Downregulation of NKG2DLs by TGF-ß in human lung cancer cells.

BACKGROUND: Transforming growth factor beta (TGF-ß) is a typical immuno-inhibitory cytokine and highly secreted by lung cancer cells. It was supposed that its immunosuppressive effects to NK cell might be related with the altered expression of activating and inhibitory molecules in lung cancer cells. In this study, we examined the expression of NKG2DLs, PD-L1 and PD-L2 in lung cancer cells after treatment of TGF-ß and a TGF-ß inhibitor, Galunisertib (LY2157299). RESULTS: TGF-ß reduced the level of surface proteins of five NKG2DLs without altered transcription levels in lung cancer cells. Galunisertib reversed the effect of TGF-ß on the expression of NKG2DLs. Since MMP inhibitors, MMPi III and MMP2 inhibitor I, restored the reduced expression of NKG2DLs after treatment of TGF-ß, it was thought that TGF-ß induced the expression of MMP2 which facilitated the shedding of the NKG2DLs in cancer cells. However, the expression of PD-L1, L2 were not changed by treatment with TGF-ß or Galunisertib. CONCLUSIONS: Therefore, inhibition of TGF-ß might reverse the immunosuppressive status on immune cells and restore NK cell mediated anticancer immune responses by upregulation of NKG2DLs in cancer cells.

Differential Effects of Histone Deacetylases on the Expression of NKG2D Ligands and NK Cell-Mediated Anticancer Immunity in Lung Cancer Cells.

Histone acetylation is an epigenetic mechanism that regulates the expression of various genes, such as natural killer group 2, member D (NKG2D) ligands. These NKG2D ligands are the key molecules that activate immune cells expressing the NKG2D receptor. It has been observed that cancer cells overexpress histone deacetylases (HDACs) and show reduced acetylation of nuclear histones. Furthermore, HDAC inhibitors are known to upregulate the expression of NKG2D ligands. Humans have 18 known HDAC enzymes that are divided into four classes. At present, it is not clear which types of HDAC are involved in the expression of NKG2D ligands. We hypothesized that specific types of HDAC genes might be responsible for altering the expression of NKG2D ligands. In this study, we monitored the expression of NKG2D ligands and major histocompatibility complex (MHC) class I molecules in lung cancer cells which were treated with six selective HDAC inhibitors and specific small interfering RNAs (siRNAs). We observed that treatment with FK228, which is a selective HDAC1/2 inhibitor, also known as Romidepsin, induced NKG2D ligand expression at the transcriptional and proteomic levels in two different lung cancer cell lines. It also caused an increase in the susceptibility of NCI-H23 cells to NK cells. Silencing HDAC1 or HDAC2 using specific siRNAs increased NKG2D ligand expression. In conclusion, it appears that HDAC1 and HDAC2 might be the key molecules regulating the expression of NKG2D ligands. These results imply that specifically inhibiting HDAC1 and HDAC2 could induce the expression of NKG2D ligands and improve the NK cell-mediated anti-cancer immunity.

COX-2- and endoplasmic reticulum stress-independent induction of ULBP-1 and enhancement of sensitivity to NK cell-mediated cytotoxicity by celecoxib in colon cancer cells.

In the present study, we investigated whether celecoxib could induce the expression of NKG2D ligands in clonogenic colon cancer cells, and increase their susceptibility to NK cell-mediated cell death. Celecoxib and its non-coxib analog, 2,5-dimethyl celecoxib, induced ULBP-1 and DR5 in both COX-2 negative HCT-15 cells and COX-2 positive HT-29 cells. Celecoxib increased their susceptibility to NK92 cells in both DELFIA assay and soft agar colony forming assay. The inducibility of ULBP-1 and DR5 by celecoxib was not different between CD44- and CD44+ HCT-15 cells, and CD133- and CD133+ HT-29 cells. Celecoxib increased the susceptibility of highly clonogenic CD44+ HCT-15 and CD133+ HT-29 cells to NK92 cells, at least comparable to less clonogenic CD44- HCT-15 and CD133- HT-29 cells, respectively. In addition, celecoxib induced CHOP, and thapsigargin, an inducer of ER (endoplasmic reticulum) stress, induced DR5 but not ULBP1 in HCT-15. Taken together, these findings suggest that celecoxib induces the expression of ULBP-1 as well as DR5 in clonogenic colon cancer cells via COX-2 and ER stress-independent pathways, and increases their susceptibility to NK cells.

Antitumor effect of dendritic cell loaded ex vivo and in vivo with tumor-associated antigens in lung cancer model.

Various ex vivo or in vivo loading protocols have been developed or evaluated for the delivery of tumor antigens to dendritic cells (DCs). We compared the antitumor effect of mature DCs electroporation-pulsed (EP/mDC) ex vivo with tumor cell lysate and immature DCs (iDCs) injected into the tumor apoptosed by ionizing radiation (IR/iDC) in lung cancer model. DCs were generated from bone marrow of C57BL/6 mice. Ionizing radiation (IR) was applied at a dose of 10 Gy to the tumor on the right thigh. iDCs were intratumorally injected into the irradiated tumor and EP/mDC was injected subcutaneously in the right flank. DC injection induced strong tumor-specific immunity against Lewis lung carcinoma, as compared with the tumor-bearing control and IR only treated mice. The growth of a distant tumor on the right and left flank was inhibited by IR/iDC and EP/mDC. Particularly, IR/iDC resulted in a more significant inhibition of tumor growth and prolonged survival time. It was related to increase of tumor-specific interferon-gamma, cytotoxicity, and decrease of regulatory T-cells. The results indicate that DCs electroporation-pulsed with tumor cell lysate induce a potent antitumor effect, but that iDCs intratumoral injected into the irradiated tumor induce a more potent antitumor effect.

Enhanced maturation and function of dendritic cells using hydrogel coated plate and antigen electroporation.

Dendritic cells (DCs) are potent antigen-presenting cells that can be matured in vitro from immature dendritic cells (iDCs) in the presence of several biological agents such as cytokine cocktail, CD40L, TNF-a and antigen loading, which are necessary and achieved using various protocols, such as lipofection, passive pulse or electroporation. However, these DCs maturation protocols may cause with a significant loss of cells because of cellular attachment and spreading during culturing. Some biomaterials that influence adhesion and development of cells have been used in cell culture techniques, and it was thought that they might be applied on the culture of DCs. In this study, we used polyHEMA, which is a hydrogel coating biomaterial that prevents DCs from adherence, and investigated whether hydrogel coating affects the maturation of iDCs. The efficiency in the generation of mDCs was improved through hydrogel coating procedure and a dendritic cell maturation marker, CD83, was significantly increased in hydrogel-coated culture condition. The antigen-loaded mDCs from electroporation were further expressed the CD83. The mDCs generated in the hydrogel-coated culture condition showed more, longer and thicker dendrites, and produced more amounts of cytokines such as IL-12 and IFN-γ. Therefore, it was suggested that the hydrogel-coated culture condition could improve function of mDCs. Cheol-Hun Son and Jae-Ho Bae contributed equally to this work.

Antitumor effects of NK cells expanded by activation pre­processing of autologous feeder cells before irradiation in colorectal cancer.

Natural killer (NK) cells play a crucial role in early immune defenses against transformed cells and are used in the therapeutic management of cancer. However, it is difficult to sufficiently obtain high purity activated NK cells for clinical application. The function of NK cells is dependent on the balance of activating and inhibitory signals. Strong and diverse stimuli are required to increase the function of NK cells. Radiotherapy modulates the expression of various immunomodulatory molecules that recruit and activate NK cells. NK cell-mediated antibody-dependent cellular cytotoxicity is one of the most potent cytotoxic effects of NK cells against target cancer cells. To generate activated and irradiated autologous peripheral blood mononuclear cells (PBMCs), cytokine and monoclonal antibody stimulation followed by ionizing radiation was performed in the present study. The expanded NK cells were cultured for 21 days using activated/irradiated autologous PBMCs. Colorectal cancer cells (SW480 and HT-29) were used to analyze the expression of NK group 2D ligands and EGFR by radiation. The cytotoxicity of radiation plus NK cell-based targeted therapy against colorectal cancer cell lines was analyzed using flow cytometry. Activated and irradiated PBMCs exhibited significantly increased expression of various activating ligands that stimulated NK cells. In total, >10,000-fold high-purity activated NK cells were obtained, with negligible T-cell contamination. To confirm the antitumor activity of the NK cells expanded by this method, the expanded NK cells were treated with cetuximab, radiotherapy, or a combination of cetuximab and radiotherapy in the presence of human colorectal cancer cells. Expanded NK cells were effective at targeting human colorectal cancer cells, particularly when combined with cetuximab and radiotherapy. Thus, in the present study, a novel method for high-purity activated NK cell expansion was developed using activated and irradiated PBMCs. In addition, combined radiotherapy and antibody-based immunotherapy with expanded NK cells may be an effective strategy to enhance the efficiency of treatment against colorectal cancer.

Combinatorial immunotherapy with gemcitabine and ex vivo-expanded NK cells induces anti-tumor effects in pancreatic cancer.

Pancreatic cancer is difficult to diagnose at the initial stage and is often discovered after metastasis to nearby organs. Gemcitabine is currently used as a standard treatment for pancreatic cancer. However, since chemotherapy for pancreatic cancer has not yet reached satisfactory therapeutic results, adjuvant chemotherapy methods are attempted. It can be expected that combining immune cell therapy with existing anticancer drug combination treatment will prevent cancer recurrence and increase survival rates. We isolated natural killer (NK) cells and co-cultured them with strongly activated autologous peripheral blood mononuclear cells (PBMCs) as feeder cells, activated using CD3 antibody, IFN-r, IL-2, and γ-radiation. NK cells expanded in this method showed greater cytotoxicity than resting NK cells, when co-cultured with pancreatic cancer cell lines. Tumor growth was effectively inhibited in a pancreatic cancer mouse xenograft model. Therapeutic efficacy was increased by using gemcitabine and erlotinib in combination. These findings suggest that NK cells cultured by the method proposed here have excellent anti-tumor activity. We demonstrate that activated NK cells can efficiently inhibit pancreatic tumors when used in combination with gemcitabine-based therapy.

Cyclophosphamide potentiates the antitumor effect of immunization with injection of immature dendritic cells into irradiated tumor.

Growth of a tumor on the left flank was suppressed by direct injection of immature DCs (iDCs) into the irradiated tumor on the right thigh (IR/DC). This antitumor immune effect of IR/DC was enhanced by pretreatment with CTX (CTX+IR/DC) and this effect was related with increased number of tumor-specific IFN-γ secreting T cells and decreased ratio of CD4(+)CD25(+)/CD4(+) T cells. The treatment with CTX+IR/DC increased or decreased the levels of IL-2 or IL-10, respectively. These results demonstrated that antitumor effect of IR/DC could be augmented by pretreatment with low-dose CTX, suggesting a new antitumor therapeutic modality of chemoradioimmunotherapy.

An inhibitor of programmed death ligand 1 enhances natural killer cell-mediated immunity against malignant melanoma cells.

Since ionizing radiation has showed the dramatic effect to kill the cancer cells through direct DNA damage as well as triggering anti-cancer immune responses including induction of NKG2D ligands, it has used for long time to treat many cancer patients. However, it has been known that radiotherapy might promote the remnant cancer cells to escape immune system and metastasis. One of the suggested ways of immune evasion is induction of a ligand for programmed death-1 (PD-L1) in head and neck cancer, bladder cancer and lung cancer cells which engages the receptor, programmed death-1 (PD-1) in immune cells. PD-1/PD-L1 axis transduces the inhibitory signal and suppresses the adaptive immunity. However, their role in innate immunity remains poorly understood. Therefore, we investigated whether ionizing radiation could change the expression of PD-L1 in malignant melanoma cells and the receptor, programmed death-1 (PD-1), in NK-92 cells. Surface PD-L1 levels on melanoma cells were increased by ionizing radiation in a dose-independent manner but the level of PD-L1 was not changed significantly in NK-92 cells. Radiation-induced PD-L1 suppressed the activity of the NK-92 cells against melanoma cells despite of upregulation of NKG2D ligands. Furthermore, activated NK cells had high level of PD-1 and could not kill PD-L1+ melanoma cells effectively. When we used PD-L1 inhibitor or silenced PD-L1 gene, inhibited PD-1/PD-L1 axis reversed the activity of the suppressed NK cells. Through these results, we supposed that PD-1/PD-L1 blockade could enhance the immune responses of NK cells against melanoma cells after radiotherapy and might overcome the PD-L1 mediated radioresistance of cancer cells.

The cryopreservation of high concentrated PBMC for dendritic cell (DC)-based cancer immunotherapy.

Peripheral blood mononuclear cells (PBMC) have been accepted as a unique material for cancer immunotherapy using dendritic cells (DC) or activated lymphocytes that are being developed as an alternative or adjuvant to conventional therapies such as surgery, chemotherapy and radiation treatment. Although successful cryopreservation of large numbers of PBMC is critical for the immunotherapy, subsequent functional study of the effects of PBMC cryopreservation on differentiation into immune cells has not been well defined. In this study, over 1.0 x 10(8)cells/ml PBMC were cryopreserved as long as 52 weeks using a controlled-rate freezer (CRF) and stored in a vapor phase of liquid nitrogen tank. The effect of PBMC cryopreservation on differentiation into DC was studied by comparing the phenotypic and functional properties of immature DC (iDC) and mature DC (mDC) derived from cryopreserved PBMC to those from fresh PBMC. The results show that cryopreservation of PBMC at a fairly high cell concentration does not significantly affect cell recovery, viability, or phenotypes of PBMC. After differentiation into DC, iDC and mDC derived from cryopreserved PBMC had their typical phenotypes and function equivalent to those derived from fresh PBMC. Therefore, the improved cryopreservation process of PBMC described in this study is available for DC-based cancer immunotherapy.

Characterization of Bacillus polyfermenticus KJS-2 as a probiotic.

The identification and characterization of Bacillus polyfermenticus KJS-2 (B. polyfermenticus KJS-2) was conducted using TEM, an API 50CHB kit, 16S rDNA sequencing, a phylogenetic tree, and catalase and oxidase testing. The conversion rate of glucose to lactic acid by B. polyfermenticus KJS-2 was found to be 60.71+/-4.9%. In addition, treatment of B. polyfermenticus KJS-2 with artificial gastric juice (pH 2.0) and bile acid (pH 6.5) for 4 h resulted in a final viability of 140+/-7.9% and 108+/-3.5%, respectively. Finally, the results of adhesion experiments using Caco-2 cells revealed that the adherence of B. polyfermenticus KJS-2 to Caco-2 cells was approximately 65+/-0.6%.

Combination Treatment of Stereotactic Body Radiation Therapy and Immature Dendritic Cell Vaccination for Augmentation of Local and Systemic Effects.

PURPOSE: The purpose of this study was to investigate the efficacy of stereotactic body radiation therapy (SBRT) as a tumor-associated antigen (TAA) presentation method for dendritic cell (DC) sensitization and evaluate its effect in combination with immunotherapy using an intratumoral injection of immature DCs (iDCs). METHODS AND MATERIALS: CT-26 colon carcinoma cell was used as a cancer cell line. Annexin V staining and phagocytosis assays were performed to determine the appropriate radiation dose and incubation time to generate TAAs. BALB/c mice were used for in vivo experiments. Cancer cells were injected into the right legs and left flanks to generate primary and metastatic tumors, respectively. The mice were subjected to radiation therapy (RT) alone, intradermal injection of electroporated DCs alone, or RT in combination with iDC intratumoral injection (RT/iDC). Tumor growth measurement and survival rate analysis were performed. Enzyme-linked immunospot and cytotoxicity assays were performed to observe the effect of different treatments on the immune system. RESULTS: Annexin V staining and phagocytosis assays showed that 15 Gy radiation dose and 48 hours of incubation was appropriate for subsequent experiments. Maximum DC sensitization and T-cell stimulation was observed with RT as compared to other TAA preparation methods. In vivo assays revealed statistically significant delay in the growth of both primary and metastatic tumors in the RT/iDC group. The overall survival rate was the highest in the RT/iDC group. CONCLUSION: The combination of SBRT and iDC vaccination may enhance treatment effects. Clinical trials and further studies are warranted in the future.

Upregulation of Myc promotes the evasion of NK cell­mediated immunity through suppression of NKG2D ligands in K562 cells.

c­Myc is a characteristic oncogene with dual functions in cell proliferation and apoptosis. Since the overexpression of the c­Myc proto­oncogene is a common event in the development and growth of various human types of cancer, the present study investigated whether oncogenic c­Myc can alter natural killer (NK) cell­mediated immunity through the expression of associated genes, using PCR, western blotting and flow cytometry assays. Furthermore, whether c­Myc could influence the expression levels of natural killer group 2 member D (NKG2D) ligands, which are well known NK activation molecules, as well as NK cell­mediated immunity, was investigated. c­Myc was inhibited by 10058­F4 treatment and small interfering RNA transfection. Upregulation of c­Myc was achieved by transfection with a pCMV6­myc vector. The inhibition of c­Myc increased MHC class I polyeptide­related sequence B and UL16 binding protein 1 expressions among NKG2D ligands, and the overexpression of c­Myc suppressed the expression of all NKG2D ligands, except MHC class I polyeptide­related sequence A. Furthermore, the alteration of c­Myc activity altered the susceptibility of K562 cells to NK cells. These results suggested that the overexpression of c­Myc may contribute to the immune escape of cancer cells and cell proliferation. Combined treatment with NK­based cancer immunotherapy and inhibition of c­Myc may achieve improved therapeutic results.

EpCAM peptide-primed dendritic cell vaccination confers significant anti-tumor immunity in hepatocellular carcinoma cells.

Cancer stem-like cells (CSCs) may play a key role in tumor initiation, self-renewal, differentiation, and resistance to current treatments. Dendritic cells (DCs) play a vital role in host immune reactions as well as antigen presentation. In this study, we explored the suitability of using CSC peptides as antigen sources for DC vaccination against human breast cancer and hepatocellular carcinoma (HCC) with the aim of achieving CSC targeting and enhancing anti-tumor immunity. CD44 is used as a CSC marker for breast cancer and EpCAM is used as a CSC marker for HCC. We selected CD44 and EpCAM peptides that bind to HLA-A2 molecules on the basis of their binding affinity, as determined by a peptide-T2 binding assay. Our data showed that CSCs express high levels of tumor-associated antigens (TAAs) as well as major histocompatibility complex (MHC) molecules. Pulsing DCs with CD44 and EpCAM peptides resulted in the efficient generation of mature DCs (mDCs), thus enhancing T cell stimulation and generating potent cytotoxic T lymphocytes (CTLs). The activation of CSC peptide-specific immune responses by the DC vaccine in combination with standard chemotherapy may provide better clinical outcomes in advanced carcinomas.

Enhancement of antitumor immunity by combination of anti-CTLA-4 antibody and radioimmunotherapy through the suppression of Tregs.

Cytotoxic T lymphocyte antigen-4 (CTLA-4) is expressed during cluster of differentiation (CD)4+ T-cell activation and terminates immune responses by interrupting CD28-enhanced activation. In addition, CTLA-4 is known to be constitutively expressed in regulatory T-cells (Tregs) and to contribute to immune suppression by enhancing the suppressive function of Tregs. However, the molecular mechanisms underlying CTLA-4-mediated Treg suppression remains incompletely understood. Furthermore, it is uncertain whether the in vivo immune suppressive functions of CTLA-4 are mediated only by a reduction in the level of conventional T-cell activity, or enhancement of Treg function. The present study demonstrated that combination therapy with an anti-CTLA-4 monoclonal antibody and dendritic cell-mediated radioimmunotherapy (IR/DC) was able to promote an antitumor response and influence Treg function in a mouse model of lung cancer. Cell surface markers, including CTLA-4, CD25 and CD4, were analyzed using flow cytometry, and T-cell activities were measured using ELISPOT and cytotoxicity assays. It was revealed that anti-CTLA-4 combined treatment with IR/DC immunotherapy may execute a more powerful and effective anti-tumor immunity through the inhibition of Treg function.

Expansion of cytotoxic natural killer cells using irradiated autologous peripheral blood mononuclear cells and anti-CD16 antibody.

Natural killer (NK) cells are considered a promising strategy for cancer treatment. Various methods for large-scale NK cell expansion have been developed, but they should guarantee that no viable cells are mixed with the expanded NK cells because most methods involve cancer cells or genetically modified cells as feeder cells. We used an anti-CD16 monoclonal antibody (mAb) and irradiated autologous peripheral blood mononuclear cells (PBMCs) (IrAPs) to provide a suitable environment (activating receptor-ligand interactions) for the NK cell expansion. This method more potently expanded NK cells, and the final product was composed of highly purified NK cells with lesser T-cell contamination. The expanded NK cells showed greater upregulation of various activation receptors, CD107a, and secreted larger amounts of interferon gamma. IrAPs expressed NKG2D ligands and CD48, and coengagement of CD16 with NKG2D and 2B4 caused potent NK cell activation and proliferation. The expanded NK cells were cytotoxic toward various cancer cells in vitro and in vivo. Moreover, irradiation or a chemotherapeutic drug further enhanced this antitumor effect. Therefore, we developed an effective in vitro culture method for large-scale expansion of highly purified cytotoxic NK cells with potent antitumor activity using IrAPs instead of cancer cell-based feeder cells.

Tumor associated macrophages provide the survival resistance of tumor cells to hypoxic microenvironmental condition through IL-6 receptor-mediated signals.

Hypoxia and infiltration of tumor-associated macrophages (TAM) are intrinsic features of the tumor microenvironment. Tumor cells that remain viable in hypoxic conditions often possess an increased survival potential and tend to grow aggressively. TAM also respond to a variety of signals in the hypoxic tumor microenvironment and express a more M2-like phenotype. In this study, the established mouse tumor tissues showed a dense infiltration of CD206+ macrophages at the junctions between the normoxic and hypoxic regions and an increased IL-6 receptor (IL-6R) expression of tumor cells in the areas of CD206+ TAM accumulation, which indicates a role of M2 phenotype TAM in survival adaptation of tumor cells preparing for an impending hypoxic injury before changes in oxygen availability. Cocultured mouse FM3A or human MCF-7 tumor cells with tumor infiltrating macrophages isolated from mouse tumor tissues and M2-polarized macrophages generated from human THP-1 cells, respectively, showed significantly decreased rate of cell death in cultures exposed to hypoxia. The acquisition of survival resistance was attributed to increased IL-6 production by M2 TAM and increased expression of IL-6R in tumor cells in the coculture system. MCF-7 cells cocultured with M2 TAM showed activated JAK1/STAT3 and Raf/MEK/JNK pathways contributing to tyrosine and serine phophorylation of STAT3, respectively. However, only tyrosine phosphorylated STAT3 was detected in the nucleus, which induced upregulation of Bcl-2 and downregulation of Bax and Bak. Finally, knockdown of IL-6R by small interfering RNA significantly counteracted coculture-induced signals and completely abolished the survival resistance to hypoxic injury. Thus, we present evidence for the role of M2 phenotype TAM in IL-6 receptor-mediated signals, particularly tyrosine phosphorylation of STAT3, responsible for the prosurvival adaptation of tumor cells to hypoxia.

Combination treatment with decitabine and ionizing radiation enhances tumor cells susceptibility of T cells.

Decitabine has been found to have anti-metabolic and anti-tumor activities in various tumor cells. Recently, the use of decitabine in combination with other conventional therapies reportedly resulted in improved anti-tumor activity against various tumors. Ionizing radiation (IR) is widely used as a cancer treatment. Decitabine and IR improve immunogenicity and susceptibility of tumor cells to immune cells by up-regulating the expression of various molecules such as major histocompatibility complex (MHC) class I; natural-killer group 2, member D (NKG2D) ligands; and co-stimulatory molecules. However, the effects of combining decitabine and IR therapies are largely unknown. Our results indicate that decitabine or IR treatment upregulates MHC class I, along with various co-stimulatory molecules in target tumor cells. Furthermore, decitabine and IR combination treatment further upregulates MHC class I, along with the co-stimulatory molecules, when compared to the effect of each treatment alone. Importantly, decitabine treatment further enhanced T cell-mediated cytotoxicity and release of IFN- γ against target tumor cells which is induced by IR. Interestingly, decitabine did not affect NKG2D ligand expression or NK cell-mediated cytotoxicity in target tumor cells. These observations suggest that decitabine may be used as a useful immunomodulator to sensitize tumor cells in combination with other tumor therapies.

Radiation-induced matrix metalloproteinases limit natural killer cell-mediated anticancer immunity in NCI-H23 lung cancer cells.

Radiotherapy has been used to treat cancer for >100 years and is required by numerous patients with cancer. Ionizing radiation effectively inhibits the growth of cancer cells by inducing cell death and increasing anticancer immunity, through the induction of natural killer group 2 member D ligands (NKG2DLs); however, adverse effects have also been reported, including the promotion of metastasis. Matrix metalloproteinases (MMPs) are induced by ionizing radiation and have an important role in the invasion and metastasis of cancer cells. Previously, MMPs were demonstrated to increase the shedding of NKG2DLs, which may reduce the surface expression of NKG2DLs on cancer cells. As a consequence, the cancer cells may escape natural killer (NK)­mediated anticancer immunity. In the present study, NCI­H23 human non­small cell lung cancer cells were used to investigate the combined effects of ionizing radiation and MMP inhibitors on the expression levels of NKG2DLs. Ionizing radiation increased the expression of MMP2 and ADAM metalloproteinase domain 10 protease, as well as NKG2DLs. The combined treatment of ionizing radiation and MMP inhibitors increased the surface expression levels of NKG2DLs and resulted in the increased susceptibility of the cancer cells to NK­92 natural killer cells. Furthermore, soluble NKG2DLs were increased in the media by ionizing radiation and blocked by MMP inhibitors. The present study suggests that radiotherapy may result in the shedding of soluble NKG2DLs, through the induction of MMP2, and combined treatment with MMP inhibitors may minimize the adverse effects of radiotherapy.

Enhanced dendritic cell-based immunotherapy using low-dose cyclophosphamide and CD25-targeted antibody for transplanted Lewis lung carcinoma cells.

Regulatory T cells (Tregs) is one of the main obstacles to the success of cancer immunotherapy. The effect of dendritic cell (DC)-based immunotherapy can be attenuated by immune suppressive functions of Tregs. We used a CD25-targeted antibody and low-dose cyclophosphamide (CTX) as immunomodulators to increase the antitumor effect of intratumoral injection of immature DCs into the irradiated tumor cells (IR/iDC). CTX or CD25-targeted antibody alone showed a significant reduction in the number of Tregs within the tumor microenvironment. When they are combined with IR/iDC, the number of Tregs was further reduced. Although IR/IDC showed strong antitumor effects such as reduction in tumor growth, increase in Th1 immune response, and improvement of survival, the therapeutic effect was further improved by combining treatments with immunomodulators. CTX and CD25-targeted antibody showed no significant difference in tumor growth when combined with IR/iDC, but CTX further increased the number of interferon (IFN)-γ-secreting T cells, cytotoxicity, and survival rate. Although irradiation induced depletion of T lymphocytes, administration of DCs recovered this depletion. Particularly, the lymphocytes were more significantly increased when CTX and IR/iDC were combined. Low-dose CTX has already been used as an immunomodulator in clinical trials, and it offers several advantages, including convenience, low-cost, and familiarity to clinicians. However, CD25-targeted antibody cannot only deplete Tregs, but also may affect IL-2-dependent effector T lymphocytes. Therefore, CTX is an effective means to inhibit Tregs, and an effective immunomodulatory agent for multimodality therapy such as combination treatment of conventional cancer therapy and immunotherapy.