Selection of Leukaemic Cell Populations by Freezing and Thawing

Abstract

THE co-existence of normal and abnormal cell populations in the peripheral blood of leukaemic patients may explain the variations in the reactivity to mitogens (discussed by Ling¹). One example is the low or delayed response of cells from chronic lymphocytic leukaemic (CLL) patients to phytohaemagglutinin (PHA) in comparison with normal cells. The variations presumably result from a combination of the response of the underlying normal population to mitogens and the different responses (inhibition, no effect or stimulation) of the abnormal cells. Analysis of abnormal cell populations and their interactions, together with the study of serum factors, is hindered by the heterogeneity of leukaemic cell suspensions. We have now investigated the differential survival of leukaemic and normal cells from leukaemic blood following freezing and thawing using controlled cooling conditions. Previously we established the cooling rate at which normal human peripheral lymphocytes are recovered optimally using dimethylsulphoxide (DMSO) as a protective additive^2,3. Lymphocytes activated by mitogen or specific antigen before freezing required different cooling rates for optimal recovery. We show here that cooling rates both faster and slower than those required for the recovery of normal lymphocytes permit the differential survival of abnormal cells from leukaemic blood and that this technique may clarify the study of serum factors.