ALS20-101 Lentiviral Gene Therapy for Beta Thalassemia

Inclusion Criteria:

1. Age 18 to 35 years at the time of consent

2. Diagnosis of transfusion dependent beta thalassemia (β0 β0, β+β0, β+β+, βEβ0, βEβ+,β0 or β+ /βA + alpha triplication(s)). Transfusion-dependent is defined as ahistory of receiving at least 120 mL/kg/year packed red blood cells or at least 8transfusions per year in the past two years. The first 2 subjects enrolled must havea non- β0 β0 genotype.

3. Genetic confirmation of α and β thalassemia diagnosis (β0β0, β+β0, β+β+, βEβ0, Eβ+dominant β-thalassemia) by a Clinical Laboratory Improvement Amendments (CLIA)certified laboratory is required.

4. Clinically stable, Karnofsky score 70, and eligible to undergo Hematopoietic StemCell Transplantation (HSCT).

5. Female subjects of childbearing potential must agree to use acceptable method(s) ofcontraception from consent through at least 6 months after CHOP-ALS20 infusion

6. Male subjects of reproductive capacity must agree to use effective contraceptionfrom start of mobilization through at least 6 months after CHOP-ALS20 infusion

Exclusion Criteria:

1. Prior receipt of HSCT or gene therapy

2. An available Human Leukocyte Antigen (HLA)-matched family donor

3. More than one alpha globin gene deletions/mutations.

4. Any prior or current malignancy (excluding adequately treated basal or squamous cellcarcinoma of the skin)

5. Known cancer predisposition syndrome

6. Positive for HIV-1, HIV-2, Human T Cell Lymphotropic Virus-1,2 (HTLV-1, HTLV-2) oractive hepatitis B or active hepatitis C infection

7. Clinically significant active bacterial, viral (including COVID-19 and influenza),fungal, or parasitic infection (temporary exclusion)

8. Clinically significant bleeding disorder

9. Evidence of cardiac dysfunction (left ventricular ejection fraction <50% orshortening fraction <27%) or clinically significant arrhythmia

10. Evidence of advanced liver disease (ALT >5x the upper limit of normal (ULN),prothrombin time >1.5 x ULN, direct bilirubin > 3x ULN) not attributable to ironchelation therapy, or evidence of bridging fibrosis on liver biopsy or fibrosisstage of F3 or higher by magnetic resonance elastography (MRE) if obtained as partof clinical care

11. Liver R2 or R2 MRI or liver biopsy with liver iron concentration 15 mg/g dw (temporary exclusion)

12. Diffusion capacity of carbon monoxide (DLco) <50% of predicted (corrected for Hb)

13. Pulse oximetry in room air <92%

14. Evidence of renal dysfunction (creatinine >1.5x ULN or Glomerular Filtration Rate (GFR) <70 ml/min/1.73 m2 based on cystatin C/creatinine equation)

15. Cardiac T2 MRI < 10 ms

16. Platelet count <100,000/mcL or absolute neutrophil count <1000/mcL except ifattributed to benign ethnic neutropenia

17. Unable to receive red cell transfusion (significant allo/auto immunization)

18. Uncontrolled systemic hypertension

19. Uncontrolled seizure disorder

20. Diagnosis of a significant psychiatric disorder that could seriously impede theability to participate in the study

21. Immediate family member with a known or suspected Familial Cancer Syndrome

22. Contraindication to anesthesia

23. For female subjects, pregnancy or breastfeeding

24. Participation in another clinical trial of an investigational drug within 30 days or 5 drug half-lives, whichever is longer, of screening (temporary exclusion)

25. Any other condition that would render the subject ineligible formobilization/apheresis and/or HSCT as determined by the investigator