I have tried to preserve the cells (following Ficol density gradient separation of MNCs) in 5% DMSO/ 95% FBS, with Mr.Frosty (isopropanol controlled temp reduction) in -80oc. Then thawing at RT until liquid starts to form, and transfer of thawed cells to large volume of warm medium (10%FBS). Best case scenario was 50% viability but after centrifugation at 200g for 10min the cells clumped to form a white cloud. 

We are considering use of DNase to prevent DNA "stickiness".

Would appreciate tips from your expirience.

Thanks