CD5 blockade enhances ex vivo CD8+ T cell activation and tumour cell cytotoxicity

CD5 is expressed on T cells and a subset of B cells (B1a). It can attenuate TCR signalling and impair CTL activation and is a therapeutic targetable tumour antigen expressed on leukemic T and B cells. However, the potential therapeutic effect of functionally blocking CD5 to increase T cell anti‐tumour activity against tumours (including solid tumours) has not been explored. CD5 knockout mice show increased anti‐tumour immunity: reducing CD5 on CTLs may be therapeutically beneficial to enhance the anti‐tumour response. Here, we show that ex vivo administration of a function‐blocking anti‐CD5 MAb to primary mouse CTLs of both tumour‐naïve mice and mice bearing murine 4T1 breast tumour homografts enhanced their capacity to respond to activation by treatment with anti‐CD3/anti‐CD28 MAbs or 4T1 tumour cell lysates. Furthermore, it enhanced TCR signalling (ERK activation) and increased markers of T cell activation, including proliferation, CD69 levels, IFN‐γ production, apoptosis and Fas receptor and Fas ligand levels. Finally, CD5 function‐blocking MAb treatment enhanced the capacity of CD8+ T cells to kill 4T1‐mouse tumour cells in an ex vivo assay. These data support the potential of blockade of CD5 function to enhance T cell‐mediated anti‐tumour immunity

Inducing DNA-Mismatch Repair Deficiency In Tumours: A Strategy To Enhance Anti-Tumour Immunity

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