IMMUNOTHERAPY OF A PLASMACYTOMA WITH ATTENUATED SALMONELLA

An attenuated strain of Salmonella typhimurium, SL3235, developed as a prototypic typhoid vaccine, is shown to retard growth of a murine pla smacytoma, TEPC-183, and to prolong survival of tumor-bearing mice. Li ve salmonella, but not acetone-killed organisms, had antitumor activit y. The immunotherapeutic effect was demonstrable when the tumor was in jected intralesionally or intraperitoneally. Increased survival, longe r mean time to death, and retardation of tumor growth were found when the salmonella were given intralesionally as late as the sixth day pos t-tumor injection. Timing of salmonella inoculation, as well as the sa lmonella dose, had an effect on treatment efficacy. Injection of salmo nella intraperitoneally exerted a strong antitumor effect when given a s late as the third day post-tumor inoculation. The highest dose (2 x 10(6)) of salmonella was less effective than doses 10- or 100-fold low er. TEPC-183 plasmacytoma is rapidly growing and highly immunosuppress ive, so the ability of the salmonella to exert therapeutic activity ag ainst it is a measure of the potency of the vaccine. These observation s are of interest, as they show that a genetically engineered, avirule nt strain of Salmonella has immunotherapeutic properties similar to th ose of BCG and other biological response modifiers, and might have cli nical potential as an antitumor agent.