MEC1 and MEC2: two new cell lines derived from B-chronic lymphocytic leukaemia in prolymphocytoid transformation

We report the establishment and characterization of two cell lines, MEC1 an d MEC2, that grew spontaneously on two subsequent occasions from the periph eral blood (PB) of a patient with B-chronic lymphocytic leukemia (B-CLL) in prolymphocytoid transformation. The patient was EBV-seropositive, his leuk emic cells were EBNA negative, but the spontaneously grown cell lines are E BNA-2 positive. In liquid culture MEC1 cells grow adherent to the vessel wa ll and as tiny clumps; MEC2 cells do not adhere and form large clumps. The doubling time of MEC1 is 40h and of MEC2 is 31h. Both cell lines express th e same light (kappa) and heavy chains (mu, delta) as the fresh parental B-C LL cells at the same high intensity, share the expression of mature B cell markers (CD19, CD20, CD21, CD22), differ in the expression of CD23 and FMC7 , are CD11a+, CD18+, CD44+, CD49d+, CD54+ and express at high levels both C D80 and CD86. CD5 is negative on MEC1 cells (as on the vast majority of par ental cells) and it has been lost by MEC2 cells after several months of cul ture. The cells have a complex karyotype. The tumour origin of MEC1 and MEC 2 has been demonstrated by Southern blot analysis of the IgH loci and by Ig gene DNA sequencing. They use the VH4 Ig family and have not undergone som atic mutations (94.8% homology with germline Ig gene 4-59). Cytofluorograph ic analysis and RT-PCR reveal that MEC1 and MEC2 overexpress Bcl-2 together with Bar, express large amounts of Bcl-xL and trace amounts of Bcl-xS. (C) 1999 Elsevier Science Ltd. All rights reserved.