FcγRIIB is a T cell checkpoint in antitumor immunity

IL-4/IL-4R axis signaling drives resistance to immunotherapy by inducing the upregulation of Fcγ receptor IIB in M2 macrophages

In recent years, immunotherapy, particularly PD-1 antibodies, have significantly enhanced the outcome of gastric cancer patients. Despite these advances, some patients do not respond well to treatment, highlighting the need to understand resistance mechanisms and develop predictive markers of treatment effectiveness. This study retrospectively analyzed data from 106 patients with stage IV gastric cancer who were treated with first-line immunotherapy in combination with chemotherapy. By comparing plasma cytokine levels between patients resistant and sensitive to PD-1 antibody therapy, the researchers identified elevated IL-4 expression in the resistant patients. Mechanical investigations revealed that IL-4 induces metabolic changes in macrophages that activate the PI3K/AKT/mTOR pathway. This alteration promotes ATP production, enhances glycolysis, increases lactic acid production, and upregulates FcγRIIB expression in macrophages. Ultimately, these changes lead to CD8+ T cell dysfunction and resistance to PD-1 antibody therapy in gastric cancer. These findings highlight the role of IL-4-induced macrophage polarization and metabolic reprogramming in immune resistance and verify IL-4 as potential targets for improving treatment outcomes in gastric cancer patients.

CD8+ T cell-derived Fgl2 regulates immunity in a cell-autonomous manner via ligation of FcγRIIB

The regulatory circuits dictating CD8+ T cell responsiveness versus exhaustion during anti-tumor immunity are incompletely understood. Here we report that tumor-infiltrating antigen-specific PD-1+ TCF-1- CD8+ T cells express the immunosuppressive cytokine Fgl2. Conditional deletion of Fgl2 specifically in mouse antigen-specific CD8+ T cells prolongs CD8+ T cell persistence, suppresses phenotypic and transcriptomic signatures of T cell exhaustion, and improves control of the tumor. In a mouse model of chronic viral infection, PD-1+ CD8+ T cell-derived Fgl2 also negatively regulates virus-specific T cell responses. In humans, CD8+ T cell-derived Fgl2 is associated with poorer survival in patients with melanoma. Mechanistically, the dampened responsiveness of WT Fgl2-expressing CD8+ T cells, when compared to Fgl2-deficient CD8+ T cells, is underpinned by the cell-intrinsic interaction of Fgl2 with CD8+ T cell-expressed FcγRIIB and concomitant caspase 3/7-mediated apoptosis. Our results thus illuminate a cell-autonomous regulatory axis by which PD-1+ CD8+ T cells both express the receptor and secrete its ligand in order to mediate suppression of anti-tumor and anti-viral immunity.

Novel and multiple targets for chimeric antigen receptor-based therapies in lymphoma

Chimeric antigen receptor (CAR) T-cell therapy targeting CD19 in B-cell non-Hodgkin lymphoma (NHL) validates the utility of CAR-based therapy for lymphomatous malignancies. Despite the success, treatment failure due to CD19 antigen loss, mutation, or down-regulation remains the main obstacle to cure. On-target, off-tumor effect of CD19-CAR T leads to side effects such as prolonged B-cell aplasia, limiting the application of therapy in indolent diseases such as chronic lymphocytic leukemia (CLL). Alternative CAR targets and multi-specific CAR are potential solutions to improving cellular therapy outcomes in B-NHL. For Hodgkin lymphoma and T-cell lymphoma, several cell surface antigens have been studied as CAR targets, some of which already showed promising results in clinical trials. Some antigens are expressed by different lymphomas and could be used for designing tumor-agnostic CAR. Here, we reviewed the antigens that have been studied for novel CAR-based therapies, as well as CARs designed to target two or more antigens in the treatment of lymphoma.

Synergistic B and T lymphocyte interaction: prognostic implications in non-small cell lung cancer

While T-cell-mediated immune responses in solid tumors have been well-established and have driven major therapeutic advances, our understanding of B-cell biology in cancer is comparatively less developed. A total of 60 lung cancer patients were included, of which 53% were diagnosed at an early stage while 47% were diagnosed at an advanced stage. Flow cytometry was used to analyze the proportion of T and B cells in all blood samples, and the levels of human serum cytokines were also assessed. Compared to the control group, cancer patients showed lower frequencies of IgD+CD27+ marginal B cells and CD32+ B cells, and higher frequencies of T cells with lower CD8+ T cells and higher central memory and naïve CD4+ T cells. Additionally, advanced-stage cancer patients exhibited higher levels of cytokines, a higher proportion of effector memory CD8+ T cells, and a lower frequency of CD27+CD28+CD4+/CD8+ T cells. Linear regression analysis revealed significant correlations between cancer stage and the frequency of B and T cell subsets, leukocyte count, and cytokine levels. Survival analysis demonstrated that patients with higher frequency of class-switched B cells had a worse prognosis, while patients with higher frequency of CD8+ effector T cells and lower frequency of CD4+57+ T cells appeared to have a better survival rate. These findings provide valuable insight into the immunological changes that occur during lung cancer progression and have the potential to inform the development of new immunotherapeutic strategies.

Unraveling T cell exhaustion in the immune microenvironment of osteosarcoma via single-cell RNA transcriptome

Osteosarcoma (OS) represents a profoundly invasive malignancy of the skeletal system. T cell exhaustion (Tex) is known to facilitate immunosuppression and tumor progression, but its role in OS remains unclear. In this study, single-cell RNA sequencing data was employed to identify exhausted T cells within the tumor immune microenvironment (TIME) of OS. We found that exhausted T cells exhibited substantial infiltration in OS samples. Pseudotime trajectory analysis revealed a progressive increase in the expression of various Tex marker genes, including PDCD1, CTLA4, LAG3, ENTPD1, and HAVCR2 in OS. GSVA showed that apoptosis, fatty acid metabolism, xenobiotic metabolism, and the interferon pathway were significantly activated in exhausted T cells in OS. Subsequently, a prognostic model was constructed using two Tex-specific genes, MYC and FCGR2B, which exhibited exceptional prognostic accuracy in two independent cohorts. Drug sensitivity analysis revealed that OS patients with a low Tex risk were responsive to Dasatinib and Pazopanib. Finally, immunohistochemistry verified that MYC and FCGR2B were significantly upregulated in OS tissues compared with adjacent tissues. This study investigates the role of Tex within the TIME of OS, and offers novel insights into the mechanisms underlying disease progression as well as the potential treatment strategies for OS.

Fibrinogen-like protein 2 promotes tumor immune suppression by regulating cholesterol metabolism in myeloid-derived suppressor cells

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) are crucial mediators of tumor-associated immune suppression. Targeting the accumulation and activation of MDSCs has been recognized as a promising approach to enhance the effectiveness of immunotherapies for different types of cancer.

METHODS

The MC38 and B16 tumor-bearing mouse models were established to investigate the role of Fgl2 during tumor progression. Fgl2 and FcγRIIB-deficient mice, adoptive cell transfer, RNA-sequencing and flow cytometry analysis were used to assess the role of Fgl2 on immunosuppressive activity and differentiation of MDSCs.

RESULTS

Here, we show that fibrinogen-like protein 2 (Fgl2) regulates the differentiation and immunosuppressive functions of MDSCs. The absence of Fgl2 leads to an increase in antitumor CD8+ T-cell responses and a decrease in granulocytic MDSC accumulation. The regulation mechanism involves Fgl2 modulating cholesterol metabolism, which promotes the accumulation of MDSCs and immunosuppression through the production of reactive oxygen species and activation of XBP1 signaling. Inhibition of Fgl2 or cholesterol metabolism in MDSCs reduces their immunosuppressive activity and enhances differentiation. Targeting Fgl2 could potentially enhance the therapeutic efficacy of anti-PD-1 antibody in immunotherapy.

CONCLUSION

These results suggest that Fgl2 plays a role in promoting immune suppression by modulating cholesterol metabolism and targeting Fgl2 combined with PD-1 checkpoint blockade provides a promising therapeutic strategy for antitumor therapy.

C-reactive protein impairs immune response of CD8+ T cells via FcγRIIb-p38MAPK-ROS axis in multiple myeloma

BACKGROUND

C-reactive protein (CRP) is a prototypical acute phase protein in humans with the function of regulating immune cells. Serum CRP levels are elevated in multiple myeloma (MM), associated with MM cell proliferation and bone destruction. However, its direct effects on T lymphocytes in MM have not been elucidated.

METHODS

Public data sets were used to explore the correlation of CRP levels with immune cell infiltration and cytotoxicity score of CD8+ T cells in MM. In vitro, repeated freeze-thaw myeloma cell lines were taken as tumor antigens to load dendritic cells (DCs) derived from HLA-A*0201-positive healthy donors. MM-specific cytotoxic T cells (MM-CTL) were obtained from T lymphocytes of the corresponding donors pulsed with these DCs. B-cell maturation antigen (BCMA)-targeted chimeric antigen receptor (CAR)-T cells were manipulated by transfecting with lentivirus encoding an anti-BCMA single-chain variable fragment. Then T cells from healthy controls, MM-CTLs and BCMA CAR-T cells were exposed to CRP and analyzed for cell proliferation, cytotoxicity, immunophenotypes. CRP binding capacity to T cells before and after Fc gamma receptors IIb (FcγRIIb) blockage, p38 mitogen-activated protein kinase (MAPK) pathway and the downstream molecules were also detected. In vivo, both normal C57BL/6J mice and the Vk*MYC myeloma mouse models were applied to confirm the impact of CRP on T cells.

RESULTS

CRP levels were negatively correlated with cell-infiltration and cytotoxicity score of CD8+ T cells in MM. In vitro experiments showed that CRP inhibited T-cell proliferation in a dose-dependent manner, impaired the cytotoxic activity and upregulated expression of senescent markers in CD8+ T cells. In vivo results validated the suppressive role of CRP in CD8+ T cells. CRP could bind to CD8+ T cells, mainly to the naïve T subset, while the binding was dramatically decreased by FcγRIIb blockage. Furthermore, CRP resulted in increased phosphorylation of p38 MAPK, elevated levels of reactive oxygen species and oxidized glutathione in CD8+ T cells.

CONCLUSIONS

We found that CRP impaired immune response of CD8+ T cells via FcγRIIb-p38MAPK-ROS signaling pathway. The study casted new insights into the role of CRP in anti-myeloma immunity, providing implications for future immunotherapy in MM.

FcγRIIB expressed on CD8+ T cells limits responsiveness to PD-1 checkpoint inhibition in cancer

Checkpoint inhibition using Fc-containing monoclonal antibodies has emerged as a powerful therapeutic approach to augment antitumor immunity. We recently showed that FcγRIIB, the only inhibitory IgG-Fc receptor, is expressed on a population of highly differentiated effector CD8+ T cells in the tumors of mice and humans, raising the possibility that CD8+ T cell responses may be directly modulated by checkpoint inhibitor binding to T cell-expressed FcγRIIB. Here, we show that despite exhibiting strong proliferative and cytokine responses at baseline, human FcγRIIBpos CD8+ T cells exhibited reduced responsiveness to both PD-1 and CTLA-4 checkpoint inhibition as compared with FcγRIIBneg CD8+ T cells in vitro. Moreover, frequencies of FcγRIIBpos CD8+ T cells were reduced after treatment of patients with melanoma with nivolumab in vivo. This reduced responsiveness was FcγRIIB dependent, because conditional genetic deletion of FcγRIIB on tumor-specific CD8+ T cells improved response to checkpoint blockade in B16 and LLC mouse models of cancer. The limited responsiveness of FcγRIIBpos CD8+ T cells was also dependent on an intact Fc region of the checkpoint inhibitor, in that treatment with Fc-devoid anti-PD-1 F(ab) fragments resulted in increased proliferation of FcγRIIBpos CD8+ T cells, without altering the response of FcγRIIBneg CD8+ T cells. Last, the addition of FcγRIIB blockade improved efficacy of PD-1 checkpoint inhibition in mouse models of melanoma, lung, and colon cancer. These results illuminate an FcγRIIB-mediated, cell-autonomous mechanism of CD8+ T cell suppression, which limits the efficacy of checkpoint inhibitors during antitumor immune responses in vivo.

Killer to cure: Expression and production costs calculation of tobacco plant-made cancer-immune checkpoint inhibitors

Immune checkpoint inhibitors (ICIs) have achieved huge clinical success. However, many still have limited response rates, and are prohibitively costly. There is a need for effective and affordable ICIs, as well as local manufacturing capacity to improve accessibility, especially to low-to-middle income countries (LMICs). Here, we have successfully expressed three key ICIs (anti-PD-1 Nivolumab, anti-NKG2A Monalizumab, and anti-LAG-3 Relatimab) transiently in Nicotiana benthamiana and Nicotiana tabacum plants. The ICIs were expressed with a combination of different Fc regions and glycosylation profiles. They were characterized in terms of protein accumulation levels, target cell binding, binding to human neonatal Fc receptors (hFcRn), human complement component C1q (hC1q) and various Fcγ receptors, as well as protein recovery during purification at 100 mg- and kg-scale. It was found that all ICIs bound to the expected target cells. Furthermore, the recovery during purification, as well as Fcγ receptor binding, can be altered depending on the Fc region used and the glycosylation profiles. This opens the possibility of using these two parameters to fine-tune the ICIs for desired effector functions. A scenario-based production cost model was also generated based on two production scenarios in hypothetical high- and low-income countries. We have shown that the product accumulation and recovery of plant production platforms were as competitive as mammalian cell-based platforms. This highlights the potential of plants to deliver ICIs that are more affordable and accessible to a widespread market, including LMICs.

Fc gamma receptor IIb in tumor-associated macrophages and dendritic cells drives poor prognosis of recurrent glioblastoma through immune-associated signaling pathways

Background: Among central nervous system tumors, glioblastoma (GBM) is considered to be the most destructive malignancy. Recurrence is one of the most fatal aspects of GBM. However, the driver molecules that trigger GBM recurrence are currently unclear. Methods: The mRNA expression data and clinical information of GBM and normal tissues were collected from the Chinese Glioma Genome Atlas The Cancer Genome Atlas (TCGA), and REpository for Molecular BRAin Neoplasia DaTa (REMBRANDT) cohorts. The DESeq2 R package was used to identify the differentially expressed genes between primary and recurrent GBM. ClueGO, Kyoto Encyclopedia of Genes and Genomes (KEGG), Biological Process in Gene ontology (GO-BP), and the Protein ANalysis THrough Evolutionary Relationships (PANTHER) pathway analyses were performed to explore the enriched signaling pathways in upregulated DEGs in recurrent GBM. A gene list that contained potential oncogenes that showed a significant negative correlation with patient survival from The Cancer Genome Atlas was used to further screen driver candidates for recurrent GBM. Univariate Cox proportional hazards regression analyses were used to investigate the risk score for the mRNA expression of the candidates. Single-cell RNA sequencing (scRNA-Seq) analyses were used to determine the cell type-specific distribution of Fc gamma receptor II b (FcγRIIb) in GBM. Immunohistochemistry (IHC) was used to confirm the FcγRIIb-positive cell populations in primary and paired recurrent GBM. Results: Through DEG analysis and overlap analysis, a total of 10 genes that are upregulated in recurrent GBM were screened. Using validation databases, FcγRIIb was identified from the 10 candidates that may serve as a driver for recurrent GBM. FCGR2B expression, not mutation, further showed a highly negative correlation with the poor prognosis of patients with recurrent GBM. Furthermore, scRNA-Seq analyses revealed that tumor-associated macrophage- and dendritic cell-specific FCGR2B was expressed. Moreover, FcγRIIb also showed a strong positive correlation coefficient with major immune-associated signaling pathways. In clinical specimens, FcγRIIb-positive cell populations were higher in recurrent GBM than in primary GBM. Conclusion: This study provides novel insights into the role of FcγRIIb in recurrent GBM and a promising strategy for treatment as an immune therapeutic target.

PCSK9 facilitates melanoma pathogenesis via a network regulating tumor immunity

BACKGROUND

PCSK9 regulates cholesterol homeostasis and promotes tumorigenesis. However, the relevance of these two actions and the mechanisms underlying PCSK9's oncogenic roles in melanoma and other cancers remain unclear.

METHODS

PCSK9's association with melanoma was analysed using the TCGA dataset. Empty vector (EV), PCSK9, gain-of-function (D374Y), and loss-of-function (Q152H) PCSK9 mutant were stably-expressed in murine melanoma B16 cells and studied for impact on B16 cell-derived oncogenesis in vitro and in vivo using syngeneic C57BL/6 and Pcsk9^-/- mice. Intratumoral accumulation of cholesterol was determined. RNA-seq was performed on individual tumor types. Differentially-expressed genes (DEGs) were derived from the comparisons of B16 PCSK9, B16 D374Y, or B16 Q152H tumors to B16 EV allografts and analysed for pathway alterations.

RESULTS

PCSK9 expression and its network negatively correlated with the survival probability of patients with melanoma. PCSK9 promoted B16 cell proliferation, migration, and growth in soft agar in vitro, formation of tumors in C57BL/6 mice in vivo, and accumulation of intratumoral cholesterol in a manner reflecting its regulation of the low-density lipoprotein receptor (LDLR): Q152H, EV, PCSK9, and D374Y. Tumor-associated T cells, CD8 + T cells, and NK cells were significantly increased in D374Y tumors along with upregulations of multiple immune checkpoints, IFNγ, and 143 genes associated with T cell dysfunction. Overlap of 36 genes between the D374Y DEGs and the PCSK9 DEGs predicted poor prognosis of melanoma and resistance to immune checkpoint blockade (ICB) therapy. CYTH4, DENND1C, AOAH, TBC1D10C, EPSTI1, GIMAP7, and FASL (FAS ligand) were novel predictors of ICB therapy and displayed high level of correlations with multiple immune checkpoints in melanoma and across 30 human cancers. We observed FAS ligand being among the most robust biomarkers of ICB treatment and constructed two novel and effective multigene panels predicting response to ICB therapy. The profiles of allografts produced by B16 EV, PCSK9, D374Y, and Q152H remained comparable in C57BL/6 and Pcsk9^-/- mice.

CONCLUSIONS

Tumor-derived PCSK9 plays a critical role in melanoma pathogenesis. PCSK9's oncogenic actions are associated with intratumoral cholesterol accumulation. PCSK9 systemically affects the immune system, contributing to melanoma immune evasion. Novel biomarkers derived from the PCSK9-network effectively predicted ICB therapy responses.

Radiotherapy-Related Gene Signature in Prostate Cancer

Simple Summary

Radiation therapy (RT) is an established therapeutic regimen for prostate cancer patients which aims for the direct elimination of tumor cells in the prostate gland and occasionally at distant anatomic sites. In this study, we performed next-generation sequencing-based gene expression analysis in peripheral blood from prostate cancer patients obtained pre- and post-radiotherapy and found six independently down-regulated genes including CCR7, FCGR2B, BTLA, CD6, CD3D, and CD3E. The analysis of the expression of the 6-genes as a signature also revealed significantly lower levels post- vs. pre-radiotherapy. Data extracted from the PRAD (PRostate ADenocarcinomas) dataset linked low levels of the 6-gene signature to better survival. More importantly, this 6-gene signature strongly correlated with a favorable prognosis regardless of poor standard clinicopathological parameters (i.e., Gleason score ≥ 8 and T3), thus highlighting its potential predictive value.

Abstract

Radiotherapy for localized prostate cancer has increased the cure and survival rates of patients. Besides its local tumoricidal effects, ionizing radiation has been linked to mechanisms leading to systemic immune activation, a phenomenon called the abscopal effect. In this study, we performed gene expression analysis on peripheral blood from prostate cancer patients obtained post- radiotherapy and showed that 6 genes, including CCR7, FCGR2B, BTLA, CD6, CD3D, and CD3E, were down-regulated by a range of 1.5–2.5-fold as compared to pre-radiotherapy samples. The expression of the signature consisting of these six genes was also significantly lower post- vs. pre-radiotherapy. These genes are involved in various tumor-promoting immune pathways and their down-regulation post-radiotherapy could be considered beneficial for patients. This is supported by the fact that low mRNA expression levels for the 6-gene signature in the prostate tumor tissue was linked to better survival. Importantly, we report that this 6-gene signature strongly correlated with a favorable prognosis regardless of poor standard clinicopathological parameters (i.e., Gleason score ≥ 8 and T3 (including T3a and T3b). Our pioneering data open the possibility that the 6-gene signature identified herein may have a predictive value, but this requires further long-term studies.

Leveraging Antibody, B Cell and Fc Receptor Interactions to Understand Heterogeneous Immune Responses in Tuberculosis

Despite over a century of research, Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), continues to kill 1.5 million people annually. Though less than 10% of infected individuals develop active disease, the specific host immune responses that lead to Mtb transmission and death, as well as those that are protective, are not yet fully defined. Recent immune correlative studies demonstrate that the spectrum of infection and disease is more heterogenous than has been classically defined. Moreover, emerging translational and animal model data attribute a diverse immune repertoire to TB outcomes. Thus, protective and detrimental immune responses to Mtb likely encompass a framework that is broader than T helper type 1 (Th1) immunity. Antibodies, Fc receptor interactions and B cells are underexplored host responses to Mtb. Poised at the interface of initial bacterial host interactions and in granulomatous lesions, antibodies and Fc receptors expressed on macrophages, neutrophils, dendritic cells, natural killer cells, T and B cells have the potential to influence local and systemic adaptive immune responses. Broadening the paradigm of protective immunity will offer new paths to improve diagnostics and vaccines to reduce the morbidity and mortality of TB.

Role of Fcγ receptors in HER2-targeted breast cancer therapy

Several therapeutic monoclonal antibodies (mAbs), including those targeting epidermal growth factor receptor, human epidermal growth factor receptor 2 (HER2), and CD20, mediate fragment crystallizable gamma receptor (FcγR)–dependent activities as part of their mechanism of action. These activities include induction of antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP), which are innate immune mechanisms of cancer cell elimination. FcγRs are distinguished by their affinity for the Fc fragment, cell distribution, and type of immune response they induce. Activating FcγRIIIa (CD16A) on natural killer cells plays a crucial role in mediating ADCC, and activating FcγRIIa (CD32A) and FcγRIIIa on macrophages are important for mediating ADCP. Polymorphisms in FcγRIIIa and FcγRIIa generate variants that bind to the Fc portion of antibodies with different affinities. This results in differential FcγR-mediated activities associated with differential therapeutic outcomes across multiple clinical settings, from early stage to metastatic disease, in patients with HER2+ breast cancer treated with the anti-HER2 mAb trastuzumab. Trastuzumab has, nonetheless, revolutionized HER2+ breast cancer treatment, and several HER2-directed mAbs have been developed using Fc glyco-engineering or Fc protein-engineering to enhance FcγR-mediated functions. An example of an approved anti-HER2 Fc-engineered chimeric mAb is margetuximab, which targets the same epitope as trastuzumab, but features five amino acid substitutions in the IgG 1 Fc domain that were deliberately introduced to increase binding to activating FcγRIIIa and decrease binding to inhibitory FcγRIIb (CD32B). Margetuximab enhances Fc-dependent ADCC in vitro more potently than the combination of pertuzumab (another approved mAb directed against an alternate HER2 epitope) and trastuzumab. Margetuximab administration also enhances HER2-specific B cell and T cell–mediated responses ex vivo in samples from patients treated with prior lines of HER2 antibody-based therapies. Stemming from these observations, a worthwhile future goal in the treatment of HER2+ breast cancer is to promote combinatorial approaches that better eradicate HER2+ cancer cells via enhanced immunological mechanisms.

FcγRIIB potentiates differentiation of myeloid-derived suppressor cells to mediate tumor immunoescape

Background: FcγRIIB, the sole inhibitory receptor of the Fc gamma receptor family, plays pivotal roles in innate and adaptive immune responses. However, the expression and function of FcγRIIB in myeloid-derived suppressor cells (MDSCs) remains unknown. This study aimed to investigate whether and how FcγRIIB regulates the immunosuppressive activity of MDSCs during cancer development. Methods: The MC38 and B16-F10 tumor-bearing mouse models were established to investigate the role of FcγRIIB during tumor progression. FcγRIIB-deficient mice, adoptive cell transfer, mRNA-sequencing and flow cytometry analysis were used to assess the role of FcγRIIB on immunosuppressive activity and differentiation of MDSCs. Results: Here we show that FcγRIIB was upregulated in tumor-infiltrated MDSCs. FcγRIIB-deficient mice showed decreased accumulation of MDSCs in the tumor microenvironment (TME) compared with wild-type mice. FcγRIIB was required for the differentiation and immunosuppressive activity of MDSCs. Mechanistically, tumor cell-derived granulocyte-macrophage colony stimulating factor (GM-CSF) increased the expression of FcγRIIB on hematopoietic progenitor cells (HPCs) by activating specificity protein 1 (Sp1), subsequently FcγRIIB promoted the generation of MDSCs from HPCs via Stat3 signaling. Furthermore, blockade of Sp1 dampened MDSC differentiation and infiltration in the TME and enhanced the anti-tumor therapeutic efficacy of gemcitabine. Conclusion: These results uncover an unrecognized regulatory role of the FcγRIIB in abnormal differentiation of MDSCs during cancer development and suggest a potential therapeutic target for anti-tumor therapy.

Intersection of FcγRIIB, the microbiome, and checkpoint inhibitors in antitumor immunity

Fc receptors (FcRs) and the microbiome are both known to have an effect on the development and progression of cancers. Checkpoint inhibitors are a novel class of therapeutics which are used to combat cancer and are integrally linked to both FcRs and the microbiome. The use of checkpoint inhibitors has grown exponentially over the past decade, although many host factors affect both the efficacy and the safety of these therapeutics. Some of these host factors, including the microbiome and the expression of FcRs, are currently being investigated. Here we discuss the current understanding of FcRs (particularly the inhibitory FcγRIIB) and the microbiome in context of T cell immunity, inflammation, cancer, and checkpoint inhibition.