Mixed leucocyte culture blocking factor activity in the plasma of patients with cancer.

Plasma samples obtained from 74 patients with malignant disease were assayed for their ability to suppress or block the mixed lymphocyte reactivity of random normal donors. 24 of the 74 patients investigated had evidence of mixed lymphocyte culture blocking factoractivity (MLC-BFA). 19 of 33 patients with disseminated disease had evidence of MLD-BFA whereas in only 5 of 41 patients with localized disease was evidence of BFA found. There was a relationship between a history of previous blood transfusion inthe 6-month period prior to study and the presence of MLC-BFA in patients' plasma. Excluding this group of patients, where previous transfusion might have been responsible for MLC-BFA and excluding, too, that group of patients with a history of past pregnancy,there remained still 11 patients with evidence of BFA in their plasma. Nine of these11 had widely disseminated and progressiv disease. MLC-BFA was found in both IgM and IgG fractions of plasma. Plasma with MLC-BFA was found to suppress normalin vitro lymphocyte responses to mitogens PWM and PHA. The MLC-BFA assay utilized in this work may provide the means of monitoring cancer patients in order to detect 'blocking' antibody.