Cryopreservation of human mesenchymal stromal cells expressing TRAIL for human anti-cancer therapy

Background aims. Mesenchymal stromal cells (MSCs) are being extensively researched for cell therapy and tissue engineering. We have engineered MSCs to express the pro-apoptotic protein tumor necrosis factor-related apoptosis inducing ligand (TRAIL) and are currently preparing this genetically modified cell therapy for a phase 1/2a clinical trial in patients with metastatic lung cancer. To do this, we need to prepare a cryopreserved allogeneic MSCTRAIL cell bank for further expansion before patient delivery. The effects of cryopreservation on a genetically modified cell therapy product have not been clearly determined. Methods. We tested different concentrations of dimethyl sulfoxide (DMSO) added to the human serum albumin ZENALB 4.5 and measured post-thaw cell viability, proliferation ability and differentiation characteristics. In addition, we examined the homing ability, TRAIL expression and cancer cell-killing capacities of cryopreserved genetically modified MSCs compared with fresh, continually cultured cells. Results. We demonstrated that the post-thaw viability of MSCs in 5% DMSO (v/v) with 95% ZENALB 4.5 (v/v) is 85.7 +/- 0.4%, which is comparable to that in conventional freezing media. We show that cryopreservation does not affect the long-term expression ofTRAIL and that cryopreservedTRAILexpressing MSCs exhibit similar levels of homing and, importantly, retain their potency in triggering cancer cell death. Conclusions. This study shows that cryopreservation is unlikely to affect the therapeutic properties of MSCTRAIL and supports the generation of a cryopreserved master cell bank.