The use of directly frozen cells in LDA assay

A method of direct freezing is described which requires a cryoprotective medium consisting of human AB serum and DMSO, an ultra-low temperature freezer and a liquid-nitrogen refrigerator. Fresh and directly frozen cells were compared in the LDA assay. Direct freezing is quite reliable for normal lymphocytes, PHA transformed lymphocytes or leukaemic blasts used as targets. However, a controlled freezing procedure may be necessary to preserve the effector cell activity.