Multiple mismatches at the low expression HLA loci DP, DQ, and DRB3/4/5 associate with adverse outcomes in hematopoietic stem cell transplantation

A single mismatch in highly expressed HLA-A, -B, -C, and -DRB1 loci (HEL) is associated with worse outcomes in hematopoietic stem cell transplantation, while less is known about the cumulative impact of mismatches in the lesser expressed HLA loci DRB3/4/5, DQ, and DP (LEL). We studied whether accumulation of LEL mismatches is associated with deleterious effects in 3853 unrelated donor transplants stratified according to number of matches in the HEL. In the 8/8 matched HEL group, LEL mismatches were not associated with any adverse outcome. Mismatches at HLA-DRB1 were associated with occurrence of multiple LEL mismatches. In the 7/8 HEL group, patients with 3 or more LEL mismatches scored in the graft-versus-host vector had a significantly higher risk of mortality (1.45 and 1.43) and transplant-related mortality (1.68 and 1.54) than the subgroups with 0 or 1 LEL mismatches. No single LEL locus had a more pronounced effect on clinical outcome. Three or more LEL mismatches are associated with lower survival after 7/8 HEL matched transplantation. Prospective evaluation of matching for HLA-DRB3/4/5, -DQ, and -DP loci is warranted to reduce posttransplant risks in donor-recipient pairs matched for 7/8 HE (read more)

Standardization and Cross Validation of Alloreactive IFNγ ELISPOT Assays Within the Clinical Trials in Organ Transplantation Consortium

Emerging evidence indicates memory donor-reactive T cells are detrimental to transplant outcome and that quantifying the frequency of IFNγ-producing, donor-reactive PBMCs by ELISPOT has potential utility as an immune monitoring tool. Nonetheless, differences in assay performance among laboratories limit the ability to compare results. In an effort to standardize assays, we prepared a panel of common cellular reagent standards, developed and cross validated a standard operating procedure (SOP) for alloreactive IFNγ ELISPOT assays in several research laboratories supported by the NIH-funded Clinical Trials in Organ Transplantation (CTOT) Consortium. We demonstrate that strict adherence to the SOP and centralized data analysis results in high reproducibility with a coefficient of variance (CV) of ∼30%. This standardization of IFNγ ELISPOTassay will facilitate interpretation of data from multicenter transplantation research studies and provide the foundation for developing clinical laboratory testing strategies to guide therapeutic decision-making in transplant patients (read more)

HLA Class I Antibodies Trigger Increased Adherence of Monocytes to Endothelial Cells by Eliciting an Increase in Endothelial P-Selectin and, Depending on Subclass, by Engaging FcγRs.

Ab-mediated rejection (AMR) of solid organ transplants is characterized by intragraft macrophages. It is incompletely understood how donor-specific Ab binding to graft endothelium promotes monocyte adhesion, and what, if any, contribution is made by the Fc region of the Ab. We investigated the mechanisms underlying monocyte recruitment by HLA class I (HLA I) Ab-activated endothelium. We used a panel of murine mAbs of different subclasses to crosslink HLA I on human aortic, venous, and microvascular endothelial cells and measured the binding of human monocytic cell lines and peripheral blood monocytes. Both anti-HLA I murine (m)IgG1 and mIgG2a induced endothelial P-selectin, which was required for monocyte adhesion to endothelium irrespective of subclass. mIgG2a but not mIgG1 could bind human FcγRs. Accordingly, HLA I mIgG2a but not mIgG1 treatment of endothelial cells significantly augmented recruitment, predominantly through FcγRI, and, to a lesser extent, FcγRIIa. Moreover, HLA I mIgG2a promoted firm adhesion of monocytes to ICAM-1 through Mac-1, which may explain the prominence of monocytes during AMR. We confirmed these observations using human HLA allele-specific mAbs and IgG purified from transplant patient sera. HLA I Abs universally elicit endothelial exocytosis leading to monocyte adherence, implying that P-selectin is a putative therapeutic target to prevent macrophage infiltration during AMR. Importantly, the subclass of donor-specific Ab may influence its pathogenesis. These results imply that human IgG1 and human IgG3 should have a greater capacity to trigger monocyte infiltration into the graft than IgG2 or IgG4 due to enhancement by FcγR interactions (read more)

Cotransplantation of MSCs and HSCs

A pilot study by Wu et al. suggests that umbilical cord–derived mesenchymal stem cells (UCMSCs) promote hematopoietic engraftment when cotransplanted with cord blood (CB) cells. The authors make good use of two somatic stem cells, both derived from umbilical cord. Together with the establishment of their UCMSC bank, their trial appears to be potentially meaningful for future development of UCMSC cotransplantation (read more)

 

Effects of Cellular Sensitization and Donor Age on Acute Rejection and Graft Function After Deceased-Donor Kidney Transplantation

Background: Allografts from older donors may be more immunogenic than those from younger donors. Pretransplantation cellular sensitization may interact with advanced donor age to increase the risk of immune injury after deceased-donor kidney transplantation.
Methods: The outcomes of 118 consecutive deceased-donor kidney transplant recipients with available pretransplantation donor-stimulated enzyme-linked immunosorbent spot (ELISPOT) assays for interferon gamma were analyzed retrospectively to determine the impact of cellular sensitization and other clinical variables, including donor age, on the incidence of acute rejection (AR) in the first year after deceased-donor transplantation and on estimated glomerular filtration rate 12 months after transplantation.
Results: The incidence of AR was higher in patients with positive pretransplantation ELISPOT assays versus those with negative assays (36% vs. 14%, P=0.009). Logistic regression indicated that the combination of donor age 50 years or older and a positive pretransplantation ELISPOT assay was more strongly associated with AR (odds ratio, 12.1; confidence interval, 1.1–133) than either variable alone. Estimated glomerular filtration 12 months after transplantation was highest in ELISPOT-negative patients receiving kidneys from donors younger than 50 years and lowest in ELISPOT-positive recipients with donors 50 years or older.
Conclusion: The combination of advanced donor age and pretransplantation cellular sensitization increases the risk of AR and poor graft function after deceased-donor kidney transplantation beyond the risk associated with each factor alone (read more)

HLA-Mismatched Renal Transplantation without Maintenance Immunosuppression

We previously reported results of our study of combined kidney and bone marrow transplantation without maintenance immunosuppression. We extended the study to include five additional patients. Here we report longer follow-up of the initial five patients and observations made after 3 years in the later cohort. Both trials were sponsored by the Immune Tolerance Network and are currently closed to further enrollment.The first five patients received the previously described conditioning regimen (regimen 1): cyclophosphamide, thymic irradiation, anti-CD2 monoclonal antibody, and an 8-to-14-month course of a calcineurin inhibitor.1 After irreversible acute humoral rejection was observed in Patient 3, who was retrospectively found to have preformed antidonor HLA class I antibodies, the regimen was modified to include two doses of rituximab before transplantation (regimen 2). Since low levels of donor-specific antibodies developed in Patients 4 and 5, the regimen was further modified to include two additional doses of rituximab (regimen 3) (read more)

Tolerance to MHC class II disparate allografts through genetic modification of bone marrow

Induction of molecular chimerism through genetic modification of bone marrow is a powerful tool for the induction of tolerance. Here, we demonstrate for the first time that expression of an allogeneic MHC class II gene in autologous bone marrow cells, resulting in a state of molecular chimerism, induces tolerance to MHC class II mismatched skin grafts, a stringent test of transplant tolerance. Reconstitution of recipients with syngeneic bone marrow transduced with retrovirus encoding H-2I-Ab (I-Ab) resulted the long-term expression of the retroviral gene product on the surface of MHC class II-expressing bone marrow-derived cell types. Mechanistically, tolerance was maintained by the presence of regulatory T cells, which prevented proliferation and cytokine production by alloreactive host T cells. Thus, the introduction of MHC class II genes into bone marrow-derived cells through genetic engineering results in tolerance. These results have the potential to extend the clinical applicability of molecular chimerism for tolerance induction (read more)

Mortality in diabetes: pancreas transplantation is associated with significant survival benefit

Background : Pancreas transplantation in complicated type 1 (insulin dependent) diabetes mellitus improves the quality of life, increases longevity and stabilizes diabetic complications. There may be clinician reticence due to perceived poor outcomes with published associated mortality rates of 5–8% due to significant co-morbidities, particularly cardiovascular impairment.
Methods : Retrospective analysis was performed on patients undergoing pancreas transplantation in a single centre since the programme's initiation [simultaneous pancreas kidney (SPK) = 148, pancreas after kidney (PAK) = 33 and pancreas transplant alone (PTA) = 11] compared with a control group accepted contemporaneously onto the waiting list. The primary endpoint was patient mortality. The risk factors including medical and diabetic history, demographics, transplant type and waiting time were analysed.
Results : The waiting list mortality was 30% (35 of 120) compared with a mortality of 9% (20 of 193) post-transplantation (P < 0.001). Deaths on the waiting list compared with transplantation up to 1 year had a relative risk of 2.67 (95% CI: 0.81–3.51; P = 0.19), whilst those surviving >1 year had a relative risk of 5.89 of dying on the waiting list (95% CI: 1.70–3.20; P < 0.0005). There were no differences in terms of cardiovascular or renal-associated risk factors, nor in other potential confounding factors other than duration of diabetes (P = 0.02). Median survival from listing was shorter in younger patients (<50; P < 0.0001).
Conclusions : Type 1 diabetics with renal failure listed for pancreas transplantation are at a significant risk of mortality even without surgery. Transplantation offers considerable survival benefits, despite associated surgical and immunosuppressive risks. In selected patients, pancreas transplantation remains the benchmark treatment for type 1 diabetes mellitus (read more)

Effect of Red Cell Transfusions on Future Kidney Transplantation

Red cell transfusions, erythropoiesis-stimulating agents (ESAs), and intravenous iron therapy all have a place in the treatment of anemia associated with CKD. Their relative merits and uses are subject to many clinical and nonclinical factors. New concerns associated with the use of ESA therapy make it likely that the use of blood transfusions will increase, refueling previous debates about their associated risks. Data on whether red cell transfusions increase sensitization to HLA antigens, rendering subsequent transplantation more problematic, are mainly derived from older literature. Older data suggested that women were more at risk of HLA sensitization than men, particularly those with previous multiple pregnancies, although recent U.S. Renal Data System data have challenged this. HLA sensitization prolongs the waiting time for transplantation and reduces graft survival. Leukocyte depletion of red cells does not appear to reduce the risk of HLA sensitization. This review summarizes much of the data on these issues, as well as highlighting the need for further research on the potential risks for blood transfusion in patients with CKD (read more)