PDCD1 and neoplasm: Figure 2 summarizes genetic and non-genetic modifications that may impair antigen presentation. Effective presentation of clonal neoantigens, which results from tumor-specific mutations, is essential for triggering T-cell immunoreactivity and enhancing the efficacy of immune checkpoint blockade. McGranahan et al. demonstrated that tumors with a greater load of clonal neoantigens exhibit better responses to PD-1 inhibitors, underscoring the importance of the effective presentation of neoantigens for the success of immunotherapy [39].