Efficient adenovector CD40 ligand immunotherapy of canine malignant melanoma

Next-generation CD40 agonists for cancer immunotherapy

INTRODUCTION

There is a need for new therapies that can enhance response rates and broaden the number of cancer indications where immunotherapies provide clinical benefit. CD40 targeting therapies provide an opportunity to meet this need by promoting priming of tumor-specific T cells and reverting the suppressive tumor microenvironment. This is supported by emerging clinical evidence demonstrating the benefits of immunotherapy with CD40 antibodies in combination with standard of care chemotherapy.

AREAS COVERED

This review is focused on the coming wave of next-generation CD40 agonists aiming to improve efficacy and safety, using new approaches and formats beyond monospecific antibodies. Further, the current understanding of the role of different CD40 expressing immune cell populations in the tumor microenvironment is reviewed.

EXPERT OPINION

There are multiple promising next-generation approaches beyond monospecific antibodies targeting CD40 in immuno-oncology. Enhancing efficacy is the most important driver for this development, and approaches that maximize the ability of CD40 to both remodel the tumor microenvironment and boost the anti-tumor T cell response provide great opportunities to benefit cancer patients. Enhanced understanding of the role of different CD40 expressing immune cells in the tumor microenvironment may facilitate more efficient clinical development of these compounds.

Treatment of Canine Oral Melanomas: A Critical Review of the Literature

Critical appraisal of the available literature for the treatment of canine oral malignant melanoma (OMM) is lacking. This critical review aimed to evaluate the current literature and provide treatment recommendations and possible suggestions for future canine OMM research. PubMed, Web of Science and Google Scholar were searched in June 2021, for terms relevant to treatment of OMM. Inclusion and exclusion criteria were applied and information on clinical response and outcome extracted. Eighty-one studies were included. The overall level of evidence supporting the various canine OMM treatment options was low. The majority of studies included confounding treatment modalities and lacked randomization, control groups and consistency in reporting clinical response and outcomes. Within these limitations, surgery remains the mainstay of therapy. Adjunctive radiotherapy provided good local control and improved median survival times (MST), chemotherapy did not offer survival benefit beyond that of surgery, while electrochemotherapy may offer a potential alternative to radiotherapy. Immunotherapy holds the most promise in extending MST in the surgical adjunctive setting, in particular the combination of gene therapy and autologous vaccination. Prospective, randomized, double-blinded clinical trials, with a lack of confounding factors and reporting based on established guidelines would allow comparison and recommendations for the treatment of canine OMM.

Adenoviral CD40 Ligand Immunotherapy in 32 Canine Malignant Melanomas-Long-Term Follow Up

Malignant melanoma is a serious disease in both humans and dogs, and the high metastatic potential results in poor prognosis for many patients. Its similarities with human melanoma make spontaneous canine melanoma an excellent model for comparative studies of novel therapies and tumor biology. Gene therapy using adenoviruses encoding the immunostimulatory gene CD40L (AdCD40L) has shown promise in initial clinical trials enrolling human patients with various malignancies including melanoma. We report a study of local AdCD40L treatment in 32 cases of canine melanoma (23 oral, 5 cutaneous, 3 ungual and 1 conjunctival). Eight patients were World Health Organization (WHO) stage I, 9 were stage II, 12 stage III, and 3 stage IV. One to six intratumoral injections of AdCD40L were given every seven days, combined with cytoreductive surgery in 20 cases and only immunotherapy in 12 cases. Tumor tissue was infiltrated with T and B lymphocytes after treatment, suggesting immune stimulation. The best overall response based on result of immunotherapy included 7 complete responses, 5 partial responses, 5 stable and 2 progressive disease statuses according to the World Health Organization response criteria. Median survival was 285 days (range 20–3435 d). Our results suggest that local AdCD40L therapy is safe and could have beneficial effects in dogs, supporting further treatment development. Clinical translation to human patients is ongoing.

Safety studies and viral shedding of intramuscular administration of oncolytic vaccinia virus TG6002 in healthy beagle dogs

BACKGROUND

Cancer is a leading cause of mortality for both humans and dogs. As spontaneous canine cancers appear to be relevant models of human cancers, developing new therapeutic approaches could benefit both species. Oncolytic virotherapy is a promising therapeutic approach in cancer treatment. TG6002 is a recombinant oncolytic vaccinia virus deleted in the thymidine kinase and ribonucleotide reductase genes and armed with the suicide gene FCU1 that encodes a protein which catalyses the conversion of the non-toxic 5-fluorocytosine into the toxic metabolite 5-fluorouracil. Previous studies have shown the ability of TG6002 to infect and replicate in canine tumor cell lines, and demonstrated its oncolytic potency in cell lines, xenograft models and canine mammary adenocarcinoma explants. Moreover, 5-fluorouracil synthesis has been confirmed in fresh canine mammary adenocarcinoma explants infected with TG6002 with 5-fluorocytosine. This study aims at assessing the safety profile and viral shedding after unique or repeated intramuscular injections of TG6002 in seven healthy Beagle dogs.

RESULTS

Repeated intramuscular administrations of TG6002 at the dose of 5 × 10⁷ PFU/kg resulted in no clinical or biological adverse effects. Residual TG6002 in blood, saliva, urine and feces of treated dogs was not detected by infectious titer assay nor by qPCR, ensuring the safety of the virus in the dogs and their environment.

CONCLUSIONS

These results establish the good tolerability of TG6002 in healthy dogs with undetectable viral shedding after multiple injections. This study supports the initiation of further studies in canine cancer patients to evaluate the oncolytic potential of TG6002 and provides critical data for clinical development of TG6002 as a human cancer therapy.

Characterization of myeloid-derived suppressor cells and cytokines GM-CSF, IL-10 and MCP-1 in dogs with malignant melanoma receiving a GD3-based immunotherapy

Melanoma in humans and canines is an aggressive and highly metastatic cancer. The mucosal forms in both species share genetic and histopathologic features, making dogs a valuable spontaneous disease animal model. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells of myeloid origin with immunosuppressive capabilities, which are increased in many human cancers and contribute to tumor immune evasion. They are a possible target to improve immunotherapy outcomes. Current information regarding MDSCs in canines is minimal, limiting their use as translational model for the study of MDSCs. The objective of this study was to characterize major MDSCs subsets (monocytic and polymorphonuclear) and the cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 10 (IL-10) and monocyte chemoattractant protein-1 (MCP-1) in canines with malignant melanoma and to evaluate changes in MDSCs and the cytokines over time in response to a GD3-based active immunotherapy. Whole blood and serum collected from 30 healthy controls and 33 patients enrolled in the University of Florida melanoma vaccine trial were analyzed by flow cytometry with canine specific CD11b, MHCII and anti-human CD14 antibodies to assess ostensibly polymorphonuclear-MDSC (CD11b⁺ MHCII^- CD14^-) and monocytic-MDSC (CD11b⁺ MHCII^- CD14⁺) subsets. IL-10, MCP-1 and both MDSCs subsets were significantly elevated in melanoma dogs versus controls. Both MDSCs subsets decreased significantly following GD3-based immunotherapy administration but no significant changes in cytokines were seen over time. To our knowledge, this is the first report documenting increased monocytic-MDSCs in canine melanoma. This is consistent with human malignant melanoma data, supporting dogs as a valuable model for therapeutic intervention studies.

Cancer Immunotherapies

The enhanced understanding of immunology experienced over the last 4 decades afforded through the tools of molecular biology has recently translated into cancer immunotherapy becoming one of the most exciting and rapidly expanding fields. Human cancer immunotherapy is now recognized as one of the pillars of treatment alongside surgery, radiation, and chemotherapy. The field of veterinary cancer immunotherapy has also rapidly advanced in the last decade with a handful of commercially available products and a plethora of investigational cancer immunotherapies that will hopefully expand the veterinary oncology treatment toolkit over time.

A Review of Immunotherapeutic Strategies in Canine Malignant Melanoma

In dogs, melanomas are relatively common tumors and the most common form of oral malignancy. Biological behavior is highly variable, usually aggressive, and frequently metastatic, with reported survival times of three months for oral or mucosal melanomas in advanced disease stages. Classical clinical management remains challenging; thus, novel and more efficacious treatment strategies are needed. Evidence-based medicine supports the role of the immune system to treat neoplastic diseases. Besides, immunotherapy offers the possibility of a precise medicinal approach to treat cancer. In recent years, multiple immunotherapeutic strategies have been developed, and are now recognized as a pillar of treatment. In addition, dogs represent a good model for translational medicine purposes. This review will cover the most relevant immunotherapeutic strategies for the treatment of canine malignant melanoma, divided among five different categories, namely, monoclonal antibodies, nonspecific immunotherapy activated by bacteria, vaccines, gene therapy, and lymphokine-activated killer cell therapy.

Oncolytic Viruses for Canine Cancer Treatment

Oncolytic virotherapy has been investigated for several decades and is emerging as a plausible biological therapy with several ongoing clinical trials and two viruses are now approved for cancer treatment in humans. The direct cytotoxicity and immune-stimulatory effects make oncolytic viruses an interesting strategy for cancer treatment. In this review, we summarize the results of in vitro and in vivo published studies of oncolytic viruses in different phases of evaluation in dogs, using PubMed and Google scholar as search platforms, without time restrictions (to date). Natural and genetically modified oncolytic viruses were evaluated with some encouraging results. The most studied viruses to date are the reovirus, myxoma virus, and vaccinia, tested mostly in solid tumors such as osteosarcomas, mammary gland tumors, soft tissue sarcomas, and mastocytomas. Although the results are promising, there are issues that need addressing such as ensuring tumor specificity, developing optimal dosing, circumventing preexisting antibodies from previous exposure or the development of antibodies during treatment, and assuring a reasonable safety profile, all of which are required in order to make this approach a successful therapy in dogs.

Oncolytic Sendai Virus Therapy of Canine Mast Cell Tumors (A Pilot Study)

Background: Canine mastocytomas (mast cell tumors) represent a common malignancy among many dog breeds. A typical treatment strategy for canine mastocytomas includes surgery, chemo- and radio-therapy, although in many cases the therapy fails and the disease progression resumes. New treatment approaches are needed. Aims: The goal of this pilot study was to examine safety and efficacy of oncolytic Sendai virus therapy administered to canine patients with cutaneous or subcutaneous mastocytomas. Materials and Methods: Six canine patients, with variable grades and stages of the disease, received virus therapy, either as a monotherapy, or in combination with surgery. The therapy included two or more virus applications administered weekly or biweekly. Each application of Sendai virus (107-108.6 EID50) consisted of multiple individual 0.01-0.1 ml injections delivered intratumorally, intradermally around a tumor, and under a tumor bed. Results: The treatment was well tolerated, with minor transitory side effects. Of the six dogs, two did not receive surgery or any other treatment besides the virus injections. The other four animals underwent radical or debulking surgeries, and in three of them the subsequent administration of Sendai virus completely cleared locally recurrent or/and remaining tumor masses. Five dogs demonstrated a complete response to the treatment, the animals remained disease free during the time of observation (2-3 years). One dog responded only partially to the virotherapy; its after-surgical recurrent tumor and some, but not all, metastases were cleared. This dog had the most advanced stage of the disease with multiple enlarged lymph nodes and cutaneous metastases. Conclusion: The results of the pilot study suggest that Sendai virus injections could be safe and efficient for the treatment of dogs affected by mastocytomas.They also suggest the need of further studies for finding optimal schemes and schedules for this kind of therapy.

Activation of myeloid and endothelial cells by CD40L gene therapy supports T-cell expansion and migration into the tumor microenvironment

CD40 is an interesting target in cancer immunotherapy due to its ability to stimulate T-helper 1 immunity via maturation of dendritic cells and to drive M2 to M1 macrophage differentiation. Pancreatic cancer has a high M2 content that has shown responsive to anti-CD40 agonist therapy and CD40 may thus be a suitable target for immune activation in these patients. In this study, a novel oncolytic adenovirus armed with a trimerized membrane-bound extracellular CD40L (TMZ-CD40L) was evaluated as a treatment of pancreatic cancer. Further, the CD40L mechanisms of action were elucidated in cancer models. The results demonstrated that the virus transferring TMZ-CD40L had oncolytic capacity in pancreatic cancer cells and could control tumor progression. TMZ-CD40L was a potent stimulator of human myeloid cells and T-cell responses. Further, CD40L-mediated stimulation increased tumor-infiltrating T cells in vivo, which may be due to a direct activation of endothelial cells to upregulate receptors for lymphocyte attachment and transmigration. In conclusion, CD40L-mediated gene therapy is an interesting concept for the treatment of tumors with high levels of M2 macrophages, such as pancreatic cancer, and an oncolytic virus as carrier of CD40L may further boost tumor killing and immune activation.

Tumor-directed immunotherapy can generate tumor-specific T cell responses through localized co-stimulation

The most important goals for the field of immuno-oncology are to improve the response rate and increase the number of tumor indications that respond to immunotherapy, without increasing adverse side effects. One approach to achieve these goals is to use tumor-directed immunotherapy, i.e., to focus the immune activation to the most relevant part of the immune system. This may improve anti-tumor efficacy as well as reduce immune-related adverse events. Tumor-directed immune activation can be achieved by local injections of immune modulators in the tumor area or by directing the immune modulator to the tumor using bispecific antibodies. In this review, we focus on therapies targeting checkpoint inhibitors and co-stimulatory receptors that can generate tumor-specific T cell responses through localized immune activation.

A retrospective review of outcome and survival following surgery and adjuvant xenogeneic DNA vaccination in 32 dogs with oral malignant melanoma

A xenogeneic DNA vaccination has been licensed for use in dogs with locally controlled stage II and III oral malignant melanoma (OMM). At present, there are limited outcome data for dogs with OMM treated with surgery and immunotherapy. The aim of this study is to retrospectively review the outcome and survival of 32 dogs affected by OMM that were treated with a combination of surgery and the xenogeneic DNA vaccination (with the addition of radiotherapy in some cases) and to determine the influence of surgical margins and delay in receiving vaccination. The overall median survival time (MST) was 335 days (95% CI: 301-540 days), and the overall median progression-free survival (PFS) was 160 days (mean 182 days, 95% CI: 132-232 days). Stage, completeness of surgical margins and delay in administration of the vaccine did not appear to statistically influence survival or PFS, although these results may reflect the low statistical power of the study due to small numbers. Further studies are required to assess whether the addition of any adjuvant treatment to surgery, including immunotherapy, is able to significantly prolong survival in cases of canine oral melanoma.

On the potential of oncolytic virotherapy for the treatment of canine cancers

Over 6 million dogs are diagnosed with cancer in the USA each year. Treatment options for many of these patients are limited. It is important that the veterinary and scientific communities begin to explore novel treatment protocols for dogs with cancer. Oncolytic viral therapy is a promising treatment option that may prove to be relatively inexpensive and effective against several types of cancer. The efficacy of oncolytic virus therapies has been clearly demonstrated in murine cancer models, but the positive outcomes observed in mice are not always seen in human cancer patients. These therapies should be thoroughly evaluated in dogs with spontaneously arising cancers to provide needed information about the potential effectiveness of virus treatment for human cancers and to promote the health of our companion animals. This article provides a review of the results of oncolytic virus treatment of canine cancers.

Immunotherapy for canine cancer--is it time to go back to the future?

Over the last 50 years, the significance of the immune system in the development and control of cancer has been much debated. However, recent discoveries provide evidence for a role of immunological mechanisms in the detection and destruction of cancer cells. Forty years ago veterinary oncologists were already investigating the feasibility of treating neoplasia by enhancing anticancer immunity. Unfortunately, this research was hindered by lack of a detailed understanding of cancer immunology, this limited the specificity and success of these early approaches. The great forward strides made in our understanding of onco-immunology in recent years have provided the impetus for a resurgence of interest in anticancer immunotherapy for canine patients. In this article both these initial trials and the exciting novel immunotherapeutics currently in development are reviewed.

Clinical trials of immunogene therapy for spontaneous tumors in companion animals

Despite the important progress obtained in the treatment of some pets' malignancies, new treatments need to be developed. Being critical in cancer control and progression, the immune system's appropriate modulation may provide effective therapeutic options. In this review we summarize the outcomes of published immunogene therapy veterinary clinical trials reported by many research centers. A variety of tumors such as canine melanoma, soft tissue sarcomas, osteosarcoma and lymphoma, feline fibrosarcoma, and equine melanoma were subjected to different treatment approaches. Both viral and mainly nonviral vectors were used to deliver gene products as cytokines, xenogeneic tumor associated antigens, specific ligands, and proapoptotic regulatory factors. In some cases autologous, allogenic, or xenogeneic transgenic cytokine producing cells were assayed. In general terms, minor or no adverse collateral effects appeared during this kind of therapies and treated patients usually displayed a better course of the disease (longer survival, delayed or suppressed recurrence or metastatic spread, and improvement of the quality of life). This suggests the utility of these methodologies as standard adjuvant treatments. The encouraging outcomes obtained in companion animals support their ready application in veterinary clinical oncology and serve as preclinical proof of concept and safety assay for future human gene therapy trials.

Self-complementary adeno-associated virus 5-mediated gene transduction of a novel CD40L mutant confers direct antitumor effects in lung carcinoma

CD40 ligand (CD40L) gene therapy offers a potentially useful option for lung cancer due to its multiple antitumor activities. However, membrane-bound CD40L may be proteolytically cleaved to form soluble CD40L (sCD40L), which results in adverse effects. In a previous study by our group, it was demonstrated that recombinant self-complementary adeno-associated virus 5 (scAAV5) efficiently delivered genes to lung cancer cells. In the present study, an scAAV5 expressing a non-cleavable human CD40L mutant (scAAV5-CD40L-M) was generated and its direct antitumor effects in lung cancer were evaluated. Transduction with scAAV5-CD40L-M resulted in effective expression of CD40L on the cell surface with low levels of cleaved sCD40L, which significantly reduced the percentage of viable cells and promoted caspase-3-dependent apoptosis of CD40-positive lung carcinoma A549 cells, compared with scAAV5-CD40L transduction (P<0.05). Furthermore, treatment with scAAV5-CD40L-M exerted a significant antitumor effect against CD40-positive A549 xenografts by inducing apoptosis (P<0.05) with few side effects. Gene therapy using an scAAV5 vector expressing non-cleavable human CD40L mutant may therefore have direct antitumor effects against CD40-positive lung cancers. These tumoricidal effects of scAAV5-CD40L-M treatment make it a promising therapeutic technique for the treatment of lung cancer.

Anti-tumour activity of oncolytic Western Reserve vaccinia viruses in canine tumour cell lines, xenografts, and fresh tumour biopsies

Cancer is one of the most common reasons for death in dogs. One promising approach is oncolytic virotherapy. We assessed the oncolytic effect of genetically modified vaccinia viruses in canine cancer cells, in freshly excised tumour biopsies, and in mice harbouring canine tumour xenografts. Tumour transduction efficacy was assessed using virus expressing luciferase or fluorescent marker genes and oncolysis was quantified by a colorimetric cell viability assay. Oncolytic efficacy in vivo was evaluated in a nude mouse xenograft model. Vaccinia virus was shown to infect most tested canine cancer cell lines and primary surgical tumour tissues. Virus infection significantly reduced tumour growth in the xenograft model. Oncolytic vaccinia virus has antitumour effects against canine cancer cells and experimental tumours and is able to replicate in freshly excised patient tumour tissue. Our results suggest that oncolytic vaccinia virus may offer an effective treatment option for otherwise incurable canine tumours.

Immunotherapy in veterinary oncology

Tumor immunology and immunotherapy is one of the most exciting and rapidly expanding fields. The immune system is divided into 2 primary components: the innate immune response and the highly specific, but more slowly developing, adaptive or acquired immune response. Immune responses are separated by whether they are induced by exposure to a foreign antigen (active response) or transferred through serum or lymphocytes from an immunized individual (passive response). The ideal cancer immunotherapy agent should discriminate between cancer and normal cells (specificity), be potent enough to kill small or large numbers of tumor cells (sensitivity), and prevent recurrence of a tumor (durability).

Oncolytic virotherapy of canine and feline cancer

Cancer is the leading cause of disease-related death in companion animals such as dogs and cats. Despite recent progress in the diagnosis and treatment of advanced canine and feline cancer, overall patient treatment outcome has not been substantially improved. Virotherapy using oncolytic viruses is one promising new strategy for cancer therapy. Oncolytic viruses (OVs) preferentially infect and lyse cancer cells, without causing excessive damage to surrounding healthy tissue, and initiate tumor-specific immunity. The current review describes the use of different oncolytic viruses for cancer therapy and their application to canine and feline cancer.

CD40L gene therapy tilts the myeloid cell profile and promotes infiltration of activated T lymphocytes

CD40 ligand (CD40L) is a potent stimulator of tumor immunity via its activation of dendritic cells, which in turn initiate T-cell activation. However, T cells are inhibited by suppressive myeloid cells, which constitute an important part of immune evasion. We hypothesized that CD40L may revert the function of suppressive myeloid cells to generate a T-cell stimulatory environment, and this was investigated in the murine bladder cancer model MB49/C57BL/6. Upon intratumoral adenoviral CD40L (AdCD40L) gene therapy, the infiltration of CD11b(+)Gr-1(+) cells was significantly reduced, whereas activated T cells were increased. In vitro, CD40L-expressing MB49 cells tilted the myeloid subpopulations in favor of granulocytic CD11b(+)Gr-1(high) myeloid cells instead of monocytic CD11b(+)Gr-1(int/low) myeloid cells. Further, the level of macrophages in splenocyte co-cultures with MB49 cells was evaluated. In cultures with MB49 cells expressing CD40L, the overall level of macrophages was reduced and the remaining cells were differentiated into M1-like cells. Hence, these data support that CD40L tilts myeloid immune cell populations in favor of anti-tumor immunity (M1) instead of immunosuppression (CD11b(+)Gr-1(int/low) and M2), and this was accompanied by an increased level of activated T cells in the tumor tissue.

CD40 ligand and tdTomato-armed vaccinia virus for induction of antitumor immune response and tumor imaging

Oncolytic vaccinia virus is an attractive platform for immunotherapy. Oncolysis releases tumor antigens and provides co-stimulatory danger signals. However, arming the virus can improve efficacy further. CD40 ligand (CD40L, CD154) can induce apoptosis of tumor cells and it also triggers several immune mechanisms. One of these is a T-helper type 1 (Th1) response that leads to activation of cytotoxic T-cells and reduction of immune suppression. Therefore, we constructed an oncolytic vaccinia virus expressing hCD40L (vvdd-hCD40L-tdTomato), which in addition features a cDNA expressing the tdTomato fluorochrome for detection of virus, potentially important for biosafety evaluation. We show effective expression of functional CD40L both in vitro and in vivo. In a xenograft model of bladder carcinoma sensitive to CD40L treatment, we show that growth of tumors was significantly inhibited by the oncolysis and apoptosis following both intravenous and intratumoral administration. In a CD40-negative model, CD40L expression did not add potency to vaccinia oncolysis. Tumors treated with vvdd-mCD40L-tdtomato showed enhanced efficacy in a syngenic mouse model and induced recruitment of antigen-presenting cells and lymphocytes at the tumor site. In summary, oncolytic vaccinia virus coding for CD40L mediates multiple antitumor effects including oncolysis, apoptosis and induction of Th1 type T-cell responses.

Locally delivered CD40 agonist antibody accumulates in secondary lymphoid organs and eradicates experimental disseminated bladder cancer

Immunotherapy with intratumoral injection of adenoviral vectors expressing CD40L has yielded positive results in experimental and clinical bladder cancer. We therefore hypothesized that anti-CD40 antibody would be effective in this setting. Agonistic CD40 antibodies were developed as vaccine adjuvants but have later been used as treatment of advanced solid tumors and hematologic cancers. Systemic anti-CD40 therapy has been associated with immune-related adverse events, such as cytokine release syndrome and liver toxicity, and local delivery is an attractive approach that could reduce toxicity. Herein, we compared local and systemic anti-CD40 antibody delivery to evaluate efficacy, toxicity, and biodistribution in the experimental MB49 bladder cancer model. Antitumor effects were confirmed in the B16 model. In terms of antitumor efficacy, local anti-CD40 antibody stimulation was superior to systemic therapy at an equivalent dose and CD8 T cells were crucial for tumor growth inhibition. Both administration routes were dependent on host CD40 expression for therapeutic efficacy. In vivo biodistribution studies revealed CD40-specific antibody accumulation in the tumor-draining lymph nodes and the spleen, most likely reflecting organs with frequent target antigen-expressing immune cells. Systemic administration led to higher antibody concentrations in the liver and blood compared with local delivery, and was associated with elevated levels of serum haptoglobin. Despite the lack of a slow-release system, local anti-CD40 therapy was dependent on tumor antigen at the injection site for clearance of distant tumors. To summarize, local low-dose administration of anti-CD40 antibody mediates antitumor effects in murine models with reduced toxicity and may represent an attractive treatment alternative in the clinic.

Production of canine soluble CD40 ligand to induce maturation of monocyte derived dendritic cells for cancer immunotherapy

CD40 ligand (CD40L) expressed by activated T cells is shown to induce maturation of immature dendritic cells (DCs) and this maturation is a vital part in DC based tumor immunotherapy. We constructed an expression vector by cloning the extracellular domain of canine CD40L fused to the signal sequence of canine IL-12p40. When PBMCs were incubated with canine granulocyte-macrophage (GM) -CSF and IL-4, expression of CD86 was significantly elevated, but the majority of cells displayed the morphology of immature DCs. Following addition of the expressed canine soluble CD40L (csCD40L) to the DC-inducing culture, the cell morphology shifted to that of mature DCs, and expression of CD80, CD86, MHC class II and CD1a was significantly enhanced. This morphological change and enhancement of expression was observed even when the csCD40L was present only in the second half period of the culture. Furthermore, the csCD40L caused a significant increase in IL-12 production from DCs. These results show that the csCD40L significantly promotes the maturation and activation of canine monocyte derived DCs.

AdCD40L--crossing the valley of death?

CD40-mediated cancer therapy has been under development since it became clear that CD40 plays a profound role in the stimulation of adaptive immune responses. Further, CD40 signaling on tumor cells may lead to growth arrest or even apoptosis that improves therapy outcome. The therapeutic window is appealing since the immune system is selective and normal cells do not apoptose upon CD40 signaling. AdCD40L is an adenoviral-based immunostimulatory gene therapy under evaluation for its efficacy to treat cancer. Because of its nature, the adenoviral backbone will stimulate TLRs while CD40L potentiates the shifts toward Th1 type of immunity. AdCD40L has shown efficacy in various murine models, and safety studies have been performed on dog patients and in human clinical trials. AdCD40L has been used for both ex vivo gene modification of tumor cell vaccines as well as for direct intratumoral injections. Lately, an oncolytic vector has been used to further increase the eradication of solid tumors that as a consequence further boosts the release of tumor antigens and creates danger signaling in the tumor micro milieu. This review discusses the currently unfolding mechanisms of action of AdCD40L gene therapy and its possibilities to reach clinical care.

Cytokine-enhanced vaccine and suicide gene therapy as surgery adjuvant treatments for spontaneous canine melanoma: 9 years of follow-up

We present here the updated results after 9 years of the beginning of a trial on canine patients with malignant melanoma. This surgery adjuvant approach combined local suicide gene therapy with a subcutaneous vaccine composed by tumor cells extracts and xenogeneic cells producing human interleukin-2 and granulocyte-macrophage colony-stimulating factor. Toxicity was absent or minimal in all patients (0≤VCOG-CTCAE grade≤1). With respect to surgery-treated controls (ST), the complete surgery (CS) arm of this combined treatment (CT) significantly increased the fraction of local disease-free patients from 13 to 81% and distant metastases free from 32 to 84%. Even though less effective than the CS arm, the partial surgery (PS) arm of this CT was significantly better controlling the disease than only surgery (14% while PS-ST: 0%, P<0.01 and CS-ST: 5%, P<0.05). In addition, CT produced a significant sevenfold (CS) and threefold (PS) increase in overall survival. The CS-CT arm significantly improved both CS-ST metastasis-free- and melanoma overall survival from 99 days (respective ranges: 11-563 and 10-568) to >2848 days (81-2848 and 35-2848). Thus, more of 50% of our CT patients died of melanoma unrelated causes, transforming a lethal disease into a chronic one. Finally, surgery adjuvant CT delayed or prevented post-surgical recurrence and distant metastasis, significantly improved disease-free and overall survival maintaining the quality of life. Long-term safety and efficacy of this treatment are supported by the high number of CT patients (283) and extensive follow-up (>9 years). The successful clinical outcome encourages the further translation of similar approaches to human gene therapy trials.

Expression of CD40 and growth-inhibitory activity of CD40 agonist in ovarian carcinoma cells

The CD40 receptor is a member of the tumour necrosis factor receptor family and is widely expressed on various cell types. The antitumour activity of CD40 agonist antibody has been observed in B-cell-derived malignancies, but its activity on ovarian cancer remains unclear. However, in this paper, we first confirmed that the anti-CD40 agonist antibody could inhibit the growth of ovarian cancer cells and induce apoptosis. This study investigated the expression of CD40 by ovarian carcinoma tissues and cell lines, at the same time, we evaluated the effect of a recombinant soluble human CD40L (rshCD40L) and an anti-CD40 agonist antibody on cell growth and apoptosis. Flow cytometry and immunohistochemistry assay demonstrated that CD40 was expressed on ovarian carcinoma cell lines and primary ovarian carcinoma cells derived from ascites, as well as on ovarian carcinoma tissues. The growth inhibition of rshCD40L and the anti-CD40 agonist antibody on ovarian carcinoma cells was examined by MTT assay, and the proportion of apoptotic tumour cells was analysed by flow cytometry and Hoechst staining. Our study showed that CD40 was expressed on all ovarian carcinoma cell lines and was examined in 86.2% (162/188) of ovarian cancer tissue samples, but not in normal ovarian tissues (n = 20). Treatment with rshCD40L or anti-CD40 agonist antibody significantly inhibited ovarian carcinoma cell growth and induced apoptosis. Theses results suggest that CD40 is expressed on ovarian carcinoma cells, moreover, that rshCD40L and anti-CD40 agonist antibody have therapeutic potential to inhibit human ovarian cancer growth.

Oncolytic virotherapy in veterinary medicine: current status and future prospects for canine patients

Oncolytic viruses refer to those that are able to eliminate malignancies by direct targeting and lysis of cancer cells, leaving non-cancerous tissues unharmed. Several oncolytic viruses including adenovirus strains, canine distemper virus and vaccinia virus strains have been used for canine cancer therapy in preclinical studies. However, in contrast to human studies, clinical trials with oncolytic viruses for canine cancer patients have not been reported. An 'ideal' virus has yet to be identified. This review is focused on the prospective use of oncolytic viruses in the treatment of canine tumors - a knowledge that will undoubtedly contribute to the development of oncolytic viral agents for canine cancer therapy in the future.

Critical role of CD40-mediated autocrine tumor necrosis factor-alpha in potentiation of cisplatin-induced cytotoxicity in cancer cells

Activation of CD40, a member of the tumor necrosis factor receptor (TNF-R) family, results in growth inhibition or apoptosis in some tumor cells, making CD40 a potential antitumor therapeutic target. Although it is known that CD40 is able to induce tumor necrosis factor-alpha (TNF-α) secretion and potentiate cisplatin's anticancer activity, whether TNF-α induction is involved in sensitizing cisplatin by CD40 has not been addressed. In this report, we provide evidence substantiating an important role of autocrine TNF-α in potentiation of cisplatin-induced apoptosis by recombinant soluble CD40 ligand (rsCD40L) in different human cancer cell lines. Activation of CD40 by rsCD40L induces two phases of autocrine TNF-α: the rapid early phase involving p38 MAP kinase and the robust and persistent late phase through enhanced tnf-α gene transcription. Blocking TNF-α with either a specific TNFR1 siRNA or a neutralizing anti-TNF-α antibody dramatically attenuated the potentiation effect of rsCD40L on cisplatin-induced cancer cell death. These results reveal an important role of TNF-α induction in CD40's chemosensitization activity and suggest that modulating TNF-α autocrine from cancer cells is an effective option for increasing the anticancer value of chemotherapeutics such as cisplatin.

Immunomodulators, immunostimulants, and immunotherapies in small animal veterinary medicine

Immunomodulators, immunostimulants, and immunotherapies are important tools used by veterinary practitioners and researchers to control and direct the immune system of small animals. This article is an overview and summary of some of the most common immunomodulatory agents used in companion animals emphasizing steroidal and nonsteroidal agents, T-cell inhibitors, cytotoxic drugs, immunostimulators and biologic response modifying agents, and neoplasia chemotherapeutic agents.

AdCD40L immunogene therapy for bladder carcinoma--the first phase I/IIa trial

PURPOSE

Immunotherapy with Bacillus Calmette-Guerin (BCG) instillation is recommended for high-risk, non-muscle invasive bladder cancer. Bacillus Calmette-Guerin is not effective in advanced tumors, and better alternatives are warranted. Immunostimulating gene therapy with adenoviral vectors expressing CD40 ligand (AdCD40L) has shown efficacy in tumor models. CD40 ligand stimulates systemic immunity and may be effective in local and invasive human disease.

EXPERIMENTAL DESIGN

Patients with invasive bladder cancer scheduled for cystectomy or patients with T(a) tumors were enrolled in a phase I/IIa trial. Patients were treated with three cycles of intrabladder Clorpactin WCS-90 prewash, followed by AdCD40L instillation 1 week apart. Safety, gene transfer, immune effects, and antitumor responses were monitored.

RESULTS

All eight recruited patients were treated as scheduled, and therapy was well tolerated. The main adverse effect was transient local pain during prewash. Postoperatively, urinary tract infections and one case of late septicemia with elevated potassium were reported. No adverse events were ascribed to vector therapy. Gene transfer was detected in biopsies, and bladders were heavily infiltrated with T cells. The effector marker IFN-gamma increased in biopsies, whereas levels of circulating T regulatory cells were reduced. Histologic evaluation indicated that AdCD40L therapy reduced the load of malignant cells.

CONCLUSIONS

To our knowledge, this is the first report on immunogene therapy in bladder cancer and the first using AdCD40L in vivo. Local AdCD40L gene therapy was safe, boosted immune activation, and should be further evaluated as a single or an adjuvant therapy for urothelial malignancies.

Cancer immunotherapy

The immune system is generally divided into 2 primary components: the innate immune response, and the highly specific but more slowly developing adaptive or acquired immune response. Immune responses can be further separated by whether they are induced by exposure to a foreign antigen (an "active" response) or whether they are transferred through serum or lymphocytes from an immunized individual (a "passive" response). The ideal cancer immunotherapy agent should be able to discriminate between cancer and normal cells (ie, specificity), be potent enough to kill small or large numbers of tumor cells (ie, sensitivity), and lastly be able to prevent recurrence of the tumor (ie, durability). Tumor immunology and immunotherapy is one of the most exciting and rapidly expanding fields at present.