Sustained Expression of High Levels of Human Factor IX from Human Cells Implanted within an Immunoisolation Device into Athymic Rodents

Abstract

Immunoisolation of allogeneic cells within a membrane-bound device is a unique approach for gene therapy. We employed an immunoisolation device that protects allograft, but not xenograft, cells from destruction, to implant a human fibroblast line (MSU 1.2) in athymic rodents. Cells, transduced with the MFG-human factor IX retroviral vector, and expressing 0.9 μg/10⁶ cells/day in vitro, were implanted in rats (four 40-μl devices, each containing 2 × 10⁷ cells, two subcutaneously, two in epididymal fat) and in mice (two 20-μl devices, each containing 2 × 10⁶ cells, subcutaneously). Plasma factor IX levels increased for 50 days, reaching maxima of 203 ng/ml (rat) and 597 ng/ml (mouse), and both continued at greater than 100 ng/ml for more than 140 days. A clone derived from the transduced cells, making 5 μg of factor IX/10⁶ cells/day, was implanted within a device (one 20-μl device containing 2.5 × 10⁶ cells), or without a device (1 × 10⁷ cells implanted freely), either subcutaneously or in epididymal fat. The freely implanted cells expressed transiently, reaching more than 100 ng/ml in each site by day 4, but dropped to zero by day 20 (subcutaneous) or day 90 (epididymal fat). In devices, levels gradually increased to 100 ng/ml (subcutaneous) or 300 ng/ml (epididymal fat), remaining high for more than 100 days. These results show long-term, high-level expression of a human protein: (1) when cells are implanted within a cell transplantation device, but not when the cells are freely implanted, and (2) from a transgene driven by a viral promoter. An alloprotective device will enable the use of cloned cell lines that can be subjected to stringent quality control assessment that is impossible to achieve with autologous approaches.

Overview summary

The success of any gene therapy approach depends on the survival of the genetically engineered cells that are implanted in the patient to deliver the therapeutic product. This study evaluates the use of a membrane device to encapsulate cells that are genetically engineered to produce human factor IX. Sustained delivery of high levels of human factor IX from these cells was observed when the cells were encapsulated within the TheraCyte^® immunoisolation device, whereas only transient expression was obtained when cells were implanted freely, without encapsulation. The results show the effectiveness of an immunoprotective device for cell transplantation from which therapeutic products may be delivered.