The difference between 5-fluorouracil and melphalan in their ability to promote antitumor immune response against MOPC-315 plasmacytoma

Thymic humoral factor-gamma 2 (THF-gamma 2) immunotherapy reduces the metastatic load and restores immunocompetence in 3LL tumor-bearing mice receiving anticancer chemotherapy

In mice bearing immunogenic tumors, adding thymic humoral factor-gamma 2 (THF-gamma 2)1 immunotherapy as an adjunct to anticancer chemotherapeutic regimens not only potentiates the antitumor activity of each drug but also repairs tumor/chemotherapy-induced damage to T-cell populations and functions. The Lewis lung carcinoma (3LL) is a weakly immunogenic, highly metastatic tumor in C57BL/6 mice. To investigate whether the immunoregulatory octapeptide is also effective against a tumor that does not elicit an antitumor immune response, we assessed the effect of combination THF-gamma 2 immunotherapy and chemotherapy in 3LL-bearing mice. The results indicate that THF-gamma 2 combined with either Melphalan or 5-Fluorouracil was more effective in reducing metastatic load than either chemotherapeutic drug alone and was characterized by massive infiltration of lymphatic cells. The combined chemoimmunotherapy treatment also prolonged the survival time in all treated animals and repaired T-cell defects and impaired in vitro cellular immune response parameters, induced either by the tumor or by chemotherapy. THF-gamma 2 immunotherapy reversed the decrease in the number of bone-marrow myeloid colonies (GM-CFU) induced by chemotherapy treatment of tumor-bearing mice, supporting the hypothesis that THF-gamma 2 directly stimulates the proliferation of myeloid stem cells. The overall results imply, that when administered as an adjunct to chemotherapy, THF-gamma 2 immunotherapy is equally effective against immunogenic and nonimmunogenic tumors.

Therapeutic effectiveness against MOPC-315 plasmacytoma of low or high doses of the synthetic thymic hormone THF-gamma 2 in combination with an "immunomodulating" or a "non-immunomodulating" drug

We reported previously that treatment of mice bearing MOPC-315 plasmacytoma with the drugs L-PAM (phenylalanine mustard) or 5-FU (5-fluorouracil), in combination with low doses of THF-gamma 2, was more effective in increasing their survival time than treatment with the drug alone. We show here that in the combined treatment using a single injection of 5-FU followed by multiple (8-15) injections of THF-gamma 2, the megadoses were more effective than the low doses in increasing the survival time of MOPC-315 tumor-bearing mice. On the other hand, in combination with L-PAM, both low and high doses of THF-gamma 2 were equally effective. The need for high doses of THF-gamma 2, when used in combination with 5-FU, could be due to the fact that 5-FU acts as a "non-immunomodulating" drug and has to be used at a high, immunosuppressive dose.

Eradication of a disseminated mouse lymphoma by 1,3-bis(2-chloroethyl)-1-nitrosourea is immunologically mediated and accompanied by de novo generation of anti-tumor cytotoxicity

The anti-tumor effect of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) was examined in BALB/c mice bearing increasing burdens of a syngeneic lymphoma (YC8). A single i.p. injection of the drug resulted in over 75% of cures when given at day 3, 5, 7 or 10 after an i.v. inoculum of 10(4) YC8 cells. The efficacy of BCNU on mice bearing large tumor burdens (from day 5 on) was not only due to its tumoricidal activity, but was immunologically mediated. Residual tumorigenic cells could be recovered in the livers of 5-day tumor bearers (TB) up to 2 weeks after BCNU treatment and only a low percentage of cures could be achieved when BCNU was administered to nude mice. In addition, BCNU-cured mice specifically rejected a lethal YC8 challenge and their splenocytes developed anti-tumor cytotoxicity in response to in vitro stimulation with YC8 cells. During kinetic experiments a 2-week period elapsed after BCNU injection before an anti-tumor cytotoxic T-lymphocyte (CTL) response could be generated by spleen cells of BCNU-treated 5-day TB. This period was characterized by immunosuppression as evaluated from impairment in the generation of lymphokine-activated killer (LAK) cells or of allospecific primary CTL responses by spleen cells from BCNU-treated 5-day TB and BCNU-treated normal mice. LAK cells first recovered and could be generated 7 days later, whereas primary allospecific CTL responses could only be detected by day 14, concomitantly with the generation of anti-tumor cytotoxicity by 5-day TB. The development of secondary in vitro CTL responses, however, was permanently abrogated. Spleen cells from BALB/c mice immunized either with YC8 or with DBA/2 minor histocompatibility antigens and treated with BCNU 1 week after the last immunization failed to mount an in vitro CTL response to their immunizing antigen, even when the cultures were supplemented with recombinant interleukin-2.

A synthetic thymic hormone, THF-gamma 2, repairs immunodeficiency of mice cured of plasmacytoma by melphalan

BALB/c mice cured of large MOPC-315 plasmacytomas by melphalan remain deficient in their spleen T-cell functions. This was manifested by impairment of the allogeneic and the antibody responses in vitro to SRBC and in decreased numbers of T-cells including their subsets CD4 and CD8. IL-2 production and specific cytotoxicity against MOPC-315 tumor cells were, on the other hand, maintained. Treatment of these cured mice by in-vivo administration of THF-gamma 2, an octapeptide from calf thymus, repaired these deficits. This was evidenced by in vitro tests with spleen cells which manifested an increased allogeneic response and elevated generation of primary antibody response, restoration of T-cell subpopulations to normal and an enhanced IL-2 production above normal levels. The potential use of THF-gamma 2 as supportive therapy in cancer treatment is suggested.

THF-gamma 2, a thymic hormone, increases immunocompetence and survival in 5-fluorouracil-treated mice bearing MOPC-315 plasmacytoma

The effect of the thymic hormone, THF-gamma 2, on the immunocompetence of 5-fluorouracil (5-FU)-treated BALB/c mice, bearing MOPC-315 tumor, was examined. Treatment of noninoculated or tumor-bearing mice with THF-gamma 2 after 5-FU injection, resulted in an increase in the antibody response to sheep red blood cells and in the allogeneic response in spleen cell cultures and had no effect on the concanavalin-A-induced interleukin-2 secretion beyond that caused by 5-FU alone. Treatment with either 5-FU alone or 5-FU and THF-gamma 2 resulted in restoration to normal values of Lyt1- and L3T4-positive populations in tumor-bearing mice. THF-gamma 2 prolonged the survival time of mice bearing MOPC-315 tumor beyond that observed in mice treated with 5-FU alone.