Early Contamination of the Dami Cell Line by HEL

To the Editor:

Dr Handin's prompt announcement1 alerting investigators to our finding of the contamination of the Dami megakaryocyte cell line by the HEL erythroleukemia cell line is to be applauded. In our experience of some 40 such instances, originators of cell lines usually prefer to ignore the problem or deny it exists. We have performed further studies that may be of use in enabling users of Dami to determine whether their stocks are likely to have been contaminated by HEL.

Using modern techniques (fluoroescence in situ hybridization [FISH] and image analysis) we karyotyped samples of Dami sourced from the American Type Culture Collection (ATCC; Rockville, MD) and found their close correspondence to the original Dami karyotype2 — transcribed using current nomenclature (ISCN 1995): 64<3n>, XY,−Y, add(1)(p21), t(1; 6)(p13; p21), t(2; 10)(10; ?) (q21; p14;)(q23; ?), add(3)(q26), t(3; 6)(p13; q16), del(4)(q25), t(4; 8)(q12; p11), t(5; 17)(q11; p11), del(6)(q21), −7, add(8)(p11), −9, t(9; ?)(?; 11)(p24; ?)(?; p15), t(9; ?)(?; 22)(p24; ?)(?; p15), −10, t(?; 11; 21)(?q11; q22), −14, add(15)(p11), −16, −18, add(18)(p11), add(19)(p11), add(19)(p13), del(20)(q12), + mar. When we examined late-passage stocks of Dami — known to yield identical DNA fingerprints with HEL — we recorded the following karyotype: 64<3n>XYY, del(1)(p21p31), −2, del(2)(q32), add(3)(q26-28), del(4)(q24), t(5; 17)(q10; q10), del(6)(q21), der(6)t(1; 6)(p13; p21), der(6)t(3; 6)(p13; q16), der(7)add(7)(p14q32), −9, add(8)(p21), der(9)t(9; ?)(?; 11)(p24; ?)(?; q13), −10, −10, del(11)(q13), −14, i(14)(q10), add(15)(p11-12), −17, −18, −18, t(18; 21)(q10; q10) ×2, −19, del(20)(q13), −21, −21, dup(21)(q11q22.3-qter), psu dic(22; 9)t(9; ?)(?; 22)(p24; ?)(?; p11-13), +2 mar.3 Stocks of HEL obtained directly from its originator4 displayed the following karyotype: 60<3n>XYY, −2, del(2)(q32), t(3; 6)(p13; q16), t(5; 17)(q10; q10), der(6)t(1; 6)(p13; p21), der(7)add(7)(p14q32), −9, der(9)t(9; ?)(?; 11)(p24; ?)(?; q13), −10, −10, del(11)(q13), −14, i(14)(q10), −17, −18, −19, del(20)(q13), r(20)(p11q11), +21, dup(21)(q11q22.3-qter), psu dic(22; 9)t(9; ?)(?; 22)(p24; ?)(?; p11-13), +2 mar.

Thus, within reasonable limits of interpretation, current ATCC stocks of Dami carry at least 16 of 18 structural chromosome rearrangements (markers) identical to those originally reported by Dr Handin's laboratory. Given that Dami's original karyotype was determined a decade ago without the aid of modern FISH technology, the degree of cytogenetic correspondence is remarkable. By the same token, the cytogenetic identity of current and original stocks indicates that Dami had been supplanted by HEL before the time of karyotyping, which was reportedly performed around July 1987² — a year before Dami was deposited with the ATCC. Thus, any stocks of Dami obtained after July 1987 are likely to have been contaminated. Stocks obtained from Dr Handin's lab before this date might possibly contain original Dami cells and should be conserved to enable their identity to be checked by single-locus DNA fingerprinting, as original Dami stocks are no longer available from their originating laboratory due to loss after a freezer accident.5 

Despite manifesting identical DNA mulilocus fingerprints, late passages of Dami and HEL share only 12 of 20 markers, indicating that this pair of cell lines represent cytogenetically distinct subclones which probably diverged because of their unusual (ie, for hematopoietic cell lines) ability to grow fom clonal seeding densities at which genetic drift by ‘bottlenecking selection’ is more likely. Given Dami's stability (1987-1997), as indicated by the near identity of late and early passage karyotypes, we are led to conjecture that most of the subclonal differences between HEL and Dami represent tumoral heterogeneity already present within the original passages from which HEL, and ultimately Dami, were established. Subclonal divergence would also fit several reports describing phenotypic differences between Dami and HEL. For these reasons we believe that the Dami cell line, while not a suitable megakaryocyte model, may be of utility in modelling tumor evolution in combination with HEL (whose identity, of course, has never been questioned).