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 treatme nt resistant disease evaluation of the CD19(+) cells during the course of h igh-dose therapy has to be a major concern. We determined the number of tum or cells in the CD19(+) as well as CD19(-) fractions of PB of eight patient s with disease sensitive to VA[I]D chemotherapy, of 10 patients who achieve d partial or complete remission post-high-dose therapy (HDT) with periphera l blood stem cell transplantation (PBSCT) and of a further seven patients w ith 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 pa tients post-transplantation were sorted for CD20(+) cells (median purity, 9 8.7%), 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 th ose of the patients post-VA[I]D (median, 1.05 vs 0.92 CD19(+) tumor cells/m l PB, P = 0.72) providing evidence for the persistence of this tumor cell f raction during the course of HDT. This was in contrast to the CD19(-) compa rtment, in which the number of tumor cells was significantly reduced in tho se patients in remission post-transplantation (median, 53 vs 0 CD19(-) tumo r cells/ml PB; P = 0.006), In patients with progressive disease the number of tumor cells in both cell fractions was significantly higher (CD19(+): me dian, 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 i n the group of patients after VA[I]D treatment, a polyclonal CD19(+) recons titution had occurred in patients responding to HDT. The tumor cell content in the CD19(+) fractions could be confirmed by the results obtained analyz ing the CD20(+) cell fractions. In conclusion, these results indicate that disease progression after PBSCT in MM is accompanied by an expansion of tum or cells in both the CD19(+) and CD19(-) fractions. Similar numbers of CD19 (+) clonotypic cells post-HDT suggest that these cells persist and thus, co ntribute to disease dissemination and relapse.