p53 (TRP53) deficiency-mediated antiapoptosis escape after 5 Gy X irradiation still induces stem cell leukemia in C3H/He mice: comparison between whole-body assay and bone marrow transplantation (BMT) assay.

Mice exposed to a lethal dose of radiation were repopulated with heterozygous p53(+/-) (TRP53(+/-)) bone marrow cells and then exposed to doses of 1, 3 and 5 Gy 1 month later. This resulted in the transplanted bone marrow-specific diseases other than competitively induced nonhematopoietic neoplasms. Interestingly, the present study showed a high frequency of stem cell leukemia, i.e., leukemias characterized by a lack of differentiation due also to p53 deficiency, even after 5 Gy irradiation. The frequencies of stem cell leukemias (and those of total hematopoietic malignancies) were 16% (24%) at 1 Gy and 45% (75%) at 3 Gy. Furthermore, markedly high incidences of stem cell leukemias were observed at 5 Gy in p53(+/-) mice, i.e., 87% (100%) in the transplantation assay and 60% (83.3%) in the whole-body assay, whereas a conventional whole-body assay induced only 14% in wild-type mice. The high incidence of stem cell leukemias observed in this study using heterozygous p53-deficient mice agrees with results of a previous study of homozygous p53-deficient mice and is consistent with the high frequency of loss of heterozygosity in the p53 wild-type allele observed in leukemias. This suggests that the target cells for radiation-induced stem cell leukemias may be p53-deficient hematopoietic stem cells.

Ex vivo expansions and transplantations of mouse bone marrow-derived hematopoietic stem/progenitor cells.

To examine the effects of co-culture with bone marrow mesenchymal stem cells on expansion of hematopoietic stem/progenitor cells and the capacities of rapid neutrophil engraftment and hematopoietic reconstitution of the expanded cells, we expanded mononuclear cells (MNCs) and CD34+/c-kit+ cells from mouse bone marrow and transplanted the expanded cells into the irradiated mice. MNCs were isolated from mouse bone marrow and CD34+/c-kit+ cells were selected from MNCs by using MoFlo Cell Sorter. MNCs and CD34+/c-kit+ cells were co-cultured with mouse bone marrow-derived mesenchymal stem cells (MSCs) under a two-step expansion. The expanded cells were then transplanted into sublethally irradiated BDF1 mice. Results showed that the co-culture with MSCs resulted in expansions of median total nucleated cells, CD34+ cells, GM-CFC and HPP-CFC respectively by 10.8-, 4.8-, 65.9- and 38.8-fold for the mononuclear cell culture, and respectively by 76.1-, 2.9-, 71.7- and 51.8-fold for the CD34+/c-kit+ cell culture. The expanded cells could rapidly engraft in the sublethally irradiated mice and reconstitute their hematopoiesis. Co-cultures with MSCs in conjunction with two-step expansion increased expansions of total nucleated cells, GM-CFC and HPP-CFC, which led us to conclude MSCs may create favorable environment for expansions of hematopoietic stem/progenitor cells. The availability of increased numbers of expanded cells by the co-culture with MSCs may result in more rapid engraftment of neutrophils following infusion to transplant recipients.

A graft-versus-tumor effect in a patient with ependymoma who received an allogenic bone marrow transplant for therapy-related leukemia. Case report.

Graft-versus-leukemia effect is an immune-mediated antitumor phenomenon associated with allogenic bone marrow transplants (BMTs) for hematological malignancies, and recent findings have indicated that a similar effect could occur in some solid tumors such as breast cancers. The authors report on a 42-year-old man with a recurrent ependymoma who received an allogenic BMT for therapy-related leukemia. After transplantation, the patient developed chronic graft-versus-host disease, which was controlled with steroid agents. Interestingly, the recurrent ependymoma regressed steadily over the next 21 months posttransplant, until the tumor became almost undetectable on magnetic resonance images. This case indicates that the graft-versus-tumor effect, mediated by cytotoxic T cells, may be able to target intraparenchymal neuroepithelial tumors, despite the brain's generally recognized status as an immunoprivileged organ.

Role of natural effector cells in the prevention of radiation-induced leukemogenesis.

Four once-weekly exposures of 225 rads (R) of whole body X-irradiation causes a high incidence of lymphoma in C57BL/6 (C57) mice. The role of natural effector cells in radiation-induced leukemogenesis was investigated. Activity of natural killer (NK) and natural cytotoxic (NC) cells was depressed in irradiated mice over a prolonged period. Transplantation of bone marrow (BM) cells from normal C57 mice to irradiated mice restored their NK responses and prevented development of lymphoma. The effect of beige BM cell transfer to irradiated mice was not clear. Unlike short-term (4-hour) assay, results of long-term (20-hour) assay suggest partial restoration of NK and full restoration of NC activity in irradiated mice. Treatment of irradiated mice with polyinosinic: polycytidillic acid (poly I:C) increased NK activity and lymphoma resistance. Administration of small repeated doses of poly I:C to irradiated mice significantly prevented the development of lymphoma as well as significantly prolonging overall survival time in irradiated mice. These observations indicate that natural effector cells mediate resistance to radiation-induced leukemogenesis.

Bone marrow transplantation for myelodysplasia and secondary acute nonlymphoblastic leukemia.

Twenty-three patients with primary myelodysplasia (MDS) or secondary myelodysplasia/acute nonlymphocytic leukemia (MDS/ANLL) were treated with allogeneic or syngeneic bone marrow transplantation (BMT). Only one patient was in a chemotherapy-induced hematologic remission. Graft-versus-host disease prophylaxis included methotrexate, methotrexate plus cyclosporine, cyclosporine, or T-cell depletion using one of two anti-CD5 monoclonal antibodies. For patients with primary MDS, the median age was 19 years (range, 11 to 41 years) and the actuarial disease-free survival was 56% +/- 21% (median follow-up, 2 years; range, 0.8 to 5 years). There were three graft failures (two with autologous recovery) and two early deaths. Outcome appeared to be related to French-American-British (FAB) classification. For patients with secondary MDS/ANLL, the median age was 28 years (range, 3 to 16 years) and the actuarial disease-free survival was 27% +/- 13% (median follow-up, 5 years; range, 2.5 to 8.5 years). There were no graft failures, two relapses, and four early deaths. The presence of marrow fibrosis per se did not predict for graft failure (P = .21); however, the use of T-cell depleted marrow in patients with marrow fibrosis resulted in graft failure in three of five individuals. Our results suggest that in patients with primary MDS or secondary MDS/ANLL, BMT should be considered early in the course of the disease, and that attempts at inducing a remission prior to BMT appeared to be unnecessary. In MDS patients with marrow fibrosis, T-cell depletion should be avoided.

Allogeneic bone marrow transplantation for acute leukemia.

Allogeneic marrow transplantation has emerged as a curative therapy for many patients with acute leukemia. The ability to cure patients of their disease is dependent on the remission status of the patient. For patients with acute myelogenous leukemia, up to 60% of patients can become long-term, disease-free survivors, whereas a similar number of patients with high-risk acute lymphoblastic leukemia can also achieve cure of their disease. The improved results with marrow transplantation have allowed the application of this therapy for patients up to the age of 50 years. Even patients with therapy-related leukemias can benefit from this approach. Although relapse is still a problem in all remission stages, current studies suggest that improved preparatory regimens, in combination with better treatment of graft-versus-host disease and prevention of cytomegalovirus pneumonia, will continue to improve the overall results of this therapy for patients with acute leukemia.