A simple method for freezing lymphocytes in microtest plates.

Freezing lymphocytes in microtest plates instead of vials for the purpose of screening sera for HLA or other cytotoxic antibodies offers the same technical advantages as freezing sera in microtest plates for tissue typing. Plate-loading errors and cell wastage are minimized, and time required for serum screening is greatly reduced. A method for freezing lymphocytes in large numbers of microtest plates for use in serum screening that is simple, reproducible, and inexpensive is described. Cryoprotected lymphocytes dispensed into microtest plates are placed on a metal table that is lowered onto a tray containing 1 cm of liquid nitrogen in a Styrofoam box. The amount of liquid nitrogen in the tray and the height of the metal table above the tray determine the freezing rate of the lymphocytes. Over 100 microtest plates can be frozen per cycle with total cooling uniformity. The materials required for this freezing device can be assembled for less than $400. Commercial freezing units typically cost over $4,000.