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Effect of cyclophosphamide on mice bearing methylcholanthrene-induced fibrosarcomas
Abstract:
Mice bearing large methylcholanthrene-induced fibrosarcomas lost the ability to respond in vitro to mitogen stimulation and to specifically neutralize autologous tumor cells in vivo. This depressed immune capability was due to active suppression, since spleen cells from advanced tumor-bearing mice could suppress the mitogen response of normal spleen cells and could inhibit tumor rejection when adoptively transferred to mice previously immunized against the tumor. Treatment with cyclophosphamide (CY) was found to affect the immune capability of the host, in addition to have a direct effect on the tumor. The number of cells in the lymph nodes and spleen, as well as their response to concanavalin A and lipopolysaccharide (but not phytohemagglutinin), decreased initially but returned to normal by Day 14. Most importantly, when CY was administered one day after tumor inoculation, the treated animals developed the ability to neutralize tumor at the same time as untreated controls but retained this capability as the tumors became advanced. Treatment with a single dose of CY as late as 11 or 20 days after tumor inoculation maintained or restored the tumor-neutralizing capacity of spleen cells. CY appears to alter the antitumor response of the host by inhibiting both cytotoxic and suppressor cells, but the cytotoxic cells recover rapidly, whereas the suppressor cells do not.
Insights
Mice with large tumors lose immune function due to suppressor cells. Cyclophosphamide (CY) treatment restores anti-tumor immunity by inhibiting these suppressor cells, enhancing anti-tumor responses.
Area of Science:
- Immunology
- Cancer Research
- Pharmacology
Background:
- Large tumors induce immune suppression in host mice, impairing responses to mitogens and tumor-specific immunity.
- This immune deficiency is mediated by active suppression, as demonstrated by spleen cell transfer experiments.
Purpose of the Study:
- To investigate the effects of cyclophosphamide (CY) on host immune capabilities in the context of methylcholanthrene-induced fibrosarcomas.
- To determine if CY can restore or maintain anti-tumor immune responses in tumor-bearing mice.
Main Methods:
- Mice bearing fibrosarcomas were treated with cyclophosphamide (CY) at various time points post-tumor inoculation.
- Immune cell populations and responses to mitogens (concanavalin A, lipopolysaccharide, phytohemagglutinin) were assessed.
- Tumor neutralization capacity was evaluated through in vivo assays and adoptive spleen cell transfer.
Main Results:
- CY treatment initially decreased lymphoid organ cellularity and mitogen responses, but these returned to normal by Day 14.
- Early CY administration (Day 1 post-inoculation) allowed mice to maintain tumor-neutralizing capacity as tumors progressed.
- Late CY administration (Days 11 or 20) also maintained or restored spleen cell tumor-neutralizing capacity.
Conclusions:
- Cyclophosphamide (CY) appears to modulate the anti-tumor immune response by inhibiting both cytotoxic and suppressor cells.
- The differential recovery kinetics of cytotoxic (rapid) and suppressor (slow) cells following CY treatment are crucial for restoring anti-tumor immunity.
