Hello Shashika Abeysekara,

There is no defined maximum number of passages for immortalized cell lines, but it is recommended to keep passages low.

Over time, immortalized cell lines may experience genetic instability and selection pressures, which can cause phenotypic and population changes. 

I suggest that if you are to use immortalized human endometrial stromal cells for any cell-based assay, you should not use them beyond passage 30.

Best.

Completely agree with what Malcolm said - therefore you should freeze a large number of cell vials for later revival as early as you can after receiving them from ATCC and ideally store 1/2 of them in a separate liquid nitrogen container in case one runs dry if at all possible (it's happened!).