54 Effect of Different Cryopreservation Protocols for Sheep Embryonic Stem Cells

Abstract

Particular attention is required to improve cryopreservation of embryonic stem cells (ESC) and study their characteristics. Stem cells were obtained from the inner cell mass of Day 5-6 blastocysts. The ESC were then cultured on mTeSR™1 medium (Stemcell Technologies, Cambridge, MA, USA). We studied the survival of ESC after slow freezing and vitrification. Slow freezing was carried out using a Planer Kryo 360-3.3 freezer (Planer plc, Sunbury-on-Thames, United Kingdom), using various cryoprotectants: 1.5 M dimethyl sulfoxide (Me₂SO), 1.5 M ethylene glycol (EG), or 1.5 M propylene glycol (PG). Six vitrification solutions (VS) were used to vitrify ESC: VS1 = 20% Me₂SO + 20% EG + 0.5 M sucrose; VS2 = 20% Me₂SO + 20% PROH + 0.5 M sucrose; VS3 = 20% EG + 20% PG + 0.5 M sucrose; VS4 = 20% Me₂SO + 20% EG + 0.5 M sucrose + 10% FCS; VS5 = 20% Me₂SO + 20% PROH + 0.5 M sucrose + 10% FCS; and VS6 = 20% EG + 20% PG + 0.5 M sucrose + 10% FCS. For the dehydration of cells and the addition of vitrification solutions, a 3-step equilibration was used. The proliferative properties of the cells were determined using an Apel PD-303S spectrophotometer (Apel Co. Ltd., Kawaguchi, Japan), using an MTT test (staining with methylthiazolyl-diphenyl tetrazolium). After slow freezing, the highest percentage of frozen–thawed cells proliferating was observed when using 1.5 M EG (P > 0.05). At the same time, the highest cell doubling after thawing was observed when using 1.5 M EG, and 1.5 M Me₂SO. After vitrification, the highest percentage of proliferation was observed in the VS2 and VS4 groups (49.7 ± 3.2% and 53.2 ± 3.8%, respectively). It should be noted that the addition of fetal calf serum to the vitrification solution also increased the proliferation of ESC after vitrification and thawing.