CD206+ tumor-associated macrophages cross-present tumor antigen and drive antitumor immunity.

In many solid cancers, tumor-associated macrophages (TAM) represent the predominant myeloid cell population. Antigen (Ag) cross-presentation leading to tumor Ag-directed cytotoxic CD8+ T cell responses is crucial for antitumor immunity. However, the role of recruited monocyte-derived macrophages, including TAM, as potential cross-presenting cells is not well understood. Here, we show that primary human as well as mouse CD206+ macrophages are effective in functional cross-presentation of soluble self-Ag and non-self-Ag, including tumor-associated Ag (TAA), as well as viral Ag. To confirm the presence of cross-presenting TAM in vivo, we performed phenotypic and functional analysis of TAM from B16-F10 and CT26 syngeneic tumor models and have identified CD11b+F4/80hiCD206+ TAM to effectively cross-present TAA. We show that CD11b+CD206+ TAM represent the dominant tumor-infiltrating myeloid cell population, expressing a unique cell surface repertoire, promoting Ag cross-presentation and Ag-specific CD8+ T cell activation comparable with cross-presenting CLEC9A+ DCs (cDC1). The presence of cross-presenting CD206+ TAM is associated with reduced tumor burden in mouse syngeneic tumor models and with improved overall survival in cutaneous melanoma patients. Therefore, the demonstration of effective Ag cross-presentation capabilities of CD206+ TAM, including their clinical relevance, expands our understanding of TAM phenotypic diversity and functional versatility.

The soluble cytoplasmic tail of CD45 regulates T-cell activation via TLR4 signaling.

The soluble cytoplasmic tail of CD45 (ct-CD45) is a cleavage fragment of CD45, that is generated during the activation of human phagocytes. Upon release to the extracellular space, ct-CD45 binds to human T cells and inhibits their activation in vitro. Here, we studied the potential role of TLR4 as a receptor for ct-CD45. Treatment of Jurkat TLR4/CD14 reporter cells with ct-CD45 induced the upregulation of the reporter gene NFκB-eGFP and could be blocked by inhibitors of TLR4 signaling. Conversely, ct-CD45 did not promote the NFκB-controlled eGFP induction in reporter cells expressing TLR1, TLR2, and TLR6 transgenes and did not lead to the activation of the transcription factors NFκB, AP-1, and NFAT in a Jurkat reporter cell line expressing endogenous TLR5. Moreover, ct-CD45 binds to recombinant TLR4 in an in vitro assay and this association was reduced in the presence of oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine. Blockade of TLR4 with mAb HTA125 partially reversed the ct-CD45-mediated inhibition of T-cell proliferation. Interestingly, targeting of TLR4 with mAb W7C11 also suppressed T-cell proliferation. In summary, the results of this study demonstrate that ct-CD45 acts via a noncanonical TLR4 activation pathway on T cells, which modulates TCR signaling.

Transferrin receptor 1 is a cellular receptor for human heme-albumin.

Iron is essential for living cells. Uptake of iron-loaded transferrin by the transferrin receptor 1 (CD71, TFR) is a major but not sufficient mechanism and an alternative iron-loaded ligand for CD71 has been assumed. Here, we demonstrate that CD71 utilizes heme-albumin as cargo to transport iron into human cells. Binding and endocytosis of heme-albumin via CD71 was sufficient to promote proliferation of various cell types in the absence of transferrin. Growth and differentiation of cells induced by heme-albumin was dependent on heme-oxygenase 1 (HO-1) function and was accompanied with an increase of the intracellular labile iron pool (LIP). Import of heme-albumin via CD71 was further found to contribute to the efficacy of albumin-based drugs such as the chemotherapeutic Abraxane. Thus, heme-albumin/CD71 interaction is a novel route to transport nutrients or drugs into cells and adds to the emerging function of CD71 as a scavenger receptor.

Iron Deprivation in Human T Cells Induces Nonproliferating Accessory Helper Cells.

Iron uptake via the transferrin receptor (CD71) is a pivotal mechanism for T cell proliferation. Yet, it is incompletely understood if targeting of CD71 also affects the differentiation and functional polarization of primary human T cells. In this study, we demonstrate that inhibition of iron ingestion with blocking mAbs against CD71 induces nonproliferating T cells, which release high amounts of IL-2. Targeting of CD71 with blocking or nonblocking mAbs did not alter major signaling pathways and the activation of the transcription factors NF-κB, NFAT, or AP-1 as analyzed in Jurkat T cells. Growth arrest in iron-deficient (Fe-def) T cells was prevented upon addition of exogenous iron in the form of ferric ammonium citrate but was not reversible by exogenous IL-2. Surprisingly, protein synthesis was found to be intact in Fe-def T cells as demonstrated by comparable levels of CD69 upregulation and cytokine production with iron-sufficient T cells upon stimulation with CD3 plus CD28 mAbs. Indeed, high amounts of IL-2 were detectable in the supernatant of Fe-def T cells, which was accompanied with a reduced cell surface expression of IL-2R. When we used such Fe-def T cells in allogeneic MLRs, we observed that these cells acquired an accessory cell function and stimulated the proliferation of bystander T cells by providing IL-2. Thus, the results of our study demonstrate that iron deprivation causes nonproliferating, altruistic T cells that can help and stimulate other immune cells by providing cytokines such as IL-2.

Landscape and Dynamics of Single Immune Cells in Hepatocellular Carcinoma.

The immune microenvironment of hepatocellular carcinoma (HCC) is poorly characterized. Combining two single-cell RNA sequencing technologies, we produced transcriptomes of CD45+ immune cells for HCC patients from five immune-relevant sites: tumor, adjacent liver, hepatic lymph node (LN), blood, and ascites. A cluster of LAMP3+ dendritic cells (DCs) appeared to be the mature form of conventional DCs and possessed the potential to migrate from tumors to LNs. LAMP3+ DCs also expressed diverse immune-relevant ligands and exhibited potential to regulate multiple subtypes of lymphocytes. Of the macrophages in tumors that exhibited distinct transcriptional states, tumor-associated macrophages (TAMs) were associated with poor prognosis, and we established the inflammatory role of SLC40A1 and GPNMB in these cells. Further, myeloid and lymphoid cells in ascites were predominantly linked to tumor and blood origins, respectively. The dynamic properties of diverse CD45+ cell types revealed by this study add new dimensions to the immune landscape of HCC.

STAT1 is a sex-specific tumor suppressor in colitis-associated colorectal cancer.

The interferon-inducible transcription factor STAT1 is a tumor suppressor in various malignancies. We investigated sex-specific STAT1 functions in colitis and colitis-associated colorectal cancer (CRC) using mice with specific STAT1 deletion in intestinal epithelial cells (STAT1∆IEC ). Male but not female STAT1∆IEC mice were more resistant to DSS-induced colitis than sex-matched STAT1flox/flox controls and displayed reduced intraepithelial infiltration of CD8+ TCRαß+ granzyme B+ T cells. Moreover, DSS treatment failed to induce expression of T-cell-attracting chemokines in intestinal epithelial cells of male but not of female STAT1∆IEC mice. Application of the AOM-DSS protocol for induction of colitis-associated CRC resulted in increased intestinal tumor load in male but not in female STAT1∆IEC mice. A sex-specific stratification of human CRC patients corroborated the data obtained in mice and revealed that reduced tumor cell-intrinsic nuclear STAT1 protein expression is a poor prognostic factor in men but not in women. These data demonstrate that epithelial STAT1 is a male-specific tumor suppressor in CRC of mice and humans.

Evaluation of Prognostic Immune Signatures in Patients with Breast, Colorectal and Pancreatic Cancer Receiving Chemotherapy.

BACKGROUND: CD97 is a member of the epidermal growth factor-seven transmembrane (EGF-TM7) receptor family and is dominantly expressed on immune cells and in a variety of malignant diseases. B7-H1 and B7-H3 are transmembrane proteins that are involved in suppression of the immune system. The aim of this study was to evaluate if these molecules are up-regulated in patients with cancer and change during chemotherapy. MATERIALS AND METHODS: We analyzed cluster of differentiation (CD) protein expression levels on tumor cell lines and in blood samples of 37 patients with solid tumors at baseline and during chemotherapy; we correlated the serum levels of CD proteins with survival outcome. RESULTS: Levels of soluble CD97 proteins were significantly elevated in all three cancer types compared to healthy controls. Patients with colorectal cancer and those with high CD97 levels had a significantly worse prognosis. CONCLUSION: This study showed a marked elevation of soluble CD97 expression in patients with certain cancer types and demonstrated definite changes in CD protein expression during chemotherapy in one patient with metastatic breast cancer.

The soluble cytoplasmic tail of CD45 (ct-CD45) in human plasma contributes to keep T cells in a quiescent state.

The cytoplasmic tail of CD45 (ct-CD45) is proteolytically cleaved and released upon activation of human phagocytes. It acts on T cells as an inhibitory, cytokine-like factor in vitro. Here, we show that ct-CD45 is abundant in human peripheral blood plasma from healthy adults compared with plasma derived from umbilical cord blood and plasma from patients with rheumatoid arthritis or systemic lupus erythematosus. Plasma depleted of ct-CD45 enhanced T-cell proliferation, while addition of exogenous ct-CD45 protein inhibited proliferation and reduced cytokine production of human T lymphocytes in response to TCR signaling. Inhibition of T-cell proliferation by ct-CD45 was overcome by costimulation via CD28. T-cell activation in the presence of ct-CD45 was associated with an upregulation of the quiescence factors Schlafen family member 12 (SLFN12) and Krueppel-like factor 2 (KLF2) as well as of the cyclin-dependent kinase (CDK) inhibitor p27kip1. In contrast, positive regulators of the cell cycle such as cyclin D2 and D3 as well as CDK2 and CDK4 were found to be downregulated in response to ct-CD45. In summary, we demonstrate that ct-CD45 is present in human plasma and sets the threshold of T-cell activation.

Engagement of distinct epitopes on CD43 induces different co-stimulatory pathways in human T cells.

Co-receptors, being either co-stimulatory or co-inhibitory, play a pivotal role in T-cell immunity. Several studies have indicated that CD43, one of the abundant T-cell surface glycoproteins, acts not only as a potent co-receptor but also as a negative regulator for T-cell activation. Here we demonstrate that co-stimulation of human peripheral blood (PB) T cells through two distinct CD43 epitopes recognized by monoclonal antibodies (mAb) CD43-6E5 (T6E5-act ) and CD43-10G7 (T10G7-act ) potently induced T-cell proliferation. However, T-cell co-stimulation through two CD43 epitopes differentially regulated activation of nuclear factor of activated T cells (NFAT) and nuclear factor-κB (NF-κB) transcription factors, T-cell cytokine production and effector function. T6E5-act produced high levels of interleukin-22 (IL-22) and interferon-γ (IFN-γ) similar to T cells activated via CD28 (TCD28-act ), whereas T10G7-act produced low levels of inflammatory cytokines but higher levels of regulatory cytokines transforming growth factor-ß (TGF-ß) and interleukin-35 (IL-35). Compared with T6E5-act or to TCD28-act , T10G7-act performed poorly in response to re-stimulation and further acquired a T-cell suppressive function. T10G7-act did not directly inhibit proliferation of responder T cells, but formed stable heterotypic clusters with dendritic cells (DC) via CD2 to constrain activation of responder T cells. Together, our data demonstrate that CD43 is a unique and polarizing regulator of T-cell function.

Expression and regulation of Schlafen (SLFN) family members in primary human monocytes, monocyte-derived dendritic cells and T cells.

Schlafen (SLFN/Slfn) family members have been investigated for their involvement in fundamental cellular processes including growth regulation, differentiation and control of viral replication. However, most research has been focused on the characterization of Slfns within the murine system or in human cell lines. Since little is known about SLFNs in primary human immune cells, we set out to analyze the expression and regulation of the six human SLFN genes in monocytes, monocyte-derived dendritic cells (moDCs) and T cells. Comparison of SLFN gene expression across these three cell types showed high mRNA expression of SLFN11 in monocytes and moDCs and high SLFN5 expression in T cells, indicating functional importance within these cell types. Differentiation of monocytes to moDCs leads to the gradual upregulation of SLFN12L and SLFN13 while SLFN12 levels were decreased by differentiation stimuli. Stimulation of moDCs via human rhinovirus, lipopolysaccharide, or IFN-α lead to strong upregulation of SLFN gene expression, while peptidoglycan poorly stimulated regulation of both SLFNs and the classical interferon-stimulated gene MxA. T cell activation was found to downregulate the expression of SLFN5, SLFN12 and SLFN12L, which was reversible upon addition of exogenous IFN-α. In conclusion, we demonstrate, that SLFN gene upregulation is mainly dependent on autocrine type I interferon signaling in primary human immune cells. Rapid decrease of SLFN expression levels following T cell receptor stimulation indicates a role of SLFNs in the regulation of human T cell quiescence.

Identification of bone morphogenetic protein 7 (BMP7) as an instructive factor for human epidermal Langerhans cell differentiation.

Human Langerhans cell (LC) precursors populate the epidermis early during prenatal development and thereafter undergo massive proliferation. The prototypic antiproliferative cytokine TGF-ß1 is required for LC differentiation from human CD34(+) hematopoietic progenitor cells and blood monocytes in vitro. Similarly, TGF-ß1 deficiency results in LC loss in vivo. However, immunohistology studies revealed that human LC niches in early prenatal epidermis and adult basal (germinal) keratinocyte layers lack detectable TGF-ß1. Here we demonstrated that these LC niches express high levels of bone morphogenetic protein 7 (BMP7) and that Bmp7-deficient mice exhibit substantially diminished LC numbers, with the remaining cells appearing less dendritic. BMP7 induces LC differentiation and proliferation by activating the BMP type-I receptor ALK3 in the absence of canonical TGF-ß1-ALK5 signaling. Conversely, TGF-ß1-induced in vitro LC differentiation is mediated via ALK3; however, co-induction of ALK5 diminished TGF-ß1-driven LC generation. Therefore, selective ALK3 signaling by BMP7 promotes high LC yields. Within epidermis, BMP7 shows an inverse expression pattern relative to TGF-ß1, the latter induced in suprabasal layers and up-regulated in outer layers. We observed that TGF-ß1 inhibits microbial activation of BMP7-generated LCs. Therefore, TGF-ß1 in suprabasal/outer epidermal layers might inhibit LC activation, resulting in LC network maintenance.