Expression Of Major Histocompatibility Antigens Research Articles

CAR T cells generated in situ using gene therapy in naturally activated lymph node T cells

Abstract T cells expressing chimeric antigen receptors (CAR T cells) are manufactured outside the body using non-physiological activation and in vitro culture protocols. The procedure takes 3 weeks and costs approximately $450,000 to administer. We have devised a scheme using mouse models for manufacturing CAR T cells in just 3 days employing a natural, polyclonal anti-viral immune response inside a lymph node (LN) using off the shelf reagents that can be applied widely in populations. CAR T cells emerge from the LN within a week, invade solid tumor, and eliminate the targeted antigen-positive tumor cells. Polyclonal activation of T cells is achieved by modifying the antigen presenting properties of lymph node resident professional antigen presenting cells (APC) through viral expression of allogeneic major histocompatibility antigens. The ensuing polyclonal activation occurs in the context of virus activated APC within the normal aarchitecture of the LN and confers robust T cell activation signals directing the development of cytolytic T cells. During the course of T cell activation, the T cells are transduced in situ with retroviruses encoding selected CARs. This approach could be applied to any number of different CARs to target a variety of tumors. T cells activated in the lymph node are functionally distinct from those activated using standard CAR T manufacturing protocols. We anticipate that CAR T cells generated in situ to natural stimuli will exhibit more normal immune regulatory properties that will impact their therapeutic utility. Because our approach uses off the shelf reagents and is administered using standard clinical procedures, cost to patients should be lowered and access to therapy increased.

Interactions between the immune system and the ruminant conceptus

Interactions of the conceptus with the immune system can involve either anti-sperm or anti-conceptus immune responses that limit the success of pregnancy of beneficial effects of cytokines released from lymphoid cells on embryonic growth and gene expression. The immune system is functional in the uterus and therefore there is the potential for anti-conceptus immune responses. However, endometrial lymphocytes are distinct in many respects from lymphoid cells at peripheral sites; one major subpopulation expresses the gamma delta T-cell receptor and may not recognize major histocompatibility antigens. There are also several control systems to limit anti-conceptus immune responses. In particular, expression of major histocompatibility antigens on the trophoblast is either absent or of limited distribution. In addition, activation of anti-conceptus immune responses leading to cytolytic responses is further limited by the presence of molecules that can inhibit lymphocyte transformation. The most well-characterized of these are prostaglandin E2 from placental and endometrial tissues, interferon-tau from the trophoblast during early pregnancy, and two endometrial proteins called the uterine milk proteins (UTMP). Progesterone plays a central role in inhibition of immune responses in actions that are mediated at least in part through endometrial secretion of UTMP. Cytokines play important roles as autocrine and paracrine regulators in many tissues including the reproductive tract. In ruminants, the best described example is interferon-tau. Other cytokines found in the reproductive tract or produced by the conceptus include interleukin-1, leukaemia inhibitory factor, granulocyte-macrophage colony stimulating factor and interleukin-6. It is possible that the major source of cytokines in the reproductive tract is non-lymphoid cells of the endometrium and trophoblast. It is not known to what extent endometrial lymphocytes contribute to the cytokine milieu because no cytokine has been identified as a product of endometrial lymphocytes. However, there is a population of granulated lymphocytes that increase in number and granularity in the luminal epithelium of the late-pregnant ewe that is a potential source of cytokines.

Effect of Dexamethasone, LPS, or INFγ on the production of TNFα, IL-12, IL-6, IL-10, CXCL8, CXCL10, and CLC3, by bovine macrophages infected in vitro with Mycobacterium avium paratuberculosis.

Effect of Dexamethasone, LPS, or INFγ on the production of TNFα, IL-12, IL-6, IL-10, CXCL8, CXCL10, and CLC3, by bovine macrophages infected in vitro with Mycobacterium avium paratuberculosis.

Foot-and-mouth disease virus 3C protease induces fragmentation of the Golgi compartment and blocks intra-Golgi transport.

Picornavirus infection can cause Golgi fragmentation and impose a block in the secretory pathway which reduces expression of major histocompatibility antigens at the plasma membrane and slows secretion of proinflammatory cytokines. In this study, we show that Golgi fragmentation and a block in secretion are induced by expression of foot-and-mouth disease virus (FMDV) 3Cpro and that this requires the protease activity of 3Cpro. 3Cpro caused fragmentation of early, medial, and late Golgi compartments, but the most marked effect was on early Golgi compartments, indicated by redistribution of ERGIC53 and membrin. Golgi fragments were dispersed in the cytoplasm and were able to receive a model membrane protein exported from the endoplasmic reticulum (ER). Golgi fragments were, however, unable to transfer the protein to the plasma membrane, indicating a block in intra-Golgi transport. Golgi fragmentation was coincident with a loss of microtubule organization resulting from an inhibition of microtubule regrowth from the centrosome. Inhibition of microtubule regrowth also required 3Cpro protease activity. The loss of microtubule organization induced by 3Cpro caused Golgi fragmentation, but loss of microtubule organization does not block intra-Golgi transport. It is likely that the block of intra-Golgi transport is imposed by separate actions of 3Cpro, possibly through degradation of proteins required for intra-Golgi transport.

A Review of Studies on Targeting Interleukin 4 Receptor for Central Nervous System Malignancy

Despite advances in biomedical sciences, the prognosis of patients with brain tumors remains poor. Effective treatment is lacking for these central nervous system (CNS) cancers. Targeted immunotoxins are a new class of therapeutic approaches that have emerged for the treatment of human cancers. In this approach, tumor antigen or cell surface receptor is targeted by a chimeric fusion protein consisting of an antibody or a ligand and a suicidal gene or toxin to kill tumor cells. In that regard, receptors for interleukin (IL)-4 (IL-4R) have been identified to be overexpressed on a variety of human CNS tumor cell lines and tissue samples including meningioma. In various studies, high grade brain tumor specimens and malignant brain tumor cell lines have been shown to overexpress high-affinity IL-4R, while normal brain samples or cell lines expressed lower levels of these receptors. The structures of IL-4R on CNS tumors have been studied, which demonstrate that these cells express predominantly type II IL-4R. These receptors are functional as IL-4 can cause signal transduction, inhibit growth of some tumor cell lines and increase expression of major histocompatibility antigens and intracellular adhesion molecular-1 (ICAM-1) on some tumor cells lines. To target IL-4R, a chimeric fusion protein composed of IL-4 and truncated Pseudomonas exotoxin has been developed. This cytotoxin is highly cytotoxic to IL-4R positive tumors in vitro and has been reported to be highly effective in pre-clinical animal model of human brain cancer. Several Phase I/II clinical trials for treatment of IL-4R positive cancers have been completed. This review article will summarize pre-clinical and clinical development of IL-4PE cytotoxin.

Cytomegalovirus infection and proinflammatory cytokine activation modulate the surface immune determinant expression and immunogenicity of cultured murine extrahepatic bile duct epithelial cells.

Murine extrahepatic bile duct epithelial cells (MEBEC) were isolated from extrahepatic bile ducts of BALB/c mice and established in primary culture. The epithelial origin was confirmed by positive cytokeratin 19 staining for these cells and the presence of microvilli and tight junctions under electron microscopy. By immunofluorescent staining with monoclonal antibodies and flow-cytometric analysis, MEBEC in culture constitutively express low levels of intercellular adhesion molecule (ICAM)-1, class I and class II major histocompatibility (MHC) antigens. The expression of ICAM-1 was significantly increased by interferon gamma (INF-gamma) or tumour necrosis factor alpha (TNF-alpha) stimulation. Class I and class II antigen expression were significantly enhanced by INF-gamma and in vitro murine cytomegalovirus (MCMV) infection. MEBEC infected with MCMV revealed a progressive cytopathic effect. MEBEC activated by INF-gamma or infected by MCMV induced a low but significant proliferation of allogeneic T cells and displayed a significant decrease in the absorbance at O.D. 550 nm in a microtitre tetrazolium assay after these treated cells were co-cultured with allogeneic T cells. These results suggest that following the up-regulation of surface MHC antigen and adhesion molecule expression with cytokines or MCMV, the MEBEC can function as antigen-presenting cells and initiate T-cell proliferation, which in turn trigger the recognition of MEBEC by effector T-cell-mediated cytotoxic responses. These findings may be implicated in the pathogenesis of virally induced, immune-mediated extrahepatic bile duct damage disorders.

Growth and major histocompatibility antigen expression regulation by IL-4, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) on human renal cell carcinoma.

We have recently shown that human renal cell carcinoma (RCC) tumour lines express high-affinity IL-4 receptors. Binding of IL-4 to RCC cells induced a growth inhibition in the range of 20-68%. To enhance the growth inhibitory effect of IL-4, we have tested the effects of two additional cytokines capable of directly affecting tumour cell growth. IFN-gamma caused a significant inhibition of RCC tumour cell growth (up to 70%) in a dose-dependent manner, whereas the effect of TNF-alpha was more limited (0-20% inhibition). The addition of IL-4 to IFN-gamma on RCC cells sensitive to IL-4 induced a greater inhibition of cell growth than that seen with each cytokine alone. IL-4 and IFN-gamma rendered RCC cells more responsive to the inhibitory effect mediated by TNF-alpha. The combination of TNF-alpha with IL-4 and IFN-gamma induced an optimal growth inhibition (up to 90-98%) of RCC cells. In addition to a direct anti-proliferative effect, we have demonstrated that these cytokines can also enhance the expression of MHC antigens on the surface of RCC tumour cell lines which may render the cells more immunogenic. All RCC lines tested expressed class I antigens, but not class II antigens. IFN-gamma induced class II expression and up-regulated the expression of class I antigens on RCC cells. Class II antigen expression was detectable following 48 h incubation, and greater after 72 h with IFN-gamma. IL-4 minimally affected class I expression, whereas TNF-alpha up-regulated class I antigen expression. IL-4 or TNF-alpha did not induce class II expression. The combination of the three cytokines slightly augmented the up-regulation of class I and class II antigens observed with IFN-gamma alone. These observations confirm the direct interaction of IL-4, IFN-gamma and TNF-alpha with RCC tumour cells, both at the level of growth regulation and MHC antigen expression, and suggest a therapeutic potential of the combination of the three cytokines for renal cell carcinoma.

Clonal Origin and Evolution of a Transmissible Cancer

The transmissible agent causing canine transmissible venereal tumor (CTVT) is thought to be the tumor cell itself. To test this hypothesis, we analyzed genetic markers including major histocompatibility (MHC) genes, microsatellites, and mitochondrial DNA (mtDNA) in naturally occurring tumors and matched blood samples. In each case, the tumor is genetically distinct from its host. Moreover, tumors collected from 40 dogs in 5 continents are derived from a single neoplastic clone that has diverged into two subclades. Phylogenetic analyses indicate that CTVT most likely originated from a wolf or an East Asian breed of dog between 200 and 2500 years ago. Although CTVT is highly aneuploid, it has a remarkably stable genotype. During progressive growth, CTVT downmodulates MHC antigen expression. Our findings have implications for understanding genome instability in cancer, natural transplantation of allografts, and the capacity of a somatic cell to evolve into a transmissible parasite.

Myocarditis

Myocarditis is clinically and pathologically defined as “inflammation of the myocardium.” Despite its rather clear-cut definition, the classification, diagnosis, and treatment of myocarditis continue to prompt considerable debate. The more routine use of endomyocardial biopsy has helped to better define the natural history of human myocarditis and to clarify clinicopathological correlations. Clinical presentations of the disease range from nonspecific systemic symptoms (fever, myalgias, palpitations, or exertional dyspnea) to fulminant hemodynamic collapse and sudden death. The extreme diversity of clinical manifestations has made the true incidence of myocarditis difficult to determine. Recent prospective postmortem data have implicated myocarditis in sudden cardiac death of young adults at rates of 8.6% to 12%.1,2 Furthermore, it has been identified as a cause of dilated cardiomyopathy in 9% of cases in a large prospective series.3 Recent molecular techniques have facilitated new insights into inflammatory autoimmune processes that affect the myocardium and ultimately result in acute or chronic dilated cardiomyopathy. Despite the well-established morbidity and mortality associated with myocarditis,4–7 clinical practice guidelines with regard to its evaluation and treatment are lacking.8 The wide variety of etiologies implicated in myocarditis and its heterogeneous clinical presentations5,7,9 have impeded patient identification and consensus on the most appropriate diagnostic criteria. The Dallas pathological criteria, published in 1986, served as the first attempt to develop standardized diagnostic guidelines for the histopathological classification of myocarditis.10 Active myocarditis is characterized by an inflammatory cellular infiltrate with evidence of myocyte necrosis (Figure 1), whereas borderline myocarditis demonstrates an inflammatory cellular infiltrate without evidence of myocyte injury (Figure 2). The inflammatory infiltrate should be further described as lymphocytic, eosinophilic, or granulomatous (Figure 3). The amount of inflammation may be mild, moderate, or severe, and its distribution may be focal, confluent, or diffuse, respectively. A retrospective study of 112 consecutive …

No cancer in cancers: Evolutionary trade-off between successful viviparity and tumor escape from the adaptive immune system

Some invertebrate species including the king crab and king squid enjoy relatively long lives of up to 20 years. Nevertheless, there are few reports of malignancies among invertebrate animals while there are many such reports in lower vertebrates such as in fishes, amphibians, and reptiles. Viviparity is characteristic of most mammalian species, although it has been observed in both vertebrate and non-vertebrate species. As adaptive immune responses evolved among the cartilaginous fishes by virtue of gene duplication, all viviparous vertebrates cope with specific immune responses to reject the fetal allograft. The escape mechanisms employed by both human and animal malignancies share common properties, which are also employed by feto-placental units, such as the expression of non-classical major histocompatibility antigens (HLA-E, HLA-F, and HLA-G in humans), accumulation of regulatory T cells, Th2-directed immune responses, Fas/FasL- and/or PD-1/PD-L1-induced apoptosis, and the expression of indoleamine 2, 3 dioxygenase which starves the local tryptophan supply that is indispensable for an effective cytotoxic T cells response. In humans, a single cancer cell requires 1-10 years to develop into a clinically remarkable tumor. For cancer cells, the genes encoding the immunoregulatory mechanisms employed by feto-placental units could be of value for escaping the host immune system. Taken together, these observations support the author's hypothesis that the evolution of viviparity resulted in an evolutionary trade-off that may have increased susceptibility to malignancies.

Inhibition of alloresponse by a human trophoblast non-coding RNA suppressing class II transactivator promoter III and major histocompatibility class II expression in murine B-lymphocytes

Trophoblasts are a model of natural allograft tolerance. A unique characteristic is the complete lack of expression of all classic major histocompatibility (MHC) antigens. We cloned a human trophoblast non-coding RNA (TncRNA) that suppresses MHC class II expression through inhibition of the class II transactivator (CIITA) promoter. We assessed the functional affects of TncRNA on an alloresponse and dissected the functional domain on CIITA promoter III. Murine B-cell line A20 was transfected with TncRNA. Class II suppressed clones were selected and characterized by flow cytometry and Northern analysis. The clones were then subjected to lymphocyte proliferation assay to assess the stimulation of T-lymphocytes. CIITA promoter III-luciferase reporter plasmids were used with TncRNA plasmids in co-transfection assays; 5'-end deletion plasmids were used to dissect the promoter. Significant suppression of I-Ad expression was seen. Northern blot scans demonstrated 84% to 93% suppression of class II transcripts. Lymphocyte proliferation assay demonstrated a 50% and 64% inhibition of lymphocyte stimulation in the 2 clones, compared to A20 wild type. Dissection of promoter III indicated that an area between bp -152 to -107 contains the functional site of TncRNA. Human TncRNA is active across species lines and significantly inhibits allogenic response to B-cells. There is concurrent suppression of constitutive class II expression in TncRNA clones mediated through a defined region of CIITA promoter III.

MHC class I manipulation on cell surfaces by gene transfer of anti-MHC class I intrabodies—a tool for decreased immunogenicity of allogeneic tissue and cell transplants

Intrabodies (IB) are suitable tools to down-regulate the expression of cell surface molecules in general. In this work, the appearance of major histocompatibility (MHC) class I molecules on the cell surface could be prevented by the expression of intracellularly localized anti-MHC class I antibodies. The expression of MHC antigens presenting intracellularly synthetised peptides on the cell surface is the predominant reason for immunologic detection and rejection of allogeneic cell and tissue transplants. Allogeneic keratinocyte sheets might be a suitable tool for skin grafting. Within this study primary rat keratinocytes have been transfected with anti-MHC I-IB. Strong IB-expressing cells showed a MHC I “knockout” phenotype. The cells did not exhibit any significant alterations compared to non-transfected cells: the cell growth and the expression of other surface molecules were unaltered. Merely an enhanced intracellular accumulation of MHC I molecules could be detected. Notably, IB-expressing keratinocytes displayed a reduced susceptibility to allogeneic cytotoxic T cells in vitro compared to unmodified cells with a normal level of MHC I surface expression. These MHC I-deficient keratinocytes might be utilized in tissue-engineered allogeneic non-immunogeneic skin transplants. The principle of MHC class I manipulation in general can be used for other allogeneic cell and tissue-engineered transplants as well.

Major histocompatibility antigen expression on the bovine placenta: its relationship to abnormal pregnancies and retained placenta

In viviparous animals, regulation of expression of major histocompatibility complex (MHC) class I antigens by the trophoblast cells, which constitute the outermost layer of the placenta, seems to be critical for maternal immunological acceptance of an allogeneic fetus. Cattle are unusual in this regard, since the bovine trophoblast cells, in specific regions of the uterine/placental interface, normally express MHC class I antigens during the third trimester of gestation. This expression appears to be biologically relevant as MHC class I compatibility between a cow and her fetus has been associated with an increased incidence of placental retention. We have found significant differences in lymphocyte populations, cytokine production, and trophoblast cell apoptosis in the placentomes of MHC-compatible and -incompatible pregnancies at parturition. This suggests that maternal immunological recognition of fetal MHC class I proteins triggers an immune/inflammatory response that contributes to placental separation at parturition in cattle. Early in pregnancy, a complete shutdown of MHC class I expression by trophoblast cells appears to be critical for normal placental development and fetal survival. In bovine somatic cell nuclear transfer (SCNT) pregnancies, there is an extremely high rate of fetal loss between days 30 and 90 of pregnancy. We have shown that in bovine SCNT pregnancies, between days 34 and 63 of gestation, there is both abnormal expression of MHC class I antigens by trophoblast cells and an abnormal accumulation of lymphocytes within the uterine stroma. Consequently, it is likely that activation of the maternal mucosal immune system, within the uterus at the same time when placentomes are being established, interferes with the process of placentome development and leads to immune-mediated abortion. Our data suggest that bovine MHC-compatible pregnancies provide a unique model for studying regulation of the uterine immune system, as well as immune-mediated placental rejection.

Resistance to Cryptococcus neoformans infection in the absence of CD4 + T cells

Previous studies of Cryptococcus neoformans infection have revealed a role for CD4+ T cells and CD8+ T cells in anticryptococcal resistance in the lungs, but such a role has been revealed only for CD4+ T cells in the brains of experimentally infected mice. In this study, we found that mice genetically engineered to lack CD4+ T cells could be successfully vaccinated to express resistance to a rechallenge with Cryptococcus neoformans, provided the challenge dose was kept to lower than 1000 organisms per mouse. The challenge infection was uniformly lethal for unvaccinated control mice. Depletion of CD8+ T cells weakened this resistance to re-challenge: both naïve and vaccinated mice that were treated with antibody raised against CD8+ T cells died significantly earlier than did mice that received an irrelevant control antibody. In vitro, purified CD8+ T cells taken from draining lymph nodes of antigen-experienced mice were less efficient than were identically prepared CD4+ T cells at stimulating the cells of a transformed microglial cell line to inhibit C. neoformans proliferation, possibly mirroring the inferiority of CD8+ T-cell-mediated protection observed in vivo. RNase protection assays showed similar IFN-gamma mRNA levels in both lymphocyte subsets. Class II major histocompatibility antigen expression was up-regulated strikingly on microglia cultured with IFN-gamma, but class I expression was less dramatically affected. Therefore microglial cell interaction may be more greatly enhanced with CD4+ cells than with CD8+ cells.

Resistance toCryptococcus neoformansinfection in the absence of CD4+T cells

Previous studies of Cryptococcus neoformans infection have revealed a role for CD4+ T cells and CD8+ T cells in anticryptococcal resistance in the lungs, but such a role has been revealed only for CD4+ T cells in the brains of experimentally infected mice. In this study, we found that mice genetically engineered to lack CD4+ T cells could be successfully vaccinated to express resistance to a re-challenge with Cryptococcus neoformans, provided the challenge dose was kept to lower than 1000 organisms per mouse. The challenge infection was uniformly lethal for unvaccinated control mice. Depletion of CD8+ T cells weakened this resistance to re-challenge: both naïve and vaccinated mice that were treated with antibody raised against CD8+ T cells died significantly earlier than did mice that received an irrelevant control antibody. In vitro, purified CD8+ T cells taken from draining lymph nodes of antigen-experienced mice were less efficient than were identically prepared CD4+ T cells at stimulating the cells of a transformed microglial cell line to inhibit C.neoformans proliferation, possibly mirroring the inferiority of CD8+ T-cell-mediated protection observed in vivo. RNase protection assays showed similar IFN-γ mRNA levels in both lymphocyte subsets. Class II major histocompatibility antigen expression was up-regulated strikingly on microglia cultured with IFN-γ, but class I expression was less dramatically affected. Therefore microglial cell interaction may be more greatly enhanced with CD4+ cells than with CD8+ cells.

Role of Interferon-α and Clonally Expanded T Cells in the Immunotherapy of Chronic Myelogenous Leukemia

Twenty five percent of patients in the chronic phase of chronic myelogenous leukemia (CML) are treated with interferon-α (IFN-α) to induce a cytogenic remission. In addition to its direct effects on leukemic cells, IFN-α has been shown to induce immunologic alterations, including upregulation of the expression of major histocompatibility (MHC) antigens in antigen-presenting cells (APCs), as well as augmentation of the activity of the lymphocytes against tumor cells. However, there has been little direct evidence supporting a causal interaction between cellular immunoreactivity and clinical responsiveness to IFN-α.We have shown that one approach to elucidate the immunological mechanisms by which IFN-α exerts its anti-CML activity is by analyzing therapy-induced modulation in T-cell receptor (TCR) Vβ chain usage, using the reverse transcription-polymerase chain reaction (RT-PCR) followed by single-strand conformation (SSCP) analysis. This method is particularly attractive, since it provides an index of antigen-specific T cell expansion, but does not require the extraction and purification of the antigens involved in the T-cell response. T cell clones that express the Vβ 10, 12, and 14 families predominate in the peripheral blood (PB) of CML patients. The enhanced expression of the Vpβ and 20 families has been detected in IFN-α responsive patients but not patients who are poorly responsive to this agent. This suggests that expansion of T cells expressing these TCR Vβ gene families may serve as a prognostic factors of the clinical responsiveness of CML patients to IFN-α.In addition, since T cell clones that express certain Vβ families may react with a discrete set of antigenic peptides presented on the surface of malignant cells, a better understanding of the immunobiology of T cells in CML may allow for the design of increasing efficacious immune therapy for this disease.

Characterization of T‐cell receptor β chain mRNA expression in IFN‐α‐responsive chronic myelogenous leukaemia patients

Interferon-alpha (IFN-alpha) has shown promise in the treatment of chronic phase of chronic myelogenous leukaemia (CML). IFN-alpha has also been found to indirectly up-regulate the expression of major histocompatibility (MHC) antigens, and to directly increase the activity of lymphocytes against tumour cells. To elucidate whether IFN-alpha induces anti-leukaemic activity of the autologous T cells in CML patients, we analysed the accumulation of T-cell receptor (TCR) in each Vbeta family using the reverse transcriptase-polymerase chain reaction (RT-PCR) followed by single-strand conformation (SSCP) analysis. We found the predominant expression of the Vbeta 10, 12, and 14 families in the peripheral blood (PB) of CML patients, in contrast to healthy donors. Especially, in IFN-alpha-responsive patients, we observed an enhancement of the accumulation of the Vbeta 9 and 20 families, suggesting that T cells enhanced by IFN-alpha may react with a discrete set of antigens on the surface of malignant cells. These findings may demonstrate that CML cells possess the heterogenous antigens and the clonal expansion of Vbeta 9+ and Vbeta 20+ T cells may be a prognostic indicator of the immune responsiveness to IFN-alpha.

Expression of porcine major histocompatibility antigens in cardiac tissue.

In this study we have used monoclonal antibodies directed against antigens of the major histocompatibility complex (MHC) class I and class II to reveal the detailed cellular distribution of swine lymphocyte alloantigens (SLA) in cardiac tissue. By applying a sensitive immunophosphatase staining reaction we detected the ubiquitous expression of SLA class I and class II on the vascular endothelium. Endothelial cells of capillaries and blood vessels were intensely stained structures in the examined swine hearts. Similar staining patterns were observed in control experiments with anti-von Willebrand factor serum and Dolichus biflorus lectin used as immunohistochemical markers for endothelial cells. The luminal layer of studied pulmonary valves exhibited a strong staining reaction with anti-SLA class I and class II antibodies. In contrast, normal cardiac myocytes failed to express immunodetectable amounts of either of the SLA determinants. Intercalated discs in porcine heart tissue did not react with either anti-SLA class I or class II antibodies. Our data showing the abundant expression of SLA molecules on endothelial cells in normal swine heart may have physiological implications in cell-mediated rejection occurring in xenotransplanted hearts.

Lack of immune responses to immediate or delayed implanted allogeneic and xenogeneic Schwann cell suspensions

Previous studies have shown that Schwann cell implantation offers a potential therapeutic approach to a variety of neurodegenerative disorders and traumatic injuries. In a clinically relevant paradigm, however, the implantation of autologous Schwann cells is problematic and the use of heterogenetic Schwann cells will be required. In the present study we addressed this important issue and analysed the immunogenicity and survival of allogeneic and xenogeneic Schwann cell suspension grafts in a prelesioned CNS fiber tract, the transected postcommissural fornix of the adult Wistar rat. Cultured Schwann cells from Wistar rat or human peripheral nerve were injected either immediately or after a delay into the transection site and the spatio-temporal pattern of leukocyte infiltration and of major histocompatibility antigen expression was characterized and semiquantified with immunocytochemical methods. Our main findings are that (1) invasive cerebral lesions induce the expression of MHC class I and II antigens, but only sparse infiltration of T-lymphocytes, (2) both allogeneic and xenogeneic discordant Schwann cell suspension grafts, from either neonatal or adult peripheral nerve, survive without any overt signs of rejection for up to 10 weeks after implantation; and (3) delayed implantation procedures have no effect on immune responses to allogeneic Schwann cell grafts. These results demonstrate that there is no marked ongoing immune reactions to heterogenetic Schwann cell suspension grafts and that long-term survival of cross-species Schwann cell grafts can be achieved in the absence of any immunsuppressive treatment. Thus the conditions for functional transplantation of Schwann cells across immunological barriers seem to be favourable and will have implications for future cross-species studies, and possibly also for clinical application.

Interactions between the immune system and the bovine conceptus

Immunological rejection of the bovine conceptus is blocked, in part, because of reduced expression of major histocompatibility (MHC) antigens on the surface of the conceptus. Also, an intrauterine environment is created during pregnancy in which maternal tissues and trophoblast secrete lymphocyte-inhibitory molecules that reduce immune reactivity. Data from other species suggest that there are also specific changes in functional activity of maternal lymphocyte populations during pregnancy that lead to 1) redirection of immune responses away from cellular immunity, 2) transient tolerance to conceptus antigens, and 3) activation of specific lymphocyte populations involved in immunosuppression or release of cytokines that stimulate placental function. Bovine trophoblast is potentially a target for maternal cytokines because placental cells express receptors for colony-stimulating factor-1 (CSF-1) and can be stimulated to proliferate in culture by lymphocyte-conditioned culture medium. Some degree of maternal recognition of conceptus antigens may be beneficial for the final stages of parturition because retained placenta occurs more frequently when dam and calf share MHC class I antigens. Methods to manipulate immunological function to enhance reproductive function remain speculative only — possibilities include alteration of uterine immune responses to reduce early embryonic mortality or to affect placental function, prevention of abortion caused by viral infection, enhancement of uterine antimicrobial defense mechanisms and reduction in frequency of retained placenta.