DNA Barcoding Reveals Habitual Clonal Dominance of Myeloma Plasma Cells in the Bone Marrow Microenvironment

Abstract

Multiple myeloma (MM) is a hematological malignancy resulting from the uncontrolled proliferation of antibody-producing plasma cells in the bone marrow. At diagnosis, independent plasma cell tumors are found throughout the skeleton. The recirculation of mutant plasma cells from the initial lesion and their recolonization of distant marrow sites are thought to occur by a process similar to solid tumor metastasis. However, the efficiency of this bone marrow homing process and the proportion of disseminated cells that actively divide and contribute to new tumor growth in MM are both unknown. We used the C57BL/KaLwRij mouse model of myeloma, lentiviral-mediated DNA barcoding of 5TGM1 myeloma cells, and next-generation sequencing to investigate the relative efficiency of plasma cell migration to, and growth within, the bone marrow. This approach revealed three major findings: firstly, establishment of metastasis within the bone marrow was extremely inefficient, with approximately 0.01% of circulating myeloma cells becoming resident long term in the bone marrow of each long bone; secondly, the individual cells of each metastasis exhibited marked differences in their proliferative fates, with the majority of final tumor burden within a bone being attributable to the progeny of between 1 and 8 cells; and, thirdly, the proliferative fate of individual clonal plasma cells differed at each bone marrow site in which the cells “landed.” These findings suggest that individual myeloma plasma cells are subjected to vastly different selection pressures within the bone marrow microenvironment, highlighting the importance of niche-driven factors, which determine the disease course and outcome.

Adaptation and selection shape clonal evolution of tumors during residual disease and recurrence

“…Each barcode serves as a molecular tag that marks all of the progeny of a particular cell. Consistent with the nomenclature used in other studies [17][18][19][20][21][22][23][24][25][26][27][28][29] , all cells marked by a particular barcode are referred to here as a clone, reflecting the fact that they arose from a single cell. It is important to note that the term clone is not meant to imply genetic differences between cells marked by different barcodes.…”

“…In this manner, it is possible to track the clonal dynamics of a cell population under different conditions. This approach has been used to study clonal dynamics in response to targeted therapies in vitro [17][18][19] and during the growth and metastatic spread of tumors in vivo [20][21][22][23][24][25][26][27][28][29] .…”

Subclonal evolution in disease progression from MGUS/SMM to multiple myeloma is characterised by clonal stability

“…Of note, a recent study from our group which used the C57BL/KaLwRij mouse model of MM, demonstrated habitual clonal dominance, where only a few establishing MM cells subsequently contributed to tumour burden while most remained dormant. This illustrates the strong selection pressures present within the BM microenvironment which plays a role in defining the clonal architecture [46].…”

Clodronate-Liposome Mediated Macrophage Depletion Abrogates Multiple Myeloma Tumor Establishment In Vivo

“…Cells within the BM produce factors such as C-X-C motif chemokine ligand 12 (CXCL12; SDF-1) that increase the migration, adhesion, and retention of MM PC [6], [7]. Recent data show that while many MM PC home to the BM, very few proliferate and contribute to the tumor burden [8], [9]. This phenomenon is, at least in part, determined by the microenvironment in which these cells colonize.…”