Mice cured from large MOPC-315
tumors by a single dose of
melphalan, 7.5 mg/kg, were examined for up to 60 days after the
drug treatment (71 days after the
tumor inoculation) for their ability to respond to mitogenic stimulation, specific and nonspecific antigenic stimulation and for their susceptibility to inoculation with an unrelated
tumor, L10
lymphoma. The response of spleen cells from cured mice to mitogenic stimulation by
phytohemagglutinin or
concanavalin A was slightly depressed at an early stage after the
drug treatment. The allogeneic response against C57BL spleen cells and the antibody response against sheep red blood cells (SRBC) of spleen cells from cured mice remained below normal levels during the whole observation period. The deficiency in response to antigenic stimulation was found to be due to impairment in T-cell function. Cured mice were also deficient in their response to SRBC immunization (antibody and delayed-type
hypersensitivity responses) and were more susceptible to inoculation with an unrelated
tumor, L10
lymphoma, than normal, noninoculated mice. On the other hand, spleen cells of cured mice developed a highly specific cytotoxic response against target MOPC-315
tumor cells and the cured mice were resistant to challenge with an otherwise highly tumorigenic dose of MOPC-315. Thus, cured mice remained deficient for a long period of time in their response to MOPC-315-unrelated
antigens but, at the same time, they showed a potent specific antitumor immunity potential in vivo and in vitro.