title: Different mechanisms for anti-tumor effects of low- and high-dose cyclophosphamide.
abstract: It is known that, besides its direct cytotoxic effect as an alkylating chemotherapeutic agent, cyclophosphamide also has immuno-modulatory effects, such as depletion of CD4+CD25+ regulatory T cells. However, its optimal concentration has not yet been fully elucidated. Therefore, we first compared the effects of different doses of cyclophosphamide on T cell subsets including CD4+CD25+ T cells in mice. Cyclophosphamide (20 mg/kg) decreased the numbers of splenocytes, CD4+ and CD8+ T cells by approximately 50%, while a decline in CD4+CD25+ T cell number was more profound, leading to the remarkably lower ratios of CD4+CD25+ T cells to CD4+ T cells. In contrast, 200 mg/kg cyclophosphamide severely decreased the numbers of all the T cell subsets by > 90% although the decreased ratios of CD4+CD25+ T cells to CD4+ T cells were still observed. Next, low-dose cyclophosphamide significantly inhibited in vivo growth of murine hepatoma MH129 tumor in immuno-competent but not immuno-deficient mice. This anti-tumor effect was abolished by CD4+CD25+ T cell repletion. In contrast, high-dose cyclophosphamide exhibited similar anti-tumor effects in both mice. In addition, contrary to antibody-mediated CD4+CD25+ T cell depletion, administration of low-dose cyclophosphamide after tumor inoculation was more efficacious than the prior administration. Our data show that low-dose cyclophosphamide selectively depletes CD4+CD25+ T cells, leading to enhanced anti-tumor effects against pre-existing tumors, while the anti-tumor effect of high-dose cyclophosphamide is solely attributed to its direct cytotoxicity. These findings appear to be highly crucial in a clinical setting of combined chemotherapy and immunotherapy for cancer treatment.
authors.affiliation: Department of Medical Gene Technology, Atomic Bomb Disease Institute, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki 852-8501, Japan.
authors.forename: Yasuhide
authors.initials: Y
authors.lastname: Motoyoshi
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Kaminoda
authors.forename: Ohki
authors.initials: O
authors.lastname: Saitoh
authors.forename: Keisuke
authors.initials: K
authors.lastname: Hamasaki
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Nakao
authors.forename: Nobuko
authors.initials: N
authors.lastname: Ishii
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nagayama
authors.forename: Katsumi
authors.initials: K
authors.lastname: Eguchi
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy*; D045744:Cell Line, Tumor; D003520:Cyclophosphamide / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D006801:Humans; D007167:Immunotherapy / Q000379:methods; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D015375:Receptors, Interleukin-2 / Q000096:biosynthesis; D013601:T-Lymphocytes / Q000378:metabolism
chemical_list: D018906:Antineoplastic Agents, Alkylating; D015375:Receptors, Interleukin-2; D003520:Cyclophosphamide