Intratumoral interferon-alpha gene transfer enhances tumor immunity after allogeneic hematopoietic stem cell transplantation

Pancreatic Cancer and Immunotherapy: Resistance Mechanisms and Proposed Solutions

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) continues to be one of the most aggressive and lethal diseases in the world. The success of immunotherapy in other types of malignancy has led to further trials to understand better the role of immunotherapy in PDAC. However, initial studies with immunotherapy, namely, the checkpoint inhibitors, in PDAC have not been met with the same outcomes. The purpose of this review is to identify and discuss the various resistance mechanisms of PDAC to immunotherapy (pancreatic stroma, genetic predisposition/epigenetics, and the immune inhibitory cells, cytokines, soluble factors, and enzymes that comprise the tumor microenvironment) and the solutions currently being studied to overcome them.

CONCLUSIONS

Various preclinical and early clinical studies have shown that immunotherapy, especially checkpoint inhibitors, in PDAC may be efficacious as part of a multi-modal treatment, in combination with other therapies that target these resistance mechanisms. Several clinical trials are ongoing to explore this concept further.

Intratumoral IFN-α gene delivery reduces tumor-infiltrating regulatory T cells through the downregulation of tumor CCL17 expression

The effect of IFN-α on the immunosuppressive tumor microenvironment is not fully understood. We previously reported that intratumoral IFN-α gene transduction decreased the frequency of regulatory T cells (Tregs) in the tumor by inducing the secretion of IL-6 from dendritic cells. In this study, we examined whether IFN-α affects the trafficking of Tregs to the tumor. Since CT26 cells expressed CCL17 among Treg-attracting chemokines, we focused on its role in IFN-α-mediated Treg suppression. IFN-α directly suppressed CCL17 production from CT26 cells in vitro, and IFN-α transduction reduced CCL17 expression in tumors in vivo. Next, to investigate whether CCL17 downregulation is related to the suppression of Treg trafficking, CCL17-downregulated CT26 cells produced using short hairpin RNA (CT26-shCCL17) were inoculated into mice. The frequency of Tregs in CT26-shCCL17 tumors was reduced and tumor growth was suppressed. Finally, to examine the combinatorial effect of IFN-α expression with CCL17 downregulation, IFN-α was transduced into CT26-shCCL17 tumors. This resulted in an elevation of CT26-specific CD8⁺ T cells and the complete eradication of tumors. This study shows a novel mechanism of IFN-α-mediated Treg suppression, and combining IFN-α gene therapy with strong CCL17 downregulation could offer a promising strategy for the treatment of cancer.

Distinguishing three subtypes of hematopoietic cells based on gene expression profiles using a support vector machine

Hematopoiesis is a complicated process involving a series of biological sub-processes that lead to the formation of various blood components. A widely accepted model of early hematopoiesis proceeds from long-term hematopoietic stem cells (LT-HSCs) to multipotent progenitors (MPPs) and then to lineage-committed progenitors. However, the molecular mechanisms of early hematopoiesis have not been fully characterized. In this study, we applied a computational strategy to identify the gene expression signatures distinguishing three types of closely related hematopoietic cells collected in recent studies: (1) hematopoietic stem cell/multipotent progenitor cells; (2) LT-HSCs; and (3) hematopoietic progenitor cells. Each cell in these cell types was represented by its gene expression profile among a total number of 20,475 genes. The expression features were analyzed by a Monte-Carlo Feature Selection (MCFS) method, resulting in a feature list. Then, the incremental feature selection (IFS) and a support vector machine (SVM) optimized with a sequential minimum optimization (SMO) algorithm were employed to access the optimal classifier with the highest Matthews correlation coefficient (MCC) value of 0.889, in which 6698 features were used to represent cells. In addition, through an updated program of MCFS method, seventeen decision rules can be obtained, which can classify the three cell types with an overall accuracy of 0.812. Using a literature review, both the rules and the top features used for building the optimal classifier were confirmed to be commonly used or potential biological markers for distinguishing the three cell types of HSPCs. This article is part of a Special Issue entitled: Accelerating Precision Medicine through Genetic and Genomic Big Data Analysis edited by Yudong Cai & Tao Huang.

Suppression of Tregs by anti-glucocorticoid induced TNF receptor antibody enhances the antitumor immunity of interferon-α gene therapy for pancreatic cancer

We have reported that interferon (IFN)-α can attack cancer cells by multiple antitumor mechanisms including the induction of direct cancer cell death and the enhancement of an immune response in several pancreatic cancer models. However, an immunotolerant microenvironment in the tumors is often responsible for the failure of the cancer immunotherapy. Here we examined whether the suppression of regulatory T cells (Tregs) within tumors can enhance an antitumor immunity induced by an intratumoral IFN-α gene transfer. First we showed that an intraperitoneal administration of an agonistic anti-glucocorticoid induced TNF receptor (GITR) monoclonal antibody (mAb), which is reported to suppress the function of Tregs, significantly inhibited subcutaneous tumor growth in a murine pancreatic cancer model. The anti-GITR mAb was then combined with the intratumoral injection of the IFN-α-adenovirus vector. The treatment with the antibody synergistically augmented the antitumor effect of IFN-α gene therapy not only in the vector-injected tumors but also in the vector-uninjected tumors. Immunostaining showed that the anti-GITR mAb decreased Foxp3⁺ cells infiltrating in the tumors, while the intratumoral IFN-α gene transfer increased CD4⁺ and CD8⁺ T cells in the tumors. Therefore, the combination therapy strongly inclined the immune balance of the tumor microenvironment in an antitumor direction, leading to a marked systemic antitumor effect. The CCR5 expression on Tregs was downregulated in the antibody-treated mice, which may explain the decrease of tumor-infiltrating Tregs. The combination of Treg-suppression by GITR mAb and the tumor immunity induction by IFN-α gene therapy could be a promising therapeutic strategy for pancreatic cancer.

Syngeneic hematopoietic stem cell transplantation enhances the antitumor immunity of intratumoral type I interferon gene transfer for sarcoma

Sarcoma at advanced stages remains a clinically challenging disease. Interferons (IFNs) can target cancer cells by multiple antitumor activities, including the induction of cancer cell death and enhancement of immune response. However, the development of an effective cancer immunotherapy is often difficult, because cancer generates an immunotolerant microenvironment against the host immune system. An autologous hematopoietic stem cell transplantation (HSCT) is expected to reconstitute a fresh immune system, and expand tumor-specific T cells through the process of homeostatic proliferation. Here we examined whether a combination of autologous HSCT and IFNs could induce an effective tumor-specific immune response against sarcoma. First, we found that a type I IFN gene transfer significantly suppressed the cell growth of various sarcoma cell lines, and that IFN-β gene transfer was more effective in inducing cell death than was IFN-α in sarcoma cells. Then, to examine the antitumor effect in vivo, human sarcoma cells were inoculated in immune-deficient mice, and a lipofection of an IFN-β-expressing plasmid was found to suppress the growth of subcutaneous tumors significantly. Finally, the IFN gene transfer was combined with syngeneic HSCT in murine osteosarcoma models. Intratumoral IFN-β gene transfer markedly suppressed the growth of vector-injected tumors and inhibited formation of spontaneous lung and liver metastases in syngeneic HSCT mice, and an infiltration of many immune cells was recognized in metastatic tumors of the treated mice. The treated mice showed no significant adverse events. A combination of intratumoral IFN gene transfer with autologous HSCT could be a promising therapeutic strategy for patients with sarcoma.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

In vivo delivery of interferon-α gene enhances tumor immunity and suppresses immunotolerance in reconstituted lymphopenic hosts

T cells recognize tumor-associated antigens under the condition of lymphopenia-induced homeostatic proliferation (HP); however, HP-driven antitumor responses gradually decay in association with tumor growth. Type I interferon (IFN) has important roles in regulating the innate and adaptive immune system. In this study we examined whether a tumor-specific immune response induced by IFN-α could enhance and sustain HP-induced antitumor immunity. An intratumoral IFN-α gene transfer resulted in marked tumor suppression when administered in the early period of syngeneic hematopoietic stem cell transplantation (synHSCT), and was evident even in distant tumors that were not transduced with the IFN-α vector. The intratumoral delivery of the IFN-α gene promoted the maturation of CD11c(+) cells in the tumors and effectively augmented the antigen-presentation capacity of the cells. An analysis of the cytokine profile showed that the CD11c(+) cells in the treated tumors secreted a large amount of immune-stimulatory cytokines including interleukin (IL)-6. The CD11c(+) cells rescued effector T-cell proliferation from regulatory T-cell-mediated suppression, and IL-6 may have a dominant role in this phenomenon. The intratumoral IFN-α gene transfer creates an environment strongly supporting the enhancement of antitumor immunity in reconstituted lymphopenic recipients through the induction of tumor-specific immunity and suppression of immunotolerance.

Administration route-dependent induction of antitumor immunity by interferon-alpha gene transfer

Type I interferon (IFN) protein is a cytokine with pleiotropic biological functions that include induction of apoptosis, inhibition of angiogenesis, and immunomodulation. We have demonstrated that intratumoral injection of an IFN-alpha-expressing adenovirus effectively induces cell death of cancer cells and elicits a systemic tumor-specific immunity in several animal models. On the other hand, reports demonstrated that an elevation of IFN in the serum following an intramuscular delivery of a vector is able to activate antitumor immunity. In this study, we compared the intratumoral and systemic routes of IFN gene transfer with regard to the effect and safety of the treatment. Intratumoral injection of an IFN-alpha adenovirus effectively activated tumor-responsive lymphocytes and caused tumor suppression not only in the gene-transduced tumors but also in distant tumors, which was more effective than the intravenous administration of the same vector. The expression of co-stimulatory molecules on CD11c(+) cells isolated from regional lymph nodes was enhanced by IFN gene transfer into the tumors. Systemic toxicity such as an elevation of hepatic enzymes was much lower in mice treated by intratumoral gene transfer than in those treated by systemic gene transfer. Our data suggest that the intratumoral route of the IFN vector is superior to intravenous administration, due to the effective induction of antitumor immunity and the lower toxicity.

Low molecular weight polyethylenimine cross-linked by 2-hydroxypropyl-gamma-cyclodextrin coupled to peptide targeting HER2 as a gene delivery vector

Gene delivery is one of the critical steps for gene therapy. Non-viral vectors have many advantages but suffered from low gene transfection efficiency. Here, in order to develop new polymeric gene vectors with low cytotoxicity and high gene transfection efficiency, we synthesized a cationic polymer composed of low molecular weight polyethylenimine (PEI) of molecular weight of 600 Da cross-linked by 2-hydroxypropyl-gamma-cyclodextrin (HP gamma-CD) and then coupled to MC-10 oligopeptide containing a sequence of Met-Ala-Arg-Ala-Lys-Glu. The oligopeptide can target to HER2, the human epidermal growth factor receptor 2, which is often over expressed in many breast and ovary cancers. The new gene vector was expected to be able to target delivery of genes to HER2 positive cancer cells for gene therapy. The new gene vector was composed of chemically bonded HP gamma-CD, PEI (600 Da), and MC-10 peptide at a molar ratio of 1:3.3:1.2. The gene vector could condense plasmid DNA at an N/P ratio of 6 or above. The particle size of HP gamma-CD-PEI-P/DNA complexes at N/P ratios 40 was around 170-200 nm, with zeta potential of about 20 mV. The gene vector showed very low cytotoxicity, strong targeting specificity to HER2 receptor, and high efficiency of delivering DNA to target cells in vitro and in vivo with the reporter genes. The delivery of therapeutic IFN-alpha gene mediated by the new gene vector and the therapeutic efficiency were also studied in mice animal model. The animal study results showed that the new gene vector HP gamma-CD-PEI-P significantly enhanced the anti-tumor effect on tumor-bearing nude mice as compared to PEI (25 kDa), HP gamma-CD-PEI, and other controls, indicating that this new polymeric gene vector is a potential candidate for cancer gene therapy.