LentiGlobin reduces transfusion dependence in young thalassemia patients

NEW ORLEANS – The gene therapy LentiGlobin can reduce transfusion dependence in children and young adults with non-beta⁰/beta⁰ thalassemia, according to two trials.

^{Jennifer Smith/MDedge News}

Dr. Timothy S. Olson

In a phase 1/2 trial, 8 of 10 of patients achieved transfusion independence at a median follow-up of 36.0 months. In a phase 3 trial, transfusion independence was achieved by 2 of 3 patients with follow-up of at least 12 months.

Timothy S. Olson, MD, PhD, of Children’s Hospital of Philadelphia, presented results from the phase 1/2 HGB-204 trial and the phase 3 HGB-207 trial at the annual meeting of the American Society of Pediatric Hematology/Oncology.

Treatment

In both trials, patients received granulocyte colony-stimulating factor and plerixafor for hematopoietic stem cell mobilization. Their cells were collected via apheresis and transduced with the betibeglogene darolentivec (BB305) lentiviral vector. The patients received busulfan (for an average of 4 days) as conditioning and were infused with the transduced cells.

The manufacturing process for LentiGlobin was refined in the HGB-207 trial, which translated to a product with a higher vector copy number and higher proportion of CD34+ cells transduced, Dr. Olson said.

The median vector copy number was 3.1 in the HGB-207 trial and 0.7 in the HGB-204 trial. The median proportion of CD34+ cells transfused was 81% and 29%, respectively. The median cell dose was 7.7 x 10⁶ CD34+ cells/kg and 7.1 x 10⁶ CD34+ cells/kg, respectively.

HGB-204 patients and efficacy

The HGB-204 trial included 10 patients with non-beta⁰/beta⁰ genotypes – 6 with beta^E/beta⁰, 1 with beta⁺/beta⁰, 2 with beta⁺/beta⁺, and 1 with an “other” genotype.

The patients’ median age at consent was 19.5 years (range, 16-34). The annualized median prestudy red blood cell (RBC) transfusion volume was 151 mL/kg per year.

At a median follow-up of 36 months, 8 of the 10 patients achieved transfusion independence. The median duration of transfusion independence was 38 months. The median weighted average hemoglobin during transfusion independence was 10.2 g/dL.

“Two patients did not achieve transfusion independence, and both patients were on the lower end of the spectrum both in terms of vector copy number per cell and the percentage of CD34+ cells that were successfully transduced,” Dr. Olson said. “Both patients actually experienced a reduction in the annualized transfusion volume requirements of between 43% and 77%.”

HGB-207 patients and efficacy

The HGB-207 trial included 16 patients with non-beta⁰/beta⁰ genotypes – 6 with beta^E/beta⁰, 7 with beta⁺/beta⁰, and 3 with the beta⁺/beta⁺ genotype.

The patients’ median age at consent was 19 years . The annualized median prestudy RBC transfusion volume was 192 mL/kg per year.

The median follow-up in this trial is 9.3 months. Ten of 11 patients with at least 3 months of follow-up are transfusion-free with hemoglobin levels greater than 11 g/dL.

Two patients have achieved transfusion independence according to the protocol definition, which is weighted average hemoglobin of 9 g/dL or greater without any RBC transfusions for at least 12 months.

“In the one patient in this study who did not achieve transfusion independence, the vector-derived hemoglobin was quite low, and this correlated with a very low vector copy number seen in circulating peripheral blood mononuclear cells,” Dr. Olson said.

It isn’t clear why this occurred, however, as the vector copy number wasn’t especially low in the LentiGlobin product the patient received. Therefore, the researchers are still investigating why this patient failed to achieve transfusion independence.