IN VITRO STUDIES OF LYMPHOCYTES FROM PATIENTS WITH PLASMA CELL MYELOMA.

Highly purified blood lymphocytes from treated and untreated patients with plasmacell myeloma were tested for the presence of *EAC lymphocytes carrying the C3 receptor surface marker using a rosette-technique and for thymus-derived (T) lymphocytes as judged by spontaneous rosette formation with sheep red blood cells. The treated patients were tested 5 weeks after a standardized 4-day treatment with melphalan and prednisolone. Untreated patients had 40-65% EAC-lymphocytes in peripheral blood while the EAC-cell level in treated patients was < 20%. A non-myeloma control group had 20-40%. The percentage of EAC-lymphocytes was correlated with different in vitro functional tests: lymphocyte-mediated lysis of target cells (Chang cell line or chicken red blood cells) treated with rabbit antibody correlated with the percentage of EAC-lymphocytes. DNA synthesis induced in lymphocytes by pokeweed mitogen (PWM) showed a biphasic dose response curve which may indicate activition of two populations of lymphocytes. A correlation was found between EAC-lymphocytes and DNA synthesis induced by a low concentration of PWM (0.1 μg/ml). The results support observations by other investigators which suggest that antibody-induced cytotoxicity requires cells in the non-T-lymphocyte population and the assumption that PWM is in part a mitogen for human bone marrow-derived lymphocytes. [ABSTRACT FROM AUTHOR]