Motoyoshi Yasuhide, Kaminoda Kazuhisa, Saitoh Ohki, Hamasaki Keisuke, Nakao Kazuhiko, Ishii Nobuko, Nagayama Yuji, Eguchi Katsumi
Department of Medical Gene Technology, Atomic Bomb Disease Institute, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki 852-8501, Japan.
Oncol Rep. 2006 Jul;16(1):141-6.
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.
已知环磷酰胺作为一种烷化剂化疗药物，除了具有直接的细胞毒性作用外，还具有免疫调节作用，如耗竭CD4+CD25+调节性T细胞。然而，其最佳浓度尚未完全阐明。因此，我们首先比较了不同剂量的环磷酰胺对小鼠T细胞亚群（包括CD4+CD25+ T细胞）的影响。环磷酰胺（20mg/kg）使脾细胞、CD4+和CD8+ T细胞数量减少约50%，而CD4+CD25+ T细胞数量的下降更为显著，导致CD4+CD25+ T细胞与CD4+ T细胞的比例明显降低。相比之下，200mg/kg环磷酰胺使所有T细胞亚群数量严重减少>90%，尽管仍观察到CD4+CD25+ T细胞与CD4+ T细胞的比例下降。接下来，低剂量环磷酰胺显著抑制免疫健全但非免疫缺陷小鼠体内鼠肝癌MH129肿瘤的生长。这种抗肿瘤作用通过补充CD4+CD25+ T细胞而被消除。相比之下，高剂量环磷酰胺在两种小鼠中均表现出类似的抗肿瘤作用。此外，与抗体介导的CD4+CD25+ T细胞耗竭相反，肿瘤接种后给予低剂量环磷酰胺比预先给予更有效。我们的数据表明，低剂量环磷酰胺选择性地耗竭CD4+CD25+ T细胞，导致对已存在肿瘤的抗肿瘤作用增强，而高剂量环磷酰胺的抗肿瘤作用仅归因于其直接细胞毒性。这些发现似乎在癌症治疗的联合化疗和免疫治疗的临床环境中至关重要。
