NCE (Year 4)

This Development Candidate Feasibility (DCF) Award seeks to address cartilage defects classified by the International Cartilage Repair Society (ICRS) as grades II-IV with the intent of halting the progression of cartilage damage before it creates arthritic changes in joint compartments. The medical significance of this project is that articular cartilage injuries and degeneration eventually lead to osteoarthritis, which costs $65B per year and affects over 25% of adults over the age of 65. The envisioned therapy would begin with a biopsy of the patient’s own skin to harvest dermis isolated, adult stem cells (DIAS cells), which would undergo processing to yield neocartilage. This neocartilage would then be implanted into the patient’s joint to restore or improve mobility.

Milestone 1 was completed, and, after reporting of preliminary data from Milestone 2, a prior approval request was submitted and approved with revised milestones. These, too, have now been completed.

For Milestone 2, three studies in the athymic mice using human DIAS neocartilage generated from foreskin, breast skin, and abdominal skin, from multiple donors were conducted to determine whether variability existed due to anatomical location and different donors. The goal was to determine whether engineered constructs would maintain stability, integrity, and viability in vivo without eliciting adverse effects. Anatomical and donor variability were found, with foreskin-derived human DIAS cells displaying constructs with the lowest level of donor variability; all of the foreskin-derived constructs retained stability, integrity, and viability. Regardless of anatomical location and donors, no DIAS cell-derived constructs elicited adverse host responses.

Milestone 3 consisted of a study to apply aggregate redifferentiation to human DIAS cells to yield cells with a chondrogenic phenotype. The aggregate redifferentiation technique, previously optimized in animal models, has also shown efficacy with human marrow-derived mesenchymal stem cells. Applied to constructs formed using human foreskin-derived DIAS cells, aggregate redifferentiation was shown to be efficacious in improving the biochemical and biomechanical properties of the constructs. Specifically, the constructs contained more cells and extracellular matrix. The compressive properties of constructs that had been formed with aggregate redifferentiated human DIAS cells were also higher than those of controls.

Milestone 4 consisted of determining whether over 75% of the engineered constructs would retain mechanical integrity after orthotopic implantation in a rabbit model. The mechanical properties of the engineered constructs were not sufficiently high to survive cycling within rabbit knees ex vivo after being placed in cartilage defects. Additional work needs to be performed to strengthen the human DIAS cell constructs for implantation; the goal would be to attain the mechanical properties currently achievable with differentiated cartilage cells derived from animal models.