Demonstration of lymphocyte blastogenesis--inhibiting factors in sera of melanoma patients.

The proliferative response of lymphocytes obtained from a healthy volunteer to the mitogens phytohemagglutinin (PHA) and concanavalin A (Con A) was evaluated in the presence of sera from 101 patients with malignant melanoma and 75 normal controls. A significant decrease in blastogenic response was observed in the presence of sera from melanoma patients. Sera from patients with advanced disease were particularly inhibitory, suggesting that the circulating immunosuppressive factors were either tumor derived or tumor induced. Our observation that sera from patients who failed to display a delayed cutaneous hypersensitivity reaction to 2,4-dinitrochlorobenzene (DNCB) are more inhibitory to mitogen stimulation than sera from patients who react to this contact allergen suggests that DNCB skin testing may identify an immunological defect mediated by circulating humoral factors.