Cartilage immunoprivilege depends on donor source and lesion location.

Area of Science:

• Musculoskeletal tissue engineering
• Immunology
• Regenerative medicine

Background:

• Cartilage repair is a major goal in tissue engineering.
• Autologous chondrocytes are scarce, making allogeneic or xenogeneic sources attractive.
• The concept of "cartilage immunoprivilege" has limited consideration of immune rejection for non-autologous cartilage.

Purpose of the Study:

• To evaluate the suitability of allogeneic and xenogeneic engineered neocartilage for cartilage repair.
• To investigate the immune response to engineered cartilage grafts in different knee joint locations.

Main Methods:

• Scaffold-free engineered articular cartilage (syngeneic, allogeneic, xenogeneic) was implanted into rabbit knee joints (n=3 per group/location).
• Immune cell infiltration and graft integration were assessed at two different locations: patella and trochlea.

Main Results:

• Xenogeneic grafts provoked strong innate and adaptive immune responses, irrespective of location.
• Allogeneic grafts elicited an immune response in the patella but negligible response in the trochlea.
• Allogeneic neocartilage survived and integrated into bone in the trochlea, comparable to microfracture controls.

Conclusions:

• Articular cartilage is not immune privileged and exhibits location-dependent immune responses.
• Immune tolerance and survival of allogeneic engineered cartilage depend on anatomical location and proximity to the synovium.