the cell culture method and its application provided by the present invention can be fully understood by the description of the following embodiments , and can be readily made by those skilled in the art , but the execution type of the present invention is not limited to the following embodiments . with the consent of the parents , fresh human umbilical cords were obtained after birth and collected in hbss buffer solution ( gibco ) at 4 ° c . humscs were obtained as previously described by hu et al . ( conversion of human umbilical cord mesenchymal stem cells in wharton &# 39 ; s jelly to dopaminergic neurons in vitro : potential therapeutic application for parkinsonism . stem cells 24 : 115 - 124 ; 2006 ). briefly , the mesenchymal tissue of wharton &# 39 ; s jelly of the umbilical cord was diced into cubes of about 0 . 5 cm 3 and centrifuged at 250 × g for 5 minutes ; and then the mesenchymal tissue was treated with collagenase type i ( sigma ) at 37 ° c . for 18 hours , washed and further digested with 2 . 5 % trypsin ( gibco ) at 37 ° c . for 30 minutes . the digested mixture was then passed through a 100 μm filter to obtain cell suspensions . then the cell suspensions were centrifuged at 250 × g for 5 minutes . the humscs culture medium consisted of dulbecco &# 39 ; s modified eagle &# 39 ; s medium / f12 ( dmem / f12 , 25 mm glucose , invitrogen ), 2 % fetal bovine serum ( invitrogen ), 1 mm glutamine , and 10 mm nicotinamide . seven - day postnatal sprague - dawley rats were used for preparation of pancreatic cells and iccs formation . the study was approved by the animal research committee of the college of medicine , national taiwan university . after rats were sacrificed , pancreases were removed and cut into small pieces , and then incubated in 2 ml medium supplemented with 3 mg collagenase for 20 min at 37 ° c . re - suspended to the collagenase - free medium and centrifuged at 1500 r . p . m . for 3 min . the final pellets were suspended in 12 ml dmem / f12 , 2 % fetal bovine serum , 1 mm glutamine , and 10 mm nicotinamide . for preparation of co - culture system , humscs were cultured in 6 - well plates with 80 % confluence at 37 ° c . place the inserts into each prepared well with the membrane towards the well bottom , ensuring no air is trapped . add 2 ml of single pancreatic cell suspensions to the interior of each insert ( pore size 3 . 0 μm or 0 . 2 μm , nunc ). during pancreatic cells culture , less than 30 % of cells attached to the dish . three days after seeding , non - adherent cells were removed by the medium change . using medium with high glucose and low serum , the pancreatic cells were gradually formed cell clusters . the cluster number was about 7 - 8 clusters / well to 25 - 30 clusters / well from third day to ninth day , and cluster size was 272 ± 44 μm at sixth day and 418 ± 72 μm at ninth day . iccs appeared on sixth day after the culture . however , after 12 days of culture , adherent cell clusters crashed , floated and died , as shown in fig1 a and fig1 b . the co - culture with humscs could promote iccs formation and survival , as shown in fig1 c , fig1 d , and fig1 e . the iccs could grow and survive steadily , although the clusters numbers in iccs / humscs co - culture had not more increase than iccs alone from day 3 to day 90 . meanwhile , humscs alone did not form cell clusters . to test whether iccs co - cultured in embodiment 2 still have functional characteristics of islets , we will inspect whether the activity of insulin secreted by cell is normal . the supernatants of iccs culture and iccs / humscs co - culture medium were harvested every 3 days for insulin detection using a rat insulin - elisa - kit ( enzyme linked immunosorbent assay kit , mercodia , sweden ). after acquiring the medium , washed plate 5 times with pbs and changed medium every 3 days . see fig2 , on day 6 , the insulin levels of iccs culture and iccs / humscs co - culture are 89 . 43 ± 3 . 32 and 89 . 97 ± 2 . 12 μg / l , respectively . however , the insulin levels in iccs culture medium rapidly declined on day 9 ( 4 . 23 ± 0 . 64 μg / l ) and day 12 ( 2 . 87 ± 0 . 09 μg / l ). meanwhile , the insulin levels in iccs / humscs co - culture still gradually increased on day 9 ( 92 . 35 ± 2 . 18 μg / l ), day 12 ( 145 . 40 ± 26 . 85 μg / l ), and even lasted to day 90 ( 160 . 30 ± 31 . 92 μg / l ). in addition , there was no human insulin detected in iccs / humscs culture medium using a specific human insulin - elisa - kit ( data not shown ). to test whether iccs co - cultured in embodiment 2 still have other activities of islets , a human cytokine protein array was used to analyze cytokines levels in the culture medium of humscs and iccs / humscs . a human cytokine protein array kit was purchased from raybiotech ( norcross , ga .) and used according to the manufacturer &# 39 ; s instructions . the protein levels could be judged through fluorescence scanning . as shown in fig3 , compared with non - culture medium , several cytokines levels showed more than a 2 - fold increase in culture medium of iccs / humscs or humscs , including interleukin - 6 ( il - 6 ), tissue inhibitor of metalloproteinases - 1 ( timp - 1 ), tissue inhibitor of metalloproteinases - 2 ( timp - 2 ), monocyte chemoattractant protein - 1 ( mcp - 1 ), growth related oncogene ( gro ), hepatocytes growth factor ( hgf ), insulin - like growth factor binding proteins 4 ( igfbp - 4 ), and interleukin - 8 ( il - 8 ). it shows these cytokines secreted by humscs have very important relationship for maintaining the survival and function of culture islet - like cell clusters . furthermore , if the above - mentioned cytokine medium ( stem cell conditioned medium ) is used to culture cells , it still can maintain the survival and activity of cells . it can be said that the culture by the stem cell medium has the same effect with respect to the co - culture of humscs , referring to embodiment 5 . firstly , a neuronal conditioned medium ( ncm ) was prepared by method described by hu et al . ( conversion of human umbilical cord mesenchymal stem cells in wharton &# 39 ; s jelly to dopaminergic neurons in vitro : potential therapeutic application for parkinsonism . stem cells 24 : 115 - 124 ; 2006 ). 10 % chloride hydrate was injected into the abdominal cavity of seven - day postnatal sprague - dawley rats . after they were anaesthetized , the brain was excised . suspended to the calcium / magnesium ion - free buffer solution ( gibco ), and centrifuged at 900 r . p . m . for 3 min . after the supernatant was removed , dmem medium with 10 % fetal bovine serum was added to the settled substance ( brain tissue ). the suspended brain tissue was ground for 15 min , in order to be dispersed into the single cell . the cells were suspended in dmem medium with 10 % fetal bovine serum ( fbs / dmem ), and cultured in 5 % co 2 , 95 % o 2 at 37 □. on day 2 , 2 μm of cytarabine , ara c ( sigma - aldrich ) was added . on day 5 , the medium was harvested as the neuronal conditioned medium used for further culture of humscs . as shown in fig4 , in order to culture and transform humscs to iccs ex viro , a stage - wise culture is performed . firstly , the undifferentiated humscs were cultured in dmem medium with 10 % fetal bovine serum for 3 - 6 days ( stage 1 ); next , humscs were cultured in neuronal conditioned medium for 7 days , and the medium was changed everyday , in order to induce the formation of nestin - positive cells ( stage 2 ); then , the cells were suspended in dmem / f12 medium with 2 % fetal bovine serum ( 25 mm glucose ), and 10 mm nicotinamide and vitamin b27 ( gibco , cat . no . 17504 - 044 ) were added , and cultured for 7 days ( stage 3 ); finally , the differentiated iccs were placed in stage 3 medium supplemented with scm and cultured for 14 days ( stage 4 ). if the stem cell conditioned medium is used to culture cells , it still can maintain the survival and activity of cells . it can be said that the culture by the stem cell medium has the similar effect with respect to the co - culture of humscs . there were many iccs generated . it was found that there were more glucagon and insulin expression of these iccs through immunostaining method . in addition , in stage 3 medium , if the concentration of glucose was adjusted , it could found that the amount of insulin secreted by cell clusters was changed . for example , the cell clusters secreted lower levels of insulin on low glucose ( 5 . 5 mm ) dmem medium , but secreted higher levels of insulin on high glucose ( 25 mm ) dmem medium as shown in fig5 . this was similar to the physiological activity of normal pancreatic islet cells . it proved that iccs transformed from the method of the invention still could maintain the function and activity of normal pancreatic islet cells . seven days before the transplantation , the streptozotocin ( stz ) was injected into the abdominal cavity of sprague - dawley rats to induce the diabetes . the injection dosage was 5 mg / kg / day , and it was continued for 2 day . before the injection of streptozotocin , every week after the injection , and 3 days after the transplantation of cell clusters , take the blood from tail vein of rat , and use sure - step blood glucose meter ( lifescan ) to determine the concentration of blood glucose . one week after the rat was injected by streptozotocin , the concentration of blood glucose would be more than 400 mg / dl . 10 % chloride hydrate was injected into the abdominal cavity of rats . after they were anaesthetized , the iccs ( about 2 × 10 6 cells ) prepared in embodiment 5 were injected into the liver parenchyma of rat slowly through # 22 syringe needle . as for the control group , the undifferentiated humscs were transplanted to the liver of rat and only the physiological salt water was injected ( false experimental group ). as the results shown in fig6 a , fig6 b and fig6 c after the iccs prepared in embodiment 5 were transplanted to streptozotocin - induced diabetic rats , the concentration of blood glucose would be reduced , and the secretion of human insulin can be detected , which showed the iccs induced and transformed according the method of the invention had the effect for inhibiting the diabetes . summarized by the above - mentioned description , according to the cell culture method of the present invention , the co - culture of humscs or the stem cell medium can be used to culture , promote or maintain the survival and function of target cells , and promote or maintain renewing , repair and proliferative capabilities of target cells . in addition , according to the method of the present invention , humscs can be induced to iccs , which possesses similar function and activity of pancreatic islet cells . it is understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention . accordingly , it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein , but rather that the claims be construed as encompassing all the features of patentable novelty that reside in the present invention , including all features that would be treated as equivalents thereof by those skilled in the art to which this invention pertains .
the invention relates to a cell culture method , particularly to a co - culture method for human mesenchymal stem cells and target animal cells , in order to solve the problem that animal cells are not easy to survive alone upon culturing . the invention also provides a method for using a stem cell conditioned medium to culture animal cells . the invention also provides a method to induce the transformation of human fetal islet - like cell clusters from human stem cells and its application thereof .