A comparative study of cartilage engineered constructs in immunocompromised, humanized and immunocompetent mice

Choosing the best ectopic in vivo model for cartilage engineering studies remains challenging and there is no clear consensus on how different models compare to one another. The use of xenogenic cells can often limit the choice to immunocompromised animals only and thus prevents the understanding of how tissue-engineered grafts perform with potential active inflammatory and immunological responses. The aim of this study was to evaluate the chondrogenic potential of a recently developed hydrogel, hyaluronan transglutaminase (HA-TG), in four mouse strains with varying immune systems: NSG, nude, NSG-SGM3 humanized and C57BL/6. The hyaluronan-based hydrogel was implanted subcutaneously for 4 weeks after an in vitro pre-culture time of 4 weeks. Scaffolds were prepared without cell seeding as the control and in combination with either human auricular chondrocytes (hAUR) or human fetal chondroprogenitor cells (hCC). We have seen that constructs were able to maintain their volumes and resisted vascularization as well as macrophage infiltration in vivo. Both hAUR and hCC maintained and produced ECM in vivo, but hAUR showed higher levels of innate collagen 2 even without mechanical stimulation. Collagen 1 and 2 deposition as well as mechanical properties of the scaffolds were comparable in all mouse strains. The C57BL/6 mouse model consistently displayed higher levels of C-reactive protein (CRP), serum amyloid A (SAA), and serum amyloid protein (SAP) in serum as a reaction to the foreign material and human cells. In addition, the number of CD68 + and CD163+ macrophages as well as CD3+ lymphocytes around the constructs in C57BL/6 mice was significantly higher than in humanized and immunocompromised mouse models. The results show that it is possible to engineer a cartilage-like graft subcutaneously not only in immunocompromised, but also in immunocompetent and humanized mouse models.