While previous reports have demonstrated that Fc engaging antagonist anti-TIGIT antibodies are efficacious in preclinical tumor models, we herewith provide specific evidence that Fc engagement is required for efficacy based on data from tumor-bearing animals treated with non-Fc engaging anti-TIGIT antibodies and TIGIT KO mice, revealing some mechanistic insight into how Fc engagement of anti-TIGIT antibodies may be contributing to anti-tumor efficacy in the mouse. The gene discussed is TIGIT; the disease is neoplasm.