RETROVIRAL-MEDIATED GENE-TRANSFER OF THE FANCONI-ANEMIA COMPLEMENTATION GROUP-C GENE TO HEMATOPOIETIC PROGENITORS OF GROUP-C PATIENTS

Fanconi anemia (FA) is a rare genetic disorder characterized by progre ssive pancytopenia, congenital abnormalities, and a predisposition to malignancy. Therapy is currently limited to allogeneic marrow transpla ntation; patients lacking a suitable donor usually die from aplasia or acute leukemia. Recently, mutation in a novel gene named FACC (Fancon i anemia C-complementing) has been identified as causing one type of F A. FACC mutations, which introduce splicing errors or stop codons, hav e been identified in similar to 15% of FA patients. We have recently b een successful in functional complementation of four FA cell lines usi ng retroviral vectors to transfer a copy of the normal FACC gene. We a lso analyzed the ability of our viral vectors to functionally correct hematopoietic progenitor cells from a patient bearing a splice donor m utation. As for the lymphoid cell lines, these CD34-enriched cells wer e extremely sensitive to MMC. After infection of these progenitor cell s with viral vectors bearing normal FACC, the progenitors gave rise to increased numbers of colonies both in the absence and presence of up to 5 nM MMC, whereas control cells were completely destroyed by 1 nM M MC. In summary, we have demonstrated that: (1) retroviral vectors can be engineered to transfer a normal FACC gene to FA(C) lymphoid cell li nes and primary hematopoietic cells; (2) introduction of a normal FACC gene into CD34(+) progenitors markedly enhances their growth in the a bsence and presence of MMC. This study is designed to determine whethe r hematopoietic progenitors transduced with the normal FACC gene can b e reinfused safely into FA(C) patients. CD34(+) cells obtained from G- CSF mobilized peripheral blood will be transduced ex vivo over a 72-ho ur period in the presence of IL-3, IL-6, and Stem Cell Factor with the FACC retroviral vector. These transduced cells will be reinfused into FA(C) patients. Patients will be monitored for toxicities as well as evidence of successful gene transfer and expression. The procedure wil l be repeated up to a total of 4 times with each treatment 2-4 months apart. Theoretically, these rescued stem cells should have a selective growth advantage within the hypoplastic FA marrow environment in vivo .