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

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.

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 demonstrates normal cytogenetics except for RPS19-deficient DBA. 4. Between 2 and 25 years of age, inclusive. 5. Eligible for allogeneic marrow or stem cell transplant for DBA (noncritical 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 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. Female subjects who are lactating/breast feeding or who plan to breastfeed within 6 months following APR-2020 infusion. 11. Male and female subjects of childbearing potential who are unwilling to practice highly effective methods of birth control from screening until ≥ 6 months after APR-2020 infusion. 12. Female subjects 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 the 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, functional, 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. 22. Has insufficient personal history of RBC transfusions over the 13 weeks prior to the end of screening.