CTLA4 and neoplasm: Since young mice expressed higher levels of CTLA-4, recapitulating a feature of adult tumor-bearing mice (Supplementary information, Figure S2), we treated perinatal human CTLA4 knock-in (Ctla4h/h) mice with control human IgG-Fc, anti-CTLA-4 mAb Ipilimumab, L3D10, anti-PD-1, anti-PD-1 + Ipilimumab or anti-PD-1 + L3D10, respectively.