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Figure 2. Cartilage matrix formation in constructs containing h MSCs and/or b ACs, 3 weeks after in-vitro culture. (A) The DNA content of none of the constructs had changed compared to their initial DNA content prior to cell- culture (dotted line). Biochemical evaluation of the sGAG (B) and collagen (C) content, 3 weeks after culture in alginate. The left graphs demonstrate the amount of matrix components per construct, whereas for the right graphs matrix production is normalized to the initially seeded primary ACs. A control condition - containing similar amounts of b ACs (0.8*10 6 nc/ml) without supplementation of h MSCs - was evaluated to determine the additional effect of h MSCs (3.2*10 6 nc/ml) on b ACs in co-cultures (dotted line). *, ** or *** indicates p -values smaller than 0.05, 0.01 or 0.001 respectively compared to the control condition. Data are shown as mean ± SD. For statistical evaluation, a mixed model was used followed by a Bonferroni's post-hoc comparisons test. h AMSC = human Adipose-tissue-derived Mesenchymal Stem Cell ( n=3 experiments with 3 independent donors) ; h BMSC = human Bone-marrow-derived Mesenchymal Stem Cell ( n=3 experiments with 3 independent donors) ; b AC = bovine Articular Chondrocyte ( n=3 experiments with 3 pools of donors). Per experiment, 3 samples were used for analyses. In vivo outcomes Cell-free alginate constructs (controls ; n=4 ) and alginate constructs containing h BMSC/ b ACs, h AMSC/ b ACs or h BMSC, h AMSC or b AC only, were generated and immediately implanted subcutaneously in athymic mice. After 8 weeks, all but 5 ( n=3 h AMSC, n=2 h BMSC) of the 40 constructs could be identified and harvested. Unfortunately however, the remaining h MSC- constructs (either h AMSCs or h BMSCs) and cell-free alginate constructs were lost during the embedding process. Constructs containing b ACs or h BMSC/ b ACs resembled cartilage tissue in both color and texture, while the appearance of constructs containing h AMSC/ b ACs was 95 AMSCs OR BMSCs FULFILL A TROPHIC ROLE IN CO-CULTURE 5