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Multiple myeloma is a hematologic malignancy of plasma cells that manifests with bone marrow tumors causing lytic bone lesions. Autologous stem cell transplantation (ASCT) after high-dose chemotherapy and followed by prolonged maintenance therapy with lenalidomide (LEN) is an effective standard-of-care therapy for multiple myeloma. However, most patients ultimately relapse. Rational combination strategies that address immune dysfunction may prolong the durability of ASCT. In this issue of the JCI, Minnie and colleagues investigated the addition of a checkpoint inhibitor to LEN maintenance therapy after ASCT. They found that the immune checkpoint TIGIT was an optimal target in patient samples. In a syngeneic, immunocompetent multiple myeloma mouse model, blockade of TIGIT synergized with LEN maintenance by inducing immune protection, characterized in part by the expansion of polyfunctional T cells in the bone marrow. The treatment enhanced durable antimyeloma efficacy and has translatable implications.

Multiple myeloma is a monoclonal tumor of plasma cells, and its development is preceded by a premalignant tumor with which it shares genetic abnormalities, including universal dysregulation of the cyclin D/retinoblastoma (cyclin D/RB) pathway. A complex interaction with the BM microenvironment, characterized by activation of osteoclasts and suppression of osteoblasts, leads to lytic bone disease. Intratumor genetic heterogeneity, which occurs in addition to intertumor heterogeneity, contributes to the rapid emergence of drug resistance in high-risk disease. Despite recent therapeutic advances, which have doubled the median survival time, myeloma continues to be a mostly incurable disease. Here we review the current understanding of myeloma pathogenesis and insight into new therapeutic strategies provided by animal models and genetic screens.

Despite significant advances in the treatment of multiple myeloma (MM), most patients succumb to disease progression. One of the major immunosuppressive mechanisms that is believed to play a role in myeloma progression is the expansion of regulatory T cells (Tregs). In this study, we demonstrate that myeloma cells drive Treg expansion and activation by secreting type 1 interferon (IFN). Blocking IFN α and β receptor 1 (IFNAR1) on Tregs significantly decreases both myeloma-associated Treg immunosuppressive function and myeloma progression. Using syngeneic transplantable murine myeloma models and bone marrow (BM) aspirates of MM patients, we found that Tregs were expanded and activated in the BM microenvironment at early stages of myeloma development. Selective depletion of Tregs led to a complete remission and prolonged survival in mice injected with myeloma cells. Further analysis of the interaction between myeloma cells and Tregs using gene sequencing and enrichment analysis uncovered a feedback loop, wherein myeloma-cell-secreted type 1 IFN induced proliferation and expansion of Tregs. By using IFNAR1-blocking antibody treatment and IFNAR1-knockout Tregs, we demonstrated a significant decrease in myeloma-associated Treg proliferation, which was associated with longer survival of myeloma-injected mice. Our results thus suggest that blocking type 1 IFN signaling represents a potential strategy to target immunosuppressive Treg function in MM.

Molecular programs that underlie precursor progression in multiple myeloma are incompletely understood. Here, we report a disease spectrum-spanning, single-cell analysis of the Vκ*MYC myeloma mouse model. Using samples obtained from mice with serologically undetectable disease, we identify malignant cells as early as 30 weeks of age and show that these tumours contain subclonal copy number variations that persist throughout progression. We detect intratumoural heterogeneity driven by transcriptional variability during active disease and show that subclonal expression programs are enriched at different times throughout early disease. We then show how one subclonal program related to GCN2 stress response is progressively activated during progression in myeloma patients. Finally, we use chemical and genetic perturbation of GCN2 in vitro to support this pathway as a therapeutic target in myeloma. These findings therefore present a model of precursor progression in Vκ*MYC mice, nominate an adaptive mechanism important for myeloma survival, and highlight the need for single-cell analyses to understand the biological underpinnings of disease progression. The molecular programs that underlie progression in multiple myeloma (MM) are incompletely understood. Here the authors use a mouse model of MM and single-cell RNA-seq to define subclonal expression programs that arise during progression and that inform targeted therapeutic strategies.

Multiple myeloma remains an incurable neoplasm of plasma cells that affects more than 20,000 people annually in the United States. There has been a veritable revolution in this disease during the past decade, with dramatic improvements in our understanding of its pathogenesis, the development of several novel agents, and a concomitant doubling in overall survival. Because multiple myeloma is a complex and wide-ranging disorder, its management must be guided by disease- and patient-related factors; emerging as one of the most influential factors is risk stratification, primarily based on cytogenetic features. A risk-adapted approach provides optimal therapy to patients, ensuring intense therapy for aggressive disease and minimizing toxic effects, providing sufficient but less intense therapy for low-risk disease. This consensus statement reflects recommendations from more than 20 Mayo Clinic myeloma physicians, providing a practical approach for newly diagnosed patients with myeloma who are not enrolled in a clinical trial.

The canonical plasma cell marker CD138 (syndecan-1) is highly expressed on the myeloma cell surface, but its functional role in vivo is unclear, as well as the ontogeny of CD138-high and CD138-negative (neg) myeloma cells. In this study we used an in vivo murine Vk*MYC myeloma model where CD138 is heterogeneously expressed depending on tumor size. We find that in comparison to CD138-neg myeloma cells, the CD138-high subset of myeloma cells is highly proliferative, less apoptotic, and enhanced IL-6R signaling, which is known to promote survival. In addition CD138-high myeloma engrafts better than its CD138-neg counterpart. In contrast, CD138-neg cells are more motile both in vitro and in vivo, and more readily disseminate and spread to other bones in vivo than CD138-high subset. Neutralizing CD138 rapidly triggers migration of myeloma cells in vivo and leads to intravasation, which results in increased dissemination to other bones. Both murine and human myeloma cells can rapidly recycle CD138 surface expression through endocytic trafficking, in response to serum levels. Blocking CD138 enhances myeloma sensitivity to bortezomib chemotherapy and significantly reduces tumor size compared to bortezomib treatment alone. Thus, our data show that CD138 surface expression dynamically regulates a switch between growth vs. dissemination for myeloma, in response to nutrient conditions.

Multiple myeloma is divided into two distinct genetic subtypes based on chromosome content. Hyperdiploid myeloma is characterized by multiple trisomies of chromosomes 3, 5, 7, 9 11, 15, 19 and 21, and lacks recurrent immunoglobulin gene translocations. Non-hyperdiploid myeloma in contrast is characterized by chromosome translocations t(4;14), t(14;16), t(14;20), t(6;14) and t(11;14). A unifying event in the pathogenesis of multiple myeloma is the dysregulated expression of a cyclin D gene, either directly by juxtaposition to an immunoglobulin enhancer, as a result of ectopic expression of a MAF family transcription factor, or indirectly by as yet unidentified mechanisms. Secondary genetic events include rearrangements of MYC, activating mutations of NRAS, KRAS or BRAF, a promiscuous array of mutations that activate NFkB and deletions of 17p. Among the poor-risk genetic features are t(4;14), t(14;16), t(14;20), del 17p and gains of 1q. Available evidence supports the use of a risk-stratified approach to the treatment of patients with multiple myeloma, with the early and prolonged use of bortezomib particularly in patients with t(4;14) and del 17p.

DNA-repair pathways defined Recruitment of p53 binding protein 1 (53BP1) to double-strand DNA breaks is an important step in the cellular response to DNA damage. Here, the histone methyltransferase MMSET is shown to be responsible for localized increases in a histone modification that is involved in recruiting 53BP1. The mechanism of MMSET recruitment to DNA damage sites is also investigated. Recruitment of 53BP1 to double-strand DNA breaks is an important step in the cellular response to DNA damage. Here, the histone methyltransferase MMSET is shown to be responsible for localized increases in a histone modification that is involved in recruiting 53BP1. The mechanism of MMSET recruitment to DNA damage sites is also investigated. p53-binding protein 1 (53BP1) is known to be an important mediator of the DNA damage response 1 , with dimethylation of histone H4 lysine 20 (H4K20me2) critical to the recruitment of 53BP1 to double-strand breaks (DSBs) 2 , 3 . However, it is not clear how 53BP1 is specifically targeted to the sites of DNA damage, as the overall level of H4K20me2 does not seem to increase following DNA damage. It has been proposed that DNA breaks may cause exposure of methylated H4K20 previously buried within the chromosome; however, experimental evidence for such a model is lacking. Here we found that H4K20 methylation actually increases locally upon the induction of DSBs and that methylation of H4K20 at DSBs is mediated by the histone methyltransferase MMSET (also known as NSD2 or WHSC1) in mammals. Downregulation of MMSET significantly decreases H4K20 methylation at DSBs and the subsequent accumulation of 53BP1. Furthermore, we found that the recruitment of MMSET to DSBs requires the γH2AX–MDC1 pathway; specifically, the interaction between the MDC1 BRCT domain and phosphorylated Ser 102 of MMSET. Thus, we propose that a pathway involving γH2AX–MDC1–MMSET regulates the induction of H4K20 methylation on histones around DSBs, which, in turn, facilitates 53BP1 recruitment.

Multiple myeloma is an incurable malignancy of plasma cells, and its pathogenesis is poorly understood. Here we report the massively parallel sequencing of 38 tumour genomes and their comparison to matched normal DNAs. Several new and unexpected oncogenic mechanisms were suggested by the pattern of somatic mutation across the data set. These include the mutation of genes involved in protein translation (seen in nearly half of the patients), genes involved in histone methylation, and genes involved in blood coagulation. In addition, a broader than anticipated role of NF-κB signalling was indicated by mutations in 11 members of the NF-κB pathway. Of potential immediate clinical relevance, activating mutations of the kinase BRAF were observed in 4% of patients, suggesting the evaluation of BRAF inhibitors in multiple myeloma clinical trials. These results indicate that cancer genome sequencing of large collections of samples will yield new insights into cancer not anticipated by existing knowledge. BRAF and other links to multiple myeloma Multiple myeloma, a malignancy of plasma cells, remains incurable and is poorly understood. Chapman et al . have used next-generation sequencing to compare 38 multiple myeloma genomes with those of normal cells from the same patients. The disease involves mutations of genes with roles in protein translation, histone methylation and blood coagulation. In terms of clinically relevant findings, unexpected activating mutations were found in the kinase BRAF, inhibitors of which have recently shown dramatic clinical activity. This suggests that BRAF inhibitors should be evaluated in patients with BRAF-mutated multiple myeloma. Multiple myeloma, a malignancy of plasma cells, remains incurable and is poorly understood. Using next-generation sequencing of several multiple myeloma genomes reveals that this disease involves mutations of genes involved in protein translation, histone methylation and blood coagulation. The study suggests that BRAF inhibitors should be evaluated in multiple myeloma clinical trials.

The gut microbiota has been causally linked to cancer, yet how intestinal microbes influence progression of extramucosal tumors is poorly understood. Here we provide evidence implying that Prevotella heparinolytica promotes the differentiation of Th17 cells colonizing the gut and migrating to the bone marrow (BM) of transgenic Vk*MYC mice, where they favor progression of multiple myeloma (MM). Lack of IL-17 in Vk*MYC mice, or disturbance of their microbiome delayed MM appearance. Similarly, in smoldering MM patients, higher levels of BM IL-17 predicted faster disease progression. IL-17 induced STAT3 phosphorylation in murine plasma cells, and activated eosinophils. Treatment of Vk*MYC mice with antibodies blocking IL-17, IL-17RA, and IL-5 reduced BM accumulation of Th17 cells and eosinophils and delayed disease progression. Thus, in Vk*MYC mice, commensal bacteria appear to unleash a paracrine signaling network between adaptive and innate immunity that accelerates progression to MM, and can be targeted by already available therapies. The mechanisms through which gut microbiota affect extramucosal tumors are poorly understood. Here the authors show that the gut microbiota promotes multiple myeloma by inducing differentiation and migration of Th17 cells in the bone marrow resulting also in increased recruitment of pro-tumorigenic eosinophils.