The promise of tumor immunotherapy to significantly improve survival in patients who are refractory to long-standing therapies, such as chemotherapy and radiation, is now being realized. While immune ...checkpoint inhibitors that target PD-1 and CTLA-4 are leading the charge in clinical efficacy, there are a number of other promising tumor immunotherapies in advanced development such as
-based vaccines. Due to its unique life cycle and ability to induce robust CTL responses, attenuated strains of
(
) have been utilized as vaccine vectors targeting both infectious disease and cancer. In fact, preclinical studies in a multitude of cancer types have found
-based vaccines to be highly effective at activating anti-tumor immunity and eradicating tumors. Several clinical trials have now recently reported their results, demonstrating promising efficacy against some cancers, and unique challenges. Development of the
-based immunotherapies continues with discovery of improved methods of attenuation, novel uses, and more effective combinatorial regimens. In this review, we provide a brief background of
as a vaccine vector, discuss recent clinical experience with
-based immunotherapies, and detail the advancements in development of improved
-based vaccine platforms and in their utilization.
Most cancer vaccines induce CTL responses to tumor-associated antigens (TAA). Killing of tumor cells occurs through TAA-specific CTL-mediated cytolysis. Here, we show that one preventive followed by ...two therapeutic immunizations with an attenuated Listeria monocytogenes (LM)-based vaccine eradicates all metastases and almost the entire primary tumor in the syngeneic, aggressive mouse breast tumor model 4T1. We provide strong evidence that this is due to the combined result of direct kill by Listeria infecting the tumor cells and by CTL responses against Listeria antigens. We showed by electron microscopy that LM expressing truncated listeriolysin O (LLO) and amino acid fragments 311 to 660 of TAA Mage-b (LM-LLO-Mage-b(311-660)) and the control strain LM-LLO infect tumor cells in vitro and in vivo. In vitro data indicate that tumor cell death occurs through activation of NADP(+) oxidase and increased intracellular Ca(2+) levels, both resulting in the production of high ROS levels. Because both LM-LLO and LM-LLO-Mage-b(311-660) showed equally strong efficacies in vivo, we concluded that LM-LLO was crucial and Mage-b was of less importance. We found strong CTL responses to LM-LLO in the spleen, and depletion of CD8 T cells in vivo resulted in significant tumor regrowth (52%) in LM-LLO-vaccinated mice, indicating that LM-LLO-specific CTL indeed partially contributed to tumor cell kill in vivo. This dual mode of action of a Listeria-based vaccine has not been described before and may provide new directions in the development of more effective vaccines against metastatic breast cancer.
Genetically encoded antibiotic peptides are evolutionarily ancient and widespread effector molecules of immune defence. Mammalian defensins, one subset of such peptides, have been implicated in the ...antimicrobial defence capacity of phagocytic leukocytes and various epithelial cells, but direct evidence of the magnitude of their in vivo effects have not been clearly demonstrated. Paneth cells, specialized epithelia of the small intestinal crypt, secrete abundant α-defensins and other antimicrobial polypeptides including human defensin 5 (HD-5; also known as DEFA5). Although antibiotic activity of HD-5 has been demonstrated in vitro, functional studies of HD-5 biology have been limited by the lack of in vivo models. To study the in vivo role of HD-5, we developed a transgenic mouse model using a 2.9-kilobase HD-5 minigene containing two HD-5 exons and 1.4 kilobases of 5′-flanking sequence. Here we show that HD-5 expression in these mice is specific to Paneth cells and reflects endogenous enteric defensin gene expression. The storage and processing of transgenic HD-5 also matches that observed in humans. HD-5 transgenic mice were markedly resistant to oral challenge with virulent Salmonella typhimurium. These findings provide support for a critical in vivo role of epithelial-derived defensins in mammalian host defence.
The high molecular weight melanoma-associated antigen (HMW-MAA), also known as melanoma chondroitin sulfate proteoglycan, has been used as a target for the immunotherapy of melanoma. This antigen is ...expressed on the cell surface and has a restricted distribution in normal tissues. Besides its expression in a broad range of transformed cells, this antigen is also found in pericytes, which are important for tumor angiogenesis. We generated a recombinant Listeria monocytogenes (Lm-LLO-HMW-MAA-C) that expresses and secretes a fragment of HMW-MAA (residues 2,160-2,258) fused to the first 441 residues of the listeriolysin O (LLO) protein. Immunization with Lm-LLO-HMW-MAA-C was able to impede the tumor growth of early established B16F10-HMW-MAA tumors in mice and both CD4(+) and CD8(+) T cells were required for therapeutic efficacy. Immune responses to a known HLA-A2 epitope present in the HMW-MAA(2160-2258) fragment was detected in the HLA-A2/K(b) transgenic mice immunized with Lm-LLO-HMW-MAA-C. Surprisingly, this vaccine also significantly impaired the in vivo growth of other tumorigenic cell lines, such as melanoma, renal carcinoma, and breast tumors, which were not engineered to express HMW-MAA. One hypothesis is that the vaccine could be targeting pericytes, which are important for tumor angiogenesis. In a breast tumor model, immunization with Lm-LLO-HMW-MAA-C caused CD8(+) T-cell infiltration in the tumor stroma and a significant decrease in the number of pericytes in the tumor blood vessels. In conclusion, a Lm-based vaccine against HMW-MAA can trigger cell-mediated immune responses to this antigen that can target not only tumor cells but also pericytes in the tumor vasculature.
Five overlapping fragments of rat HER-2/neu have been expressed in recombinant Listeria monocytogenes. Each fragment of HER-2/neu is secreted as a fusion protein with a truncated, nonhemolytic form ...of listeriolysin O (LLO). Lm-LLO-EC1, Lm-LLO-EC2, and Lm-LLO-EC3 overlap the extracellular domain of HER-2/neu, whereas Lm-LLO-IC1 and Lm-LLO-IC2 span the intracellular domain. All five strains controlled the growth of established NT-2 tumors, a rat HER-2/neu-expressing tumor line derived from a spontaneously arising mammary tumor in a FVB/N HER-2/neu-transgenic mouse. The antitumor effect of each of these vaccine constructs was abrogated by the in vivo depletion of CD8(+) T cells, although only one known epitope has been defined previously and is present in Lm-LLO-EC2. Anti-HER-2/neu CTL responses were generated by each of the rLm vaccine constructs. With the use of a panel of 3T3 cell lines expressing overlapping fragments of HER-2/neu, regions of HER-2/neu with potential CD8(+) T cell epitopes have been defined. DNA vaccines expressing either a fragment or full-length HER-2/neu were constructed in LLO-fused and non-LLO-fused forms. CTL analysis of the DNA vaccines revealed a broadening in the regions of HER-2/neu recognizable as targets when the target Ag is fused to LLO. These studies show the efficacy of L. monocytogenes-based HER-2/neu vaccines in a murine model of breast cancer and also that the immunogenicity of self-Ags can be increased by fusion to LLO and delivery by L. monocytogenes revealing subdominant epitopes.
Because of its cytosolic localization, Listeria monocytogenes (LM) has long been considered an attractive tool for delivering tumor-associated antigens (TAA) antigens in vivoto combat cancer. LM ...directly infects antigen-presenting cells (APC) such as monocytes, macrophages and dendritic cells (DC), thereby delivering the TAA into their cytoplasm, resulting in processing, and presentation of the antigen to the immune system. This activates adaptive and innate immune responses to the TAA, mediating tumor cell cytolysis. Recently we discovered additional pathways by which Listeria can be harnessedto induce tumor cell death, which suggest new directions in the development of vaccines or therapies against cancer. In one approach, we have used Listeria to induce immune responses that destroy tumor vasculature. Another new pathway involves selective infection of cancer cells with Listeria, followed by tumor cell death through the production of high levels of reactive oxygen species (ROS) and through Listeria-specific cytotoxic T lymphocytes (CTL). This review will focus on the most recent studies on the multiple pathways of LM and how they can be harnessed in the battle against cancer.
Interleukin 17 (IL-17) is produced during infection with Listeria monocytogenes and is also an important regulator of tumor development with both pro- and anti-tumorigenic effects. αβ T cells and γδ ...T cells are among the principle producers of IL-17 in response to infection and other proinflammatory conditions. Listeria-based cancer immunotherapies induce IFNγ directed Th1 dependent tumor regression; however, the role of IL-17 in Listeria based immunotherapy has not been addressed. Therefore, we investigated the ability of attenuated Listeria-based immunotherapy to induce IL-17 producing cells in a model of cervical cancer and the potential impact that these cells have on anti-tumor vaccine efficacy. Here we show that vaccination of tumor bearing mice with Listeria vaccines resulted in elevated levels of intratumoral IL-17 and increased IL-17 production by γδ TCR
+
cells, exclusively. IL-17 producing cells were lacking in tumors of γδ T-cell-deficient mice; however, the absence of γδ T cells, including IL-17
+
γδ T cells, did not alter tumor progression or abrogate the efficacy of the Listeria-based vaccine indicating that αβ T cells are key for clearance of the tumor. Th1 responses, known to be responsible for anti-tumor Listeria-based vaccine efficacy, appear to be sufficient for tumor regression in γδ T-cell-deficient mice. We conclude that the efficacy of Listeria-based vaccine does not rely on γδ T cells (or IL-17 produced by them) in a TC.1 tumor model; however, Listeria-based immunotherapy can be used to induce IL-17
+
γδ T cells that are important for regression observed in alternative cancer models.
The aim of this study was to efficiently design a novel vaccine for human Her-2/neu-positive (hHer-2/neu) breast cancer using the live, attenuated bacterial vector Listeria monocytogenes.
Three ...recombinant L. monocytogenes-based vaccines were generated that could express and secrete extracellular and intracellular fragments of the hHer-2/neu protein. In addition, we generated a fourth construct fusing selected portions of each individual fragment that contained most of the human leukocyte antigen (HLA) epitopes as a combination vaccine (L. monocytogenes-hHer-2/neu chimera).
Each individual vaccine was able to either fully regress or slow tumor growth in a mouse model for Her-2/neu-positive tumors. All three vaccines could elicit immune responses directed toward human leukocyte antigen-A2 epitopes of hHer-2/neu. The L. monocytogenes-hHer-2/neu chimera was able to mimic responses generated by the three separate vaccines and prevent spontaneous outgrowth of tumors in an autochthonous model for Her-2/neu-positive breast cancer, induce tumor regression in transplantable models, and prevent seeding of experimental lung metastases in a murine model for metastatic breast cancer.
This novel L. monocytogenes-hHer-2/neu chimera vaccine proves to be just as effective as the individual vaccines but combines the strength of all three in a single vaccination. These encouraging results support future clinical trials using this chimera vaccine and may be applicable to other cancer types expressing the Her-2/neu molecule such as colorectal and pancreatic cancer.
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