Peripheral blood stem and progenitor cell collection in pediatric candidates for ex vivo gene therapy: a 10-year series

Abstract

Hematopoietic stem and progenitor cell (HSPC)-based gene therapy (GT) requires the collection of a large number of cells. While bone marrow (BM) is the most common source of HSPCs in pediatric donors, the collection of autologous peripheral blood stem cells (PBSCs) is an attractive alternative for GT. We present safety and efficacy data of a 10year cohort of 45 pediatric patients who underwent PBSC collection for backup and/or purification of CD34 + cells for ex vivo gene transfer. Median age was 3.7 years and median weight 15.8 kg. After mobilization with lenograstim/plerixafor (n = 41) or lenograstim alone (n = 4) and 1À3 cycles of leukapheresis, median collection was 37 Â 10 6 CD34 + cells/kg. The procedures were well tolerated. Patients who collected R7 and R13 Â 10 6 CD34 + cells/kg in the first cycle had pre-apheresis circulating counts of at R42 and R86 CD34 + cells/mL, respectively. Weight-adjusted CD34 + cell yield was positively correlated with peripheral CD34 + cell counts and influenced by female gender, disease, and drug dosage. All patients received a GT product above the minimum target, ranging from 4 to 30.9 Â 10 6 CD34 + cells/kg. Pediatric PBSC collection compares well to BM harvest in terms of CD34 + cell yields for the purpose of GT, with a favorable safety profile.

Mobilization-based chemotherapy-free engraftment of gene-edited human hematopoietic stem cells

“…M-HSCT with autologous cells corrected by gene editing might represent a promising option, where the use of engraftment enhancers might also compensate for the limited efficiency of HDR in primitive HSPCs (Vavassori et al, 2021). We estimated the total CD34 + cells available in the BM and the median number of mobilized CD34 + cells following mobilization with G-CSF and AMD3100, according to reported findings (Canarutto et al, 2021;Orkin et al, 2015) and then determined the expected extent of BM vacancy. Based on the assumptions that: (1) mobilized HSPCs found in the circulation account for all BM-egressed cells and (2) mobilized and infused HSPCs compete equally, we estimate that upon infusion of 35 3 10 6 CD34 + /kg, a dose close to the upper range of those used in the clinic, one could reach a chimerism of 15%.…”

Genotoxic effects of base and prime editing in human hematopoietic stem cells

“…The substantial amount of DNA DSBs in HSPCs emphasizes a concrete liability of nickase-based editing and CBE in particular, which were originally described as spared from potentially genotoxic events and thus defined as ‘DSB-free’, rather than ‘DSB-less’, systems. Although the frequencies of deletions and translocations were lower after nickase-based editing than after nuclease-based editing, these figures remain relevant considering that several hundred million HSPCs are treated and infused in clinical applications of HSPC gene therapy (>2 × 10 6 CD34 + cells per kg) 38 . Hence, the potential occurrence and in vivo persistence of large genomic rearrangements should be considered in the preclinical and clinical risk assessment of base and prime editing and, even more stringently, when aiming for multiplex editing approaches.…”

Hematopoietic reconstitution dynamics of mobilized- and bone marrow-derived human hematopoietic stem cells after gene therapy

“…MPB is widely employed as HSPC source for ex vivo gene-correction approaches and HSCT 10 , 30 , 31 , 53 , 54 . Our analyses provide insights into the kinetic of reconstitution, longevity and lineage output of primitive and committed HSPC in 13 WAS-GT patients receiving either engineered purified MPB- or BM-HSPC.…”

“…Collection of MPB HSPC for clinical HSCT purposes is currently based on Granulocyte-Colony Stimulating Factor (G-CSF) administration. In poor mobilizer subjects or in GT trials, G-CSF is used in combination with the C-X-C Chemokine receptor type 4 (CXCR4) antagonist Plerixafor 10 , 14 , 29 – 31 , in order to increase the amount of retrieved HSPC. The outcome of G-CSF MPB vs. BM-based allogeneic transplantation has been characterized from the clinical point of view 32 , with G-CSF MPB source displaying rapid recovery from neutropenia, reduced time of platelet-transfusion dependency and similar long-term reconstitution performance.…”