Myd88 knockdown with RNA interference induces in vitro immune hyporesponsiveness in dendritic cells from rhesus monkeys.

Immature dendritic cells (imDCs) are activated and mature to initiate an adaptive immune response, resulting in allograft rejection and transplantation failure. Myeloid differentiation factor 88 (Myd88) is a key factor in the Toll-like receptor (TLR) signaling pathway. Here, we investigated the effect of Myd88 silencing on DC function and immune response. CD34 + cells were isolated from the bone marrow of rhesus monkeys by the immunomagnetic bead method and then infected with an adenovirus expressing Myd88-specific short hairpin RNA (sh-Myd88). sh-NC (nontargeting negative control)- or sh-Myd88-infected DCs were treated with lipopolysaccharide (LPS) for another 48 h to induce DCS maturation. The maturation of DCs was identified by immunofluorescence staining for MHCII, CD80, and CD86. DC apoptosis was examined using Annexin V/PI staining. DC-related cytokine levels (IFN-γ and IL-12) were assessed by ELISA. A mixed lymphocyte reaction (MLR) was performed to test the effect of Myd88-silenced DCs on T lymphocytes in vitro. The results showed that compared with control or sh-NC-infected DCs, Myd88-silenced DCs had lower MHCII, CD80, CD86, and DC-related cytokine (IFN-γ and IL-12) levels. Myd88 did not affect the apoptosis of DCs. MLR demonstrated that Myd88 silencing could effectively block LPS-activated T cell proliferation in vitro. These data were consistent with the characteristics of tolerogenic DCs. In conclusion, our data indicated that Myd88 silencing could inhibit the maturation of imDCs and alleviate immune rejection, which provides a reference for immune tolerance in clinical liver transplantation.

The Effect of Akkermansia muciniphila and Its Outer Membrane Vesicles on MicroRNAs Expression of Inflammatory and Anti-inflammatory Pathways in Human Dendritic Cells.

Probiotics play a crucial role in immunomodulation by regulating dendritic cell (DC) maturation and inducing tolerogenic DCs. Akkermansia muciniphila affects inflammatory response by elevating inhibitory cytokines. We aimed to evaluate whether Akkermansia muciniphila and its outer membrane vesicles (OMVs) affect microRNA-155, microRNA-146a, microRNA-34a, and let-7i expression of inflammatory and anti-inflammatory pathways. Peripheral blood mononuclear cells (PBMCs) were isolated from the healthy volunteers. To produce DCs, monocytes were cultivated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). DCs were allocated into six subgroups: DC + Lipopolysaccharide (LPS), DC + dexamethasone, DC + A. muciniphila (MOI 100, 50), DC + OMVs (50 µg/ml), and DC + PBS. The surface expression of human leukocyte antigen-antigen D related (HLA-DR), CD86, CD80, CD83, CD11c, and CD14 was examined using flow cytometry, and the expression of microRNAs was assessed using qRT-PCR, and the levels of IL-12 and IL-10 were measured using ELISA. A. muciniphila (MOIs 50, 100) could significantly decrease IL-12 levels relative to the LPS group. The IL-10 levels were decreased in the DC + LPS group than the DC + dexamethasone group. Treatment with A. muciniphila (MOI 100) and OMVs could elevate the concentrations of IL-10. DC treatment with LPS led to a significant increment in the expression of microRNA-155, microRNA-34a, and microRNA-146a. The expression of these microRNAs was reversed by A. muciniphilia and its OMVs treatment. Let-7i increased in treatment groups compared to the DC + LPS group. A. muciniphilia (MOI 50) had a substantial effect on the expression of HLA-DR, CD80, and CD83 on DCs. Therefore, DCs treatment with A. muciniphila led to induce tolerogenic DCs and the production of anti-inflammatory IL-10.

Differential induction of IL-17, IL-10, and IL-9 in human T helper cells by B7h and B7.1.

ICOS and CD28 are expressed by T cells and are involved in costimulation of cytokine production in T helper (TH) cells. ICOS binds B7h expressed by several cell types, whereas CD28 binds B7.1 and B7.2 expressed by activated antigen presenting cells. This work investigated the role of B7h and B7.1 in TH17 and TH9 cell differentiation by assessing activity of recombinant B7h-Fc and B7.1-Fc on human naïve TH cells activated in the presence of different combinations of exogenous cytokines. In the presence of TGF-ß1 and IL-1ß (TH17 promoting condition), B7h-Fc was more effective than B7.1-Fc in inducing IL-17A and IL-10 secretion, whereas B7.1-Fc was more effective in inducing IL-17F. Dual costimulation with B7h-Fc and B7.1-Fc displayed an intermediate pattern with predominance of IL-17F over IL-17A, secretion of high levels of IL-10, and secretion of IL-9 levels lower than those induced by B7.1-Fc alone. In the presence of TGF-ß1 and IL-4 (TH9 promoting condition), B7h-Fc induced IL-17A only, whereas B7.1-Fc induced also IL-17F, IL-10, and high levels of IL-9. Experiments on memory TH cells showed that B7h-Fc mainly supported secretion of IL-17A and IL-10, whereas B7.1-Fc supported secretion of IL-17A, IL-17F, IL-10, and IL-9. These data indicate that B7h and B7.1 play different roles in modulation of TH17 and TH9 differentiation. This plasticity might be important in the immune response to pathogens and tumors, and in the development of autoimmune diseases, and should be taken in consideration in designing of immunotherapeutic protocols triggering ICOS or CD28.

[Effect of Xijiao Dihuang Combined Prescription on Human Dendritic Cell Function Induced by Lipopolysaccharide].

OBJECTIVE: To observe the effects of drug-containing serum of Xijiao Dihuang combined prescription(XJDH) on the related functions of dendritic cells(DCs) induced in vitro, and to explore the mechanisms underlying the effectiveness of XJDH treatment on primary immune thrombocytopenia(ITP). METHODS: Peripheral blood samples were colle-ted from 6 healthy volunteers. Mononuclear cells were isolated by density gradient centrifugation, and CD14+ mononuclear cells were collected by the magnetic separation technique. CD14+ mononuclear cells were induced into immature DCs by recombinant human granulocyte-macrophage colony stimulating factor (GM-CSF) and recombinant human interleukin 4 (IL-4). Immature DCs were divided into three groups: control group, model group and XJDH group. CCK-8 assay was used to determine the intervention concentration and time of drug-containing serum. Lipopolysaccharide(LPS) with the final concentration of 1 µg/ml was added to model group and XJDH group respectively for 24 h to induce DCs maturation. Normal rat serum was added to control group and model group, and XJDH was added to XJDH group for 24 h. Flow cytometry was used to detect the levels of CD80, CD83 and HLA-DR on the surface of DCs. Western blot was used to detect the expression of TLR4 and NF-κB, and levels of IL-6, IL-12 and TNF-α in cell supernatant was detected by ELISA. RESULTS: Compared with the control group, LPS stimulation increased the expression of CD80, CD83 and HLA-DR, with subsequent increasing expression of TLR4 and NF-κB, as well as IL-6, IL-12 and TNF-α increased(P<0.05). In comparison with model group, the expression of DCs surface molecules CD80, CD83 and HLA-DR, DCs' expression of TLR4 and NF-κB protein, and the levels of IL-6, IL-12 and TNF-α in the cell supernatant of XJDH group decreased after the intervention of XJDH (P<0.05). CONCLUSION: Drug containing serum of Xijiao Dihuang combined prescription can down-regulate TLR4/NF-κB signaling pathway related protein expression, inhibit DCs maturation, and reduce proinflammatory factor secretion, which may be one of the mechanisms of drug-containing serum of Xijiao Dihuang combined prescription in the treatment of immune thrombocytopenia.

Programmed death-1/B7-H1 negative costimulation protects mouse liver against ischemia and reperfusion injury.

UNLABELLED: Programmed death-1 (PD-1)/B7-H1 costimulation acts as a negative regulator of host alloimmune responses. Although CD4 T cells mediate innate immunity-dominated ischemia and reperfusion injury (IRI) in the liver, the underlying mechanisms remain to be elucidated. This study focused on the role of PD-1/B7-H1 negative signaling in liver IRI. We used an established mouse model of partial liver warm ischemia (90 minutes) followed by reperfusion (6 hours). Although disruption of PD-1 signaling after anti-B7-H1 monoclonal antibody treatment augmented hepatocellular damage, its stimulation following B7-H1 immunoglobulin (B7-H1Ig) fusion protected livers from IRI, as evidenced by low serum alanine aminotransferase levels and well-preserved liver architecture. The therapeutic potential of B7-H1 engagement was evident by diminished intrahepatic T lymphocyte, neutrophil, and macrophage infiltration/activation; reduced cell necrosis/apoptosis but enhanced anti-necrotic/apoptotic Bcl-2/Bcl-xl; and decreased proinflammatory chemokine/cytokine gene expression in parallel with selectively increased interleukin (IL)-10. Neutralization of IL-10 re-created liver IRI and rendered B7-H1Ig-treated hosts susceptible to IRI. These findings were confirmed in T cell-macrophage in vitro coculture in which B7-H1Ig diminished tumor necrosis factor-α/IL-6 levels in an IL-10-dependent manner. Our novel findings document the essential role of the PD-1/B7-H1 pathway in liver IRI. CONCLUSION: This study is the first to demonstrate that stimulating PD-1 signals ameliorated liver IRI by inhibiting T cell activation and Kupffer cell/macrophage function. Harnessing mechanisms of negative costimulation by PD-1 upon T cell-Kupffer cell cross-talk may be instrumental in the maintenance of hepatic homeostasis by minimizing organ damage and promoting IL-10-dependent cytoprotection.

B7 blockade alters the balance between regulatory T cells and tumor-reactive T cells for immunotherapy of cancer.

PURPOSE: In prostate cancer-bearing host, regulatory T (Treg) cells restrain activity of tumor antigen-specific T cells. Because B7:CD28 interactions are needed for both function of CD4+CD25+ Treg cells and CD8+ effective T cells, targeting this pathway may help to overcome the immunotherapy barriers. EXPERIMENTAL DESIGN: The anti-B7-1/B7-2 monoclonal antibodies were administered to a transgenic mouse model of prostate cancer (TRAMP) ectopically expressing SV40 large T antigen in different tumor development stages for prevention and therapy of prostate cancer. The treatment was also tested in treating transplanted MC38 colon adenocarcinoma in mice. RESULTS: Here, we showed that short-term administration of anti-B7-1/B7-2 monoclonal antibodies in TRAMP mice leads to significant inhibited primary tumor growth and the size of metastatic lesions. The treatment is effective to inhibit MC38 colon cancer growth. Correspondingly, this treatment results in a transient reduction of Treg in both thymus and the periphery. In vivo cytotoxicity assay revealed T antigen-specific CTL effectors in anti-B7-treated but not control IgG-treated TRAMP mice. CONCLUSIONS: Transient blockade of B7-1/B7-2 alters the balance between Treg and cancer-reactive T cells to enhance cancer immunotherapy.

VSIG4, a B7 family-related protein, is a negative regulator of T cell activation.

T cell activation by APCs is positively and negatively regulated by members of the B7 family. We have identified a previously unknown function for B7 family-related protein V-set and Ig domain-containing 4 (VSIG4). In vitro experiments using VSIG4-Ig fusion molecules showed that VSIG4 is a strong negative regulator of murine and human T cell proliferation and IL-2 production. Administration to mice of soluble VSIG4-Ig fusion molecules reduced the induction of T cell responses in vivo and inhibited the production of Th cell-dependent IgG responses. Unlike that of B7 family members, surface expression of VSIG4 was restricted to resting tissue macrophages and absent upon activation by LPS or in autoimmune inflammatory foci. The specific expression of VSIG4 on resting macrophages in tissue suggests that this inhibitory ligand may be important for the maintenance of T cell unresponsiveness in healthy tissues.

Soluble CD80 Protein Delays Tumor Growth and Promotes Tumor-Infiltrating Lymphocytes.

Tumor cells use various immune-suppressive strategies to overcome antitumor immunity. One such method is tumor expression of programmed death ligand-1 (PD-L1), which triggers apoptotic death or anergy upon binding programmed death-1 (PD-1) on T cells. Our previous in vitro cellular studies with human and mouse PD-L1+ tumor cells demonstrated that a soluble form of the costimulatory molecule CD80 prevented PD-L1-mediated immune suppression and restored T-cell activation by binding PD-L1 and blocking interaction with PD-1. We now report that in vivo treatment of established syngeneic PD-L1+ CT26 colon carcinoma and B16F10 melanoma tumors with CD80-Fc delays tumor growth and promotes tumor-infiltrating T cells. Studies with PD-1-/- and CD28-/- mice demonstrate that soluble CD80 acts in vivo by simultaneously neutralizing PD-1 suppression and activating through CD28. We also report that soluble CD80 mediates its effects by activating transcription factors EGR1-4, NF-κB, and MAPK, downstream signaling components of the CD28 and T-cell receptor pathways. Soluble CD80 binds to CTLA-4 on activated human peripheral blood mononuclear cells. However, increasing quantities of CTLA-4 antagonist antibodies do not increase T-cell activation. These results indicate that soluble CD80 does not suppress T-cell function through CTLA-4 and suggest that CTLA-4 acts as a decoy receptor for CD80, rather than functioning as a suppressive signaling receptor. Collectively, these studies demonstrate that soluble CD80 has therapeutic efficacy in vivo in mouse tumor systems and that its effects are due to its ability to inhibit PD-1-mediated suppression while concurrently activating T cells through CD28. Cancer Immunol Res; 6(1); 59-68. ©2017 AACR.

Induction of a gene expression program in dendritic cells with a cross-linking IgM antibody to the co-stimulatory molecule B7-DC.

While bivalent antibodies can block ligand-receptor interactions, IgM pentamers efficiently cross-link cell surface targets and evoke physiological responses. We have described one such interaction between an IgM antibody (Ab) and the B7-DC costimulatory molecule expressed by dendritic cells that induces strong antitumor immunity and modulates pathogenic responses associated with allergic asthma. Progressive changes in gene expression in dendritic cells activated by an IgM B7-DC cross-linking Ab resulted in the increased expression in 350 genes and decreased expression of more than 200 genes over the course of 24 h following Ab treatment. In particular, up-regulation of the caspase inhibitor FLIP and the chemokine receptor CCR7, and the down-regulation of the CXCR4 receptor provide a mechanistic basis of Ab-induced survival and enhanced migration into draining lymph nodes. Increased expression of both cell surface and secreted molecules known to be mediators of the immunomodulatory properties of dendritic cells was detected at both the levels of RNA and protein expression. This analysis documents the ability of IgM Ab to activate a gene expression cascade leading to important biological changes in cellular function and provides mechanistic insight into the potent immunomodulatory properties attributed to this Ab.

Adenoviral B7-H3 therapy induces tumor specific immune responses and reduces secondary metastasis in a murine model of colon cancer.

Current cancer gene therapies aim at the induction of systemic antitumor immune responses. Tumors may deliver antigens to T-cells, but may lack the costimulatory signals necessary for mounting an effective response. The purpose of this study was to evaluate the efficacy of an adenoviral delivery of the B7-H3 costimulatory molecule in mice to induce antitumor immune responses. Colon cancers were established by orthotopic injection of syngeneic colon cancer cells into the cecum on Balb/c mice. After two weeks, these mice were treated by intratumoral injection of an adenovirus expressing mouse B7-H3 (Ad-B7-H3-GFP) or a control virus (Ad-GFP). Ad-B7-H3-GFP treatment resulted in a reduction of tumor size compared to the controls. In addition, the occurrence of secondary metastasis was significantly reduced in B7-H3 treated mice compared to control animals (lymph node 7/10 vs. 10/10; liver 2/10 vs. 8/10, p

High-level expression of B7-H1 molecules by dendritic cells suppresses the function of activated T cells and desensitizes allergen-primed animals.

A body of evidence indicates that expression of the programmed cell death 1 (PD-1) receptor by activated T cells plays an important role in the down-regulation of immune responses; however, the functions of its known ligands, B7-H1 (PD-L1) and B7-dendritic cell (DC; PD-L2), at the effector phase of immune responses are less clear. In the current study, we investigated the roles of B7-H1 in DC-mediated regulation of hapten-activated T cells and the delayed-type contact hypersensitivity response in primed animals. We found that the expression of B7-H1 and B7-DC was induced on activation of DC by hapten stimulation. Blockade of B7-H1, but not B7-DC, enhanced the activity of hapten-specific T cells. Interaction with a DC line that expresses high cell-surface levels of B7-H1 (B7-H1/DC) suppressed the proliferation of, and cytokine production by, activated T cells. In vivo administration of hapten-carrying B7-H1/DC desensitized the response of sensitized animals to hapten challenge, and this desensitization was hapten-specific. These data indicate that B7-H1 expressed by DC mediates inhibitory signals for activated T cells and suppresses the elicitation of immune responses. The ability of B7-H1/DC to inhibit the function of preactivated T cells in vivo suggests novel strategies for the treatment of immune response-mediated disorders.

Characterization of polysaccharides extracted from Platycodon grandiflorus (Jacq.) A.DC. affecting activation of chicken peritoneal macrophages.

Polysaccharides were isolated from Platycodon grandiflorus (Jacq.) A.DC. (PG) and the effects of three polysaccharides (PGPS80, PGPS60, PGPSt) on their immunological activities were studied. The structure identification of PGPSs was assessed using physicochemical and spectral methods. Results showed that PGPSt(2.67×105Da) compared to PGPS80(1.01×105Da) and PGPS60(1.12×105Da) has relatively higher average molecular weight(Mw) at the first peak with a narrower molecular weight distribution and all consisted of glucose, mannose, arabinose, galactose, xylose and rhamnose in different mass percentages. PGPS80 and PGPSt linked mainly by 1,3-and 1,6-ß-d-Galp residues. The immunological efficacy of PGPSs was performed on chicken peritoneal macrophages. Results showed that PGPSt significantly increased phagocytic rates, proliferation and NO production, stimulated macrophages to produce cytokines, including TNF-α, IL-1ß and IL-6 as well as stimulated macrophages to express the maturation markers CD80 and CD86. These findings suggest that PGPSt exerted significant immunological activity and might be associated with special characters.

Influence of CD80, interleukin-2, and interleukin-7 expression in human renal cell carcinoma on the expansion, function, and survival of tumor-specific CTLs.

PURPOSE: A renal cell carcinoma (RCC) line, RCC-26, has been identified as a suitable candidate for development of an allogeneic tumor cell vaccine based on its expression of a variety of tumor-associated antigens (TAA). To improve immunogenicity, RCC-26 cells were genetically engineered to express CD80 alone or in combination with interleukin (IL)-2 or IL-7. The effect of these modifications on proliferation, function, and survival of autologous and allogeneic tumor-specific CTLs was assessed. EXPERIMENTAL DESIGN: RCC-26 sublines expressing different transgenes were tested for their capacity to reactivate cytokine secretion and cytotoxicity in autologous tumor-infiltrating lymphocytes, to improve proliferation and survival of tumor-associated T cells present in autologous peripheral blood, and to induce tumor-associated responses in naive allogeneic lymphocytes. The expression of several common TAA was quantitated in the RCC-26 sublines using reverse transcription-PCR to identify surrogate markers for immune monitoring in clinical trials. RESULTS: Gene-modified RCC-26 cells showed enhanced immunogenicity. CD80 expression was necessary to induce RCC-associated CTL in blood of healthy allogeneic donors. It also improved proliferation of autologous effector-memory T cells. Further enhancement was achieved with IL-2 through induction of the antiapoptosis protein Bcl-x(L). The candidate vaccine lines overexpressed several common TAA that are suitable markers for immune monitoring. CONCLUSIONS: RCC-26 cells coexpressing CD80 and cytokine transgenes display improved immunogenic characteristics, supporting their use as allogeneic tumor cell vaccines for HLA-A2-matched patients with metastatic RCC.

Generation of immunostimulatory dendritic cells from human CD34+ hematopoietic progenitor cells of the bone marrow and peripheral blood.

Dendritic antigen-presenting cells are considered to be the most effective stimulators of T cell immunity. The use of dendritic cells has been proposed to generate therapeutic T cell responses to tumor antigens in cancer patients. One limitation is that the number of dendritic cells in peripheral blood is exceedingly low. Dendritic cells originate from CD34+ hematopoietic progenitor cells (HPC) which are present in the bone marrow and in small numbers in peripheral blood. CD34+ HPC can be mobilized into the peripheral blood by in vivo administration of granulocyte-colony-stimulating factor. The aim of the current study was to determine whether functional dendritic cells could be elicited and grown in vitro from CD34+ HPC derived from bone marrow or granulocyte-colony-stimulating factor-mobilized peripheral blood. Culture of CD34+ HPC with granulocyte-macrophage-colony-stimulating factor and tumor necrosis factor alpha yielded a heterogeneous cell population containing cells with typical dendritic morphology. Phenotypic studies demonstrated a loss of the CD34 molecule over 1 week and an increase in cells expressing surface markers associated with dendritic cells, CD1a, CD80 (B7/BB1), CD4, CD14, HLA-DR, and CD64 (Fc gamma RI). Function was validated in experiments showing that cultured cells could stimulate proliferation of allogeneic CD4+ and CD8+ T lymphocytes. Antigen-presenting capacity was further confirmed in experiments showing that cultured cells could effectively stimulate tetanus toxoid-specific responses and HER-2/neu peptide-specific responses. The derivation and expansion of dendritic cells from cultured bone marrow or granulocyte-colony-stimulating factor-mobilized CD34+ HPC may provide adequate numbers for testing of dendritic cells in clinical studies, such as vaccine and T cell therapy trials.

CD40-CD40L interactions provide "third-party" costimulation for T cell response against B7-1-transfected human breast tumor cells.

In this study we provide evidence that a human breast carcinoma cell line, MDA-MB-231 (MDA), can be made immunogenic following B7 transfection and that full T cell activation is obtained through cooperation of T-B lymphocytes via CD40-CD40L interactions. Tumor cells transfected with either B7 gene (MDAB7), neomycin-resistant gene only (MDAneo), or untransfected (MDA) were used in an allogeneic mixed lymphocyte tumor culture (MLTC) to investigate their ability to stimulate T cell proliferation and generate cytotoxic T lymphocytes (CTL). MDAB7 induced moderate T cell proliferation while MDAneo or MDA did not. Substantial T cell proliferation and de novo generation of cytolytic T cells was obtained only in response to MDAB7 when B cells were present during the MLTC. CD8+-purified T + B cells proliferated to a greater extent than whole T cell populations + B or CD4+ + B in response to MDAB7. Addition of alpha-B7-1 or alpha-CD40 in the MLTC inhibited T cell proliferation by 65 and 40%, respectively, whereas T cell proliferation and generation of CTL was completely abrogated when MLTC was performed in the presence of both antibodies. These data suggest that the engagement of CD40L on T cells with CD40 on B cells provides a costimulatory signal which, in synergism with TCR-dependent MDAB7-T cell recognition (signal 1) and B7/CD28 interactions (signal 2), leads to full T cell activation.

Tumor suppressive effects of WEE1 gene silencing could not enhance immunopotentiation effects of CD80 and 4-1BBL co-stimulation in human T cells.

BACKGROUND: Activation of T cells against tumors by recruiting co-stimulatory molecules has been an attractive approach for cancer immunotherapy. Reports suggested that targeting different genes in tumors might also boost T cell-mediated tumor destruction. AIMS: We investigated whether in vitro WEE1 gene silencing in MDA-MB-468 and MCF7 breast cancer cell lines could enhance immunopotentiating effects of CD80 and 4-1BBL co-stimulation in human T cells. MATERIALS AND METHODS: WEE1 gene was specifically silenced in the cancer cells using shRNA technology. The co-stimulatory molecules were over-expressed on the surface of the cancer cells by recombinant non-replicative adenoviruses. The immune reaction of T cells in the co-culture with tumor cells was studied. IFN-g production was assessed by intracellular staining of T cells. To assess cytotoxic activity of CD8+ T cells, the CD107a mobilization-degranulation assay was performed. Expression of granzyme B, perforin and fasl were examined by real time PCR. RESULTS: T cell dual co-stimulation led to a significant increase in the frequency of IFN-g producing cells and higher percentages of degranulation in CD8+ T cells. It also resulted in higher expression levels of the cytotoxicity-related genes. WEE1 gene silencing in the target cells alone however, could not produce significant immune reactivation in the cultured T cells. Likewise, the immune responses of T cells neither improved nor suppressed when dually co-stimulated PBMCs were exposed to the cancer cells with silenced WEE1. CONCLUSIONS: In spite of antitumor effects of WEE1 silencing, combination of this approach with immune co-stimulation could not boost the reactivity of cultured T cells against the tested breast cancer cells.

B7-1 amplifies the response to interleukin-2-secreting tumor vaccines in vivo, but fails to induce a response by naive cells in vitro.

Parental and interleukin-2 (IL-2)-secreting CMS5 tumor cells were transfected with the B7-1 costimulatory molecule to amplify anti-tumor responses. CMS5 cells transfected with B7-1 grew more slowly in vivo than did parental CMS5 cells. Moreover, tumor cells secreting levels of IL-2 too low to cause rejection alone were rejected following transfection with B7-1. To determine whether the expression of B7-1 enabled the tumor cells to activate T cells directly, their ability to stimulate in vitro functional responses by T cells was examined. We found that neither B7-1+ nor IL-2-secreting, B7-1+ CMS5 cells stimulated naive spleen cells to proliferate or to become cytotoxic. In contrast, restimulation of primed T cells by B7-1+ CMS5 cells resulted in stronger cytotoxicity responses than seen following restimulation by parental CMS5 cells. Lysis was even higher if the B7-1+ tumor cells also secreted IL-2. Our results suggest that the expression of costimulatory molecules can augment responses generated by vaccinating with IL-2-secreting tumor cells. Furthermore, they are consistent with the hypothesis that the initiation of an anti-tumor response by naive T cells may depend upon initial antigen presentation by another unidentified cell and that the major action of IL-2-secreting and/or B7-1+ tumor cell vaccines might be to potentiate the response of already primed cells.

Vector-driven hyperexpression of a triad of costimulatory molecules confers enhanced T-cell stimulatory capacity to DC precursors.

Activation of T cells requires at least two signals: signal 1, via the T-cell receptor, and signal 2, in which a costimulatory molecule on the antigen presenting cell (APC) interacts with a ligand on the T cell. Dendritic cells (DCs) are the most potent APCs in part due to their expression of costimulatory molecules. DCs, however, constitute only a minor percentage of APCs in the body, and the in vitro preparation of DCs is both costly and time consuming. The studies reported here demonstrate that one can utilize other APCs, such as bone marrow progenitor cells (BMPCs) and make them markedly more effective as APCs; this was accomplished by their infection with recombinant poxviruses (either the replication-defective avipox or vaccinia), which contain transgenes for a triad of costimulatory molecules (B7-1, ICAM-1 and LFA-3, designated TRICOM). APCs infected with TRICOM vectors are shown to significantly enhance the activation of both naive and effector CD4(+) and CD8(+) T-cell populations. The use of TRICOM vectors in vaccine strategies is discussed.

Differential down-regulation of CD28 by B7-1 and B7-2 engagement.

Physiologically relevant full activation of T cells requires signal transduction through the T cell receptor and additional costimulatory cell surface molecules. Best understood of these costimulatory interactions are those between CD28 and its ligands B7-1 (CD80) and B7-2 (CD86). While B7-1 and B7-2 bind the same receptors (CD28 and CTLA-4), they share only 25% sequence homology, are expressed at different times during immune responses, and in some systems have been shown to differentially affect T cell cytokine expression. Although CD28 is an activation antigen, its expression is down-regulated after engagement by B7-1. Here we show that B7-2 engagement is considerably less effective at down-regulating CD28, which indicates a differential effect of these two CD28 ligands on activated T cells.

Keratinocytes induce local tolerance to skin graft by activating interleukin-10-secreting T cells in the context of costimulation molecule B7-H1.

BACKGROUND: Intermingled skin grafting using autologous skin islets inlaid in allogeneic skin sheets was found to delay graft rejection, contributing to a significant reduction in mortality for patients with severe burns. In this study we examine the down-regulatory mechanisms underlying the effect of the autologous skin islets. METHODS: Mixed culture of lymphocytes with epidermal cells of autologous and allogeneic origin were performed with a comparing of cell activity from cytokine-knockout mice. And the Th1/Th2-related cytokine profiles were examined. RESULTS: Autologous keratinocytes act as potent inducers of suppression in the mixed culture by making a shift of the cytokine profile from Th1 to Th2. The observed suppression is predominantly mediated by interleukin (IL)-10, because the effect could be reversed by application of a neutralizing antibody to IL-10. The results of reconstitution experiments in BALB/c mice, with or without IL-10 gene-knockout, are consistent with this finding. These demonstrated that T cells were main effective components for the IL-10-related suppression. Furthermore, a newly identified member of the human B7 family (B7-H1) is found to play an important role in activating human IL-10-secreting lymphocytes. When transfected with the CD80 gene, autologous keratinocytes lost the ability to down-regulate the mixed cell culture, which effect could be reversed by introduction of the anti-CD80 antibody. CONCLUSIONS: Our study provides new evidence that autologous keratinocytes present in intermingled skin grafts are inducers for local immune tolerance by expression of B1-H1 in their activation of the IL-10-secreting T cells.