1. ? Allow the cells to encyst.? To detach cysts from the flask or test tube, rub the bottom with a sterile cotton swab.
2. ? If the cyst concentration exceeds the required level do not centrifuge, but adjust the concentration to 2 x106 cysts/ml with fresh medium.? If the concentration is too low, centrifuge at 600 x g for 5 min and resuspend the pellet in the volume of fresh medium required to yield the desired concentration.
3.?? While cells are centrifuging prepare a 15% (v/v) solution of sterile DMSO as follows: Add the required volume of DMSO to a glass screw-capped test tube and place it in an ice bath.? Allow the DMSO to solidify.? Add the required volume of refrigerated medium.? Dissolve the DMSO by inverting the tube several times.?
????? *NOTE: If the DMSO solution is not prepared on ice, an exothermic reaction will occur that may precipitate certain components of the medium.
4.? Mix the cell preparation and the DMSO in equal portions. Thus, the final concentration will be 106 - 107 and 7.5% (v/v) DMSO. The time from the mixing of the cell preparation and DMSO stock solution before the freezing process is begun should no less than 15 min and no longer than 60 min.
5.?? Dispense in 0.5 ml aliquots into 1.0 - 2.0 ml sterile plastic screw-capped cryules (special plastic vials for cryopreservation).
6.? Place vials in a controlled rate freezing unit. From room temperature cool at -1°C/min to -40°C. If freezing unit can compensate for the heat of fusion, maintain rate at?? -1°C/min through heat of fusion. At -40°C plunge ampules into liquid nitrogen.
7.? The frozen preparations are stored in either the vapor or liquid phase of a nitrogen freezer.
8.?? To establish a culture from the frozen state place an ampule in a water bath set at 35°C (2-3 min). Immerse the vial just sufficient to cover the frozen material. Do not agitate the vial.
9.?? Immediately after thawing, aseptically remove the contents of the ampule and inoculate into 5.0 ml of fresh ATCC medium 712 in a T-25 tissue culture flask or plastic 16 x 125 mm screw-capped test tube.? Incubate at 25°C.
