交替半身照射消除体内残留白血病细胞的实验研究

Experimental Studies on the Elimination of Minimal Residual Leukemia In Vivo by Alternate Half Body Irradiation

用BN大鼠粒细胞白血病模型(BNML),于白血病强化疗后交替进行半身照射,不用骨髓移植,以代替全身照射移植自身骨髓。结果表明,实验动物能耐受这一新的治疗措施,骨髓造血能自行重建,无1只大鼠死于造血衰竭,而且实验动物生存时间比单用化疗动物明显延长。

The purpose of this study is to develop a new way for leukemia patients to tolerate an ablative chemoradiotherapy without BMT. Previous studies had demonstrated that only a few leukemia cells remained in the body during rem- ission phase following chemotherapy and did not migrate to distant organs via the circulation until they had given rise to 3～4×10~5 new cells. The period required for such growth was about 20 days. However, hematopoietic stem cells migrate earlier than do leukemia cells. Therefore, alternate half body irradiation (HBI) within this period would kill the residual leukemia cells, but hematopoietic stem cells would migrate from shielded marrow to irradiated marrow and reconstruct hematopoiesis. BN rats were injected i. v. with 10 BNML subline LT12nl #15 cells, which had been transfected with the E.coli Lac-Z and Neo genes by retrovirusmediated gene transfer. Cytochemical X-gal staining was used to identify the leukemia cells in agar culture. At day 9 after inoculation of leukemia cells, the rats were treated with cyclophosphamide (Cy 120 mg/kg), and 3 days later irradiated with 10 Gy (2 Gy/min, 6 MV, X-rays) on the upper half body, with the lower body shielded by a lead brick. They were then irradiated with the same dosage in the lower body with the upper half body shielded a week later. The preliminary results were as follow: At day 9 after inoculation, the cellularity of bone marrow (humerus, sternum, femur and tibia) was in the normal range, and the number of L-CFU ranged from 3.6×10^(-5) to 9.0×10^(-5) in agar culture. At day 4 after Cy treatment, the cellularity of bone marrow was greatly decreased and remained at only 1％～3％ of that before treatment. No leukemia cell colony could be found in the agar culture of L-CFU. At the 17th day after HBI treatment, the number of bone marrow cells was recovered. The cellularity of humerus bone marrow included in the first HBI area reached the level before treatment, while the cellularity of femur and tibia marrow included in the second HBI area was still hypoplastic. No leukemia cell colony was found among 10~6 bone marrow cells plated in agar culture. The animals tolerated Cy+HBI, none died of hematopoietic failure. They survived 70～170 d, with an average of 117.9+20.4 d. In the control group treated by Cy alone, the survival time averaged 70.7+20.4 d. The difference was statistically significant (P<0.05). It seems that alternat HBI after chemotherapy is a promising new strategy for eliminating minimal residual leukemia.