Considerations for drug delivery utilizing encapsulated cells: Factors for optimal cell behavior

Background Drug delivery is an important aspect for clinical therapies, but drug delivery to the brain tissue may be restricted by the blood‐brain barrier (BBB), which limits the passage of many molecules when administered peripherally. To achieve direct brain delivery of biological drugs, various techniques have been developed, including encapsulation of live cells within membranes to limit immune mediated host‐rejection (1,2), forming the basis for cell replacement therapies (3,4). Interestingly, the dynamics of cells within the encapsulated membrane (limited space) have been less understood and determinants (prolonged cell proliferation, contact inhibition, cell death, re‐population, debris clearance) which can affect cellular health and its long‐term biological function need more attention. Studying cells (NGC0211) previously used in encapsulated cell‐biodelivery (ECB) devices to treat Alzheimer’s disease (AD) patients (5), the population dynamics of cells when cultured in limited space were investigated. Method Human retinal epithelial cells obtained from the ARPE‐19 cell line and genetically modified to release NGF (termed NGC0211) were cultured in 35mm dishes in different conditions (serum containing or serum free) and monitored overtime using light microscope. Cells were cultured for prolonged periods (3‐4 weeks) continuously without splitting to induce space constraints and monitored under the microscope. Simultaneously, medium was changed at different intervals (weekly or every 2 days) to observe effects of nutrient deprivation. To check debris clearance, dying cells were labelled with CFSE and plated on healthy cells stained with CellMask™ Deep Red plasma membrane stain or dye. To check the impact of inflammation, NGC0211 cells were exposed to inflammatory cytokines for various time points. Result Cellular dynamics and morphology of NGC0211 cells changed overtime with repeated cycles of cell death and simultaneous re‐population, indicating the prime role of phasic cell proliferation to maintain a constant population. Inflammatory cytokines affected NGC0211 cell proliferation, indicating the negative impact of inflammation on cellular re‐population. Conclusion Long‐term stability and clinical therapy using encapsulated cells can be affected by the internal dynamics of the cells itself. Inflammation may reduce clinical efficacy by affecting cellular re‐population, thereby reducing the number of viable cells within the encapsulated device overtime.