In the present study, an ascitic tumor of NALM-6, a human pre-B acute lymphoblastic leukemia cell line, was established in nude mice which had not been subjected to any preconditioning such as X-irradiation and/or splenectomy. The ascitic tumor was also established in X-irradiated mice. Under various conditions, the tumor transplantability was 100%. NALM-6 cells were initially inoculated i.p. into 8-day-old nude mice after being admixed with X-irradiated HT-1080, a human fibrosarcoma cell line. Then, the in vivo grown (for 10 wk) tumor cells were serially transplanted i.p. into X-irradiated adult (10 to 12 wk old) nude mice. After the serial passages, we succeeded in establishing a highly transplantable NALM-6 ascitic tumor in nonpreconditioned as well as X-irradiated nude mice without the addition of HT-1080 cells. The ascitic tumor cells do not lose transplantability after in vitro culture for 20 days. Cellular radioimmunoassay and fluorescence-activated cell sorter analysis indicated that the in vivo established NALM-6 tumor cells retained the antigenic phenotype of the parental NALM-6 cells. Titration experiments revealed a reciprocal relationship between survival time of the mice and the number of tumor cells inoculated. When appropriate numbers of tumor cells (e.g., 4 × 106 cells) were used for the inoculation, survival times of individual mice fell within a relatively narrow range; this narrow range will facilitate the experiments where the present tumor model is used for evaluating the in vivo efficacy of antitumor agents. The present ascitic tumor models, particularly the one established in nonpreconditioned nude mice, will be useful for evaluating the in vivo efficacy of anti-human leukemia agents as well as for studying the in vivo biological behavior of the transplanted leukemia cells.

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This work was supported by USPHS Grants CA19304 and CA42683 awarded by the National Cancer Institute.

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