Low-Dose Cyclophosphamide Inhibition of Transplantable Fibrosarcoma Growth by Augmentation of The Host Immune Response2

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Abstract
Preinjection of a low dose of cyclophosphamide (Cy) (500 μg/mouse) either delayed or inhibited tumor appearance following the inoculation of transplantable 3-methylcholanthrene-induced fibrosarcomas in inbred male C3H/HeJ mice. This dose of Cy decreased the spleen weight by 13% and the total spleen cell count by 23%. However, the same dose could potentiate the footpad swelling reaction (FPSR) measured against Staphylococcus aureus antigen. Splenic lymphocytes from Cy-treated animals showed increased blastogenic response against phytohemagglutinin-M and bacterial lipopolysaccharide. Thus 500 μg Cy/animal may have depleted suppressor cell populations leading to: a) an increase in FPSR, b) increased blastogenic transformation of lymphocytes, and c) tumor growth inhibition.