Dissecting the mechanisms of immune checkpoint therapy.

Abstract

Immune checkpoint therapy with antibodies targeting CTLA4 or PD1/PDL1 has led to durable regression of disease and cures for a subset of patients with cancer, which has led to increased efforts to develop combination immunotherapy strategies to benefit an even greater number of patients. However, questions remain as to which combinations should be used and in which population of patients. In 2019, several studies reported on the differential impact of targeting CTLA4 and/or PD1 on T cell responses, with clear evidence that both CD4+ and CD8+ T cell responses are needed. These data highlight the complementary nature of targeting CTLA4 and PD1 to drive both CD4+ and CD8+ effector T cell responses, which should be considered in future treatment strategies. Furthermore, reverse translational studies, which provide immune response data from patients receiving immune checkpoint therapy, have revealed resistance mechanisms that indicate relevant targets for combination strategies. Taken together, future treatments will likely consist of anti-CTLA4 plus anti-PD1 with addition of individualized therapy on the basis of tumour type and site of metastatic disease. Studies of immune checkpoint therapy for cancer in 2019 uncovered critical insights into the differences between targeting CTLA4 versus PD1 and the role of particular T cell subsets in immune responses to cancer. Moreover, reverse translational studies are informing our understanding of resistance and response mechanisms in patients.