Late immune and haemopoietic functions in plasmacytoma-bearing mice cured by melphalan

Alkylating agents can cause latent and permanent damage to the bone marrow. We compared the long term effects of melphalan on a number of immune and haemopoietic functions of plasmacytoma bearing BALB/c mice with that of normal mice treated with a similar dose of melphalan. The drug administered orally at a dose of 250 micrograms and 400 micrograms on day 14 and 24 following i.m. inoculation of MOPC-315 plasmacytoma cells resulted in cure of the mice. Their spleen cells showed a permanent impairment of MLR activity, T-cell number and IL-2 production as well as a mild suppression of NK activity for one year after cessation of melphalan therapy. The number of B cells was elevated. In contrast, plasmacytoma-free mice treated with melphalan retained long term normal immune functions, although shortly after melphalan therapy a temporary suppression was noted. On the other hand, melphalan was responsible for bone marrow myeloid stem cell damage since the number of myeloid progenitor cell (CFU-GM) colonies was reduced in both melphalan-treated groups compared to untreated normal controls. Plasmacytoma bearing mice had a shorter survival. These results demonstrate that some late sequelae of alkylating agents are not due to the drug alone; shorter survival and T-cell deficiency are related to the previous presence of the tumour.