4-1BB co-stimulation enhances human CD8(+) T cell priming by augmenting the proliferation and survival of effector CD8(+) T cells

Interactions between 4-1BB and its ligand, 4-1BBL, enhance CD8(+) T cell-mediated antiviral and antitumor immunity in vivo. However, mechanisms regulating the priming of CD8(+) T cell responses by 4-1BB remain unclear, particularly in humans. The 4-1BB receptor was undetectable on naive or resting human CD8(+) T cells and induced in vitro by TCR triggering. Naive cord blood cells were therefore primed in vitro against peptides or cellular antigens and then co-stimulated with 4-1BBL or agonistic antibodies. Co-stimulation enhanced effector function such as IFN-gamma production and cytotoxicity by augmenting numbers of antigen-specific and effector CD8(+) T cells. OKT3 responses also showed reduced cell death and revealed that the proliferation of CD8(+) T cells required two independently regulated events. One, the induction of IL-2 production, could be directly triggered by 4-1BB engagement on CD8(+) T cells in the absence of accessory cells. The other, expression of CD25, was induced with variable efficacy by accessory cells. Thus, suboptimal accessory cells and 4-1BB co-stimulation combined their effects to enhance IL-2 production and proliferation. Reduced apoptosis observed after co-stimulation in the presence of accessory cells correlated with increased levels of Bcl-X(L) in CD8(+) T cells, while Bcl-2 expression remained unchanged. Altogether, 4-1BB enhanced expansion, survival and effector functions of newly primed CD8(+) T cells, acting in part directly on these cells. As 4-1BB triggering could be protracted from the TCR signal, 4-1BB agonists may function through these mechanisms to enhance or rescue suboptimal immune responses.     

协同刺激分子4-1BB和CD28对人外周血不同T细胞亚群的激活作用

目的 :探讨 4 1BB/ 4 1BBL协同刺激信号在CD4 和CD8 T细胞活化、增殖中的作用 ,并与CD2 8/B7信号作比较。方法 :用抗CD3单抗 (mAb)刺激人外周血单个核细胞 (PBMC)。用阻断型抗 4 1BBLmAb和抗CD80mAb ,分别阻断 4 1BB/ 4 1BBL和CD2 8/B7 1协同刺激信号。利用流式细胞术 (FCM)检测CD4 T细胞、CD8 T细胞的增殖率、CD8/CD4T细胞的比值变化和细胞分泌IFN γ的情况。结果 :用抗 4 1BBLmAb和抗CD80mAb阻断相应的协同刺激途径后 ,CD4 和CD8 T细胞的增殖和细胞分泌IFN γ的水平均明显下降。培养 8d,抗CD3mAb单独刺激组CD8/CD4T细胞的比值为 1.98± 0 .0 6 ;抗 4 1BBLmAb阻断组CD8/CD4T细胞的比值下降为 0 .96±0 .0 3;而在抗CD80mAb阻断组 ,其比值上升为 2 .6 9± 0 .16。结论 :4 1BB分子可在CD4 T细胞和CD8 T细胞的活化、增殖中提供协同刺激信号。 4 1BB分子所介导的协同刺激信号 ,在CD8 T细胞活化及增殖中发挥了更为重要的作用 ;而CD2 8分子所介导的协同刺激信号则更有利于CD4 T细胞的活化     

Expression and function of 4-1BB and 4-1BB ligand on murine dendritic cells

4-1BB (CDw137) and its ligand (4-1BBL) have been implicated in cellular immune responses. To further characterize the expression and function of 4-1BBL, we newly generated an anti-mouse 4-1BBL mAb (TKS-1), which can inhibit the interaction of 4-1BBL with 4-1BB. Flow cytometric analyses using TKS-1 and an anti-mouse 4-1BB mAb indicated that 4-1BB was inducible on both CD4(+) and CD8(+) splenic T cells by stimulation with immobilized anti-CD3 mAb, but 4-1BBL was not expressed on resting or activated T cells. 4-1BBL expression was inducible on splenic B cells by stimulation with anti-IgM antibody plus anti-CD40 mAb, on peritoneal macrophages by stimulation with lipopolysaccharide (LPS) and on splenic dendritic cells (DC) by stimulation with anti-CD40 mAb or LPS. Interestingly, splenic DC expressed 4-1BB constitutively, which was down-regulated by anti-CD40 stimulation. Co-culture of splenic DC with 4-1BBL-transfected cells or 4-1BBL-expressing tumor cell lines led to cytokine (IL-6 and IL-12) production and co-stimulatory molecule up-regulation by splenic DC, indicating that 4-1BBL can directly activate DC. Moreover, IL-12 production by anti-CD40-stimulated DC was partially inhibited by TKS-1. These results suggest that 4-1BB expressed on DC may be involved in DC activation through DC--tumor interaction and DC--DC interaction.     

Involvement of 4-1BB (CD137)-4-1BBligand interaction in the modulation of CD4 T cell-mediated inflammatory colitis

4-1BB ligand (4-1BBL) expressed on antigen-presenting cells interacts with 4-1BB on activated T cells (especially CD8+ cells) and co-stimulates the latter to secrete cytokines and to proliferate. The role of 4-1BB-4-1BBL interaction was studied here in a model of colitis based on naive CD4+ T cell transfer to SCID mice, a disease model in which CD8 cells do not take part. We found that CD4+ T cells from 4-1BB-deficient mice, after transfer in SCID mice, proliferated more rapidly compared to wild-type CD4+ T cells. Mice reconstituted with naive CD4+ T cells from 4-1BB-deficient mice developed colitis, however, with a mixed Th1/Th2 response, in contrast to the Th1-type response in mice reconstituted with wild-type naive CD4+ T cells. Importantly, this altered cytokine response did not temper colitis severity. Although it has been reported previously that 4-1BB co-stimulation may contribute to regulatory T cell functioning, we found that CD4+CD25+ regulatory T cells from 4-1BB-deficient mice were perfectly able to prevent naive CD4+ T cell-induced colitis. In conclusion, our data provide evidence that 4-1BB-4-1BBL interaction modulates the effector CD4+ T cell-driven immune response and cytokine production in experimental colitis without affecting regulatory T cell function.     

HBcAg-induced upregulated 4-1BB ligand on B cells contributes to B-cell hyperactivation during chronic hepatitis B infection

During the natural history of chronic hepatitis B infection (CHB), the function of B cells is still obscure. Several limited studies have suggested that B cells are highly active in patients with CHB. In the present study, we reported that the 4-1BB ligand (4-1BBL) expression on B cells was significantly higher in patients with CHB than that in healthy subjects, meanwhile, the patients with CHB had higher serological IgG levels. Further, after being stimulated with sCD40L or hepatitis B core antigen (HBcAg), B cells had higher levels of 4-1BBL. After being cocultured with 4-1BBL+ B cells, the expressions of CD69 and 4-1BB on CD4+ T cells were significantly higher than that cocultured with 4-1BB− B cells. Cytokines including interleukin (IL)-2, IL-4, and IL-6 were significantly higher in the supernatant from 4-1BBL+ B cells coculture group than those from coculture group of 4-1BBL− B cell group, respectively; while IFN-γ and TNF-α in cocultured supernatant of 4-1BBL+ B cell group were significantly lower. Consistently, the total IgG levels in culture supernatant were significantly higher in 4-1BBL+ B cell group. Thus, hyperactive status of B cells in patients with CHB could be partially derived from the higher 4-1BBL expression on B cells triggered by HBcAg. 4-1BBL signaling pathway is involved in B cells activation, and further regulates B cell-T cell interaction by modulating the cytokines secretion, which might be critical in B cells dysfunction during CHB infection.     

Expression and function of 4-1BB during CD4 versus CD8 T cell responses in vivo

4-1BBL(-/-) mice have a defect in recall CD8+ T cell responses to viruses, whereas CD4+ T cell responses to virus are unimpaired in these mice. In contrast, both CD4+ and CD8+ T cells respond to 4-1BB ligand (4-1BBL) in vitro. To clarify the role of 4-1BB/4-1BBL in CD4+ versus CD8+ T cell responses in vivo, we compared CD4 (OT-II) and CD8 (OT-I) TCR transgenic T cells responding to the same antigen in an in vivo adoptive transfer model in 4-1BBL(+/+) versus 4-1BBL(-/-) mice. During primary and secondary responses, expression of 4-1BB on in vivo-activated TCR transgenic T cells was earlier and more transient than previously observed in vitro, correlating with expression of the early activation antigen CD69 and preceding the transition to the CD44hi state. Although 4-1BB is expressed early in the primary response, there was no effect of 4-1BBL deficiency on initial CD8 T cell expansion and only a minor effect on initial CD4 T cell expansion. The major effect of 4-1BB/4-1BBL interaction is on the T cell recall response. This is due to effects of 4-1BBL on maintenance of T cell numbers at the end of the primary response with additional effects of 4-1BBL on secondary expansion of T cells.     

Mechanism of enhanced antigen presentation by B cells activated with anti-μ plus interferon-γ: Role of B7-2 in the activation of naive and memory CD4+ T cells

B cells activated with anti-γ antibody plus interferon (IFN)-γ exerted strong antigen presentation activity for T cell proliferation. The enhanced antigen presentation function was shown to be due to the increase in B7-2 expression. When B cells were stimulated with anti-μ, expression of MHC major histocompatibility complex class II, heat-stable antigen (HSA), ICAM-1 and B7-2 was increased. The presence of IFN-γ further augmented the expression of B7-2 on anti-μ-stimulated B cells. B7-1 was not expressed on B cells under these conditions. The participation of B7-2 in the elicitation of the proliferative response of T cells was confirmed by the inclusion of anti-B7-2 antibody in cultures. The enhanced expression of either HSA or ICAM-1 was shown not to play a major role in the increased B cell antigen presentation capacity. The major T cell population responding to this activated B cell antigen presentation was shown to be CD44^low naive CD4⁺ T cells, whereas CD45RB^low memory CD4⁺ T cells responded only weakly. The difference in proliferative responses between naive and memory CD4⁺ T cells was explained by the different efficiency in IL-2 production of these cell populations in response to antigen presentation by B cells activated by anti-μ plus IFN-γ. These results suggest that IFN-γ plays an important role in recruitment of naive T cells for an immune response.     

Increased soluble 4-1BB ligand (4-1BBL) levels in peripheral blood of patients with multiple sclerosis

4-1BB ligand (4-1BBL; CD137L) is a member of the tumour necrosis factor superfamily expressed primarily on antigen presenting cells such as B cells, macrophages and dendritic cells. Its engagement with the receptor 4-1BB (CD137) has been shown to promote T-cell activation and regulate proliferation and survival of T cells. The role of the costimulatory molecule in multiple sclerosis (MS) remains unclear. In this study, the expression of 4-1BBL and soluble 4-1BBL (s4-1BBL) protein levels were analysed in peripheral blood of MS patients. Compared with healthy controls, MS patients had an increase in both plasma s4-1BBL protein levels and expression of 4-1BBL in CD14(+) monocytes. In contrast, myelin basic protein-reactive T-cell proliferation was not found to be inhibited by the use of an anti-4-1BBL antibody. The elevated s4-1BBL protein levels in the MS patients may function as a self-regulatory mechanism of 4-1BB/4-1BBL interaction and costimulation.     

Functional expression of 4-1BB (CD137) in the inflammatory tissue in Crohn's disease

4-1BB ligand (L) expressed on antigen presenting cells (APC) interacts with 4-1BB, expressed on activated T cells and this interaction costimulates T cells to secrete cytokines and to proliferate. We investigated whether 4-1BB/4-1BBL interactions might be involved in the pathogenesis of Crohn's disease (CD). In immunohistochemistry, we found 4-1BB expression on lamina propria (LP) cells in inflamed and to a lesser extend in non-inflamed gut tissue from CD patients. mRNA levels for 4-1BB were also elevated in intestinal CD tissue. In contrast, only few 4-1BB-expressing cells were found in inflamed tissue from ulcerative colitis (UC) patients and almost no positive cells were found in control intestinal tissue. 4-1BB expression was better sustained on in vitro activated lamina propria T cells from CD patients compared to controls. Finally, agonistic anti-4-1BB antibody enhanced interferon-gamma (IFN-gamma) production and proliferation of lamina propria T cells from CD patients. Taken together, our data suggest that 4-1BB/4-1BBL interactions contribute to the persistence of gut inflammation in CD.     

The combination of 4-1BBL and CD40L strongly enhances the capacity of dendritic cells to stimulate HIV-specific T cell responses

One of the consequences of HIV infection is a progressive loss of T cell functions, resulting in decreased cytokine secretion and proliferation and an increased sensitivity to apoptosis. Therefore, successful therapeutic vaccination approaches should aim at restoring the functionality of existing HIV-specific T cells, as well as to efficiently induce potent, HIV-specific T cells from na?ve T cells. In this study, we wanted to determine the stimulatory capacity of DCs coelectroporated with mRNA encoding for different costimulatory molecules of the TNFSF, together with HIV antigen-encoding mRNA. We show that DCs electroporated with 4-1BBL can enhance the proliferation, functionality, cytokine production, and survival of HIV-specific CD8(+) T cells. Furthermore, we are the first to show that a combination of 4-1BBL and CD40L overexpression on DCs dramatically enhances CD4(+) and CD8(+) T cell responses. Finally, we demonstrate that signaling through 4-1BB, but not through CD40, can alleviate the suppressive effect of Tregs on CD8(+) T cell proliferation. Thus, the combination of 4-1BBL and CD40L enhances HIV-specific CD8(+) T cell responses in a synergistic way, resulting in enhanced proliferation of CD4(+) and CD8(+) T cell subsets, an increased cytokine secretion, and a reduced sensitivity to Treg-mediated immune suppression.     

Amplification of tumor immunity by gene transfer of the co-stimulatory 4-1BB ligand: synergy with the CD28 co-stimulatory pathway

We have explored the role of an activation-induced T cell molecule, 4-1BB (CDw137), in the amplification of tumor immunity by retrovirus-mediated transduction of the 4-1BB ligand (4-1BBL) into tumor cells. Mice inoculated with P815 tumor cells expressing 4-1BBL developed a strong cytotoxic T lymphocyte (CTL) response and long-term immunity against wild-type tumor. The optimal effect of 4-1BBL in CTL stimulation required B7-CD28 interaction since blockade of this interaction by antibodies down-regulated the expression of 4-1BB on T cells and decreased CTL activity. Furthermore, co-expression of 4-1BBL and B7-1 in the poorly immunogenic AG104A sarcoma enhanced the induction of effector CTL and the rejection of the wild-type tumor while neither 4-1BBL nor B7-1 single transfectants were effective, suggesting a synergistic effect between the 4-1BB and the CD28 co-stimulatory pathways. Our results underscore the importance of the 4-1BB T cell stimulation pathway in the amplification of an antitumor immune response.     

Differential clonal expansion of CD4 and CD8 T cells in response to 4-1BB ligation: contribution of 4-1BB during inflammatory responses

Cell surface proteins of the tumor necrosis factor (TNF) family of receptors have been intimately involved in inducing T cell death. A feature of these family members that is less well studied is their ability to rescue T cells from apoptosis. One such member is 4-1BB; an activation induced surface receptor on CD4 and CD8 T cells. This study demonstrates that the costimulatory effects of 4-1BB, which was found to enhance clonal expansion, required cross-linking of the receptor. The survival of the activated CD8 T cells following expansion was not associated with an increase in Bcl-2 expression. Provided that 4-1BB signaling was present, the amplification of activated CD8 T cell growth in vivo was independent of CD28 ligation. In vivo clonal expansion of activated CD4 T cells, however, was not as responsive to 4-1BB cross-linking. Moreover, 4-1BB-induced expansion was comparable to that mediated by LPS which can incite multiple costimulatory signals. Furthermore, LPS-mediated growth and survival of superantigen (SAg) stimulated T cells appeared to be partially dependent on interactions between 4-1BB and 4-1BB ligand (4-1BBL).     

4-1BB （CD137） Ligand Enhanced Anti-Tumor Immune Response against Mouse Forestomach Carcinoma In Vivo

Cancer occurrence and development has been demonstrated to be associated with escape from immune surveillance, and low eostimulatory molecules expression has been considered as one of the important reasons for cancer evading the immune system. 4-1BB （CD137） is a costimulatory molecule expressed on the surface of activated T cells. Interaction of 4-1BB with its natural ligand （4-1BBL） expressed on antigen presenting cells （APCs） has been shown to amplify T-cell mediated immunity. We therefore examined whether murine cancer cells expressing 4-1BBL could produce antitumor effects in inoculated mice. Mouse forestomach carcinoma （MFC） cells were transfected with 4-1BBL gene （MFC/4-1BBL）. The proliferation of the transduced cells in vitro was not different from that of parental cells. However, MFC/4-1BBL cells developed small tumors and induced higher cytotoxicity of tumor infiltration lymphocyte （TIL）. Production of cytokines （IFN-γ TNF-α and IL-2） in serum and cytotoxic T lymphocyte （CTL） activity of splenocytes from mice immunized with mitomycin C （MMC）-treated MFC/4-1BBL cells were significantly higher than that from mice immunized with MMC-treated parental MFC and MFC/ pMKITneo cells. These results suggest that modification of cancer cells with 4-1BBL gene can produce antitumor immune responses.     

Naive CD4+ T Cells Can be Sensitized with IL-7

We addressed the question whether it is possible to lower the threshold for naive T cells to respond to antigens. Purified adult and cord blood derived CD4+ CD45RA+ naive T cells were incubated in the presence of various cytokines for two days ("primed T cells"), after which the cytokines were removed by extensive washing. Primed and unprimed cells were activated with solid phase-coupled anti-CD3 and soluble anti-CD28 monoclonal antibodies (MoAb). Naive T cells, primed with interleukin(IL)-7 proliferated more vigorously than unprimed cells. Primed cells required 6 h for antigenic stimulation, whereas unprimed cells required 20 h. The priming also shifted the threshold of naive T cells in order to stimulate the antigen concentration to a lower level. The addition of IL-10 almost completely abrogated the enhancing effect of IL-7 on naive T cells. Other cytokines (IL-1, IL-2, IL-6, IL-12, interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha had less effect on the cell proliferation. However, priming of naive T cells with IL-7 had no impact on the proliferation to allogeneic immature or mature dendritic cells (DC). We conclude that the antigen-independent activation of naive T cells with IL-7 prior to antigen stimulation sensitizes cells, and may be of help in trying to stimulate immune responses against weak antigens. This approach, however, does not enhance proliferative responses stimulated by DC.     

Contribution of 4–1BBL on radioresistant cells in providing survival signals through 4–1BB expressed on CD8+ memory T cells in the bone marrow

The persistence of memory lymphocytes is a critical feature of adaptive immunity. The TNF family ligand 4–1BBL supports the antigen‐independent survival of CD8+ memory T cells. Here, we show that mice lacking 4–1BB only on αβ T cells show a similar defect in CD8+ T‐cell recall responses, as previously shown in 4–1BBL‐deficient mice. We show that 4–1BB is selectively expressed on BM CD8+ but not CD4 + memory T cells of unimmunized mice. Its ligand, 4–1BBL, is found on VCAM‐1+ stromal cells, CD11c+ cells, and a Gr1^lo myeloid population in unimmunized mice. Adoptive transfer of in vitro generated memory T cells into mice lacking 4–1BBL only on radioresistant cells recapitulates the defect in CD8 + T‐cell survival seen in the complete knockout mice, with smaller effects of 4–1BBL on hematopoietic cells. In BM, adoptively transferred DsRed CD8+ memory T cells are most often found in proximity to VCAM‐1+ cells or Gr1+ cells, followed by B220+ cells and to a much lesser extent near CD11c+ cells. Thus, a VCAM‐1+CD45^? stromal cell is a plausible candidate for the radioresistant cell that provides 4–1BBL to CD8+ memory T cells in the BM.     

Morphological Interactions of Interdigitating Dendritic Cells with B and T Cells in Human Mesenteric Lymph Nodes

Interdigitating dendritic cells (IDC) of the human mesenteric lymph nodes (LN) were examined by two-color immunofluorescent microscopy and flow cytometry to clarify their exact localization, immunophenotype, and relationships with T and B cells. IDC were identified as HLA-DR(bright) large dendriform cells of the T cell areas co-expressing CD40, CD54 (ICAM-1), CD80 (B7/B7-1), CD83, and CD86 (B70/B7-2). The majority of IDC directly attached to a few IgD+ naive B cells as well as to numerous CD4+ T cells. When LN cells were singly suspended and briefly incubated in vitro, IDC formed clusters with IgD+ IgM+ naive B cells, but not with IgA+ or IgG+ B cells. When suspended LN cells were cultured, clustered B cells disappeared within 7 days, and on prolonged culture, some IDC developed into extensively dendriform cells forming stable complexes with several or sometimes numerous CD4+ IL-2R+ CD40L+ activated T cells. These findings indicate that resting naive B cells actually interact with IDC directly in T cell areas of human secondary lymphoid tissues. IDC have a non-antigen (Ag)-specific, strong affinity for resting naive B cells, but this affinity is transient and IDC cannot form stable complexes with B cells, although they can form stable complexes with activated T cells. It is suggested that the stable IDC/Ag-activated T cell complexes make it possible to capture and to stimulate rare Ag-specific resting naive B cells with high efficiency.     

4-1BB (CD137) controls the clonal expansion and survival of CD8 T cells in vivo but does not contribute to the development of cytotoxicity

4-1BB is expressed on activated T cells. We analyzed the role of 4-1BB during the CD8 T cell response of OT-I TCR-transgenic T cells to ovalbumin. In vitro, blocking 4-1BB during peptide presentation reduced proliferation of naive CD8 T cells, but did not affect the generation of CTL. Using an in vivo adoptive transfer model, clonal expansion of CD8 T cells to whole protein in adjuvant was significantly reduced when 4-1BB was blocked, with 50-70% fewer CD8 T cells accumulating. This was due to a reduction in T cell division and to enhanced apoptosis of CD8 T cells that had undergone many divisions. T cells generated in the absence of 4-1BB were impaired in their ability to secrete IFN-gamma whereas CTL activity of the T cells that survived was unaffected. These findings demonstrate that 4-1BB contributes to clonal expansion, survival, and development of Tc1 cells when protein antigen is encountered by primary CD8 T cells in an inflammatory environment in vivo.     

Activated B cells modified by electroporation of multiple mRNAs encoding immune stimulatory molecules are comparable to mature dendritic cells in inducing in vitro antigen-specific T-cell responses

Ex-vivo-activated B cells are an alternative source of antigen-presenting cells (APCs) and a potential replacement for dendritic cells (DCs) in immunotherapy. However, the ability of ex-vivo-activated B cells to function as potent APCs has been a concern, especially when compared to DCs. Our study investigated whether modification of activated B cells with immune stimulatory molecules could enhance the ability of activated B cells to stimulate T cells. We show that murine splenic B cells, activated with a combination of Toll-like receptor agonist and agonistic anti-CD40, stimulated antigen-specific CD8+ T cells more efficiently than cells activated with Toll-like receptor agonist or anti-CD40 alone, probably by down-regulation of the immune regulatory cytokine interleukin-10 (IL-10). However, the activated B cells were still poor T-cell stimulators compared to mature DCs. Therefore, we modified the activated B cells by simultaneous electroporation of multiple messenger RNAs encoding costimulatory molecules (OX40L and 4-1BBL), cytokines (IL-12p35 and IL-12p40) and antigen. We found that de novo expression or overexpression of OX40L, 4-1BBL and IL-12p70 on activated B cells synergistically enhanced proliferation as well as IL-2 and interferon-gamma production by CD8+ T cells. Furthermore, the RNA-modified activated B cells induced antigen-specific cytotoxic T lymphocyte responses as efficiently as mature DCs in vitro. Unexpectedly, modified activated B cells were inferior to mature DCs at in vivo induction of CD8+ T-cell responses. In summary, activated B cells modified to express immune stimulatory molecules are a potent alternative to DCs in immunotherapy.     

4-1BB在人外周血γδT细胞活化中的协同刺激作用

采用结核杆菌(Mtb)低分子多肽刺激人外周血单个核细胞,流式细胞术(FCM)检测不同活化时相γδT细胞膜表面4-1BB分子的表达;用阻断型4-1BB配体(4-1BBL)单抗阻断4-1BB/4-1BBL信号,FCM检测γδT细胞的增殖比率和细胞内产生IFN-γ的情况,同时与阻断CD28/B7-1信号相比较。结果显示,静止的γδT细胞膜表面不表达4-1BB分子,Mtb抗原刺激后6 h,4-1BB即有明显表达(29.71%),48 h达到高峰(49.79%);与未阻断组相比,阻断4-1BB/4-1BBL信号,γδT细胞的增殖效应和细胞内IFN-γ的产生均明显下降(P<0.01),与CD28/B7-1信号阻断组相比,差异无显著性(P>0.05)。提示4-1BB/4-1BBL信号同CD28/B7-1信号一样,可为γδT细胞活化提供协同刺激作用。     

CD28 ligands CD80 (B7-1) and CD86 (B7-2) induce long-term autocrine growth of CD4+ T cells and induce similar patterns of cytokine secretion in vitro

The interaction of CD28 and its ligands is critical for antigen-inducedT cell activation. Recent studies have demonstrated the existenceof at least two members of the B7 receptor family. In this report,the co-stimulatory signals provided by CD80 (B7-1) or CD86 (B7-2)were compared to CD28 ligation by mAb. We demonstrate that thekinetics of induction of T cell proliferation after anti-CD3stimulation was similar regardless of the form of co-stimulation.Similarly, B7-1 and B7-2 could both maintain long-term expansionof CD4 cells. The co-stimulatory effects of both B7-1 and B7-2were dependent on CD28 cross-linking, based on complete inhibitionof proliferation by CD28 antibody Fab fragments. Co-stimulationwith B7-1 and B7-2 induced high levels of cytokine secretionby resting T cells, and the effects of B7-1 and B7-2 could notbe distinguished. This conclusion is based on analysis of theinitial activation of CD28⁺ T cells. as well as T cell subpopulationsconsisting of CD4⁺ and CD8⁺ T cells. Both B7-1 and B7-2 couldelicit IL-4 secretion from CD4⁺ T cells while anti-CD28 antibodyinduced substantially less IL-4 secretion. Furthermore, bothB7-1 and B7-2 could stimulate high levels of IFN- and IL-4 fromCD4⁺CD45RO⁺ cells, while neither B7 receptor could co-stimulateIFN- and IL-4 secretion from CD4⁺CD45RA⁺ T cells. B7-1 and B7-2could, however, co-stimulate CD4⁺CD45RA⁺ T cells to secreteIL-2. By contrast, when previously activated T cells were tested,re-stimulation of CD4⁺ T cell blasts with B7-1 or B7-2 resultedin higher secretion of IL-4 and IL-5 than anti-CD28, while re-stimulationwith anti-CD28 antibody maintained a higher level of secretionof IL-2 and IFN- than B7-1 or B7-2. These observations may haveimportant implications because they suggest that the mannerof CD28 ligation can be a critical determinant in the developmentof cytokine secretion that corresponds to T_h1- and T_h2-likepatterns of differentiation. Together these observations suggestthat there are no Intrinsic differences between B7-1 and B7-2in their ability to co-stimulate the populations of cells thatwe have tested.