MKI67 and neoplasm: Additionally, the lack of immune-mediated cytotoxic effect of CD8+ T cells present in tumors of treated animals, as indicated by the lack of a reduction in the number of Ki67+ cells, could possibly be attributed to the B16-F10 tumor model features, considering that these cells suffer from low levels of major histocompatibility complex I (MHCI) markers, thus impacting the presentation of tumor antigens and consequently initiation of the cellular anti-tumor response [61].