Inducing DNA-Mismatch Repair Deficiency In Tumours: A Strategy To Enhance Anti-Tumour Immunity
Abstract
Immunotherapy has improved patient outcomes in advanced or metastatic settings across a number of cancers. Patients with tumours deficient in the DNA mismatch repair (DNA-MMR) pathway often show high response rates to immune checkpoint inhibitors (ICIs) with a rise in immune surveillance. However, little is known about the immune sensitization effects of inducing DNA- MMR-deficiency in low tumour mutational burden (TMB) cancers, such as ICI refractory neuroblastoma. In addition, the dynamic T-cell profile that results from such a DNA-MMR inactivation, and whether this may confer a therapeutic benefit, is poorly understood. Here we used CRISPR/CAS9 genome editing technology to knock out (KO) MLH1, a crucial molecule in the DNA-MMR pathway, in mouse neuroblastoma (neuro-2a) cells – a low TMB pediatric cancer refractory to ICIs – to induce MMR deficiency. To analyze tumour growth inhibition in response to ICIs and immunophenotype the tumour-infiltrating lymphocytes (TILs), tumours with intact or induced MMR deficiency were injected subcutaneously into immunocompetent mice. Tumour growth were measured after treatment with anti-PD1 antibodies and TILs were analyzed for activation, exhaustion, and effector markers, allowing for an in-depth flow cytometric analysis of T-cell subsets in these tumours. Our study shows that inducing MMR-deficiency induces a robust anti-tumour response in a low TMB cancer. Moreover, this sensitization was accompanied by specific phenotypic changes of T-cells in response to anti-PD1 therapy in the tumour.