Finally, PCNA+ proliferating cells were more abundant in lymph nodes from both tumor-bearing and anti-mPD-1-treated mice compared with those from tumor-free mice, showing uniform distribution across T cell zones and marked accumulation within the medullary sinus (Fig. 4A, B, D), which implies that a substantial proportion of these proliferating cells are activated T cells. Here, PCNA is linked to neoplasm.