Induction of potent antitumor response by vaccination with tumor lysate-pulsed macrophages engineered to secrete macrophage colony-stimulating factor and interferon-gamma

Neoepitopes as cancer immunotherapy targets: key challenges and opportunities

Over the last half century, it has become well established that cancers can elicit a host immune response that can target them with high specificity. Only within the last decade, with the advances in high-throughput gene sequencing and bioinformatics approaches, are we now on the forefront of harnessing the host's immune system to treat cancer. Recently, some strides have been taken toward understanding effective tumor-specific MHC I restricted epitopes or neoepitopes. However, many fundamental questions still remain to be addressed before this therapy can live up to its full clinical potential. In this review, we discuss the major hurdles that lie ahead and the work being done to address them.

Bu Fei Decoction attenuates the tumor associated macrophage stimulated proliferation, migration, invasion and immunosuppression of non-small cell lung cancer, partially via IL-10 and PD-L1 regulation

Macrophages play a pivotal role in tumor microenvironment. Bu-Fei Decoction (BFD) is a classical formula of traditional Chinese medicine (TCM) to alleviate lung cancer related symptoms, whether it has antitumor effect or could influence cancer microenvironment deserves further study. The aim of the present study was to examine the antitumor effect of BFD on non-small cell lung cancer (NSCLC), and to investigate the underlying mechanisms through tumor associated macrophages (TAMs). M2-polarized TAMs were induced by Phorbol 12-myristate 13-acetate (PMA) and interleukin 4 (IL-4). The antitumor activity of BFD in vitro was investigated in A549 and H1975 cells using MTT assay. The in vivo anticancer effect of BFD was evaluated in athymic nude mouse xenograft model. The invasive and migration properties of NSCLC cells were measured using Transwell. The protein expression was assessed using western blotting, ELISA and immunohistochemistry. The gene expression was examined using RT-PCR. TAMs was successfully established. Conditioned medium from TAMs increased cell proliferation, migration and invasion in NSCLC cells (p<0.05). BFD showed dose-dependent inhibitory effect on cell proliferation, migration and invasion abilities induced by TAMs. TAMs and rhIL-10 promoted the mRNA and protein expression of PD-L1 in NSCLC cells (p<0.01). Anti-IL-10 antibodies inhibited the elevated PD-L1 expression induced by TAMs. In vitro, the expression of PD-L1 and IL-10 was inhibited by BFD dose-dependently. In vivo, BFD suppressed A549 and H1975 tumor growth and decreased the expression of IL-10, PD-L1 and CD206. The results showed that TAMs play an important role in tumor progression of NSCLC, which was associated with tumor proliferation, migration, invasion and immunosuppression. Moreover, the antitumor mechanism of BFD is related to interruption of the link between TAMs and cancer cells by inhibiting the expression of IL-10 and PD-L1 in vitro and in vivo. Our results demonstrated BFD's potential as a novel treatment for NSCLC.

Enhanced performance of macrophage-encapsulated nanoparticle albumin-bound-paclitaxel in hypo-perfused cancer lesions

Hypovascularization in tumors such as liver metastases originating from breast and other organs correlates with poor chemotherapeutic response and higher mortality. Poor prognosis is linked to impaired transport of both low- and high-molecular weight drugs into the lesions and to high washout rate. Nanoparticle albumin-bound-paclitaxel (nAb-PTX) has demonstrated benefits in clinical trials when compared to paclitaxel and docetaxel. However, its therapeutic efficacy for breast cancer liver metastasis is disappointing. As macrophages are the most abundant cells in the liver tumor microenvironment, we design a multistage system employing macrophages to deliver drugs into hypovascularized metastatic lesions, and perform in vitro, in vivo, and in silico evaluation. The system encapsulates nAb-PTX into nanoporous biocompatible and biodegradable multistage vectors (MSV), thus promoting nAb-PTX retention in macrophages. We develop a 3D in vitro model to simulate clinically observed hypo-perfused tumor lesions surrounded by macrophages. This model enables evaluation of nAb-PTX and MSV-nab PTX efficacy as a function of transport barriers. Addition of macrophages to this system significantly increases MSV-nAb-PTX efficacy, revealing the role of macrophages in drug transport. In the in vivo model, a significant increase in macrophage number, as compared to unaffected liver, is observed in mice, confirming the in vitro findings. Further, a mathematical model linking drug release and retention from macrophages is implemented to project MSV-nAb-PTX efficacy in a clinical setting. Based on macrophage presence detected via liver tumor imaging and biopsy, the proposed experimental/computational approach could enable prediction of MSV-nab PTX performance to treat metastatic cancer in the liver.

Macrophage-tumor cell interactions regulate the function of nitric oxide

Tumor cell-macrophage interactions change as the tumor progresses, and the generation of nitric oxide (NO) by the inducible nitric oxide synthase (iNOS) plays a major role in this interplay. In early stages, macrophages employ their killing mechanisms, particularly the generation of high concentrations of NO and its derivative reactive nitrogen species (RNS) to initiate tumor cell apoptosis and destroy emerging transformed cells. If the tumor escapes the immune system and grows, macrophages that infiltrate it are reprogramed in situ by the tumor microenvironment. Low oxygen tensions (hypoxia) and immunosuppressive cytokines inhibit iNOS activity and lead to production of low amounts of NO/RNS, which are pro-angiogenic and support tumor growth and metastasis by inducing growth factors (e.g., VEGF) and matrix metalloproteinases (MMPs). We review here the different roles of NO/RNS in tumor progression and inhibition, and the mechanisms that regulate iNOS expression and NO production, highlighting the role of different subtypes of macrophages and the microenvironment. We finally claim that some tumor cells may become resistant to macrophage-induced death by increasing their expression of microRNA-146a (miR-146a), which leads to inhibition of iNOS translation. This implies that some cooperation between tumor cells and macrophages is required to induce tumor cell death, and that tumor cells may control their fate. Thus, in order to induce susceptibility of tumors cells to macrophage-induced death, we suggest a new therapeutic approach that couples manipulation of miR-146a levels in tumors with macrophage therapy, which relies on ex vivo stimulation of macrophages and their re-introduction to tumors.

Epstein-Barr virus-encoded BARF1 protein is a decoy receptor for macrophage colony stimulating factor and interferes with macrophage differentiation and activation

Epstein-Barr virus (EBV), like many other persistent herpes viruses, has acquired numerous mechanisms for subverting or evading immune surveillance. This study investigates the role of secreted EBV-encoded BARF1 protein (sBARF1) in creating an immune evasive microenvironment. Wild-type consensus BARF1 was expressed in the human 293 cell line and purified. This native hexameric sBARF1 had inhibitory capacity on macrophage colony stimulating factor (M-CSF)-stimulated, and not on granulocyte macrophage-colony stimulating factor (GM-CSF)-stimulated growth and differentiation of myeloid cells. Antibodies specific to hexameric sBARF1 were able to block this effect. M-CSF was shown to interact with sBARF1 via the protruding N-terminal loops involving Val38 and Ala84. Each BARF1 hexamer was capable of binding three M-CSF dimers. Mutations in the BARF1 loops greatly affected M-CSF interaction, and showed loss of growth inhibition. Analysis of the activation state of the M-CSF receptor c-fms and its downstream kinase pathways showed that sBARF1 prevented M-CSF-induced downstream phosphorylation. Since M-CSF is an important factor in macrophage differentiation, the effect of sBARF1 on the function of monocyte-derived macrophages was evaluated. sBARF1 affected overall survival and morphology and significantly reduced expression of macrophage differentiation surface markers such as CD14, CD11b, CD16, and CD169. Macrophages differentiating in the presence of sBARF1 showed impaired responses to lipopolysaccharide and decreased oxygen radical formation as well as reduced phagocytosis of apoptotic cells. In conclusion, EBV sBARF1 protein is a potent decoy receptor for M-CSF, hampering the function and differentiation of macrophages. These results suggest that sBARF1 contributes to the modulation of immune responses in the microenvironment of EBV-positive carcinomas.

Macrophages in tumor microenvironments and the progression of tumors

Macrophages are widely distributed innate immune cells that play indispensable roles in the innate and adaptive immune response to pathogens and in-tissue homeostasis. Macrophages can be activated by a variety of stimuli and polarized to functionally different phenotypes. Two distinct subsets of macrophages have been proposed, including classically activated (M1) and alternatively activated (M2) macrophages. M1 macrophages express a series of proinflammatory cytokines, chemokines, and effector molecules, such as IL-12, IL-23, TNF-α, iNOS and MHCI/II. In contrast, M2 macrophages express a wide array of anti-inflammatory molecules, such as IL-10, TGF-β, and arginase1. In most tumors, the infiltrated macrophages are considered to be of the M2 phenotype, which provides an immunosuppressive microenvironment for tumor growth. Furthermore, tumor-associated macrophages secrete many cytokines, chemokines, and proteases, which promote tumor angiogenesis, growth, metastasis, and immunosuppression. Recently, it was also found that tumor-associated macrophages interact with cancer stem cells. This interaction leads to tumorigenesis, metastasis, and drug resistance. So mediating macrophage to resist tumors is considered to be potential therapy.

Glucocorticoids suppress cystathionine gamma-lyase expression and H2S production in lipopolysaccharide-treated macrophages

Hydrogen sulfide (H(2)S) plays an important role in inflammation. We showed that macrophages expressed the H(2)S-forming enzyme cystathionine gamma-lyase (CSE) and produced H(2)S. Lipopolysaccharide (LPS) stimulated the CSE expression and H(2)S production rate. l-cysteine reduced LPS-induced nitric oxide (NO) production. CSE inhibitor blocked the inhibitory effect of l-cysteine. CSE knockdown increased, whereas CSE overexpression decreased LPS-induced NO production. Dexamethasone suppressed LPS-induced CSE expression and the H(2)S production rate as well as NO production. l-arginine increased, whereas N(G)-nitro-l-arginine methyl ester (l-NAME) decreased LPS-induced CSE expression and H(2)S production. Dexamethasone plus l-NAME significantly decreased LPS-induced CSE expression and H(2)S production compared to l-NAME. Our results suggest that macrophages are one of the H(2)S producing sources. H(2)S might exert anti-inflammatory effects by inhibiting NO production. Dexamethasone may directly inhibit CSE expression and H(2)S production, besides the NO-dependent way. Inhibition of H(2)S and NO production may be a mechanism by which glucocorticoids coordinate the balance between pro- and anti-inflammatory mediators during inflammation.

Tumor-associated macrophages: effectors of angiogenesis and tumor progression

Tumor-associated macrophages (TAMs) are a prominent inflammatory cell population in many tumor types residing in both perivascular and avascular, hypoxic regions of these tissues. Analysis of TAMs in human tumor biopsies has shown that they express a variety of tumor-promoting factors and evidence from transgenic murine tumor models has provided unequivocal evidence for the importance of these cells in driving angiogenesis, lymphangiogenesis, immunosuppression, and metastasis. This review will summarize the mechanisms by which monocytes are recruited into tumors, their myriad, tumor-promoting functions within tumors, and the influence of the tumor microenvironment in driving these activities. We also discuss recent attempts to both target/destroy TAMs and exploit them as delivery vehicles for anti-cancer gene therapy.

Monocyte/macrophage infiltration in tumors: modulators of angiogenesis

The role of a tumor immune infiltrate in cancer progression and metastasis has been debated frequently. Although often considered to be associated with improved prognosis and leading to the enhanced survival of cancer patients, inflammatory cells have also been described to assist the tumor's capabilities to progress, proliferate, and metastasize. Tumor-associated macrophages (TAMs), for example, have been shown to be symbiotically related to tumor cells: Tumor cells recruit TAMs and provide them with survival factors, and TAMs in turn produce a variety of angiogenic factors in response to the tumor microenvironment. This review will describe the composition of an immune infiltrate in tumors and the angiogenic and angiostatic properties of the cells present. Special emphasis will be on the angiogenesis-associated activities of TAMs. The development of immunotherapy and gene therapy using TAMs to mediate tumor cytotoxicity or to deliver gene constructs will be discussed as well. As immunotherapy has so far not been as effective as anticipated, a combination therapy in which angiostatic agents are used as well is put forward as a novel strategy to treat cancer.

Extracellular accumulation of recombinant proteins fused to the carrier protein YebF in Escherichia coli

Bacterial protein secretion is important in the life cycles of most bacteria, in which it contributes to the formation of pili and flagella and makes available extracellular enzymes to digest polymers for nutritional purposes and toxins to kill host cells in infections of humans, animals and plants. It is generally accepted that nonpathogenic laboratory strains of Escherichia coli, particularly K12 strains, do not secrete proteins into the extracellular medium under routine growth conditions. In this study, we report that commonly used laboratory strains secrete YebF, a small (10.8 kDa in the native form), soluble endogenous protein into the medium, challenging the status quo view that laboratory strains do not secrete proteins to the medium. We further show that 'passenger' proteins linked to the carboxyl end of YebF are efficiently secreted. The function of YebF is unknown, but its use as a carrier for transgenic proteins provides a tool to circumvent toxicity and other contamination issues associated with protein production in E. coli.

Colony-stimulating factor-1 in immunity and inflammation

Colony-stimulating factor-1 (CSF-1, also known as macrophage-CSF) is the primary regulator of the survival, proliferation, differentiation and function of mononuclear phagocytes. Studies that involve CSF-1-deficient mice demonstrate that there is a variable requirement for CSF-1 in the development of individual mononuclear phagocyte populations. However, these cells uniformly express the CSF-1 receptor, and their morphology, phagocytosis and responsiveness to infectious and non-infectious stimuli is regulated by CSF-1. CSF-1 plays important roles in innate immunity, cancer and inflammatory diseases, including systemic lupus erythematosus, arthritis, atherosclerosis and obesity. In several conditions, activation of macrophages involves a CSF-1 autocrine loop. In addition, secreted and cell-surface isoforms of CSF-1 can have differential effects in inflammation and immunity.

Potential of albumin nanoparticles as carriers for interferon gamma

Although interferon gamma (IFN-gamma has been extensively studied as a potent activator for macrophages and as a promising adjuvant in vaccines, its rapid biodegradation and clearance have severely limited its clinical efficacy. Our major objective in this work was to develop formulation conditions to get high association of the cytokine to albumin nanoparticles, without leading any conformational changes and subsequent loss of activity. To achieve this objective, two different formulations were prepared by either 1) incubation between the cytokine and the newly prepared nanoparticles (IFN-NPA) or 2) between the protein and IFN-gamma prior coacervation (IFN-NPB). Steady-state fluorescence emission spectra revealed that the environment of the tryptophan (Trp) residue was not affected by conditions of mechanical stress required for preparing nanoparticles. A bioassay for antiproliferative activity with Hela cells indicated that the cytokine, after their desorption from the surface of nanoparticles (IFN-NPA), fully retained its activity. It also indicated that the cytokine was principally associated with nanoparticles via electrostatic interactions and confirmed by desorption experiments carried out in media with different pH and ionic strength, with burst effect ranked in the order pH 5 > pH 7.4 > pH 8.5. Also, the adsorption of IFN-gamma onto these carriers was able to improve the priming effects of IFN-gamma on the nitric oxide production (NO) by RAW macrophages. On the contrary, when we incubated the cytokine with the albumin solution prior to the desolvation process for preparing nanoparticles (IFN-NPB), we obtained better encapsulation efficiencies (around 100%), but the cytokine was inactive: it was not detected by ELISA or bioassay in Hela cells and unable to stimulate NO production by macrophages.

Intratumoral injection of interferon-gamma gene-modified dendritic cells elicits potent antitumor effects: effective induction of tumor-specific CD8+ CTL response

PURPOSE

To examine the antitumor efficacy of intratumoral injection of interferon-gamma gene-modified dendritic cells (DC-IFN-gamma) in a B16 melanoma model and to investigate its related immunological mechanisms.

METHODS

C57BL/6 mice-derived DC were transfected with adenovirus encoding IFN-gamma or beta-galactosidase (DC-LacZ). Secretion of IFN-gamma and TNF-alpha by DC was detected by ELISA. Nitric oxide (NO) production was measured by Griess reaction. Cytotoxicity of DC against tumor cell lines and activity of cytotoxic T lymphocytes (CTLs) were determined by 51Cr-release assay. TRP-2aa180-188-specific CD8+ CTLs in tumor-bearing mice with different treatment were determined by ELISPOT.

RESULTS

DC-IFN-gamma could secrete high levels of IFN-gamma, NO and TNF-alpha. DC-IFN-gamma were cytolytic to B16 melanoma cells in vitro, but DC-LacZ and DC were not. Significant inhibition of tumor growth and prolonged survival were achieved in tumor-bearing mice intratumorally injected with DC-IFN-gamma when compared with those in tumor-bearing mice intratumorally injected with DC, DC-LacZ, fibroblasts, IFN-gamma gene-modified fibroblasts or PBS. After treatment with DC-IFN-gamma, enhanced Th1 and decreased Th2 responses were observed, and B16 melanoma antigen TRP-2aa180-188-specific CD8+ CTLs were induced significantly in the tumor-bearing mice.

CONCLUSIONS

Intratumorally injected DC-IFN-gamma can uptake tumor antigens in situ and cross-present tumor antigens to specific CD8+ T cells, hereby eliciting effective antitumor effects in murine model with preestablished B16 melanoma.

Mechanisms regulating the recruitment of macrophages into hypoxic areas of tumors and other ischemic tissues

The mechanisms responsible for recruiting monocytes from the bloodstream into solid tumors are now well characterized. However, recent evidence has shown that these cells then differentiate into macrophages and accumulate in large numbers in avascular and necrotic areas where they are exposed to hypoxia. This parallels their tendency to congregate in ischemic areas of other diseased tissues such as atherosclerotic plaques and arthritic joints. In tumors, macrophages appear to undergo marked phenotypic changes when exposed to hypoxia and to switch on their expression of a number of mitogenic and proangiogenic cytokines and enzymes. This then promotes tumor growth, angiogenesis, and metastasis. Here, we compare the various mechanisms responsible for monocyte recruitment into tumors with those regulating the accumulation of macrophages in hypoxic/necrotic areas. Because the latter are best characterized in human tumors, we focus mainly on these but also discuss their relevance to macrophage migration in ischemic areas of other diseased tissues. Finally, we discuss the relevance of these mechanisms to the development of novel cancer therapies, both in providing targets to reduce the proangiogenic contribution made by hypoxic macrophages in tumors and in developing the use of macrophages to deliver therapeutic gene constructs to hypoxic areas of diseased tissues.

Interferon-gamma is an autocrine mediator for dendritic cell maturation

Maturation of dendritic cells (DC) is critical for efficient antigen presentation and initiation of an immune response. Interferon-gamma (IFN-gamma) is an important Th1 cytokine. In this study, we investigated the role of IFN-gamma in DC maturation using either IFN-gamma receptor deficient- or IFN-gamma overexpression-models. We showed that immature DC generated in vitro from bone marrow (BM) progenitor cells produced low level of IFN-gamma. After LPS stimulation, DC produced more IFN-gamma, and IFN-gamma productions were at comparable levels among C57BL/6 mice-derived DC (C57BL/6 DC), wild-type 129 mice-derived DC (129 DC) and IFN-gamma receptor deficient 129 mice-derived DC (IFN-gammaR-/-DC). We found that IFN-gammaR-/-DC exhibited decreased expression of CD54, CD86, reduced capacity to secrete IL-1beta and IL-12p70, and impaired capacity to stimulate alloreactive T cells and to drive Th1 differentiation. Transfection of IFN-gamma gene into DC promoted DC to express higher CD40, CD54, CD80, CD86, CCR7 and I-Ab, secrete more IL-1beta and IL-12p70, and more potently activate both CD4 and CD8 T cells. These data suggest that IFN-gamma signaling pathway is important for the maturation of DC in an autocrine fashion.

Picolinic acid- or desferrioxamine-inducible autocrine activation of macrophages engineered to produce IFNγ: an approach for gene therapy

Macrophage (Mphi)-based vectors are highly mobile cellular shuttles designed to deliver therapeutic genes within the tissues. We engineered a mouse Mphi cell line to express the murine interferon-gamma (IFNgamma) under the control of an inducible promoter containing the hypoxia-responsive element, which can be triggered by hypoxia and other stimuli. We show that this Mphi vector can be induced to produce IFNgamma under normoxic conditions by stimulation with picolinic acid (PA), a catabolite of tryptophan, or desferrioxamine (DFX), an iron-chelating drug. The Mphi vector responds to IFNgamma with the induction of IRF-1 and of other IFNgamma-inducible genes, the expression of Ia antigens and induction of phagocytic activity. Inducible nitric oxygen synthase gene expression, nitric oxide production, as well as TNFalpha secretion were enhanced by PA or DFX as the sole stimuli. None of the above responses could be triggered individually by PA or DFX in control, normal Mphi, indicating that the Mphi vector overcame the need for costimulatory molecules derived from the immune system for its full activation. Furthermore, we demonstrate that extracellular iron can downregulate such response, thereby identifying an additional tool for the fine tuning of the Mphi vector response to stimulation.

Tumor-associated macrophages in breast cancer

Neoplastic cells form only one part of a complex network of cell types that make up a breast tumor. The normal cell types that make up the nonneoplastic components of tumors include fibroblasts, endothelium, and inflammatory cells, such as tumor associated macrophages (TAMs). TAMs have the potential to carry out both anti- and protumor activities In their antitumor role TAMs can present tumor antigens to cytotoxic T-cells and are capable of being directly cytotoxic to neoplastic cells. Conversely, TAMs are also able to promote tumor growth directly by secreting breast tumor mitogens, such as epidermal growth factor, and indirectly by stimulating tumor angiogenesis and metastasis. Recent studies have indicated that in breast cancers the protumor role of TAMs is dominant, and that TAMs may be executing a "wound healing" type of process in response to stimuli found in the tumor microenvironment, such as hypoxia. As such, TAMs may provide opportunities for future therapeutic interventions.

The role of tumour-associated macrophages in tumour progression: implications for new anticancer therapies

The role of macrophages in tumour growth and development is complex and multifaceted. Whilst there is limited evidence that tumour-associated macrophages (TAMs) can be directly tumouricidal and stimulate the anti-tumour activity of T cells, there is now contrasting evidence that tumour cells are able to block or evade the activity of TAMs at the tumour site. In some cases, tumour-derived molecules even redirect TAM activities to promote tumour survival and growth. Indeed, evidence has emerged for a symbiotic relationship between tumour cells and TAMs, in which tumour cells attract TAMs and sustain their survival, with TAMs then responding to micro-environmental factors in tumours such as hypoxia (low oxygen tension) by producing important mitogens as well as various growth factors and enzymes that stimulate tumour angiogenesis. This review presents evidence for the number and/or distribution of TAMs being linked to prognosis in different types of human malignancy. It also outlines the range of pro- and anti-tumour functions performed by TAMs, and the novel therapies recently devised using TAMs to stimulate host immune responses or deliver therapeutic gene constructs to solid tumours.

Interferon-gamma therapy: evaluation of routes of administration and delivery systems

Although different routes and delivery systems have been used to deliver interferon-gamma (IFN-gamma) for the treatment of a variety of viral and neoplastic diseases, little has been reported regarding the most efficient and least toxic routes and drug delivery modes required to achieve these goals. To have a greater understanding of the best strategies to use to administer this cytokine in an efficient, stable, and safe manner, this review details aspects of IFN-gamma concerning its mechanism of action, physical properties, and pharmacokinetics. One important conclusion that is drawn from this analysis is that a consistent, local concentration of IFN-gamma is necessary to achieve an optimal therapeutic response. A critical discussion covering the advantages and limitations of the currently used methodologies to deliver IFN-gamma in such a fashion is presented.

Engineering of macrophages to produce IFN-gamma in response to hypoxia

Activation of murine macrophages (Mphi) requires the collaboration of signals derived from the immune system and the environment. In this study, we engineered a murine Mphi cell line to become activated in response to an environmental signal, hypoxia, as the sole stimulus. Hypoxia is a condition of low oxygen tension, occurring in several pathological tissues, which acts in synergy with IFN-gamma to induce full Mphi activation. We transfected the ANA-1 murine Mphi cell line with a construct containing the IFN-gamma gene controlled by a synthetic promoter inducible by hypoxia (HRE3x-Tk), and we characterized the cellular and molecular biology of the engineered Mphi under normoxia or hypoxia. Engineered Mphi in normoxia expressed basal levels of IFN-gamma mRNA and protein that were strongly augmented by shifting the cells to hypoxia. Furthermore, they responded to the synthesized IFN-gamma with induction of IFN-responsive factor-1 and 2'-5'-oligoadenylate synthase expression. Under normoxic conditions, the engineered Mphi had a significant constitutive level of Ia Ags and Fc receptors. Hypoxia induced further augmentation of Ia and Fc expression. Finally, hypoxia induced inducible NO synthase expression, and subsequent reoxygenation led to the production of NO. In conclusion, the engineered Mphi, which produce IFN-gamma in an inducible manner, express new biochemical and functional properties in response to low oxygen environment as the sole stimulus, thereby circumventing the need for costimulation by other immune system-derived signals.

Intratumoral IL-18 gene transfer improves therapeutic efficacy of antibody-targeted superantigen in established murine melanoma

Antibody-targeted superantigen C215Fab-SEA is a fusion protein of staphylococcal enterotoxin A (SEA) and the Fab region of the tumor-reactive C215 mAb. It can trigger CTL against C215 antigen-positive tumor cells and induce tumor-suppressive cytokines. However, the antitumor effect of C215Fab-SEA is not satisfactory because of suboptimal production of Th1 cytokines after repeated administration. Interleukin 18 (IL-18) is a novel cytokine with profound effects on Th1 cellular response. In this study, we showed that adenovirus-mediated intratumoral IL-18 gene transfer strongly improved the therapeutic efficacy of C215Fab-SEA in the pre-established C215 antigen-expressing B16 melanoma murine model. More significant tumor inhibition and prolonged survival time were observed in tumor-bearing mice received combined therapy of C215Fab-SEA and Ad IL-18 than those of mice treated with C215Fab-SEA or AdIL-18 alone. Combination therapy augmented NK and CTL activities of tumor-bearing mice more markedly. The production of IL-2 and IFN-gamma also increased more significantly. More potent antitumor effect of combined therapy was observed in IL-10 KO mice with enhanced Th1 response. Our data demonstrated that the antitumor effect of C215Fab-SEA immunotherapy could be potentiated significantly by combination with intratumoral IL-18 gene transfer through more efficient activation of Th1 immune responses.

Generation of high-titer retroviral vector-producing macrophages as vehicles for in vivo gene transfer

The goal of this project was to develop a novel gene transfer system based on macrophages (Mphi) as shuttles of recombinant retroviral vectors carrying therapeutic or marker genes. The murine Mphi cell line WGL5 was used as a source of Mphi for this study. We generated retrovirus-producing Mphi by transducing the WGL5 cells with a replication-defective retroviral vector carrying the enhanced green fluorescent protein (EGFP) reporter gene and the Moloney murine leukemia virus (MoMLV) as helper virus. We demonstrated stable integration of the recombinant retrovirus in the Mphi genome, efficient recombinant retrovirus production, and EGFP gene delivery to different cell lines in vitro. To evaluate Mphi-mediated EGFP gene transfer in vivo, allogeneic mice were injected s.c. with the retrovirus-producing WGL5 Mphi, that gave rise to solid tumor masses at the injection site, highly infiltrated with host leukocytes. We observed EGFP fluorescence in tumor-infiltrating CD4(+) and CD8(+) host T lymphocytes, providing direct evidence of the ability of engineered Mphi to mediate EGFP gene delivery to host cells in vivo. Moreover, we showed that retrovirus-producing Mphi could home to different organs in vivo following i.v. injection into mice. These data demonstrate that Mphi can be engineered as cellular vehicles for recombinant retroviruses carrying heterologous genes and suggest potential applications of this novel vector system for gene therapy.