Genetically engineered macrophages expressing IFN-γ restore alveolar immune function in scid mice

Reversal of immunodeficiency in the lung by gene therapy is limited in part by the difficulty of transfecting lung cells in vivo. Many options exist for successfully transfecting cells in vitro, but they are not easily adapted to the in vivo condition. To overcome this limitation, we transduced macrophages in vitro with the murine IFN-γ (mIFN-γ) gene and intratracheally delivered the macrophages to express mIFN-γ in vivo. A recombinant retroviral vector pSF91 system was modified to encode mIFN-γ and enhanced green fluorescent protein (EGFP). A murine macrophage cell line J774A.1 transduced with the retroviral supernatant increased secretion from undetectable levels to 131.6 ± 4.2 μg/ml mIFN-γ at 24 h in vitro. The mIFN-γ-producing macrophages were intratracheally instilled into mechanically ventilated scid mice. mIFN-γ levels in the bronchoalveolar lavage increased from undetectable levels at baseline to 158.8 ± 5.1 pg/ml at 48 h (P < 0.001). Analysis of the lavaged cells for EGFP expression revealed that EGFP expression was directly proportional to the number of transduced macrophages instilled into the lung. Immune function was partially restored in the alveolar spaces of scid mice with evidence of enhanced MHC class II antigen expression and increased phagocytosis (P < 0.05). Tumor necrosis factor α was increased from undetectable at baseline to 103.5 ± 11.4 pg/ml. In contrast, i.p. administration of the engineered macrophages did not enhance IFN-γ levels in the lung. Our study suggests airway delivery of genetically engineered macrophages expressing mIFN-γ gene can partially restore significant immune activity in the lungs of immunodeficient mice.