Induction of alloantigen-specific hyporesponsiveness in human T lymphocytes by blocking interaction of CD28 with its natural ligand B7/BB1

Impaired Ca/calcineurin pathway in in vivo anergized CD4 T cells

Clonal anergy is one of the mechanisms that may account for self tolerance induced in T cells in the periphery. In this study we used the well-documented system of in vivo administration of a superantigen, staphylococcal enterotoxin B (SEB), to induce a state of hyporesponsiveness (anergy) in murine peripheral T cells to decipher the intracellular biochemical basis for this process. The TCR-induced Ca response of in vitro activated T cells was found to be impaired with significant defects in the phosphorylation of phospholipase C-gamma 1. Experiments with calcium ionophore and newly established transgenic mouse lines that express an active form of calcineurin suggested that in vivo SEB-induced anergy is established and/or maintained by a selective impairment in the TCR-induced activation of the Ca/calcineurin pathway.

Anergic T cells generated in vitro suppress rejection response to islet allografts

BACKGROUND

Induction of antigen-specific unresponsiveness to grafts is the ultimate goal for organ transplantation. It has been shown that anergic T cells generated in vivo can be transferred as suppressor cells. Anergic cells generated in vitro have never been successfully used to prevent allograft rejection in vivo. We examined whether anergic cells generated in vitro by blocking CD28/B7 costimulatory pathway can suppress allograft rejection in vivo.

METHODS

Anergic T cells were generated in vitro by the addition of anti-B7-1 and anti-B7-2 monoclonal antibodies (mAbs) to primary mixed lymphocyte reaction (MLR) consisting of C57BL/6 (B6) splenocytes as responder and irradiated BALB/c splenocytes as stimulator. We tested the ability of these cells to respond to various stimuli and to suppress alloreactive T-cell responses in vitro. For in vivo studies, 4x10(7) anergic cells were injected intravenously immediately after transplantation of BALB/c islets under the renal subcapsular space of streptozotocin-induced diabetic and 2.5-Gy X-irradiated B6 mice.

RESULTS

Anergic cells treated with both mAbs in the primary MLR did not proliferate in secondary MLR against BALB/c and third-party C3H/He stimulators. The cells also failed to respond to immobilized anti-CD3 mAb, although they proliferated in response to concanavalin A or phorbol myristate acetate + ionomycin. The anergic state was reversed by the addition of exogenous IL-2. Furthermore, these cells suppressed the proliferation of naive B6 T cells against either the same (BALB/c) or third-party (C3H/He) stimulator cells. In in vivo studies, irradiated B6 mice rejected BALB/c islet allografts acutely with a mean survival time of 27.0+/-8.3 days, whereas two of six animals injected with the anergic cells accepted the allografts indefinitely (>100 days) with a mean survival time of 52.0+/-38.2 days.

CONCLUSIONS

Anergic cells generated in vitro by blocking CD28/B7 costimulatory pathway suppress islet allograft rejection after adoptive transfer. This procedure might be clinically useful for promoting allograft survival.

Blockade of CD86 and CD40 induces alloantigen-specific immunoregulatory T cells that remain anergic even after reversal of hyporesponsiveness

The generation of immunoregulatory T cells that block the B7(CD86/CD80)-CD28 and/or CD40-CD154 costimulatory pathways has great potential for the induction of long-term transplantation tolerance. In a human polyclonal in vitro model, combined monoclonal antibody (mAb) blocking of the costimulatory ligands CD40 and CD86 lead to allospecific T-cell anergy that cannot be reversed by antigenic rechallenge in the presence of IL-2. Although antigenic restimulation with IL-2 restored the proliferative response, subsequent antigenic restimulation of the restored anergic cells in a tertiary mixed lymphocyte culture still resulted in nonresponsiveness. Importantly, these anergic T cells suppress the response of naive alloreactive T cells in an antigen-specific way via linked recognition. Suppression may partially depend on local IL-10 production, while transforming growth factor–β (TGF-β) did not play a role. Irrespective of the monoclonal antibody combination used, blast formation occurred in a subset of CD4+ cells. These cells were characterized by a sustained CD45RA expression, an increased T-cell receptor density, and a lower level of CD4 expression. A reduced number of CD45RO+/CD8+ T cells was observed whenever anti-CD86 was combined with anti-CD40, which was reflected by an even more attenuated cytotoxic T-cell function. This indicates the importance of CD40-CD154 in the generation of cytotoxic T cells in this transplantation model. We hypothesize that in our model, anergy is induced in the CD4+ T-cell subset, whereby CD8+ cytotoxic effector function is impaired by the lack of both CD40-CD154 signaling and cytokine-mediated help. This costimulatory ligand–directed mAb approach might well be used for the ex vivo generation of antigen-specific immunoregulatory T cells applicable in adoptive immunotherapy.

Blockade of CD86 and CD40 induces alloantigen-specific immunoregulatory T cells that remain anergic even after reversal of hyporesponsiveness

The generation of immunoregulatory T cells that block the B7(CD86/CD80)-CD28 and/or CD40-CD154 costimulatory pathways has great potential for the induction of long-term transplantation tolerance. In a human polyclonal in vitro model, combined monoclonal antibody (mAb) blocking of the costimulatory ligands CD40 and CD86 lead to allospecific T-cell anergy that cannot be reversed by antigenic rechallenge in the presence of IL-2. Although antigenic restimulation with IL-2 restored the proliferative response, subsequent antigenic restimulation of the restored anergic cells in a tertiary mixed lymphocyte culture still resulted in nonresponsiveness. Importantly, these anergic T cells suppress the response of naive alloreactive T cells in an antigen-specific way via linked recognition. Suppression may partially depend on local IL-10 production, while transforming growth factor–β (TGF-β) did not play a role. Irrespective of the monoclonal antibody combination used, blast formation occurred in a subset of CD4+ cells. These cells were characterized by a sustained CD45RA expression, an increased T-cell receptor density, and a lower level of CD4 expression. A reduced number of CD45RO+/CD8+ T cells was observed whenever anti-CD86 was combined with anti-CD40, which was reflected by an even more attenuated cytotoxic T-cell function. This indicates the importance of CD40-CD154 in the generation of cytotoxic T cells in this transplantation model. We hypothesize that in our model, anergy is induced in the CD4+ T-cell subset, whereby CD8+ cytotoxic effector function is impaired by the lack of both CD40-CD154 signaling and cytokine-mediated help. This costimulatory ligand–directed mAb approach might well be used for the ex vivo generation of antigen-specific immunoregulatory T cells applicable in adoptive immunotherapy.

A native soluble form of CTLA-4

CTLA-4 is an immunoregulatory receptor expressed on the surface of activated T and B lymphocytes. The counterreceptors for CTLA-4 are the B7 family molecules. We describe alternatively spliced mRNAs expressed in hematolymphoid tissues of humans, mice, and rats that lack the transmembrane domain coded by exon 3 of the CTLA-4 gene. These alternate transcripts were detected by RT-PCR in B cells and resting T cells of both the CD4 and the CD8 phenotype. Activation of human blood mononuclear cells with PHA or anti-CD3 + anti-CD28 monoclonal antibodies appears to effect a decrease in the amount of the alternative transcript relative to the full-length transcript. Recombinant sCTLA-4 is a B7-binding protein and has immunomodulatory effects as measured by inhibition of the mixed leukocyte response. Human serum contains immunoreactive material consistent with a native soluble form of CTLA-4.

Adenovirus-mediated gene therapy for mucopolysaccharidosis VII: involvement of cross-correction in wide-spread distribution of the gene products and long-term effects of CTLA-4Ig coexpression

Recombinant adenoviruses expressing human beta-glucuronidase (AxCAhGUS) and CTLA-4Ig (AxCACTLA-4Ig) were generated and therapeutic efficacy was investigated using a murine model of mucopolysaccharidosis type VII (MPSVII). Seven days after the intravenous administration of AxCAhGUS, high levels of beta-glucuronidase (GUSB) activity were observed in the liver, spleen, heart, lung, kidney, and serum, while viral DNA was predominantly detected in the liver. To investigate the contribution of in vivo cross-correction of GUSB between the liver and other organs, we injected the serum obtained from the transduced mice into untreated MPSVII mice. Similar distributions of GUSB activity were observed in the serum-injected mice, suggesting that GUSB activities detected in the extrahepatic organs were due to the cross-correction rather than the direct gene transduction. This result also suggested that maintaining high levels of GUSB in the systemic circulation was essential for the effective treatment of MPSVII. To achieve this, we injected AxCAhGUS and AxCACTLA-4Ig into MPSVII mice. Serum GUSB activity was sustained at high levels for more than 200 days and morphological normalization of the liver and spleen was observed for a year. This suggests that long-term therapeutic efficacy in visceral organs of MPSVII is achievable by coexpression of CTLA-4Ig through an in vivo cross-correction pathway.

Tolerance and hematopoietic stem cell transplantation 50 years after Burnet's theory

OBJECTIVE

In 1949, the original formulation of Burnet's theory on the mechanisms responsible for the capacity of the immune system to discriminate between foreign antigens (i.e., the "non-self") and the cells of its own body (i.e., the "self") was published. Since then, further refinements and reconsiderations of the basic concepts underlying the achievement of a state of tolerance toward a certain antigen have been reported. Here, we attempt to analyze critically new clinical and experimental strategies aimed at inducing alloantigen-specific unresponsiveness.

DATA SOURCES

The data discussed in this review are drawn from articles and abstracts published in journals covered by the Science Citation Index and Medline.

STATE OF THE ART

Induction of tolerance toward alloantigens still remains one of the most elusive goals of clinical immunology. Until now, nonspecific immunosuppressive drugs have been used to successfully perform both solid organ and hematopoietic stem cell transplantation. However, using this approach, patients given an allograft are exposed to the threat of infections, tumors, and other side effects. Moreover, in solid organ transplant recipients, permanent tolerance toward the graft's alloantigens is never achieved. Recently, considerable progress has been made in expanding our knowledge of transplant tolerance. The traditional model of central tolerance, derived from Burnet's concept, has been complemented by knowledge of mechanisms of peripheral tolerance.

CONCLUSIONS

New experimental and therapeutic trials based on the blockade of costimulatory molecules, as well as on generation and infusion of either regulatory or nonimmunogenic cells, have been recently proposed for inducing alloantigen-specific tolerance.The achievements obtained in understanding the mechanisms of unresponsiveness toward non-self antigens are fundamental prerequisites for successful allogeneic transplants, and they could open a new exciting era of specific, immunosuppressive therapies.

Activation of alloreactive T cells by allogeneic nonprofessional antigen-presenting cells and interleukin-12 from bystander autologous professional antigen-presenting cells

BACKGROUND

After solid organ transplantation most alloantigens are presented to the recipient's immune system by normal tissue cells, which can be considered to act as nonprofessional antigen-presenting cells (APC). It is well accepted that such nonprofessional APC fail to activate recipient resting T cells due to their inability to deliver costimulatory activity. In our study, we tested a hypothesis that such costimulatory activity may be provided by "bystander" recipient professional APC.

METHODS

We set up mixed lymphocyte cultures (MLC) of purified T cell responders and T cell stimulator cells, the latter as nonprofessional APC carrying allogeneic MHC class I and II, and tested if responder-type autologous APC could facilitate responder T cell proliferation. In this assay also the effects of anti-CD28 antibody and interleukin- (IL) 1beta, IL-6, or IL-12 mediated costimulation on responder T cell proliferation and IL-2 production were investigated.

RESULTS

Autologous APC, i.e., monocytes, were found to facilitate the proliferative response of resting T cells stimulated by allogeneic nonprofessional APC. IL-12 was identified as the most important costimulatory factor for induction of proliferation. IL-1beta enhanced IL-2 production and proliferation of allostimulated resting T cells but its presence was not essential. Although CD28 triggering alone was ineffective, this costimulatory pathway enhanced IL-2 production and proliferation when combined with IL-12 or IL-1beta.

CONCLUSIONS

We conclude that costimulatory activity for activation of resting human T cells by nonprofessional donor APC can be delivered through activity of bystander recipient-type autologous APC. This mechanism of allostimulation may contribute to the induction and perpetuation of alloreactivity "in vivo" in a time frame when intragraft professional donor-type APC have been replaced with professional recipient-type APC.

Pancreatic islet xenograft tolerance after short-term costimulation blockade is associated with increased CD4+ T cell apoptosis but not immune deviation

BACKGROUND

Our purpose was to determine if short-term inhibition of the CD40/CD40L and CD28/B7 costimulatory pathways was capable of inducing specific unresponsiveness to pancreatic islet xenografts and to ascertain the mechanism of tolerance induction.

METHODS

Diabetic B6AF1 mice were transplanted with Wistar or DA rat islets and were treated short term with CTLA4-Fc and anti-CD40L mAb (MR1).

RESULTS

Coadministration of CTLA4-Fc with MR1, resulted in indefinite rat islet xenograft survival in mice. Tolerance was species but not strain specific as long-term surviving recipients rejected third party BALB/c islet allografts but accepted a second rat islet xenograft from the same or different donor strain. Tolerance induction was associated with a large leukocyte infiltrate that did not exhibit features of immune deviation as intragraft T cell-specific cytokine gene expression was globally reduced. In particular, interleukin-4 gene expression was markedly suppressed. There was a complete inhibition of anti-donor IgG, IgG1, and IgM antibody in the serum of CTLA4-Fc/MR1- treated animals. Tolerance induction was associated with increased CD4+ T cell apoptosis as there was an increased proportion of annexin-V staining and Fas expressing CD4+ T cells and a decrease in CD4+ T cell Bcl-2 expression in the grafts and draining lymph nodes of CTLA4-Fc/MR1-treated recipients.

CONCLUSION

Combined costimulatory blockade was capable of producing tolerance to pancreatic islet xenografts. The induction of this tolerant state was associated with increased T cell apoptosis, whereas the maintenance phase of tolerance was associated with the accumulation of a large number of inactive lymphocytes within the graft.

Blockade of CD28-B7, but not CD40-CD154, prevents costimulation of allogeneic porcine and xenogeneic human anti-porcine T cell responses

Despite increasing use of swine in transplantation research, the ability to block costimulation of allogeneic T cell responses has not been demonstrated in swine, and the effects of costimulatory blockade on xenogeneic human anti-porcine T cell responses are also not clear. We have compared the in vitro effects of anti-human CD154 mAb and human CTLA4IgG4 on allogeneic pig T cell responses and xenogeneic human anti-pig T cell responses. Both anti-CD154 mAb and CTLA4IgG4 cross-reacted on pig cells. While anti-CD154 mAb and CTLA4IgG4 both inhibited the primary allogeneic pig MLRs, CTLA4IgG4 (7.88 microg/ml) was considerably more inhibitory than anti-CD154 mAb (100 microg/ml) at optimal doses. Anti-CD154 mAb inhibited the production of IFN-gamma by 75%, but did not inhibit IL-10 production, while CTLA4IgG4 completely inhibited the production of both IFN-gamma and IL-10. In secondary allogeneic pig MLRs, CTLA4IgG4, but not anti-CD154 mAb, induced Ag-specific T cell anergy. CTLAIgG4 completely blocked the indirect pathway of allorecognition, while anti-CD154 mAb blocked the indirect response by approximately 50%. The generation of porcine CTLs was inhibited by CTLA4IgG4, but not by anti-CD154 mAb. Human anti-porcine xenogeneic MLRs were blocked by CTLA4IgG4, but only minimally by anti-CD154 mAb. Finally, CTLA4IgG4 prevented secondary xenogeneic human anti-porcine T cell responses. These data indicate that blockade of the B7-CD28 pathway was more effective than blockade of the CD40-CD154 pathway in inhibiting allogeneic pig T cell responses and xenogeneic human anti-pig T cell responses in vitro. These findings have implications for inhibiting cell-mediated immune responses in pig-to-human xenotransplantation.

Blocking the CD28-B7 T-cell costimulatory pathway abrogates the development of obliterative bronchiolitis in a murine heterotopic airway model

BACKGROUND

CTLA4IgG that binds to B7 effectively inhibits the signaling of CD28/B7 pathway and induces antigen-specific T-cell unresponsiveness in vitro and in vivo. We examined whether the development of obliterative bronchiolitis in a murine heterotopic airway transplantation model is T cell dependent and whether CTLA4IgG abrogates the development of obliterative bronchiolitis.

METHODS

Tracheae with main bronchi from C3H/He (H2k), BALB/C (H2d), or C57BL/6 (H2b) mice were transplanted heterotopically into subcutaneous pockets on the backs of BALB/C or BALB/C nu/nu mice on day 0. Recipient mice were untreated or intraperitoneally treated with either CTLA4IgG or human IgG with different time and dose schedules.

RESULTS

The development of obliterative bronchiolitis, which leads to luminal obliteration by fibrous tissue in a murine heterotopic airway transplantation model, was T cell dependent and the development of obliterative bronchiolitis was significantly abrogated by the CTLA4IgG treatment. However, the normal ciliated columnar respiratory epithelial cells in allografts were lost and replaced by flattened attenuated epithelial cells even after the CTLA4IgG treatment. We further demonstrated that CTLA4IgG treatment did not result in the induction of donor-specific unresponsiveness.

CONCLUSIONS

We demonstrated that the development of obliterative bronchiolitis in a murine heterotopic airway model involves both CD28/B7-dependent and -independent processes. The luminal obliteration by fibrous tissue is clearly CD28/B7 dependent and can be inhibited by CTLA4IgG. The luminal obliteration of allografted trachea by fibrous tissues and the loss of ciliated columnar respiratory epithelial cells represent distinct disease processes.

Induction of T cell anergy in the absence of CTLA-4/B7 interaction

Immunologic tolerance in T lymphocytes is maintained through both thymic and peripheral contributions. One peripheral tolerance mechanism is the induction of T cell anergy, a form of nonresponsiveness resulting from incomplete T cell activation, such as stimulation through the TCR in the absence of costimulation. Recent reports have suggested that engagement of the inhibitory receptor CTLA-4 by its B7 ligand is critical for the initiation of anergy. We tested the importance of CTLA-4 in anergy induction in primary T cells with an in vitro anergy system. Using both CTLA-4/B7-blocking agents and CTLA-4-deficient T cells, we found that T cell anergy can be established in the absence of CTLA-4 expression and/or function. Even in the absence of CTLA-4 signal transduction, T cells activated solely through TCR ligation lose the ability to proliferate as a result of autocrine IL-2 production upon subsequent receptor engagement. Thus, CTLA-4 signaling is not required for the development of T cell anergy.

Cytokine upregulation of the antigen presenting function of acute myeloid leukemia cells

Acute myeloid leukemia (AML) cells are malignant counterparts of normal myeloid pathway progenitors. Myeloid progenitors differentiate into professional antigen presenting cells (APC) under the essential influence of GM-CSF along with additional cytokines. Twelve cases of human AML were tested for ability to be differentiated toward a professional APC phenotype in short-term culture with addition of GM-CSF and the following recombinant proteins: TNFalpha, IL-4, CD40 ligand, Flt3 ligand and SCF. Significant upregulation of CD80 (B7-1) and enhancement of alloantigen presentation was seen with the addition of GM-CSF and TNFalpha alone or with additional cytokines. The combination of GM-CSF and TNFalpha, either alone or in combination with an additional cytokine, resulted in enhancing alloantigen presentation by at least two-fold over the media control group in 10/12 patients studied, and resulted in CD80 expression of greater than 15% in 11/12 patients studied. In AML cultures with GM-CSF and TNFalpha, coexpression of CD80 and either CD34 or an aberrant surface marker (CD56) was seen. In one case, sorted CD80, cells retained a characteristic cytogenetic marker and CD34 expression, proving their derivation from an AML precursor. These studies verify other reports of in vitro differentiation of human AML precursors into enhanced APC, suggesting that this phenomenon could be utilized for immunotherapy strategies aimed at enhancing presentation of leukemia antigens to T cells.

Cytotoxic T lymphocyte antigen 4-immunoglobulin fusion protein combined with methotrexate/cyclosporine as graft-versus-host disease prevention in a canine dog leukocyte antigen-nonidentical marrow transplant model

BACKGROUND

We studied whether blocking of the T cell costimulatory signal from B7-->CD28 by cytotoxic T lymphocyte antigen 4-immunoglobulin fusion protein would, either by itself or when added to methotrexate/cyclosporine, result in improved graft-versus-host disease prevention after dog leukocyte antigen nonidentical canine hematopoietic stem cell transplantation after 920 cGy total body irradiation.

RESULTS AND CONCLUSIONS

Survivals of cytotoxic T lymphocyte antigen 4-immunoglobulin fusion protein-treated dogs were only slightly prolonged over controls. It appeared that the addition of cytotoxic T lymphocyte antigen 4-immunoglobulin fusion protein failed to induce graft-host tolerance in this model beyond that achieved with methotrexate/cyclosporine alone.

Naive CD8+ T cells do not require costimulation for proliferation and differentiation into cytotoxic effector cells

Most current models of T cell activation postulate a requirement for two distinct signals. One signal is delivered through the TCR by engagement with peptide/MHC complexes, and the second is delivered by interaction between costimulatory molecules such as CD28 and its ligands CD80 and CD86. Soluble peptide/MHC tetramers provide an opportunity to test whether naive CD8+ T cells can be activated via the signal generated through the TCR-alphabeta in the absence of any potential costimulatory molecules. Using T cells from two different TCR transgenic mice in vitro, we find that TCR engagement by peptide/MHC tetramers is sufficient for the activation of naive CD8+ T cells. Furthermore, these T cells proliferate, produce cytokines, and differentiate into cytolytic effectors. Under the conditions where anti-CD28 is able to enhance proliferation of normal B6 CD4+, CD8+, and TCR transgenic CD8+ T cells with anti-CD3, we see no effect of anti-CD28 on proliferation induced by tetramers. The results of this experiment argue that given a strong signal delivered through the TCR by an authentic ligand, no costimulation is required.

Analysis of the requirements for the induction of CD4+ T cell alloantigen hyporesponsiveness by ex vivo anti-CD40 ligand antibody

A major goal of the transplant field is to selectively tolerize only those donor T cells recognizing host alloantigen and mediating graft-vs-host disease (GVHD). Recently, we described an ex vivo approach in which the blockade of the CD40 ligand (CD40L):CD40 costimulatory pathway in bulk MLR cultures induces donor CD4+ T cells to become specifically tolerant to MHC class II-disparate alloantigenic-bearing stimulators, resulting in a profound reduction in GVHD generation in vivo. In studies presented in this work, we investigated the ex vivo requirements for tolerance induction. We found that CD4+ T cells become profoundly more hyporesponsive to alloantigen restimulation with prolonged culture duration such that 7 to 10 but not 4 days is needed to achieve maximum alloantigen hyporesponsiveness as assessed in secondary MLR cultures and GVHD generation. By day 7, both primed and tolerized cells had substantially increased blastogenesis and CD25 expression. Primed but not tolerized cells substantially down-regulated L-selectin expression, indicating that the tolerized cells do not become fully Ag experienced. Both Th1 and Th2 cytokine production is severely impaired by CD40L:CD40 blockade. Analysis of culture supernatants and results from IL-4 and IL-10 knockout mice indicated that GVHD prevention was not mediated by a skewing toward a Th2 phenotype. The addition of IL-4 to the cultures as a survival factor precluded the induction of tolerance in the anti-CD40L-cultured cells. These data provide further impetus for the ex vivo use of anti-CD40L mAb to block GVHD generation.

Development of human T-cell leukemia virus type 1-transformed tumors in rats following suppression of T-cell immunity by CD80 and CD86 blockade

Host immunity influences clinical manifestations of human T-cell leukemia virus type 1 (HTLV-1) infection. In this study, we demonstrated that HTLV-1-transformed tumors could develop in immunocompetent rats by blocking a costimulatory signal for T-cell immune responses. Four-week-old WKA/HKm rats were treated with monoclonal antibodies (MAbs) to CD80 and CD86 and subcutaneously inoculated with syngeneic HTLV-1-infected TARS-1 cells. During MAb treatment for 14 days, TARS-1 inoculation resulted in the development of solid tumors at the site of inoculation, which metastasized to the lungs. In contrast, rats not treated with MAbs promptly rejected tumor cells. Splenic T cells from MAb-treated rats indicated impairment of proliferative and cytotoxic T-lymphocyte responses against TARS-1 in vitro compared to untreated rats. However, tumors grown in MAb-treated rats regressed following withdrawal of MAb therapy. Recovery of TARS-1-specific T-cell immune responses was associated with tumor regression in these rats. Our results suggest that HTLV-1-specific cell-mediated immunity plays a critical role in immunosurveillance against HTLV-1-transformed tumor development in vivo.

Cultures derived from peripheral blood CD34+ progenitor cells of head and neck cancer patients and from cord blood are functionally different

Patients with head and neck squamous cell carcinoma (HNSCC) have profound immune defects mediated, in part, by an increased number of immune suppressive CD34+ progenitor cells in their peripheral blood and tumor. One means of overcoming this immune suppression is to stimulate the CD34+ cells to differentiate into more mature, nonsuppressive progeny such as dendritic cells or monocytes. This study determined that CD34+ cells from the peripheral blood of HNSCC patients have the same potential to differentiate into dendritic cells as do human umbilical cord blood CD34+ cells following 12-16 days of culture with a cytokine cocktail. When compared functionally, the cultures that developed from CD34+ cells of cord blood were able to induce an allostimulatory response in naive T-cells, while the cultures that developed from patient CD34+ cells lacked allostimulatory ability. Both cultures expressed class II MHC (HLA-DR), but the proportion of cells expressing the costimulatory molecules CD80 and CD86 was significantly less in cultures that developed from HNSCC-patient CD34+ cells. Therefore, although the CD34+ cells from the peripheral blood of HNSCC patients can differentiate into dendritic cells, their allostimulatory capabilities are impaired, raising the question of their potential effectiveness in stimulating antitumor immune responses.

Antigen presentation by parenchymal cells: a route to peripheral tolerance?

T-cell activation and the development of efficient immune responses requires the delivery, by the antigen-presenting cell, of two distinct signals. The first results from the engagement of the TCR:CD3:CD4 complex, and the second from the interaction of CD28 with the B7 family of co-stimulatory molecules. In this context, the physiological significance and the functional consequences of antigen presentation by B7-deficient parenchymal cells, which express MHC class II molecules as a result of inflammation, remains a matter of debate. In this paper we have attempted to critically review the often conflicting reports on the functional effects of antigen presentation by epithelial and endothelial cells to T cells, both in vitro and in vivo. Our own findings are summarised in a model which is consistent with the suggestion of an important role for antigen presentation by parenchymal cells in the induction and the maintenance of peripheral tolerance.

Investigational treatments in rheumatoid arthritis

The active search for new treatment modalities of established rheumatoid arthritis have created a dynamic period for rheumatology. Both promising pharmaceutical products and targeted interventions with products of the biotechnology industry are being developed. Leflunomide and the selective blockade of the cytokine tumour necrosis factor (TNF) have recently been registered in several countries and others will follow. Like all new therapeutic strategies much remains to be learned about the optimal use of these therapies and their possible limitations. The success of these interventions have shown that a complex disease such as rheumatoid arthritis that is refractory to conventional treatment can be modulated by new therapeutic strategies. This experience has also resulted in further searches for new drugs that influence those pathogenetic pathways affected by the interventions found to be effective.

Anti-CD154 or CTLA4Ig obviates the need for thymic irradiation in a non-myeloablative conditioning regimen for the induction of mixed hematopoietic chimerism and tolerance

BACKGROUND

Thymic irradiation (TI) or repeated administration of T cell-depleting monoclonal antibodies (TCD mAbs) is required in a previously described non-myeloablative regimen allowing allogeneic marrow engraftment with stable mixed chimerism and tolerance. As both treatments might be associated with toxicity in the clinical setting, we evaluated whether T-cell costimulatory blockade could be used to replace them.

METHODS

C57BL/6 mice received depleting anti-CD4 and anti-CD8 mAbs on day -5, 3 Gy whole body irradiation (day 0), and 15x10(6) fully MHC-mismatched, B10.A bone marrow cells. In addition, hosts were injected with an anti-CD154 mAb (day 0) and/or CTLA4Ig (day +2). Chimerism in peripheral blood was followed by flow cytometric (FACS) analysis, and tolerance was assessed by skin grafting, and also by mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML) assays. The frequency of certain Vbeta families was determined by FACS to assess deletion of donor-reactive T cells.

RESULTS

Chimerism was transient and tolerance was not present in animals receiving TCD mAbs on day -5 without costimulatory blockade. The addition of anti-CD154 and CTLA4Ig, alone or in combination, reliably permitted induction of high levels of stable (>6 months) multi-lineage chimerism, with specific tolerance to skin grafts and donor antigens by MLR and CML assays. Long-term chimeras showed deletion of donor-reactive CD4+ peripheral blood lymphocytes, splenocytes, and mature thymocytes. Administration of TCD mAbs only 1 day before bone marrow transplantation plus anti-CD154 also allowed induction of permanent chimerism and tolerance.

CONCLUSIONS

One injection of anti-CD154 or CTLA4Ig overcomes the need for TI or prolonged host TCD in a preclinical model for the induction of mixed chimerism and deletional tolerance and thus further decreases the toxicity of this protocol. Achievement of tolerance with conditioning given over 24 hr suggests applicability to cadaveric organ transplantation.

Expression and characterization of glycolipid-anchored B7-1 (CD80) from baculovirus-infected insect cells: protein transfer onto tumor cells

Tumor cells can be modified to express immunostimulatory molecules such as B7-1 by protein transfer using purified glycosylphosphatidylinositol-anchored B7-1 (GPI-B7-1). In this study recombinant baculovirus encoding GPI-B7-1 (vBacB7-1(GPI)) was established to obtain large quantities of purified GPI-B7-1 to modify tumor cells by protein transfer. vBacB7-1(GPI)-infected insect cells showed high-level cell surface expression of GPI-B7-1 that was susceptible to PIPLC treatment. GPI-B7-1 expressed in insect cells (Bac-GPI-B7-1) mediated T cell proliferation, indicating that the GPI-B7-1 retains costimulatory activity. Moreover, Bac-GPI-B7-1 was completely solubilized in Triton X-100 at 4 degrees C compared to 22% solubilization of GPI-B7-1 expressed in CHOK1 cells, suggesting that GPI-anchored proteins expressed in insect cells may not be clustered into the detergent-insoluble fraction. SDS-PAGE analysis of Bac-GPI-B7-1 showed faster mobility (45 kDa) compared to GPI-B7-1 from CHOK1 (68 kDa) and this difference may be due to a difference in glycosylation. Cell binding assays showed that immunoaffinity-purified Bac-GPI-B7-1 retained its functional ability to bind CD28(+) cells. Moreover, when human tumor cells were incubated with this functionally active purified GPI-B7-1, an efficient transfer of B7-1 onto tumor cells was observed. These results demonstrate that GPI-B7-1 can be expressed in insect cells in a functionally active form and can be used to modify tumor cells for immunotherapeutic applications.

The role of T cell costimulation by CD80 in the initiation and maintenance of the immune response to human leukemia

Most human myeloid leukemias express both class I and class II HLA and it has been postulated that leukemia-associated peptides are presented by those molecules. It is possible, however, that leukemia cells escape the immune surveillance by lacking expression of "costimulatory" molecules required for activating the immune response. Human erythroleukemia line (HEL) has been the subject of previous detailed studies demonstrating surface expression of bona fide HLA molecules but inability to stimulate allogeneic response of proliferative or cytolytic T cells. We found that an HLA-DR+ subclone (HEL-DR+) expresses LFA-1, LFA-3, ICAM-1, ICAM-3, but neither CD80 nor CD86 on the surface. Transfection of CD80 cDNA into HEL-DR+ cells induced the allogeneic response of purified T cells from both cord blood and peripheral blood of adult donors, demonstrating that CD80 expression could lead to accessory cell-independent activation of naive T cells. Priming allogeneic peripheral blood T cells by HEL-DR+/CD80+ also lead to generation of cytotoxic T lymphocytes that lysed both HEL-DR+/CD80+ and wild type HEL-DR+ equally well, confirming CD80 expression is required only in the CTL induction phase but not in the CTL effector phase. We established and maintained alloproliferative T cell clones from adult blood by stimulation with the HEL-DR+/CD80+ line. The clones could respond not only to HEL-DR+/CD80+ line but also to the HEL-DR+ line; however, the proliferative response to HEL-DR+/CD80+ was amplified and sustained compared to the short-lived response to wild type HEL-DR+ cells. Therefore, expression of CD80 by HEL-DR+ cells was determinant both to initiate and sustain the T cell response. These experiments support the hypothesis that lack of expression of "costimulatory" molecules for T cells contributes to leukemia escape from immune surveillance, and provide preliminary data for the use of CD80 transfection in the immunotherapy of human leukemia.

Intercellular adhesion molecule-1/leukocyte function associated antigen-1 blockade inhibits alloantigen specific human T cell effector functions without inducing anergy

BACKGROUND

Intercellular adhesion molecule (ICAM-1) is important in leukocyte adhesion-dependent events and some data suggest that ICAM-1 provides T cell costimulation. We anlayzed the role of the ICAM-1 and leukocyte function associated antigen-1 (LFA-1) interaction in human T cell alloreactivity in vitro.

METHODS

Allo-antigen-induced T cell proliferation and cytotoxic T lymphocyte lytic activity were assessed by mixed lymphocyte reaction assay and 51 Chromium release assay, respectively. Immunostaining and flow cytometry were used to assess the expression of receptors on activated T cells.

RESULTS

Alloantigen-induced T cell proliferation and cytotoxic T lymphocyte activity were markedly inhibited by antibodies to ICAM-1 and LFA-1. These antibodies had to be present at the time of initial T cell receptor/antigen engagement to inhibit proliferation. Neither IL-2 nor IL-4 were involved in the observed inhibition by antibodies. Inhibition was not associated with altered cell surface expression of receptors such as CD3, CD4, ICAM-1, LFA-1, CD25, and HLA-DR however, these antibodies did impede the ability of generation of functionally active T cells. Interestingly, these antibodies inhibited soluble, but not immobilized OKT3-induced proliferation of peripheral blood leukocytes. Antibody-mediated inhibition of proliferation failed to impair the ability of T cells to subsequently proliferate in response to stimulation by the original or third party alloantigen or mobilize [Ca++]i in response to CD3 or LFA-1 receptor ligation.

CONCLUSIONS

These data demonstrate that blockade of ICAM-1/LFA-1 binding at the time of allorecognition potently blocks initial T cell effector functions that could be due to lack of effective T cell/APC engagement.

Inhibition of CD28 Expression by Oligonucleotide Decoys to the Regulatory Element in Exon 1 of the CD28 Gene

Ligation of CD28 provides a costimulatory signal essential for Ag-mediated T cell activation via the TCR. Previously we demonstrated that inhibition of human and murine CD28 expression by a guanosine (G)-rich oligonucleotide (ODN), GR1, led to immunosuppression in vitro and in vivo. The bioactivity of GR1 was dependent on a G-rich DNA sequence motif consisting of two G tetrads separated by four nucleotides, (G4N4G4). We have shown recently that a G-rich region, designated CD28GR, in exon 1 of the CD28 gene is such a motif and is a positive regulatory element that binds the transcription factors Sp1 and EGR-1. Here we showed that the bioactivity of GR1 and the related GR2 correlated with the sequence-specific formation of distinct nuclear protein complexes and a high degree of ODN secondary structure. In addition, these ODN blocked transcription factor binding to CD28GR (also in a sequence-specific manner) and prevented CD28GR from driving transcription of a reporter gene. Interestingly, GR1 potently inhibited CD28, but not the expression of other Sp1- and EGR-1-regulated genes, an effect associated with lower Sp1 protein binding affinity of GR1 and GR2 compared with that of canonical Sp1 sites. These data show that DNA sequences that contain the G-rich sequence motif, G4N4G4, such as GR1 and GR2, can functionally mimic the regulatory protein binding ability of CD28GR. Thus, GR1 and GR2 act as molecular decoys to selectively interfere with transcriptional regulation of the CD28 gene.

Refolding and characterization of recombinant human soluble CTLA-4 expressed in Escherichia coli

CD28 and CTLA-4 are homologous cell surface proteins expressed by T cells. CD28 is constitutively expressed by most T cells, whereas CTLA-4 is expressed by activated T cells. Both proteins are ligands for the costimulatory molecules CD80 and CD86 expressed by activated B cells, macrophages, and dendritic cells. A fusion protein comprising the CTLA-4 extracellular domain joined to a human immunoglobulin heavy chain constant region (CTLA4Ig) binds CD80 and CD-86 with high affinity and inhibits CD80/CD86-dependent immune responses in vitro and in vivo. Attempts at producing the CTLA-4 extracellular domain as an unfused protein have met with limited success. Here we describe the expression and purification of the CTLA-4 extracellular domain as a nonfused protein in Escherichia coli. The 12.5-kDa CTLA-4 extracellular domain was insoluble when expressed in E. coli and required denaturation, reduction, and refolding steps to become soluble and assume its proper conformation. The protein refolded into a mixture of monomers, disulfide-linked dimers, and higher order disulfide-linked aggregates. sCTLA-4 dimers were the predominant refold form when air was used as the oxidizing agent during the refold procedure. Purified sCTLA-4 dimers were 10- to 50-fold more potent than sCTLA-4 monomers at inhibiting T cell activation using a CD80-dependent in vitro bioassay.

Human Fibroblasts Transduced with CD80 or CD86 Efficiently trans-Costimulate CD4+ and CD8+ T Lymphocytes in HLA-Restricted Reactions: Implications for Immune Augmentation Cancer Therapy and Autoimmunity

Augmenting immunogenicity by genetically modifying tumor cells to express costimulatory molecules has proven to be a promising therapeutic strategy in murine tumor models and is currently under investigation in human clinical trials for metastatic cancer. However, there are significant technical and logistic problems associated with implementing strategies requiring direct gene modification of primary tumor cells. In an effort to circumvent these problems, we are developing a strategy in which the costimulatory signal required for tumor-specific T lymphocyte activation is provided by a genetically modified human fibroblast (trans-costimulation). We have evaluated the efficiency of CD80- and CD86-mediated trans-costimulation in the activation of human CD8+ and CD4+ T lymphocytes in MHC class I- and class II-restricted lymphoproliferation reactions. Our studies demonstrate that the efficiency of CD80- or CD86-mediated trans-costimulation of purified human CD8+ and CD4+ T lymphocytes is comparable to cis-costimulation under defined conditions. Moreover, a dose-response relationship consistent with the predicted two-hit kinetics of the reaction was evident in trans-costimulation reactions in which the ratio of target cells expressing either signal 1 or signal 2 was varied incrementally from 1:10 to 10:1. Importantly, the level of cell-surface CD86 required for trans-costimulation is equivalent to that constitutively expressed by human peripheral blood monocytes. These results may have significant implications for the clinical implementation of this type of cancer immunotherapy and also raise questions about the possibility of trans-costimulating autoreactive T lymphocytes in vivo.

HgCl(2)-induced human lymphocyte activation in vitro: a superantigenic mechanism?

Mercuric chloride (HgCl(2)) has been proposed to be a mitogen for human blood lymphocytes in vitro. In our previous study, we demonstrated that HgCl(2) preferentially stimulates the CD4+ T cell subset to blast transformation and DNA synthesis and that the reaction is dependent on CD14+ accessory cells. In order to characterise the responding cells further and to elucidate the mechanism of T cell activation, the T cell receptor (TCR) Vbeta chain expression of the blast-transformed cells was analysed by monoclonal antibodies and flow cytometry. The 22 TCR-Vbeta-specific antibodies used were found to react with 55-80% of the naive CD4+ and CD8+ blood T cells from the different donors. Six to 18% of the lymphocytes, mainly CD4+ T cells, were blast transformed after addition of HgCl(2). The distribution of the lymphoblasts carrying certain TCR Vbeta chains were skewed, and 15-40% expressed the TCR Vbeta2 chain. Furthermore, if cells were pretreated for 5 days with HgCl(2), whereafter recombinant interleukin-2 in fresh medium was added, the TCR Vbeta7+ T cell subset was also stimulated to blast transformation. The superantigen staphyloccal enterotoxin B, as a control, induced blast transformation in 10-26% of the lymphocytes, mainly CD4+ T cells, which were, as expected, positive for Vbeta3, Vbeta12, Vbeta14 or Vbeta17. We conclude that HgCl(2) has characteristics of a superantigen, activating the human lymphocytes in a Vbeta-chain-selective manner in vitro.

Gene transfer of the Co-stimulatory molecules B7-1 and B7-2 enhances the immunogenicity of human renal cell carcinoma to a different extent

Stimulation of a specific antitumour immune response with recruitment and induction of T-cell effector functions represents an attractive concept in human cancer therapy. Different cytokines and the B7 co-stimulatory molecules are both able to provide proliferation and activation signals for T cells. In the present study, we first demonstrated the absence of both B7-1 and B7-2 expression in human renal cell carcinoma (RCC) cell lines. The lack of B7 expression was associated with a low or absent proliferative response of allogeneic and autologous T cells upon stimulation with tumour cells. In order to investigate the role of B7-1 and B7-2, the human RCC cell line, MZ1257RC, which expresses normal levels of adhesion molecules and major histocompatibility complex (MHC) class I surface antigens, was transfected with B7-1 and B7-2 expression vectors, respectively. The B7-1- and B7-2-transduced MZ1257RC cells were potent stimulators of allogeneic and autologous T-cell proliferation. B7-2 transfectants were approximately two- to threefold more effective in the induction of primary T-cell activation than B7-1-transduced cells. Interleukin (IL)-12 synergized with the B7/CD28 interaction to enhance allogeneic T-cell proliferation, independently of the B7 molecule transduced. In contrast, IL-2 only co-operatively increased T-cell activation in the presence of B7-2. Our results suggest the following: first, that co-stimulatory molecules are required for efficient T-cell responses directed against RCC; second, that B7-2 appears to be a more potent stimulator of tumour immunity as compared to B7-1; and third, that B7 molecules selectively co-operate with different T-cell stimulatory cytokines. The different activity of B7-1 and B7-2 molecules on the immunogenicity of RCC will have implications for the development and optimization of RCC-specific cancer vaccines.

Immunohistochemical localization of B7 costimulating molecules and major histocompatibility complex class II antigen in pulmonary sarcoidosis

BACKGROUND

Alveolar macrophages (AM) of sarcoidosis have an enhanced capacity to mediate antigen-induced T lymphocyte proliferation. To induce an effective immune response, antigen-presenting cells have to not only present antigenic peptide with MHC molecules to T lymphocytes, but also express B7 costimulating molecules.

OBJECTIVE

The purpose of this study was to investigate the expression of B7 and MHC molecules in lung tissues from patients with sarcoidosis.

METHODS

We performed immunohistochemistry for B7-1, B7-2 and MHC class II antigens using transbronchial lung biopsy specimens obtained from patients with sarcoidosis and normal lung parenchyma obtained by lobectomy for solitary pulmonary nodule as controls.

RESULTS

B7-1, B7-2 and MHC class II antigen were expressed in epithelioid cells in granulomas in 14 (93.3%), 2 (13.3%) and 9 (60.0%) of 15 patients with sarcoidosis, respectively. These were also expressed in AM in 14 (93. 3%), 5 (33.3%) and 12 (80.0%) of 15 patients with sarcoidosis, respectively. The positivity of B7-1 was significantly higher than that of B7-2 in both epithelioid cells and AM in sarcoidosis (p < 0. 01). Positive signals for B7-1, B7-2 and MHC class II antigen were also found in AM in 9 (90%), 8 (80%) and 8 (80%) of 15 of controls, respectively. However, the intensity of positive signals for B7-1, but not B7-2 or MHC class II antigen in AM was significantly increased in sarcoidosis compared to controls (p < 0.05).

CONCLUSIONS

These results suggested that epithelioid cells in granulomas and AM from patients with sarcoidosis had the capability to act as accessory cells and that the accessory function of these cells was shifted to B7-1 rather than B7-2 in sarcoidosis.

IL-2-Independent Activation and Proliferation in Human T Cells Induced by CD28

Although the role of CD28 in T cell costimulation is firmly established, the mechanisms by which it exerts its costimulatory actions are less clear. In many circumstances it is difficult to distinguish the effects of CD28 from subsequent actions of cytokines, such as IL-2, on T cell proliferation. Here, we report a model of CD28 costimulation using PMA plus the natural ligand CD80 that resulted in very limited stimulation of IL-2, as evidenced by both cytokine production and IL-2 promoter stimulation. Promoter assays revealed CD28-dependent effects on both NF-κB and AP-1, but not on NF-AT or the intact IL-2 promoter. In addition, T cell proliferation was completely resistant to the actions of the immunosuppressant cyclosporin A (CsA). Moreover T cell proliferation was unaffected by the addition of blocking Abs to both IL-2 and the IL-2 receptor, demonstrating that this form of costimulation by CD28 was independent of IL-2. We also investigated the effects of stimulating T cell blasts with CD80 alone and found that there was a limited requirement for IL-2 in this system. We conclude that CD28 costimulation can cause substantial T cell proliferation in the absence of IL-2, which is driven by a soluble factor independent of NF-AT transactivation.

Transplantation tolerance: the concept and its applicability

Recent advances have enabled researchers to induce tolerance in animal transplant models. Although it has been relatively easy to do so in rodents, it has been much more difficult to translate such strategies into primates. Understanding the cellular and molecular mechanisms of the alloimmune response has prompted the development of novel strategies that may obviate the need for immunosuppression in humans. Mechanisms of tolerance and promising new therapies, as well as the inherent difficulties in bringing them into clinical practice, are reviewed.

Blocking CD40 - CD154 and CD80/CD86 - CD28 interactions during primary allogeneic stimulation results in T cell anergy and high IL-10 production

Although CD28 triggering provides an important co-stimulatory signal to T cells, blocking the CD80/CD86 - CD28 interaction with CTLA-4lg fusion protein is not sufficient for tolerance induction in vivo or in vitro. According to more recent data, interruption of the CD40 - CD154 interaction might complement the effect of CTLA-4lg and induce graft acceptance. We studied the effects of a blocking anti-CD40 monoclonal antibody (mAb) and/or blocking anti-CD80/anti-CD86 mAb in cultures of human peripheral blood mononuclear cells (PBMC) stimulated with allogeneic PBMC. T cells activated by alloantigens in the presence of anti-CD80, anti-CD86 and anti-CD40 entered a state of alloantigen-specific non-responsiveness as evidenced upon restimulation by lack of proliferation, cytotoxic activity, and IL-2, IL-5 and IL-13 production. IFN-gamma production during restimulation was less than in the control cultures, while the production of IL-10 was enhanced. Addition of recombinant IL-2 during the restimulation rescued alloantigen-specific activity. We conclude that the simultaneous blocking of the CD40 - CD154 and CD80/CD86 - CD28 interaction during allogeneic T cell activation induces T cell anergy. Since anergic cells induced by this treatment still produce high levels of IL-10, the latter could contribute to modulation of antigen-presenting cell activity and to bystander suppression of residual reactive T cells.

The role of B7 costimulation in T-cell immunity

CD4+ T cells are considered to be the major controlling element of the adaptive immune response. They recognize foreign peptides by interaction of the T cell receptor (TCR) with peptide complexed to major histocompatibility complex (MHC) class II molecules on the surface of antigen presenting cells (APC). Once activated, CD4+ T cells orchestrate the various phases of the immune response. They are responsible for the production of numerous cytokines, which activate specific immune effector cell populations including B cells, eosinophils, mast cells and macrophages. Not surprisingly, the activation of CD4+ T cells needs to be tightly regulated and is subject to finely tuned control mechanisms. The requirement for a second or 'costimulatory' signal, in addition to the antigenic signal, provides a key element for the exquisite control of T cell activation. One of the major signalling pathways responsible for delivery of this costimulatory signal is induced by interaction of CD28 on T cells with B7 molecules found only on APC. The present review outlines our current understanding of the physiological role of B7 costimulatory signals in regulating CD4+ T cell responses.

Recently activated T cells are costimulation-dependent in vitro

While the prominent role of B7-mediated signaling in the activation of naive and resting T cells has been exhaustively demonstrated, it is unclear whether costimulation is required in the amplification of an initiated immune response. In this study we have developed a multistep culture system to investigate the costimulation requirements of recently activated alloreactive CD4(+) T cells and the outcome of allorecognition of B7-deficient, MHC class-II-expressing epithelial cells. The results show that following in vitro "priming" with allogeneic costimulation rich antigen presenting cells, T cells can be reactivated to proliferate only if B7-mediated costimulation is provided. Furthermore, recognition of antigen on B7-negative epithelial cells induced allospecific nonresponsiveness in the responder T cells. Finally, the nonresponsive state was not accompanied by IL-4 secretion and appeared to be reversible, since T cell reactivity could be restored by short-term culture in the presence of IL-2. These observations suggest that "primed" T cells remain B7-dependent in vitro and are susceptible to functional inactivation following costimulation-deficient antigen presentation.

Acceptance of skin allografts in pigs by portal venous injection of donor bone marrow cells

OBJECTIVE

To confirm in pigs whether a new method for organ allografts, originally established in mice by the authors, might be applicable to humans.

SUMMARY BACKGROUND DATA

The authors recently established a new method for organ allografts in mice that includes the injection of donor bone marrow cells (BMCs) using the portal vein (PV), followed by the administration of cyclosporin A (CsA) on days 2 and 5, and the intravenous injection of BMCs on day 5. In the present study, they modify this method (a single-day protocol) and apply it to pigs.

METHODS

Allogeneic BMCs of donor pigs were injected using the PV (a superior mesenteric vein). The skin grafting was carried out on the day of the PV injection. The recipient pigs received donor grafts, autologous grafts, and third-party grafts at the same time. In addition, an open wound was made as the epithelized control. Full-thickness skin grafts were harvested from the dorsal wall of the donors. CsA (10 mg/kg) was injected intramuscularly into recipient pigs on days 2 and 5 after the PV injection.

RESULTS

One hundred percent of skin grafts survived for >300 days when donor BMCs were injected using the PV (n = 6). However, the skin grafts of the three pigs that had received BMCs using the intravenous route were rejected within 3 to 4 weeks after transplantation. The third-party skin grafts showed necrotic changes on day 21 after transplantation.

CONCLUSIONS

One hundred percent of skin allografts can be obtained, even in pigs, by injecting donor BMCs using the PV, carrying out skin allografts, and administering CsA on days 2 and 5. This single-day protocol would be of great advantage for human organ transplantation.

Antigen presenting cells integrate opposing signals from CD4+ and CD8+ regulatory T lymphocytes to arbitrate the outcomes of immune responses

An individual's set of polymorphic HLA class II and I molecules is known to select the T cell repertoire in the thymus and to present processed antigenic peptides (pAg) to mature peripheral CD4+ T helper (Th) and CD8+ T cytotoxic (Th) cells in the periphery. This review highlights new studies which address how antigen presenting cells (APC) integrate the responses of cognate Th and T suppressor (Ts) cells to determine the outcome of immune responses. Together with other findings, these studies emphasize that understanding the mechanism of immune processes requires consideration of HLA molecules in the context of the peptides they bind, the antigen presenting cells (APC) that express them and the T lymphocytes that recognize them. The activities of lymphocyte and APC surface structures are becoming integrated into a physiological understanding of the cellular interactions between regulatory and effector T cells with APC.

Absence of co-stimulation and not the intensity of TCR signaling is critical for the induction of T cell unresponsiveness in vivo

Understanding the mechanisms of T cell activation versus induction of unresponsiveness is of critical importance for the rational modulation of immune responses. Efficient T cell activation is critical for vaccination purposes, while the inhibition of T cell responses is potentially important for the ablation of autoimmune diseases. Modulation of co-stimulation and changing TCR-mediated signaling using altered peptide ligands (APL) have been shown to result in clonal T cell unresponsiveness. This study compares for the first time the efficiency of the two approaches for the induction of CD8+ T cell unresponsiveness in vivo for naive and memory T cells using TCR-transgenic mice. The results demonstrate that inhibition of CD28-mediated co-stimulation in the presence of a strong TCR-mediated signal most efficiently induces T cell unresponsiveness. In contrast, APL that are capable of weak TCR triggering fail to interfere with T cell responsiveness in vivo and are ignored by T cells. Thus, short-term blockage of CD28 during antigenic stimulation rather than the use of APL is the most promising way to actively down-modulate responsiveness of naive CD8+ T cells at least in the particular TCR-transgenic mouse model analyzed in this study.

CD28/CTLA-4 and CD80/CD86 families: signaling and function

T cell stimulation in the absence of a second, costimulatory signal can lead to anergy or the induction of cell death. CD28 is a major T cell costimulatory receptor, the coengagement of which can prevent anergy and cell death. The CD28 receptor is a member of a complex family of polypeptides that includes at least two receptors and two ligands. Cytotoxic lymphocyte-associated molecule-4 (CTLA-4, CD152) is the second member of the CD28 receptor family. The ligands or counterreceptors for these two proteins are the B7 family members, CD80 (B7-1) and CD86 (B7-2). This article reviews the CD28/CTLA4 and CD80/CD86 families, and outlines the functional outcomes and biochemical signaling pathways recruited after CD28 ligation.

Interaction between B.7 and CD28 costimulatory molecules is essential for the activation of effector function mediating spontaneous tumour regression

The spontaneous regression of a rat histiocytoma, AK-5, is mediated by activated natural killer cells through antibody-dependent cellular cytotoxicity. In addition to the Fc-FcR interaction between the target and the effector cells demonstrated previously, we show the participation of costimulatory molecules B7 and CD28 in the efficient killing of the tumour cell. Blockade of the costimulatory interaction in vivo using anti-CD28 led to increased tumour growth and a suppressed cytokine response. Anti-CD28 antibody administration in vivo also diminished the cytotoxic potential of NK cells against AK-5 cells in vitro. Our studies also demonstrate the expression of B7.1 and B7.2 antigen on AK-5 tumour cells. The cytotoxic activity of natural killer cells was significantly inhibited when the effector/target cells were cultured in the presence of antibodies raised against B7.1, B7.2 and CD28. Administration of anti-CD28 in vivo also affected the efficiency of the formation of effector/target conjugates in vitro. Similarly, anti-CD28 injections affected expression of the adhesion molecules LFA 1 and ICAM 1 by splenocytes. Administration of anti-B7.1 and B7. 2 antibodies in AK-5 tumour-bearing animals showed a differential response. The cytotoxicity of natural killer cells was significantly inhibited after anti-B7.2 administration, suggesting the preferential participation of B7.2 molecules in vivo. These observations suggest an important role for B7-CD28 interaction in AK-5 tumour regression.

Persistent tolerance induced after portal venous injection of allogeneic cells plus cyclophosphamide treatment

The injection of allogeneic cells via the portal vein (p.v.) is known to reduce responses to donor-alloantigens. In the present study, we have obtained persistent tolerance across Mls and multiple minor histocompatibility complexes by p.v. preimmunization followed by the administration of cyclophosphamide (CY). A hundred percent survival of (BALB/c x DBA/2)F1 (CDF1) skin grafts for more than 200 days was observed when BALB/c mice were preimmunized with spleen cells of CDF1 (3 x 10(7)) via the p.v. and administered 300 mg/Kg CY 2 days after the p.v. injection. Comparable survival of the skin graft was observed when bone marrow cells instead of spleen cells were p.v. preimmunized. However, the survival rate was significantly decreased when LPS-stimulated blastic cells were p.v. preimmunized. Microchimerism has been observed in the liver, thymus, bone marrow and peripheral blood of recipients. V beta 6+ cells decreased in CD4+ cells of recipients of the p.v. preimmunization plus CY treatment. However, there was no difference in the decrease in V beta 6+ cells between recipients accepting the CDF1 skin grafts and recipients that had rejected the skin grafts. Furthermore, no intrathymic depletion of the V beta 6+ cells was observed. From these results, it is suggested that, rather than clonal deletion, other mechanisms such as clonal anergy or suppression may be involved in the induction of persistent tolerance after the p.v. preimmunization plus CY treatment.

Expression of B7-1, B7-2, and interleukin-12 in anti-Fas antibody-induced pulmonary fibrosis in mice

BACKGROUND

We have previously reported that the inhalation of anti-Fas antibody induced pulmonary fibrosis in mice. To induce an effective immune response, antigen-presenting cells have to not only present antigenic peptide with MHC molecules to T lymphocytes, but also express B7 costimulating molecules. The purpose of this study is to investigate whether B7 family costimulating molecules and interleukin-12 (IL-12), which primarily promote cellular immunity, are associated with anti-Fas antibody-induced pulmonary fibrosis.

METHODS

We examined the expression of B7-1, B7-2, and IL-12 using the revese transcription-polymerase chain reaction (RT-PCR), RT-in situ PCR, and immunohistochemistry.

RESULTS

We observed the upregulation of B7-1, B7-2, and IL-12 p40 mRNA after anti-Fas antibody inhalation. B7-2 and IL-12 p40 mRNA appeared to be expressed in mononuclear cells, while B7-1 mRNA and protein were expressed in bronchiolar epithelial cells as well as macrophages.

CONCLUSION

These findings indicate that the T-cell-mediated immune response in this model involved the upregulation of B7-1, B7-2, and IL-12, and that the aberrant expression of B7-1 in bronchiolar epithelial cells may induce autoreactive T cell proliferation against themselves.

Loss of antiviral cytotoxic T-lymphocyte activity during high-level antigen stimulation

High levels of antigenic stimulation can result in deactivation of CD8+ T cells through a variety of mechanisms, including insufficient T-cell help. In the present study, an adoptive transfer system was established in which ovalbumin (OVA)-specific CD8+ T cells were transferred to irradiated mice infected with a recombinant vaccinia virus encoding OVA (VV-OVA). Prolonged activation of OVA-specific CD8+ T cells resulted in a proliferative block in these cells, although cytotoxic function was maintained. Unlike naive and recently activated OVA-specific T cells, these nonproliferative cytotoxic CD8+ T cells did not have antiviral activity following further transfer to mice infected with VV-OVA. Provision of interleukin-2 (IL-2) at the site of virus infection using a recombinant virus encoding antigen and IL-2, as well as the addition of helper T cells, had no effect on the generation of these dysfunctional T cells. Thus, there was no evidence that lack of T-cell help was responsible for CD8+ T-cell deactivation in this model.

Costimulatory molecules B7-1 and B7-2 on CSF cells in multiple sclerosis and optic neuritis

The aberrant expression of B7 costimulatory molecules is involved in the pathogenesis of autoimmune diseases and overexpression of B7-1 was found in inflammatory multiple sclerosis (MS) lesions. We here report that costimulatory molecules B7-1 and B7-2 are expressed on cerebrospinal fluid (CSF) monocytes and B-lymphocytes from patients with MS, optic neuritis (ON) and other inflammatory central nervous system (CNS) diseases. In patients with ON but not MS, increased expression of B7-2 was detected as compared to non-inflammatory controls. The expression of B7-1 in MS and ON patients correlates with disease duration but not with relapses in patients with MS indicating a role in early disease but not as a reliable marker of disease activity at later stages of MS.

CTLA4IgG treatment induces long-term acceptance of rat small bowel allografts

BACKGROUND

CTLA4 immunoglobulin (Ig)G that binds to B7 effectively inhibits the signaling of CD28/CTLA4-B7 pathway and induces antigen specific T cell unresponsiveness in vitro and in vivo. Using CTLA4IgG, we examined induction of long-term graft survival and the mechanism of maintenance of tolerance in rat allogeneic small bowel transplantation.

METHODS

Small bowels of Brown-Norway rats (RT1n) were heterotopically transplanted into Lewis rats (RT1l). Recipients were treated with an i.p. injection of either CTLA4IgG or control IgG for 7 days.

RESULTS

Long-term survival was observed in rats treated with CTLA4IgG, whereas control rats died within 16 days after transplantation. To examine whether a tolerant state was established in long-term survival rats, secondary transplantation was performed using small bowels of Brown-Norway rats or ACI (RT1b) rats. It was demonstrated that small bowels of Brown-Norway rats were accepted; however, those of ACI rats were rejected within 10 days. Serum concentrations of interleukin (IL)-4 were maintained at >50 microg/ml for 7 days after transplantation in rats treated with CTLA4IgG but <15 microg/ml in control rats. IL-2 concentration was reduced to half in CTLA4IgG-treated rats compared with that in control recipients. Serum IFN-gamma in CTLA4IgG-treated recipients increased after transplantation and was not distinguishable from that of control recipients during the first 7 days after transplantation. Conclusion. We demonstrated that CTLA4IgG treatment alone for 7 days induced a long-term donor specific tolerance in rat allogeneic small bowel transplantation. The induction of long-term acceptance of small bowel allografts by CTLA4IgG is not caused by simply the shift of anti-alloimmune responses from Thl to Th2 cytokine production.