Prevalence of proliferating CD8⁺ cells in normal lymphatic tissues, inflammation and cancer

CD8⁺ cytotoxic T-lymphocytes are essential components of the anti-tumor immunity. To better understand the expansion of CD8⁺ T-cells we used multiplex fluorescence immunohistochemistry to study Ki67⁺CD8⁺ cells in normal lymphoid tissues, selected inflammatory diseases and cancers in 41 large sections/ microenvironment tissue microarrays (TMAs) as well as 765 samples in a conventional TMA format. The evaluation of more than 20 different compartments of normal lymphoid tissues revealed that the percentage of proliferating (ki67⁺) CD8⁺ cells did commonly not exceed 3%. In inflammations, the percentage of Ki67⁺CD8⁺ cells was more variable and higher compared to normal tissues. In cancers, the percentage of Ki67⁺CD8⁺ cells was higher in the tumor center than at the invasive margin. In the tumor center of 765 colorectal cancers, the density of Ki67⁺CD8⁺ cells and the percentage of proliferating CD8⁺ cytotoxic T-cells was significantly associated with microsatellite instability (p<0.0001), pT (p<0.0002) and pN category (p<0.0098). In summary, these data show that the percentage of Ki67⁺CD8⁺ cells is usually at a baseline proliferation rate below 3% in healthy secondary lymphoid organs. This rate is often markedly higher in inflammatory and neoplastic diseases compared to normal tissues. The striking link with unfavorable tumor features in colorectal cancer suggest a potential clinical utility of assessing the percentage of Ki67⁺CD8⁺ cells to predict patients outcome.