The relative proliferation index as a more sensitive parameter for evaluating lymphoproliferative responses of cancer patients to mitogens and alloantigens

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Abstract
Lymphocyte proliferation (LP)6 assays were performed in microculture using the T‐cell mitogens phytohemagglutinin (PHA) and concanavalin A (Con A); the T+B cell mitogens, pokeweed mitogen (PWM) and staphylococcal phage lysate (SPL); and a pool of allogeneic stimulating leukocytes in oneway mixed leukocyte cultures (MLC) in lung and breast cancer patients and normal individuals. The resultant data were expressed in three different ways: (1) as mean counts per minute (CPM) of tritiated thymidine incorporation; (2) as a stimulation index (SI) and (3) as a relative proliferation index (RPI). The RPI is defined as the ratio of net CPM (nCPM) in experimental cultures with stimulant (E) minus medium control cultures (C) of a test individual to the mean nCPM of three or more normal individuals examined in the same assay on the same day. These expressions were then compared for their ability to discriminate between LP responses in cancer patients and normal individuals. The RPI value and selected cut‐off values gave the most sensitive measure for the determination of depressed proliferative responses. These analyses demonstrated that lung carcinoma patients were depressed to PHA (50%), MLC (47%), PWM (43%) and Con A (40%). To a lesser degree, breast carcinoma patients were also depressed to MLC (36%), PHA (31%), PWM (27%) and Con A (19%). Our data indicate that the use of the RPI in the analysis of LP response represents an improved method for detecting impaired response of lymphocytes to general mitogens and alloantigens which can consistently reveal immunosuppression in many cancer patients and may be useful for serial monitoring of individual patients.