RP-L301, a Lentiviral-Mediated Gene Therapy for Pyruvate Kinase Deficiency (PKD): A Phase 2 Clinical Trial Design

Introduction: Red cell pyruvate kinase deficiency (PKD) is a rare, autosomal recessive, non-spherocytic hemolytic anemia caused by mutations in the pyruvate kinase liver and red blood cell (PKLR) gene, resulting in a glycolytic defect, causing increased red cell destruction, hyperbilirubinemia, splenomegaly, and iron overload. Splenectomy increases hemoglobin (on average 1.6 g/dL) but is associated with increased infection and thromboembolic risk, and 10-15% of patients with PKD will remain transfusion dependent despite splenectomy. Mitapivat, an allosteric PKLR activator, is approved for the treatment of adult patients, however hemoglobin increases of at least 1.5 g/dL were infrequent in splenectomized patients and/or those with more severe anemia. There is a high unmet medical need for patients with severe PKD who are transfusion dependent. RP-L301 is a gene therapy consisting of autologous CD34+ hematopoietic cells transduced with a lentiviral vector (LV) carrying the codon optimized red cell pyruvate kinase (coRPK) gene. As demonstrated in the RP-L301 Phase 1 study, infusion of genetically corrected autologous hematopoietic cells was associated with favorable safety (there were no RP-L301 associated serious adverse events) and conferred sustained hemoglobin increases and eliminated RBC transfusion requirements. Hb improvement and hemolysis reduction were observed in both adult and pediatric patients with PKD; all patients remain transfusion independent following hematopoietic engraftment; 3 of 4 patients demonstrate sustained normal-range Hb levels with up to 3 years follow-up. These results indicate that RP-L301 has the potential to address the significant unmet need in PKD.

Study Design and Methods: This is a single-arm, open-label, global (US, Denmark, Netherlands and Spain) Phase 2 (NCT06422351) clinical trial evaluating a single infusion of RP-L301 in splenectomized pediatric and adult patients (ages 8-55 years) with PKD. Key inclusion criteria include confirmed PKLR mutation, significant anemia and/or RBC transfusion requirements, and adequate organ function. Key exclusion criteria include presence of other causes of hemolysis and previous hematopoietic cell transplant.

The primary objective is to evaluate efficacy; the primary endpoint is a Hb increase of >1.5 g/dL at 12 months post-infusion compared to baseline levels. Secondary and exploratory objectives include resolution of anemia to normal range, reduction in transfusion requirements including transfusion-independence, improvement in hemolysis parameters, PKD symptoms and patient-reported outcomes, iron overload reduction, genetic correction, safety, tolerability, and durability of efficacy results.

Autologous CD34+ hematopoietic cells are mobilized using granulocyte-colony stimulating factor (G-CSF) and plerixafor and then collected via apheresis, followed by CD34+ cell enrichment by immunoselection and transduction with the LV containing coRPK. RP-L301 is infused following myeloablative busulfan conditioning. Efficacy and safety will be assessed through 24 months post-infusion and patients will have the option for long-term follow-up enrollment up to 15 years. Approximately 10 patients will participate.

Conclusion: Based on the favorable efficacy and safety data from the Phase 1 study, this registrational Phase 2 study is designed to enable comprehensive evaluation of the potential of RP-L301 autologous gene therapy to substantively reverse the disease phenotype in pediatric and adult patients with PKD.