A2/A2B to B Renal Transplantation: Past, Present, and Future Directions

One component of the new national kidney allocation system (KAS) in the United States that was implemented on December 4, 2014, was the allocation of kidneys from A2 and A2B (A, non-A1 and AB, non-A1B) deceased donors into blood group B candidates (A2/A2B to B). In so far as this is an important component of the new KAS that has the potential to further increase the access to transplantation for blood group B candidates on the waiting list, most of whom are minority candidates, we will review the body of evidence and historical perspectives that led to its inclusion in the new KAS. This review will also describe prospects for more widespread use of A2/A2B to B transplantation and a novel mechanism of humoral immunosuppression in B patients before and after transplantation with an A2 or A2B kidney (read more)

EpViX: A cloud-based tool for epitope reactivity analysis and epitope virtual crossmatching to identify low immunologic risk donors for sensitized recipients

One of the challenges facing solid organ transplantation programs globally is the identification of low immunological risk donors for sensitized recipients by HLA allele genotype. Because recognition of donor HLA alleles by host antibodies is at the core of organ rejection, the objective of this work was to develop a new version of the EpHLA software, named EpViX, which uses an HLAMatchmaker algorithm and performs automated epitope virtual crossmatching at the initiation of the organ donation process. EpViX is a free, web-based application developed for use over the internet on a tablet, smartphone or computer. This program was developed using the Ruby programming language and the Ruby-on-Rails framework. To improve the user experience, the EpViX software interface was developed based on the best human–computer interface practices. To simplify epitope analysis and virtual crossmatching, the program was integrated with important available web-based resources, such as OPTN, IMGT/HLA and the International HLA Epitope Registry. We successfully developed a program that allows people to work collaboratively and effectively during the donation process by accurately predicting negative crossmatches, saving time and other resources (read more)

New Immunosuppressive Cell Therapy to Prolong Survival of Induced Pluripotent Stem Cell–Derived Allografts

Background: Induced pluripotent stem cell (iPSC) technology provides new opportunities in regenerative medicine to generate grafts from donors for transplantation. However, particularly when allogeneic iPSCs are used, immune suppression is required to avoid rejection of iPSC-derived grafts. In this study, we examine a concept that protection of iPSCs-derived allografts can be achieved when transplantation is accompanied with the administration of immunosuppressive cells generated from the same iPSCs resource.
Methods: Mouse iPSCs were differentiated into immunosuppressive cells by a culture protocol using granulocyte macrophage-colony-stimulating factor, macrophage-colony-stimulating factor, IL-4, and lipopolysaccharide. Adherent clusters were collected and examined for the ability to suppress allogeneic T- and B-cell responses, as well as for the contribution to prolonged allogeneic graft survival in transplantation models.
Results: Myeloid cells with immunosuppressive features were successfully induced from iPSCs, and thus referred to as iPSC-derived suppressor cells (iPS-SCs). The iPS-SCs resemble macrophages in terms of cell surface molecules and gene expressions. Furthermore, iPS-SCs efficiently suppressed allogeneic T- and B-cell proliferation in a nitric oxide–dependent manner, and iPS-SCs were found to suppress alloantibody production and prolong substantially the survival of iPSC-derived grafts, such as embryoid bodies and cardiomyocytes, in in vivo allogeneic transplantation models.
Conclusions: A certain fraction of macrophage-like cells with immunosuppressive functions can be generated from donor iPSCs, which contribute to the prolonged survival of grafts derived from the same iPSCs in allogeneic recipients. These results suggest a new immunosuppressive strategy of combined donor iPSC-derived graft and immunosuppressive cell transplantation in regenerative medicine using iPSCs (read more)

Predicted Indirectly Recognizable HLA Epitopes Presented by HLA-DRB1 Are Related to HLA Antibody Formation During Pregnancy

Pregnancy can prime maternal immune responses against inherited paternal HLA of the fetus, leading to the production of child-specific HLA antibodies. We previously demonstrated that donor-specific HLA antibody formation after kidney transplantation is associated with donor-derived HLA epitopes presented by recipient HLA class II (predicted indirectly recognizable HLA epitopes presented by HLA class II [PIRCHE-II]). In the present study, we evaluated the role of PIRCHE-II in child-specific HLA antibody formation during pregnancy. A total of 229 mother–child pairs were HLA typed. For all mismatched HLA class I molecules of the child, we subsequently predicted the number of HLA epitopes that could be presented by maternal HLA class II molecules. Child-specific antigens were classified as either immunogenic or nonimmunogenic HLA based on the presence of specific antibodies and correlated to PIRCHE-II numbers. Immunogenic HLA contained higher PIRCHE-II numbers than nonimmunogenic HLA. Moreover, the probability of antibody production during pregnancy increased with the number of PIRCHE-II. In conclusion, our data suggest that the number of PIRCHE-II is related to the formation of child-specific HLA antibodies during pregnancy. Present confirmation of the role of PIRCHE-II in antibody formation outside the transplantation setting suggests the PIRCHE-II concept is universal (read more and editorial)

Discarded Human Thymus Is a Novel Source of Stable and Long-Lived Therapeutic Regulatory T Cells

Regulatory T cell (Treg)–based therapy is a promising approach to treat many immune-mediated disorders such as autoimmune diseases, organ transplant rejection, and graft-versus-host disease (GVHD). Challenges to successful clinical implementation of adoptive Treg therapy include difficulties isolating homogeneous cell populations and developing expansion protocols that result in adequate numbers of cells that remain stable, even under inflammatory conditions. We investigated the potential of discarded human thymuses, routinely removed during pediatric cardiac surgery, to be used as a novel source of therapeutic Tregs. Here, we show that large numbers of FOXP3+ Tregs can be isolated and expanded from a single thymus. Expanded thymic Tregs had stable FOXP3 expression and long telomeres, and suppressed proliferation and cytokine production of activated allogeneic T cells in vitro. Moreover, expanded thymic Tregs delayed development of xenogeneic GVHD in vivo more effectively than expanded Tregs isolated based on CD25 expression from peripheral blood. Importantly, in contrast to expanded blood Tregs, expanded thymic Tregs remained stable under inflammatory conditions. Our results demonstrate that discarded pediatric thymuses are an excellent source of therapeutic Tregs, having the potential to overcome limitations currently hindering the use of Tregs derived from peripheral or cord blood (read more)

Evaluation of the iBeads assay as a tool for identifying class I HLA antibodies.

In addition to antibodies targeting native class I human leukocyte antigens (HLA), the single antigen flow beads assay (SAFB) detects antibodies recognizing denatured forms (anti-dHLA). Acid treated SAFB and the modified SAFB reagent named iBeads are expected to distinguish anti-native (anti-nHLA) from anti-dHLA. Sera from 280 class I HLA-sensitized SAFB-positive kidney transplant candidates were retested with acid-treated SAFB and iBeads. Concordance between SAFB and iBeads, taking into account acid-treatment results, was described at global and locus levels. T-lymphocyte flow cytometry crossmatches (FCXM) were performed to identify an accurate iBeads MFI threshold allowing predicting FCXM results. Concordance between acid-treatment and iBeads assays was observed for 86.9% of alleles. The iBeads MFI were lower than for classical SAFB, especially for HLA-B and C alleles. Anti-dHLA identified with acid-treated SAFB were more frequently negative with iBeads for HLA-B and -C alleles. An iBeads MFI threshold of 1000 allowed predicting positive FCXM with 95.6% sensitivity, 91.6% negative predictive value and 0.08 negative likelihood ratio. The iBeads assay still has limitations, but might represent an invaluable alternative to SAFB for virtual crossmatch strategies in organ transplant allocation programs (read more)

Donor-specific antibody to trans-encoded donor HLA-DQ heterodimer

The majority of de novo donor specific HLA antibodies (DSAs) in transplant patients are directed to HLA-DQ antigens, which consist of a heterodimer of alpha and beta chains. Although a heterodimer can theoretically be cis- or trans-encoded, the sensitizing forms appear to be generally cis-forms. DSA to DQ trans-heterodimer has never been reported. We reviewed 360 post-kidney transplant recipients (transplant: 2002-2013; follow-up: 5.6±3.3years). DQ DSA was detected in 46 of 57 patients who developed DSA. DSA specificity was consistent with donor mismatched DQ trans-heterodimers in three patients: DQ2.5 (DQB1*02, DQA1*05), DQ2.3 (DQB1*02, DQA1*03), and DQ4.3 (DQB1*04, DQA1*03). Two of them eventually lost grafts (2 and 5years later) with allograft nephropathy. In conclusion, post-transplant patients may develop DSA to donor DQ trans-heterodimers. Further studies are warranted to determine the clinical significance of such DSAs (read more)