Production of IL-10 by alloreactive sibling donor cells and its influence on the development of acute GVHD

Modulation of the secretion of mesenchymal stem cell immunoregulatory factors by hydrolyzed fish collagen

The aim of the present study was to investigate the possible immunomodulatory effects of osteogenically differentiated bone marrow mesenchymal stem cells induced by hydrolyzed fish collagen. Marine biomaterials have attracted significant attention for their environmental friendliness and renewability. Hydrolyzed fish collagen (HFC) has been discovered to induce the osteoblastic differentiation of stem cells, which underlies the foundation for its application in tissue engineering. Stem cells and their biomaterial carriers face acute immune rejection mediated by host macrophages. A potential strategy for combatting rejection in stem cell therapy is to modify the polarization of macrophages. However, whether HFC-induced mesenchymal stem cells maintain their immunomodulatory ability remains to be determined. To understand this phenomenon, a co-culture model of direct contact was established between bone marrow mesenchymal stem cells (BMSCs) and RAW264.7 macrophages, where the secretion of nitrous oxide from macrophages was measured using Griess colorimetric assay. ELISAs were performed to measure the secretion of interleukin (IL)-1β, IL-6, transforming growth factor (TGF)-β and IL-10, whilst reverse transcription-quantitative PCR was used to assess the expression levels of IL-1β, IL-6, CD206, resistin-like molecule α (FIZZ1) and prostaglandin E2 receptor 4 (EP4). In addition, the expression levels of relevant proteins in the phosphorylated-cyclic AMP-responsive element-binding protein-CCAAT/enhancer-binding protein β (EBPβ) pathway were investigated using western blotting. HFC-induced BMSCs were found to suppress the expression levels of IL-1β and IL-6, whilst increasing the expression levels of CD206 and FIZZ1 in RAW264.7 macrophages. HFC-induced BMSCs also inhibited the secretion of IL-1β and IL-6, whilst promoting the secretion of TGF-β and IL-10 secretion from RAW264.7 macrophages. Mechanistic studies using western blotting discovered that HFC stimulated the secretion of prostaglandin E2 from BMSCs, which subsequently increased the expression of EP4 on the macrophages. EP4 then increased the expression levels of C/EBPβ and arginase 1 further. In conclusion, results from the present study suggested that following induction with HFC, BMSCs maintain their immunomodulatory activity.

Interleukin-10 mediated immune regulation after stem cell transplantation: Mechanisms and implications for therapeutic intervention

Interleukin-10 (IL-10) is a multi-faceted anti-inflammatory cytokine which plays an essential role in immune tolerance. Indeed, deficiency of IL-10 or its receptor results in aberrant immune responses that lead to immunopathology. Graft-versus-host disease (GVHD) is the limiting complication of allogeneic stem cell transplantation (SCT) and results from an imbalance in pathological versus regulatory immune networks. A number of immune cells exert their immunomodulatory role through secretion of IL-10 or induction of IL-10-secreting cells after SCT. Type-1 regulatory T cells (Tr1 cells) and FoxP3⁺ regulatory T cells (T_regs) are predominant sources of IL-10 after SCT and the critical role of this cytokine in preventing GVHD is now established. Recently, intriguing interactions among IL-10, immune cells, commensal microbes and host tissues in the gastrointestinal (GI) tract and other barrier surfaces have been uncovered. We now understand that IL-10 secretion is dynamically modulated by the availability of antigen, co-stimulatory signals, cytokines, commensal microbes and their metabolites in the microenvironment. In this review, we provide an overview of the control of IL-10 secretion and signaling after SCT and the therapeutic interventions, with a focus on Tr1 cells.

Seeking biomarkers for acute graft-versus-host disease: where we are and where we are heading?

Acute graft-versus-host disease (aGVHD) is one of the most important complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT), which would seriously affect the clinical outcomes of patients. Early diagnosis and early intervention are keys for improving its curative efficacy. Thus, seeking the biomarkers of aGVHD that can accurately identify and diagnose aGVHD is very important to guiding the intervention and treatment of aGVHD. For the past decades, many studies have focused on searching for aGVHD-related biological markers to assist in diagnosis, early warning, and risk stratification. Unfortunately, until now, no reliable aGVHD biomarker is available that is recognized and widely used in clinical practice. With the continuous development of biological technology, as well as our in-depth understanding of the pathophysiologic mechanism of aGVHD, the selection, examination and application of biological markers have changed much. In this review, we summarized the progress of aGVHD biological marker screening, identification, preliminary clinical application, and look forward to a promising development direction in the future.

IL-35 mitigates murine acute graft-versus-host disease with retention of graft-versus-leukemia effects

IL-35 is a newly discovered inhibitory cytokine secreted by regulatory T cells (Tregs) and may have therapeutic potential in several inflammatory disorders. Acute graft-versus-host disease (aGVHD) is a major complication of allogeneic hematopoietic stem cell transplantation and caused by donor T cells and inflammatory cytokines. The role of IL-35 in aGVHD is still unknown. Here we demonstrate that IL-35 overexpression suppresses CD4(+) effector T-cell activation, leading to a reduction in alloreactive T-cell responses and aGVHD severity. It also leads to the expansion of CD4(+)Foxp3(+) Tregs in the aGVHD target organs. Furthermore, IL-35 overexpression results in a selective decrease in the frequency of Th1 cells and an increase of IL-10-producing CD4(+) T cells in aGVHD target tissues. Serum levels of TNF-α, IFN-γ, IL-6, IL-22 and IL-23 decrease and IL-10 increases in response to IL-35. Most importantly, IL-35 preserves graft-versus-leukemia effect. Finally, aGVHD grade 2-4 patients have decreased serum IL-35 levels comparing with time-matched patients with aGVHD grade 0-1. Our findings indicate that IL-35 has an important role in reducing aGVHD through promoting the expansion of Tregs and repressing Th1 responses, and should be investigated as the therapeutic strategy for aGVHD.

Harnessing the power of alloreactivity without triggering graft-versus-host disease: how non-engrafting alloreactive cellular therapy might change the landscape of acute myeloid leukemia treatment

Human leukocyte antigen-mismatched leukocyte infusions outside of the context of transplantation are a promising strategy for acute myeloid leukemia. Recent studies using such non-engrafting alloreactive cellular therapy (NEACT) revealed that survival of elderly patients increased from 10% to 39% when NEACT was given following chemotherapy, and that durable complete remissions were achieved in about a third of patients with relapsed or chemorefractory disease. We review the clinical reports of different NEACT approaches to date and describe how although T-cell and NK alloreactivity could generate immediate anti-leukemic effects, long-term disease control may be achieved by stimulating recipient-derived T-cell responses against tumor-associated antigens. Other variables likely impacting NEACT such as the release of pro-inflammatory cytokines from donor-host bidirectional alloreactivity and the choice of chemotherapeutics as well as future avenues for improving NEACT, such as optimizing the cell dose and potential synergies with adjuvant pharmacologic immune checkpoint blockade, are discussed.

Increased Level of IFN-γ and IL-4 Spot-Forming Cells on ELISPOT Assay as Biomarkers for Acute Graft-Versus-Host Disease and Concurrent Infections

Acute graft-versus-host disease (aGVHD) remains a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Infections may coexist and in certain circumstances aggravate aGVHD. It was described that type 1 as well as type 2 cytokines are important mediators of aGVHD. We measured spot-forming cells (SFCs) for interferon (IFN)-γ, interleukin (IL)-4, IL-10, and IL-17 in unstimulated peripheral blood from 80 patients with hematological disorders who underwent allogeneic hematopoietic stem cell transplantation by using the enzyme-linked immunospot (ELISPOT) assay that reflects the ongoing in vivo immune status. A serial monitoring showed that both type 1 and type 2 cytokine SFCs were correlated with aGVHD activity. The numbers of IFN-γ and IL-4 SFCs in patients with grade II-IV aGVHD were significantly higher than those in patients with grade 0 and/or I aGVHD. Elevation of IFN-γ and IL-4 SFCs was significantly correlated with the severity of aGVHD, but not with infection itself, e.g., cytomegalovirus infection. Cytokine SFCs are clinically relevant biomarkers for the diagnostic and therapeutic evaluation of aGVHD and concurrent infection.

Making sense of regulatory T cell suppressive function

Several types of regulatory T cells maintain self-tolerance and control excessive immune responses to foreign antigens. The major regulatory T subsets described over the past decade and novel function in transplantation will be covered in this review with a focus on CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells. Multiple mechanisms have been proposed to explain how Treg cells inhibit effector cells but none can completely explain the observed effects in toto. Proposed mechanisms to explain suppressive activity of Treg cells include the generation of inhibitory cytokines, induced death of effector cells by cytokine deprivation or cytolysis, local metabolic perturbation of target cells mediated by changes in extracellular nucleotide/nucleoside fluxes with alterations in intracellular signaling molecules such as cyclic AMP, and finally inhibition of dendritic cell functions. A better understanding of how Treg cells operate at the molecular level could result in novel and safer therapeutic approaches in transplantation and immune-mediated diseases.

Arginine-enriched total parenteral nutrition improves survival in peritonitis by normalizing NFkappaB activation in peritoneal resident and exudative leukocytes

BACKGROUND

Enteral nutrition maintains peritoneal defense more effectively than parenteral nutrition, at least partly by preserving NFkappaB activation in peritoneal cells. We hypothesized that arginine (ARG)-enriched parenteral nutrition would normalize NFkappaB activation in peritoneal leukocytes, thereby improving the survival of peritonitis models.

METHODS

A total of 105 ICR mice were randomized to chow (n=33), IV feeding of a standard (STD) total parenteral nutrition (STD-TPN) solution (ARG 0.3%) (n=35), or 1% ARG-TPN solution (n=37), and fed accordingly for 5 days.Experiment 1: Thirty mice were used for intranuclear NFkappaB measurement in peritoneal resident cells (PRCs). After incubation with lipopolysaccharide (LPS: 0, 1, 10 microg/mL) for 30 minutes, intranuclear NFkappaB activity was examined by laser scanning cytometry.Experiment 2: Fifty-one mice were injected with 2 mL of 1% glycogen intraperitoneally. Peritoneal exudative cells (PECs) were obtained at 2 or 4 hours after glycogen administration for NFkappaB measurement. Cytokine (TNFalpha, IL-10) levels in peritoneal lavage fluid were also determined by ELISA.Experiment 3: After 5 days of feeding, 24 mice underwent cecal ligation and puncture. Survival was observed up to 5 days.

RESULTS

Experiment 1: Intranuclear NFkappaB levels in the ARG-TPN and chow groups increased dose-dependently after LPS stimulation, while the level in the STD-TPN group was unchanged.Experiment 2: Intranuclear NFkappaB level was significantly higher at 2 hours in the chow than in the STD-TPN group, whereas in the ARG-TPN mice the level was midway between those of the chow and STD-TPN groups. TNFalpha and IL-10 levels of the chow group were significantly higher than those of STD-TPN mice at 2 hours. TNFalpha was significantly higher in the ARG-TPN group than in the STD-TPN group, but the IL-10 level showed no recovery.Experiment 3: Survival times were significantly reduced in the STD-TPN as compared with the chow group, though ARG-TPN improved survival.

CONCLUSION

ARG-enriched TPN is a surrogate for enteral feeding which maintains peritoneal defense by preserving NFkappaB activation in peritoneal resident and exudative leukocytes.

Immunization with host-type CD8{alpha}+ dendritic cells reduces experimental acute GVHD in an IL-10-dependent manner

Little is known about the role of active immunization in suppressing undesirable immune responses. Because CD8alpha(+) dendritic cells (DCs) suppress certain immune responses, we tested the hypothesis that immunization of donors with host-derived CD8alpha(+) DCs will reduce host-specific donor T-cell responses. BALB/c T cells from the animals that were immunized with B6 CD8alpha(+) DCs demonstrated, in vitro and in vivo, significantly reduced proliferation and secretion of inflammatory cytokines but showed enhanced secretion of interleukin-10 (IL-10). The responses against third-party and model antigens were preserved demonstrating antigen specificity. The in vivo relevance was further demonstrated by the reduction on graft-versus-host disease (GVHD) in both a major histocompatibility complex-mismatched clinically relevant BALB/c --> B6 model and major histocompatibility complex-matched, minor-mismatched C3H.SW --> B6 model of GVHD. Immunization of the donors that were deficient in IL-10 (IL-10(-/-)) or with CD8alpha(+) DCs from B6 class II (class II(-/-)) failed to reduce T-cell responses, demonstrating (1) a critical role for secretion of IL-10 by donor T cells and (2) a direct contact between the T cells and the CD8alpha(+) DCs. Together, these data may represent a novel strategy for reducing GVHD and suggest a broad counterintuitive role for vaccination strategies in mitigating undesirable immune responses in an antigen-specific manner.

Type 1 regulatory T cells are associated with persistent split erythroid/lymphoid chimerism after allogeneic hematopoietic stem cell transplantation for thalassemia

BACKGROUND

Thalassemia major can be cured with allogeneic hematopoietic stem cell transplantation. Persistent mixed chimerism develops in around 10% of transplanted thalassemic patients, but the biological mechanisms underlying this phenomenon are poorly understood.

DESIGN AND METHODS

The presence of interleukin-10-producing T cells in the peripheral blood of eight patients with persistent mixed chimerism and five with full donor chimerism was investigated. A detailed characterization was then performed, by T-cell cloning, of the effector and regulatory T-cell repertoire of one patient with persistent mixed chimerism, who developed stable split erythroid/lymphoid chimerism after a hematopoietic stem cell transplant from an HLA-matched unrelated donor.

RESULTS

Higher levels of interleukin-10 were produced by peripheral blood mononuclear cells from patients with persistent mixed chimerism than by the same cells from patients with complete donor chimerism or normal donors. T-cell clones of both host and donor origin could be isolated from the peripheral blood of one, selected patient with persistent mixed chimerism. Together with effector T-cell clones reactive against host or donor alloantigens, regulatory T-cell clones with a cytokine secretion profile typical of type 1 regulatory cells were identified at high frequencies. Type 1 regulatory cell clones, of both donor and host origin, were able to inhibit the function of effector T cells of either donor or host origin in vitro.

CONCLUSIONS

Overall these results suggest that interleukin-10 and type 1 regulatory cells are associated with persistent mixed chimerism and may play an important role in sustaining long-term tolerance in vivo. These data provide new insights into the mechanisms of peripheral tolerance in chimeric patients and support the use of cellular therapy with regulatory T cells following hematopoietic stem cell transplantation.

Allograft-specific cytokine profiles associate with clinical outcome after islet cell transplantation

Islet cell transplantation can cure type 1 diabetes, but allograft rejection and recurrent autoimmunity may contribute to decreasing insulin independence over time. In this study we report the association of allograft-specific proliferative and cytokine profiles with clinical outcome. Peripheral blood mononuclear cells were obtained of 20 islet recipients. Cytokine values in mixed lymphocyte cultures (MLC) were determined using stimulator cells with graft-specific HLA class II. Qualitative and quantitative cytokine profiles were determined before and after islet transplantation, blinded from clinical outcome. Cytotoxic T Lymphocyte precursor (CTLp) assays were performed to determine HLA class I alloreactivity. Allograft-specific cytokine profiles were skewed toward a Th2 or regulatory (Treg) phenotype after transplantation in insulin-independent, but not in insulin-requiring recipients. IFNgamma/IL10 ratio and MLC proliferation decreased after transplantation in insulin-independent recipients (p = 0.006 and p = 0.01, respectively). Production of the Treg cytokine IL10 inversely correlated with proliferation in alloreactive MLC (p = 0.008) and CTLp (p = 0.005). Production of IL10 combined with low-MLC reactivity associated significantly with insulin independence. The significant correlation between allograft-specific cytokine profiles and clinical outcome may reflect the induction of immune regulation in successfully transplanted recipients. Islet donor-specific IL10 production correlates with low alloreactivity and superior islet function.

A functional role for soluble HLA-G antigens in immune modulation mediated by mesenchymal stromal cells

BACKGROUND

It has been suggested that soluble factors produced by bone marrow (BM) mesenchymal stromal cells (MSC) play a fundamental role in mediating immune modulation. HLA-G antigens (Ag) are major histocompatibility complex (MHC) class Ib molecules characterized by a limited polymorphism and a splicing mechanism that regulates the production of membrane-bound and soluble isoforms. Interleukin-10 (IL-10) cytokine is one of the main up-modulators of soluble HLA-G Ag (sHLA-G) production by CD14+ peripheral blood monocyte cells and increased IL-10 levels are reported to be associated with MSC immune modulation.

METHODS

We investigated, by specific enzyme-linked immunosorbent assay (ELISA), the possible role of sHLA-G molecules in the inhibition of the peripheral blood mononuclear cell (PBMC) response to phytohemagglutinin (PHA) mediated by MSC from different sources.

RESULTS

There was a significant correlation between the presence of increased levels of sHLA-G and IL-10 in the MSC/PBMC/PHA culture supernatants and lymphoproliferative inhibition. Neutralizing experiments performed with monoclonal Ab directed against HLA-G and IL-10 molecules confirmed the inhibitory ability of sHLA-G Ag. Furthermore, exogenous IL-10 induced sHLA-G molecule secretion by MSC alone in a polymorphic way, while a longitudinal analysis confirmed the loss of MSC inhibitory functions in relation to in vitro MSC aging.

DISCUSSION

Overall the results obtained suggest a functional role for sHLA-G molecules in inhibiting the PBMC response mediated by MSC. Moreover, the ability of IL-10 to induce sHLA-G Ag production by MSC alone could be proposed as a marker of MSC functional ability.

Cholera toxin B subunit promotes the induction of regulatory T cells by preventing human dendritic cell maturation

Cholera toxin B subunit (CTB) is an efficient mucosal carrier molecule for the generation of immune responses to linked antigens. There is also good evidence that CTB acts as an immunosuppressant, as it is able to down-modulate human monocyte/macrophage cell line activation and to suppress Th1-type responses. In the present study, we examined the possibility that recombinant CTB (rCTB) may affect human dendritic cell (DC) functions in response to LPS stimulation and may induce the generation of DC with the capacity to generate CD4(+) regulatory T cells (Tregs). Our findings show that rCTB partially prevents the LPS-induced maturation process of monocyte-derived DC (MDDC) and decreases their IL-12 production with no relevant effect on IL-10 production. LPS-stimulated MDDC pretreated with rCTB are able to promote the induction of low proliferating T cells, which show an enhanced IL-10 production associated with a reduced IFN-gamma production and the same high levels of TGF-beta as the control. These T cells suppress proliferation of activated autologous T cells. Transwell experiments and blockade of IL-10R and TGF-beta showed that the immunomodulatory effect is mediated by soluble factors. Thus, T cells induced by rCTB-conditioned MDDC acquire a regulatory phenotype and activity similar to those described for type 1 Tregs.

Regulatory T-cell immunotherapy for tolerance to self antigens and alloantigens in humans

Substantial progress in understanding the biology of regulatory T cells and their roles in health and disease has been achieved in the past 10 years. This has led to an increasing interest in the possibility of using regulatory T cells as a biological therapy to preserve and restore tolerance to self antigens and alloantigens. Immunotherapy by the adoptive transfer of regulatory T cells may have several advantages over conventional treatments. However, several hurdles have to be overcome before such a therapy can enter clinical practice. This Review summarizes our current knowledge of regulatory T cells, illustrates the ongoing regulatory T-cell-based clinical trials, analyses the strengths and pitfalls of this new therapeutic approach, and highlights the future perspectives.

Blood eosinophilia as a marker of favorable outcome after allogeneic stem cell transplantation

Eosinophilia is observed in a variety of disorders including acute and chronic graft-versus-host disease (GVHD). The clinical records of 237 patients who underwent allogeneic stem cell transplantation (allo-SCT) were retrospectively reviewed. Eosinophilia, defined as a relative eosinophil count>4% within the first 100 days, was observed in 135 patients (57%). The incidence of grades II-IV acute GVHD was significantly higher in patients without eosinophilia than in those with eosinophilia (68% vs. 43%; P<0.001). The incidence of chronic GVHD was significantly higher in patients without eosinophilia than in those with eosinophilia (73% vs. 56%; P=0.011). Relapse rate was similar between patients with and without eosinophilia (33% vs. 27%; P=0.438). The probability of nonrelapse mortality was 10% in patients with eosinophilia, which was significantly lower than that in patients without eosinophilia (31%; P<0.001), and the overall survival (OS) at 3 years was 67% in patients with eosinophilia, which was significantly higher than that in patients without eosinophilia (51%; P=0.003). Multivariate analysis identified older age, high-risk disease, acute GVHD, sex disparity between patient and donor, and the absence of eosinophilia as significant factors for reduced OS. These data lead us to conclude that eosinophilia after allo-SCT may serve as a favorable prognostic marker.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

A DNA vaccine encoding CCL4/MIP-1β enhances myocarditis in experimental Trypanosoma cruzi infection in rats

Chagas' disease, caused by Trypanosoma cruzi, is a major cause of cardiovascular disease in Latin America. Exacerbated inflammation disproportional to parasite load characterizes chronic myocardial lesions in chagasic patients. Chemokines and their receptors are expected to account for the renewed inflammatory processes after the inoculation of the parasite, but their potential unique functions are far from being clear. Herein, we evaluated the effect of a DNA vaccine encoding CCL4/MIP-1beta, a CC-chemokine, in T. cruzi-elicited myocarditis in rats. Holtzman rats were given intramuscularly cardiotoxin and the CCL4/MIP-1beta DNA-containing plasmid (100microg) was delivered in this muscular site four times. Fourteen days after last immunization, animals were inoculated with a myotropical CL-Brener T. cruzi clone. Peak of parasitism was observed at day 15 after infection, preceding the peak of myocardial inflammation at day 20. Myocarditis was still intense at day 30, but the inflammatory infiltrates showed a more focal distribution. The expression of CCL2/MCP-1 and CCL4/MIP-1beta correlated closely with the kinetics of myocardial inflammation. The CCL4/MIP-1beta DNA vaccine induced an increase of the levels of the anti-CCL4/MIP-1beta observed in T. cruzi-infected animals. This was associated with an exacerbation of myocardial inflammation and fibrosis, although alterations in parasitemia and myocardial parasitism were not observed. Our data suggest that CCL4/MIP-1beta plays a role in preventing excessive inflammation and pathology rather than in controlling parasite replication.

Beyond HLA: the significance of genomic variation for allogeneic hematopoietic stem cell transplantation

The last 2 years have seen much excitement in the field of genetics with the identification of a formerly unappreciated level of “structural variation” within the normal human genome. Genetic structural variants include deletions, duplications, and inversions in addition to the recently discovered, copy number variants. Single nucleotide polymorphisms are the most extensively evaluated variant within the genome to date. Combining our knowledge from these studies with our rapidly accumulating understanding of structural variants, it is apparent that the extent of genetic dissimilarity between any 2 individuals is considerable and much greater than that which was previously recognized. Clearly, this more diverse view of the genome has significant implications for allogeneic hematopoietic stem cell transplantation, not least in the generation of transplant antigens but also in terms of individual susceptibility to transplant-related toxicities. With advances in DNA sequencing technology we now have the capacity to perform genome-wide analysis in a high throughput fashion, permitting a detailed genetic analysis of patient and donor prior to transplantation. Understanding the significance of this additional genetic information and applying it in a clinically meaningful way will be one of the challenges faced by transplant clinicians in the future.

The Ratio of Interferon-γ and Interleukin-10 Producing Donor-Specific Cells as an In Vitro Monitoring Tool for Renal Transplant Patients

If in vitro tools can be used to predict which renal transplant patients are at risk for rejection and which patients are more predisposed to tolerance, the immunosuppressive regimen can be adjusted to prevent rejection before it becomes clinically apparent or, in case of a tolerant patient, medication can be reduced or even stopped. Peripheral blood mononuclear cells (PBMC) of patients with persistent stable graft function and of patients with (biopsy-confirmed) acute rejection were stimulated with donor cells and tested with Elispot analysis. A significantly higher number of donor-specific interferon (IFN)-gamma producing cells were found in patients with rejection, as determined with Elispot analysis. Furthermore, a trend towards a higher number of interleukin (IL)-10 producing cells was found in patients with stable graft function. The ratio of IFN-gamma/IL-10 producing cells showed to be the best tool to discriminate between nonrejecting patients and rejecting patients.