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Pulmonary alveolar proteinosis (PAP) due to deficiency of the common beta-chain (beta(c)) of the interleukin-3 (IL-3)/IL-5/granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors is a rare monogeneic disease characterized by functional insufficiency of pulmonary macrophages. Hematopoietic stem cell gene therapy for restoring expression of beta(c)-protein in the hematopoietic system may offer a curative approach. Toward this end, we generated a retroviral construct expressing the murine beta(c) (mbeta(c)) gene and conducted investigations in a murine model of beta(c)-deficient PAP. Functional correction of mbeta(c) activity in mbeta(c)(-/-) bone marrow (BM) cells was demonstrated by restoration of in vitro colony formation in response to GM-CSF. In addition, in a murine in vivo model of mbeta(c)-deficient PAP mbeta(c) gene transfer to hematopoietic stem cells not only restored the GM-CSF-sensitivity of hematopoietic progenitor cells but also, within a period of 12 weeks, almost completely reversed the morphologic features of surfactant accumulation. These results were obtained despite modest transduction levels (10-20%) and, in comparison to wild-type mice, clearly reduced beta(c) expression levels were detected in hematopoietic cells. Therefore, our data demonstrating genetic and functional correction of mbeta(c)(-/-) deficiency in vitro as well as in a murine in vivo model of PAP strongly suggest gene therapy as a potential new treatment modality in beta(c)-deficient PAP.

The SFFV LTR seems to allow a high expression of transgenes, as long as the transgene is not expressed downstream of an internal ribosomal entry site. Internal promoters may be useful for targeted gene expression in specific cell types, but the reduced level of expression from some internal promoters has to be taken into consideration.

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