Intrapulmonary IFN-beta gene therapy using an adenoviral vector is highly effective in a murine orthotopic model of bronchogenic adenocarcinoma of the lung

Given previous work showing that an adenoviral vector expressing IFN-beta (Ad.IFNbeta) was highly effective in eradicating i.p. mesothelioma tumors, the antitumor efficacy of this agent was evaluated in an orthotopic model of bronchogenic adenocarcinoma of the lung. These transgenic mice have a conditionally expressed, oncogenic K-rasG12D allele that can be activated by intratracheal administration of an adenovirus expressing Cre recombinase (Ad.Cre). K-rasG12D mutant mice were given Ad.Cre intranasally to activate the oncogene. Mice were then given 10(9) plaque-forming units of a control vector (Ad.LacZ) or Ad.IFNbeta intranasally 3 and 4 weeks later, a time when lung tumors had been established. Cells derived from K-ras-mutated lung tumors were also grown in the flanks of mice to study mechanisms of therapeutic responses. In two separate experiments, untreated tumor-bearing mice all died by day 57 (median survival, 49 days). Ad.LacZ-treated mice all died by day 71 (median survival, 65 days). In contrast, 90% to 100% of mice treated with Ad.IFNbeta were long-term survivors (>120 days; P < 0.001). In addition, immunity to re-challenge with tumor cells was induced. In vitro and flank tumor studies showed that Ad.IFNbeta induced direct tumor cell killing and that depleting natural killer or CD8+ T cells, but not CD4+ T cells, with antibodies attenuated the effect of Ad.IFNbeta. These studies, showing remarkable antitumor activity in this orthotopic lung cancer model, provide strong preclinical support for a trial of Ad.IFNbeta to treat human non-small cell lung cancer.     

Induction of potent antitumor immunity by intratumoral injection of interleukin 23-transduced dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells that play a critical role in priming immune responses to tumor. Interleukin (IL)-23 can act directly on DC to promote immunogenic presentation of tumor peptide in vitro. Here, we evaluated the combination of bone marrow-derived DC and IL-23 on the induction of antitumor immunity in a mouse intracranial glioma model. DCs can be transduced by an adenoviral vector coding single-chain mouse IL-23 to express high levels of bioactive IL-23. Intratumoral implantation of IL-23-expressing DCs produced a protective effect on intracranial tumor-bearing mice. The mice consequently gained systemic immunity against the same tumor rechallenge. The protective effect of IL-23-expressing DCs was comparable with or even better than that of IL-12-expressing DCs. IL-23-transduced DC (DC-IL-23) treatment resulted in robust intratumoral CD8(+) and CD4(+) T-cell infiltration and induced a specific TH1-type response to the tumor in regional lymph nodes and spleen at levels greater than those of nontransduced DCs. Moreover, splenocytes from animals treated with DC-IL-23 showed heightened levels of specific CTL activity. In vivo lymphocyte depletion experiments showed that the antitumor immunity induced by DC-IL-23 was mainly dependent on CD8(+) T cells and that CD4(+) T cells and natural killer cells were also involved. In summary, i.t. injection of DC-IL-23 resulted in significant and effective systemic antitumor immunity in intracranial tumor-bearing mice. These findings suggest a new approach to induce potent tumor-specific immunity to intracranial tumors. This approach may have therapeutic potential for treating human glioma.     

Gemcitabine selectively eliminates splenic Gr-1+/CD11b+ myeloid suppressor cells in tumor-bearing animals and enhances antitumor immune activity.

PURPOSE: Myeloid suppressor (Gr-1(+)/CD11b(+)) cells accumulate in the spleens of tumor-bearing mice where they contribute to immunosuppression by inhibiting the function of CD8(+) T cells and by promoting tumor angiogenesis. Elimination of these myeloid suppressor cells may thus significantly improve antitumor responses and enhance effects of cancer immunotherapy, although to date few practical options exist. EXPERIMENTAL DESIGN: The effect of the chemotherapy drug gemcitabine on the number of (Gr-1(+)/CD11b(+)) cells in the spleens of animals bearing large tumors derived from five cancer lines grown in both C57Bl/6 and BALB/c mice was analyzed. Suppressive activity of splenocytes from gemcitabine-treated and control animals was measured in natural killer (NK) cell lysis and Winn assays. The impact of myeloid suppressor cell activity was determined in an immunogene therapy model using an adenovirus expressing IFN-beta. RESULTS: This study shows that the chemotherapeutic drug gemcitabine, given at a dose similar to the equivalent dose used in patients, was able to dramatically and specifically reduce the number of myeloid suppressor cells found in the spleens of animals bearing large tumors with no significant reductions in CD4(+) T cells, CD8(+) T cells, NK cells, macrophages, or B cells. The loss of myeloid suppressor cells was accompanied by an increase in the antitumor activity of CD8(+) T cells and activated NK cells. Combining gemcitabine with cytokine immunogene therapy using IFN-beta markedly enhanced antitumor efficacy. CONCLUSIONS: These results suggest that gemcitabine may be a practical strategy for the reduction of myeloid suppressor cells and should be evaluated in conjunction with a variety of immunotherapy approaches.     

Eradication of primary murine fibrosarcomas and induction of systemic immunity by adenovirus-mediated interferon beta gene therapy.

We determined whether an adenoviral vector-mediated murine IFN-beta gene therapy could eradicate established s.c. tumors produced by murine UV-2237m fibrosarcoma cells. The tumor cells were highly susceptible to infection by adenoviral vectors. Cells infected with 10 or 100 multiplicity of infection of AdCIFN-beta, an adenoviral vector encoding murine IFN-beta driven by the human cytomegalovirus promoter, expressed high levels of steady-state IFN-beta mRNA and produced 500 or 7,000 units of IFN-beta activity/10(6) cells/24 h, respectively. Infection of tumor cells with 30 multiplicity of infection of AdCIFN-beta (but not control AdCLacZ vector) inhibited in vitro tumor cell proliferation by 40-45%. Intralesional injection of 5 x 10(8) plaque-forming units of AdCIFN-beta (but not AdLacZ) eradicated established s.c. fibrosarcomas in syngeneic mice but not fibrosarcomas in nude mice. Mice cured of the disease developed systemic immunity against rechallenge with UV-2237m cells but not against another syngeneic tumor, the K-1735 M2 melanoma. Immunohistochemical analysis revealed that tumors injected with AdCIFN-beta contained more macrophages and CD4+ and CD8+ cells than did tumors injected with AdCLacZ or saline. Most cells in the PBS- and AdCLacZ-treated tumors stained positive for proliferating cell nuclear antigen, and few cells stained for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling. In sharp contrast, AdCIFN-beta-treated tumors contained few proliferating cell nuclear antigen-positive cells and many terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling-positive cells. Taken together, our data demonstrate that IFN-beta gene therapy delivered by adenoviral vectors can be effective against fibrosarcomas.     

Use of cyclooxygenase-2 inhibition to enhance the efficacy of immunotherapy

Antitumor effects of cyclooxygenase-2 (COX-2) inhibition have been reported in a wide variety of tumor models and in human cancers, both as chemoprevention and therapy. Human mesothelioma tumors have been shown to overexpress COX-2 and high levels of COX-2 protein have been demonstrated to be a prognostic factor, indicating poor outcome in this tumor. In this study, we determined that inhibition of COX-2 by oral administration of Rofecoxib significantly slowed but did not cure the growth of small tumors in mesothelioma-bearing mice. Large tumors were unaffected. This effect was dependent on the presence of CD8+ T cells and was associated with increased tumor-infiltrating lymphocytes. Because these activities are consistent with a mechanism that results in a decrease in the immunosuppressive environment of the tumor, we additionally examined the effect of COX-2 blockade combined with Ad.IFN-beta therapy, a treatment that we have previously demonstrated results in expansion of antitumor CD8+ CTLs and cures a high percentage of small mesothelioma tumors in mice. Ad.IFN-beta therapy combined with COX-2 inhibition was associated with an increased number of T cells within tumors and resulted in cures of small tumors, significant inhibition of the growth of large established tumors, and inhibition of the growth of metastatic tumor foci after surgical debulking. The additive effects of these modes of treatment suggests that it would be rational to combine COX-2 inhibition with immuno- and immunogene therapy approaches (perhaps in conjunction with surgical debulking) in human clinical trials of treatment of mesothelioma and other tumors.     

Cycloxygenase-2 inhibition augments the efficacy of a cancer vaccine.

Tumor-derived cyclooxygenase-2 (COX-2) and its product, prostaglandin E2, exert strong immunoinhibitory effects that block dendritic cell function and CD4+ and CD8+ T-cell proliferation and function. We have shown previously that the addition of an oral COX-2 inhibitor to immunogene therapy using IFN-beta markedly augmented therapeutic efficacy in murine tumor models. In this study, we hypothesized that COX-2 inhibition might also augment an antitumor vaccination strategy. Mice bearing tumors derived from TC1 cells, a tumor line that expresses the human papillomavirus (HPV) E7 protein, were thus vaccinated with an adenoviral vector expressing HPV E7 protein (Ad.E7). This vaccine approach effectively generated E7-specific CD8+ cells and slowed the growth of small tumors but had little effect on large tumors. However, feeding mice with the COX-2 inhibitor, rofecoxib, restored the effectiveness of the vaccine against large tumors and prolonged survival. This effect was accompanied by a larger percentage of E7-specific CD8+ cells in the regional draining lymph nodes and a markedly increased number of tumor-infiltrating E7-specific CD8+ cells (as determined by flow cytometry) and total CD8+ T cells (as determined by immunohistochemical staining). Increased immunocyte trafficking was likely mediated by the generation of a Th1-type tumor microenvironment because COX-2 inhibition increased expression levels of mRNA for IFN-gamma, interleukin-12, IP-10, and MIG while lowering the expression of vascular endothelial growth factor within tumors. This study shows that the effectiveness of a cancer vaccine can be significantly improved by adding COX-2 inhibition.     

Soluble type II transforming growth factor-beta receptor inhibits established murine malignant mesothelioma tumor growth by augmenting host antitumor immunity.

PURPOSE: Transforming growth factor (TGF)-beta blockade has been proposed as an anticancer therapy; however, understanding which tumor patients might benefit most from such therapy is crucial. An ideal target of such inhibitory therapy might be malignant mesothelioma (MM), a highly lethal, treatment-resistant malignancy of mesothelial cells of the pleura and peritoneum that produces large amounts of TGF-beta. The purpose of this study was to explore the possible therapeutic utility of TGF-beta blockade on MM. EXPERIMENTAL DESIGN: To evaluate this hypothesis, we tested the effects of a soluble TGF-beta type II receptor (sTGF-beta R) that specifically inhibits TGF-beta1 and TGF-beta 3 in three different murine MM tumor models, AB12 and AC29 (which produce large amounts of TGF-beta) and AB1 (which does not produce TGF-beta). RESULTS: Tumor growth of both established AB12 and AC29 tumors was inhibited by sTGF-beta R. In contrast, AB1 tumors showed little response to sTGF-beta R. The mechanism of these antitumor effects was evaluated and determined to be primarily dependent on immune-mediated responses because (a) the antitumor effects were markedly diminished in severe combined immunodeficient mice or mice depleted of CD8(+) T cells and (b) CD8(+) T cells isolated from spleens of mice treated with sTGF-beta R showed strong antitumor cytolytic effects, whereas CD8(+) T cells isolated from spleens of tumor-bearing mice treated with of control IgG2a showed no antitumor cytolytic effects. CONCLUSIONS: Our data suggest that TGF-beta blockade of established TGF-beta-secreting MM should be explored as a promising strategy to treat patients with MM and other tumors that produce TGF-beta.     

A novel small-molecule inhibitor of transforming growth factor beta type I receptor kinase (SM16) inhibits murine mesothelioma tumor growth in vivo and prevents tumor recurrence after surgical resection

Malignant mesothelioma is an aggressive and lethal pleural cancer that overexpresses transforming growth factor beta (TGFbeta). We investigated the efficacy of a novel small-molecule TGFbeta type I receptor (ALK5) kinase inhibitor, SM16, in the AB12 syngeneic model of malignant mesothelioma. SM16 inhibited TGFbeta signaling seen as decreased phosphorylated Smad2/3 levels in cultured AB12 cells (IC(50), approximately 200 nmol/L). SM16 penetrated tumor cells in vivo, suppressing tumor phosphorylated Smad2/3 levels for at least 3 h following treatment of tumor-bearing mice with a single i.p. bolus of 20 mg/kg SM16. The growth of established AB12 tumors was significantly inhibited by 5 mg/kg/d SM16 (P < 0.001) delivered via s.c. miniosmotic pumps over 28 days. The efficacy of SM16 was a result of a CD8+ antitumor response because (a) the antitumor effects were markedly diminished in severe combined immunodeficient mice and (b) CD8+ T cells isolated from spleens of mice treated with SM16 showed strong antitumor cytolytic effects whereas CD8+ T cells isolated from spleens of tumor-bearing mice treated with control vehicle showed minimal activity. Treatment of mice bearing large tumors with 5 mg/kg/d SM16 after debulking surgery reduced the extent of tumor recurrence from 80% to <20% (P < 0.05). SM16 was also highly effective in blocking and regressing tumors when given p.o. at doses of 0.45 or 0.65 g/kg in mouse chow. Thus, SM16 shows potent activity against established AB12 malignant mesothelioma tumors using an immune-mediated mechanism and can significantly prevent tumor recurrence after resection of bulky AB12 malignant mesothelioma tumors. These data suggest that ALK5 inhibitors, such as SM16, offer significant potential for the treatment of malignant mesothelioma and possibly other cancers.     

Large nontransplanted hepatocellular carcinoma in woodchucks: treatment with adenovirus-mediated delivery of interleukin 12/B7.1 genes

BACKGROUND: Cytokine-based gene therapy strategies efficiently stimulate immune responses against many established transplanted tumors, leading to rejection of the tumor. In this study, we investigated the therapeutic potential of cancer immunotherapy in a clinically more relevant model, woodchucks with primary hepatocellular carcinomas induced by woodchuck hepatitis virus. METHODS: Large (2-5 cm), established intrahepatic tumors were given an injection once with 1 x 10(9) plaque-forming units of AdIL-12/B7.1, an adenovirus vector carrying genes for murine interleukin 12 and B7.1, or of AdEGFP, the control virus, and regression of the tumors was then monitored. Five animals were used in total. RESULTS: In four tumor-bearing animals, the antitumor response was assessed by autopsy and histologic analysis within 1-2 weeks after treatment. In all animals treated with AdIL-12/B7.1 therapy versus AdEGFP therapy, we observed substantial tumor regression (P =.006; two-sided unpaired Student's t test) accompanied by a massive infiltration of T lymphocytes. These tumors also contained increased levels of CD4(+) and CD8(+) T cells and interferon gamma (IFN gamma). In continuously growing tumor nodules given an injection of the control virus or in nontumoral liver, no such effects (i.e., tumor regression and increased levels of CD4(+) and CD8(+) T cells and IFN gamma) were detected. In the fifth animal, monitored for long-term antitumor efficacy by magnetic resonance imaging (MRI) after intratumoral vector administration by MRI guidance, the tumor was almost completely eliminated (> or = 95%) 7 weeks after treatment. CONCLUSION: Adenovirus vector-based immunotherapy appears to be an effective treatment of large nontransplanted (orthotopic) tumors that acquire malignant characteristics in a stepwise process, reflecting the real-world scenario of hepatocellular carcinoma in humans.     

Anti-tumor activity of an anti-endoglin monoclonal antibody is enhanced in immunocompetent mice

In the present study, we investigated the mechanisms by which anti-endoglin (EDG; CD105) monoclonal antibodies (mAbs) suppress angiogenesis and tumor growth. Antihuman EDG mAb SN6j specifically bound to murine endothelial cells and was internalized into the cells in vitro. SN6j effectively suppressed angiogenesis in mice in the Matrigel plug assay. We found that SN6j is more effective for tumor suppression in immunocompetent mice than in SCID mice. We hypothesized that T cell immunity is important for effective antitumor efficacy of SN6j in vivo. To test this hypothesis, we investigated effects of CpG oligodeoxynucleotides (ODN) and depletion of CD4(+) T cells and/or CD8(+) T cells on antitumor efficacy of SN6j in mice. Systemic (i.v.) administration of a relatively small dose (0.6 mug/g body weight/dose) of SN6j suppressed growth of established s.c. tumors of colon-26 in BALB/c mice and improved survival of the tumor-bearing mice. Addition of CpG ODN to SN6j synergistically enhanced antitumor efficacy of SN6j. In contrast, such enhancing effects of CpG ODN were not detected in SCID mice. Antitumor efficacy of SN6j in BALB/c mice was abrogated when CD4(+) T cells and/or CD8(+) T cells were depleted; effect of CD8(+) T cell depletion was stronger. Interestingly, CD4-depletion decreased tumor growth while CD8-depletion enhanced tumor growth in the absence of SN6j. SN6j induced apoptosis in human umbilical vein endothelial cells in a dose-dependent manner which indicates an additional mechanism of antiangiogenesis by SN6j. (c) 2008 Wiley-Liss, Inc.     

Cationic lipid:bacterial DNA complexes elicit adaptive cellular immunity in murine intraperitoneal tumor models

Previous studies with a mycobacterial heat shock protein (hsp-65) have demonstrated some efficacy using cationic liposome-mediated gene transfer in murine i.p. sarcoma models. To further analyze the efficacy of hsp-65 immunotherapy in clinically relevant models of localized cancer, immunocompetent mice bearing i.p. murine mesothelioma were treated with four i.p. doses of a cationic lipid complexed with plasmid DNA (pDNA) containing hsp65, LacZ, or a null plasmid. We observed >90% long-term survival (median survival, 150 days versus approximately 25 days, treated versus saline control, respectively) in a syngeneic, i.p. murine mesothelioma model (AC29). Long-term survivors were observed in all groups treated with lipid complexed with any pDNA. Lipid alone or DNA alone provided no demonstrable survival advantage. In a more aggressive i.p. model of mesothelioma (AB12), we observed >40% long-term survival in groups treated with lipid:pDNA complexes, again irrespective of the transgene. To ask whether these antitumor effects had led to an adaptive immune response against the tumor cell, we rechallenged long-term survivors in both murine models s.c. with the parental tumor cell line. Specific, long-lasting systemic immunity against the tumor was readily demonstrated in both models (AB12 and AC29). Consistent with these results, splenocytes from long-term survivors specifically lysed the parental tumor cell lines. Depleting the CD8+ T-cells from the splenocyte pool eliminated this lytic activity. Lipid:pDNA treatment of athymic, SCID, and SCID/Beige mice bearing a murine i.p. mesothelioma (AC29) resulted in only a slight survival advantage, but there were no long-term survivors. Treatment of immunocompetent mice depleted of specific immune effector cells demonstrated roles for CD8+ and natural killer cells. Although the exact mechanism(s) responsible for these antitumor effects is unclear, the results are consistent with roles for both innate and adaptive immune responses. An initial tumor cell killing stimulated by cationic lipid:pDNA complexes appears to be translated into long-term, systemic immunity against the tumor cell. These results are the first to demonstrate that adaptive immunity against a tumor cell can be induced by the administration of lipid:pDNA complexes. Multiple administrations of cationic lipid complexed with pDNA lacking an expressed transgene could provide a promising generalized immune-mediated modality for treating cancer.     

MHC class I and class II presentation of tumor antigen in retrovirally and adenovirally transduced dendritic cells

The unique antigen-presenting capabilities of dendritic cells (DCs) make them an attractive means with which to initiate an antitumor immune response. Using DCs transduced with tumor antigens for immunotherapy has several theoretical advantages over peptide-pulsed DCs including the possibility that transduced DCs are capable of presenting epitopes on both class I and class II MHC molecules. To test this theory, we inserted the human tumor antigen gp100 into mouse DCs transgenic for HLA-DRbeta1*0401 using either adenoviral vector or a VSV-G pseudotyped retroviral vector. DCs transduced with tumor antigen were able to be recognized by both a murine CD8(+) T-cell clone and a murine CD4(+) T-cell line in a cytokine release assay, thereby demonstrating presentation of both MHC class I and class II gp100 epitopes. This study describes the simultaneous presentation of a tumor-associated antigen to both CD4(+) and CD8(+) T cells and lends support to the use of gene-modified DCs as a means to initiate both CD4(+) and CD8(+) antitumor responses.     

Long-term follow-up of patients with malignant pleural mesothelioma receiving high-dose adenovirus herpes simplex thymidine kinase/ganciclovir suicide gene therapy.

PURPOSE: Delineation of the long-term follow-up data on a series of patients with malignant mesothelioma, who received a single intrapleural dose of a nonreplicative adenoviral (Ad) vector encoding the herpes simplex virus thymidine kinase "suicide gene" (Ad.HSVtk) in combination with systemic ganciclovir. EXPERIMENTAL DESIGN: This report focuses on the 21 patients receiving "high-dose" therapy, defined by an intrapleural dose of vector (> or =1.6 x 10(13) viral particles), where transgene-encoded tk protein was reliably identified on immunohistochemical staining. In 13 patients, the vector was deleted in the E1 and E3 regions of the Ad; in the other eight patients, the vector had deletions in the Ad genes E1 and E4. Safety, immunologic responses, transgene expression, and clinical responses were evaluated. RESULTS: Both the E1/E3-deleted vector and the E1/E4-deleted vector were well tolerated and safe, although production of the E1/E4 vector was more difficult. Posttreatment antibody responses against the tumors were consistently seen. Interestingly, we observed a number of clinical responses in our patients, including two long-term (>6.5 year) survivors, both of whom were treated with the E1/E4-deleted vector. CONCLUSIONS: Intrapleural Ad.HSVtk/ganciclovir is safe and well tolerated in mesothelioma patients and resulted in long-term durable responses in two patients. Given the limited amount of gene transfer observed, we postulate that Ad.HSVtk may have been effective due to induction of antitumor immune responses. We hypothesize that approaches aiming to augment the immune effects of Ad gene transfer (i.e., with the use of cytokines) may lead to increased numbers of therapeutic responses in otherwise untreatable pleural malignancies.     

Recombinant adenoviral vector expressing human wild-type p53, GM-CSF,and B7-1 genes suppresses the growth of glioma in vivo

Malignant gliomas are the most common of primary brain tumors and have been proven incurable with conventional treatments. Evidence have shown that a recombinant adenoviral vector expressing human wild-type p53, granulocyte-macrophage colony-stimulating factor (GM-CSF), and B7-1 genes (BB-102) may have antitumor effects in vitro. In this study, we investigated the effects of BB-102-based vaccine on glioma in vivo. An animal model using nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice with human immune system was established. The mice were vaccinated with inactivated U251 glioma cells transduced with BB-102 or adenoviral vector expressing green fluorescence protein (Ad-GFP) as a control and followed by the challenge of live U251 glioma cells. Tumor growth and antitumor responses were measured. Data showed that mice vaccinated with BB-102 had significantly reduced local tumor growth compared to mice with Ad-GFP vaccination or the control group. Histopathological analysis displayed low tumor cell density and significant infiltration of human peripheral blood lymphocytes (HuPBLs) in the tumor tissues of mice transduced with BB-102. Immunohistochemical analysis showed that mutant p53 was not expressed in tumor tissues of mice with BB-102 vaccination, and the expression level of Ki67 was significantly lower in the tumor tissues of the BB-102 group than those in the Ad-GFP group or the control group. Further study demonstrated that mice with BB-102 vaccination had significantly increased total T cell numbers, total T cell proportion, CD4+ T cell proportion, and CD8+ T cell proportion in spleens, as well as higher value of IgG, IgA, and IgE in sera. These data suggest that the recombinant adenoviral vector expressing human wild-type p53, GM-CSF, and B7-1 genes could suppress glioma in NOD/SCID mice model and might be considered as a novel strategy for glioma therapy.     

Low‐dose paclitaxel improves the therapeutic efficacy of recombinant adenovirus encoding CCL21 chemokine against murine cancer

Secondary lymphoid tissue chemokine (SLC/CCL21), one of the CC chemokines, exerts potent antitumor immunity by co‐localizing T cells and dendritic cells at the tumor site and is currently tested against human solid tumors. Here, we investigated whether the combination of recombinant adenovirus encoding murine CCL21 (Ad‐mCCL21) with low‐dose paclitaxel would improve therapeutic efficacy against murine cancer. Immunocompetent mice bearing B16‐F10 melanoma or 4T1 breast carcinoma were treated with either Ad‐mCCL21, paclitaxel, or both agents together. Our results showed that Ad‐mCCL21 + low‐dose paclitaxel more effectively reduced the growth of tumors as compared with either treatment alone and significantly prolonged survival time of the tumor‐bearing animals. These antitumor effects of the combined therapy were linked to altered cytokine network at the tumor site, enhanced apoptosis of tumor cells, and decreased formation of new vessels in tumors. Importantly, the combined therapy elicited a strong therapeutic antitumor immunity, which could be partly abrogated by the depletion of CD4⁺ or CD8⁺ T lymphocytes. Collectively, these preclinical evaluations may provide a combined strategy for antitumor immunity and should be considered for testing in clinical trials.     

Activation of tumor-specific CD8+ T Cells after intratumoral Ad5-TRAIL/CpG oligodeoxynucleotide combination therapy

CD8(+) T-cell activation via cross-presentation of antigens from apoptotic tumor cells is controversial. Dendritic cells capture naturally shed tumor antigens and cross-present them to CD8(+) T cells; unfortunately, the frequency of activated CD8(+) T cells is often too low to mount an effective response against the tumor. By increasing the amount of antigen for presentation, a larger T-cell response can be theoretically elicited. We used a recombinant adenovirus encoding full-length murine tumor necrosis factor-related apoptosis-inducing ligand (Ad5-mTRAIL) to induce tumor cell apoptosis, and when given intratumorally to mice bearing experimental renal cell carcinoma (Renca) tumors, Ad5-mTRAIL minimally prolonged survival and induced a low level of CTL activity. To enhance dendritic cell efficiency, an immunostimulatory CpG oligodeoxynucleotide (CpG ODN) was combined with Ad5-mTRAIL. This combination therapy significantly augmented in vivo antigen-specific T-cell proliferation and CTL activity, as well as prolonged survival of Renca tumor-bearing mice. Interestingly, depletion of CD4(+) or CD25(+) cells before therapy further enhanced survival and in vivo CTL activity. In addition, tumor-free mice depleted of CD4(+) cells were also able to reject a subsequent challenge of Renca cells, but not MHC-matched RM-11 prostate tumor cells, demonstrating the existence of immunologic memory. These results collectively show that local treatment with Ad5-mTRAIL and CpG ODN can augment tumor antigen cross-presentation resulting in T-cell proliferation, enhanced CTL activity, and increased animal survival.