CTLA4 and viral infectious disease: Based on the data presented in this review and in line with the recommendations of the Study Group for Infections in Compromised Hosts, we assume that PD-1/PD-L1- and/or CTLA-4-based ICI treatment does not seem to independently enhance the risk of infection or cause more virulent course of disease.27 Hence, the above discussed viral infections should not be considered as contraindications per se for patients who are scheduled for or are on ICI.