The immunogenomics of minor histocompatibility antigens

Pathways of Antigen Recognition by T Cells in Allograft Rejection

The adaptive immune response leading to the rejection of allogeneic transplants is initiated and orchestrated by recipient T cells recognizing donor antigens. T-cell allorecognition is mediated via 3 distinct mechanisms: the direct pathway in which T cells recognize allogeneic major histocompatibility complex (MHC) molecules on donor cells, the indirect pathway through which T cells interact with donor peptides bound with self-MHC molecules on recipient antigen-presenting cells, and the recently described semidirect pathway whereby T cells recognize donor MHC proteins on recipient antigen-presenting cells. In this article, we present a description of each of these allorecognition pathways and discuss their role in acute and chronic rejection of allogeneic transplants.

Association of blood donor's biological characteristics on outcomes of cardiac surgery patients receiving red blood cells transfusion

OBJECTIVES

This study aimed to assess the association of blood donor variables on the outcome of patients undergoing cardiac surgery.

STUDY DESIGN AND METHODS

A retrospective observational study was conducted on patients who had cardiac surgery between January 2018 and December 2020. Blood donor characteristics such as age (≤ or >30 years), sex, and body mass index (BMI) (≤ or >25 kg/m²) were analyzed for association with patient outcomes (length of hospital stay (LOS), mortality, and readmission). Sex matching was done as fully match, fully mismatch, and partial mismatch. Cox regression and Linear regression models were used to study the association with mortality and readmission, and LOS.

RESULTS

During the study period, 5788 patients had cardiac surgery; receiving a total of 20,348 red cell units. Of which, 522 (9%) died, 531 (9.2%) re-admitted and median LOS was 11 days (IQR 7-18). BMI >25 kg/m² (β, 2.96; p = 0.000), female to male transfusion (partial mismatch: β, 4.42; p = 0.001; fully mismatch: β, 9.0; p = 0.02) negatively affected LOS. BMI >25 kg/m² (HR, 2.07; p = 0.00) and partial mismatch transfusion to male patients (HR, 1.60; p = 0.01) increased mortality. Fully mismatch transfusion to female patients (HR, 1.24; p = 0.01) and partial mismatch to male patients (HR, 1.86; p = 0.01) increased readmission. No association of donor age on patient outcome was observed.

DISCUSSION

Blood donor sex, and BMI can influence mortality and LOS in cardiac surgery patients. The use of computer tools to match the patient's and donor's characteristics can assist to eliminate these types of adverse consequences.

Effects of biological sex mismatch on neural progenitor cell transplantation for spinal cord injury in mice

Despite advancement of neural progenitor cell transplantation to spinal cord injury clinical trials, there remains a lack of understanding of how biological sex of transplanted cells influences outcomes after transplantation. To address this, we transplanted GFP-expressing sex-matched, sex-mismatched, or mixed donor cells into sites of spinal cord injury in adult male and female mice. Biological sex of the donor cells does not influence graft neuron density, glial differentiation, formation of the reactive glial cell border, or graft axon outgrowth. However, male grafts in female hosts feature extensive hypervascularization accompanied by increased vascular diameter and perivascular cell density. We show greater T-cell infiltration within male-to-female grafts than other graft types. Together, these findings indicate a biological sex-specific immune response of female mice to male donor cells. Our work suggests that biological sex should be considered in the design of future clinical trials for cell transplantation in human injury.

In this study, Pitonak et al. report that transplantation of neural progenitor cells derived from male donors trigger an immune rejection response following transplantation into sites of spinal cord injury in female mice.

Antibody Responses to Minor Histocompatibility Antigens After Solid Organ Transplantation

Antibody-mediated rejection (AMR) is a major barrier to long-term graft survival following solid organ transplantation (SOT). Major histocompatibility antigens mismatched between donor and recipient are well-recognized targets of humoral alloimmunity in SOT and thought to drive most cases of AMR. In contrast, the implication of minor histocompatibility antigens (mHAs) in AMR has not been fully investigated, and their clinical relevance remains controversial. Recent technological advances, allowing for genome-wide comparisons between donors and recipients, have uncovered novel, polymorphic mHA targets with potential influence on the graft outcome following SOT. Here, we review these latest studies relating to mHAs and discuss their clinical significance.

Endocan in Acute Leukemia: Current Knowledge and Future Perspectives

Endocan is a soluble dermatan sulfate proteoglycan expressed by endothelial cells and detected in serum/plasma. Its expression is increased in tumors/tumor vessels in several human malignancies, and high expression (high serum/plasma levels or tumor levels) has an adverse prognostic impact in several malignancies. The p14 endocan degradation product can also be detected in serum/plasma, but previous clinical studies as well as previously unpublished results presented in this review suggest that endocan and p14 endocan fragment levels reflect different biological characteristics, and the endocan levels seem to reflect the disease heterogeneity in acute leukemia better than the p14 fragment levels. Furthermore, decreased systemic endocan levels in previously immunocompetent sepsis patients are associated with later severe respiratory complications, but it is not known whether this is true also for immunocompromised acute leukemia patients. Finally, endocan is associated with increased early nonrelapse mortality in (acute leukemia) patients receiving allogeneic stem cell transplantation, and this adverse prognostic impact seems to be independent of the adverse impact of excessive fluid overload. Systemic endocan levels may also become important to predict cytokine release syndrome after immunotherapy/haploidentical transplantation, and in the long-term follow-up of acute leukemia survivors with regard to cardiovascular risk. Therapeutic targeting of endocan is now possible, and the possible role of endocan in acute leukemia should be further investigated to clarify whether the therapeutic strategy should also be considered.

Consequence of Histoincompatibility beyond GvH-Reaction in Cytomegalovirus Disease Associated with Allogeneic Hematopoietic Cell Transplantation: Change of Paradigm

Hematopoietic cell (HC) transplantation (HCT) is the last resort to cure hematopoietic malignancies that are refractory to standard therapies. Hematoablative treatment aims at wiping out tumor cells as completely as possible to avoid leukemia/lymphoma relapse. This treatment inevitably co-depletes cells of hematopoietic cell lineages, including differentiated cells that constitute the immune system. HCT reconstitutes hematopoiesis and thus, eventually, also antiviral effector cells. In cases of an unrelated donor, that is, in allogeneic HCT, HLA-matching is performed to minimize the risk of graft-versus-host reaction and disease (GvHR/D), but a mismatch in minor histocompatibility antigens (minor HAg) is unavoidable. The transient immunodeficiency in the period between hematoablative treatment and reconstitution by HCT gives latent cytomegalovirus (CMV) the chance to reactivate from latently infected donor HC or from latently infected organs of the recipient, or from both. Clinical experience shows that HLA and/or minor-HAg mismatches increase the risk of complications from CMV. Recent results challenge the widespread, though never proven, view of a mechanistic link between GvHR/D and CMV. Instead, new evidence suggests that histoincompatibility promotes CMV disease by inducing non-cognate transplantation tolerance that inhibits an efficient reconstitution of high-avidity CD8⁺ T cells capable of recognizing and resolving cytopathogenic tissue infection.

Vaccine and Cell-based Therapeutic Approaches in Acute Myeloid Leukemia

Over the past decade, our increased understanding of the interactions between the immune system and cancer cells has led to paradigm shifts in the clinical management of solid and hematologic malignancies. The incorporation of immune-targeted strategies into the treatment landscape of acute myeloid leukemia (AML), however, has been challenging. While this is in part due to the inability of the immune system to mount an effective tumor-specific immunogenic response against the heterogeneous nature of AML, the decreased immunogenicity of AML cells also represents a major obstacle in the effort to design effective immunotherapeutic strategies. In fact, AML cells have been shown to employ sophisticated escape mechanisms to evade elimination, such as direct immunosuppression of natural killer cells and decreased surface receptor expression leading to impaired recognition by the immune system. Yet, cellular and humoral immune reactions against tumor-associated antigens (TAA) of acute leukemia cells have been reported and the success of allogeneic stem cell transplantation and monoclonal antibodies in the treatment of AML clearly provides proof that an immunotherapeutic approach is feasible in the management of this disease. This review discusses the recent progress and persisting challenges in cellular immunotherapy for patients with AML.

MSCs Become Collagen-Type I Producing Cells with Different Phenotype in Allogeneic and Syngeneic Bone Marrow Transplantation

Mesenchymal stem cells (MSCs) have been widely used in therapeutic applications for many decades. However, more and more evidence suggests that factors such as the site of origin and pre-implantation treatment have a crucial impact on the result. This study investigates the role of freshly isolated MSCs in the lacrimal gland after allogeneic transplantation. For this purpose, MSCs from transgenic GFP mice were isolated and transplanted into allogeneic and syngeneic recipients. While the syngeneic MSCs maintained a spherical shape, allogeneic MSCs engrafted into the tissue as spindle-shaped cells in the interstitial stroma. Furthermore, the MSCs produced collagen type I in more than 85% to 95% of the detected GFP+ MSCs in the recipients of both models, supposedly contributing to pathogenic fibrosis in allogeneic recipients compared to syngeneic models. These findings indicate that allogeneic MSCs act completely differently from syngeneic MSCs, highlighting the importance of understanding the exact mechanisms behind MSCs.

T-Cell Dysfunction as a Limitation of Adoptive Immunotherapy: Current Concepts and Mitigation Strategies

Simple Summary

T cells are immune cells that can be used to target infections or cancers. Adoptive T-cell immunotherapy leverages these properties and/or confers new features to T cells through ex vivo manipulations prior to their use in patients. However, as a “living drug,” the function of these cells can be hampered by several built-in physiological constraints and external factors that limit their efficacy. Manipulating T cells ex vivo can impart dysfunctional features to T cells through repeated stimulations and expansion, but it also offers many opportunities to improve the therapeutic potential of these cells, including emerging interventions to prevent or reverse T-cell dysfunction developing ex vivo or after transfer in patients. This review outlines the various forms of T-cell dysfunction, emphasizes how it affects various types of T-cell immunotherapy approaches, and describes current and anticipated strategies to limit T-cell dysfunction.

Abstract

Over the last decades, cellular immunotherapy has revealed its curative potential. However, inherent physiological characteristics of immune cells can limit the potency of this approach. Best defined in T cells, dysfunction associated with terminal differentiation, exhaustion, senescence, and activation-induced cell death, undermine adoptive cell therapies. In this review, we concentrate on how the multiple mechanisms that articulate the various forms of immune dysfunction impact cellular therapies primarily involving conventional T cells, but also other lymphoid subtypes. The repercussions of immune cell dysfunction across the full life cycle of cell therapy, from the source material, during manufacturing, and after adoptive transfer, are discussed, with an emphasis on strategies used during ex vivo manipulations to limit T-cell dysfunction. Applicable to cellular products prepared from native and unmodified immune cells, as well as genetically engineered therapeutics, the understanding and potential modulation of dysfunctional features are key to the development of improved cellular immunotherapies.

Genetic background and transplantation outcomes: insights from genome-wide association studies

PURPOSE OF REVIEW

The current review summarizes recent advances in the genetic studies of transplantation outcomes, including new genome-wide association studies for acute rejection, allograft survival, pharmacogenomics, and common transplant comorbidities.

RECENT FINDINGS

Genetic studies of kidney transplantation outcomes have begun to address the question of genetic compatibility beyond human leukocyte antigens, including the role of genome-wide mismatches in missense variants, and the 'genomic collision' hypothesis under which the risk of rejection may be increased in recipients homozygous for loss-of-function variants with grafts from nonhomozygous donors. In recent pilot studies, missense mismatch scores for transmembrane and secreted proteins were associated with antibodies against the mismatched peptides and reduced allograft survival. A 'genomic collision' at the LIMS1 locus involving a common deletion near LIMS1 gene was associated with anti-LIMS1 antibody response and increased risk of rejection. Additional genetic factors under active investigation include genome-wide polygenic risk scores for renal function and apolipoprotein L1 risk genotypes in African-American kidney donors. Due to the heterogeneity and complexity of clinical outcomes, new genome-wide association studies for rejection, allograft survival, and specific transplant comorbidities will require larger multicenter meta-analyses.

SUMMARY

Genetic compatibilities between donor and recipient represent an important determinant of rejection and long-term allograft survival. Genetic background of transplant donors may be additionally predictive of allograft function, while recipient's genomes are likely determinant of a wide range of transplantation outcomes, from rejection susceptibility to pharmacogenetics and various comorbidities related to prolonged immunosuppression.

Alloimmunity in pancreas transplantation

PURPOSE OF REVIEW

Despite significant improvement in pancreas allograft survival, rejection continues to be a major clinical problem. This review will focus on emerging literature related to the impact of pretransplant and de-novo DSA (dnDSA) in pancreas transplant recipients, and the diagnosis and treatment of T-cell-medicated rejection (TCMR) and antibody-mediated rejection (ABMR) in this complex group of patients.

RECENT FINDINGS

Recent data suggest that pretransplant DSA and the emergence of dnDSA in pancreas transplant recipients are both associated with increased risk of ABMR. The pancreas allograft biopsy is essential for the specific diagnosis of TCMR and/or ABMR, distinguish rejection from other causes of graft dysfunction, and to guide-targeted therapy. This distinction is important especially in the setting of solitary pancreas transplants but also in simultaneous pancreas-kidney transplants where solid evidence has now emerged demonstrating discordant biopsy findings. Treatment of rejection in a functioning pancreas can prolong allograft survival.

SUMMARY

The accurate and timely diagnosis of active alloimmune destruction in pancreas transplant recipients is paramount to preserving graft function in the long term. This review will discuss new, rapidly evolving information that is valuable for the physician caring for these patients to achieve optimal immunological outcomes.

H60: A Unique Murine Hematopoietic Cell-Restricted Minor Histocompatibility Antigen for Graft-versus-Leukemia Effect

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an important treatment for many types of hematological malignancies. Matching of donor and recipient for the major histocompatibility complex (MHC) improves the HSCT reconstitution, but donor-derived T cells reactive to non-MHC encoded minor histocompatibility antigens (MiHAs) can induce graft-versus-host disease (GVHD) while also being needed for graft-versus-leukemia (GVL) effects. MiHAs are allelically variant self-peptides presented conventionally on MHC molecules, but are alloantigenic in transplantation settings. Immunodominant MiHAs are most strongly associated with GVHD and GVL. There is need for mouse paradigms to understand these contradictory effects. H60 is a highly immunodominant mouse MiHA with hematopoietic cell-restricted expression. Immunodominance of H60 is tightly associated with its allelic nature (presence vs. absence of the transcripts), and the qualitative (TCR diversity) and quantitative (frequency) traits of the reactive T cells. The identity as a hematopoietic cell-restricted antigen (HRA) of H60 assists the appearance of the immunodominace in allo-HSCT circumstances, and generation of GVL effects without induction of serious GVHD after adoptive T cell transfer. Also it allows the low avidity T cells to escape thymic negative selection and exert GVL effect in the periphery, which is a previously unevaluated finding related to HRAs. In this review, we describe the molecular features and immunobiology in detail through which H60 selectively exerts its potent GVL effect. We further describe how lessons learned can be extrapolated to human allo-HCST.

Enhancement of Antigen Presentation by Deletion of Viral Immune Evasion Genes Prevents Lethal Cytomegalovirus Disease in Minor Histocompatibility Antigen-Mismatched Hematopoietic Cell Transplantation

Hematoablative treatment followed by hematopoietic cell transplantation (HCT) for reconstituting the co-ablated immune system is a therapeutic option to cure aggressive forms of hematopoietic malignancies. In cases of family donors or unrelated donors, immunogenetic mismatches in major histocompatibility complex (MHC) and/or minor histocompatibility (minor-H) loci are unavoidable and bear a risk of graft-vs.-host reaction and disease (GvHR/D). Transient immunodeficiency inherent to the HCT protocol favors a productive reactivation of latent cytomegalovirus (CMV) that can result in multiple-organ CMV disease. In addition, there exists evidence from a mouse model of MHC class-I-mismatched GvH-HCT to propose that mismatches interfere with an efficient reconstitution of antiviral immunity. Here we used a mouse model of MHC-matched HCT with C57BL/6 donors and MHC-congenic BALB.B recipients that only differ in polymorphic autosomal background genes, including minor-H loci coding for minor-H antigens (minor-HAg). Minor-HAg mismatch is found to promote lethal CMV disease in absence of a detectable GvH response to an immunodominant minor-HAg, the H60 locus-encoded antigenic peptide LYL8. Lethality of infection correlates with inefficient reconstitution of viral epitope-specific CD8⁺ T cells. Notably, lethality is prevented and control of cytopathogenic infection is restored when viral antigen presentation is enhanced by deletion of immune evasion genes from the infecting virus. We hypothesize that any kind of mismatch in GvH-HCT can induce "non-cognate transplantation tolerance" that dampens not only a mismatch-specific GvH response, which is beneficial, but adversely affects also responses to mismatch-unrelated antigens, such as CMV antigens in the specific case, with the consequence of lethal CMV disease.

Differential gene analysis during the development of obliterative bronchiolitis in a murine orthotopic lung transplantation model: A comprehensive transcriptome-based analysis

BACKGROUND

Obliterative bronchiolitis (OB) is a known issue during minor histocompatibility antigen (mHA) disparity during lung transplantation. This study evaluated gene expression in a murine orthotropic lung transplantation model using microarray analysis.

METHODS

Left lungs from C57BL/10(H-2b) donor mice were transplanted into mHA-mismatched C57BL/6(H-2b) recipient mice. Three groups (OB, non-OB, and sham controls) were confirmed pathologically and analyzed. Gene expression changes in the lung grafts were determined by microarray and immunohistochemical staining, and genes were verified by quantitative PCR in the lungs and mediastinal lymph nodes (LNs).

RESULTS

A total of 1343 genes were upregulated in the OB lungs compared to the sham group. Significant upregulation was observed for genes related to innate, e.g. Tlr2 and CCL3 and adaptive immunity, e.g. H2-ab1 and Il-21. Positive labeling for MHC class II antigen was observed in the bronchial epithelium of OB accompanied with B cells. We found increased Tlr2, Ccl3, H2-ab1, Il-21, Ighg3, Ifng, and Pdcd1 mRNA expression in the OB lung, and increased Il-21, Ighg3, and Pdcd1 expression in the OB LNs.

CONCLUSIONS

Adaptive and innate immune reactions were involved in OB after lung transplantation, and genetic examination of related genes could be used for detection of OB.

T-Cell Immunotherapies Targeting Histocompatibility and Tumor Antigens in Hematological Malignancies

Over the last decades, T-cell immunotherapy has revealed itself as a powerful, and often curative, strategy to treat blood cancers. In hematopoietic cell transplantation, most of the so-called graft-vs.-leukemia (GVL) effect hinges on the recognition of histocompatibility antigens that reflect immunologically relevant genetic variants between donors and recipients. Whether other variants acquired during the neoplastic transformation, or the aberrant expression of gene products can yield antigenic targets of similar relevance as the minor histocompatibility antigens is actively being pursued. Modern genomics and proteomics have enabled the high throughput identification of candidate antigens for immunotherapy in both autologous and allogeneic settings. As such, these major histocompatibility complex-associated tumor-specific (TSA) and tumor-associated antigens (TAA) can allow for the targeting of multiple blood neoplasms, which is a limitation for other immunotherapeutic approaches, such as chimeric antigen receptor (CAR)-modified T cells. We review the current strategies taken to translate these discoveries into T-cell therapies and propose how these could be introduced in clinical practice. Specifically, we discuss the criteria that are used to select the antigens with the greatest therapeutic value and we review the various T-cell manufacturing approaches in place to either expand antigen-specific T cells from the native repertoire or genetically engineer T cells with minor histocompatibility antigen or TSA/TAA-specific recombinant T-cell receptors. Finally, we elaborate on the current and future incorporation of these therapeutic T-cell products into the treatment of hematological malignancies.

Novel insights into non-HLA alloimmunity in kidney transplantation

Recognition of non‐self structures on donor cells represents the main immunological barrier in solid organ transplantation. The human leukocyte antigens (HLA) are considered the most important non‐self (allo)antigens in transplantation. Long‐term graft attrition is mainly caused by the formation of alloreactive antibodies that are directed against non‐self structures (i.e., epitopes) on cell surface proteins. Recently published data provided evidence for a similar importance of non‐HLA mismatches between donors and recipients in acute rejection as well as long‐term kidney allograft survival. These data suggest a broader concept of immunological non‐self that goes beyond HLA incompatibility and expands the current concept of polymorphic non‐self epitopes on cell surface molecules from HLA to non‐HLA targets. Amino acid substitutions caused by single nucleotide variants in protein‐coding genes or complete loss of gene expression represent the basis for polymorphic residues in both HLA and non‐HLA molecules. To better understand these novel insights in non‐HLA alloimmunity, we will first review basic principles of the alloimmune response with a focus on the HLA epitope concept in donor‐specific antibody formation before discussing key publications on non‐HLA antibodies.

The mouse curly whiskers (cw) mutations are recessive alleles of hephaestin-like 1 (Hephl1)

The spontaneous, curly whiskers mutation (abbreviated cw) generates kinky, brittle vibrissae in homozygous mice. Although cw has been mapped to the centromeric end of mouse Chromosome 9, no particular gene has been causally implicated, and this lack of genetic assignment has stymied cw's complete molecular and functional analysis. As a foundation for its positional cloning, we have fine-mapped cw to a small, 0.57 Mb interval that contains only three skin-expressed genes, including hephaestin-like 1 (Hephl1), which encodes a membrane-bound, multi-copper ferroxidase. Sequence analysis of all Hephl1 coding regions in cw/cw mutants revealed a single-base-pair substitution that alters Hephl1 mRNA splicing, and is specific to the cw allele, only. Sequence analysis of a second, independent, re-mutation to curly whiskers (that we verified by complementation testing with cw and have designated cw^2J) revealed a distinct defect in Hephl1 (a frame-shifting, single-base-pair insertion) that is specific to cw^2J. The results presented strongly suggest that defects in the Hephl1 gene are the molecular basis of the classical, curly-whiskers mutant phenotypes.

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Genetic mapping identifies a small number of candidates for the mouse cw mutation.

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Sequence analysis of one of these candidates, Hephl1, reveals a cw-specific defect.

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Analysis of skin mRNA indicates that the Hephl1^cw transcript is aberrantly spliced.

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Complementation testing identifies a distinct re-mutation to curly whiskers, cw^2J.

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Sequence analysis of Hephl1 reveals a cw^2J-specific, frameshifting insertion.

Contribution of non-HLA incompatibility between donor and recipient to kidney allograft survival: genome-wide analysis in a prospective cohort

BACKGROUND

The introduction of HLA matching of donors and recipients was a breakthrough in kidney transplantation. However, half of all transplanted kidneys still fail within 15 years after transplantation. Epidemiological data suggest a fundamental role of non-HLA alloimmunity.

METHODS

We genotyped 477 pairs of deceased donors and first kidney transplant recipients with stable graft function at three months that were transplanted between Dec 1, 2005, and April 30, 2015. Genome-wide genetic mismatches in non-synonymous single nucleotide polymorphisms (nsSNPs) were calculated to identify incompatibilities in transmembrane and secreted proteins. We estimated the association between nsSNP mismatch and graft loss in a Cox proportional hazard model, adjusting for HLA mismatch and clinical covariates. Customised peptide arrays were generated to screen for antibodies against genotype-derived mismatched epitopes in 25 patients with biopsy-confirmed chronic antibody-mediated rejection.

FINDINGS

59 268 nsSNPs affecting a transmembrane or secreted protein were analysed. The median number of nsSNP mismatches in immune-accessible transmembrane and secreted proteins between donors and recipients was 1892 (IQR 1850-1936). The degree of nsSNP mismatch was independently associated with graft loss in a multivariable model adjusted for HLA eplet mismatch (HLA-A, HLA-B, HLA-C, HLA-DP, HLA-DQ, and HLA-DR). Each increase by a unit of one IQR had an HR of 1·68 (95% CI 1·17-2·41, p=0·005). 5-year death censored graft survival was 98% in the quartile with the lowest mismatch, 91% in the second quartile, 89% in the third quartile, and 82% in the highest quartile (p=0·003, log-rank test). Customised peptide arrays verified a donor-specific alloimmune response to genetically predicted mismatched epitopes.

INTERPRETATION

Genetic mismatch of non-HLA haplotypes coding for transmembrane or secreted proteins is associated with an increased risk of functional graft loss independently of HLA incompatibility. As in HLA alloimmunity, donor-specific alloantibodies can be identified against genotype derived non-HLA epitopes.

FUNDING

Austrian Science Fund, WWTF (Vienna Science and Technology Fund), and Ministry of Health of the Czech Republic.

Human Embryonic Stem Cell Derived from Early Stage Fertilized Ovum: Non Immunogenic and Universal, Neuronal and Non-neuronal Cell Lines

Background

Human embryonic stem cells (hESCs) have the potential to treat various human disorders currently labeled as incurable and/or terminal illness. However, the fear that the patients' immune system would recognize them as non self and lead to an immune rejection has hampered their use. The main cause for immune rejection is usually the incompatibility of both donor and recipient's major histocompatibility complex (MHC).

Methods

We describe a hESC line developed through a patented technology that does not lead to immune reaction upon transplantation. We have transplanted these cells in ＞1,400 patients with chronic/terminal conditions and did not observe any immune reaction. No immunosuppressant were administered to these patients. We analyzed the expression levels of MHC-I and MHC-II on the surface of these hESCs using microarray technology. The gene targets for miRNA were analyzed using Gene ontology and DAVID database and pathways for these genes were determined using Reactome and Panther databases.

Results

Our results showed that the levels of expression of MHC-I and MHC-II on hESCs is almost negligible and thus the hESCs are less susceptible to an immune rejection.

Conclusions

The hESCs cultured at our facility expresses low levels of MHC-I and do not produce an immune reaction. These can be administered universally and need no cross matching before transplantation.

Comparison of the MHC I Immunopeptidome Repertoire of B-Cell Lymphoblasts Using Two Isolation Methods

Significant technological advances in both affinity chromatography and mass spectrometry have facilitated the identification of peptides associated with the major histocompatibility complex class I (MHC I) molecules, and enabled a greater understanding of the dynamic nature of the immunopeptidome of normal and neoplastic cells. While the isolation of MHC I-associated peptides (MIPs) typically used mild acid elution (MAE) or immunoprecipitation (IP), limited information currently exists regarding their respective analytical merits. Here, a comparison of these approaches for the isolation of two different B-cell lymphoblast cell models is presented, and it is reported on the recovery, reproducibility, scalability, and complementarity of identification from each method. Both approaches yielded reproducible datasets for peptide extracts obtained from 2 to 100 million cells, with 2016 to 5093 MIPs, respectively. The IP typically provides up to 6.4-fold increase in MIPs compared to the MAE. The comprehensiveness of these immunopeptidome analyses is extended using personalized genomic database of B-cell lymphoblasts, and it is discovered that 0.4% of their respective MIP repertoire harbored nonsynonymous single nucleotide variations (also known as minor histocompatibility antigens, MiHAs).

Escape from thymic deletion and anti-leukemic effects of T cells specific for hematopoietic cell-restricted antigen

Whether hematopoietic cell-restricted distribution of antigens affects the degree of thymic negative selection has not been investigated in detail. Here, we show that T cells specific for hematopoietic cell-restricted antigens (HRA) are not completely deleted in the thymus, using the mouse minor histocompatibility antigen H60, the expression of which is restricted to hematopoietic cells. As a result, low avidity T cells escape from thymic deletion. This incomplete thymic deletion occurs to the T cells developing de novo in the thymus of H60-positive recipients in H60-mismatched bone marrow transplantation (BMT). H60-specific thymic deletion escapee CD8⁺ T cells exhibit effector differentiation potentials in the periphery and contribute to graft-versus-leukemia effects in the recipients of H60-mismatched BMT, regressing H60⁺ hematological tumors. These results provide information essential for understanding thymic negative selection and developing a strategy to treat hematological tumors.

Major and minor histocompatibility antigens to NIMA: Prediction of a tolerogenic NIMA effect

The immunologic effects of developmental exposure to non-inherited maternal antigens (NIMA) are heterogeneous, either tolerogenic or immunogenic. The role of minor histocompatibility antigens (MiHA) in NIMA effects is unknown. We have recently reported that the NIMA effect can be classified into two distinct reactivities, low and high responder, to NIMA in utero and during nursing depending on the degree of maternal microchimerism (MMc) and Foxp3 expression of peripheral blood CD4(+)CD25(+) cells after graft-versus-host disease (GVHD) induction. These reactivities were predictable before transplantation, using an MLR-ELISPOT (mixed lymphocyte reaction; enzyme-linked immunospot) assay by comparing the number of IFNγ-producing cells stimulated with NIMA. Moreover, this assay was also applicable in both major and minor NIMA-mismatched setting. These observations are clinically relevant and suggest that it is possible to predict the immunological tolerance to NIMA.

Role of major histocompatibility complex variation in graft-versus-host disease after hematopoietic cell transplantation

Graft-versus-host disease (GVHD) remains a significant potentially life-threatening complication of allogeneic hematopoietic cell transplantation (HCT). Since the discovery of the human leukocyte antigen (HLA) system over 50 years ago, significant advances have clarified the nature of HLA variation between transplant recipients and donors as a chief etiology of GVHD. New information on coding and non-coding gene variation and GVHD risk provides clinicians with options to consider selected mismatched donors when matched donors are not available. These advances have increased the availability of unrelated donors for patients in need of a transplant and have lowered the overall morbidity and mortality of HCT.

Minor Antigen Disparities Impede Induction of Long Lasting Chimerism and Tolerance through Bone Marrow Transplantation with Costimulation Blockade

Mixed chimerism and tolerance can be successfully induced in rodents through allogeneic bone marrow transplantation (BMT) with costimulation blockade (CB), but varying success rates have been reported with distinct models and protocols. We therefore investigated the impact of minor antigen disparities on the induction of mixed chimerism and tolerance. C57BL/6 (H2^b) mice received nonmyeloablative total body irradiation (3 Gy), costimulation blockade (anti-CD40L mAb and CTLA4Ig), and 2 × 10⁷ bone marrow cells (BMC) from either of three donor strains: Balb/c (H2^d) (MHC plus multiple minor histocompatibility antigen (mHAg) mismatched), B10.D2 (H2^d) or B10.A (H2^a) (both MHC mismatched, but mHAg matched). Macrochimerism was followed over time by flow cytometry and tolerance was tested by skin grafting. 20 of 21 recipients of B10.D2 BMC but only 13 of 18 of Balb/c BMC and 13 of 20 of B10.A BMC developed stable long-term multilineage chimerism (p < 0.05 for each donor strain versus B10.D2). Significantly superior donor skin graft survival was observed in successfully established long-term chimeras after mHAg matched BMT compared to mHAg mismatched BMT (p < 0.05). Both minor and major antigen disparities pose a substantial barrier for the induction of chimerism while the maintenance of tolerance after nonmyeloablative BMT and costimulation blockade is negatively influenced by minor antigen disparities.        

Immunological Properties of Corneal Epithelial-Like Cells Derived from Human Embryonic Stem Cells

Transplantation of ex vivo expanded corneal limbal stem cells (LSCs) has been the main treatment for limbal stem cell deficiency, although the shortage of donor corneal tissues remains a major concern for its wide application. Due to the development of tissue engineering, embryonic stem cells (ESCs)-derived corneal epithelial-like cells (ESC-CECs) become a new direction for this issue. However, the immunogenicity of ESC-CECs is a critical matter to be solved. In the present study, we explored the immunological properties of ESC-CECs, which were differentiated from ESCs. The results showed that ESC-CECs had a similar character and function with LSCs both in vitro and in vivo. In ESC-CECs, a large number of genes related with immune response were down-regulated. The expressions of MHC-I, MHC-II, and co-stimulatory molecules were low, but the expression of HLA-G was high. The ESC-CECs were less responsible for T cell proliferation and NK cell lysis in vitro, and there was less immune cell infiltration after transplantation in vivo compared with LSCs. Moreover, the immunological properties were not affected by interferon-γ. All these results indicated a low immunogenicity of ESC-CECs, and they can be promising in clinical use.

Proteogenomic-based discovery of minor histocompatibility antigens with suitable features for immunotherapy of hematologic cancers

Pre-clinical studies have shown that injection of allogeneic T cells primed against a single minor histocompatibility antigen (MiHA) could cure hematologic cancers (HC) without causing any toxicity to the host. However, translation of this approach in humans has been hampered by the paucity of molecularly defined human MiHAs. Using a novel proteogenomic approach, we have analyzed cells from 13 volunteers and discovered a vast repertoire of MiHAs presented by the most common HLA haplotype in European Americans: HLA-A*02:01;B*44:03. Notably, out of >6000 MiHAs, we have identified a set of 39 MiHAs that share optimal features for immunotherapy of HCs. These 'optimal MiHAs' are coded by common alleles of genes that are preferentially expressed in hematopoietic cells. Bioinformatic modeling based on MiHA allelic frequencies showed that the 39 optimal MiHAs would enable MiHA-targeted immunotherapy of practically all HLA-A*02:01;B*44:03 patients. Further extension of this strategy to a few additional HLA haplotypes would allow treatment of almost all patients.

A novel approach to measuring cell-mediated lympholysis using quantitative flow and imaging cytometry

In this study, we established a novel isotope-free approach for the detection of cell-mediated lympholysis (CML) in MHC defined peripheral blood mononuclear cells (PBMCs) using multiparameter flow and imaging cytometry. CML is an established in vitro assay to detect the presence of cytotoxic effector T-lymphocytes precursors (CTLp). Current methods employed in the identification of CTLp in the context of transplantation are based upon the quantification of chromium ((51)Cr) released from target cells. In order to adapt the assay to flow cytometry, primary porcine PBMC targets were labeled with eFluor670 and incubated with major histocompatibility complex (MHC) mismatched effector cytotoxic lymphocytes (CTLs). With this method, we were able to detect target-specific lysis that was comparable to that observed with the (51)Cr-based assay. In addition, the use of quantitative cell imaging demonstrates the presence of accessory cells involved in the cytotoxic pathway. This innovative technique improves upon the standard (51)Cr release assay by eliminating the need for radioisotopes and provides enhanced characterization of the interactions between effector and target cells. This technique has wide applicability to numerous experimental and clinical models involved with effector-cell interactions.

Selection of Thymocytes Expressing Transgenic TCR Specific for a Minor Histocompatibility Antigen, H60

Minor histocompatibility antigens are MHC-bound peptides and contribute to the generation of allo-responses after allogeneic transplantation. H60 is a dominant minor H antigen that induces a strong CD8 T-cell response in MHC-matched allogeneic transplantation settings. Here, we report establishment of a TCR transgenic mouse line named J15, wherein T cells express TCRs specific for H60 in complex with H-2K(b), and different fates of the thymocytes expressing J15 TCRs in various thymic antigenic environments. Thymocytes expressing the J15 TCRs were positively selected and differentiated into CD8(+) single positive (SP) cells in the thymus of C57BL/6 mice, wherein the cognate antigen H60 is not expressed. However, thymocytes were negatively selected in thymus tissue where H60 was transgenically expressed under the control of the actin promoter, with double-positive stages of cells being deleted. Despite the ability of the H60H peptide (LTFHYRNL) variant to induce cytotoxic activity from H60-specific CTL lines at ~50% of the activity induced by normal H60 peptides (LTFNYRNL), J15-expressing thymocytes were positively selected in the thymus where the variant H60H was transgenically expressed. These results demonstrate that a single amino-acid change in the H60 epitope peptide influences the fate of thymocytes expressing the cognate TCR.

Tolerance induction using nanoparticles bearing HY peptides in bone marrow transplantation

Allogeneic cell therapies have either proven effective or have great potential in numerous applications, though the required systemic, life-long immunosuppression presents significant health risks. Inducing tolerance to allogeneic cells offers the potential to reduce or eliminate chronic immunosuppression. Herein, we investigated antigen-loaded nanoparticles for their ability to promote transplant tolerance in the minor histocompatibility antigen sex-mismatched C57BL/6 model of bone marrow transplantation. In this model, the peptide antigens Dby and Uty mediate rejection of male bone marrow transplants by female CD4+ and CD8+ T cells, respectively, and we investigated the action of nanoparticles on these T cell subsets. Antigens were coupled to or encapsulated within poly(lactide-co-glycolide) (PLG) nanoparticles with an approximate diameter of 500 nm. Delivery of the CD4-encoded Dby epitope either coupled to or encapsulated within PLG particles prevented transplant rejection, promoted donor-host chimerism, and suppressed proliferative and IFN-γ responses in tolerized recipients. Nanoparticles modified with the Uty peptide did not induce tolerance. The dosing regimen was investigated with Dby coupled particles, and a single dose delivered the day after bone marrow transplant was sufficient for tolerance induction. The engraftment of cells was significantly affected by PD-1/PDL-1 costimluation, as blockade of PD-1 reduced engraftment by ∼50%. In contrast, blockade of regulatory T cells did not impact the level of chimerism. The delivery of antigen on PLG nanoparticles promoted long-term engraftment of bone marrow in a model with a minor antigen mismatch in the absence of immunosuppression, and this represents a promising platform for developing a translatable, donor-specific tolerance strategy.

Memory programming in CD8(+) T-cell differentiation is intrinsic and is not determined by CD4 help

CD8⁺ T cells activated without CD4⁺ T-cell help are impaired in memory expansion. To understand the underlying cellular mechanism, here we track the dynamics of helper-deficient CD8⁺ T-cell response to a minor histocompatibility antigen by phenotypic and in vivo imaging analyses. Helper-deficient CD8⁺ T cells show reduced burst expansion, rapid peripheral egress, delayed antigen clearance and continuous activation, and are eventually exhausted. Contrary to the general consensus that CD4 help encodes memory programmes in CD8⁺ T cells and helper-deficient CD8⁺ T cells are abortive, these cells can differentiate into effectors and memory precursors. Importantly, accelerating antigen clearance or simply increasing the burst effector size enables generation of memory cells by CD8⁺ T cells, regardless of CD4 help. These results suggest that the memory programme is CD8⁺ T-cell-intrinsic, and provide insight into the role of CD4 help in CD8⁺ T-cell responses.

Persistent antigen stimulation can cause exhaustion and unresponsiveness of CD8 cells, impairing the immune response. Here the authors show that increasing the number of CD8 cells, decreasing the antigen load or providing CD4 help can overcome the exhaustion and establish a memory response.

Subdominant H60 antigen-specific CD8 T-cell response precedes dominant H4 antigen-specific response during the initial phase of allogenic skin graft rejection

In allogeneic transplantation, including the B6 anti-BALB.B settings, H60 and H4 are two representative dominant minor histocompatibility antigens that induce strong CD8 T-cell responses. With different distribution patterns, H60 expression is restricted to hematopoietic cells, whereas H4 is ubiquitously expressed. H60-specific CD8 T-cell response has been known to be dominant in most cases of B6 anti-BALB.B allo-responses, except in the case of skin transplantation. To understand the mechanism underlying the subdominance of H60 during allogeneic skin transplantation, we investigated the dynamics of the H60-specific CD8 T cells in B6 mice transplanted with allogeneic BALB.B tail skin. Unexpectedly, longitudinal bioluminescence imaging and flow cytometric analyses revealed that H60-specific CD8 T cells were not always subdominant to H4-specific cells but instead showed a brief dominance before the H4 response became predominant. H60-specific CD8 T cells could expand in the draining lymph node and migrate to the BALB.B allografts, indicating their active participation in the anti-BALB.B allo-response. Enhancing the frequencies of H60-reactive CD8 T cells prior to skin transplantation reversed the immune hierarchy between H60 and H4. Additionally, H60 became predominant when antigen presentation was limited to the direct pathway. However, when antigen presentation was restricted to the indirect pathway, the expansion of H60-specific CD8 T cells was limited, whereas H4-specific CD8 T cells expanded significantly, suggesting that the temporary immunodominance and eventual subdominance of H60 could be due to their reliance on the direct antigen presentation pathway. These results enhance our understanding of the immunodominance phenomenon following allogeneic tissue transplantation.

Impact of genomic polymorphisms on the repertoire of human MHC class I-associated peptides

For decades, the global impact of genomic polymorphisms on the repertoire of peptides presented by major histocompatibility complex (MHC) has remained a matter of speculation. Here we present a novel approach that enables high-throughput discovery of polymorphic MHC class I-associated peptides (MIPs), which play a major role in allorecognition. On the basis of comprehensive analyses of the genomic landscape of MIPs eluted from B lymphoblasts of two MHC-identical siblings, we show that 0.5% of non-synonymous single nucleotide variations are represented in the MIP repertoire. The 34 polymorphic MIPs found in our subjects are encoded by bi-allelic loci with dominant and recessive alleles. Our analyses show that, at the population level, 12% of the MIP-coding exome is polymorphic. Our method provides fundamental insights into the relationship between the genomic self and the immune self and accelerates the discovery of polymorphic MIPs (also known as minor histocompatibility antigens).

Mass spectrometry (MS) has furthered our understanding of MHC class I-associated peptides (MIPs), but the technique is inadequate for studying MIP-associated polymorphisms. Here, the authors combine high-throughput MS with exome and transcriptome sequencing to identify polymorphic MIPs from two female siblings.

Transplantation genetics: current status and prospects

Over the last decade, advances in genetic technologies have accelerated our understanding of the genetic diversity across individuals and populations. Case-control and population-based studies have led to several thousand genetic associations across a range of phenotypes and traits being unveiled. Despite widespread and successful use of organ transplantation as a curative therapy for organ failure, genetic research has yet to make a major impact on transplantation practice aside from HLA matching. New studies indicate that non-HLA loci, termed minor histocompatibility antigens (mHAs), may play an important role in graft rejection. With several million common and rare polymorphisms observed between any two unrelated individuals, a number of these polymorphisms represent mHAs, and may underpin transplantation rejection. Genetic variation is also recognized as contributing to clinical outcomes including response to immunosuppressants, introducing the possibility of genotype-guided prescribing in the very near future. This review summarizes existing knowledge of the impact of genetics on transplantation outcomes and therapeutic responses, and highlights the translational potential that new genomic knowledge may bring to this field.

Immune response to mutant neo-antigens: Cancer's lessons for aging

Extending observations on the immunogenicity of neo-antigens that arise in the course of oncogenesis and tumor progression, we suggest that somatic mutations affecting normal tissues also lead to generation of new epitopes. We hypothesize that, at least under inflammatory conditions, immune responses against such neo-antigens may lead to the elimination or functional impairment of normal cells, thus contributing to aging.

Deletion of naïve T cells recognizing the minor histocompatibility antigen HY with toxin-coupled peptide-MHC class I tetramers inhibits cognate CTL responses and alters immunodominance

Alloreactive T-cell responses directed against minor histocompatibility (H) antigens, which arise from diverse genetic disparities between donor and recipient outside the MHC, are an important cause of rejection of MHC-matched grafts. Because clinically significant responses appear to be directed at only a few antigens, the selective deletion of naïve T cells recognizing donor-specific, immunodominant minor H antigens in recipients before transplantation may be a useful tolerogenic strategy. We have previously demonstrated that peptide-MHC class I tetramers coupled to a toxin can efficiently eliminate specific TCR-transgenic T cells in vivo. Here, using the minor histocompatibility antigen HY as a model, we investigated whether toxic tetramers could inhibit the subsequent priming of the two H2-D(b)-restricted, immunodominant T-cell responses by deleting precursor CTL. Immunization of female mice with male bone marrow elicited robust CTL activity against the Uty and Smcy epitopes, with Uty constituting the major response. As hypothesized, toxic tetramer administration prior to immunization increased survival of cognate peptide-pulsed cells in an in vivo CTL assay, and reduced the frequency of corresponding T cells. However, tetramer-mediated decreases in either T-cell population magnified CTL responses against the non-targeted epitope, suggesting that D(b)-Uty(+) and D(b)-Smcy(+) T cells compete for a limited common resource during priming. Toxic tetramers conceivably could be used in combination to dissect manipulate CD8(+) T-cell immunodominance hierarchies, and to prevent the induction of donor-specific, minor H antigen CTL responses in allotransplantation.

Rejection of leukemic cells requires antigen-specific T cells with high functional avidity

In a context where injection of antigen (Ag)-specific T cells probably represents the future of leukemia immunotherapy, identification of optimal target Ags is crucial. We therefore sought to discover a reliable marker for selection of the most potent Ags. To this end, (1) we immunized mice against 8 individual Ags: 4 minor histocompatibility Ags (miHAs) and 4 leukemia-associated Ags (LAAs) that were overexpressed on leukemic relative to normal thymocytes; (2) we assessed their ability to reject EL4 leukemic cells; and (3) we correlated the properties of our Ags (and their cognate T cells) with their ability to induce protective antileukemic responses. Overall, individual miHAs instigated more potent antileukemic responses than LAAs. Three features had no influence on the ability of primed T cells to reject leukemic cells: (1) MHC-peptide affinity; (2) the stability of MHC-peptide complexes; and (3) epitope density at the surface of leukemic cells, as assessed using mass spectrometry. The cardinal feature of successful Ags is that they were recognized by high-avidity CD8 T cells that proliferated extensively in vivo. Our work suggests that in vitro evaluation of functional avidity represents the best criterion for selection of Ags, which should be prioritized in clinical trials of leukemia immunotherapy.

Transfusion-induced bone marrow transplant rejection due to minor histocompatibility antigens

Traditionally, alloimmunization to transfused blood products has focused exclusively on recipient antibodies recognizing donor alloantigens present on the cell surface. Accordingly, the immunologic sequelae of alloimmunization have been antibody mediated effects (ie, hemolytic transfusion reactions, platelet refractoriness, anti-HLA and anti-HNA effects, etc). However, in addition to the above sequelae, there is also a correlation between the number of antecedent transfusions in humans and the rate of bone marrow transplant (BMT) rejection-under reduced intensity conditioning with HLA-matched or HLA-identical marrow. Bone marrow transplant of this nature is the only existing cure for a series of nonmalignant hematologic diseases (eg, sickle cell disease, thalassemias, etc); however, rejection remains a clinical problem. It has been hypothesized that transfusion induces subsequent BMT rejection through immunization. Studies in animal models have observed the same effect and have demonstrated that transfusion-induced BMT rejection can occur in response to alloimmunization. However, unlike traditional antibody responses, sensitization in this case results in cellular immune effects, involving populations such as T cell or natural killer cells. In this case, rejection occurs in the absence of alloantibodies and would not be detected by existing immune-hematologic methods. We review human and animal studies in light of the hypothesis that, for distinct clinical populations, enhanced rejection of BMT may be an unappreciated adverse consequence of transfusion, which current blood bank methodologies are unable to detect.

Immunogenicity of pluripotent stem cells and their derivatives

The ability of pluripotent stem cells to self-renew and differentiate into all somatic cell types brings great prospects to regenerative medicine and human health. However, before clinical applications, much translational research is necessary to ensure that their therapeutic progenies are functional and nontumorigenic, that they are stable and do not dedifferentiate, and that they do not elicit immune responses that could threaten their survival in vivo. For this, an in-depth understanding of their biology, genetic, and epigenetic make-up and of their antigenic repertoire is critical for predicting their immunogenicity and for developing strategies needed to assure successful long-term engraftment. Recently, the expectation that reprogrammed somatic cells would provide an autologous cell therapy for personalized medicine has been questioned. Induced pluripotent stem cells display several genetic and epigenetic abnormalities that could promote tumorigenicity and immunogenicity in vivo. Understanding the persistence and effects of these abnormalities in induced pluripotent stem cell derivatives is critical to allow clinicians to predict graft fate after transplantation, and to take requisite measures to prevent immune rejection. With clinical trials of pluripotent stem cell therapy on the horizon, the importance of understanding immunologic barriers and devising safe, effective strategies to bypass them is further underscored. This approach to overcome immunologic barriers to stem cell therapy can take advantage of the validated knowledge acquired from decades of hematopoietic stem cell transplantation.

Gene expression profiling of allogeneic islet grafts in an experimental mouse model before rejection or tolerance phenotypes arise

BACKGROUND

It has been reported that an HY antigen-mismatched islet transplantation can induce peripheral tolerance. However, the factors that initiate the peripheral tolerance are not clear. This study was designed to examine which genes were most important for the induction of peripheral tolerance.

METHODS

Islets from female Balb/c and male C57BL/6 mice were transplanted underneath the left perirenal capsule of female C57BL/6 recipient mice rendered diabetic by intraperitoneal injection of streptozotocin. Before rejection or tolerance phenotypes arose, we harvested islet grafts for cDNA microarray analysis.

RESULTS

Minor antigen-mismatched islets transplanted into recipient mice showed no rejection or tolerance phenotypes until 12 days posttransplantation. When we confirmed, decreased functional islet grafts and increased inflammatory cell infiltration. Gene expression profiles revealed differences in expression among groups. Major histocompatibility complex-mismatched islets induced upregulation of 209 genes and downregulation of 10 genes compared with the HY antigen-mismatched islet (2-fold; P < .05). Of these, 3 genes exhibited significant changes in expression levels in Balb/c donor islet grafts compared with C57BL/6 donor islet grafts: Gad1, Gdf10, and Scg2 (P < .01).

CONCLUSIONS

The present study suggested that 3 genes showed a significant relationship to protection against graft rejection. The identification of these genes may help to understand signaling pathways, involved in the communication between transplanted islet grafts and recipients in vivo.

Social discrimination by quantitative assessment of immunogenetic similarity

Genes of the major histocompatibility complex (MHC) that underlie the adaptive immune system may allow vertebrates to recognize their kin. True kin-recognition genes should produce signalling products to which organisms can respond. Allelic variation in the peptide-binding region (PBR) of MHC molecules determines the pool of peptides that can be presented to trigger an immune response. To examine whether these MHC peptides also might underlie assessments of genetic similarity, we tested whether Xenopus laevis tadpoles socially discriminate between pairs of siblings with which they differed in PBR amino acid sequences. We found that tadpoles (four sibships, n = 854) associated preferentially with siblings with which they were more similar in PBR amino acid sequence. Moreover, the strength of their preference for a conspecific was directly proportional to the sequence similarity between them. Discrimination was graded, and correlated more closely with functional sequence differences encoded by MHC class I and class II alleles than with numbers of shared haplotypes. Our results thus suggest that haplotype analyses may fail to reveal fine-scale behavioural responses to divergence in functionally expressed sequences. We conclude that MHC-PBR gene products mediate quantitative social assessment of immunogenetic similarity that may facilitate kin recognition in vertebrates.

The impact of frequent HLA haplotypes in high linkage disequilibrium on donor search and clinical outcome after unrelated haematopoietic SCT

The MHC region on chromosome 6 contains a large number of non-HLA genes next to the HLA genes. Matching for HLA in unrelated hematopoietic SCT (HSCT) does not necessarily mean that these non-HLA genes are also matched. We selected 348 Northwest European patients transplanted with an HLA-A-, -B-, -C-, -DRB1-, -DQB1-matched unrelated donor (MUD) between 1987 and 2008. Patients' haplotypes were identified via descend. We were unable to determine the haplotypes of the donor; therefore we used frequent haplotypes (FH) in high linkage disequilibrium (LD) as a proxy for haplotype matching. Presence of a FH in a patient positively affected the probability and speed of identifying a matched unrelated donor. Competing risk survival analysis showed that patients with one or two FH have a statistically significantly decreased probability of developing ≥ grade II acute GVDH (aGVHD) without increased risk of relapse compared to patients without FH (HR (95% CI): 0.53 (0.31-0.91)). This association was strongest for those FH with the highest LD between both HLA-A and -C or -B, and HLA-C or -B and -DRB1 (HR (95% CI): 0.49 (0.26-0.92)). These results extend evidence that non-HLA allele coding regions have a significant impact on development of ≥ grade II aGVHD. We conclude that there is more to successful HSCT than matching for HLA genes.

Requirement of CD4 help for induction of CD8 T cell response specific for virally derived h60

CD40-CD40L-mediated help from CD4 T cells is essential to induce primary CD8 T cell responses specific to the non-inflammatory cell-based antigen H60. In this study, using H60 as a model antigen, we generated recombinant vaccinia viruses (rVVs) expressing the H60 CD8 epitope and investigated whether CD4 help was required to activate the CD8 T cell response specific to the virally expressed H60. The immune response after infection with rVVs expressing H60 was similar to that after immunization with H60 congenic splenocytes, with a peak frequency of H60-specific CD8 T cells detected in the blood on day 10 post-infection. A CD8 T cell response specific for virally derived H60 was not induced in CD4-depleted mice, but was in CD40-deficient mice. These results provide insights into the characterization of the CD8 T cell response specifically for antigens originating from cellular sources compared to viral sources.