Tumor-dendritic cell fusion as a basis for cancer immunotherapy

Gene Expression Profile of Dendritic Cell-Tumor Cell Hybrids Determined by Microarrays and Its Implications for Cancer Immunotherapy

Background. Dendritic cell- (DC-) tumor fusion cells stimulate effective in vivo antitumor responses. However, therapeutic approaches are dependent upon the coadministration of exogenous 3rd signals. The purpose of this study was to determine the mechanisms for inadequate 3rd signaling by electrofused DC-tumor cell hybrids. Methods. Murine melanoma cells were fused with DCs derived from C57BL/6 mice. Quantitative real-time PCR (qPCR) was used to determine relative changes in Th (T helper) 1 and Th2 cytokine gene expression. In addition, changes in gene expression of fusion cells were determined by microarray. Last, cytokine secretion by fusion cells upon inhibition of signaling pathways was analyzed by ELISA. Results. qPCR analyses revealed that fusion cells exhibited a downregulation of Th1 associated cytokines IL-12 and IL-15 and an upregulation of the Th2 cytokine IL-4. Microarray studies further showed that the expression of chemokines, costimulatory molecules, and matrix-metalloproteinases was deregulated in fusion cells. Lastly, inhibitor studies demonstrate that inhibition of the PI3K/Akt/mTOR signaling pathway could restore the secretion of bioactive IL-12p70 by fusion cells. Conclusion. Our results suggest that combining fusion cell-based vaccination with administration of inhibitors of the PI3K/Akt/mTOR signaling pathway may enhance antitumor responses in patients.

Can dendritic cells improve whole cancer cell vaccines based on immunogenically killed cancer cells?

Immunogenic cell death (ICD) offers interesting opportunities in cancer cell (CC) vaccine manufacture, as it increases the immunogenicity of the dead CC. Furthermore, fusion of CCs with dendritic cells (DCs) is considered a superior method for generating whole CC vaccines. Therefore, in this work, we determined in naive mice whether immunogenically killed CCs per se (CC vaccine) elicit an antitumoral immune response different from the response observed when immunogenically killed CCs are associated with DCs through fusion (fusion vaccine) or through co-incubation (co-incubation vaccine). After tumor inoculation, the type of immune response in the prophylactically vaccinated mice differed between the groups. In more detail, fusion vaccines elicited a humoral anticancer response, whereas the co-incubation and CC vaccine mainly induced a cellular response. Despite these differences, all three approaches offered a prophylactic protection against tumor development in the murine mammary carcinoma model. In summary, it can be concluded that whole CC vaccines based on immunogenically killed CCs may not necessarily require association with DCs to elicit a protective anticancer immune response. If this finding can be endorsed in other cancer models, the manufacture of CC vaccines would greatly benefit from this new insight, as production of DC-based vaccines is laborious, time-consuming and expensive.

Purified dendritic cell-tumor fusion hybrids supplemented with non-adherent dendritic cells fraction are superior activators of antitumor immunity

Background

Strong evidence supports the DC-tumor fusion hybrid vaccination strategy, but the best fusion product components to use remains controversial. Fusion products contain DC-tumor fusion hybrids, unfused DCs and unfused tumor cells. Various fractions have been used in previous studies, including purified hybrids, the adherent cell fraction or the whole fusion mixture. The extent to which the hybrids themselves or other components are responsible for antitumor immunity or which components should be used to maximize the antitumor immunity remains unknown.

Methods

Patient-derived breast tumor cells and DCs were electro-fused and purified. The antitumor immune responses induced by the purified hybrids and the other components were compared.

Results

Except for DC-tumor hybrids, the non-adherent cell fraction containing mainly unfused DCs also contributed a lot in antitumor immunity. Purified hybrids supplemented with the non-adherent cell population elicited the most powerful antitumor immune response. After irradiation and electro-fusion, tumor cells underwent necrosis, and the unfused DCs phagocytosed the necrotic tumor cells or tumor debris, which resulted in significant DC maturation. This may be the immunogenicity mechanism of the non-adherent unfused DCs fraction.

Conclusions

The non-adherent cell fraction (containing mainly unfused DCs) from total DC/tumor fusion products had enhanced immunogenicity that resulted from apoptotic/necrotic tumor cell phagocytosis and increased DC maturation. Purified fusion hybrids supplemented with the non-adherent cell population enhanced the antitumor immune responses, avoiding unnecessary use of the tumor cell fraction, which has many drawbacks. Purified hybrids supplemented with the non-adherent cell fraction may represent a better approach to the DC-tumor fusion hybrid vaccination strategy.

Local secretion of IL-12 augments the therapeutic impact of dendritic cell-tumor cell fusion vaccination

BACKGROUND

The development of dendritic cell (DC)-tumor fusion vaccines is a promising approach in cancer immunotherapy. Using fusion vaccines allows a broad spectrum of known and unidentified tumor-associated antigens to be presented in the context of MHC class I and class II molecules, with potent co-stimulation provided by the DCs. Although DC-tumor fusion cells are immunogenic, murine studies have shown that effective immunotherapy requires a third signal, which can be provided by exogenous interleukin 12 (IL-12). Unfortunately, systemic administration of IL-12 induces severe toxicity in cancer patients, potentially precluding clinical use of this cytokine to augment fusion vaccine efficacy. To overcome this limitation, we developed a novel approach in which DC-tumor fusion cells locally secrete IL-12, then evaluated the effectiveness of this approach in a murine B16 melanoma model.

MATERIALS AND METHODS

Tumor cells were stably transduced to secrete murine IL-12p70. These tumor cells were then electrofused to DC to form DC-tumor heterokaryons. These cells were used to treat established B16 pulmonary metastases. Enumeration of these metastases was performed and compared between experimental groups using Wilcoxon rank sum test. Interferon γ enzyme-linked immunosorbent spot assay was performed on splenocytes from treated mice.

RESULTS

We show that vaccination with DCs fused to syngeneic melanoma cells that stably express murine IL-12p70 significantly reduces counts of established lung metastases in treated animals when compared with DC-tumor alone (P = 0.029). Interferon γ enzyme-linked immunosorbent spot assays suggest that this antitumor response is mediated by CD4(+) T cells, in the absence of a tumor-specific CD8(+) T cell response, and that the concomitant induction of antitumor CD4(+) and CD8(+) T cell responses required exogenous IL-12.

CONCLUSIONS

This study is, to the best of our knowledge, the first report that investigates the impact of local secretion of IL-12 on antitumor immunity induced by a DC-tumor fusion cell vaccine in a melanoma model and may aid the rational design of future clinical trials.

Allogeneic tumor vaccine produced by electrofusion between osteosarcoma cell line and dendritic cells in the induction of antitumor immunity

OBJECTIVE

Fusion of dendritic cells, DCs, with tumor cells is an effective approach for delivering tumor antigens to DCs, and DC-tumor fusion cells are potent stimulators of T cells. However, the integration of allogeneic DC-osteosarcoma fusion cells has not been fully examined. This study was designed to investigate the antitumor effects of tumor vaccine produced by electrofusion between rat osteosarcoma cells and allogeneic DCs.

METHODS

In the present study, we electrofused Wistar rat bone marrow-derived DCs to SD rat osteosarcoma cells (UMR106) and purified them by monoclonal antibody OX62 and magnetic beads. Coculture of SD or Wistar bone marrow derived T lymphocytes with DC-tumor fusion cells resulted in activation of T cells, and the proportion of CD8(+), CD4(+) cells was determined using flow cytometry. Then cytotoxic T lymphocytes, CTLs, assay was assessed according to results of MTT assay.

RESULTS

After T cells were cultured with allogeneic DC-osteosarcoma fusion cells, DOF, and effective activation of T cells was observed. The proportion of CD8(+) cells in the SD T cell group increases from 34.16% before induction to 74.85%, while that of CD4(+) cells is from 63.35% to 71.75% in Wistar T cell group. The immunization using allogeneic DC-osteosarcoma vaccine induced UMR106-specific CTL responses which were statistically significant (P < 0.05) and the cytotoxic activity was inhibited by the treatment with anti-CD8 and anti-MHC-class I monoclonal antibodies but not with anti-CD4 and anti-MHC-class II antibodies.

CONCLUSION

The present study provided valid evidence of integration of rat allogeneic DCs electrofused with tumor cells and analyzed their properties in T cell activation. The fusion cells may thus represent a promising strategy for DC-based immunotherapy of patients with osteosarcoma.

Dendritic cell-tumor cell hybrids and immunotherapy: what's next?

Dendritic cells (DC) are professional antigen-presenting cells currently being used as a cellular adjuvant in cancer immunotherapy strategies. Unfortunately, DC-based vaccines have not demonstrated spectacular clinical results. DC loading with tumor antigens and DC differentiation and activation still require optimization. An alternative technique for providing antigens to DC consists of the direct fusion of dendritic cells with tumor cells. These resulting hybrid cells may express both major histocompatibility complex (MHC) class I and II molecules associated with tumor antigens and the appropriate co-stimulatory molecules required for T-cell activation. Initially tested in animal models, this approach has now been evaluated in clinical trials, although with limited success. We summarize and discuss the results from the animal studies and first clinical trials. We also present a new approach to inducing hybrid formation by expression of viral fusogenic membrane glycoproteins.

Immunotherapy using allogeneic squamous cell tumor-dendritic cell fusion hybrids

BACKGROUND

Tumor-associated antigens (TAAs) are known to be immunotherapy targets; thus tumor-sharing TAA may be used as a fusion hybrid partner to confer protection against subsequent tumor challenge.

METHODS

The squamous cell carcinomas (SCCs), SCCVII and B4B8, were used in C3H/HEN mice: SCCVII (H-2(k)) is syngeneic, B4B8 (H-2(d)) is allogeneic. Experiments using tumor alone included hyperimmunization schedule, subdermal and intranodal routes. Mice were challenged 2 weeks later. Fusion hybrids were created from both SCC tumor cell lines and syngeneic dendritic cells (DCs). These were delivered intranodally for immunization, and mice were challenged with tumor 2 weeks later.

RESULTS

Only syngeneic tumor given subdermally was able to protect after tumor challenge 2 weeks later. Hyperimmunization schedule did not alter these findings. However, fusion hybrid immunization from both allogeneic and syngeneic SCCs conferred protection after tumor challenge.

CONCLUSIONS

Allogeneic tumor-DC fusion hybrids targeting TAA can protect against subsequent tumor challenge.

Toll-like receptor agonists as third signals for dendritic cell-tumor fusion vaccines

BACKGROUND

The aim of the present study was to evaluate the therapeutic efficacy of dendritic cell (DC)-tumor fusion hybrids with Toll-like receptor (TLR) agonists.

METHODS

DC-tumor fusion hybrids were generated by electrofusion and injected into the inguinal lymph nodes of C57BL/6 mice with 3-day established pulmonary metastases. Paired TLR agonists polyinosine:polycytadilic acid [poly(I:C)] and cytosine-phosphate-guanine (CpG) were then injected intraperitoneally. Enzyme-linked immunosorbent assay (ELISA) was used to evaluate interleukin (IL)-12 production from the DC-tumor fusion hybrids in vitro.

RESULTS

Fusion + TLR agonists (60 metastases) had significantly fewer metastases than did the untreated control (262 metastases, p = .0001) and fusion alone (150 metastases, p = .02). ELISA showed that the DC-tumor fusion hybrids yielded 90 pg of IL-12 after TLR stimulation compared with 1610 pg from dendritic cells alone.

CONCLUSIONS

CpG and poly(I:C) administered as a third signal with fusion hybrids as described significantly reduce melanoma metastasis compared with fusion hybrids alone. Fusion hybrids do not appear to be a significant source for IL-12 secretion.

Induction of antitumor immunity by semi-allogeneic and fully allogeneic electrofusion products of tumor cells and dendritic cells

Immunization with the electrofusion product of tumor cells and dendritic cells (DCs) is a promising approach to cancer immunotherapy. Production of electrofusion vaccines currently requires the acquisition of tumor material and must be tailored to each individual. Alternative vaccine configurations were explored in this study. Results indicated that fusion vaccines with fully syngeneic, semi-allogeneic or fully allogeneic components, were all effective in inducing specific, long-lasting antitumor immunity. This previously undescribed activity of a fully allogeneic fusion product introduces the possibility of using defined allogeneic tumor and DC lines to simplify vaccine manufacturing.

Potential side effects of dendritic cells pulsed with allogenic melanoma cell lysate in mice

An attempt has been made to investigate the toxicity of cancer immunotherapy based on the dendritic cells pulsed with lysate of allogenic melanoma cell, DM401. Dendritic cells pulsed with lysate of clone M3 were subcutaneously administered once a week eight times to C57BL/6 mice at 0, 2.5, 5, and 10 x 10(7) cells/kg. No changes attributable to the administration were observed in clinical signs and food and water consumption. The administration induced slight increases in body weights, white blood cells, total protein, total cholesterol, triglyceride, phospholipids, and absolute spleen weights, but a slight decrease in albumin/globulin ratio. Microscopic examinations revealed the infiltration of inflammatory cells in the lung, mainly in the pulmonary arteriole, in which the tunica media thickened, and in the pulmonary alveoli and alveolar space. Thickened tunica media of pulmonary arteriole was observed in both males and females at all selected doses. In addition, the subcutis at the test substance-application site showed inflammation and fibrosis. In conclusion, lung is a target organ of DM401, and most of the changes including the findings in lung are considered as the immunomodulatory functions of dendritic cells.

Dendritic cells fused with allogeneic breast cancer cell line induce tumor antigen-specific CTL responses against autologous breast cancer cells

Dendritic cell (DC)/tumor cell fusion vaccine has been revealed as a promising tool for the antitumor immunotherapy. Previous research has shown that fusion hybrids of human DCs and autologous tumor cells can induce cytotoxic T lymphocyte (CTL) responses against autologous tumor cells in animal models and human clinical trials. However, a major restriction factor for the clinical use is the difficulty for preparation of sufficient amount of autologous tumor cells especially for the patients with metastasis cancer whose primary tumor lesion is not clear or has been resected. In this study, allogeneic breast cancer cell line MCF-7 cells were electrofused to autologous DCs from patient with breast cancer as a strategy to deliver shared breast cancer antigens to DCs. Fusion cells generated by autologous DCs and allogeneic MCF-7 were able to induce autologous T lymphocytes proliferation, high levels of IFN-gamma production and CTL responses. CTLs induced by DCs/allogeneic MCF-7 fusion cells were able to kill autologous breast cancer cells in an antigen specific and HLA restriction manner. Our study may provide the experiment basis for the use of allogeneic breast cancer cell line in the DC/tumor cell fusion cell vaccination strategy.

A biophysical approach to the optimisation of dendritic-tumour cell electrofusion

Electrofusion of tumour and dendritic cells (DCs) is a promising approach for production of DC-based anti-tumour vaccines. Although human DCs are well characterised immunologically, little is known about their biophysical properties, including dielectric and osmotic parameters, both of which are essential for the development of efficient electrofusion protocols. In the present study, human DCs from the peripheral blood along with a tumour cell line used as a model fusion partner were examined by means of time-resolved cell volumetry and electrorotation. Based on the biophysical cell data, the electrofusion protocol could be rapidly optimised with respect to the sugar composition of the fusion medium, duration of hypotonic treatment, frequency range for stable cell alignment, and field strengths of breakdown pulses triggering membrane fusion. The hypotonic electrofusion consistently gave a tumour-DC hybrid rate of up to 19%, as determined by counting dually labelled fluorescent hybrids in a microscope. This fusion rate is nearly twice as high as that usually reported in the literature for isotonic media. The experimental findings and biophysical approach presented here are generally useful for the development of efficient electrofusion protocols, especially for rare and valuable human cells.