Cell‐mediated and serum blocking reactivity to tumor antigens in patients with malignant melanoma

The reactivity of human lymphocytes, separated from peripheral blood by procedures involving sedimentation through plasmagel and settling on a glass surface, on survival or growth of melanoma tumor cells is reported. Assay of reactivity was by either a colony inhibition in dilute agar (GEL) technique or a microcytotoxicity assay (MC). In 54 experiments with lymphocytes from normal donors, inhibition of melanoma cell viability, as compared to growth in medium alone, was seen 25 (46.3%) times, stimulation was observed seven (12.9%) times and no effect 22 (40.7%) times. These results were not influenced by matching of the lymphocyte and tumor-cell donor for ABO blood group. Inhibition was seen less often, however, in tests with the GEL method than in those with the MC assay. Eighty-two experiments assessed the effect of lymphocytes from melanoma patients on melanoma cell viability. Inhibition to an extent greater than that of normal lymphocytes tested at the same time was seen 65 (79.3%) times. There was no difference in the frequency of detection of inhibition with lymphocytes from patients with local, regional, or widespread disease, although the percentage inhibition was less in the latter group. No differences were seen between patients with clinically active versus inactive disease. Only one of five patients who were within a week of death was reactive. Reactivity was detected as frequently with allogeneic as with autochthonous melanoma target cells. Serum blocking factor (SBF), capable of inhibiting in vitro cell-mediated reactivity to melanoma tumor cells, was assayed in serum from melanoma patients at various stages of disease. SBF was detected at some time in 30% of patients with local, 88.9% with regional, and 80.0% with widespread disease. It was found in 42.9% of those with clinically inactive and 70.6% with active melanoma. However, detection of SBF was found to fluctuate from sample to sample taken at different times during the course of disease in individual patients regardless of clinical status. The importance of sequential determinations of SBF activity for patient assessment is stressed.