RESUMO
Trogocytosis is the uptake of membrane fragments from one cell by another and has been described for immune cells in mice and humans. Functional consequences of trogocytosis are emerging, but a dramatic immune function has still to be associated with it. Here we show that some resting, and most activated, CD4+ and CD8+ T cells acquire immunosuppressive HLA-G1 from antigen-presenting cells (APCs) in a few minutes. Acquisition of HLA-G through membrane transfers does not change the real nature of the T cells but immediately reverses their function from effectors to regulatory cells. These regulatory cells can inhibit allo-proliferative responses through HLA-G1 that they acquired. These data demonstrate that trogocytosis of HLA-G1 leads to instant generation of a new type of regulatory cells, which act through cell-surface molecules they temporarily display but do not express themselves. Such regulatory cells whose existence is most likely limited in space and time might constitute an "emergency" immune suppression mechanism used by HLA-G-expressing tissues to protect themselves against immune aggression. In addition, T cells acquire from HLA-G-expressing APCs their HLA-G-dependent capability to induce the slower differentiation of regulatory cells that act independently of HLA-G. These data re-emphasize the significance of HLA-G expression in normal and pathologic situations.
Assuntos
Comunicação Celular/imunologia , Antígenos HLA/metabolismo , Antígenos de Histocompatibilidade Classe I/metabolismo , Linfócitos T Reguladores/imunologia , Linfócitos T Reguladores/metabolismo , Células Apresentadoras de Antígenos/imunologia , Diferenciação Celular , Células Cultivadas , Antígenos HLA/imunologia , Antígenos HLA-G , Antígenos de Histocompatibilidade Classe I/imunologia , Humanos , Ativação Linfocitária/imunologia , Linfócitos T Reguladores/citologiaRESUMO
HLA-G is a tolerogenic molecule whose detection in sera and within allografted tissues is associated with better graft acceptance. HLA-G mediates T-cell differentiation into suppressor cells, which are thought to promote tolerance. Here, we investigated such T cells phenotypically and functionally and assessed their clinical relevance in the peripheral blood of patients who have undergone transplantation. Our results demonstrate that HLA-G expressed by antigen-presenting cells or present as soluble protein down-regulates the expression of CD4 and CD8 on allostimulated T cells at both transcriptional and posttranslational levels. These CD3(+)CD4(low) and CD3(+)CD8(low) T-cell subsets are characterized by an increased proportion of cells expressing CD45RA and HLA-DR, and a decreased number of cells expressing CD62L. In addition, these HLA-G-induced CD3(+)CD4(low) and CD3(+)CD8(low) subpopulations are Foxp3-negative suppressor T cells whose function involves IL-10. Biologic relevance came from analysis of patients who underwent transplantation, with high HLA-G plasma concentrations associated with better graft survival. Peripheral blood from these patients contains increased levels of IL-10 concomitantly to an enhanced representation of CD3(+)CD4(low) and CD3(+)CD8(low) T cells compared with HLA-G-negative patients who underwent transplantation and healthy individuals. These data define novel immunosuppressive subpopulations of peripheral blood T cells induced by HLA-G with potent implications in peripheral tolerance.
Assuntos
Complexo CD3/imunologia , Antígenos CD4/imunologia , Antígenos CD8/imunologia , Linfócitos T CD8-Positivos/imunologia , Sobrevivência de Enxerto/imunologia , Antígenos HLA/imunologia , Antígenos de Histocompatibilidade Classe I/imunologia , Transplante de Rim/imunologia , Transplante de Fígado/imunologia , Tolerância ao Transplante , Adulto , Células Apresentadoras de Antígenos/imunologia , Células Apresentadoras de Antígenos/metabolismo , Complexo CD3/biossíntese , Antígenos CD4/biossíntese , Antígenos CD8/biossíntese , Linfócitos T CD8-Positivos/metabolismo , Feminino , Fatores de Transcrição Forkhead/biossíntese , Fatores de Transcrição Forkhead/imunologia , Regulação da Expressão Gênica/imunologia , Antígenos HLA/sangue , Antígenos HLA-G , Antígenos de Histocompatibilidade Classe I/sangue , Humanos , Interleucina-10/biossíntese , Interleucina-10/imunologia , Selectina L/biossíntese , Selectina L/imunologia , Masculino , Pessoa de Meia-IdadeRESUMO
The soluble HLA-G5 isoform encoded by intron-4 retaining spliced transcript has been previously detected in vivo in sera and grafts from transplanted patients who had significantly better graft acceptance. These findings led us to investigate the role of HLA-G5 in tolerance induction in vitro and its biological relevance in allograft acceptance in vivo. We demonstrated that engagement of Ig-like transcript-2 and Ig-like transcript-4 receptors by HLA-G5 is involved in inhibition of T cell alloproliferative responses. Naive T cells sensitized in vitro with HLA-G5, for as little as 18 h, 1) lost their ability to respond to subsequent allogeneic stimulus, and 2) acquired regulatory properties because they inhibited the reactivity of other T cells. These HLA-G5-induced T cells act in an Ag-nonspecific fashion and through soluble factors. Biological relevance was provided by ex vivo analyzes of samples from liver-kidney cotransplanted patients who had high HLA-G5 serum levels and no graft rejection. We showed that addition of HLA-G5-containing sera from these patients inhibited T cell alloresponses and that serum HLA-G5 was responsible for this inhibition. Notably, PBMC from transplanted patients exposed to high levels of circulating HLA-G5 did not respond to allostimulation and inhibited alloreactivity of other T cells. These results demonstrate that HLA-G5-mediated tolerance involves the induction of immunosuppressive T cells. These findings provide evidence supporting the tolerogenic properties of HLA-G and emphasize its potential application as a relevant therapeutic candidate capable of limiting allograft rejection.
Assuntos
Diferenciação Celular/imunologia , Sobrevivência de Enxerto/imunologia , Antígenos HLA/fisiologia , Antígenos de Histocompatibilidade Classe I/fisiologia , Ativação Linfocitária/imunologia , Linfócitos T Reguladores/imunologia , Tolerância ao Transplante/imunologia , Antígenos CD/fisiologia , Proliferação de Células , Células Cultivadas , Feminino , Antígenos HLA-G , Humanos , Transplante de Rim/imunologia , Receptor B1 de Leucócitos Semelhante a Imunoglobulina , Transplante de Fígado/imunologia , Masculino , Glicoproteínas de Membrana/fisiologia , Pessoa de Meia-Idade , Receptores Imunológicos/fisiologia , Linfócitos T Reguladores/metabolismo , Transplante HomólogoRESUMO
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.
Assuntos
Antígenos HLA/imunologia , Antígenos de Histocompatibilidade Classe I/imunologia , Tolerância Imunológica/imunologia , Indolamina-Pirrol 2,3,-Dioxigenase/imunologia , Linfócitos T/imunologia , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Ensaio de Imunoadsorção Enzimática/métodos , Antígenos HLA/sangue , Antígenos HLA-G , Antígenos de Histocompatibilidade Classe I/sangue , Humanos , Cinurenina/farmacologia , Ativação Linfocitária , Teste de Cultura Mista de Linfócitos , Transdução de Sinais/imunologia , Linfócitos T/efeitos dos fármacos , Regulação para Cima/imunologiaRESUMO
Nonclassical human leukocyte antigen (HLA) class I molecule HLA-G and indoleamine 2,3 dioxygenase (INDO) in humans and mice, respectively, have been shown to play crucial immunosuppressive roles in fetal-maternal tolerance. HLA-G inhibits natural killer and T cell function by high-affinity interaction with inhibitory receptors, and INDO acts by depleting the surrounding microenvironment of the essential amino acid tryptophan, thus inhibiting T cell proliferation. We investigated whether HLA-G expression and INDO function were linked. Working with antigen-presenting cell (APC) lines and monocytes, we found that functional inhibition of INDO by 1-methyl-tryptophan induced cell surface expression of HLA-G1 by HLA-G1-negative APCs that were originally cell-surface negative, and that in reverse, the functional boost of INDO by high concentrations of tryptophan induced a complete loss of HLA-G1 cell surface expression by APCs that were originally cell-surface HLA-G1-positive. This mechanism was shown to be posttranslational because HLA-G protein cell contents remained unaffected by the treatments used. Furthermore, HLA-G cell surface expression regulation by INDO seems to relate to INDO function, but not to tryptophan catabolism itself. Potential implications in fetal-maternal tolerance are discussed.
Assuntos
Antígenos HLA/biossíntese , Antígenos de Histocompatibilidade Classe I/biossíntese , Processamento de Proteína Pós-Traducional/fisiologia , Triptofano Oxigenase/metabolismo , Linhagem Celular , Antígenos HLA-G , Humanos , Monócitos/imunologia , Processamento de Proteína Pós-Traducional/efeitos dos fármacos , Triptofano/análogos & derivados , Triptofano/farmacologia , Triptofano/fisiologia , Regulação para CimaRESUMO
Most types of cancer are difficult to eradicate, and some, like hepatocellular carcinoma, are almost always fatal. Among various interventions to improve the survival of patients with cancer, immunotherapy seems to hold some promises. However, it requires relevant animal models for preclinical development. In this study we report a new and relevant experimental model where liver tumors grow inside a nontumoral parenchyma of adult mice. This model is based on the intrasplenic injection in syngeneic recipient mice of hepatocytes from transgenic mice expressing SV40 large T oncogene specifically in the liver. Using this model where no apparent spontaneous cellular immune response was observed, immunization using a single injection of monoepitopic SV40 T Ag short peptide was sufficient to provoke liver tumor destruction, leading rapidly to complete remission. Tumor regression was associated with the induction of a long-lasting CD8+ T cell response, observed not only in the spleen but also, more importantly, in the tumoral liver. These results show the efficacy of peptide immunotherapy in the treatment of liver cancer.
Assuntos
Antígenos Transformantes de Poliomavirus/imunologia , Linfócitos T CD8-Positivos/imunologia , Neoplasias Hepáticas Experimentais/terapia , Fragmentos de Peptídeos/imunologia , Animais , Movimento Celular , Imunização , Imunoterapia , Interferon gama/biossíntese , Neoplasias Hepáticas Experimentais/imunologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos TransgênicosRESUMO
HLA-G displays immunotolerogenic properties towards the main effector cells involved in graft rejection through inhibition of NK- and CTL-mediated cytolysis and CD4+ T cell alloproliferation. HLA-G expression is restricted in healthy tissues to trophoblast and thymus but is extended to various tissues under pathological conditions. HLA-G was detected in allograft biopsies and sera from transplanted patients who displayed a better graft acceptance. However, the cells involved in such de novo expression of HLA-G remain to be characterized. By flow cytometry and confocal microscopy, we demonstrated that, following allogeneic stimulation in vitro, both CD4+ and CD8+ T cell subsets can express membrane-bound HLA-G1 and/or soluble HLA-G5 molecules. Such HLA-G1/-G5 expression is regulated at the transcriptional level. Soluble HLA-G5 could be detected by using a novel monoclonal antibody, 5A6G7, specific for the intron 4-retaining sequence of HLA-G5. Finally, the biological relevance of these data was provided by analysis of transplanted patients in whom we identified both CD4+ and CD8+ T cells expressing HLA-G. The HLA-G-positive T cells we describe here may constitute a cellular source of HLA-G after allotransplantation and may be involved in the improved graft acceptance which is observed in HLA-G-positive transplanted patients.