Off topic:Why this change in morphology in endothelial colony forming cells (ECFC)?

Question

[charlesgwellem]

Dear colleagues, I culture on 2% PAN-biotech gelatine, cord blood MNCs into endothelial colony forming cells (ECFCs), using Endopan 3 kit medium. 

For many of my samples, I obtain a change in morphology of my ECFCs during culture, and these "new looking"  ECFCs no longer proliferate. The cells now look enlarged , elongated and lose their cobble-stone morphology (see page 47 of the in below) and can not be used for my further purposes. I am worried about this phenomenon and I want to solve and or avoid it.

I thank you in advance for any suggestions as to why this happens and how I can help the situation.

link : https://pure.tue.nl/ws/files/3791909/762770.pdf