Reduced intensity conditioning for allogeneic hematopoietic stem-cell transplant determines the kinetics of acute graft-versus-host disease

FL/GCSF/AMD3100-mobilized Hematopoietic Stem Cells Induce Mixed Chimerism With Nonmyeloablative Conditioning and Transplantation Tolerance

BACKGROUND

Mobilization of hematopoietic stem cells (HSCs) has become the preferred approach for HSC transplantation. AMD3100, a competitive inhibitor of C-X-C motif chemokine receptor-4, has been found to be a rapid mobilizing agent. The present study evaluated approaches to optimize the product collected.

METHODS

Mobilized peripheral blood mononuclear cells (mPBMCs) from B6 mice were transplanted to recipient BALB/c mice conditioned with ablative or nonmyeloablative approaches.

RESULTS

The optimal dose of AMD3100 was found to be 5.0 mg/kg. Optimal HSC mobilization was observed when AMD3100 (day 10) was coadministered with Flt3 ligand (FL) (days 1-10) and granulocyte colony-stimulating factor (GCSF) (days 4-10). There was a 228.8-fold increase of HSC with FL/GCSF/AMD3100 compared with AMD3100 treatment alone. When unmodified mPBMCs were transplanted into ablated allogeneic recipients, all recipients expired by day 40 from severe acute graft versus host disease (GVHD). When T cells were depleted from mPBMC, long-term survival and engraftment were achieved in majority of the recipients. When PBMC mobilized by FL/GCSF/AMD3100 were transplanted into recipients conditioned nonmyeloablatively with anti-CD154/rapamycin plus 100, 200, and 300 cGy of total body irradiation, 42.9%, 85.7%, and 100% of mice engrafted, respectively. Donor chimerism was durable, multilineage, and stable. Lymphocytes from mixed chimeras showed no response to host or donor antigens, suggesting functional bidirection T-cell tolerance in vitro. Most importantly, none of the engrafted mice exhibited clinical features of GVHD.

CONCLUSIONS

FL/GCSF/AMD3100 is an efficient treatment to maximally mobilize HSC. Durable engraftment and donor-specific tolerance can be achieved with mPBMC in nonmyeloablative conditioning without GVHD.

Cutaneous graft-versus-host disease after hematopoietic stem cell transplant - a review

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplants (allo-HSCT) associated with significant morbidity and mortality. The earliest and most common manifestation is cutaneous graft-versus-host disease. This review focuses on the pathophysiology, clinical features, prevention and treatment of cutaneous graft-versus-host disease. We discuss various insights into the disease's mechanisms and the different treatments for acute and chronic skin graft-versus-host disease.

Bone Marrow Graft-Versus-Host Disease in Major Histocompatibility Complex-Matched Murine Reduced-Intensity Allogeneic Hemopoietic Cell Transplantation

BACKGROUND

Most clinical allogeneic hemopoietic cell transplants (alloHCT) are now performed using reduced-intensity conditioning (RIC) instead of myeloablative conditioning (MAC); however, the biology underlying this treatment remains incompletely understood.

METHODS

We investigated a murine model of major histocompatibility complex-matched multiple minor histocompatibility antigen-mismatched alloHCT using bone marrow (BM) cells and splenocytes from B6 (H-2) donor mice transplanted into BALB.B (H-2) recipients after RIC with fludarabine of 100 mg/kg per day for 5 days, cyclophosphamide of 60 mg/kg per day for 2 days, and total body irradiation (TBI).

RESULTS

The lowest TBI dose capable of achieving complete donor chimerism in this mouse strain combination was 325 cGy given as a single fraction. Mice that underwent RIC had a reduced incidence and delayed onset of graft-versus-host disease (GVHD) and significantly prolonged survival compared with MAC-transplanted recipients (TBI of 850 cGy plus cyclophosphamide of 60 mg/kg per day for 2 days). Compared with syngeneic controls, RIC mice with GVHD showed evidence of BM suppression, have anemia, reduced BM cellularity, and showed profound reduction in BM B cell lymphopoiesis associated with damage to the endosteal BM niche. This was associated with an increase in BM CD8 effector T cells in RIC mice and elevated blood and BM plasma levels of T helper1 cytokines. Increasing doses of splenocytes resulted in increased incidence of GVHD in RIC mice.

CONCLUSIONS

We demonstrate that the BM is a major target organ of GVHD in an informative clinically relevant RIC mouse major histocompatibility complex-matched alloHCT model by a process that seems to be driven by CD8 effector T cells.

Unique patterns of CD8+ T-cell-mediated organ damage in the Act-mOVA/OT-I model of acute graft-versus-host disease

T-cell receptor (TCR)-transgenic models of acute graft-versus-host disease (aGvHD) offer a straightforward and highly controlled approach to study the mechanisms and consequences of T-cell activation following allogeneic hematopoietic stem cell transplantation (aHSCT). Here, we report that aHSCT involving OT-I mice as donors, carrying an ovalbumin-specific CD8+ TCR, and Act-mOVA mice as recipients, expressing membrane-bound ovalbumin driven by the β-actin promoter, induces lethal aGvHD in a CD8+ T-cell-dependent, highly reproducible manner, within 4-7 days. Tracking of UBC-GFP/OT-I graft CD8+ T cells disclosed heavy infiltration of the gastrointestinal tract, liver, and lungs at the onset of the disease, and histology confirmed hallmark features of gastrointestinal aGVHD, hepatic aGvHD, and aGvHD-associated lymphocytic bronchitis in infiltrated organs. However, T-cell infiltration was virtually absent in the skin, a key target organ of human aGvHD, and histology confirmed the absence of cutaneous aGVHD, as well. We show that the model allows studying CD8+ T-cell responses in situ, as selective recovery of graft CD45.1/OT-I CD8+ T cells from target organs is simple and feasible by automated tissue dissociation and subsequent cell sorting. Assessment of interferon-gamma production by flow cytometry, granzyme-B release by ELISA, TREC assay, and whole-genome gene expression profiling confirmed that isolated graft CD8+ T cells remained intact, underwent clonal expansion, and exerted effector functions in all affected tissues. Taken together, these data demonstrate that the OT-I/Act-mOVA model is suitable to study the CD8+ T-cell-mediated effector mechanisms in a disease closely resembling fatal human gastrointestinal and hepatic aGVHD that may develop after aHSCT using HLA-matched unrelated donors.

Immunosuppressive human anti-CD83 monoclonal antibody depletion of activated dendritic cells in transplantation

Current immunosuppressive/anti-inflammatory agents target the responding effector arm of the immune response and their nonspecific action increases the risk of infection and malignancy. These effects impact on their use in allogeneic haematopoietic cell transplantation and other forms of transplantation. Interventions that target activated dendritic cells (DCs) have the potential to suppress the induction of undesired immune responses (for example, graft versus host disease (GVHD) or transplant rejection) and to leave protective T-cell immune responses intact (for example, cytomegalovirus (CMV) immunity). We developed a human IgG1 monoclonal antibody (mAb), 3C12, specific for CD83, which is expressed on activated but not resting DC. The 3C12 mAb and an affinity improved version, 3C12C, depleted CD83(+) cells by CD16(+) NK cell-mediated antibody-dependent cellular cytotoxicity, and inhibited allogeneic T-cell proliferation in vitro. A single dose of 3C12C prevented human peripheral blood mononuclear cell-induced acute GVHD in SCID mouse recipients. The mAb 3C12C depleted CMRF-44(+)CD83(bright) activated DC but spared CD83(dim/-) DC in vivo. It reduced human T-cell activation in vivo and maintained the proportion of CD4(+) FoxP3(+) CD25(+) Treg cells and also viral-specific CD8(+) T cells. The anti-CD83 mAb, 3C12C, merits further evaluation as a new immunosuppressive agent in transplantation.

Insights into the pathogenesis of GvHD: what mice can teach us about man

Acute graft-vs-host disease (GvHD) is a life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT). Most of the knowledge about the biology of GvHD is derived from mouse models of this disease and therefore a critical analysis of potential advantages and disadvantages of the murine GvHD models is important to classify and understand the findings made in these models. The central events leading up to GvHD were characterized in three phases which includes the tissue damage-phase, the T cell priming-phase and the effector-phase, when the disease becomes clinically overt. The role of individual cytokines, chemokines, transcription factor or receptors was studied in these models by using gene deficient or transgenic mice in the donor or recipient compartments. Besides, numerous studies have been performed in these models to prevent or treat GvHD. Several recent clinical trials were all based on previously reported findings from the mouse model of GvHD such as the trials on CCR5-blockade, donor statin treatment, vorinostat treatment or adoptive transfer of regulatory T cells for GvHD prevention. The different mouse models for GvHD and graft-vs-leukemia effects are critically reviewed and their impact on current clinical practice is discussed.

Neutrophil granulocytes recruited upon translocation of intestinal bacteria enhance graft-versus-host disease via tissue damage

Acute graft-versus-host disease (GVHD) considerably limits wider usage of allogeneic hematopoietic cell transplantation (allo-HCT). Antigen-presenting cells and T cells are populations customarily associated with GVHD pathogenesis. Of note, neutrophils are the largest human white blood cell population. The cells cleave chemokines and produce reactive oxygen species, thereby promoting T cell activation. Therefore, during an allogeneic immune response, neutrophils could amplify tissue damage caused by conditioning regimens. We analyzed neutrophil infiltration of the mouse ileum after allo-HCT by in vivo myeloperoxidase imaging and found that infiltration levels were dependent on the local microbial flora and were not detectable under germ-free conditions. Physical or genetic depletion of neutrophils reduced GVHD-related mortality. The contribution of neutrophils to GVHD severity required reactive oxygen species (ROS) because selective Cybb (encoding cytochrome b-245, beta polypeptide, also known as NOX2) deficiency in neutrophils impairing ROS production led to lower levels of tissue damage, GVHD-related mortality and effector phenotype T cells. Enhanced survival of Bcl-xL transgenic neutrophils increased GVHD severity. In contrast, when we transferred neutrophils lacking Toll-like receptor-2 (TLR2), TLR3, TLR4, TLR7 and TLR9, which are normally less strongly activated by translocating bacteria, into wild-type C57BL/6 mice, GVHD severity was reduced. In humans, severity of intestinal GVHD strongly correlated with levels of neutrophils present in GVHD lesions. This study describes a new potential role for neutrophils in the pathogenesis of GVHD in both mice and humans.

Post-transplantation B cell activating factor and B cell recovery before onset of chronic graft-versus-host disease

Excessive levels of B cell activating factor (BAFF) are found in patients with active chronic graft-versus-host disease (cGVHD). In mice, BAFF has been shown to be essential for B cell recovery after myeloablation. To assess how BAFF levels relate to transplantation factors and subsequent development of cGVHD, we prospectively monitored 412 patients in the first year after allogeneic peripheral blood or bone marrow hematopoietic stem cell transplantation (HSCT) and censored data at time of cGVHD onset. In patients who did not develop cGVHD, we affirmed a temporal pattern of gradually decreasing BAFF levels as B cell numbers increase after myeloablative conditioning. In contrast, after reduced-intensity conditioning, BAFF levels remained high throughout the first post-HSCT year, suggesting that the degree of myeloablation resulted in delayed B cell recovery associated with persistence of higher BAFF levels. Given that high BAFF/B cell ratios have been associated with active cGVHD, we examined differences in early BAFF/B cell ratios and found significantly different BAFF/B cell ratios at 3 months post-HSCT only after myeloablative conditioning in patients who subsequently developed cGVHD. In addition to HSCT conditioning type, the use of sirolimus was significantly associated with higher BAFF levels after HSCT, and this also was potentially related to lower B cell numbers. Taken together, our results are important for interpreting BAFF measurements in cGVHD biomarker studies.

IL-1β and TLR4 signaling are involved in the aggravated murine acute graft-versus-host disease caused by delayed bortezomib administration

It was shown that the proteasome inhibitor, bortezomib, administered immediately following allogeneic bone marrow transplantation resulted in marked inhibition of acute graft-versus-host disease (aGVHD), with retention of graft-versus-tumor effects. However, continuous bortezomib administration resulted in significant acceleration of graft-versus-host disease-dependent morbidity. We carried out studies to dissect the mechanisms of aggravated aGVHD caused by delayed bortezomib administration. First, we demonstrated that IL-1β was critically involved, and the subsequent aGVHD could be alleviated by IL-1β blockade. Bortezomib treatment after dendritic cell (DC) activation resulted in drastically elevated IL-1β production, whereas bortezomib treatment before DC activation inhibited IL-1β production, suggesting that the timing of bortezomib administration significantly affected IL-1β production by DCs. We further demonstrated that delayed administration of bortezomib accelerated aGVHD through TLR4 signaling. Because the LPS levels were much lower with reduced-intensity conditioning compared with high-dose irradiation, the accelerated graft-versus-host disease-dependent morbidity with delayed bortezomib administration could be rescued by reduced-intensity conditioning. Our studies suggested that TLR4 pathway activation and delayed bortezomib administration amplified the production of IL-1β and other inflammatory cytokines, which resulted in accelerated aGVHD-dependent morbidity. These results indicated that decreased toxicity of continuous bortezomib administration could be achieved by reduced-intensity conditioning or by inhibiting IL-1β.

The Nlrp3 inflammasome regulates acute graft-versus-host disease

Conditioning therapies before transplantation induce the release of uric acid, which triggers the NLRP3 inflammasome and IL-1β production contributing to graft-versus-host disease.

The success of allogeneic hematopoietic cell transplantation is limited by acute graft-versus-host disease (GvHD), a severe complication accompanied by high mortality rates. Yet, the molecular mechanisms initiating this disease remain poorly defined. In this study, we show that, after conditioning therapy, intestinal commensal bacteria and the damage-associated molecular pattern uric acid contribute to Nlrp3 inflammasome–mediated IL-1β production and that gastrointestinal decontamination and uric acid depletion reduced GvHD severity. Early blockade of IL-1β or genetic deficiency of the IL-1 receptor in dendritic cells (DCs) and T cells improved survival. The Nlrp3 inflammasome components Nlrp3 and Asc, which are required for pro–IL-1β cleavage, were critical for the full manifestation of GvHD. In transplanted mice, IL-1β originated from multiple intestinal cell compartments and exerted its effects on DCs and T cells, the latter being preferentially skewed toward Th17. Compatible with these mouse data, increased levels of active caspase-1 and IL-1β were found in circulating leukocytes and intestinal GvHD lesions of patients. Thus, the identification of a crucial role for the Nlrp3 inflammasome sheds new light on the pathogenesis of GvHD and opens a potential new avenue for the targeted therapy of this severe complication.

Endothelial and epithelial barriers in graft-versus-host disease

Endothelial and epithelial cells form selectively permeable barriers that separate tissue compartments. These cells coordinate movement between the lumen and tissue via the transcellular and paracellular pathways. The primary determinant of paracellular permeability is the tight junction, which forms an apical belt-like structure around endothelial and epithelial cells. This chapter discusses endothelial and epithelial barriers in graft-versus-host disease after allogeneic bone marrow transplantation, with a focus on the tight junction and its role in regulating paracellular permeability. Recent studies suggest that in graft-versus-host disease, pathological increases in paracellular permeability, or barrier dysfunction, are initiated by pretransplant conditioning and sustained by alloreactive cells and the proinflammatory milieu. The intestinal epithelium is a significant focus, as it is a target organ of graft-versus-host disease, and the mechanisms of barrier regulation in intestinal epithelium have been well characterized. Finally, we propose a model that incorporates endothelial and epithelial barrier dysfunction in graft-versus-host disease and discuss modulating barrier properties as a therapeutic approach.

Mesenchymal stem cell transplantation to promote bone healing

An overall decline in the availability of osteogenic precursor cells and growth factors in the bone marrow microenvironment have been associated with impaired bone formation and osteopenia in humans. The objective of the current study was to determine if transplantation of mesenchymal stromal cells (MSC) from a healthy, young donor mouse into an osteopenic recipient mouse could enhance osseointegration of a femoral implant. MSC harvested from normal young adult mice differentiated into bone forming osteoblasts when cultured on implant grade titanium surfaces ex vivo and promoted bone formation around titanium-coated rods implanted in the femoral canal of osteopenic recipient mice. Micro computed tomographic imaging and histological analyses showed more, better quality, bone in the femur that received the MSC transplant compared with the contra-lateral control femur that received carrier alone. These results provide pre-clinical evidence that MSC transplantation promotes peri-implant bone regeneration and suggest the approach could be used in a clinical setting to enhance bone regeneration and healing in patients with poor quality bone.

Dendritic cells and regulation of graft-versus-host disease and graft-versus-leukemia activity

Hematopoietic stem cell transplantation is the only curative treatment for many malignant hematologic diseases, with an often critical graft-versus-leukemia effect. Despite peritransplant prophylaxis, GVHD remains a significant cause of posthematopoietic stem cell transplantation morbidity and mortality. Traditional therapies have targeted T cells, yet immunostimulatory dendritic cells (DCs) are critical in the pathogenesis of GVHD. Furthermore, DCs also have tolerogenic properties. Monitoring of DC characteristics may be predictive of outcome, and therapies that target DCs are innovative and promising. DCs may be targeted in vivo or tolerogenic (tol) DCs may be generated in vitro and given in the peritransplant period. Other cellular therapies, notably regulatory T cells (T(reg)) and mesenchymal stem cells, mediate important effects through DCs and show promise for the prevention and treatment of GVHD in early human studies. Therapies are likely to be more effective if they have synergistic effects or target both DCs and T cells in vivo, such as tolDCs or T(reg). Given the effectiveness of tolDCs in experimental models of GVHD and their safety in early human studies for type 1 diabetes, it is crucial that tolDCs be investigated in the prevention and treatment of human GVHD while ensuring conservation of graft-versus-leukemia effects.

Low incidence and severity of graft-versus-host disease after outpatient allogeneic peripheral blood stem cell transplantation employing a reduced-intensity conditioning

BACKGROUND

The prevalence and features of graft-versus-host disease (GVHD) in patients receiving allografts using peripheral blood stem cells (PBSCs) after a reduced-intensity conditioning (RIC) regimen are not well known. Several features of GVHD in patients at two institutions using RIC were assessed.

METHODS

We analysed the overall survival (OS) and prevalence of GVHD in patients who underwent outpatient allogeneic PBSC transplantation after RIC between October 1998 and July 2008.

RESULTS

We included 301 patients with a median age of 30 yrs (range, 1-71 yrs). In 37 cases, allogeneic peripheral blood stem cell transplantation was indicated for non-malignant disease, and in 264 for malignant disease. The median OS was 35 months. The estimated 3-yr OS was 48%. A total of 154 patients developed GVHD: there were 64 acute, 50 chronic and 40 cases that progressed from acute to chronic. Of the 104 patients with acute GVHD (aGVHD), 40% had grade I and 60% had grades II-IV. Of the 90 patients with chronic GVHD (cGVHD), 67% had limited and 33% had extensive forms. A total of 160 patients died, 40 as a result of GVHD (24 from aGVHD and 16 from cGVHD), 50 as a result of progressive disease and 70 from diverse causes.

CONCLUSIONS

The incidence of GVHD was lower than in other series using conventional myeloablative preparative regimens. Most importantly, the severity of GVHD did not significantly affect the long-term survival.

A prospective dose-finding trial using a modified continual reassessment method for optimization of fludarabine plus melphalan conditioning for marrow transplantation from unrelated donors in patients with hematopoietic malignancies

BACKGROUND

Because of the less graft-facilitating effect by bone marrow (BM), we need to assess a dosage of conditioning more accurately particularly in combination with reduced-intensity conditioning. Thus we examined that modified continual reassessment method (mCRM) is applicable for deciding appropriate conditioning of allogeneic BM transplantation.

PATIENTS AND METHODS

The conditioning regimen consisted of i.v. fludarabine (125 mg/m2) plus an examination dose of i.v. melphalan. The primary endpoint was a donor-type T-cell chimerism at day 28 with successful engraftment defined as >90% donor cells. Five patients per dose level were planned to be accrued and chimerism data were used to determine the next dose.

RESULTS

Seventeen patients were enrolled at doses between 130 and 160 mg/m2. The dose was changed from 160 to 130 mg/m(2) (second level) after five full-donor chimerisms. With one patient of 0% chimera in the second level, the dose was increased to 135 mg/m2 (third level). Following five full-donor chimerisms in the third level, the study was complete as projected.

CONCLUSIONS

mCRM was shown to be a relevant method for dose-finding of conditioning regimen. The melphalan dose of 135 mg/m2 was determined as the recommended phase II dose to induce initial full-donor chimerism.

Intestinal damage determines the inflammatory response and early complications in patients receiving conditioning for a stem cell transplantation

Background

Stem cell transplantation (SCT) is still complicated by the occurrence of fever and inflammatory complications attributed to neutropenia and subsequent infectious complications. The role of mucosal barrier injury (MBI) of the intestinal tract therein has received little attention.

Methods

We performed a retrospective analysis in 163 SCT recipients of which data had been collected prospectively on intestinal damage (citrulline), inflammation (C-reactive protein), and neutrophil count. Six different conditioning regimens were studied; 5 myeloablative (MA) and 1 non-myeloablative (NMA). Linear mixed model multivariate and AUC analyses were used to define the role of intestinal damage in post-SCT inflammation. We also studied the relationship between the degree of intestinal damage and the occurrence of early post-SCT complications.

Results

In the 5 MA regimen there was a striking pattern of inflammatory response that coincided with the occurrence of severe intestinal damage. This contrasted with a modest inflammatory response seen in the NMA regimen in which intestinal damage was limited. With linear mixed model analysis the degree of intestinal damage was shown the most important determinant of the inflammatory response, and both neutropenia and bacteremia had only a minor impact. AUC analysis revealed a strong correlation between citrulline and CRP (Pearson correlation r = 0.96). Intestinal damage was associated with the occurrence of bacteremia and acute lung injury, and influenced the kinetics of acute graft-versus-host disease.

Conclusion

The degree of intestinal damage after myeloablative conditioning appeared to be the most important determined the inflammatory response following SCT, and was associated with inflammatory complications. Studies should explore ways to ameliorate cytotoxic therapy-induced intestinal damage in order to reduce complications associated with myeloablative conditioning therapy.

UVA (UVA-1) therapy for the treatment of acute GVHD of the skin

Long-wavelength UVA (340-400 nm UVA-1) phototherapy has been reported to be effective in atopic dermatitis, localized scleroderma and T-cell-derived skin diseases. We retrospectively investigated 70 patients with acute cutaneous GVHD after allogeneic haematopoietic cell transplantation or donor lymphocyte infusion. Complete and partial responses with a median duration of 10 months were achieved in 49 (70%) and 17 (24.3%) patients, respectively. Overall, 47 (67.1%) patients were not treated with systemic steroids. Furthermore, immunosuppression could be tapered in 24 (34.3%) patients while they were receiving UVA-1 treatment. Responses were seen irrespective of age or type of conditioning. Treatment was very well tolerated. After a median follow-up of 18 (range 10-60) months, three patients developed epithelial skin neoplasia. We conclude that UVA-1 therapy is feasible, well tolerated and can be an effective treatment for acute GVHD of the skin, thereby avoiding the use of systemic steroids and/or allowing a more rapid tapering of systemic immunosuppression in a substantial number of patients. The results of this retrospective analysis warrant larger, prospective studies and the effectiveness of UVA-1 therapy should be compared with other established treatment modalities.

Mesenchymal stromal cells transiently alter the inflammatory milieu post-transplant to delay graft-versus-host disease

BACKGROUND

Multipotent mesenchymal stromal cells suppress T-cell function in vitro, a property that has underpinned their use in treating clinical steroid-refractory graft-versus-host disease after allogeneic hematopoietic stem cell transplantation. However the potential of mesenchymal stromal cells to resolve graft-versus-host disease is confounded by a paucity of pre-clinical data delineating their immunomodulatory effects in vivo.

DESIGN AND METHODS

We examined the influence of timing and dose of donor-derived mesenchymal stromal cells on the kinetics of graft-versus-host disease in two murine models of graft-versus-host disease (major histocompatibility complex-mismatched: UBI-GFP/BL6 [H-2(b)]→BALB/c [H-2(d)] and the sibling transplant mimic, UBI-GFP/BL6 [H-2(b)]→BALB.B [H-2(b)]) using clinically relevant conditioning regimens. We also examined the effect of mesenchymal stromal cell infusion on bone marrow and spleen cellular composition and cytokine secretion in transplant recipients.

RESULTS

Despite T-cell suppression in vitro, mesenchymal stromal cells delayed but did not prevent graft-versus-host disease in the major histocompatibility complex-mismatched model. In the sibling transplant model, however, 30% of mesenchymal stromal cell-treated mice did not develop graft-versus-host disease. The timing of administration and dose of the mesenchymal stromal cells influenced their effectiveness in attenuating graft-versus-host disease, such that a low dose of mesenchymal stromal cells administered early was more effective than a high dose of mesenchymal stromal cells given late. Compared to control-treated mice, mesenchymal stromal cell-treated mice had significant reductions in serum and splenic interferon-γ, an important mediator of graft-versus-host disease.

CONCLUSIONS

Mesenchymal stromal cells appear to delay death from graft-versus-host disease by transiently altering the inflammatory milieu and reducing levels of interferon-γ. Our data suggest that both the timing of infusion and the dose of mesenchymal stromal cells likely influence these cells' effectiveness in attenuating graft-versus-host disease.

Isolation of clonogenic, long-term self renewing embryonic renal stem cells

A tissue stem cell should exhibit long-term self-renewal, clonogenicity and a capacity to differentiate into the tissue of origin. Such a postnatal renal stem cell has not been formally identified. The metanephric mesenchyme (MM) of the developing kidney gives rise to both the renal interstitium and the nephrons and is regarded as the progenitor population of the developing kidney. However, isolated MM does not self renew and requires immortalization for survival in culture. Here we report the isolation and sustained culture of long-term repopulating, clonal progenitors from the embryonic kidney as free floating nephrospheres. Such cells displayed clonal self renewal for in excess of twenty passages when cultured with bFGF and thrombin, showed broad mesodermal multipotentiality, but retained expression of key renal transcription factors (Wt1, Sall1, Eya1, Six1, Six2, Osr1 and Hoxa11). While these cells did display limited capacity to contribute to developing embryonic kidney explants, nephrospheres did not display in vitro renal epithelial capacity. Nephrospheres could be cultured from both Sall1(+) and Sall1(-) fractions of embryonic kidney, suggesting that they were derived from the MM as a whole and not specifically the MM-derived cap mesenchyme committed to nephron formation. This embryonic renal stem cell population was not able to be isolated from postnatal kidney confirming that while the embryonic MM represents a mulitpotent stem cell population, this does not persist after birth.