HUMAN COLORECTAL TUMOR-INFILTRATING LYMPHOCYTES EXPRESS ACTIVATION MARKERS AND THE CD45RO MOLECULE, SHOWING A PRIMED POPULATION OF LYMPHOCYTES IN THE TUMOR AREA

This study investigated the phenotype of freshly isolated human tumour infiltrating lymphocytes (TIL) from 14 patients with colorectal tumou rs, and compared them with lymphocytes derived from the lamina propria of the unaffected mucosa and with lymphocytes derived from peripheral blood of the same patients. It was found that TIL expressed the activ ation markers CD25 and HLA-DR to a higher extent than the peripheral b lood lymphocytes (p=0.01), and that both lamina propria lymphocytes an d TIL preferentially expressed the CD45RO+phenotype, associated with m emory cells, in contrast with lamina propria lymphocytes. Both lamina propria lymphocytes and TIL contained few natural killer (NK) cells (C D3-CD56+) compared with peripheral blood lymphocytes (p=0.001), and th is was reflected in the cytotoxicity assays. After 1 to 2 weeks in cul ture with interleukin-2 100 U/ml, lymphocytes from all three compartme nts had a high cytolytic activity against all targets tested, consiste nt with the lymphokine activated killer cell phenomenon. No increase i n the number of NK cells was noted after culture, but 20-30% of the T cells now coexpressed the CD56 molecule. This was most prominent in th e CD8+ subset, but lymphokine activated killer cell activity was found in both CD4+ and CD8+ subsets. Possible tumour escape mechanisms are discussed.