Hematopoietic Engraftment of Fanconi Anemia Patients through 3 Years after Gene Therapy

Nine Fanconi anemia patients complementation group A (FA-A), age 2-6 years, have been infused with autologous hematopoietic cells after genetic correction with the therapeutic PGK-FANCA.Wpre* lentiviral vector. In all instances patients underwent CD34⁺ cell mobilization with G-CSF and plerixafor and were subsequently infused in the absence of any pre-conditioning regimen, in order to avoid genotoxic side effects in a population characterized by DNA repair defects and cancer predisposition. The first four patients were treated between January 2016 and March 2017 and were infused with an estimated number of 170,000 and 410,000 transduced CD34⁺ cells/Kg. The other five patients were treated more recently with cell numbers that ranged between 50,000 to 1.6x10⁶ corrected CD34⁺ cells/kg. The analyses of the first four patients showed the presence of corrected cells both in BM and PB after six months post-infusion and progressive increases of gene marking were observed thereafter in all these patients until the most recent follow-up (2 to >3 years post-infusion). Gene marking in BM CD34⁺ cells correlated with the survival of the CFCs to mitomycin-C, with levels up to 70% at 3 years post-infusion. Additionally, progressive decreases in the percentage of PB T cells with diepoxybutane-induced chromosomal breaks were observed in the patients with higher levels of gene marking. Similarly, stabilized PB cell counts have been observed in patients with higher percentages of gene corrected cells. Insertion site analyses revealed the absence of genotoxic events, and demonstrated the engraftment of pluripotent HSCs and a pattern of oligoclonal reconstitution, consistent with the number of infused corrected CD34⁺ cells and the absence of conditioning. In the five additional patients treated more recently, the presence of gene corrected PB cells has been confirmed; levels of gene marking have been consistent with data observed in the first four treated patients and with the number of infused CD34⁺ cells. Our results confirm the engraftment of gene corrected HSCs in non-conditioned FA-A patients, in some cases through more than 3 years of follow-up, suggesting the relevance of this therapeutic approach in FA.