Matrix Metalloproteinase-9 in Monocytic Myeloid-Derived Suppressor Cells Correlate with Early Infections and Clinical Outcomes in Allogeneic Hematopoietic Stem Cell Transplantation

Dual roles of myeloid-derived suppressor cells in various diseases: a review

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that originate from bone marrow stem cells. In pathological conditions, such as autoimmune disorders, allergies, infections, and cancer, normal myelopoiesis is altered to facilitate the formation of MDSCs. MDSCs were first shown to promote cancer initiation and progression by immunosuppression with the assistance of various chemokines and cytokines. Recently, various studies have demonstrated that MDSCs play two distinct roles depending on the physiological and pathological conditions. MDSCs have protective roles in autoimmune disorders (such as uveoretinitis, multiple sclerosis, rheumatoid arthritis, ankylosing spondylitis, type 1 diabetes, autoimmune hepatitis, inflammatory bowel disease, alopecia areata, and systemic lupus erythematosus), allergies, and organ transplantation. However, they play negative roles in infections and various cancers. Several immunosuppressive functions and mechanisms of MDSCs have been determined in different disease conditions. This review comprehensively discusses the associations between MDSCs and various pathological conditions and briefly describes therapeutic approaches.

Highly immunosuppressive myeloid cells correlate with early relapse after allogeneic stem cell transplantation

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative treatment for myeloid malignancies such as some acute myeloid leukemias (AML) and high-risk myelodysplastic syndromes (MDS). It aims to eradicate the malignant clone using immunocompetent donor cells (graft-versus-leukemia effect, GVL). Unfortunately, relapse is the primary cause of transplant failure mainly related on HLA loss or downregulation and upregulation of inhibitory ligands on blasts which result in donor immune effector dysfunctions.

METHODS

Between 2018 and 2021, we conducted a monocentric prospective study including 61 consecutive patients transplanted for AML or high-risk MDS. We longitudinally investigated immune cells at days + 30, + 90 and + 180 post-transplant from bone marrow and peripheral blood. We assessed the dynamics between myeloid derived suppressor cells (MDSCs) and T-cells.

RESULTS

Among the 61 patients, 45 did not relapse over the first 12 months while 16 relapsed during the first year post-transplant. Through months 1 to 6, comparison with healthy donors revealed an heterogenous increase in MDSC frequency. In all recipients, the predominant MDSC subset was granulocytic with no specific phenotypic relapse signature. However, in relapsed patients, in vitro and in vivo functional analyses revealed that MDSCs from peripheral blood were highly immunosuppressive from day + 30 onwards, with an activated NLRP3 inflammasome signature. Only circulating immunosuppressive MDSCs were statistically correlated to circulating double-positive Tim3+LAG3+ exhausted T cells.

CONCLUSION

Our simple in vitro functional assay defining MDSC immunosuppressive properties might serve as an early biomarker of relapse and raise the question of new preventive treatments targeting MDSCs in the future. Trial registration NCT03357172.

Assessment of monocytic-myeloid-derived suppressive cells (M-MDSC) before and after allogeneic hematopoietic stem cell transplantation in acute leukemia patients

In this monocentric prospective study, the influence on long-term outcomes of peripheral blood levels of monocytic-myeloid-derived suppressive cells (M-MDSC) was investigated in 56 patients with acute leukemia (myeloid n = 47; lymphoid n = 9) before and after (Days+60/+90) allogeneic hematopoietic stem cell transplantation (Allo-HSCT). A risk of relapse was found to be associated with a level of pregraft M-MDSC above 1.4% by ROC curve analysis. In multivariate analysis, this threshold retained a strong statistical significance (HR: 5.94 [2.09-16.87], p = 0.001). Considering only the group of patients who were in complete remission prior to Allo-HSCT (n = 44), a significant prediction of relapse was found to be associated, in multivariate analysis, with a level of pregraft M-MDSC above 1.4% (HR: 55.01 [14.95-202.37], p < 0.001) together with pregraft-positive measurable -residual disease (MRD) (HR: 11.04 [1.89-64.67], p = 0.008). A poorer OS (HR: 6.05 [1.24-29.59], p = 0.026) and disease-free survival (HR: 6.52 [1.41-30.19], p = 0.016) were also associated with higher levels of pregraft M-MDSC. Remarkably, no relapse occurred in patients with pregraft-negative MRD and ≤1.4% of M-MDSC (vs. a 3-year relapse rate of 60% for others, p = 0.004). Patients developing grade 3-4 acute graft-versus-host-disease (GVHD, median occurrence: day+30 posttransplant) showed significantly higher levels of M-MDSC% at days +60 and +90, suggesting a possible amplification of these immunosuppressive cells as a reaction to GVHD. In conclusion, this prospective study demonstrates a negative impact of higher proportions of peripheral M-MDSC before Allo-HSCT in leukemic patients. This paves the way to potential therapeutic intervention to decrease M-MDSC levels before Allo-HSCT and thus perhaps the incidence of relapse in such patients.

Modulation of T-cell function by myeloid-derived suppressor cells in hematological malignancies

Myeloid-derived suppressor cells (MDSCs) are pathologically activated neutrophils and monocytes that negatively regulate the immune response to cancer and chronic infections. Abnormal myelopoiesis and pathological activation of myeloid cells generate this heterogeneous population of myeloid-derived suppressor cells. They are characterized by their distinct transcription, phenotypic, biochemical, and functional features. In the tumor microenvironment (TME), myeloid-derived suppressor cells represent an important class of immunosuppressive cells that correlate with tumor burden, stage, and a poor prognosis. Myeloid-derived suppressor cells exert a strong immunosuppressive effect on T-cells (and a broad range of other immune cells), by blocking lymphocyte homing, increasing production of reactive oxygen and nitrogen species, promoting secretion of various cytokines, chemokines, and immune regulatory molecules, stimulation of other immunosuppressive cells, depletion of various metabolites, and upregulation of immune checkpoint molecules. Additionally, the heterogeneity of myeloid-derived suppressor cells in cancer makes their identification challenging. Overall, they serve as a major obstacle for many cancer immunotherapies and targeting them could be a favorable strategy to improve the effectiveness of immunotherapeutic interventions. However, in hematological malignancies, particularly B-cell malignancies, the clinical outcomes of targeting these myeloid-derived suppressor cells is a field that is still to be explored. This review summarizes the complex biology of myeloid-derived suppressor cells with an emphasis on the immunosuppressive pathways used by myeloid-derived suppressor cells to modulate T-cell function in hematological malignancies. In addition, we describe the challenges, therapeutic strategies, and clinical relevance of targeting myeloid-derived suppressor cells in these diseases.

Single-cell transcriptome profiling reveals heterogeneous neutrophils with prognostic values in sepsis

Neutrophils constitute the largest proportion of nucleated peripheral blood cells, and neutrophils have substantial heterogeneity. We profiled nearly 300,000 human peripheral blood cells in this study using single-cell RNA sequencing. A large proportion (>50%) of these cells were annotated as neutrophils. Neutrophils were further clustered into four subtypes, including Neu1, Neu2, Neu3, and Neu4. Neu1 is characterized by high expression of MMP9, HP, and RGL4. Neu1 was associated with septic shock and significantly correlated with the sequential organ failure assessment (SOFA) score. A gene expression module in Neu1 named Neu1_C (characterized by expression of NFKBIA, CXCL8, G0S2, and FTH1) was highly predictive of septic shock with an area under the curve of 0.81. The results were extensively validated in external bulk datasets by using single-cell deconvolution methods. In summary, our study establishes a general framework for studying neutrophil-related mechanisms, prognostic biomarkers, and potential therapeutic targets for septic shock.

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Neutrophils were clustered into four subtypes, including Neu1, Neu2, Neu3, and Neu4

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Neu1 was associated with septic shock

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Neu1 was correlated with the sequential organ failure assessment (SOFA) score

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A gene expression module in Neu1 named Neu1_C was highly predictive of septic shock

Myeloid-derived suppressor cells in hematologic malignancies: two sides of the same coin

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of bone marrow cells originating from immature myeloid cells. They exert potent immunosuppressive activity and are closely associated with the development of various diseases such as malignancies, infections, and inflammation. In malignant tumors, MDSCs, one of the most dominant cellular components comprising the tumor microenvironment, play a crucial role in tumor growth, drug resistance, recurrence, and immune escape. Although the role of MDSCs in solid tumors is currently being extensively studied, little is known about their role in hematologic malignancies. In this review, we comprehensively summarized and reviewed the different roles of MDSCs in hematologic malignancies and hematopoietic stem cell transplantation, and finally discussed current targeted therapeutic strategies.Affiliation: Kindly check and confirm the processed affiliations are correct. Amend if any.correct

Potential Strategies to Improve the Effectiveness of Drug Therapy by Changing Factors Related to Tumor Microenvironment

A tumor microenvironment (TME) is composed of various cell types and extracellular components. It contains tumor cells and is nourished by a network of blood vessels. The TME not only plays a significant role in the occurrence, development, and metastasis of tumors but also has a far-reaching impact on the effect of therapeutics. Continuous interaction between tumor cells and the environment, which is mediated by their environment, may lead to drug resistance. In this review, we focus on the key cellular components of the TME and the potential strategies to improve the effectiveness of drug therapy by changing their related factors.

IDO1 scavenges reactive oxygen species in myeloid-derived suppressor cells to prevent graft-versus-host disease

This study reveals that the tryptophan-degrading reaction catalyzed by indoleamine 2,3-dioxygenase 1 (IDO1) is linked to reactive oxygen species (ROS) scavenging in Gr-1⁺CD11b⁺ myeloid cells. The IDO1-mediated ROS scavenging promotes myeloid-derived suppressor cell characteristics in Gr-1⁺CD11b⁺ cells, suppressing their differentiation into proinflammatory neutrophils. These results could explain the increased lethality in graft-versus-host disease as well as the enhanced proinflammatory and reduced regulatory T cell responses after transplantation of IDO1-deficient bone marrow cells. Our findings provide a mechanistic insight into the immune-modulatory roles of IDO1.

Tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase 1 (IDO1) also has an immunological function to suppress T cell activation in inflammatory circumstances, including graft-versus-host disease (GVHD), a fatal complication after allogeneic bone marrow transplantation (allo-BMT). Although the mononuclear cell expression of IDO1 has been associated with improved outcomes in GVHD, the underlying mechanisms remain unclear. Herein, we used IDO-deficient (Ido1^−/−) BMT to understand why myeloid IDO limits the severity of GVHD. Hosts with Ido1^−/− BM exhibited increased lethality, with enhanced proinflammatory and reduced regulatory T cell responses compared with wild type (WT) allo-BMT controls. Despite the comparable expression of the myeloid-derived suppressor cell (MDSC) mediators, arginase-1, inducible nitric oxide synthase, and interleukin 10, Ido1^−/− Gr-1⁺CD11b⁺ cells from allo-BMT or in vitro BM culture showed compromised immune-suppressive functions and were skewed toward the Ly6C^lowLy6G^hi subset, compared with the WT counterparts. Importantly, Ido1^−/−Gr-1⁺CD11b⁺ cells exhibited elevated levels of reactive oxygen species (ROS) and neutrophil numbers. These characteristics were rescued by human IDO1 with intact heme-binding and catalytic activities and were recapitulated by the treatment of WT cells with the IDO1 inhibitor L1-methyl tryptophan. ROS scavenging by N-acetylcysteine reverted the Ido1^−/−Gr-1⁺CD11b⁺ composition and function to an MDSC state, as well as improved the survival of GVHD hosts with Ido1^−/− BM. In summary, myeloid-derived IDO1 enhances GVHD survival by regulating ROS levels and limiting the ability of Gr-1⁺CD11b⁺ MDSCs to differentiate into proinflammatory neutrophils. Our findings provide a mechanistic insight into the immune-regulatory roles of the metabolic enzyme IDO1.

Cytokine Overproduction and Immune System Dysregulation in alloHSCT and COVID-19 Patients

The COVID-19 pathomechanism depends on (i) the pathogenicity of the virus, (ii) ability of the immune system to respond to the cytopathic effect of the virus infection, (iii) co-morbidities. Inflammatory cytokine production constitutes a hallmark of COVID-19 that is facilitated by inability of adaptive immunity to control virus invasion. The effect of cytokine release syndrome is deleterious, but the severity of it depends on other confounding factors: age and comorbidities. In this study, we analyze the literature data on the post-transplant course of allogeneic hematopoietic stem cell transplanted (alloHSCT) patients, which is affected by generated inflammatory cytokines. The sequence of events boosting cytokine production was analyzed in relation to clinical and laboratory data highlighting the impact of cytokine generation on the post-transplant course. The collected data were compared to those from studies on COVID-19 patients. The similarities are: (i) the damage/pathogen-associated molecular pattern (DAMP/PAMP) stage is similar except for the initiation hit being sterile in alloHSCT (toxic damage of conditioning regimen) and viral in COVID-19; (ii) genetic host-derived factors play a role; (iii) adaptive immunity fails, DAMP signal(s) increases, over-production of cytokines occurs; (iv) monocytes lacking HLADR expression emerge, being suppressor cells hampering adaptive immunity; (v) immune system homeostasis is broken, the patient's status deteriorates to bed dependency, leading to hypo-oxygenation and malnutrition, which in turn stimulates the intracellular alert pathways with vigorous transcription of cytokine genes. All starts with the interaction between DAMPs with appropriate receptors, which leads to the production of pro-inflammatory cytokines, the inflammatory process spreads, tissue is damaged, DAMPs are released and a vicious cycle occurs. Attempts to modify intracellular signaling pathways in patients with post-alloHSCT graft vs host disease have already been undertaken. The similarities documented in this study show that this approach may also be used in COVID-19 patients for tuning signal transduction processes to interrupt the cycle that powers the cytokine overproduction.

The Role of Myeloid-Derived Suppressor Cells (MDSCs) in Graft-versus-Host Disease (GVHD)

Background: Myeloid-derived suppressor cells (MDSCs) are implicated in the complex interplay involving graft-versus-leukemia (GVL) effects and graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HCT) in hematologic malignancies. Methods: A review of literature through PubMed was undertaken to summarize the published evidence on the pathophysiology and clinical implications of MDSCs in allo-HCT. Literature sources published in English since 1978 were searched, using the terms Natural Suppressor (NS) cells, MDSCs, GVHD, and allo-HCT. Results: In vivo studies demonstrated that MDSCs derived from mobilization protocols could strongly suppress allo-responses mediated by T cells and enhance T-Reg activity, thus inhibiting GVHD toxicity. However, the influence of MDSCs on the GVL effect is not fully defined. Conclusions: The induction or maintenance of MDSC suppressive function would be advantageous in suppressing inflammation associated with GVHD. Pathways involved in MDSC metabolism and the inflammasome signaling are a promising field of study to elucidate the function of MDSCs in the pathogenesis of GVHD and translate these findings to a clinical setting.

Dietary conjugated linoleic acid links reduced intestinal inflammation to amelioration of CNS autoimmunity

A close interaction between gut immune responses and distant organ-specific autoimmunity including the CNS in multiple sclerosis has been established in recent years. This so-called gut–CNS axis can be shaped by dietary factors, either directly or via indirect modulation of the gut microbiome and its metabolites. Here, we report that dietary supplementation with conjugated linoleic acid, a mixture of linoleic acid isomers, ameliorates CNS autoimmunity in a spontaneous mouse model of multiple sclerosis, accompanied by an attenuation of intestinal barrier dysfunction and inflammation as well as an increase in intestinal myeloid-derived suppressor-like cells. Protective effects of dietary supplementation with conjugated linoleic acid were not abrogated upon microbiota eradication, indicating that the microbiome is dispensable for these conjugated linoleic acid-mediated effects. Instead, we observed a range of direct anti-inflammatory effects of conjugated linoleic acid on murine myeloid cells including an enhanced IL10 production and the capacity to suppress T-cell proliferation. Finally, in a human pilot study in patients with multiple sclerosis (n = 15, under first-line disease-modifying treatment), dietary conjugated linoleic acid-supplementation for 6 months significantly enhanced the anti-inflammatory profiles as well as functional signatures of circulating myeloid cells. Together, our results identify conjugated linoleic acid as a potent modulator of the gut–CNS axis by targeting myeloid cells in the intestine, which in turn control encephalitogenic T-cell responses.

The diverse roles of myeloid derived suppressor cells in mucosal immunity

The mucosal immune system plays a vital role in protecting the host from the external environment. Its major challenge is to balance immune responses against harmful and harmless agents and serve as a 'homeostatic gate keeper'. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of undifferentiated cells that are characterized by an immunoregulatory and immunosuppressive phenotype. Herein we postulate that MDSCs may be involved in shaping immune responses related to mucosal immunity, due to their immunomodulatory and tissue remodeling functions. Until recently, MDSCs were investigated mainly in cancerous diseases, where they induce and contribute to an immunosuppressive and inflammatory environment that favors tumor development. However, it is now becoming clear that MDSCs participate in non-cancerous conditions such as chronic infections, autoimmune diseases, pregnancy, aging processes and immune tolerance to commensal microbiota at mucosal sites. Since MDSCs are found in the periphery only in small numbers under normal conditions, their role is highlighted during pathologies characterized by acute or chronic inflammation, when they accumulate and become activated. In this review, we describe several aspects of the current knowledge characterizing MDSCs and their involvement in the regulation of the mucosal epithelial barrier, their crosstalk with commensal microbiota and pathogenic microorganisms, and their complex interactions with a variety of surrounding regulatory and effector immune cells. Finally, we discuss the beneficial and harmful outcomes of the MDSC regulatory functions in diseases affecting mucosal tissues. We wish to illuminate the pivotal role of MDSCs in mucosal immunity, the limitations in our understanding of all the players and the intricate challenges stemming from the complex interactions of MDSCs with their environment.

Long-Term Results of Total Hip Arthroplasty in Young Patients With Osteonecrosis After Allogeneic Bone Marrow Transplantation for Hematological Disease: A Multicenter, Propensity-Matched Cohort Study With a Mean 11-Year Follow-Up

BACKGROUND

The number of young patients with hematological disease requiring total hip arthroplasty (THA) is expected to increase. We aimed to investigate the long-term THA outcomes in patients with osteonecrosis of the femoral head (ONFH) following allogeneic bone marrow transplantation (BMT) for hematological disease.

METHODS

All patients who underwent THA for osteonecrosis after BMT from 1997 to 2012 were identified at 2 institutions. Using propensity scores, 75 THAs in 45 patients were matched for age, gender, body mass index, American Society of Anesthesiologists score, and year of surgery with 75 THAs in 58 patients with idiopathic ONFH without a history of hematological disease (1:1 ratio). The mean age at surgery was 36.7 years and 52% were men. Clinical and radiographic evaluations were performed and clinical scores were obtained at last follow-up. Kaplan-Meier analyses were used to compare survivorship.

RESULTS

At a mean follow-up of 10.6 ± 3.5 years, clinical, radiographic, and survivorship outcomes, and the Harris hip scores were similar between both groups. The 13-year survivorship for all-cause revision was 93.4% for the BMT group and 95% for the control group (P = .928). No significant differences were observed between groups in the rates of reoperation (4% vs 5.3%, P = 1.000), 90-day readmission (all 5.3%), or overall mortality (4.4% vs 1.7%, P = .681). No hips had periprosthetic joint infection or septic loosening in either group. Osteolysis occurred in none of the BMT patients and in 2 hips (2.7%) of the control patients (P = .497).

CONCLUSION

This large cohort multicenter survey at 11-year follow-up shows that contemporary cementless THA in young hematological disease patients after allogeneic BMT is not associated with a higher risk for surgical complications, revision, reoperation, readmission, and mortality compared to a matched cohort of idiopathic ONFH.

Cellular therapies for graft-versus-host disease: a tale of tissue repair and tolerance

The success of allogeneic hematopoietic cell transplantation depends heavily on the delicate balance between the activity of the donor immune system against malignant and nonmalignant cells of the recipient. Abrogation of alloreactivity will lead to disease relapse, whereas untamed allo-immune responses will lead to lethal graft-versus-host disease (GVHD). A number of cell types have been identified that can be used to suppress alloreactive immune cells and prevent lethal GVHD in mice. Of those, mesenchymal stromal cells and, to a lesser extent, regulatory T cells have demonstrated efficacy in humans. Ideally, cellular therapy for GVHD will not affect alloreactive immune responses against tumor cells. The importance of tissue damage in the pathophysiology of GVHD rationalizes the development of cells that support tissue homeostasis and repair, such as innate lymphoid cells. We discuss recent developments in the field of cellular therapy to prevent and treat acute and chronic GVHD, in the context of GVHD pathophysiology.

Early Posttransplant Mobilization of Monocytic Myeloid-derived Suppressor Cell Correlates With Increase in Soluble Immunosuppressive Factors and Predicts Cancer in Kidney Recipients

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) increase in patients with cancer and are associated with poor prognosis; however, their role in transplantation is not yet understood. Here we aimed to study the MDSC effects on the evolution of kidney transplant recipients (KTRs).

METHODS

A cohort of 229 KTRs was prospectively analyzed. Two myeloid cells subsets. CD11bCD33CD14CD15HLA-DR (monocytic MDSC [M-MDSC]) and CD11bCD33CD14CD15HLA-DR (monocytes), were defined by flow cytometry. The suppressive capacity of myeloid cells was tested in cocultures with autologous lymphocytes. Suppressive soluble factors, cytokines, anti-HLA antibodies, and total antioxidant capacity were quantified in plasma.

RESULTS

Pretransplant, M-MDSC, and monocytes were similar in KTRs and healthy volunteers. M-MDSCs increased immediately posttransplantation and suppressed CD4 and CD8 T cells proliferation. M-MDSCs remained high for 1 y posttransplantation. Higher M-MDSC counts at day 14 posttransplant were observed in patients who subsequently developed cancer, and KTRs with higher M-MDSC at day 14 had significantly lower malignancy-free survival. Day 14 M-MDSC >179.2 per microliter conferred 6.98 times (95% confidence interval, 1.28-37.69) more risk to develop cancer, independently from age, gender, and immunosuppression. Early posttransplant M-MDSCs were lower in patients with enhanced alloimmune response as represented by anti-HLA sensitization. M-MDSC counts correlated with higher circulatory suppressive factors arginase-1 and interleukin-10, and lower total antioxidant capacity.

CONCLUSIONS

Early posttransplant mobilization of M-MDSCs predicts cancer and adds risk as an independent factor. M-MDSC may favor an immunosuppressive environment that promotes tumoral development.

CD14 + HLADR - blood values in patients after alloHSCT are highly predictive of survival and infectious complications

BACKGROUND

Cytokine storm described in patients after allogeneic haematopoietic stem cell transplantation (alloHSCT) is associated with the appearance of CD14 + HLADR - in the blood.

METHODS

To study the role of CD14 + HLADR - cells 223 patients after alloHSCT followed from 1 month to 15 years. The methods used included flow cytometry for blood cells profiling, nucleic acid tests for viral reactivation, and physician care according to the Polish and international guidelines.

RESULTS

We found that CD14 + HLADR - peak values determined during the first 60 post-transplant days were higher in the patients who died than in those who survived in this time interval (mean ± SEM: 3.78 ± 0.67% vs 2.38 ± 0.65%, p < 0.001). Receiver operating characteristic (ROC) analysis showed that CD14 + HLADR - cells level in the blood at cut-off point at 0.71% discriminated the patients as to survival; the patients above the threshold had poorer survival (Kaplan-Meier curve covering 15-year observation) than those below (0.19 vs 0.46, p < 0.001). Infections prevailed other causes of death in the high blood CD14 + HLADR - group (0.61 vs 0.38, p = 0.057). ROC analysis defined the CD4+ blood level at 17.70% as not significantly associated with survival. Multivariate analysis revealed that CD14 + HLADR - cells (HR = 3.47, p < 0.001) and the presence of acute graft-versus-host disease (aGvHD) grade ≥ 3 (HR = 3.82, p = 0.005) adversely impacted the survival.

CONCLUSIONS

CD14 + HLADR - cells can serve as a biomarker for the risk of fatal complications frequently associated with infections.

Correlation between MDSC and Immune Tolerance in Transplantation: Cytokines, Pathways and Cell-cell Interaction

MDSCs play an important role in the induction of immune tolerance. Cytokines and chemokines (GM-CSF, IL-6) contributed to the expansion, accumulation of MDSCs, and MDSCs function through iNOS, arginase and PD-L1. MDSCs are recruited and regulated through JAK/STAT, mTOR and Raf/MEK/ERK signaling pathways. MDSCs' immunosuppressive functions were realized through Tregs-mediated pathways and their direct suppression of immune cells. All of the above contribute to the MDSC-related immune tolerance in transplantation. MDSCs have huge potential in prolonging graft survival and reducing rejection through different ways and many other factors worthy to be further investigated are also introduced.

Myeloid-Derived Suppressor Cells in the Context of Allogeneic Hematopoietic Stem Cell Transplantation

Myeloid-derived suppressor cells (MDSCs) are innate immune cells that acquire the capacity to suppress adaptive immune responses. In the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT), MDSCs (in the donor graft and in the recipient, after allo-HSCT) might mediate immune suppression through multiple mechanisms. However, it remains unclear how MDSCs can be distinguished from their normal myeloid counterparts in the hematopoietic stem cell donor graft and during immune reconstitution after allo-HSCT in the recipient. Our ability to understand their exact role in allo-HSCT is limited by the absence of a specific gene signature or surface markers for identifying MDSCs among myeloid cells and by their plasticity in different microenvironments. According to various studies, MDSCs might induce transplant tolerance and control graft vs. host disease (GVHD), but their impact on the graft vs. tumor effect (GVT) is not fully understood. In fact, we know that MDSCs commonly expand in patients with cancer, and they are thought to promote hematological malignancy progression. However, little is known about whether depleting them might be an effective strategy for enhancing GVT effects. Here, we review data published over the past 40 years on allo-HSCT to delineate the different MDSC subsets, and their abilities to induce transplant tolerance and preserve the GVT effect. This review will provide a basis for determining whether one MDSC subset might be proposed as the most appropriate candidate for cellular therapies, due to its ability to modulate GVHD.

DNA methylation in the promoters of PD-L1, MMP9, ARG1, galectin-9, TIM-3, VISTA and TGF-β genes in HLA-DR- myeloid cells, compared with HLA-DR+ antigen-presenting cells

Myeloid cells, including antigen-presenting cells (APCs) and myeloid-derived suppressor cells (MDSCs) play opposing roles to orchestrate innate and adaptive immune responses during physiological and pathological conditions. We investigated the role of DNA methylation in regulating the transcription of inhibitory/suppressive molecules in myeloid suppressive cells (identified as CD33⁺HLA-DR^-) in comparison to APCs. We selected a number of immune checkpoints (ICs), IC ligands, and immunosuppressive molecules that have been implicated in MDSC function, including PD-L1, TIM-3, VISTA, galectin-9, TGF-β, ARG1 and MMP9. We examined their mRNA expression levels, and investigated whether DNA methylation regulates their transcription in sorted myeloid cell subpopulations. We found that mRNA levels of PD-L1, TIM-3, TGF-β, ARG1 and MMP9 in CD33⁺HLA-DR^- cells were higher than APCs. However, VISTA and galectin-9 mRNA levels were relatively similar in both myeloid subpopulations. CpG islands in the promoter regions of TGF-β1, TIM-3 and ARG1 were highly unmethylated in CD33⁺HLA-DR^-cells, compared with APCs, suggesting that DNA methylation is one of the key mechanisms, which regulate their expression. However, we did not find differences in the methylation status of PD-L1 and MMP9 between CD33⁺HLA-DR^- and APCs, suggesting that their transcription could be regulated via other genetic and epigenetic mechanisms. The promoter methylation status of VISTA was relatively similar in both myeloid subpopulations. This study provides novel insights into the epigenetic mechanisms, which control the expression of inhibitory/suppressive molecules in circulating CD33⁺HLA-DR^- cells in a steady-state condition, possibly to maintain immune tolerance and haemostasis.

Lung resided monocytic myeloid-derived suppressor cells contribute to premetastatic niche formation by enhancing MMP-9 expression

In cancer patients, the prevalence of myeloid-derived suppressor cells (MDSCs) is correlated with the degree of malignancy. In the present study, we investigated the role of circulating M-MDSCs in premetastatic niche formation using a mouse syngeneic tumor model and found that there was an increased frequency of M-MDSCs in the peripheral blood of tumor-bearing mice. M-MDSCs tracking and lung tissue histological analyses revealed that the malignant conditions promote the residence of circulating M-MDSCs and increased tumor cell arrest in the lungs. We further found that MMP-9 expression was increased in the circulating M-MDSCs and the administration of an MMP-9 inhibitor suppressed M-MDSCs transplantation-induced tumor cell arrest in the lung. Therefore, our findings suggest that the expansion of circulating M-MDSCs during tumor progression contributes to premetastatic niche formation by increasing MMP-9 expression.

Alteration of the Intestinal Microbiota by Broad-Spectrum Antibiotic Use Correlates with the Occurrence of Intestinal Graft-versus-Host Disease

Patients undergoing hematopoietic stem cell transplantation (HSCT) frequently receive empiric antibiotics during the neutropenic period before engraftment. Several recent studies have shown that anaerobes in the intestine are important mediators of intestinal homeostasis, and that commensal bacteria can be potent modulators of the severity of acute graft-versus-host disease (aGVHD). However, the relationships among the type of antibiotic used during the neutropenic period, changes in the intestinal microbiota, and subsequent occurrence of aGVHD are not clear. In this study, a total of 211 patients undergoing HSCT were stratified into 3 groups: patients not treated with any antibiotics during the neutropenic period (group 1; n = 43), patients treated with cefepime only (group 2; n = 87), and patients treated with carbapenem antibiotics, defined as meropenem or prepenem with or without previous cefepime therapy (group 3; n = 81). Intestinal microbiota analyses were performed on pre- and post-HSCT stool samples, and immunophenotypic analyses were performed on pre- and post-HSCT peripheral blood samples. Among the 211 patients, 95 (45%) developed aGVHD (grade ≥II), including 54 with intestinal GVHD. The incidence of intestinal GVHD was higher in group 3 compared with group 1 and group 2 (32.1%, 11.6%, and 26.4%, respectively; P = .044). After adjusting for potentially significant variables identified by univariate analysis, multivariate analyses identified broad-spectrum antibiotic use during the neutropenic period as associated with the occurrence of intestinal GVHD (hazard ratio, 3.25; 95% confidence interval, 1.13 to 9.34; P = .029). Accordingly, loss of bacterial diversity in terms of alterations in intestinal microbiota after HSCT was observed in patients who received broad-spectrum antibiotics. Moreover, alterations in the frequencies of several intestinal bacteria phyla were associated with the occurrence of intestinal GVHD. Evaluation of circulating immune cell subsets according to type of antibiotic used during the neutropenic period revealed delayed recovery of myeloid-derived suppressor cells in the broad-spectrum antibiotic use group. Our data indicate that the use of broad-spectrum antibiotics during the neutropenic period is associated with a higher incidence of intestinal GVHD via loss of microbiome diversity. Further studies are needed to determine whether maintaining bacterial diversity can help prevent the development of aGVHD.

Predictive Role of Circulating Immune Cell Subtypes Early after Allogeneic Hematopoietic Stem Cell Transplantation in Patients with Acute Leukemia

Background and Objectives

Cells of innate immunity normally recover in the first weeks to months after allogenenic hematopoietic stem cell transplantation (allo-HSCT). Their relevance in terms of graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effect is largely unknown. The predictive role of early recovery in the immune cells on acute GVHD and GVL effect after allo-HSCT was investigated in patients with acute leukemia who achieved the first complete remission.

Methods

Peripheral blood samples were taken at the median of 14 days (range, 12~29 days) after allo-HSCT. A cohort including 119 samples and characteristics of patients were analyzed. Immune cell populations were identified by flow cytometry.

Results

The median age was 49.0 years (range, 21~69) at transplantation. Univariate analysis showed that age less than 40 years old, lower frequencies of CD8⁺ T cells, invariant natural killer T (iNKT) cells, monocytic myeloid derived suppressor cells (M-MDSCs) and higher frequency of immature MDSCs were associated with occurrence of grade III–IV acute GVHD. Multivariate analyses showed that iNKT cells (hazard ratio (HR), 0.453, 95% CI, 0.091~0.844, p=0.024) and M-MDSCs (HR, 0.271, 95% CI, 0.078~0.937, p=0.039) were independent factors. Combination of higher frequencies of both cell subsets was associated with lower incidence of grade III–IV acute GVHD, whereas patients with lower frequency of iNKT cells and higher frequency of M-MDSCs showed significant higher probability of relapse.

Conclusions

iNKT cells and M-MDSCs could be relevant cell biomarkers for predicting acute GVHD and/or relapse in acute leukemia patients treated with allo-HSCT.

Expression and Activity of Matrix Metalloproteinases in Leukemia

Matrix metalloproteinases (MMPs) are responsible for the degradation of extracellular matrix components and hence play a crucial role in physiological and pathologic processes. The imbalance between the expression of MMPs and their inhibitors can be effective in leukemic cell processes such as migration, angiogenesis, survival, and apoptosis, playing a key role in the progression and prognosis of leukemia. In this review, we discuss the potential involvement of MMPs and their inhibitors in the pathogenesis and progression of leukemia by examining their role in the prognosis of leukemia. Inducing leukemic cell growth, migration, invasiveness, and angiogenesis are the main roles of MMPs in leukemia progression mediated by their degradative activity. Given the important role of MMPs in leukemia progression, further clinical trials are needed to confirm the link between MMPs' expressions and leukemia prognosis. It is hoped to use MMPs as therapeutic targets to improve patients' health by recognizing the prognostic value of MMPs in leukemia and their effect on the progression of these malignancies and their response to treatment.

Different role of circulating myeloid-derived suppressor cells in patients with multiple myeloma undergoing autologous stem cell transplantation

Background

The aim of this study is to evaluate the prognostic impact of myeloid-derived suppressor cells (MDSCs) in multiple myeloma (MM) in the context of autologous stem cell transplantation (ASCT).

Methods

Peripheral blood samples were collected for measuring monocytic (M-) MDSCs (CD14^posHLA-DR^low/neg) and early-stage (E-) MDSCs (Lin^negHLA-DR^negCD33^posCD11b^pos) before and after ASCT. Clinical outcomes following ASCT differed according to the frequency of each MDSC phenotype.

Results

In the pre-ASCT analyses, lower M-MDSCs (<median) but not E-MDSCs were associated with a longer time to progression (TTP), whereas both MDSC phenotypes post-ASCT did not have a role in TTP. Both MDSC phenotypes pre-ASCT but not post-ASCT similarly suppressed in vitro autologous T and natural killer T cell proliferation. Importantly, pre-ASCT M-MDSCs more strongly inhibited the in vitro cytotoxic effect of melphalan compared with pre-ASCT E-MDSCs. Transcriptome analysis of each isolated MDSC subtype showed that expression of osteoclastic differentiation factors, particularly colony-stimulating factor 1 receptor (CSF1R), was significantly increased in M-MDSCs pre-ASCT. Finally, blockade of CSF1R substantially recovered the melphalan-induced cytotoxicity reduced by pre-ASCT M-MDSCs.

Conclusions

Our data demonstrate that pre-ASCT M-MDSCs are correlated with poor clinical outcomes after ASCT through reduced cytotoxicity of melphalan. We propose that targeting CSF1R on these cells may improve the results of ASCT in MM.

Electronic supplementary material

The online version of this article (10.1186/s40425-018-0491-y) contains supplementary material, which is available to authorized users.

Early Plasma Matrix Metalloproteinase Profiles. A Novel Pathway in Pediatric Acute Respiratory Distress Syndrome

RATIONALE

MMPs (Matrix metalloproteinases) and their endogenous tissue inhibitors may contribute to lung injury through extracellular matrix degradation and modulation of inflammation and fibrosis.

OBJECTIVES

To test for an association between MMP pathway proteins and inflammation, endothelial dysfunction, and clinical outcomes.

METHODS

We measured MMPs in plasma collected on acute respiratory distress syndrome (ARDS) Day 1 from 235 children at five hospitals between 2008 and 2017. We used latent class analysis to identify patients with distinct MMP profiles and then associated those profiles with markers of inflammation (IL-1RA, -6, -8, -10, and -18; macrophage inflammatory protein-1α and -1β; tumor necrosis factor-α and -R2), endothelial injury (angiopoietin-2, von Willebrand factor, soluble thrombomodulin), impaired oxygenation (PaO2/FiO2 [P/F] ratio, oxygenation index), morbidity, and mortality.

MEASUREMENTS AND MAIN RESULTS

In geographically distinct derivation and validation cohorts, approximately one-third of patients demonstrated an MMP profile characterized by elevated MMP-1, -2, -3, -7, and -8 and tissue inhibitor of metalloproteinase-1 and -2; and depressed active and total MMP-9. This MMP profile was associated with multiple markers of inflammation, endothelial injury, and impaired oxygenation on Day 1 of ARDS, and conferred fourfold increased odds of mortality or severe morbidity independent of the P/F ratio and other confounders (95% confidence interval, 2.1-7.6; P < 0.001). Logistic regression using both the P/F ratio and MMP profiles was superior to the P/F ratio alone in prognosticating mortality or severe morbidity (area under the receiver operating characteristic curve, 0.75; 95% confidence interval, 0.68-0.82 vs. area under the receiver operating characteristic curve, 0.66; 95% confidence interval, 0.58-0.73; P = 0.009).

CONCLUSIONS

Pediatric patients with ARDS have specific plasma MMP profiles associated with inflammation, endothelial injury, morbidity, and mortality. MMPs may play a role in the pathobiology of children with ARDS.

Engineering CAR-T Cells for Improved Function Against Solid Tumors

Genetic engineering T cells to create clinically applied chimeric antigen receptor (CAR) T cells has led to improved patient outcomes for some forms of hematopoietic malignancies. While this has inspired the biomedical community to develop similar strategies to treat solid tumor patients, challenges such as the immunosuppressive character of the tumor microenvironment, CAR-T cell persistence and trafficking to the tumor seem to limit CAR-T cell efficacy in solid cancers. This review provides an overview of mechanisms that tumors exploit to evade eradication by CAR-T cells as well as emerging approaches that incorporate genetic engineering technologies to improve CAR-T cell activity against solid tumors.

Persistent accumulation of circulating monocytic myeloid-derived suppressor cells contributes to post-infectious immunosuppression in renal transplant recipients with bacterial infection: A pilot study

INTRODUCTION

Post-infectious immunosuppression is disadvantageous to patients' long-term outcomes, especially in transplant recipients receiving large doses of immunosuppressants. A growing body of evidence indicates the immunoregulatory ability of myeloid-derived suppressor cells (MDSCs). We herein investigate the characteristics of monocytic-MDSCs (M-MDSCs) in a cohort of renal transplant recipients with/without infection to clarify the potential involvement in post-infectious immunosuppression.

METHODS

The study prospectively included 28 adult recipients who underwent allogeneic ABO-compatible renal transplant. Blood samples were drawn at day 0, 7, 14, 28, 60 and 90 postoperation. The incidence of infection and treatment strategies were recorded. The frequency and absolute number of peripheral blood M-MDSCs as well as other immune cells were determined by flow cytometry. Immnosuppressive functions of M-MDSCs were analyzed by inhibition of T cells proliferation. mRNA levels of immunosuppressive molecules in sorted M-MDSCs were also examined.

RESULTS

7 recipients were diagnosed with bacterial (n = 5) or viral (n = 2) infection and 3/5 of bacterial-infected recipients suffered from secondary infection during further follow-up. In the non-infected group, M-MDSCs numbers increased transiently during the early postoperative period, however, bacterial but not viral infection led to significant and persistent accumulation of M-MDSCs that remained at high levels after anti-infective treatments. M-MDSCs from infected recipients demonstrated potent ability to suppress T cells proliferation in vitro and negatively correlated with lymphocytes in vivo, yet not in the non-infected group. Inducible nitric oxide synthase (iNOS) mRNA levels were higher in sorted M-MDSCs when compared with monocytes, and suppressive activity was reversed by addition of a NOS inhibitor.

CONCLUSIONS

Circulating M-MDSCs underwent significant and persistent increases after bacterial infection in renal transplant recipients, contributing to post-infectious immunodeficiency. Therefore, special attention should be given to M-MDSCs during the monitoring of immune status and infection management.