* Waldenstrom’s macroglobulinemia (WM) is a lymphoplasmacytic lymphoma characterized by small malignant lymphocytes, plasmacytoid lymphocytes, and/or plasma cells that primarily invade the bone marrow and secrete a monoclonal immunoglobulin M (IgM). Due to the infiltration of tumor cells, patients with WM may present with clinical features of lymphadenopathy, hepatosplenomegaly or pancytopenia. WM is a relatively rare malignancy with an incidence of 3 to 5 per million people per year. Due to the rarity of the disease and the paucity of reliable preclinical models, many facets of the molecular, phenotypic and microenvironmental architecture of WM remain incompletely understood.
(i) Analysis of the WM molecular and microenvironmental landscape (D Roos-Weil, F Nguyen-Khac).
Our previous work using multi-omics techniques (high-throughput DNA sequencing, methylome, transcriptome) in WM identified prognostic biomarkers (Roos-Weil et al., Cancer Discov 2019; Roos-Weil et al., Blood 2020; Krzisch et al., Am J Hematol 2021; Forgeard et al. Haematologica 2022), but only partially addressed the heterogeneity and causes of therapeutic resistance in WM. As a consequence, our current research project focuses on the role of the tumor microenvironment (TME), which has been little studied in WM, in therapeutic resistance. More precisely, we aim to define the composition and phenotype of TME cells using the innovative slide-based mass cytometry technology (Hyperion imaging) coupled with single-cell RNAseq analysis on bone marrow samples from WM patients. We seek to identify subgroups with distinct characteristics and to define interactions between tumor and TEM cells (interactome). By establishing new local collaborations (Sorbonne University CyPS platform, CHIC CRC platform and Sorbonne University iGenSeq platform), the first part of our work was to optimize the Hyperion technology on WM samples at different stages of the disease (n=70). This initial approach has identified different cell populations enriched according to disease stage (more CD31+ endothelial cells, CD8+ T lymphocytes and fewer myeloid/monocytic cells in advanced vs. early stages) as well as different modes of intercellular organization (B/T lymphocyte colocalization and myeloid/monocytic cell exclusion, in advanced stages). Based on these very encouraging data, our goal now is to confirm them in a validation cohort and to establish correlations with intrinsic genetic markers and patient prognosis. To do that, we will take advantage of samples from prospective protocols as well as from our local database (Pitié-Salpêtrière Hospital, Paris), which is annotated at clinical, phenotypic, cytogenetic and molecular levels.
(ii) Assessment of the WM specific BCR structure (M Armand, C Bravetti, F Davi, D Roos-Weil).
As with CLL, we propose to apply Oxford Nanopore technology to search for genetic abnormalities that may occur downstream of immunoglobulin (Ig) variable region genes, in particular recombinations with other genes, deletions/insertions or mutations between variable and constant regions. These events are still poorly understood in WM. We expect that this approach should enable us to discover new mechanisms of oncogenesis in this rare pathology, with potential therapeutic implications. In particular, the identification of new genetic abnormalities should help us to better understand the response to treatment, and ultimately guide therapeutic choice. Moreover, we will be able to correlate the data obtained from long fragment sequencing with patients’ clinical characteristics, other biological abnormalities and disease progression, with the aim of improving understanding of disease pathophysiology and defining a prognostic impact.