We have demonstrated that histone deacetylase inhibitors (HDACi) can reinstate immune reactivity in colorectal cancer cells by upregulation of elements of the machinery of immune presentation, including MHC class1. We went on to show that the combination of an HDACi with an immune checkpoint inhibitor delivered synergistic anticancer effects in a syngeneic colorectal cancer (CRC) mouse model. We have performed a clinical trial to test this hypothesis in patients with advanced, refractory CRC with positive results. We have adapted our AI/digital pathology programme to develop a biomarker to select CRC patients who are more likely to benefit from this combination immunotherapy and plan to incorporate this into a prospective clinical trial.