An in vitro evaluation of the potential suitability of peripheral blood CD14+ and bone marrow CD34+-derived dendritic cells for a tolerance inducing regimen in the primate

Generation and functional assessment of nonhuman primate regulatory dendritic cells and their therapeutic efficacy in renal transplantation

Nonhuman primates (NHP) are important pre-clinical models for evaluation of the safety and efficacy of the most promising potential therapeutic advances in organ transplantation based on rodent studies. Although rare, dendritic cells (DC) play important roles in preservation of self tolerance and DC with immunoregulatory properties (regulatory DC; DCreg) can promote transplant tolerance in rodents when adoptively transferred to allograft recipients. NHP DCreg can be generated ex vivo from bone marrow precursors or blood monocytes of cynomolgus or rhesus macaques or baboons. NHP DCreg generated in the presence of anti-inflammatory factors that confer stability and resistance to maturation, subvert alloreactive T cell responses. When infused into rhesus renal allograft recipients before transplant, they safely prolong MHC mis-matched graft survival, associated with attenuation of anti-donor immune reactivity. In this concise review we describe the properties of NHP DCreg and discuss their influence on T cell responses, alloimmunity and organ transplant survival.

Advances and challenges in immunotherapy for solid organ and hematopoietic stem cell transplantation

Although major advances have been made in solid organ and hematopoietic stem cell transplantation in the last 50 years, big challenges remain. This review outlines the current immunological limitations for hematopoietic stem cell and solid organ transplantation and discusses new immune-modulating therapies in preclinical development and in clinical trials that may allow these obstacles to be overcome.

Tolerogenic dendritic cells and negative vaccination in transplantation: from rodents to clinical trials

The use of immunosuppressive (IS) drugs to treat transplant recipients has markedly reduced the incidence of acute rejection and early graft loss. However, such treatments have numerous adverse side effects and fail to prevent chronic allograft dysfunction. In this context, therapies based on the adoptive transfer of regulatory cells are promising strategies to induce indefinite transplant survival. The use of tolerogenic dendritic cells (DC) has shown great potential, as preliminary experiments in rodents have demonstrated that administration of tolerogenic DC prolongs graft survival. Recipient DC, Donor DC, or Donor Ag-pulsed recipient DC have been used in preclinical studies and administration of these cells with suboptimal immunosuppression increases their tolerogenic potential. We have demonstrated that autologous unpulsed tolerogenic DC injected in the presence of suboptimal immunosuppression are able to induce Ag-specific allograft tolerance. We derived similar tolerogenic DC in different animal models (mice and non-human primates) and confirmed their protective abilities in vitro and in vivo. The mechanisms involved in the tolerance induced by autologous tolerogenic DC were also investigated. With the aim of using autologous DC in kidney transplant patients, we have developed and characterized tolerogenic monocyte-derived DC in humans. In this review, we will discuss the preclinical studies and describe our recent results from the generation and characterization of tolerogenic monocyte-derived DC in humans for a clinical application. We will also discuss the limits and difficulties in translating preclinical experiments to theclinic.

Non-human primate dendritic cells

Non-human primates (NHP) are essential translational models for biomedical research. Dendritic cells (DC) are a group of antigen presenting cells (APC) that play pivotal roles in the immunobiology of health and disease and are attractive cells for adoptive immunotherapy to stimulate and suppress immunity. DC have been studied extensively in humans and mice but until recently, have not been well characterized in NHP. This review considers the available data about DC across a range of NHP species and summarizes the understanding of in vitro-propagated DC and in vivo-isolated DC, which is now established. It is clear that although NHP DC exist within the paradigm of human DC, there are important functional and phenotypic differences when compared with human DC subsets. These differences need to be taken into account when designing preclinical, translational studies of DC therapy using NHP models.

Design of a real-time quantitative polymerase chain reaction to assess human complement regulatory protein gene expression in polytransgenic xenograft pigs

OBJECTIVE

To design a real-time quantitative polymerase chain reaction (q-PCR) to assess gene expression for hCD55, hCD59, and hCD46 in polytransgenic (PT) pigs used as xenograft donors for orthotopic liver xenotransplantation using a pig-to-baboon model.

MATERIALS AND METHODS

Three pairs of primers were designed using PrimerBlast and mRNA of hCD55, hCD59, and hCD46 sequences. Blood samples from five PT pigs (two males and three females) were used to isolated peripheral blood mononuclear cells (PBMCs) by means of Ficoll gradients. After DNAase digestion of isolated mRNA, we synthesized cDNA. Using SYBR-Green chemistry of q-PCR, we constructed a standard curve. Two wild-type (WT) pigs were used as negative controls, and PBMCs from two healthy human volunteers as positive controls. The amplicon length was assessed by means of agarose gel electrophoresis and PCR products, sequenced.

RESULTS

We observed amplification for hCD55, hCD59, and hCD46 in all samples from the five PT pigs except for hCD55 and hCD46 in one male PT pig. Neither the human samples nor the negative controls showed amplification. The expected amplicon length was confirmed; sequencing showed high homology with human mRNA for the three proteins and no match with any known pig sequence.

CONCLUSIONS

The q-PCR allowed detection of animals with the highest gene expression for hCD55, hCD59, and hCD46 for xenograft donors in transplantation experiments.

Dendritic cells and regulation of alloimmune responses: relevance to outcome and therapy of organ transplantation

Dendritic cells are uniquely well-equipped for antigen capture, processing and presentation. They are highly-efficient antigen-presenting cells that induce and regulate T-cell reactivity. Due to their inherent tolerogenicity, immature dendritic cells offer considerable potential as candidate cellular vaccines for negative regulation of immune reactivity/promotion of tolerance. Both classic myeloid and, more recently, characterized plasmacytoid dendritic cells, exhibit tolerogenic properties. Manipulation of dendritic cells differentiation/ maturation in the laboratory using cytokines, pharmacologic agents or genetic engineering approaches can render stably immature dendritic cells that promote organ transplant tolerance in rodents. There are also indications from human studies of the ability of dendritic cells to promote T-cell tolerance and induce T-regulatory cells, with potential for therapeutic application in organ transplantation. In addition, recent clinical observations suggest that modulation of dendritic cell function (e.g., by immunosuppressive drugs) affects the outcome of transplantation. The challenge confronting applied dendritic cell biology is the identification of optimal strategies and therapeutic regimens to allow the potential of these powerful immune regulatory cells to be realized in the clinic.

Propagation and characterisation of dendritic cells from G-CSF mobilised peripheral blood monocytes and stem cells in common marmoset monkeys

The common marmoset is a small New World Primate that has been used as an immunological model for a number of human diseases. Dendritic cells (DC) have not been extensively characterised in this species and in particular protocols to derive DC from living donors without the need for animal sacrifice are presently lacking. This study establishes new protocols to generate substantial numbers of marmoset DC for use in cell therapy studies. Recombinant human G-CSF was used to mobilise peripheral blood monocytes and CD34(+) stem cells in sufficient numbers for large scale in-vitro DC propagation using cytokine conditioning including IL-4, GM-CSF, FLT3-L, stem cell factor and thrombopoietin. Marmoset DC exhibited morphology similar to human DC, were capable of antigen uptake and presentation and had moderate allo-stimulatory ability. Monocyte-derived DC had a maturation-resistant immature phenotype, whereas haematopoietic precursor-derived DC were semi-mature in phenotype and function. This study confirms the feasibility of the marmoset as a unique small primate model in which to pursue DC-based immunotherapy strategies.

Tribbles-1 as a novel biomarker of chronic antibody-mediated rejection

Diagnosis of the specific cause of late allograft injury is necessary if more personalized and efficient immunosuppressive regimens are to be introduced. This study sought previously unrecognized biomarkers for specific histologic diagnoses of late graft scarring by comparison of gene sets from published microarray studies. Tribbles-1 (TRIB1), a human homolog of Drosophila tribbles, was identified to be a potentially informative biomarker. For testing this, mRNA expression in 76 graft biopsies, 71 blood samples, and 11 urine samples were profiled from independent cohorts of renal transplant patients with different histologic diagnoses recruited at two European centers. TRIB1 but not TRIB2 or TRIB3 was found to be a potential blood and tissue biomarker of chronic antibody-mediated rejection, an active immune-mediated form of chronic allograft failure associated with a poor prognosis. TRIB1 mRNA levels in peripheral blood mononuclear cells discriminated patients with chronic antibody-mediated rejection from those with other types of late allograft injury with high sensitivity and specificity. TRIB1 was also upregulated in a rodent model of chronic cardiac vasculopathy, suggesting that this biomarker may be useful in other solid-organ transplants and across species. It was determined that TRIB1 is expressed primarily by antigen-presenting cells and activated endothelial cells. Overall, these data support the potential use of TRIB1 as a biomarker of chronic antibody-mediated allograft failure.

Implication of matrix metalloproteinase 7 and the noncanonical wingless-type signaling pathway in a model of kidney allograft tolerance induced by the administration of anti-donor class II antibodies

In rats, tolerance to MHC-incompatible renal allografts can be induced by the administration of anti-donor class II Abs on the day of transplantation. In this study we explored the mechanisms involved in the maintenance phase of this tolerance by analyzing intragraft gene expression profiles by microarray in long-term accepted kidneys. Comparison of the gene expression patterns of tolerated to syngeneic kidneys revealed 5,954 differentially expressed genes (p < 0.05). Further analysis of this gene set revealed a key role for the wingless-type (WNT) signaling pathway, one of the pivotal pathways involved in cell regulation that has not yet been implicated in transplantation. Several genes within this pathway were significantly up-regulated in the tolerated grafts, particularly matrix metalloproteinase 7 (MMP7; fold change > 40). Analysis of several other pathway-related molecules indicated that MMP7 overexpression was the result of the noncanonical WNT signaling pathway. MMP7 expression was restricted to vascular smooth muscle cells and was specific to anti-class II Ab-induced tolerance, as it was undetectable in other models of renal and heart transplant tolerance and chronic rejection induced across the same strain combination. These results suggest a novel role for noncanonical WNT signaling in maintaining kidney transplant tolerance in this model, with MMP7 being a key target. Determining the mechanisms whereby MMP7 contributes to transplant tolerance may help in the development of new strategies to improve long-term graft outcome.

Isolation and characterization of dendritic cells from common marmosets for preclinical cell therapy studies

Dendritic cells (DCs) have important functions as modulators of immune responses, and their ability to activate T cells is of great value in cancer immunotherapy. The isolation of DCs from the peripheral blood of rhesus and African green monkeys has been reported, but the immune system in the common marmoset remains poorly characterized, although it offers many potential advantages for preclinical studies. In the present study, we devised methods, based on techniques developed for mouse and human DC preparation, for isolating DCs from three major tissue sources in the common marmoset: bone marrow (BM), spleen and peripheral blood. Each set of separated cells was analysed using the cell surface DC-associated markers CD11c, CD80, CD83, CD86 and human leucocyte antigen (HLA)-DR, all of which are antibodies against human antigens, and the cells were further characterized both functionally and morphologically as antigen-presenting cells. BM proved to be an excellent cell source for the isolation of DCs intended for preclinical studies on cell therapy, for which large quantities of cells are required. In the BM-derived CD11c(+) cell population, cells exhibiting the characteristic features of DCs were enriched, with the typical DC morphology and the abilities to undergo endocytosis, to secrete interleukin (IL)-12, and to stimulate Xenogenic T cells. Moreover, BM-derived DCs produced the neurotrophic factor NT-3, which is also found in murine splenic DCs. These results suggest that BM-derived DCs from the common marmoset may be useful for biological analysis and for preclinical studies on cell therapy for central nervous system diseases and cancer.

Immunophenotype and functions of fetal baboon bone-marrow derived dendritic cells

Dendritic cells (DCs) are unique antigen-presenting cells that can take up pathogens, pathogens-derived and stress-antigens and stimulate antigen-specific immune response. Here we investigated the immunobiology of fetal DCs and compared their phenotype and activation status against infectious stimuli with those of young and adult baboons. The DCs were obtained from femoral bone-marrow (BMDCs) of fetus (140 and 175 days of gestation), young (4-5 years old) and mature adult (10-35 years old) baboons. The cells were cultured in the presence of GM-CSF and IL-4. To study phagocytic ability of BMDCs, the cells were harvested on 6th day and incubated with fluorescent-labeled Escherichia coli bioparticles. The BMDCs were also treated with E. coli O111:B4 lipopolysaccharide (LPS) for 24h and changes in expression of cell-surface markers and IL-12 were studied using distinct immunoassays. We found that the phenotype and morphology of BMDCs from fetal, young and adult baboons were similar and showed increased expression of HLA-DP, DQ, DR and T cell co-stimulatory molecules upon LPS treatment. However, significant differences were observed in phagocytic activity and IL-12 secretion among BMDCs from these sources. The ability of fetal baboon BMDCs to phagocytose E. coli bioparticles was significantly lower and they secreted lower level of LPS-stimulated IL-12 as compared to the BMDCs from adult baboon. These results suggest that compared to adult BMDCs, fetal baboon BMDCs are less efficient in mounting immune response against Gram-negative bacterial stimuli.

Dendritic cells: tools and targets for transplant tolerance

Our knowledge of the role of dendritic cells (DC) in the generation and maintenance of T-cell tolerance has expanded rapidly and is now a key area of research in basic and applied DC biology. This minireview highlights recent developments in the field that are leading to new avenues for exploiting DC in the promotion of transplant tolerance.