Degenerative diseases of the retina represent a popular target for emerging cell-based therapeutics and initial data from early stage clinical trials suggest that short-term safety objectives can be met in at least some cases. The question of efficacy will require additional time and testing to be adequately resolved.
Rapid progress has been made in the development of novel cell-based approaches for the potential treatment of retinal degenerative diseases. As a result, one must consider carefully the conditions under which these therapeutics are manufactured if they are to be used in clinical studies or, ultimately, be approved as licensed cellular therapeutics.
Here, we describe the principles behind the manufacturing of clinical-grade cellular products, as well as potential methods for large-scale expansion and processing according to Good Manufacturing Practice (GMP) standards sets by the United States Food and Drug Administration. Standards for personnel, materials, procedures and facilities required for such manufacturing processes are reviewed.
We also discuss current and future scale-up methods for the manufacturing of large doses of cellular therapeutics under GMP conditions and compare the use of conventional culture methods such as tissue culture flasks and multi-layered cell factories with novel systems such as closed system hollow-fiber bioreactors. Incorporation of these novel bioreactor systems into GMP facilities may enable us to provide adequate cell numbers for multi-center clinical trials and paves the way for development of cellular therapeutics with the potential to treat very large numbers of patients.
Transplantation of adult mouse iPS cell-derived photoreceptor precursors restores retinal structure and function in degenerative mice
This study was designed to determine whether adult mouse induced pluripotent stem cells (iPSCs), could be used to produce retinal precursors and subsequently photoreceptor cells for retinal transplantation to restore retinal function in degenerative hosts. iPSCs were generated using adult dsRed mouse dermal fibroblasts via retroviral induction of the transcription factors Oct4, Sox2, KLF4 and c-Myc. As with normal mouse ES cells, adult dsRed iPSCs expressed the pluripotency genes SSEA1, Oct4, Sox2, KLF4, c-Myc and Nanog.
Following transplantation into the eye of immune-compromised retinal degenerative mice these cells proceeded to form teratomas containing tissue comprising all three germ layers. At 33 days post-differentiation a large proportion of the cells expressed the retinal progenitor cell marker Pax6 and went on to express the photoreceptor markers, CRX, recoverin, and rhodopsin. When tested using calcium imaging these cells were shown to exhibit characteristics of normal retinal physiology, responding to delivery of neurotransmitters. Following subretinal transplantation into degenerative hosts differentiated iPSCs took up residence in the retinal outer nuclear layer and gave rise to increased electro retinal function as determined by ERG and functional anatomy.
As such, adult fibroblast-derived iPSCs provide a viable source for the production of retinal precursors to be used for transplantation and treatment of retinal degenerative disease.
Engineering retinal progenitor cell and scrollable poly(glycerol-sebacate) composites for expansion and subretinal transplantation
Retinal degenerations cause permanent visual loss and affect millions world-wide. Presently, a novel treatment highlights the potential of using biodegradable polymer scaffolds to induce differentiation and deliver retinal progenitor cells for cell replacement therapy.
In this study, we engineered and analyzed a micro-fabricated polymer, poly(glycerol sebacate) (PGS) scaffold, whose useful properties include biocompatibility, elasticity, porosity, and a microtopology conducive to mouse retinal progenitor cell (mRPC) differentiation. In vitro proliferation assays revealed that PGS held up to 86,610 (+/-9993) mRPCs per square millimeter, which were retained through simulated transplantations. mRPCs adherent to PGS differentiated toward mature phenotypes as evidenced by changes in mRNA, protein levels, and enhanced sensitivity to glutamate.
Transplanted composites demonstrated long-term mRPC survival and migrated cells exhibited mature marker expression in host retina. These results suggest that combining mRPCs with PGS scaffolds for subretinal transplantation is a practical strategy for advancing retinal tissue engineering as a restorative therapy.