CTLA4 and neoplasm: Tumor growth and mean tumor doubling times (TDTs) in these groups (IL-2: 9.7 days, α-PD-1/α-CTLA-4: 6 days, α-PD-1: 8.7 days, α-CD137: 11.7 days, α-PD-1/α-CD137: 11 days) were statistically not significant from Control-treated mice that had a mean TDT of 9.2 days (Fig. 3).