4-1BB ligand, a member of the TNF family, is important for the generation of antiviral CD8 T cell responses.

4-1BB (CD137) is a costimulatory molecule expressed on activated T cells and interacts with 4-1BB ligand (4-1BBL) on APCs. To investigate the role of 4-1BB costimulation for the development of primary immune responses, 4-1BBL-deficient (4-1BBL-/-) mice were infected with lymphocytic choriomeningitis virus (LCMV). 4-1BBL-/- mice were able to generate CTL and eliminate acute LCMV infection with normal kinetics, but CD8 T cell expansion was 2- to 3-fold lower than in wild-type (+/+) mice. In the same mice, virus-specific CD4 Th and B cell responses were minimally affected, indicating that 4-1BB costimulation preferentially affects CD8 T cell responses. This result contrasts with our earlier work with CD40L-deficient (CD40L-/-) mice, in which the CD8 T cell response was unaffected and the CD4 T cell response was markedly impaired. When both 4-1BBL- and B7-dependent signals were absent, CD8 T cell expansion was further reduced, resulting in lower CTL activity and impairing their ability to clear LCMV. Altogether, these results indicate that T cells have distinct costimulatory requirements: optimal CD8 responses require 4-1BBL-dependent interactions, whereas CD4 responses are minimally affected by 4-1BB costimulation, but require CD40-CD40L and B7-dependent interactions.     

4-1BB costimulation is required for protective anti-viral immunity after peptide vaccination

Peptide vaccination induces T cell activation and cytotoxic T cell development. In an effort to understand what factors can improve immune responses to peptide vaccination, the role of 4-1BB (CD137) costimulation was examined, since 4-1BB has been shown to promote T cell responses in other systems. 4-1BBL-deficient (-/-) and wild-type (+/+) mice were immunized with a lipidated lymphocytic choriomeningitis virus (LCMV) peptide NP396-404. Analysis of peptide-specific responses early after immunization by CTL assay, intracellular IFN-gamma staining, and IFN-gamma enzyme-linked immunospot assay (ELISPOT) indicated that CD8 T cell responses were reduced 3- to 10-fold in the absence of 4-1BB costimulation. Moreover, when agonistic anti-4-1BB Ab was given, CD8 T cell responses in 4-1BBL-/- mice were augmented to levels similar to those in 4-1BBL+/+ mice. Two months after immunization, 4-1BBL+/+ mice still had epitope-specific cells and were protected against viral challenge, demonstrating that peptide vaccination can induce long-term protection. In fact, 70% of CD8 T cells were specific for the immunizing peptide after viral challenge, demonstrating that strong, epitope-specific CD8 T cell responses are generated after peptide vaccination. In contrast, peptide-immunized 4-1BBL-/- mice had fewer epitope-specific cells and were impaired in their ability to resolve the infection. These results show that immunization with a single LCMV peptide provides long term protection against LCMV infection and point to costimulatory molecules such as 4-1BB as important components for generating protective immunity after vaccination.     

Temporal segregation of 4-1BB versus CD28-mediated costimulation: 4-1BB ligand influences T cell numbers late in the primary response and regulates the size of the T cell memory response following influenza infection

In this report, we demonstrate that CD28(-/-) mice are severely impaired in the initial expansion of D(b)/NP366-374-specific CD8 T cells in response to influenza virus infection, whereas 4-1BB ligand (4-1BBL)(-/-) mice show no defect in primary T cell expansion to influenza virus. In contrast, 4-1BBL(-/-) mice show a decrease in D(b)/NP366-374-specific T cells late in the primary response. Upon secondary challenge with influenza virus, 4-1BBL(-/-) mice show a decrease in the number of D(b)/NP366-374-specific T cells compared to wild-type mice such that the level of the CD8 T cell expansion during the in vivo secondary response is reduced to the level of a primary response, with concomitant reduction of CTL effector function. In contrast, Ab responses, as well as secondary CD4 T cell responses, to influenza are unaffected by 4-1BBL deficiency. Thus, CD28 is critical for initial T cell expansion, whereas 4-1BB/4-1BBL signaling affects T cell numbers much later in the response and is essential for the survival and/or responsiveness of the memory CD8 T cell pool.     

A switch in costimulation from CD28 to 4-1BB during primary versus secondary CD8 T cell response to influenza in vivo

4-1BBL(-/-) mice exhibit normal primary CD8 T cell responses to influenza virus, but show decreased CD8 T cell numbers late in the primary response as well as decreased secondary responses. In contrast, CD28(-/-) mice are defective in initial CD8 T cell expansion. Using agonistic anti-4-1BB Ab to replace the CD28 or 4-1BB signal, we examined the timing of the required signals for CD28 vs 4-1BB costimulation. A single dose of agonistic anti-4-1BB Ab added only during priming restores the secondary CD8 T cell response in CD28(-/-) mice. Once the T cell numbers in the primary response reach a minimum threshold, a full secondary response is achieved even in the absence of CD28. In contrast, anti-4-1BB added during priming fails to correct the defective secondary response in 4-1BBL(-/-) mice, whereas addition of anti-4-1BB during challenge fully restores this response. Thus, there is a switch in costimulatory requirement from CD28 to 4-1BB during primary vs recall responses. Adoptive transfer studies show that T cells primed in 4-1BBL(-/-) or wild-type mice are equally capable of re-expansion when rechallenged in wild-type mice. These studies rule out a model in which signals delivered through 4-1BB during priming program the T cells to give a full recall response and suggest that 4-1BB-4-1BBL interactions take place at later stages in the immune response. The results indicate that anti-4-1BB or 4-1BBL therapy will be most effective during the boost phase of a prime-boost vaccination strategy.     

Cooperation between 4-1BB and ICOS in the immune response to influenza virus revealed by studies of CD28/ICOS-deficient mice

CD28, ICOS, and 4-1BB each play distinct roles in the CD8 T cell response to influenza virus. CD28-/- mice are severely impaired in primary CD8 T cell expansion and fail to mount a secondary response to influenza. Influenza-specific CD8 T cells expand normally in ICOS-/- mice, with only a small and transient defect late in the primary response and an unimpaired secondary response. Conversely, 4-1BB/4-1BBL interaction is dispensable for the primary CD8 T cell response to influenza, but maintains CD8 T cell survival and controls the size of the secondary response. Previous results showed that a single dose of agonistic anti-4-1BB Ab at priming allowed partial restoration of primary CD8 T cell expansion and full recovery of the secondary CD8 T cell responses to influenza in CD28-/- mice. In this study we show that anti-4-1BB fails to correct the CD8 T cell defect in CD28-/-ICOS-/- mice, suggesting that ICOS partially compensates for CD28 in this model. In support of this hypothesis, we found that anti-4-1BB enhances ICOS expression on both T cell subsets and that anti-4-1BB and anti-ICOS can synergistically activate CD4 and CD8 T cells. Furthermore, ICOS and 4-1BB can cooperate to directly stimulate isolated CD28-/- CD8 T cells. These results reveal a novel interaction between the ICOS and 4-1BB costimulatory pathways as well as unexpected redundancy between CD28 and ICOS in primary CD8 T cell expansion. These findings have implications for costimulation of human T cell responses in diseases such as AIDS or rheumatoid arthritis, in which CD28- T cells accumulate.     

4-1BB and OX40 act independently to facilitate robust CD8 and CD4 recall responses

Mice deficient in OX40 or 4-1BB costimulatory pathways show defects in T cell recall responses, with predominant effects on CD4 vs CD8 T cells, respectively. However, OX40L can also stimulate CD8 T cells and 4-1BBL can influence CD4 T cells, raising the possibility of redundancy between the two TNFR family costimulators. To test this possibility, we generated mice deficient in both 4-1BBL and OX40L. In an adoptive transfer model, CD4 T cells expressed 4-1BB and OX40 sequentially in response to immunization, with little or no overlap in the timing of their expression. Under the same conditions, CD8 T cells expressed 4-1BB, but no detectable OX40. Thus, in vivo expression of 4-1BB and OX40 can be temporally and spatially segregated. In the absence of OX40L, there were decreased CD4 T cells late in the primary response and no detectable secondary expansion of adoptively transferred CD4 T cells under conditions in which primary expansion was unaffected. The 4-1BBL had a minor effect on the primary response of CD4 T cells in this model, but showed larger effects on the secondary response, although 4-1BBL(-/-) mice show less impairment in CD4 secondary responses than OX40L(-/-) mice. The 4-1BBL(-/-) and double knockout mice were similarly impaired in the CD8 T cell response, whereas OX40L(-/-) and double knockout mice were similarly impaired in the CD4 T cell response to both protein Ag and influenza virus. Thus, 4-1BB and OX40 act independently and nonredundantly to facilitate robust CD4 and CD8 recall responses.     

IL-15-dependent induction of 4-1BB promotes antigen-independent CD8 memory T cell survival

Mice lacking CD137L (4-1BBL) show normal primary expansion and contraction of the CD8+ T cell response to influenza virus, but exhibit a defect in Ag-specific CD8+ T cell numbers at 3-6 wk postinfection. Previous results showed that the decrease in CD8+ T cell numbers in this model is not due to a programming defect during primary expansion. Thus, it appears that 4-1BB/4-1BBL interactions control the number of surviving CD8+ effector memory cells, late in the primary response. In this report, we asked how 4-1BB on T cells could play a role after Ag has apparently been cleared from the host. We show that IL-15, a cytokine involved in regulation of CD8+ memory T cell survival, induces the expression of 4-1BB on CD8+CD44(high) memory phenotype T cells, but not on CD4+ T cells. The Ag-independent induction of 4-1BB by IL-15 was dependent on MAPK p38 and ERK activation. Transfer of in vitro-generated OT-I CD8+ memory T cells into unimmunized wild-type or 4-1BBL-deficient hosts revealed a 2- to 3-fold survival advantage when 4-1BBL was present, recapitulating the effect seen in the endogenous response to influenza in mice. Decreases in the overall number of memory CD8+ T cells were also observed in the bone marrow of unmanipulated 4-1BBL-deficient mice. These data suggest a model whereby 4-1BB expression on memory CD8+ T cells, perhaps due to encounter with IL-15 in the bone marrow, allows 4-1BB/4-1BBL interactions to maintain memory CD8 T cell survival in the absence of Ag.     

4-1BB ligand induces cell division, sustains survival, and enhances effector function of CD4 and CD8 T cells with similar efficacy

A costimulatory member of the TNFR family, 4-1BB, is expressed on activated T cells. Although some reports have suggested that 4-1BB is primarily involved in CD8 T cell activation, in this report we demonstrate that both CD4 and CD8 T cells respond to 4-1BB ligand (4-1BBL) with similar efficacy. CD4 and CD8 TCR transgenic T cells up-regulate 4-1BB, OX40, and CD27 and respond to 4-1BBL-mediated costimulation during a primary response to peptide Ag. 4-1BBL enhanced proliferation, cytokine production, and CTL effector function of TCR transgenic T cells. To compare CD4 vs CD8 responses to 4-1BBL under similar conditions of antigenic stimulation, we performed MLRs with purified CD4 or CD8 responders from CD28(+/+) and CD28(-/-) mice. We found that CD8 T cells produced IL-2 and IFN-gamma in a 4-1BBL-dependent manner, whereas under the same conditions the CD4 T cells produced IL-2 and IL-4. 4-1BBL promoted survival of CD4 and CD8 T cells, particularly at late stages of the MLR. CD4 and CD8 T cells both responded to anti-CD3 plus s4-1BBL with a similar cytokine profile as observed in the MLR. CD4 and CD8 T cells exhibited enhanced proliferation and earlier cell division when stimulated with anti-CD3 plus anti-CD28 compared with anti-CD3 plus 4-1BBL, and both subsets responded comparably to anti-CD3 plus 4-1BBL. These data support the idea that CD28 plays a primary role in initial T cell expansion, whereas 4-1BB/4-1BBL sustains both CD4 and CD8 T cell responses, as well as enhances cell division and T cell effector function.     

4-1BB ligand-mediated costimulation of human T cells induces CD4 and CD8 T cell expansion, cytokine production, and the development of cytolytic effector function

4-1BB (CD137) is a costimulatory member of the TNFR family expressed on activated T cells. Its ligand, 4-1BBL, is expressed on activated APC. In the mouse, CD8 T cells are preferentially activated by agonistic anti-murine 4-1BB Abs. However, murine 4-1BBL can stimulate both CD4 and CD8 T cells. To date, there are only limited data on the effects of 4-1BBL on human T cell responses. To further understand the role of 4-1BBL in human T cell responses, we compared human CD4 and CD8 T cell responses to transfected human 4-1BBL plus TCR-mediated stimulation. Both human CD4 and CD8 T cells responded to 4-1BBL. The presence of 4-1BBL on the APC led to increased expansion, cytokine production, and the development of cytolytic effector function by human T cells. In unfractionated T cell cultures, CD4 and CD8 T cells could expand to a similar extent in response to signals through the TCR and 4-1BB, as measured by CFSE labeling and by quantitating T cell numbers in the cultures. In contrast to the results with total T cells, isolated CD8 T cells produced less IL-2 and expanded to a lesser extent than isolated CD4 T cells responding to 4-1BBL. Thus, 4-1BBL is most effective when both CD4 and CD8 T cells are included in the cultures. CD28 and 4-1BB were found to synergize in the induction of IL-2 by human T cells, and CTLA-Ig partially blocked 4-1BBL-dependent IL-2 production. However, a portion of the 4-1BBL-mediated effects were independent of CD28-B7 interaction.     

Immune responses in 4-1BB (CD137)-deficient mice

The 4-1BB (a TNFR superfamily member) is an inducible costimulatory molecule that can exert regulatory effects on T cells independently of CD28 stimulation. The in vitro expression of 4-1BB (CD137) is induced following activation of T cells with various stimuli, including anti-TCR mAbs, lectins, and a combination of PMA and ionomycin. To delineate further the physiological role of 4-1BB in immunity, mice deficient in this receptor were generated. These mutant mice developed normally, and were viable and fertile. Humoral responses to vesicular stomatitis virus were comparable with those seen in wild-type mice, whereas the IgG2a and IgG3 isotype responses to keyhole limpet hemocyanin were somewhat reduced in the mutant mice. The 4-1BB-deficient mice demonstrated enhanced T cell proliferation in response to mitogens or anti-CD3 even in the environment of reduced ability to secrete growth-supporting cytokines (IL-2 and IL-4). Although T cells from 4-1BB-deficient mice showed enhanced proliferation, the T cell immune responses of these animals, such as cytokine production and CTL activity, were diminished. In addition, 4-1BB deletion appears to play a role in the regulation of myeloid progenitor cell growth, leading to an increase in these precursor cells in peripheral blood, bone marrow, and spleen.     

4-1BBL enhances anti-tumor responses in the presence or absence of CD28 but CD28 is required for protective immunity against parental tumors

A20 is an aggressive BALB/c B cell lymphoma that, despite its expression of B7-2, rapidly forms tumors in syngeneic mice. We have generated A20 transfectants expressing elevated levels of B7-2 (A20/B7-2high) or 4-1BBL (A20/4-1BBL(low,mod,high)) and found that mice which were able to reject the A20/B7-2 or A20/4-1BBL transfectants were also resistant to subsequent systemic challenge with the parental cell line. To assess whether the effectiveness of 4-1BBL in enhancing anti-tumor immunogenicity was dependent on additional signals from B7-CD28 interaction, we injected the A20 variants into BALB/c CD28(-/-) mice. We found that CD28(-/-) mice were able to reject the A20/4-1BBL variants while A20/B7-2 cells formed tumors. However, when the A20/4-1BBL resistant CD28(-/-) mice were systemically challenged with the A20 parental line, tumors formed rapidly. Upon restimulation in vitro, splenocytes from A20/4-1BBL immunized CD28(+/+) mice were able to kill parental tumors whereas splenocytes from CD28(-/-) mice showed a reduction in CTL activity against A20 or A20/4-1BBL targets. Examination of cytokine production by the immunized animals indicated that the CD28(-/-) splenocytes secreted substantially less IL-2 as well as reduced levels of IFN-gamma compared with their CD28(+/+) counterparts. Thus, 4-1BBL expressing tumors are capable of priming CTL responses against 4-1BBL transfected as well as parental tumors in the absence of CD28. However, in the absence of CD28 signaling, the production of cytokines and particularly IL-2 was lower, resulting in a weaker CTL recall response and reduced ability to survive challenge with parental tumor.     

Progressive depletion of peripheral B lymphocytes in 4-1BB (CD137) ligand/I-Ealpha)-transgenic mice

Interaction of 4-1BB (CD137) and its ligand (4-1BBL) is thought to positively regulate cell-mediated and humoral immune responses. We have prepared transgenic mouse strains that express 4-1BBL cDNA under the control of MHC class II I-Ealpha promoter. The 4-1BBL-transgenic mice show progressive splenomegaly and selective depletion of B220(+) B cells accompanied with low levels of circulating IgG and defective humoral responses to Ag challenge. In addition, splenocytes from the transgenic mice fail to provide stimulation for allogeneic T cells in both lymphoproliferative and CTL responses in vitro, whereas their T cells remain functionally normal. Our results reveal unexpected functions of 4-1BBL in the regulation of humoral immune responses and Ag presentation.     

Enhanced establishment of a virus carrier state in adult CD4+ T-cell-deficient mice.

CD4+ T cells play an important role in regulating the immune response; their contribution to virus clearance is variable. Mice that lack CD4+ T cells (CD4-/- mice) and are therefore unable to produce neutralizing antibodies cleared viscero-lymphotropic lymphocytic choriomeningitis virus (LCMV) strain WE when infected intravenously with a low dose (2 x 10(2) PFU) because of an effective CD8+ cytotoxic T-cell (CTL) response. In contrast, infection with a high dose (2 x 10(6) PFU) of LCMV strain WE led to expansion of antiviral CTL, which disappeared in CD4-/- mice; in contrast, CD4+ T-cell-competent mice developed antiviral memory CTL. This exhaustion of specific CTL caused viral persistence in CD4-/- mice, whereas CD4+ T-cell-competent mice eliminated the virus. After infection of CD4-/- mice with the faster-replicating LCMV strain DOCILE, abrogation of CTL response and establishment of viral persistence developed after infection with a low dose (5 x 10(2) PFU), i.e., an about 100-fold lower dose than in CD(4+)-competent control mice. These results show that absence of T help enhances establishment of an LCMV carrier state in selected situations.     

Extracellular domain of human 4-1BBL enhanced the function of cytotoxic T-lymphocyte induced by dendritic cell

Interaction of costimulatory molecules and their receptors is crucial for tumor lysate-pulsed dendritic cells (sensitized DC, sDC) to promote T cell activation, clonal expansion and its antitumor immunity. To augment the costimulatory signal may regulate the interaction between DC and cytotoxic T lymphocyte (CTL) and consequently enhance the antitumor response. The costimulatory ligand and receptor pair of 4-1BB/4-1BBL is one of the main factors in the costimulation of CTL. We explored the adjuvant role of a recombinant human 4-1BBL extracellular domain (ex4-1BBL) in modulating CTL activation induced by HepG2 antigen-loaded DC (sDC). The augment effects of sDC in combination with ex4-1BBL on the proliferation, activation, cell survival and cytotoxicity against HepG2 cells of CTL were examined. In the presence of ex4-1BBL, sDC exhibited markedly augmented effects on the above four functions of CTL. These results demonstrate that ex4-1BBL plays an important role in the costimulation pathway for DC-mediated CTL’s activation, which might be a useful adjuvant factor for DC-based cancer biotherapy.     

4-1BB is superior to CD28 costimulation for generating CD8+ cytotoxic lymphocytes for adoptive immunotherapy

Artificial APCs (aAPCs) genetically modified to express selective costimulatory molecules provide a reproducible, cost-effective, and convenient method for polyclonal and Ag-specific expansion of human T cells for adoptive immunotherapy. Among the variety of aAPCs that have been studied, acellular beads expressing anti-CD3/anti-CD28 efficiently expand CD4+ cells, but not CD8+ T cells. Cell-based aAPCs can effectively expand cytolytic CD8+ cells, but optimal costimulatory signals have not been defined. 4-1BB, a costimulatory molecule expressed by a minority of resting CD8+ T cells, is transiently up-regulated by all CD8+ T cells following activation. We compared expansion of human cytolytic CD8+ T cells using cell-based aAPCs providing costimulation via 4-1BB vs CD28. Whereas anti-CD3/anti-CD28 aAPCs mostly expand naive cells, anti-CD3/4-1BBL aAPCs preferentially expand memory cells, resulting in superior enrichment of Ag-reactive T cells which recognize previously primed Ags and efficient expansion of electronically sorted CD8+ populations reactive toward viral or self-Ags. Using HLA-A2-Fc fusion proteins linked to 4-1BBL aAPCs, 3-log expansion of Ag-specific CD8+ CTL was induced over 14 days, whereas similar Ag-specific CD8+ T cell expansion did not occur using HLA-A2-Fc/anti-CD28 aAPCs. Furthermore, when compared with cytolytic T cells expanded using CD28 costimulation, CTL expanded using 4-1BB costimulation mediate enhanced cytolytic capacity due, in part, to NKG2D up-regulation. These results demonstrate that 4-1BB costimulation is essential for expanding memory CD8+ T cells ex vivo and is superior to CD28 costimulation for generating Ag-specific products for adoptive cell therapy.     

Enhanced CD4 T cell responsiveness in the absence of 4-1BB

The 4-1BB (CD137) is a member of the TNFR superfamily, and is expressed on several cell types, including activated T cells. Although 4-1BB ligation by agonistic Ab or 4-1BB ligand-expressing APCs can costimulate T cells, the physiological significance of 4-1BB expression in vivo during T cell responses is still being elucidated. In this study, we have addressed the impact on CD4 T cell priming when 4-1BB is absent after gene targeting. Surprisingly, 4-1BB(-/-) mice generated more enhanced effector CD4 T cell responses to OVA protein in adjuvant, even though Ab responses in 4-1BB(-/-) mice were normal. Using an adoptive transfer system with OT-II TCR transgenic CD4 T cells, we found that 4-1BB(-/-) CD4 cells responding in a 4-1BB-sufficient environment had enhanced cell division compared with wild-type cells and displayed augmented clonal expansion during the primary response. This was not due to a developmental defect as 4-1BB-deficient CD4 cells could respond normally to Ag in vitro. These results demonstrate that the absence of 4-1BB can make CD4 T cells hyperresponsive to protein Ag in vivo, suggesting a new unappreciated negative regulatory role of 4-1BB when expressed on a T cell.     

An altered T cell repertoire in MECL-1-deficient mice

Immunoproteasome subunits low-molecular mass polypeptide (LMP)2 and LMP7 affect Ag presentation by MHC class I molecules. In the present study, we investigated the function of the third immunosubunit LMP10/multicatalytic endopeptidase complex-like (MECL)-1 (beta2i) in MECL-1 gene-targeted mice. The number of CD8+ splenocytes in MECL-1-/- mice was 20% lower than in wild-type mice. Infection with lymphocytic choriomeningitis virus (LCMV) elicited a markedly reduced cytotoxic T cell (CTL) response to the LCMV epitopes GP276-286/Db and NP205-212/Kb in MECL-1-/- mice. The weak CTL response to GP276-286/Db was not due to an impaired generation of this epitope but was attributed to a decreased precursor frequency of GP276-286/Db-specific T cells. The expansion of TCR-Vbeta10+ T cells, which contain GP276-286/Db-specific cells, was reduced in LCMV-infected MECL-1-/- mice. Taken together, our data reveal an in vivo function of MECL-1 in codetermining the T cell repertoire for an antiviral CTL response.     

Blocking 4-1BB/4-1BB ligand interactions prevents herpetic stromal keratitis

Herpetic stromal keratitis (HSK) is a chronic inflammatory process in corneal stroma that results from recurrent HSV type 1 infection. We used the murine model of HSK to demonstrate the importance of the interaction between an inducible T cell costimulatory receptor, 4-1BB, and its ligand, 4-1BB ligand (4-1BBL), in the development of this disease. In BALB/c mice, HSK ordinarily induced by infection with the RE strain of herpes was prevented by blocking 4-1BB/4-1BBL interaction, either by deleting 4-1BB (in mutant 4-1BB(-/-) mice) or by introducing mAbs against 4-1BBL. The majority of T cells infiltrating the infected corneas were 4-1BB(+) activated effector cells that expressed cell surface markers CD44, CD25, and/or CD62L, as well as chemokine receptors CCR1, CCR2, and CCR5, and a limited number of TCR Vbeta chains (Vbeta8.1/8.2, Vbeta8.3, Vbeta10b, and Vbeta5.1/5.2, in order of abundance). Analysis of cell surface phenotypes showed that the failure to develop HSK in the 4-1BB(-/-) mice was associated with a reduced expression of CD62L at the time of T cell migration into the corneal stroma.     

4-1BBL通过激活Wnt/β-catenin信号通路促进人胃癌细胞的增殖和迁移

4-1BB和4-1BB配体(4-1BBL),又被称为CD137和CD137配体,分别属于肿瘤坏死因子(TNF)受体和配体家族的成员。4-1BBL 与4-1BB相互作用可以激活T细胞免疫应答。因此,4-1BBL一直在抗肿瘤免疫应答中发挥经典的免疫共刺激分子作用。近期研究发现,4-1BBL在肿瘤细胞中另有其他的生物学功能,但4-1BBL在胃癌进展过程中的功能尚不明确。本文探讨了4-1BBL在人胃癌细胞中的生物学功能和分子作用机制。首先,通过检索TCGA和Kaplan Meier plotter数据库发现,4-1BBL在胃癌组织中的表达显著高于癌旁组织（P<0.001）,且4-1BBL的高表达与胃癌的不良预后正相关（P<0.05）。细胞生物学的结果显示,敲除4-1BBL明显抑制胃癌细胞的增殖（P<0.05）、侵袭和迁移（P<0.05）,促进胃癌细胞的凋亡（P<0.05）;另外,蛋白质免疫印迹结果表明,敲除4-1BBL可使β-联蛋白、c-Myc和细胞周期蛋白D1(cyclin D1)的蛋白质表达水平下降,抑制Wnt/β-catenin信号通路。相反,过表达4-1BBL则显著促进胃癌细胞增殖（P<0.05）、侵袭和迁移（P<0.05）,减少胃癌细胞的凋亡（P<0.05）;且过表达4-1BBL促进β-联蛋白(β-catenin)、c-Myc和细胞周期蛋白D1的蛋白质表达,激活Wnt/β-catenin信号通路。综上所述,4-1BBL可通过激活Wnt/β-catenin信号通路促进人胃癌细胞的增殖和迁移。     

CD8+ T cell dysfunction and increase in murine gammaherpesvirus latent viral burden in the absence of 4-1BB ligand

Studies of costimulatory receptors belonging to the TNFR family have revealed their diverse roles in affecting different stages of the T cell response. The 4-1BB ligand (4-1BBL)/4-1BB pathway has emerged as a receptor-ligand pair that impacts not the initial priming, but later phases of the T cell response, such as sustaining clonal expansion and survival, maintaining memory CD8(+) T cells, and supporting secondary expansion upon Ag challenge. Although the role of this costimulatory pathway in CD8(+) T cell responses to acute viral infections has been well-studied, its role in controlling chronic viral infections in vivo is not known to date. Using the murine gammaherpesvirus-68 (MHV-68) model, we show that 4-1BBL-deficient mice lack control of MHV-68 during latency and show significantly increased latent viral loads. In contrast to acute influenza infection, the numbers of MHV-68-specific memory CD8(+) T cells were maintained during latency. However, the virus-specific CD8(+) T cells showed defects in function, including decreased cytolytic function and impaired secondary expansion. Thus, 4-1BBL deficiency significantly affects the function, but not the number, of virus-specific CD8(+) T cells during gammaherpesvirus latency, and its absence results in an increased viral burden. Our study suggests that the 4-1BB costimulatory pathway plays an important role in controlling chronic viral infections.