Friday, April 26, 2013

Literature Review of Passenger Lymphocyte Syndrome Following Renal Transplantation and Two Case Reports

Passenger lymphocyte syndrome (PLS) is an immune-mediated hemolysis. It occurs following ABO blood group mismatched solid organ and/or bone marrow transplantation between donor and recipient. We report two cases of PLS occurring after renal transplantation. Both recipients received live related kidney transplants; one from his mother and the other from his brother. The direction of blood group transfer, from donor to recipient, was O Rh D+ to A Rh D+ in both cases. Approximately 12 days after transplantation, both recipients showed a rapid fall in their hemoglobin levels with no identifiable bleeding source. DAT positive hemolysis was confirmed and anti-A antibodies were detected in recipient sera, confirming a diagnosis of PLS. Both cases required blood transfusion support to maintain their hemoglobin and both had good renal outcomes. We have identified 99 PLS cases following renal transplant in the English literature. Previous ABO sensitization, donor blood group O to recipient blood group A or B transfer, and ciclosporin treatment have been identified as risk factors for PLS. Clinical outcomes in general are good; nonetheless, cases of graft failure and deaths have been reported. Early diagnosis and appropriate treatment are important in at risk individuals (read more)

Induction Therapy With Basiliximab and Full HLA Mismatch

Introduction: Induction therapy reduces rejection episodes among patients at high immunologic risk. Antithymocyte globulins appear to be superior to basiliximab in this population, despite the greater potential risk of infection and neoplasia. The aim of this study was to evaluate graft function and acute rejection episodes in 6 HLA-mismatched patients who underwent induction with basiliximab but had no other immunologic risk factors.
Methods: We analyzed retrospectively patients who were transplanted using basiliximab for induction therapy during a 4 year period, comparing patients with full HLA mismatches with those who had 5 or fewer mismatches. None of the patients had other immunological risk factors for rejection.
Results: We observed no significant differences between the groups concerning demographic features, cold ischemia times, and panel reactive antibodies. Graft function at 12 and 24 months was not different between both groups. Acute rejection episodes were also not different between groups.
Discussion: In this population of full HLA mismatches and no other immunological risk factors, induction immunosuppression therapy with basiliximab was safe in terms of graft function and acute rejection episodes (read more)

Preferential HLA-DRB1*11-dependent presentation of CUB2-derived peptides by ADAMTS13-pulsed dendritic cells

Autoantibodies directed against ADAMTS13 prohibit the processing of von Willebrand factor multimers, initiating a rare and life-threatening disorder called acquired thrombotic thrombocytopenic purpura (TTP). Recently, HLA-DRB1*11 has been identified as a risk factor for the development of acquired TTP. Here, we identified ADAMTS13-derived peptides presented on MHC class II alleles from 17 healthy donors. Dendritic cells from a panel of both HLA-DRB1*11–positive and -negative donors were pulsed with ADAMTS13, and the HLA-DR–presented peptide repertoire was analyzed by mass spectrometry. Interestingly, at low antigen concentrations, HLA-DRB1*11- or DRB1*03-positive donors presented a limited number of CUB2-derived peptides. Pulsing of dendritic cells using higher concentrations of ADAMTS13 resulted in the presentation of larger numbers of ADAMTS13-derived peptides by both HLA-DRB1*11–positive and -negative donors. Although the presented peptides were derived from several ADAMTS13 domains, inspection of the peptide profiles revealed that CUB2 domain–derived peptides were presented with a higher efficiency when compared with other peptides. Remarkably, dendritic cells from DRB1*11 donors pulsed with higher concentrations of ADAMTS13-present derivatives of a single CUB2-derived peptide. We hypothesize that functional presentation of CUB2-derived peptides on HLA-DRB1*11 contributes to the onset of acquired TTP by stimulating low-affinity, self-reactive CD4+ T cells (read more)

Wednesday, April 24, 2013

Low-level HLA antibodies do not predict platelet transfusion failure in TRAP study participants

In the Trial to Reduce Alloimmunization to Platelets (TRAP) study, 101 of 530 participants became refractory to platelet transfusions without evidence of HLA or human platelet antigen (HPA) antibodies. We used a more sensitive bead-based assay to detect and quantify HLA antibodies and a qualitative solid-phase enzyme-linked immunosorbet assay for HPA to determine whether low-level antibodies could predict refractoriness in longitudinal panels from 170 lymphocytotoxicity assay (LCA) and 20 LCA+ TRAP participants. All TRAP recipients who previously tested LCA+ were HLA antibody+, using the bead-based system. Levels of HLA or HPA antibodies did not predict refractoriness among LCA recipients, although higher levels of HLA antibodies were associated with refractoriness among LCA+ recipients. These data demonstrate that weak to moderate HLA antibody levels detectable by modern binding assays are not associated with platelet refractoriness (read more)

Plasmapheresis Adjusts Inflammatory Responses in Potential Kidney Transplant Recipients

imageBackground: Plasmapheresis (PP) has been used in the treatment of various immunologic disorders, and its efficacy has mainly been attributed to the removal of humoral factors and autoantibodies. Besides these effects, PP may induce modifications of the cellular immunologic status, contributing to the restoration of impaired immunologic function. The effect of PP on lymphocyte subpopulations, plasma neopterin, and cytokines in renal transplant recipients was investigated in this study.
Methods: We compared pre-PP and post-PP lymphocyte subpopulations and plasma neopterin in 37, and cytokine plasma levels in 30, potential renal transplant recipients. Plasma neopterin and cytokines were measured by enzyme-linked immunosorbent assay kits, lymphocyte subsets were determined using four-color fluorescence flow cytometry.
Results: Lymphocyte subpopulation counts and ratios including CD45+/μL (P=0.005), CD3+/μL (P=0.02), CD4+DR+/μL (P=0.002), CD8+/μL (P=0.01), and CD8+DR+/μL (P=0.005) T cells; CD4+DR+/CD4+ (P=0.009) and CD8+DR+/CD8+ (P=0.0004) ratios; DR+ cells:μL (P=0.003); CD19+ B lymphocytes/μL (P=0.001); and plasma levels of neopterin (P<;0.0001), soluble interleukin-1 receptor antagonist (P<;0.0001), IL-8 (P=0.0001), and tumor necrosis factor-α (P=0.008) were significantly decreased after PP as compared with before PP. The results indicate a decrease of activated DR+, CD4+, and CD8+ T lymphocytes and B lymphocytes, and a decrease of monocyte and macrophage activation as a result of PP.
Conclusion: Based on these results, we conclude that PP not only removes antibodies from the plasma but, in addition, modulates T-lymphocyte activation and the inflammatory response by decreasing plasma proinflammatory cytokines (read more)

A new approach to HLA typing designed for solid organ transplantation: epityping and its application to the HLA-A locus

HLA-specific antibodies bind discrete clusters of amino acids called epitopes, but serological assignment of antibody specificities makes no reference to this. As HLA typing for solid organ transplantation is provided at only medium (serologically equivalent) resolution, this means that recipient HLA antibodies to donor HLA epitopes may not be identified. We have designed a novel and rapid HLA-A epitope typing method (epityping) using a two-stage PCR-SSP-based method to detect the HLA-A locus epitopes described by El Awar et al. 2007, Transplantation, 84, 532. The initial PCR step utilizes HLA-A locus-specific primers; the product is cleaned using the QIAquick Spin Purification procedure. The purified product is tested using our in-house epitope-specific primer panel, the results being visualized using gel electrophoresis. Twenty two UCLA DNA Exchange samples were epityped, blinded to the HLA type. Of the 75 primer pairs, the mean correlation coefficient was 0.95 with each sample giving 67 or more correct primer results. In all cases, it was possible to derive the first field classic HLA type from the epityping results. These results indicate that a method for identification of HLA epitopes which is comparable in time, cost and technical expertise to current HLA typing methods is achievable. Redesigning HLA typing to correlate with what the antibody binds should minimize inappropriate organ allocation. We suggest that epityping provides a more effective method than standard HLA typing for solid organ transplantation (read more)

Umbilical Cord Blood Transplantation Supported by Third-Party Donor Cells: Rationale, Results, and Applications

Low incidence of graft-versus-host disease provides the major rational for pursuing umbilical cord blood (UCB) stem cell transplantation (SCT). Considerable evidence also suggests a lower rate of recurrence after UCB SCT than after transplantation from adult donors. Recent advances in understanding of the human fetal immune development provide a rational underpinning for these clinical outcomes. The fetal immune system is geared toward maintaining tolerance to foreign antigens, particularly to the maternal antigens to which it is exposed throughout gestation. To this purpose it is dominated by a unique population of peripheral T regulatory cells that actively maintain tolerance. This and other features of the UCB lymphoid system explains the low incidence of graft-versus-host disease and superior outcomes of UCB SCT with noninherited maternal antigen–matched grafts. At the same time, highly sensitized maternal microchimeric cells are frequently detected in UCB and likely contribute to superior graft-versus-leukemia effects and low rates of disease recurrence in inherited paternal antigen–matched UCB recipients. However, historically erratic and slow hematopoietic recovery after UCB SCT leads to increased early morbidity and mortality, excessive hospitalization, and increased costs. This has held up the widespread utilization of UCB SCT in adults. Here we summarize recent data on UCB SCT with an emphasis on studies of co-infusion of adult CD34 selected hematopoietic stem cells with UCB SCT. This procedure, through transient engraftment of adult hematopoietic stem cells, largely overcomes the problem of delayed engraftment. It also results in predictable engraftment of a UCB with the desired characteristics. We also briefly discuss unresolved issues and possible future applications of this technology (read more)

Chimerism Patterns of Long-Term Stable Mixed Chimeras Posthematopoietic Stem Cell Transplantation in Patients with Nonmalignant Diseases: Follow-Up of Long-Term Stable Mixed Chimerism Patients

Long-term stable mixed chimerism (MC) is a rare phenomenon after hematopoietic stem cell transplantation (HSCT) characterized by 5% to 95% residual recipient hematopoietic cells. The underlying mechanisms of MC are largely unknown. In this study we compared full donor chimerism with long-lasting stable MC for a median of 9.5 years (range, 5 to 16.5) post-HSCT in patients with nonmalignant diseases. Several factors significantly associated with the likelihood of stable MC development were identified by univariate analysis, eg, younger donor age, sibling donor, and conditioning regimen. Despite a limited patient cohort, our multivariate analysis could confirm that a sibling donor was associated with stable MC development. Furthermore, development of acute-graft-versus-host disease and blood stream infection was significantly more prevalent in the full donor chimerism patient group. Additionally, significant fluctuations in the recipient-to-donor chimerism ratio decreased over time after HSCT in MC patients (read more)

Sunday, April 14, 2013

Perivascular support of human hematopoietic stem/progenitor cells

Hematopoietic stem and progenitor cells (HSPCs) emerge and develop adjacent to blood vessel walls in the yolk sac, aorta-gonad-mesonephros region, embryonic liver, and fetal bone marrow. In adult mouse bone marrow, perivascular cells shape a "niche" for HSPCs. Mesenchymal stem/stromal cells (MSCs), which support hematopoiesis in culture, are themselves derived in part from perivascular cells. In order to define their direct role in hematopoiesis, we tested the ability of purified human CD146+ perivascular cells, as compared with unfractionated MSCs and CD146 cells, to sustain human HSPCs in coculture. CD146+ perivascular cells support the long-term persistence, through cell-to-cell contact and at least partly via Notch activation, of human myelolymphoid HSPCs able to engraft primary and secondary immunodeficient mice. Conversely, unfractionated MSCs and CD146 cells induce differentiation and compromise ex vivo maintenance of HSPCs. Moreover, CD146+ perivascular cells express, natively and in culture, molecular markers of the vascular hematopoietic niche. Unexpectedly, this dramatic, previously undocumented ability to support hematopoietic stem cells is present in CD146+ perivascular cells extracted from the nonhematopoietic adipose tissue (read more)

Wednesday, April 10, 2013

A Single Dose of Rituximab Does Not Deplete B Cells in Secondary Lymphoid Organs but Alters Phenotype and Function

A single dose of the anti-CD20 monoclonal antibody rituximab induces a nearly complete B cell depletion in peripheral blood, but not in secondary lymphoid organs. Modulation of this remaining B cell population due to rituximab treatment may contribute to the therapeutic effects of rituximab. To assess the in vivo effects of rituximab we used lymph nodes (LNs) collected during renal transplant surgery in patients who had received rituximab 4 weeks earlier in preparation for an ABO-incompatible transplantation. Rituximab treatment resulted in a lower percentage of naïve (IgD+CD27) and a higher percentage of switched memory (IgDCD27+) B cells. Remarkably, transitional (CD24++CD38++) B cells were virtually lacking in the LNs of rituximab-treated patients. Moreover, LN-derived B cells from rituximab-treated patients produced different amounts of various Ig-subclasses after anti-CD40/IL-21 stimulation ex vivo. Finally, after stimulation of allogeneic T cells with LN-derived B cells from rituximab-treated patients, the proliferated T cells showed a decreased production of IL-17. In conclusion, after treatment with rituximab there remains a B cell population with different functional capacities. Consequently, the effect of rituximab on the immune response will not only be determined by the extent of B cell depletion, but also by the functional properties of the remaining B cells (read more)

The Effect of Rabbit Anti-Thymocyte Globulin on Human Mesenchymal Stem Cells

Background : Mesenchymal stem cells (MSCs) possess immunomodulatory properties which are of key interest for their application in autoimmunity and transplantation. In transplantation, administration of MSCs has shown promising results in preclinical models and has recently moved to clinical trials. Therefore it is important to study the interactions between MSCs and immunosuppressive drugs currently used in transplantation. We aimed to analyze the effect of rabbit anti-thymocyte globulin (rATG) MSCs.
Methods : MSCs were obtained from perirenal fat of kidney donors and exposed to ranging doses of rATG (Thymoglobulin®, Genzyme;0.5ug/ml-100ug/ml). Binding of rATG, effects on viability and susceptibility to be killed by cytotoxic lymphocytes as well as effects on their immunosuppressive potential of MSCs were tested.
Results : rATG binds dose-dependently to MSCs. This binding was associated with slightly impaired viability after 48 and 72 hours when compared to non-exposed MSCs. In contrast to non-treated MSCs, rATG pre-exposed MSCs were susceptible to be lysed by cytokine-activated CD8+ cytotoxic cells and NKT cells. The capacity of MSCs to suppress the proliferation of anti-CD3/CD28 activated CD4 and CD8 T cells was reduced by the presence of rATG in the culture.
Conclusion : rATG reduces the viability and anti-proliferative capacity of MSCs in a dose dependent manner and converts them into targets for CD8 T cells and NKT cell lysis (read more)

Friday, April 5, 2013

Efficacy of HLA-matched platelet transfusions for patients with hypoproliferative thrombocytopenia: a systematic review

BACKGROUND: HLA-matched platelets (PLTs) are widely used to transfuse patients but the effectiveness of HLA matching has not been well defined and the cost is approximately five times the cost of preparing the random-donor PLTs. The objective of this systematic review was to determine whether HLA-matched PLTs lead to a reduction in mortality; reduction in frequency or severity of hemorrhage; reduction in HLA alloimmunization, refractoriness, or PLT utilization; or improvement in PLT count increment in patients with hypoproliferative thrombocytopenia.
STUDY DESIGN AND METHODS: We conducted a literature search of MEDLINE, Cochrane Controlled Register of Clinical Trials, EMBASE, and PubMed databases to April 2012.
RESULTS: A total of 788 citations were reviewed and 30 reports were included in the analysis. Most studies did not include technologies currently in use for HLA typing or detection of HLA antibodies as 75% were conducted before the year 2000. None of the studies were adequately powered to detect an effect on mortality or hemorrhage. HLA-matched PLTs did not reduce alloimmunization and refractoriness rates beyond that offered by leukoreduction, and utilization was not consistently improved. HLA-matched PLTs led to better 1-hour posttransfusion count increments and percentage of PLT recovery in refractory patients; however, the effect at 24 hours was inconsistent.
CONCLUSION: The correlation of the PLT increment with other clinical outcomes and the effect of leukoreduction on HLA-matched PLT transfusion could not be determined. Prospective studies utilizing current technology and examining clinical outcomes are necessary to demonstrate the effectiveness of HLA-matched PLT transfusion (read more)

Thursday, April 4, 2013

De Novo Donor-Specific HLA Antibodies Decrease Patient and Graft Survival in Liver Transplant Recipients

The role of de novo donor-specific HLA antibodies (DSA) in liver transplantation remains unknown as most of the previous studies have only focused on preformed HLA antibodies. To understand the significance of de novo DSA, we designed a retrospective cohort study of 749 adult liver transplant recipients with pre- and posttransplant serum samples that were analyzed for DSA. We found that 8.1% of patients developed de novo DSA 1 year after transplant; almost all de novo DSAs were against HLA class II antigens, and the majority were against DQ antigens. In multivariable modeling, the use of cyclosporine (as opposed to tacrolimus) and low calcineurin inhibitor levels increased the risk of de novo DSA formation, while a calculated MELD score >15 at transplant and recipient age >60 years old reduced the risk. Multivariable analysis also demonstrated that patients with de novo DSA at 1-year had significantly lower patient and graft survival. In conclusion, we demonstrate that de novo DSA development after liver transplantation is an independent risk factor for patient death and graft loss (read more)