Frequency of natural regulatory T cells specific for factor VIII in the peripheral blood of healthy donors.

Tolerance to self-proteins involves multiple mechanisms, including conventional CD4+ T-cell (Tconv) deletion in the thymus and the recruitment of natural regulatory T cells (nTregs). The significant incidence of autoantibodies specific for the blood coagulation factor VIII (FVIII) in healthy donors illustrates that tolerance to self-proteins is not always complete. In contrast to FVIII-specific Tconvs, FVIII-specific nTregs have never been revealed and characterized. To determine the frequency of FVIII-specific Tregs in human peripheral blood, we assessed the specificity of in vitro expanded Tregs by the membrane expression of the CD137 activation marker. Amplified Tregs maintain high levels of FOXP3 expression and exhibit almost complete demethylation of the FOXP3 Treg-specific demethylated region. The cells retained FOXP3 expression after long-term culture in vitro, strongly suggesting that FVIII-specific Tregs are derived from the thymus. From eleven healthy donors, we estimated the frequencies of FVIII-specific Tregs at 0.17 cells per million, which is about 10-fold lower than the frequency of FVIII-specific CD4+ T cells we previously published. Our results shed light on the mechanisms of FVIII tolerance by a renewed approach that could be extended to other self- or non-self-antigens.

A wave of bipotent T/ILC-restricted progenitors shapes the embryonic thymus microenvironment in a time-dependent manner.

During embryonic development, multiple waves of hematopoietic progenitors with distinct lineage potential are differentially regulated in time and space. Two different waves of thymic progenitors colonize the fetal thymus where they contribute to thymic organogenesis and homeostasis. The origin, the lineage differentiation potential of the first wave, and their relative contribution in shaping the thymus architecture, remained, however, unclear. Here, we show that the first wave of thymic progenitors comprises a unique population of bipotent T and innatel lymphoid cells (T/ILC), generating a lymphoid tissue inducer cells (LTi's), in addition to invariant Vγ5+ T cells. Transcriptional analysis revealed that innate lymphoid gene signatures and, more precisely, the LTi-associated transcripts were expressed in the first, but not in the second, wave of thymic progenitors. Depletion of early thymic progenitors in a temporally controlled manner showed that the progeny of the first wave is indispensable for the differentiation of autoimmune regulator-expressing medullary thymic epithelial cells (mTECs). We further show that these progenitors are of strict hematopoietic stem cell origin, despite the overlap between lymphopoiesis initiation and the transient expression of lymphoid-associated transcripts in yolk sac (YS) erythromyeloid-restricted precursors. Our work highlights the relevance of the developmental timing on the emergence of different lymphoid subsets, required for the establishment of a functionally diverse immune system.

Maintenance of Type 2 Response by CXCR6-Deficient ILC2 in Papain-Induced Lung Inflammation.

Innate lymphoid cells (ILC) are important players of early immune defenses in situations like lymphoid organogenesis or in case of immune response to inflammation, infection and cancer. Th1 and Th2 antagonism is crucial for the regulation of immune responses, however mechanisms are still unclear for ILC functions. ILC2 and NK cells were reported to be both involved in allergic airway diseases and were shown to be able to interplay in the regulation of the immune response. CXCR6 is a common chemokine receptor expressed by all ILC, and its deficiency affects ILC2 and ILC1/NK cell numbers and functions in lungs in both steady-state and inflammatory conditions. We determined that the absence of a specific ILC2 KLRG1+ST2- subset in CXCR6-deficient mice is probably dependent on CXCR6 for its recruitment to the lung under inflammation. We show that despite their decreased numbers, lung CXCR6-deficient ILC2 are even more activated cells producing large amount of type 2 cytokines that could drive eosinophilia. This is strongly associated to the decrease of the lung Th1 response in CXCR6-deficient mice.

Microtubule assembly during mitosis - from distinct origins to distinct functions?

The mitotic spindle is structurally and functionally defined by its main component, the microtubules (MTs). The MTs making up the spindle have various functions, organization and dynamics: astral MTs emanate from the centrosome and reach the cell cortex, and thus have a major role in spindle positioning; interpolar MTs are the main constituent of the spindle and are key for the establishment of spindle bipolarity, chromosome congression and central spindle assembly; and kinetochore-fibers are MT bundles that connect the kinetochores with the spindle poles and segregate the sister chromatids during anaphase. The duplicated centrosomes were long thought to be the origin of all of these MTs. However, in the last decade, a number of studies have contributed to the identification of non-centrosomal pathways that drive MT assembly in dividing cells. These pathways are now known to be essential for successful spindle assembly and to participate in various processes such as K-fiber formation and central spindle assembly. In this Commentary, we review the recent advances in the field and discuss how different MT assembly pathways might cooperate to successfully form the mitotic spindle.

Bone marrow monocytes sustain NK cell-poiesis during non-alcoholic steatohepatitis.

Natural killer (NK) cells are the predominant lymphocyte population in the liver. At the onset of non-alcoholic steatohepatitis (NASH), an accumulation of activated NK cells is observed in the liver in parallel with inflammatory monocyte recruitment and an increased systemic inflammation. Using in vivo and in vitro experiments, we unveil a specific stimulation of NK cell-poiesis during NASH by medullary monocytes that trans-present interleukin-15 (IL-15) and secrete osteopontin, a biomarker for patients with NASH. This cellular dialogue leads to increased survival and maturation of NK precursors that are recruited to the liver, where they dampen the inflammatory monocyte infiltration. The increase in the production of both osteopontin and the IL-15/IL-15Rα complex by bone marrow monocytes is induced by endotoxemia. We propose a tripartite gut-liver-bone marrow axis regulating the immune population dynamics and effector functions during liver inflammation.

Infliximab aggregates produced in severe and mild elevated temperature stress conditions induce an extended specific CD4 T-cell response.

Aggregation has been widely described as a factor contributing to therapeutic antibody immunogenicity. Although production of high-affinity anti-drug antibodies depends on the activation of CD4 T lymphocytes, little is known about the T-cell response induced by antibody aggregates, especially for aggregates produced in mild conditions resulting from minor handling errors of vials. Large insoluble infliximab (IFX) aggregates produced in severe elevated temperature stress conditions have been previously shown to induce human monocyte-derived dendritic cell (moDC) maturation. We here showed that large IFX aggregates recruit in vitro a significantly higher number of CD4 T-cells compared to native IFX. Moreover, a larger array of T-cell epitopes encompassing the entire variable regions was evidenced compared to the native antibody. We then compared the responses of moDCs to different types of aggregates generated by submitting IFX to mild conditions of various times of incubation at an elevated temperature. Decreasing stress duration reduced aggregate size and quantity, and subsequently altered moDC activation. Of importance, IFX aggregates generated in mild conditions and not altering moDC phenotype generated an in vitro T-cell response with a higher frequency of CD4 T cells compared to native IFX. Moreover, cross-reactivity studies of aggregate-specific T cells showed that some T cells could recognize both native and aggregated IFX, while others responded only to IFX aggregates. Taken together, our results suggest that aggregation of antibodies in mild elevated temperature stress conditions is sufficient to alter moDC phenotype in a dose-dependent manner and to increase T-cell response.

Pegylation Reduces the Uptake of Certolizumab Pegol by Dendritic Cells and Epitope Presentation to T-Cells.

Pegylation of biopharmaceuticals is the most common strategy to increase their half-life in the blood and is associated with a reduced immunogenicity. As antigen presentation is a primary event in the activation of CD4 T-cells and initiation of Anti-Drug Antibody (ADA) response, we investigated the role of the PEG molecule on the T-cell reactivity of certolizumab pegol (CZP), a pegylated anti-TNFα Fab. We generated T-cell lines raised against CZP and its non-pegylated form (CZNP) and demonstrated CZP primed few T-cells in comparison to CZNP. CZP-primed lines from 3 donors responded to a total of 5 epitopes, while CZNP-primed lines from 3 donors responded to a total of 7 epitopes, 4 epitopes were recognized by both CZP- and CZNP-primed lines. In line with this difference of T-cell reactivity, CZP is less internalized by the dendritic cells than CZNP. In vitro digestion assay of CZP by Cathepsin B showed a rapid removal of the PEG moiety, suggesting a limited influence of PEG on CZP proteolysis. We therefore demonstrate that pegylation diminishes antigen capture by dendritic cells, peptide presentation to T-cells and T-cell priming. This mechanism might reduce immunogenicity and contribute to the long half-life of CZP and possibly of other pegylated molecules.

Nucleolin Therapeutic Targeting Decreases Pancreatic Cancer Immunosuppression.

Background: The pancreatic ductal adenocarcinoma (PDAC) microenvironment is highly fibrotic and hypoxic, with poor immune cell infiltration. Recently, we showed that nucleolin (NCL) inhibition normalizes tumour vessels and impairs PDAC growth. Methods: Immunocompetent mouse models of PDAC were treated by the pseudopeptide N6L, which selectively inhibits NCL. Tumour-infiltrating immune cells and changes in the tumour microenvironment were analysed. Results: N6L reduced the proportion of regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) and increased tumour-infiltrated T lymphocytes (TILs) with an activated phenotype. Low-dose anti-VEGFR2 treatment normalized PDAC vessels but did not modulate the immune suppressive microenvironment. RNAseq analysis of N6L-treated PDAC tumours revealed a reduction of cancer-associated fibroblast (CAF) expansion in vivo and in vitro. Notably, N6L treatment decreased IL-6 levels both in tumour tissues and in serum. Treating mPDAC by an antibody blocking IL-6 reduced the proportion of Tregs and MDSCs and increased the amount of TILs, thus mimicking the effects of N6L. Conclusions: These results demonstrate that NCL inhibition blocks the amplification of lymphoid and myeloid immunosuppressive cells and promotes T cell activation in PDAC through a new mechanism of action dependent on the direct inhibition of the tumoral stroma.

Correction: Ponzo et al. Nucleolin Therapeutic Targeting Decreases Pancreatic Cancer Immunosuppression. Cancers 2022, 14, 4265.

In the original publication [...].

Pivotal role of translokin/CEP57 in the unconventional secretion versus nuclear translocation of FGF2.

Intracellular trafficking of fibroblast growth factor 2 (FGF2) exhibits two unusual features: (i) it is secreted despite the lack of signal peptide and (ii) it can translocate to the nucleus after interaction with high- and low-affinity receptors on the cell surface, although it does not possess any classical nuclear localization signal. This nuclear translocation constitutes an important part of the response to the growth factor. Previously, we identified Translokin/CEP57, an FGF2 binding partner, as an intracellular mediator of FGF2 trafficking, which is essential for the nuclear translocation of the growth factor. Here, we report the identification of four Translokin partners: sorting nexin 6, Ran-binding protein M and the kinesins KIF3A and KIF3B. These proteins, through their interaction with Translokin, are involved in two exclusive complexes allowing the bidirectional trafficking of FGF2. Thus, Translokin plays a pivotal role in this original mechanism. In addition, we show that FGF2 secretion is regulated by a negative loop, retro-controlled by FGF receptor and involving FGF2 itself.

Translokin is an intracellular mediator of FGF-2 trafficking.

Basic fibroblast growth factor (bFGF or FGF-2) exerts its pleiotropic activities both as an exogenous and an intracellular factor. FGF-1 and FGF-2 are prototypes for this dual signalling, but the mechanisms of their intracellular actions remain unknown. Here we show that Translokin, a cytoplasmic protein of relative molecular mass 55,000 (M(r) 55K), interacts specifically with the 18K form of FGF-2. Translokin is ubiquitously expressed and colocalizes with the microtubular network. As Translokin does not interact with FGF-1, we used a strategy based on FGF-1-FGF-2 chimaeras to map the interacting regions in FGF-2 and to generate Nb1a2, a non-interacting variant of FGF-2. Although most of the FGF-2 properties are preserved in Nb1a2, this variant is defective in intracellular translocation and in stimulating proliferation. The fusion of a nuclear localization signal to Nb1a2 restores its mitogenic activity and its nuclear association. Inhibiting Translokin expression by RNA interference reduces the translocation of FGF-2 without affecting the intracellular trafficking of FGF-1. Our data show that the nuclear association of internalized FGF-2 is essential for its mitogenic activity and that Translokin is important in this translocation pathway.

Specificity of the T Cell Response to Protein Biopharmaceuticals.

The anti-drug antibody (ADA) response is an undesired humoral response raised against protein biopharmaceuticals (BPs) which can dramatically disturb their therapeutic properties. One particularity of the ADA response resides in the nature of the immunogens, which are usually human(ized) proteins and are therefore expected to be tolerated. CD4 T cells initiate, maintain and regulate the ADA response and are therefore key players of this immune response. Over the last decade, advances have been made in characterizing the T cell responses developed by patients treated with BPs. Epitope specificity and phenotypes of BP-specific T cells have been reported and highlight the effector and regulatory roles of T cells in the ADA response. BP-specific T cell responses are assessed in healthy subjects to anticipate the immunogenicity of BP prior to their testing in clinical trials. Immunogenicity prediction, also called preclinical immunogenicity assessment, aims at identifying immunogenic BPs and immunogenic BP sequences before any BP injection in humans. All of the approaches that have been developed to date rely on the detection of BP-specific T cells in donors who have never been exposed to BPs. The number of BP-specific T cells circulating in the blood of these donors is therefore limited. T cell assays using cells collected from healthy donors might reveal the weak tolerance induced by BPs, whose endogenous form is expressed at a low level. These BPs have a complete human sequence, but the level of their endogenous form appears insufficient to promote the negative selection of autoreactive T cell clones. Multiple T cell epitopes have also been identified in therapeutic antibodies and some other BPs. The pattern of identified T cell epitopes differs across the antibodies, notwithstanding their humanized, human or chimeric nature. However, in all antibodies, the non-germline amino acid sequences mainly found in the CDRs appear to be the main driver of immunogenicity, provided they can be presented by HLA class II molecules. Considering the fact that the BP field is expanding to include new formats and gene and cell therapies, we face new challenges in understanding and mastering the immunogenicity of new biological products.

The Notch Signaling Pathway Is Balancing Type 1 Innate Lymphoid Cell Immune Functions.

The Notch pathway is one of the canonical signaling pathways implicated in the development of various solid tumors. During carcinogenesis, the Notch pathway dysregulation induces tumor expression of Notch receptor ligands participating to escape the immune surveillance. The Notch pathway conditions both the development and the functional regulation of lymphoid subsets. Its importance on T cell subset polarization has been documented contrary to its action on innate lymphoid cells (ILC). We aim to analyze the effect of the Notch pathway on type 1 ILC polarization and functions after disruption of the RBPJk-dependent Notch signaling cascade. Indeed, type 1 ILC comprises conventional NK (cNK) cells and type 1 helper innate lymphoid cells (ILC1) that share Notch-related functional characteristics such as the IFNg secretion downstream of T-bet expression. cNK cells have strong antitumor properties. However, data are controversial concerning ILC1 functions during carcinogenesis with models showing antitumoral capacities and others reporting ILC1 inability to control tumor growth. Using various mouse models of Notch signaling pathway depletion, we analyze the effects of its absence on type 1 ILC differentiation and cytotoxic functions. We also provide clues into its role in the maintenance of immune homeostasis in tissues. We show that modulating the Notch pathway is not only acting on tumor-specific T cell activity but also on ILC immune subset functions. Hence, our study uncovers the intrinsic Notch signaling pathway in ILC1/cNK populations and their response in case of abnormal Notch ligand expression. This study help evaluating the possible side effects mediated by immune cells different from T cells, in case of multivalent forms of the Notch receptor ligand delta 1 treatments. In definitive, it should help determining the best novel combination of therapeutic strategies in case of solid tumors.

CD4 T cells specific for factor VIII are present at high frequency in healthy donors and comprise naïve and memory cells.

We investigated the frequency and subset origin of circulating factor VIII (FVIII)-specific CD4 T cells in healthy donors. Total CD4 T cells and purified CD4 T-cell subsets were stimulated with FVIII-loaded autologous dendritic cells and challenged for specificity in interferon-γ enzyme-linked immunospots. The number of specific T-cell lines allowed estimation of the frequency of T cells circulating in the blood of the donors. All the 16 healthy donors generated strong in vitro T-cell responses, leading to the generation of 154 FVIII-specific T-cell lines. The mean frequency of FVIII-specific CD4 T cells in healthy donors was similar to that of T cells specific for foreign antigens and greater than that of T cells specific for known immunogenic therapeutic proteins. Normal levels of endogenous FVIII in healthy donors therefore do not prevent a significant escape of FVIII-specific CD4 T cells from negative thymic selection. FVIII-specific T cells mainly originated from both the naïve and central memory cell subsets, but their frequencies remained low as compared with those of cells specific for foreign antigens in immunized donors. The observation of a spontaneous generation of FVIII-specific memory T cells without a global expansion suggests peculiar peripheral tolerance mechanisms to FVIII in healthy donors.

Characterization of CD4 T Cell Epitopes of Infliximab and Rituximab Identified from Healthy Donors.

The chimeric antibodies anti-CD20 rituximab (Rtx) and anti-TNFα infliximab (Ifx) induce antidrug antibodies (ADAs) in many patients with inflammatory diseases. Because of the key role of CD4 T lymphocytes in the initiation of antibody responses, we localized the CD4 T cell epitopes of Rtx and Ifx. With the perspective to anticipate immunogenicity of therapeutic antibodies, identification of the CD4 T cell epitopes was performed using cells collected in healthy donors. Nine T cell epitopes were identified in the variable chains of both antibodies by deriving CD4 T cell lines raised against either Rtx or Ifx. The T cell epitopes often exhibited a good affinity for human leukocyte antigen (HLA)-DR molecules and were part of the peptides identified by MHC-associated peptide proteomics assay from HLA-DR molecules of dendritic cells (DCs) loaded with the antibodies. Two-third of the T cell epitopes identified from the healthy donors stimulated peripheral blood mononuclear cells from patients having developed ADAs against Rtx or Ifx and promoted the secretion of a diversity of cytokines. These data emphasize the predictive value of evaluating the T cell repertoire of healthy donors and the composition of peptides bound to HLA-DR of DCs to anticipate and prevent immunogenicity of therapeutic antibodies.

Acentrosomal Microtubule Assembly in Mitosis: The Where, When, and How.

In mitosis the cell assembles the bipolar spindle, a microtubule (MT)-based apparatus that segregates the duplicated chromosomes into two daughter cells. Most animal cells enter mitosis with duplicated centrosomes that provide an active source of dynamic MTs. However, it is now established that spindle assembly relies on the nucleation of acentrosomal MTs occurring around the chromosomes after nuclear envelope breakdown, and on pre-existing microtubules. Where chromosome-dependent MT nucleation occurs, when MT amplification takes place and how the two pathways function are still key questions that generate some controversies. We reconcile the data and present an integrated model accounting for acentrosomal microtubule assembly in the dividing cell.

Aurora-A regulates MCRS1 function during mitosis.

The mitotic spindle is made of microtubules (MTs) nucleated through different pathways involving the centrosomes, the chromosomes or the walls of pre-existing MTs. MCRS1 is a RanGTP target that specifically associates with the chromosome-driven MTs protecting them from MT depolymerases. MCRS1 is also needed for the control of kinetochore fiber (K-fiber) MT minus-ends dynamics in metaphase. Here, we investigated the regulation of MCRS1 activity in M-phase. We show that MCRS1 is phosphorylated by the Aurora-A kinase in mitosis on Ser35/36. Although this phosphorylation has no role on MCRS1 localization to chromosomal MTs and K-fiber minus-ends, we show that it regulates MCRS1 activity in mitosis. We conclude that Aurora-A activity is particularly important in the tuning of K-fiber minus-ends dynamics in mitosis.

FAM65B controls the proliferation of transformed and primary T cells.

Cell quiescence is controlled by regulated genome-encoded programs that actively express genes which are often down-regulated or inactivated in transformed cells. Among them is FoxO1, a transcription factor that imposes quiescence in several cell types, including T lymphocytes. In these cells, the FAM65B encoding gene is a major target of FOXO1. Here, we show that forced expression of FAM65B in transformed cells blocks their mitosis because of a defect of the mitotic spindle, leading to G2 cell cycle arrest and apoptosis. Upon cell proliferation arrest, FAM65B is engaged in a complex containing two proteins well known to be involved in cell proliferation i.e. the HDAC6 deacetylase and the 14.3.3 scaffolding protein. In primary T cells, FAM65B is down-regulated upon T cell receptor engagement, and maintaining its expression blocks their proliferation, establishing that the decrease of FAM65B expression is required for proliferation. Conversely, inhibiting FAM65B expression in naive T lymphocytes decreases their activation threshold. These results identify FAM65B as a potential new target for controlling proliferation of both transformed and normal cells.

Microtubule nucleation in mitosis by a RanGTP-dependent protein complex.

BACKGROUND: The γ-tubulin ring complex (γTuRC) is a multisubunit complex responsible for microtubule (MT) nucleation in eukaryotic cells. During mitosis, its spatial and temporal regulation promotes MT nucleation through different pathways. One of them is triggered around the chromosomes by RanGTP. Chromosomal MTs are essential for functional spindle assembly, but the mechanism by which RanGTP activates MT nucleation has not yet been resolved. RESULTS: We used a combination of Xenopus egg extracts and in vitro experiments to dissect the mechanism by which RanGTP triggers MT nucleation. In egg extracts, NEDD1-coated beads promote MT nucleation only in the presence of RanGTP. We show that RanGTP promotes a direct interaction between one of its targets, TPX2, and XRHAMM that defines a specific γTuRC subcomplex. Through depletion/add-back experiments using mutant forms of TPX2 and NEDD1, we show that the activation of MT nucleation by RanGTP requires both NEDD1 phosphorylation on S405 by the TPX2-activated Aurora A and the recruitment of the complex through a TPX2-dependent mechanism. CONCLUSIONS: The XRHAMM-γTuRC complex is the target for activation by RanGTP that promotes an interaction between TPX2 and XRHAMM. The resulting TPX2-RHAMM-γTuRC supracomplex fulfills the two essential requirements for the activation of MT nucleation by RanGTP: NEDD1 phosphorylation on S405 by the TPX2-activated Aurora A and the recruitment of the complex onto a TPX2-dependent scaffold. Our data identify TPX2 as the only direct RanGTP target and NEDD1 as the only Aurora A substrate essential for the activation of the RanGTP-dependent MT nucleation pathway.