MDSC in Mice and Men: Mechanisms of Immunosuppression in Cancer

Engagement of sialylated glycans with Siglec receptors on suppressive myeloid cells inhibits anticancer immunity via CCL2

The overexpression of sialic acids on glycans, called hypersialylation, is a common alteration found in cancer cells. Sialylated glycans can enhance immune evasion by interacting with sialic acid-binding immunoglobulin-like lectin (Siglec) receptors on tumor-infiltrating immune cells. Here, we investigated the effect of sialylated glycans and their interaction with Siglec receptors on myeloid-derived suppressor cells (MDSCs). We found that MDSCs derived from the blood of lung cancer patients and tumor-bearing mice strongly express inhibitory Siglec receptors and are highly sialylated. In murine cancer models of emergency myelopoiesis, Siglec-E knockout in myeloid cells resulted in prolonged survival and increased tumor infiltration of activated T cells. Targeting suppressive myeloid cells by blocking Siglec receptors or desialylation strongly reduced their suppressive potential. We further identified CCL2 as a mediator involved in T-cell suppression upon interaction between sialoglycans and Siglec receptors on MDSCs. Our results demonstrated that sialylated glycans inhibit anticancer immunity by modulating CCL2 expression.

Simple protocol for measuring CD11b+ GR-1+ (Ly6C+/Ly6G+) myeloid cells from a minimum volume of mouse peripheral blood

Myeloid-derived suppressor cells (MDSCs) comprise a heterogeneous population of myeloid origin and immature state, whose hallmark is the capacity to suppress T cells and other immune populations. In mice, the first approach to identify MDSCs relies in the measurement of their phenotypical markers: CD11b and GR-1. In addition, two main subtypes of MDSCs have been defined based on the expression of the following markers: CD11b+ Ly6G- Ly6C+ (monocytic-MDSCs, M-MDSCs) and CD11b+ Ly6G+ Ly6C+/low (polymorphonuclear-MDSCs, PMN-MDSCs). Since CD11b+ GR-1+ (Ly6C+/Ly6G+) MDSCs can increase significantly in peripheral blood during numerous acute or chronic processes, measuring alterations in the phenotypic markers CD11b and GR-1 could be important as a first step before assessing the suppressive function of the cells. In many cases it could be necessary to measure CD11b+ Gr-1+ cells from a minimum volume of peripheral blood cells without greatly affecting animal viability, since this approach would allow for further studies to be conducted on subsequent days, such as measuring parameters of the immune response or even survival in the context of the pathology under study. The following protocol describes a simple and optimized protocol for measuring the presence of CD11b+ GR-1+ (Ly6C+/Ly6G+) myeloid cells using 2+ channel flow cytometry, from a minimum volume of mouse peripheral blood obtained by facial vein puncture.

MDSC-targeted liposomal all-trans retinoic acid suppresses mMdscs and improves immunotherapy in HBV infection

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) are evolving as a prominent determinant in cancer occurrence and development and are functionally found to suppress T cells in cancer. Not much research is done regarding its involvement in viral infections. This research was designed to investigate the role of MDSCs in hepatitis B virus (HBV) infection and how targeting these cells with our novel all-trans retinoic acid encapsulated liposomal formulation could improve immunotherapy in C57BL/6 mice.

METHODS

Ten micrograms (10 μg) of plasmid adeno-associated virus (pAAV/HBV 1.2, genotype A) was injected hydrodynamically via the tail vein of C57BL/6 mice. An all-trans retinoic acid encapsulated liposomal formulation (L-ATRA) with sustained release properties was used in combination with tenofovir disoproxil fumarate (TDF), a nucleotide analog reverse transcriptase inhibitor (nRTI) to treat the HBV infection. The L-ATRA formulation was given at a dose of 5 mg/kg intravenously (IV) twice a week. The TDF was given orally at 30 mg/kg daily.

RESULTS

Our results revealed that L-ATRA suppresses MDSCs in HBV infected mice and enhanced T-cell proliferation in vitro. In vivo studies showed higher and improved immunotherapeutic effect in mice that received L-ATRA and TDF concurrently in comparison with the groups that received monotherapy. Lower HBV DNA copies, lower concentrations of HBsAg and HBeAg, lower levels of ALT and AST and less liver damage were seen in the mice that received the combination therapy of L-ATRA + TDF.

CONCLUSIONS

In effect, targeting MDSCs with the combination of L-ATRA and TDF effectively reduced mMDSC and improved immunotherapy in the HBV infected mice. Targeting MDSCs could provide a breakthrough in the fight against hepatitis B virus infection.

Polysaccharide isolated from Grifola frondosa eliminates myeloid-derived suppressor cells and inhibits tumor growth by enhancing T cells responses

Myeloid derived suppressor cells (MDSCs) are known to accumulate in cancer patients and tumor-bearing mice, playing a significant role in promoting tumor growth. Depleting MDSCs has emerged as a potential therapeutic strategy for cancer. Here, we demonstrated that a fungal polysaccharide, extracted from Grifola frondosa, can effectively suppress breast tumorigenesis in mice by reducing the accumulation of MDSCs. Treatment with Grifola frondosa polysaccharide (GFI) leads to a substantial decrease in MDSCs in the blood and tumor tissue, and a potent inhibition of tumor growth. GFI treatment significantly reduces the number and proportion of MDSCs in the spleen, although this effect is not observed in the bone marrow. Further analysis reveals that GFI treatment primarily targets PMN-MDSCs, sparing M-MDSCs. Our research also highlights that GFI treatment has the dual effect of restoring and activating CD8+T cells, achieved through the downregulation of TIGIT expression and the upregulation of Granzyme B. Taken together, our findings suggest that GFI treatment effectively eliminates PMN-MDSCs in the spleen, leading to a reduction in MDSC numbers in circulation and tumor tissues, ultimately enhancing the antitumor immune response of CD8+T cells and inhibiting tumor growth. This study introduces a promising therapeutic agent for breast cancer.

Immunosuppressive low-density neutrophils in the blood of cancer patients display a mature phenotype

The presence of human neutrophils in the tumor microenvironment is strongly correlated to poor overall survival. Most previous studies have focused on the immunosuppressive capacities of low-density neutrophils (LDN), also referred to as granulocytic myeloid-derived suppressor cells, which are elevated in number in the blood of many cancer patients. We observed two types of LDN in the blood of lung cancer and ovarian carcinoma patients: CD45high LDN, which suppressed T-cell proliferation and displayed mature morphology, and CD45low LDN, which were immature and non-suppressive. We simultaneously evaluated the classical normal-density neutrophils (NDN) and, when available, tumor-associated neutrophils. We observed that NDN from cancer patients suppressed T-cell proliferation, and NDN from healthy donors did not, despite few transcriptomic differences. Hence, the immunosuppression mediated by neutrophils in the blood of cancer patients is not dependent on the cells' density but rather on their maturity.

Sulforaphane Attenuates AOM/DSS-Induced Colorectal Tumorigenesis in Mice via Inhibition of Intestinal Inflammation

Sulforaphane (SFN) is a compound derived from cruciferous plants. It has received considerable attention in recent years due to its effectiveness in cancer prevention and anti-inflammatory properties. The purpose of this study was to evaluate the antitumor potential of sulforaphane on colitis-associated carcinogenesis (CAC) through the establishment of a mouse model with AOM/DSS. First, AOM/DSS and DSS-induced model were established and administered SFN for 10 wk, and then the severity of colitis-associated colon cancer was examined macroscopically and histologically. Subsequently, immune cells and cytokines in the tumor microenvironment (TME) were quantified. Finally, the influence of sulforaphane was also investigated using different colon cell lines. We found that sulforaphane treatment decreased tumor volume, myeloid-derived suppressor cells (MDSC) expansion, the expression of the proinflammatory cytokine IL-1β, and the level of IL-10 in serum. Also, it enhanced the antitumor activities of CD8+ T cells and significantly reduced tumorigenesis as induced by AOM/DSS. SFN also attenuated intestinal inflammation in DSS-induced chronic colitis by reshaping the inflammatory microenvironment. This work demonstrates that sulforaphane suppresses carcinogenesis-associated intestinal inflammation and prevents AOM/DSS-induced intestinal tumorigenesis and progression.

Flow cytometric detection of CD11b+ Gr-1+ cells in nontumor-bearing mice: A propolis-elicited model

Myeloid-derived suppressor cells (MDSCs) are a heterogenous myeloid lineage population whose conventional surface phenotype is CD11b+ Gr-1+. Due to their rarity and fragility, analyses using primary isolated MDSCs are extremely difficult. However, counting CD11b+ Gr-1+ cells in associated tissues such as tumors and inflammatory lesions provides critical information regarding MDSC involvement in immune disorders in the tissues. Specific MDSC markers have not been identified, limiting our ability to apply histochemical approaches during MDSCs research. However, profiling surface antigens using multi-colorimetric flow cytometry enables us to easily monitor the abundance of MDSCs in vivo. Monitoring of mouse MDSCs and their subpopulations using flow cytometry is well established. In this article, I exemplify a conventional method of monitoring CD11b+ Gr-1+ cells in mouse adipose tissue after administration of Brazilian propolis ethanol extract, which is a strong inducer of MDSCs.

Polymorphonuclear myeloid-derived suppressor cells and phosphatidylinositol-3 kinase gamma are critical to tobacco-mimicking oral carcinogenesis in mice

BACKGROUND

Oral squamous cell carcinoma (OSCC) is a devastating disease most often associated with tobacco consumption that induces a field of mutations from which a tumor arises. Identification of ways to prevent the emergence of cancer in high-risk patients is an ultimate goal for combatting all types of cancer, including OSCC.

METHODS

Our study employs a mouse model of tongue carcinogenesis induced by tobacco carcinogen mimetic, 4-nitroquinoline 1-oxide (4NQO), to establish tongue dysplasia and OSCC. We use conventional histology, immunohistochemistry, multispectral imaging, mass cytometry, novel cell lines, pharmaceutical inhibition of PI3Kγ, T-cell suppression assays and mouse transplant models in our functional experimentation.

RESULTS

In our study, we identify Ly6G+ granulocytes as the most abundant immune cell type in a model of tongue carcinogenesis induced by tobacco carcinogen mimetic 4NQO. Targeting Ly6G+ granulocytes with a pharmacologic inhibitor of PI3Kγ, an isoform of PI3K exclusively expressed by myeloid cells, resulted in reduced tongue dysplasia severity, and reduced rates of OSCC. Importantly, we performed functional assays with the Ly6G+ granulocytes induced in cell line models of 4NQO carcinogenesis to demonstrate that these granulocytes have increased polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) activity against T-cell proliferation and these PMN-MDSCs play a functional role in promoting tumor formation by inhibiting tumor regression in a PI3Kγ-dependent manner.

CONCLUSIONS

Overall, our data suggest that recruitment of PMN-MDSCs to sites of dysplasia is critical to immune suppression of CD8 T cells, thereby permitting malignancy, and PI3Kγ inhibitors are one mechanism to reduce PMN-MDSC recruitment, immunosuppression and tumorigenesis in OSCC.

Long Non-Coding RNAs in Colorectal Cancer: Navigating the Intersections of Immunity, Intercellular Communication, and Therapeutic Potential

This comprehensive review elucidates the intricate roles of long non-coding RNAs (lncRNAs) within the colorectal cancer (CRC) microenvironment, intersecting the domains of immunity, intercellular communication, and therapeutic potential. lncRNAs, which are significantly involved in the pathogenesis of CRC, immune evasion, and the treatment response to CRC, have crucial implications in inflammation and serve as promising candidates for novel therapeutic strategies and biomarkers. This review scrutinizes the interaction of lncRNAs with the Consensus Molecular Subtypes (CMSs) of CRC, their complex interplay with the tumor stroma affecting immunity and inflammation, and their conveyance via extracellular vesicles, particularly exosomes. Furthermore, we delve into the intricate relationship between lncRNAs and other non-coding RNAs, including microRNAs and circular RNAs, in mediating cell-to-cell communication within the CRC microenvironment. Lastly, we propose potential strategies to manipulate lncRNAs to enhance anti-tumor immunity, thereby underlining the significance of lncRNAs in devising innovative therapeutic interventions in CRC.

Myeloid-derived suppressor cells impair CD4+ T cell responses during chronic Staphylococcus aureus infection via lactate metabolism

Staphylococcus aureus is an important cause of chronic infections resulting from the failure of the host to eliminate the pathogen. Effective S. aureus clearance requires CD4+ T cell-mediated immunity. We previously showed that myeloid-derived suppressor cells (MDSC) expand during staphylococcal infections and support infection chronicity by inhibiting CD4+ T cell responses. The aim of this study was to elucidate the mechanisms underlying the suppressive effect exerted by MDSC on CD4+ T cells during chronic S. aureus infection. It is well known that activated CD4+ T cells undergo metabolic reprogramming from oxidative metabolism to aerobic glycolysis to meet their increased bioenergetic requirements. In this process, pyruvate is largely transformed into lactate by lactate dehydrogenase with the concomitant regeneration of NAD+, which is necessary for continued glycolysis. The by-product lactate needs to be excreted to maintain the glycolytic flux. Using SCENITH (single-cell energetic metabolism by profiling translation inhibition), we demonstrated here that MDSC inhibit CD4+ T cell responses by interfering with their metabolic activity. MDSC are highly glycolytic and excrete large amount of lactate in the local environment that alters the transmembrane concentration gradient and prevent removal of lactate by activated CD4+ T. Accumulation of endogenous lactate impedes the regeneration of NAD+, inhibit NAD-dependent glycolytic enzymes and stop glycolysis. Together, the results of this study have uncovered a role for metabolism on MDSC suppression of CD4+ T cell responses. Thus, reestablishment of their metabolic activity may represent a mean to improve the functionality of CD4+ T cells during chronic S. aureus infection.

Monocytic MDSCs exhibit superior immune suppression via adenosine and depletion of adenosine improves efficacy of immunotherapy

Immune checkpoint inhibitor (ICI) therapy is effective against many cancers for a subset of patients; a large percentage of patients remain unresponsive to this therapy. One contributing factor to ICI resistance is accumulation of monocytic myeloid-derived suppressor cells (M-MDSCs), a subset of innate immune cells with potent immunosuppressive activity against T lymphocytes. Here, using lung, melanoma, and breast cancer mouse models, we show that CD73-expressing M-MDSCs in the tumor microenvironment (TME) exhibit superior T cell suppressor function. Tumor-derived PGE2, a prostaglandin, directly induces CD73 expression in M-MDSCs via both Stat3 and CREB. The resulting CD73 overexpression induces elevated levels of adenosine, a nucleoside with T cell-suppressive activity, culminating in suppression of antitumor CD8+ T cell activity. Depletion of adenosine in the TME by the repurposed drug PEGylated adenosine deaminase (PEG-ADA) increases CD8+ T cell activity and enhances response to ICI therapy. Use of PEG-ADA can therefore be a therapeutic option to overcome resistance to ICIs in cancer patients.

The role of myeloid-derived suppressor cells in liver cancer

MDSCs are immature myeloid immune cells, which accumulate in models of liver cancer to reduce effector immune cell activity, contribute to immune escape and treatment resistance. The accumulation of MDSCs suppresses the role of CTL and the killing effects of NK cells, induces the accumulation of Treg cells, and blocks the antigen presentation of DCs, thus promoting the progression of liver cancer. Recently, immunotherapy has emerged a valuable approach following chemoradiotherapy in the therapy of advanced liver cancer. A considerable increasing of researches had proved that targeting MDSCs has become one of the therapeutic targets to enhance tumor immunity. In preclinical study models, targeting MDSCs have shown encouraging results in both alone and in combination administration. In this paper, we elaborated immune microenvironment of the liver, function and regulatory mechanisms of MDSCs, and therapeutic approaches to target MDSCs. We also expect these strategies to supply new views for future immunotherapy for the treatment of liver cancer.

Fluorescent Detection of Peroxynitrite Produced by Myeloid-Derived Suppressor Cells in Cancer and Inhibition by Dasatinib

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells that expand dramatically in many cancer patients. This expansion contributes to immunosuppression in cancer and reduces the efficacy of immune-based cancer therapies. One mechanism of immunosuppression mediated by MDSCs involves production of the reactive nitrogen species peroxynitrite (PNT), where this strong oxidant inactivates immune effector cells through destructive nitration of tyrosine residues in immune signal transduction pathways. As an alternative to analysis of nitrotyrosines indirectly generated by PNT, we used an endoplasmic reticulum (ER)-targeted fluorescent sensor termed PS3 that allows direct detection of PNT produced by MDSCs. When the MDSC-like cell line MSC2 and primary MDSCs from mice and humans were treated with PS3 and antibody-opsonized TentaGel microspheres, phagocytosis of these beads led to production of PNT and generation of a highly fluorescent product. Using this method, we show that splenocytes from a EMT6 mouse model of cancer, but not normal control mice, produce high levels of PNT due to elevated numbers of granulocytic (PMN) MDSCs. Similarly, peripheral blood mononuclear cells (PBMCs) isolated from blood of human melanoma patients produced substantially higher levels of PNT than healthy human volunteers, coincident with higher peripheral MDSC levels. The kinase inhibitor dasatinib was found to potently block the production of PNT both by inhibiting phagocytosis in vitro and by reducing the number of granulocytic MDSCs in mice in vivo, providing a chemical tool to modulate the production of this reactive nitrogen species (RNS) in the tumor microenvironment.

Precancerous Lesions of the Head and Neck Region and Their Stromal Aberrations: Piecemeal Data

Head and neck squamous cell carcinomas (HNSCCs) develop through a series of precancerous stages from a pool of potentially malignant disorders (PMDs). Although we understand the genetic changes that lead to HNSCC, our understanding of the role of the stroma in the progression from precancer to cancer is limited. The stroma is the primary battleground between the forces that prevent and promote cancer growth. Targeting the stroma has yielded promising cancer therapies. However, the stroma at the precancerous stage of HNSCCs is poorly defined, and we may miss opportunities for chemopreventive interventions. PMDs already exhibit many features of the HNSCC stroma, such as inflammation, neovascularization, and immune suppression. Still, they do not induce cancer-associated fibroblasts or destroy the basal lamina, the stroma's initial structure. Our review aims to summarize the current understanding of the transition from precancer to cancer stroma and how this knowledge can reveal opportunities and limitations for diagnostic, prognostic, and therapeutic decisions to benefit patients. We will discuss what may be needed to fulfill the promise of the precancerous stroma as a target to prevent progression to cancer.

Tumor cell integrin β4 and tumor stroma E-/P-selectin cooperatively regulate tumor growth in vivo

BACKGROUND

The immunological composition of the tumor microenvironment has a decisive influence on the biological course of cancer and is therefore of profound clinical relevance. In this study, we analyzed the cooperative effects of integrin β4 (ITGB4) on tumor cells and E-/P-selectin on endothelial cells within the tumor stroma for regulating tumor growth by shaping the local and systemic immune environment.

METHODS

We used several preclinical mouse models for different solid human cancer types (xenograft and syngeneic) to explore the role of ITGB4 (shRNA-mediated knockdown in tumor cells) and E-/P-selectins (knockout in mice) for tumor growth; effects on apoptosis, proliferation and intratumoral signaling pathways were determined by histological and biochemical methods and 3D in vitro experiments; changes in the intratumoral and systemic immune cell composition were determined by flow cytometry and immunohistochemistry; chemokine levels and their attracting potential were measured by ELISA and 3D invasion assays.

RESULTS

We observed a very robust synergism between ITGB4 and E-/P-selectin for the regulation of tumor growth, accompanied by an increased recruitment of CD11b⁺ Gr-1^Hi cells with low granularity (i.e., myeloid-derived suppressor cells, MDSCs) specifically into ITGB4-depleted tumors. ITGB4-depleted tumors undergo apoptosis and actively attract MDSCs, well-known to promote tumor growth in several cancers, via increased secretion of different chemokines. MDSC trafficking into tumors crucially depends on E-/P-selectin expression. Analyses of clinical samples confirmed an inverse relationship between ITGB4 expression in tumors and number of tumor-infiltrating leukocytes.

CONCLUSIONS

These findings suggest a distinct vulnerability of ITGB4^Lo tumors for MDSC-directed immunotherapies.

Diverse Neutrophil Functions in Cancer and Promising Neutrophil-Based Cancer Therapies

Neutrophils represent the most abundant cell type of leukocytes in the human blood and have been considered a vital player in the innate immune system and the first line of defense against invading pathogens. Recently, several studies showed that neutrophils play an active role in the immune response during cancer development. They exhibited both pro-oncogenic and anti-tumor activities under the influence of various mediators in the tumor microenvironment. Neutrophils can be divided into several subpopulations, thus contradicting the traditional concept of neutrophils as a homogeneous population with a specific function in the innate immunity and opening new horizons for cancer therapy. Despite the promising achievements in this field, a full understanding of tumor-neutrophil interplay is currently lacking. In this review, we try to summarize the current view on neutrophil heterogeneity in cancer, discuss the different communication pathways between tumors and neutrophils, and focus on the implementation of these new findings to develop promising neutrophil-based cancer therapies.

Local and Systemic Injections of Human Cord Blood Myeloid-Derived Suppressor Cells to Prevent Graft Rejection in Corneal Transplantation

Myeloid-derived suppressor cells (MDSCs) are therapeutic agents to prevent graft rejection in organ transplants by modulating inflammation. Herein, the immunosuppressive effect of human cord blood MDSCs on corneal allograft models was confirmed. CB-MDSCs were locally (subconjuctival, 5 × 10⁵) or systemically (intravenous, 1 × 10⁶) injected twice on days 0 and 7. A corneal transplantation model was established using C57BL/6 and BALB/c mice, and corneal graft opacity was measured to evaluate graft rejection up to 6 weeks. Results showed that graft survival in the MDSCs groups increased compared to vehicle groups after 42 days. Systemic and local MDSC administration inhibited the maturation (MHC-II^hi CD11c+) of dendritic cells (DCs) and the differentiation of interferon γ+ CD4+ Th1 in draining lymph nodes (LNs). However, vehicle groups increased the infiltration of CD3+ T cells and F4/80+ macrophages and produced prominent neovascular and lymphatic vessels into the graft site with increased mRNA expression of VEGF-A/C and VEGFR-1/R-3. Local MDSCs administration showed prominent anti-angiogenic/anti-lymphangiogenic effects even at lower MDSCs doses. Thus, CB-MDSCs could relatively suppress the infiltration of pathological T cells/macrophages into the corneas and the migration of mature DCs into draining LNs Therefore, ocular and systemic MDSCs administration showed therapeutic potential for preventing corneal allograft rejection.

The inflammasomes: crosstalk between innate immunity and hematology

BACKGROUND

The inflammasome is a cytosolic multi-protein complex responsible for the proteolytic maturation of pro-inflammatory cytokines IL-1ß and IL-18 and of gasdermin-D, which mediates membrane pore formation and the cytokines release, or eventually a lytic cell death known as pyroptosis. Inflammation has long been accepted as a key component of hematologic conditions, either oncological or benign diseases.

OBJECTIVES

This study aims to review the current knowledge about the contribution of inflammasome in hematologic diseases. We attempted to depict the participation of specific inflammasome receptors, and the possible cell-specific consequence of complex activation, as well as the use of anti-inflammasome therapies.

METHODS

We performed a keyword-based search in public databases (Pubmed.gov, ClinicalTrials.gov.).

CONCLUSION

Different blood cells variably express inflammasome components. Considering the immunosuppression associated with both the disease and the treatment of some hematologic diseases, and a microenvironment that allows neoplastic cell proliferation, inflammasomes could be a link between innate immunity and disease progression, as well as an interesting therapeutic target.

Myeloid-derived Suppressor Cells Activate Liver Natural Killer Cells in a Murine Model in Uveal Melanoma

OBJECTIVE

Elevated myeloid-derived suppressor cells (MDSCs) in many malignancies are associated with the increased risk for metastases and poor prognosis. Therefore, a mouse model of intraocular melanoma was established to explore how MDSCs influence liver metastases.

METHODS

In this study, murine B16LS melanoma cells were transplanted into the posterior compartment (PC) of the eye of C57BL/6 mice. Leucocytes from the liver of naive mice and mice bearing melanoma liver metastasis were isolated using isotonic Percoll centrifugation, examined by flow cytometry for their expression of Gr1, CD11b, F4/80, RAE-1, and Mult-1, and further isolated for MDSCs and natural killer (NK) cells. The effects of MDSCs on NK cells were tested by coculturing and assessing the ability of NK cells to produce interferon-gamma (IFN-γ) by ELISA and NK cell cytotoxicity by ³H-thymidine incorporation assay. The impact of IFN-γ on liver metastases was examined via selectively depleting IFN-γ in vivo.

RESULTS

The results showed that mice with liver metastases had increased levels of CD11b⁺Gr1⁺F4/80⁺ as well as CD11b⁺Gr1⁺F4/80^- MDSCs. MDSCs significantly enhanced the generation of IFN-γ together with the cytotoxicity of the NK cells. Furthermore, these effects were cell-cell contact-dependent. Although IFN-γ was not of a toxic nature to the melanoma cells, it profoundly inhibited B16LS cell proliferation. Depleting IFN-γ in vivo led to increased liver metastases.

CONCLUSION

All these findings first revealed that MDSCs accumulated in liver metastasis of intraocular melanoma could activate the NK cells to produce an effective anti-tumor immune response. Thus, the MDSCs' performance in different tumor models would need more investigation to boost current immunotherapy modalities.

TIGIT is the central player in T-cell suppression associated with CAR T-cell relapse in mantle cell lymphoma

BACKGROUND

Chimeric antigen receptor (CAR) T-cell therapy using brexucabtagene autoleucel (BA) induces remission in many patients with mantle cell lymphoma (MCL), and BA is the only CAR T-cell therapy approved by the FDA for MCL. However, development of relapses to BA is recognized with poor patient outcomes. Multiple CAR T-cell therapies have been approved for other lymphomas and the resistance mechanisms have been investigated. However, the mechanisms underlying BA relapse in MCL have not been investigated and whether any previously reported resistance mechanisms apply to BA-relapsed patients with MCL is unknown.

METHODS

To interrogate BA resistance mechanisms in MCL, we performed single-cell RNA sequencing on 39 longitudinally collected samples from 15 BA-treated patients, and multiplex cytokine profiling on 80 serial samples from 20 patients.

RESULTS

We demonstrate that after BA relapse, the proportion of T cells, especially cytotoxic T cells (CTLs), decreased among non-tumor cells, while the proportion of myeloid cells correspondingly increased. TIGIT, LAG3, and CD96 were the predominant checkpoint molecules expressed on exhausted T cells and CTLs; only TIGIT was significantly increased after relapse. CTLs expanded during remission, and then contracted during relapse with upregulated TIGIT expression. Tumor cells also acquired TIGIT expression after relapse, leading to the enhanced interaction of tumor cell TIGIT with monocyte CD155/PVR. In myeloid cells, post-relapse HLA-II expression was reduced relative to pretreatment and during remission. Myeloid-derived suppressor cells (MDSCs) were enriched after relapse with elevated expression of activation markers, including CLU (clusterin) and VCAN (versican). Extracellular chemokines (CCL4, CXCL9, CXCL13), soluble checkpoint inhibitors (sPD-L1, sTIM3, s4-1BB), and soluble receptors (sIL-2R, sTNFRII) were decreased during remission but elevated after relapse.

CONCLUSIONS

Our data demonstrate that multiple tumor-intrinsic and -extrinsic factors are associated with T-cell suppression and BA relapse. Among these, TIGIT appears to be the central player given its elevated expression after BA relapse in not only CTLs but also MCL cells. The acquisition of TIGIT expression on tumor cells is MCL-specific and has not been reported in other CAR T-treated diseases. Together, our data suggest that co-targeting TIGIT may prevent CAR T relapses and thus promote long-term progression-free survival in MCL patients.

New Perspectives on Myeloid-Derived Suppressor Cells and Their Emerging Role in Haematology

Myeloid-derived suppressor cells (MDSCs) are immature cells of myeloid origin that have gained researchers’ attention, as they constitute promising biomarkers and targets for novel therapeutic strategies (i.e., blockage of development, differentiation, depletion, and deactivation) in several conditions, including neoplastic, autoimmune, infective, and inflammatory diseases, as well as pregnancy, obesity, and graft rejection. They are characterised in humans by the typical immunophenotype of CD11b⁺CD33⁺HLA-DR^–/low and immune-modulating properties leading to decreased T-cell proliferation, induction of T-regulatory cells (T-regs), hindering of natural killer (NK) cell functionality, and macrophage M2-polarisation. The research in the field is challenging, as there are still difficulties in defining cell-surface markers and gating strategies that uniquely identify the different populations of MDSCs, and the currently available functional assays are highly demanding. There is evidence that MDSCs display altered frequency and/or functionality and could be targeted in immune-mediated and malignant haematologic diseases, although there is a large variability of techniques and results between different laboratories. This review presents the current literature concerning MDSCs in a clinical point of view in an attempt to trigger future investigation by serving as a guide to the clinical haematologist in order to apply them in the context of precision medicine as well as the researcher in the field of experimental haematology.

Radiotherapy combined with immunotherapy: the dawn of cancer treatment

Radiotherapy (RT) is delivered for purposes of local control, but can also exert systemic effect on remote and non-irradiated tumor deposits, which is called abscopal effect. The view of RT as a simple local treatment has dramatically changed in recent years, and it is now widely accepted that RT can provoke a systemic immune response which gives a strong rationale for the combination of RT and immunotherapy (iRT). Nevertheless, several points remain to be addressed such as the interaction of RT and immune system, the identification of the best schedules for combination with immunotherapy (IO), the expansion of abscopal effect and the mechanism to amplify iRT. To answer these crucial questions, we roundly summarize underlying rationale showing the whole immune landscape in RT and clinical trials to attempt to identify the best schedules of iRT. In consideration of the rarity of abscopal effect, we propose that the occurrence of abscopal effect induced by radiation can be promoted to 100% in view of molecular and genetic level. Furthermore, the “radscopal effect” which refers to using low-dose radiation to reprogram the tumor microenvironment may amplify the occurrence of abscopal effect and overcome the resistance of iRT. Taken together, RT could be regarded as a trigger of systemic antitumor immune response, and with the help of IO can be used as a radical and systemic treatment and be added into current standard regimen of patients with metastatic cancer.

Phototheranostics of Splenic Myeloid-Derived Suppressor Cells and Its Impact on Spleen Metabolism in Tumor-Bearing Mice

(1) Background: MDSCs play an active role in the immune surveillance escape of cancer cells. Because MDSCs in mice are CD11b⁺Gr1⁺, near-infrared photoimmunotherapy (NIR-PIT) using the NIR dye IR700 conjugated to an MDSC-binding antibody provides an opportunity for targeted elimination of MDSCs. (2) Methods: The efficacy of Gr1-IR700-mediated NIR-PIT was evaluated in vitro using magnetically separated CD11b⁺Gr1⁺ MDSCs from spleens of 4T1-luc tumor-bearing (TB) mice. For in vivo evaluation, spleens of Gr1-IR700-injected 4T1-luc TB mice were irradiated with NIR light, and splenocyte viability was determined using CCK-8 assays. Metabolic profiling of NIR-PIT-irradiated spleens was performed using ¹H MRS. (3) Results: Flow cytometric analysis confirmed a ten-fold increase in splenic MDSCs in 4T1-luc TB mice. Gr1-IR700-mediated NIR-PIT eliminated tumor-induced splenic MDSCs in culture. Ex vivo fluorescence imaging revealed an 8- and 9-fold increase in mean fluorescence intensity (MFI) in the spleen and lungs of Gr1-IR700-injected compared to IgG-IR700-injected TB mice. Splenocytes from Gr1-IR700-injected TB mice exposed in vivo to NIR-PIT demonstrated significantly lower viability compared to no light exposure or untreated control groups. Significant metabolic changes were observed in spleens following NIR-PIT. (4) Conclusions: Our data confirm the ability of NIR-PIT to eliminate splenic MDSCs, identifying its potential to eliminate MDSCs in tumors to reduce immune suppression. The metabolic changes observed may identify potential biomarkers of splenic MDSC depletion as well as potential metabolic targets of MDSCs.

Mesenchymal stem cell transplantation alleviated atherosclerosis in systemic lupus erythematosus through reducing MDSCs

Objective

The mechanism by which mesenchymal stem cell (MSC) transplantation alleviates atherosclerosis in systemic lupus erythematosus (SLE) remains elusive. In this study, we aim to explore the efficacy and mechanism of MSC in ameliorating atherosclerosis in SLE.

Methods

ApoE^−/− and Fas^−/− mice on the B6 background were cross-bred to generate SLE mice with atherosclerosis. Myeloid-derived suppressor cells (MDSCs) were sorted and quantified. The apoE^−/−Fas^−/− mice were either treated with anti-Gr antibody or injected with MDSCs. The lupus-like autoimmunity and atherosclerotic lesions were evaluated. Furthermore, the apoE^−/−Fas^−/− mice were transplanted with MSCs and lupus-like autoimmunity and atherosclerotic lesions were assessed.

Results

MDSCs in peripheral blood, spleen, draining lymph nodes increased in apoE^−/−Fas^−/− mice compared with B6 mice. Moreover, the adoptive transfer of MDSCs aggravated both atherosclerosis and SLE pathologies, whereas depleting MDSCs ameliorated those pathologies in apoE^−/−Fas^−/− mice. MSC transplantation in apoE^−/−Fas^−/− mice decreased the percentage of MDSCs, alleviated the typical atherosclerotic lesions, including atherosclerotic lesions in aortae and liver, and reduced serum cholesterol, triglyceride and low-density lipoprotein levels. MSC transplantation also reduced SLE pathologies, including splenomegaly, glomerular lesions, anti-dsDNA antibody in serum, urine protein and serum creatinine. Moreover, MSC transplantation regulated the generation and function of MDSCs through secreting prostaglandin E 2 (PGE2).

Conclusion

Taken together, these results indicated that the increased MDSCs contributed to atherosclerosis in SLE. MSC transplantation ameliorated the atherosclerosis and SLE through reducing MDSCs by secreting PGE2.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03002-y.

Intranasal Delivery of Recombinant S100A8 Protein Delays Lung Cancer Growth by Remodeling the Lung Immune Microenvironment

Lung cancer is the leading cause of cancer-related death worldwide. Increasing evidence indicates a critical role for chronic inflammation in lung carcinogenesis. S100A8 is a protein with reported pro- and anti-inflammatory functions. It is highly expressed in myeloid-derived suppressor cells (MDSC) that accumulate in the tumor microenvironment and abrogate effective anti-cancer immune responses. Mechanisms of MDSC-mediated immunosuppression include production of reactive oxygen species and nitric oxide, and depletion of L-arginine required for T cell function. Although S100A8 is expressed in MDSC, its role in the lung tumor microenvironment is largely unknown. To address this, mouse recombinant S100A8 was repeatedly administered intranasally to mice bearing orthotopic lung cancers. S100A8 treatment prolonged survival from 19 days to 28 days (p < 0.001). At midpoint of survival, whole lungs and bronchoalveolar lavage fluid (BALF) were collected and relevant genes/proteins measured. We found that S100A8 significantly lowered expression of cytokine genes and proteins that promote expansion and activation of MDSC in lungs and BALF from cancer-bearing mice. Moreover, S100A8 enhanced activities of antioxidant enzymes and suppressed production of nitrite to create a lung microenvironment conducive to cytotoxic lymphocyte expansion and function. In support of this, we found decreased MDSC numbers, and increased numbers of CD4⁺ T cells and natural killer T (NK-T) cells in lungs from cancer-bearing mice treated with S100A8. Ex-vivo treatment of splenocytes with S100A8 protein activated NK cells. Our results indicate that treatment with S100A8 may favourably modify the lung microenvironment to promote an effective immune response in lungs, thereby representing a new strategy that could complement current immunotherapies in lung cancer.

Metformin combined with local irradiation provokes abscopal effects in a murine rectal cancer model

Although preoperative chemoradiation therapy can down-stage locally advanced rectal cancer (LARC), it has little effect on distant metastases. Metformin exerts an anti-cancer effect partly through the activation of host immunity. LuM1, a highly lung metastatic subclone of colon 26, was injected subcutaneously (sc) in BALB/c mice and treated with metformin and/or local radiation (RT). Lung metastases and the primary tumors were evaluated and the phenotypes of immune cells in the spleen and lung metastases were examined with flow cytometry and immunohistochemistry. Local RT, but not metformin, partially delayed the growth of sc tumor which was augmented with metformin. Lung metastases were unchanged in metformin or RT alone, but significantly reduced in the combined therapy. The ratios of splenic T cells tended to be low in the RT group, which were increased by the addition of metformin. IFN-γ production of the splenic CD4(+) and CD8(+) T cells was enhanced and CD49b (+) CD335(+) activated NK cells was increased after combined treatment group. Density of NK cells infiltrating in lung metastases was increased after combination treatment. Metformin effectively enhances local and abscopal effects of RT though the activation of cell-mediated immunity and might be clinically useful for LARC.

Klebsiella pneumoniae induces host metabolic stress that promotes tolerance to pulmonary infection

K. pneumoniae sequence type 258 (Kp ST258) is a major cause of healthcare-associated pneumonia. However, it remains unclear how it causes protracted courses of infection in spite of its expression of immunostimulatory lipopolysaccharide, which should activate a brisk inflammatory response and bacterial clearance. We predicted that the metabolic stress induced by the bacteria in the host cells shapes an immune response that tolerates infection. We combined in situ metabolic imaging and transcriptional analyses to demonstrate that Kp ST258 activates host glutaminolysis and fatty acid oxidation. This response creates an oxidant-rich microenvironment conducive to the accumulation of anti-inflammatory myeloid cells. In this setting, metabolically active Kp ST258 elicits a disease-tolerant immune response. The bacteria, in turn, adapt to airway oxidants by upregulating the type VI secretion system, which is highly conserved across ST258 strains worldwide. Thus, much of the global success of Kp ST258 in hospital settings can be explained by the metabolic activity provoked in the host that promotes disease tolerance.

New Discovery of Myeloid-Derived Suppressor Cell's Tale on Viral Infection and COVID-19

Myeloid-derived suppressor cells (MDSCs) are generated under biological stress such as cancer, inflammatory tissue damage, and viral infection. In recent years, with occurrence of global infectious diseases, new discovery on MDSCs functions has been significantly expanded during viral infection and COVID-19. For a successful viral infection, pathogens viruses develop immune evasion strategies to avoid immune recognition. Numerous viruses induce the differentiation and expansion of MDSCs in order to suppress host immune responses including natural killer cells, antigen presenting cells, and T-cells. Moreover, MDSCs play an important role in regulation of immunopathogenesis by balancing viral infection and tissue damage. In this review article, we describe the overview of immunomodulation and genetic regulation of MDSCs during viral infection in the animal model and human studies. In addition, we include up-to-date review of role of MDSCs in SARS-CoV-2 infection and COVID-19. Finally, we discuss potential therapeutics targeting MDSCs.

Myeloid-Derived Suppressor Cells (MDSC) in the Umbilical Cord Blood: Biological Significance and Possible Therapeutic Applications

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of myeloid cells that suppress immune responses in cancer, infection, and trauma. They mainly act by inhibiting T-cells, natural-killer cells, and dendritic cells, and also by inducing T-regulatory cells, and modulating macrophages. Although they are mostly associated with adverse prognosis of the underlying disease entity, they may display positive effects in specific situations, such as in allogeneic hematopoietic stem cell transplantation (HSCT), where they suppress graft-versus-host disease (GVHD). They also contribute to the feto-maternal tolerance, and in the fetus growth process, whereas several pregnancy complications have been associated with their defects. Human umbilical cord blood (UCB) is a source rich in MDSCs and their myeloid progenitor cells. Recently, a number of studies have investigated the generation, isolation, and expansion of UCB-MDSCs for potential clinical application associated with their immunosuppressive properties, such as GVHD, and autoimmune and inflammatory diseases. Given that a significant proportion of UCB units in cord blood banks are not suitable for clinical use in HSCT, they might be used as a significant source of MDSCs for research and clinical purposes. The current review summarizes the roles of MDSCs in the UCB, as well as their promising applications.

Myeloid-Derived Suppressor Cells Mediate T Cell Dysfunction in Nonhuman Primate TB Granulomas

Myeloid-derived suppressor cells (MDSCs) represent an innate immune cell population comprised of immature myeloid cells and myeloid progenitors with very potent immunosuppressive potential. MDSCs are reported to be abundant in the lungs of active tuberculosis (TB) patients. We sought to perform an in-depth study of MDSCs during latent TB infection (LTBI) and active TB (ATB) using the nonhuman primate (NHP) model of pulmonary TB. We found a higher proportion of granulocytic, polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in the lungs of ATB animals compared to those with LTBI or naive control animals. Active disease in the lung, but not LTBI, was furthermore associated with higher proliferation, expansion, and immunosuppressive capabilities of PMN-MDSCs, as shown by enhanced expression of Ki67, indoleamine 2,3-dioxygenase (IDO1), interleukin-10 (IL-10), matrix metallopeptidase 9 (MMP-9), inducible nitric oxide synthase (iNOS), and programmed death-ligand 1 (PD-L1). These immunosuppressive PMN-MDSCs specifically localized to the lymphocytic cuff at the periphery of the granulomas in animals with ATB. Conversely, these cells were scarcely distributed in interstitial lung tissue and the inner core of granulomas. This spatial regulation suggests an important immunomodulatory role of PMN-MDSCs by restricting T cell access to the TB granuloma core and can potentially explain dysfunctional anti-TB responses in active granuloma. Our results raise the possibility that the presence of MDSCs can serve as a biomarker for ATB, while their disappearance can indicate successful therapy. Furthermore, MDSCs may serve as a potential target cell for adjunctive TB therapy.

Giving Oncolytic Viruses a Free Ride: Carrier Cells for Oncolytic Virotherapy

Oncolytic viruses (OVs) are an emerging class of therapeutics which combine multiple mechanisms of action, including direct cancer cell-killing, immunotherapy and gene therapy. A growing number of clinical trials have indicated that OVs have an excellent safety profile and provide some degree of efficacy, but to date only a single OV drug, HSV-1 talimogene laherparepvec (T-Vec), has achieved marketing approval in the US and Europe. An important issue to consider in order to accelerate the clinical advancement of OV agents is the development of an effective delivery system. Currently, the most commonly employed OV delivery route is intratumoral; however, to target metastatic diseases and tumors that cannot be directly accessed, it is of great interest to develop effective approaches for the systemic delivery of OVs, such as the use of carrier cells. In general, the ideal carrier cell should have a tropism towards the tumor microenvironment (TME), and it must be susceptible to OV infection but remain viable long enough to allow migration and finally release of the OV within the tumor bed. Mesenchymal stem cells (MSCs) have been heavily investigated as carrier cells due to their inherent tumor tropism, in spite of some disadvantages in biodistribution. This review focuses on the other promising candidate carrier cells under development and discusses their interaction with specific OVs and future research lines.

Mild and Asymptomatic COVID-19 Convalescents Present Long-Term Endotype of Immunosuppression Associated With Neutrophil Subsets Possessing Regulatory Functions

The SARS-CoV-2 infection [coronavirus disease 2019 (COVID-19)] is associated with severe lymphopenia and impaired immune response, including expansion of myeloid cells with regulatory functions, e.g., so-called low-density neutrophils, containing granulocytic myeloid-derived suppressor cells (LDNs/PMN-MDSCs). These cells have been described in both infections and cancer and are known for their immunosuppressive activity. In the case of COVID-19, long-term complications have been frequently observed (long-COVID). In this context, we aimed to investigate the immune response of COVID-19 convalescents after a mild or asymptomatic course of disease. We enrolled 13 convalescents who underwent a mild or asymptomatic infection with SARS-CoV-2, confirmed by a positive result of the PCR test, and 13 healthy donors without SARS-CoV-2 infection in the past. Whole blood was used for T-cell subpopulation and LDNs/PMN-MDSCs analysis. LDNs/PMN-MDSCs and normal density neutrophils (NDNs) were sorted out by FACS and used for T-cell proliferation assay with autologous T cells activated with anti-CD3 mAb. Serum samples were used for the detection of anti-SARS-CoV-2 neutralizing IgG and GM-CSF concentration. Our results showed that in convalescents, even 3 months after infection, an elevated level of LDNs/PMN-MDSCs is still maintained in the blood, which correlates negatively with the level of CD8+ and double-negative T cells. Moreover, LDNs/PMN-MDSCs and NDNs showed a tendency for affecting the production of anti-SARS-CoV-2 S1 neutralizing antibodies. Surprisingly, our data showed that in addition to LDNs/PMN-MDSCs, NDNs from convalescents also inhibit proliferation of autologous T cells. Additionally, in the convalescent sera, we detected significantly higher concentrations of GM-CSF, indicating the role of emergency granulopoiesis. We conclude that in mild or asymptomatic COVID-19 convalescents, the neutrophil dysfunction, including propagation of PD-L1-positive LDNs/PMN-MDSCs and NDNs, is responsible for long-term endotype of immunosuppression.