COEXISTENCE OF ANEUPLOID SUBCLONES WITHIN A MYELOMA CELL-LINE THAT EXHIBITS CLONAL IMMUNOGLOBULIN GENE REARRANGEMENT - CLINICAL IMPLICATIONS

A new human myeloma cell line, ANBL-6, was established and characteriz ed at the genotypic and phenotypic levels. The cells exhibit a clonall y rearranged immunoglobulin gene locus and resemble plasma cells morph ologically. The ANBL-6 cells also exhibited an absolute dependence on exogenous interleukin 6 for growth. Of interest, DNA ploidy analysis s uggested the existence of a near-diploid as well as a near-tetraploid population in this cell line. Cytogenetic studies confirmed the existe nce of two aneuploid karyotypes and further revealed a clonal relation ship between the two karyotypes, as evidenced by numerous shared struc tural abnormalities. To determine whether the near-diploid cells funct ioned as stem cells for the near-tetraploid population, the near-diplo id population was separated via flow cytometry and recultured prior to ploidy analysis. This population was observed to remain predominantly near-diploid over time, suggesting that these cells did not function as stem cells for the near-tetraploid population. However, the near-te traploid cells did exhibit a growth advantage in vitro. Moreover, sequ ential ploidy analysis performed retrospectively on fresh bone marrow cells from the patient also suggested that there was an expansion of t he near-tetraploid population during clinical relapse. These results s uggest that both populations are self-regenerating and reflect the con sequences of clonal evolution in the myeloma tumor. The coexistence of clonally related subclones with shared chromosomal abnormalities, how ever, suggests that the near-tetraploid subclone was derived from the near-diploid subclone at an unknown time during tumorigenesis.