Non-genotoxic conditioning facilitates hematopoietic stem cell gene therapy for hemophilia A using bioengineered factor VIII.

Hematopoietic stem and progenitor cell (HSPC) lentiviral gene therapy is a promising strategy toward a lifelong cure for hemophilia A (HA). The primary risks associated with this approach center on the requirement for pre-transplantation conditioning necessary to make space for, and provide immune suppression against, stem cells and blood coagulation factor VIII, respectively. Traditional conditioning agents utilize genotoxic mechanisms of action, such as DNA alkylation, that increase risk of sterility, infection, and developing secondary malignancies. In the current study, we describe a non-genotoxic conditioning protocol using an immunotoxin targeting CD117 (c-kit) to achieve endogenous hematopoietic stem cell depletion and a cocktail of monoclonal antibodies to provide transient immune suppression against the transgene product in a murine HA gene therapy model. This strategy provides high-level engraftment of hematopoietic stem cells genetically modified ex vivo using recombinant lentiviral vector (LV) encoding a bioengineered high-expression factor VIII variant, termed ET3. Factor VIII procoagulant activity levels were durably elevated into the normal range and phenotypic correction achieved. Furthermore, no immunological rejection or development of anti-ET3 immunity was observed. These preclinical data support clinical translation of non-genotoxic antibody-based conditioning in HSPC LV gene therapy for HA.

Feasibility, potency, and safety of growing human mesenchymal stem cells in space for clinical application.

Growing stem cells on Earth is very challenging and limited to a few population doublings. The standard two-dimensional (2D) culture environment is an unnatural condition for cell growth. Therefore, culturing stem cells aboard the International Space Station (ISS) under a microgravity environment may provide a more natural three-dimensional environment for stem cell expansion and organ development. In this study, human-derived mesenchymal stem cells (MSCs) grown in space were evaluated to determine their potential use for future clinical applications on Earth and during long-term spaceflight. MSCs were flown in Plate Habitats for transportation to the ISS. The MSCs were imaged every 24-48 h and harvested at 7 and 14 days. Conditioned media samples were frozen at -80 °C and cells were either cryopreserved in 5% dimethyl sulfoxide, RNAprotect, or paraformaldehyde. After return to Earth, MSCs were characterized to establish their identity and cell cycle status. In addition, cell proliferation, differentiation, cytokines, and growth factors' secretion were assessed. To evaluate the risk of malignant transformation, the space-grown MSCs were subjected to chromosomal, DNA damage, and tumorigenicity assays. We found that microgravity had significant impact on the MSC capacity to secrete cytokines and growth factors. They appeared to be more potent in terms of immunosuppressive capacity compared to their identical ground control. Chromosomal, DNA damage, and tumorigenicity assays showed no evidence of malignant transformation. Therefore, it is feasible and potentially safe to grow MSCs aboard the ISS for potential future clinical applications.

Characterization and cost-benefit analysis of automated bioreactor-expanded mesenchymal stem cells for clinical applications.

BACKGROUND: Expanding quantities of mesenchymal stem cells (MSCs) sufficient to treat large numbers of patients in cellular therapy and regenerative medicine clinical trials is an ongoing challenge for cell manufacturing facilities. STUDY DESIGN AND METHODS: We evaluated options for scaling up large quantities of bone marrow-derived MSCs (BM-MSCs) using methods that can be performed in compliance with Good Manufacturing Practices (GMP). We expanded BM-MSCs from fresh marrow aspirate in αMEM supplemented with 5% human platelet lysate using both an automated cell expansion system (Quantum, Terumo BCT) and a manual flask-based method using multilayer flasks. We compared MSCs expanded using both methods and assessed their differentiation to adipogenic and osteogenic tissue, capacity to suppress T-cell proliferation, cytokines, and growth factor secretion profile and cost-effectiveness of manufacturing enough BM-MSCs to administer a single dose of 100 × 106 cells per subject in a clinical trial of 100 subjects. RESULTS: We have established that large quantities of clinical-grade BM-MSCs manufactured with an automated hollow-fiber bioreactor were phenotypically (CD73, CD90, CD105) and functionally (adipogenic and osteogenic differentiation and cytokine and growth factor secretion) similar to manually expanded BM-MSCs. In addition, MSC manufacturing costs significantly less and required less time and effort when using the Quantum automated cell expansion system over the manual multilayer flasks method. CONCLUSION: MSCs manufactured by an automated bioreactor are physically and functionally equivalent to the MSCs manufactured by the manual flask method and have met the standards required for clinical application.

Modifiers of mesenchymal stem cell quantity and quality.

BACKGROUND: Clinical trials involving mesenchymal stem cell (MSC) therapy have variable outcomes. We hypothesize this is largely attributed to donor-to-donor variability and tissue of origin. STUDY DESIGN AND METHODS: We examined proliferation rates, cytokine secretion profiles, and differentiation capability of seven bone marrow-derived MSCs (BM-MSCs) and 16 adipose tissue-derived MSCs (AD-MSCs) from 23 donors. RESULTS: AD-MSCs had the capacity to undergo more than 40 population doublings, while the BM-MSC proliferation rate was found to be considerably slower. We observed more donor-to-donor variability in proliferation rates of BM-MSCs than with AD-MSCs. Cytokine analysis revealed that secretion of eight cytokines was significantly increased by AD-MSCs at Passage (P)3 compared with P1, while for BM-MSCs at P3 relative to P1, only interleukin-8 and RANTES secretion was significantly increased. By P5, secretion of all cytokines by AD-MSCs was either decreased or unchanged relative to P1. In contrast, cytokine secretion by BM-MSCs at P5 was mostly unchanged, although secretion of six cytokines was significantly increased relative to P1. When we compared cytokine secretion between AD-MSCs and BM-MSCs at P3, AD-MSCs significantly secreted higher concentrations of cytokines than BM-MSCs while the opposite was observed at P5. This suggests that BM-MSCs are relatively more potent at P5 while AD-MSCs are relatively more potent at P3. AD-MSCs and BM-MSCs exhibited the capacity for chondrogenic differentiation. AD-MSCs and BM-MSCs appeared to display a more enhanced inclination toward adipogenic and osteogenic differentiation, respectively. CONCLUSION: MSC physiology is significantly influenced by donor variability and tissue of origin and this should be considered when designing clinical trials.