The human mixed lymphocyte-tumor cell interaction test. I. Positive autologous lymphocyte proliferative responses can be stimulated by tumor cells as well as by cells from normal tissues.

Co-culture of cancer patients' nonadherent peripheral blood lymphocytes with irradiated autologous fresh tumor cells, termed the mixed lymphocyte-tumor interaction (MLTI) test, resulted in significant stimulation of 3H-Tdr in corporation on day 6 in 19 of 37 autologous combinations. The MLTI test was performed in a microtiter wells (0.2 ml) and a variety of solid tumor cells (sarcomas and carcinomas) were used. Tumor cells were dissociated from the fresh biopsy tissue by nontrypsin enzymatic digestion (deoxyribonuclease, hyaluronidase, and collagenase) and the tumor cells enriched by depletion of macrophages using adherence procedures. Occasionally, further tumor cell purification was achieved by separation of cells on the basis of size on dis-continuous gradients. Positive MLTI resulted in stimulation as high as 20-fold over the backgrounds of PBL and tumor cells cultured alone. Mean positive MLTI was SI of 7.7. The negative MLTI were not a reflection of generalized immunosuppression, because tumor cell preparations that did not stimulate autologous PBL did stimulate allogeneic PBL. In an additional patient, PBL not responding in the autologous MLTI did respond to allogeneic tumors. MLTI using cryopreserved cells reproduced the MLTI results using fresh cells in 11 of 16 tests; the other five tests were all positive in the fresh MLTI and negative when using cryopreserved cells. Despite reports from many other groups it appears that positive MLTI were not tumor-specific. In 14 experiments we were able to simultaneously test the proliferative response to autologous tumor as well as to an autologous normal tissue (lung, liver, colon, and bowel). In eight of these experiments positive responses were obtained with tumor stimulators and in seven of these, positive proliferation was also obtained with normal tissue.