Nonconditioned ADA-SCID gene therapy reveals ADA requirement in the hematopoietic system and clonal dominance of vector-marked clones

Toru Uchiyama; Sirirat Takahashi; Kazuhiko Nakabayashi; Kohji Okamura; Kaori Edasawa; Masafumi Yamada; Nobuyuki Watanabe; Emi Mochizuki; Toru Yasuda; Akane Miura; Motohiro Kato; Daisuke Tomizawa; Makoto Otsu; Tadashi Ariga; Masafumi Onodera

doi:10.1016/j.omtm.2021.10.003

Nonconditioned ADA-SCID gene therapy reveals ADA requirement in the hematopoietic system and clonal dominance of vector-marked clones

Mol Ther Methods Clin Dev. 2021 Oct 16:23:424-433. doi: 10.1016/j.omtm.2021.10.003. eCollection 2021 Dec 10.

Authors

Affiliations

¹ Department of Human Genetics, National Center for Child Health and Development, Tokyo, Japan.
² Department of Maternal-Fetal Biology, National Center for Child Health and Development, Tokyo, Japan.
³ Department of System Biomedicine, National Center for Child Health and Development, Tokyo, Japan.
⁴ Department of Pediatrics, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
⁵ Department of Pediatric Hematology and Oncology Research, National Center for Child Health and Development, Tokyo, Japan.
⁶ Children's Cancer Center, National Center for Child Health and Development, Tokyo, Japan.
⁷ Department of Transfusion and Cell Transplantation, Kitasato University School of Medicine, Kanagawa, Japan.

Abstract

Two patients with adenosine deaminase (ADA)-deficient severe combined immunodeficiency (ADA-SCID) received stem cell-based gene therapy (SCGT) using GCsapM-ADA retroviral vectors without preconditioning in 2003 and 2004. The first patient (Pt1) was treated at 4.7 years old, and the second patient (Pt2), who had previously received T cell gene therapy (TCGT), was treated at 13 years old. More than 10 years after SCGT, T cells showed a higher vector copy number (VCN) than other lineages. Moreover, the VCN increased with differentiation toward memory T and B cells. The distribution of vector-marked cells reflected variable levels of ADA requirements in hematopoietic subpopulations. Although neither patient developed leukemia, clonal expansion of SCGT-derived clones was observed in both patients. The use of retroviral vectors yielded clonal dominance of vector-marked clones, irrespective of the lack of leukemic changes. Vector integration sites common to all hematopoietic lineages suggested the engraftment of gene-marked progenitors in Pt1, who showed severe osteoblast (OB) insufficiency compared to Pt2, which might cause a reduction in the stem/progenitor cells in the bone marrow (BM). The impaired BM microenvironment due to metabolic abnormalities may create space for the engraftment of vector-marked cells in ADA-SCID, despite the lack of preconditioning.

Keywords: ADA activity; ADA-SCID; bone marrow microenvironment; clonal dominance; insertional mutagenesis; nonconditioned gene therapy; retroviral vector.