Assessing the Safety, Tolerability, and Efficacy of APR-2020 in Pediatric and Adolescent Subjects With RPS19 Deficient Diamond-Blackfan Anemia

A Phase 1, Open-label, Single-arm Study of APR 2020 in Transfusion Dependent, Steroid Resistant Pediatric and Adolescent Subjects With RPS19 Deficient Diamond Blackfan Anemia by Transplantation of Autologous CD34+ Stem Cells Transduced With CLIN LV EFS coRPS19 PRE* (APR-2020)

Brief summary

The goal of this clinical trial is to learn if APR-2020 is safe and can help treat Diamond-Blackfan Anemia (DBA) in adolescents and children. The main questions it aims to answer are:

• Is APR-2020 safe and well tolerated?
• Does APR-2020 modify or correct an underlying genetic condition which causes DBA?
• Does APR-2020 reduce or eliminate the need for blood transfusions and/or restore certain blood counts affected by DBA?

Participants will:

• Take the drug one time as an infusion.
• Undergo two rounds of a cellular harvest procedure in which their own cells will be used in the manufacturing of their own participant-specific product.
• Initially return to the clinic for two years of follow up at increasingly sparse intervals.

Study Overview

• Status: Recruiting
• Conditions: RPS19 Deficient Diamond-Blackfan Anemia
• Intervention / Treatment: Biological: APR-2020

Detailed Description

This open-label, single-arm study evaluates the safety and efficacy of APR-2020 in transfusion-dependent, steroid-resistant pediatric and adolescent patients with RPS19-deficient Diamond-Blackfan Anemia (DBA).

Disease Background: DBA is a congenital bone marrow (BM) failure syndrome characterized by early-onset hypoplastic anemia secondary to selective erythroid aplasia. The cardinal hematologic manifestation is a severe normochromic, macrocytic anemia in the presence of preserved leukocyte and platelet counts. In approximately 90% of affected individuals, hematologic abnormalities manifest within the first year of life; the median age at clinical presentation is approximately 2 months, with a median age at diagnosis of 3 months (Sieff 2023).

Genotype-phenotype data have demonstrated substantial clinical heterogeneity both within and across molecular subtypes. Accordingly, the term DBA syndrome has been adopted to reflect the broader phenotypic spectrum, encompassing classic DBA-estimated to occur at an incidence of 5 to 10 per million live births with no significant sex predilection-as well as non-classical or attenuated presentations. Most patients exhibit a reticulocytopenic (hyporegenerative) anemia, consistent with impaired erythroid progenitor differentiation and maturation, with or without associated congenital anomalies or growth abnormalities (Vlachos et al. 2018).

DBA is primarily caused by heterozygous pathogenic variants in genes encoding ribosomal proteins (RPs), resulting in ribosomal haploinsufficiency and defective ribosome biogenesis. The most frequently implicated genes include RPS19 (25-30%), RPL5 (7-12%), RPS26 (6-9%), RPL11 (5-7%), RPS24 (2-3%), and RPS10 (1-3%). Additional RP gene variants have been identified at lower frequencies (Sieff 2023; Wlodarski et al. 2024). RPS19 remains the most commonly mutated gene in DBA (Da Costa et al. 2020; Sieff 2023; Wlodarski et al. 2024). Rare pathogenic variants in non-ribosomal protein genes associated with DBA-like phenotypes-such as GATA1, TSR2, and EPO-have also been described but collectively account for fewer than 1% of cases (Da Costa et al. 2020; Wlodarski et al. 2024).

Patients eligible for inclusion in the present study have a confirmed diagnosis of DBA attributable to pathogenic variants in RPS19.

Study Population: The protocol will enroll 4 subjects with genetically confirmed RPS19-deficient DBA who demonstrate transfusion-dependent, corticosteroid-refractory disease.

Study Drug: The study drug, APR-2020 is a gene therapy that consists of autologous cluster of differentiation (CD)34+ hematopoietic stem and progenitor cells (HSPCs) derived from mobilized peripheral blood (PB) from subjects with RPS19-deficient DBA. These CD34+ cells will be exposed ex-vivo to the Sponsor's highly purified and concentrated third generation self-inactivating (SIN) lentiviral vector (LVV), which provides the functioning RPS19 gene.

The efficacy of APR-2020 was demonstrated through a rescue of the DBA phenotype in the RPS19-deficient DBA mouse model and through in vitro and in vivo RPS19 gene transfer to RPS19-deficient mouse hematopoietic stem and progenitor cells using Apriligen's proprietary vector. (Liu et al. 2022).

APR-2020 is intended to supplement haploinsufficiency of RPS19 gene expression in patients with DBA. APR-2020 provides gene-corrected multipotent progenitor cells with a fitness advantage which is expected to enable engraftment and clonal expansion of corrected cells without the need for myeloablative conditioning, thereby eliminating conditioning-related toxicity in this vulnerable pediatric population. The aforementioned preclinical studies generated data that support evaluating APR-2020 without any genotoxic conditioning. (Dahl et al. 2021; Garelli et al. 2019; Yoshida et al. 2025)

Expression of the RPS19 protein has the potential to restore impaired erythroid differentiation and proliferation of erythroid progenitors potentially eliminating the need for RBC transfusions. After APR-2020 infusion, transduced CD34+ HSPCs are expected to engraft in the BM, which will be measured by presence of RPS19 and vector copy number (VCN).

Healthy erythroid progenitors have a significant capacity to increase output of RBCs: In healthy individuals, the rate of erythropoiesis can be increased > 10 fold in response to increased demand, involving physiological signals such as tissue hypoxia and increased production of erythropoietin (Flygare et al. 2011, Peslak et al. 2012). With this 10-fold over capacity, it is possible that just 10% of healthy amounts of gene-corrected erythroid progenitors is sufficient to sustain healthy erythropoiesis.

Immunologically matched DBA mouse models can be cured by healthy stem cell transplantation without conditioning: Successful disease correction in RPL11 and RPS19 deficient mouse models using non genotoxic antibody-based conditioning prior to HSCT has been demonstrated (Dahl et al. 2021, Swartzrock et al. 2024). These studies showed that even with minimal donor engraftment, unconditioned transplantation effectively normalized hemoglobin levels in DBA mice.

Further, the molecular efficacy report by Freiman et al. 2025 demonstrates induction of pro-apoptotic gene expression programs in multipotent progenitors from patients with DBA that is significantly downregulated after gene therapy. This suggests APR 2020 derived multipotent progenitors expressing RPS19 will have a healthy fitness advantage over the uncorrected progenitors, allowing for selective expansion even without myeloablative conditioning. In addition, Venugopal et al. 2017 documented a case of self reverting mutations in a patient with DBA that partially corrected the blood phenotype. The expansion of reversion events arising independently suggests a selective advantage over the defective cell population with likely contribution to correcting the phenotypic defect. This clinical case provides real-world validation that reversion in just a fraction of HSCs can achieve significant clinical improvement, supporting a non-myeloablative approach for APR 2020 gene therapy.

Collectively, these findings provide a strong scientific rationale for initially attempting APR 2020 gene therapy without genotoxic conditioning. The converging evidence demonstrates that even limited engraftment of gene-corrected cells can provide clinical benefit in DBA due to the selective advantage of corrected cells, the amplification capacity of erythroid progenitors, and the effectiveness of even low-level RPS19 expression in rescuing cellular function; this approach prioritizes patient safety by avoiding the serious risks associated with myeloablative conditioning, including organ toxicity, infertility, and secondary malignancies, while still offering potential for therapeutic benefit.

In RPS19-associated DBA, haploinsufficiency resulting from monoallelic loss-of-function leads to defective ribosome biogenesis and erythroid failure. Therefore, the emergence of circulating reticulocytes following gene-based intervention implies successful in vivo transgene expression and functional rescue of erythroid progenitors.

Reticulocyte-based response criteria serve as a direct measure of restored endogenous erythropoiesis and function as an early biological marker that precedes and predicts subsequent increases in hemoglobin (Wlodarski et al 2024). Because DBA is characterized by a primary defect in erythroid progenitor proliferation and differentiation, impaired RBC production occurs upstream of reticulocyte formation. Accordingly, baseline reticulocyte counts in eligible subjects are anticipated to be profoundly reduced or near absent. For these reasons, the Sponsor considers the appearance of reticulocytes to be a critical early indicator of therapeutic activity following treatment with APR-2020, representing mechanistic correction of erythropoiesis and a leading signal of subsequent hemoglobin recovery.

Clinical Significance: This study represents a potentially transformative approach for transfusion-dependent, steroid-resistant RPS19-deficient DBA patients who currently face lifelong transfusion dependence with associated iron overload, or high-risk allogeneic HSCT as their only alternatives. The non-genotoxic conditioning strategy, paired with an autologous gene therapy, if successful, could establish a new paradigm for gene therapy in inherited bone marrow failure syndromes where corrected cells possess intrinsic selective advantage.

• Study Type: Interventional
• Enrollment (Estimated): 4
• Phase: Phase 1

Contacts and Locations

• Study Contact: Name: Nova Silver; Phone Number: 617-306-3020; Email: nsilver@apriligen.com

Study Locations

• United States
  • California
    • Stanford, California, United States, 94304
      • Recruiting
      • Stanford University - Stanford Children's Health
      • Contact: Research Nurse; Phone Number: 650-724-6055; Email: scgt_clinical_trials_office@lists.stanford.edu
  • Massachusetts
    • Boston, Massachusetts, United States, 02215
      • Recruiting
      • Boston Children's Hospital
      • Contact: Emily Morris; Phone Number: 617-632-1954; Email: gene.therapy@childrens.harvard.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child; Adult
• Accepts Healthy Volunteers: No

Description

Key Inclusion Criteria:

1. Confirmed diagnosis of RPS19-deficient DBA.
2. Signed informed consent by the subject or legally authorized representative.
3. Bone marrow analysis demonstrating normal cytogenetics except for RPS19-deficient DBA.
4. Subjects are between 2 and 18 years of age, inclusive.
5. Eligible for allogeneic marrow or stem cell transplant for DBA (non-critical cardiac and hepatic iron overload).
6. Corticosteroid resistance
7. Transfusion-dependent anemia
8. Willingness to return for long-term follow-up
9. Adequate renal and pulmonary function
10. Able to undergo hematopoietic stem cell transplant (HSCT) mobilization and apheresis procedures.

Key Exclusion Criteria:

1. Availability of a suitable, consenting HLA-identical sibling donor.
2. Positive viral serology.
3. Clinically significant, active bacterial, viral, or fungal infection.
4. Any prior or current malignancy, myeloproliferative disorder, or myelodysplastic syndrome, except where therapy was curative excision (ie, in situ squamous cell carcinoma).
5. Any concerning molecular or cytogenetic abnormalities in hematopoietic cells.
6. Previous receipt of an allogeneic transplant or gene therapy.
7. Immediate family member with a known or suspected Familial Cancer Syndrome (including, but not limited to breast, colorectal, ovarian, prostate, and pancreatic cancers, excluding DBA).
8. Diagnosis of significant psychiatric disorder that could impact the subject's ability to participate in the study, in the opinion of the Investigator.
9. History of complex allo-immunization, as determined by the Investigator.
10. Women who are lactating/breast feeding or who plan to breastfeed within 6 months following APR-2020 infusion.
11. Men and females of childbearing potential who are unwilling to practice highly effective methods of birth control through the duration of the study.
12. Females with a positive serum pregnancy test at Screening or who are planning to become pregnant during the study period.
13. Liver disease, as evidenced by critical iron overload with magnetic resonance imaging (MRI)
14. Heart disease or Type 1 diabetes.
15. Evidence of significant pulmonary hypertension, per Investigator assessment.
16. Any other condition that would render the subject ineligible for HSCT, as determined by Investigator.
17. Contraindication to stem cell or bone marrow aspiration, mobilization or collection including allergies to filgrastim or plerixafor.
18. Currently enrolled in another investigational drug study or received an investigational study drug or procedure within 90 days of study enrollment.
19. A physical or emotional status that would prevent giving informed consent, protocol compliance, or adequate follow-up.
20. An assessment by the Investigator that the subject or parents of the subject will not comply with the study procedures outlined in the study protocol.
21. Taking prohibited medications.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: APR-2020	Biological: APR-2020; The drug product (DP) is designated as APR-2020 and is composed of autologous human CD34+ cells derived from each clinical patient with RPS19-deficient DBA that have been transduced ex vivo with the drug substance.; Other Names: Cell Therapy

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incidence of protocol-defined dose limiting toxicities (DLTs) for APR-2020		30 Days
Incidence and severity of treatment emergent adverse events, assessed by the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE)		24 Months
Monitoring of laboratory parameters, frequency and severity of clinical adverse events (AEs), assessed by the NCI CTCAE		24 Months
Fraction of reticulocytes greater than the baseline value where reticulocyte increases are sustained over 3 consecutive measurements within 4 weeks	Baseline is defined as the average of 3 measurements prior to APR-2020 infusion	24 Months
Proportion of subjects with hemoglobin level of at least 8 g/dL starting 90 days after last RBC transfusion, sustained over 2 consecutive measurements that are approximately 1 month apart		24 Months

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Number of subjects who achieve engraftment	Engraftment is defined by: Fraction of reticulocytes greater than the baseline value AND; Any one of the following:At least 0.002 therapeutic vector copies per nucleated cell of patient bone marrow (BM); ORAt least 0.002 therapeutic vector copies per nucleated cell of patient peripheral blood (PB); OR At least 0.2% gene marked CD34+ cells in BM or PB.	24 Months
Incidence of treatment related mortality		100 Days, 1 Year and 2 Years
Change from baseline in the frequency and/or dose of iron chelation therapy		12 and 24 Months
Change from baseline in iron stores present in cardiac and hepatic tissue		6, 12, and 24 Months
Change from baseline in subject and family responses on the QoL survey	PedsQL(TM) hematology/oncology and family impact	12 Months
Change from baseline in erythroid progenitors		6 and 24 Months
Change from baseline in vector copy number in mononuclear cells	Peripheral blood monthly for the first 6 months, then every 6 months for 2 years. Bone marrow at 6 and 24 months post treatment.	24 Months

Collaborators and Investigators

• Sponsor: Apriligen, Inc.

Publications and helpful links

General Publications

• Vlachos A, Osorio DS, Atsidaftos E, Kang J, Lababidi ML, Seiden HS, Gruber D, Glader BE, Onel K, Farrar JE, Bodine DM, Aspesi A, Dianzani I, Ramenghi U, Ellis SR, Lipton JM. Increased Prevalence of Congenital Heart Disease in Children With Diamond Blackfan Anemia Suggests Unrecognized Diamond Blackfan Anemia as a Cause of Congenital Heart Disease in the General Population: A Report of the Diamond Blackfan Anemia Registry. Circ Genom Precis Med. 2018 May;11(5):e002044. doi: 10.1161/CIRCGENETICS.117.002044. No abstract available.
• Da Costa L, Leblanc T, Mohandas N. Diamond-Blackfan anemia. Blood. 2020 Sep 10;136(11):1262-1273. doi: 10.1182/blood.2019000947.
• Dahl M, Warsi S, Liu Y, Debnath S, Billing M, Siva K, Flygare J, Karlsson S. Bone marrow transplantation without myeloablative conditioning in a mouse model for Diamond-Blackfan anemia corrects the disease phenotype. Exp Hematol. 2021 Jul;99:44-53.e2. doi: 10.1016/j.exphem.2021.06.002. Epub 2021 Jun 12.
• Garelli E, Quarello P, Giorgio E, Carando A, Menegatti E, Mancini C, Di Gregorio E, Crescenzio N, Palumbo O, Carella M, Dimartino P, Pippucci T, Dianzani I, Ramenghi U, Brusco A. Spontaneous remission in a Diamond-Blackfan anaemia patient due to a revertant uniparental disomy ablating a de novo RPS19 mutation. Br J Haematol. 2019 Jun;185(5):994-998. doi: 10.1111/bjh.15688. Epub 2018 Nov 20. No abstract available.
• Flygare J, Rayon Estrada V, Shin C, Gupta S, Lodish HF. HIF1alpha synergizes with glucocorticoids to promote BFU-E progenitor self-renewal. Blood. 2011 Mar 24;117(12):3435-44. doi: 10.1182/blood-2010-07-295550. Epub 2010 Dec 21.
• Freiman S, Chen J, Baudet A et al. Ex Vivo APR 2020 Molecular Efficacy Report. 2025. Lund University.
• Jillella AP, Ustun C. What is the optimum number of CD34+ peripheral blood stem cells for an autologous transplant? Stem Cells Dev. 2004 Dec;13(6):598-606. doi: 10.1089/scd.2004.13.598.
• Liu Y, Dahl M, Debnath S, Rothe M, Smith EM, Grahn THM, Warsi S, Chen J, Flygare J, Schambach A, Karlsson S. Successful gene therapy of Diamond-Blackfan anemia in a mouse model and human CD34+ cord blood hematopoietic stem cells using a clinically applicable lentiviral vector. Haematologica. 2022 Feb 1;107(2):446-456. doi: 10.3324/haematol.2020.269142.
• Moreno-Carranza B, Gentsch M, Stein S, Schambach A, Santilli G, Rudolf E, Ryser MF, Haria S, Thrasher AJ, Baum C, Brenner S, Grez M. Transgene optimization significantly improves SIN vector titers, gp91phox expression and reconstitution of superoxide production in X-CGD cells. Gene Ther. 2009 Jan;16(1):111-8. doi: 10.1038/gt.2008.143. Epub 2008 Sep 11.
• Peslak SA, Wenger J, Bemis JC, Kingsley PD, Koniski AD, McGrath KE, Palis J. EPO-mediated expansion of late-stage erythroid progenitors in the bone marrow initiates recovery from sublethal radiation stress. Blood. 2012 Sep 20;120(12):2501-11. doi: 10.1182/blood-2011-11-394304. Epub 2012 Aug 13.
• Sieff C. DBA Syndrome.GeneReviews. Accessed April 2025. Retrieved from: https://www.ncbi.nlm.nih.gov/books/NBK7047/#:~:text=Diamond%2DBlackfan%20anemia%20(DBA),in%
• Swartzrock L, Liu YL, Hoang H, et al. Disease correction of a diamond blackfan anemia mouse model using non genotoxic conditioning and hematopoietic stem cell transplantation. Blood 2024;144(Suppl 1):194 5.
• Yoshida M, Bhoopala, S, Toki T, et al. Polyclonal somatic gene rescue via uniparental disomy confers multilineage hematopoietic potential in treatment-independent patients with DBA syndrome. Blood 2025;146(1):746.
• Venugopal P, Moore S, Lawrence DM, George AJ, Hannan RD, Bray SC, To LB, D'Andrea RJ, Feng J, Tirimacco A, Yeoman AL, Young CC, Fine M, Schreiber AW, Hahn CN, Barnett C, Saxon B, Scott HS. Self-reverting mutations partially correct the blood phenotype in a Diamond Blackfan anemia patient. Haematologica. 2017 Dec;102(12):e506-e509. doi: 10.3324/haematol.2017.166678. Epub 2017 Sep 29. No abstract available.
• Wlodarski MW, Vlachos A, Farrar JE, Da Costa LM, Kattamis A, Dianzani I, Belendez C, Unal S, Tamary H, Pasauliene R, Pospisilova D, de la Fuente J, Iskander D, Wolfe L, Liu JM, Shimamura A, Albrecht K, Lausen B, Bechensteen AG, Tedgard U, Puzik A, Quarello P, Ramenghi U, Bartels M, Hengartner H, Farah RA, Al Saleh M, Hamidieh AA, Yang W, Ito E, Kook H, Ovsyannikova G, Kager L, Gleizes PE, Dalle JH, Strahm B, Niemeyer CM, Lipton JM, Leblanc TM; international Diamond-Blackfan anaemia syndrome guideline panel. Diagnosis, treatment, and surveillance of Diamond-Blackfan anaemia syndrome: international consensus statement. Lancet Haematol. 2024 May;11(5):e368-e382. doi: 10.1016/S2352-3026(24)00063-2.

Helpful Links

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Study record dates

Study Major Dates

• Study Start (Actual): April 16, 2026
• Primary Completion (Estimated): April 1, 2027
• Study Completion (Estimated): September 1, 2028

Study Registration Dates

• First Submitted: March 12, 2026
• First Submitted That Met QC Criteria: March 12, 2026
• First Posted (Actual): March 17, 2026

Study Record Updates

• Last Update Posted (Actual): May 15, 2026
• Last Update Submitted That Met QC Criteria: May 13, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Diamond-Blackfan Anemia; DBA; RPS19
• Additional Relevant MeSH Terms: Congenital Bone Marrow Failure Syndromes; Bone Marrow Failure Disorders; Genetic Diseases, Inborn; Hematologic Diseases; Bone Marrow Diseases; Anemia; Anemia, Hypoplastic, Congenital; Red-Cell Aplasia, Pure; Anemia, Aplastic; Congenital, Hereditary, and Neonatal Diseases and Abnormalities; Hemic and Lymphatic Diseases; Anemia, Diamond-Blackfan; Therapeutics; Biological Therapy; Cell- and Tissue-Based Therapy
• Other Study ID Numbers: APR-2020-001

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No