Soluble total human leukocyte antigen class I and human leukocyte antigen-G molecules in kidney and kidney/pancreas transplantation

Biological Characteristics of HLA-G and Its Role in Solid Organ Transplantation

Organ transplantation is a lifesaving option for patients with advanced diseases. Rejection is regarded as one of the most severe risk factors post-transplantation. A molecule that contributes to immune tolerance and resisting rejection is human leukocyte antigen (HLA)-G, which belongs to the non-classical major histocompatibility complex class (MHC) I family. HLA-G was originally found to play a role during pregnancy to maintain immune tolerance between mother and child. It is expressed in the placenta and detected in several body fluids as soluble factor as well as different membrane isoforms on cells. Recent findings on HLA-G show that it can also play multifaceted roles during transplantation. This review will explain the general characteristics and biological function of HLA-G and summarize the views supporting the tolerogenic and other roles of HLA-G to better understand its role in solid organ transplantation (SOT) and its complications. Finally, we will discuss potential future research on the role of HLA-G in prevention, diagnosis, and treatment in SOT.

HLA-G1+ Expression in GGTA1KO Pigs Suppresses Human and Monkey Anti-Pig T, B and NK Cell Responses

The human leukocyte antigen G1 (HLA-G1), a non-classical class I major histocompatibility complex (MHC-I) protein, is a potent immunomodulatory molecule at the maternal/fetal interface and other environments to regulate the cellular immune response. We created GGTA1-/HLAG1+ pigs to explore their use as organ and cell donors that may extend xenograft survival and function in both preclinical nonhuman primate (NHP) models and future clinical trials. In the present study, HLA-G1 was expressed from the porcine ROSA26 locus by homology directed repair (HDR) mediated knock-in (KI) with simultaneous deletion of α-1-3-galactotransferase gene (GGTA1; GTKO) using the clustered regularly interspersed palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas9) gene-editing system. GTKO/HLAG1+ pigs showing immune inhibitory functions were generated through somatic cell nuclear transfer (SCNT). The presence of HLA-G1 at the ROSA26 locus and the deletion of GGTA1 were confirmed by next generation sequencing (NGS) and Sanger's sequencing. Fibroblasts from piglets, biopsies from transplantable organs, and islets were positive for HLA-G1 expression by confocal microscopy, flow cytometry, or q-PCR. The expression of cell surface HLA-G1 molecule associated with endogenous β2-microglobulin (β2m) was confirmed by staining genetically engineered cells with fluorescently labeled recombinant ILT2 protein. Fibroblasts obtained from GTKO/HLAG1+ pigs were shown to modulate the immune response by lowering IFN-γ production by T cells and proliferation of CD4+ and CD8+ T cells, B cells and natural killer (NK) cells, as well as by augmenting phosphorylation of Src homology region 2 domain-containing phosphatase-2 (SHP-2), which plays a central role in immune suppression. Islets isolated from GTKO/HLA-G1+ genetically engineered pigs and transplanted into streptozotocin-diabetic nude mice restored normoglycemia, suggesting that the expression of HLA-G1 did not interfere with their ability to reverse diabetes. The findings presented here suggest that the HLA-G1+ transgene can be stably expressed from the ROSA26 locus of non-fetal maternal tissue at the cell surface. By providing an immunomodulatory signal, expression of HLA-G1+ may extend survival of porcine pancreatic islet and organ xenografts.

New markers for predictions of acute and chronic rejection and graft outcomes in kidney transplant recipients; HLA-G gene 3'UTR 14 bp polymorphism and sHLA-G

The aim of this study was to evaluate the relation of Human Leukocyte Antigen-G (HLA-G) 14 bp ins/del (insertion/deletion) polymorphism and soluble HLA-G (sHLA-G) level with rejection in kidney transplant recipients. The study was planned as a case-control study involving two hundred fifty kidney transplant recipients. The case group consisted of 125 (female/male: 56/69) kidney transplant recipients diagnosed with acute (n = 52) and chronic rejection (n = 73). The control group consisted of one hundred twenty-five kidney transplant patients with no acute or chronic rejection matched by gender and age in the case group. The sHLA-G level in the recipient's plasma (at the time of rejection for the case, the same time as the case after the transplant for control) was analyzed by Enzyme-Linked Immunosorbent Assay (ELISA). HLA-G 3' untranslated region (3'UTR) polymorphism of recipient and donor was determined using agarose gel electrophoresis and DNA sequencing method. In our study, it was shown that acute rejection rate increased 1.06 times and chronic rejection rate increased 1.14 times in kidney transplant recipients with low serum sHLA-G levels. The rejection patients with the HLA-G 14 bp del/del genotype had higher sHLA-G levels post-transplantation. The frequency of acute rejection was lower in patients with HLA-G 14 bp del/del polymorphism than those with ins/ins and ins/del polymorphisms. This study proposes that HLA-G 3'UTR polymorphism and sHLA-G level might be useful in prediction of rejection in kidney transplant recipients.

Role and expression of non-classical human leukocyte antigen-G in renal transplanted allografts

BACKGROUND

The non-classical class I molecule human leukocyte antigen-G (HLA-G) has great potential to modulate the immune response. However, the mechanism underlying HLA-G induction remains unknown. Therefore, this study aimed to determine the factors that induce HLA-G expression on proximal tubular epithelial cells (pTECs) in renal transplanted allografts in vivo and in vitro.

METHODS

This study included 40 adult Japanese patients with renal allografts (35 and five patients with kidneys from living and deceased donors, respectively) who survived for at least 1 year. We evaluated HLA-G1/5 expression using an immunofluorescence method and investigated the induction of HLA-G expression in primary cultured human pTECs by cytokines and immunosuppressants.

RESULTS

The HLA-G expression was identified in the perinuclear region or on the basement membrane of pTECs of renal biopsy tissue in 12 (30%) of 40 patients at 2-4 weeks and at 1 year following transplantation. A reduction of 30% in the estimated glomerular filtration rate was lower in the HLA-G-positive group than that of the negative group (p = 0.016). Cox proportional hazard models also demonstrated that HLA-G1/5 expression on pTECs was an independent predictor of improved renal allograft function (hazard ratio, 0.189; 95% CI 0.041-0.850, p = 0.030). Interferon-beta was the most powerful inducer of HLA-G expression in vitro, whereas the immunosuppressants everolimus, tacrolimus, cyclosporin, and dexamethasone did not induce any expression.

CONCLUSION

Unlike immunosuppressants, acquired HLA-G expression might confer long-term renal preservation effects in renal transplanted allografts.

Association of HLA-G Polymorphisms in the 3'UTR Region and Soluble HLA-G with Kidney Graft Outcome

Background: Human leukocyte antigen G (HLA-G) belongs to nonclassical HLA I molecule involving in the suppression of immune response. Besides its profound effect to induce fetal tolerance, HLA-G expression has been associated with allograft acceptance. For the regulation of HLA-G levels, polymorphic sites within the 3' untranslated region (3'UTR) are of crucial importance. The aim of the study was to analyze the association between several HLA-G 3'UTR variants (+3003T/C, +3010C/G, +3027C/A, +3035C/T, +3142G/C, +3187A/G, and +3196C/G), soluble HLA-G (sHLA-G) level, and kidney graft outcome in the Slovak Caucasian population. Methods: We investigated 69 kidney transplant recipients (45 males, 24 females) of age 27-65 years. Out of this group, 37 recipients developed acute rejection that was biopsy proven. Recipient's plasma was obtained at 1 day before transplantation and analyzed by ELISA. The HLA-G 3'UTR polymorphisms were typed by direct sequencing. Results: In the recipients with stable allograft function, significantly higher values of sHLA-G were found in the homozygous +3010GG, +3142CC, +3187GG, and +3196CC carriers in comparison to the acute rejection recipients (P = 0.01-0.05). Conclusion: The study demonstrated genetic association between HLA-G 3'UTR variants and sHLA-G level in kidney recipients leading to graft acceptance. We suggest to monitor the pretransplantation sHLA-G level as additional marker to predict kidney graft outcome. Abbreviations: AMR: Antibody-mediated rejection; APC: antigen-presenting cell; CD: cluster of designation; del: deletion; HLA: human leukocyte antigen; ILT: immunoglobulin-like transcript; ins: insertion; KIR: killer-cell immunoglobulin-like receptor; NK: natural killer; sHLA-G: soluble HLA-G; SNP: single nucleotide polymorphism; TCMR: T cell-mediated rejection; URR: upstream regulatory region; UTR: untranslated region.

Effects of recombinant thrombomodulin therapy and soluble human leukocyte antigen-G levels during hematopoietic stem cell transplantation

BACKGROUND

Conditioning chemotherapies for hematopoietic stem cell transplantation (HSCT), especially those that include total body irradiation, can result in serious complications such as graft-versus-host disease (GVHD). Human leukocyte antigen G (HLA-G) is a non-classical class I molecule with multiple immunoregulatory functions.

METHODS

We measured interleukin (IL)-10, transforming growth factor (TGF)β₁, and soluble HLA-G (sHLA-G) in HSCT patients and examined the relationship between sHLA-G levels and acute GVHD (aGVHD). Additionally, we investigated the effect of recombinant soluble thrombomodulin (rTM) therapy on sHLA-G levels. Our study cohort included 135 patients who underwent allogeneic HSCT at several institutions in Japan.

RESULTS

Serum levels of IL-10 and TGFβ₁ exhibited no significant changes following HSCT. In contrast, levels of sHLA-G were significantly increased at days 21 and 28 post-HSCT. For patients with confirmed complications, the frequency of aGVHD was significantly lower in those with a > 2.8-fold increase in sHLA-G levels at day 28 relative to day 7 post-HSCT. sHLA-G levels in patients who received rTM therapy were significantly higher at days 21 and 28 post-HSCT compared with those in patients who did not receive rTM therapy.

CONCLUSION

These data suggest that HLA-G/sHLA-G participate in prevention of GVHD, and that rTM may prevent aGVHD following HSCT by promoting elevation of sHLA-G.

Immunological biomarkers of tolerance in human kidney transplantation: An updated literature review

The half-life of transplanted kidneys is <10 years. Acute or chronic rejections have a negative impact on transplant outcome. Therefore, achieving to allograft tolerance for improving long-term transplant outcome is a desirable goal of transplantation field. In contrast, there are evidence that distinct immunological characteristics lead to tolerance in some transplant recipients. In contrast, the main reason for allograft loss is immunological responses. Various immune cells including T cells, B cells, dendritic cells, macrophages, natural killer, and myeloid-derived suppressor cells damage graft tissue and, thereby, graft loss happens. Therefore, being armed with the comprehensive knowledge about either preimmunological or postimmunological characteristics of renal transplant patients may help us to achieve an operational tolerance. In the present study, we are going to review and discuss immunological characteristics of renal transplant recipients with rejection and compare them with tolerant subjects.

HLA-G and anti-HCV in patients on the waiting list for kidney transplantation

PURPOSE

Human leukocyte antigen (HLA)-G is a non-classic major histocompatibility complex HLA class I molecule. HLA-G may have tolerogenic properties which are linked to epigenetic-sensitive pathways. There is a correlation of sHLA-G levels and graft acceptance in transplantation studies. There are previous data on correlation of sHLA-G with graft rejection as well as with viral infections such as hepatitis C virus (HCV) in kidney transplanted patients. Here, we report the sHLA-G expression in patients on the waiting list for kidney transplantation, with and without anti-HCV compared to a control group.

METHODS

Serum of 67 patients on the waiting list for kidney transplantation (n = 43 with anti-HCV and n = 24 without anti-HCV) was analyzed. Among these patients, n = 39 were on the waiting list for the first transplantation, while n = 28 were patients who returned in the list. The control group included n = 23 blood donors with anti-HCV (n = 13) and without anti-HCV (n = 10).

RESULTS

The expression of sHLA-G was significantly lower in the control group (39.6 ± 34.1 U/ml) compared to both - patients on the waiting list for the first transplantation (62.5 ± 42.4 U/ml, p=0.031) and patients who returned in the list (76.7 ± 53.9 U/ml, p=0.006). No significant differences were observed in all anti-HCV positive groups. A positive linear correlation between sHLA-G and TNF-α, and patient age was observed.

CONCLUSIONS

Serum sHLA-G values were significantly increased in both - patients on the waiting list for the first transplantation and patients who returned in the list, as compared to control group. Our findings confirm the key tolerogenic role of sHLA-G levels as epigenetic-related marker for measuring the state of kidney allograft acceptance.

Recipient HLA-G +3142 CC Genotype and Concentrations of Soluble HLA-G Impact on Occurrence of CMV Infection after Living-Donor Kidney Transplantation

The expression modulation of the immunosuppressive non-classical Human leukocyte antigen-G (HLA-G) molecule and its soluble isoforms is an immune evasion strategy being deployed by cytomegalovirus (CMV). The +3142 C>G single nucleotide polymorphism (SNP) located within the 3′ untranslated region (3′UTR) is of crucial importance for the regulation of HLA-G expression. Therefore, we analyzed the influence of the +3142 C>G HLA-G SNP on the occurrence of CMV infection in a cohort of 178 living-donor kidney recipients and their 178 corresponding donors. In addition, soluble HLA-G (sHLA-G) levels were quantified before and after transplantation. The presence of the HLA-G +3142 CC genotype in recipients, but not donors of our cohort as along with elevated sHLA-G levels (≥6.1 ng/mL) were associated with higher susceptibility to CMV infection after transplantation. Our results provided evidence that (i) HLA-G is implicated in the establishment of CMV after living-donor kidney transplantation and (ii) recipient HLA-G +3142 CC genotype and sHLA-G concentration levels could represent important predictive risk markers for CMV infection.

The Mechanisms of Human Renal Epithelial Cell Modulation of Autologous Dendritic Cell Phenotype and Function

Proximal tubule epithelial cells (PTEC) of the kidney line the proximal tubule downstream of the glomerulus and play a major role in the re-absorption of small molecular weight proteins that may pass through the glomerular filtration process. In the perturbed disease state PTEC also contribute to the inflammatory disease process via both positive and negative mechanisms via the production of inflammatory cytokines which chemo-attract leukocytes and the subsequent down-modulation of these cells to prevent uncontrolled inflammatory responses. It is well established that dendritic cells are responsible for the initiation and direction of adaptive immune responses. Both resident and infiltrating dendritic cells are localised within the tubulointerstitium of the renal cortex, in close apposition to PTEC, in inflammatory disease states. We previously demonstrated that inflammatory PTEC are able to modulate autologous human dendritic cell phenotype and functional responses. Here we extend these findings to characterise the mechanisms of this PTEC immune-modulation using primary human PTEC and autologous monocyte-derived dendritic cells (MoDC) as the model system. We demonstrate that PTEC express three inhibitory molecules: (i) cell surface PD-L1 that induces MoDC expression of PD-L1; (ii) intracellular IDO that maintains the expression of MoDC CD14, drives the expression of CD80, PD-L1 and IL-10 by MoDC and inhibits T cell stimulatory capacity; and (iii) soluble HLA-G (sHLA-G) that inhibits HLA-DR and induces IL-10 expression by MoDC. Collectively the results demonstrate that primary human PTEC are able to modulate autologous DC phenotype and function via multiple complex pathways. Further dissection of these pathways is essential to target therapeutic strategies in the treatment of inflammatory kidney disorders.

HLA-G as a tolerogenic molecule in transplantation and pregnancy

HLA-G is a nonclassical HLA class I molecule. In allogeneic situations such as pregnancy or allograft transplantation, the expression of HLA-G has been related to a better acceptance of the fetus or the allograft. Thus, it seems that HLA-G is crucially involved in mechanisms shaping an allogeneic immune response into tolerance. In this contribution we focus on (i) how HLA-G is involved in transplantation and human reproduction, (ii) how HLA-G is regulated by genetic and microenvironmental factors, and (iii) how HLA-G can offer novel perspectives with respect to therapy.

HLA-G polymorphism (rs16375) and acute rejection in liver transplant recipients

Background. HLA-G molecules exhibit immunomodulatory properties that can delay graft rejection. The 14 bp insertion/deletion polymorphism (INDEL) (rs16375) influences the stability of final HLA-G mRNA and its soluble isoforms. Objective. The present study aimed to investigate the possible association between this polymorphism and the incidence of acute rejection in Iranian liver transplant recipients. Methods. Different genotypes were evaluated by PCR. The patients who had acute rejection within 6 months after transplantation were classified as acute rejection (AR) group, while others were considered as nonacute rejection (NAR) group. Results. Among the recipients, 21 patients (21%) had at least one episode of AR, while the other 79 patients (79%) had normal liver function. No significant differences were found between the two groups regarding sex, MELD score, and primary liver disease. Also, no difference was observed concerning rs16375 genotype and allele frequency (P = 0.44, OR: 0.69; CI: 0.21–2.10). Conclusion. The study results revealed no significant difference between the AR and the NAR groups regarding the 14 bp INDEL genotypes and alleles. Further studies are recommended to be conducted on other polymorphic sites as well as monitoring of serum HLA-G concentration in order to ascertain the potential implications of this marker in our population.

Soluble human leukocyte antigen G molecule expression in allogeneic hematopoietic stem cell transplantation: good predictor of acute graft-versus-host disease

BACKGROUND

Graft-versus-host disease (GVHD) remains a main complication of allogeneic hematopoietic stem cell transplantation (allo-HSCT). Human leukocyte antigen G (HLA-G) is a non-classical class I molecule exerting multiple immunoregulatory functions. The aim of this study was to explore the relationship between soluble HLA-G (sHLA-G) and GVHD after allo-HSCT.

METHODS

The sHLA-G levels were examined using enzyme-linked immunosorbent assay in patients with hematological malignancies (n = 106) before transplantation, on days +15 and +30 after transplantation, as well as healthy volunteers (n = 10).

RESULTS

The levels of sHLA-G5, sHLA-G6 and sHLA-G7 in patients on days +15 and +30 after transplantation were all significantly higher than those before transplantation (all p ≤ 0.001). The increased levels of sHLA-G5 on days +15 and +30 after transplantation were both significantly higher in patients with grade 0-I acute GVHD (aGVHD) compared to those with grade II-IV aGVHD (both p < 0.001). The increased levels of sHLA-G5 on days +15 and +30 after transplantation were both negatively correlated with the severity of aGVHD (both p < 0.001).

CONCLUSION

sHLA-G5 might be a predictor of the occurrence and severity of aGVHD, which may help to establish individual prophylaxis against aGVHD and improve the survival for patients after allo-HSCT.

The plasma levels of soluble HLA-G molecules correlate directly with CD34+ cell concentration and HLA-G 14bp insertion/insertion polymorphism in cord blood donors

BACKGROUND

Cord blood provides haematopoietic stem cells for allogeneic transplantation and, thanks to the naivety of its immune system, has several advantages over other sources of stem cells. In the transplantation setting, the presence of immunosuppressive human leucocyte antigen (HLA)-G molecules has been advocated to prevent both rejection and Graft-versus-Host disease. HLA-G is physiologically expressed throughout pregnancy and is contained in cord blood at birth. Moreover, it has recently been reported that not only cord blood mesenchymal cells, but also CD34+ cell progenies produce soluble HLA-G (sHLA-G). We tried to identify the largest producer of sHLA-G among 85 healthy cord blood donors at Pavia Cord Blood Bank, correlating the sHLA-G concentration with the HLA-G 14bp insertion/deletion (INS/DEL) genotype and CD34+ cell concentration.

MATERIALS AND METHODS

We measured sHLA-G levels in 36 cord blood plasma stored at -20 °C for 2 months and 49 cord blood plasma stored at -196 °C for 4-6 years, by enzyme-linked immunosorbent assay. All cord blood donors were genotyped for the HLA-G 14bp INS/DEL polymorphism by polymerase chain reaction. For each cord blood unit, we measured the cell concentration by flow cytometry.

RESULTS

We did not find differences in sHLA-G levels between cord blood plasma aliquots stored for 4-6 years at -196 °C and cord blood plasma aliquots stored for 2 months at -20 °C. We observed a higher sHLA-G concentration in cord blood plasma donors who carried the HLA-G 14bp INS/INS genotype and had higher CD34+ cell concentrations (P=0.006).

DISCUSSION

This is the first report showing that the best cord blood stem cell donor is also the best sHLA-G producer, particularly if genetically characterized by the HLA-G 14bp INS/INS genotype. If the therapeutic role of sHLA-G molecules were to be finally established in the transplantation setting, our data suggest that cord blood plasma donors can provide a safe source of allogeneic sHLA-G immunosuppressive molecules ready for transfusion.

Identification of a novel HLA-G+ regulatory population in blood: expansion after allogeneic transplantation and de novo HLA-G expression at graft-versus-host disease sites

BACKGROUND

The human leukocyte antigen-G (HLA-G) has been considered to be an important tolerogeneic molecule playing an essential role in maternal-fetal tolerance, which constitutes the perfect example of successful physiological immunotolerance of semi-allografts. In this context, we investigated the putative role of this molecule in the allogeneic hematopoietic cell transplantation setting.

DESIGN AND METHODS

The percentage of HLA-G(+) cells in peripheral blood of healthy donors and allo-transplanted patients was evaluated by flow cytometry. Their immunoregulatory and tolerogeneic properties were investigated in in vitro immunostimulatory and immunosuppression assays. Immunohistochemical analysis for HLA-G expression was performed in skin biopsies from allo-transplanted patients and correlated with the occurrence of graft-versus-host disease.

RESULTS

We identified a CD14(+)HLA-G(pos) population with an HLA-DR(low) phenotype and decreased in vitro immunostimulatory capacity circulating in peripheral blood of healthy individuals. Naturally occurring CD14(+)HLA-G(pos) cells suppressed T-cell responses and exerted an immunotolerogenic action on T cells by rendering them hyporesponsive and immunosuppressive in vitro. After allogeneic hematopoietic cell transplantation, HLA-G(pos) cells increase in blood. Interestingly, besides an increase in CD14(+)HLA-G(pos) cells, there was also a pronounced expansion of CD3(+)HLA-G(pos) cells. Of note, CD3(+)HLA-G(pos) and CD14(+)HLA-G(pos) cells from transplanted patients were suppressive in in vitro lymphoproliferation assays. Furthermore, we found an upregulation of HLA-G expression in skin specimens from transplanted patients that correlated with graft-versus-host disease. Inflammatory cells infiltrating the dermis of transplanted patients were also HLA-G(pos).

CONCLUSIONS

We report the presence of naturally occurring HLA-G(pos) monocytic cells with in vitro suppressive properties. HLA-G expressing regulatory blood cells were found in increased numbers after allogeneic transplantation. Epithelial cells in skin affected by graft-versus-host disease revealed elevated HLA-G expression.

HLA-G in organ transplantation: towards clinical applications

HLA-G plays a particular role during pregnancy in which its expression at the feto-maternal barrier participates into the tolerance of the allogenic foetus. HLA-G has also been demonstrated to be expressed in some transplanted patients, suggesting that it regulates the allogenic response. In vitro data indicate that HLA-G modulates NK cells, T cells, and DC maturation through its interactions with various inhibitory receptors. In this paper, we will review the data reporting the HLA-G involvement of HLA-G in human organ transplantation, then factors that can modulate HLA-G, and finally the use of HLA-G as a therapeutic tool in organ transplantation.

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.

Expression of soluble HLA-G identifies favorable outcomes in liver transplant recipients

BACKGROUND

Human leukocyte antigen (HLA)-G displays immunotolerogenic properties toward the main effector cells involved in graft rejection through inhibition of natural killer cell- and cytotoxic T-lymphocyte-mediated cytolysis, and CD4 T-cell alloproliferation. An increase in serum and graft levels of HLA-G has been noted in transplant patients with improved allograft survival. However, the clinical relevance of soluble serum HLA-G molecules in tolerant pediatric and young adult liver transplant patients remains to be studied.

METHODS

We examined the serum HLA-G levels in 42 pediatric and young adult liver transplant patients with a mean age of 15 years; 13 patients had operational tolerance (TOL), with complete immunosuppression withdrawal for 2.3 to 13.2 years.

RESULTS

Median HLA-G level in patients with acute rejection (AR) was similar to the level in pediatric healthy volunteers (9.9 vs. 4.2 U/mL, P=0.13). HLA-G was higher in patients with stable liver function on immunosuppression (54.6 U/mL) than in patients with AR (P=0.01) and healthy volunteers (P=0.003), but almost 6-fold lower than in TOL patients (325.4 U/mL). HLA-G did not correlate with clinical confounders or a history of posttransplant lymphoproliferative disease or Epstein-Barr virus; although levels in the TOL group were negatively correlated with time after immunosuppression withdrawal (r=-0.75, P=0.003). In rejectors, HLA-G levels trended to negatively correlate with a higher number (r=-0.58) and greater severity of AR episodes (r=-0.56) after 1 year posttransplantation.

CONCLUSIONS

Increased serum HLA-G levels track with operational tolerance of liver grafts and support favorable outcomes in pediatric and young adult recipients.

Human mesenchymal stem cells and renal tubular epithelial cells differentially influence monocyte-derived dendritic cell differentiation and maturation

Mesenchymal stem cells (MSCs) possess immunosuppressive properties. But also fully differentiated human renal tubular epithelial cells (RTECs) are able to modulate T-cell proliferation in vitro. In this study we compared two MSC populations, human adipose derived stem cells (ASCs) and human amniotic mesenchymal stromal cells (hAMSCs), and RTECs regarding their potential to inhibit monocyte-derived dendritic cell (DC) differentiation and maturation in indirect co-culture. In the presence of hAMSCs and RTECs, monocytes stimulated to undergo DC differentiation were inhibited to acquire surface phenotype of immature and mature DCs. In contrast, ASCs showed only limited suppressive capacity. Secretion of IL-12p70 was suppressed in hAMSC co-cultures and high IL-10 levels were detected in all co-cultures. Prostaglandin E(2) was found in ASC and hAMSC co-cultures, whereas soluble human leukocyte antigen-G was highly elevated only in RTEC co-cultures. Thus, inhibition of DC generation by MSCs and RTECs might be mediated by different soluble factors.