In vivo CRISPR screening identifies Ptpn2 as a cancer immunotherapy target

Immunotherapy with PD-1 checkpoint blockade is effective in only a minority of patients with cancer, suggesting that additional treatment strategies are needed. Here we use a pooled in vivo genetic screening approach using CRISPR–Cas9 genome editing in transplantable tumours in mice treated with immunotherapy to discover previously undescribed immunotherapy targets. We tested 2,368 genes expressed by melanoma cells to identify those that synergize with or cause resistance to checkpoint blockade. We recovered the known immune evasion molecules PD-L1 and CD47, and confirmed that defects in interferon-γ signalling caused resistance to immunotherapy. Tumours were sensitized to immunotherapy by deletion of genes involved in several diverse pathways, including NF-κB signalling, antigen presentation and the unfolded protein response. In addition, deletion of the protein tyrosine phosphatase PTPN2 in tumour cells increased the efficacy of immunotherapy by enhancing interferon-γ-mediated effects on antigen presentation and growth suppression. In vivo genetic screens in tumour models can identify new immunotherapy targets in unanticipated pathways. In vivo CRISPR screening reveals that loss of Ptpn2 increases the response of tumour cells to immunotherapy and increases IFNγ signalling, suggesting that PTPN2 inhibition may potentiate the effect of immunotherapies that invoke an IFNγ response. Cancer immunotherapy treatments, such as PD-1 checkpoint blockade, are only effective in a minority of patients, suggesting the need to investigate new treatment strategies. Nicholas Haining and colleagues describe a functional genomics approach using the CRISPR–Cas9 system to identify genes that affect the response to immune checkpoint blockade in the B16 mouse transplantable tumour model. They show that loss of function of the phosphatase PTPN2 in tumour cells enhances interferon-γ-mediated effects on antigen presentation and growth suppression. This finding suggests that PTPN2 is a potential target for cancer immunotherapy and that in vivo genetic screenings of tumour models could help identify other possible targets.