Total Body Irradiation May Detrimentally Induce Cytogenetic Abnormalities of Bone Marrow Derived Mesenchymal Stem Cell.

Total body irradiation (TBI) is routinely used before allogeneic transplantation to kill the leukemic cells as well as to suppress the immunity of recipient to ensure donor hematopoietic stem cell engraftment. TBI is associated with a lot of long-term adverse effects on normal cells, including radiation-induced sarcoma. Mesenchymal stem cells (MSCs) are the stromal stem cells in the bone marrow (BM) and other mesenchymal tissue and are extensively studied in the clinical application as cell therapy for tissue repair. Nevertheless, some in vitro and animal studies had pointed out that sarcoma could be derived from cultured or in vitro manipulated MSCs. We therefore conduct this study to see whether irradiation using the dosing schedule similar to TBI can induce malignant transformation of BM-MSCs.

Ex vivo expanded (passage 3 to 5) BM-MSCs from two normal adults were irradiated with 1200 cGy (200cGy twice a day for consecutive 3 days, mimicking TBI clinically). Each of them was kept ex vivo culture for 6 and 12 passages respectively. The cells were then subjected to investigate morphology, phenotype, differentiation potential, and cytogenetic analysis using traditional G-banding technique and also spectral karyotyping (SKY). Ex vivo expanded (passage 3 to 5) BM-MSCs from five leukemic patients obtained before and after TBI (1200cGy)-conditioned allogeneic transplantation were also examined in the same way. The differences in the characteristic of BM-MSCs before and after irradiation (or TBI) were evaluated and the effects of TBI on MSCs were determined.

BM-MSCs from normal adults or transplant patients after irradiation or TBI are still fibroblast-like and are CD29+, CD44+, CD73+, CD90+, CD105+, CD166+, CD14-, CD34-, and CD45-, which are just the same to normal BM-MSCs. However, the proliferation and multi-differentiation ability are markedly decreased in BM-MSCs after irradiation or TBI. Of the Two BM-MSCs obtained from normal adults and having normal karyotype, cytogenetic abnormalities can be easily identified on SKY after irradiation with 1200cGy. Besides, the same cytogenetic abnormality can be detected in both passage 6 and passage 12 MSCs. Interestingly, cytogenetic clonal evolution was detected in 1 of them. In sex-mismatched allogeneic transplant, the cytogenetic studies showed all the BM-MSCs remain recipient-origin after transplant. Nevertheless, of the five BM-MSCs isolated from transplant patients who had received TBI conditioning, cytogenetic abnormalities were detected in all of them. More importantly, cytogenetic clonal evolution was also found in 1 of them.

BM-MSCs can not be eradicated by myeloablative, TBI-based conditioning chemoradiotherapy and they remain recipient-origin. The cellular morphology and surface antigen expression did not differed significantly after irradiation. However, TBI significantly reduced the proliferation and differentiation potential of BM-MSCs. Most important of all, TBI induced clonal cytogenetic abnormality on BM-MSCs, which is evident not only from ex vivo irradiation study but also from clinical patients' specimens. Besides, cytogenetic clonal evolution, a unique feature of malignant process, was found in some of them. TBI is known to be an important risk factor for soft tissue sarcoma in transplant survivors, our study further provides the direct evidence that TBI-exposed BM-MSCs may have clonal cytogenetic abnormality and the tumorigenic potential of these cells merits extensive study. Taking together, the BM-MSCs isolated from patients who had received TBI have defective proliferation and differentiation potential. Moreover, because of cytogenetic abnormality, these cells should not be considered for any clinical application.

No relevant conflicts of interest to declare.