PDCD1 and Opportunistic infection: A previous review [36] summarized that there are two main reasons for infection events associated with immune checkpoint inhibitors: one is opportunistic infections associated with immune-related adverse events treatment (such as glucocorticoids, corticosteroids or immunosuppressants); the other one is infections due to dysregulated immunity, such as cases of atypical mycobacterium infection following PD-1/PD-L1 immunotherapy in the absence of immunosuppression [37].