Clinical Focus

  • Hematopoietic Stem Cell Transplantation
  • Immune Regulatory Disorders
  • Severe Aplastic Anemia
  • Leukemia/Lymphoma
  • Pediatric Hematology-Oncology

Academic Appointments

Boards, Advisory Committees, Professional Organizations

  • Chair, Medical Committee, Camp Ramah Darom (2018 - Present)
  • Medical Advisory Board, Rally Foundation for Childhood Cancer (2017 - Present)

Professional Education

  • Board Certification: American Board of Pediatrics, Pediatric Hematology-Oncology (2017)
  • Fellowship: Johns Hopkins Medicine Pediatric Hematology and Oncology Program (2016) MD
  • Fellowship, National Institutes of Health, National Cancer Institute Pediatric Oncology Branch, Pediatric Hematology-Oncology (2015)
  • Board Certification: American Board of Pediatrics, Pediatrics (2012)
  • Residency: Icahn School of Medicine at Mount Sinai Pediatric Residency (2012) NY
  • Medical Education: Icahn School of Medicine at Mount Sinai (2009) NY

Clinical Trials

  • CD4^LVFOXP3 in Participants With IPEX Recruiting

    This first-in-human, Phase 1 clinical trial will test the feasibility of the manufacturing and the safety of the administration of CD4^LVFOXP3 in up to 36 evaluable human participants with IPEX and evaluate the impact of the CD4^LVFOXP3 infusion on the disease.

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  • Early Trial of Allogeneic Hematopoietic Stem Cell Transplantation for Patients Who Will Receive a Kidney Transplant From the Same Donor Recruiting

    This is a single center, non-randomized, non-controlled open-label phase 1b/2a trial of performing sequential αβdepleted-HSCT and KT in patients requiring KT to prevent kidney rejection post-KT, in the absence of any post-KT immunosuppression, to abrogate the need for lifelong immunosuppression, the risk of chronic rejection and, ultimately, the need for repeated transplantation.

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  • Posoleucel (ALVR105) for the Treatment of Adenovirus Infection in Pediatric and Adult Participants Receiving Standard of Care Following Allogeneic Hematopoietic Cell Transplantation Recruiting

    This study will assess the safety and efficacy of Posoleucel for the treatment of adenovirus (AdV) infection in pediatric and adult allo-HCT recipients receiving standard of care (SoC).

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  • Study of Posoleucel (ALVR105,Viralym-M) for Multi-Virus Prevention in Patients Post-Allogeneic Hematopoietic Cell Transplant Recruiting

    This is a Phase 3 study to evaluate posoleucel (ALVR105, Viralym-M); an allogeneic, off-the-shelf multi-virus specific T cell therapy that targets six viral pathogens: BK virus, cytomegalovirus, adenovirus, Epstein-Barr virus, human herpesvirus 6 and JC virus.

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All Publications

  • Defibrotide modulates pulmonary endothelial cell activation and protects against lung inflammation in pre-clinical models of LPS-induced lung injury and idiopathic pneumonia syndrome FRONTIERS IN IMMUNOLOGY Klein, O. R., Ktena, Y. P., Pierce, E., Fu, H., Haile, A., Liu, C., Cooke, K. R. 2023; 14: 1186422


    A multiple organ dysfunction syndrome (MODS) workshop convened by the National Institute of Child Health and Human Development in 2015 identified acute respiratory distress syndrome (ARDS) and complications of allogeneic blood and marrow transplantation (allo-BMT) as contributors to MODS in pediatric patients. Pulmonary dysfunction also remains a significant complication of allo-BMT. Idiopathic pneumonia syndrome (IPS) defines non-infectious, acute, lung injury that occurs post-transplant. Injury and activation to endothelial cells (ECs) contribute to each form of lung inflammation.Two murine models were employed. In an ARDS model, naïve B6 mice receive an intravenous (i.v.) injection of lipopolysaccharide (LPS). In the established model of IPS, naïve B6D2F1 mice receive lethal total body irradiation followed by BMT from either allogeneic (B6) or syngeneic (B6D2F1) donors. Lung inflammation was subsequently assessed in each scenario.Intravenous injection of LPS to B6 mice resulted in enhanced mRNA expression of TNFα, IL-6, Ang-2, E-, and P-selectin in whole lung homogenates. The expression of Ang-2 in this context is regulated in part by TNFα. Additionally, EC activation was associated with increased total protein and cellularity in broncho-alveolar lavage fluid (BALF). Similar findings were noted during the development of experimental IPS. We hypothesized that interventions maintaining EC integrity would reduce the severity of ARDS and IPS. Defibrotide (DF) is FDA approved for the treatment of BMT patients with sinusoidal obstruction syndrome and renal or pulmonary dysfunction. DF stabilizes activated ECs and protect them from further injury. Intravenous administration of DF before and after LPS injection significantly reduced mRNA expression of TNFα, IL6, Ang-2, E-, and P-selectin compared to controls. BALF showed decreased cellularity, reflecting less EC damage and leak. Allogeneic BMT mice were treated from day -1 through day 14 with DF intraperitoneally, and lungs were harvested at 3 weeks. Compared to controls, DF treatment reduced mRNA expression of TNFα, IL6, Ang-2, E-, and P- selectin, BALF cellularity, and lung histopathology.The administration of DF modulates EC injury in models of ARDS and IPS. Cytokine inhibition in combination with agents that stabilize EC integrity may be an attractive strategy for patients in each setting.

    View details for DOI 10.3389/fimmu.2023.1186422

    View details for Web of Science ID 001023536600001

    View details for PubMedID 37441074

    View details for PubMedCentralID PMC10335747

  • Transplant for non-malignant disorders: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee report on the role of alternative donors, stem cell sources and graft engineering. Cytotherapy Klein, O. R., Bonfim, C., Abraham, A., Ruggeri, A., Purtill, D., Cohen, S., Wynn, R., Russell, A., Sharma, A., Ciccocioppo, R., Prockop, S., Boelens, J. J., Bertaina, A. 2023


    Hematopoietic stem cell transplantation (HSCT) is curative for many non-malignant disorders. As HSCT and supportive care technologies improve, this life-saving treatment may be offered to more and more patients. With the development of new preparative regimens, expanded alternative donor availability, and graft manipulation techniques, there are many options when choosing the best regimen for patients. Herein the authors review transplant considerations, transplant goals, conditioning regimens, donor choice, and graft manipulation strategies for patients with non-malignant disorders undergoing HSCT.

    View details for DOI 10.1016/j.jcyt.2022.12.005

    View details for PubMedID 36710227

  • Reduced Intensity Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Pediatric Inherited Immune Deficiencies and Bone Marrow Failure Syndromes JOURNAL OF CLINICAL IMMUNOLOGY Klein, O. R., Bapty, S., Lederman, H. M., Younger, M. M., Zambidis, E. T., Jones, R. J., Cooke, K. R., Symons, H. J. 2021; 41 (2): 414-426


    Allogeneic bone marrow transplantation (alloBMT) is the only cure for many primary immune deficiency disorders (PIDD), primary immune regulatory disorders (PIRD), and inherited bone marrow failure syndromes (IBMFS).We report the results of 25 patients who underwent alloBMT using reduced intensity conditioning (RIC), alternative donors, and post-transplantation cyclophosphamide (PTCy). In an attempt to reduce regimen-related toxicities, we removed low-dose TBI from the prep and added mycophenolate mofetil and tacrolimus for graft-versus-host disease (GVHD) prophylaxis for all donor types in the latter 14 patients. Donors were haploidentical related (n = 14), matched unrelated (n = 9), or mismatched unrelated (n = 2). The median age was 9 years (range 5 months-21 years).With a median follow-up of 26 months (range 7 months-9 years), the 2-year overall survival is 92%. There were two deaths, one from infection, and one from complications after a second myeloablative BMT. Three patients developed secondary graft failure, one at 2 years and two at >3 years, successfully treated with CD34 cell boost in one or second BMT in two. The remaining 20 patients have full or stable mixed donor chimerism and are disease-free. The incidence of mixed chimerism is increased since removing TBI from the prep. The 6-month cumulative incidence of grade II acute GVHD is 17%, with no grade III-IV. The 1-year cumulative incidence of chronic GVHD is 14%, with severe of 5%.This alloBMT platform using alternative donors, RIC, and PTCy is associated with excellent rates of engraftment and low rates of GVHD and non-relapse mortality, and offers a curative option for patients with PIDD, PIRD, and Identifier: NCT04232085.

    View details for DOI 10.1007/s10875-020-00898-0

    View details for Web of Science ID 000587090700001

    View details for PubMedID 33159275

    View details for PubMedCentralID PMC7647188

  • Myeloablative haploidentical BMT with posttransplant cyclophosphamide for hematologic malignancies in children and adults BLOOD ADVANCES Symons, H. J., Zahurak, M., Cao, Y., Chen, A., Cooke, K., Gamper, C., Klein, O., Llosa, N., Zambidis, E. T., Ambinder, R., Bolanos-Meade, J., Borrello, I., Brodsky, R., DeZern, A., Gojo, I., Showel, M., Swinnen, L., Smith, B., Luznik, L., Jones, R. J., Fuchs, E. J. 2020; 4 (16): 3913-3925


    Promising results have been reported for patients with high-risk hematologic malignancies undergoing HLA-haploidentical bone marrow transplantation (haploBMT) with posttransplantation cyclophosphamide (PTCy), but there are few data on outcomes with myeloablative conditioning in this context. We report the results of a single-institution, prospective phase 2 trial of myeloablative haploBMT using busulfan-based or total body irradiation-based conditioning in 96 children or adults (median age, 42 years; range, 1-65 years) with high-risk hematologic malignancies. Recovery of neutrophils and platelets occurred at a median of 24 and 29 days. Engraftment of donor cells with chimerism >95% was achieved in 91%. The cumulative incidence of acute graft-versus-host disease (GVHD) grades II to IV and grades III to IV at day 100 was 11% and 4%, and of chronic GVHD at 6 and 12 months was 4% and 15%, with 6% moderate to severe. The cumulative incidence of nonrelapse mortality was 6% at 100 days and 11% at 1 year (19% in those aged >55 years). The cumulative incidence of relapse at 1 year was 35%; at 3 years, it was 43%. In multivariable analysis, relapse was associated with increased age (P = .02 for age 20-55 years and P = .02 for age >55 years) and with minimal residual disease before transplantation (P = .05). The overall survival at 1 and 3 years is 73% and 54%, and event-free survival at 1 and 3 years is 57% and 49%. We show that haploBMT with PTCy after myeloablative conditioning is safe and efficacious for adult and pediatric patients with hematologic malignancies. Careful consideration must be given to using myeloablative conditioning in patients age >55 years. This trial was registered at as #NCT00796562.

    View details for DOI 10.1182/bloodadvances.2020001648

    View details for Web of Science ID 000562892100013

    View details for PubMedID 32813874

    View details for PubMedCentralID PMC7448587

  • T-ALLO10 INFUSION AFTER A.DEPLETED-HSCT IN CHILDREN AND YOUNG ADULTS WITH HEMATOLOGIC MALIGNANCIES: IMPROVED IMMUNE RECONSTITUTION IN THE ABSENCE OF SEVERE GVHD Bertaina, A., Bacchetta, R., Shyr, D., Saini, G., Lee, J., Kristovich, K., Agarwal-Hashmi, R., Klein, O., Melsop, K., Tate, K., Barbarito, G., Oppizzi, L., Chen, P., Cepika, A., Roncarolo, M. SPRINGERNATURE. 2023: 232-234
  • Precision Delivery of Steroids as a Rescue Therapy for Gastrointestinal Graft-versus-Host Disease in Pediatric Stem Cell Transplant Recipients Journal of Clinical Medicine Levitte, s., Ganguly, A., Frolik, S., Guevara-Tique, A., et al 2023; 12 (4229)

    View details for DOI 10.3390/jcm12134229

  • Volumetric modulated arc therapy total body irradiation in pediatric and adolescent/young adult patients undergoing stem cell transplantation: Early outcomes and toxicities. Pediatric blood & cancer Marquez, C., Hui, C., Simiele, E., Blomain, E., Oh, J., Bertaina, A., Klein, O., Shyr, D., Jiang, A., Hoppe, R. T., Kovalchuk, N., Hiniker, S. M. 2022: e29689


    INTRODUCTION: Total body irradiation (TBI) is an important component of many conditioning regimens for hematopoietic stem cell transplantation (HSCT), most commonly used in pediatric and adolescent/young adult (AYA) patients. We aimed to evaluate outcomes and toxicities among pediatric and AYA patients treated with TBI utilizing volumetric modulated arc therapy total body irradiation (VMAT-TBI).METHODS: We reviewed pediatric and AYA patients treated with VMAT-TBI at our institution from 2019 to 2021. Data on patient and disease characteristics, treatment details, outcomes and toxicities were collected. Overall survival (OS) and relapse-free survival (RFS) were analyzed using the Kaplan-Meier method.RESULTS: Among 38 patients, 16 (42.1%) were treated with myeloablative regimens and 22 (57.9%) with nonmyeloablative regimens. Median age was 7.2 years (range: 1-27) and median follow-up was 8.7 months (range: 1-21). Lungs Dmean was 7.3 ± 0.3Gy for myeloablative regimens (range: 6.8-7.8). Kidneys were spared to average mean dose of 71.4 ± 4.8% of prescription dose. Gonadal sparing was achieved for patients treated for nonmalignant diseases to Dmean of 0.7 ± 0.1Gy. No patient experienced primary graft failure; one (2.6%) experienced secondary graft failure. The most common grade 1-2 acute toxicities were nausea (68.4%) and fatigue (55.3%). Mucositis was the most common grade 3-4 acute toxicity, affecting 39.5% of patients. There were no cases of pneumonitis or nephrotoxicity attributable to TBI.CONCLUSION: VMAT-TBI offers increased ability to spare organs at risk in pediatric and AYA patients undergoing HSCT, with a favorable acute/subacute toxicity profile and excellent disease control.

    View details for DOI 10.1002/pbc.29689

    View details for PubMedID 35373904

  • Outcomes of pediatric patients with oncologic disease or following hematopoietic stem cell transplant supported on extracorporeal membrane oxygenation: The PEDECOR experience PEDIATRIC BLOOD & CANCER Steppan, D. A., Coleman, R. D., Viamonte, H. K., Hanson, S. J., Carroll, M. K., Klein, O. K., Cooke, K. R., Spinella, P. C., Steiner, M. E., Loftis, L. L., Bembea, M. M., Pediat Acute Lung Injury Sepsis In, ELSO 2020; 67 (10): e28403


    Outcomes for patients with oncologic disease and/or after hematopoietic stem cell transplant (HSCT) requiring intensive care unit admission have improved, but indications for and outcomes after extracorporeal membrane oxygenation (ECMO) support in this population are poorly characterized.We analyzed data from consecutive patients < 18 years with oncologic disease and/or after HSCT reported to a pediatric ECMO registry by nine pediatric centers in the United States between 2011 and 2018.We identified 18 ECMO patients with oncologic disease and/or HSCT, and 415 ECMO controls matched with a propensity score algorithm based on age, gender, race, severity of illness at admission, and reason for ECMO. The primary indication for ECMO was respiratory failure in 66.7% in the oncologic disease and/or HSCT group, and in 70.7% in the matched ECMO control group. Eleven of 18 patients survived to hospital discharge (61.1%), similar to the matched control group (60.8%), P = 0.979. Children with oncologic disease and/or HSCT had lower mean platelet counts during ECMO and received higher volumes of platelets compared with the control group, mean 14.6 mL/kg/day (standard deviations [SD], 9.8) versus mean 9.3 mL/kg/day (SD, 10.4), P = 0.001. Of the 11 surviving children with oncologic disease and/or HSCT, five sustained new neurologic disorders (45.5%) versus 45 of 222 (20.3%) in the control group, P = 0.061. Bleeding complications were similar in the two groups.Outcomes of patients with oncologic disease and/or HSCT supported on ECMO in the current era are not significantly different compared with matched ECMO controls and are improved from previously published reports.

    View details for DOI 10.1002/pbc.28403

    View details for Web of Science ID 000539018400001

    View details for PubMedID 32519430

  • Reduced-Intensity Haploidentical Bone Marrow Transplantation with Post-Transplant Cyclophosphamide for Solid Tumors in Pediatric and Young Adult Patients BIOLOGY OF BLOOD AND MARROW TRANSPLANTATION Llosa, N. J., Chen, A. R., Gamper, C. J., Klein, O. R., Zambidis, E. T., Luber, B., Rosner, G., Siegel, N., Holuba, M., Robey, N., Hayashi, M., Jones, R. J., Fuchs, E., Holdhoff, M., Loeb, D. M., Symons, H. J. 2017; 23 (12): 2127-2136


    High-risk, recurrent, or refractory solid tumors in pediatric, adolescent, and young adult (AYA) patients have an extremely poor prognosis despite current intensive treatment regimens. We piloted an allogeneic bone marrow transplant platform using reduced-intensity conditioning (RIC) and partially HLA-mismatched (haploidentical) related donors for this population of pediatric and AYA solid tumor patients. Sixteen patients received fludarabine, cyclophosphamide, melphalan, and low-dose total body irradiation RIC haploidentical BMT (haploBMT) followed by post-transplantation cyclophosphamide (PTCy), mycophenolate mofetil, and sirolimus. All assessable patients were full donor chimeras on day 30 with a median neutrophil recovery of 19 days and platelet recovery of 21 days. One patient (7%) exhibited secondary graft failure associated with concomitant infection. The median follow-up time was 15 months. Overall survival was 88%, 56%, and 21% at 6, 12, and 24 months, respectively. Median survival from transplant date was 14 months with a median progression-free survival 7 months. We observed limited graft-versus-host disease in 3 patients and nonrelapse mortality in 1 patient. We demonstrated that RIC haploBMT with PTCy is feasible and has acceptable toxicities in patients with incurable pediatric and AYA solid tumors; thus, this approach serves as a platform for post-transplant strategies to prevent relapse and optimize progression-free survival.

    View details for DOI 10.1016/j.bbmt.2017.08.012

    View details for Web of Science ID 000418309000016

    View details for PubMedID 28807769

    View details for PubMedCentralID PMC5986177

  • Adoptive immunotherapy for primary immunodeficiency disorders with virus-specific T lymphocytes JOURNAL OF ALLERGY AND CLINICAL IMMUNOLOGY Naik, S., Nicholas, S. K., Martinez, C. A., Leen, A. M., Hanley, P. J., Gottschalk, S. M., Rooney, C. M., Hanson, I., Krance, R. A., Shpall, E. J., Cruz, C. R., Amrolia, P., Lucchini, G., Bunin, N., Heimall, J., Klein, O. R., Gennery, A. R., Slatter, M. A., Vickers, M. A., Orange, J. S., Heslop, H. E., Bollard, C. M., Keller, M. D. 2016; 137 (5): 1498-+


    Viral infections are a leading fatal complication for patients with primary immunodeficiencies (PIDs) who require hematopoietic stem cell transplantation (HSCT). Use of virus-specific T lymphocytes (VSTs) has been successful for the treatment and prevention of viral infections after HSCT for malignant and nonmalignant conditions. Here we describe the clinical use of VSTs in patients with PIDs at 4 centers.We sought to evaluate the safety and efficacy of VSTs for treatment of viral infections in patients with PIDs.Patients with PIDs who have received VST therapy on previous or current protocols were reviewed in aggregate. Clinical information, including transplantation details, viral infections, and use of antiviral and immunosuppressive pharmacotherapy, were evaluated. Data regarding VST production, infusions, and adverse reactions were compared.Thirty-six patients with 12 classes of PID diagnoses received 37 VST products before or after HSCT. Twenty-six (72%) patients had received a diagnosis of infection with cytomegalovirus, EBV, adenovirus, BK virus, and/or human herpesvirus 6. Two patients were treated before HSCT because of EBV-associated lymphoproliferative disease. Partial or complete responses against targeted viruses occurred in 81% of patients overall. Time to response varied from 2 weeks to 3 months (median, 28 days). Overall survival at 6 months after therapy was 80%. Four patients had graft-versus-host disease in the 45 days after VST infusion, which in most cases was therapy responsive.VSTs derived from either stem cell donors or third-party donors are likely safe and effective for the treatment of viral infections in patients with PIDs.

    View details for DOI 10.1016/j.jaci.2015.12.1311

    View details for Web of Science ID 000376180200026

    View details for PubMedID 26920464

    View details for PubMedCentralID PMC4860050

  • Idiopathic pneumonia syndrome following hematopoietic stem cell transplantation JOURNAL OF PEDIATRIC INTENSIVE CARE Klein, O. R., Cooke, K. R. 2014; 3 (3): 147-157


    Non-infectious lung injury following hematopoietic stem cell transplant may be driven by either immune or non-immune pathways of inflammation. Common alloimmune lung complications include idiopathic pneumonia syndrome (IPS), transfusion related lung injury, diffuse alveolar hemorrhage, and peri-engraftment respiratory distress syndrome, with both diffuse alveolar hemorrhage and peri-engraftment respiratory distress syndrome existing as subsets of IPS when infection is absent. This review will discuss the definitions, risk factors, and pathogeneses of IPS and highlight the diagnostic work-up and novel approaches to treatment.

    View details for DOI 10.3233/PIC-14098

    View details for Web of Science ID 000218845900007

    View details for PubMedID 31214462

    View details for PubMedCentralID PMC6530755