Effect of GM-CSF and IL-2 co-expression on the anti-tumor immune response

We evaluated the effect of potential therapeutic genes, GM-CSF and IL-2 respectively, or in combination of both cytokines, on the activation of systemic antitumor responses. CT26 tumor cells were modified to secrete GM-CSF and/or IL-2. The growth rate of the modified tumor cells versus the parental CT26 cells did not show any difference. When we implanted the CT26 tumor cells which secrete either GM-CSF or IL-2, delayed and suppressed tumorigenicity was observed. However, another CT26 cell line which expresses both GM-CSF and IL-2 (CT26/GMCSF/IL-2) did not form any tumor mass in the immunocompetent syngeneic Balb/c mice, showing the potential immune responses. Immunohistochemical examination of the modified tumor masses implanted with the cells expressing GM-CSF or IL-2 showed increased necrosis and infiltration of NK (CD56+) lineage cells and macrophage/monocytes. In the vaccination model, the growth of rechallenged wild-type CT26 was more suppressed int he mice which were injected with GM-CSF or IL-2, however, the wild-type CT26 tumor formed normal tumor mass in the mice vaccinated with CT26/GM-CSF/IL-2 showing acute non-T-cell mediated immune response. As a treatment, we injected those modified tumor cells into the established tumor. There we could find tumor growth suppression by the injection of cytokine-modified CT26 cells, especially by the CT26/GM-CSF/IL-2. In the present study we could induce the eradication of tumorigenicity by the transfection of both GM-CSF and IL-2 genes and a potent role in the growth suppression of an established tumor.     

Inhibition of tumor growth and enhancement of metastasis after transfection of the γ-interferon gene

Cells from the spontaneous metastatic TS/A mammary adenocarcinoma of a BALB/c mouse were transfected with the murine γ-interferon (IFN-γ) gene. Six clones (IFN-γ clones) releasing between 2 and 6,000 international units (IU) of IFN-γ/ml culture medium, were compared to TS/A parental cells (TS/A-pc) and to cells transfected with neomycin resistance gene only (NEO cells). Autocrine IFN-γ up-regulated membrane expression of H-2 class-1 and Ly-6 glycoproteins, but did not alter cellular proliferation in vitro. All IFN-γ clones gave rise to progressive tumors with a growth rate significantly slower than that of tumors induced by TS/A-pc and NEO cells, and inversely correlated with the amount of IFN-γ secreted. TS/A-pc and NEO tumors displayed a marginal reactive infiltrate, whereas those formed by IFN-γy clones were massively infiltrated mostly by macrophages. In T- and NK-deficient mice the growth of tumors formed by I FN-y clones was not enhanced. In vitro tests showed that IFN-γ clone cells were markedly more lysed by macrophages than TS/A-pc and NEO cells, while they remained poorly sensitive to NK and LAK cells. These data as a whole suggest that the development of solid tumors by IFN-γ clones is primarily hampered by macrophages and not by T-lymphocytes or NK cells. When spontaneous metastatic ability was compared, 2 IFN-γ clones releasing 2-4 IFN-γ lU/ml were significantly more metastatic, while most IFN-γ clones appeared to be as metastatic as NEO cells. By contrast, following intravenous challenge, all IFN-γ clones produced 5-10 times more experimental metastases than NEO cells. The higher metastatic ability of IFN-γ clones was attributed to increased resistance to NK cells since, in NK-depleted BALB/c mice, metastatic spread of IFN-γ clones was not enhanced, whereas a 50-fold increase in the number of metastases was found upon injection of NEO cells.     

Systemic effects of cytokines released by gene-transduced tumor cells: Marked hyperplasia induced in small bowel by γ-interferon transfectants through host lymphocytes

Cells transduced with cytokine genes are currently used to enhance the anti-tumor and immunomodulatory effects of these molecules in cancer therapy. The sustained release of cytokine thus obtained can perturb many homeostatk systems of the host. We have previously shown that the murine mammary adenocarcinoma TS/A transfected with the murine γ-in-terferon (IFN-γ) gene stimulates a strong immune response that impairs tumor growth. Mice bearing tiny tumors have serum IFN-γ levels constantly exceeding 100 IU/ml. Therefore, we asked which systemic effects can be triggered in mice by such transfectants. BALB/c mice bearing tumors produced by clone 16.6000 cells (which release 6,000 IU/ml of IFN-γ in culture) were compared to normal mice and to mice with tumors produced by parent cells transfected with the neomycin resistance gene (NEO cells, no IFN-γ release). Histological studies revealed a marked hyperplasia of small bowel tn mice bearing 16.6000 tumors; the villi and crypts of these mice were >1.5 times longer than those of normal mice and of mice bearing NEO tumors. In vivo administration of bromodeoxyuridine evidenced a 2.5–3 times increase in the proliferative score of the intestinal crypts of mice bearing 16.6000 tumors compared to control mice. No intestinal alterations were observed in nude mice bearing 16.6000 tumors. T lymphocytes thus appear to play a causal role in this phenomenon. © 1995 Wiley-Liss, Inc.     

IL-12基因联合吡柔比星治疗裸鼠膀胱癌移植瘤的实验

目的 探讨联合应用白细胞介素12(IL-12)质粒和吡柔比星（THP）对人膀胱癌裸鼠移植瘤生长的抑制作用。方法 将人EJ膀胱癌细胞株裸鼠腋下接种,成瘤后设4组（每组6只）：联合组于骨骼肌注射IL-12真核表达质粒pcAGGS-mIL-12和腹腔注射THP;IL-12组骨骼肌注射pcAGGS-mIL-12;THP组腹腔注射THP;对照组肌肉及腹腔注射0.9%氯化钠溶液,以上注射每周2次,共4次。观察各组裸鼠肿瘤大小变化。4周后处死荷瘤鼠。免疫组织化学法检测肿瘤内VEGF 表达。ELISA法测定血液及肿瘤组织中IL-12和γ-干扰素(IFN-γ)的表达。结果 联合组肿瘤生长明显抑制,瘤重及体积明显小于其他组。ELISA法表明IL-12组和联合组 IL-12和IFN-γ都高表达。免疫组织化学法表明联合组VEGF基因表达量明显低于其他组（P<0.05）。结论 联合应用IL-12真核表达质粒pCAGGS-mIL-12和THP,对人膀胱癌裸鼠移植瘤的抑制作用明显强于单独应用IL-12和THP。     

ENHANCED METASTASIS OF AMOUSE MAMMARY ADENOCARCINOMA AFTER INVITRO TREATMENT WITHγ－INTERFERON

ＥＮＨＡＮＣＥＤＭＥＴＡＳＴＡＳＩＳＯＦＡＭＯＵＳＥＭＡＭＭＡＲＹＡＤＥＮＯＣＡＲＣＩＮＯＭＡＡＦＴＥＲＩＮＶＩＴＲＯＴＲＥＡＴＭＥＮＴＷＩＴＨγ－ＩＮＴＥＲＦＥＲＯＮＬｕｏＬｉｑｕｎ；罗利群ＺｈａｎｇＹｏｕｈｕｉ；张友会（Ｃａｎｃｅｒｉｎｓｔｉｔｕ...     

Gene transfer of NK4, an angiogenesis inhibitor,induces CT26 tumor regression via tumor‐specific T lymphocyte activation

Hepatocyte growth factor (HGF) has been shown to be involved in malignant behaviors, such as invasion and metastasis, in different tumors. Hence, HGF could be a target molecule for control of the malignant potential of cancer. NK4 is a competitive antagonist for HGF and exerts an antitumor activity, not only by HGF antagonism but also by antiangiogenesis. Here, we studied the participation of cellular immunity in CT26 tumor regression by NK4 gene transfer. In vivo experiments showed that NK4‐induced inhibition of subcutaneous tumor growth (as demonstrated in immunocompetent BALB/c mice) was weakened in T lymphocyte‐deficient nude mice. In addition, the immunocompetent BALB/c mice that had shown complete regression of CT26‐NK4 tumors generated an immune memory against repeated challenge with the same tumor antigen. Immunohistochemistry of tumor‐infiltrating lymphocytes showed that the ratio of CD8/CD4 in CT26‐NK4 tumors was significantly higher than that in control tumors. Also, the presence of tumor‐specific cytotoxic T lymphocytes (CTL) was demonstrated by cytotoxicity assays. Depletion of CD8+ T lymphocytes markedly abrogated the antitumor activity of NK4. However, NK4 had no direct effect on the in vitro cellular immune system. Taken together, these data indicate that NK4 expression by gene transfer, at the tumor site, triggers tumor‐specific CTL activation, resulting in complete CT26 tumor regression in vivo. This action was considered to be due to apoptosis induced by NK4's potent antiangiogenic and HGF antagonistic effects. © 2009 UICC     

The boosting effect of co-transduction with cytokine genes on cancer vaccine therapy using genetically modified dendritic cells expressing tumor-associated antigen

The T-helper 1 (Th1) immune reaction is most important in dendritic cell (DC)-based immunotherapy. Interleukin 12 (IL-12) and granulocyte macrophage colony-stimulating factor (GM-CSF) play a pivotal role in inducing Th1 and cytotoxic T lymphocyte (CTL) responses. In this study, DCs expressing the natural tumor antigen gp70 of BALB/c-derived CT26 were adenovirally transduced with the IL-12 gene and/or GM-CSF gene, and it was examined whether vaccinations using these genetically engineered DCs can induce strong therapeutic antitumor immunity. Mice were immunized once by subcutaneous (s.c.) injection with genetically modified DCs. The cytotoxic activity of splenocytes against CT26 was assayed in a 51Cr-release assay 14 days after immunization. The therapeutic efficacy of the vaccination was examined in s.c. tumor models. The cytotoxic activity of CTLs against CT26 in mice immunized with DCs expressing gp70 (DC-AxCAgp70) was significantly augmented by co-transduction with the GM-CSF/IL-12 gene (p<0.0001) and remarkably reduced by the depletion of CD4+ or CD8+ cells (p<0.01). The cytotoxic activity against CT26 of the plain spleen cells in mice immunized with DC-AxCAgp70/GM-CSF/IL-12 was significantly higher than that in mice immunized with DC-AxCAgp70 (p<0.0001), and this activity decreased to almost 50% upon the depletion of NK cells. Vaccinations using DC-AxCAgp70/GM-CSF/IL-12 or DC-AxCAgp70/IL-12 could elicit potent therapeutic immunity in s.c. tumor models; tumor-free mice were observed in these vaccination groups. However, there was no significant difference between these two groups. A vaccination therapy using DCs co-transduced with the TAA gene and Th 1-type cytokine genes, especially the IL-12 gene, is ideal for immunotherapy in terms of the activation of DCs, NK cells, CD4+ T cells and CD8+ T cells, and may be useful in the clinical application of a cancer vaccine therapy.     

Early activation and interferon-γ production of tumor-infiltrating mature CD27 high natural killer cells

Natural killer (NK) cells are known to be critically involved in the control of tumors through their direct cytotoxic function, but have also been proposed as an initial source of interferon (IFN)-γ that primes subsequent adaptive tumor-specific immune responses. Although mounting evidence supports the importance of NK cells in antitumor immune responses, the immunological characteristics of NK cells infiltrating the tumor microenvironment and the mechanisms that regulate this process remain unclear. In the present study, we found that NK cells infiltrate early developing MCA205 tumors, and further showed that mature CD27(high) NK cells were the predominant subpopulation of NK cells accumulating in the tumor microenvironment. The tumor-infiltrating NK cells displayed an activated cell surface phenotype and provided an early source of IFN-γ. Importantly, we also found that host IFN-γ was critical for NK cell infiltration into the local tumor site and that the tumor-infiltrating NK cells mainly suppressed tumor growth via the IFN-γ pathway. This work implicates the importance of IFN-γ as a positive regulatory factor for NK cell recruitment into the tumor microenvironment and an effective antitumor immune effector response.     

Granulocyte-macrophage colony-stimulating factor and interleukin-2 fusion cDNA for cancer gene immunotherapy

Genetic engineering of tumor cells to express both granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-2 can induce synergistic immune antitumor effects. Paradoxically, the combination has also been reported to down-regulate certain immune functions, highlighting the unpredictability of dual cytokine use. We hypothesized that a GM-CSF and IL-2 fusion transgene (GIFT) could circumvent such limitations yet preserve synergistic features. We designed a fusion cDNA of murine GM-CSF and IL-2. Protein structure computer modeling of GIFT protein predicted for intact ligand binding domains for both cytokines. B16 mouse melanoma cells were gene modified to express GIFT (B16GIFT), and these cells were unable to form tumors in C57bl/6 mice. Irradiated B16GIFT whole-cell tumor vaccine could also induce absolute protective immunity against challenge by live B16 cells. In mice with established melanoma, B16GIFT therapeutic cellular vaccine significantly improved tumor-free survival when compared with B16 expressing both IL-2 and GM-CSF. We show that GIFT induced a significantly greater tumor site recruitment of macrophages than combined GM-CSF and IL-2 and that macrophage recruitment arises from novel chemotactic feature of GIFT. In contrast to suppression by GM-CSF of natural killer (NK) cell recruitment despite coexpression of IL-2, GIFT leads to significant functional NK cell infiltration as confirmed in NK-defective beige mice. In conclusion, we demonstrated that a fusion between GM-CSF and IL-2 can invoke greater antitumor effect than both cytokines in combination, and novel immunobiological properties can arise from such chimeric constructs.     

THE BIOLOGICAL CHARACTERISTICS OF ADENOVIRUS-MEDIATED IL-18 GENE-MODIFIED MURINE COLORECTAL ADENOCARCINOMA CELL IN VIVO AND IN VITRO

Interleukin 18 (IL-18) has multiple biological activities, such as promoting the generation of Th1 cytokines and GM-CSF, activating NK cells and CTL, which contributes to its anti-tumor activity.[1(5] So IL-18 might have promising application in the immunotherapy and gene therapy of cancer. To confirm the anti-tumor activity of IL-18, we constructed the recombinant adenovirus encoding IL-18 gene, observed preliminarily the biological characteristics of IL-18-modified murine colorectal …     

Synergistic effects of co-expression of the Th1 cytokines il-2 and IFNγ on generation of murine tumor-reactive cytotoxic cells

While the effect of cytokines on the generation of tumor-reactive cytotoxic cells has been a topic of active investigation, the effect of physiological cytokine combinations has not been determined. We have investigated the effect of co-expression of IL-2 and IFN-γ on the generation of cytotoxic cells against the murine line 1 tumor in vivo. These cytokines were selected because they are normally produced in concert by a subset of T-helper cells called T-helper 1 (Th1). We transfected the line 1 murine carcinoma with cDNA for IL-2 and IFN-γ, alone or combined. IFN-γ alone does not elicit rejection of the transfectant, but IL-2 increases the tumorigenic dose by 10,000-fold above the parental cells. Co-expression of IFN-γ and IL-2 increases this rejection to at least 100,000-fold above parental line 1. Unlike IL-2 transfectants, tumor cells expressing both IFN-γ and IL-2 can also elicit rejection of admixed parental tumor cells. Finally, the IFN-γ/IL-2 transfectants are more effective at generating memory cells that are cytolytic for the parental tumor. Our results show that synergistic interactions of Th1 cytokines can remarkably enhance the cytotoxic response to tumors. © 1995 Wiley-Liss, Inc.     

Effects of hMIP-1beta gene modification on in vivo tumorigenicity and vaccine efficacy of tumor cells

OBJECTIVE To explore the effects of human macrophage inflammatory protein-1 beta (hMIP-1beta) modification on the in vivo tumorigenicity and vaccine efficacy of tumor cells. METHODS: Murine colorectal adenocarcinoma CT26 cells were transfected with a recombinant adenovirus carring the hMIP-1beta gene (AdhMIP-1beta). The efficacy of gene transfection was tested by X-gal staining. The hMIP-1beta level in the supernatant of hMIP-1beta gene-modified CT26 cells was assayed by ELISA, and the chemotactic activity for CD4+ T cells, CD8+ T cells, NK cells and immature dendritic cells (imDCs) were assayed by a transwell chamber. The changes of growth characteristics and in vivo tumorigenicity of hMIP-1beta gene-modified CT26 cells were also assessed. BALB/c mice were immunized with hMIP-1beta gene-modified CT26 tumor vaccine and the antitumor effect was evaluated. RESULTS: hMIP-1beta gene could be transfected into CT26 cells by AdhMIP-1beta with an efficiency over 95%. The level of hMIP-1beta in the culture supernatant of hMIP-1beta gene-modified CT26 cells was 980 pg/ml and the supernatant displayed ramarkable chemotactic activity to CD4+ T cells, CD8+ T cells, NK cells and imDCs compared with LacZ gene-modified CT26 cells and control. When the hMIP-1beta gene-modifited CT26 cells were subcutaneously inoculated in BALB/c mice, the tumorigencity was delayed and suppressed, and overt necrosis and lymphocyte infiltration were observed in the tumor tissue, but not in those inoculated with LacZ gene-modified CT26 cells or parental CT26 cells. The mice immunized with hMIP-1beta gene-modified CT26 tumor vaccine could induce tumor specific CTL activity and nonspecific NK activity, and exhibited resistance to later challenge with wild-type CT26 cells. CONCLUSION: hMIP-1beta gene-modified CT26 cells exhibit decreased tumorigenicity, and hMIP-1beta gene-modified tumor vaccine may induce a powerful specific and nonspecific antitumor response. The data suggested that hMIP-1beta gene-modified tumor vaccine may play a potent role in prevention of metastasis and recurrence of malignant tumors.     

Establishment of Nude Mice Lacking NK Cells and Their Application for Human Tumor Xenografts

Objective: Nude mice are used as a recipient for human tumor cell xenografts. However, the success rate of xenotransplantation is unsatisfactory due to high natural killer (NK) activity. To overcome this limitation, we established nude mice with no NK cells, and compared the transplantation efficiency with that in nude mice. Methods: BALB/c Nude Jak3-/- (Nude-J) mice were established by crossing BALB/c Nude mice and BALB/c Jak-3-/- mice. Hematopoietic malignant cell lines (BCBL-1 and Z138) were implanted subcutaneously to compare the tumorigenicity in Nude-J mice with Nude Rag-2/Jak3 double deficient (Nude RJ) mice and nude mice. Results: Nude-J mice showed complete loss of NK and T lymphocytes, whereas B lymphocytes remained. Both BCBL-1 and Z138 human lymphoid malignant cell lines formed almost the same sizes of subcutaneous tumors in Nude-J and Nude RJ mice, whereas they formed no or only small tumors in nude mice. Splenocytes from Nude-J mice showed no cytotoxic activity in vitro. Conclusion: Nude-J mice can be a valuable tool for human tumor cell transplantation studies.     

Growth suppression of subcutaneous tumor by CT26 expressing NK4 in syngeneic mice

An HGF antagonist, NK4, inhibits not only invasion and metastasis of tumor cells driven by HGF-Met receptor binding, but also tumor angiogenesis. To address the antitumor activities of NK4, we investigated the biological behaviors of CT26 transfected with the NK4 gene (CT26-NK4) in vitro and in vivo. In the in vitro assay, the invasion in MOCK transfected cells (control) was stimulated by HGF; however, in CT26-NK4 cells, these effects were completely inhibited. In the in vivo assay, the tumor growth of CT26-NK4 was strongly suppressed and the survival of CT26-NK4 tumor-bearing mice was significantly prolonged. Immunohistochemical analysis revealed that while proliferating cells (PCNA immunostaining) of CT26-NK4 tumors were weakly suppressed, the micro-vessel number (CD31/PECAM-1 immunostaining) in those tumors was significantly suppressed as compared with the control tumors. In conclusion, NK4 exerts potent antitumor effects via anti-angiogenesis rather than inhibition of biological events of tumor cells stimulated by HGF.     

The level of MHC class I expression on murine adenocarcinoma can change the antitumor effector mechanism of immunocytokine therapy

The huKS1/4-IL2 fusion protein, directed against the human epithelial cell adhesion molecule (huEpCAM) has been shown to induce a strong CD8+ T-cell-dependent, natural killer (NK) cell-independent, antitumor response in mice bearing the huEp-CAM-transfected CT26 colon cancer CT26-EpCAM. Here we investigate the effectiveness of huKS1/4-IL2 against CT26-Ep21.6, a subclone of CT26-EpCAM, expressing low levels of MHC class I. In vitro antibody-dependent cellular cytotoxicity (ADCC) assays in the presence of huKS1/4-IL2 demonstrate that murine NK cells from spleen and blood can kill CT26-Ep21.6 significantly better than they kill CT26-EpCAM. NK-mediated ADCC of CT26-EpCAM can be enhanced by blocking the murine NK cell-inhibitory receptor, Ly-49C. A potent in vivo antitumor effect was observed when BALB/c mice bearing experimental metastases of CT26-Ep21.6 were treated with huKS1/4-IL2. The depletion of NK cells during huKS1/4-IL2 treatment significantly reduced the antitumor effect against CT26-Ep21.6. Together our in vitro and in vivo data in the huEp-CAM-transfected CT26 models indicate that the amount of MHC class I expressed on the tumor target cell plays a critical role in the in vivo antitumor mechanism of huKS1/4-IL2 immunotherapy. A low MHC class I level favors NK cells as effectors, whereas a high level of MHC class I favors T cells as effectors. Given the heterogeneity of MHC class I expression seen in human tumors and the prevailing T-cell suppression in many cancer patients, the observation that huKS1/4-IL2 has the potential to effectively activate an NK cell-based antitumor response may be of potential clinical relevance.     

A comparative study on the xenotransplantability of human solid tumors into mice with different genetic immune deficiencies

These experiments set out to assess the role of NK and B cells in the resistance of nude mice to human tumor xenotransplantation. The transplantability of 9 fresh and 8 cultured human tumors was compared in 2 strains of mice with different genetic immune deficiencies: athymic NCr/Sed (nu/nu) nude mice, and nude-beige-xid (N:NIH-nu-bg-xid/Sed mice). Flow cytometric studies showed both strains to be deficient in Thy. 1.2 (T) cells and unresponsive to stimulation by Concanavalin A (Con A) or direct T-cell-receptor triggering with anti-CD3. The number of B cells was similar in the 2 strains, but the response to lipopolysaccharide (LPS) was markedly reduced in the nude-beige-xid animals. The number of asialoGM1-positive cells (predominantly NK) detected by flow cytometry was also reduced in the nude-beige-xid mice. The transplantability of the human tumors was found to be equivalent in the 2 strains. Quantitative cell-transplantation assays performed for 2 of the tumor cell lines did not reveal any subtle transplantation advantage for the more broadly immune-deficient animals. No evidence could, therefore, be found to suggest that NK or B cells were major determinants of human tumor xenotransplantability in these strains of mice.     

Therapeutic potential of human mesenchymal stem cells producing IL-12 in a mouse xenograft model of renal cell carcinoma

Mesenchymal stem cells (MSCs) represent a new tool for delivery of therapeutic agents to cancer. The cytokine interleukin-12 (IL-12) has demonstrated a potent anti-tumor activity in a variety of mouse tumor models. In this study, human MSCs were isolated from human bone marrow and identified by phenotype analysis and differentiation assays. The anti-tumor activity of human MSCs stably transduced with a recombinant adenoviral vector expressing the murine IL-12 (MSC/IL-12) were evaluated in a mouse xenograft model of renal cell carcinoma (RCC). Expression and bioactivity of the transgenic protein IL-12 from adenoviral vector were confirmed prior to in vivo studies. A nude mouse model of RCC was developed by subcutaneously injection of 786-0 cells into nude mice. MSC/IL-12 was injected into the lateral tail vein with single dose. Results indicated that systemic administration of MSC/IL-12 reduced the growth of 786-0 RCC and significantly prolonged mouse survival. These transfected cells could home to tumors after intravenous injection and largely produce local IL-12 protein. In contrast, systemic level of IL-12 was modestly elevated. Further studies showed that the anti-tumor activity of the MSC/IL-12 was dependent on the presence of natural killer (NK) cells and IFN-γ in this experimental setting. These data demonstrate the potential of adult MSC constitutively producing IL-12 to reduce the growth of RCC and enhance the tumor-bearing mouse survival.     

Oncolytic virotherapy with an HSV amplicon vector expressing granulocyte-macrophage colony-stimulating factor using the replication-competent HSV type 1 mutant HF10 as a helper virus

Direct viral infection of solid tumors can cause tumor cell death, but these techniques offer the opportunity to express exogenous factors to enhance the antitumor response. We investigated the antitumor effects of a herpes simplex virus (HSV) amplicon expressing mouse granulocyte-macrophage colony-stimulating factor (mGM-CSF) using the replication-competent HSV type 1 mutant HF10 as a helper virus. HF10-packaged mGM-CSF-expressing amplicon (mGM-CSF amplicon) was used to infect subcutaneously inoculated murine colorectal tumor cells (CT26 cells) and the antitumor effects were compared to tumors treated with only HF10. The mGM-CSF amplicon efficiently replicated in CT26 cells with similar oncolytic activity to HF10 in vitro. However, when mice subcutaneously inoculated with CT26 cells were intratumorally injected with HF10 or mGM-CSF amplicon, greater tumor regression was seen in mGM-CSF amplicon-treated animals. Furthermore, mGM-CSF amplicon treatment prolonged mouse survival. Immunohistochemical analysis revealed increased inflammatory cell infiltration in the solid tumor in the mGM-CSF amplicon-treated animals. These results suggest that expression of GM-CSF enhances the antitumor effects of HF10, and HF10-packaged GM-CSF-expressing amplicon is a promising agent for the treatment of subcutaneous tumors.     

Tumor vaccine therapy against recrudescent tumor using dendritic cells simultaneously transfected with tumor RNA and granulocyte macrophage colony-stimulating factor RNA

Recently, dendritic cells (DC) transfected with tumor RNA have been used as a cancer vaccine. The efficacy of a cancer vaccine using DC transfected tumor RNA was examined. Of particular interest was whether a vaccine using DC transfected with recrudescent tumor RNA is effective for the treatment of a regrowing tumor after prior immunotherapy. In addition, the usefulness of co-transfection of granulocyte macrophage colony-stimulating factor (GM-CSF) mRNA to augment the DC vaccine was examined. CT26 tumor-bearing mice were immunized by s.c. injection with DC transfected with CT26 mRNA (DC-CT26). The cytotoxic activity against CT26 in mice immunized with DC-CT26 was significantly higher than that in the control group ( P  < 0.001) and was augmented by GM-CSF mRNA co-transfection ( P  < 0.05), resulting in remarkable therapeutic efficacy in CT26 s.c. tumor models. Cytotoxic T lymphocytes induced by the vaccination using DC transfected with mRNA from the recrudescent tumor showed a potent cytotoxicity against the recrudescent CT26 tumor cells, which was significantly higher than the cytotoxicity induced by the vaccination using DC-CT26 ( P  < 0.05). In addition, in a recrudescent tumor model, this vaccination suppressed the regrowing s.c. tumors, and was augmented by GM-CSF mRNA co-transfection ( P  < 0.05). These results suggested that vaccination therapy using DC simultaneously transfected with whole tumor RNA and GM-CSF mRNA could generate therapeutic immune responses even against recrudescent tumor after prior vaccination. ( Cancer Sci 2008; 99: 407–413)