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(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 2022

Tumor cells use different mechanisms to avoid immune recognition. One of these is the induction of the enzymes indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3 dioxygenase (TDO) responsible for catabolizing the essential amino acid tryptophan into kynurenine. The aim of this work was to elucidate the pathway that translates these metabolic changes into T-lymphocyte malfunction within the tumor microenvironment. We show that through the aryl hydrocarbon receptor (AHR), CD4+ T lymphocytes from DBA/2 mice, differentiate significantly more into immunosuppressive regulatory T cells (Treg) when cultured in absence of tryptophan. More importantly, we found that under tryptophan-depleted conditions, AHR was significantly upregulated rendering it more sensitive to ligands such as kynurenine. Overall, our findings provide new insights into the respective role of tryptophan depletion and kynurenine production in IDO1/TDO-mediated immunosuppression., (BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 2022

Lors de leur exposition prolongée avec leur antigène, les lymphocytes T CD8 ont une capacité atténuée à proliférer, produire des cytokines, et expriment le récepteur PD-1. Ils sont nommés « épuisés ». Le rôle des facteurs de transcription impliqués dans l’épuisement est incertain car il est difficile de distinguer les changements qui relèvent de l’activation d’un lymphocyte T, de ceux qui conduisent à leur épuisement. De plus, la majorité des études réalisées compare des lymphocytes T CD8 épuisés, donc chroniquement activés, à des lymphocytes T CD8 au repos. Dans cette thèse, nous avons examiné le rôle du facteur de transcription IRF4 sur la fonction des lymphocytes T CD8 humains en forçant son expression par transduction lentivirale ou en l’invalidant par CRISPR/Cas9. Puis, nous avons analysé si les lymphocytes T CD8 infiltrés dans des tumeurs ovariennes humaines co-expriment des marqueurs d’épuisement et d’activation, ainsi que le facteur de transcription IRF4., (BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 2022

Malignant mesothelioma is a disease caused by inhalation of needle-like shaped particles and whose pathogenesis is not yet fully elucidated. A long-lasting general inflammation caused by persistent mesotheliomagenic particles is not sufficient to explain mesothelioma onset. Indeed, challenging data have shown that mesothelioma occurs without chronic inflammation. Our research team previously helped to discover that, beside inflammation, particles such as silica also induce a selective, rapid and sustained accumulation of immunosuppressive cells (regulatory T lymphocytes, myeloid derived suppressive cells and M2/regulatory macrophages) participating to fibrogenesis. To determine whether carcinogenic particles such as asbestos and carbon nanotubes (CNT) also elicit immunosuppressive responses, we investigated the impact of these particles on macrophage turnover, phenotype and immunosuppressive activity. With that purpose, we intraperitoneally injected mesotheliomagenic CNT-7 (needle-like, Mitsui & Co) and non-mesotheliomagenic CNT-T (tangled, Nagoya University) particles in Wistar rats and compared the effects on peritoneal macrophage subpopulations. We showed that macrophages die very rapidly in the attempt to phagocyte mesotheliomagenic CNT. They are later replenished by monocytic-derived small peritoneal macrophages (SPM-like macrophages) possessing comparable immunosuppressive functions and signatures to Tumor-Associated Macrophages (TAM), which infiltrate mesothelioma and block T cell antitumor activities. Early immunosuppressive SPM-like macrophages express and release the shed form of the immunoregulatory syndecan-1 glycoprotein, which could explain the immunosuppression that they exert on T cells. Non-mesotheliomagenic peritoneal responses induced by CNT-T are, in contrast, characterized by a recruitment of self-proliferating large peritoneal macrophages (LPM-like macrophages) that correspond to homeostatic macrophages without immunosuppressive activity. Our o, (BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 2021

Current immunotherapy is less effective in breast cancer than in melanoma. However, “TILs” (tumor-infiltrating lymphocytes) are a prognostic factor and a predictive biomarker for chemotherapy response but few are really tumor-specific. TILs are also observed in ductal carcinoma in situ (DCIS), the earliest stage of breast cancer. We cannot predict which DCIS will progress towards invasive breast cancer (IBC). As DCIS could be more immunogenic than IBC, we studied the specificity of CD8+ and Treg (regulatory T cell) TILs extracted from 17 DCIS by reconstructing their TCR and screening them for recognition of various tumor antigens. For the CD8 TCRs, the results were negative. For Tregs TCRs, we observed the recognition of a mutated antigen by the most predominant clonotype of one tumor. Moreover, we observed activated Tregs in 64% of our DCIS samples. These results suggest that the tumor micro-environnement could already be immunosuppressive at the in situ stage of breast cancer., (BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 2021

Myeloid-derived suppressor cells (MDSCs) expand during pathological conditions in both humans and mice and their presence is linked to poor clinical outcomes for cancer patients. Studying MDSC immunosuppression is restricted by MDSCs' rarity, short lifespan, heterogeneity, poor viability after freezing and the lack of MDSC-specific markers. In this review, we will compare identification and isolation strategies for human and murine MDSCs. We will also assess what direct and indirect immunosuppressive mechanisms have been attributed to MDSCs. While some immunosuppressive mechanisms are well-documented in mice, e.g., generation of ROS, direct evidence is still lacking in humans. In future, bulk or single-cell genomics could elucidate which phenotypic and functional phenotypes MDSCs adopt in particular microenvironments and help to identify potential targets for therapy.

Amino acids blood levels are remarkably constant, in spite of fasting periods and large variations in diet supply. Systemic homeostasis is particularly important for tryptophan, given its key role in many cellular processes, including immunity and neuronal activity. In humans, tryptophanemia is maintained around 60µM. Here, we showed that tryptophan homeostasis is largely controlled by the post-translational stability of tryptophan 2,3-dioxygenase (TDO), the hepatic enzyme catalyzing the first step of tryptophan catabolism along the kynurenine pathway. TDO, located at the strategic crossroad of the portal and systemic circulation, degrades more than 90% of food-derived tryptophan. High tryptophan levels stabilize the active tetrameric conformation of TDO through binding non-catalytic exosites, promoting rapid blood tryptophan catabolism. In low tryptophan, the lack of tryptophan binding in the exosites destabilizes the tetramer into inactive monomers and dimers, and unmasks a degron. This triggers the polyubiquitination of TDO by SKP1-CUL1-F-box complexes, resulting in proteasome-mediated degradation of TDO and rapid interruption of tryptophan catabolism. Artificial stabilization of tetrameric TDO with the non-metabolizable analog alpha-methyl-tryptophan in vivo stably reduces blood tryptophan levels. Our results uncover a mechanism allowing a rapid adaptation of tryptophan catabolism to ensure quick degradation of excess tryptophan while preventing further catabolism below physiological levels. This ensures a tight control of tryptophanemia, as required for both neurological and immune homeostasis., La concentration plasmatique des acides aminés est remarquablement constante en dépit des variations de nos apports alimentaires. L’homéostasie systémique des acides aminés est particulièrement importante pour le tryptophane, en raison de son rôle clef dans de nombreux processus biologiques, incluant l’immunité et l’activité neuronale. Chez l’homme, la tryptophanémie est en permanence maintenue à 60µM. Nos découvertes révèlent que l’homéostasie du tryptophane est majoritairement contrôlée par la stabilité post-traductionnelle de la tryptophane 2,3-dioxygenase (TDO), l’enzyme hépatique catalysant la première réaction du catabolisme du tryptophane dans la voie métabolique de la kynurénine. Localisée au carrefour de l’artère hépatique et de la veine porte, la protéine TDO occupe une position stratégique pour filtrer le sang et dégrade plus de 90% du tryptophane d’origine alimentaire. Lorsque la tryptophanémie augmente, le tryptophane active la protéine TDO en stabilisant sa conformation tétramérique au moyen de quatre exosites non catalytiques, promouvant ainsi le catabolisme du tryptophane plasmatique. Une fois la tryptophanémie faible, le tryptophane libère les exosites et provoque la déstabilisation du tétramère en dimères et en monomères inactifs, libérant ainsi un motif de dégradation ou dégron reconnu par des ubiquitines ligases SKP1-CUL1-F-box. Elles déclenchent alors la polyubiquitination de TDO, laquelle conduit à la dégradation de l’enzyme par le protéasome et à l’arrêt du catabolisme du tryptophane. In vivo, la stabilisation de la protéine TDO hépatique avec un analogue non métabolisable, l’alpha-méthyl-tryptophane, réduit de manière permanente la concentration plasmatique du tryptophane. Nos résultats décrivent un mécanisme d’adaptation rapide du catabolisme du tryptophane permettant une dégradation de l’acide aminé en excès et prévenant son catabolisme en dessous de sa teneur physiologique. Cette boucle de rétrocontrôle assure une régulation fine de la try, (BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 2021

The transcription factor HELIOS is best known for being expressed in CD4 regulatory T cells and in murine exhausted CD8 T cells. However, data on human HELIOS+ CD8 T cells are scarce and contradictory. In blood, 21% of human CD8 T cells are HELIOS+. The two main CD8 T cell subpopulations that express HELIOS are Tc17 and Tc1 effectors that recognize viral peptides presented by HLA-E. HELIOS+ Tc1 effectors produce lower amounts of IFN-g and TNF-a compared to their HELIOS- counterparts. It remains to be understood why so many individuals maintain in their blood high amounts of Tc1 effectors that secrete low amounts of cytokines and what the connection between HELIOS and HLA-E restriction means. In ovarian carcinomas, we found TOX+ CD8 T cells that express HELIOS, suggesting the existence of either HLA-E-restricted anti-tumor CD8 T cells or two populations of exhausted T cells, namely TOX+ HELIOS- and TOX+ HELIOS+., Le facteur de transcription HELIOS est connu pour être exprimé par les lymphocytes T CD4 régulateurs et des T CD8 épuisés murins. Cependant, les données sur la nature des lymphocytes T CD8 humains HELIOS+ sont rares et contradictoires. Nous montrons ici que les lymphocytes T CD8 HELIOS+ représentent 21% des lymphocytes T CD8 du sang et contiennent deux sous-populations: des Tc17 et des Tc1 effecteurs spécifiques de peptides viraux présentés par HLA-E. Les Tc1 effecteurs HELIOS+ produisent peu d’IFN-g et de TNF-a par rapport aux HELIOS-. Il reste à comprendre pourquoi tant de Tc1 effecteurs sanguins sécrètent peu de cytokines après activation et le lien entre l’expression d’HELIOS et la restriction HLA-E. Dans des carcinomes ovariens, certains lymphocytes T CD8 TOX+ expriment HELIOS, suggérant l’existence de lymphocytes T CD8 anti-tumeur restreints par HLA-E, ou la présence de deux populations de lymphocytes T épuisés : TOX+ HELIOS- / TOX+ HELIOS+., (BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 2021