## 4 Discussion
Interestingly, we observed a strong staining intensity and more chondrogenic-like phenotype, including chondrones and a cell-poor extracellular matrix (ECM), in the alcian blue staining of pellets, derived from arthritic MSC-like cells, which were derived from hyaline cartilage and BM-MSCs. At the same time, hypertrophic differentiation was least evident in cell pellets containing MSC-like cells from arthritic hyal cartilage and the SM. When examining the multipotent differentiation capacity of different MSC-subpopulations, BM-MSCs are often viewed as the gold standard, which is used for comparison. Matching our current findings, earlier studies showed that the qualitative multipotent differentiation potential of MSC-like cells isolated from arthritic hyal cartilage and the IPF does not differ from that of BM-MSCs, and these subpopulations offer promising potential for clinical transition [33; 34; 39]. [PERSON] et al. and others showed that the treatment of patients with late-stage OA of the knee with adipose-derived MSCs led to improved clinical and functional outcome [46]. While the MSC-like cells isolated in our study showed limited proliferative capacity, they showed great chondrogenic differentiation potential, when analyzing the histological and immunohistochemical stainings, as well as the expression of chondrogenic marker genes. In contrast, MSC-like cells isolated from the SM have been shown to possess a greater chondrogenic differentiation capacity than BM-MSCs [18; 35]. Since chondrogenic differentiation potential was evaluated by measuring pellet dry weight and size, we could not directly compare the results observed in our current study, since these variables were not evaluated in our current study [18]. Few studies have also reported on the multipotent differentiation capacity of cells derived from different intraarticular ligaments [19; 22; 43]. When examining histological and immunohistochemical stainings, we found a slightly superior chondrogenic differentiation potential in MSC-like cells isolated from the ACL, when compared to BM-MSCs [22]. Surprisingly, [PERSON] et al. described a similar chondrogenic but an inferior osteogenic differentiation capacity when comparing ACL-derived MSC-like cells to BM-MSCs [41]. Finally, [PERSON] et al. reported that MSC-like cells, isolated from meniscal tissue, present extensive multipotent differentiation capacity [21]. According to our findings, [PERSON] et al. previously showed that their qualitative adipogenic, osteogenic, and chondrogenic potential did not differ significantly from MSCs isolated from the SM, intraarticular ligaments, or BM of the same knee joints [44]. In summary, MSC-like cells were isolated from the BM, SM, IPF, ACL, and meniscal tissue of arthritic knee joints. Interestingly, all subpopulations of MSC-like cells, isolated from the same donor, did not differ, regarding their qualitative in vitro multipotent differentiation potential. Although cells isolated from hyaline cartilage showed the clear expression of MSC-like surface antigens, plastic-adherent growth, and great multipotent differentiation capacity, [PERSON] et al. found that most of the isolated cells from hyaline cartilage are not progenitors after prolonged expansion in vitro but, rather, a mixed population of chondrocytes and multipotent progenitor cells [34]. All of the examined tissues are routinely removed during primary TKA. Interestingly, the SM, IPF, ACL, and meniscal tissue are also easily accessible via minimal-invasive surgery. The number of MSC-like cells that can be harvested during surgery often differs between native tissues and is larger for soft tissues, such as adipose and synovial tissue [37; 47]. In contrast, BM, cartilage, and ligamentous tissues often only offer a limited number of cells, resulting in major challenges for clinical transition during both tissue harvesting and TE, since clinical cell-based therapy often requires large amounts of MSC-like cells for tissue repair [29; 37; 48].