Targeting the immune microenvironment in Waldenström macroglobulinemia via halting the CD40/CD40-ligand axis.

Recent investigations have improved our understanding of the molecular aberrations supporting Waldenström macroglobulinemia (WM) biology; however, whether the immune microenvironment contributes to WM pathogenesis remains unanswered. First, we showed how a transgenic murine model of human-like lymphoplasmacytic lymphoma/WM exhibits an increased number of regulatory T cells (Tregs) relative to control mice. These findings were translated into the WM clinical setting, in which the transcriptomic profiling of Tregs derived from patients with WM unveiled a peculiar WM-devoted messenger RNA signature, with significant enrichment for genes related to nuclear factor κB-mediated tumor necrosis factor α signaling, MAPK, and PI3K/AKT, which was paralleled by a different Treg functional phenotype. We demonstrated significantly higher Treg induction, expansion, and proliferation triggered by WM cells, compared with their normal cellular counterpart; with a more profound effect within the context of CXCR4C1013G-mutated WM cells. By investigating the B-cell-to-T-cell cross talk at single-cell level, we identified the CD40/CD40-ligand as a potentially relevant axis that supports WM cell-Tregs interaction. Our findings demonstrate the existence of a Treg-mediated immunosuppressive phenotype in WM, which can be therapeutically reversed by blocking the CD40L/CD40 axis to inhibit WM cell growth.

Halting the FGF/FGFR axis leads to antitumor activity in Waldenström macroglobulinemia by silencing MYD88.

The human fibroblast growth factor/fibroblast growth factor receptor (FGF/FGFR) axis deregulation is largely involved in supporting the pathogenesis of hematologic malignancies, including Waldenström macroglobulinemia (WM). WM is still an incurable disease, and patients succumb because of disease progression. Therefore, novel therapeutics designed to specifically target deregulated signaling pathways in WM are required. We aimed to investigate the role of FGF/FGFR system blockade in WM by using a pan-FGF trap molecule (NSC12). Wide-transcriptome profiling confirmed inhibition of FGFR signaling in NSC12-treated WM cells; unveiling a significant inhibition of MYD88 was also confirmed at the protein level. Importantly, the NSC12-dependent silencing of MYD88 was functionally active, as it led to inhibition of MYD88-driven pathways, such as BTK and SYK, as well as the MYD88-downstream target HCK. Of note, both canonical and noncanonical NF-κB cascades were downregulated in WM cells upon NSC12 treatment. Functional sequelae exerted by NSC12 in WM cells were studied, demonstrating significant inhibition of WM cell growth, induction of WM cell apoptosis, halting MAPK, JAK/STAT3, and PI3K-Akt pathways. Importantly, NSC12 exerted an anti-WM effect even in the presence of bone marrow microenvironment, both in vitro and in vivo. Our studies provide the evidence for using NSC12 as a specific FGF/FGFR system inhibitor, thus representing a novel therapeutic strategy in WM.

Progression signature underlies clonal evolution and dissemination of multiple myeloma.

Clonal evolution drives tumor progression, dissemination, and relapse in multiple myeloma (MM), with most patients dying of relapsed disease. This multistage process requires tumor cells to enter the circulation, extravasate, and colonize distant bone marrow (BM) sites. Here, we developed a fluorescent or DNA-barcode clone-tracking system on MM PrEDiCT (progression through evolution and dissemination of clonal tumor cells) xenograft mouse model to study clonal behavior within the BM microenvironment. We showed that only the few clones that successfully adapt to the BM microenvironment can enter the circulation and colonize distant BM sites. RNA sequencing of primary and distant-site MM tumor cells revealed a progression signature sequentially activated along human MM progression and significantly associated with overall survival when evaluated against patient data sets. A total of 28 genes were then computationally predicted to be master regulators (MRs) of MM progression. HMGA1 and PA2G4 were validated in vivo using CRISPR-Cas9 in the PrEDiCT model and were shown to be significantly depleted in distant BM sites, indicating their role in MM progression and dissemination. Loss of HMGA1 and PA2G4 also compromised the proliferation, migration, and adhesion abilities of MM cells in vitro. Overall, our model successfully recapitulates key characteristics of human MM disease progression and identified potential new therapeutic targets for MM.

Phase 1 study of ibrutinib and the CXCR4 antagonist ulocuplumab in CXCR4-mutated Waldenström macroglobulinemia.

MYD88 and CXCR4 mutations are common in Waldenström macroglobulinemia (WM). Mutated CXCR4 (CXCR4Mut) impacts BTK-inhibitor response. We conducted a phase 1 trial of the CXCR4-antagonist ulocuplumab with ibrutinib in this first-ever study to target CXCR4Mut in WM. Ibrutinib was initiated at 420 mg/d with cycle 1 and continued until intolerance or progression; ulocuplumab was given cycles 1 to 6, with a 3 + 3 dose-escalation design. Each cycle was 4 weeks. Thirteen symptomatic patients, of whom 9 were treatment-naive patients were enrolled. Twelve were evaluable for response. At best response, their median serum immunoglobulin M declined from 5574 to 1114 mg/dL; bone marrow disease decreased from 65% to 10%, and hemoglobin increased from 10.1 to 14.2 g/dL (P < .001). The major and VGPR response rates were 100% and 33%, respectively, with VGPRs observed at lower ulocuplumab dose cohorts. Median times to minor and major responses were 0.9 and 1.2 months, respectively. With a median follow-up of 22.4 months, the estimated 2-year progression-free survival was 90%. The most frequent recurring grade ≥2 adverse events included reversible thrombocytopenia, rash, and skin infections. Ulocuplumab dose-escalation did not impact adverse events. The study demonstrates the feasibility of combining a CXCR4-antagonist with ibrutinib and provides support for the development of CXCR4-antagonists for CXCR4Mut WM. This trial was registered at www.clinicaltrials.gov as #NCT03225716.

Specific targeting of the KRAS mutational landscape in myeloma as a tool to unveil the elicited antitumor activity.

Alterations in KRAS have been identified as the most recurring somatic variants in the multiple myeloma (MM) mutational landscape. Combining DNA and RNA sequencing, we studied 756 patients and observed KRAS as the most frequently mutated gene in patients at diagnosis; in addition, we demonstrated the persistence or de novo occurrence of the KRAS aberration at disease relapse. Small-molecule inhibitors targeting KRAS have been developed; however, they are selective for tumors carrying the KRASG12C mutation. Therefore, there is still a need to develop novel therapeutic approaches to target the KRAS mutational events found in other tumor types, including MM. We used AZD4785, a potent and selective antisense oligonucleotide that selectively targets and downregulates all KRAS isoforms, as a tool to dissect the functional sequelae secondary to KRAS silencing in MM within the context of the bone marrow niche and demonstrated its ability to significantly silence KRAS, leading to inhibition of MM tumor growth, both in vitro and in vivo, and confirming KRAS as a driver and therapeutic target in MM.

The role of clonal hematopoiesis as driver of therapy-related myeloid neoplasms after autologous stem cell transplantation.

Therapy-related myeloid neoplasm (t-MN) is a threatening complication of autologous stem cell transplantation (ASCT). Detecting clonal hematopoiesis (CH) mutations in cryopreserved cells before ASCT has been associated with a higher risk of t-MN, but the evolution of molecular abnormalities from pre-ASCT to t-MN, within the same patient, remains to be elucidated. We evaluated the mutational profile of 19 lymphoma/myeloma patients, at both pre-ASCT and t-MN diagnosis, using a targeted NGS approach; 26 non-developing t-MN control patients were also studied pre-ASCT. At ASCT, we found a higher frequency of CH in patients developing t-MN (58%) than in those who did not (23%) (P = 0.029); mutations in epigenetic (DNMT3A, TET2, and ASXL1) and DNA repair genes (PPM1D, RAD21, TP53, and STAG2) were the most represented. At t-MN, CH increased to 82% of patients. Cumulative mutational burden and variant allele frequency (VAF) also increased at t-MN. CH clones detected at ASCT were found at t-MN in eight out of 16 patients, mainly with stable VAF. Among the new driver mutations appeared at t-MN, TP53 increased from one to 13 mutations, in nine patients; being associated with complex karyotype. Mutations in transcription factor (RUNX1, CEBPA) and intracellular signaling genes (FLT3, RAS genes) also increased from three to 17 mutations in eight patients, presenting with a normal karyotype. Overall, we found that preexisting CH at ASCT rarely causes t-MN directly, but may rather facilitate the appearance of new mutations, especially those involving TP53, RUNX1, and RAS, that can drive the evolution to t-MN of at least two distinct types.

Surfactant therapy for COVID-19 related ARDS: a retrospective case-control pilot study.

BACKGROUND: COVID-19 causes acute respiratory distress syndrome (ARDS) and depletes the lungs of surfactant, leading to prolonged mechanical ventilation and death. The feasibility and safety of surfactant delivery in COVID-19 ARDS patients have not been established. METHODS: We performed retrospective analyses of data from patients receiving off-label use of exogenous natural surfactant during the COVID-19 pandemic. Seven COVID-19 PCR positive ARDS patients received liquid Curosurf (720 mg) in 150 ml normal saline, divided into five 30 ml aliquots) and delivered via a bronchoscope into second-generation bronchi. Patients were matched with 14 comparable subjects receiving supportive care for ARDS during the same time period. Feasibility and safety were examined as well as the duration of mechanical ventilation and mortality. RESULTS: Patients showed no evidence of acute decompensation following surfactant installation into minor bronchi. Cox regression showed a reduction of 28-days mortality within the surfactant group, though not significant. The surfactant did not increase the duration of ventilation, and health care providers did not convert to COVID-19 positive. CONCLUSIONS: Surfactant delivery through bronchoscopy at a dose of 720 mg in 150 ml normal saline is feasible and safe for COVID-19 ARDS patients and health care providers during the pandemic. Surfactant administration did not cause acute decompensation, may reduce mortality and mechanical ventilation duration in COVID-19 ARDS patients. This study supports the future performance of randomized clinical trials evaluating the efficacy of meticulous sub-bronchial lavage with surfactant as treatment for patients with COVID-19 ARDS.

Clinical characteristics and risk factors for mortality in hematologic patients affected by COVID-19.

BACKGROUND: Patients with cancer are considered highly vulnerable to the recent coronavirus disease 2019 (COVID-19) pandemic. However, there are still few data on COVID-19 occurring in hematologic patients. METHODS: One hundred two patients with COVID-19 symptoms and a nasopharyngeal swab positive for severe acute respiratory syndrome coronavirus 2 seen at 2 hematologic departments located in Lombardy, Italy, during March 2020 were studied. Risk factors for acquiring COVID-19 were analyzed by comparisons of patients with COVID-19 and the standard hematologic population managed at the same institutions in 2019. Thirty-day survival was compared with the survival of matched uninfected control patients with similar hematologic disorders and nonhematologic patients affected by COVID-19. RESULTS: Male sex was significantly more prevalent in patients with COVID-19. The infection occurred across all different types of hematologic disease; however, the risk of acquiring a COVID-19 infection was lower for patients with chronic myeloproliferative neoplasms, including chronic myeloid leukemia, and higher for patients with immune-mediated anemia on immunosuppressive-related treatments. The 30-day mortality rate was 39.2%, which was higher than the rates for nonhematologic patients with COVID-19 (23.5%; P = .02) and uninfected hematologic controls (3%; P < .001). The severity of the respiratory syndrome at presentation and active hematologic treatment were independently associated with a worse prognosis. Neither diagnosis nor disease status affected the prognosis. The worst prognosis was demonstrated among patients on active hematologic treatment and those with more severe respiratory syndrome at COVID-19 presentation. CONCLUSIONS: During the COVID-19 pandemic, patients should be advised to seek medical attention at the earliest signs of dyspnea and/or respiratory infection. Physicians should perform a risk-benefit analysis to determine the impact of temporarily deferring nonlifesaving treatments versus the risk of adverse outcomes associated with COVID-19. LAY SUMMARY: Coronavirus disease 2019 (COVID-19) infection occurs across all different types of hematologic disease; however, the risk of acquiring it is lower for patients with chronic myeloproliferative neoplasms, including chronic myeloid leukemia, and higher for patients with immune-mediated anemia on immunosuppressive treatment. The 30-day mortality rate is 39.2%, which is far higher than the rates for both uninfected hematologic controls (3%; P < .001) and nonhematologic patients with COVID-19 (23.5%; P = .02) despite matching for age, sex, comorbidities, and severity of disease. Variables independently associated with a worse prognosis are the severity of the respiratory syndrome at presentation and any type of active hematologic treatment. Neither diagnosis nor disease status influence the prognosis.

Prognostic role of circulating exosomal miRNAs in multiple myeloma.

Exosomes, secreted by several cell types, including cancer cells, can be isolated from the peripheral blood and have been shown to be powerful markers of disease progression in cancer. In this study, we examined the prognostic significance of circulating exosomal microRNAs (miRNAs) in multiple myeloma (MM). A cohort of 156 patients with newly diagnosed MM, uniformly treated and followed, was studied. Circulating exosomal miRNAs were isolated and used to perform a small RNA sequencing analysis on 10 samples and a quantitative reverse transcription polymerase chain reaction (qRT-PCR) array on 156 samples. We studied the relationship between miRNA levels and patient outcomes, including progression-free survival (PFS) and overall survival (OS). We identified miRNAs as the most predominant small RNAs present in exosomes isolated from the serum of patients with MM and healthy controls by small RNA sequencing of circulating exosomes. We then analyzed exosomes isolated from serum samples of 156 patients using a qRT-PCR array for 22 miRNAs. Two of these miRNAs, let-7b and miR-18a, were significantly associated with both PFS and OS in the univariate analysis and were still statistically significant after adjusting for the International Staging System and adverse cytogenetics in the multivariate analysis. Our findings support the use of circulating exosomal miRNAs to improve the identification of patients with newly diagnosed MM with poor outcomes. The results require further validation in other independent prospective MM cohorts.

Targeting the bone marrow microenvironment in multiple myeloma.

Multiple myeloma (MM) is characterized by clonal expansion of malignant plasma cells in the bone marrow (BM). Despite the significant advances in treatment, MM is still a fatal malignancy. This is mainly due to the supportive role of the BM microenvironment in differentiation, migration, proliferation, survival, and drug resistance of the malignant plasma cells. The BM microenvironment is composed of a cellular compartment (stromal cells, osteoblasts, osteoclasts, endothelial cells, and immune cells) and a non-cellular compartment. In this review, we discuss the interaction between the malignant plasma cell and the BM microenvironment and the strategy to target them.

Exome sequencing reveals recurrent germ line variants in patients with familial Waldenström macroglobulinemia.

Familial aggregation of Waldenström macroglobulinemia (WM) cases, and the clustering of B-cell lymphoproliferative disorders among first-degree relatives of WM patients, has been reported. Nevertheless, the possible contribution of inherited susceptibility to familial WM remains unrevealed. We performed whole exome sequencing on germ line DNA obtained from 4 family members in which coinheritance for WM was documented in 3 of them, and screened additional independent 246 cases by using gene-specific mutation sequencing. Among the shared germ line variants, LAPTM5(c403t) and HCLS1(g496a) were the most recurrent, being present in 3/3 affected members of the index family, detected in 8% of the unrelated familial cases, and present in 0.5% of the nonfamilial cases and in <0.05 of a control population. LAPTM5 and HCLS1 appeared as relevant WM candidate genes that characterized familial WM individuals and were also functionally relevant to the tumor clone. These findings highlight potentially novel contributors for the genetic predisposition to familial WM and indicate that LAPTM5(c403t) and HCLS1(g496a) may represent predisposition alleles in patients with familial WM.

Detection of newly produced T and B lymphocytes by digital PCR in blood stored dry on nylon flocked swabs.

BACKGROUND: A normal number of T-cell receptor excision circles (TRECs) and K-deleting recombination excision circles (KRECs) is considered a biomarker for adequate new T- and B-cell production. In newborns, detection of TRECs and KRECs by real time PCR from dried blood spotted on filter paper is used for the screening of severe immunodeficiency. In adults, elderly and during diseases, where the number of TRECs is lower than in newborns and children, a large amount of DNA and a sensitive method of amplification are necessary to identify newly produced lymphocytes. METHODS: DNA was prepared from blood of 203 healthy adults (range: 18-91 years old) absorbed for 10 s on flocked swabs and let to dry, or from peripheral blood mononuclear cells. DNA was subjected to digital PCR and to well established conventional real time PCR-based method using TREC- and KREC-specific primers and probes. The number of TRECs and KRECs was expressed per mL of blood. Statistical analysis was performed by nested ANOVA, Pearson coefficient of determination, and by linear regression tests. RESULTS: The novel method for the storage of dried blood on nylon flocked swabs and the use of digital PCR allow quantification of TRECs and KRECs with high degree of sensitivity, specificity, accuracy, and precision. TRECs and KRECs were amplified by digital PCR in all tested blood samples, including those obtained from elderly individuals (>70 years old) and that were negative by real time PCR. Furthermore, values of TRECs and KRECs obtained by digital PCR were in the range of those acquired by real time PCR. CONCLUSIONS: Our findings demonstrate that DNA isolation from dried blood on flocked swabs followed by digital PCR-based analysis represents a useful tool for studying new lymphocyte production in adults and elderly individuals. This suggests the potential use of the methodology when monitoring of clinical variables is limited by the number of molecules that can be amplified and detected, such as in patients with immunodeficiency or under immunosuppressive therapies.

A novel in vivo model for studying conditional dual loss of BLIMP-1 and p53 in B-cells, leading to tumor transformation.

The tumor suppressors B-lymphocyte-induced maturation protein-1 (BLIMP-1) and p53 play a crucial role in B-cell lymphomas, and their inactivation contributes to the pathogenesis of a wide spectrum of lymphoid malignancies, including diffuse large B-cell lymphomas (DLBCLs). Patients with activated B-cell-like (ABC) DLBCL may present with loss of BLIMP-1, c-Myc over-expression, decreased p53, and poor prognosis. Nevertheless, there is a lack of in vivo models recapitulating the biology of high-grade ABC DLBCL. We therefore aimed to develop an in vivo model aiming to recapitulate the phenotype observed in this cohort of patients. A Cre-Lox approach was used to achieve inactivation of both p53 and BLIMP-1 in murine B-cells. Contextual ablation of BLIMP-1 and p53 led to development of IgM-positive B-cell lymphoma with an aggressive phenotype, supported by c-Myc up-regulation, and accumulation of somatic mutations, as demonstrated by whole exome sequencing. Sensitivity of B-tumor cells to BTK inhibition was demonstrated. This model mirrors what reported in patients with ABC DLBLC, and therefore represents a novel model for studying the biology of ABC-DLBCL harboring the dual loss of BLIMP-1/p53 and c-Myc over-expression.

Bone Marrow Stroma and Vascular Contributions to Myeloma Bone Homing.

PURPOSE OF THE REVIEW: Herein we dissect mechanisms behind the dissemination of cancer cells from primary tumor site to the bone marrow, which are necessary for metastasis development, with a specific focus on multiple myeloma. RECENT FINDINGS: The ability of tumor cells to invade vessels and reach the systemic circulation is a fundamental process for metastasis development; however, the interaction between clonal cells and the surrounding microenvironment is equally important for supporting colonization, survival, and growth in the secondary sites of dissemination. The intrinsic propensity of tumor cells to recognize a favorable milieu where to establish secondary growth is the basis of the "seed and soil" theory. This theory assumes that certain tumor cells (the "seeds") have a specific affinity for the milieu of certain organs (the "soil"). Recent literature has highlighted the important contributions of the vascular niche to the hospitable "soil" within the bone marrow. In this review, we discuss the crucial role of stromal cells and endothelial cells in supporting primary growth, homing, and metastasis to the bone marrow, in the context of multiple myeloma, a plasma cell malignancy with the unique propensity to primarily grow and metastasize to the bone marrow.

Engineered nanomedicine for myeloma and bone microenvironment targeting.

Bone is a favorable microenvironment for tumor growth and a frequent destination for metastatic cancer cells. Targeting cancers within the bone marrow remains a crucial oncologic challenge due to issues of drug availability and microenvironment-induced resistance. Herein, we engineered bone-homing polymeric nanoparticles (NPs) for spatiotemporally controlled delivery of therapeutics to bone, which diminish off-target effects and increase local drug concentrations. The NPs consist of poly(D,L-lactic-co-glycolic acid) (PLGA), polyethylene glycol (PEG), and bisphosphonate (or alendronate, a targeting ligand). The engineered NPs were formulated by blending varying ratios of the synthesized polymers: PLGA-b-PEG and alendronate-conjugated polymer PLGA-b-PEG-Ald, which ensured long circulation and targeting capabilities, respectively. The bone-binding ability of Ald-PEG-PLGA NPs was investigated by hydroxyapatite binding assays and ex vivo imaging of adherence to bone fragments. In vivo biodistribution of fluorescently labeled NPs showed higher retention, accumulation, and bone homing of targeted Ald-PEG-PLGA NPs, compared with nontargeted PEG-PLGA NPs. A library of bortezomib-loaded NPs (bone-targeted Ald-Bort-NPs and nontargeted Bort-NPs) were developed and screened for optimal physiochemical properties, drug loading, and release profiles. Ald-Bort-NPs were tested for efficacy in mouse models of multiple myeloma (MM). Results demonstrated significantly enhanced survival and decreased tumor burden in mice pretreated with Ald-Bort-NPs versus Ald-Empty-NPs (no drug) or the free drug. We also observed that bortezomib, as a pretreatment regimen, modified the bone microenvironment and enhanced bone strength and volume. Our findings suggest that NP-based anticancer therapies with bone-targeting specificity comprise a clinically relevant method of drug delivery that can inhibit tumor progression in MM.

Cell autonomous and microenvironmental regulation of tumor progression in precursor states of multiple myeloma.

PURPOSE OF REVIEW: Multiple myeloma is a plasma cell malignancy evolving in the bone marrow and leading to end organ damage such as bone lesions, cytopenias, and kidney failure. This review delineates recent advances in the molecular mechanisms leading to tumor progression in multiple myeloma. Two different aspects enable tumor expansion: cell autonomous through genomic alterations in the tumor clone and noncell autonomous deregulations in the bone marrow tumor microenvironment. These alterations provide the framework for the continuous progression of multiple myeloma from early precursor conditions such as monoclonal gammopathy of undetermined significance and smoldering multiple myeloma to overt multiple myeloma. RECENT FINDINGS: In this review, we discuss recent findings in the genomic alterations that occur in the tumor clone such as somatic genomic mutations, copy number variation and chromosomal translocation, and delineate noncell autonomous deregulations in which tumor cells take advantage of a permissive microenvironment to further proliferate. The latter compartment includes interaction with bone marrow stromal cells, osteoblasts, osteoclasts, and immune escape. SUMMARY: Understanding the mechanisms that lead tumor progression from early stages to overt multiple myeloma could guide to more effective therapies and therefore prevent disease progression.

CXCR7-dependent angiogenic mononuclear cell trafficking regulates tumor progression in multiple myeloma.

The CXCR4/stromal cell-derived factor-1 (SDF-1) axis is essential for cell trafficking and has been shown to regulate tumor progression and metastasis in many tumors including multiple myeloma (MM). A second chemokine receptor for SDF-1, CXCR7 was discovered recently and found on activated endothelial cells. We examined the role of CXCR7 in angiogenic mononuclear cells (AMCs) trafficking in MM. Our data demonstrate that AMCs are circulating in patients with MM and in vivo studies show that they specifically home to areas of MM tumor growth. CXCR7 expression is important for regulating trafficking and homing of AMCs into areas of MM tumor growth and neoangiogenesis. We demonstrate that the CXCR7 inhibitor, POL6926, abrogated trafficking of AMCs to areas of MM tumor progression leading to a significant inhibition of tumor progression. These effects were through regulation of endothelial cells and not through a direct tumor effect, indicating that targeting a bone marrow microenvironmental cell can lead to a delay in MM tumor progression. In conclusion, our studies demonstrate that CXCR7 may play an important role in the regulation of tumor progression in MM through an indirect effect on the recruitment of AMCs to areas of MM tumor growth in the bone marrow niche.

C1013G/CXCR4 acts as a driver mutation of tumor progression and modulator of drug resistance in lymphoplasmacytic lymphoma.

The C-X-C chemokine receptor type 4 (CXCR4) plays a crucial role in modulating cell trafficking in hematopoietic stem cells and clonal B cells. We screened 418 patients with B-cell lymphoproliferative disorders and described the presence of the C1013G/CXCR4 warts, hypogammaglobulinemia, infections, and myelokathexis-associated mutation in 28.2% (37/131) of patients with lymphoplasmacytic lymphoma (Waldenström macroglobulinemia [WM]), being either absent or present in only 7% of other B-cell lymphomas. In vivo functional characterization demonstrates its activating role in WM cells, as demonstrated by significant tumor proliferation and dissemination to extramedullary organs, leading to disease progression and decreased survival. The use of a monoclonal antibody anti-CXCR4 led to significant tumor reduction in a C1013G/CXCR4 WM model, whereas drug resistance was observed in mutated WM cells exposed to Bruton's tyrosine kinase, mammalian target of rapamycin, and phosphatidylinositol 3-kinase inhibitors, but not proteasome inhibitors. These findings demonstrate that C1013G/CXCR4 is an activating mutation in WM and support its role as a critical regulator of WM molecular pathogenesis and as an important therapeutic target.