Gene therapy/bone marrow transplantation in ADA-deficient mice: roles of enzyme-replacement therapy and cytoreduction

Abstract

<jats:title>Abstract</jats:title><jats:p>Gene therapy (GT) for adenosine deaminase–deficient severe combined immune deficiency (ADA-SCID) can provide significant long-term benefit when patients are given nonmyeloablative conditioning and ADA enzyme-replacement therapy (ERT) is withheld before autologous transplantation of γ-retroviral vector-transduced BM CD34+ cells. To determine the contributions of conditioning and discontinuation of ERT to the therapeutic effects, we analyzed these factors in Ada gene knockout mice (Ada−/−). Mice were transplanted with ADA-deficient marrow transduced with an ADA-expressing γ-retroviral vector without preconditioning or after 200 cGy or 900 cGy total-body irradiation and evaluated after 4 months. In all tissues analyzed, vector copy numbers (VCNs) were 100- to 1000-fold greater in mice receiving 900 cGy compared with 200 cGy (P &lt; .05). In mice receiving 200 cGy, VCN was similar whether ERT was stopped or given for 1 or 4 months after GT. In unconditioned mice, there was decreased survival with and without ERT, and VCN was very low to undetectable. When recipients were conditioned with 200 cGy and received transduced lineage-depleted marrow, only recipients receiving ERT (1 or 4 months) had detectable vector sequences in thymocytes. In conclusion, cytoreduction is important for the engraftment of gene-transduced HSC, and short-term ERT after GT did not diminish the capacity of gene-corrected cells to engraft and persist.</jats:p>

Outcomes in Two Japanese Adenosine Deaminase-Deficiency Patients Treated by Stem Cell Gene Therapy with No Cytoreductive Conditioning

“…In addition, the idea has emerged that ERT at some points after SCGT may benefit patient outcomes [19,34,41], thus suggesting another combination of two variables for future clinical protocols (i.e., with cytoreductive conditioning, while on PEG-ADA).…”

Stem cell transplantation in the context of HIV – how can we cure HIV infection?

“…For HIV-infected patients who have not developed cancer, it is envisioned that a low-dose chemotherapy ablation regimen can be used. As observed with ADA-severe combined immunodeficiency patients in recent clinical trials, only a reduced intensity conditioning regimen needs to be applied for reliable engraftment of gene modified cells to occur [21][22][23]. Therefore, HIV-infected patients could receive a non-lethal dose of chemotherapy to make space in the bone marrow for the anti-HIV gene modified cells.…”

Cytoreductive conditioning intensity predicts clonal diversity in ADA-SCID retroviral gene therapy patients

“…4,6 One can speculate that the myeloid abnormalities that have been observed in ADA-deficiency may limit leukoproliferation. 44 Alternatively, the trans-correction of the metabolic abnormalities in ADA-SCID, the basis for immune reconstitution with enzyme replacement therapy, decreases the proliferative pressure on the gene-corrected stem cells (or lymphoid progenitors) by allowing some noncorrected cells to survive. Potentially, the lack of cytoreductive conditioning in SCID-X1 trials led to strong competition and proliferative stress of corrected clones, which is absent in ADA-SCID because of the inability of corrected clones to engraft efficiently without conditioning.…”

“…Unlike SCID-X1 gene therapy, in which a strong selection for corrected cells exists because of the lack of growth factor receptors on uncorrected cells, ADA-SCID gene therapy in humans has required the use of chemotherapeutic conditioning agents, such as busulfan or melphalan in order to achieve long-term and efficient engraftment of corrected cells. 2,5,44 We therefore focused on the delivered dose of busulfan, which we estimated by high-performance liquid chromatography measurement of busulfan concentrations at successive times after administration of the drug, and transduced bone marrow cell dose.…”