The expression of CD70 and CD80 by gene-modified tumor cells induces an antitumor response depending on the MHC status

Coordinating Effect of VEGFC and Oleic Acid Participates to Tumor Lymphangiogenesis

Simple Summary

In cancer, the lymphatic system is hijacked by tumor cells that escape from primary tumor and metastasize to the sentinel lymph nodes. Tumor lymphangiogenesis is stimulated by the vascular endothelial growth factors-C (VEGFC) after binding to its receptor VEGFR-3. However, how VEGFC cooperates with other molecules to promote lymphatic neovessel growth has not been fully determined. Here, we showed that tumor lymphangiogenesis developed in tumoral lesions and in their surrounding adipose tissue (AT). Interestingly, lymphatic vessel density correlated with an increase in circulating free fatty acids (FFA) in the lymph from tumor-bearing mice. We showed that adipocyte-released FFA are uploaded by lymphatic endothelial cells (LEC) to stimulate their sprouting. Lipidomic analysis identified the monounsaturated oleic acid (OA) as the major circulating FFA in the lymph in a tumoral context. OA transporters FATP-3, -6 and CD36 were only upregulated on LEC in the presence of VEGFC showing a collaborative effect of these molecules. OA released from adipocytes is taken up by LECs to stimulate the fatty acid β-oxidation, leading to increased adipose tissue lymphangiogenesis. Our results provide new insights on the dialogue between tumors and adipocytes via the lymphatic system and identify a key role for adipocyte-derived FFA in the promotion of lymphangiogenesis, revealing novel therapeutic opportunities for inhibitors of lymphangiogenesis in cancer.

Abstract

In cancer, the lymphatic system is hijacked by tumor cells that escape from primary tumor and metastasize to the sentinel lymph nodes. Tumor lymphangiogenesis is stimulated by the vascular endothelial growth factors-C (VEGFC) after binding to its receptor VEGFR-3. However, how VEGFC cooperates with other molecules to promote lymphatics growth has not been fully determined. We showed that lymphangiogenesis developed in tumoral lesions and in surrounding adipose tissue (AT). Interestingly, lymphatic vessel density correlated with an increase in circulating free fatty acids (FFA) in the lymph from tumor-bearing mice. We showed that adipocyte-released FFA are uploaded by lymphatic endothelial cells (LEC) to stimulate their sprouting. Lipidomic analysis identified the monounsaturated oleic acid (OA) as the major circulating FFA in the lymph in a tumoral context. OA transporters FATP-3, -6 and CD36 were only upregulated on LEC in the presence of VEGFC showing a collaborative effect of these molecules. OA stimulates fatty acid β-oxidation in LECs, leading to increased AT lymphangiogenesis. Our results provide new insights on the dialogue between tumors and adipocytes via the lymphatic system and identify a key role for adipocyte-derived FFA in the promotion of lymphangiogenesis, revealing novel therapeutic opportunities for inhibitors of lymphangiogenesis in cancer.

Human cancer germline antigen-specific cytotoxic T cell-what can we learn from patient

In this review, we will highlight the importance of cancer germline antigen-specific cytotoxic CD8⁺ T lymphocytes (CTL) and the factors affecting antitumor CTL responses. In light of cancer immunotherapy, we will emphasis the need to further understand the features, characteristics, and actions of modulatory receptors of human cancer germline-specific CTLs, in order to determine the optimal conditions for antitumor CTL responses.

Intratumoral Gene Electrotransfer of Plasmid DNA Encoding shRNA against Melanoma Cell Adhesion Molecule Radiosensitizes Tumors by Antivascular Effects and Activation of an Immune Response

In this study, radiotherapy was combined with the gene electrotransfer (GET) of plasmid encoding shRNA against melanoma cell adhesion molecule (pMCAM) with dual action, which was a vascular-targeted effect mediated by the silencing of MCAM and an immunological effect mediated by the presence of plasmid DNA in the cytosol-activating DNA sensors. The effects and underlying mechanisms of therapy were evaluated in more immunogenic B16F10 melanoma and less immunogenic TS/A carcinoma. The silencing of MCAM potentiated the effect of irradiation (IR) in both tumor models. Combined therapy resulted in 81% complete responses (CR) in melanoma and 27% CR in carcinoma. Moreover, after the secondary challenge of cured mice, 59% of mice were resistant to challenge with melanoma cells, and none were resistant to carcinoma. Combined therapy reduced the number of blood vessels; induced hypoxia, apoptosis, and necrosis; and reduced cell proliferation in both tumor models. In addition, the significant increase of infiltrating immune cells was observed in both tumor models but more so in melanoma, where the expression of IL-12 and TNF-α was determined as well. Our results indicate that the combined therapy exerts both antiangiogenic and immune responses that contribute to the antitumor effect. However, tumor immunological status is crucial for a sufficient immune system contribution to the overall antitumor effect.

Bioprofiling TS/A Murine Mammary Cancer for a Functional Precision Experimental Model

The TS/A cell line was established in 1983 from a spontaneous mammary tumor arisen in an inbred BALB/c female mouse. Its features (heterogeneity, low immunogenicity and metastatic ability) rendered the TS/A cell line suitable as a preclinical model for studies on tumor-host interactions and for gene therapy approaches. The integrated biological profile of TS/A resulting from the review of the literature could be a path towards the description of a precision experimental model of mammary cancer.

TGF-β upregulates CD70 expression and induces exhaustion of effector memory T cells in B-cell non-Hodgkin's lymphoma

Transforming growth factor beta (TGF-β) has an important role in mediating T-cell suppression in B-cell non-Hodgkin lymphoma (NHL). However, the underlying mechanism responsible for TGF-β-mediated inhibition of effector memory T (Tm) cells is largely unknown. As reported here, we show that exhaustion is a major mechanism by which TGF-β inhibits Tm cells, and TGF-β mediated exhaustion is associated with upregulation of CD70. We found that TGF-β upregulates CD70 expression on effector Tm cells while it preferentially induces Foxp3 expression in naive T cells. CD70 induction by TGF-β is Smad3-dependent and involves IL-2/Stat5 signaling. CD70+ T cells account for TGF-β-induced exhaustion of effector Tm cells. Both TGF-β-induced and preexisting intratumoral CD70+ effector Tm cells from B-cell NHL have an exhausted phenotype and express higher levels of PD-1 and TIM-3 compared with CD70- T cells. Signaling transduction, proliferation and cytokine production are profoundly decreased in these cells, and they are highly susceptible to apoptosis. Clinically, intratumoral CD70-expressing T cells are prevalent in follicular B-cell lymphoma (FL) biopsy specimens, and increased numbers of intratumoral CD70+ T cells correlate with an inferior patient outcome. These findings confirm TGF-β-mediated effector Tm cell exhaustion as an important mechanism of immune suppression in B-cell NHL.

The costimulatory molecule CD70 is regulated by distinct molecular mechanisms and is associated with overall survival in diffuse large B-cell lymphoma

In diffuse large B-cell lymphomas (DLBCL), a recurrent deletion of the 19p13 region has recently been described. CD70 and TNFSF9 genes are suspected tumor suppressor genes, but previous studies suggest an oncogenic role for CD70. Therefore, we studied the consequences of variation in CD70 copy number and epigenetic modifications on CD70 expression. Copy-number variation was investigated in 144 de novo DLBCL tissues by comparative genomic hybridization array and quantitative multiplex PCR. Gene expression was assessed by quantitative RT-PCR, and CD70 promoter methylation was determined by pyrosequencing. The 19p13.3.2 region was deleted in 21 (14.6%) cases, which allowed the minimal commonly deleted region of 57 Kb that exclusively includes the CD70 gene to be defined. Homozygous deletions were observed in four (2.7%) cases, and acquired single-nucleotide variations of CD70 were detected in nine (6.3%) cases. CD70 was highly expressed in both germinal centre B-cell-like (GCB) and activated B-cell-like (ABC) DLBCL compared to normal tissue, with distinct molecular mechanisms of mRNA expression regulation. A gene dosage effect was observed in the GCB subtype, whereas promoter methylation was the predominant mechanism of down regulation in the ABC subtype. However, high CD70 expression levels correlated to shorter overall survival in both the GCB (P = 0.0021) and the ABC (P =0.0158) subtypes. In conclusion, CD70 is targeted by recurrent deletions, somatic mutations and promoter hypermethylation, but its high level of expression is related to an unfavorable outcome, indicating that this molecule may constitute a potential therapeutic target in selected DLBCL.

Development of a human monoclonal antibody for potential therapy of CD27-expressing lymphoma and leukemia

PURPOSE

The TNF receptor superfamily member CD27 is best known for its important role in T-cell immunity but is also recognized as a cell-surface marker on a number of B- and T-cell malignancies. In this article, we describe a novel human monoclonal antibody (mAb) specific for CD27 with properties that suggest a potential utility against malignancies that express CD27.

EXPERIMENTAL DESIGN

The fully human mAb 1F5 was generated using human Ig transgenic mice and characterized by analytical and functional assays in vitro. Severe combined immunodeficient (SCID) mice inoculated with human CD27-expressing lymphoma cells were administered 1F5 to investigate direct antitumor effects. A pilot study of 1F5 was conducted in non-human primates to assess toxicity.

RESULTS

1F5 binds with high affinity and specificity to human and macaque CD27 and competes with ligand binding. 1F5 activates T cells only in combination with T-cell receptor stimulation and does not induce proliferation of primary CD27-expressing tumor cells. 1F5 significantly enhanced the survival of SCID mice bearing Raji or Daudi tumors, which may be mediated through direct effector mechanisms such as antibody-dependent cellular cytotoxicity. Importantly, administration of up to 10 mg/kg of 1F5 to cynomolgus monkeys was well tolerated without evidence of significant toxicity or depletion of circulating lymphocytes.

CONCLUSIONS

Collectively, the data suggest that the human mAb 1F5, which has recently entered clinical development under the name CDX-1127, may provide direct antitumor activity against CD27-expressing lymphoma or leukemia, independent of its potential to enhance immunity through its agonistic properties.

Stromal estrogen receptor-α promotes tumor growth by normalizing an increased angiogenesis

Estrogens directly promote the growth of breast cancers that express the estrogen receptor α (ERα). However, the contribution of stromal expression of ERα in the tumor microenvironment to the protumoral effects of estrogen has never been explored. In this study, we evaluated the molecular and cellular mechanisms by which 17β-estradiol (E2) impacts the microenvironment and modulates tumor development of ERα-negative tumors. Using different mouse models of ER-negative cancer cells grafted subcutaneously into syngeneic ovariectomized immunocompetent mice, we found that E2 potentiates tumor growth, increases intratumoral vessel density, and modifies tumor vasculature into a more regularly organized structure, thereby improving vessel stabilization to prevent tumor hypoxia and necrosis. These E2-induced effects were completely abrogated in ERα-deficient mice, showing a critical role of host ERα. Notably, E2 did not accelerate tumor growth when ERα was deficient in Tie2-positive cells, even in mice grafted with wild-type bone marrow. These results were extended by clinical evidence of ERα-positive stromal cell labeling in the microenvironment of human breast cancers. Together, our findings therefore show that E2 promotes the growth of ERα-negative cancer cells through the activation of stromal ERα (extra-hematopoietic Tie-2 positive cells), which normalizes tumor angiogenesis and allows an adaptation of blood supply to tumors, thereby preventing hypoxia and necrosis. These findings significantly deepen mechanistic insights into the impact of E2 on tumor development with potential consequences for cancer treatment.

Immunotherapy of MHC class I-deficient tumors

MHC class I downregulation is a general mechanism by which tumor cells can escape from T-cell-mediated immunity. This downregulation also represents a serious obstacle to the development of effective antitumor immunotherapy or vaccination. Therefore, successful immunotherapeutic and vaccination protocols should be optimized against tumors with distinct cell surface expression of the MHC class I molecules. Mechanisms leading to protective immunity may vary in different models with respect to the particular tumors (e.g., in their levels of residual expression of the MHC class I molecules on tumor cells or inducibility of MHC class I expression). Notably, both CD8+ cell-mediated immunity and MHC class I-unrestricted mechanisms can take place against MHC class I-deficient tumors. Since MHC class I downregulation is frequently reversible by cytokines and also by the activation of epigenetically silenced genes, an attractive strategy is to elicit specific cell-mediated immunity combined with restoration of MHC class I expression on tumor cells.

Role of CD27/CD70 pathway of activation in immunity and tolerance

The CD70/CD27 axis has gained increasing interest among the immunologists, because of its capacity to regulate immunity versus tolerance. Recent studies clearly show that expression of CD70 may prevent tolerance induced by antigen presentation in the steady-state, i.e., by nonactivated DCs. In addition, CD27 signaling appears critical for T cell expansion and survival and therefore, induction of long-term memory. It contributes to germinal center formation, B cell activation, and production of neutralizing antibodies but can also be subverted by viruses, in particular, during chronic infections. The potential role of the CD27/CD70 pathway in the course of inflammatory diseases, as in EAE, arthritis, and inflammatory bowel disease models, suggests that CD70 may be a target for immune intervention. Conversely, the potency of costimulation through CD27 suggests that the CD27/CD70 axis could be exploited for the design of anti-cancer vaccines.

Epigenetic silencing of TNFSF7 (CD70) by DNA methylation during progression to breast cancer

To escape the immune system, tumor cells may remove surface molecules such as the major histocompatibility complex (MHC) and co-stimulatory molecules, which are essential for recognition by lymphocytes. Down-regulation of the co-stimulatory molecules CD70 (TNFSF7) and CD80 may contribute to tumor cell survival; however, the mechanism of down-regulation of the TNFSF7 gene during tumorigenesis is poorly understood. Here we present evidence indicating that TNFSF7 gene expression is epigenetically down-regulated via DNA hypermethylation within its promoter region during progression in breast cancer cells in the isogenic MCF10 model. Bisulfite sequencing revealed that the CpG pairs at the proximal region of the TNFSF7 promoter are heavily methylated during progression of breast cancer cells but that methylation of the more distal sequences was not changed considerably. Thus, this epigenetic silencing of the TNFSF7 gene via hypermethylation of its proximal region may allow the benign and invasive MCF10 variants to escape immune surveillance.

In vitro evidence for a new therapeutic approach in renal cell carcinoma

PURPOSE

Renal cell carcinoma (RCC) is the most lethal among the common urologic malignancies, comprising 3% of all human neoplasias; approximately 40% of patients eventually die of cancer progression. One third of patients who present with metastatic disease and up to 40% treated for localized disease generally experience recurrence. RCCs are characterized by high resistance to chemo-, radio- and immunotherapy. We recently discovered an endogenous enzymatic activity, which is particularly expressed in tumorigenic cell, endogenous non-telomerase reverse transcriptase (RT) of retrotrasposon / retroviral origin, as a specific target to induce proliferation arrest in a number of human carcinogenesis in vitro culture cell lines.

METHODS

To address this possibility, we have employed RCC primary cell culture testing pharmacological inhibition, in vitro, by two characterized non nucleosidic RT inhibitors, nevirapine and efavirenz; next, we assessed morphological effects and analyzed putative modulation on gene expression profile.

RESULTS

Both treatments reduced cell proliferation rate and induced morphological differentiation and gene expression reprogramming in different RCC analyzed tumor biomarkers.

CONCLUSION

In this study we describe a new potential therapeutic approach to obtain considerable future benefits in renal carcinoma cure and attempt to establish a new possible pharmacological therapy based on oral drugs administration in renal RCC treatment.

The role of TNF superfamily members in T-cell function and diseases

Interactions that occur between several tumour necrosis factor (TNF)-TNF receptors that are expressed by T cells and various other immune and non-immune cell types are central to T-cell function. In this Review, I discuss the biology of four different ligand-receptor interactions - OX40 ligand and OX40, 4-1BB ligand and 4-1BB, CD70 and CD27, and TL1A and death receptor 3 - and their potential to be exploited for therapeutic benefit. Manipulating these interactions can be effective for treating diseases in which T cells have an important role, including inflammatory conditions, autoimmunity and cancer. Here, I explore how blocking or inducing the signalling pathways that are triggered by these different interactions can be an effective way to modulate immune responses.

The CD70/CD27 pathway is critical for stimulation of an effective cytotoxic T cell response against B cell precursor acute lymphoblastic leukemia

For effective immunotherapy, maintaining the frequency and cytotoxic potential of effector cells is critical. In this context costimulation via the CD70/CD27 pathway has been proven essential. CD70 has been reported to be expressed to varying degrees on malignant B cells. However, in B cell precursor acute lymphoblastic leukemia, the most common childhood malignancy, the role of CD70 in stimulation of antileukemic T cell responses has so far not been delineated. Herein we demonstrate that in B cell precursor acute lymphoblastic leukemia expression of CD70 is low but can be induced upon blast activation via CD40. Both CD70 and CD80/CD86 up-regulated on CD40-stimulated blasts contribute to primary stimulation of T cell proliferation and cytokine production in an additive manner. These two signals also cooperate in the prevention of T cell anergy. In contrast to blockade of CD70 during the effector phase, inhibition of CD70-mediated costimulation during generation of antileukemic T cells prevents effector cell proliferation and reduces their cytotoxic capacity. Modulation of the CD70/CD27 pathway may thus represent a novel therapeutic approach for augmenting magnitude and quality of the antileukemic response in B cell precursor acute lymphoblastic leukemia.

Local gene delivery of tumor necrosis factor alpha can impact primary tumor growth and metastases through a host-mediated response

TNFerade is a replication incompetent adenovector designed to express human TNFalpha under control of the Egr-1 radiation and chemotherapy enhanced promoter, and is currently in Phase II/III clinical testing. Data from Phase I clinical testing of TNFerade in a limited set of melanoma patients suggested the potential to impact distal metastases following intratumoral injections of TNFerade. These clinical observations and the multiple potential mechanisms of TNFerade led us to hypothesize local treatment with TNFerade + radiation may impact metastatic disease. We explored this hypothesis in preclinical models using the spontaneously metastatic, syngeneic B16F10 murine melanoma model. Established subcutaneous B16F10 tumors were treated with intratumoral injections of TNFerade and localized 2 Gy fractionated radiation therapy, modeling the clinical treatment regimen. Following 10-14 days of treatment, mice were evaluated for metastases development in the iliac and axillary lymph nodes. Comparisons of metastatic burden to control groups indicated TNFerade +/- radiation suppressed the formation of metastases in the lymph nodes. Additional experiments in TNF receptor knockout mice, where the only possible effects are on tumor cells containing the TNFalpha receptor, indicate TNFerade's local and distal activities are critically dependent on a host-mediated response. These data provide direct preclinical evidence local therapy of a solid tumor with TNFerade can also reduce metastatic disease, in addition to effects on the treated lesion. Furthermore, our finding of a host dependant response(s) for TNFerade at both the treated tumor and on lymph node metastases suggest the potential for broad activity independent of tumor histology.

Identification of CD70 as a diagnostic biomarker for clear cell renal cell carcinoma by gene expression profiling, real-time RT-PCR and immunohistochemistry

The underlying molecular mechanisms of renal cell carcinoma (RCC) are poorly understood and more reliable markers for early diagnosis are needed. Hence, alternative strategies for biomarker discovery with appropriate validation technologies have to be performed. To elucidate genesis and progression of RCC we used high parallel chip based gene expression profiling comparing normal and tumour tissues. We compared corresponding control and tumour tissue samples from 10 patients with clear cell RCC. We isolated RNA from histologically well characterised tissue sections and performed reverse transcription, labelling and linear RNA amplification. Samples were hybridised on microarrays containing 642 human cDNAs. Of the 352 differentially expressed genes found, CD70 and FRA2 were selected for further evaluation by real-time RT-PCR. The analysis all showed a high potential to discriminate between normal and tumour tissue. Moreover, increased CD70 mRNA expression in tumour cells could be correlated to its expression at the protein level. Immunohistochemistry (IHC) showed very strong expression of CD70 in all tumour samples but no expression in adjacent normal kidney tissue. With our combined approach we were able to identify CD70 as a new marker for RCC, which may be useful in the future for improved immunohistochemical diagnosis.

Geranylgeranyl transferase inhibition stimulates antimelanoma immune response through MHC class I and costimulatory molecule expression

Defective antitumor immune responses are frequent consequences of defects in the expression of major histocompatibility complex (MHC) class I and costimulatory molecules. We demonstrated that statins, inhibitors of HMGCoA reductase, enhance mIFN-gamma induced expression of MHC class I antigens on murine B16F10 melanoma. GGTI-298, a geranylgeranyl transferase I inhibitor, but not FTI-277, a farnesyl transferase inhibitor, mimics this effect of statins. This effect is related to peptide transporter protein TAP1 up-regulation. Simultaneously, GGTI-298 induces the expression of CD80 and CD86 costimulatory molecules. C3 exoenzyme, which selectively inactivates Rho proteins, phenocopies the effects of GGTI-298, indicating a role for Rho proteins in these events. Furthermore, the treatment of B16F10 cells with GGTI-298 or C3 exoenzyme associated with mIFN-gamma induces in vivo tumor growth slowing down in immunocompetent but not in nu/nu syngeneic mice. Both in vivo injections and in vitro restimulation of splenocytes with GGTI-298- and mIFN-gamma-treated B16F10 cells induces an enhancement of specific CD8 T lymphocytes labeled by TRP-2/H-2K(b) tetramers. Finally, these effects are not limited to mouse models since they were also reproduced in two human melanoma cell lines. These observations indicate that protein geranylgeranylation as well as Rho protein are critical for costimulatory and IFN-gamma-dependent MHC class I molecule expression in melanoma.

Induction of T-cell antitumor immunity and protection against tumor growth by secretion of soluble human CD70 molecules

One of the strategies to promote an antitumor response is the genetic modification of tumor cells to induce expression of costimulatory molecules. We have tested the capacity of a soluble form of CD70 molecule (sCD70). After construction of a vector carrying the sCD70, we obtained stable sCD70-secreting TS/A tumor cells and allogenic MC57 fibroblasts. In all, 45% of wild-type (wt) tumors were rejected in immunocompetent mice when transfected sCD70-secreting cells were injected three times in the periphery of the wt tumors. Furthermore, the sCD70-secreting TS/A cells induced a protective memory against wt TS/A tumor growth: 70% of the wt tumors used for the challenge were rejected by mice, which had rejected tumors 45 days before in the presence of sCD70-secreting TS/A cells. It was also shown that in vitro mock TS/A tumor cell proliferation was inhibited by splenocytes harvested from mice injected with TS/A cells expressing CD70. Growth kinetics of wt TS/A tumors in immunocompetent versus nude mice suggested that T lymphocytes were implicated in the antitumor response, which was confirmed by membrane expression of specific markers. The data suggest that injection of genetically transfected cells secreting sCD70 in the periphery of wt TS/A tumors induces T-cell-mediated inhibition of tumor growth and builds up a protective antitumor memory.

CD70 Signaling Is Critical for CD28-Independent CD8+T Cell-Mediated Alloimmune Responses In Vivo

The inability to reproducibly induce robust and durable transplant tolerance using CD28-B7 pathway blockade is in part related to the persistence of alloreactive effector/memory CD8(+) T cells that are less dependent on this pathway for their cellular activation. We studied the role of the novel T cell costimulatory pathway, CD27-CD70, in alloimmunity in the presence and absence of CD28-B7 signaling. CD70 blockade prolonged survival of fully mismatched vascularized cardiac allografts in wild-type murine recipients, and in CD28-deficient mice induced long-term survival while significantly preventing the development of chronic allograft vasculopathy. CD70 blockade had little effect on CD4(+) T cell function but prevented CD8(+) T cell-mediated rejection, inhibited the proliferation and activation of effector CD8(+) T cells, and diminished the expansion of effector and memory CD8(+) T cells in vivo. Thus, the CD27-CD70 pathway is critical for CD28-independent effector/memory CD8(+) alloreactive T cell activation in vivo. These novel findings have important implications for the development of transplantation tolerance-inducing strategies in primates and humans, in which CD8(+) T cell depletion is currently mandatory.

Tamoxifen long-term treatment in vitro alters the apoptotic response of MCF-7 breast cancer cells

In this study, we examined alterations in the apoptotic response of tamoxifen (TAM)-resistant breast cancer cells. We used an in vitro selection approach for TAM resistance by means of long-term culture of MCF-7 breast cancer cells with increasing concentrations of TAM. The apoptotic response to TAM was determined by means of ELISA measurement of apoptotic DNA-histone complexes in cytoplasm and by Annexin-V staining. MCF-7(LT) cells isolated after 5 months of long-term treatment with TAM exhibited a significantly reduced apoptotic response to this drug, even if administered in high concentrations up to 20 microM. This reduced apoptotic response was also observed after treatment with the topoisomerase II inhibitor etoposide, a pro-apoptotic antineoplastic drug. Microarray experiments comparing the transcriptome of MCF-7(LT) and wild-type cells revealed both the down-regulated expression of several genes coding for pro-apoptotic proteins and the up-regulation of genes coding for apoptosis inhibitors. Further experiments to determine expression changes of the receptor tyrosine kinases HER2 and epidermal growth factor receptor did not reveal any alterations in MCF-7(LT) if compared to wild-type cells. Our findings suggest that long-term treatment with TAM in vitro does not necessarily change the expression of receptor tyrosine kinases, but can modulate the expression of apoptotic key genes impairing the apoptotic response of MCF-7 breast cancer cells.

Use and comparison of different internal ribosomal entry sites (IRES) in tricistronic retroviral vectors

BACKGROUND

Polycistronic retroviral vectors that contain several therapeutic genes linked via internal ribosome entry sites (IRES), provide new and effective tools for the co-expression of exogenous cDNAs in clinical gene therapy protocols. For example, tricistronic retroviral vectors could be used to genetically modify antigen presenting cells, enabling them to express different co-stimulatory molecules known to enhance tumor cell immunogenicity.

RESULTS

We have constructed and compared different retroviral vectors containing two co-stimulatory molecules (CD70, CD80) and selectable marker genes linked to different IRES sequences (IRES from EMCV, c-myc, FGF-2 and HTLV-1). The tricistronic recombinant amphotropic viruses containing the IRES from EMCV, FGF-2 or HTLV-1 were equally efficient in inducing the expression of an exogenous gene in the transduced murine or human cells, without displaying any cell type specificity. The simultaneous presence of several IRESes on the same mRNA, however, can induce the differential expression of the various cistrons. Here we show that the IRESes of HTLV-1 and EMCV interfere with the translation induced by other IRESes in mouse melanoma cells. The IRES from FGF-2 did however induce the expression of exogenous cDNA in human melanoma cells without any positive or negative regulation from the other IRESs present within the vectors. Tumor cells that were genetically modified with the tricistronic retroviral vectors, were able to induce an in vivo anti-tumor immune response in murine models.

CONCLUSION

Translation of the exogenous gene is directed by the IRES and its high level of expression not only depends on the type of cell that is transduced but also on the presence of other genetic elements within the vector.

Pharmacological-based translational induction of transgene expression in mammalian cells

In the quest for the development of pharmacological switches that control gene expression, no system has been reported that regulates at the translational level. To permit small-molecule control of transgene translation, we have constructed a farnesyl transferase inhibitor-responsive translation initiation factor. This artificial protein is a three-component chimaera consisting of the ribosome recruitment core of the eIF4G1 eukaryotic translation initiation factor, the RNA-binding domain of the R17 bacteriophage coat protein and the plasma membrane localization CAAX motif of farnesylated H-Ras. This membrane-delocalized translation factor is inactive unless liberated in the cytosol. Farnesyl transferase inhibitor FTI-277 prevents the membrane association of the CAAX motif and thus increases the cytoplasmic levels of the eIF4G fusion protein, which is then capable of inducing translation of the second cistron of a bicistronic messenger RNA containing an R17-binding site in its intercistronic space. Such direct translational control by farnesyl transferase inhibitors provides a system for fast, graded and reversible regulation of transgene expression.

Vaccine Therapy for Murine Glioma Using Tumor Cells Genetically Modified to Express B7.1

OBJECTIVE

In a syngeneic mouse brain tumor model, we tested the hypothesis that vaccination with tumor cells genetically modified to express B7.1 molecules induces tumor-specific T cells and immunological antitumor effects.

METHODS

Malignant glioma cells (RSV-MG) derived from a C3H/He mouse induced by Schmidt-Ruppin Rous sarcoma virus (RSV) were infected with an adenovirus encoding the B7.1 gene (AdB7). To investigate the effects of B7.1 expression on the tumorigenicity of RSV-MG cells, infected cells were implanted subcutaneously into C3H/He mice. The C3H/He mice were vaccinated with AdB7 transfectants injected subcutaneously and 2 weeks later were challenged intracerebrally with wild-type RSV-MG cells to determine whether or not the expression of B7.1 would enhance the immunogenicity of RSV-MG cells.

RESULTS

Immunocytochemistry confirmed the expression of B7.1 and major histocompatibility complex Class I antigen on the infected cells. The growth of subcutaneous tumors was markedly retarded in the AdB7 group, whereas tumors had formed and progressively increased in size in the other control groups. In the vaccine experiments, the mice immunized with AdB7 transfectants survived longer than did the mice of the other groups, and a significant difference in survival times was noted. Immunocytochemistry revealed that brain tumors in mice previously vaccinated with AdB7 infectants had been infiltrated by a larger number of CD3(+) lymphocytes and that these CD3(+) lymphocytes contained not only CD4(+) and CD8(+) T cells but also CD25(+)-activated T cells. In addition, a cytotoxicity assay confirmed that vaccination with the AdB7 transfectants induced tumor-specific cytotoxicity.

CONCLUSION

These results demonstrate the therapeutic potential of vaccination with tumor cells expressing B7.1 for the treatment of malignant glioma.

Failure of B7.1-modified tumor to evoke full activation of CD8+ tumor-infiltrating lymphocytes in the central nervous system: prevention of parental tumor growth in the subcutaneous environment

OBJECT

It is well known that the central nervous system (CNS) is an immunologically privileged site. To characterize CD8+ tumor-infiltrating lymphocytes (TILs) recovered from the CNS, the authors compared these cells with TILs recovered from subcutaneous tissue by using a B7.1 gene-modified tumor implantation model.

METHODS

The authors established a B7.1 gene-modified EL4 murine lymphoma cell line (EL4-B7.1) and implanted the cells into the CNS to observe the duration of tumor-free survival. Although EL4-B7.1 cells were completely rejected in a subcutaneous implantation model, 40% of animals died after the CNS implantation (all animals in which the parent tumor was implanted died within 16 days). Therefore, the authors isolated TILs from each implantation site and analyzed the expressions of activation antigens CD25 and CD69 by performing the anti-CD8 magnetic beads separation method and flow cytometric analysis. After implantation of the parent tumor, there was no difference in the number of TILs from each site (CD25 1.7-3.2%, CD69 21.9-34.3%). After implantation of the B7.1-modified tumor, the CD25-expressing TIL population from the subcutaneous site was 4.68 times higher than that from the CNS site (17.8% compared with 3.8%). Based on these findings, the authors used a mitomycin C-treated EL4-B7.1 subcutaneous vaccination with various protocols. Vaccination before tumor challenge was sufficient to prevent the development of the tumor. For animals with established tumor, the vaccination protocol was able to prolong host survival (p = 0.0053).

CONCLUSIONS

The data clearly demonstrate that the CNS environment fails to activate CD8+ TILs fully. These are the first data indicating in detail a difference between CD8+ TILs from the CNS and those from other sites based on a B7.1-modified tumor model.

CD80-mediated induction of immunostimulation in two ocular melanoma cell lines is augmented by interferon-gamma

Although the transfection of the T-cell costimulatory molecule CD80 cDNA into human tumours can augment their immunogenicity in vitro, its expression alone is ineffective in many tumour systems. We evaluated the influence of CD80 expression on the immunostimulatory activity of ocular melanoma cell lines and determined whether IFN-gamma could enhance the effect. Two ocular melanoma cell lines were transfected with CD80 cDNA. The immunostimulatory capacity of the CD80+ transfectants was determined by their ability to stimulate the proliferation of allogeneic peripheral blood mononuclear cells (PBMC). The influence of additional accessory molecules on PBMC proliferation was assessed by pre-treating the CD80 transfectants with IFN-gamma. The CD80+ transfectants induced proliferation of allogeneic PBMC. IFN-gamma treatment of the tumour cells induced upregulated expression of MHC class I, de novo expression of MHC class II and CD54, and enhanced the ability of the CD80+ transfectants to stimulate PBMC proliferation. CD4+ T cells were not required for the proliferative response against untreated CD80+ tumour cells but were necessary for the augmentation of proliferation observed following IFN-gamma treatment. CD80+ ocular melanoma cells possess immunostimulatory potential which is augmented by IFN-gamma induced upregulation of cell surface molecules. Further studies on the role of costimulatory molecules in inducing anti-tumour immunity in ocular melanoma may help to define new strategies for application of immunotherapeutic approaches to treat this aggressive disease.

In vivo induction of antitumor immunity and protection against tumor growth by injection of CD154-expressing tumor cells

As they should enhance tumor-specific antigen presentation by dendritic cells, tumor cell lines genetically modified to express CD154 molecules have been used in an attempt to induce protective antitumor immunity. Two murine models were used: the major histocompatibility complex (MHC) class I negative melanoma B16F10 and the MHC class I positive mammary adenocarcinoma TS/A. CD154 or mock-transfected B16F10 or TS/A cells were injected subcutaneously into H-2-compatible B6D2 mice. CD154 expression by tumor cells induced a complete rejection (in the TS/A model) or a striking reduction (in the B16F10 model) of modified tumors growth, but also a significant protection against the growth of mock tumor cells injected simultaneously, either mixed with the CD154-expressing tumor cells, or in the other flank of mice. Thirty days after CD154-expressing tumor rejection, splenic lymphocytes from surviving tumor-free mice were able to inhibit tumor proliferation in vitro and significant amounts of IFN-gamma were detected in the sera of these mice. Growth kinetics of mock and CD154-expressing tumors in immunocompetent versus nude mice suggest that T lymphocytes and natural killer cells responses are implicated in this antitumor immunity. The injection of CD154-expressing tumor cell induced an antitumor protective response, both locally and distant from the injection site. The effect was most pronounced in MHC class I expressing TS/A tumor model.