Continuous in vivo infusion of interferon-gamma (IFN-gamma) enhances engraftment of syngeneic wild-type cells in Fanca-/- and Fancg-/- mice

Abstract

Fanconi anemia (FA) is a heterogeneous genetic disorder characterized by bone marrow (BM) failure and cancer susceptibility. Identification of the cDNAs of 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. However, strategies to enhance the mobilization, transduction, and engraftment of exogenous stem cells are required to optimize efficacy prior to widespread clinical use. Hypersensitivity of Fancc-/- cells to interferon-gamma (IFN-gamma), a nongenotoxic immune-regulatory cytokine, enhances engraftment of syngeneic wild-type (WT) cells in Fancc-/- mice. However, whether this phenotype is of broad relevance in other FA complementation groups is unresolved. Here we show that primitive and mature myeloid progenitors in Fanca-/- and Fancg-/- mice are hypersensitive to IFN-gamma and that in vivo infusion of IFN-gamma at clinically relevant concentrations was sufficient to allow consistent long-term engraftment of isogenic WT repopulating stem cells. Given that FANCA, FANCC, and FANCG complementation groups account for more than 90% of all FA patients, these data provide evidence that IFN-gamma conditioning may be a useful nongenotoxic strategy for myelopreparation in FA patients.

Figure 1.

Evaluation of the sensitivity of Fanca^–/– and Fancg^–/– myeloid progenitors to IFN-γ. Methylcellulose cultures that promote the growth of myeloid progenitors from FA-deficient bone marrow were established containing a range of concentrations of IFN-γ in triplicate wells. The respective genotypes are indicated. Data represent the mean ± standard error of the mean (SEM) of 4 independent experiments. *P < .01 comparing the IFN-γ–dependent reduction in myeloid progenitors of Fancc^–/–, Fanca^–/–, and Fancg^–/– myeloid progenitors to wild-type controls using analysis of variance.

Figure 2.

Effects of in vivo IFN-γ treatment on peripheral white blood cell (WBC) counts and bone marrow cellularity. (A) Peripheral nucleated cell counts were obtained from experimental mice following completion of IFN-γ treatment (closed symbols) or the phosphate-buffered saline vehicle, PBS (open symbols). Each symbol represents total nucleated white blood cells from individual mice. Bars represent the mean WBC count of all experimental mice in the respective treatment group. *P < .01 comparing white blood cell counts of IFN-γ–treated mice to vehicle-treated control mice with the same genotype. (B) BM cellularity following IFN-γ treatment. Symbols represent bone marrow cellularity of individual mice. Bars represent the mean BM cellularity of all mice in the experimental group. *P < .01 comparing bone marrow cellularity of IFN-γ–treated mice versus vehicle-treated controls of the same genotype.

Figure 3.

Evaluation of IFN-γ on primitive and mature myeloid progenitor numbers isolated from the BM of Fanca^–/–, Fancg^–/–, and Fancc^–/– mice. (A) Evaluation of myeloid progenitors from WT, Fancc^–/– , Fanca^–/–, and Fancg^–/– bone marrow. Hematopoietic cells derived from the bone marrow LDMNCs from mice of each respective genotype were cultured in triplicate to evaluate growth of high proliferating potential colony-forming cells (HPP-CFCs) and low proliferating potential colony-forming cells (LPP-CFCs). Data represent the mean ± standard error of the mean (SEM) of 3 independent experiments. (B) Bone marrow cells from WT, Fancc^–/–, Fanca^–/–, and Fancg^–/– mice previously treated with a 7-day course of 400 μg/kg per day IFN-γ or vehicle control were cultured at 2 × 10⁴ BM LDMNCs/mL to determine the reduction in the respective populations of progenitors. Data represent the mean ± standard error of the mean (SEM) of 3 independent experiments.

Figure 4.

IFN-γ treatment of Fanca^–/– and Fancg^–/– recipients is sufficient to allow engraftment of syngeneic WT bone marrow cells. (A) CD45.1⁺ WT BM nucleated cells (10⁷) were injected into the tail vein of Fanca^–/– and Fancg^–/– C57Bl/6 recipients that express the CD45.2 antigen. Recipients were pretreated with IFN-γ or vehicle control. The percentage of CD45.1⁺ cells in the peripheral blood was determined by fluorescence cytometry 6 months following transplantation. WT and Fancc^–/– mice treated with PBS or IFN-γ were used as controls. Data points represent CD45.1⁺ chimerism of individual mice. Bars represent the mean CD45.1⁺ chimerism. *P < .001 comparing chimerism of Fanca^–/– or Fancg^–/– recipients treated with IFN-γ versus vehicle-treated Fanca^–/– recipients and Fancg^–/– recipients. Multilineage analysis of donor CD45.1 cells in representative (B) Fanca^–/– and (C) Fancg^–/– mice. The percentage of WT CD45.1⁺ lymphoid (CD3 and B220) and myeloid (Gr1 and Mac1) cells is shown in the top right corner of each fluorescence-activated cell sorter (FACS) profile.

Figure 5.

IFN-γ treatment of Fanca^–/– recipients is sufficient to allow long-term engraftment of syngeneic WT bone marrow cells. Six months following transplantation with CD45.1⁺ WT donor BM nucleated cells, selected recipients from a second cohort of (A) Fanca^–/– or (B) Fancg^–/– mice received transplants from secondary recipients to verify that the engrafting CD45.1 donor cells were long-term repopulating stem cells. The CD45.1⁺ chimerism of each primary recipient (left panels) and the chimerism of 3 secondary recipients (right panels) from each respective primary recipient are indicated. Bars represent the mean CD45.1⁺ chimerism. *P < .001 comparing chimerism of Fanca^–/– and Fancg^–/– recipients treated with IFN-γ versus vehicle-treated Fanca^–/– and Fancg^–/– recipients.