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Sepsis-induced immunosuppression increases the risk of chronic infection and reduces survival. Myeloid-derived suppressor cells (MDSCs) expand in the bone marrow and spleen during murine polymicrobial sepsis, contributing to immunosuppression. A better understanding of molecular controls of MDSC production is needed to identify treatment targets. We previously reported that miR-21 and miR-181b couple with transcription factor NFI-A to induce MDSCs during murine sepsis. Here, we expand upon these observations by showing that conditional deletion of the Nfia gene in the myeloid lineage precludes MDSC development. NFI-A-deficient Gr1+CD11b+ myeloid cells are not immunosuppressive and differentiate normally into macrophages and dendritic cells. In contrast, ectopically expressed NFI-A prevents differentiation of these immature Gr1+CD11b+ cells, while converting them into MDSCs. In addition, NFI-A-deficient Gr1+CD11b+ cells decreased, and cells transfected with NFI-A increase expression of miR-21 and miR181b. Our results support a myeloid cell loop in which NFI-A and miR-21 and miR-181b sustain Gr1+CD11b+ MDSC-dependent immunosuppression during sepsis.

RUNX1 overlapping RNA (RUNXOR) is a long noncoding RNA and a key regulator of myeloid-derived suppressor cells (MDSCs) via targeting runt-related transcription factor 1 (RUNX1). We and others have previously reported MDSC expansion and inhibition of host immune responses during viral infections; however, the mechanisms regulating MDSC differentiation and suppressive functions, especially the role of RUNXOR-RUNX1 in the regulation of MDSCs in people living with HIV (PLHIV), remain unknown. In this study, we demonstrate that RUNXOR and RUNX1 expressions are upregulated in MDSCs that expand and accumulate in human PBMCs derived from PLHIV. We found that the upregulation of RUNXOR and RUNX1 is associated with the expressions of several key immunosuppressive molecules, including arginase 1, inducible NO synthase, STAT3, IL-6, and reactive oxygen species. RUNXOR and RUNX1 could positively regulate each other's expression and control the expressions of these suppressive mediators. Specifically, silencing RUNXOR or RUNX1 expression in MDSCs from PLHIV attenuated MDSC expansion and immunosuppressive mediator expressions, whereas overexpressing RUNXOR in CD33+ myeloid precursors from healthy subjects promoted their differentiation into MDSCs and enhanced the expression of these mediators. Moreover, loss of RUNXOR-RUNX1 function in MDSCs improved IFN-γ production from cocultured autologous CD4 T cells derived from PLHIV. These results suggest that the RUNXOR-RUNX1 axis promotes the differentiation and suppressive functions of MDSCs via regulating multiple immunosuppressive signaling molecules and may represent a potential target for immunotherapy in conjunction with antiviral therapy in PLHIV.

Sepsis-induced myeloid-derived suppressor cells (MDSCs) increase mortality risk. We previously identified that long non-coding RNA Hotairm1 supports myeloid precursor shifts to Gr1+CD11b+ MDSCs during mouse sepsis. A major unanswered question is what molecular processes control Hotairm1 expression. In this study, we found by a genetic deletion that a specific PU.1-binding site is indispensable in controlling Hotairm1 transcription. We then identified H3K4me3 and H3K27me3 at the PU.1 site on the Hotairm1 promoter. Controlling an epigenetic switch of Hotairm1 transcription by PU.1 was histone KDM6A demethylase for H3K27me3 that derepressed its transcription with possible contributions from Ezh2 methyltransferase for H3K27me3. KDM6A knockdown in MDSCs increased H3K27me3, decreased H3K4me3, and inhibited Hotairm1 transcription activation by PU.1. These results enlighten clinical translation research of PU.1 epigenetic regulation as a potential sepsis immune-checkpoint treatment site.

Virus-infected cells can regulate non-permissive bystander cells, but the precise mechanisms remain incompletely understood. Here we report that this process can be mediated by transfer of viral RNA-loaded exosomes shed from infected cells to myeloid-derived suppressor cells (MDSCs), which in turn regulate the differentiation and function of T cells during viral infection. Specifically, we demonstrated that patients with chronic hepatitis C virus (HCV) infection exhibited significant increases in T follicular regulatory (TFR) cells and decreases in T follicular helper (TFH) cells. These MDSC-mediated T-cell dysregulations resulted in an increased ratio of TFR/TFH and IL-10 production in peripheral blood. Specifically, co-culture of MDSCs derived from HCV patients with healthy peripheral blood mononuclear cells (PBMCs) induced expansion of TFR, whereas depletion of MDSCs from PBMCs of HCV patients reduced the increases in TFR frequency and IL-10 production, and promoted the differentiation of IFN-γ-producing TFH cells. Importantly, we found that exosomes isolated from the plasma of HCV patients and supernatant of HCV-infected hepatocytes could drive monocytic myeloid cell differentiation into MDSCs. These exosomes were enriched in tetraspanins, such as CD63 and CD81, and contained HCV RNA, but exosomes isolated from patients with antiviral treatment contained no HCV RNA and could not induce MDSC differentiation. Notably, these HCV RNA-containing exosomes (HCV-Exo) were sufficient to induce MDSCs. Furthermore, incubation of healthy myeloid cells with these HCV-Exo inhibited the expression of miR−124, whereas reconstitution of PBMCs with miR−124 abolished the effects of HCV−Exo on MDSC induction. Taken together, these results indicate that HCV-associated exosomes can transfer immunomodulatory viral RNA from infected cells to neighboring immune cells and trigger MDSC expansion, which subsequently promotes TFR differentiation and inhibits TFH function. This study reveals a previously unrecognized path that represents a novel mechanism of immune dysregulation during chronic viral infection.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells identified in mice as Gr-1+CD11b+ cells with the ability to inhibit T cell function. MDSC are emerging as important regulators of T cell mediated immune responses. Current paradigm suggests that despite heterogeneity, all Gr-1+CD11b+ cells are suppressive when exposed to inflammatory stimuli. In vitro evaluation shows MDSC from multiple tissue sites have suppressive activity, and in vivo inhibition of MDSCenhances T cell function. However, the relative capacity of MDSC present at localized inflammatory sites or in peripheral tissues to suppress T cell responses in vivo has not been directly evaluated. Using a tissue specific acute inflammatory prostatitis model, we demonstrate that MDSC inhibition of CD8+ T-cell proliferation is restricted to the inflammatory site.Further, MDSC from inflammatory sites possess immediate capacity to inhibit T-cell function, whereas those isolated from peripheral tissues (spleens and liver) were not suppressive without activation of iNOS by exposure to IFN-_.Using two mouse models of prostate cancer, we extend these findings to thetumor micro-environment. During a chronic inflammatory response induced by tumorgrowth, we show Gr-1+CD11b+ cells from the tumor site possess immediate capacity toregulate effector T cell function whereas those from the spleen do not. In both tumormodels and in our prostatitis model, long term culture of activated T cells with splenicGr-1+CD11b+ cells converted precursor cells into functional MDSC during standard in vitro suppression assays. These data highlight the importance of MDSC in the prostate, and demonstrate the function of MDSC during a localized inflammatory response isrestricted to the site of an ongoing immune responseGrowing evidence suggests that prostatitis associated with chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is mediated in part by the loss of T cell and B cell tolerance to prostate antigens. Clinical data demonstrates the presence of T cell proliferative responses to prostate auto-antigens in CP/CPPS patients. However, the mechanisms leading to this loss of tolerance are not clearly understood, largely because of a lack of available animal models. We report the development of a new mouse model for the study of chronic prostate inflammation (CPI), the Prostate Ovalbumin Expressing Transgenic-3 (POET-3) model. Adoptive transfer of antigen specific OT-I T cells induces CPI characterized by infiltration of exogenous (OT-I) and endogenous T cells into the prostate persisting as long as 45 days after transfer. In vitro and in vivo data demonstrate inflammation induced loss of T cell tolerance to prostate auto-antigens. Auto-antibody responses to prostate antigens were detected in POET-3 mice after induction of CPI. These data have important therapeutic implications for treatment of CPI.

Surgery-induced myeloid derived suppressor cells (sxMDSC)s mediate postoperative suppression of Natural Killer (NK) cells, which enables postoperative cancer recurrence and metastases. Currently, no therapeutics against sxMDSCs have been developed. Recent research has identified that the myeloid-restricted PI3K isoform (PI3Kγ) mediates MDSC activity. I targeted PI3Kγ in sxMDSCs as a therapeutic to reduce postoperative NK cell suppression and metastatic burden. Additionally, I investigated the efficacy of a sxMDSC-specific antibody-drug conjugate (ADC) with a PI3Kγ inhibitor payload. Pharmacological inhibition of PI3Kγ in sxMDSCs led to reduced AKT phosphorylation and reduced suppression of NK cytotoxicity in human and murine models. PI3Kγ inhibition also reduced postoperative metastatic burden. Despite the novelty of the sxMDSC-specific ADC, it didn’t provide considerable benefits in reducing NK cell suppression compared to the unconjugated PI3Kγ inhibitor. However, this is a “first iteration” in what could be a powerful approach to targeting sxMDSCs, thereby preventing postoperative metastatic burden.

The present study has considered cellular and molecular requirements in T cell responses. The central role of T cell growth factors (TCGF) in T cell responses prompted us to study the regulatory events directing TCGF production in lectin stimulated cultures. It was found that normal spleen cells, activated with Concanavalin A for 24 h, develop suppressive cells that block de novo TCGF production by fresh spleen cells. The induction time for effector suppressor cells (nonadherent, Lyt-2-positive T cells) was found to be 18 h and to parallel the termination of TCGF production in situ. The suppressive mechanism is neither iji situ absorption of TCGF produced at control rates nor killing of TCGF producing cells. These results suggest that suppression of TCGF production is an active process which directly and reversibly blocks TCGF-producing cells. This study also indicated that ConA induced a very limited proliferation of Lyt-2- T helper cells (TH) in unselected T cell populations. The activation and growth requirements of Lyt-1+ TH cells were directly investigated and compared with those of Lyt-2+ cytotoxic T lymphocytes (CTL), as defined by the selective expression of Lyt differentiation antigens and functional activities. This analysis revealed a profound difference in activation and growth requirements between these T cell subsets. Thus, while Lyt-2+ CTL precursors can be induced to TCGF reactivity by soluble lectins, in the absence of specialized accessory cells,; Lyt-2" TH cell precursors show a strict accessory cell requirement both for activation and proliteration. Finally, the low level of TH cell effector function, detected in a primary responses to allo-MHC-antigens or lectins, appears to be due to the development of suppressive Lyt2+ T cells. The functional relevance of Lyt-2 antigens expressed on CTL membranes was further assessed in the last part of this study. Two distinct activation systems were used, namely MHC-antigens, provided as UV-irradiated stimulator cells or polyclonal induction by a 4 h pulse, with lectins. Both procedures were shown to selectively induce Lyt-2+ CTL precursors into TCGF reactivity without leading to mitosis, unless TCGF was added. In both cases it was found that monoclonal anti-Lyt-2 antibodies inhibited the two antigen- dependent phases of CTL responses namely, the initial induction step and target cytolysis. The analogy observed between antigen specific and lectin mediated indueton and target cytolysis, with regard to the susceptibility of inhibition by anti-Lyt-2 antibodies has lead to a general hypothesis on CTL activation. / <p>[4] s., s. 1-58: sammanfattning, s. 59-130, [12] s.: 6 uppsatser</p> / digitalisering@umu