Conditioning-related Toxicity Research Articles

A Multicentre, Randomized, Double-Blinded, Phase 2b Study Evaluating the Efficacy and Safety of MaaT033, an Oral, Pooled Microbiome Ecosystem Therapy in Patients Undergoing Allogenic Hematopoietic Cell Transplantation to Improve Overall Survival: The Phoebus Trial

Background and significance: Allogenic hematopoietic cell transplantation (alloHCT) is a well-established therapy for various life-threatening hematologic malignancies. The use of alloHCT is constantly increasing, with nearly 20 000 transplantations reported to the European Society for Blood and Marrow Transplantation (EBMT) per year. However, this treatment is limited by high morbidity and mortality, mainly related to relapse, infection, graft-versus-host disease (GvHD), and conditioning-related toxicity. Several pioneering studies have shown that the diversity of the gut microbiota of patients not only correlates with the occurrence of medical complications after alloHCT, including GvHD (Jenq et al. 2012, Stein-Thoeringer et al. 2019) and bloodstream infections (Taur et al. 2012), but also with relapse of the underlying disease (Peled et al. 2017). Gut microbiota diversity restoration with fecal microbiotherapy could be an effective treatment to improve patients' clinical outcomes including overall survival (OS) after alloHCT, through the prevention and resolution of gut microbiota dysbiosis. MaaT033 is a freeze-dried, full-ecosystem, high-diversity, fecal microbiota medicinal product, formulated as delayed-release capsules and derived from pooled allogenic human fecal material. The PHOEBUS trial is a phase 2b study to evaluate the efficacy of MaaT033 in improving survival of adult alloHCT patients (Clinicaltrials.gov identifier: NCT05762211) Study design and Methods: 387 subjects aged ≥ 50 years with hematologic malignancies for which an alloHCT is indicated will be randomized 1:1 to receive either MaaT033 (experimental arm) or placebo (control arm) before initiation of the conditioning regimen and after hematopoietic recovery following alloHCT. Stratification of patients will be performed based on disease risk index (low-intermediate versus high-very high) and donor-host compatibility (HLA-identical versus HLA-mismatch). Inclusion criteria include age ≥ 50 years, alloHCT with a reduced-toxicity or reduced-intensity conditioning regimen, neutrophils > 0.5 G/L, and administration of broad-spectrum antibiotics within the last 90 days prior to inclusion. Exclusion criteria comprise non-myeloablative conditioning regimen, conventional myeloablative conditioning regimen, in-vitro T-cell depletion, alloHCT with cord blood cells, alloHCT from an unrelated donor with ≥ 3/10 HLA-mismatches, use of alemtuzumab, vedolizumab or abatacept for GvHD prophylaxis, history of chronic digestive disease. The primary endpoint is to evaluate OS at 12 months after randomization. Secondary endpoints will include evaluation of the safety of MaaT033, GvHD-free survival, cumulative incidence of acute GvHD and chronic GvHD, non-relapse mortality, relapse-free survival, GvHD-free, relapse-free survival, the proportion of patients with severe infections, gut microbiota composition, and quality of life. Exploratory endpoints will describe the impact of MaaT013 on immune recovery, the nutritional status of the patients, and resource utilization. Patients will receive MaaT033 or placebo (3 capsules per day) for 1 week before the start of the conditioning regimen. Experimental treatment (3 capsules per day) will be resumed at neutrophil recovery and pursued up to 90 days after alloHCT. Patients will be followed monthly up to 6 months post alloHCT and then every 3 months up to 12 months. The study is approved in France and Germany; expansion to other countries is planned for 2024. Study start is expected in September 2023.

Safety and survival analysis of haplo-identical hematopoietic stem cell transplantation in patients with severe aplastic anemia who had previous failure to antithymoglobulin treatment

Objective: To investigate the safety and efficacy of haplo-identical hematopoietic stem cell transplantation (haplo-HSCT) conditioning with the same dosage form of antithymoglobulin (ATG) in patients with severe aplastic anemia (SAA) failure to ATG. Methods: This was a retrospective cohort study. A total of 65 patients with SAA who failed ATG treatment and received haplo-HSCT conditioning with the same dosage of ATG at the Institute of Hematology, Peking University People's Hospital between July 2008 and October 2020 were included as the ATG treatment failure group. An additional 65 SAA patients who applied ATG for the first time during haplo-HSCT were randomly selected by stratified sampling as the first-line haplo-HSCT group. Baseline clinical data and follow-up data of the two groups were collected. Conditioning-related toxicity within 10 days after ATG application and long-term prognosis were analyzed. The Kaplan-Meier was used to calculate the overall survival rate, and the Log-rank test was applied to compare the rates of the two groups. Results: In the ATG treatment failure group, there were 36 males and 29 females, and the age at the time of transplantation [M (Q1, Q3)] was 16 (8, 25) years. In the first-line haplo-HSCT group, there were 35 males and 30 females, with a median age of 17 (7, 26) years. Within 10 days of ATG application, the incidence of noninfectious fever, noninfectious diarrhea, and liver injury in the ATG treatment failure group was 78% (51 cases), 45% (29 cases), and 28% (18 cases), respectively, and in the first-line haplo-HSCT group was 74% (48 cases), 54% (35 cases), and 25% (16 cases), respectively; the difference between the two groups was not statistically significant for any of these three parameters (all P>0.05). For graft-versus-host disease (GVHD), there was no significant difference between the ATG treatment failure group and the first-line haplo-HSCT group in the development of 100 day Ⅱ to Ⅳ acute GVHD (29.51%±0.35% vs. 25.42%±0.33%), Ⅲ to Ⅳ acute GVHD (6.56%±0.10% vs. 6.78%±0.11%), and 3-year chronic GVHD (26.73%±0.36% vs. 21.15%±0.30%) (all P>0.05). Three-year overall survival (79.6%±5.1% vs. 84.6%±4.5%) and 3-year failure-free survival (79.6%±5.1% vs. 81.5%±4.8%) were also comparable between these two groups (both P>0.05). Conclusions: Compared with no exposure to ATG before HSCT, similar early adverse effects and comparable survival outcomes were achieved in patients with SAA who failed previous ATG treatment and received haplo-HSCT conditioning with the same dosage form of ATG. This might indicate that previous failure of ATG treatment does not significantly impact the efficacy and safety of salvaging haplo-HSCT in patients with SAA.

259 PERICARDITIS AND PERICARDIAL EFFUSION IN CHRONIC GRAFT-VERSUS-HOST DISEASE AFTER ALLOGENIC HEMATOPOIETIC STEM CELL TRANSPLANTATION

Abstract Background Pericarditis and pericardial effusion (PE) are rare but potentially life-threatening complications in chronic graft-vs-host disease (cGVHD). Limited data are currently available in this setting, based on small single-center retrospective studies. The purpose of this study is to characterize the clinical presentation, management, and outcomes of pericarditis and PE complicating cGVHD in allogeneic hematopoietic cell transplant recipients. Material and Methods We included all consecutive patients referred to our pericardial diseases referral center from 1st May 2008 to 1st May 2022. All patients had no previous cardiovascular or autoimmune diseases and suffered from severe cGVHD with involvement of at least 2 organs. Pericarditis and PE were diagnosed according to ESC guidelines. Conditioning-related toxicity and infections were carefully excluded. Results Pericarditis was diagnosed in 4 patients (2 males, mean age 48.5 ±9.0 years), of whom 2 developed mild PE. PE without pericarditis was diagnosed in 5 patients (80% male, aged 53.2 ±8.9 years), in 2 patients it was reported as severe, requiring pericardial drainage. The average time after allogeneic hematopoietic stem cell transplantation was 22 months (range, 4 to 58 months). All patients required escalation of the corticosteroid therapy they were chronically taking, and in 4 cases the therapy was boosted with non-steroidal anti-inflammatory drugs. Only one patient developed a recurrence and died of multiorgan failure associated with severe cGVHD (involving eyes, mucous membranes, skin, joints, liver, pleuro-pericardial effusion) refractory to immunosuppressive therapy. Overall survival was 89% and no patient developed constrictive pericarditis. Mean follow-up was 69±55 months. Conclusions Pericarditis and PE related to cGVHD typically occur with mild clinical signs in the context of severe cGVHD, however in our study 22% of patients required pericardial drainage at diagnosis. The mainstay of treatment is high-dose steroids and usually the majority of patients have a favorable outcome.

Safety and Efficacy of Aru-1801 in Patients with Sickle Cell Disease: Early Results from the Phase 1/2 Momentum Study of a Modified Gamma Globin Gene Therapy and Reduced Intensity Conditioning

▪Introduction: Sickle cell disease (SCD) is a genetic red blood cell (RBC) disorder that causes chronic hemolytic anemia, progressive organ damage, and life-threatening acute complications such as painful vaso-occlusive crises. Allogeneic hematopoietic stem cell transplant (allo-HSCT) with myeloablative conditioning remains the only curative therapy for SCD but has several limitations including low donor availability and conditioning-related toxicity. Genetic modification of autologous hematopoietic system cells (HSCs) with reduced-intensity conditioning (RIC) using a high-potency drug product may address these limitations.ARU-1801 is a gene therapy that uses a modified γ-globin lentiviral vector to produce HbF G16D within autologous CD34+ HSCs. Preclinical studies in SCD mice have shown the G16D mutation enables γ-globin G16D to bind α-globin with higher affinity; lentiviral transfer of γ-globin G16D resulted in 1.5-2x more HbF per vector copy number (VCN) compared to analogous wild-type γ-globin vector. Early studies also suggested HbF G16D may be more potent for anti-sickling than HbF, lowering reticulocyte counts in SCD mice to a greater extent at similar protein levels. We hypothesize ARU-1801 with RIC could lessen toxicities and resource utilization relative to myeloablative approaches, allowing expanded access to gene therapy for a broader group of SCD patients. Updated data from patients in the ongoing Phase 1/2 study (NCT02186418) including laboratory and clinical markers of efficacy are presented here.Methods: Adults (18-45 years old) with severe SCD (defined by recurrent vaso-occlusive events [VOE] and acute chest syndrome) were screened for eligibility. Prior to ARU-1801 drug product (DP) infusion, all patients received a single IV dose of RIC melphalan (140 mg/m 2). Endpoints included measures of safety, engraftment, VCN, hemoglobin sub-fractions, and SCD-related outcomes. Patients were weaned off transfusions 3-6 months after DP infusion. Levels of anti-sickling globins (including HbF G16D) are presented as proportions of non-transfused total hemoglobin.Results: As of 28 July 2021, four patients (mean, 26 [19-35] years old) have been treated with ARU-1801 gene therapy for SCD with three patients followed for ≥12 months post-transplant. Transient neutropenia and thrombocytopenia were the predominant adverse events, lasting a median seven days each. There have been no other serious adverse events related to chemotherapy or ARU-1801 to date.At 36 months post-transplant, Patient 1 has shown stable HbF expression (27%) and 64% F-cells. Patient 2 has maintained 14% HbF and 37% F-cells at 36 months despite lower engraftment of ARU-1801 due to renal hyperfiltration (eGFR = 200 mL/min/1.73 m 2) at time of conditioning, which resulted in lower melphalan exposure. Both patients saw marked improvements in SCD manifestations, including 93% and 85% fewer annualized VOEs, respectively, in the two years after receiving ARU-1801 gene therapy compared to two years prior.Patient 3 received ARU-1801 manufactured with several process modifications (including improvements of HSC collection timing and lentiviral production) and has maintained 36% HbF at month 15 with pancellular distribution (96% F-cells). To date, Patient 3 has had no VOEs since ARU-1801 administration, representing 100% reduction from baseline.Conclusion: Amelioration of SCD phenotype and engraftment of ARU-1801 gene-modified HSCs is possible with a single RIC dose of melphalan, as demonstrated in three patients. The first patient shows 27% HbF expression at three years, and 93% reduction in VOEs. The second patient had lower HSC engraftment due to below-target melphalan exposure (likely caused by renal hyperfiltration), with 14% HbF and 5% HbA2 at three years. Nonetheless, an 85% reduction in VOEs in Patient 2 demonstrates significant clinical benefit. Dose-adjusted melphalan has the potential to improve engraftment in SCD patients with renal hyperfiltration. Following manufacturing process improvements, the third patient has shown the highest HbF (36%) at one year, the highest F-cells (96%), and no VOEs since receiving ARU-1801. ARU-1801, with RIC melphalan conditioning, is a promising alternative to myeloablative transplants for achieving durable responses with a favorable safety profile in patients with severe SCD. Longer follow-up and additional patients will be presented. [Display omitted] DisclosuresAsnani: Avicanna Ltd.: Research Funding; Aruvant Sciences: Research Funding. Lutzko: Aruvant Sciences: Patents & Royalties: preclinical vector development. Quinn: Forma Therapeutics: Consultancy; Emmaus Medical: Research Funding; Novo Nordisk: Consultancy; Aruvant: Research Funding. Lo: Aruvant Sciences: Current Employment. Little: Aruvant Sciences: Current Employment. Dong: Aruvant Sciences: Current Employment. Malik: Aruvant Sciences: Consultancy; Forma Therapeutics: Consultancy; Aruvant Sciences: Patents & Royalties; CSL Behring: Patents & Royalties. OffLabel Disclosure:Plerixafor was used for stem cell mobilization. Melphalan was used as chemotherapy conditioning prior to autologous transplant with ARU-1801

Venetoclax or Ruxolitinib in Pre-Transplant Conditioning Lowers the Engraftment Barrier by Different Mechanisms in Allogeneic Stem Cell Transplant Recipients.

Allogeneic stem cell transplantation (alloSCT) is utilised to cure haematological malignancies through a combination of conditioning regimen intensity and immunological disease control via the graft versus tumour (GVT) effect. Currently, conventional myeloablative chemotherapeutic or chemoradiation conditioning regimens are associated with significant side effects including graft versus host disease (GVHD), infection, and organ toxicity. Conversely, more tolerable reduced intensity conditioning (RIC) regimens are associated with unacceptably higher rates of disease relapse, partly through an excess incidence of mixed chimerism. Improvement in post-alloSCT outcomes therefore depends on promotion of the GVT effect whilst simultaneously reducing conditioning-related toxicity. We have previously shown that this could be achieved through BCL-2 inhibition, and in this study, we explored the modulation of JAK1/2 as a strategy to lower the barrier to donor engraftment in the setting of RIC. We investigated the impact of short-term treatment of BCL2 (venetoclax) or JAK1/2 (ruxolitinib) inhibition on recipient natural killer and T cell immunity and the subsequent effect on donor engraftment. We identified striking differences in mechanism of action of these two drugs on immune cell subsets in the bone marrow of recipients, and in the regulation of MHC class-II and interferon-inducible gene expression, leading to different rates of GVHD. This study demonstrates that the repurposed use of ruxolitinib or venetoclax can be utilised as pre-transplant immune-modulators to promote the efficacy of alloSCT, whilst reducing its toxicity.

1032TiP A phase I, first-in-human, study of TILT-123, a tumor-selective oncolytic adenovirus encoding TNFa and IL-2, in participants with advanced melanoma receiving adoptive T-cell therapy with tumor-infiltrating lymphocytes

Adoptive T-cell therapy using tumor-infiltrating lymphocytes (TIL) has demonstrated that potent and long-lasting antitumor responses can be achieved with cellular cancer immunotherapy in solid tumor patients. Yet, the therapy yields various toxicities, due to toxic lymphodepleting preconditioning and IL-2 postconditioning. With the intent of decreasing conditioning-related toxicities, while retaining efficacy, we developed TILT-123 (Ad5/3-E2F-D24-hTNFa-IRES-hIL2), a novel oncolytic adenovirus designed to reinvigorate antitumor T-cells.

Characterization of Pericarditis following Allogeneic Hematopoietic Cell Transplantation

Pericarditis is an uncommon cardiac complication following allogeneic hematopoietic cell transplantation (alloHCT), with limited data characterizing its incidence, presentation, and management. The etiology of pericarditis in this setting is poorly understood and may include conditioning-related toxicity, infection, or graft-versus-host disease (GVHD). The objective of the present study was to characterize the clinical presentation, management, and outcomes of post-alloHCT pericarditis observed at a single center. This retrospective case-control study of consecutive adults undergoing alloHCT over 5 years was conducted to identify patients who developed pericarditis. Pericarditis was diagnosed using clinical, electrocardiography, and echocardiography findings. Identified cases were compared with a cohort of patients who underwent alloHCT during the same period but did not develop pericarditis. A total of 620 patients underwent alloHCT over the 5-year period, 20 of whom developed pericarditis (3.2% incidence). One patient had a pre-alloHCT history of pericarditis. All but 3 patients had received anthracycline therapy and 1 patient had received chest irradiation before undergoing alloHCT. Patients with pericarditis were more likely than patients without pericarditis to have received total body irradiation (odds ratio [OR], 4.57; P=.003) or cyclophosphamide (OR, 2.35; P=.07) as conditioning or GVHD prophylaxis. Fourteen patients experienced their initial episode of pericarditis before day +100 post-alloHCT, with a median time to onset at day +7. Six patients had their initial episode on day +100 or later, with a median time to onset at day +268. Only 1 patient had active, previously diagnosed GVHD, and 3 patients were on systemic steroid therapy at the time of pericarditis diagnosis. Pericarditis was treated primarily with colchicine (median duration 91 days). Seven episodes of recurrence occurred in 5 patients. Two patients experienced cardiac tamponade following their initial diagnosis, and 3 developed tamponade at recurrence. Recurrence was more common in patients who received no or <90 days of colchicine compared with those who received ≥90 days (45.5% vs 0%; P=.02). No cardiac-related deaths occurred. Overall survival was 85% at a median follow-up of 30 months post-alloHCT. Pericarditis occurred in 3.2% of patients in this single-center study, with cases observed both before and after day +100 and some cases occurring ≥1 year after alloHCT. Colchicine was an effective intervention, with ≥90 days of treatment associated with reduced recurrence. Pericarditis should be considered in patients presenting with chest pain following alloHCT.

Antibody-Drug Conjugates Targeting CD45 Plus Janus Kinase (JAK) Inhibitors As Conditioning for Allogeneic Hematopoietic Stem Cell Transplantation

<h3>Introduction</h3> Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a potentially curative therapy for the treatment of hematologic diseases. AlloHSCT is associated with significant treatment-related morbidity and mortality from conditioning-related toxicities and graft-versus-host disease (GvHD), which limits its use to the most life-threatening indications, such as acute myeloid leukemia (AML). However, for conditions like AML that are primarily diagnosed in elderly patients, alloHSCT may be contraindicated due to poor patient functional status or medical comorbidities. Thus, an unmet clinical need exists for novel, highly-effective alloHSCT conditioning regimens with greater tolerability and minimal toxicity. <h3>Objectives</h3> Previously, antibody-drug conjugates (ADCs) composed of a CD45.2 antibody bound to the ribosome-inactivating protein saporin (CD45-SAP) were shown to allow high-level engraftment of syngeneic murine hematopoietic stem cells (HSCs). Here, we describe ADC-based conditioning regimens for murine alloHSCT which overcome immune barriers to engraftment imposed by minor histocompatibility antigen (miHA) and major histocompatibility complex (MHC) mismatches. <h3>Methods</h3> Mice were conditioned for HSCT with 3 mg/kg CD45-SAP 7 days prior to infusion of 10 × 10⁶ bone marrow cells. Haploidentical F1-to-parent (CB6F1→B6) and miHA-mismatched (BALB/c→DBA/2) HSCT models were used. For GvHD studies, a parent-to-F1 (B6→CB6F1) model was used in which recipients were infused with 25 × 10⁶ donor splenocytes after CD45-SAP treatment or sublethal irradiation. <h3>Results</h3> CD45-SAP combined with T cell depletion was sufficient for high-level engraftment in our alloHSCT models (Fig 1). The selective Janus kinase (JAK) inhibitor baricitinib, previously shown by our lab to prevent GvHD, also permitted HSC engraftment when mice received the drug during the peri-transplant period (Fig 2A-B). Graft stability in baricitinib-treated mice was optimized by either combining daily baricitinib treatment with pre-transplant T cell depletion, or by delivering baricitinib via continuous infusion (Fig 2C-D). Notably, CD45-SAP conditioned mice showed minimal morbidity or mortality from GvHD when infused with allogeneic splenocytes, whereas mice conditioned with sublethal irradiation developed acute GvHD. (Fig 3). <h3>Conclusion</h3> CD45-SAP combined with T cell depletion and/or pharmacologic immunomodulation with baricitinib effectively conditioned mice for engraftment of mismatched HSCs. Strikingly, mice conditioned with CD45-SAP did not develop GvHD even when infused with high doses of allogeneic splenocytes. These studies provide proof-of-principle evidence that targeted immunotherapeutics (ADCs plus JAK inhibitors) can prepare HSCT recipients for engraftment of allogeneic donor HSCs with minimal toxicities and without development of GvHD.

Proof of Concept for Repair of Sickle Cell Disease By Non-Myeloablative MHC Disparate T Cell Depleted HSCT Combined with Donor-Derived Veto Cells

Although life extending medical treatments are available for sickle cell disease (SCD), allogenic hematopoietic stem cell transplantation (HSCT) is considered a treatment of choice (Ozdogu et al., Bone Marrow Transplant 2018; 53(7): 880-890). However, HSCT is associated with several limitations, including conditioning-related toxicity and graft-versus-host disease (GvHD), especially when using MHC disparate transplants. Thus, the development of safe transplantation protocols for MHC disparate HSCT in sickle cell disease is vital. While the risk of GvHD and conditioning toxicity can be effectively reduced by the use of T-cell-depleted HSCT (TD-HSCT) under reduced intensity conditioning (RIC), rejection of TD-HSCT remains a challenge. We previously demonstrated in wild type mice that this barrier can be overcome using donor-derived veto cells. Here, we demonstrate the safety and efficacy of this approach in a well-defined murine model for sickle cells disease. Veto activity is based on the ability of certain cells to attack host CTL-precursors (CTLp) which are directed against antigens expressed on the veto cells themselves, sparing cells that are not targeted against the veto cells including T cells needed for defense against pathogens. Central memory CD8 T cells exhibit the most robust veto activity upon transplantation; however, these cells are also endowed with marked GvH activity. We overcame this issue by expanding naïve or memory CD8 T cells against 3rd party MHC or viral antigens, respectively, under culture conditions favoring expression of central memory phenotype. Such anti-3rd party central memoryCD8 T cells (Tcm), which are endowed with marked veto activity, also exhibit reduced risk for GvHD in fully mis-matched recipients (Reviewed in Reisner Y, Or-Geva N. Semin Hematol. 2019; 56(3): 173-182.) To generate Tcm veto cells, splenocytes obtained from Balb/c donors (H2d) were cultured against irradiated third-party splenocytes (FVB; H2q) under cytokine deprivation. The selective expansion of CD8 mouse T cells against 3rd party stimulators leads to selective 'death by neglect' of bystander anti-host T cell clones potentialy mediating GvHD, and these are further diluted out by subsequent expansion of anti-3rd party T clones during continued culture in the presence of IL-15. Apart from selective loss of GvH reactive T cells, these culture conditions induce a central memory phenotype shown to be important for attaining robust veto activity in vivo (Ophir et al., Blood. 2013; 121(7): 1220-8). We first calibrated the optimal irradiation dose for sickle mice (Berkeley model, H2b), comparing 4.5 Gy versus 5 Gy TBI in a conditioning protocol also including short term rapmycin treatment (Scheme 1). Higher levels of engraftment and chimerism were found in the group receiving 5Gy TBI (Fig. 1). All mice of both treatment groups survived &gt;140 days with no evidence of GvHD. To further evaluate this treatment approach, 8 week old sickle mice (N=7) were given bone marrow transplants using the protocol described in Scheme 1, including conditioning with 5 Gy TBI (day -1), rapamycin treatment (day -1 to day 4), and transplantation of NuBM (day 0) plus veto cells (day 7; Scheme 1). Notably, at 44 days post-transplant, 6 out of 7 mice receiving NuBM + TCM + Rapa (85.7%) showed donor chimerism in the peripheral blood, ranging between 77-94% (Fig.2A-B), while no chimerism was detected in mice receiving conditioning alone, or conditioning and transplantation with only NuBM or only veto cells . All mice in all groups survived (N=26) , and no GvHD was detected with a follow up of 77 days, even in the transplanted group which exhibited high donor-derived chimerism. Furthermore, reversal of sickle disease symptoms was observed, including reticulocyte levels (p=0.001;Fig.2C) and expression of wild type hemoglobin ( Fig.2D) in all engrafted mice. Our results offer a proof of concept for the treatment of sickle disease by MHC disparate non-myeloablative T cell depleted HSCT in conjunction with anti-3rd party central memory veto CD8 T cells. A clinical trial testing the safety and efficacy of anti-3rd party veto cells in the context of low toxicity non-myeloablative TD-HSCT in hematological malignancies is currently ongoing at MD Anderson Cancer Center. If successful, our present results support further evaluation of this platform for sickle cell disease. Disclosures Lustig: Yeda Ltd.: Patents &amp; Royalties. Reisner:Cell Source, Inc.: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties.

Haematopoietic Stem Cell Transplantation for Primary Haemophagocytic Lymphohistiocytosis.

Haematopoietic stem cell transplantation currently remains the only curative treatment of primary forms of haemophagocytic lymphohistiocytosis (HLH). Rapid diagnosis, efficient primary treatment of hyperinflammation, and conditioning regimens tailored to this demanding condition have substantially improved prognosis in the past 40 years. However, refractory hyperinflammation, central nervous system (CNS) involvement, unavailability of matched donors, susceptibility to conditioning-related toxicities, and a high frequency of mixed chimaerism remain a challenge in a substantial proportion of patients. Gene therapeutic approaches for several genetic defects of primary HLH are being developed at pre-clinical and translational levels.

ST2 and REG3α as Predictive Biomarkers After Haploidentical Stem Cell Transplantation Using Post-transplantation High-Dose Cyclophosphamide.

Allogenic hematopoietic stem cell transplantation (allo-HSCT) is a curative procedure for several hematological malignancies. Haploidentical HSCT (haplo-HSCT) using high-dose post-transplantation cyclophosphamide (PTCy) makes transplantation possible for patients with no HLA-matched sibling donor. However, this treatment can cause complications, mainly infection, graft-vs.-host disease (GVHD), and conditioning-related toxicity. In recent years, different biomarkers in the form of tissue-specific proteins have been investigated; these may help us to predict complications of allo-HSCT. In this study we explored two such biomarkers, suppression of tumorigenicity 2 (ST2) and regenerating islet-derived 3α (REG3α), in the largest series reported of T cell–replete haplo-HSCT with PTCy. Plasma samples drawn from 87 patients at days +15 and +30 were analyzed. ST2 and REG3α levels at day +15 were not associated with post-transplant complications. ST2 levels at day +30 were higher in patients with grade II-IV acute GVHD, mainly those who received reduced intensity conditioning (RIC; median 2,503 vs. 1,830 ng/ml; p = 0.04). Of note, patients with higher plasma ST2 levels at day +30 also presented a higher incidence of non-relapse mortality (HR, 7.9; p = 0.004) and lower 2-year overall survival (25 vs. 44 months; p = 0.02) than patients with lower levels. Patients with REG3α levels higher than 1,989 pg/ml at day +30 presented a higher incidence of acute gastrointestinal GVHD in the whole cohort (HR, 8.37; p = 0.003) and in the RIC cohort (HR 6.59; p = 0.01). These data suggest that measurement of ST2 and REG3α might be useful for the prognosis and prediction of complications in patients undergoing haplo-HSCT with PTCy.

PF757 REDUCED INTENSITY CONDITIONING AND AVOIDING USE OF BROAD SPECTRUM ANTIBIOTHERAPY ACTIVE AGAINST GRAM‐NEGATIVE BACTERIA MIGHT HAVE A CUMULATIVE IMPACT IN REDUCING INTESTINAL MICROBIOTA MISBALANCE

Background:Intestinal microbiota misbalance of allo‐HCT recipients is characterized by loss of alfa‐diversity and domination of microbial communities by single organisms. These injury patterns have been associated with poor survival and might be attributable to regimen‐related mucosal injury, antibiotic exposure and nutritional alterations, between others. We hypothesized that potential sources of microbiome insult may vary with time and that conditioning related toxicity and specific antibiotic pressure may have a sequential and possibly cumulative impact, leading to poor survival trough increase rate and severity of acute graft versus host disease.Aims:to perform an exploratory preliminary analysis aiming at identifying possible trends in microbiota misbalance after 1) myeloablative vs. reduced conditioning and 2) broad‐spectrum antibiotherapy active against Gram‐negative bacteria vs. not receiving it.Methods:We prospectively recruited a multicenter cohort of 24 consecutive recipients of allo‐HCT after signing informed consent form from January through September 2018. We performed 16S rRNA gene profiling of 87 stool samples collected at the following time points: pre‐conditioning (sample1), day0 (sple2), day+7 (sple3), day of fever whenever it occurred (sample 4/inconstant), day of antibiotic discontinuation (sple5). Most frequent diagnosis was AML (41%) and variables of interest are summarized in table 1. Phylogenetic diversity analyses were performed using Qiime2 and in‐house R scripts. No statistical comparison between groups was performed due to small sample size and operational taxonomic units (OUT) in each sample were obtained by using Silva database. Secondary analyses were performed for calculating Shannon's and inverse Simpsońs diversity indexes for alpha and beta diversity. Patients received antibiotherapy per local policy along with other usual standards of care.Results:Median follow‐up 9 months (4–13). Six patients died (3 from relapse, 1 from TRM, 2 from other causes). Five patients had grade III‐IV aGVHD. Seven patients received broad‐spectrum antibiotherapy against Gram‐negative bacteria. Following trends were identified: a) patients receiving myeloablative conditioning (MAC) had greater reduction in microbiota diversity between sample 1 (pre‐conditioning) and sample 2 (day 0) vs. patients receiving reduced intensity conditioning (RIC) (figure, higher panel). b) patients receiving broad‐spectrum antibiotherapy against Gram‐negative bacteria had greater reduction in microbiota diversity between sample 4 (day of starting antibiotherapy) and sample 5 (day of antibiotherapy withdrawal) vs. patients that received reduced spectrum antibiotherapy or no antibiotherapy (figure, medium panel). c) patients developing grade III‐IV aGVHD had greater reduction in microbiota diversity for each collection time‐point vs. patients having grade I‐II aGVHD or no aGVHD.Summary/Conclusion:1) This exploratory preliminary analysis showed in a small prospective multicenter cohort of adult recipients of allo‐HCT that MAC and use of broad spectrum antibiotherapy active against Gram‐negative bacteria might have a sequential cumulative impact in reducing the diversity of intestinal microbiota.image2) This hypothesis merits further testing in a bigger cohort of patients. Our clinical research group is carrying out this study and data will be updated.3) If the hypothesis is confirmed this could be used for designing co‐ordinated strategies targeting at the same time conditioning and antibiotherapy in selected individual patients.

Clinical Efficacy of Autologous Hematopoietic Stem Cell Transplantation Using Tumor-ablative Conditioning Regimen for Patients with Refractory/Relapsed Non-Hodgkin's Lymphoma

To investigate the safety and effectiveness of autologous hematopoietic stem cell transplantation (auto-HSCT) using tumor-ablative conditioning regiment for patients with refractory/relapsed non-Hodgkin's lymphoma. The clinical data of 16 patients with refractory/relapsed non-Hodgkin's lymphoma received above-mentioned therapeutic regimen from January 2013 to July 2015 was analyzed retrospectively, and conditioning-related toxicity, engraftment, infection, relapse and survival rate were evaluated. No conditioning-related organs' failure and mortality were found. Only 1 patient had not been engrafted, and the engraftment rate was 93.7%. The incidence of serious infection was 31.2%. The median follow-up was 20.5(1-30) months, and 3 patients died, out of them 2 patients died of relapse. Two year overall survival (OS) , disease-free survival (DFS) and relapse rates were 80.2%, 74.5% and 20.6% respectively. Auto-HSCT using tumor-ablative conditioning regimen is safe and effective for patients with refractory/relapsed non-Hodgkin's lymphoma, and it possess a certain effect for reducing disease relapse after transplantation.

Immunotoxin Enables Non-Genotoxic Conditioning for Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) can cure non-malignant hemoglobinopathies, congenital immunodeficiencies and, perhaps, AIDS, diseases that affect millions of people worldwide; yet, it's use is limited outside of malignancies largely because allogeneic transplantation can be complicated by serious conditioning-related toxicities and graft-versus-host disease (GVHD). The advent of highly efficient gene editing technology promises to enable autologous HSCT while avoiding GVHD. However, conditioning-related toxicities will remain a significant barrier to patient accrual unless addressed.Current conditioning approaches rely on genotoxic methods such as total body irradiation (TBI) and/or chemotherapy. These non-targeted methods induce cytopenias, adversely affect niche cells and may damage other organ systems including germ cells. To fully realize the curative potential of HSCT, the development of mild-conditioning methods that preserve immunity while enabling efficient donor engraftment is essential. Efforts to develop mild non-genotoxic approaches (e.g. CD117 antagonist ACK2 antibody) have thus far been met with efficacy limited to immunocompromised animals with very poor engraftment in immunocompetent settings.While extensively explored in cancer therapy, protein-based internalizing immunotoxins (ITs) that induce cell death by inhibiting protein synthesis have not been explored as a conditioning strategy. By creating saporin-based ITs against various antigens present on HSCs, we identified an immunotoxin against CD45 receptor (CD45-IT) that potently depleted hematopoietic cells in vitro (40-70 picomolar IC50) and achieved efficient HSC depletion (>98% depletion in vivo)in fully immunocompetent mice when administered as a single dose. Following CD45-IT administration, transplantation of whole bone marrow donor cells enabled efficient donor engraftment (>90% chimerism). A wide engraftment window was tolerated as transplantation anywhere between 2-12 days post CD45-IT resulted in equivalent engraftment. Immune reconstitution was multi-lineage, durable (maintained for >15 months) and transferrable to secondary recipients, indicative of true stem cell engraftment. Using sickle cell disease mice, we demonstrated CD45-IT conditioning enabled >90% healthy donor cell engraftment resulting in complete disease correction (n=18 sickle mice).We next compared the toxicities induced by CD45-IT and conventional TBI (sub-lethal) in non-transplanted mice over a 120-day period. CD45-IT was non-lethal as mice survived long-term without requiring transplantation (n=12 mice). In contrast to TBI, CD45-IT had significantly less adverse effects on marrow hematopoietic progenitors, vascular integrity and overall marrow cellularity, which recovered faster than in TBI-treated mice. While peripheral B and T-cells were efficiently depleted by both CD45-IT and TBI immediately after treatment, unusually rapid lymphocyte recovery was observed following CD45-IT (12-18 days for T- and B-cell recovery) in comparison to TBI (48 days for recovery). Histology of thymi revealed CD45-IT does not induce thymic atrophy (unlike TBI) as the cortical region continued to support T-cell development as confirmed by T-cell receptor excision circle (TREC) analysis.Whereas TBI reduced peripheral neutrophil counts versus control, CD45-IT induced a rapid expansion of neutrophils (3-fold higher than naïve control). To test innate immunity, we performed a systemic challenge of candida albicans (a clinically relevant fungal strain). Candida challenge in TBI-conditioned mice proved lethal (100% death in 3 days, p value < 0.0001, n=10 mice). In contrast, CD45-IT treated mice were significantly immune to candida challenge with comparable survival to naïve controls (60% survival for CD45-IT, n=10 mice per group).To summarize, a protein-based immunotoxin targeting CD45 enables efficient HSCT in fully immunocompetent animals. The targeted immunotoxin avoids numerous toxicities associated with current genotoxic conditioning approaches and preserves innate immunity, thymic integrity and enables quicker recovery of adaptive immune cells while avoiding loss of vascular integrity, undesirable anemia, and prolonged cytopenias. Given these advantages, CD45-IT may be useful for conditioning of non-malignant transplant patients. DisclosuresHoggatt:Harvard University: Patents & Royalties.

Mucocutaneous Engraftment and Type VII Collagen (C7) Replacement after Allogeneic Hematopoietic Cell Transplantation (HCT) in Patients with Recessive Dystrophic Epidermolysis Bullosa (RDEB)

In RDEB-an incurable, often fatal, blistering genodermatosis-loss-of-function mutations in the COL7A1 gene result in diminished or absent C7, lack of attachment between the epidermal basement membrane and the dermal matrix, and a poor quality of life and early death as a result of chronic mucocutaneous blistering.In 2010, we reported the results of a 'first-in-human' study on the use of HCT in 6 patients with RDEB, suggesting that increased C7 expression and mucocutaneous wound healing paralleled integumentary donor cell engraftment (NEJM 363:629, 2010). However, myeloablative conditioning (MAC) resulted in high incidence of renal, pulmonary and hepatic complications, as well as opportunistic infections due to chemotherapy-induced mucocutaneous toxicity. Therefore, subsequent patients with RDEB received reduced intensity conditioning (RIC) and the addition of bone marrow (BM)-derived mesenchymal stem/stromal cells (MSC) in an attempt to reduce the conditioning-related toxicities and enhance tissue recovery.After 2010, 20 patients aged 0.4-20 years with generalized severe RDEB underwent allogeneic HCT at the University of Minnesota. Of these, 7 were treated with MAC (busulfan IV 0.8 mg/kg for >12 kg and 1.1 mg/kg for those <12 kg of body weight q6h on days -9 to -6, with pharmacokinetic targeting 1,000 mmol/min for the area under curve; fludarabine [FLU] IV 25 mg/m2/day on days -5 to -3, and cyclophosphamide [CY] IV 50 mg/kg/day on days -5 to -2). Subsequently, 13 were treated with RIC (CY IV 50 mg/kg/day on day -6, FLU IV 40 mg/m2/day on days -6 to -2, anti-thymocyte globulin IV 30 mg/kg/day on days -4 to -2, and total body irradiation [TBI] 200 cGy or 300 cGy on day -1). Uniform GvHD prophylaxis used was cyclosporine A and mycophenolate mofetil. The hematopoietic graft was HLA-matched related BM (N=10), unrelated BM (N=7) or umbilical cord blood (UCB, N=3). In addition, a single infusion of third-party HLA-mismatched MSC (dose: 2 x 106/kg) was administered on day 0 (7 with MAC; 13 with RIC).The probability of 2-year survival was 90% (95% CI, 47-99%) in recipients of RIC as compared to 69% (95% CI, 37-87%) in recipients of MAC (p=0.3). 3 individuals (2 MAC; 1 RIC) died within one year after treatment as a result of veno-occlusive disease (N=1) and fungal sepsis (N=2), and one patient treated with MAC died after one year from extensive chronic GvHD. Interestingly, acute GVHD was rare (overall grade 2, N=2). There were no statistically significant survival differences in comparison of related vs. unrelated grafts, BM vs. UCB grafts, and those who received additional MSC vs. those who did not. Complete hematopoietic chimerism was achieved in all patients after MAC; however, RIC was associated with partial engraftment-mean 31% (range, 0-93%) in the CD15 compartment and 55% (range, 25-100%) in the CD3 compartment by day 100 after HCT. Wild-type levels of C7 in the skin believed to be sufficient to protect from extensive blistering are 10-30%. The skin chimerism was a mean 37% (range, 0-97%) after MAC in contrast to 13% (range, 0-47%) after RIC with a trend to slightly higher proportion in recipients of TBI 300cGy relative to 200cGy TBI. The primary endpoint of the analysis was survival with objective evidence of reduced mucocutaneous blistering. When compared to MAC, RIC was better tolerated with reduced risks of end organ toxicities and infections: cumulative incidence was 63% (95% CI, 34-92%) in recipients of RIC as compared to 92% (95% CI, 65-100%) in recipients of MAC, (p=0.06). For the entire cohort of engrafted, surviving subjects with RDEB thus far (N=18 of 26), 14 individuals demonstrated partial to marked biochemical and clinical improvement in mucocutaneous disease as evidenced by >50% reduction in affected body surface area, and/or C7 expression; example from RIC-treated individual is shown in Figure 1 (nuclei are blue, epidermis [top] and dermis [bottom of each panel] with C7 expression [red] at the dermal-epidermal junction).These results suggest that [1] RIC is associated with less toxicity and potentially improved survival; [2] HCT can result in improved expression of C7 protein, with reduced mucocutaneous blistering characteristic of generalized severe RDEB; and [3] these observations set the stage for exploratory studies with hematopoietic cell therapy for tissue repair and regeneration in extramedullary sites, extending their use into treatment of a broad spectrum of non-hematologic disorders. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Anti-thymocyte globulin could improve the outcome of allogeneic hematopoietic stem cell transplantation in patients with highly aggressive T-cell tumors

The early experiment result in our hospital showed that anti-thymocyte globulin (ATG) inhibited the proliferation of lymphoid tumor cells in the T-cell tumors. We used the ATG as the part of the conditioning regimen and to evaluate the long-term anti-leukemia effect, the safety and complication in the patients with highly aggressive T-cell lymphomas. Twenty-three patients were enrolled into this study. At the time of transplant, six patients reached first or subsequent complete response, three patients had a partial remission and 14 patients had relapsed or primary refractory disease. The conditioning regimen consisted of ATG, total body irradiation, toposide and cyclophosphamide. The complete remission rate after transplant was 95.7%. At a median follow-up time of 25 months, 16 (69.6%) patients are alive and free from diseases, including nine patients in refractory and progressive disease. Seven patients died after transplant, five from relapse and two from treatment-related complications. The incidence of grades II–IV acute graft-vs-host disease (GvHD) was 39.1%. The maximum cumulative incidence of chronic GvHD was 30%. The most frequent and severe conditioning-related toxicities observed in 8 out of 23 patients were grades III/IV infections during cytopenia. Thus, ATG-based conditioning is a feasible and effective alternative for patients with highly aggressive T-cell tumors.

Immunology of Hematopoietic Stem Cell Transplant

Hematopoietic stem cell transplantation (HSCT) is a procedure in which infusion of hematopoietic stem cells is used to reestablish hematopoietic function in patients with damaged or defective bone marrow or immune systems. Early and late complications following allogeneic HSCT include acute and chronic graft-versus-host disease (GVHD), donor rejection, graft failure, relapse of primary malignancy, conditioning-related toxicity, immunodeficiency and infections. Immunology has a central role in allogeneic hematopoietic cell transplantation. Any appreciation of the immunological mechanism involved in engraftment, GVHD, the development of tolerance, immune reconstitution, and the control of malignancy requires some understanding of the immunologic basis for immune reactions provoked by grafting tissue from one individual to another. In the future it should be possible to learn what gene(s) must be activated and which must be repressed to force stem cells into division without maturation; to engineer a mechanism into the cells that stops proliferation and sets the stage for amplification; to search if there could be a universal donor cell line, neatly packaged and stabilized in sealed vials and distributed by the pharmaceutical industry; to modify the transplanted cells in such a way that they have a proliferative advantage over those of the host and to deliver the lethal blow against the neoplasm, perhaps the cells that are infused will be engineered in such a way as to be able to distinguish between normal host cells and tumor.

Safety and effectiveness of tumor-ablative chemotherapy combined with low intensity modified conditioning regimen for 30 patients with hematologic malignancies receiving allogeneic hematopoietic stem cell transplantation

This study was aimed to investigate the safety and effectiveness of tumor-ablative Chemotherapy combined with low intensity conditioning regiment BUCy/TBICy for patients with hematologic malignancies receiving allogeneic hematopoietic stem cell transplantation (allo-HSCT). The clinical data of 30 patients with hematologic malignancies received above-mentioned therapeutic method from January 2012 to January 2013 was analyzed retrospectively, and the engraftment, GVHD, infection, conditioning-related toxicity, relapse and survival rates were evaluated. All the patients signed the informed consent before transplantation. The median follow-up duration was 20.5 (16.3-27.3) months. The results indicated that all the patients had been engrafted successfully. One year overall survival (OS) and disease-free survival (DFS) rates were 93.3% and 83.3% respectively. No conditioning-related toxicity occurred. The incidences of II-IV grade aGVHD was 37.9%, among which incidence of III-IV grade aGVHD was 3.4%; incidence of extensive cGVHD was 13.8%. So far, 1 case relapsed, 1 case displayed graft rejection, and poor function of graft occurred in 1 case, death occurred in 2 cases(6.7%). It is concluded that tumor-ablative chemotherapy combined with low intensity-modified BUCy/TBICy is safe and effective in allogeneic hematopoietic stem cell transplantation for hematologic malignancies, and it is useful to reduce relapse of hematologic malignancies after transplantation.

Rapid Expansion of Naive CD4+ Cord Blood Lymphocytes Restores Adaptive Immunity within 2 Months After Unrelated Cord Blood Transplantation

AbstractAbstract 2337Viral infections remain a significant problem following haematopoietic cell transplantation (HCT). Recovery of CD4+ T-cells only occurs with return of thymopoiesis 6–12 months after HCT. In an attempt to improve immune reconstitution and reduce viral infections following unrelated cord blood transplantation (CBT), serotherapy was omitted from conditioning.26 children, median age 19 months (range 1–147) underwent unrelated CBT for immunodeficiency (13) or high risk/relapsed leukemia (13). Pre-transplant co-morbidities included lung aspergillosis (2), adenoviraemia (1), Paraflu3 respiratory tract infection (3). Conditioning was myeloablative in 25 patients. HLA matching was 6/6, 5/6 and 4/6 in 13, 14 and 3 cases respectively (4 double cords). GvHD prophylaxis was mostly cyclosporine/mycophenolate mofetil (24). The median number of nucleated, CD34+ and CD3+ cells infused was 8.12 × 107/kg (range, 4.7–17.72), 3.5 × 105/kg (range, 1.23–11.95) and 5.63 × 106/kg (range, 1.9–24.45).Median time to myeloid and platelet engraftment was 22 (range, 13–38) and 39 (range, 21–110) days. One patient died from conditioning related toxicity and 3 patients died after leukaemia relapse. 22 patients are alive and in remission with a median follow up of 12 months (range 3–66). 18 patients have full donor engraftment while 4 patients are mixed chimeras.Acute GvHD > grade I occurred in 16 patients (grade II n=11; grade III-IV n=5) but in general this responded to steroids and only 1 child developed cGvHD. There was no infection-related mortality, despite early adenoviraemia (4), CMV viraemia (4), HHV6 encephalitis (1) and RSV/Paraflu3 respiratory tract infections (3).The most striking finding was a rapid and sustained CD4+ T-cell expansion with conversion from naive to memory/effector phenotype. The median CD3+, CD4+ and CD8+ counts at 2 months post CBT was 0.85 ×109cells/L (range, 0.44–2.44), 0.55 ×109cells/L (range, 0.06–1.89), and 0.21 ×109cells/L (range, 0.01–1.21) respectively. As a comparison, the median CD4+ T-cell count at 2 months post a HCT from a matched sibling donor was 0.24 ×109cells/L in 23 children evaluated in our institution.In 3 patients who developed adenoviral/CMV reactivation virus-specific T cells were detected by ELISPOT/IFN-g assays as early as 45 days post transplant, and viral infections resolved rapidly.Unrelated CBT without serotherapy results in rapid “peripheral” expansion of naive/memory CD4+ T-cells, and restores cell-mediated immunity in children faster than any other HCT donor source. Disclosures:No relevant conflicts of interest to declare.

Fludarabine, amsacrine, high-dose cytarabine and 12 Gy total body irradiation followed by allogeneic hematopoietic stem cell transplantation is effective in patients with relapsed or high-risk acute lymphoblastic leukemia

In this prospective study, we examined the toxicity and efficacy of an intensified conditioning regimen for treatment of patients with relapsed or high-risk acute lymphoblastic leukemia who undergo allogeneic hematopoietic stem cell transplantation. Fifteen patients received fludarabine 30 mg/m(2), cytarabine 2000 mg/m(2), amsacrine 100 mg/m(2) on days -10, -9, -8 and -7, anti-thymocyte globulin (ATG-Fresenius) 20 mg/kg body weight on days -6, -5 and -4 and fractionated total body irradiation 2 x 2 Gy on days -3, -2 and -1 (FLAMSA-ATG-TBI) before allogeneic hematopoietic stem cell transplantation. At the time of hematopoietic stem cell transplantation, 10 patients were in complete remission (8 CR1; 2 CR2), 3 with primary refractory and 2 suffered from refractory relapse. All patients achieved a complete remission after hematopoietic stem cell transplantation; and after a median follow-up time of 1091 days (range, 334-1554 days), nine patients (60%) are alive and free from disease, including three patients with prior refractory disease. Three patients died due to treatment-related mortality. The most frequent and severe conditioning-related toxicities observed in 9 out of 15 patients were grade III/IV infections according to common toxicity criteria. Thus, conditioning with the FLAMSA-ATG-TBI regimen is a feasible and effective alternative for patients with relapsed or high-risk acute lymphoblastic leukemia.