Bioprocessing Research For Cellular Products

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This project aims to develop novel preservation platform technologies required for the successful banking of human cells, an absolute prerequisite for their use as products. Many regenerative medicine products rely on the delivery of live cells to patients. At present this is exemplified by established therapeutic interventions such as bone marrow transplantation, blood transfusion and corneal grafting; future generations of products may include bio-artificial matrices that incorporate donor stem cells, for example bone replacement and repair devices, and artificial 'mini-organs' such as pancreas or liver. Current cryopreservation of stem cell based products results from historic work, using DMSO as a cryopreserving agent which is largely unsubstantiated with respect to final biological activity. DMSO can be toxic to cells, lead to low viabilities post thaw and both genetic and epigenetic instability (i.e loss of pluripotency) over long term culture. Cryopreservation of blood cells has been attempted previously, with limited success due to loss of cell integrity, primarily due to the breakdown of the cell membrane and consequent loss of overall cell structure. A variety of techniques have been investigated for delivering trehalose, a membrane impermeable cryoprotectant, into mammalian cells, including microinjection, ion channel stimulation, pore formation using mutant bacterial toxins, fluid phase endocytosis, and internal trehalose synthesis via genetic engineering but intracellular trehalose concentrations achieved in erythrocytes has not exceeded 50 mM and is therefore below thresholds for cryoprotection. Biopolymer mediated cell loading achieves substantially increased intracellular trehalose concentrations of up to 251 mM and a concomitant improvement of erythrocyte cryosurvival of up to 20.4 % as compared with conventional methods of loading trehalose into cells. The technology utilizes novel amphiphilic biopolymers that interact with the external cell membrane to enable penetration and retention of cryoprotectant agents into the cells. Membrane permeabilisation by these Cell Permeating Polymers (CPPs) is rapid and completely reversible via washing with buffer. Cellular uptake of trehalose is dependent on polymer molecular structure, concentration, pH, external trehalose concentration, incubation temperature and time. Optimization of these parameters imparts cellular osmoprotection. Overall, a total cell recovery through a single freeze-thaw cycle at -80oC of 82.6 % has been achieved, which compares with a recovery of only 0.8 % for cells frozen in PBS. This proposal aims to explore the CPP mediated loading of preservation agents into stem cells, to examine preservation by freezing and dessication and to arrive at integrated processing routes for the preparation of optimally stable stem cells.