Protective specific immunity induced by doxorubicin plus TNF-α combination treatment of EL4 lymphoma-bearing C57BL/6 mice

The therapeutic efficacy of a single (day 8), moderate dose (4 mg/kg, i.v.) of doxorubicin (DOX, Adriamycin) combined with recombinant human TNF-α (3 different doses and 5 different schedules, i.v.) was evaluated in C57BL/6 mice bearing an implant (s.c.) of the DOX-sensitive, TNF-α-resistant EL4 lymphoma. In parallel to monitoring survival, the levels of several host anti-tumor cytolytic effector functions of splenocytes and thymocytes were evaluated throughout the treatment period and in long-term survivors (LTS). DOX treatment alone resulted in a moderate (approx. 20%) increase in life span but no cures. TNF-α alone, at any tested dose or schedule, had little or no positive effect on survival. The combinations of DOX and TNF-α were only slightly better than DOX alone with respect to the time to death of mice that died (approx. 29% increase); however, each of the combinations involving 1,000 U TNF-α/injection produced a fraction (20% to 80%) of LTS. The host defense activities examined included those of splenic and thymic cytolytic T lymphocytes (CTL) and lymphokine-activated killer cells as well as splenic tumoricidal macrophages. Although most activities were modulated by tumor growth and/or treatment, only CTL responsiveness appeared to correlate with survival. CTL activity in the treated groups with LTS was significantly higher than in control groups late in the treatment period. Finally, ex vivo analyses of splenocytes and thymocytes together with the rejection of implanted tumor at 17 months established that LTS displayed specific long-term immune memory. Int. J. Cancer 87:101–109, 2000. © 2000 Wiley-Liss, Inc.