Edgardo D. Carosella

Altered HLA-G transcription in pre-eclampsia is associated with allele specific inheritance: possible role of the HLA-G gene in susceptibility to the disease

Abstract: Pre-eclampsia is a disorder of human pregnancy occuring in 5-10 % of all births, and represents the leading cause of infant morbidity and mortality and maternal death. In pre-eclampsia, invasion of fetal trophoblasts into maternal arteries during early pregnancy is shallow or absent. Here we examined the hypothesis that HLA-G, a non-classical class I HLA expressed in cytotrophoblasts, may act as a key gene in pre-eclampsia. We analysed HLA-G at the level of transcription and genotyped a silent CAC-CAT polymorphism in exon 3 and a 14-bp insertion/deletion in the 3′ untranslated region. A deficit in levels of the HLA-G3 transcript was observed in mild pre-eclampsia compared to normal placentas. The distribution of HLA-G polymorphisms was different between normal and pre-eclampsia samples. A correlation between the alteration in transcription of the HLA-G gene and certain HLA-G genotypes was also observed. Thus we provide the first evidence for a possible role of HLA-G in genetic susceptibility to, and pathogenesis of pre-eclampsia.

Modulation of dendritic cell differentiation by HLA-G and ILT4 requires the IL-6—STAT3 signaling pathway

The expression of Ig-like transcript (ILT) inhibitory receptors is a characteristic of tolerogenic dendritic cells (DCs). However, the mechanisms of modulation of DCs via ILT receptors remain poorly defined. HLA-G is a preferential ligand for several ILTs. Recently, we demonstrated that triggering of ILT4 by HLA-G1 inhibits maturation of human monocyte-derived conventional DCs and murine DCs from ILT4 transgenic mice, resulting in diminished expression of MHC class II molecules, CD80 and CD86 costimulatory molecules, and prolongation of skin allograft survival. Different isoforms of HLA-G have diverse effects on the efficiency to induce ILT-mediated signaling. In this work, we show that HLA-G1 tetrameric complex and HLA-G5 dimer, but not HLA-G5 monomer, induce strong ILT-mediated signaling. We determined that the arrest of maturation of ILT4-positive DCs by HLA-G ligands involves the IL-6 signaling pathway and STAT3 activation. Ligation of ILT4 with HLA-G on DCs results in recruitment of SHP-1 and SHP-2 protein tyrosine phosphatases. We propose a model where SHP-2 and the IL-6–STAT3 signaling pathway play critical roles in the modulation of DC differentiation by ILT4 and HLA-G.

The immunosuppressive molecule HLA-G and its clinical implications

Human leukocyte antigen G (HLA-G) is a non-classical major histocompatibility complex (MHC) class I molecule that, through interaction with its receptors, exerts important tolerogenic functions. Its main physiological expression occurs in placenta where it seems to participate in the maternal tolerance toward the fetus. HLA-G has been studied as a marker of pregnancy complications such as abortion or pre-eclapmsia. Although HLA-G is not expressed in most adult tissues, its ectopic expression has been observed in some diseases such as viral infections, autoimmune disorders, and especially cancer. HLA-G neo-expression in cancer is associated with the capability of tumor cells to evade the immune control. In this review, we will summarize HLA-G biology and how it participates in these physiopathological processes. Special attention will be paid to its role as a diagnostic tool and also as a therapeutic target.

A Systematic Review of Immunotherapy in Urologic Cancer: Evolving Roles for Targeting of CTLA-4, PD-1/PD-L1, and HLA-G

CONTEXTnOverexpression of immune checkpoint molecules affects tumor-specific T-cell immunity in the cancer microenvironment, and can reshape tumor progression and metastasis. Antibodies targeting checkpoints could restore antitumor immunity by blocking the inhibitory receptor-ligand interaction.nnnOBJECTIVEnTo analyze data and current trends in immune checkpoint targeting therapy for urologic cancers.nnnEVIDENCE ACQUISITIONnSystematic literature search for clinical trials in the PubMed and Cochrane databases up to August 2014 according to Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Endpoints included oncologic results, tumor response rates, safety, and tolerability.nnnEVIDENCE SYNTHESISnAnti-CTLA-4 monotherapy has demonstrated biochemical responses in prostate cancer. One phase 3 trial assessing ipilimumab efficacy in castration-resistant disease was negative overall. Nevertheless, ipilimumab may significantly improve overall survival compared with placebo in subgroups of patients with favorable prognostic features. In renal cancer, phase 1 trials showed interesting stabilization or long-lasting objective response rates approaching 50% using anti-PD-1/PD-L1 drugs in heavily pretreated metastatic patients. In bladder cancer, one phase 2 trial indicated a good safety profile for ipilimumab as a neoadjuvant drug before radical cystectomy. Overall, immune-related effects such as colitis and dermatitis were common and well tolerated.nnnCONCLUSIONSnOur systematic review shows that antibodies blocking immune checkpoints offer interesting and long-lasting response rates in heavily pretreated patients with advanced urologic cancers. More promising results are currently provided by anti-CTLA-4 antibodies in prostate cancer and by PD-1/PD-L1 inhibitors in renal cancer. These should encourage new clinical trials of immune therapy combinations and immunotherapy monotherapy combined with conventional anticancer drugs. In bladder cancer, the use of targeted immunotherapy still remains underevaluated; however, preliminary results reported at recent conferences seem encouraging.nnnPATIENT SUMMARYnData from studies support the activity and safety of immune checkpoint inhibitors in urologic cancers, alone or in combination with conventional cancer therapies. Encouraging data in other oncologic fields could translate into interesting responses in urological cancers.

HLA-G: An Immune Checkpoint Molecule

HLA-G is a molecule that was first known to confer protection to the fetus from destruction by the immune system of its mother, thus critically contributing to fetal-maternal tolerance. The first functional finding constituted the basis for HLA-G research and can be summarized as such: HLA-G, membrane-bound or soluble, strongly binds its inhibitory receptors on immune cells (NK, T, B, monocytes/dendritic cells), inhibits the functions of these effectors, and so induces immune inhibition. HLA-G function may therefore be beneficial because when expressed by a fetus or a transplant it protects them from rejection, or deleterious because when expressed by a tumor, it also protects it from antitumor immunity. This is the primary HLA-G function: that of a checkpoint molecule. Great work has been done in the past years to characterize HLA-G itself, its regulation, its functions and mechanisms of action, and its pathological relevance. We will review this here, focusing on transplantation and oncology because these pathological contexts have been studied the most and also because they best represent the two opposite sides of HLA-G: beneficial to be promoted, or deleterious to be blocked.

Recent advances on the non‐classical major histocompatibility complex class I HLA‐G molecule

The human leukocyte antigen (HLA)-G non-classical major histocompatibility complex (MHC) class I molecule was originally described in first-trimester trophoblasts at the fetal-maternal interface in 1990. Eight years later, the First International Conference on this molecule was inaugurated by Prof Jean Dausset, recipient of the Nobel Prize in Medicine. The Fifth International Conference on HLA-G, held in Paris on July 2009, began with a tribute to Prof Jean Dausset who left us recently. This conference was co-chaired by Dr Edgardo D. Carosella and Prof Hans Grosse-Wilde, included 57 oral presentations and was attended by approximately 140 delegates from 16 countries. We summarize here the major advances on the HLA-G molecule that were reported, including findings on its biological activity and characterization of new mechanisms of action, notably through mesenchymal stem cells and regulatory cells, and the previously unexplored role of HLA-G on immune cells such as gammadelta T-cells and B lymphocytes. Furthermore, the role of HLA-G during pregnancy was revisited and its impact in pathologies such as cancer, autoimmune disorders and transplantation was further extended.

The tolerogenic molecule HLA-G.

Three recent publications review the basic immunological, clincal, and regulation aspects of HLA-G [1–3]. Briefly, HLA-G is haracterized by a low amount of polymorphism and a tissueestricted expression that can be induced in transplantation, nflammatory diseases, cancers, multiple sclerosis, and viral infecions. The expression regulation of the HLA-G gene is regulated hrough epigenetic mechanisms, and occurs at the transcriptional nd post-transcriptional levels. The HLA-G primary transcript ields the production of 7 isoforms, four of which are membraneound (HLA-G1 through HLA-G4), and three are soluble (HLA-G5 hrough HLA-G7). Functionally, HLA-G inhibits the cytolytic function of NK cells nd T lymphocytes, the alloproliferative response of CD4+ T cells, he on-going proliferation of T cells and NK cells, the maturation f dendritic cells, and induces regulatory T cells. HLA-G binds the nhibitory receptors ILT2 (CD85j/LILRB1), ILT4 (CD85d/LILRB2), and IR2DL4 (CD158d). Clinically, the expression of HLA-G has been correlated with the olerance of the fetus by its mother, the acceptance of solid organ ransplants, and the immune escape of tumors and virus-infected ells.

Human leukocyte antigen–G is expressed in advanced-stage ovarian carcinoma of high-grade histology

HLA-G is a nonclassical MHC class I molecule with restricted normal tissue distribution, but whose expression is induced in pathologic situations such as cancer. In regard to the its immunosuppressive properties, it has been suggested that HLA-G could be a way for tumors to escape immunosurveillance. HLA-G has been described in almost all types of cancer, whatever their origins. Ovarian cancer is the second leading cause of death among women with gynecologic cancers, after breast cancer. The high mortality rate of this pathology is linked to its late discovery resulting from discreet symptomatology at early stages and the current paucity of highly sensitive and specific biomarkers. The aim of the present study was to analyze, in a French, retrospectively based study, whether HLA-G could be a marker for the detection of ovarian cancer and the prediction of clinical evolution. For this purpose, we looked for HLA-G expression in ovarian carcinoma lesions from low to high grade and stage, and we showed that HLA-G is selectively expressed in advanced-stage disease of high-grade histology.

Indoleamine 2,3 dioxygenase and human leucocyte antigen-G inhibit the T-cell alloproliferative response through two independent pathways

Both human leucocyte antigen (HLA)‐G and indoleamine 2,3 dioxygenase (IDO) are key molecules involved in immune tolerance. HLA‐G is a non‐classical HLA class I molecule that can be expressed in both membrane‐bound (HLA‐G1) and soluble (HLA‐G5) forms, both of which exhibit tolerogenic properties via interaction with inhibitory receptors present on natural killer (NK) cells, T cells and antigen‐presenting cells (APC). IDO is an enzyme that acts by depleting the surrounding microenvironment of the essential amino acid, tryptophan, thereby inhibiting T‐cell proliferation. Our present study was aimed at analysing the potential link that may exist between IDO and HLA‐G. Our results showed that during allogeneic reactions, soluble HLA‐G expression was not regulated by the addition of IDO substrate (i.e. tryptophan), metabolite (i.e. kynurenine) or inhibitor (i.e. 1‐methyl‐tryptophan), that IDO activity was not altered by HLA‐G5 treatment, and that HLA‐G5‐mediated inhibition of the T‐cell alloproliferative response was neither affected by the presence of tryptophan and kynurenine nor reversed after IDO activity blockage, demonstrating that HLA‐G5 can exert its function in the absence of functional IDO. Similarly, inhibition of the T‐cell alloresponse, induced by HLA‐G1‐expressing antigen‐presenting cells, was not altered by IDO metabolites or inhibitor. Taken together, these findings show that the function and expression of IDO and HLA‐G5 are not mutually influenced, but rather inhibit the T‐cell alloproliferative response through two independent pathways. IDO and HLA‐G are thus complementary for inducing and maintaining immune tolerance in physiological (pregnancy) and pathological (tumour and allograft) situations.

HLA‐G1 and HLA‐G5 active dimers are present in malignant cells and effusions: The influence of the tumor microenvironment

Dimers of the nonclassical HLA‐G class I molecule have recently been shown to be active structures that mediate inhibition of NK‐cell cytotoxic activity through interaction with the immunoglobulin‐like transcript (ILT)‐2 inhibitory receptor. However, this has only been proven in trophoblasts and HLA‐G transfectants. Here, we document for the first time the existence of HLA‐G dimers in cancer. Indeed, we identified both surface and soluble HLA‐G dimers in tumor cells and malignant ascites respectively. Interestingly, factors from the tumor microenvironment, such as interferons, enhanced the formation of HLA‐G dimers and increased the protection of tumors from NK cell‐mediated lysis. These data emphasize the impact of HLA‐G conformation on its efficiency at inhibiting the antitumor response and thus favoring tumor progression. In view of these results, the effect of the tumor microenvironment on upregulation of HLA‐G function deserves particular attention when designing cancer immunotherapy protocols.