Effect of cyclophosphamide and levan treatment on bone marrow and peripheral blood cells in B16-F10 melanoma-bearing mice

Immunotherapeutic agents have often been found to provoke opposite effects on tumor growth--inhibitory or stimulatory--depending on dose, timing or route of administration. The reason for these opposite effects is not yet known. Levan (polyfructose), an immunomodulatory polysaccharide, has been found to exert opposite effects on the growth of the F10 variant of B16 melanoma. Low doses inhibit and high doses enhance the growth of this tumor. Cyclophosphamide (CY) augments the inhibitory effect of the polysaccharide. In order to elucidate the mechanism of these opposite effects, we tried to determine the changes induced by levan at inhibitory and stimulatory doses, alone or in conjunction with CY, on the lymphatic and hematopoietic systems of B16-F10 melanoma-bearing mice. In a previous study we reported the effect of these treatments on the morphology of spleen and lymph nodes (Leibovici, Kopel, Siegal & Gal-Mor (1986). Int. J. Immunopharmac., 8, 391). In the present study, we examined the effect of the treatments on bone marrow and peripheral blood composition. The growth of the tumor itself, as well as the various treatments, induced very marked changes in both bone marrow and blood. Tumor inoculation produced a sharp leukopenia and anemia followed by a restoration of both white and red blood cells. In the bone marrow, the tumor caused a gradual decrease in lymphocyte number. CY accentuated the severe leukopenia caused by the tumor. Lymphocyte depletion was prolonged, while restoration of granulocytes was achieved by day 7. A similar pattern of changes was observed in the bone marrow. With levan, opposite effects were observed in blood and bone marrow with the two doses in relation to the number of the cells of the lymphoid and myeloid lines: while 0.1 mg (tumor inhibitory) doses caused a more active restoration of lymphocytes as compared to 10 mg (tumor stimulatory) doses, an opposite effect was seen on the myeloid series--the high dose induced a more pronounced granulocytosis than the low dose. In the combined treatment, the low levan dose accelerated lymphocyte restoration in bone marrow compared to CY, while the high dose delayed the recovery of these cells. The results of the present study in conjunction with our previous study may explain the basis of the intriguing tumor inhibitory-stimulatory effects of some immunomodulators. Moderate increases in myeloid cell series appear to favor tumor inhibition and high increases favor tumor stimulation. In addition, the results of this study suggest that a regulatory relation might exist between the proliferation of the lymphoid and myeloid cell series.