Mesenchymal progenitor cells in red and yellow bone marrow

Marrow cavities in all bones of newborn mammals contain haematopoietic tissue and stromal microenvironment that support haematopoiesis (haematopoietic microenvironment), known as red bone marrow (BM). From the early postnatal period onwards, the haematopoietic microenvironment, mainly in tubular bones of the extremities, is replaced by mesenchymal cells that accumulate lipid drops, known as yellow BM, whereas haematopoietic tissue gradually disappears. We analysed the ability of mesenchymal cell progenitors in red and yellow BM to produce bone and haematopoietic microenvironment in vivo after transplantation into normal or haematopoietically deficient (irradiated and old) recipients. We found that (1) normal substitution of red with yellow BM results from a gradual loss of mesenchymal stem cells (MSCs) capable of developing bone and haematopoietic microenvironment; (2) the mesenchymal cell population in tubular bones still containing active haematopoietic tissue gradually becomes depleted of MSCs, starting from a young age; (3) haematopoietic microenvironment is incapable of self-maintenance and its renewal depends on the presence of precursor cells; (4) the mesenchymal cell population remaining in areas with yellow BM contains cells able to develop functionally active haematopoietic microenvironment in conditions of haematopoietic insufficiency. Our data also indicate the possible existence of bi-potential stromal precursor cells producing either bone in normal, or bone together with active haematopoietic microenvironment in irradiated or old recipients. This study opens a spectrum of opportunities for the extension of haematopoietic territories by substituting the fat contents of BM cavities with haematopoietic tissue, thereby improving haematopoiesis compromised by cytotoxic treatments, irradiation, ageing, etc.

Immunotherapy of hematologic malignancies and metastatic solid tumors in experimental animals and man

Following engraftment of donor hematopoietic cells and induction of host-versus-graft tolerance, immunocompetent lymphocytes of donor origin can induce graft-versus-leukemia (GVL) and graft-versus-tumor (GVT) effects. Engraftment of allogeneic bone marrow cells can be accomplished following non-myeloablative conditioning while possibly controlling graft-versus-host disease (GVHD). GVL and GVT effects may thus be successfully accomplished following non-myeloablative stem cell transplantation (NST) as shown by data derived from experimental animals and man.

Transplantation of allogeneic or xenogeneic bone marrow within the donor stromal microenvironment

Successful engraftment of hematopoietic stem cells requires a supportive hematopoietic stromal microenvironment (HSM). Defects in the HSM associated with aplastic anemia, myelofibrosis, or caused by intensive ionizing radiation and chemotherapy generally result in failure of bone marrow (BM) engraftment. Transplantation of donor BM within donor HSM may therefore provide optimal conditions for allogeneic BM transplantation. We have transplanted donor hematopoietic cells together with their own HSM to improve acceptance of allogeneic or xenogeneic BM. The non-myeloablative treatment used induced tolerance to murine allografts and provided conditions for the life-long acceptance of allogeneic HSM. Allogeneic BM transplanted within it's own HSM under the kidney capsule caused less graft-versus-host disease than BM transplanted i.v. Tolerance in mice to xenogeneic (rat) HSM was less complete. Ectopic ossicles were small and contained fewer hematopoietic cells. However, simultaneous transplantation of rat BM and HSM to preconditioned mice improved engraftment of rat BM compared with transplantation of BM alone. Donor hematopoietic cells survived longer on their own HSM than on HSM of recipients.

Nonmyeloablative conditioning to induce bilateral tolerance after allogeneic bone marrow transplantation in mice

We recently described a new nonmyeloablative method to induce stable and specific transplantation tolerance to allogeneic tissues in adult mice. It included total lymphoid irradiation (TLI) of recipients with six fractions of 200 cGy each, inoculation with donor bone marrow (BM) cells and cyclophosphamide (Cy) for selective elimination or inactivation of residual donor-reactive cells of the host, and infusion with T-cell depleted donor BM cells after Cy. Here, we investigated the possibility to induce stable bilateral graft-vs-host and host-vs-graft transplantation tolerance using non-T-cell depleted allogeneic BM. Our results show that the dose of BM required for the induction of transplantation tolerance was inversely correlated with the intensity of the conditioning. Transfer of a low dose (3 x 10(6)) of total donor BM cells to recipients preconditioned with a less intensive regimen (two or three TLI fractions instead of six) diminished graft-vs-host disease (GVHD)-related mortality of recipients to 40% and converted 89% of the survivors into GVHD-free mixed hematopoietic chimeras that maintained donor skin allografts >180 days. A tenfold increase in the number of donor BM cells (3 x 10(7) instead of 3 x 10(6)) reduced the rate of GVHD-related mortality of recipients to 20% and resulted in bilateral transplantation tolerance in 100% of nonirradiated survivors.

Induction of bilateral transplantation tolerance to cellular and perfused allografts and xenografts with donor hematopoietic cells

We have recently introduced a new approach for induction of transplantation tolerance to donor alloantigens using well-tolerated non-myeloablative conditioning across MHC and xenogeneic barriers in mice. Our regimen consists of no or very low doses of total lymphoid irradiation (TLI), previously shown to be tolerogenic because of profound yet non-myeloablative immunosuppression, followed by deletion of donor-reactive host lymphocytes activated in vivo with donor hematopoietic cells with a single dose of cyclophosphamide. Recipients of immunosuppressive regimen with lower intensity (e.g., no or one single dose of TLI) required a larger inoculum of donor bone marrow cells; the reverse was also true, both regimens resulting in stable mixed chimerism. A combination of low-dose TLI followed by depletion of donor-reactive host cells with cyclophosphamide resulted in consistent engraftment of even low numbers of T-cell-depleted donor-derived hematopoietic cells, known to be much more difficult to engraft, with consistent induction of permanent and donor-specific transplantation tolerance to donor skin allografts with signs of similar success across xenogeneic barriers.

Permanent and specific transplantation tolerance induced by a nonmyeloablative treatment to a wide variety of allogeneic tissues: I. Induction of tolerance by a short course of total lymphoid irradiation and selective elimination of the donor-specific host lymphocytes

The long-term success of organ transplantation is limited by complications resulting from consistent nonspecific immunosuppression. Induction of stable, donor-specific tolerance remains the main goal of transplantation immunology. In this article, a new, nonmyeloablative method is described for induction of transplantation tolerance to fully mismatched bone marrow cells (BMC), bone marrow stromal precursors, heart muscle, and skin allografts. The method is based on pretransplant conditioning with no postgraft immunosuppression, and consists of a short course (six daily fractions of 200 cGy) of total lymphoid irradiation (sTLI), followed by selective elimination of donor-specific alloreactive cells of the host escaping low-dose sTLI. Donor-specific alloreactive cells were activated by intravenous inoculation with a high dose of donor BMC (3 x 10(7) cells) 1 day after sTLI, and eliminated by a single intraperitoneal dose (200 mg/kg) of cyclophosphamide given 1 day after cell transfer. Infusion of a low number of T cell-depleted BMC (3 x 10(6) cells) after tolerogenic preconditioning converted recipients to stable mixed chimeras free of graft-versus-host disease. The same treatment provided long-lasting acceptance of heterotopically transplanted allografts of the heart muscle and of the stromal precursors to the hematopoietic microenvironment. This treatment also led to acceptance and life-long survival of full-thickness donor skin allografts. However, skin allografts survived only in mice that received donor T cell-depleted BMC after cyclophosphamide and had 20-50% donor cells in the blood. Our results suggest that after sTLI, additional selective clonal deletion of residual host cells induces a state of long-lasting specific tolerance to a wide variety of donor-derived tissues.

Osteogenic growth peptide increases blood and bone marrow cellularity and enhances engraftment of bone marrow transplants in mice

The osteogenic growth peptide (OGP) was characterized recently in regenerating bone marrow (BM) and normal serum. In vitro, the OGP regulates stromal-cell proliferation and differentiated functions. In vivo, an increase in serum OGP accompanies the osteogenic phase of postablation BM regeneration. The present results in normal mice show that OGP induces a balanced increase in WBC counts and overall BM cellularity. In mice receiving myeloablative irradiation and syngeneic or semiallogeneic BM transplants, OGP stimulates hematopoietic reconstruction and doubles the survival rate; these effects are dependent on initiating the OGP administration before irradiation. Chimerism measurements in semiallogeneic graft recipients suggest no preferential effect of OGP on residual host cells. The data implicate OGP in the acceleration of hematopoiesis secondary to expansion of the stromal microenvironment and/or enhancement of stroma-derived signals to stem cells. The low-dose effectiveness of OGP is explained by the demonstration of an autocrine positive feedback loop that together with the OGP-binding protein sustains high serum levels of the peptide. A potential OGP-based treatment in combination with chemoradiotherapy is attractive because of the OGP-induced balanced multi-lineage enhancement of hematopoiesis and possible replacement of expensive recombinant cytokines by a readily synthesized peptide.

Eosinophils activation in post-autologous bone marrow transplanted patients treated with subcutaneous interleukin-2 and interferon-alpha 2A immunotherapy

We evaluated eosinophils morphology, physical properties and antileukemic activity in autologous bone marrow transplanted (ABMT) patients treated with subcutaneous recombinant interleukin 2 (rIL-2) and recombinant human interferon alpha 2a (IFN alpha) given as outpatient immunotherapy. All patients receiving rIL-2/IFN alpha therapy developed peripheral blood eosinophilia of 20-40% peaking at 2-4 weeks of therapy. While on rIL-2/IFN alpha therapy the eosinophils became hypodense and hypersegmented. The antibody dependent cell-mediated cytotoxic activity (ADCC) of the eosinophils against the human B-cell lymphoma cell line (Raji) was depressed post-ABMT. Prolonged (28 days) in vivo rIL-2/IFN alpha immunotherapy enhanced ADCC activity of the eosinophils and brought them to normal levels. Similarly, rIL-2/IFN alpha immunotherapy enhanced the depressed cytotoxic activity of neutrophils post-ABMT to normal levels. Thus, eosinophils and neutrophils from rIL-2/IFN alpha-treated ABMT recipients may be targeted toward tumor cells by antibody, and express tumoricidal activity. No effect of rIL-2/IFN alpha was observed on monocyte-dependent ADCC activity which remained normal post-ABMT. We conclude that in addition to their effect on lymphocytes, cytokine-mediated immunotherapy consisting of subcutaneous low doses of riL-2 and IFN alpha may mediate their therapeutic effects in cancer therapy by increasing the number of eosinophils and enhancing the antitumor activity of eosinophils and neutrophils, provided that tumor-specific or tumor-associated antibodies are present.

Bone formation by marrow osteogenic cells (MBA-15) is not accompanied by osteoclastogenesis and generation of hematopoietic supportive microenvironment

This study was aimed at elucidating the relationship between osteogenic activity of marrow stromal cells and their ability to support hematopoiesis followed by the bone-remodeling process. We used the MBA-15 cell line, which expresses osteoblastic phenotype in vitro and forms bone in diffusion chamber. We have compared bone formation and hematopoietic responses elicited in vivo by these cells with the implantation of freshly isolated bone marrow cells (BMC) or demineralized tooth matrix (DTM). Both MBA-15 cells and BMC, implanted under the kidney capsule, yielded intramembraneous bone, but DTM, implanted subcutaneously, elicited endochondral bone. MBA-15 formed primary bone, mimicking only the initial sequential stages of the ossification process. Neither histologic signs of bone resorption and remodeling nor tartrate-resistant acid phosphatase (TRAP)-positive cells and marrow formation were observed. Bone formation was monitored biochemically. Functions for hematopoietic stem and committed cell content were measured by GM-CFU and BFU-E assays that confirmed the morphologic observations. In both BMC and DTM implantation, bone formation was followed by hematopoietic activity, osteoclastogenesis, and remodeling. We conclude that MBA-15 osteoprogenitor cells, despite their extensive bone formation ability, are unable to form a microenvironment supportive for hematopoiesis and osteoclastogenesis or to initiate bone remodeling.

Ability of the hemopoietic microenvironment in the induced bone to maintain the proliferative potential of early hemopoietic precursors

A comparison of proliferative potential was made between spleen colony forming unit (CFU-S) from skeletal bones and those from ectopically induced ossicles. To this end, mice having two types of ectopic ossicles were used. Each animal was implanted s.c. with demineralized tooth matrix (which served as a source of bone-inducing activity) and again beneath the renal capsule with a femoral bone marrow plug (which was a source of viable osteogenic cells). Those recipient mice that had developed ectopic ossicles were lethally irradiated and then reconstituted with syngeneic bone marrow cells. At various times post-reconstitution, the proliferative potential (PP) of CFU-S in skeletal bones and ectopic ossicles of mice was studied in a double spleen colony test. Hemopoietic cells from each source were injected into lethally irradiated mice; in 11 days, spleen colonies were cut out, and their cells were reinjected into secondary irradiated recipients. The PP of CFU-S was evaluated by examining the development of daughter CFU-S. It was found that, in the hemopoietic microenvironment of induced ossicles, skeletal bone and ectopic ossicles developed by viable osteogenic cells, the PP of CFU-S is maintained to the same extent.