PD1/CTLA‐4 BsAb demonstrated significant tumor accumulation, with a 6.3‐fold increase compared to PLG‐Fc‐III‐4C‐IgG in MC38‐bearing mice, and significantly reduced the adverse colitis event related to toxicity observed with aPD1 + aCTLA‐4 in healthy mice (Scheme 1). Here, CTLA4 is linked to colitis.