Prevention of diabetes in nonobese diabetic mice by nonmyeloablative allogeneic bone marrow transplantation

Stability of Chimerism in Non-Obese Diabetic Mice Achieved By Rapid T Cell Depletion Is Associated With High Levels of Donor Cells Very Early After Transplant

Stable mixed hematopoietic chimerism is a robust method for inducing donor-specific tolerance with the potential to prevent rejection of donor islets in recipients with autoimmune type-1 diabetes. However, with reduced intensity conditioning, fully allogeneic chimerism in a tolerance resistant autoimmune-prone non-obese diabetic (NOD) recipient has rarely been successful. In this setting, successful multilineage chimerism has required either partial major histocompatability complex matching, mega doses of bone marrow, or conditioning approaches that are not currently clinically feasible. Irradiation free protocols with moderate bone marrow doses have not generated full tolerance; donor skin grafts were rejected. We tested whether more efficient recipient T cell depletion would generate a more robust tolerance. We show that a combination of donor-specific transfusion-cyclophosphamide and multiple T cell depleting antibodies could induce stable high levels of fully allogeneic chimerism in NOD recipients. Less effective T cell depletion was associated with instability of chimerism. Stable chimeras appeared fully donor-specific tolerant, with clonal deletion of allospecific T cells and acceptance of donor skin grafts, while recovering substantial immunocompetence. The loss of chimerism months after transplant was significantly associated with a lower level of chimerism and donor T cells within the first 2 weeks after transplant. Thus, rapid and robust recipient T cell depletion allows for stable high levels of fully allogeneic chimerism and robust donor-specific tolerance in the stringent NOD model while using a clinically feasible protocol. In addition, these findings open the possibility of identifying recipients whose chimerism will later fail, stratifying patients for early intervention.

The hematopoietic system in the context of regenerative medicine

Hematopoietic stem cells (HSC) represent the prototype stem cell within the body. Since their discovery, HSC have been the focus of intensive research, and have proven invaluable clinically to restore hematopoiesis following inadvertent radiation exposure and following radio/chemotherapy to eliminate hematologic tumors. While they were originally discovered in the bone marrow, HSC can also be isolated from umbilical cord blood and can be "mobilized" peripheral blood, making them readily available in relatively large quantities. While their ability to repopulate the entire hematopoietic system would already guarantee HSC a valuable place in regenerative medicine, the finding that hematopoietic chimerism can induce immunological tolerance to solid organs and correct autoimmune diseases has dramatically broadened their clinical utility. The demonstration that these cells, through a variety of mechanisms, can also promote repair/regeneration of non-hematopoietic tissues as diverse as liver, heart, and brain has further increased their clinical value. The goal of this review is to provide the reader with a brief glimpse into the remarkable potential HSC possess, and to highlight their tremendous value as therapeutics in regenerative medicine.

Immunological Basis for Rapid Progression of Diabetes in Older NOD Mouse Recipients Post BM-HSC Transplantation

Type I diabetes (T1D), mediated by autoreactive T cell destruction of insulin-producing islet beta cells, has been treated with bone marrow-derived hematopoietic stem cell (BM-HSC) transplantation. Older non-obese diabetic (NOD) mice recipients (3m, at disease-onset stage) receiving syngeneic BM-HSC progressed more rapidly to end-stage diabetes post-transplantation than younger recipients (4-6w, at disease-initiation stage). FACS analyses showed a higher percentage and absolute number of regulatory T cells (Treg) and lower proportion of proliferating T conventional cells (Tcon) in pancreatic lymph nodes from the resistant mice among the younger recipients compared to the rapid progressors among the older recipients. Treg distribution in spleen, mesenteric lymph nodes (MLN), blood and thymus between the two groups was similar. However, the percentage of thymic Tcon and the proliferation of Tcon in MLN and blood were lower in the young resistants. These results suggest recipient age and associated disease stage as a variable to consider in BM-HSC transplantation for treating T1D.

Regimen-specific effects of RNA-modified chimeric antigen receptor T cells in mice with advanced leukemia

Cytotoxic T lymphocytes modified with chimeric antigen receptors (CARs) for adoptive immunotherapy of hematologic malignancies have demonstrated activity in early phase clinical trials. While T cells bearing stably expressed CARs are efficacious and have potential long-term persistence, temporary expression of a CAR via RNA electroporation is also potentially efficacious in preclinical models. Temporary CAR expression using RNA presents a method of testing CARs clinically with additional safety where there may be concerns about possible chronic "on-target, off-tumor" toxic effects, as the degradation of RNA ensures complete removal of the CAR over time without relying on suicide induction systems. CD19-directed RNA CAR T cells were tested in vivo for efficacy and comparison to lentiviral vector (LV)-generated stable CAR T cells. We tested the hypothesis that multiple infusions of RNA CAR T cells preceded by lymphodepleting chemotherapy could mediate improved survival and sustained antitumor responses in a robust leukemia xenograft model. The saturation strategy using rationally designed multiple infusions of RNA CARs based on multiple model iterations approached the efficacy of a stable LV expression method. Two-color imaging revealed that relapse was a locoregional phenomenon in both the temporary and the stable expression models. In marked contrast to stably expressed CARs with retroviral or LV technology, the efficacy of RNA CARs appears independent of the costimulatory signaling endodomains likely because they more influence proliferation and persistence rather than short-term efficacy. The efficacy of the RNA CAR infusions may approach that of stably expressed CARs, offer theoretically safer initial clinical testing in addition to suicide systems, and allow for rapid and effective iterative preclinical modeling for the testing of new targets.

Tolerance-inducing strategies in islet transplantation

Allogeneic islet transplantation is a promising approach for restoring normoglycemia in type 1 diabetic patients. Current use of immunosuppressive therapies for management of islet transplant recipients can be counterintuitive to islet function and can lead to complications in the long term. The induction of donor-specific tolerance eliminates the dependency on immunosuppression and allows recipients to retain responses to foreign antigens. The mechanisms by which tolerance is achieved involve the deletion of donor-reactive T cells, induction of T-cell anergy, immune deviation, and generation of regulatory T cells. This review will outline the various methods used for inducing donor-specific tolerance in islet transplantation and will highlight the previously unforeseen potential of tissue stromal cells in promoting islet engraftment.

Preimplantation factor (PIF) analog prevents type I diabetes mellitus (TIDM) development by preserving pancreatic function in NOD mice

Preimplantation factor (PIF) is a novel embryo-secreted immunomodulatory peptide. Its synthetic analog (sPIF) modulates maternal immunity without suppression. There is an urgent need to develop agents that could prevent the development of type 1 diabetes mellitus (TIDM). Herein, we examine sPIF's preventive effect on TIDM development by using acute adoptive-transfer (ATDM) and spontaneously developing (SDM) in non-obese diabetic (NOD) murine models. Diabetes was evaluated by urinary and plasma glucose, intraperitoneal glucose tolerance test (IPGTT), pancreatic islets insulin staining by immunohistochemistry and by pancreatic proteome evaluation using mass spectrometry, followed by signal pathway analysis. Continuous administration of sPIF for 4-weeks prevents diabetes development in ATDM model in >90% of recipients demonstrated by normal IPGTT, preserved islets architecture, number, and insulin staining. (P < 0.01). sPIF effect was specific; its protective effects are not replicated by scrambled PIF (χ(2) = 0.009) control. sPIF led also to increased circulating Th2 and Th1 cytokines. In SDM model, 4-week continuous sPIF administration prevented onset of diabetes for 21 weeks post-therapy (P < 0.01). Low-dose sPIF administration for 16 weeks prevented diabetes development up to 14 weeks post-therapy, evidenced by preserved islets architecture and insulin staining. In SDM model, pancreatic proteome pathway analysis demonstrated that sPIF regulates protein traffic, prevents protein misfolding and aggregation, and reduces oxidative stress and islets apoptosis, leading to preserved insulin staining. sPIF further increased insulin receptor expression and reduced actin and tubulin proteins, thereby blocking neutrophil invasion and inflammation. Exocrine pancreatic function was also preserved. sPIF administration results in marked prevention of spontaneous and induced adoptive-transfer diabetes suggesting its potential effectiveness in treating early-stage TIDM.

Immunosuppressive therapy exacerbates autoimmunity in NOD mice and diminishes the protective activity of regulatory T cells

Mounting evidence indicates that immunosuppressive therapy and autologous bone marrow transplantation are relatively inefficient approaches to treat autoimmune diabetes. In this study we assessed the impact of immunosuppression on inflammatory insulitis in NOD mice, and the effect of radiation on immunomodulation mediated by adoptive transfer of various cell subsets. Sublethal radiation of NOD females at the age of 14 weeks (onset of hyperglycemia) delayed the onset of hyperglycemia, however two thirds of the mice became diabetic. Adoptive transfer of splenocytes into irradiated NON and NOD mice precipitated disease onset despite increased contents of CD25(+)FoxP3(+) T cells in the pancreas and regional lymphatics. Similar phenotypic changes were observed when CD25(+) T cells were infused after radiation, which also delayed disease onset without affecting its incidence. Importantly, irradiation increased the susceptibility to diabetes in NOD and NON mice (71-84%) as compared to immunomodulation with splenocytes and CD25(+) T cells in naïve recipients (44-50%). Although irradiation had significant and durable influence on pancreatic infiltrates and the fractions of functional CD25(+)FoxP3(+) Treg cells were elevated by adoptive cell transfer, this approach conferred no protection from disease progression. Irradiation was ineffective both in debulking of pathogenic clones and in restoring immune homeostasis, and the consequent homeostatic expansion evolves as an unfavorable factor in attempts to restore self-tolerance and might even provoke uncontrolled proliferation of pathogenic clones. The obstacles imposed by immunosuppression on abrogation of autoimmune insulitis require replacement of non-specific immunosuppressive therapy by selective immunomodulation that does not cause lymphopenia.

Preventive effects of syngeneic bone marrow transplantation on diabetic nephropathy in mice

Treatment with autologous bone marrow transplantation (ABMT) can change the natural history of diabetes in patients with new-onset Type 1 diabetes (T1D). Effects of syngeneic bone marrow transplantation (syn-BMT) on diabetic nephropathy were studied in streptozotocin-induced diabetic mice. Diabetic mice received sibling's bone marrow on days 3, 10, 20, or 40 after T1D onset, respectively. Renal pathology, levels of oxidative stress, and the expressions of angiotensinogen (AGT), monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor beta 1 (Tgf-beta1) mRNA were investigated. Treatment with syn-BMT when disease was early-onset reduced mesangial area expansion and kidney enlargement; besides, if it is given on day 10, syn-BMT attenuated glomerular hypertrophy. Oxidative stress factors such as catalase (CAT) and superoxide radical anion O(2-) (O(2-)) were markedly maintained by syn-BMT compared to mice without treatment. In diabetic mice without treatment, renal AGT and MCP-1 mRNA were increased, while they were effectively suppressed by syn-BMT. But it showed no changes or even increment in Tgf-beta1 mRNA after syn-BMT. Syn-BMT, if applied when disease was early-onset, ameliorated diabetic renal injury. These preventive effects could be partly via maintaining oxidative stress and expression of AGT and MCP-1 in kidney in streptozotocin-diabetic mice.

Time point is important for effects of syngeneic bone marrow transplantation for type 1 diabetes in mice

OBJECTIVES

Autologous hematopoietic stem cell transplantation (HSCT) has recently become a novel therapy for patients with new-onset type 1 diabetes (T1D). However, the optimal time points for HSCT are still unknown.

METHODS

By using multiple low-dose streptozotocin (STZ)-induced T1D mice models, we performed syngeneic bone marrow transplantation (syn-BMT) in diabetic mice at various time points new-onset day 3 (n = 12); new-onset day 10 (n = 13); later-onset day 20 (n = 12); and day 40 (n = 7), respectively. At 120 days after syn-BMT, we examined pancreata histology, serum insulin, and CD4(+)CD25(+)FoxP3(+) T regulatory lymphocytes (Tregs).

RESULTS

Our previous results showed that syn-BMT can overcome diabetes when performed on day 10, but not at day 40. Our new data showed BMT only attenuated diabetes when done on day 3 or day 20. Moreover, the percentage of Tregs in the spleen correlated with the attenuation of hyperglycemia.

SIGNIFICANCE

These results indicated that syn-BMT should be performed, when diabetes is neither too new-onset nor too late-stage. Tregs represent one mechanism for syn-BMT-induced restoration of immune tolerance in STZ-diabetic mice.

Resolving the conundrum of islet transplantation by linking metabolic dysregulation, inflammation, and immune regulation

Although type 1 diabetes cannot be prevented or reversed, replacement of insulin production by transplantation of the pancreas or pancreatic islets represents a definitive solution. At present, transplantation can restore euglycemia, but this restoration is short-lived, requires islets from multiple donors, and necessitates lifelong immunosuppression. An emerging paradigm in transplantation and autoimmunity indicates that systemic inflammation contributes to tissue injury while disrupting immune tolerance. We identify multiple barriers to successful islet transplantation, each of which either contributes to the inflammatory state or is augmented by it. To optimize islet transplantation for diabetes reversal, we suggest that targeting these interacting barriers and the accompanying inflammation may represent an improved approach to achieve successful clinical islet transplantation by enhancing islet survival, regeneration or neogenesis potential, and tolerance induction. Overall, we consider the proinflammatory effects of important technical, immunological, and metabolic barriers including: 1) islet isolation and transplantation, including selection of implantation site; 2) recurrent autoimmunity, alloimmune rejection, and unique features of the autoimmune-prone immune system; and 3) the deranged metabolism of the islet transplant recipient. Consideration of these themes reveals that each is interrelated to and exacerbated by the other and that this connection is mediated by a systemic inflammatory state. This inflammatory state may form the central barrier to successful islet transplantation. Overall, there remains substantial promise in islet transplantation with several avenues of ongoing promising research. This review focuses on interactions between the technical, immunological, and metabolic barriers that must be overcome to optimize the success of this important therapeutic approach.

Reversal of new-onset type 1 diabetes in mice by syngeneic bone marrow transplantation

Autologous hematopoietic stem cell transplantation (HSCT) has recently been performed as a novel strategy to treat patients with new-onset type 1 diabetes (T1D). However, the mechanism of autologous HSCT-induced remission of diabetes remains unknown. In order to help clarify the mechanism of remission-induction following autologous HSCT in patients with T1D, mice treated with multiple low doses of streptozotocin to induce diabetes were used as both donors (n=20) and recipients (n=20). Compared to streptozocin-treated mice not receiving transplantation, syngeneic bone marrow transplantation (syn-BMT) from a streptozocin-treated diabetic donor, if applied during new-onset T1D (day 10 after diabetes onset), can reverse hyperglycemia without relapse (P<0.001), maintain normal blood insulin levels (P<0.001), and preserve islet cell mass. Compared to diabetic mice not undergoing HSCT, syn-BMT, results in restoration of Tregs in spleens (P<0.01), increased Foxp3 mRNA expression (P<0.01) and increased Foxp3 protein expression (P<0.05). This diabetic-remission-inducing effect occurred in mice receiving bone marrow from either streptozocin-treated diabetic or non-diabetic normal donors. We conclude that autologous HSCT remission of diabetes is more than transient immune suppression, and is capable of prolonged remission-induction via regeneration of CD4+CD25+FoxP3+ Tregs.

Blood and Marrow Transplant Clinical Trials Network State of the Science Symposium 2007

Outcomes of hematopoietic cell transplantation are steadily improving. New techniques have reduced transplant toxicities, and there are new sources of hematopoietic stem cells from unrelated donors. In June 2007 the Blood and Marrow Transplant Clinical Trials Network convened a State of the Science Symposium of more than 200 participants in Ann Arbor to identify the most compelling clinical research opportunities in the field. This report summarizes the symposium's discussions and identifies eleven high priority clinical trials that the network plans to pursue over the course of the next several years.

Deletion of Donor-Reactive Cells as a New Conditioning Regimen for Allogeneic Bone Marrow Transplantation

Progress in the development of less toxic conditioning for bone marrow transplantation (BMT) came with the understanding that acceptance of mismatched BM does not require myeloablation of recipients. Lymphocyte deletion by a cocktail of immunosuppressive drugs is generally sufficient to ensure engraftment of compatible BM cells. However, reduced intensity conditioning (RIC) protocols available today do not provide robust tolerance to mismatched allogeneic BM. Herein we discuss 2 new experimental approaches to RIC protocols with the aim of facilitating allogeneic BM engraftment. Both conditioning regimens are based on selective deletion/inactivation of donor-reactive cells before BMT. Our data show that the first conditioning protocol, comprising priming of recipients by a donor-specific lymphocyte transfusion (DST) on day -2 and a single injection of cyclophosphamide, a drug that is predominantly toxic for proliferating cells, on day -1, consistently improves engraftment of allogeneic BM (day 0) in all experimental models tested. The second engraftment enhancing approach is based on the blockade by antagonistic reagents of the signaling pathways that govern the antigen-induced immune response. Combining the signaling blockade with the deletion of activated donor-reactive cells by cytoreductive agents provides additional benefits for transplantation across major histocompatibility barriers.

Diabetes impairs endothelial progenitor cell-mediated blood vessel formation in response to hypoxia

BACKGROUND

Diabetics suffer from vascular dysfunction with increased risks of coronary artery disease and peripheral vascular disease secondary to an impaired ability to respond to tissue ischemia. Because endothelial progenitor cells are known to home to sites of ischemia and participate in new blood vessel growth, the authors examined the effects of diabetes on human endothelial progenitor cell function and peripheral tissue signaling in hypoxia, and determined whether these cells might be a useful cell-based therapy for diabetic vascular complications.

METHODS

Circulating human endothelial progenitor cells from type 2 diabetic patients and controls were isolated and subjected to in vitro adhesion, migration, and proliferation assays (n = 5). Cell mobilization and recruitment were studied in vivo in diabetic and nondiabetic environments (n = 6). Exogenous human diabetic and normal cells were analyzed for therapeutic efficacy in a murine ischemia model (n = 6).

RESULTS

Adhesion, migration, and proliferation of human diabetic endothelial progenitor cells in response to hypoxia was significantly reduced compared with controls. In diabetic mice, cell mobilization from the bone marrow and recruitment into ischemic tissue was significantly reduced compared with controls. Normal cells injected systemically as replacement therapy in a diabetic mouse increased but did not normalize ischemic tissue survival.

CONCLUSIONS

These findings suggest that diabetes causes defects in both the endothelial progenitor cell and peripheral tissue responses to hypoxia. These changes in endothelial progenitor cell function and signaling offer a novel explanation for the poor clinical outcome of type 2 diabetics following ischemic events. Based on these findings, it is unlikely that endothelial progenitor cell-based cellular therapies will be able to prevent diabetic complications.

Approaches towards endogenous pancreatic regeneration

The phenomenon of pancreatic regeneration in mammals has been well documented. It has been shown that pancreatic tissue is able to regenerate in several species of mammal after surgical insult. This tissue is also known to have the potential to maintain or increase its beta-cell mass in response to metabolic demands during pregnancy and obesity. Since deficiency in beta-cell mass is the hallmark of most forms of diabetes, it is worthwhile understanding pancreatic regeneration in the context of this disease. With this view in mind, this article aims to discuss the potential use in clinical strategies of knowledge that we obtained from studies carried out in animal models of diabetes. Approaches to achieve this goal involve the use of biomolecules, adult stem cells and gene therapy. Various molecules, such as glucagon-like peptide-1, beta-cellulin, nicotinamide, gastrin, epidermal growth factor-1 and thyroid hormone, play major roles in the initiation of endogenous islet regeneration in diabetes. The most accepted hypothesis is that these molecules stimulate islet precursor cells to undergo neogenesis or to induce replication of existing beta-cells, emphasizing the importance of pancreas-resident stem/progenitor cells in islet regeneration. Moreover, the potential of adult stem cell population from bone marrow, umbilical cord blood, liver, spleen, or amniotic membrane, is also discussed with regard to their potential to induce pancreatic regeneration.

Bone marrow transplantation combined with gene therapy to induce antigen-specific tolerance and ameliorate EAE

Hematopoietic stem cell (HSC) transplantation is a potential therapy that can offer multiple sclerosis patients a radical, potentially curative treatment. Using experimental autoimmune encephalomyelitis (EAE) as a model, we previously reported that retrovirally transduced B cells expressing myelin basic protein (MBP), MBP Ac1-11, or myelin oligodendrocyte glycoprotein p35-55 induced tolerance and reduced symptoms. Here, we extend our tolerance approach using bone marrow (BM) cells expressing full-length phospholipid protein (PLP) in a model for relapsing, remitting EAE. Using GFP expression as a marker, we found that up to 50% of cells were positive for transgene expression in peripheral blood after 900 rad irradiation and transduced BM transplantation, and expression was stable in hematopoietic lineages for over 10 weeks. Upon challenge, T cell proliferation in response to PLP p139-151 was reduced and EAE was completely abolished in a pretreatment protocol. In addition, protection from EAE could be achieved with PLP-transduced BM cells given on day 12 after immunization, a potential therapeutic protocol. Finally, the protective effect of PLP-expressing BM could also be observed using a nonmyeloablative protocol, albeit with lower efficacy. Our results suggest that HSC may be useful to achieve long-lasting tolerance to protect mice from EAE and possibly to promote CNS repair in ongoing EAE.

Nonmyeloablative stem cell transplantation and cell therapy for malignant and non-malignant diseases

The conditioning prior to allogeneic stem cell transplantation was originally designed as a myeloablative conditioning, designed to eliminate malignant or genetically abnormal cells and then use the transplant procedure for rescue of the patients or to replace missing bone marrow products. However, allografts can induce effective graft vs. malignancy effects and can also eliminate undesirable hematopoietic stem cells in patients with genetic disorders and autoimmune diseases, thus documenting that alloreactive effects mediated by donor lymphocytes post-grafting can play a major role in eliminating hematopoietic cell of host origin, as well as provide effective immunotherapy for the treatment of disease recurrence. The efficacy of donor lymphocyte infusion (DLI) could be improved by activation with rIL-2 or by donor immunization. The cumulative experience over the years suggesting that alloreactive donor lymphocytes were most effective in eliminating tumor cells of host origin resulted in an attempt to reduce the intensity of the conditioning in preparation for the transplant procedure used for the treatment of hematological and other malignancies as well as life-threatening non-malignant disorders for which allogeneic stem cell transplantation may be indicated. Our working hypothesis proposed that the myeloablative conditioning which is hazardous and may be associated with early and late side effects, may not be required for treatment of patients with any indication for allogeneic stem cell transplantation. Instead, nonmyeloablative conditioning based on the use of reduced intensive preparatory regimen, also known as nonmyeloablative stem cell transplantation, may be sufficient for engraftment of donor stem cells while avoiding procedure-related toxicity and mortality, followed by elimination of undesirable cells of host origin by post-transplant effects mediated by alloreactive donor lymphocytes infused along with donor stem cells or administered subsequently as DLI. Improvement of the immediate outcome of stem cell transplantation using NST due to a significant decrease in transplant related mortality has broadened the spectrum of patients eligible for allogeneic stem cell transplantation, including elderly patients and other patients with less than optimal performance status. Likewise, the safer use of stem cell transplantation prompted expanding the scope of potential indications for allogeneic stem cell transplantation, such as metastatic solid tumors and autoimmune disorders, which now are slowly becoming much more acceptable. Current strategies focus on the need to improve the capacity of donor lymphocytes to eliminate undesirable malignant and non-malignant hematopoietic cells of host origin, replacing abnormal or malignant stem cells or their products with normal hematopoietic stem cells of donor origin, while minimizing procedure-related toxicity and mortality and improving the quality of life by reducing the incidence and severity of hazardous acute and chronic GVHD.

Depletion of alloantigen-primed lymphocytes overcomes resistance to allogeneic bone marrow in mildly conditioned recipients

OBJECTIVE

Successful implantation of allogeneic bone marrow (BM) cells after nonmyeloablative conditioning would allow to compensate for the inadequate supply of compatible grafts and to reduce mortality of graft-vs.-host disease (GVHD). Recently, we proposed to facilitate engraftment of mismatched BM by conditioning for alloantigen-primed lymphocyte depletion (APLD) with cyclophosphamide (CY). Here we summarize the experimental results obtained by this approach.

MATERIALS AND METHODS

Naive or mildly irradiated BALB/c mice were primed with C57BL/6 BM cells (day 0), treated with CY (day 1) to deplete alloantigen-primed lymphocytes, and given a second C57BL/6 BM transplant (day 2) for engraftment. Recipients were repeatedly tested for chimerism in the blood and followed for GVHD and survival. The protocol was also tested for inducing tolerance to donor tissue and organ allografts, and for treatment of leukemia, breast cancer, and autoimmune diabetes in NOD mice.

RESULTS

APLD by 200 mg/kg CY provided engraftment of allogeneic BM from the same donor in 100% mildly irradiated recipients. Eighty percent chimeras remained GVHD-free more 200 days. All chimeras accepted permanently donor skin grafts and donor hematopoietic stromal progenitors. Allogeneic BM transplantation (BMT) after APLD had a strong therapeutic potential in BALB/c mice harboring malignant cells and in autoimmune NOD recipients. Tolerance-inducing CY dose could be reduced to 100 mg/kg. Conditioning for APLD resulted in engraftment of allogeneic BM after a significantly lower radiation dose than treatment with radiation and CY alone.

CONCLUSION

Our results demonstrate that conditioning for APLD has a definite advantage over general immunosuppression with CY and radiation therapy.