Tolerogenic Function of Dimeric Forms of HLA-G Recombinant Proteins: A Comparative Study In Vivo

HLA-G is a natural tolerogenic molecule involved in the best example of tolerance to foreign tissues there is: the maternal-fetal tolerance. The further involvement of HLA-G in the tolerance of allogeneic transplants has also been demonstrated and some of its mechanisms of action have been elucidated. For these reasons, therapeutic HLA-G molecules for tolerance induction in transplantation are actively investigated. In the present study, we studied the tolerogenic functions of three different HLA-G recombinant proteins: HLA-G heavy chain fused to β2-microglobulin (B2M), HLA-G heavy chain fused to B2M and to the Fc portion of an immunoglobulin, and HLA-G alpha-1 domain either fused to the Fc part of an immunoglobulin or as a synthetic peptide. Our results demonstrate the tolerogenic function of B2M-HLA-G fusion proteins, and especially of B2M-HLA-G5, which were capable of significantly delaying allogeneic skin graft rejection in a murine in vivo transplantation model. The results from our studies suggest that HLA-G recombinant proteins are relevant candidates for tolerance induction in human transplantation

Testing the theory of immune selection in cancers that break the rules of transplantation

Modification of cancer cells likely to reduce their immunogenicity, including loss or down-regulation of MHC molecules, is now well documented and has become the main support for the concept of immune surveillance. The evidence that these modifications, in fact, result from selection by the immune system is less clear, since the possibility that they may result from reorganized metabolism associated with proliferation or from cell de-differentiation remains. Here, we (a) survey old and new transplantation experiments that test the possibility of selection and (b) survey how transmissible tumours of dogs and Tasmanian devils provide naturally evolved tests of immune surveillance

Long-Lasting Inhibitory Effects of Fetal Liver Mesenchymal Stem Cells on T-Lymphocyte Proliferation

Human bone marrow mesenchymal stem cells (BM-MSC) are multipotent progenitor cells that have transient immunomodulatory properties on Natural Killer (NK) cells, Dendritic Cells (DC), and T cells. This study compared the use of MSC isolated from bone marrow and fetal liver (FL-MSC) to determine which displayed the most efficient immunosuppressive effects on T cell activation. Although both types of MSC exhibit similar phenotype profile, FL-MSC displays a much more extended in vitro life-span and immunomodulatory properties. When co-cultured with CD3/CD28-stimulated T cells, both BM-MSC and FL-MSC affected T cell proliferation by inhibiting their entry into the cell cycle, by inducing the down-regulation of phospho-retinoblastoma (pRb), cyclins A and D1, as well as up-regulating p27kip1expression. The T cell inhibition by MSC was not due to the soluble HLA-G5 isoform, but to the surface expression of HLA-G1, as shown by the need of cell-cell contact and by the use of neutralizing anti-HLA-G antibodies. To note, in a HLA-G-mediated fashion, MSC facilitated the expansion of a CD4low/CD8low T subset that had decreased secretion of IFN-γ, and an induced secretion of the immunomodulatory cytokine IL-10. Because of their longer lasting in vitro immunosuppressive properties, mainly mediated by HLA-G, and their more efficient induction of IL-10 production and T cell apoptosis, fetal liver MSC could be considered a new tool for MSC therapy to prevent allograft rejection

MiRNA-Mediated Control of HLA-G Expression and Function

HLA-G is a non-classical HLA class-Ib molecule expressed mainly by the extravillous cytotrophoblasts (EVT) of the placenta. The expression of HLA-G on these fetal cells protects the EVT cells from immune rejection and is therefore important for a healthy pregnancy. The mechanisms controlling HLA-G expression are largely unknown. Here we demonstrate that miR-148a and miR-152 down-regulate HLA-G expression by binding its 3′UTR and that this down-regulation of HLA-G affects LILRB1 recognition and consequently, abolishes the LILRB1-mediated inhibition of NK cell killing. We further demonstrate that the C/G polymorphism at position +3142 of HLA-G 3′UTR has no effect on the miRNA targeting of HLA-G. We show that in the placenta both miR-148a and miR-152 miRNAs are expressed at relatively low levels, compared to other healthy tissues, and that the mRNA levels of HLA-G are particularly high and we therefore suggest that this might enable the tissue specific expression of HLA-G

Breast cancer stroma frequently recruits fetal derived cells during pregnancy

Breast carcinomas associated with pregnancy display a high frequency of inflammatory types, multifocal lesions and lymph node metastasis. Because pregnancy results in transfer to mothers of foetal stem cells that can migrate and differentiate into various tissues, we addressed the issue of whether such cells are present in breast carcinoma associated with pregnancy

A Novel Mechanism of Soluble HLA-G Mediated Immune Modulation: Downregulation of T Cell Chemokine Receptor Expression and Impairment of Chemotaxis

BACKGROUND: In recent years, many immunoregulatory functions have been ascribed to soluble HLA-G (sHLA-G). Since chemotaxis is crucial for an efficient immune response, we have investigated for the first time the effects of sHLA-G on chemokine receptor expression and function in different human T cell populations. METHODOLOGY/PRINCIPAL FINDINGS: T cell populations isolated from peripheral blood were stimulated in the presence or absence of sHLA-G. Chemokine receptors expression was evaluated by flow cytometry. sHLA-G downregulated expression of i) CCR2, CXCR3 and CXCR5 in CD4(+) T cells, ii) CXCR3 in CD8(+) T cells, iii) CXCR3 in Th1 clones iv) CXCR3 in TCR Vdelta2gamma9 T cells, and upregulated CXCR4 expression in TCR Vdelta2gamma9 T cells. sHLA-G inhibited in vitro chemotaxis of i) CD4(+) T cells towards CCL2, CCL8, CXCL10 and CXCL11, ii) CD8(+) T cells towards CXCL10 and CXCL11, iii) Th1 clones towards CXCL10, and iv) TCR Vdelta2gamma9 T cells towards CXCL10 and CXCL11. Downregulation of CXCR3 expression on CD4+ T cells by sHLA-G was partially reverted by adding a blocking antibody against ILT2/CD85j, a receptor for sHLA-G, suggesting that sHLA-G downregulated chemokine receptor expression mainly through the interaction with ILT2/CD85j. Follicular helper T cells (T(FH)) were isolated from human tonsils and stimulated as described above. sHLA-G impaired CXCR5 expression in T(FH) and chemotaxis of the latter cells towards CXCL13. Moreover, sHLA-G expression was detected in tonsils by immunohistochemistry, suggesting a role of sHLA-G in local control of T(FH) cell chemotaxis. Intracellular pathways were investigated by Western Blot analysis on total extracts from CD4+ T cells. Phosphorylation of Stat5, p70 s6k, beta-arrestin and SHP2 was modulated by sHLA-G treatment. CONCLUSIONS/SIGNIFICANCE: Our data demonstrated that sHLA-G impairs expression and functionality of different chemokine receptors in T cells. These findings delineate a novel mechanism whereby sHLA-G modulates T cell recruitment in physiological and pathological conditions

Implications of the polymorphism of HLA-G on its function, regulation, evolution and disease association

The HLA-G gene displays several peculiarities that are distinct from those of classical HLA class I genes. The unique structure of the HLA-G molecule permits a restricted peptide presentation and allows the modulation of the cells of the immune system. Although polymorphic sites may potentially influence all biological functions of HLA-G, those present at the promoter and 3′ untranslated regions have been particularly studied in experimental and pathological conditions. The relatively low polymorphism observed in the MHC-G coding region both in humans and apes may represent a strong selective pressure for invariance, whereas, in regulatory regions several lines of evidence support the role of balancing selection. Since HLA-G has immunomodulatory properties, the understanding of gene regulation and the role of polymorphic sites on gene function may permit an individualized approach for the future use of HLA-G for therapeutic purposes

The HLA-G non classical MHC class I molecule is expressed in cancer with poor prognosis. Implications in tumour escape from immune system and clinical applications

Deep insight on The HLA-G non classical MHC class I molecule is expressed in cancer with poor prognosis. Implications in tumour escape from immune system and clinical applications