BACKGROUND Lymphocytes obtained from tumor-draining lymph nodes (DLN) can have potent in vivo antitumor activity after in vitro activation with bryostatin 1 and ionomycin. However, the presence of visceral metastases in the donor can inhibit the effectiveness of such lymphocytes. In the present study, we tested the ability of low-dose cyclophosphamide to overcome metastasis-induced immunosuppression in a murine model. METHODS Mice were injected with MCA-105 sarcoma cells in the footpad alone or in the footpad and the tail vein to establish lung metastases. Cyclophosphamide was given i.p. 1 day before harvesting the draining popliteal lymph nodes. For all donor groups, DLN cells were activated with 5 nM bryostatin 1 and 1 microM ionomycin and cultured for 7 days in 20 U/ml IL-2. Activated DLN cells were then adoptively transferred to syngeneic mice with 3-day lung metastases. RESULTS The adoptive transfer of DLN cells from mice with footpad tumors only significantly reduced the number of lung metastases compared to untreated mice. However, activated DLN cells obtained from mice with both footpad and lung tumors were significantly less effective. Treatment of similar donor mice with 10 mg/kg cyclophosphamide significantly improved the anti-tumor activity of adoptively transferred cells. This dose of cyclophosphamide did not reduce the number of cells obtained from each lymph node or the expansion of cell numbers in vitro. CONCLUSIONS These results suggest that the administration of low-dose cyclophosphamide prior to harvesting DLN cells may improve the success of adoptive immunotherapy in cancer patients.