Mechanistically, a 6.3‐fold increase in PD1/CTLA‐4 BsAb accumulation in tumors due to the tumor targeting ability of aPD1, and the PD1/CTLA‐4 BsAb significantly reduces the adverse colitis event in healthy mice, compared to aPD1 and aCTLA‐4. Here, CTLA4 is linked to colitis.