Analysis of circulating tumor cells in patients with multiple myeloma during the course of high-dose therapy with peripheral blood stem cell transplantation

In multiple myeloma (MM) circulating CD19(+) cells have been considered as myeloma precursors. As these cells are also possibly a reservoir of treatment resistant disease evaluation of the CD19(+) cells during the course of high-dose therapy has to be a major concern. We determined the number of tumor cells in the CD19(+) as well as CD19(-) fractions of PB of eight patients with disease sensitive to VA[I]D chemotherapy, of 10 patients who achieved partial or complete remission post-high-dose therapy (HDT) with peripheral blood stem cell transplantation (PBSCT) and of a further seven patients with disease progression :post-transplantation. CD19(+) fell fractions were obtained by preparative sequential magnetic and fluorescence activated cell sorting With a median purity of 97.1%. In addition, PB samples of seven patients post-transplantation were sorted for CD20(+) cells (median purity, 98.7%), The number of tumor cells in the CD19(+), the CD19(-) and the CD20(+) fractions were determined using a quantitative CDR3 PCR assay. The number of CD19(+) tumor cells in patients in remission post-HDT was similar to those of the patients post-VA[I]D (median, 1.05 vs 0.92 CD19(+) tumor cells/ml PB, P = 0.72) providing evidence for the persistence of this tumor cell fraction during the course of HDT. This was in contrast to the CD19(-) compartment, in which the number of tumor cells was significantly reduced in those patients in remission post-transplantation (median, 53 vs 0 CD19(-) tumor cells/ml PB; P = 0.006), In patients with progressive disease the number of tumor cells in both cell fractions was significantly higher (CD19(+): median, 1.05 vs 21 tumor cells/ml PB, P = 0.05; CD19(-): 0 vs 63 tumor cells/ml PB, P = 0.008). While the absolute number of CD19(+) cells was reduced in the group of patients after VA[I]D treatment, a polyclonal CD19(+) reconstitution had occurred in patients responding to HDT. The tumor cell content in the CD19(+) fractions could be confirmed by the results obtained analyzing the CD20(+) cell fractions. In conclusion, these results indicate that disease progression after PBSCT in MM is accompanied by an expansion of tumor cells in both the CD19(+) and CD19(-) fractions. Similar numbers of CD19(+) clonotypic cells post-HDT suggest that these cells persist and thus, contribute to disease dissemination and relapse.