ECM Based Hydrogel Delivery Vehicles and 3D In Vitro Injection Model for Human Retinal Progenitor Cells Transplantation

Retinal degenerative diseases caused by photoreceptor cell loss and damage are the leading cause of blindness worldwide1. Treatments, including gene therapy, drug, and neuroprotective approach, mainly focus on slowing down the degeneration process rather than reversing it. Retinal cells implanted into the subretinal space have been shown to integrate within host retina, improving visual function in models of retinal degeneration1. One barrier to clinical success is the loss, through efflux and death, of the majority (&gt;99%) of implanted cells2. A factor likely contributing to cell death is the host microenvironment of the subretinal space after a high cell density (~105 cells/ul) bolus injection (e.g., lacking oxygen/nutrients, missing physical support, and chemical cues). Recent studies have demonstrated that the delivery of retinal progenitor cells (RPCs) using polymer scaffolds results in improved cell survival and differentiation with associated increases in RPC integration3-4. However, current polymer scaffolds still result in minimal overall integration (&lt;2%). We have established an in vitro bolus injection model mimicking clinical subretinal injection to explore the impact of bolus injection on human RPCs viability. Studies using this model have revealed that indeed RPCs are damaged during the injection process, leading to cell death. To better understand what cues may improve survival of RPCs in the post-injection bolus microenvironment, inert hydrogel systems (oxidized low viscosity alginate) were employed in conjunction with retinal ECM cues including glycosaminoglycans (GAGs): hyaluronic acid (HA) and chondroitin sulfate (CS), laminin (important component of basement membrane), and RGDS (adhesive peptides). The effects of the stiffness and chemical modifications of the delivery vehicles on cell survival/death mechanisms in the bolus injection environment were investigated using fractional factorial design, revealing advantages of stiffer substrates and laminin in promoting RPC survival. Ultimately, this information can be used to guide design of cell delivery vehicles for human RPCs transplantation with improved post-injection survival.<br/><br/><b>References:</b><br/>1.Qiu et al., Exp. Eye Res. 2005; 80(4): 515-525.<br/>2.Redenti et al., Ocular Biol Dis Inform. 2008; 1:19-29.<br/>3.Yao et al., Polymers 2011, 3, 899-914.<br/>4.Tucker et al., Biomaterials. 2010; 31(1): 9-19.