Bone marrow derived mesenchymal stem cells (MSC) have been shown to be progenitor cells for mesenchymal tissues. These cells may also provide a potential therapy for bone repair. Our previous studies showed that MSC engineered with the gene for bone morphogenetic protein 2 (BMP-2), a growth factor for bone cells, were capable of differentiating into osteoblast lineage and inducing autologous bone formation in several animal models. Culturing individual MSC for autologous implantation, however, remains problematic. The number of human MSC with osteogenic potential decreases with age, and, in certain diseases, the patient's marrow may be damaged or the healthy cells reduced in number. In this study, we used rats with a femoral segmental defect to investigate whether allogeneic BMP-2 engineered MSC would facilitate bone healing. We show that BMP-2 engineered allogeneic MSC can repair critical bone defects to the same degree as rats treated with BMP-2 engineered autologous MSC, if the allogeneic group receives short-term treatment with immunosuppressant FK506. We also show that allogeneic gene transferred MSC are directly involved in bone repair, in addition to acting as gene deliverers.

Continuous in vitro exposure of human bone marrow cells to acyclovir (-200 ,uM) or human leukocyte interferon (-250 U/ml) caused 50% inhibition of granulocyte colony-forming cell differentiation. Colonies expressed in the presence of either agent were reduced both in size and number. Erythroid progenitors were more resistant than granulocyte progenitors to the antiproliferative effects of acyclovir. Progenitor cells of patients recovering from cytotoxic chemotherapy were no more sensitive to the effects of acyclovir or interferon than were cells obtained from patients before chemotherapy.Acyclovir (ACV) [9-(2-hydroxyethoxymethyl)guanine] is being evaluated as topical or systemic therapy in local and disseminated herpesvirus infection. ACV inhibits herpes simplex virus types I and II and varicella-zoster virus at concentrations that have little effect on the division of mammalian fibroblasts (1,4,6,19,24) or lymphocytes (25). In mice, rabbits, and guinea pigs infected with herpes simplex virus types I and II ACV is both effective and nontoxic (7,12,20,24). The favorable therapeutic effect of ACV is explained by its efficient phosphorylation to an active form by cells which contain virusspecified kinases (6, 8) and the high affinity of herpesvirus-specified DNA polymerase for this active ACV triphosphate (6). Although ACV is highly selective in comparison with other antimetabolites, we previously found that human fibroblasts and mitogen-and antigen-stimulated human lymphocytes can be inhibited by higher levels (100 to 200 ,uM) of ACV (14). McGuffin et al. (15) recently reported -20% inhibition of human granulocyte colony-forming unit (CFU-C) differentiation at ACV concentrations of 100 puM. Because higher doses of ACV may be required to treat more resistant herpesviruses in patients myelosuppressed by chemotherapy, we have measured the effect of higher doses of ACV on human CFU-Cs. The myelosuppression caused by ACV was compared with that of human leukocyte interferon which is known to be myelosuppressive in man. To determine whether the kinetic state of the marrow altered the susceptibility of myeloid precursors we studied samples obtained before and after chemotherapy. We also determined possible effects of ACV on the immature erythroid progenitor, the erythroid burst-forming unit (BFU-E), and its progeny, the erythroid colony-forming unit (CFU-E).MATERIALS AND METHODS Patient samples. Bone marrow cells were obtained from seven patients (five with glioblastoma, one with melanoma, one with oat-cell carcinoma) before treatment with intensive chemotherapy and autologous bone marrow infusion. Marrow cells were also obtained from three patients with oat-cell carcinoma after combination chemotherapy, from one patient with acute lymphocytic leukemia in remission, and from two normal donors. Peripheral blood cells enriched for granulocyte progenitors during the period of leukocyte recovery after chemotherapy (23) were obtained from two patients with oat-cell carcinoma. Peripheral blood cells were also obtained from...