ORIGIN OF CD57(-CELLS WHICH INCREASE AT TUMOR SITES IN PATIENTS WITH COLORECTAL-CANCER() T)

Human T cells carrying natural killer (NK) markers, CD57 or CD56 antig ens, appear to be distinguishable from other T cell subsets in terms o f their granular lymphocyte morphology and their numerical increase in patients with AIDS and in recipients of bone marrow transplantation. At the begining of this study, we observed that CD57(+) T cells as wel l as CD56(+) T cells were abundant at tumour sites in many patients wi th colorectal cancer. Since all these findings for CD57(+) T cells are quite similar to those of extrathymic T cells seen in mice, we invest igated how CD57(+) T cells are distributed to various immune organs in humans. They were found to be present mainly in the bone marrow and l iver, but to be completely absent in the thymus. Similar to the case o f extrathymic T cells in mice, they were observed to consist of double -negative CD4(-)8(-) subsets as well as single-positive subsets (prepo nderance of CD8(+) cells), and to contain a considerable proportion of gamma delta T cells. These features are striking when compared with t hose of CD57(-) T cells, which are characterized by an abundance of CD 4(+) subsets and alpha beta T cells. Not only at tumour sites but also in the peripheral blood, some patients with colorectal cancer display ed elevated levels of CD57(+) cells. These results suggest that CD57() T cells may be of extrathymic origin, possibly originating in the bo ne marrow and liver, and may be associated with tumour immunity, simil ar to another extrathymic population of CD56(+) T cells in humans.