Antimetabolites synergize with non-genotoxic antibody drug conjugate conditioning in hematopoietic stem cell lentiviral gene therapy.

Authors

Jennifer Okalova, Jordan S Alexander, Seema R Patel, Gianna M Branella, Carlos Barichello de Quevedo, W Hunter Baldwin, Chengyu Prince, Shanmuganathan Chandrakasan, Harrison C Brown, Christopher B Doering, H Trent Spencer

Published in

Molecular therapy. Advances. Volume 34. Issue 3. Pages 201780. Sep 10, 2026. Epub Jun 11, 2026.

Abstract

Hematopoietic stem cell transplantation (HSCT) of genetically engineered cells is a promising treatment modality for monogenic diseases. However, hematopoietic stem cell (HSC)-directed lentiviral vector (LV) gene therapies remain limited by genotoxicities associated with standard non-targeted conditioning using irradiation or alkylating chemotherapy. We and others developed an antibody drug conjugate (ADC) with anti-CD117 and saporin (sap), which selectively depletes CD117-expressing HSC and progenitor cells (HSPCs). Since anti-CD117-sap does not generally provide engraftment comparable to conventional conditioning, we investigated the hypothesis anti-CD117-sap is not effective as a single conditioning agent due to insufficient HSPC depletion. We show anti-CD117-sap induces nearly complete residual HSPC entry into a non-G₀ proliferative state and postulated agents targeting cycling cells would enhance engraftment. When we administered the antimetabolite 5-fluorouracil with anti-CD117-sap, anti-thymocyte globulin, and an immunoglobulin-degrading enzyme, we achieved >90% peripheral blood chimerism of unmodified cultured donor cells. Additional immunosuppression combined with an increase in transplanted cells further permitted ∼70% engraftment of HSPCs transduced with an LV encoding a high-expression, immunogenic factor VIII (FVIII) transgene. Copy numbers of ∼1.0 and normal FVIII plasma activity levels (>50%) by 6 months post-HSCT were achieved. Collectively, we show ADC and antimetabolite administration can augment LV-engineered HSPC engraftment by targeting cycling cells.

PMID:
42436858
Bibliographic data and abstract were imported from PubMed on 12 Jul 2026.

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