Identification of a mouse male-specific transplantation antigen, H-Y

Sex Matters-Insights from Testing Drug Efficacy in an Animal Model of Pancreatic Cancer

Preclinical studies rarely test the efficacy of therapies in both sexes. The field of oncology is no exception in this regard. In a model of syngeneic, orthotopic, metastasized pancreatic ductal adenocarcinoma we evaluated the impact of sex on pathological features of this disease as well as on the efficacy and possible adverse side effects of a novel, small molecule-based therapy inhibiting KRAS:SOS1, MEK1/2 and PI3K signaling in male and female C57BL/6J mice. Male mice had less tumor infiltration of CD8-positive cells, developed bigger tumors, had more lung metastasis and a lower probability of survival compared to female mice. These more severe pathological features in male animals were accompanied by higher distress at the end of the experiment. The evaluated inhibitors BI-3406, trametinib and BKM120 showed synergistic effects in vitro. This combinatorial therapy reduced tumor weight more efficiently in male animals, although the drug concentrations were similar in the tumors of both sexes. These results underline the importance of sex-specific preclinical research and at the same time provide a solid basis for future studies with the tested compounds.

The catalytic inhibitor epacadostat can affect the non-enzymatic function of IDO1

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan metabolizing enzyme chronically activated in many cancer patients and its expression and activity correlate with a poor prognosis. In fact, it acts as an immune regulator and contributes to tumor-induced immunosuppression by determining tryptophan deprivation and producing immunosuppressive metabolites named kynurenines. These findings made IDO1 an attractive target for cancer immunotherapy and small-molecule inhibitors, such as epacadostat, have been developed to block its enzymatic activity. Although epacadostat was effective in preclinical models and in early phase trials, it gave negative results in a metastatic melanoma randomized phase III study to test the benefit of adding epacadostat to the reference pembrolizumab therapy. However, the reason for the epacadostat failure in this clinical trial has never been understood. Our data suggest that a possible explanation of epacadostat ineffectiveness may rely on the ability of this drug to enhance the other IDO1 immunoregulatory mechanism, involving intracellular signaling function. These findings open up a new perspective for IDO1 inhibitors developed as new anticancer drugs, which should be carefully evaluated for their ability to block not only the catalytic but also the signaling activity of IDO1.

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.

Alternative Sexual Orientation in Humans: What Is Known and What Needs to Be Known Further

Since the 20th century, multiple studies have linked the variations in human sexual orientation, from heterosexuality to bisexuality or homosexuality, to a wide range of biological factors. However, a clear mechanism that leads to the development of these variations has not been established yet. This review consolidates various comprehensive studies on the possible biological factors in the fields of genetics, epigenetics, uterine environment, hormones, neuroanatomy, and neurobiology that lead to these variations. One intriguing question that 'homosexuality phenotype' faces is its ability to avoid elimination by Darwinian selection. This review tries to explain why natural selection is not eliminating the genetic factors associated with homosexuality even at the cost of the evolutionary fitness of homosexual individuals. Studies supporting certain strong candidates for alternative sexual orientation (ASO) are highlighted, which can become new research avenues for investigators in this field. Further, a novel speculation is proposed that might be contributing to the development of variation in human sexuality.

Gender medicine in corneal transplantation: influence of sex mismatch on rejection episodes and graft survival in a prospective cohort of patients

To evaluate the effect of donor-to-recipient sex mismatched (male donor corneas to female recipients) on the incidence of rejection episodes and failures up to 1 year after corneal transplantation. Prospective observational cohort study, with donor corneas randomly assigned and surgeons blind to the sex of donor. A unique eye bank retrieved and selected the donor corneas transplanted in 4 ophthalmic units in patients with clinical indication for primary or repeated keratoplasty for optical reasons, perforating or lamellar, either anterior or posterior. Rejection episode defined as any reversible or irreversible endothelial, epithelial or stromal sign, with or without development of corneal edema, and graft failure as a permanently cloudy graft or a regraft for any reason detected or acknowledged during a postoperative ophthalmic visit at any time up to 1 year after surgery were recorded.156 (28.6%) patients resulted donor-to-recipient gender mismatched for H-Y antigen (male donor to female recipient). During the 12 months follow-up, 83 (14.7%, 95% CI 12.0-17.9) grafts showed at least 1 rejection episode and 17 (3.2%, 95% CI 2.0-5.0) failed after immune rejection, among 54 (9.6%, 95% CI 7.4-12.3) grafts failed for all causes. No significant differences between matched and mismatched patients were found for cumulative incidence of both rejection episodes (15.2% and 13.5%) and graft failures following rejection (3.2% and 2.6%), respectively. Multivariable analyses showed that H-Y matching either is not a predictive factor for rejection or graft failure nor seems to influence incidence of failures on respect to patient's risk category. The lack of influence of donor-to-recipient mismatched on the rate of rejections and graft failures resulting from this study do not support the adoption of donor-recipient matching in the allocation of corneas for transplantation.

The Impact of Sex on Alloimmunity

Transplantation outcomes are known to be affected by multiple factors, including donor and recipient sex. Aside from the physiological characteristics of male and female donor allografts, accumulating evidence suggests that additional features underlie sex-specific immune responses that affect graft survival. We discuss here aspects of innate and adaptive alloimmunity that are specific to males and females in the context of underlying genetic and hormonal factors. These differences likely contribute to the observed disparities in graft survival. Understanding these features in more detail may lead to improved strategies for optimizing the results of organ transplantation.

Alloantigen expression on malignant cells and healthy host tissue influences graft-versus-tumor reactions after allogeneic hematopoietic stem cell transplantation

Durable remissions of hematological malignancies regularly observed following allogeneic hematopoietic stem cell transplantation (aHSCT) are due to the conditioning regimen, as well as an immunological phenomenon called graft-versus-leukemia (GVL) or graft-versus-tumor (GVT) effect. The development of GVL is closely linked to graft-versus-host disease (GVHD), the main side effect associated with aHSCT. Both, GVHD and GVL are mediated by donor T cells that are initially activated by antigen-presenting cells that present recipient-derived alloantigens in the context of either matched or mismatched MHC class I molecules. Using murine models of aHSCT we show that ubiquitously expressed minor histocompatibility alloantigens (mHAg) are no relevant target for GVT effects. Interestingly, certain ubiquitously expressed MHC alloantigens augmented GVT effects early after transplantation, while others did not. The magnitude of GVT effects correlated with tumor infiltration by CD8+ cytotoxic T cells and tumor cell apoptosis. Furthermore, the immune response underlying GVHD and GVT was oligoclonal, highlighting that immunodominance is an important factor during alloimmune responses. These results emphasize that alloantigen expression on non-hematopoietic tissues can influence GVT effects in a previously unrecognized fashion. These findings bear significance for harnessing optimal GVL effects in patients receiving aHSCT.

Involvement of Male-Specific Minor Histocompatibility Antigen H-Y in Epidermal Equivalent Allograft Rejection

This study describes the involvement of male-specific minor histocompatibility antigen H-Y in vitro cultured epidermal equivalent (EE) rejection. Male and female Balb/c or C3H/HeN keratinocytes were isolated and cultured separately. Male EE were grafted onto adult male (isografts) and adult female (H-Y allografts) mice. As controls, Balb/c EE were grafted onto adult C3H/HeN (complete allografts) mice. Fourteen, 21, and 30 days postgrafting, histological studies showed well-organized cutaneous tissues with complete basement membranes (laminin and type IV collagen deposition) in H-Y allografts compared to the isografts. This cutaneous organization was altered 150 days postgrafting, which is a sign of the H-Y EE allograft rejection. Complete allografts were totally rejected 21 days postgrafting. Immunological studies revealed leucocyte infiltration of H-Y allografts. Significant infiltration was detected even 150 days postgrafting. Leucocyte phenotyping revealed the presence of Mac-1+, CD8+ and CD4+ cells in the H-Y allografts. Humoral immune analysis revealed the presence of circulating anti-H-Y allogeneic keratinocyte cytotoxic antibodies in female recipient sera. Our data suggest that male-specific minor histocompatibility antigen H-Y induces cellular and humoral activation of the recipient immune system even after grafting EE free of cutaneous active immune cells such as T lymphocytes and Langerhans cells.

The Influence of Donor and Recipient Gender Incompatibility on Corneal Transplant Rejection and Failure

In vascularized organ transplants, gender mismatches have higher rates of immunological rejection. We investigated the influence of gender incompatibility, including H-Y incompatibility, on corneal transplant graft rejection and failure. Patients were included who had undergone a first corneal transplant for keratoconus (KC), Fuchs endothelial dystrophy (FED), pseudophakic bullous keratopathy (PBK), infection and other indications. A Cox regression model was fitted for each indication to determine factors affecting graft failure and rejection at 5 years. The impact of gender, including H-Y, matching was analyzed after accounting for other factors, including known risk factors. Of 18 171 patients, 4314 had undergone a transplant for FED, 4783 for KC, 3669 for PBK, 1903 for infection and 3502 for other disorders. H-Y mismatched (male [M]→female [F]) corneas were at greater risk of graft failure or rejection. For FED, F→F were 40% less likely to fail (p < 0.0001) and 30% less likely to reject (p = 0.01); M→M were 20% less likely to fail (p = 0.04) and 30% less likely to reject (p = 0.01). For KC, M→M matched corneas were 30% less likely to fail (p = 0.05) and 20% less likely to reject (p = 0.01) compared with H-Y mismatches. H-Y antigen mismatched (M→F) patients were at greater risk of rejection or graft failure.

Protective and Destructive Immunity in the Periodontium: Part 2—T-cell-mediated Immunity in the Periodontium

Based on the results of recent research in the field and Part 1 of this article (in this issue), the present paper will discuss the protective and destructive aspects of the T-cell-mediated adaptive immunity associated with the bacterial virulent factors or antigenic determinants during periodontal pathogenesis. Attention will be focused on: (i) osteoimmunology and periodontal disease; (ii) some molecular techniques developed and applied to identify critical microbial virulence factors or antigens associated with host immunity (with Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis as the model species); and (iii) summarizing the identified virulence factors/antigens associated with periodontal immunity. Thus, further understanding of the molecular mechanisms of the host’s T-cell-mediated immune responses and the critical microbial antigens related to disease pathogenesis will facilitate the development of novel therapeutics or protocols for future periodontal treatments. Abbreviations used in the paper are as follows: A. actinomycetemcomitans ( Aa), Actinobacillus actinomycetemcomitans; Ab, antibody; DC, dendritic cells; mAb, monoclonal antibody; pAb, polyclonal antibody; OC, osteoclast; PAMP, pathogen-associated molecular patterns; P. gingivalis ( Pg), Porphyromonas gingivalis; RANK, receptor activator of NF-κB; RANKL, receptor activator of NF-κB ligand; OPG, osteoprotegerin; TCR, T-cell-receptors; TLR, Toll-like receptors.

Medawar's legacy to cellular immunology and clinical transplantation: a commentary on Billingham, Brent and Medawar (1956) 'Quantitative studies on tissue transplantation immunity. III. Actively acquired tolerance'

‘Quantitative studies on tissue transplantation immunity. III. Actively acquired tolerance’, published in Philosophical Transactions B in 1956 by Peter Medawar and his colleagues, PhD graduate Leslie Brent and postdoctoral fellow Rupert Billingham, is a full description of the concept of acquired transplantation tolerance. Their 1953 Nature paper (Billingham RE et al. 1953 Nature172, 603–606. (doi:10.1038/172603a0)) had provided initial evidence with experimental results from a small number of neonatal mice, with mention of similar findings in chicks. The Philosophical Transactions B 1956 paper is clothed with an astonishing amount of further experimental detail. It is written in Peter Medawar's landmark style: witty, perceptive and full of images that can be recalled even when details of the supporting information have faded. Those images are provided not just by a series of 20 colour plates showing skin graft recipient mice, rats, rabbits, chickens and duck, bearing fur or plumage of donor origin, but by his choice of metaphor, simile and analogy to express the questions being addressed and the interpretation of their results, along with those of relevant published data and his prescient ideas of what the results might portend. This work influenced both immunology researchers and clinicians and helped to lay the foundations for successful transplantation programmes. It led to the award of a Nobel prize in 1960 to Medawar, and subsequently to several scientists who advanced these areas. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

The bm12 Inducible Model of Systemic Lupus Erythematosus (SLE) in C57BL/6 Mice

Systemic lupus erythematosus (SLE) is an autoimmune disease with diverse clinical and immunological manifestations. Several spontaneous and inducible animal models mirror common components of human disease, including the bm12 transfer model. Upon transfer of bm12 splenocytes or purified CD4 T cells, C57BL/6 mice rapidly develop large frequencies of T follicular helper cells (Tfh), germinal center (GC) B cells, and plasma cells followed by high levels of circulating anti-nuclear antibodies. Since this model utilizes mice on a pure C57BL/6 background, researchers can quickly and easily study disease progression in transgenic or knockout mouse strains in a relatively short period of time. Here we describe protocols for the induction of the model and the quantitation Tfh, GC B cells, and plasma cells by multi-color flow cytometry. Importantly, these protocols can also be used to characterize disease in most mouse models of SLE and identify Tfh, GC B cells, and plasma cells in other disease models.

Physical and functional interactions between the histone H3K4 demethylase KDM5A and the nucleosome remodeling and deacetylase (NuRD) complex

Histone H3K4 methylation has been linked to transcriptional activation. KDM5A (also known as RBP2 or JARID1A), a member of the KDM5 protein family, is an H3K4 demethylase, previously implicated in the regulation of transcription and differentiation. Here, we show that KDM5A is physically and functionally associated with two histone deacetylase complexes. Immunoaffinity purification of KDM5A confirmed a previously described association with the SIN3B-containing histone deacetylase complex and revealed an association with the nucleosome remodeling and deacetylase (NuRD) complex. Sucrose density gradient and sequential immunoprecipitation analyses further confirmed the stable association of KDM5A with these two histone deacetylase complexes. KDM5A depletion led to changes in the expression of hundreds of genes, two-thirds of which were also controlled by CHD4, the NuRD catalytic subunit. Gene ontology analysis confirmed that the genes commonly regulated by both KDM5A and CHD4 were categorized as developmentally regulated genes. ChIP analyses suggested that CHD4 modulates H3K4 methylation levels at the promoter and coding regions of target genes. We further demonstrated that the Caenorhabditis elegans homologues of KDM5 and CHD4 function in the same pathway during vulva development. These results suggest that KDM5A and the NuRD complex cooperatively function to control developmentally regulated genes.

To drive or be driven: the path of a mouse model of recurrent pregnancy loss

This review is an example of the use of an animal model to try to understand the immune biology of pregnancy. A well-known model of recurrent spontaneous pregnancy loss is put in clinical, historical, and theoretical context, with emphasis on T cell biology.

Local immunostimulation leading to rejection of accepted male skin grafts by female mice as a model for cancer immunotherapy

Female mice of inbred strain CBA do not reject syngeneic male skin grafts even though they mount a T-cell response against the male-specific HY antigen. We show that local immunostimulation performed by injecting cytokines and Toll-like receptor ligands in close vicinity to the graft causes rejection. We feel that this approach should be tested in tumor-bearing human patients in combination with antitumor vaccination. Relief of intratumor immunosuppression may increase considerably the fraction of patients who respond to vaccination directed against tumor antigens recognized by T cells.

The roles of Jumonji-type oxygenases in human disease

The iron- and 2-oxoglutarate-dependent oxygenases constitute a phylogenetically conserved class of enzymes that catalyze hydroxylation reactions in humans by acting on various types of substrates, including metabolic intermediates, amino acid residues in different proteins and various types of nucleic acids. The discovery of jumonji (Jmj), the founding member of a class of Jmj-type chromatin modifying enzymes and transcriptional regulators, has culminated in the discovery of several branches of histone lysine demethylases, with essential functions in regulating the epigenetic landscape of the chromatin environment. This work has now been considerably expanded into other aspects of epigenetic biology and includes the discovery of enzymatic steps required for methyl-cytosine demethylation as well as modification of RNA and ribosomal proteins. This overview aims to summarize the current knowledge on the human Jmj-type enzymes and their involvement in human pathological processes, including development, cancer, inflammation and metabolic diseases.

Distinct in vivo CD8 and CD4 T cell responses against normal and malignant tissues

Normal tissue and tumour grafts expressing the same alloantigens often elicit distinct immune responses whereby only normal tissue is rejected. To investigate the mechanisms that underlie these distinct outcomes, we compared the responses of adoptively transferred HY-specific conventional (CD8 and CD4) or regulatory T (Treg) cells in mice bearing HY-expressing tumour, syngeneic male skin graft or both. For local T cell priming, T cell re-circulation, graft localization and retention, skin grafts were more efficient than tumours. Skin grafts were also capable of differentiating CD4 T cells into functional Th1 cells. Donor T cell responses were inversely correlated with tumour progression. When skin graft and tumour transplants were performed sequentially, contemporary graft and tumour burden enhanced CD8 but reduced CD4 T cell responses causing accelerated skin-graft rejection without influencing tumour growth. Although both skin grafts and tumours were able to expand HY-specific Treg cells in draining lymph node (dLN), the proportion of tumour-infiltrating Treg cells was significantly higher than that within skin grafts, correlating with accelerated tumour growth. Moreover, there was a higher level of HY antigen presentation by host APC in tumour-dLN than in graft-dLN. Finally, tumour tissues expressed a significant higher level of IDO, TGFβ, IL10 and Arginase I than skin grafts, indicating that malignant but not normal tissue represents a stronger immunosuppressive environment. These comparisons provide important insight into the in vivo mechanisms that conspire to compromise tumour-specific adaptive immunity and identify new targets for cancer immunotherapy.

The T-cell receptor is not hardwired to engage MHC ligands

The bias of αβ T cells for MHC ligands has been proposed to be intrinsic to the T-cell receptor (TCR). Equally, the CD4 and CD8 coreceptors contribute to ligand restriction by colocalizing Lck with the TCR when MHC ligands are engaged. To determine the importance of intrinsic ligand bias, the germ-line TCR complementarity determining regions were extensively diversified in vivo. We show that engagement with MHC ligands during thymocyte selection and peripheral T-cell activation imposes remarkably little constraint over TCR structure. Such versatility is more consistent with an opportunist, rather than a predetermined, mode of interface formation. This hypothesis was experimentally confirmed by expressing a hybrid TCR containing TCR-γ chain germ-line complementarity determining regions, which engaged efficiently with MHC ligands.

Role of H3K4 demethylases in complex neurodevelopmental diseases

Significant neurological disorders can result from subtle perturbations of gene regulation that are often linked to epigenetic regulation. Proteins that regulate the methylation of lysine 4 of histone H3 (H3K4) and play a central role in epigenetic regulation, and mutations in genes encoding these enzymes have been identified in both autism and Rett syndrome. The H3K4 demethylases remove methyl groups from lysine 4 leading to loss of RNA polymerase binding and transcriptional repression. When these proteins are mutated, brain development is altered. Currently, little is known regarding how these gene regulators function at the genomic level. In this article, we will discuss findings that link H3K4 demethylases to neurodevelopment and neurological disease.

Transient modification within a pool of CD4 T cells in the maternal spleen

Classic models suggest maternal tolerance is dependent on regulation of fetal antigen-specific T cell responses. We hypothesize that factors unique to a particular fetal antigen-specific T cell, rather than the state of pregnancy per se, are important determinants of T cell fate during pregnancy. To investigate the fate of fetal antigen-specific CD4 T cells in the systemic circulation, we examined spleen cells in a CD4 T cell receptor transgenic mouse specific for the male antigen H-Y. We observed a transient decrease in CD4(+) Vβ6(+) cell numbers and, due to transient internalization of CD4, an increase in CD4(-) Vβ6(+) T cells. Antigen-specific in vitro responsiveness was not depressed by pregnancy. These data suggest that pregnancy supports fluidity in this particular CD4 T cell pool that may, in turn, help to meet competing requirements of maternal immune responsiveness and fetal tolerance.

Minor histocompatibility antigens: presentation principles, recognition logic and the potential for a healing hand

PURPOSE OF REVIEW

There is ample evidence indicating a pathologic role for minor histocompatibility antigens in inciting graft-versus-host disease in major histocompatibility complex (MHC)-matched bone marrow transplantation and rejection of solid organ allografts. Here we review the current knowledge of the genetic and biochemical bases for the cause of minor histoincompatibility and the structural basis for the recognition of the resulting alloantigens by the T-cell receptor.

RECENT FINDINGS

Recent evidence indicates that we as independently conceived individuals are genetically unique, thus, offering a mechanism for minor histoincompatibility between MHC-identical donor-recipient pairs. Furthermore, advances in delineating the mechanisms underlying antigen cross-presentation by MHC class I molecules and a critical role for autophagy in presenting cytoplasmic antigens by MHC class II molecules have been made. These new insights coupled with the X-ray crystallographic solution of several peptide/MHC-T-cell receptor structures have revealed mechanisms of histoincompatibility.

SUMMARY

On the basis of these new insights, ways to test for allograft compatibility and concoction of immunotherapies are discussed.

Concomitant tumor and minor histocompatibility antigen-specific immunity initiate rejection and maintain remission from established spontaneous solid tumors

Nonmyeloablative hematopoietic cell transplantation can cure patients with hematologic malignancies but has reported limited success against solid tumors. This is possibly because of profound peripheral tolerance mechanisms and/or suboptimal tumor recognition by effector T lymphocytes. We report that in mice developing spontaneous prostate cancer, nonmyeloablative minor histocompatibility mismatched hematopoietic stem cell transplantation, and donor lymphocyte infusion of unmanipulated lymphocytes combined with posttransplant tumor-specific vaccination circumvents tumor-specific tolerance, allowing acute tumor rejection and the establishment of protective immunosurveillance. Although donor-derived tumor-specific T cells readily differentiated into effector cells and infiltrated the tumor soon after infusion, they were alone insufficient for tumor eradication, which instead required the concomitance of minor histocompatibiltiy antigen-specific CD8(+) T-cell responses. The establishment of protective immunosurveillance was best induced by posttransplant tumor-specific vaccination. Hence, these results provide the proof of principle that tumor-specific T-cell responses have to be harnessed together with minor histocompatibility responses and sustained by posttransplant tumor-specific vaccination to improve the efficacy of allotransplantion for the cure of solid tumors.

Peptide-specific, TCR-alpha-driven, coreceptor-independent negative selection in TCR alpha-chain transgenic mice

As thymocytes differentiate, Ag sensitivity declines, with immature CD4-CD8- double-negative (DN) cells being most susceptible to TCR signaling events. We show that expression of alphabetaTCR from the DN3 stage lowers the threshold for activation, allowing recognition of MHC peptides independently of the TCR beta-chain and without either T cell coreceptor. The MHC class I-restricted C6 TCR recognizes the Y-chromosome-derived Ag HYK(k)Smcy. Positive selection in C6 alphabetaTCR females is skewed to the CD8 compartment, whereas transgenic male mice exhibit early clonal deletion of thymocytes. We investigated the effect of the HYK(k)Smcy complex on developing thymocytes expressing the C6 TCR alpha-chain on a TCR-alpha(-/-) background. On the original selecting haplotype, the skew to the CD8 lineage is preserved. This is MHC dependent, as the normal bias to the CD4 subset is seen on an H2b background. In male H2k C6 alpha-only mice, the presence of the HYK(k)Smcy complex leads to a substantial deletion of thymocytes from the DN subset. This phenotype is replicated in H2k C6 alpha-only female mice expressing an Smcy transgene. Deletion is not dependent on the beta variable segment of the C6 TCR or on a restricted TCR-beta repertoire. In contrast, binding of HYK(k)Smcy and Ag-specific activation of mature CD8+ T cells is strictly dependent on the original C6 beta-chain. These data demonstrate that, in comparison with mature T cells, alphabetaTCR+ immature thymocytes can recognize and transduce signals in response to specific MHC-peptide complexes with relaxed binding requirements.

Assessment of graft function in rodent models of heart transplantation

Heterotopic heart transplantation in rats and mice is the most commonly used model to study allograft immune response and to test immunosuppressive drugs and tolerance induction protocols. Standardization of both the surgical procedure and the evaluation of graft function is essential for data interpretation. The most popular way to monitor graft function has been the palpation method. However, there are some proposal for more objective assessment methods like electrocardiogram and echocardiogram. Although, complementary tests might add some relevant information when assessing minor effects of immunosuppressive therapy, palpation by an experienced investigator is very predictive and so far the simplest method to determine heart allograft function. Minor complications during the surgical procedure and unreliable assessment can have a major impact on the interpretation of experiment results. Here, the author reviews the literature and presents some suggestions that help eliminating biases on the assessment of heart allograft function.

Dendritic cells: a family portrait at mid-gestation

Recent advances in our understanding of dendritic cells (DCs) and their role in tolerance and immunity has fuelled study of their normal development and function within the reproductive tract. The common hypothesis that pregnancy is a state of immune suppression or deviation now includes the idea that alterations in DC phenotype and function are critical for maternal tolerance. We chose to study DCs in the uterus and lymphoid tissue in non-pregnant and pregnant mice at mid-gestation to understand what DC-related factors may be involved in premature birth. We used a mouse model where the mother's immune system has been shown to respond to the male antigen H-Y. Observed differences among DCs in the uterus, uterine draining nodes and spleen, even in non-pregnant mice, suggest the existence of a specialized uterus-specific subset of DCs. We further found that, amongst CD45(+) CD11c(+) cells in the uterus and peripheral lymphoid tissue of pregnant mice, expression of major histocompatibility complex class II (MHC II) and costimulatory molecules (i.e. CD80) was similar to that in the non-pregnant state. Moreover, there was no pregnancy-related decrease in the proportion of CD11c(+) cells in the uterus or in the uterine node that were CD11b(-) CD8(+). Pregnancy increased the CD11b(+) subsets and the expression of chemokine (C-C motif) ligand 6 (CCL6) in DCs of the uterine draining nodes. Finally, DC subsets showed variable expression, with respect to tissue and pregnancy, of the cytokine interleukin-15, which is important in lymphoid cell homeostasis. For DCs, pregnancy is not a state of immune paralysis, but of dynamic developmental change.

Sexually dimorphic gene expression in mammalian somatic tissue

BACKGROUND

The sexually dimorphic differentiation of the bipotential gonad into testis or ovary initiates the sexually dimorphic development of mammals and leads to divergent hormone concentrations between the sexes throughout life. However, despite the fact that anatomic and hormonal differences between the sexes are well described, only a few studies have investigated the manifestation of these differences at the transcriptional level in mammalian somatic tissue.

OBJECTIVE

This review focuses on basic regulatory mechanisms of sex-specific gene expression and examines recent gene expression profiling studies to outline basic differences between the sexes at the transcriptome level in somatic tissues.

METHODS

To identify gene expression profiling studies addressing sexually dimorphic gene expression, the PubMed database was searched using the terms sex and dimorp and gene expression not drosophila not elegans. Abstracts of all identified publications were screened for studies explicitly using microarrays to identify sex differences in somatic tissues of rodents or humans. The search was restricted to English-language articles published in the past 5 years. Reference lists of identified articles as well as microarray databases (Gene Expression Omnibus and ArrayExpress) were also used.

RESULTS

The application of microarray technology has enabled the systematic assessment of sex-biased gene expression on the transcriptome level, indicating that the regulatory pathways underlying sexual differentiation give rise to extensive differences in somatic gene expression across organisms.

CONCLUSION

Sustainable annotation of sex-biased gene expression provides a key to understanding basic physiological differences between healthy males and females as well as those with diseases.

DDX3Y encodes a class I MHC-restricted H-Y antigen that is expressed in leukemic stem cells

The Y chromosome encodes male-specific minor histocompatibility (H-Y) antigens that stimulate T- and B-lymphocyte responses after sex-mismatched allogeneic hematopoietic cell transplantation (HCT). A CD8(+) cytotoxic T lymphocyte (CTL) clone that recognizes a novel HLA-B*2705-restricted H-Y antigen encoded by the DDX3Y gene was isolated from a male who had received a hematopoietic cell graft from his human leukocyte antigen (HLA)-identical sister. The antigenic peptide is a decamer that differs from the homologous DDX3X-encoded peptide at 4 positions. Expression of DDX3Y and of the H-Y epitope that it encodes was examined by quantitative polymerase chain reaction (PCR) and by CTL recognition assays. Expression of DDX3Y is detected in all myeloid and lymphoid leukemic cells that carry an intact Y chromosome. Moreover, the DDX3Y-encoded H-Y epitope is presented on the surface of both myeloid and lymphoid leukemic cells from male HLA-B*2705(+) patients. DDX3Y-specific CTLs prevent engraftment of human acute leukemia in nonobese diabetic/severe combined immune deficient mice, demonstrating that the DDX3Y-encoded H-Y antigen is also expressed in leukemic stem cells. These results demonstrate that CD8(+) T-cell responses against DDX3Y have the potential to contribute to graft-versus-leukemia (GVL) activity after female into male allogeneic HCT. This study is registered at http://clinicaltrials.gov as NCT00107354.

Sensitization to enhanced green fluorescence protein minor histocompatibility antigen by gene transduction into dendritic cells and peritoneal exudate macrophages

Enhanced green fluorescence protein (EGFP) has been widely applied to gene transduction in cellular and molecular biology as a reporter element. When applied to cell transplantation, it raises fundamental issues concerning cell-associated antigens, in particular, a model of minor histocompatibility antigen(s). Although it is well known that immunological behavior of minor histocompatibility antigens mimic tumor associated antigens (TAA), identified genes coding minor histocompatibility antigens are few and far between. Inasmuch as immunity and tolerance to TAA are provided by immunological behavior of minor histocompatibility antigen such as histocompatibility antigen of the Y chromosome, H-Y, it occurs to us that transgenic as well as transduced EGFP provides a useful model system to be applied to tumor immunology. In this respect, genetic modification of specialized antigen-presenting cells (APC), i.e., dendritic cells (DC), such as gene transduction of EGFP into DC, would provide one of the most important strategies in transplantation as well as tumor immunology inasmuch as DC play a key role in initiating primary immune responses, As far as gene transduction into DC is concerned, others have reported that successful gene transduction occurs in DC by adenoviral vector systems. However, our previous studies concerning EGFP transduction into DC suggested that this view should be carefully examined and interpreted. Employing adenoviral and lentiviral vector systems as well as specialized APC of rat DC and peritoneal exudate macrophages (PEM), EGFP-transduced APC were examined to determine whether and to what extent the EGFP-transduced APC were able to sensitize non-transgenic littermates against transgenic EGFP as antigen(s). Thus EGFP-transgenic cardiac isografts were transplanted to non-transgenic littermates and examined to determine if sensitization of non-transgenic littermate recipients with the EGFP-transduced APC was able to reject the test grafts in an accelerated manner. In this study, we examined this and provide further evidence that widely used viral vector systems are unable to transfer the reporter gene EGFP into mature rat DC generated from bone marrow cells (BMC), driven by Flt3/Flk2 ligand and IL-6. Nevertheless, successful gene transduction was obtained by either applying a lentiviral vector system to the developing DC progenitor cells during a long-term culture of rat BMC or by applying an adenoviral vector system to PEM. Thus, successful gene transduction into specialized APC was verified by in vivo priming of non-transgenic littermates with the EGFP-transduced APC, followed by accelerated rejection of EGFP-transgenic cardiac isografts.

Sexually dimorphic gene expression in the heart of mice and men

The prevalence and clinical manifestation of several cardiovascular diseases vary considerably with sex and age. Thus, a better understanding of the molecular basis of these differences may represent a starting point for an improved gender-specific medicine. Despite the fact that sex-specific differences have been observed in the cardiovascular system of humans and animal models, systematic analyses of sexual dimorphisms at the transcriptional level in the healthy heart are missing. Therefore we performed gene expression profiling on mouse and human cardiac samples of both sexes and young as well as aged individuals and verified our results for a subset of genes using real-time polymerase chain reaction in independent left ventricular samples. To tackle the question whether sex differences are evolutionarily conserved, we also compared sexually dimorphic genes between both species. We found that genes located on sex chromosomes were the most abundant ones among the sexually dimorphic genes. Male-specific expression of Y-linked genes was observed in mouse hearts as well as in the human myocardium (e.g. Ddx3y, Eif2s3y and Jarid1d). Higher expression levels of X-linked genes were detected in female mice for Xist, Timp1 and Car5b and XIST, EIF2S3X and GPM6B in women. Furthermore, genes on autosomal chromosomes encoding cytochromes of the monoxygenase family (e.g. Cyp2b10), carbonic anhydrases (e.g. Car2 and Car3) and natriuretic peptides (e.g. Nppb) were identified with sex- and/or age-specific expression levels. This study underlines the relevance of sex and age as modifiers of cardiac gene expression.

Graft-versus-host disease

Allogeneic haematopoietic stem-cell transplantation (SCT) is a curative therapy for haematological malignancies and inherited disorders of blood cells, such as sickle-cell anaemia. Mature alphabeta T cells that are contained in the allografts reconstitute T-cell immunity and can eradicate malignant cells in the recipient. Unfortunately, these T cells recognize the recipient as 'non-self' and employ a wide range of immune mechanisms to attack recipient tissues in a process known as graft-versus-host disease (GVHD). The full therapeutic potential of allogeneic haematopoietic SCT will not be realized until approaches to minimize GVHD, while maintaining the positive contributions of donor T cells, are developed. This Review focuses on research in mouse models pursued to achieve this goal.

Natural Regulation of Immunity to Minor Histocompatibility Antigens

MHC-matched hemopoietic stem cell transplantation is commonly used for the treatment of some forms of leukemia. Conditioning regimens before transplant act to reduce the burden of leukemic cells and the graft-vs-leukemia (GvL) effect can eliminate residual disease. The GvL effect results largely from the recognition of minor histocompatibility Ags by donor T cells on recipient tissues. These Ags are generally widely expressed and also provoke graft-vs-host (GvH) disease. Manipulation of immunity to promote GvL while curtailing GvH would greatly improve clinical outcome. To develop strategies that may achieve this, the parameters which control immunity to minor histocompatibility Ags need to be defined. In this study, we have analyzed responses to the mouse HY minor histocompatibility Ag using hemopoietic cell and skin grafts as surrogate GvL and GvH targets, respectively. We show that natural regulation of CD8 T cell responses to HY operates at multiple levels. First, CD4 T cell help is required for primary CD8 responses directed at hemopoietic cells. However, although CD4 T cells of H2(k) mouse strains recognize HY, they provide ineffective help associated with a proportion of recipients developing tolerance. This was further investigated using TCR-transgenic mice which revealed H2(k)-restricted HY-specific CD4 T cells are highly susceptible to regulation by CD25(+) regulatory T cells which expand in tolerant recipients. A second level of regulation, operating in the context of skin grafts, involves direct inhibition of CD8 T cell responses by CD94/NKG2 engagement of the nonclassical MHC class I molecule Qa1.

The X-linked mental retardation gene SMCX/JARID1C defines a family of histone H3 lysine 4 demethylases

Histone methylation regulates chromatin structure and transcription. The recently identified histone demethylase lysine-specific demethylase 1 (LSD1) is chemically restricted to demethylation of only mono- and di- but not trimethylated histone H3 lysine 4 (H3K4me3). We show that the X-linked mental retardation (XLMR) gene SMCX (JARID1C), which encodes a JmjC-domain protein, reversed H3K4me3 to di- and mono- but not unmethylated products. Other SMCX family members, including SMCY, RBP2, and PLU-1, also demethylated H3K4me3. SMCX bound H3K9me3 via its N-terminal PHD (plant homeodomain) finger, which may help coordinate H3K4 demethylation and H3K9 methylation in transcriptional repression. Significantly, several XLMR-patient point mutations reduced SMCX demethylase activity and binding to H3K9me3 peptides, respectively. Importantly, studies in zebrafish and primary mammalian neurons demonstrated a role for SMCX in neuronal survival and dendritic development and a link to the demethylase activity. Our findings thus identify a family of H3K4me3 demethylases and uncover a critical link between histone modifications and XLMR.

Differential effects of immunosuppressive drugs on T-cell motility

The best-characterized mechanism of the action of immunosuppressive drugs is to prevent T-cell clonal expansion, thus containing the magnitude of the ensuing immune response. As T-cell recruitment to the inflammatory site is another key step in the development of T-cell-mediated inflammation, we analyzed and compared the effects of two commonly used immunosuppressants, cyclosporin A (CsA) and the rapamycin-related compound SDZ-RAD, on the motility of human CD4+ T cells. We show that CsA, but not SDZ-RAD, inhibits T-cell transendothelial migration in vitro. CsA selectively impaired chemokine-induced T-cell chemotaxis while integrin-mediated migration was unaffected. The inhibition of T-cell chemotaxis correlated with reduced AKT/PKB but not ERK activation following exposure to the chemokine CXCL-12/SDF-1. In addition, CsA, but not SDZ-RAD, prevents some T-cell receptor-mediated effects on T-cell motility. Finally, we show that CsA, but not SDZ-RAD inhibits tissue infiltration by T cells in vivo. Our data suggest a prominent antiinflammatory role for CsA in T-cell-mediated tissue damage, by inhibiting T-cell trafficking into tissues in addition to containing clonal expansion.

JmjC-domain-containing proteins and histone demethylation

Histone methylation has important roles in regulating gene expression and forms part of the epigenetic memory system that regulates cell fate and identity. Enzymes that directly remove methyl marks from histones have recently been identified, revealing a new level of plasticity within this epigenetic modification system. Here we analyse the evolutionary relationship between Jumonji C (JmjC)-domain-containing proteins and discuss their cellular functions in relation to their potential enzymatic activities.

Role of immunoproteasomes in cross-presentation

The evidence that proteasomes are involved in the processing of cross-presented proteins is indirect and based on the in vitro use of proteasome inhibitors. It remains, therefore, unclear whether cross-presentation of MHC class I peptide epitopes can occur entirely within phagolysosomes or whether it requires proteasome degradation. To address this question, we studied in vivo cross-presentation of an immunoproteasome-dependent epitope. First, we demonstrated that generation of the immunodominant HY Uty(246-254) epitope is LMP7 dependent, resulting in the lack of rejection of male LMP7-deficient (LMP7(-/-)) skin grafts by female LMP7(-/-) mice. Second, we ruled out an altered Uty(246-254)-specific T cell repertoire in LMP7(-/-) female mice and demonstrated efficient Uty(246-254) presentation by re-expressing LMP7 in male LMP7(-/-) cells. Finally, we observed that LMP7 expression significantly enhanced cross-priming of Uty(246-254)-specific T cells in vivo. The observations that male skin grafts are not rejected by LMP7(-/-) female mice and that presentation of a proteasome-dependent peptide is not efficiently rescued by alternative cross-presentation pathways provide strong evidence that proteasomes play an important role in cross-priming events.

CD8 T Cells Specific for a Donor-Derived, Self-Restricted Transplant Antigen Are Nonpathogenic Bystanders after Vascularized Heart Transplantation in Mice

CD8 T cell cross-priming, an established mechanism of protective antiviral immunity, was originally discovered during studies involving minor transplantation Ags. It is unclear whether or how cross-primed CD8 T cells, reactive to donor-derived, but recipient class I MHC-restricted epitopes, could injure a fully MHC-disparate, vascularized transplant. To address this question we studied host class I MHC-restricted, male transplantation Ag-reactive T cell responses in female recipients of fully MHC-disparate, male heart transplants. Cross-priming to the immune-dominant determinant HYUtyp occurred at low frequency after heart transplantation. CD8 T cell preactivation through immunization with HYUtyp mixed in CFA did not alter the kinetics of acute rejection. Furthermore, neither HYUtyp immunization nor adoptive transfer of HYUtyp-specific TCR-transgenic T cells affected outcome in 1) a model of chronic rejection in the absence of immunosuppression or 2) a model of allograft acceptance induced by costimulatory blockade. The results support the contention that CD8 T cells reactive to host-restricted, but donor-derived, Ags are highly specific and are nonpathogenic bystanders during rejection of MHC-disparate cardiac allografts.

Inefficient purifying selection: the mammalian Y chromosome in the rodent genus Mus

Two related genes with potentially similar functions, one on the Y chromosome and one on the X chromosome, were examined to determine if they evolved differently because of their chromosomal positions. Six hundred fifty-seven base pairs of coding sequence of Jarid1d (Smcy) on the Y chromosome and Jarid1c (Smcx) on the X chromosome were sequenced in 13 rodent taxa. An analysis of replacement and silent substitutions, using a counting method designed for samples with small evolutionary distances, showed a significant difference between the two genes. The different patterns of replacement and silent substitutions within Jarid1d and Jarid1c may be a result of evolutionary mechanisms that are particularly strong on the Y chromosome because of its unique properties. These findings are similar to results of previous studies of Y chromosomal genes in these and other mammalian taxa, suggesting that genes on the mammalian Y evolve in a chromosome-specific manner.

Identification of the immunodominant HY H2-D(k) epitope and evaluation of the role of direct and indirect antigen presentation in HY responses

Minor histocompatibility Ags derive from self-proteins and provoke allograft rejection and graft-vs-host disease in MHC-matched donor-recipient combinations. In this study, we define the HYD(k) epitope of the HY minor histocompatibility Ag as the 8mer peptide RRLRKTLL derived from the Smcy gene. Using HY tetramers, the response to this peptide was found to be immunodominant among the four characterized MHC class I-restricted HY epitopes (HYD(k)Smcy (defined here), HYK(k)Smcy, HYD(b)Uty, and HYD(b)Smcy). Indirect presentation stimulated a robust primary HYD(k)Smcy response. Indirect presentation and priming of HY-specific CD8+ T cells is also operative in the presence of a full MHC mismatch. To determine whether the indirect route of Ag presentation is required for HY priming, female parent into F1 (H2bxk) female recipient bone marrow chimeras were immunized with male cells of the other parental haplotype, limiting presentation to the direct pathway. The dominant H2b HY response (HYD(b)Uty) was dependent on indirect presentation. However, the dominant H2k HY response (HYD(k)Smcy) could be stimulated efficiently by the direct pathway. In contrast, secondary expansion of both HYD(k)Smcy and HYD(b)Uty-specific CD8+ T cells was effective only when Ag was presented by the direct route. Transgenic overproduction of Smcy mRNA within the immunizing cells resulted in a corresponding increase in the HYD(k)Smcy, HYD(b)Smcy, and HYK(k)Smcy-specific CD8+ T cell responses when presented via the direct pathway but did not enhance indirect presentation demonstrating the independent regulation of MHC class I-peptide occupancy in the two Ag-processing pathways.

Membrane phosphatidylserine distribution as a non-apoptotic signalling mechanism in lymphocytes

Phosphatidylserine (PS) exposure is normally associated with apoptosis and the removal of dying cells. We observed that PS is exposed constitutively at high levels on T lymphocytes that express low levels of the transmembrane tyrosine phosphatase CD45RB. CD45 was shown to be a negative regulator of PS translocation in response to various signals, including activation of the ATP receptor P2X(7). Changes in PS distribution were shown to modulate several membrane activities: Ca(2+) and Na(+) uptake through the P2X(7) cation channel itself; P2X(7)-stimulated shedding of the homing receptor CD62L; and reversal of activity of the multidrug transporter P-glycoprotein. The data identify a role for PS distribution changes in signal transduction, rapidly modulating the activities of several membrane proteins. This seems to be an all-or-none effect, coordinating the activity of most or all the molecules of a target protein in each cell. The data also suggest a new approach to circumventing multidrug resistance.

Engraftment of Allogeneic Hematopoietic Stem Cells Requires Both Inhibition of Host-Versus-Graft Responses and ‘Space' for Homeostatic Expansion

BACKGROUND

The establishment of host-versus-graft (HvG) tolerance is the primary aim of reduced intensity conditioning (RIC) regimens for allogeneic stem cell transplantation (SCT). It remains to be clarified to what extent recipient myeloablation is fundamental in the establishment of donor chimerism.

METHODS

We have addressed this question in a murine model of RIC SCT in which the donor-recipient combination produces HvG against the male specific minor histocompatibility antigen HY. In this system engraftment can be monitored by RT-PCR and HvG effectors enumerated by tetramer analysis.

RESULTS

We demonstrate that the dose of irradiation influences donor hemopoietic engraftment and affects generation of anti-donor specific T cells. Chimeric recipients do not mount a HvG immune response, becoming selectively tolerant, as demonstrated by the long term acceptance of skin grafts of donor but not third party origin. However, HvG tolerance is not sufficient to secure engraftment since, even in the absence of HvG, partial myeloablation was still required. The "space" produced by myeloablation and the consequent potential for donor cell expansion could also affect HvG tolerance, since its induction is severely impaired when donor hematopoietic cells have reduced proliferative capacity.

CONCLUSIONS

We conclude that both some degree of myeloablation and HvG tolerance are required for successful engraftment, and that the capacity of donor cells to proliferate influences the induction of HvG tolerance.

Bone marrow mesenchymal stem cells induce division arrest anergy of activated T cells

It has been shown that mesenchymal stem cells (MSCs) induce T cells to become unresponsive. We characterized the phenotype of these T cells by dissecting the effect of MSCs on T-cell activation, proliferation, and effector function. For this purpose, an in vitro murine model was used in which T-cell responses were generated against the male HY minor histocompatibility antigen. In the presence of MSCs, the expression of early activation markers CD25 and CD69 was unaffected but interferon-γ (IFN-γ) production was reduced. The inhibitory effect of MSCs was directed mainly at the level of cell proliferation. Analysis of the cell cycle showed that T cells, stimulated in the presence of MSCs, were arrested at the G1 phase. At the molecular level, cyclin D2 expression was profoundly inhibited, whereas p27kip1 was up-regulated. When MSCs were removed from the cultures and restimulated with the cognate peptide, T cells produced IFN-γ but failed to proliferate. The addition of exogenous interleukin-2 (IL-2) did not restore proliferation. MSCs did not preferentially target any T-cell subset, and the inhibition was also extended to B cells. MSC-mediated inhibition induces an unresponsive T-cell profile that is fully consistent with that observed in division arrest anergy.

Escape from immune surveillance does not result in tolerance to tumor-associated antigens

Despite expression of tumor-associated or tumor-specific antigens by most tumors, evasion of protective T-cell immunity is the rule rather than the exception. Understanding whether tumor immune escape primarily represents T-cell neglect, anergy/tolerance, or quantitative limits of an existent immune response is central to developing new strategies to enhance antitumor immunity. The authors studied the immune response to MB49, a tumor that naturally expresses HY. Immune surveillance was effective following low-dose tumor inocula, since normal female mice showed a diminished incidence and slower growth rate of MB49 compared with T-cell-depleted female mice and male mice. Following high-dose tumor inoculation, females developed large, progressive tumors but continued to demonstrate immune responses to class I and class II restricted HY epitopes. The HY reactive T cells remained capable of executing HY immune responses since T cells adoptively transferred from MB49-bearing animals mediated accelerated HY skin graft rejection compared with those taken from naive mice. Thus, MB49 does not induce immune tolerance to HY but rather escapes immune surveillance largely due to quantitative limits of the immune response. Treatment of tumor-bearing animals with rhIL7 significantly increased the number of T cells responding to HY but did not alter tumor growth rate. These results demonstrate that escape from immune surveillance does not necessarily imply immune tolerance to tumor antigens and that immunotherapy need not overcome tumor-induced tolerance per se, and suggest that substantial opportunities remain in tumor-bearing hosts to amplify weak but persistent antitumor immune responses.

X-linked mental retardation

Genetic factors have an important role in the aetiology of mental retardation. However, their contribution is often underestimated because in developed countries, severely affected patients are mainly sporadic cases and familial cases are rare. X-chromosomal mental retardation is the exception to this rule, and this is one of the reasons why research into the genetic and molecular causes of mental retardation has focused almost entirely on the X-chromosome. Here, we review the remarkable recent progress in this field, its promise for understanding neural function, learning and memory, and the implications of this research for health care.