Engraftment Of Bone Marrow Cells Research Articles

Transplantation studies in C3-deficient animals reveal a novel role of the third complement component (C3) in engraftment of bone marrow cells.

Mice deficient in complement C3 (C3(-/-)) are hematologically normal under steady-state conditions, and yet displayed a significant delay in hematopoietic recovery from either irradiation or transplantation of wild-type (WT) hematopoietic stem/progenitor cells (HSPC). Transplantation of histocompatible WT Sca-1(+) cells into C3(-/-) mice resulted in a (i) decrease in day 12 CFU-S, (ii) 5-7-day delay in platelet and leukocyte recovery, and (iii) reduced number of BM CFU-GM progenitors at day 16 after transplantation. Nevertheless, HSPC from C3(-/-) mice engrafted normally into irradiated WT mice, suggesting that there was a defect in the hematopoietic environment of C3(-/-) mice. Since C3(-/-) mice cannot activate/cleave C3, the C3 fragments C3a, C3a(des-Arg), and iC3b were examined for a role in HSPC engraftment. Liquid-phase C3a and C3a(des-Arg) increased CXCR4 incorporation into membrane lipid rafts (thus potentiating HSPC responses to SDF-1 gradients), whereas iC3b was deposited onto irradiated BM cells and functioned to tether CR3(CD11b/CD18)(+)HSPC to damaged stroma. The activity of C3a(des-Arg) suggested that C3aR(+)HSPC also expressed the C5L2 (receptor for C3a and C3a(des-Arg)) and this was confirmed. In conclusion, a novel mechanism for HSC engraftment was identified, which involves complement activation and specific C3 fragments that promote conditioning for transplantation and enhance HSPC engraftment.

Enhancement of allogeneic hematopoietic stem cell engraftment and prevention of GVHD by intra-bone marrow bone marrow transplantation plus donor lymphocyte infusion.

We examined the effect of intra-bone marrow (IBM)-bone marrow transplantation (BMT) in conjunction with donor lymphocyte infusion (DLI) on the engraftment of allogeneic bone marrow cells (BMCs) in mice. Recipients that had received 6 Gy of radiation completely rejected donor BMCs, even when IBM-BMT was carried out. However, when BMCs were IBM injected and donor peripheral blood mononuclear cells (PBMNCs) were simultaneously injected intravenously (DLI), donor cell engraftment was observed 7 days after BMT and complete donor chimerism continued thereafter. It is of interest that the cells of recipient origin did not recover, and that the hematolymphoid cells, including progenitor cells (Lin-/c-kit+ cells) in the recipients, were fully reconstituted with cells of donor origin. The cells in the PBMNCs responsible for the donor BMC engraftment were CD8+. Recipients that had received 6 Gy of radiation, IBM-BMT, and DLI showed only a slight loss of body weight, due to radiation side effects, and had no macroscopic or microscopic symptoms of graft-versus-host disease. These findings suggest that IBM-BMT in conjunction with DLI will be a valuable strategy for allogeneic BMT in humans.

B-cell deficiency and reduced B-cell reconstitution in hemoglobin-deficit mice

Objective To study the effect of persistent hemoglobin-deficit mutation ( hbd/hbd) on hematopoiesis and the function of hematopoietic stem cells (HSCs). Methods Young and old mice homozygous for the spontaneous hbd/hbd mutation were compared to young and old wild-type control mice, all on the C57BL/6 background, over cellular composition in blood and bone marrow (BM) using cell counting, complete blood counts, and flow cytometry. BM cells from hbd/hbd mutants and normal controls were also tested for HSC engraftment in vivo using the competitive repopulation assay. Results Both young and old hbd/hbd mutants exhibited a microcytic anemia with significantly ( p<0.01) lower levels of hemoglobin and mean corpuscular volume. There were significant declines in CD45R + B cells in both blood ( p<0.01) and BM ( p<0.05) in old hbd/hbd mice, suggesting that B-cell homeostasis was compromised. Total BM cells per mouse was significantly increased ( p<0.05) in old hbd/hbd mice. In the competitive repopulation assay in vivo, BM cells from old hbd/hbd donors showed slightly decreased contribution to T cells and myeloid cells but a significantly ( p<0.01) decreased engraftment in B lymphocytes, indicating that B-cell hematopoiesis was compromised in old hbd/hbd mice. These data differ from results previously obtained from normal C57BL/6 mice in which BM cell engraftment ability does not decrease with donor age. Conclusion Persistent hbd/hbd mutation causes hematopoiesis defects in the B cell lineage.

Participation of bone marrow derived cells in cutaneous wound healing.

Bone marrow has long been known to be a source of stem cells capable of regeneration of the hematopoeitic system. Recent reports, however, have indicated that bone marrow might also contain early stem cells that can differentiate into other organ tissues such as skin. While these studies have illustrated that bone marrow stem cells could find their way to the skin, they have not addressed the dynamics of how bone marrow stem cells might participate in the homeostatis and regeneration of skin. In this report we followed green fluorescent protein (GFP) labeled bone marrow transplanted into non-GFP mice in order to determine the participation of bone marrow stem cells in cutaneous wounds. Our results indicate that there are a significant number of bone marrow cells that traffic through both wounded and non-wounded skin. Wounding stimulated the engraftment of bone marrow cells to the skin and induced bone marrow derived cells to incorporate into and differentiate into non-hematopoietic skin structures. This report thus illustrates that bone marrow might be a valuable source of stem cells for the skin and possibly other organs. Wounding could be a stimulus for bone marrow derived stem cells to travel to organs and aid in the regeneration of damaged tissue.

Nonlethal conditioning for the induction of allogeneic chimerism and tolerance to islet allografts.

We reported that tolerance to skin grafts can be achieved by chimerism induction by way of nonlethal conditioning. In the present study, we evaluated the outcome of islet allografts implanted either simultaneously or after donor bone marrow cell (BMC) infusion when nonlethal conditioning was used. B10 (H-2b) mice were conditioned with antilymphocyte serum (ALS), 100 cGy total body irradiation (TBI), and given 30 x 10(6) allogeneic (B10.BR, H-2k) BMC on day 0. On day 2, cyclophosphamide was given intraperitoneally (IP), followed by a second BMC infusion on day 3. After chimeras were typed for allogeneic BMC engraftment on day 28, animals were rendered diabetic chemically and transplanted under the kidney capsule with islet allografts genetically matched or disparate to the BM. Donor-specific islet grafts were accepted (median survival time [MST] > 180 days, n=6), whereas all major histocompatibility complex (MHC)-disparate third-party BALB/c (H-2d) islet grafts were rejected (MST=13.8 days, n=4). When B10.BR BMC and islets were given simultaneously, graft acceptance (MST >140 days, n=4) was observed. Surprisingly, when MHC-disparate third-party islets (BALB/c) were given together with B10.BR BMC, long-term survival was also observed (MST >100 days, n=3). These findings suggested that conditioning alone at the time of islet implant might induce long-term engraftment without further treatment. However, only chimeric animals accepted a second-set donor-specific graft, whereas all other groups rejected it. Our data indicates that stable allogeneic chimerism and islet indefinite survival can be achieved by the use of a nonmyeloablative protocol. The results of the conditioning-only experiments are consistent with the possibility of graft accommodation.

Plastic adult stem cells: will they graduate from the school of hard knocks?

Notwithstanding the fact that adult bone marrow cell engraftment to epithelial organs seems a somewhat uncommon event, there is no doubt it does occur, and under appropriate conditions of a strong and positive selection pressure these cells will expand clonally and make a significant contribution to tissue replacement. Likewise, bone-marrow-derived cells can be amplified in vitro and differentiated into a multitude of tissues. These in essence are the goals of regenerative medicine using any source of stem cells, be it embryonic or adult. Despite such irrefutable evidence of what is possible, a veritable chorus of detractors of adult stem cell plasticity has emerged, some doubting its very existence, motivated perhaps by more than a little self-interest. The issues that have led to this state of affairs have included the inability to reproduce certain widely quoted data, one case where the apparent transdifferentiation was due to contamination of the donor tissue with haematopoietic cells and, most notoriously, extrapolating from the behaviour of embryonic stem cells to suggest that adult bone marrow cells simply fuse with other cells and adopt their phenotype. While these issues need resolving, slamming this whole new field because not everything is crystal clear is not good science. The fact that a phenomenon is quite rare in no way mitigates against its very existence: asteroid collisions with the Earth are rare, but try telling the dinosaurs they do not occur! When such events do occur (transdifferentiation or collision), they certainly can make an impact.

Efficacy of donor splenocytes mixed with bone marrow cells for induction of tolerance in sublethally irradiated mice

Background: High dose of bone marrow cells (BMCs) has been reported to be essential to establish donor-specific tolerance. In clinical settings, a large quantity of BMCs is very difficult to be obtained. Our previous report demonstrated that even a low dose of BMCs could establish donor-specific tolerance if mixed with splenocytes (SPLCs). In the present study, various components of SPLCs were purified or removed and were investigated their contribution for enhancement of bone marrow engraftment leading to donor-specific tolerance in sublethally irradiated mice. Methods: Sublethally irradiated C57BL/6 recipient mice were intravenously injected 3×10 6 BMCs mixed with various components and various numbers of SPLCs harvested from BALB/c donor mice. One week after injection, skin grafting was performed. The degree of chimerism in peripheral blood lymphocytes (PBLs) and in SPLCs was analyzed by FACS 3 months after transplantation. Results: Recipients receiving 3×10 6 BMCs mixed with 10×10 6 T cell-enriched SPLCs established chimerism. Recipients receiving BMCs mixed with macrophage-depleted SPLCs also showed chimeirism and donor-specific tolerance. B cell-enriched SPLCs did not help small dose of BMCs to establish chimerism. Irradiated SPLCs were not effective to induce tolerance even with additional infusion to recipients. Conclusions: Active effects of splenic T cells were more important to help engraftment of small dose of BMCs than B cells, but the interaction between T and B cells might play some roles to enhance BMC engraftment. Splenic macrophages or dendritic cells might have some adverse effects against tolerance induction. Fatal graft-versus-host disease (GVHD) might be avoided by depleting adherent cells from SPLCs, so macrophages or dendritic cells were also considered as key components to induce donor-specific tolerance and prevent GVHD in this model.

Functional defects of NK cells treated with chloroquine mimic the lytic defects observed in perforin-deficient mice.

NK cells are the primary effectors mediating acute rejection of incompatible bone marrow cell grafts. To reduce rejection, we evaluated the ability of chloroquine (CHQ) to prevent perforin-dependent NK cell activity. Perforin is a key cytotoxic component released from the lytic granules of activated NK cells. Generation of functional perforin requires an acidic protease activity that occurs in the secretory, lytic lysosomes. Our hypothesis was that CHQ, a lysosomotropic reagent, would raise the pH of the acidic compartment in which perforin is processed and thereby block perforin maturation and cytotoxicity. We have measured NK cytotoxicity in vivo by clearance of YAC-1 tumor cells from the lungs and by rejection of incompatible bone marrow transplants and in vitro by cytolysis of YAC-1 and Jurkat cells. The engraftment of bone marrow cells was monitored by recolonization of the spleen with hemopoietic cells from transplants of MHC class I-deficient bone marrow cells into lethally irradiated recipient mice. Transplant rejection was compared in two inbred strains of mice: 129, which apparently use perforin-dependent cytotoxicity, and C57BL/6, in which rejection can be perforin-independent. CHQ treatment reduced NK cell activity in 129 mice in which perforin is important for mediating rejection. CHQ affected the fraction of NK cell cytolysis that was Fas independent. In addition, we found that CHQ prevents perforin processing by LAK cells in vitro. These data indicate that CHQ may impair rejection of incompatible bone marrow transplants and other functions mediated by NK and cytotoxic T cells.

MHC class Ia molecules alone control NK-mediated bone marrow graft rejection

Mice with functionally deleted genes encoding MHC class I heavy (H-2Kb, H-2Db) and light (β2-microglobulin) chains were used in bone marrow cell transfer experiments to study the role of class Ia and Ib molecules in NK cell function. Absence of H-2Kb and absence of H-2Db on bone marrow cells resulted in complete and in almost complete NK-mediated rejection, respectively. Absence of either H-2 class Ib (at least when expressed in H-2 class Ia-deficient mice) or cell surface class Ia free heavy chains did not result in bone marrow rejection. Thus, in C57BL / 6 adult mice, the inactivation of NK cells required for bone marrow cell engraftment relies entirely upon-H-2 class Ia molecules. These results imply the existence of an inhibitory receptor which recognizes either directly or indirectly H-2Db molecules and further suggest that in C57BL / 6 mice the NK cells which do not express a H-2Kb specific inhibitory receptor necessarily express an H-2Db-specific one.

MHC class Ia molecules alone control NK-mediated bone marrow graft rejection.

Mice with functionally deleted genes encoding MHC class I heavy (H-2K(b), H-2D(b)) and light (beta2-microglobulin) chains were used in bone marrow cell transfer experiments to study the role of class Ia and Ib molecules in NK cell function. Absence of H-2K(b) and absence of H-2D(b) on bone marrow cells resulted in complete and in almost complete NK-mediated rejection, respectively. Absence of either H-2 class Ib (at least when expressed in H-2 class Ia-deficient mice) or cell surface class Ia free heavy chains did not result in bone marrow rejection. Thus, in C57BL/6 adult mice, the inactivation of NK cells required for bone marrow cell engraftment relies entirely upon-H-2 class Ia molecules. These results imply the existence of an inhibitory receptor which recognizes either directly or indirectly H-2D(b) molecules and further suggest that in C57BL/6 mice the NK cells which do not express a H-2K(b) specific inhibitory receptor necessarily express an H-2D(b)-specific one.

VLA-5 is expressed by mouse and human long-term repopulating hematopoietic cells and mediates adhesion to extracellular matrix protein fibronectin.

Fibronectin (FN), an extracellular matrix protein, is involved in the adhesion and migration of hematopoietic cells and has been shown to enhance retroviral gene transfer into primitive hematopoietic cells by co-localization of target cells and retrovirus when used as a substrate in vitro. We have previously found that mouse hematopoietic stem cells could be transduced on a FN fragment that included the recognition sequence Arg-Gly-Asp (RGD), suggesting that stem cells may express the integrin very late antigen (VLA)-5. To address this, we investigated the binding of mouse and human hematopoietic cells to recombinant peptides that contained one or a combination of the three principle cell-binding domains of FN. These domains included the VLA-5- binding sequence RGD, the VLA-4-binding site CS1, and the high affinity heparin-binding domain. Here we show that mouse long-term in vivo repopulating stem cells, as well as primitive human NOD/SCID mouse repopulating cells, can bind extracellular matrix protein FN by using integrin VLA-5 in vitro. This binding is specific and can be inhibited by antibodies to VLA-5. In addition, preincubation of BM cells with peptide CH-296, which contains all three primary FN-binding domains, decreased the engraftment of cells in the bone marrow in vivo, while intravenous injection of the same peptide induced an increase of progenitor cells in the spleen. In summary, our data demonstrate that VLA-5 is expressed on primitive mouse and human hematopoietic cells and suggest that there may be significant cooperation between integrin receptors and proteoglycan molecules in the engraftment of bone marrow cells and hematopoietic cell adhesion in vivo.

Cytomegalovirus inhibits the engraftment of donor bone marrow cells by downregulation of hemopoietin gene expression in recipient stroma.

Cytomegalovirus (CMV) disease after bone marrow (BM) transplantation is often associated with BM graft failure. There are two possible reasons for such a correlation. First, a poor hematopoietic reconstitution of unrelated etiology could promote the progression of CMV infection by the lack of immune control. Alternatively, CMV infection could interfere with the engraftment of donor BM cells in recipient BM stroma. Evidence for a causative role of CMV in BM aplasia came from studies in long-term BM cultures and from the murine in vivo model of CMV-induced aplastic anemia. A deficiency in the expression of essential stromal hemopoietins, such as stem cell factor (SCF), has indicated a functional insufficiency of the stromal microenvironment. It remained open to question whether CMV mediates a negative regulation of hemopoietin gene expression (the downregulation model) or whether it causes the default of a positive regulator (the lack-of-induction model). Further, even though implicitly assumed, it has never been formally documented that CMV directly interferes with the engraftment of a BM cell transplant. We addressed these problems in a murine model of CMV infection after experimental male-into-female BM transplantation. The data indicate that the downregulation model applies. Quantitation of the male-sex-determining gene tdy demonstrated an impaired engraftment of donor BM cells in the BM stroma of the female recipients. This graft failure was reflected by a diminished population of SCF-receptor-expressing hematopoietic progenitor cells and correlated with a reduced level of stromal SCF gene expression. Interestingly, high doses of BM cells protected against stromal insufficiency by a mechanism unrelated to control of infection.

Treatment of mice with anti-CD44 after allogeneic bone marrow cell transplantation is lethal.

Because CD44 is known to be of functional importance in hematopoiesis, we were interested in whether anti-CD44 would interfere with syngeneic or allogeneic bone marrow cell engraftment. Syngeneic and allogeneic grafts were accepted by over 80% of mice. In both the syngeneic and the allogeneic host, homing, repopulation, and regain of immunoreactivity was delayed by anti-CD44 treatment. But in the syngeneic host the overall survival rate was unaltered. Instead, less than 25% of anti-CD44-treated, allogeneically reconstituted mice survived by recovery of the host's hematopoietic system, i.e. graft acceptance was close to 0%. The mice died between 4 and 15 days after engraftment and showed severe alterations of the gut. The high death rate of the allogeneically reconstituted mice was specific for anti-CD44 treatment. It did not depend on an ADCC mechanism, could not be abrogated by depletion of T cells, and was only mitigated by depletion of NK cells. According to the histological appearance of the gut, anti-CD44 strengthens a local (gut-associated) graft versus host reaction, which is not mediated by alphabeta T cells and at least not exclusively by NK cells. Because gut death is one of the major reasons for failure in allogeneic bone marrow transplantation, the model of anti-CD44-induced lethality offers itself to clarify the underlying mechanism.

Differential Effects of the Rejection of Bone Marrow Allografts by the Depletion of Activating Versus Inhibiting Ly-49 Natural Killer Cell Subsets

Natural killer cells mediate the specific rejection of bone marrow cell (BMC) allografts in lethally irradiated mice. The Ly-49 family of molecules present on subsets of murine NK cells appears capable of binding class I MHC molecules, resulting in transmission of an inhibitory signal to the NK cell. These Ly-49 family members have been shown to have an immunoreceptor tyrosine-based inhibitory motif that is responsible for the inhibitory signal. However, a new Ly-49 family member was found that lacks this motif, Ly-49D, and evidence suggests that this may be an activating receptor. We therefore compared the role of the activating Ly-49 member with NK cells bearing inhibitory Ly-49 receptors in BMC rejection. Depletion of Ly-49D+ NK cells in H-2b mice abrogated their ability to reject H-2d BMC allografts. Similarly, Ly-49C+ NK cells also were shown to mediate the specific rejection of H-2d BMC. When both subsets were depleted, an additive enhancement of BMC engraftment was observed, indicating that both subsets play a role in the rejection of allogeneic H-2-homozygous H-2d BMC. However, rejection of H-2(b x d) or D8 (H-2b, Dd transgene) BMC allografts was unaffected by Ly-49C+ NK cell depletion in H-2b mice. In marked contrast, depletion of Ly-49D+ NK cells in H-2b mice totally abrogated the rejection of H-2(b x d) heterozygous BMC in support of in vitro data suggesting that Ly-49D+ NK cells receive activating signals. Therefore, NK subsets demonstrate a differential ability to reject H-2 homozygous and heterozygous BMC.

Engraftment of discordant xenogeneic swine bone marrow cells in immunodeficient mice

Abstract: We have recently demonstrated that swine bone marrow cells (BMC) can engraft in C.B‐17 scid mice. While engraftment is enhanced by providing donor‐specific porcine cytokines, the level of swine hematopoiesis declines between 3 and 6 weeks post‐transplant. In the present study, the utility of several strains of immunodeficient mice as recipients of swine hematopoietic cells has been determined by comparing levels of swine bone marrow engraftment at 3 weeks after bone marrow transplant. Irradiated recipients were injected with lxlO8 swine BMC and were treated daily with porcine cytokines. The presence of swine cells in BMT recipients was detected by flow cytometry and marrow colony‐forming assays. Recombination activating gene‐1 (RAG‐1)‐deficient mice were not permissive for the engraftment of swine BMC, even with administration of increased doses of whole body irradiation, or with depleting anti‐NK cell antibody. In contrast, NOD‐scid mice showed improved swine BMC engraftment compared to C.B‐17 scid mice. Levels of swine class I+, myeloid, and CD2+ cells in bone marrow, spleen, and peripheral blood, and the number of porcine myeloid progenitor cells was significantly higher in NOD‐scid recipients than in simultaneous C.B‐17 scid recipients. In addition, the sera from C.B‐17 scid mice markedly inhibited the proliferation of swine BMC in vitro. A weaker inhibitory effect was also mediated by sera from RAG‐1‐deficient mice, but not by sera from NOD‐scid mice. Together, our results indicate that multiple host elements resist xenogeneic hematopoietic engraftment and function, some of which are clearly independent of host T, B, or NK cells. Understanding the basis for the advantage of NODscid mice as recipients of discordant xenogeneic porcine BMC will help to identify these elements.

A substantial level of mixed chimerism is required for the induction of permanent transplantation tolerance

The induction of donor-specific transplantation tolerance is a major goal in organ transplantation, in order to eliminate the requirement for lifelong immunosuppressive therapy. Previously, we have developed a murine bone marrow transplantation model in which recipient mice were treated with a single dose of anti-CD3 and low dose whole body irradiation (WBI). Transfusion of donor bone marrow cells across a full H-2 disparity resulted in induction of high levels of stable mixed chimerism, specific T cell non-responsiveness and indefinite skin allograft survival. The present study has focused on manipulation of the level of chimerism in this model by varying the number of infused bone marrow cells, varying the dose of WBI and addition of syngeneic bone marrow cells. Our results indicate that a substantial level of chimerism is needed for induction of transplantation tolerance. In addition, in the semi-allogeneic donor-recipient combination an even lower dose of WBI was sufficient for engraftment of bone marrow cells and subsequent tolerance induction. We suggest that sharing of MHC antigens between donor and recipient might play an important role in facilitating the development of chimerism and tolerance in organ transplantation.

Lymphocyte Development in Irradiated Thymuses: Dynamics of Colonization by Progenitor Cells and Regeneration of Resident Cells

Lymphocyte development in irradiated thymuses was analyzed using two complementary strategies: anin vitroexperimental model and computer simulations. In thein vitromodel, fetal thymus lobes were irradiated and the regeneration of cells that survived irradiation were examined, with the results compared to those of reconstruction of the thymus by donor bone marrow cells and their competition with the thymic resident cells.In vitromeasurements of resident cell kinetics showed that cell proliferation is slowed down significantly after a relatively low (10 Gy) irradiation dose. Although the number of thymocytes that survived irradiation remained low for several days post-irradiation, further colonization by donor cells was not possible unless performed within 6 h after irradiation. These experimental results, coupled with the analysis by computer simulations, suggest that bone marrow cell engraftment in the irradiated thymus may be limited by the presence of radiation-surviving thymic resident cells and the reduced availability of seeding niches.

Engraftment of bone marrow cells into normal unprepared hosts: effects of 5-fluorouracil and cell cycle status

Bone marrow from animals treated with 5-fluorouracil (5FU) competes equally with normal marrow when assessed in vivo in an irradiated mouse, but shows markedly defective engraftment when transplanted into noncytoablated hosts. Using Southern Blot analysis and a Y-chromosome specific probe, we determined the level of engraftment of male donor cells in the bone marrow, spleen, and thymus of unprepared female hosts. We have confirmed the defective engraftment of marrow harvested 6 days after 5FU (FU-6) and transplanted into unprepared hosts and shown that this defect is transient; by 35 days after 5FU (FU-35), engraftment has returned to levels seen with normal marrow. FU-6 marrow represents an actively cycling population of stem cells, and we hypothesize that the cycle status of the stem cell may relate to its capacity to engraft in the nonirradiated host. Accordingly, we have evaluated the cycle status of engrafting normal and FU-6 marrow into normal hosts using an in vivo hydroxyurea technique. We have shown that those cells engrafting from normal marrow and over 70% of the cells engrafting from FU-6 marrow were quiescent, demonstrating no killing with hydroxyurea. We have also used fluorescent in situ hybridization (FISH) analysis with a Y-chromosome probe and demonstrated that normal and post-5FU engraftment patterns in peripheral blood were similar to those seen in bone marrow, spleen, and thymus. Altogether these data indicate that cells engrafting in normal, unprepared hosts are dormant, and the defect that occurs after 5FU is concomitant with the induction of these cells to transit the cell cycle.

Engraftment of Bone Marrow Cells Into Normal Unprepared Hosts: Effects of 5-Fluorouracil and Cell Cycle Status

Bone marrow from animals treated with 5-fluorouracil (5FU) competes equally with normal marrow when assessed in vivo in an irradiated mouse, but shows markedly defective engraftment when transplanted into noncytoablated hosts. Using Southern Blot analysis and a Y-chromosome specific probe, we determined the level of engraftment of male donor cells in the bone marrow, spleen, and thymus of unprepared female hosts. We have confirmed the defective engraftment of marrow harvested 6 days after 5FU (FU-6) and transplanted into unprepared hosts and shown that this defect is transient; by 35 days after 5FU (FU-35), engraftment has returned to levels seen with normal marrow. FU-6 marrow represents an actively cycling population of stem cells, and we hypothesize that the cycle status of the stem cell may relate to its capacity to engraft in the nonirradiated host. Accordingly, we have evaluated the cycle status of engrafting normal and FU-6 marrow into normal hosts using an in vivo hydroxyurea technique. We have shown that those cells engrafting from normal marrow and over 70% of the cells engrafting from FU-6 marrow were quiescent, demonstrating no killing with hydroxyurea. We have also used fluorescent in situ hybridization (FISH) analysis with a Y-chromosome probe and demonstrated that normal and post-5FU engraftment patterns in peripheral blood were similar to those seen in bone marrow, spleen, and thymus. Altogether these data indicate that cells engrafting in normal, unprepared hosts are dormant, and the defect that occurs after 5FU is concomitant with the induction of these cells to transit the cell cycle.

Recombinant human IL-7 administration in mice affects colony-forming units-spleen and lymphoid precursor cell localization and accelerates engraftment of bone marrow transplants

Murine reconstitution assays were used to investigate the effects of recombinant human interleukin-7 (rhIL-7) on myeloid and lymphoid precursors and on bone marrow engraftment. Reconstitution with bone marrow from rhIL-7-treated mice results in a 3.4-fold decrease in total colony-forming unit-spleen (CFU-S) activity (day 9) and an 18.1- and 11.9-fold decrease in its ability to generate thymocytes and splenic B lineage cells, respectively. In contrast, after reconstitution with splenocytes from rhIL-7-treated mice, CFU-S activity increased 23.6-fold (day 9) and the thymocyte and splenic B lineage cell regenerative capacity increased by 4.0- and 3.2-fold, respectively. In addition, CD43low+, B220low+ cells that contain pre-pro-B cells and pro-B cells were expanded two- to threefold and Ig mu-, B220+, CD2- and Ig mu-, B220+, CD2+ B lineage cells were expanded approximately 10-fold and 10- to 45-fold (depending on the tissue examined), respectively, after rhIL-7 treatment. Administration of rhIL-7 to irradiated mice transplanted with bone marrow resulted in accelerated T cell and B cell reconstitution by up to 2-4 weeks. Thus, rhIL-7 administration affects the distribution of myeloid and lymphoid precursors. Moreover, rhIL-7 administration accelerates murine bone marrow cell engraftment and therefore may be useful in reducing the engraftment time in bone marrow transplant patients.