Hematopoietic Stem Cell Transplantation Model Research Articles

Therapeutic Inducers of Natural Killer cell Killing (ThINKK): preclinical assessment of safety and efficacy in allogeneic hematopoietic stem cell transplant settings

BackgroundAllogeneic hematopoietic stem cell transplantation (HSCT) remains the standard of care for chemotherapy-refractory leukemia patients, but cure rates are still dismal. To prevent leukemia relapse following HSCT, we aim to...

Mesenchymal stem cell-derived exosomes can alleviate GVHD and preserve the GVL effect in allogeneic stem cell transplantation animal models.

Mesenchymal stem cells (MSCs) can alleviate graft-versus-host disease (GVHD) in hematopoietic stem cell transplantation (HSCT). MSCs-derived exosomes (MEXs) can mirror the biological function of their parent cells. Whether MEXs can alleviate GVHD like their parent cells or not is unclear. In this study, we investigate the effects of MEXs on GVHD and graft-versus-leukemia (GVL) effect in vitro and in HSCT animal models. MSCs were produced using bone marrow mononuclear cells (MNCs), and MEXs were separated from the supernatants of MSCs. Electron microscopy, western blot, and nanoparticle tracking analysis (NTA) were used to determine the characteristics of MEXs. The immunomodulatory function of MEXs and their effects on GVHD and GVL were examined in vitro and in vivo. Like other cell-type derived exosomes, our data revealed that MEXs were also disc-shaped vesicles with a diameter of 100-200 nm under electron microscopy and were positive for the exosomal hallmark proteins. MEXs can notably inhibit the expression of costimulatory molecules and functional cytokine secretion of dendritic cells (DCs). Meanwhile, MEXs can exert suppressive effects on T lymphocyte proliferation and activation. Moreover, MEXs can also encourage the polarization of macrophages toward the M2 type. In animal HSCT models, MEXs can promote the differentiation of Treg cells in spleens, decrease the GVHD score, increase the survival rate of mice, and preserve the cytotoxic antileukemia effects of CD8+ T lymphocytes from recipient mice. These findings showed that MEXs exert their effects by inhibiting the immunomodulatory function of DCs, macrophages, and T lymphocytes. In the animal model, MEXs ameliorate the clinical symptoms of GVHD, while maintaining the antitumor effects of CD8+ T lymphocytes. Therefore, it can be inferred that MEXs can separate GVHD from GVL in HSCT. Our study suggests that MEXs have broad clinical application potential in the prevention and treatment of GVHD in HSCT in the near future.

Pegylated Long-Acting Interferon Gamma Treatment Enhances MHC Class II Expression and the Graft-Versus-Leukemia Effect in Preclinical Models of AML Relapse

Relapse after allogeneic hematopoietic stem cell transplantation (HCT)represents the most common type of treatment failure and is thought to result in part from AML cell escape from immune pressure exerted by donor immune cells (the “Graft-versus-leukemia” effect, GvL). We and others have previously reported downregulation of MHC class II (MHC-II) expression in up to half of AML cases relapsing after transplantation, but it is unclear whether a) loss of MHC-II contributes mechanistically to loss of GvL, and b) whether reversal of MHC-II downregulation can restore GvL. We tested the role of MHC-II in mediating GvL in a mouse model of minor-antigen mismatch HCT where C57BL/6 mice (B6) bearing syngeneic AML cells (H-2b) were co-transplanted with or without CD3+ T cells from C3.SW-H2b/SnJ mice (H-2b). Since murine AML cells do not generally express MHC-II at baseline, we transduced MLL-AF9-driven B6 AML cells with a fluorescently-tagged retrovirus expressing CIITA the main transcriptional regulator of MHC-II genes. MHC-II-expressing AML cells were selectively deleted when co-transplanted with donor T cells, in contrast to animals that received no T cells (Figure 1, right) or mice that received AML cells transduced with empty vector (Figure 1, left). To extend these findings to human cells, we used both MHC-II blocking antibodies and CRISPR-mediated disruption of CIITA in human AML cell lines and primary samples. Loss or blocking of MHC-II led to diminished the ability of AML cells to stimulate MHC-mismatched donor T cells in a mixed lymphocyte reaction. Loss of MHC-II expression in AML cells can be reversed in vitro by Interferon gamma (IFNG). We tested the ability of IFNG to enhance the GvL by culturing AML cell lines and primary patient samples with or without IFNG for 48 hours. IFNG-treatment enhanced the ability of AML cells from some-but not all-samples to stimulate third-party T cells. Interestingly, enhanced stimulation was observed in both CD4 and CD8 cells, suggesting that IFNG may also potentiate GvL through MHC-II-independent pathways. Since the use of IFNG in vivo may be limited by its short half-life, we tested a novel long-acting pegylated human interferon gamma (peg-IFNG, Bolder BioTechnology) in a xenograft model of AML. Immunodeficient mice were engrafted with MHC-II-low human AML cells. After engraftment, mice (n=3 each group) received six doses of IFNG, peg-IFNG, or vehicle (15mcg given s.c. M-W-F). After treatment, mice were sacrificed and MHC-II expression was quantified on human AML cells isolated from bone marrow of treated mice. IFNG treatment increased MHC-II expression modestly compared to vehicle (2.7-fold, p=0.04), while peg-IFNG much more robustly stimulated MHC-II stimulation on human AML cells in this xenograft model (12-fold, p=0.02). Finally, we tested whether peg-IFNG can enhance AML cell clearance in a xenograft model. Luciferin-labelled THP1 cells (low MHC-II expression) were injected on day 0 into immundeficient mice (n=8-9 each group). On day 7, mice started treatment with peg-IFNG or vehicle (15mcg given s.c. M-W-F for two weeks). On day 21, baseline tumor burden was measured using bioluminescence, and healthy third-party donor T cells were injected. Mice were followed with weekly CBC and bioluminescence measurments, and moribund mice were sacrificed and banked. Mice treated with peg-IFNG plus T cells had decreased tumor burden during the course of the experiment compared to untreated controls as well as mice treated with T cells plus vehicle only (Figure 2, p<0.01 by ANOVA for both comparisons). In addition, mice treated with peg-IFNG had significantly improved survival compared to control groups (median survival 79 days compared to 63 days and 67 days, p<0.05 by Log-Rank test). Together, these findings suggest that long-acting IFNG analogues may effectively enhance GvL in AML patients after HCT.

Extracellular Release of Damaged Mitochondria Induced By Cytotoxic Conditioning Exacerbates Graft-Versus-Host Disease

Despite therapeutic advancements, graft versus host disease (GVHD) is a major complication of hematopoietic stem cell transplantation (HSCT). Pathogen and damage associated molecular patterns released following pre-transplant conditioning have an important role in the initiation of GVHD. However, the role of extracellular mitochondria (exMito) as an endogenous danger signal has not been explored. Herein, we report that cytotoxic conditioning with radiation leads to mitochondrial fission and impaired PINK-1/PARKIN-dependent mitophagy in the intestinal mucosal layer. This was coupled with extracellular release of damaged mitochondria in the plasma of BALB/c mice following irradiation. Sublethal irradiation of the Caco-2 epithelial cell line confirmed the in vivo expulsion of mitochondria in a cell-death independent manner. exMito released upon irradiation were damaged, and had impaired ATP production. Incubation of splenocytes with damaged exMito increased the cell surface expression of immune stimulatory molecules and induced Th1 cytokine release. Furthermore, in mixed lymphocyte reactions, exMito pre-treated BALB/c stimulator cells increased the activation and proliferation of C57BL6/J responder T cells. Finally, co-transplantation of isolated damaged mitochondria in a C57BL6/J to BALB/c mouse HSCT model aggravated GVHD. The translational relevance of these findings was studied in a cohort of pediatric patients who underwent HSCT. Fractionated irradiation given with their conditioning regimen increased the abundance of circulating exMito and correlated with the incidence of GVHD. Our results suggest that modulation of exMito release could be a novel therapeutic target to prevent GVHD after HSCT.

Calcineurin inhibitor inhibits tolerance induction by suppressing terminal exhaustion of donor T cells after allo-HCT

AbstractCalcineurin inhibitor–based graft-versus-host disease (GVHD) prophylaxis is standard in allogeneic hematopoietic stem cell transplantation (HCT) but fails to induce long-term tolerance without chronic GVHD (cGVHD) in a considerable number of patients. In this study, we addressed this long-standing question in mouse models of HCT. After HCT, alloreactive donor T cells rapidly differentiated into PD-1+ TIGIT+ terminally exhausted T cells (terminal Tex). GVHD prophylaxis with cyclosporine (CSP) suppressed donor T-cell expression of TOX, a master regulator to promote differentiation of transitory exhausted T cells (transitory Tex), expressing both inhibitory receptors and effector molecules, into terminal Tex, and inhibited tolerance induction. Adoptive transfer of transitory Tex, but not terminal Tex, into secondary recipients developed cGVHD. Transitory Tex maintained alloreactivity and thus PD-1 blockade restored graft-versus-leukemia (GVL) activity of transitory Tex and not terminal Tex. In conclusion, CSP inhibits tolerance induction by suppressing the terminal exhaustion of donor T cells, while maintaining GVL effects to suppress leukemia relapse.

Research Highlights.

Research Highlights.

Posttransplant cyclophosphamide contributes to the impairment of the graft-versus-leukemia effect and the amelioration of graft-versus-host disease with the suppression of alloreactive T cells in a murine stem cell transplant model

Posttransplant cyclophosphamide (PTCy) is an effective prophylaxis for graft-versus-host disease (GVHD) due to its suppression of donor-derived alloreactive T cells in allogeneic hematopoietic stem cell transplantation (HSCT). The graft-versus-leukemia (GVL) effect is an antileukemia effect induced by donor-derived alloreactive T cells, similar to GVHD, whereas no studies have demonstrated the association between the dynamics of donor-derived alloreactive T cells and impairment of the GVL effect after HSCT with PTCy. We herein evaluated the dynamics of donor-derived T cells expressing a functional marker for alloreactivity, programmed cell death-1 (PD-1), in a murine HSCT model with PTCy. We showed that PTCy was associated with the development of leukemia cells and the decreased survival probability in an HSCT model with leukemia cells, whereas PTCy could ameliorate GVHD and increased the survival probability in the HSCT model without leukemia cells. We revealed that the percentages of PD-1 expressing donor-derived CD8+/CD4+ alloreactive T cells, with the exception of CD44+ memory T cells, in the recipient spleen were suppressed with PTCy, and that donor T-cell chimerism levels were decreased early after HSCT with PTCy. Our results suggest that PTCy correlated with the impairment of the GVL effect and the amelioration of GVHD through the suppression of PD-1 expressing donor-derived CD8+/CD4+ alloreactive T cells after HSCT.

Experimental Models of Mouse and Human Hematopoietic Stem Cell Transplantation.

Experimental hematopoietic stem cell transplantation (HSCT) is an invaluable tool in determining the function and characteristics of hematopoietic stem cells (HSC) from experimental mouse and human donor groups. These groups could include, but are not limited to, genetically altered populations (gene knockout/knockin models), ex vivo manipulated cell populations, or in vivo modulated cell populations. The basic fundamentals of this process involve taking cells from a mouse/human donor source and putting them into another mouse (recipient) after preconditioning of the recipient with either total body irradiation (TBI) for mouse donor cells or into sublethally irradiated immune-deficient mice for human donor cells. Then, at pre-determined time pointspost-transplant, sampling a small amount of peripheral blood (PB) and at the termination of the evalaution, bone marrow (BM) to determine donor contribution and function by phenotypic analysis. Exploiting the congenic mouse strains of C57BL/6 (CD45.1- CD45.2+), BoyJ (CD45.1+ CD45.2-), and their F1-crossed hybrid C57BL/6×BoyJ (CD45.1+ CD45.2+), we are able to quantify donor, competitor, and recipient mouse cell contributions to the engraftment state. Human donor cell engraftment (e.g., from the cord blood [CB], mobilized PB, or BM) is assessed by human cell phenotyping in sublethally irradiated immune-deficient mouse recipients (e.g., NOD scid gamma mice that are deficient in B cells, T cells, and natural killer cells and have defective dendritic cells and macrophages). Engraftment of cells from primary mouse recipients into secondary mice allows for an estimation of the self-renewal capacity of the original donor HSC. This chapter outlines concepts, methods, and techniques for mouse and human cell models of HSCT and for assessment of donor cells collected and processed in hypoxia versus ambient air.

Addition of romiplostim to conditioning prior to HSCT allows chemotherapy reduction while maintaining engraftment levels

AbstractAllogeneic hematopoietic stem cell transplantation (HSCT) offers a curative treatment approach for certain benign and malignant hematologic diseases. The actual HSCT is preceded by a conditioning therapy that reduces host-vs-HSCT graft rejection and creates niche space for transplanted hematopoietic stem and progenitor cells (HSPCs). Conditioning consists of chemotherapy with or without irradiation and is a major cause of side effects in HSCT. However, reduction of the intensity of cytotoxic conditioning leads to higher rates of engraftment failure and increased rates of relapse. We here tested if the addition of an HSC cycling inducing agent during conditioning allows to diminish the dose of conditioning drugs without reducing subsequent transplanted HSC engraftment in a mouse HSCT model. The thrombopoietin receptor agonist romiplostim was shown to induce cell cycling activity in hematopoietic stem cells (HSCs). We thus tested if the addition of romiplostim to the clinically applied conditioning chemotherapy regimen cyclophosphamide and busulfan leads to increased efficacy of the chemotherapeutic regimen. We found that romiplostim not only sensitizes HSCs to chemotherapy but also enables a reduction of the main chemotherapeutic component busulfan by half while HSC engraftment levels are maintained in long-term, serial transplantation assays.

The Reconstitution Dynamics of Cultivated Hematopoietic Stem Cells and Progenitors Is Independent of Age.

Hematopoietic stem cell transplantation (HSCT) represents the only curative treatment option for numerous hematologic malignancies. While the influence of donor age and the composition of the graft have already been examined in clinical and preclinical studies, little information is available on the extent to which different hematological subpopulations contribute to the dynamics of the reconstitution process and on whether and how these contributions are altered with age. In a murine model of HSCT, we therefore simultaneously tracked different cultivated and transduced hematopoietic stem and progenitor cell (HSPC) populations using a multicolor-coded barcode system (BC32). We studied a series of age-matched and age-mismatched transplantations and compared the influence of age on the reconstitution dynamics. We show that reconstitution from these cultured and assembled grafts was substantially driven by hematopoietic stem cells (HSCs) and multipotent progenitors (MPPs) independent of age. The reconstitution patterns were polyclonal and stable in all age groups independently of the variability between individual animals, with higher output rates from MPPs than from HSCs. Our experiments suggest that the dynamics of reconstitution and the contribution of cultured and individually transduced HSPC subpopulations are largely independent of age. Our findings support ongoing efforts to expand the application of HSCT in older individuals as a promising strategy to combat hematological diseases, including gene therapy applications.

Single Agent CD117-Targeted Antibody Drug Conjugate in Combination with Lymphodepleting Antibodies Enables Allogenic Hematopoietic Stem Cell Transplantation in Mice without Chemotherapy or Radiation

Hematopoietic stem cell transplant (HSCT) is a highly effective and potentially curative treatment for malignant and non-malignant blood disorders. However, patient eligibility for this procedure can be limited due to the mortality and morbidity risks associated with current conditioning regimens, including organ toxicity, infertility, and secondary malignancies. We have developed a novel anti-CD117 antibody drug conjugate (ADC) that, in combination with lymphodepleting antibodies, can effectively condition mice to support a full allogeneic (allo) transplant. Specifically, we used a tool anti-mouse (anti-m) CD117-PBD ADC in combination with anti-mCD4 and CD8 depleting antibodies and assessed the ability of the combination to successfully condition in a murine model of allo-HSCT.Our tool ADC, anti-mCD117-PBD, was engineered for rapid clearance to enable a timely HSCT following conditioning. A single dose of 1 mg/kg robustly depleted long-term hematopoietic stem cells (LT-HSC) by 97% compared to PBS controls in C57BL/6 mice. We first evaluated the ability of single doses of 1 and 3 mg/kg anti-mCD117-PBD to condition for transplant in a congenic mouse model (C57BL/6 hosts [CD45.2+] with B6.SJL-Ptprca Pepcb/boyJ donors [CD45.1+]). We then evaluated conditioning with a single dose of 3 mg/kg anti-mCD117-PBD, in combination with 250 μg/mouse anti-mCD4 (GK1.5) and anti-mCD8 (YTS 169.4) antibody, in a fully mismatched allo transplant model (C57BL/6 hosts [CD45.2+] with CByJ.SJL(B6)-ptprca/J donors [CD45.1+]). In both studies, a dose matched non-targeted isotype-PBD (iso-PBD) was used as a negative control, while 9 Gy total body irradiation (TBI) was used as a fully myeloablative positive control. Anti-rat (anti-r) IgG isotype (LTF-2) was used as a negative lymphodepletion control antibody in the allo-HSCT study. Conditioned mice were transplanted with 2e7 whole BM cells. Lymphodepleting antibodies were dosed daily for three consecutive days before transplant. Peripheral blood chimerism was assessed over 16 weeks (congenic model) to 24 weeks (allo model), at which time donor HSC chimerism was evaluated in the terminal bone marrow.In the congenic HSCT model, conditioning recipient mice with a single dose of 3 mg/kg anti-mCD117-PBD enabled robust donor chimerism in the peripheral blood and bone marrow, as well as reconstitution of the T-, B- and myeloid cell compartments, that was comparable to the 9 Gy TBI positive control for myeloablative conditioning. Treatment with the iso-PBD control at 3 mg/kg was not effective at enabling HSC engraftment. In the fully mismatched allo-HSCT model, recipient mice conditioned with 3 mg/kg anti-mCD117-PBD in combination with 250 μg/mouse lymphodepleting anti-mCD4 + anti-mCD8 antibodies enabled full donor chimerism, achieving >90% engraftment by week 12 in the peripheral blood which was sustained through the end of the study at week 24 (Figure 1A). Multilineage reconstitution of immune cell subsets was also observed in this study, with >90% donor chimerism seen in the B cell and myeloid compartments and T cell reconstitution above 75% (Figure 1B-D). There was 99% donor HSC engraftment in the bone marrow at study termination (Figures 1E & F). These results were comparable to the chimerism observed in the 9 Gy TBI positive control mice. Groups conditioned with the non-targeting iso-PBD or anti-rIgG isotype antibody controls did not support donor engraftment in the model.In conclusion, conditioning with 3 mg/kg anti-mCD117-PBD, in combination with lymphodepleting antibodies anti-mCD4 and anti-mCD8, enables complete donor chimerism in a fully mismatched allo-HSCT murine model. This targeted conditioning approach could offer a more favorable risk-benefit profile over currently available conditioning regimens and could extend the curative potential of allo-HSCT to more patients with malignant and non-malignant diseases who otherwise would not be eligible for HSCT. [Display omitted] DisclosuresLanieri: Magenta Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Lamothe: Magenta Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Bhattarai: Magenta Therapeutics: Current Employment, Current holder of stock options in a privately-held company. Palchaudhuri: Magenta Therapeutics: Current Employment, Current holder of stock options in a privately-held company, Patents & Royalties. Olson: Magenta Therapeutics: Current Employment, Current holder of stock options in a privately-held company.

Donor-derived M2 macrophages attenuate GVHD after allogeneic hematopoietic stem cell transplantation.

IntroductionGraft‐versus‐host disease (GVHD) is frequent and fatal complication following allogeneic hematopoietic stem cell transplantation (HSCT) and characteristically involves skin, gut, and liver. Macrophages promote tissue regeneration and mediate immunomodulation. Macrophages are divided into two different phenotypes, classically activated M1 (pro‐inflammatory or immune‐reactive macrophages) and alternatively activated M2 (anti‐inflammatory or immune‐suppressive macrophages). The anti‐inflammatory effect of M2 macrophage led us to test its effect in the pathophysiology of GVHD.MethodsGVHD was induced in lethally irradiated BALB/c mice. M2 macrophages derived from donor bone marrow (BM) were administered intravenously, while controls received donor BM‐mononuclear cells and splenocytes. Animals were monitored for clinical GVHD and analyzed.ResultsWe confirmed that administering donor BM‐derived M2 macrophages attenuated GVHD severity and prolonged survival after HSCT. Moreover, donor BM‐derived M2 macrophages significantly suppressed donor T cell proliferation by cell‐to‐cell contact in vitro.ConclusionsWe showed the protective effects of donor‐derived M2 macrophages on GVHD and improved survival in a model of HSCT. Our data suggest that donor‐derived M2 macrophages offer the potential for cell‐based therapy to treat GVHD.

GVHD Pathogenesis, Prevention and Treatment: Lessons From Humanized Mouse Transplant Models.

Graft-vs-host disease (GVHD) is the most common cause of non-relapse mortality following allogeneic hematopoietic stem cell transplantation (HSCT) despite advances in conditioning regimens, HLA genotyping and immune suppression. While murine studies have yielded important insights into the cellular responses of GVHD, differences between murine and human biology has hindered the translation of novel therapies into the clinic. Recently, the field has expanded the ability to investigate primary human T cell responses through the transplantation of human T cells into immunodeficient mice. These xenogeneic HSCT models benefit from the human T cell receptors, CD4 and CD8 proteins having cross-reactivity to murine MHC in addition to several cytokines and co-stimulatory proteins. This has allowed for the direct assessment of key factors in GVHD pathogenesis to be investigated prior to entering clinical trials. In this review, we will summarize the current state of clinical GVHD research and discuss how xenogeneic HSCT models will aid in advancing the current pipeline of novel GVHD prophylaxis therapies into the clinic.

Essential Role of Regulatory T Cells on Early B Cell Reconstitution after Haploidentical BMT with Posttransplant Cyclophosphamide

Posttransplant cyclophosphamide (PTCy) is an effective prophylaxis for both acute and chronic graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT). Recent studies reported that PTCy has been associated with low incidence of viral infections or EBV-related posttransplantation lymphoproliferative disease (EB-LPD), suggesting PTCy-based immune modulation leads the favorable immune reconstitution after transplant. Recently, we studied the immune reconstitution dynamics of each lymphocyte subset after transplant using PTCy and reported that PTCy-based immune-modulation strongly promoted Treg-dominant T-cell reconstitution and stem cell-derived mature B-cell generation by using murine model of haploidentical HSCT with PTCy. TCR- and BCR- repertoire analysis demonstrated that PTCy resulted in the broader diversity of both T cell and B cell repertoire than non-PTCy controls. However, the mechanism of coordination of increased Tregs and B cells after PTCy-based HSCT has not well studied. To address this issue, we here investgated the impact and role of PTCy on Tregs and B cell recovery and the mutual influence between the two important subsets by using murine BMT model. Irradiated B6D2F1 mice were transplanted with 5x106 spleen cells from the CD45.1 B6 mice together with 5x106 TCD-BM from CD45.2 B6 donors. Cyclophosphamide 100mg/kg or control vehicle was administered at day 3 after transplant. Peripheral blood mononuclear cells (PBMCs) and splenic cells were sequentially obtained at day21. The chimeric balances among host-residual H-2kd+ cells, donor graft-derived cells and donor BM-derived cells in Tregs and B cells were monitored separately. To evaluate the homeostatic stability, proliferation marker Ki-67 and anti-apoptotic BCL-2 were also quantitatively examined respectively. To examine the detailed phenotype of Tcells, CD4, CD8, CD25, Foxp3, ICOS, CXCR5 were tested. Also, to examine the detailed phenotype of B cells, the expression of B220, CD21, CD23, CD24 were tested. At day21 after HSCT, the number of Treg cell in spleen was significantly higher on PTCy-treated recipients than that of non-PTCy control (P < 0.05). We also checked the emergence of donor-derived follicular helper T cells (Tfh) in lymph node because recent studies have shown that Tfh could contribute B cell differentiation after HSCT. In our analysis at day21 in this PTCy model, Tfh cells were still few in both PTCy group and non-PTCy group, suggesting the early T cell recovery after PTCy did not promote B cell differentiation into pathological plasmablast. The number of B cell was markedly higher in PTCy-treated recipients than that of non-PTCy control (P < 0.01). The increased B cell population was mainly transitional-1 phenotype suggesting these B cells were recent emigrants from bone marrow. In consistent with low recovery of Tfh cells, plasmablast-like phenotype of B cells were not observed. Next, to evaluate the impact of graft-derived Treg recovery on B cell reconstitution, we depleted Treg from spleen cells of B6 donors by using CD25+ magnetic beads. After the depletion, residual Treg cell in the graft was under 1% of total CD4 T cells. At day21, splenic Treg cells is under 3% of total CD4 T cells in Treg-depleted group, that is much lower than Treg in Treg-repleted group. Interestingly, the number of B cells at day21 in PTCy-treated recipients was equivalent to that of non-PTCy recipients when we depleted Treg from donor graft, suggesting that well-balaced B cell recovery promoted by PTCy was completely abolished by Treg-depletion. Taken together, our data suggested that PTCy could induce the expansion of Treg recovery and naïve B cell recovery without urging early emergence of Tfh cells in lymph node, resulting in well-diversed T and B cell reconstitution. Treg appears to contribute to promote naïve B cell emergence from bone marrow, indicating the T and B cell recovery might be mutually influenced. Moreover, slow recovery of Tfh cells in lymph node could be advantage for preventing B cell from forced differentiation into plasmablast causing GVHD. These data provide the important information for understanding the immunological reconstitution after PTCy-based haploidentical HSCT. DisclosuresMaeda:Toko Pharmaceutical Industries: Other: Investigational drug is provided free of charge.

Iron Overload Decreases Engraftment of Mice Receiving Allogeneic or Syngeneic Bone Marrow Transplant

Background:Transfusional iron overload is a poor prognostic factor in patients undergoing hematopoietic stem cell transplantation (HSCT). In multiple clinical studies, elevated serum ferritin correlated with inferior transplant outcomes; however, ferritin is an imperfect marker of iron burden and may not correlate with other markers, such as liver iron content. These studies are also confounded because increased transfusional need often reflects more severe disease, an independent predictor of worse outcome. Thus, it remains unclear whether the correlation between iron status and transplant outcome is due to transfusional iron overload alone, or is more reflective of other comorbidities. We developed a mouse model of parenteral iron overload followed by high dose chemotherapy and allogeneic or syngeneic HSCT to study, in isolation, the effects of iron overload on engraftment and survival after transplant.Methods:Cohorts of female C57BL/6 (H-2Kb) recipients received 0, 5, 25, or 50mg iron dextran, in divided doses over 2 weeks. Mice were then conditioned with busulfan (20mg/kg daily x 5 days) and cyclophosphamide (100mg/kg daily for the last 3 days). Two days later, mice received 30 x 106 bone marrow cells from female BALB/c (H-2Kd) donors (allogeneic HSCT) or 5 x 106 bone marrow cells from female UBC-GFP (H-2Kb) donors (syngeneic HSCT). Mice received enrofloxacin (10mg/kg daily x 5 days) after transplant. Engraftment was evaluated by flow cytometry as the proportion of donor cells in blood or bone marrow. Iron-related parameters were measured at the time of euthanasia (Day +28 post-transplant). Statistical analysis was performed with GraphPad Prism.Results:Our model of iron overload using iron dextran at escalating doses showed a dose-dependent increase in markers of iron load, such as total liver iron (R2=0.86) and ferritin (R2=0.84)(Fig. 1A-B; both P<0.0001 for linear trend). After allogeneic HSCT, there was a statistically significant decrease in overall survival in all groups receiving iron dextran (range: 47-63%), as compared to the saline control (90%)(Fig 1C; P<0.05); this effect was not dose-dependent. Data from 3 pooled experiments (N=30 mice per group) showed an engraftment rate of 59% in the saline group, and 47%, 42%, and 21% in the 5mg, 25mg, and 50mg iron dextran groups, respectively, suggesting a dose-dependent effect of iron overload on engraftment (Fig. 1D). In the syngeneic HSCT model, iron overload prior to transplant similarly resulted in delayed RBC and platelet engraftment and decreased rates of overall engraftment (Fig. 1E,F,G).Conclusions:Iron overload had a dose-dependent negative effect on overall engraftment after allogeneic and syngeneic HSCT. For allogeneic HSCT, there was also a decrease in overall survival in all the groups receiving iron dextran. For syngeneic HSCT, in which graft rejection cannot occur, iron overload still negatively affected post-transplant engraftment, suggesting that this effect is not due solely to potential immunomodulatory effects of excess iron on graft rejection. The mechanism(s) underlying the effects of iron overload on survival and engraftment rates in allogeneic and syngeneic HSCT, along with the potential benefit of chelation therapy, remain to be determined.Figure 1: Effect of iron overload on survival and engraftment. Mean ± S.D. for (A) total liver iron and (B) ferritin for allogeneic HSCT. Kaplan-Meier survival estimates for (C) mortality and (D) percent of mice not engrafting >50% of nucleated cells for allogeneic HSCT (N=10 mice per group per replicate; 30 mice total per group). Mean ± S.D. for (E) percent red cell engraftment over time and (F) percent platelet engraftment of time in syngeneic HSCT. Kaplan-Meier survival estimates for (F) percent of mice not engrafting >50% of red blood cells (N=10 mice per group per replicate; 20 mice total per group). *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001 as compared to the saline control or as specified. Arrow denotes day of transplant. [Display omitted] DisclosuresSpitalnik:New Health Sciences: Consultancy, Membership on an entity's Board of Directors or advisory committees.

The Anti-Viral Compound Cosalane Attenuates Acute Graft-Versus-Host Disease in Murine Hematopoietic Stem Cell Transplant Models

Introduction : Acute graft-versus-host disease (aGVHD) remains a major barrier to the success of allogeneic hematopoietic stem cell transplantation (HSCT). Mechanistically, aGVHD depends on the trafficking of donor conventional T cells (Tcons) into host secondary lymphoid tissues (SLT) where they are activated by host antigens. Previously our group demonstrated that donor Tcons deficient in the lymphoid trafficking receptor CC-Chemokine Receptor 7 (CCR7) generated attenuated aGVHD responses but retained their graft-versus-leukemia (GVL) potential (Coghill JM et al. Blood. 2010; 115(23): 4914-22). This suggested that the receptor might be targeted therapeutically. Since there were no drugs affecting the CCR7 axis, we undertook a high throughput screen (HTS) of over 200,000 compounds to identify small molecule antagonists of the receptor. This effort demonstrated that cosalane, a compound originally developed as a novel HIV therapeutic but with additional activity against numerous other enveloped viruses including cytomegalovirus and herpes simplex virus, also possessed an intrinsic ability to block human and murine CCR7 signaling in response to both of its ligands. As a result, we examined the ability of cosalane to modulate aGVHD in vivo in mouse HSCT models.Results : Cosalane did not substantially alter aGVHD outcomes when dosed intravenously post-transplant to murine recipients in a standard C57BL/6 “B6” (H-2b) into C57BL/6-DBA2 F1 “B6D2” (H-2bxd) haplotype matched HSCT model. However, when donor Tcons were incubated with cosalane in vitro for one hour prior to transplant, aGVHD was significantly attenuated and survival was prolonged compared to cells incubated with DMSO vehicle (Figure 1A, *P=0.004 for curve comparison between BM with Tcons and BM with Tcons/cosalane groups by log rank test). Cosalane exposure did not appear to result in any cytotoxicity, and did not affect Tcon activation and expansion in vitro in response to CD3 stimulation in the presence of supplemental IL-2. Furthermore, when the entire stem cell product (bone marrow cells plus Tcons) was incubated with cosalane prior to transplant, myeloid engraftment was unaffected and survival times were once again improved with no evidence of bone marrow aplasia (Figure 1B, **P=0.001 for curve comparison by log rank test).While cosalane was originally identified as an inhibitor of CCR7, its effects on donor Tcon trafficking into host lymphoid sites post-transplant were surprisingly modest. No major differences in donor Tcon accumulation within the host inguinal lymph nodes, mesenteric lymph nodes, or spleen were noted on either transplant day +7 or day +14. A strong trend for reduced Tcon numbers was noted, however, within the host colon and liver by the second week post-transplant, implying an additional mechanism of action beyond its activity against CCR7.Cosalane's effects did not appear to be strain dependent, as survival times were also improved in a completely MHC mismatched B6 into BALB/c (H-2d) model system, although to a lesser extent. In addition, cosalane pretreatment of human peripheral blood mononuclear cells resulted in prolonged survival times in a mouse xenogeneic aGVHD transplant model. We went on to examine cosalane's effects on beneficial GVL effects using a well described luciferase transduced p815 (H-2d) murine mastocytoma model. Here survival times were prolonged in B6D2 mice receiving cosalane treated B6 Tcons/tumor versus those receiving DMSO treated B6 Tcons/tumor (who all succumbed to aGVHD) and those receiving bone marrow alone/tumor (who all died from malignancy). We have found cosalane's effects on aGVHD to be dose dependent in a B6 into B6D2 system (treatment range 13uM-39uM), and additional work is ongoing to optimize its administration so as to maximize anti-inflammatory effects while sparing anti-tumor immunity.Conclusions : The anti-viral compound cosalane is able to attenuate aGVHD in multiple allogeneic and xenogeneic model systems after a brief incubation with the donor Tcon and/or bone marrow product in vitro prior to transplant. Although identified in our HTS as a CCR7 antagonist, its effects on lymphoid trafficking after HSCT have thus far been limited, and additional mechanistic studies are currently ongoing. Given its known anti-viral effects against numerous pathogens common to the HSCT setting, we are also exploring its anti-infective properties in murine model systems. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Naive T-cell depletion in stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HCT) is curative in many patients with advanced hematopoietic malignancies. Donor T cells not only facilitate engraftment and protect against opportunistic pathogens and residual disease, but can also cause graft-versus-host disease (GVHD), with significant morbidity and mortality. Complete T-cell depletion can not only substantially reduce GVHD rates but can also delay immune reconstitution and increase rates of opportunistic infections and relapse. Murine models have shown that naive T cells (TNs) consistently cause severe GVHD, whereas memory T cells cause milder or no GVHD and have critical graft-versus-tumor function. Informed by experiments performed in murine models of HCT, clinical trials are being conducted to evaluate TN-depleted peripheral blood stem cell (PBSC) grafts. These trials are showing very low rates of chronic GVHD and of serious acute GVHD in the HLA-matched HCT setting, with lower frequencies of opportunistic infections than after fully T-cell-depleted HCT and no apparent increase in relapse rates. Randomized clinical trials are ongoing, comparing standard unselected HCT with TN-depleted PBSCs and other promising GVHD-reduction strategies. Correlative laboratory studies will clarify how antitumor function is retained in TN-depleted HCT and inform strategies to further augment graft-versus-leukemia in patients at a high risk of relapse. TN depletion of donor lymphocyte infusions and of haploidentical stem cell grafts is also being investigated.

Effects of Combined Infusion of Mesenchymal Stem Cells and Endothelial Progenitor Cells on Lung Injury after Hematopoietic Stem Cell Transplantation

To investigate the effects of combined infusion of mesenchymal stem cells (MSC) and endothelial progenitor cells (EPC) on lung injury after hematopoietic stem cell transplantation (HSCT). The experiment was divided into normal control group, irradiation group, bone marrow cell transplantation group (BMT group), BMT+EPC group, BMT+MSC group and BMT+EPC+MSC group. The model of HSCT was established, on the 30th day after transplantation, the mice were sacrificed. Then lung tissue was taken for testing. The mRNA expression levels of VEGF, IL-18, IL-12b were detected by RT-PCR, and protein expression level of NLRP3 was detected by Western blot. The expression of MPO and CD146 was observed by immunohistochemistry assay. The expression level of VEGF gene in BMT+EPC+MSC group was significantly higher than that in other groups (P＜0.01). The expression level of IL-18 and IL-12b gene was the highest in BMT group and the lowest in BMT+EPC+MSC group, and the difference was statistically significant (P＜0.05). HSCT could increase the expression of NLRP3 protein, and the BMT+EPC+MSC could significantly reduce the level of NLRP3 protein in lung cells, tending to normal. Compared with normal tissues, the BMT+EPC+MSC could improve the lung tissue structure more effectively, the expression of MPO positive cells was lower, and the expression of VEGF positive cells was higher. The combined infusion of MSC and EPC can promote capillary regeneration, alleviate inflammation and promote lung repair after HSCT, which is superior to single EPC or MSC infusion.

Establishing a Novel High-Throughput Conditioning-Free HSC Transplant Model in Zebrafish

Hematopoietic stem cell (HSC) transplantation is a widely successful treatment, but the risk of mortality remains. Preclinical modeling is critical to uncover the biological components that underlie poor patient outcomes. Zebrafish is a vertebrate animal with high genetic and cellular conservation with human hematopoiesis with many advantages to discover regulators of HSC transplant biology, such as high fecundity and short generation time. We developed a novel HSC transplant model using bloodless runx1 W84X mutant zebrafish which are devoid of endogenous HSCs. Most embryos die 8-12 days post fertilization (dpf) due to the absence of definitive hematopoiesis. We hypothesized that the empty HSC niche and lack of an immune system would prevent graft rejection, making robust HSC engraftment possible. We transplanted donor marrow ubiquitously expressing green fluorescent protein (ubi:GFP) via intravascular injection into runx1 homozygous mutants and heterozygotes at 2dpf. Sham-injected and uninjected embryos served as negative controls. We transplanted an average of 100-200 recipients per experimental day. Survival was significantly improved in transplanted runx1 mutants, with 64% surviving in the transplanted cohort compared to 5% in the sham-injected controls, suggesting HSC transplantation likely supplied these fish with a functional hematopoietic compartment critical for survival. Chimerism was quantified by flow cytometry 8 weeks post-transplant. Successful engraftment was defined as >5% GFP+ myeloid cells. Over 99% of animals meeting this criterion also showed robust multi-lineage engraftment. Over 70% of runx1 mutant recipients were engrafted compared to only 3% of the runx1 heterozygotes. The myeloid chimerism of engrafted mutant fish was 84% (+/-25%), while the engrafted heterozygous control had only 21% myeloid chimerism. Transplanted fish remain robustly engrafted >6 months post-transplant. The runx1 mutants supported HSC self-renewal, as the GFP+ marrow cells from primary recipients were able to robustly engraft secondary runx1 mutant hosts. We also demonstrated that competitive transplantation in runx1 mutants can be used to measure HSC frequency, a critical feature needed to functionally and quantitatively assess HSC potential following genetic or pharmacological perturbations. These data demonstrate that the runx1 mutant zebrafish is an advantageous HSC transplant host that allows quantification of long-term serially-repopulating true HSCs. The advantages of our zebrafish transplant model allow the real-time visualization of stem cell trafficking and homing in a healthy, uninjured niche and the ability to perform large-scale screens to identify drugs that modify engraftment. This will provide unprecedented insight into both the donor and host factors needed for robust HSC engraftment that will be helpful in improving human HSC graft outcomes.

Viral opportunistic infections in Mauritian cynomolgus macaques undergoing allogeneic stem cell transplantation mirror human transplant infectious disease complications.

Allogeneic hematopoietic stem cell transplantation (HSCT) and xenotransplantation are accompanied by viral reactivations and virus-associated complications resulting from immune deficiency. Here, in a Mauritian cynomolgus macaque model of fully MHC-matched allogeneic HSCT, we report reactivations of cynomolgus polyomavirus, lymphocryptovirus, and cytomegalovirus, macaque viruses analogous to HSCT-associated human counterparts BK virus, Epstein-Barr virus, and human cytomegalovirus. Viral replication in recipient macaques resulted in characteristic disease manifestations observed in HSCT patients, such as polyomavirus-associated hemorrhagic cystitis and tubulointerstitial nephritis or lymphocryptovirus-associated post-transplant lymphoproliferative disorder. However, in most cases, the reconstituted immune system, alone or in combination with short-term pharmacological intervention, exerted control over viral replication, suggesting engraftment of functional donor-derived immunity. Indeed, the donor-derived reconstituted immune systems of two long-term engrafted HSCT recipient macaques responded to live attenuated yellow fever 17D vaccine (YFV 17D) indistinguishably from untransplanted controls, mounting 17D-targeted neutralizing antibody responses and clearing YFV 17D within 14days. Together, these data demonstrate that this macaque model of allogeneic HSCT recapitulates clinical situations of opportunistic viral infections in transplant patients and provides a pre-clinical model to test novel prophylactic and therapeutic modalities.