Tumor-infiltrating DCs suppress nucleic acid-mediated innate immune responses through interactions between the receptor TIM-3 and the alarmin HMGB1.

The mechanisms by which tumor microenvironments modulate nucleic acid-mediated innate immunity remain unknown. Here we identify the receptor TIM-3 as key in circumventing the stimulatory effects of nucleic acids in tumor immunity. Tumor-associated dendritic cells (DCs) in mouse tumors and patients with cancer had high expression of TIM-3. DC-derived TIM-3 suppressed innate immune responses through the recognition of nucleic acids by Toll-like receptors and cytosolic sensors via a galectin-9-independent mechanism. In contrast, TIM-3 interacted with the alarmin HMGB1 to interfere with the recruitment of nucleic acids into DC endosomes and attenuated the therapeutic efficacy of DNA vaccination and chemotherapy by diminishing the immunogenicity of nucleic acids released from dying tumor cells. Our findings define a mechanism whereby tumor microenvironments suppress antitumor immunity mediated by nucleic acids.

TIM-4 glycoprotein-mediated degradation of dying tumor cells by autophagy leads to reduced antigen presentation and increased immune tolerance.

Phagocytosis of apoptotic cells by myeloid cells has been implicated in the maintenance of immune homeostasis. In this study, we found that T cell immunoglobulin- and mucin domain-containing molecule-4 (TIM-4) repressed tumor-specific immunity triggered by chemotherapy-induced tumor cell death. TIM-4 was found to be highly expressed on tumor-associated myeloid cells such as macrophages (TAMs) and dendritic cells (TADCs) and danger-associated molecular patterns (DAMPs) released from chemotherapy-damaged tumor cells induced TIM-4 on tumor-associated myeloid cells recruited from bone marrow-derived precursors. TIM-4 directly interacted with AMPKα1 and activated autophagy-mediated degradation of ingested tumors, leading to reduced antigen presentation and impaired CTL responses. Consistently, blockade of the TIM-4-AMPKα1-autophagy pathway augmented the antitumor effect of chemotherapeutics by enhancing tumor-specific CTL responses. Our finding provides insight into the immune tolerance mediated by phagocytosis of dying cells, and targeting of the TIM-4-AMPKα1 interaction constitutes a unique strategy for augmenting antitumor immunity and improving cancer chemotherapy.

Sleeve Gastrectomy and Cholecystectomy are Safe in Obese Patients with Asymptomatic Cholelithiasis. A Multicenter Randomized Trial.

BACKGROUND: Obesity is a severe health problem. Gallstones may symptomatize after sleeve gastrectomy (SG). Concomitant laparoscopic cholecystectomy (LC) with SG is controversial. The effects of SG and LC versus delayed LC following SG in obese patients with asymptomatic gallbladder stones were evaluated. METHODS: A randomized trial of 222 morbidly obese patients with gallbladder stones divided them into two equal groups: SG + LC and SG-only. This multicenter study conducted from January 2016 to January 2019. RESULTS: Except for operative time and postoperative hospital stay, there was no statistically significant difference between LSG + LC group and SG group (P < 0.001). In SG + LC group, LC added 40.7 min to SG, three patients (3%) required conversion, early postoperative complications occurred in 9 cases (9/111, 9%), three cases required re-intervention (3%). In SG group, the complicated cases required LC were 61 cases (61/111, 55%). Acute cholecystitis (26/61, 42.7%) was the most common gallstone symptoms. Most complicated cases occurred in the first-year follow-up (52/61, 85%). In the delayed LC group (61 patients), operative time was 50.13 ± 1.99 min, open conversion occurred in 2 cases (2/61, 3.2%), early postoperative complications occurred in four patients (4/61, 6.4%) and postoperative re-intervention were due to bile leaks and cystic artery bleeding (2/61, 3.2%). CONCLUSIONS: SG with LC prolongs the operative time and hospital stay, but the perioperative complications are the same as delayed LC; LC with SG minimizes the need for a second surgery. Concomitant LC with SG is safe.

Interleukin-34 expression in ovarian cancer: a possible correlation with disease progression.

Ovarian cancer is the second-most lethal gynecological malignancy and the seventh-commonest cause of cancer-related death in women around the world. Most of the ovarian cancer patients are diagnosed at advanced stages and suffer from recurrence after primary cytoreductive surgery and standard first-line chemotherapy. Thus, the successful management of ovarian cancer patients requires the identification of factors that contribute to progression and relapse. Interleukin-34 (IL-34) is a novel cytokine that acts as a tissue-specific ligand of colony-stimulating factor-1 receptor (CSF-1R). In cancer, IL-34 exerts pro-tumorigenic functions that promote tumor growth, metastasis, angiogenesis, immune suppression and therapeutic resistance. In this study, we evaluate the impact of IL-34 on progression and survival of ovarian cancer patients. First, IL-34 was found to be expressed in several human ovarian cancer cell lines and cancer tissues from patients. The expression of IL-34 was enhanced by cytotoxic chemotherapy in ovarian cancer cell lines and cancer tissues from chemotherapy-treated ovarian cancer patients. Importantly, high IL-34 expression correlated with worse progression-free survival (PFS) and overall survival in different cohorts. The assessment of PFS based on a combination between IL34 expression and other related genes such as CSF1R and CD163 helped further to reach more statistical significance compared with IL34 alone. Furthermore, in the murine ovarian cancer cell HM-1 in vivo model, it was suggested that IL-34-derived tumor cells was correlated with tumor progression and survival by modulating the immune environment. Collectively, these findings indicate a possible correlation between IL-34 expression and disease progression in ovarian cancer patients and the mouse model.

Transcriptional regulator Bhlhe40 works as a cofactor of T-bet in the regulation of IFN-γ production in iNKT cells.

Invariant natural killer T (iNKT) cells are a subset of innate-like T cells that act as important mediators of immune responses. In particular, iNKT cells have the ability to immediately produce large amounts of IFN-γ upon activation and thus initiate immune responses in various pathological conditions. However, molecular mechanisms that control IFN-γ production in iNKT cells are not fully understood. Here, we report that basic helix-loop-helix transcription factor family, member e40 (Bhlhe40), is an important regulator for IFN-γ production in iNKT cells. Bhlhe40 is highly expressed in stage 3 thymic iNKT cells and iNKT1 subsets, and the level of Bhlhe40 mRNA expression is correlated with Ifng mRNA expression in the resting state. Although Bhlhe40-deficient mice show normal iNKT cell development, Bhlhe40-deficient iNKT cells show significant impairment of IFN-γ production and antitumor effects. Bhlhe40 alone shows no significant effects on Ifng promoter activities but contributes to enhance T-box transcription factor Tbx21 (T-bet)-mediated Ifng promoter activation. Chromatin immunoprecipitation analysis revealed that Bhlhe40 accumulates in the T-box region of the Ifng locus and contributes to histone H3-lysine 9 acetylation of the Ifng locus, which is impaired without T-bet conditions. These results indicate that Bhlhe40 works as a cofactor of T-bet for enhancing IFN-γ production in iNKT cells.

Interleukin 34, from pathogenesis to clinical applications.

Interleukin-34 (IL-34) is a hematopoietic cytokine that was described for the first time in 2008 as a second ligand of CSF1R in addition to M-CSF. IL-34 and M-CSF share no sequence homology, but have similar functions, affecting the biology of myeloid cell lineage. In contrast to M-CSF, IL-34 shows unique signaling and expression patterns. Physiologically, IL-34 expression is restricted to epidermis and CNS, acting as a regulator of Langerhans cells and microglia, respectively. However, IL-34 expression can be induced and regulated by NF-κB under pathological conditions. Importantly, growing evidence indicates a correlation between IL-34 and disease severity, chronicity and progression. In addition to its promising roles as a novel diagnostic and prognostic biomarker of disease, IL-34 may also serve as a powerful target for therapeutic intervention. Here, we review the current knowledge regarding the emerging roles of IL-34 in disease, and focus on the clinical applications of IL-34 in medicine.

Myeloid molecular characteristics of human γδ T cells support their acquisition of tumor antigen-presenting capacity.

Human T cells expressing γδ T cell receptor have a potential to show antigen-presenting cell-like phenotype and function upon their activation. However, the mechanisms that underlie the alterations in human γδ T cells remain largely unclear. In this study, we have investigated the molecular characteristics of human γδ T cells related to their acquisition of antigen-presenting capacity in comparison with activated αß T cells. We found that activated γδ but not αß T cells upregulated cell surface expression of a scavenger receptor, CD36, which seemed to be mediated by signaling through mitogen-activated protein kinase and/or NF-κB pathways. Confocal microscopical analysis revealed that activated γδ T cells can phagocytose protein antigens. Activated γδ T cells could induce tumor antigen-specific CD8(+) T cells using both apoptotic and live tumor cells as antigen resources. Furthermore, we detected that C/EBPα, a critical transcription factor for the development of myeloid-lineage cells, is expressed much higher in γδ T cells than in αß T cells. These results unveiled the molecular mechanisms for the elicitation of antigen-presenting functions in γδ T cells and would also help designing new approaches for γδ T cell-mediated human cancer immunotherapy.

Combined blockade of TIM-3 and TIM-4 augments cancer vaccine efficacy against established melanomas.

Cancer vaccines have been developed to instruct the endogenous immune responses to autologous tumors and to generate durable clinical responses. However, the therapeutic benefits of cancer vaccines remain insufficient due to the multiple immunosuppressive signals delivered by tumors. Thus, to improve the clinical efficacy of cancer immunotherapy, it is important to develop new modalities to overcome immunosuppressive tumor microenvironments and elicit effective antitumor immune responses. In this study, we show that novel monoclonal antibodies (mAbs) specifically targeting either T cell immunoglobulin mucin protein-3 (TIM-3) or T cell immunoglobulin mucin protein-4 (TIM-4) enhance the therapeutic effects of vaccination against established B16 murine melanomas. This is true for vaccination with irradiated B16 melanoma cells engineered to express the flt3 ligand gene (FVAX). More importantly, combining anti-TIM-3 and anti-TIM-4 mAbs markedly increased vaccine-induced antitumor responses against established B16 melanoma. TIM-3 blockade mainly stimulated antitumor effector activities via natural killer cell-dependent mechanisms, while CD8(+) T cells served as the main effectors induced by anti-TIM-4 mAb. Our findings reveal that therapeutic manipulation of TIM-3 and TIM-4 may provide a novel strategy for improving the clinical efficacy of cancer immunotherapy.

A prospective multicentre study evaluating the outcomes of the abdominal wall dehiscence repair using posterior component separation with transversus abdominis muscle release reinforced by a retro-muscular mesh: filling a step.

BACKGROUND: This study aimed to evaluate the results of posterior component separation (CS) and transversus abdominis muscle release (TAR) with retro-muscular mesh reinforcement in patients with primary abdominal wall dehiscence (AWD). The secondary aims were to detect the incidence of postoperative surgical site occurrence and risk factors of incisional hernia (IH) development following AWD repair with posterior CS with TAR reinforced by retromuscular mesh. METHODS: Between June 2014 and April 2018, 202 patients with grade IA primary AWD (Björck's first classification) following midline laparotomies were treated using posterior CS with TAR release reinforced by a retro-muscular mesh in a prospective multicenter cohort study. RESULTS: The mean age was 42 ± 10 years, with female predominance (59.9%). The mean time from index surgery (midline laparotomy) to primary AWD was 7 ± 3 days. The mean vertical length of primary AWD was 16 ± 2 cm. The median time from primary AWD occurrence to posterior CS + TAR surgery was 3 ± 1 days. The mean operative time of posterior CS + TAR was 95 ± 12 min. No recurrent AWD occurred. Surgical site infections (SSI), seroma, hematoma, IH, and infected mesh occurred in 7.9%, 12.4%, 2%, 8.9%, and 3%, respectively. Mortality was reported in 2.5%. Old age, male gender, smoking, albumin level < 3.5 gm%, time from AWD to posterior CS + TAR surgery, SSI, ileus, and infected mesh were significantly higher in IH. IH rate was 0.5% and 8.9% at two and three years, respectively. In multivariate logistic regression analyses, the predictors of IH were time from AWD till posterior CS + TAR surgical intervention, ileus, SSI, and infected mesh. CONCLUSION: Posterior CS with TAR reinforced by retro-muscular mesh insertion resulted in no AWD recurrence, low IH rates, and low mortality of 2.5%. Trial registration Clinical trial: NCT05278117.

Hepatobiliary manifestations following two-stages elective laparoscopic restorative proctocolectomy for patients with ulcerative colitis: A prospective observational study.

BACKGROUND: Hepatobiliary manifestations occur in ulcerative colitis (UC) patients. The effect of laparoscopic restorative proctocolectomy (LRP) with ileal pouch anal anastomosis (IPAA) on hepatobiliary manifestations is debated. AIM: To evaluate hepatobiliary changes after two-stages elective laparoscopic restorative proctocolectomy for patients with UC. METHODS: Between June 2013 and June 2018, 167 patients with hepatobiliary symptoms underwent two-stage elective LRP for UC in a prospective observational study. Patients with UC and having at least one hepatobiliary manifestation who underwent LRP with IPAA were included in the study. The patients were followed up for four years to assess the outcomes of hepatobiliary manifestations. RESULTS: The patients' mean age was 36 ± 8 years, and males predominated (67.1%). The most common hepatobiliary diagnostic method was liver biopsy (85.6%), followed by Magnetic resonance cholangiopancreatography (63.5%), Antineutrophil cytoplasmic antibodies (62.5%), abdominal ultrasonography (35.9%), and Endoscopic retrograde cholangiopancreatography (6%). The most common hepatobiliary symptom was Primary sclerosing cholangitis (PSC) (62.3%), followed by fatty liver (16.8%) and gallbladder stone (10.2%). 66.4% of patients showed a stable course after surgery. Progressive or regressive courses occurred in 16.8% of each. Mortality was 6%, and recurrence or progression of symptoms required surgery for 15%. Most PSC patients (87.5%) had a stable course, and only 12.5% became worse. Two-thirds (64.3%) of fatty liver patients showed a regressive course, while one-third (35.7%) showed a stable course. Survival rates were 98.8%, 97%, 95.8%, and 94% at 12 mo, 24 mo, 36 mo, and at the end of the follow-up. CONCLUSION: In patients with UC who had LRP, there is a positive impact on hepatobiliary disease. It caused an improvement in PSC and fatty liver disease. The most prevalent unchanged course was PSC, while the most common improvement was fatty liver disease.

Erratum: Interleukin-34 Limits the Therapeutic Effects of Immune Checkpoint Blockade.

[This corrects the article DOI: 10.1016/j.isci.2020.101584.].

Recurrent appendicitis following successful drainage of appendicular abscess in adult without interval appendectomy during COVID-19. Prospective cohort study.

BACKGROUND: COVID-19 infection is a global pandemic that affected routine health services and made patients fear to consult for medical health problems, even acute abdominal pain. Subsequently, the incidence of complicated appendicitis increased during the Covid-19 pandemic. This study aimed to evaluate recurrent appendicitis after successful drainage of appendicular abscess during COVID-19. MATERIAL AND METHODS: A prospective cohort study conducted in the surgical emergency units of our Universities' Hospitals between March 15, 2020 to August 15, 2020 including patients who were admitted with the diagnosis of an appendicular abscess and who underwent open or radiological drainage. Main outcomes included incidence, severity, and risk factors of recurrent appendicitis in patients without interval appendectomy. RESULTS: A total of 316 patients were included for analysis. The mean age of the patients was 37 years (SD ± 13). About two-thirds of patients were males (60.1%). More than one-third (39.6%) had co-morbidities; type 2 diabetes mellitus (T2DM) (22.5%) and hypertension (17.1%) were the most frequent. Approximately one quarter (25.6%) had confirmed COVID 19 infection. About one-third of the patients (30.4%) had recurrent appendicitis. More than half of them (56.3%) showed recurrence after three months, and 43.8% of patients showed recurrence in the first three months. The most frequent grade was grade I (63.5%). Most patients (77.1%) underwent open surgery. Age, T2DM, hypertension, COVID-19 infection and abscess size >3 cm were significantly risking predictors for recurrent appendicitis. CONCLUSIONS: Interval appendectomy is suggested to prevent 56.3% of recurrent appendicitis that occurs after 3 months. We recommend performing interval appendectomy in older age, people with diabetes, COVID-19 infected, and abscesses more than 3 cm in diameter. RESEARCH QUESTION: Is interval appendectomy preventing a high incidence of recurrent appendicitis after successful drainage of appendicular abscess during COVID-19 pandemic?

Bromodomain-containing protein 4 regulates interleukin-34 expression in mouse ovarian cancer cells.

BACKGROUND: Interleukin (IL)-34 acts as an alternative ligand for the colony-stimulating factor-1 receptor and controls the biology of myeloid cells, including survival, proliferation, and differentiation. IL-34 has been reported to be expressed in cancer cells and to promote tumor progression and metastasis of certain cancers via the promotion of angiogenesis and immunosuppressive macrophage differentiation. We have shown in our previous reports that targeting IL-34 in chemo-resistant tumors in vitro resulted in a remarkable inhibition of tumor growth. Also, we reported poor prognosis in patients with IL-34-expressing tumor. Therefore, blocking of IL-34 is considered as a promising therapeutic strategy to suppress tumor progression. However, the molecular mechanisms that control IL-34 production are still largely unknown. METHODS: IL-34 producing ovarian cancer cell line HM-1 was treated by bromodomain and extra terminal inhibitor JQ1. The mRNA and protein expression of IL-34 was evaluated after JQ1 treatment. Chromatin immunoprecipitation was performed to confirm the involvement of bromodomain-containing protein 4 (Brd4) in the regulation of the Il34 gene. Anti-tumor effect of JQ1 was evaluated in mouse tumor model. RESULTS: We identified Brd4 as one of the critical molecules that regulate Il34 expression in cancer cells. Consistent with this, we found that JQ1 is capable of efficiently suppressing the recruitment of Brd4 to the promotor region of Il34 gene. Additionally, JQ1 treatment of mice bearing IL-34-producing tumor inhibited the tumor growth along with decreasing Il34 expression in the tumor. CONCLUSION: The results unveiled for the first time the responsible molecule Brd4 that regulates Il34 expression in cancer cells and suggested its possibility as a treatment target.

Induction of macrophage-like immunosuppressive cells from common marmoset ES cells by stepwise differentiation with DZNep.

Recent progress in regenerative medicine has enabled the utilization of pluripotent stem cells (PSCs) as the resource of therapeutic cells/tissue. However, immune suppression is still needed when the donor-recipient combination is allogeneic. We have reported previously that mouse PSCs-derived immunosuppressive cells contribute to prolonged survival of grafts derived from the same mouse PSCs in allogeneic recipients. For its clinical application, a preclinical study using non-human primates such as common marmoset must be performed. In this study, we established the induction protocol of immunosuppressive cells from common marmoset ES cells. Although similar immunosuppressive macrophages could not be induced by same protocol as that for mouse PSCs, we employed an inhibitor for histone methyltransferase, DZNep, and succeeded to induce them. The DZNep-treated macrophage-like cells expressed several immunosuppressive molecules and significantly inhibited allogeneic mixed lymphocyte reaction. The immunosuppressive cells from non-human primate ESCs will help to establish an immunoregulating strategy in regenerative medicine using PSCs.

Efficient generation of thymic epithelium from induced pluripotent stem cells that prolongs allograft survival.

The thymus plays a significant role in establishing immunological self-tolerance. Previous studies have revealed that host immune reaction to allogeneic transplants could be regulated by thymus transplantation. However, physiological thymus involution hinders the clinical application of these insights. Here, we report an efficient generation of thymic epithelial-like tissue derived from induced pluripotent stem cells (iPSCs) and its potential to regulate immune reaction in allogeneic transplantation. We established an iPSC line which constitutively expresses mouse Foxn1 gene and examined the effect of its expression during in vitro differentiation of thymic epithelial cells (TECs). We found that Foxn1 expression enhances the differentiation induction of cells expressing TEC-related cell surface molecules along with upregulation of endogenous Foxn1. iPSC-derived TECs (iPSC-TECs) generated T cells in nude recipient mice after renal subcapsular transplantation. Moreover, iPSC-TEC transplantation to immuno-competent recipients significantly prolonged the survival of allogeneic skin. Our study provides a novel concept for allogeneic transplantation in the setting of regenerative medicine.

Interleukin-34 Limits the Therapeutic Effects of Immune Checkpoint Blockade.

Interleukin-34 (IL-34) is an alternative ligand to colony-stimulating factor-1 (CSF-1) for the CSF-1 receptor that acts as a key regulator of monocyte/macrophage lineage. In this study, we show that tumor-derived IL-34 mediates resistance to immune checkpoint blockade regardless of CSF-1 existence in various murine cancer models. Consistent with its immunosuppressive characteristics, the expression of IL-34 in tumors correlates with decreased frequencies of cellular (such as CD8+ and CD4+ T cells and M1-biased macrophages) and molecular (including various cytokines and chemokines) effectors at the tumor microenvironment. Then, a neutralizing antibody against IL-34 improved the therapeutic effects of the immune checkpoint blockade in combinatorial therapeutic models, including a patient-derived xenograft model. Collectively, we revealed that tumor-derived IL-34 inhibits the efficacy of immune checkpoint blockade and proposed the utility of IL-34 blockade as a new strategy for cancer therapy.

Prognostic value of IL-34 in colorectal cancer patients.

The mortality of colorectal cancer is expected to increase in some countries including the United States, which necessitates the identification of new molecules that help in prognosis assessment and survival improvement. In this brief report, we evaluated the potential of interleukin-34 (IL-34) as a prognostic factor in colorectal cancer. IL-34 was reported for the first time in 2008 as a novel cytokine that controls the biology of the myeloid cell lineage. Accumulating evidence suggests important roles for IL-34 in modifying the tumor microenvironment and enhancing therapeutic resistance of cancer. In this study, we found that IL-34 expression was detectable in various colorectal cancer cell lines in addition to primary cancer tissues from a cohort of Japanese colorectal cancer patients, ranging from high to absent. A Kaplan-Meier analysis showed that high expression of IL-34 correlated with poor survival of colorectal cancer patients. Importantly, in both univariate and multivariate analysis, high IL-34 expression correlated with unfavorable prognosis. A similar relationship between IL-34 expression and the poorer prognosis was also observed in a cohort of colorectal cancer patients registered at The Cancer Genome Atlas. Together, these findings indicate a potential role for IL-34 as a prognostic factor in colorectal cancer.

Flow cytometric identification and cell-line establishment of macrophages in naked mole-rats.

Naked mole rats (NMRs) have extraordinarily long lifespans and anti-tumorigenic capability. Recent studies of humans and mice have shown that many age-related diseases, including cancer, are strongly correlated with immunity, and macrophages play particularly important roles in immune regulation. Therefore, NMR macrophages may contribute to their unique phenotypes. However, studies of the roles of macrophages are limited by material restrictions and the lack of an established experimental strategy. In this study, we developed a flow cytometric strategy to identify NMR macrophages. The NMR macrophages were extractable using an off-the-shelf anti-CD11b antibody, M1/70, and forward/side scatter data obtained by flow cytometry. NMR macrophages proliferated in response to human/mouse recombinant M-CSF and engulfed Escherichia coli particles. Interestingly, the majority of NMR macrophages exhibited co-staining with an anti-NK1.1 antibody, PK136. NK1.1 antigen crosslinking with PK136 results in mouse NK cell stimulation; similarly, NMR macrophages proliferated in response to NK1.1 antibody treatment. Furthermore, we successfully established an NMR macrophage cell line, NPM1, by transduction of Simian virus 40 early region that proliferated indefinitely without cytokines and retained its phagocytotic capacity. The NPM1 would contribute to further studies on the immunity of NMRs.

A role for IL-34 in osteolytic disease of multiple myeloma.

Multiple myeloma (MM) is a hematological malignancy that grows in multiple sites of the axial skeleton and causes debilitating osteolytic disease. Interleukin-34 (IL-34) is a newly discovered cytokine that acts as a ligand of colony-stimulating factor-1 (CSF-1) receptor and can replace CSF-1 for osteoclast differentiation. In this study, we identify IL-34 as an osteoclastogenic cytokine that accelerates osteolytic disease in MM. IL-34 was found to be expressed in the murine MM cell line MOPC315.BM, and the expression of IL-34 was enhanced by stimulation with proinflammatory cytokines or by bone marrow (BM) stromal cells. MM-cell-derived IL-34 promoted osteoclast formation from mouse BM cells in vitro. Targeting Il34 by specific small interfering RNA impaired osteoclast formation in vitro and attenuated osteolytic disease in vivo. In BM aspirates from MM patients, the expression levels of IL-34 in CD138+ populations vary among patients from high to weak to absent. MM cell-derived IL-34 promoted osteoclast formation from human CD14+ monocytes, which was reduced by a neutralizing antibody against IL-34. Taken together, this study describes for the first time the expression of IL-34 in MM cells, indicating that it may enhance osteolysis and suggesting IL-34 as a potential therapeutic target to control pathological osteoclastogenesis in MM patients.