Antibody-mediated allograft rejection: the emerging role of endothelial cell signalling and transcription factors

Memory B cells and long-lived plasma cells in AMR

Antibody-mediated rejection (AMR) has a strongly negative impact on long-term renal allograft survival. Currently, no recognized effective treatments are available, especially for chronic antibody-mediated rejection (CAMR). Donor-specific antibodies (DSAs) secreted by long-lived plasma cells and memory B cells are acknowledged as biomarkers of AMR. Nevertheless, it may be too late for the DSA routine examination production since DSAs may have binded to graft vascular endothelial cells through complement-dependent or complement-independent pathways. Therefore, methods to effectively monitor memory B cells and long-lived plasma cells and subsequently prevent DSA production are key to reducing the adverse effects of AMR. Therefore, this review mainly summarizes the production pathways of memory B cells and long-lived plasma cells and provides suggestions for the prevention of AMR after transplantation.

Stimulation by Exosomes from Hypoxia Preconditioned Human Umbilical Vein Endothelial Cells Facilitates Mesenchymal Stem Cells Angiogenic Function for Spinal Cord Repair

Revascularization treatment is a critical measure for tissue engineering therapies like spinal cord repair. As multipotent stem cells, mesenchymal stem cells (MSCs) have proven to regulate the lesion microenvironment through feedback to the microenvironment signals. The angiogenic capacities of MSCs have been reported to be facilitated by vein endothelial cells in the niche. As emerging evidence demonstrated the roles of exosomes in cell-cell and cell-microenvironment communications, to cope with the ischemia complication for treatment of traumatic spinal cord injury, the study extracts the microenvironment factors to stimulate angiogenic MSCs through using exosomes (EX) derived from hypoxic preconditioned (HPC) human umbilical vein endothelial cells (HUVEC). The HPC treatment with a hypoxia time segment of only 15 min efficiently enhanced the function of EX in facilitating MSCs angiogenesis activity. MSCs stimulated by HPC-EX showed significant tube formation within 2 h, and the in vivo transplantation of the stimulated MSCs elicited effective nerve tissue repair after rat spinal cord transection, which could be attributed to the pro-angiogenic and anti-inflammatory impacts of the MSCs. Through the simulation of MSCs using HPC-tailored HUVEC exosomes, the results proposed an efficient angiogenic nerve tissue repair strategy for spinal cord injury treatment and could provide inspiration for therapies based on stem cells and exosomes.

Critical role of sensitized serum in rejection of allogeneic bone marrow cells

Objective: Humoral immunity has been clearly implicated in solid organ transplantation, but little is known about the relationship between humoral immunity and hematopoietic stem cell transplantation. This study was designed to investigate that relationship.

Materials and Methods: Sensitized serum was obtained from a sensitized murine model established by allogeneic splenocyte transfusion. Sensitized serum was incubated with allogeneic bone marrow cells (BMCs) in vitro and the cytotoxicity was evaluated by the complement-dependent cytotoxicity method. Mice were transplanted with allogeneic BMCs incubated with sensitized serum after lethal irradiation. The engraftment was assayed by hematopoietic recovery and chimera analysis. Moreover, mice received passive transfer of sensitized serum 1 day prior to transplantation. Mortality was scored daily after bone marrow transplantation.

Results: The in vitro experiments showed that sensitized serum was capable of impairing allogeneic BMCs through the complement-dependent cytotoxicity pathway. The animal studies showed that BMCs incubated with sensitized serum failed to rescue mice from lethal irradiation. The engraftment assay showed that the allogeneic BMCs incubated with sensitized serum were rejected with time in the recipients. Furthermore, the mice died of marrow graft rejection by transfer of sensitized serum prior to transplantation.

Conclusion: Taken together, our results indicated that sensitized serum played a critical role in graft rejection during hematopoietic stem cell transplantation.

Impact of HLA antibodies on graft survival in long-term renal recipients with functional grafts

OBJECTIVES

Accumulating evidence supports the hypothesis that HLA antibodies play an important role in early renal allograft injury. However, the effects of HLA antibodies on long-term graft survival are still poorly understood. In this study, we examined the impact of HLA antibodies on graft survival in long-term renal recipients with functional grafts for 10 years.

MATERIAL AND METHODS

In this retrospective study, long-term renal recipients were defined as kidney transplant recipients who had normally functioning renal grafts (serum creatinine level <2.0 mg/dl) for 10 years. Posttransplant serum samples from a total of 92 long-term renal allograft recipients on cyclosporine-based triple maintenance drug therapy (121.6 ± 0.886 months) were screened for the specificities of anti-HLA antibodies. The results of HLA antibodies before the transplantation, assessed using the same test method, were compared with those after their transplantations. Moreover, these 92 patients who received cadaveric renal transplant between January 2000 and December 2002 were followed up for about 10 years (range 107-135 months).

RESULTS

27 patients had HLA-I antibodies and 16 patients had HLA-II antibodies before the transplantation, whereas 12 patients had HLA-I antibodies and 18 patients had HLA-II antibodies after the transplantation. Moreover, the types of HLA antibodies were different from those found before the transplantation. In these renal recipients with functioning renal grafts, the estimated glomerular filtration rate was 66.52 ± 14.52 ml/min/1.73 m(2) in the HLA antibody-positive group (n = 23) and 69.09 ± 25.54 ml/min/1.73 m(2) negative in the HLA antibody-negative group (n = 69, p > 0.05). Three patients (3.26%) (3 out of 92) had donor-specific anti-HLA antibodies (DSA). The frequency of DSA in this study was lower than that in the general Chinese Han renal recipient population.

CONCLUSIONS

We find that all HLA antibodies in the long-term renal grafts are newly formed after the transplantation. The HLA antibody status has little impact on the renal graft function in the long-term renal recipients.

Concise review: immunologic lessons from solid organ transplantation for stem cell-based therapies

Clinical organ transplantation became possible only after powerful immunosuppressive drugs became available to suppress the alloimmune response. After decades of solid organ transplantation, organ rejection is still a major challenge. However, significant insight into allorecognition has emerged from this vast experience and should be used to inform future stem cell-based therapies. For this reason, we review the current understanding of selected topics in transplant immunology that have not been prominent in the stem cell literature, including immune responses to ischemia/reperfusion injuries, natural killer cells, the adaptive immune response, some unresolved issues in T-cell allorecognition, costimulatory molecules, and the anticipated role of regulatory T cells in graft tolerance.

Antibodies against dengue virus nonstructural protein-1 induce heme oxygenase-1 via a redox-dependent pathway in human endothelial cells

Heme oxygenase (HO)-1, the inducible isoform of the first and rate-limiting enzyme of heme degradation, affords anti-inflammatory protection via its cell-type-specific effects in endothelial cells (ECs). In dengue hemorrhagic fever (DHF), which is the life-threatening form of dengue virus (DV) infection, endothelial interactions of cross-reactive antibodies against the DV nonstructural glycoprotein-1 (NS1) are associated with endothelial dysfunction. In this study, we investigated whether anti-NS1 antibodies might regulate HO-1 gene expression in human ECs. Serum from DHF patients with high anti-NS1 titers and a monoclonal anti-NS1 antibody upregulated HO-1 gene expression in human umbilical vein ECs, which was blocked by purified NS1 antigen. Immunoprecipitation studies showed that anti-NS1 antibodies specifically bound to the oxidoreductase protein disulfide isomerase (PDI) on ECs. Moreover, anti-NS1-mediated HO-1 induction was reduced by inhibition of PDI enzyme activity. Reactive oxygen species, which were generated by NADPH oxidase and in turn activated the phosphatidylinositol 3-kinase (PI3K)/Akt cascade, were involved in this upregulation of HO-1 gene expression. Finally, apoptosis of ECs caused by anti-NS1 antibodies was increased by pharmacological inhibition of HO-1 enzyme activity. In conclusion, HO-1 gene expression is upregulated by anti-NS1 antibodies via activation of a redox-dependent PDI/PI3K/Akt-mediated pathway in human ECs.

HLA class I antibody-mediated endothelial and smooth muscle cell activation

PURPOSE OF REVIEW

Advances in immunosuppression and patient management have successfully improved 1-year transplant outcome. Unfortunately, antibody-mediated rejection is a major barrier to long-term graft survival. This study summarizes the effects of antibodies on endothelial cell and smooth muscle cell (SMC) migration, proliferation and leukocyte recruitment, emphasizing the intracellular signaling pathways that orchestrate these distinct functional outcomes.

RECENT FINDINGS

Several studies have provided further insight into the effects of human leukocyte antigen (HLA) class I antibodies on vascular cells. We found that HLA I molecules partner with integrin β4 to transduce proliferative signaling, and identified proteins that associate with the cytoskeleton after HLA class I crosslinking. Natural killer cells have been strongly implicated in a murine model of donor-specific major histocompatibility complex I antibody-triggered neointimal thickening. A recently developed human arterial graft model revealed the role of matrix metalloproteinases in SMC mitogenesis by HLA class I antibodies. Using a donor transgenic for HLA-A2, Fukami et al. investigated the mechanisms of accommodation induced by low titers of HLA class I antibodies.

SUMMARY

Ligation of HLA class I molecules with antibodies leads to the activation of intracellular signals in endothelial cells and SMCs, which in turn promote actin cytoskeletal remodeling, survival, proliferation, and recruitment of leukocytes.