Immunotherapy of established tumors in mice by intratumoral injection of an adenovirus vector harboring the human IL-2 cDNA: induction of CD8(+) T-cell immunity and NK activity

Oncolytic ImmunoViroTherapy: A long history of crosstalk between viruses and immune system for cancer treatment

Cancer Immunotherapy relies on harnessing a patient's immune system to fine-tune specific anti-tumor responses and ultimately eradicate cancer. Among diverse therapeutic approaches, oncolytic viruses (OVs) have emerged as a novel form of cancer immunotherapy. OVs are a naturally occurring or genetically modified class of viruses able to selectively kill cancer cells, leaving healthy cells unharmed; in the last two decades, the role of OVs has been redefined to act beyond their oncolytic activity. Indeed, the immunogenic cancer cell death mediated by OVs induces the release of tumor antigens that in turn induces anti-tumor immunity, allowing OVs to act as in situ therapeutic cancer vaccines. Additionally, OVs can be engineered for intratumoral delivery of immunostimulatory molecules such as tumor antigens or cytokines to further enhance anti-tumor response. Moreover, OVs can be used in combination with other cancer immunotherapeutic approaches such as Immune Checkpoint Inhibitors and CAR-T cells. The current review first defines the three main mechanisms of action (MOA) of OVs currently used in cancer therapy that are: i) Oncolysis, ii) OV-induced cancer-specific immune activation, and iii) Exploiting pre-existing anti-viral immunity to enhance cancer therapy. Secondly, we focus on how OVs can induce and/or improve anti-cancer immunity in a specific or unspecific fashion, highlighting the importance of these approaches. Finally, the last part of the review analyses OVs combined with other cancer immunotherapies, revising present and future clinical applications.

Blockade of transforming growth factor β2 by anti-sense oligonucleotide improves immunotherapeutic potential of IL-2 against melanoma in a humanized mouse model

BACKGROUND AIMS

IL-2 is a potent cytokine that activates natural killer cells and CD8+ cytotoxic T lymphocytes (CTLs) and has been approved for the treatment of metastatic renal cell carcinoma and metastatic melanoma. However, the medical use of IL-2 is restricted because of its narrow therapeutic window and potential side effects, including the expansion of regulatory T cells (Tregs).

METHODS

In this study, the authors investigated the complementary effects of transforming growth factor-β2 (TGF-β2) anti-sense oligodeoxynucleotide (TASO) on the immunotherapeutic potential of IL-2 in a melanoma-bearing humanized mouse model.

RESULTS

The authors observed that the combination of TASO and IL-2 facilitated infiltration of CTLs into the tumor, thereby potentiating the tumor killing function of CTLs associated with increased granzyme B expression. In addition, TASO attenuated the increase in Tregs by IL-2 in the peripheral blood and spleen and also inhibited infiltration of Tregs into the tumor, which was partly due to decreased CCL22. Alteration of T-cell constituents at the periphery by TGF-β2 inhibition combined with IL-2 might be associated with the synergistic augmentation of serum pro-inflammatory cytokines (such as interferon γ and tumor necrosis factor α) and decreased ratio of Tregs to CTLs in tumor tissues, which consequently results in significant inhibition of tumor growth CONCLUSIONS: These results indicate that the application of TASO improves IL-2-mediated anti-tumor immunity, thus implying that blockade of TGF-β2 in combination with IL-2 may be a promising immunotherapeutic strategy for melanoma.

Localized Interleukin-12 for Cancer Immunotherapy

Interleukin-12 (IL-12) is a potent, pro-inflammatory type 1 cytokine that has long been studied as a potential immunotherapy for cancer. Unfortunately, IL-12's remarkable antitumor efficacy in preclinical models has yet to be replicated in humans. Early clinical trials in the mid-1990's showed that systemic delivery of IL-12 incurred dose-limiting toxicities. Nevertheless, IL-12's pleiotropic activity, i.e., its ability to engage multiple effector mechanisms and reverse tumor-induced immunosuppression, continues to entice cancer researchers. The development of strategies which maximize IL-12 delivery to the tumor microenvironment while minimizing systemic exposure are of increasing interest. Diverse IL-12 delivery systems, from immunocytokine fusions to polymeric nanoparticles, have demonstrated robust antitumor immunity with reduced adverse events in preclinical studies. Several localized IL-12 delivery approaches have recently reached the clinical stage with several more at the precipice of translation. Taken together, localized delivery systems are supporting an IL-12 renaissance which may finally allow this potent cytokine to fulfill its considerable clinical potential. This review begins with a brief historical account of cytokine monotherapies and describes how IL-12 went from promising new cure to ostracized black sheep following multiple on-study deaths. The bulk of this comprehensive review focuses on developments in diverse localized delivery strategies for IL-12-based cancer immunotherapies. Advantages and limitations of different delivery technologies are highlighted. Finally, perspectives on how IL-12-based immunotherapies may be utilized for widespread clinical application in the very near future are offered.

In situ vaccination for the treatment of cancer

Vaccination has had a tremendous impact on human health by harnessing the immune system to prevent and eradicate infectious diseases and this same approach might be used in cancer therapy. Cancer vaccine development has been slowed hindered by the paucity of universal tumor-associated antigens and the difficulty in isolating and preparing individualized vaccines ex vivo. Another approach has been to initiate or stimulate an immune response in situ (at the tumor site) and thus exploit the potentially numerous tumor-associated antigens there. Here, we review the many approaches that have attempted to accomplish effective in situ vaccination, using intratumoral administration of immunomodulators to increase the numbers or activation state of either antigen present cells or T cells within the tumor.

In situ vaccination: Cancer immunotherapy both personalized and off-the-shelf

As cancer immunotherapy continues to benefit from novel approaches which cut immune 'brake pedals' (e.g. anti-PD1 and anti-CTLA4 antibodies) and push immune cell gas pedals (e.g. IL2, and IFNα) there will be increasing need to develop immune 'steering wheels' such as vaccines to guide the immune system specifically toward tumor associated antigens. Two primary hurdles in cancer vaccines have been: identification of universal antigens to be used in 'off-the-shelf' vaccines for common cancers, and 2) logistical hurdles of ex vivo production of individualized whole tumor cell vaccines. Here we summarize approaches using 'in situ vaccination' in which intratumoral administration of off-the-shelf immunomodulators have been developed to specifically induce (or amplify) T cell responses to each patient's individual tumor. Clinical studies have confirmed the induction of systemic immune and clinical responses to such approaches and preclinical models have suggested ways to further potentiate the translation of in situ vaccine trials for our patients.

Targeting the tumor microenvironment to enhance antitumor immune responses

The identification of tumor-specific antigens and the immune responses directed against them has instigated the development of therapies to enhance antitumor immune responses. Most of these cancer immunotherapies are administered systemically rather than directly to tumors. Nonetheless, numerous studies have demonstrated that intratumoral therapy is an attractive approach, both for immunization and immunomodulation purposes. Injection, recruitment and/or activation of antigen-presenting cells in the tumor nest have been extensively studied as strategies to cross-prime immune responses. Moreover, delivery of stimulatory cytokines, blockade of inhibitory cytokines and immune checkpoint blockade have been explored to restore immunological fitness at the tumor site. These tumor-targeted therapies have the potential to induce systemic immunity without the toxicity that is often associated with systemic treatments. We review the most promising intratumoral immunotherapies, how these affect systemic antitumor immunity such that disseminated tumor cells are eliminated, and which approaches have been proven successful in animal models and patients.

Effective melanoma immunotherapy with interleukin-2 delivered by a novel polymeric nanoparticle

Interleukin-2 (IL-2) has been shown to possess antitumor activity in numerous preclinical and clinical studies. However, the short half-life of recombinant IL-2 protein in serum requires repeated high-dose injections, resulting in severe side effects. Although adenovirus-mediated IL-2 gene therapy has shown antitumor efficacy, the host antibody response to adenoviral particles and potential biosafety concerns still obstruct its clinical applications. Here we report a novel nanopolymer for IL-2 delivery, consisting of low molecular weight polyethylenimine (600 Da) linked by β-cyclodextrin and conjugated with folate (named H1). H1 was mixed with IL-2 plasmid to form H1/pIL-2 polyplexes of around 100 nm in diameter. Peritumoral injection of these polyplexes suppressed the tumor growth and prolonged the survival of C57/BL6 mice bearing B16-F1 melanoma grafts. Importantly, the antitumor effects of H1/pIL-2 (50 μg DNA) were similar to those of recombinant adenoviruses expressing IL-2 (rAdv-IL-2; 2 × 10(8) pfu). Furthermore, we showed that H1/pIL-2 stimulated the activation and proliferation of CD8+, CD4+ T cell, and natural killer cells in peripheral blood and increased the infiltration of CD8+, CD4+ Tcells, and natural killer cells into the tumor environment. In conclusion, these results show that H1/pIL-2 is an effective and safe melanoma therapeutic with an efficacy comparable to that of rAdv-IL-2. This treatment represents an alternative gene therapy strategy for melanoma.

Direct and indirect antitumor effects by human peripheral blood lymphocytes expressing both chimeric immune receptor and interleukin-2 in ovarian cancer xenograft model

Human peripheral blood lymphocytes (PBLs) electroporated with RNA encoding anti-Her-2/neu-specific chimeric immune receptor (CIR) have been reported to elicit potent immune responses against SKOV3 tumors in a nude mouse model. However, CIR-electroporated PBL (CIR-PBL) did not proliferate, and the cell number rapidly decreased in the absence of exogenous interleukin-2 (IL-2). In this study, PBLs electroporated with both CIR and IL-2 RNA (CIR/IL-2-PBL) were studied to determine whether antitumor effects could be improved by adoptive immunotherapy. CIR and IL-2 were expressed in CIR/IL-2-PBL at levels similar to PBLs electroporated, with IL-2 RNA (IL-2-PBL) or CIR-PBL. Transfer of IL-2 RNA induced proliferation and prolonged survival of PBLs in vitro. In a xenograft model, both IL-2-PBL and CIR/IL-2-PBL showed significantly higher antitumor effects than CIR-PBL. The number of tumor-infiltrating natural killer (NK) cells was significantly increased in IL-2-PBL and CIR/IL-2-PBL. After NK cell depletion, IL-2-PBL showed significantly lower antitumor effects than CIR/IL-2-PBL. These results suggest that transfer of IL-2 RNA to CIR-PBL can promote NK cell infiltration of tumors and prolong survival of infused PBLs in vivo. RNA electroporated PBLs may represent efficient tools for delivery of functional molecules to tumors by multiple gene transfer.

Phase I and biodistribution study of recombinant adenovirus vector-mediated herpes simplex virus thymidine kinase gene and ganciclovir administration in patients with head and neck cancer and other malignant tumors

In this study, we investigated the safety and efficacy in cancer patients of a single intra-tumor injection of recombinant adenovirus vector-mediated herpes simplex virus thymidine kinase gene (AdV/TK) followed by systemic administration of ganciclovir (GCV). In 18 patients with malignant tumors refractory to standard treatment, AdV/TK was injected on day 1 with dose escalation from 2.5 x 10(11) to 1 x 10(12) virus particles (VP), and GCV (5 mg kg(-1)) was delivered intravenously every 12 h from days 2 to 15. The most common treatment-related toxicities were transient fever (10/18) and local injection site reaction (10/18), and most adverse events were WHO grade I/II. Anti-adenovirus antibody levels increased continuously during treatment, but anti-HSV antibody levels remained stable. One patient had a PR at the injection site but PD was found in the primary site (lung cancer), one patient with fibrosarcoma of the neck had an MR, five patients had SD, and 10 patients had PD. In conclusion, AdV/TK followed by GCV can be administered safely to Chinese cancer patients, and achieved a local response with few environmental effects. Because the response was localized, single regional tumor relapse, especially after radiation, may be an indication for this suicide gene therapy.

Type I IFN innate immune response to adenovirus-mediated IFN-gamma gene transfer contributes to the regression of cutaneous lymphomas

The fact that adenoviral vectors activate innate immunity and induce type I IFNs has not been fully appreciated in the context of cancer gene therapy. Type I IFNs influence different aspects of human immune response and are believed to be crucial for efficient tumor rejection. We performed transcriptional profiling to characterize the response of cutaneous lymphomas to intralesional adenovirus-mediated IFN-gamma (Ad-IFN-gamma) gene transfer. Gene expression profiles of skin lesions obtained from 19 cutaneous lymphoma patients before and after treatment with Ad-IFN-gamma revealed a distinct gene signature consisting of IFN-gamma- and numerous IFN-alpha-inducible genes (type II- and type I-inducible genes, respectively). The type I IFN response appears to have been induced by the vector itself, and its complexity, in terms of immune activation, was potentiated by the IFN-gamma gene insert. Intralesional IFN-gamma expression together with the induction of a combined type I/II IFN response to Ad-IFN-gamma gene transfer seem to underlie the objective (measurable) clinical response of the treated lesions. Biological effects of type I IFNs seem to enhance those set in motion by the transgene, in our case IFN-gamma. This combination may prove to be of therapeutic importance in cytokine gene transfer using Ads.

MCP-3 (CCL7) delivered by parvovirus MVMp reduces tumorigenicity of mouse melanoma cells through activation of T lymphocytes and NK cells

Monocyte chemotactic protein 3 (MCP-3/CCL7), a CC chemokine able to attract and activate a large panel of leukocytes including natural killer cells and T lymphocytes, could be beneficial in antitumor therapy. Vectors were constructed based on the autonomous parvovirus minute virus of mice (MVMp), carrying the human (MCP-3) cDNA. These vectors were subsequently evaluated in the poorly immunogenic mouse melanoma model B78/H1. The infection of the tumor cells with MCP3-transducing vector at low virus input multiplicities, but not with wild-type virus, strongly inhibited tumor growth after implantation in euthymic mice. In a therapeutic B78/H1 model, repeated intratumoral injections of MCP3-tranducing virus prevented further tumor expansion as long as the treatment was pursued. The antitumor effects of the MCP-3-transducing vector were not restricted to this tumor model since they could also be observed in the K1735 melanoma. The depletion of CD4, CD8, NK cells and of interferon gamma (IFNgamma) in mice implanted with MVMp/MCP3-infected B78/H1 cells abolished the antitumor activity of the vector. The latter data, together with tumor growth in nude mice and reverse-transcriptase (RT)-PCR analyses of MVMp/MCP3-treated tumors, clearly showed that activated CD4, CD8 and NK cells were indispensable for the antineoplastic effect in the B78/H1 tumor. Altogether, our results show that MCP3-transducing parvovirus vectors may be quite potent against poorly or nonimmunogenic tumors, even in conditions where only a fraction of the tumor cell population is efficiently infected with recombinant parvoviruses.

A phase I trial of hyperthermia-induced interleukin-12 gene therapy in spontaneously arising feline soft tissue sarcomas

Interleukin-12 (IL-12), a proinflammatory cytokine, shows anticancer properties. Systemically administered IL-12 causes dose-dependent toxicity. To achieve localized intratumoral gene expression, an adenoviral gene therapy vector with IL-12 controlled by a heat-inducible promoter (heat shock promoter 70B) was developed and tested in a phase I clinical trial in cats with spontaneously arising soft tissue sarcoma. A feasibility study was done in 16 cats with soft tissue sarcoma using murine IL-12 and/or enhanced green fluorescent protein adenoviral vectors under cytomegalovirus or heat shock promoter 70 control. Subsequently, we conducted a phase I clinical trial using an adenoviral feline IL-12 construct in 13 cats with soft tissue sarcoma. The soft tissue sarcomas were irradiated (48 Gy/16 fractions) followed by intratumoral injection of adenovirus. Twenty-four hours postinjection, tumors were heated (41 degrees C, 60 min). Tumor expression of feline IL-12 and IFN-gamma was determined. Cats were monitored for systemic toxicity. For the murine IL-12 construct, an association was noted between viral dose and murine IL-12 levels within tumor, whereas serum levels were minimal. Mild toxicity was noted at 10(11) plaque-forming units (pfu). With the feline IL-12 construct, high levels of feline IL-12 mRNA were detected in tumor biopsies with low or absent IFN-gamma mRNA following gene therapy. Hematologic and hepatic toxicities were noted at the highest viral doses and were associated with detection of IFN-gamma mRNA in tumor. It is possible to localize gene expression and limit systemic toxicity of IL-12 using the hyperthermia-induced gene therapy approach. The maximum tolerated dose of the feline IL-12 adenoviral vector was 10(10) pfu/tumor as dose-limiting toxicities were noted at the 4 x 10(10) pfu dose.

Cytokine gene transfer for cancer therapy

The possibility of inducing a strong immune response to impair tumor growth by ectopically expressing cytokines, followed by the generation of an antitumor memory raised great hopes and enthusiasm as a therapeutic approach. However, the efficacy of this strategy on established tumor models appeared low and the initial results in the clinics were disappointing. Recently, new evidence indicates that cytokine gene combination or the combined use of cytokine genes with additional gene therapy approaches induces a synergistic effect supporting the use of cytokine gene therapy to improve the clinical outcome for cancer patients.

Targeting of products of genes to tumor sites using adoptively transferred A-NK and T-LAK cells

Despite successes in animals, cytokine gene expression selectively in human tumors is difficult to achieve owing to lack of efficient delivery methods. Since interleukin (IL)-2-activated natural killer (A-NK) and phytohemagglutinin and IL-2 activated killer T (T-LAK) cells, as previously demonstrated, localize and accumulate in murine lung tumor metastases following adoptive transfer, we transduced them to test their ability to deliver products of genes selectively to tumors. Assessments of transduction efficiency in vitro demonstrated that adenoviral transduction consistently resulted in high (>60%) transduction rates and substantial expression of transgenes such as GFP, Red2, luciferase, beta-galactosidase and mIL-12 for at least 4 days. In vivo experiments illustrated that Ad-GFP transduced A-NK and Ad-Red2 (RFP) transduced T-LAK or mIL-12 transduced A-NK cells localized 10-50-fold more or survived significantly better than mock transduced cells, respectively, within lung metastases than in the surrounding normal lung tissue. Most importantly, mIL-12 transduced A-NK cells provided a significantly greater antitumor response than non-transduced A-NK cells. Thus, adoptive transfer of A-NK and T-LAK cells represents an efficient method for targeting products of genes to tumor sites.

Blockade of TNF-alpha decreases both inflammation and efficacy of intrapulmonary Ad.IFNbeta immunotherapy in an orthotopic model of bronchogenic lung cancer

Adenoviral immuno-gene therapy using interferon-beta has been effective in an orthotopic model of lung cancer. However, pulmonary inflammation induced by adenoviral (Ad) vectors will almost certainly limit the maximally tolerated dose. On the other hand, the strong innate immune response generated by the vector may be helpful in initiating the adaptive immune response required for efficacy. The goals of this study were to develop an effective approach to inhibit Ad.IFNbeta-mediated acute pulmonary inflammation and to determine whether this reduction of Ad-mediated inflammation decreased the therapeutic efficacy of Ad.IFNbeta in a mouse model of bronchioloalveolar cancer. Our data show that anti-TNF-alpha antibodies can blunt the innate pulmonary immune response induced by Ad vectors, even in sensitized animals. However, this effect also inhibited the ability of the animal to generate anti-tumor immune responses and reduced survival in an orthotopic lung cancer model responsive to Ad.IFNbeta treatment. Interestingly, in a flank model of tumor using a cell line derived from the lung tumor, TNF-alpha blockade did not inhibit efficacy. These data suggest that the innate immune response to adenovirus in the lung may be important in immuno-gene therapy of lung cancer. Therapeutic application of anti-inflammatory therapy in immuno-gene therapy strategies should thus be undertaken with caution.

Gene therapy for carcinoma of the breast

In view of the limited success of available treatment modalities for breast cancer, alternative and complementary strategies need to be developed. The delineation of the molecular basis of breast cancer provides the possibility of specific intervention by gene therapy through the introduction of genetic material for therapeutic purposes. In this regard, several gene therapy approaches for carcinoma of the breast have been developed. These approaches can be divided into six broad categories: (1) mutation compensation, (2) molecular chemotherapy, (3) proapoptotic gene therapy, (4) antiangiogenic gene therapy, (5) genetic immunopotentiation, and (6) genetic modulation of resistance/sensitivity. Clinical trials for breast cancer have been initiated to evaluate safety, toxicity, and efficacy. Combined modality therapy with gene therapy and chemotherapy or radiation therapy has shown promising results. It is expected that as new therapeutic targets and approaches are identified and advances in vector design are realized, gene therapy will play an increasing role in clinical breast cancer treatment.

Fusokine Interleukin-2/Interleukin-18, a Novel Potent Innate and Adaptive Immune Stimulator with Decreased Toxicity

To redress the immune imbalances created by pathologies such as cancer, it would be beneficial to create novel cytokine molecules, which combine desired cytokine activities with reduced toxicities. Due to their divergent but complementary activities, it is of interest to combine interleukin-2 (IL-2) and IL-18 into one recombinant molecule for immunotherapy. Evaluation of a fusokine protein that combines murine IL-2/IL-18 shows that it is stable, maintains IL-2 and IL-18 bioactivities, has notably reduced IL-2 associated toxicities, and has a novel lymphocyte-stimulating activity. An adeno-viral expression system was used to explore the biology of this "fusokine". Inclusion of the IL-18 prosequence (proIL-18) increases the expression, secretion, and potency of this fusokine. In vivo gene transfer experiments show that Ad-IL-2/proIL-18 dramatically outdoes Ad-IL-2, Ad-proIL-18, or the combination of both, by inducing high rates of tumor rejection in several murine models. Both innate and adaptive effector mechanisms are required for this antitumor activity.

Secretomers as a new tool for the monitoring of CTL responses

Efforts to follow tumor-specific immune responses in patients are often thwarted by lack of knowledge of the appropriate tumor antigens and the CTL epitopes of those antigens. There is, therefore, a growing need for techniques to monitor tumor-specific immune responses in settings where tumor antigens, and antigenic epitopes, remain unidentified. Here we describe a novel system to follow tumor-specific CTL immune responses. A truncated, soluble murine class I MHC (H-2Db) molecule was fused with a rat IgG2a Fc, in order to allow secretion of the complex. Tumor-specific CTL could then be detected as a result of the complex fastening to specific T cell receptors (TCR). These constructs were inserted into the genome of a recombinant adenovirus vector. Infection of tumor cells with these adenovirus constructs results in the secretion of the complexes into the culture supernatant. These soluble divalent class I MHC molecules were used to detect and activate specific CTL populations.

In vivoanti-tumour activity of recombinant MVM parvoviral vectors carrying the human interleukin-2 cDNA

BACKGROUND

The natural oncotropism and oncotoxicity of vectors derived from the autonomous parvovirus, minute virus of mice (prototype strain) [MVM(p)], combined with the immunotherapeutic properties of cytokine transgenes, make them interesting candidates for cancer gene therapy.

METHODS

The in vivo anti-tumour activity of a recombinant parvoviral vector, MVM-IL2, was evaluated in a syngeneic mouse melanoma model that is relatively resistant in vitro to the intrinsic cytotoxicity of wild-type MVM(p).

RESULTS

In vitro infection of the K1735 melanoma cells prior to their injection resulted in loss of tumorigenicity in 70% of mice (7/10). Tumour-free mice were protected against a challenge with non-infected parental cells. In addition, MVM-IL2-infected tumour cells induced an anti-tumour activity on parental cells injected at a distant location. These non-infected tumour cells were injected either at the same time or 7 days before the injection of MVM-IL2-infected cells. In the latter setting, which mimics a therapeutic model for small tumours, 4/10 mice were still tumour-free after 4 months.

CONCLUSIONS

Our results show that (i) the MVM-IL2 parvoviral vector efficiently transduces tumour cells; and (ii) the low multiplicity of infection (MOI = 1) used in our experiments was sufficient to elicit an anti-tumour effect on distant cells, which supports further studies on this vector as a new tool for cancer gene therapy.

Gene-based vaccines and immunotherapeutics

DNA vaccines, comprised of plasmid DNA encoding proteins from pathogens, allergens, and tumors, are being evaluated as prophylactic vaccines and therapeutic treatments for infectious diseases, allergies, and cancer; plasmids encoding normal human proteins are likewise being tested as vaccines and treatments for autoimmune diseases. Examples of in vivo prophylaxis and immunotherapy, based on different types of immune responses (humoral and cellular), in a variety of disease models and under evaluation in early phase human clinical trials are presented. Viral vectors continue to show better levels of expression than those achieved by DNA plasmid vectors. We have focused our clinical efforts, at this time, on the use of recombinant viral vectors for both vaccine as well as cytokine gene transfer studies. We currently have four clinical programs in cancer immunotherapy. Two nonspecific immunotherapy programs are underway that apply adenoviral vectors for the transfer of cytokine genes into tumors in situ. An adenovirus-IFN gamma construct (TG1042) is currently being tested in phase II clinical trials in cutaneous lymphoma. A similar construct, adenovirus-IL2 (TG1024), also injected directly into solid tumors, is currently being tested in patients with solid tumors (about one-half of which are melanoma). Encouraging results are seen in both programs. Two cancer vaccine immunotherapy programs focus on two cancer-associated antigens: human papilloma virus E6 and E7 proteins and the epithelial cancer-associated antigen MUC1. Both are encoded by a highly attenuated vaccinia virus vector [modified vaccinia Ankara (MVA)] and both are coexpressed with IL-2. Encouraging results seen in both of these programs are described.

Adenovirus-mediated intralesional interferon-γ gene transfer induces tumor regressions in cutaneous lymphomas

Primary cutaneous lymphomas have been successfully treated with interferons (IFNs), counterbalancing the T-helper 2 (Th2)-skewing state. We undertook a phase 1, open-label, dose-escalating trial of repeated intratumoral administration of TG1042 in patients with advanced primary cutaneous T-cell lymphomas (CTCLs) and multilesional cutaneous B-cell lymphomas (CBCLs). TG1042 is a third-generation, nonreplicating human adenovirus vector containing a human IFN-γ cDNA insert. Nine patients (7 CTCL, 2 CBCL) were enrolled at the following TG1042 doses: 3 × 109, 3 × 1010, and 3 × 1011 total particles. Local clinical response was observed in 5 of 9 treated patients (3 patients with complete response [CR] and 2 patients with partial response [PR]). Out of these, 3 patients showed systemic CR with the clearance of other noninjected skin lesions. Clinical response lasted for a median of 3 months (range, 1-6 months). Adverse events were mostly of grades 1 and 2. Seven of 9 treated patients had a detectable TG1042-derived IFN-γ message in injected lesions after the first treatment cycle. A TG1042-IFN-γ message was also detectable after several treatment cycles. We demonstrate the induction of humoral immune response to lymphoma tumor-antigen se70-2 after treatment. Our study shows that intralesional injections of TG1042 are both safe and well tolerated. (Blood. 2004;104:1631-1638)

Human cytokine-induced killer cells have enhanced in vitro cytolytic activity via non-viral interleukin-2 gene transfer

Modulation of the immune system by genetically modified immunological effector cells is of potential therapeutic value in the treatment of malignancies. Interleukin-2 (IL-2) is a crucial cytokine which induces potent antitumor response. Cytokine-induced killer cells (CIK) have been described as highly efficient cytotoxic effector cells capable of lysing tumor cell targets and are capable of recognizing these cells in a non-MHC restricted fashion. Dendritic cells (DC) are the major antigen presenting cells. This study evaluated the antitumor effect of CIK cells which were non-virally transfected with IL-2 and co-cultured with pulsed and unpulsed DC. Human CIK cells generated from peripheral blood were transfected in vitro with plasmid encoding for the human IL-2. Transfection involved a combination of electrical parameters and a specific solution to deliver plasmid directly to the cell nucleus by using the Nucleofector^® electroporation system. Nucleofection resulted in the production of IL-2 with a mean of 478.5 pg/10⁶ cells (range of 107.6–1079.3 pg /10⁶ cells/24 h) compared to mock transfected CIK cells (31 pg/10⁶ cells) (P = 0.05). After co-culturing with DC their functional ability was assessed in vitro by a cytotoxicity assay. On comparison with non-transfected CIK cells co-cultured with DCs (36.5 ± 5.3 %), transfected CIK cells co-cultured with DC had a significantly higher lytic activity of 58.5 ± 3.2% (P = 0.03) against Dan G cells, a human pancreatic carcinoma cell line.

Tumor irradiation followed by intratumoral cytokine gene therapy for murine renal adenocarcinoma

To circumvent the toxicity caused by systemic injection of cytokines, cytokine cDNA genes encoding the human interleukin IL-2 cDNA (Ad-IL-2) and murine interferon IFN-gamma gene (Ad- IFN-gamma) were inserted into adenoviral vectors. These constructs were used for intratumoral gene therapy of murine renal adenocarcinoma Renca tumors. Treatment with three doses of Ad-IL-2 or Ad- IFN-gamma, given a day apart, was more effective than single-dose gene therapy. We found that tumor irradiation enhanced the therapeutic efficacy of Ad-IL-2 and Ad-IFN-gamma intratumoral gene therapy. Tumor irradiation, administered 1 day prior to three doses of Ad-IL-2 treatment, was more effective than radiation or Ad-IL-2 alone, resulting in tumor growth arrest in all mice, increased survival and a consistent increase in complete tumor regression response rate. Complete responders rejected Renca tumor challenge and demonstrated specific cytotoxic T-cell activity, indicative of specific tumor immunity. The effect of radiation combined with three doses of Ad-IFN-gamma was less pronounced and did not lead to tumor immunity. Histological observations showed that irradiation of the tumor prior to gene therapy increased tumor destruction and inflammatory infiltrates in the tumor nodules. These findings demonstrate that tumor irradiation improves the efficacy of Ad-IL-2 gene therapy for induction of antitumor immune response.

Dendritic cell vaccine therapy by immunization with fusion cells of interleukin-2 gene-transduced, spleen-derived dendritic cells and tumour cells

We examined the preventive and therapeutic effects of fusion cells prepared from spleen-derived dendritic cells (DCs) transduced with the interleukin-2 (IL-2) gene and QRsP fibrosarcoma cells in a mouse lung metastasis model. The IL-2 or LacZ gene was introduced into spleen-derived DCs using an adenoviral vector. Irradiated QRsP tumour cells were fused with IL-2 gene-transduced DCs (fusion/IL-2) or LacZ gene-transduced DCs (fusion/LacZ) by polyethylene glycol. These fusion cells expressed major histocompatibility complexes (MHC) class I and II, CD86, CD11c and CD8alpha. Splenocytes from mice vaccinated with fusion cells showed increased production of interferon-gamma (IFN-gamma) and cytotoxic T-lymphocyte (CTL) activity as compared with those vaccinated with DCs or tumour cells alone, and CTL levels were higher in fusion/IL-2-vaccinated mice than in fusion/LacZ-vaccinated mice. In our experiments on the protective and therapeutic effects on lung metastasis, mice vaccinated with fusion/IL-2 fusion/LacZ or fusion showed a significant reduction in pulmonary metastasis compared with those given DCs, tumour or phosphate-buffered saline. The introduction of the IL-2 gene into fusion cells produced more potent preventive and therapeutic effects. These results suggest that immunization with fusion cells prepared from spleen-derived DCs and tumour cells is capable of inducing preventive and therapeutic anti-tumour immunity against lung metastasis, and modification by the IL-2 gene may increase anti-tumour efficacy.

Recombinant avian adenovirus CELO expressing the human interleukin-2: characterization in vitro, in ovo and in vivo

In our study, a recombinant adenovirus based on the avian adenovirus CELO genome, has been constructed that contains the human interleukin-2 gene. We have shown the production of biologically active recombinant interleukin-2 in vitro (LMH and 293 cells) and in ovo (chicken embryos) infected with recombinant virus CELO-IL2. An increase in the median survival time of C57BL/6 mice carrying B16 melanoma tumors has been demonstrated after multiple intra-tumors injections of the recombinant adenovirus CELO-IL2.

Generating MHC Class II+/Ii- phenotype after adenoviral delivery of both an expressible gene for MHC Class II inducer and an antisense Ii-RNA construct in tumor cells

Tumor cells engineered by gene transduction to be MHC Class II+/Ii- are novel APCs capable of presenting endogenous tumor antigen epitopes to activate T helper cells. The MHC Class II+/Ii- tumor cell phenotype is created by transfecting genes for either CIITA or IFN-gamma, and inhibiting induced Ii mRNA by an Ii reverse gene construct (Ii-RGC). Adenoviral vectors are preferred for the delivery of such genes because of high infection efficiency and ubiquity of the adenoviral receptor on many cell types and tumors. Here we show that at 5 MOI (multiplicity of infection), recombinant adenoviruses with CIITA or IFN-gamma genes converted virtually all MC-38 colon adenocarcinoma cells and Renca renal carcinoma cells in culture to MHC Class II+/Ii+ cells. A single recombinant adenovirus with both genes for IFN-gamma and Ii-RGC (rAV/IFN-gamma/Ii-RGC) efficiently induced the MHC Class II+/Ii- phenotype. Injection of tumor nodules with rAV/Ii-RGC and rAV/CIITA/IFN-gamma combined with a suboptimal dose of rAV/IL-2 induced a potent antitumor immune response. The methods are adaptable for producing enhanced genetic vaccines, attenuated virus vaccines (eg, vaccinia), and ex vivo cell-based vaccines (dendritic and tumor cells).

Adenovirus and adeno-associated virus vectors

Recombinant adenovirus (rAd) and recombinant adeno-associated virus (rAAV) are among the most extensively used vectors in gene therapy studies to date. These two vectors share some similar features such as a broad host range and ability to infect both proliferating and quiescent cells. However, they also possess their own unique set of properties that render them particularly attractive for gene therapy applications. rAd vectors can accommodate larger inserts, mediate transient but high levels of protein expression, and can be easily produced at high titers. Development of gutted rAd vectors has further increased the cloning capacity of these vectors. The gaining popularity of rAAV use in gene therapy can be attributed to its lack of pathogenicity and added safety due to its replication defectiveness, and its ability to mediate long-term expression in a variety of tissues. Site-specific integration, as occurs with wild-type AAV, will be a unique and valuable feature if incorporated into rAAV vectors, further improving their safety. This paper describes these properties of rAd and rAAV vectors, and discusses further development and vector improvements that continue to extend the utility of these vectors, such as cell retargeting by capsid modification, differential transduction by use of serotypes, and extension of the cloning capacity of rAAV vectors by dual vector heterodimerization.

Augmentation of local antitumor immunity in liver by interleukin-2 gene transfer via portal vein

Metastasis to the liver remains an important problem in the treatment of patients with gastrointestinal cancer. We examined the mechanism and effect on liver metastasis of in vivo interleukin-2 (IL-2) gene transfer to the liver. RCN-9 cells derived from F344 rat colon adenocarcinoma were injected into syngeneic rats via the ileocecal vein to induce liver tumors. A total of 2.5x10(9) pfu of adenovirus vector harboring the human IL-2 gene (AdCMVhIL-2), or 2.5x10(9) pfu of control vector encoding beta-galactosidase was administered before RCN-9 cell challenge. On day 14, mean tumor weight was 4.0+/-2.4 g in the control group, whereas IL-2-transduced livers had no tumors. Survival of AdCMVhIL-2-treated rats was significantly longer than that of control rats (P<.01). Flow cytometry demonstrated that the proportion of natural killer (NK) cells had increased among sinusoidal cells collected from IL-2-transduced livers. These cells were highly cytotoxic to RCN-9 cells in vitro in the presence of a physiological high concentration of recombinant IL-2. Preventative effects of IL-2 transduction of the liver against liver metastasis were lost after depletion of NK cells by treatment with anti-asialo GM1 antibodies. Our results indicate that IL-2 gene transfer to the liver prevents liver metastasis by continuously providing physiological high concentrations of IL-2 in the liver, thereby activating sinusoidal NK cells.

IL-2 Plasmid Therapy of Murine Ovarian Carcinoma Inhibits the Growth of Tumor Ascites and Alters Its Cytokine Profile

We have evaluated whether i.p. murine ovarian tumors could be treated with an IL-2 plasmid DNA complexed with the cationic lipid, (±)-N-(2-hydroxyethyl)-N,N-dimethyl-2,3-bis(tetradecyloxy)-1-propanaminium bromide/dioleoylphosphatidylethanolamine (DMRIE/DOPE). Reporter gene studies were initially conducted in which mice bearing i.p. murine ovarian teratocarcinoma (MOT) were injected i.p. with reporter gene plasmid DNA (pDNA):DMRIE/DOPE. Histochemical analyses revealed that transfection occurred primarily in the tumor cells of the ascites, with only a minority of other ascitic cells or surrounding tissues transfected. IL-2 levels in the MOT ascites were determined after i.p. injection of either IL-2 pDNA:DMRIE/DOPE or recombinant IL-2 protein. IL-2 was detected in tumor ascites for up to 10 days after a single i.p. injection of IL-2 pDNA:DMRIE/DOPE, but was undetectable 24 h after a single i.p. injection of IL-2 protein. In an antitumor efficacy study, MOT tumor-bearing mice injected i.p. with IL-2 pDNA:DMRIE/DOPE on days 5, 8, and 11 after tumor cell implant had a significant inhibition of tumor ascites (p = 0.001) as well as a significant increase in survival (p = 0.008). A cytokine profile of the MOT tumor ascites revealed that mice treated with IL-2 pDNA:DMRIE/DOPE had an IL-2-specific increase in the levels of IFN-γ and GM-CSF. Taken together, these findings indicate that i.p. treatment of ovarian tumors with IL-2 pDNA:DMRIE/DOPE can lead to an increase in local IL-2 levels, a change in the cytokine profile of the tumor ascites, and a significant antitumor effect.

Immunotherapy of advanced malignancy by direct gene transfer of an interleukin-2 DNA/DMRIE/DOPE lipid complex: phase I/II experience

PURPOSE

We have completed a phase I study, followed by three phase I/II studies, in patients with metastatic melanoma, renal cell carcinoma (RCC), and sarcoma in order to evaluate the safety, toxicity, and antitumor activity of Leuvectin (Vical Inc, San Diego, CA), a gene transfer product containing a plasmid encoding human interleukin (IL)-2 formulated with the cationic lipid 1, 2-dimyristyloxypropyl-3-dimethyl-hydroxyethyl ammonium bromide/dioleyl-phosphatidyl-ethanolamine (DMRIE/DOPE) and administered intratumorally.

PATIENTS AND METHODS

Twenty-four patients were treated in the phase I study. Leuvectin doses were 10 microg, 30 microg, or 300 microg weekly for 6 weeks. In three subsequent phase I/II studies, a total of 52 patients (18 with melanoma, 17 with RCC, and 17 with sarcoma) were treated with further escalating doses of Leuvectin: 300 microg twice a week for 3 weeks, 750 microg weekly for 6 weeks, and 1,500 microg weekly for 6 weeks.

RESULTS

There were no drug-related grade 4 toxicities and only one grade 3 toxicity, but the majority of patients experienced mild constitutional symptoms after treatment. In the phase I/II studies, 45 patients were assessable for response (14 with RCC, 16 with melanoma, and 15 with sarcoma). Two patients with RCC and one with melanoma have achieved partial responses lasting from 16 to 19 months and continuing. In addition, two RCC, three melanoma, and six sarcoma patients had stable disease lasting from 3 to 18 months and continuing. The plasmid was detected by polymerase chain reaction assay in the posttreatment samples of 29 of 46 evaluated patients. Immunohistochemistry studies on serial biopsy specimens showed increased IL-2 expression and CD8(+) infiltration after treatment in the tumor samples of several patients (12 and 16, respectively).

CONCLUSION

Direct intratumoral injection of Leuvectin is a safe and possibly effective immunotherapeutic approach in the treatment of certain tumor types.