Provision of 4-1BB ligand enhances effector and memory CTL responses generated by immunization with dendritic cells expressing a human tumor-associated antigen

Development and characterization of a novel human CD137 agonistic antibody with anti-tumor activity and a good safety profile in non-human primates

CD137 (4-1BB, TNFRSF9), an inducible T-cell costimulatory receptor, is expressed on activated T cells, activated NK cells, Treg cells, and several innate immune cells, including DCs, monocytes, neutrophils, mast cells, and eosinophils. In animal models and clinical trials, anti-CD137 agonistic monoclonal antibodies have shown anti-tumor potential, but balancing the efficacy and toxicity of anti-CD137 agonistic monoclonal antibodies is a considerable hindrance for clinical applications. Here, we describe a novel fully human CD137 agonistic antibody (PE0116) generated from immunized harbor H2L2 human transgenic mice. PE0116 is a ligand blocker, which is also the case for Utomilumab (one of the leading CD137 agonistic drugs); PE0116 partially overlaps with Urelumab's recognized epitope. In vitro, PE0116 activates NF-κB signaling, significantly promotes T-cell proliferation, and increases cytokine secretion in the presence of cross-linking. Importantly, PE0116 possesses robust anti-tumor activity in the MC38 tumor model. In vivo, PE0116 exhibits a good safety profile and has typical pharmacokinetic characteristics of an IgG antibody in preclinical studies of non-human primates. In summary, PE0116 is a promising anti-CD137 antibody with a good safety profile in preclinical studies.

CD137 and PD-L1 targeting with immunovirotherapy induces a potent and durable antitumor immune response in glioblastoma models

Background

Glioblastoma (GBM) is a devastating primary brain tumor with a highly immunosuppressive tumor microenvironment, and treatment with oncolytic viruses (OVs) has emerged as a promising strategy for these tumors. Our group constructed a new OV named Delta-24-ACT, which was based on the Delta-24-RGD platform armed with 4-1BB ligand (4-1BBL). In this study, we evaluated the antitumor effect of Delta-24-ACT alone or in combination with an immune checkpoint inhibitor (ICI) in preclinical models of glioma.

Methods

The in vitro effect of Delta-24-ACT was characterized through analyses of its infectivity, replication and cytotoxicity by flow cytometry, immunofluorescence (IF) and MTS assays, respectively. The antitumor effect and therapeutic mechanism were evaluated in vivo using several immunocompetent murine glioma models. The tumor microenvironment was studied by flow cytometry, immunohistochemistry and IF.

Results

Delta-24-ACT was able to infect and exert a cytotoxic effect on murine and human glioma cell lines. Moreover, Delta-24-ACT expressed functional 4-1BBL that was able to costimulate T lymphocytes in vitro and in vivo. Delta-24-ACT elicited a more potent antitumor effect in GBM murine models than Delta-24-RGD, as demonstrated by significant increases in median survival and the percentage of long-term survivors. Furthermore, Delta-24-ACT modulated the tumor microenvironment, which led to lymphocyte infiltration and alteration of their immune phenotype, as characterized by increases in the expression of Programmed Death 1 (PD-1) on T cells and Programmed Death-ligand 1 (PD-L1) on different myeloid cell populations. Because Delta-24-ACT did not induce an immune memory response in long-term survivors, as indicated by rechallenge experiments, we combined Delta-24-ACT with an anti-PD-L1 antibody. In GL261 tumor-bearing mice, this combination showed superior efficacy compared with either monotherapy. Specifically, this combination not only increased the median survival but also generated immune memory, which allowed long-term survival and thus tumor rejection on rechallenge.

Conclusions

In summary, our data demonstrated the efficacy of Delta-24-ACT combined with a PD-L1 inhibitor in murine glioma models. Moreover, the data underscore the potential to combine local immunovirotherapy with ICIs as an effective therapy for poorly infiltrated tumors.

4-1BB Agonism Averts TIL Exhaustion and Licenses PD-1 Blockade in Glioblastoma and Other Intracranial Cancers

PURPOSE

The success of checkpoint blockade against glioblastoma (GBM) has been disappointing. Anti-PD-1 strategies may be hampered by severe T-cell exhaustion. We sought to develop a strategy that might license new efficacy for checkpoint blockade in GBM.

EXPERIMENTAL DESIGN

We characterized 4-1BB expression in tumor-infiltrating lymphocytes (TIL) from human GBM. We implanted murine tumor models including glioma (CT2A), melanoma (B16), breast (E0771), and lung carcinomas intracranially and subcutaneously, characterized 4-1BB expression, and tested checkpoint blockade strategies in vivo.

RESULTS

Our data reveal that 4-1BB is frequently present on nonexhausted CD8⁺ TILs in human and murine GBM. In murine gliomas, 4-1BB agonism and PD-1 blockade demonstrate a synergistic survival benefit in a CD8⁺ T-cell-dependent manner. The combination decreases TIL exhaustion and improves TIL functionality. This strategy proves most successful against intracranial CT2A gliomas. Efficacy in all instances correlates with the levels of 4-1BB expression on CD8⁺ TILs, rather than with histology or with intracranial versus subcutaneous tumor location. Proffering 4-1BB expression to T cells licenses combination 4-1BB agonism and PD-1 blockade in models where TIL 4-1BB levels had previously been low and the treatment ineffective.

CONCLUSIONS

Although poor T-cell activation and severe T-cell exhaustion appear to be limiting factors for checkpoint blockade in GBM, 4-1BB agonism obviates these limitations and produces long-term survival when combined with anti-PD-1 therapy. Furthermore, this combination therapy is limited by TIL 4-1BB expression, but not by the intracranial compartment, and therefore may be particularly well-suited to GBM.

4-1BBL enhances CD8+ T cell responses induced by vectored vaccines in mice but fails to improve immunogenicity in rhesus macaques

T cells play a central role in the immune response to many of the world's major infectious diseases. In this study we investigated the tumour necrosis factor receptor superfamily costimulatory molecule, 4-1BBL (CD137L, TNFSF9), for its ability to increase T cell immunogenicity induced by a variety of recombinant vectored vaccines. To efficiently test this hypothesis, we assessed a number of promoters and developed a stable bi-cistronic vector expressing both the antigen and adjuvant. Co-expression of 4-1BBL, together with our model antigen TIP, was shown to increase the frequency of murine antigen-specific IFN-γ secreting CD8(+) T cells in three vector platforms examined. Enhancement of the response was not limited by co-expression with the antigen, as an increase in CD8(+) immunogenicity was also observed by co-administration of two vectors each expressing only the antigen or adjuvant. However, when this regimen was tested in non-human primates using a clinical malaria vaccine candidate, no adjuvant effect of 4-1BBL was observed limiting its potential use as a single adjuvant for translation into a clinical vaccine.

Differential impact of CD27 and 4-1BB costimulation on effector and memory CD8 T cell generation following peptide immunization

The factors that determine differentiation of naive CD8 T cells into memory cells are not well understood. A greater understanding of how memory cells are generated will inform of ways to improve vaccination strategies. In this study, we analyzed the CD8 T cell response elicited by two experimental vaccines comprising a peptide/protein Ag and an agonist that delivers a costimulatory signal via CD27 or 4-1BB. Both agonists increased expansion of Ag-specific CD8 T cells compared with Ag alone. However, their capacity to stimulate differentiation into effector and memory cells differed. CD27 agonists promoted increased expression of perforin and the generation of short-lived memory cells, whereas stimulation with 4-1BB agonists favored generation of stable memory. The memory-promoting effects of 4-1BB were independent of CD4 T cells and were the result of programing within the first 2 d of priming. Consistent with this conclusion, CD27 and 4-1BB-stimulated CD8 T cells expressed disparate amounts of IL-2, IFN-γ, CD25, CD71, and Gp49b as early as 3 d after in vivo activation. In addition, memory CD8 T cells, generated through priming with CD27 agonists, proliferated more extensively than did 4-1BB-generated memory cells, but these cells failed to persist. These data demonstrate a previously unanticipated link between the rates of homeostatic proliferation and memory cell attrition. Our study highlights a role for these receptors in skewing CD8 T cell differentiation into effector and memory cells and provides an approach to optimize vaccines that elicit CD8 T cell responses.

Fine-tuning of dendritic cell biology by the TNF superfamily

Members of the tumour necrosis factor (TNF) superfamily have been implicated in a wide range of biological functions, and their expression by cells of the immune system makes them appealing targets for immunomodulation. One common theme for TNF superfamily members is their coordinated expression at the interface between antigen-specific T cells and antigen-presenting dendritic cells and, by virtue of this expression pattern, TNF superfamily members can shape T cell immune responses. Understanding how to manipulate such functions of the TNF superfamily may allow us to tip the balance between immunity and tolerance in the context of human disease.

Tolerogenic dendritic cells generated by RelB silencing using shRNA prevent acute rejection

It is well known that adoptive transfer of donor-derived tolerogenic dendritic cells (DCs) helps to induce immune tolerance. RelB, one of NF-κB subunits, is a critical element involved in DC maturation. In the present study, our results showed tolerogenic DCs could be acquired via silencing RelB using small interfering RNA. Compared with imDCs, the tolerogenic DCs had more potent ability to inhibit mixed lymphocyte reaction (MLR) and down-regulate Th1 cytokines and prompt the production of Th2 cytokines. They both mediated immune tolerance via the increased of T cell apoptosis and generation of regulatory T cells. Administration of donor-derived tolerogenic DCs significantly prevented the allograft rejection and prolonged the survival time in a murine heart transplantation model. Our results demonstrate donor-derived, RelB-shRNA induced tolerogenic DCs can significantly induce immune tolerance in vitro and in vivo.

Lentiviral-mediated shRNA against RelB induces the generation of tolerogenic dendritic cells

OBJECTIVE

Lentiviral-mediated shRNA against RelB was used to produce tolerogenic dendritic cells from murine bone marrow derived dendritic cells (BMDCs).

METHOD

RelB expression in the BMDCs was silenced by lentivirus carrying RelB shRNA. The apoptosis rate and surface markers of DCs were assessed by flow cytometry. IL-12,IL-10,TGF-β1 secreted by DCs and DNA binding capacity of NF-κB subunits in the nucleus were measured by ELISA, independently. MLR was used to analyze the capacity of DCs to inhibit immune response.

RESULTS

RelB expression was significantly inhibited in DCs following lentiviral mediated delivery of RelB specific shRNA. The RelB shRNA-DC produced lower IL-12 and higher IL-10 than mature dendritic cells (mDCs) and silencing control DCs. There was no difference in the apoptosis rate between shRNA RelB-DCs and mDCs. The expression levels of co-stimulatory molecules (CD80, CD86 and CD83) and MHC-II class molecule were lower in the RelB shRNA-DCs than in the mDCs and silencing control DCs. In addition, RelB shRNA also inhibited the RelB DNA binding capacity but had no effect on other NF-κB subunits. The shRNA RelB-DCs can significantly inhibit mixed lymphocyte reaction (MLR) and down-regulate Th1 cytokines and prompt the production of Th2 cytokines.

CONCLUSION

Our results indicate RelB shRNA transfection of DCs can induce the immature status, and produce tolerogenic DCs.

Engineering dendritic cells to enhance cancer immunotherapy

Cancer immunotherapy aims to establish immune-mediated control of tumor growth by priming T-cell responses to target tumor-associated antigens. Three signals are required for T-cell activation: (i) presentation of cognate antigen in self MHC molecules; (ii) costimulation by membrane-bound receptor-ligand pairs; and (iii) soluble factors to direct polarization of the ensuing immune response. The ability of dendritic cells (DCs) to provide all three signals required for T-cell activation makes them an ideal cancer vaccine platform. Several strategies have been developed to enhance and control antigen presentation, costimulation, and cytokine production. In this review, we discuss progress toward developing DC-based cancer vaccines by genetic modification using RNA, DNA, and recombinant viruses. Furthermore, the ability of DC-based vaccines to activate natural killer (NK) and B-cells, and the impact of gene modification strategies on these populations is described. Clinical trials using gene-modified DCs have shown modest results, therefore, further considerations for DC manipulation to enhance their clinical efficacy are also discussed.

CTLA4 is expressed on mature dendritic cells derived from human monocytes and influences their maturation and antigen presentation

Background

Dendritic cells (DCs) initiate immune responses through their direct interaction with effector cells. However, the mechanism by which DC activity is regulated is not well defined. Previous studies have shown that CTLA4 on T cells regulates DCs function by "cross-talk". We investigated whether there is an intrinsic regulatory mechanism in DCs, with CTLA4 as a candidate regulator.

Results

We confirmed via RT-PCR and flow cytometry the natural expression of CTLA4 on mature DCs derived from human monocytes. Approximately 8% CD1a-positive cells express CTLA4 both on surface and intracellular, whereas 10% CD1a-negative cells express CTLA4 intracellularly, but little expression was observed on the cell surface. The cross-linking of CTLA4 inhibits DCs maturation and antigen presentation in vitro, but does not inhibit endocytosis.

Conclusions

CTLA4 is expressed by DCs and plays an inhibitory role. CTLA4-expressing DCs may represent a group of regulatory DCs. Because of its wide distribution on different cell types, CTLA4 may play a general role in regulating immune responses.

Generation of an immune microenvironment as a novel mechanism for myotoxins to potentiate genetic vaccines

We recently reported that administration of low doses of myotoxins at vaccination sites potentiated antigen-specific T-cell immunity induced by genetic cancer vaccines in mice, an effect which was superior to TLR agonists. In the current study, we found unexpectedly that the mechanism of this potent adjuvant effect was immune-mediated. Myotoxins induced sterile inflammation at vaccination sites, associated with a predominant infiltration of dendritic cells (DC). Inhibition of DC recruitment abrogated the immune stimulation effect of myotoxins, suggesting the requirement for DC. Genetic profiling of myotoxin-treated tissues revealed characteristics of an immune microenvironment with up-regulation of chemokines, proinflammatory cytokines, Toll-like receptors (TLR) and their endogenous ligands, and activation of innate immunity. Mechanistic experiments in vivo also elucidated the requirement for genes triggering DC maturation including TLR signaling and CD40. These studies suggest that myotoxins-induced sterile inflammation generates a favorable microenvironment that promotes multiple stages in the development of adaptive immunity. This novel mechanism of immune potentiation may be exploited for development of adjuvants for genetic vaccines against infectious pathogens and cancer.

Construction of a recombinant adenovirus co-expressing truncated human prostate-specific membrane antigen and mouse 4-1BBL genes and its effect on dendritic cells

Our aim was to construct a recombinant adenovirus co-expressing truncated human prostate-specific membrane antigen (tPSMA) and mouse 4-1BBL genes and to determine its effect on dendritic cells (DCs) generated from bone marrow suspensions harvested from C57BL/6 mice for which the effect of 4-1BBL on DCs is not clear, especially during DCs processing tumor-associated antigen. Replication deficient adenovirus AdMax™ Expression System was used to construct recombinant adenovirus Ad-tPSMA-internal ribosome entry site-mouse 4-1BBL (Ad-tPSMA-IRES-m4-1BBL) and Ad-enhanced green fluorescent protein. Day 7 proliferating DC aggregates generated from C57BL/6 mice were collected as immature DCs and further mature DCs were obtained by lipopolysaccharide activated immature DCs. After DCs were exposed to the recombinant adenovirus with 250 multiplicity of infection, the expression of tPSMA and m4-1BBL proteins were detected by Western blot, and the apoptosis and phenotype of DCs were analyzed by flow cytometry. Cytokines (IL-6 and IL-12) in the supernatant were detected by enzyme-linked immunosorbent assay (ELISA). Proliferation of T cells was detected by allogeneic mixed lymphocyte reactions. The tPSMA and m4-1BBL proteins were expressed correctly. The apoptosis rate of DCs transfected with Ad-tPSMA-IRES-m4-1BBL was 14.6%, lower than that of control DCs. The expression of co-stimulatory molecules [CD80 (81.6 ± 5.4%) and CD86 (80.13 ± 2.81%)] up-regulated in Ad-tPSMA-IRES-m4-1BBL-pulsed DCs, and the level of IL-6 (3960.2 ± 50.54 pg/mL) and IL-12 (249.57 ± 12.51 pg/mL) production in Ad-tPSMA-IRES-m4-1BBL-transduced DCs were significantly higher (P < 0.05) than those in control DCs. Ad-tPSMA-IRES-m4-1BBL induced higher T-cell proliferation (OD(450) = 0.614 ± 0.018), indicating that this recombinant adenovirus can effectively enhance the activity of DCs.

CD137 ligand, a member of the tumor necrosis factor family, regulates immune responses via reverse signal transduction

CD137 (4-1BB, TNFR superfamily 9) and its ligand are members of the TNFR and TNF families, respectively, and are involved in the regulation of a wide range of immune activities. CD137 ligand cross-links its receptor, CD137, which is expressed on activated T cells, and costimulates T cell activities. CD137 ligand can also be expressed as a transmembrane protein on the cell surface and transmit signals into the cells on which it is expressed (reverse signaling). CD137 ligand expression is found on most types of leukocytes and on some nonimmune cells. In monocytic cells (monocytes, macrophages, and DCs), CD137 ligand signaling induces activation, migration, survival, and differentiation. The activities of T cells, B cells, hematopoietic progenitor cells, and some malignant cells are also influenced by CD137 ligand, but the physiological significance is understood only partly. As CD137 and CD137 ligand are regarded as valuable targets for immunotherapy, it is pivotal to determine which biological effects are mediated by which of the 2 molecules.

The change of immunoactivity of dendritic cells induced by mouse 4-1BBL recombinant adenovirus

PURPOSE

The purpose of this study is to construct a recombinant adenovirus vector carrying mouse 4-1BBL and observe its effects in dendritic cells.

MATERIALS AND METHODS

Mouse 4-1BBL cDNA was taken from the plasmid pcDNA3-m4- 1BBL and subcloned into adenovirus shuttle plasmid pAdTrack-CMV, and then transformed into competent BJ5183 with plasmid pAdEasy-1. After recombination in E.coli, Ad-4-1BBL was packaged and amplified in HEK 293 cells. The expression of 4-1BBL in Ad-4-1BBL-transfected mouse prostate cancer cell line RM-1 was detected by reverse transcription polymerase chain reaction (RT-PCR) and Western blot. After the co-culture of dendritic cells (DCs) with Ad-4-1BBL-transfected RM-1 cells, interleukin (IL)-6 and IL-12 production were assessed by enzyme-linked immunosorbent assay (ELISA) and co-stimulatary molecules (CD80 and CD86) on DCs were analyzed by flow cytometry.

RESULTS

The levels of IL-6 (3,960 pg/mL) and IL-12 (249 pg/mL) production in Ad-m4-1BBL-pulsed DCs were more than those in none-pulsed DCs. The differences were statistically significant (p < 0.05). The expression of co-stimulatary molecules (CD80 and CD86) was up-regulated in Ad-m4-1BBL-pulsed DCs.

CONCLUSION

The results indicated the recombinant mouse 4-1BBL can effectively activate DCs.

Anti-tumor immune response induced by dendritic cells transduced with truncated PSMA IRES 4-1BBL recombinant adenoviruses

Up-regulation of receptor-ligand pairs during interaction of a peptide-bound MHC complex on dendritic cells (DCs) with cognate TCR may amplify, sustain, and drive diversity in the ensuing T cell immune response. Members of the TNF ligand superfamily and the TNFR superfamily contribute to this costimulatory molecule signaling. In the present study, we used replication deficient adenoviruses to introduce a tumor-associated Ag (a truncated human prostate-specific membrane antigen (tPSMA)) and the T cell costimulatory molecule 4-1BBL into murine DCs, and observed the ability of these recombinant DCs to elicit tPSMA-directed T-cell responses in vitro and anti-tumor immunity to RM-1-tPSMA in a murine tumor model. Infection of DCs with Ad-tPSMA-IRES-m4-1BBL induced tPSMA-specific proliferative responses and up-regulated CD80 and CD86 s signaling molecules. The cytotoxic T lymphocytes activated by the Ad-tPSMA-IRES-m4-1BBL-transfected DCs showed significantly higher IFN-gamma production and cytotoxicity against the RM-1 cells transfected with tPSMA. Moreover, vaccination of mice with Ad-tPSMA-IRES-m4-1BBL-transfected DCs induced a potent protective and therapeutic anti-tumor immunity to RM-1-tPSMA in a tumor model. These results demonstrated that development of DCs engineered to express tPSMA and 4-1BBL by recombinant adenovirus-mediated gene transfer may offer a new strategy for prostate cancer immunotherapy.

Evaluating maturation and genetic modification of human dendritic cells in a new polyolefin cell culture bag system

BACKGROUND

Dendritic cells (DCs) are applied worldwide in several clinical studies of immune therapy of malignancies, autoimmune diseases, and transplantations. Most legislative bodies are demanding high standards for cultivation and transduction of cells. Closed-cell cultivating systems like cell culture bags would simplify and greatly improve the ability to reach these cultivation standards. We investigated if a new polyolefin cell culture bag enables maturation and adenoviral modification of human DCs in a closed system and compare the results with standard polystyrene flasks.

STUDY DESIGN AND METHODS

Mononuclear cells were isolated from HLA-A*0201-positive blood donors by leukapheresis. A commercially available separation system (CliniMACS, Miltenyi Biotec) was used to isolate monocytes by positive selection using CD14-specific immunomagnetic beads. The essentially homogenous starting cell population was cultivated in the presence of granulocyte-macrophage-colony-stimulating factor and interleukin-4 in a closed-bag system in parallel to the standard flask cultivation system. Genetic modification was performed on Day 4. After induction of maturation on Day 5, mature DCs could be harvested and cryopreserved on Day 7. During the cultivation period comparative quality control was performed using flow cytometry, gene expression profiling, and functional assays.

RESULTS

Both flasks and bags generated mature genetically modified DCs in similar yields. Surface membrane markers, expression profiles, and functional testing results were comparable. The use of a closed-bag system facilitated clinical applicability of genetically modified DCs.

CONCLUSIONS

The polyolefin bag-based culture system yields DCs qualitatively and quantitatively comparable to the standard flask preparation. All steps including cryopreservation can be performed in a closed system facilitating standardized, safe, and reproducible preparation of therapeutic cells.

Adjuvantive effects of anti-4-1BB agonist Ab and 4-1BBL DNA for a HIV-1 Gag DNA vaccine: different effects on cellular and humoral immunity

Plasmid DNA immunizations induce low levels but a broad spectrum of cellular and humoral immune responses. Here, we investigate the potential of co-stimulation through 4-1BB as an adjuvant for a HIV-1 DNA vaccine in mice. We designed plasmid DNAs expressing either the membrane bound or soluble form of 4-1BBL, and compared with the agonistic anti-4-1BB Ab for their ability to adjuvant the Gag DNA vaccine. Both, anti-4-1BB agonistic Ab as well as 4-1BBL DNA enhanced the Gag-specific cellular immune responses. However, in complete contrast to the agonistic Ab that suppressed humoral immunity to Gag, 4-1BBL DNA adjuvanted vaccines enhanced Gag-specific IgG responses. Importantly, the expression of Gag and 4-1BBL from the same plasmid was critical for the adjuvant activity. Collectively, our data suggest that for a HIV-1 vaccine where both antigen-specific cellular and humoral immunity are desirable, 4-1BBL expressed by a DNA vaccine is a superior adjuvant than anti-4-1BB agonistic Ab.

Clinical and immunologic effects of intranodal autologous tumor lysate-dendritic cell vaccine with Aldesleukin (Interleukin 2) and IFN-{alpha}2a therapy in metastatic renal cell carcinoma patients

PURPOSE

To evaluate the clinical and immunologic outcomes of DC (dendritic cell) vaccine with interleukin (IL)-2 and IFN-alpha 2a in metastatic renal cell carcinoma patients.

EXPERIMENTAL DESIGN

Eighteen consented and eligible patients were treated. Peripheral blood monocytes were cultured ex vivo into mature DCs and loaded with autologous tumor lysate. Treatment consisted of five cycles of intranodal vaccination of DCs (1 x 10(7) cells/1 mL Lactated Ringer's solution), 5-day continuous i.v. infusion of IL-2 (18MiU/m2), and three s.c. injections of IFN-alpha 2a (6MiU) every other day. Response Evaluation Criteria in Solid Tumors criteria were used for disease assessment. Correlative immunologic end points included peripheral blood lymphocyte cell phenotype and function as well as peripheral blood anti-renal cell carcinoma antibody and cytokine levels.

RESULTS

All patients received between two and five treatment cycles. Toxicities consisted of known and expected cytokine side effects. Overall objective clinical response rate was 50% with three complete responses. Median time to progression for all patients was 8 months, and median survival has not been reached (median follow up of 37+ months). Treatment-related changes in correlative immunologic end points were noted and the level of circulating CD4(+) T regulatory cells had a strong association with outcome. Pre-IP-10 serum levels approached significance for predicting outcome.

CONCLUSIONS

The clinical and immunologic responses observed in this trial suggest an interaction between DC vaccination and cytokine therapy. Our data support the hypothesis that modulation of inflammatory, regulatory, and angiogenic pathways are necessary to optimize therapeutic benefit in renal cell carcinoma patients. Further exploration of this approach is warranted.

In vivo anti-melanoma efficacy of allo-restricted CTLs specific for melanoma expanded by artificial antigen-presenting cells

Cytotoxic CD8(+) T cells are key effectors in the immunotherapy of malignant and viral diseases. However, autologous T cell responses to tumor antigens presented by self-MHC are usually weak and ineffective. Allo-restricted T cells represent a potent source of tumor-specific T cells for adoptive immunotherapy. This study reports in vivo anti-melanoma efficacy of the pTRP2-specific allo-restricted CTLs expanded from the BALB/c splenocytes by multiple stimulations with aAPCs made by coating H-2K(b)-Ig/pTRP2 dimeric complexes, anti-CD28 antibody, 4-1BBL molecules and CD83 molecules to cell-sized latex beads. The induced allo-restricted CTLs exhibited specific lysis against RMA-S cells pulsed with the peptide pTRP2 and H-2K(b+) melanoma cells expressing TRP2, while a murine Lewis lung carcinoma cell line 3LL could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-H-2K(b) monoclonal antibody Y3. Adoptive transfer of the allo-restricted CTLs specific for malignant melanoma expanded by the aAPCs can mediate effective anti-melanoma response in vivo. These results suggested that the specific allo-restricted CTLs expanded by aAPCs coated with an MHC-Ig/peptide complex, anti-CD28 antibody, 4-1BBL and CD83 could be a potential option of specific immunotherapy for patients with malignant melanoma.

Costimulatory ligand CD70 allows induction of CD8+ T-cell immunity by immature dendritic cells in a vaccination setting

The use of dendritic cells (DCs) as anticancer vaccines holds promise for therapy but requires optimization. We have explored the potential of costimulatory ligand CD70 to boost the capacity of DCs to evoke effective CD8(+) T-cell immunity. We show that immature conventional DCs, when endowed with CD70 expression by transgenesis, are converted from a tolerogenic state into an immunogenic state. Adoptively transferred CD70-expressing immature DCs could prime CD8(+) T cells, by CD27, to become tumor-eradicating cytolytic effectors and memory cells with a capacity for robust secondary expansion. The CD8(+) T-cell response, including memory programming, was independent of CD4(+) T-cell help, because the transferred immature DCs were loaded with major histocompatibility complex class I-restricted peptide only. Without CD70 expression, the DCs generated abortive clonal expansion, dysfunctional antitumor responses, and no CD8(+) T-cell memory. CD70-expressing CD8(+) DCs were the primary subset responsible for CD8(+) T-cell priming and performed comparably to fully matured DCs. These data highlight the importance of CD27/CD70 interactions at the T-cell/DC interface and indicate that CD70 should be considered in the design of DC vaccination strategies.

Recombinant attenuated Salmonella harboring 4-1BB ligand gene enhances cellular immunity

OBJECTIVE

To transfect antigen presenting cells (APCs) with 4-1BB ligand DNA by attenuated Salmonella enterica serovar Typhimurium in vivo, and to observe the effects of ectogenous 4-1BBL on the immune functions of infected rats.

METHODS

Attenuated Salmonella typhimurium (vaccine strain) carrying plasmids pIRES2-EGFP-4-1BBL was constructed and used to infect HepG2 hepatoma cells. The expression of reporter gene, green fluorescent protein (GFP) and rat 4-1BBL in the transfected cells was detected by double-immunofluorescence staining. Rats were fed with the recombinant bacteria intragastrically on three occasions in 2 weeks, and were then sacrificed. The transcription and expression of GFP and 4-1BBL genes in splenocytes were measured by RT-PCR and flow cytometry. The phenotypes of T cells in peripheral blood and splenocytes were determined by flow cytometry. The content of IFN-gamma in the cultural supernatant of splenocytes stimulated by PHA was measured by ELISA.

RESULTS

The recombinant bacteria harboring 4-1BBL had the same invasive abilities as the original bacteria, and it was able to deliver exogenous genes into HepG2 cells, where the GFP and 4-1BBL were successfully expressed. There were significant upregulations of CD3(+)CD8(+) T cells (P=0.018) and CD3(+)CD25(+) T cells (P=0.019) in the peripheral blood cells as well as CD3(+)CD8(+) T cells (P=0.022), and CD3(+)CD25(+) T cells (P=0.008) in splenocytes of the infected rats. The rats had more 4-1BBL expression detected in the spleen. IFN-gamma released by PHA-stimulated splenocytes increased significantly by the recombinant bacteria as compared with controls (P=0.002).

CONCLUSION

Salmonella serovar Typhimurium containing 4-1BBL can transfect target genes into antigen presenting cells in vivo, and the expression of exogenous 4-1BBL enhances cellular immunity markedly.

PR1 vaccination in myeloid malignancies

The graft-versus-leukemia (GVL) effect following allogeneic stem cell transplantation is testament to the effectiveness of the immune system in recognizing and eliminating leukemia cells. The successful identification of a range of leukemia-associated antigens (LAAs) that drive the GVL response in recent years has stimulated research in the development of vaccines to treat hematological malignancies. Here, we review the current experience with the PR1 vaccine. PR1 is a nine amino acid, HLA-A(*)0201-restricted peptide, shared by two myeloid LAAs, proteinase (PR)3 and neutrophil elastase (NE). PR3 and NE are found in the primary (azurophil) granule proteins of normal granulocytes and are overexpressed in myeloid leukemia cells. PR1 induces powerful HLA-A(*)0201-restricted CD8+ T-cell responses that selectively kill myeloid leukemia cells in vitro. The detection of low frequencies of PR1-specific CD8+ T cells in patients with chronic myeloid leukemia and at higher frequencies in patients entering molecular remission after allogeneic stem cell transplantation supports the concept that there is natural immunity to PR1, which can be boosted further by vaccination to enhance immunity to leukemia. Preliminary reports indicate that PR1 peptide vaccination induces significant increases in PR1-specific CD8+ T cells, with rapid and durable remissions in some patients with myeloid leukemia. These promising early results point the way to optimizing the administration of peptide vaccines to improve the treatment of otherwise refractory myeloid leukemias.

Adoptive transfer of pTRP2-specific CTLs expanding by bead-based artificial antigen-presenting cells mediates anti-melanoma response

Cytotoxic CD8(+) T cells are key effectors in the immunotherapy of malignant and viral diseases. However, the lack of efficient methods for their in vitro priming and expansion has become a bottleneck to the development of vaccines and adoptive transfer strategies. Synthetic artificial antigen-presenting cells (aAPCs) are now emerging as an attractive tool for eliciting and expanding CTL responses. This study reported a novel approach for targeting malignant melanoma with pTRP2-specific cytotoxic T lymphocytes (CTLs) expanded from the C57BL/6 splenocytes by multiple stimulations with aAPCs made by coating H-2K(b)-Ig/pTRP2 dimeric complexes, anti-CD28 antibody, 4-1BBL molecules and CD83 molecules to cell-sized latex beads. The induced CTLs exhibited specific lysis against RMA-S cells pulsed with the peptide pTRP2 and H-2K(b+) melanoma cells expressing TRP2, while a murine Lewis lung carcinoma cell line 3LL could not be recognized by the CTLs. The peptide-specific activity was inhibited by anti-H-2K(b) monoclonal antibody Y3. Adoptive Transfer of CTLs specific for malignant melanoma expanding by the aAPCs can mediate effective anti-melanoma response. These results suggested the bead-based aAPCs coated with an MHC-Ig/peptide complex, anti-CD28 antibody, 4-1BBL and CD83 could provide a useful tool for the reproducible expansion of specific CTLs for adoptive immunotherapy.

CD137 ligand reverse signaling has multiple functions in human dendritic cells during an adaptive immune response

T cell activation via dendritic cells (DC) is an important step in the adaptive immune response, which requires DC maturation, migration to lymph nodes and presentation of antigen to T cells. CD137 receptor expressed on activated T cells is a potent costimulatory molecule. Here, we investigated the functions of CD137 ligand (CD137L) in human monocyte-derived DC during an immune response. Cross-linking of CD137L on DC leads to cell maturation in an autocrine fashion, mostly via release of TNF-alpha. Reverse signaling of CD137L also mediates migration of DC via up-regulation of the CCR7 chemokine receptor, demonstrated by an in vivo MIP-3beta-dependent SCID mouse migration model. Finally, CD137L-activated DC induce differentiation of human T cells into potent Th1 effectors. Cocultivation of autologous T cells and CD137L-activated DC in an antigen-specific reaction leads to T cell proliferation and the release of IL-12p70 and IFN-gamma. These findings deliver new insights into the multiple effects of reverse signaling of CD137L in human DC during the initiation of an adaptive immune response, including the key features of DC maturation, migration and, ultimately, antigen-specific T cell differentiation.

Multiple copies of a tumor epitope in a recombinant hepatitis B surface antigen (HBsAg) vaccine enhance CTL responses, but not tumor protection

We propose the replacement of endogenous epitopes with foreign epitopes to exploit the highly immunogenic hepatitis B surface antigen (HBsAg) as a vaccine vector to elicit disease-protective cytotoxic T-lymphocyte (CTL) responses. Locations were defined within the HBsAg gene where replacements of DNA encoding HBsAg epitopes may be made to generate functional recombinant (r) HBsAg DNA vaccines. We demonstrate that rHBsAg DNA vaccines encoding multiple copies of a model tumor epitope from human papillomavirus (HPV) elicit enhanced CTL responses compared to rHBsAg DNA vaccines encoding a single copy. We show that rHBsAg DNA vaccines elicit a marked prophylactic and long-lived therapeutic protection against epitope expressing tumor, although protective efficacy was not improved by increasing the number of copies of the tumor epitope DNA. These results demonstrate the efficacy of HBsAg as a vector for the delivery of foreign CTL epitopes using the epitope replacement strategy, and have implications for rHBsAg vaccine design. The results also have implications for the derivation of a therapeutic vaccine for HPV-associated squamous carcinoma.

Optimizing adoptive polyclonal T cell immunotherapy of lymphomas, using a chimeric T cell receptor possessing CD28 and CD137 costimulatory domains

We previously demonstrated the feasibility of generating therapeutic numbers of cytotoxic T lymphocyte (CTL) clones expressing a CD20-specific scFvFc:CD3zeta chimeric T cell receptor (cTCR), making them specifically cytotoxic for CD20+ B lymphoma cells. However, the process of generating and expanding he CTL clones was laborious, the CTL clones expressed the cTCR at low surface density, and they exhibited suboptimal proliferation and cytotoxicity. To improve the performance of the CTLs in vitro and in vivo, we engineered "second-generation'' plasmid constructs containing a translational enhancer (SP163) and CD28 and CD137 costimulatory domains in cis with the CD3zeta intracellular signaling domain of the cTCR gene. Furthermore, we verified the superiority of generating genetically modified polyclonal T cells expressing the second-generation cTCR rather than T cell clones. Our results demonstrate that SP163 enhances the surface expression of the cTCR; that the second-generation cTCR improves CTL activation, proliferation, and cytotoxicity; and that polyclonal T cells proliferate rapidly in vitro and mediate potent CD20-specific cytotoxicity. This study provides the preclinical basis for a clinical trial of adoptive T cell immunotherapy for patients with relapsed CD20+ mantle cell lymphoma and indolent lymphomas.

Co-immunisation with DNA encoding RANK/RANKL or 4-1BBL costimulatory molecules does not enhance effector or memory CTL responses afforded by immunisation with a tumour antigen-encoding DNA vaccine

T cell mediated immune responses are induced following interaction of MHC-presented epitope on professional antigen presenting cells such as dendritic cells (DCs) with cognate T cell receptor. Up-regulation of receptor-ligand pairs of costimulatory molecules linking DC to T cell enhances the resulting T cell responses. This 'second signalling' occurs through the B7 molecules CD80/86 expressed by DCs, and importantly through members of the TNF ligand/TNF receptor superfamilies. We have previously shown that co-expression of RANK/RANKL or 41BB-L in addition to tumour antigen in dendritic cells augmented cognate effector and memory tumour antigen-directed cytotoxic T cell responses when the DCs were used to immunise mice. Here, we examined whether co-immunisation with naked plasmid DNAs encoding antigen and these costimulatory molecule(s), would enhance antigen specific T cell responses. We demonstrate that co-immunisation with DNAs encoding tumour antigen and costimulatory molecules failed to enhance antigen-directed CTL responses, or tumour protection, afforded by immunisation with DNA encoding tumour antigen alone.

Cytokine production of lung cancer cell lines: Correlation between their production and the inflammatory/immunological responses both in vivo and in vitro

Cytokines produced by tumor cells may have various effects on antitumor immune responses and tumor growth. In the present study, the cytokine production of 31 lung cancer cell lines was evaluated, while any correlation with the histological type, the induction of tumor-specific cytotoxic T lymphocytes (CTL) in vitro, and angiogenesis and the infiltration of inflammatory cells in tumor tissues were also examined. Production of interleukin (IL)-1alpha, IL-1beta, IL-4, IL-6, IL-8, IL-10, tumor necrosis factor (TNF)-alpha, granulocyte macrophage colony stimulating factor (GM-CSF), granulocyte colony stimulating factor, transforming growth factor (TGF)-beta and vascular endothelial growth factor (VEGF) in the culture supernatant was measured using enzyme-linked immunosorbent assay. Each cytokine was produced in a substantial number of the tumor cell lines. In particular, IL-6, IL-8, TGF-beta and VEGF were produced in 18 (55%), 29 (94%), 31 (100%) and 28 (90%) of 31 cell lines, respectively. However, neither IL-4 nor TNF-alpha was produced at all by any tumor cell line. TGF-beta production was significantly higher in adenocarcinoma than in squamous cell carcinoma (P = 0.03). Immunohistochemical staining revealed the magnitude of macrophage infiltration, and angiogenesis in surgically resected tumor tissue specimens correlated well with GM-CSF and IL-8 production from the corresponding cell lines. Among six lung cancer cell lines, CTL were induced in the three lung cancer cell lines that produced a lower amount of TGF-beta (<100 pg/mL). These findings suggested that TGF-beta produced by tumor cells could inhibit the induction of CTL in vitro. The present results suggest that the production of various cytokines from tumor cells might exert various paracrine effects both in vivo and in vitro.

Recent developments in the use of adenoviruses and immunotoxins in cancer gene therapy

Despite setbacks in the past and apparent hurdles ahead, gene therapy is advancing toward reality. The past several years have witnessed this new field of biomedicine developing rapidly both in breadth and depth, especially for the treatment of cancer, thanks largely to the better understanding of molecular and genetic basis of oncogenesis and the development of new and improved vectors and technologies for gene delivery and targeting. This article is intended to provide a brief review of recent advances in cancer gene therapy using adenoviruses, both as vectors and as oncolytic agents, and some of the recent progress in the development of immunotoxins for use in cancer gene therapy.

Developing a rational tumor vaccine therapy for renal cell carcinoma: immune yin and yang

In patients with progressive malignancy, the natural balance between proinflammatory (Yang) and inhibitory (regulatory or Yin) immune pathways is disrupted and favors cancer-specific immune suppression. Therapy with interleukin 2 (IL-2) can mobilize immune effector cells that recognize and destroy cancer. High-dose IL-2 is the only therapy that has consistently induced complete durable remissions in patients with metastatic renal cell carcinoma (RCC) but only in a few of them. The lack of benefit in most metastatic RCC patients is likely due to the ineffective manipulation of other immune circuits critical in regulating tumor cytotoxic pathways. The limited clinical activity of IL-2, RCC vaccines, and other immune therapies to date leads us to postulate that effective clinical treatment strategies will need to simultaneously enhance proinflammatory pathways and disrupt regulatory pathways. We present preliminary studies in RCC patients to highlight the complexity of the regulatory pathways and our approach to shifting the balance of proinflammatory and regulatory immune pathways using dendritic cell-tumor lysate vaccine followed by cytokine therapy.

Soluble PD-1 Facilitates 4-1BBL–Triggered Antitumor Immunity against Murine H22 Hepatocarcinoma In vivo

PURPOSE

The use of costimulatory molecules targeting distinct T-cell signaling pathways has provided a means for triggering and enhancing antitumor immunity; however, it is still not fully understood what types of costimulatory molecules are suitable for the combination in tumor therapy. Our purpose in this study is to establish an effective antitumor immune approach by using costimulatory molecule 4-1BBL in combination with soluble PD-1.

EXPERIMENTAL DESIGN

The murine H22 hepatocarcinoma served as an ectopic tumor model. Local gene transfer was done by injection with naked plasmid p4-1BBL and/or psPD-1. The synergistic mechanism of dual-gene therapy was elucidated by detecting the change of gene expression of immunoregulatory factors in tumor microenvironment. The effects of immunotherapy were evaluated by testing the function of tumor-specific T cells, measuring tumor weight or volume, survival of mice, and H&E staining of tissues.

RESULTS

4-1BBL expressed by normal nonimmune cells effectively enhanced antitumor immune response but up-regulated PD-L1 and did not reduce IL-10 and transforming growth factor-beta (TGF-beta). sPD-1 synergized with 4-1BBL to establish efficient antitumor immune environment, including down-regulation of IL-10 and TGF-beta, further up-regulation of interleukin (IL)-2 and IFN-gamma, and higher CD8(+) T-cell infiltration. The combined treatment by 4-1BBL/sPD-1 eradicated tumors from mice with small amounts of preexistent tumor cells or tumors from approximately 60% of individuals with larger amounts of preexistent tumor cells.

CONCLUSIONS

Our findings in this report imply a great potential of 4-1BBL in combination with sPD-1 in tumor therapeutics with the in vivo existent tumor cells as antigens.

Leukemia-Specific T-Cell Reactivity Induced by Leukemic Dendritic Cells Is Augmented by 4-1BB Targeting

PURPOSE

Acute myelogenous leukemia (AML) blasts are able to differentiate into leukemia-derived dendritic cells (AML-DC), thereby enabling efficient presentation of known and unknown leukemic antigens. Advances in culture techniques and AML-DC characterization justify clinical application. However, additional measures are likely needed to potentiate vaccines and overcome the intrinsic tolerant state of the patients' immune system. Engagement of the costimulatory molecule 4-1BB can break immunologic tolerance and increase CTL responses. In this study, we examined the role of the 4-1BB ligand (4-1BBL) on T-cell responses induced by AML-DC.

EXPERIMENTAL DESIGN

In allogeneic and autologous cocultures of T cells and AML-DC, the effect of the addition of 4-1BBL on T-cell proliferation, T-cell subpopulations, and T-cell function was determined.

RESULTS

Addition of 4-1BBL to cocultures of AML-DC and T cells induced a preferential increase in the proliferation of CD8(+) T cells. Increased differentiation into effector and central memory populations was observed in both CD4(+) and CD8(+) T cells in the presence of 4-1BBL. AML-DC induce a T helper 1 response, characterized by high IFN-gamma production, which is significantly increased by targeting 4-1BB. T cells primed in the presence of 4-1BBL show specificity for the leukemia-associated antigen Wilms' tumor 1, whereas cytotoxicity assays with leukemic blast targets showed the cytolytic potential of T cells primed in the presence of 4-1BBL.

CONCLUSION

We conclude that 4-1BBL is an effective adjuvant to enhance T-cell responses elicited by AML-DC.

Approaches to studying costimulation of human antiviral T cell responses: prospects for immunotherapeutic vaccines

The generation of strong and specific CD8 T cell responses is important in the control of viral infections. Costimulatory molecules provide signals necessary for the development or maintenance of these responses. A major focus of our laboratory is to investigate the role of costimulatory molecules of the TNFR and CD28 families in antiviral responses. Our aim is to translate information obtained using murine models to the study of these molecules using human cells. We have devised an in vitro system using recombinant replication- deficient adenovirus to deliver costimulatory molecules to antigen-presenting cells that are then used to stimulate autologous T cells from both healthy and HIV-infected individuals. Here we describe our findings and discuss the implications of incorporating costimulatory molecules into viral vector vaccine strategies.

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.

CD25+ CD4+ regulatory T-cells in cancer

Regulatory T-cells (Treg) protect the host from autoimmune disease by suppressing self-reactive immune cells. As such, Treg may also block antitumor immune responses. Recent observations by us and others showed that the prevalence of Treg is increased in cancer patients, particularly in the tumor environment. Our studies in a mouse pancreas cancer model suggest that the tumor actively promotes the accrual of Treg through several mechanisms involving activation of naturally occurring Treg as well as conversion of non-Treg into Treg. Our studies focus on further defining these mechanisms with the ultimate goal of designing strategies that block Treg-mediated suppression in cancer patients.

Immunotherapy targeting 4-1BB and its ligand

T-cell activation in the absence of costimulation is futile because T-cells deprived of costimulatory signals enter a state of unresponsiveness or anergy. The interaction of 4-1BB and 4-1BB ligand (4-1BBL) activates an important costimulatory pathway with diverse and important roles in immune regulation. Signals relayed through 4-1BB generate strong CD8(+) T-cell responses rather than CD4(+) T-cell responses; this action results in cytokine induction and promotes T-cell survival. In recent years, 4-1BB-mediated immune regulation has gained great significance because of the seemingly contradictory dual roles of agonistic anti-4-1BB in vivo disease models. To date, agonistic 4-1BB monoclonal antibody has shown therapeutic potential against a variety of tumors, CD4(+) T-cell-mediated autoimmune diseases, and chronic graft-versus-host disease. In addition, blockade of 4-1BB/4-1BBL interaction has produced therapeutic effects against coxsackievirus-induced myocardial inflammation, herpetic stromal keratitis, and graft rejection. We propose that the dual roles of agonistic anti-4-1BB--an enhanced effector function and a suppressor function--are mediated by a novel CD11c(+)CD8(+) T-cell population.

The challenge of inhibiting alloreactive T-cell memory

Memory T cells specific for donor antigens present a unique challenge in transplantation. In addition to expressing rapid and robust immune responses to a transplanted organ, memory T cells may be resistant to the effects of currently used graft-prolonging therapies. The increasing recognition that alloreactive memory T cells participate in transplant rejection is driving new lines of research focusing on understanding the immunobiology of alloreactive memory T cells and on designing novel therapies to specifically target memory T cells. The purpose of this review is to summarize the effects of existing immunosuppressive drugs and costimulatory blockade on functions of alloreactive memory T cells that undermine allograft survival.

4-1BB ligand enhances tumor-specific immunity of poxvirus vaccines

PURPOSE

Recombinant poxvirus vaccines have been explored as tumor vaccines. The immunogenicity of these vaccines can be enhanced by co-expressing costimulatory molecules and tumor-associated antigens. While the B7-CD28 interaction has been most comprehensively investigated, other costimulatory molecules utilize different signaling pathways and might provide further cooperation in T cell priming and survival. 4-1BB (CD137) is a TNF family member and is critical for activation and long-term maintenance of primed T cells. This study was conducted to determine if a poxvirus expressing the ligand for 4-1BB (4-1BBL) could further improve the immune and therapeutic responses of a previously reported poxvirus vaccine expressing a triad of costimulatory molecules (B7.1, ICAM-1, and LFA-3).

EXPERIMENTAL DESIGN

A recombinant vaccinia virus expressing 4-1BBL was generated and characterized in an in vitro infection system. This vaccine was then used alone or in combination with a vaccinia virus expressing CEA, B7.1, ICAM-1, and LFA-3 in CEA-transgenic mice bearing established MC38 tumors. Tumor growth and immune responses against CEA and other tumor-associated antigens were determined. The level of anti-apoptotic proteins in responding T cells was determined by flow cytometry on tetramer selected T cells.

RESULTS

The combination of 4-1BBL with B7.1-based poxvirus vaccination resulted in significantly enhanced therapeutic effects against CEA-expressing tumors in a CEA-transgenic mouse model. This was associated with an increased level of CEA-specific CD4(+) and CD8(+) T cell responses, induction of antigen spreading to p53 and gp70, increased accumulation of CEA-specific T cells in the tumor microenvironment, and increased expression of bcl-X(L) and bcl-2 in CD4(+) and CD8(+) T cells in vaccinated mice.

CONCLUSION

4-1BBL cooperates with B7 in enhancing anti-tumor and immunologic responses in a recombinant poxvirus vaccine model. The inclusion of costimulatory molecules targeting distinct T cell signaling pathways provides a mechanism for enhancing the therapeutic effectiveness of tumor vaccines.

Critical, but conditional, role of OX40 in memory T cell-mediated rejection

Memory T cells can be a significant barrier to the induction of transplant tolerance. However, the molecular pathways that can regulate memory T cell-mediated rejection are poorly defined. In the present study we tested the hypothesis that the novel alternative costimulatory molecules (i.e., ICOS, 4-1BB, OX40, or CD30) may play a critical role in memory T cell activation and memory T cell-mediated rejection. We found that memory T cells, generated by either homeostatic proliferation or donor Ag priming, induced prompt skin allograft rejection regardless of CD28/CD154 blockade. Phenotypic analysis showed that, in contrast to naive T cells, such memory T cells expressed high levels of OX40, 4-1BB, and ICOS on the cell surface. In a skin transplant model in which rejection was mediated by memory T cells, blocking the OX40/OX40 ligand pathway alone did not prolong the skin allograft survival, but blocking OX40 costimulation in combination with CD28/CD154 blockade induced long-term skin allograft survival, and 40% of the recipients accepted their skin allograft for >100 days. In contrast, blocking the ICOS/ICOS ligand and the 4-1BB/4-1BBL pathways alone or combined with CD28/CD154 blockade had no effect in preventing skin allograft rejection. OX40 blockade did not affect the homeostatic proliferation of T cells in vivo, but markedly inhibited the effector functions of memory T cells. Our data demonstrate that memory T cells resisting to CD28/CD154 blockade in transplant rejection are sensitive to OX40 blockade and suggest that OX40 is a key therapeutic target in memory T cell-mediated rejection.

Application of a reversible immortalization system for the generation of proliferation-controlled cell lines

To employ physiological mechanisms to control cell growth primary cells were reversibly immortalized using the SV40 TAg. The cells showed a fibroblast-like morphology. When the expression of the TAg was turned off, the cells arrested in the G0/G1 cell cycle phase. The cell culture could be kept for over 1 week in the proliferation-controlled state while the growth arrest remained fully reversible. The regulation was highly efficacious in that the arrested cell population did not spontaneously resume growth, suggesting that in the absence of the immortalizing gene expression endogenous growth-control mechanisms can keep these cells in a viable state for a prolonged time. Recombinant protein expression increased in growth-controlled cells when compared to conventionally cultured cells. Analysis of a secreted pharmaceutical protein revealed high product integrity without any signs of degradation. Therefore, it is feasible to apply genetic regulation of cell immortalization to obtain proliferation-controlled cell lines and this technique may be of interest to generate novel biotechnological producer cells.

Cotransfection of dendritic cells with RNA coding for HER-2/neu and 4-1BBL increases the induction of tumor antigen specific cytotoxic T lymphocytes

Ribonucleic acid (RNA) transfection of dendritic cells (DCs) was shown to be highly efficient in eliciting CD8+ and CD4+ T-cell responses. We analyzed whether electroporation of DCs with RNA coding for a tumor-associated antigen (TAA) would elicit antigen-specific effector cytotoxic T lymphocyte (CTL) responses and whether these responses could be modulated by cotransfection with a second specific synthetic RNA. Therefore in vitro generated human monocyte-derived DCs were electroporated with in vitro transcribed RNA (in vitro transcript, IVT) encoding the TAA HER-2/neu. Additionally, these cells were cotransfected with IVT coding for human 4-1BBL. Transfection of DCs with 4-1BBL-IVT did not alter their typical phenotype. However, it increased the expression of the costimulatory molecules CD80 and CD40. Coadministration of HER-2/neu- and 4-1BBL-IVT resulted in an increased specific lysis of target cells by the in vitro induced CTL lines, indicating that 4-1BBL enhances their ability to elicit primary CTL responses. Interestingly, transfection of DCs with 4-1BBL-IVT did not augment their capacity to stimulate allogeneic lymphocyte responses. The here established approach of cotransfection of DCs with tumor-RNA and a second specific IVT could improve and optimize the in vitro manipulation of DCs for the induction of antigen-specific CTL responses.

Defective DNA mismatch repair determines a characteristic transcriptional profile in proximal colon cancers

BACKGROUND & AIMS

Colon cancers with defective DNA mismatch repair (MMR) have peculiar molecular, pathologic, and clinical features, including high-level microsatellite instability, conspicuous lymphocytic infiltration, preferential location in the proximal colon, and better prognosis. Our aim was to characterize the transcriptional profile of this colon cancer subset.

METHODS

An oligonucleotide microarray containing 12,625 probes was used to evaluate gene expression in 25 proximal colon cancers, 10 samples of normal colon mucosa, and 14 colon cancer cell lines. Transcriptional profiles of MMR-deficient cancers and cell lines were compared with those of their MMR-proficient counterparts.

RESULTS

Unsupervised analysis of microarray data showed that MMR status exerts a predominant influence on the gene expression profile of proximal colon cancers. Hierarchical clustering divided the cancers into 2 groups corresponding almost perfectly with their MMR status. Supervised analysis identified numerous gene expression changes that represent a genetic signature of MMR-deficient colon cancers. Changes in genes involved in apoptosis and the immune response were consistent with the better prognosis of MMR-deficient cancers. In MMR-deficient cancers and cell lines, 4-1BBL, a crucial gene in the anti-tumor immune response, was, respectively, 2.4 and 6.0 times more expressed than in their MMR-proficient counterparts. This difference was confirmed by quantitative reverse-transcription polymerase chain reaction and flow cytometric assessment of 4-1BBL protein expression in colon cancer cell lines. Our analysis also showed novel possible gene targets of microsatellite instability.

CONCLUSIONS

MMR inactivation produces distinct changes in the cellular messenger RNA pool, which is consistent with a unique tumorigenesis pathway.

Modulation of cord blood CD8+ T-cell effector differentiation by TGF-β1 and 4-1BB costimulation

Transforming growth factor-β1 (TGF-β1), an immunosuppressive cytokine, inhibits cytotoxic T cell (CTL) immune responses. In contrast, 4-1BB (CD137), a costimulatory molecule in the tumor necrosis factor (TNF) receptor family, amplifies CTL-mediated antitumor immune responses. We investigated whether TGF-β1 responses could be reversed by 4-1BB costimulation during in vitro differentiation of naive CD8+ T cells into effector CTL cells. TGF-β1 potently suppressed CTL differentiation of human cord blood naive CD8+ T cells as determined by reduced induction of characteristic phenotypes of effector cells and cytotoxic activity. TGF-β1-mediated suppression of CTL differentiation was abrogated by 4-1BB costimulation but not by CD28 or another member in the TNF receptor family, CD30. 4-1BB costimulation suppressed Smad2 phosphorylation induced by TGF-β1, suggesting that 4-1BB effects were at the level of TGF-β1 signaling. 4-1BB effects on the TGF-β1-mediated suppression were enhanced by interleukin 12 (IL-12) but counteracted by IL-4; 4-1BB expression was up- or down-regulated, respectively, by IL-12 and IL-4. IL-4 was more dominant than IL-12 when both cytokines were present during 4-1BB costimulation in the presence of TGF-β1. This indicates critical roles for IL-4 and IL-12 in regulating 4-1BB effects on TGF-β1-mediated suppression. (Blood. 2005;105:274-281)

Role of 4-1BB:4-1BB ligand in cancer immunotherapy

The activation of T cells plays a central role in antitumor immunity. In order to activate naïve T cells, two key signals are required. Signal one is provided through the T-cell receptor (TCR) while signal two is that of costimulation. The CD28:B7 molecules are one of the best-studied costimulatory pathways, thought to be the main mechanism through which primary T-cell stimulation occurs. However, a number of molecules have been identified which serve to amplify and diversify the T-cell response, following initial T-cell activation. These include the more recently described 4-1BB:4-1BB ligand (4-1BBL) molecules. 4-1BB:4-1BBL are a member of the TNFR:TNF ligand family, which are expressed on T cells and antigen-presenting cells (APCs), respectively. Therapies utilizing the 4-1BB:4-1BBL signaling pathway have been shown to have antitumor effects in a number of model systems. In this paper, we focus on the 4-1BB:4-1BBL costimulatory molecules. In particular, we will describe the structure and function of the 4-1BB molecule, its receptor and how 4-1BB:4-1BBL costimulation has and may be used for the immunotherapy of cancer.

Phosphatidylserine regulates the maturation of human dendritic cells

Phosphatidylserine (PS), which is exposed on the surface of apoptotic cells, has been implicated in immune regulation. However, the effects of PS on the maturation and function of dendritic cells (DCs), which play a central role in both immune activation and regulation, have not been described. Large unilamellar liposomes containing PS or phosphatidylcholine were used to model the plasma membrane phospholipid composition of apoptotic and live cells, respectively. PS liposomes inhibited the up-regulation of HLA-ABC, HLA-DR, CD80, CD86, CD40, and CD83, as well as the production of IL-12p70 by human DCs in response to LPS. PS did not affect DC viability directly but predisposed DCs to apoptosis in response to LPS. DCs exposed to PS had diminished capacity to stimulate allogeneic T cell proliferation and to activate IFN-gamma-producing CD4(+) T cells. Exogenous IL-12 restored IFN-gamma production by CD4(+) T cells. Furthermore, activated CTLs proliferated poorly to cognate Ag presented by DCs exposed to PS. Our findings suggest that PS exposure provides a sufficient signal to inhibit DC maturation and to modulate adaptive immune responses.

Manipulating dendritic cell biology for the active immunotherapy of cancer

Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) that have an unequaled capacity to initiate primary immune responses, including tolerogenic responses. Because of the importance of DCs in the induction and control of immunity, an understanding of their biology is central to the development of potent immunotherapies for cancer, chronic infections, autoimmune disease, and induction of transplantation tolerance. This review discusses recent advances in DC research and the application of this knowledge toward new strategies for the clinical manipulation of DCs for cancer immunotherapy.