Heterogeneity of natural killer lymphocyte abnormalities in colon cancer patients

The monoclonal antibody HNK-1 reacts exclusively with human granular lymphocytes that comprise 16 ± 1.4% of blood mononuclear cells. In normal individuals, almost all natural killer (NK) and killer (K) cell function resides in this lymphocyte subset. The level of HNK-1⁺ granular lymphocytes, their stage of differentiation, and NK cell function were examined in 70 colon cancer patients and the results compared with data for 114 age-matched normal individuals. Median levels of granular lymphocytes were significantly depressed in colon cancer patients compared to controls (9% versus 16.5%, P < 0.0001). Despite the depressed numbers of circulating HNK-1⁺ cells, NK cell function in the colon cancer patients was essentially the same as in normals (P = 0.78). The HNK-1⁺ lymphocyte level correlated with NK cell function in about two thirds of normal individuals but only one third of colon cancer patients (P = 0.025). Three possible mechanisms for this dichotomy were examined. First, lymphoid cell subpopulations purified with a fluorescence-activated cell sorter (FACS) were examined for altered NK cell functional activity. HNK-1⁺ cells from the colon cancer patients exhibited significantly less NK functional activity compared to normals (796 versus 1046 lytic units, P = 0.04). Interestingly, the HNK-1^- fraction (predominantly T lymphocytes) had increased NK cell functional activity in the colon cancer patients compared to normals (373 versus 218 lytic units, P = 0.0001). Purified monocytes did not contribute to NK cell functional activity. Second, the functional maturity of the HNK-1⁺ lymphocytes was correlated with NK activity. Two subsets of HNK-1⁺ cells were identified by surface membrane markers and purified with the FACS. The more mature HNK-1⁺ subset (i.e., HNK⁺Leu-4M1⁺) exhibited almost ten times more NK cell functional activity than did the less mature cell fraction (i.e., HNK⁺Leu-4⁺M1^-) cells in normal individuals (2230 versus 286 lytic units/10⁷ cells). Further analysis demonstrated that the ratio of mature to immature HNK⁺ cells in normal individuals was 3:1, while it was decreased to 1:1 ratio in colon cancer patients (P = 0.005). Third, the influence of prostaglandin-mediated suppression on NK cell activity was examined. PGE₂ did not appear to influence NK cell function, since NK cell function was unchanged in vitro in the presence of a prostaglandin synthesis inhibitor. Thus, compared to normal individuals, colon cancer patients had (1) a profound depression in the numbers of HNK-1 granular lymphocytes with a concomitant decrease in their NK cell functional capability (on a per cell basis), (2) a shift in the subsets of HNK⁺ cells with a significant decrease in the more functionally efficient (i.e., mature) HNK⁺ cells, and (3) no regulatory influence by prostaglandin-producing suppressor monocytes on NK cell function. This monoclonal HNK-1 antibody thus identified a heterogeneity of NK cell abnormalities and provided some insights into abnormal host defenses in colon cancer patients.