The Role of Lymphoid Neogenesis in Allografts

De novo induction of organized lymphoid aggregates at non-lymphoid sites has been observed in many chronic inflammatory conditions where foreign antigens such as infectious agents, auto- or alloantigens, persist. The prevailing opinion in the field of transplantation is that lymphoid neogenesis within allografts is detrimental to the establishment of immune tolerance. These structures, commonly referred to as tertiary lymphoid organs (TLOs), are thought to contribute to graft rejection by generating and propagating local alloimmune responses. However, recent studies have shown that TLOs rich in regulatory Foxp3+ cells are present in long term accepting allografts. The notion that TLOs can contribute to the local downregulation of immune responses has been corroborated in other chronic inflammation models. These findings suggest that contrary to previous suggestions that the induction of TLOs in allografts is necessarily harmful, the induction of “tolerogenic” TLOs may prove advantageous. In this review, we discuss our current understanding of how TLOs are induced and how they regulate immune responses with a particular focus on alloimmunity (read more)

Renal Transplantation with Final Allocation Based on the Virtual Crossmatch

Solid phase immunoassays (SPI) are now routinely used to detect HLA antibodies. However the flow cytometric crossmatch (FCXM) remains the established method for assessing final donor-recipient compatibility. Since 2005 we have followed a protocol whereby the final allocation decision for renal transplantation is based on SPI (not the FCXM). Here we report long term graft outcomes for 508 consecutive kidney transplants using this protocol. All recipients were negative for donor specific antibody by SPI. Primary outcomes are graft survival and incidence of acute rejection within one year (AR<1yr) for FCXM+ (n=54) and FCXM- (n=454) recipients. Median follow up is 7.1 years. FCXM+ recipients were significantly different from FCXM- recipients for the following risk factors: living donor (24% vs 39%, p=0.03), duration of dialysis (31.0 months vs 13.5 months, p=0.008), retransplants (17% vs 7.3%, p=0.04), % sensitized (63% vs 19%, p=0.001) and PRA>80% (20% vs 4.8%, p=0.001). Despite these differences, 5 year actual graft survival rates are 87 and 84% respectively. AR<1yr occurred in 13% FCXM+ and 12% FCXM- recipients. Crossmatch status was not associated with graft outcomes in any univariate or multivariate model. Renal transplantation can be performed successfully, using SPI as the definitive test for donor-recipient compatibility (read more)

ABH-glycan microarray characterizes ABO subtype antibodies: fine specificity of immune tolerance after ABO-incompatible transplantation

Organ transplantation from ABO blood group-incompatible (ABOi) donors requires accurate detection, effective removal and subsequent surveillance of anti-donor antibodies. Because ABH antigen subtypes are expressed differently in various cells and organs, measurement of antibodies specific for the antigen subtypes in the graft is essential. Erythrocyte agglutination, the century-old assay used clinically, does not discriminate subtype-specific ABO antibodies and provides limited information on antibody isotypes. We designed and created an ABO-glycan microarray and demonstrate here the precise assessment of the presence and, importantly, the absence of donor-specific antibodies in an international study of pediatric heart transplant patients. Specific IgM, IgG and IgA isotype antibodies to non-self ABH-subtypes were detected in controls and recipients of ABO-compatible (ABOc) transplants. Conversely, in children who received ABOi transplants, antibodies specific for A-subtype-II and/or B-subtype-II antigens, the only ABH antigen subtypes expressed in heart tissue, were absent, demonstrating the fine specificity of B-cell tolerance to donor/graft blood group antigens. In contrast to the hemagglutination assay, the ABO-glycan microarray allows detailed characterization of donor-specific antibodies necessary for effective transplant management, representing a major step forward in precise ABO antibody detection (read more)

Humanized Mouse Models for Transplant Immunology

Our understanding of the molecular pathways that control immune responses, particularly immunomodulatory molecules that control the extent and duration of an immune response, have led to new approaches in the field of transplantation immunology to induce allograft survival. These molecular pathways are being defined precisely in murine models and translated into clinical practice; however, many of the newly available drugs are human-specific reagents. Furthermore, many species-specific differences exist between mouse and human immune systems. Recent advances in the development of humanized mice, namely, immunodeficient mice engrafted with functional human immune systems, have led to the availability of a small animal model for the study of human immune responses. Humanized mice represent an important preclinical model system for evaluation of new drugs and identification of the mechanisms underlying human allograft rejection without putting patients at risk. This review highlights recent advances in the development of humanized mice and their use as preclinical models for the study of human allograft responses (read more).

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)