Cellular drug resistance in fresh and cryopreserved lymphocytes and lymphoblasts

The aim of the study was to comparison of in vitro drug resistance in normal peripheral blood lymphocytes (NPBL) before and after cryopreservation as well as comparison of drug resistance between NPBL and lymphoblasts from adult acute lymphoblastic leukemia (ALL). Chemosensitivity of lymphocytes of 11 healthy adult volunteers and lymphoblasts of 21 adults with acute lymphoblastic leukemia (ALL) on initial diagnosis was compared. To make this comparison the MTT assay was used. The MTT assay measures the endpoint of the action of anticancer drugs i.e. cell kill, regardless of the mechanisms of cell kill and mechanisms of drug resistance. The following twelve drugs were tested: cytosine arabinoside, actinomycine, L-asparaginase, daunorubicin, doxorubicin, 4-HOO-ifosfamide, mitoxantrone, prednisolone, 6-thioguanine, vincristine and vepesid. The success rate of the assay after cryopreservation of cells, measured by survival of ≥ 70% control cells, was 100% for lymphocytes and 47,6% for lymphoblasts. A high resistance was found in fresh normal lymphocytes to all twelve drugs tested. However, in contrast to leukemic samples, the chemosensitivity of lymphocytes changed after cryopreservation and then the LC50 values were lower, from > 3,2-fold to > 222-fold (P ≤ 0.001), becoming comparable in sensitivity of lymphoblasts for daunorubicin and even more sensitive than lymphoblasts for ifosfamide (P = 0.002), cytosine arabinoside, mitoxantrone and vepesid.