiotherapy (RT), or immunoradiotherapy, is a promising therapeutic strategy in preclinical cancer models. However, the results of immunoradiotherapy clinical trials in locally-advanced head and neck squamous cell carcinoma (HNSCC) have been disappointing. This warrants re-evaluation of the translation between preclinical and clinical work. Standard-of-care treatment for unresected locally-advanced HNSCC is chemoradiation (CRT); OC-0264 Clinical immunomodulation by ATR inhibition combined with radiation M. Dillon 1 , E. Patin 1 , M. McLaughlin 1 , L. Grove 1 , P. Nenclares 1 , K. Harrington 1 1 The Institute of Cancer Research, Radiotherapy and Imaging, London, United Kingdom