## 3 Results
### Surface Markers of Isolated MSCs  
To define the expression of the surface markers CD44, CD73, CD90, and CD105, flow cytometry was performed on cells derived from six different tissues of a single, representatively chosen donor (Figure 2). The co-expression of CD73, CD90, and CD105 is viewed as highly characteristic, but not specific, for MSCs.  
CD44, CD90, and CD105 were present on more than 95% of all isolated cells. CD73 was expressed by over 95% of cells derived from BM, while cells derived from other tissues showed a lower expression of CD73, with none of the samples reaching more than 60% positivity for the surface marker.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Gene** & **Primer Sequence (5’-3’)** & **Anneal. Temp. (\({}^{\circ}\)C)** & **Product Size (bp)** & **Cycles** \\ \hline \multicolumn{5}{c}{**Markers of adipogenesis**} \\ \hline \multirow{3}{*}{_LPL_} & Sense: GAGATTCTCTGTATGGCAC & 51.0 & 250 & 30 \\  & Antisense: CTGCAAATGAGACACTTTC & 61.0 & 380 & 35 \\  & Antisense: ATAAGGGTGGAGATGCAGGCTC & & & \\ \hline \multicolumn{5}{c}{**Markers of chondrogenesis**} \\ \hline \multirow{3}{*}{_COL2A1_} & Sense: TTTCCCAGGTCAAGATGCTC & 58.0 & 374 & 35 \\  & Antisense: CTTCAGCACCTCTCTCCACCA & & & \\ \hline \multirow{3}{*}{_AGN_} & Sense: TGAGAGGGCTGGAAACA & 54.0 & 392 & 30 \\  & Antisense: GGAGGTGTAATTGCAGGGAACA & 58.0 & 263 & 35 \\ \hline \multicolumn{5}{c}{**Markers of osteogenesis**} \\ \hline \multirow{3}{*}{_COL1A2_} & Sense: GGACACAATGGATTGCAAAGG & 54.0 & 461 & 32 \\  & Antisense: TAACACCTGTCTCACTCTG & & & \\ \hline \multirow{3}{*}{_OC_} & Sense: ATGAGAGCCCTCACACCTCTC & 59.0 & 387 & 35 \\  & Antisense: GCCGTAGAACGCCCGATAGGC & & & \\ \hline \multirow{3}{*}{_ALP_} & Sense: TGAGACTTCAGAAAGCTCAACCCA & 51.0 & 454 & 35 \\  & Antisense: TCTCGTGTGTGTGTACCAGTCC & & & \\ \hline \multicolumn{5}{c}{**Internal control**} \\ \hline \multirow{3}{*}{_EEF1A1_} & Sense: AGGTATTACCTGAACCATCC & 54.0 & 234 & 25 \\  & Antisense: AAAGGTGGATAGCTCTGGAAAGC & & & \\ \hline \end{tabular}
\end{table}
Table 3: Primer details for semiquantitative RT-PCR.  
Figure 1: Cumulative population doublings of cells derived from all native tissues, between isolation and after primary passage, pictured as median \(\pm\) standard deviation (error bars). Cells derived from bone marrow (BM), hyaline cartilage, the meniscus, the anterior cruciate ligament (ACL), the synovial membrane (SM), and the infrapatellar fat pad (IPF) were counted, following primary isolation from all six native tissues. After primary passage and before initiating the following experiments, cells were harvested and counted again. Cumulative population doubling (CPD) was calculated using the formula CPD = log10/(N/N0) \(\times\) 3.33. N was the number of cells at the end of passage one, and N0 was the number of cells derived from primary isolation of native tissues. The median of CPD is pictured, respectively. Error bars picture the standard deviation.  
Figure 2: Flow cytometry analysis of the expression of surface antigens on cells isolated from all six tissues of one single patient. Cells from bone marrow (**a**), hyaline cartilage (**b**), the meniscus (**c**), the  
-interior cruciate ligament (ACL) (**d**), the synovial membrane (SM) (**e**), and the infrapatellar fat pad (IPF) (**f**) were examined for the co-expression of surface antigens cluster of differentiation (CD)44, CD73 (CD44/CD73), CD90, and CD105 (CD90/CD105). The results were pictured using the Flowlo 10.5.3 software by Flowlo, LLC. While almost all cells (\(\geq\)95%) were positive for the surface markers CD44, CD90, and CD105, the percentage of CD73+ cells ranged from about 13-99%, depending on the donor tissue.