Effect of melphalan in vitro on induction of murine suppressor T cells by ConA

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.

THF-gamma 2, a synthetic thymic hormone, increases effectiveness of combined chemotherapy and immunotherapy against RPC-5 murine plasmacytoma

The effect of a synthetic thymic hormone, THF-gamma 2, on the anti-tumor activity of spleen cells was studied in mice immunized against the RPC-5 tumor. Following two courses of the THF-gamma 2 treatment, the mean RPC-5 specific cytotoxic response of immune spleen cells was significantly increased when compared to normal cells (P less than 0.001) and to untreated immune spleen cells (P less than 0.04). In addition, THF-gamma 2 treatment improved the competence of immune spleen cells in adoptive immunotherapy (AIT) when performed in combination with chemotherapy by melphalan. Recipients of spleen cells from THF-gamma 2 treated mice showed a 35% increase in survival when compared to AIT with immune cells alone. The results suggest that THF-gamma 2 treatment of donors for AIT might be applicable to cancer therapy in humans.

Differences in sensitivity to melphalan between con A-activated and nonactivated human T-cell subsets

In vitro treatment with melphalan (L-PAM, L-phenylalanine mustard), 2 micrograms/2 X 10(6) cells, significantly decreased the total number of E-rosette-positive (E+) T lymphocytes from peripheral blood (PBL) of healthy human donors as well as those of the OKT4 (precursor suppressor/helper/inducer T cells) and OKT17 populations (suppressor cells within the OKT4 subset). The OKT8 population (cytotoxic/mature suppressor cells) was not affected by a similar L-PAM treatment. The sensitivity of concanavalin A (Con A)-activated E+ T-cell populations to subsequent L-PAM treatment in vitro was different from that of Con A-untreated T cells: Thus, L-PAM treatment did not affect the expression of OKT3 and OKT4 antigens, increased the percentage of OKT17 cells, and inhibited the expression of OKT8 antigen. Depletion of OKT8 from Con A-activated E+ T cells (OKT4+-OKT8(-)-OKT17+) did not affect their suppressive activity on PHA stimulation in L-PAM-treated as well as untreated cells. Further depletion of OKT17+ cells from the OKT4+-OKT8(-)-OKT17+ subset (OKT4+-OKT8(-)-OKT17-) abolished the suppressive effect on PHA stimulation. Suppressive activity of the OKT4+-OKT8(-)-OKT17- subset was again evident after treatment of this population with L-PAM. The results obtained indicate that the sensitivity to L-PAM treatment of various T-cell phenotypes is changed by Con A activation and that after depletion of specific T suppressor cells L-PAM seems affect the immunoregulatory circuit within the Con A-activated OKT4 subset.

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

The anticancer chemotherapeutic drugs melphalan (L-phenylalanine mustard; L-PAM), 5-fluorouracil (5-FU), methotrexate (MTX), and daunorubicin (DAU) were tested for their toxic activity against MOPC-315 tumor cells in vitro. L-PAM, 5-FU, and DAU had a marked toxic effect whereas MTX did not affect the rate of thymidine incorporation in the tumor cells. L-PAM (7.5 mg/kg) induced permanent regression of large s.c. MOPC-315 plasmacytoma tumors, 5-FU (200-250 mg/kg) induced transient regression of MOPC-315 tumors with reappearance starting on the 6th day after the 5-FU injection and DAU (5 mg/kg) was not effective. L-PAM treatment restored the cytotoxic potential of spleen cells of tumor-bearing mice against target MOPC-315 tumor cells whereas spleen cells from tumor-bearing mice treated with 5-FU were unable to mount a cytotoxic response. L-PAM and 5-FU were also assayed for their effect in vitro on induction of suppressor T cells by ConA. L-PAM treatment in vitro markedly reduced the induction of suppressor T cells by ConA whereas 5-FU had no effect. It is suggested that anticancer chemotherapeutic drugs can be classified in "immunopromoting" (L-PAM as prototype) and "nonimmunopromoting" (5-FU as prototype) on the basis of their effect in vivo on established tumors and their effect on induction of suppressor T cells by ConA.