Immunologic tolerance: collaboration between antigen and lymphokines

Memory B Cells and Long-lived Plasma Cells

The importance of B cell and antibody-mediated immune response in the acute and long-term persistence of transplanted solid organs has become increasingly evident in recent years. A variety of therapeutic innovations target antibodies directed toward HLA or blood groups (ABO) to allow better allocation and posttransplant longevity of organs. Antibodies originate from plasma cells (PCs), which are terminally differentiated B cells. Long-term production and persistence of these antibodies is partly due to fast reactivation of previously generated memory B cells; however, there is increasing evidence that some differentiated PCs can persist independently in the bone marrow for years or even decades, producing specific antibodies or even experiencing regeneration without proliferation without need to be replaced by newly differentiating B cells. This review outlines the currently presumed pathways of differentiation, antibody, and memory generation on both B-cell and PC levels. On this background, current therapeutic concepts for antibody reduction before and after solid organ transplantation are considered, to better understand their mechanisms, possible synergisms, and specific risks. Specific differences in regards to ABO versus HLA antibodies as well as practical relevance for generation of desensitization and posttransplant antibody-directed therapy protocols are discussed.

A20 deficiency in B cells enhances B-cell proliferation and results in the development of autoantibodies

A20/TNFAIP3 is an ubiquitin-editing enzyme, important for the regulation of the NF-κB pathway. Mutations in the TNFAIP3 gene have been linked to different human autoimmune disorders. In human B-cell lymphomas, the inactivation of A20 results in constitutive NF-κB activation. Recent studies demonstrate that in mice the germline inactivation of A20 leads to early lethality, due to inflammation in multiple organs of the body. In this report, we describe a new mouse strain allowing for the tissue-specific deletion of A20. We show that B-cell-specific deletion of A20 results in a dramatic reduction in marginal zone B cells. Furthermore, A20-deficient B cells display a hyperactive phenotype represented by enhanced proliferation upon activation. Finally, these mice develop higher levels of serum immunoglobulins, resulting in an excessive production of self-reactive autoantibodies.

Do parasitic infections break T-cell tolerance and trigger autoimmune disease?

Burnet and Fenner originally defined 'tolerance' as 'unresponsiveness against self'. It is now generally accepted that the phenomenon of tolerance is required to protect on individual from potentially autoreactive cells. Recent experiments have independently shown that parasite infection or interleukin 2 (IL-2) can reverse an established T-cell tolerance in vivo. Breaking T-cell tolerance restores the capacity of T cells to be stimulated by their specific antigen and, in the case of a self-antigen, may be followed by autoimmune disease. In this review, Martin Röcken and Ethan Shevach briefly describe the potential pathways for generating T-cell tolerance in vivo, and focus on recently described mechanisms by which parasitic infections may circumvent or abrogate the tolerant state.

Engagement of membrane immunoglobulin enhances Id3 promoter activity in WEHI-231 B lymphoma cells

AIM

We have recently shown that engagement of membrane immunoglobulin (mIg) induced upregulation of inhibitor of differentiation 3 (Id3) mRNA, resulting in growth arrest at G1 phase in WEHI-231 cells. In the present study, we examined whether engagement of mIg will affect promoter activity of the Id3 gene in WEHI-231 cells.

METHODS

DNA fragments corresponding to the 5'-flanking region of mId3 gene were amplified by polymerase chain reaction (PCR) using genomic DNA as the template. Three DNA fragments upstream of the transcription start site (+1) of the mId3 gene were subcloned into the luciferase reporter vector PGV-B2. The recombinant constructs were transiently transfected into WEHI-231 cells by an electroporation method. After incubation for 24 h, WEHI-231 cells were stimulated with 10 mg/L anti-IgM or irradiated CD40L-expressing NIH3T3 cells or control NIH3T3 cells for further 24 h, followed by assay for luciferase activity.

RESULTS

The luciferase analysis demonstrated that basal promoter activity of the Id3 gene was found in the region between -200 and +54. The Id3 promoter activity was increased 2-fold following stimulation with anti-IgM, but not CD40L, compared with medium alone.

CONCLUSION

The mIg-mediated upregulation of Id3 expression is controlled, at least in part, through transcriptional regulation, as assessed by luciferase assay.

CD40 Ligand Rescues Inhibitor of Differentiation 3-Mediated G1 Arrest Induced by Anti-IgM in WEHI-231 B Lymphoma Cells

The engagement of membrane-bound Igs (mIgs) results in growth arrest, accompanied by apoptosis, in the WEHI-231 murine B lymphoma cells, a cell line model representative of primary immature B cells. Inhibitor of differentiation (Id) proteins, members of the helix-loop-helix protein family, functions in proliferation, differentiation, and apoptosis in a variety of cell types. In this study, we analyzed the involvement of Id protein in mIg-induced growth arrest and apoptosis in WEHI-231 cells. Following stimulation with anti-IgM, expression of Id3 was up-regulated at both the mRNA and protein levels; this up-regulation could be reversed by CD40L treatment. Retrovirus-mediated transduction of the Id3 gene into WEHI-231 cells resulted in an accumulation of the cells in G(1) phase, but did not induce apoptosis. E box-binding activity decreased in response to anti-IgM administration, but increased after stimulation with either CD40L alone or anti-IgM plus CD40L, suggesting that E box-binding activity correlates with cell cycle progression. WEHI-231 cells overexpressing Id3 accumulated in G(1) phase, which was accompanied by reduced levels of cyclin D2, cyclin E, and cyclin A, and a reciprocal up-regulation of p27(Kip1). Both the helix-loop-helix and the C-terminal regions of Id3 were required for growth-suppressive activity. These data suggest that Id3 mimics mIg-mediated G(1) arrest in WEHI-231 cells.

Evidence against humoral immune attack as the cause of sheep-goat interspecies and hybrid pregnancy failure in the DOE

The failure of interspecies and hybrid pregnancies between the domestic sheep (Ovis aries) and goat (Capra hircus) is not completely understood. The sheep-goat hematopoietic chimera is a unique model for studying the role of the maternal immune response in failure of interspecies and hybrid pregnancies between these species. Hematopoietic chimeras were created by in utero transplantation of sheep fetal liver cells into goat fetuses. The resulting chimeric females were recipients of sheep demi-embryos genetically identical to their sheep cells and/or were bred to a ram to create a hybrid pregnancy. Pregnancy sera were analyzed for the presence of anti-species antibodies (Ab) using a lymphocyte microcytotoxicity assay. None of the concepti survived to term. Gross and histological evaluations of two interspecies sheep concepti revealed abnormal placentome formation. The humoral immune response of several hematopoietic chimeras to the challenging concepti differed from control animals. We observed delayed onset of Ab production, low and absent titers, and persistent Ab titers with delayed fetal death. Ultrasonography typically revealed normal fetal development associated with high volumes of placental fluids and retarded placentome development. We conclude that fetal death was associated with abnormal placental development that was not the result of maternal humoral immune attack.

A fully human antibody neutralising biologically active human TGFbeta2 for use in therapy

Phage display provides a methodology for obtaining fully human antibodies directed against human transforming growth factor-beta (TGFbeta) suitable for the treatment of fibrotic disorders. The strategy employed was to isolate a human single chain Fv (scFv) fragment that neutralises human TGFbeta2 from a phage display repertoire, convert it into a human IgG4 and then determine its TGFbeta binding and neutralisation properties and its physical characteristics. Several scFv fragments binding to TGFbeta2 were isolated by panning of an antibody phage display repertoire, and subsequent chain shuffling of the selected V(H) domains with a library of V(L) domains. The three most potent neutralising antibodies were chosen for conversion to IgG4 format. The IgG4 antibodies were ranked for their ability to neutralise TGFbeta2 and the most potent, 6B1 IgG4, was chosen for further characterisation. 6B1 IgG4 has a high affinity for TGFbeta2 with a dissociation constant of 0.89 nM as determined using the BIAcore biosensor and only 9% cross-reactivity with TGFbeta3 (dissociation constant, 10 nM). There was no detectable binding to TGFbeta1. 6B1 IgG4 strongly neutralises (IC50 = 2 nM) the anti-proliferative effect of TGFbeta2 in bioassays using TF1 human erythroleukaemia cells. Similarly, there was strong inhibition of binding of TGFbeta2 to cell surface receptors in a radioreceptor assay using A549 cells. 6B1 IgG4 shows no detectable cross-reactivity with related or unrelated antigens by immunocytochemistry or ELISA. The 6B1 V(L) domain has entirely germline framework regions and the V(H) domain has only three non-germline framework amino acids. This, together with its fully human nature, should minimise any potential immunogenicity of 6B1 IgG4 when used in therapy of fibrotic diseases mediated by TGFbeta2.

Differential Th1 and Th2 cell regulation of murine cardiac allograft acceptance by blocking cell adhesion of ICAM-1/LFA-1 and VCAM-1/VLA-4

Administration of anti-intercellular adhesion molecule (ICAM)-1 monoclonal antibody (mAb) plus anti-lymphocyte function associated antigen (LFA)-1 mAb induces tolerance in murine cardiac transplantation, while anti-vascular cell adhesion molecule (VCAM)-1 mAb plus anti-very late antigen (VLA)-4 mAb administration prolongs graft survival, but leads to tolerance only in some cases. BALB/c mice hearts were transplanted into C3H/He recipients. Each combination of anti-VCAM-1 plus anti-VLA-4 mAbs (100 microg each/day, i.p.) or anti-ICAM-1 plus anti-LFA-1 mAbs (50 microg each/day, i.p.) was administered for 5 days. For control study, third group mice received daily with FK506 administration (1 mg/kg/day). The cardiac allografts and recipients' spleens were harvested on day 7; the expression of cytokines were detected using immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) and in situ RT-PCR. Th2 cytokines (IL-4 and IL-10) were markedly enhanced and Th1 cytokines (IFN-gamma and IL-2) were suppressed in recipients treated with anti-ICAM-1 mAb plus anti-LFA-1 mAb, while poor Th2 cytokine expression allowed persistent Th1 cytokine expression in recipient mice with anti-VCAM-1 mAb plus anti-VLA-4 mAb treatment. Both Th1 and Th2 cytokine expression was suppressed in FK506-treated mice. It is concluded that immunological tolerance and prolonged graft survival induced by blocking cell adhesion is regulated by different cytokine expression.

Gene therapy for breast cancer

Gene therapy for breast cancer is still in the very early stages of development. Many of the molecular strategies that have been proposed are also being developed for other cancers. Their application to breast cancer, however, needs to address several issues specific to this disease such as the widespread nature of metastases, the indolent growth of the tumor cells, and the production by the tumor of immunosuppressive agents. Nonetheless, these approaches appear promising, particularly those that employ a combination of strategies. Gene therapies that affect the biology of breast cancer cells or regulate host immune mechanisms have been most successful and may be paired with existing therapies for breast cancer.

Mechanisms of recovery from experimental autoimmune encephalomyelitis: T cell deletion and immune deviation in myelin basic protein T cell receptor transgenic mice

Experimental autoimmune encephalomyelitis (EAE) is a Th1-type cell-mediated autoimmune disease directed against central nervous system (CNS) myelin antigens such as myelin basic protein (MBP). EaE is usually characterized by spontaneous remission of clinical disease and immune pathology despite the persistence of self myelin antigens in the central nervous system. Following induction of an acute episode of EAE, spontaneous remission also occurs in MBP T cell receptor (TCR) transgenic mice even through most T cells express a TCT specific for MBP. To investigate the mechanisms of recovery associated with EAE, we examined the behavior of MBP-specific T cells in the MBP TCR transgenic mouse model during disease progression and recovery. We found that recovery from EAE was associated with three major immunologic changes: (1) deletion of encephalitogenic T cells in the brain; (2) deviation of MBP-specific transgenic (Tg+) T cells both in the periphery and in the central nervous system from INF- gamma secretin Th1 type cells to cells that secrete IL-4, IL-10, and TGF- beta ; and (3) deletion of Tg+ T cells in the thymus through apoptosis. Thus spontaneous recovery from a classic Th1 type organ specific autoimmune disease is associated with two mechanisms of immune tolerance, deletion of autoreactive cells and immune deviation of autoreactive cells to a non-pathogenic phenotype.

Autoimmunity, immunologic tolerance, and gene therapy

Research in our laboratory focuses on three major themes: 1. Costimulation and cell death in autoimmunity. 2. Molecular mechanisms of immunologic tolerance. 3. Gene therapy of autoimmune diseases. We have performed a large series of experiments using T cell receptor (TCR) transgenic mice examining mechanisms of autoimmunity and peripheral T cell tolerance. A major focus of our current research is to understand the roles of costimulation and cell death in T cell tolerance and T cell-mediated autoimmune diseases. This involves studies of the TCR, the costimulatory molecules, and the cytokines. We are also exploring novel strategies for the treatment of autoimmune diseases by gene transfer.

Polyclonal T cell elimination by prolonged immunostimulation in an experimental model

An experimental model of immunological deficiency obtained by treating mice for 6 months with serum of human blood drawn from different healthy individuals has been studied. The results show that an alteration of a circulating lymphocyte population with alterations of the ratio CD4+/CD8+ appeared in mice stimulated for a long period with immunogens. Mice treated for 2-4 months showed an increase in B lymphocytes and a decrease in the total number of T lymphocytes, with a decrease in CD4+ lymphocytes and an increase in CD8+ lymphocytes. After 4 months, the CD8+ lymphocyte population started to decrease, with a ratio of CD4+/CD8+ reaching almost 1. In animals treated for 2-3 months, the mean survival time (MST) following experimental infection with Salmonella typhimurium presented a decrease to 5 days, and after 5-6 months of treatment presented a decrease to 3-2.5 days. The bacteraemia was modified in comparison with controls. Prolonged exposure to antigens also induced lymphocyte apoptosis: cells of animals treated for 4-6 months presented increased levels of apoptosis with a percentage that reached 30-35%. A semiquantitative evaluation of the level of heat shock protein (hsp) in splenic lymphocytes showed an increase in the presence of hsp60 and hsp70 in the first 3 months of treatment, which then remained constant for up to 6 months.

Suppression of anti-thyrocyte autoreactivity by the lymphocytes of normal fetal lambs

We have devised an experimental strategy to determine whether the developing immune system of normal fetal animals can spontaneously acquire the capacity to inhibit autoimmune responses by its cells as it matures. Whilst the existence of cells with the capacity to exert negative regulation and to curtail autoimmune responses has been demonstrated previously in response to the experimental induction of these responses, the relevance of such regulatory processes to the prevention of overt autoimmunity in normal animals has not been established. We have produced pairs of identical twin fetal lambs by splitting blastocysts and have subsequently deprived one of each pair of exposure to thyroid-specific antigens by surgical thyroidectomy before development of immunological self recognition. Thyroidectomized fetuses developed T lymphocytes autoreactive against self thyrocytes. However, their normal, identical co-twins were found to acquire a class of T lymphocytes with the capacity to block anti-thyrocyte autoreactive cells from the thyroidectomized fetal co-twin. Blocking of anti-thyroid autoreactivity required preliminary contact between these normal T lymphocytes and the target thyrocytes. Substitution of an allograft of fetal thyroid tissue for a fetal lamb's own thyroid gland failed to prevent the development of autoreactivity against autologous thyrocytes by the recipient's lymphocytes. However, the reactivity of those lymphocytes against thyrocytes from the specific allogeneic thyroid donor was markedly curtailed.

Immunobiology and immunopharmacology of organ allograft rejection

Much has been learned regarding immunobiological mechanisms responsible for the rejection of histoincompatible allografts. There has also been considerable progress in our understanding of mechanisms responsible for tolerance. The new knowledge gained regarding graft destructive alloimmunity process and the mechanisms of action of immunosuppressants have resulted in solid organ graft survival rates that are in excess of 80% at one year posttransplantation. The principles of tolerance mechanism are yet to be successfully applied in the clinic. In this review, molecular and cellular mechanisms of action of clinically useful immunosuppressive drugs are reviewed from the perspective of regulation of the anti-allograft repertory.

Fibroblasts as efficient antigen-presenting cells in lymphoid organs

Only so-called "professional" antigen-presenting cells (APCs) of hematopoietic origin are believed capable of inducing T lymphocyte responses. However, fibroblasts transfected with viral proteins directly induced antiviral cytotoxic T lymphocyte responses in vivo, without involvement of host APCs. Fibroblasts induced T cells only in the milieu of lymphoid organs. Thus, antigen localization affects self-nonself discrimination and cell-based vaccine strategies.

Pancreatic islet beta cells drive T cell-immune responses in the nonobese diabetic mouse model

The role of autoantigens and that of target organs in which tissue lesions develop remains elusive in most spontaneous models of autoimmune diseases. Whether the presence of target autoantigens is required for the recruitment of autoreactive lymphocytes is unknown in most cases. To evaluate the importance of islet cells in the development of autoimmunity in the nonobese diabetic (NOD) mouse, we generated beta cell-deprived mice by injecting a high dose of alloxan, a toxic agent specific for beta cells. In contrast with spleen cells from 6-mo-old naive NOD mice which transfer diabetes in irradiated 8-mo-old male recipients, spleen cells from age-matched NOD mice which received a single injection of alloxan at 3 wk of age did not transfer diabetes. With the exception of the ability to transfer diabetes, beta cell-deprived NOD mice showed maintained immune competence. Furthermore, sialitis developed with the expected intensity and prevalence in beta cell-deprived mice. Already committed "diabetogenic" spleen cells collected from spontaneously diabetic mice also showed a reduced capacity to transfer diabetes after their removal from the diabetic mice and transient "parking" in beta cell-deprived mice. Taken together, our data bring evidence that involvement of autoreactive T cells detected by the capacity to transfer diabetes requires the presence of target beta cells.

Generation of monoclonal antibodies against autologous proteins in gene-inactivated mice

Induction of an immune response is strongly dependent on the phylogenetic distance between antigen and recipient. In general, antibodies will not be raised against self-antigens nor against highly conserved domains. In the present study we describe the production and characterization of murine monoclonal "auto-antibodies" against murine tissue-type plasminogen activator (t-PA) raised in "knock-out" mice, homozygously deficient of the functional gene. 203 stable hybridomas were obtained producing murine monoclonal antibodies against murine t-PA. Analysis of the species reactivity revealed that 182 cross-reacted with one or more (t-)PAs originating from other species including rat t-PA, human t-PA, and vampire bat-PA. 121 reacted with epitopes conserved among murine, rat, and human t-PA. In addition, 31 of the monoclonal antibodies were directed against domains present in all four species. Epitope mapping indicated a high frequency of specificity toward diverse epitopes that are highly conserved across species. Comparative analysis of their influence on the enzymatic activity of t-PA and their species cross-reactivity clearly demonstrated that the domains required for the biological activity of plasminogen activators are more conserved (p < 0.02) than non-functional domains. The availability of such unique antibodies against a wide variety of conserved epitopes may facilitate studies on the structural homologies between (t-)PAs isolated from various species. The present approach should also apply to various other classes of proteins, allowing the generation of monoclonal antibodies, against conserved epitopes, which could not be raised in wild-type animals because of their "self-antigen" nature.

T helper cell unresponsiveness: rapid induction in antigen-transgenic and reversion in non-transgenic mice

T cell tolerance is usually established by clonal deletion of self-specific T cells in the thymus, or some times, in the periphery. Alternatively, tolerance may also be achieved by induction of clonal T cell unresponsiveness by a poorly understood mechanism called "anergy". We found that transgenic mice expressing a soluble form of vesicular stomatitis virus (VSV) glycoprotein (G) predominantly in liver and kidney exhibited normal B cell responses. VSV-G-specific T help-independent neutralizing IgM responses were within normal ranges, but no T help-dependent neutralizing IgG antibodies were generated upon immunization with recombinant VSV-G protein and recombinant vaccinia virus expressing VSV-G. This demonstrated absence of B cell tolerance but presence of T helper cell unresponsiveness. After adoptive transfer of transgenic spleen cells into thymectomized immuno-incompetent hosts, the unresponsive T helper cells regained function and switched the neutralizing IgM response to IgG, comparably to control T helper cells, within 7 days. Conversely, when naive non-transgenic spleen cells were transferred into transgenic mice, VSV-G-specific T helper cells became unresponsive within 3-4 days. These results suggest that VSV-G-specific T helper cells are rendered unresponsive within a few days in the VSV-G transgenic host also outside of the thymus and that this unresponsiveness was reversed by transfer into antigen-free recipients.

Induction of anergy or active suppression following oral tolerance is determined by antigen dosage

Oral tolerance was generated to hen egg white lysozyme in the mouse or to guinea pig myelin basic protein in the rat by a low-dose (1 mg) or a high-dose (5-20 mg) feeding regimen. High doses of antigen induced tolerance characterized by anergy with little or no active suppression and increased secretion of interleukin 4 (IL-4). Anergy was shown by an increase in frequency of IL-2-secreting cells following culture in recombinant IL-2. Low doses of antigen induced tolerance characterized by antigen-driven active suppression with increased secretion of transforming growth factor beta (TGF-beta) and IL-4 and minimal anergy. Without further immunization, spleen cells from animals orally tolerized by both regimens secreted increased levels of IL-4 and TGF-beta in an antigen-specific manner. Animals fed high doses secreted more IL-4 and less TGF-beta, whereas those fed low doses secreted more TGF-beta and less IL-4. These results demonstrate that the two feeding regimens induced cell populations that differed in their cytokine secretion profile and their capacity to actively suppress in vitro and to induce anergy. Our results provide a basis for distinguishing different forms of antigen-driven peripheral tolerance and have important implications for orally induced antigen-specific modulation of human autoimmune diseases.

Tumor immunogenicity determines the effect of B7 costimulation on T cell-mediated tumor immunity

A costimulatory signal through B7 to its counter-receptor CD28 on T cells enhances T cell activation. We have generated recombinant retroviruses containing cDNA for murine B7 and transduced a panel of murine tumor lines with varying immunogenicity to study the effect of B7 costimulation on antitumor immunity. In contrast to the progressive outgrowth of all wild-type (B7-) tumors in unimmunized syngeneic mice, four immunogenic tumors, lymphoma RMA, EL4, mastocytoma P815, and melanoma E6B2, regressed completely when transduced with the B7 gene. In contrast, four nonimmunogenic tumors, sarcomas MCA101, MCA102, and Ag104, and melanoma B16, remained tumorigenic after transduction of the B7 gene. Immunization with B7-transduced immunogenic tumors enhanced protective immunity and increased specific cytotoxic T lymphocyte (CTL) activity against the respective wild-type tumors as compared to immunization with nontransduced or mock-transduced tumors. Moreover, cocultivation of CTL with B7-transduced EL4 cells augmented the specificity of tumor-reactive CTL in long-term cultures. Treatment by injection of B7-transduced tumor cells cured 60% of mice with established wild-type EL4 lymphoma. In contrast, immunization with nonimmunogenic tumors transduced with B7 did not provide protective immunity and did not increase specific CTL activity. Our results show that tumor immunogenicity is critical to the outcome of costimulation of T cell-mediated tumor immunity by B7.

Role of antibody and T cells in the long-term inhibition of IgE synthesis

We have shown that the long-term inhibition of IgE synthesis associated with perinatal inoculation of syngeneic IgE is accompanied by the synthesis of autoantibodies to IgE. Synthesis of IgE can also be inhibited by passive transfer of syngeneic anti-IgE antibodies. In the present investigation we made use of adoptive transfer experiments to assess the relative roles of antibodies and T cells in the inhibitory process. It was found that spleen cells from IgE-suppressed mice (synthesizing anti-IgE antibodies) could adoptively transfer the state of inhibition to syngeneic adult mice. The inhibition occurred only under conditions in which the recipient mice synthesized anti-IgE antibodies. Separated B cells, CD4+ T cells, CD8+ T cells, or a mixture of B and CD8+ T cells were ineffective. However, strong inhibition of IgE synthesis (as indicated by serum levels and numbers of IgE-secreting cells in the spleen) was observed after transfer of a mixture of B cells and CD4+ (helper) T cells. The results indicate that in this experimental model anti-IgE antibodies are the suppressive agent and that T cells do not play a role other than that of providing help to B cells for anti-IgE synthesis.

Somatic gene therapy for cancer: the utility of transferrinfection in generating 'tumor vaccines'

The last few years have seen the development of a branch of somatic gene therapy which aims at strengthening the immune surveillance of the body, leading to eradication of disseminated cancer tumor cells and occult micrometastases after surgical removal of the primary tumor. Such a tumor vaccination protocol calls for cultivation of the primary tumor tissue and the insertion of one of three types of genes into the isolated cultured tumor cells followed by irradiation of the transfected or transduced cells to render them incapable of further proliferation. The cells so treated constitute the 'tumor vaccine'. A review of the literature suggests that for mouse models, in the initial period after inoculation, rejection of the tumor cells is usually effected by non-T-cell immunity, whereas the long-term systemic immune response is based on cytotoxic T-cells. High expression of the gene inserted into the tumor cells may be critical for the success of the vaccination procedure. Examples are given which indicate that transferrinfection, a procedure to introduce genes by adenovirus-augmented receptor-mediated endocytosis, meets some important prerequisites for successful application of this type of gene therapy.

Suppression of anti-erythrocyte autoantibody-producing B cells by a physiological IgG-anti-F(ab')2 antibody and escape from suppression by tumour transformation; a model relevant for the pathogenesis of autoimmune haemolytic anaemia

We showed previously that broadly reactive IgG anti-immunoglobulin autoantibodies produced by rats during the immune response suppress the B cell response. We report here on the effect of a similar human antibody on self-reactive human B cells. IgG anti-F(ab')2 was added to cultures of anti-erythrocyte autoantibody-producing B cells derived from healthy donors. A dose-dependent suppression of the antibody response was obtained (maximum at 1.3 ng IgG/10(6) cells). This effect was competitively inhibited by F(ab')2 gamma. Autoimmune haemolytic anaemia can be caused by chronic monoclonal B cell proliferation. To reproduce this condition in vitro we immortalized B cells with Epstein-Barr virus (EBV) and raised a B cell population with anti-erythrocyte autoantibody activity. These cells were electrically fused with CB-F7 tumour cells and an IgG1 cold-reactive anti-erythrocyte autoantibody-producing B cell line was established. Surprisingly, the tumour cells were not suppressed by IgG anti-F(ab')2. It is known that anti-immunoglobulins selectively suppress antigen-receptor (AgR)-occupied B cells by a Fc gamma-receptor (Fc gamma R)-mediated mechanism. To occupy their AgR, we preincubated the tumour cells with anti-AgR antibody. In spite of this, their susceptibility to suppression was not restored. As shown by rabbit IgG-sensitized ox erythrocyte (EA)-rosetting, this refractoriness was not due to a loss of Fc gamma R. Our experiments delineate a mechanism of peripheral B cell suppression to autoantigens, and show a way of escape from control relevant for the pathogenesis of autoimmune haemolytic anaemia.

Oncogene transformation can induce tolerogenicity in murine macrophages after down-regulation of immunogenicity without altering major histocompatibility complex antigen expression

In vitro studies on cell lines may allow analyses of the mechanisms of immunogenicity and tolerogenicity in cells. We used a model of oncogenic transformation of an established murine macrophage cell line and report here that one v-mos-transformed clone expressing unaltered high amounts of MHC class I and II antigens does not induce proliferation of unprimed T cells in primary mixed lymphocyte reactions, in sharp contrast to its non-transformed parental cells. Interestingly, this clone induces specific unresponsiveness, as revealed by the lack of responsiveness of MHC-specific T cells when subsequently exposed to the pertinent MHC alloantigens in immunogenic form but unaltered MHC-third party responsiveness of the naive spleen T cells. Furthermore, the accessory function of this clone is strongly reduced. These functional defects could be overcome by the addition of exogenous interleukin-1 alpha (IL-1 alpha). Analysis of mRNA expression showed a significant and selective reduction of IL-1 alpha mRNA levels when compared with parental cells.

Blood transfusion and immunomodulation: a possible mechanism

To induce an immunogenic response in vivo, an antigen-presenting (stimulator) cell must present both antigen-specific (class II MHC) and an accessory signal to the CD4 T cell. Failure to express the accessory signal has been shown in vitro to induce a state of specific unresponsiveness (anergy) in the T cell. We have shown that although stimulator cells in blood continue to express class II MHC molecules during refrigerated storage, their ability to present the accessory signal diminishes, reaching zero in all units tested by about 13 days. This implies that blood in excess of 2 weeks old should not alloimmunize but could induce some degree of immunosuppression. UV-B irradiation and, to a lesser extent, gamma-irradiation, were also shown to inhibit expression of the accessory signal by stimulator cells in blood.

An evaluation of the potential to use tumor-associated antigens as targets for antitumor T cell therapy using transgenic mice expressing a retroviral tumor antigen in normal lymphoid tissues

A major obstacle to the development of T cell therapy for the treatment of human tumors has been the difficulty generating T cells specifically reactive with the tumor. Most of the characterized human tumor antigens have been classified as tumor associated, because of demonstrable expression at low levels in some normal cells, and thus have not been extensively studied as potential targets of a therapeutic immune response. However, the quantitative difference in expression of such antigens between the tumor and normal cells might permit the generation of antigen-specific T cells capable of selective antitumor and not autoimmune activity. To address this issue, transgenic (TG) mice were generated that expressed low levels of Friend murine leukemia virus (FMuLV) envelope protein in lymphoid cells under the control of an immunoglobulin promoter. This protein is expressed at high levels by a Friend virus-induced erythroleukemia of C57BL/6 (B6) origin, FBL, and has been shown to serve as an efficient tumor-specific rejection antigen in B6 mice. The env-TG mice were tolerant to envelope, as reflected by the failure to detect an envelope-specific response after in vivo priming and in vitro stimulation with preparations of FMuLV envelope. However, adoptively transferred envelope-specific T cells from immunized non-TG B6 mice mediated complete eradication of FBL tumor cells in TG mice, and did not induce detectable autoimmune damage to TG lymphoid tissues. The transferred immune cells were not permanently inactivated in the TG mice, since donor T cells responded to envelope after removal from the TG mice. The lack of autoimmune injury did not reflect inadequate expression of envelope by TG lymphocytes for recognition by T cells, since TG lymphocytes functioned effectively in vitro as stimulators for envelope-specific T cells. The results suggest that this and analogous strains of TG mice may prove useful for elucidating principles for the generation and therapeutic use of tumor-reactive T cells specific for tumor-associated antigens.

Genesis and evolution of antichromatin autoantibodies in murine lupus implicates T-dependent immunization with self antigen

Autoantibodies reacting with chromatin and its components, histones and DNA, are characteristic of the human autoimmune disease SLE and drug-induced lupus, but the mechanisms of their induction remain unknown. Serial serum samples collected over short intervals from lupus-prone MRL/MP-lpr/lpr and BXSB mice were tested by ELISA on chromatin and its substructures to characterize the initial autoimmune response to these antigens. Direct binding studies demonstrated that the early autoantibodies recognized discontinuous epitopes on native chromatin and the (H2A-H2B)-DNA subnucleosome. As the immune response progressed, native DNA and other chromatin constituents generally became antigenic. Based on adsorption studies and IgG subclass restriction, antibodies to native DNA were more related to chromatin than to denatured DNA. The kinetics of autoantibody appearance and the Ig class distribution were similar to the kinetics and distribution seen in antibodies induced by immunization with an exogenous T-dependent antigen. These results are most consistent with the view that autoantibodies reacting with chromatin are generated by autoimmunization with chromatin, and antibodies to native DNA are a subset of the wide spectrum of antichromatin autoantibodies.

Production of human antibodies using bacteriophage

The immune system produces antibodies by a process of antigen-driven selection. An in vitro process of antigen-driven selection, based on the display of antibody fragments on filamentous bacteriophage, has recently been developed. This enables human antibody fragments of high affinity and specificity to be produced without immunization.

Receptor editing: an approach by autoreactive B cells to escape tolerance

To determine the fate of anti-DNA antibody-bearing B cells in normal mice, we generated transgenic mice bearing the heavy (H) and light (L) chain genes of a well-characterized anti-double-stranded DNA antibody. This antibody was originally isolated from a diseased MRL/lpr mouse and has characteristics common to spontaneously arising anti-DNA antibodies. Results show that the H/L transgene (tg) immunoglobulin receptor is not expressed by animals bearing both tgs, although single tg animals (H or L) express their transgenes. Young H/L tg animals express few B cells, whereas adult H/L tg animals maintain almost normal B cell numbers. Analysis of the immunoglobulin receptors used by adult B cells shows that all contain the tg H chain in association with endogenous L chains. These B cells transcribe the L tg as well as the rearranged endogenous L chain gene, and loss of endogenous L chain gene transcription results in resurrection of the 3H9 H/L tg product. Examination of the endogenous L chains used by these cells shows that they represent a highly restricted subset of V genes. Taken together, these data suggest that autoreactive transgenic B cells can rearrange endogenous L chain genes to alter surface receptors. Those L chains that compete successfully with the L tg for H chain binding, and that create a nonautoreactive receptor, allow the B cell to escape deletion. We suggest that this receptor editing is a mechanism used by immature autoreactive B cells to escape tolerance.

Synergism between the endogenous viral loci ev6 and ev9 in inducing immunological tolerance to avian leukosis virus

1. The course of infection by exogenous avian leukosis virus was followed in a commercial strain of White Leghorn domestic fowls by measuring viral antigen in feather pulp and egg albumin. Ten days after hatching, 2 out of 360 birds tested positive and at 286 days of age about 60% of the birds had been antigen positive at least once. 2. Among the antigen positive birds, two groups could be distinguished: those which permanently and those which transiently expressed viral antigen. Permanent antigen expression was associated with low antibody titres, while transient antigen expression was associated with high antibody titres. 3. The strain segregated for the two endogenous viral genes ev6 and ev9, both of which express endogenous viral envelope protein, and have been implicated in affecting immune-responsiveness. The antibody titre in individuals positive for both ev6 and ev9, was significantly lower than in those which had none or only one of the two ev-genes. In addition, individuals positive for both ev-genes occurred more frequently in the group permanently positive for viral antigen than in the group transiently antigen positive. 4. The results indicate that there was a strong synergism between ev6 and ev9 in reducing the antibody response to exogenous avian leukosis virus infection, perhaps by inducing immune tolerance or interfering with antibody formation.

Tolerance of sheep-goat chimeras to their component cells

Four sheep-goat chimeras with a goat or sheep sibling having an identical genotype to one of the two component species of cells were tested for tolerance through mixed lymphocyte response (MLR) and skin grafts. None of the four chimeras showed a response to its sib in MLR and three of the four accepted sib skin grafts. This demonstrates that the chimerism exhibited by these animals was sufficient to render the chimera tolerant to antigens expressed by the sib. Two of the four sibs showed positive responses to their chimeric sibs in MLR and two did not; one negative response was expected because the chimera's lymphocytes were essentially all the same species as the sib's. Chimeric skin grafts were partially accepted by two of the four sibs, suggesting the presence of both sheep and goat cells in the skin grafts derived from the chimeras. Two of the four sibs did not accept chimeric skin grafts, possibly due to lack of compatible cells in the graft. Neither differences between an allo- and xenoresponse in MLR nor time differences in the rejection of allo- and xenografts were observed.

In vivo role of interleukin 4 in T cell tolerance induced by aqueous protein antigen

High doses of aqueous protein antigens induce a form of immunological tolerance in which interleukin 2 (IL-2)- and interferon gamma (IFN-gamma)-secreting T helper type 1 (Th1) cells are inhibited, but IL-4-secreting (Th2) cells are not. This is manifested by reduced proliferation of antigen-specific T cells upon in vitro restimulation, and marked suppression of specific antibody responses of the immunoglobulin (Ig)G2a, IgG2b, and IgG3 isotypes, but not of IgG1 and IgE. The role of the immunomodulatory cytokine IL-4 in this model of unresponsiveness to protein antigens has been examined. Administration of tolerizing antigen itself primes splenic CD4+ T cells for secretion of lymphokines, both IL-2 and IL-4. Neutralization of IL-4 in vivo with the anti-IL-4 antibody 11B11 during tolerance induction augments IFN-gamma production by T cells of tolerant mice, and reverses the suppression of IgG2a, IgG2b, and IgG3. This blockade of IL-4 function does not, however, restore the proliferative responses of T cells, suggesting that reduced T cell proliferation is due to direct T cell inactivation or anergy. Inhibiting the activity of IL-4 in vivo also inhibits the expansion of antigen-specific Th2-like cells, which are resistant to the induction of unresponsiveness. Thus, the immunologic consequences of high-dose tolerance are due to a combination of clonal T cell anergy and IL-4-mediated immune regulation.

Costimulation of antitumor immunity by the B7 counterreceptor for the T lymphocyte molecules CD28 and CTLA-4

Interaction of the B7 molecule on antigen-presenting cells with its receptors CD28 and CTLA-4 on T cells provides costimulatory signals for T cell activation. We have studied the effects of B7 on antitumor immunity to a murine melanoma that expresses a rejection antigen associated with the E7 gene product of human papillomavirus 16. While this E7+ tumor grows progressively in immunocompetent hosts, cotransfection of its cells with B7 led to tumor regression by a B7-dependent immune response mediated by CD8+ cytolytic T lymphocytes. The immune response induced by E7+B7+ tumor cells also caused regression of E7+B7- tumors at distant sites and was curative for established E7+B7- micrometastases. Our findings suggest that increasing T cell costimulation through the CD28 and CTLA-4 receptors may have therapeutic usefulness for generating immunity against tumors expressing viral antigens.

Self tolerance to human A and B histo-blood group antigens exists at the B cell level and cannot be broken by potent polyclonal B cell activation in vitro

It is generally considered that tolerance to self antigens is less complete in B than in T lymphocytes. However, B cell tolerance through either functional inactivation (anergy) or clonal deletion has been demonstrated in transgenic mice. In the present study, we investigated whether B cells specific for self A/B histo-blood group antigens can be detected in normal humans. It is a key feature of the ABO system that all normal individuals make natural antibodies against those A or B carbohydrates which are not present in their organism. To detect B cells by the limiting dilution approach we used a specific enzyme-linked immunosorbent assay for the quantitation of anti-A/B antibodies, and a culture system in which polyclonal B cell activation occurs through cell contact with EL4 thymoma cells. As was reported for other B cell studies, we frequently detected "polyreactive" immunoglobulin (Ig)M (but not IgG) with apparent autoreactivity but of uncertain significance regarding physiologic conditions. However, A- or B-specific B cell responses occurred with selective patterns in agreement with classical blood group serology in 14 individuals with A, B, AB or 0 blood group phenotypes: 1/11,600 B cells made anti-allo A/B IgM and 1/26,500 B cells such as IgG, while only 1/104,000 B cells apparently made anti-self A/B IgM and 1/350,000 B cells such as IgG. This shows self tolerance at the B cell level. Since anergy of B cells can frequently be broken by polyclonal B cell activation in vitro, and EL4 cells are potent B cell stimulators, the present results argue for either a highly resistant anergic state or for clonal deletion of self-A/B histo-blood group-specific human B cells.