Probing the underlying immune and molecular mechanisms of MKI67 by xCell algorithm, TIMER algorithm, correlation analysis, and enrichment analysis, our results suggested that MKI67 expression was significantly correlated with the level of tumor-infiltrating immune cells across several cancer types, including B cells, CD4+ T cells, CD8+ T cells, DC infiltrates, neutrophils, and macrophages. The gene discussed is CD4; the disease is cancer.