Fanconi anemia (FA) is characterized by bone marrow (BM) failure and cancer susceptibility. Identification of the cDNAs of many FA complementation types allows the potential of using gene transfer technology to introduce functional cDNAs as transgenes into autologous stem cells and provide a cure for the BM failure in FA patients. Previous studies in FA murine models and in a phase 1 clinical trial suggest that myelopreparation is required for significant engraftment of exogenous, genetically corrected stem cells. Since myeloid progenitors from Fancc^-/- mice and human Fanconi anemia group C protein (FANCC) patients have increased apoptosis in response to interferon γ (IFN-γ) in vitro, we hypothesized that IFN-γ may be useful as a nongenotoxic, myelopreparative conditioning agent. To test this hypothesis, IFN-γ was administered as a continuous infusion to Fancc^-/- and wild-type (WT) mice for 1 week. Primitive and mature myeloid lineages were preferentially reduced in IFN-γ-treated Fancc^-/- mice. Further, IFN-γ conditioning of Fancc^-/- recipients was sufficient as a myelopreparative regimen to allow consistent engraftment of isogenic WT repopulating stem cells. Collectively, these data demonstrate that Fancc^-/- hematopoietic cell populations have increased hypersensitivity to IFN-γ in vivo and that IFN-γ conditioning may be useful as a nongenotoxic strategy for myelopreparation in this disorder. (Blood. 2004;104:1204-1209)