Relative Frequencies of Alloantigen-Specific Helper CD4 T Cells and B Cells Determine Mode of Antibody-Mediated Allograft Rejection

Humoral alloimmunity is now recognized as a major determinant of transplant outcome. MHC glycoprotein is considered a typical T-dependent antigen, but the nature of the T cell alloresponse that underpins alloantibody generation remains poorly understood. Here, we examine how the relative frequencies of alloantigen-specific B cells and helper CD4 T cells influence the humoral alloimmune response and how this relates to antibody-mediated rejection (AMR). An MHC-mismatched murine model of cardiac AMR was developed, in which T cell help for alloantibody responses in T cell deficient (Tcrbd-/-) C57BL/6 recipients against donor H-2Kd MHC class I alloantigen was provided by adoptively transferred "TCR75" CD4 T cells that recognize processed H-2Kd allopeptide via the indirect-pathway. Transfer of large numbers (5 × 105) of TCR75 CD4 T cells was associated with rapid development of robust class-switched anti-H-2Kd humoral alloimmunity and BALB/c heart grafts were rejected promptly (MST 9 days). Grafts were not rejected in T and B cell deficient Rag2-/- recipients that were reconstituted with TCR75 CD4 T cells or in control (non-reconstituted) Tcrbd-/- recipients, suggesting that the transferred TCR75 CD4 T cells were mediating graft rejection principally by providing help for effector alloantibody responses. In support, acutely rejecting BALB/c heart grafts exhibited hallmark features of acute AMR, with widespread complement C4d deposition, whereas cellular rejection was not evident. In addition, passive transfer of immune serum from rejecting mice to Rag2-/- recipients resulted in eventual BALB/c heart allograft rejection (MST 20 days). Despite being long-lived, the alloantibody responses observed at rejection of the BALB/c heart grafts were predominantly generated by extrafollicular foci: splenic germinal center (GC) activity had not yet developed; IgG secreting cells were confined to the splenic red pulp and bridging channels; and, most convincingly, rapid graft rejection still occurred when recipients were reconstituted with similar numbers of Sh2d1a-/- TCR75 CD4 T cells that are genetically incapable of providing T follicular helper cell function for generating GC alloimmunity. Similarly, alloantibody responses generated in Tcrbd-/- recipients reconstituted with smaller number of wild-type TCR75 CD4 T cells (103), although long-lasting, did not have a discernible extrafollicular component, and grafts were rejected much more slowly (MST 50 days). By modeling antibody responses to Hen Egg Lysozyme protein, we confirm that a high ratio of antigen-specific helper T cells to B cells favors development of the extrafollicular response, whereas GC activity is favored by a relatively high ratio of B cells. In summary, a relative abundance of helper CD4 T cells favors development of strong extrafollicular alloantibody responses that mediate acute humoral rejection, without requirement for GC activity. This work is composed of two parts, of which this is Part I. Please read also Part II: Chhabra et al., 2019.

Functional amyloidogenesis in immunocytes from the colonial ascidian Botryllus schlosseri: Evolutionary perspective

Cytotoxic morula cells (MCs) and phagocytes are the circulating immunocytes of the colonial ascidian Botryllus schlosseri: Both these cells can synthesise amyloid fibrils, supporting the idea that physiological amyloidogenesis is involved in inflammation and modulation of immune responses. Intriguingly, amyloid of B. schlosseri immunocytes is made of two different proteins. MCs, the first cells to sense non-self and involved in the allorejection reaction between contacting genetically incompatible colonies, use melanin encapsulation as the principal method to fight non-self. They release amyloid fibrils formed by p102 protein that allow the packaging and deposit of melanin and other toxic molecules nearby the invader or in the contact region of incompatible colonies. Phagocytes release amyloid-based extracellular traps when challenged with microbes: their amyloid fibrils harbour BsAPP, an orthologue of the vertebrate amyloidogeneic protein APP. This strategy of immune response, present also in human neutrophils, allows phagocytes to block and engulf bacteria and fungi.

Complement Inhibitor CRIg/FH Ameliorates Renal Ischemia Reperfusion Injury via Activation of PI3K/AKT Signaling

Complement activation is involved in the pathogenesis of ischemia reperfusion injury (IRI), which is an inevitable process during kidney transplantation. Therefore, complement-targeted therapeutics hold great potential in protecting the allografts from IRI. We observed universal deposition of C3d and membrane attack complex in human renal allografts with delayed graft function or biopsy-proved rejection, which confirmed the involvement of complement in IRI. Using FB-, C3-, C4-, C5-, C5aR1-, C5aR2-, and C6-deficient mice, we found that all components, except C5aR2 deficiency, significantly alleviated renal IRI to varying degrees. These gene deficiencies reduced local (deposition of C3d and membrane attack complex) and systemic (serum levels of C3a and C5a) complement activation, attenuated pathological damage, suppressed apoptosis, and restored the levels of multiple local cytokines (e.g., reduced IL-1β, IL-9, and IL-12p40 and increased IL-4, IL-5, IL-10, and IL-13) in various gene-deficient mice, which resulted in the eventual recovery of renal function. In addition, we demonstrated that CRIg/FH, which is a targeted complement inhibitor for the classical and primarily alternative pathways, exerted a robust renoprotective effect that was comparable to gene deficiency using similar mechanisms. Further, we revealed that PI3K/AKT activation, predominantly in glomeruli that was remarkably inhibited by IRI, played an essential role in the CRIg/FH renoprotective effect. The specific PI3K antagonist duvelisib almost completely abrogated AKT phosphorylation, thus abolishing the renoprotective role of CRIg/FH. Our findings suggested that complement activation at multiple stages induced renal IRI, and CRIg/FH and/or PI3K/AKT agonists may hold the potential in ameliorating renal IRI.

A Functionally Different Immune Phenotype in Cattle Is Associated With Higher Mastitis Incidence

A novel vaccine against bovine viral diarrhea (BVD) induced pathogenic antibody production in 5-10% of BVD-vaccinated cows. Transfer of these antibodies via colostrum caused Bovine neonatal pancytopenia (BNP) in calves, with a lethality rate of 90%. The exact immunological mechanisms behind the onset of BNP are not fully understood to date. To gain further insight into these mechanisms, we analyzed the immune proteome from alloreactive antibody producers (BNP cows) and non-responders. After in vitro stimulation of peripheral blood derived lymphocytes (PBL), we detected distinctly deviant expression levels of several master regulators of immune responses in BNP cells, pointing to a changed immune phenotype with severe dysregulation of immune response in BNP cows. Interestingly, we also found this response pattern in 22% of non-BVD-vaccinated cows, indicating a genetic predisposition of this immune deviant (ID) phenotype in cattle. We additionally analyzed the functional correlation of the ID phenotype with 10 health parameters and 6 diseases in a retrospective study over 38 months. The significantly increased prevalence of mastitis among ID cows emphasizes the clinical relevance of this deviant immune response and its potential impact on the ability to fight infections.

Complex mammalian-like haematopoietic system found in a colonial chordate

Haematopoiesis is an essential process that evolved in multicellular animals. At the heart of this process are haematopoietic stem cells (HSCs), which are multipotent and self-renewing, and generate the entire repertoire of blood and immune cells throughout an animal's life1. Although there have been comprehensive studies on self-renewal, differentiation, physiological regulation and niche occupation in vertebrate HSCs, relatively little is known about the evolutionary origin and niches of these cells. Here we describe the haematopoietic system of Botryllus schlosseri, a colonial tunicate that has a vasculature and circulating blood cells, and interesting stem-cell biology and immunity characteristics2-8. Self-recognition between genetically compatible B. schlosseri colonies leads to the formation of natural parabionts with shared circulation, whereas incompatible colonies reject each other3,4,7. Using flow cytometry, whole-transcriptome sequencing of defined cell populations and diverse functional assays, we identify HSCs, progenitors, immune effector cells and an HSC niche, and demonstrate that self-recognition inhibits allospecific cytotoxic reactions. Our results show that HSC and myeloid lineage immune cells emerged in a common ancestor of tunicates and vertebrates, and also suggest that haematopoietic bone marrow and the B. schlosseri endostyle niche evolved from a common origin.

Notch signaling mediated by Delta-like ligands 1 and 4 controls the pathogenesis of chronic GVHD in mice

Chronic graft-versus-host disease (cGVHD) is a major complication of allogeneic hematopoietic cell transplantation (allo-HCT) and remains an area of unmet clinical need with few treatment options available. Notch blockade prevents acute GVHD in multiple mouse models, but the impact of Notch signaling on cGVHD remains unknown. Using genetic and antibody-mediated strategies of Notch inhibition, we investigated the role of Notch signaling in complementary mouse cGVHD models that mimic several aspects of human cGVHD in search of candidate therapeutics. In the B10.D2→BALB/c model of sclerodermatous cGVHD, Delta-like ligand 4 (Dll4)-driven Notch signaling was essential for disease development. Antibody-mediated Dll4 inhibition conferred maximum benefits when pursued early in a preventative fashion, with anti-Dll1 enhancing early protection. Notch-deficient alloantigen-specific T cells showed no early defects in proliferation or helper polarization in vivo but subsequently exhibited markedly decreased cytokine secretion and enhanced accumulation of FoxP3+ regulatory T cells. In the B6→B10.BR major histocompatibility complex-mismatched model with multi-organ system cGVHD and prominent bronchiolitis obliterans (BO), but not skin manifestations, absence of Notch signaling in T cells provided long-lasting disease protection that was replicated by systemic targeting of Dll1, Dll4, or both Notch ligands, even during established disease. Notch inhibition decreased target organ damage and germinal center formation. Moreover, decreased BO-cGVHD was observed upon inactivation of Notch1 and/or Notch2 in T cells. Systemic targeting of Notch2 alone was safe and conferred therapeutic benefits. Altogether, Notch ligands and receptors regulate key pathogenic steps in cGVHD and emerge as novel druggable targets to prevent or treat different forms of cGVHD.

Antibody-mediated immune suppression by antigen modulation is antigen-specific

Alloantibodies developing after exposure to red blood cell (RBC) alloantigens can complicate pregnancy and transfusion therapy. The only method currently available to actively inhibit RBC alloantibody formation is administration of antigen-specific antibodies, a phenomenon termed antibody-mediated immune suppression (AMIS). A well-known example of AMIS is RhD immune globulin prophylaxis to prevent anti-D formation in RhD- individuals. However, whether AMIS is specific or impacts alloimmunization to other antigens on the same RBC remains unclear. To evaluate the specificity of AMIS, we passively immunized antigen-negative recipients with anti-KEL or anti-hen egg lysozyme (HEL) antibodies, followed by transfusion of murine RBC expressing both the HEL-ovalbumin-Duffy (HOD) and human KEL antigens (HOD × KEL RBC). Significant immunoglobulin G deposition on transfused HOD × KEL RBC occurred in all passively immunized recipients. Complement deposition and antigen modulation of the KEL antigen occurred on transfused RBC only in anti-KEL-treated recipients, whereas HEL antigen levels decreased only in the presence of anti-HEL antibodies. Western blot analysis confirmed the specificity of antigen loss, which was not attributable to RBC endocytosis and appears distinct for the 2 antigens. Specifically, removal of KEL was attenuated by clodronate treatment, whereas loss of HEL was unaffected by clodronate in vivo but sensitive to protease treatment in vitro. Antigen-specific modulation correlated with antigen-specific AMIS, with anti-KEL treated recipients forming antibodies to the HOD antigen and anti-HEL-treated recipients developing antibodies to the KEL antigen. Together, these results demonstrate that passively administered antibodies can selectively inhibit the immune response to a specific antigen.

Determining the Quantitative Principles of T Cell Response to Antigenic Disparity in Stem Cell Transplantation

Alloreactivity compromising clinical outcomes in stem cell transplantation is observed despite HLA matching of donors and recipients. This has its origin in the variation between the exomes of the two, which provides the basis for minor histocompatibility antigens (mHA). The mHA presented on the HLA class I and II molecules and the ensuing T cell response to these antigens results in graft vs. host disease. In this paper, results of a whole exome sequencing study are presented, with resulting alloreactive polymorphic peptides and their HLA class I and HLA class II (DRB1) binding affinity quantified. Large libraries of potentially alloreactive recipient peptides binding both sets of molecules were identified, with HLA-DRB1 generally presenting a greater number of peptides. These results are used to develop a quantitative framework to understand the immunobiology of transplantation. A tensor-based approach is used to derive the equations needed to determine the alloreactive donor T cell response from the mHA-HLA binding affinity and protein expression data. This approach may be used in future studies to simulate the magnitude of expected donor T cell response and determine the risk for alloreactive complications in HLA matched or mismatched hematopoietic cell and solid organ transplantation.

Regulatory T cells in embryo implantation and the immune response to pregnancy

At implantation, the embryo expresses paternally derived alloantigens and evokes inflammation that can threaten reproductive success. To ensure a robust placenta and sustainable pregnancy, an active state of maternal immune tolerance mediated by CD4+ regulatory T cells (Tregs) is essential. Tregs operate to inhibit effector immunity, contain inflammation, and support maternal vascular adaptations, thereby facilitating trophoblast invasion and placental access to the maternal blood supply. Insufficient Treg numbers or inadequate functional competence are implicated in idiopathic infertility and recurrent miscarriage as well as later-onset pregnancy complications stemming from placental insufficiency, including preeclampsia and fetal growth restriction. In this Review, we summarize the mechanisms acting in the conception environment to drive the Treg response and discuss prospects for targeting the T cell compartment to alleviate immune-based reproductive disorders.

Bioimaging of alloantigen-stimulated regulatory T cells in rat vascularized composite allotransplantation

Background

Tipping the balance toward regulatory T cells (Tregs) through adoptive cell therapy has shown promise to induce transplantation tolerance. Although such strategy has been explored in many mice organ transplantation studies, less knowledge was available in rat systems. Furthermore, the behaviors of the transferred cells have not been well studied in real-time fashion.

Methods

Tregs from naïve LEW rats were purified in two steps with the autoMACS system. Immunosuppression potential of these cells was examined with mixed lymphocyte reaction. Following stimulation by the alloantigen in vitro, the purified Tregs were infused into the recipients of vascularized composite allotransplantation (VCA). Secondary allogeneic skin grafting challenge was performed on the recipients with long-term survived VCA. Live optical imaging was performed to track luciferase-expressing Tregs following infusion to the VCA recipients. Expression of relevant molecules was studied by flow cytometry or quantitative RT-PCR.

Results

Rat Tregs were enriched following two-step cell sorting and showed immunosuppressive capacity. Upon infusion into the VCA recipients that have been treated with antilymphocyte serum and short-term Cyclosporin A, the antigen-stimulated Tregs significantly prolonged VCA survival and induced donor-specific tolerance. Tracking of the infused bioluminescent Tregs showed their specific homing to lymph nodes, and then to the VCAs. Following secondary skin grafting, Tregs specifically gathered at the donor-derived skin that was not rejected by the recipient. The in vivo migratory pattern coincided with the altered expression of cell surface molecules of CD62L, CD103, CD134, and CD278, following donor-antigen stimulation. Elevated expression of CCR4 and CCL22 in allograft may also participate in recruiting Tregs for maintenance of VCA survival and promoting donor-specific tolerance.

Conclusion

Sorted Tregs induced donor-specific tolerance to VCA in rats. Live cell tracking demonstrated that activated CD4⁺CD25⁺FoxP3⁺ Tregs targeted primarily to the lymph nodes and VCA. The Tregs migrated to the secondary grafted donor skin and contributed to the maintenance of donor-specific tolerance. These behaviors were associated with phenotypic changes induced by donor antigen stimulation. Increased expression of CCR4 and CCL22 in VCA skin may also be relevant.

Quantifying size and diversity of the human T cell alloresponse

Alloreactive T lymphocytes are the primary mediators of immune responses in transplantation, both in the graft-versus-host and host-versus-graft directions. While essentially all clones comprising the human T cell repertoire have been selected on self-peptide presented by self-human leukocyte antigens (self-HLAs), much remains to be understood about the nature of clones capable of responding to allo-HLA molecules. Quantitative tools to study these cells are critical to understand fundamental features of this important response; however, the large size and diversity of the alloreactive T cell repertoire in humans presents a great technical challenge. We have developed a high-throughput T cell receptor (TCR) sequencing approach to characterize the human alloresponse. We present a statistical method to model T cell clonal frequency distribution and quantify repertoire diversity. Using these approaches, we measured the diversity and frequency of distinct alloreactive CD4+ and CD8+ T cell populations in HLA-mismatched responder-stimulator pairs. Our findings indicate that the alloimmune repertoire is highly specific for a given pair of individuals, that most alloreactive clones circulate at low frequencies, and that a high proportion of TCRs is likely able to recognize alloantigens.

Growth Inhibition of Murine Colonic Adenocarcinoma by Tumor Immune but not by IL-2-Activated or Alloactivated Lymphocytes

The antigenic profile of C-26 and C-51 BALB/c colonic adenocarcinomas was examined by in vivo and in vitro assays. Mice immunized with irradiated C-26 or C-51 tumor cells from freshly excised tumor nodules or from in vitro-growing cell lines were able to reject a challenge of both tumors. Spleen lymphocytes of immune but not of normal mice were effective in cross-inhibiting tumor growth in vivo in a Winn assay. Tissue-associated antigens common to C-26 and C-51 and to their metastases but not to other syngeneic neoplasms were detected in vitro by cytotoxic T lymphocytes obtained after 5 days of a secondary culture of immune lymphocytes and irradiated tumor cells. Activated lymphocytes were obtained by exposure of spleen cells to interleukin 2 or by allostimulation. Such lymphocytes, although cytotoxic in vitro on C-26 and C-51 carcinomas, were unable to significantly reduce in vivo tumor growth in the Winn assay.

Human Neutrophil Alloantigen Genotype Frequencies Among Syrian Population

BACKGROUND

Human neutrophil antigens (HNA) are able to provoke allo- and autoimmune antibodies which lead to reactions like autoimmune and neonatal neutropenia. However, until now no data about HNA genotype distribution in Syrian population exists. The aim of this study was to determine the HNA allele frequencies in the largest group asking for asylum in Germany since 2015. Allele frequencies were compared to data from German blood donors. Therefore, we calculated the risk of alloimmunization and associated transfusion reactions, as well as the risk of developing neonatal neutropenia for newborns of mixed race couples.

METHODS

We isolated DNA from blood samples of 100 Syrian volunteers and typed them for HNA-1, -3, -4, and -5 by using a commercial polymerase chain reaction kit with sequence-specific primers (SSP-PCR). Then, we compared the HNA genotype distribution with data from Germans and different populations from literature.

RESULTS

In Syrian population the gene frequencies for HNA-1a, HNA-1b, and HNA-1c were 0.375, 0.580, and 0.040, for HNA-3a and -3b 0.742 and 0.258, for HNA-4a and -4b 0.860 and 0.140, and for HNA-5a and -5bw 0.660 and 0.340, respectively. No statistically significant differences between Syrian and German gene frequencies were found.

CONCLUSIONS

This study is the first to report HNA gene frequencies in Syrian population. There is no significant difference of HNA genotype frequencies compared to the German population. Therefore, no elevated alloimmunization risks in transfusion of blood and blood components and in pregnancy of mixed race couples exist.

Kidney Transplantation: The Challenge of Human Leukocyte Antigen and Its Therapeutic Strategies

Kidney transplantation remains the treatment of choice for end-stage renal failure. When the immune system of the recipient recognizes the transplanted kidney as a foreign object, graft rejection occurs. As part of the host immune defense mechanism, human leukocyte antigen (HLA) is a major challenge for graft rejection in transplantation therapy. The impact of HLA mismatches between the donor and the potential recipient prolongs the time for renal transplantation therapy, tethered to dialysis, latter reduces graft survival, and increases mortality. The formation of pretransplant alloantibodies against HLA class I and II molecules can be sensitized through exposures to blood transfusions, prior transplants, and pregnancy. These preformed HLA antibodies are associated with rejection in kidney transplantation. On the other hand, the development of de novo antibodies may increase the risk for acute and chronic rejections. Allograft rejection results from a complex interplay involving both the innate and the adaptive immune systems. Thus, further insights into the mechanisms of tissue rejection and the risk of HLA sensitization is crucial in developing new therapies that may blunt the immune system against transplanted organs. Therefore, the purpose of this review is to highlight facts about HLA and its sensitization, various mechanisms of allograft rejection, the current immunosuppressive approaches, and the directions for future therapy.

In vitro induction of T regulatory cells by a methylated CpG DNA sequence in humans: Potential therapeutic applications in allergic and autoimmune diseases

BACKGROUND

Allergic and autoimmune diseases comprise a group of inflammatory disorders caused by aberrant immune responses in which CD25+ Forkhead box P3-positive (FOXP3+) T regulatory (Treg) cells that normally suppress inflammatory events are often poorly functioning. This has stimulated an intensive investigative effort to find ways of increasing Tregs as a method of therapy for these conditions. One such line of investigation includes the study of how ligation of Toll-like receptors (TLRs) by CpG oligonucleotides (ODN) results in an immunostimulatory cascade that leads to induction of T-helper (Th) type 1 and Treg-type immune responses.

OBJECTIVE

The present study investigated the mechanisms by which calf thymus mammalian double-stranded DNA (CT-DNA) and a synthetic methylated DNA CpG ODN sequence suppress in vitro lymphoproliferative responses to antigens, mitogens, and alloantigens when measured by [3H]-thymidine incorporation and promote FoxP3 expression in human CD4+ T cells in the presence of transforming growth factor (TGF) beta and interleukin-2 (IL-2).

METHODS

Lymphoproliferative responses of peripheral blood mononuclear cells from four healthy subjects or nine subjects with systemic lupus erythematosus to CT-DNA or phytohemagglutinin (PHA) was measured by tritiated thymidine ([3H]-TdR) incorporation expressed as a stimulation index. Mechanisms of immunosuppressive effects of CT-DNA were evaluated by measurement of the degree of inhibition to lymphoproliferative responses to streptokinase-streptodornase, phytohemagglutinin (PHA), concanavalin A (Con A), pokeweed mitogen (PWM), or alloantigens by a Con A suppressor assay. The effects of CpG methylation on induction of FoxP3 expression in human T cells were measured by comparing inhibitory responses of synthetic methylated and nonmethylated 8-mer CpG ODN sequences by using cell sorting, in vitro stimulation, and suppressor assay.

RESULTS

Here, we showed that CT-DNA and a synthetic methylated DNA 8-mer sequence could suppress antigen-, mitogen-, and alloantigen-induced lymphoproliferation in vitro when measured by [3H]-thymidine. The synthetic methylated DNA CpG ODN but not an unmethylated CpG ODN sequence was shown to promote FoxP3 expression in human CD4+ T cells in the presence of TGF beta and IL-2. The induction of FoxP3+ suppressor cells is dose dependent and offers a potential clinical therapeutic application in allergic and autoimmune and inflammatory diseases.

CONCLUSION

The use of this methylated CpG ODN offers a broad clinical application as a novel therapeutic method for Treg induction and, because of its low cost and small size, should facilitate delivery via nasal, respiratory, gastrointestinal routes, and/or by injection, routes of administration important for vaccine delivery to target sites responsible for respiratory, gastrointestinal, and systemic forms of allergic and autoimmune disease.

Indoleamine 2, 3-dioxygenase Up-regulates Hypoxia-inducible Factor-1α Expression by Degrading L-tryptophan but Not Its Activity in Human Alloreactive T-cells

Indoleamine 2, 3-dioxygenase (IDO) suppresses T-cell function at least in part by altering cell metabolism. Hypoxia-inducible factor-1 (HIF-1) increases upon T-cell activation and alters cell metabolism favoring their differentiation to effector cells. The effect of IDO on HIF-1α expression and activity was evaluated. For this purpose, mixed lymphocyte reaction (MLR) was performed using the IDO inhibitor 1-DL-methyl-tryptophan and the p53 inhibitor pifithrin-α. L-tryptophan degradation and cell proliferation were assessed by enzyme-linked immunosorbent assay, whereas the expression of proteins of interest by western blotting. IDO inhibited cell proliferation, and in MLR-derived T-cells increased HIF-1α and p53, whereas it decreased c-Myc. Inhibition of p53 abrogated IDO-induced HIF-1α upregulation. IDO increased the p53 transcriptional targets p21 and TP53-induced glycolysis and apoptosis regulator. The transcriptional targets of both HIF-1α and c-Myc, hexokinase II and lactate dehydrogenase-A were decreased by IDO. Phosphorylated pyruvate dehydrogenase remained unaffected indicating that pyruvate dehydrogenase kinase, a transcriptional target of HIF-1α, is not affected by IDO. In human alloreactive T-cells, IDO up-regulates HIF-1α, by inducing p53 overexpression. However, HIF-1α remains transcriptionally inactive.

Immunocontraceptive target repertoire defined by systematic identification of sperm membrane alloantigens in a single species

Sperm competence in animal fertilization requires the collective activities of numerous sperm-specific proteins that are typically alloimmunogenic in females. Consequently, sperm membrane alloantigens are potential targets for contraceptives that act by blocking the proteins' functions in gamete interactions. Here we used a targeted proteomics approach to identify the major alloantigens in swine sperm membranes and lipid rafts, and thereby systematically defined the repertoire of these sperm-specific proteins in a single species. Gilts with high alloantibody reactivity to proteins in sperm membranes or lipid rafts produced fewer offspring (73% decrease) than adjuvant-only or nonimmune control animals. Alloantisera recognized more than 20 potentially unique sperm membrane proteins and five sperm lipid raft proteins resolved on two-dimensional immunoblots with or without prior enrichment by anion exchange chromatography. Dominant sperm membrane alloantigens identified by mass spectrometry included the ADAMs fertilin α, fertilin ß, and cyritestin. Less abundant alloantigens included ATP synthase F1 β subunit, myo-inositol monophosphatase-1, and zymogen granule membrane glycoprotein-2. Immunodominant sperm lipid raft alloantigens included SAMP14, lymphocyte antigen 6K, and the epididymal sperm protein E12. Of the fifteen unique membrane alloantigens identified, eleven were known sperm-specific proteins with uncertain functions in fertilization, and four were not previously suspected to exist as sperm-specific isoforms. De novo sequences of tryptic peptides from sperm membrane alloantigen "M6" displayed no evident homology to known proteins, so is a newly discovered sperm-specific gene product in swine. We conclude that alloimmunizing gilts with sperm membranes or lipid rafts evokes formation of antibodies to a relatively small number of dominant alloantigens that include known and novel sperm-specific proteins with possible functions in fertilization and potential utility as targets for immunocontraception.

In-vitro blockade of the CD4 receptor co-signal in antigen-specific T-cell stimulation cultures induces the outgrowth of potent CD4 independent T-cell effectors

T-cell receptor (TCR) redirected T cells are promising tools for adoptive cancer immunotherapy. Since not only CD8 but also CD4 T cells are key players for efficient antitumor responses, the targeted redirection of both subsets with the same antigen-specific TCR comes more and more into focus. Although rapidly evolving technologies enable the reliable genetic re-programming of T cells, the limited availability of TCRs that induce T-cell activation in both T-cell subsets without CD4/CD8 co-receptor contribution hampers the broad application of this approach. We developed a novel stimulation approach, which drives the activation and proliferation of CD4 T-cell populations capable of inducing effector functions in a CD4-independent manner. Naive-enriched CD4 T cells were stimulated against dendritic cells (DC) expressing allogeneic HLA-DP antigens upon RNA transfection and CD4/HLA interactions were blocked by the addition of CD4 binding antibody. Evolving CD4 T-cell populations were specifically activated independent of the CD4 co-signal and induced strong TCR-mediated IFN-γ secretion as well as cytolysis upon recognition of leukemia cells expressing HLA-DP antigen. Our novel stimulation approach may facilitate the generation of CD4 T cells as source for co-receptor independent TCRs for future immunotherapies.

Visualization of Immune Responses in the Cornea

The eye has become a useful site for the investigation and understanding of local and systemic immune responses. The ease of access and transparency of the cornea permits direct visualization of ocular structures, blood vessels, and lymphatic vessels, allowing for the tracking of normal and pathological biological processes in real time. As a window to the immune system, we have used the eye to dissect the mechanisms of corneal inflammatory reactions that include innate and adaptive immune responses. We have identified that the ocular microenvironment regulates these immune responses by recruiting different populations of inflammatory cells to the cornea through local production of selected chemokines. Moreover, crosstalk between T cells and macrophages is a common and crucial step in the development of ocular immune responses to corneal alloantigens. This review summarizes the data generated by our group using intravital fluorescent confocal microscopy to capture the tempo, magnitude, and function of innate and adaptive corneal immune responses.

Ibrutinib suppresses alloantibody responses in a mouse model of allosensitization

BACKGROUND

Ibrutinib is a Bruton's tyrosine Kinase (BTK) antagonist that inhibits B cell receptor (BCR) signaling. Complete BTK deficiency is associated with absence of B-cells. Ibrutinb is currently approved by FDA for treatment of B-cell malignancies, including Waldenström macroglobulinaemia. We recently carried out studies to determine if ibrutinib could modify alloantibody responses.

MATERIALS AND METHODS

A mouse model of allogenic sensitization using a C57BL/6 mouse as the recipient of a skin allograft from an HLA-A2 transgenic mouse was utilized to examine the effects of ibrutinib on alloantibody responses and B cell effector functions. Donor-specific antibody (DSA) levels were measured in a flow-cytometric antibody binding assay. Splenic T and B cell subsets and plasma cells were analyzed in flow cytometry.

RESULTS

Control mice developed peak levels of DSA IgM at day 14 PTx while the ibrutinib treated mice had significantly lower levels of DSA IgM (p=0.0047). Control mice developed HLA.A2-specific IgG antibodies at day 14 (230±60 MFI) and reached peak levels at day 21 (426±61 MFI). In contrast, mice in the treatment group had low levels of HLA.A2-specific IgG at day 14 (109±59 MFI, p=0.004) and day 21 (241±86 MFI, p=0.003). FACS analysis found a reduction of B220⁺ or CD19⁺ B cell population (p<0.05). In addition, ibrutinib attenuated recall DSA IgG responses to re-sensitization (p<0.05) and reduced CD38⁺CD138⁺ plasma cells (p<0.05) in the spleens.

CONCLUSIONS

Ibrutinib is effective in suppressing alloantibody responses through blocking BTK-mediated BCR signaling, leading to reduction of B cells and short-lived plasma cells in the spleens. Use of ibrutinib may provide benefits to HLA-sensitized transplant patients for alloantibody suppression.

Pulmonary Involvement of Acute Myeloid Leukemia Mimicking Transfusion-related Acute Lung Injury

Transfusion-related acute lung injury (TRALI) is defined as a new episode of acute lung injury (ALI) occurring during transfusion or within 6 hours of transfusion completion. A 66-year-old man suffering from acute myeloid leukemia developed acute respiratory distress syndrome after platelet transfusion. TRALI was diagnosed clinically, but an autopsy showed leukemic cells in diffuse pulmonary edema. Anti-human neutrophil antigen (HNA)-3a antibodies were detected in the donor serum, and the HNA-3 genotype of the patient was identified as a/a. This case was considered to represent pulmonary involvement of acute myeloid leukemia, rather than TRALI. A revision of the definition of TRALI accounting for hematological malignancies should therefore be considered.

Induction of Immunological Tolerance to Islet Allografts

T-cell dependent activation of resting B cells involves the interaction of gp39 on T cells with its receptor, CD40, on B cells. We administered either a combination of T-cell-depleted splenic lymphocytes and anti-gp39 monoclonal antibody or antibody alone to establish islet allografts in mice without continuous immunosuppression. Fully allogeneic H-2q FVB islets were permanently accepted by chemically diabetic H-2b C57BL/6 mice provided that the recipients were pretreated with both T-cell-depleted donor spleen cells and anti-gp39 antibody. Antibody alone was less effective in prolonging allograft survival, but we did observe that anti-gp39 mAb alone can exert an independent, primary effect on islet allograft survival that was dose dependent. Targeting gp39, in combination with lymphocyte transfusion, might prove suitable for tolerance induction and allotransplantation without immunosuppression.

Differences in the Contribution of CD4+ T Cells to Proislet and Islet Allograft Rejection Correlate with Constitutive Class II MHC Alloantigen Expression

Allografts of BALB/c (H-2d) fetal proislets facilitated long-term (>100 days) reversal of streptozotocin-induced diabetes in CBA/H (H-2k) mice treated with a combination of anti-CD4 and anti-CD8 mAbs. Anti-CD8 monotherapy was partially effective in restoring normoglycemia but anti-CD4 mAb treatment of host animals failed to promote allograft function. In contrast, allografts of BALB/c adult islets demonstrated indefinite reversal of diabetes in recipient mice treated only with anti-CD8 mAb. Anti-CD4 monotherapy resulted in only transient restoration of normoglycemia. These findings clearly demonstrate (1) a critical role for CD8 T cells in the acute rejection of pancreatic islet tissue allografts and (2) tissue-specific differences in the participation of CD4 T cells as primary effectors in the rejection reaction. Immunohistochemical studies showed that the capacity for CD4 T cells to initiate the rejection of proislet but not adult islet allografts correlates with the presence/absence, respectively, of graft parenchymal cells that constitutively express Class II MHC alloantigens. Proislet grafts, unlike transplants of purified adult islets, contain heterogeneous tissue components including Class II MHC+ve duct epithelium. Thus, the participation of CD8 and CD4 T cells as primary effectors of graft rejection depends on which class or classes of MHC antigens are constitutively expressed on graft parenchymal cells and are available for recognition. Islet tissue in both rejecting proislet and islet allografts showed de novo induction of Class II MHC alloantigens only after severe disruption to islet architecture had been achieved by infiltrating mononuclear cells. Thus, at this stage of advanced allograft injury, CD4 T cells have the potential to act as secondary effectors, possibly by amplifying the inflammatory reaction and thus accelerating graft destruction. The capacity for antirejection mAb therapy to establish transplant tolerance was facilitated in the islet allograft model where it was necessary to target only the CD8 T cell subpopulation.

Cytokines affecting CD4+T regulatory cells in transplant tolerance. II. Interferon gamma (IFN-γ) promotes survival of alloantigen-specific CD4+T regulatory cells

CD4+T cells that transfer alloantigen-specific transplant tolerance are short lived in culture unless stimulated with specific-donor alloantigen and lymphocyte derived cytokines. Here, we examined if IFN-γ maintained survival of tolerance transferring CD4+T cells. Alloantigen-specific transplant tolerance was induced in DA rats with heterotopic adult PVG heart allografts by a short course of immunosuppression and these grafts functioned for >100days with no further immunosuppression. In previous studies, we found the CD4+T cells from tolerant rats that transfer tolerance to an irradiated DA host grafted with a PVG heart, lose their tolerance transferring ability after 3days of culture, either with or without donor alloantigen, and effect rejection of specific-donor grafts. If cultures with specific-donor alloantigen are supplemented by supernatant from ConA activated lymphocytes the tolerance transferring cells survive, suggesting these cells depend on cytokines for their survival. In this study, we found addition of rIFN-γ to MLC with specific-donor alloantigen maintained the capacity of tolerant CD4+T cells to transfer alloantigen-specific tolerance and their ability to suppress PVG allograft rejection mediated by co-administered naïve CD4+T cells. IFN-γ suppressed the in vitro proliferation of tolerant CD4+T cells. Tolerant CD4+CD25+T cells did not proliferate in MLC to PVG stimulator cells with no cytokine added, but did when IFN-γ was present. IFN-γ did not alter proliferation of tolerant CD4+CD25+T cells to third-party Lewis. Tolerant CD4+CD25+T cells' expression of IFN-γ receptor (IFNGR) was maintained in culture when IFN-γ was present. This study suggested that IFN-γ maintained tolerance mediating alloantigen-specific CD4+CD25+T cells.

Divergent Function of Programmed Death-Ligand 1 in Donor Tissue versus Recipient Immune System in a Murine Model of Bronchiolitis Obliterans

Costimulatory molecules, such as the programmed death ligand (PD-L1), might exert differential effects on T-cell function, depending on the clinical setting and/or immunological environment. Given the impact of T cells on bronchiolitis obliterans (BO) in lung transplantation, we used an established tracheal transplant model inducing BO-like lesions to investigate the impact of PD-L1 on alloimmune responses and histopathological outcome in BO. In contrast to other transplant models in which PD-L1 generally shows protective functions, we demonstrated that PD-L1 has divergent effects depending on its location in donor versus recipient tissue. Although PD-L1 deficiency in donor tissue worsened histopathological outcome, and increased systemic inflammatory response, recipient PD-L1 deficiency induced opposite effects. Mechanistic studies revealed PD-L1-deficient recipients were hyporesponsive toward alloantigen, despite increased numbers of CD8+ effector T cells. The function of PD-L1 on T cells after unspecific stimulation was dependent on both cell type and strength of stimulation. This novel function of recipient PD-L1 may result from the high degree of T-cell activation within the highly immunogenic milieu of the transplanted tissue. In this model, both decreased T-cell alloimmune responses and the reduction of BO in PD-L1-deficient recipients suggest a potential therapeutic role of selectively blocking PD-L1 in the recipient. Further investigation is warranted to determine the impact of this finding embedded in the complex pathophysiological context of BO.