Anu Wallecha

Construction and Characterization of an Attenuated Listeria monocytogenes Strain for Clinical Use in Cancer Immunotherapy

ABSTRACT Listeria monocytogenes has been exploited previously as a vaccine vector for the delivery of heterologous proteins such as tumor-specific antigens for active cancer immunotherapy. However, for effective use of live vector in clinics, safety is a major concern. In the present study, we describe an irreversibly attenuated and highly immunogenic L. monocytogenes platform, the L. monocytogenes dal-, dat-, and actA-deleted strain that expresses the human prostate-specific antigen (PSA) using an antibiotic resistance marker-free plasmid (the dal dat ΔactA 142 strain expressing PSA). Despite limited in vivo survival, the dal dat ΔactA 142 strain was able to elicit efficient immune responses required for tumor clearance. Our results showed that immunization of mice with the dal dat ΔactA 142 strain caused the regression of the tumors established by the prostate adenocarcinoma cell line expressing PSA. An evaluation of immunologic potency indicated that the dal dat ΔactA 142 strain elicits a high frequency of PSA-specific immune responses. Interestingly, immunization with the dal dat ΔactA 142 strain induced significant infiltration of PSA-specific T cells in the intratumoral milieu. Collectively, our data suggest that the dal dat ΔactA 142 strain is a safe and potent vector for clinical use and that this platform may be further exploited as a potential candidate to express other single or multiple antigens for cancer immunotherapy.

A Novel Human Her-2/neu Chimeric Molecule Expressed by Listeria monocytogenes Can Elicit Potent HLA-A2 Restricted CD8-positive T cell Responses and Impact the Growth and Spread of Her-2/neu-positive Breast Tumors

Purpose: 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. Experimental Design: 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). Results: 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. Conclusion: 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.

Phase Variation of Ag43 Is Independent of the Oxidation State of OxyR

OxyR is a DNA binding protein that differentially regulates a cells response to hydrogen peroxide-mediated oxidative stress. We previously reported that the reduced form of OxyR is sufficient for repression of transcription of agn43 from unmethylated template DNA, which is essential for deoxyadenosine methylase (Dam)- and OxyR-dependent phase variation of agn43. Here we provide evidence that the oxidized form of OxyR [OxyR(ox)] also represses agn43 transcription. In vivo, we found that exogenous addition of hydrogen peroxide, sufficient to oxidize OxyR, did not affect the expression of agn43. OxyR(ox) repressed in vitro transcription but only from an unmethylated agn43 template. The -10 sequence of the promoter and three Dam target sequences were protected in an in vitro DNase I footprint assay by OxyR(ox). Furthermore, OxyR(ox) bound to the agn43 regulatory region DNA with an affinity similar to that for the regulatory regions of katG and oxyS, which are activated by OxyR(ox), indicating that binding at agn43 can occur at biologically relevant concentrations. OxyR-dependent regulation of Ag43 expression is therefore unusual in firstly that OxyR binding at agn43 is dependent on the methylation state of Dam target sequences in its binding site and secondly that OxyR-dependent repression appears to be independent of hydrogen-peroxide mediated oxidative stress and the oxidation state of OxyR.

Lm-LLO-Based Immunotherapies and HPV-Associated Disease

HPV infection is a direct cause of neoplasia and malignancy. Cellular immunologic activity against cells expressing HPV E6 and E7 is sufficient to eliminate the presence of dysplastic or neoplastic tissue driven by HPV infection. Live attenuated Listeria monocytogenes- (Lm-) based immunotherapy (ADXS11-001) has been developed for the treatment of HPV-associated diseases. ADXS11-001 secretes an antigen-adjuvant fusion (Lm-LLO) protein consisting of a truncated fragment of the Lm protein listeriolysin O (LLO) fused to HPV-16 E7. In preclinical models, this construct has been found to stimulate immune responses and affect therapeutic outcome. ADXS11-001 is currently being evaluated in Phase 2 clinical trials for cervical intraepithelial neoplasia, cervical cancer, and HPV-positive head and neck cancer. The use of a live attenuated bacterium is a more complex and complete method of cancer immunotherapy, as over millennia Lm has evolved to infect humans and humans have evolved to prevent and reject this infection over millennia. This evolution has resulted in profound pathogen-associated immune mechanisms which are genetically conserved, highly efficacious, resistant to tolerance, and can be uniquely invoked using this novel platform technology.

Cancer immunotherapy using recombinant Listeria monocytogenes: transition from bench to clinic.

Cancer immunotherapy has developed into a field of intense study as aspects of the immune system involved in the eradication of cancer have become delineated. Listeria monocytogenes is a gram-positive, facultative intracellular bacterium which infects antigen presenting cells (APC), and is being used as a cancer vaccine to deliver tumor antigens directly to the APC. This results in the generation of a strong immune response towards the tumor associated antigen and direct targeting of the tumor by the immune system. Advances in this field have led to the development of a series of L. monocytogenes-based cancer vaccines, which are currently in clinical trials. A phase I study has shown these vaccines can be safely administered and well-tolerated in terminal stage cancer patients and an efficacy signal was observed in patients who did not respond to other therapies. Additional data on the efficacy of these vaccines is expected in the near-term.

Listeria monocytogenes (Lm)-LLO immunotherapies reduce the immunosuppressive activity of myeloid-derived suppressor cells and regulatory T cells in the tumor microenvironment.

Myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) are major components of the immune suppressive cells that potentially limit the effectiveness of an immunotherapy-based treatment. Both of these suppressive cell types have been shown to expand in tumor models and promote T-cell dysfunction that in turn favors tumor progression. This study demonstrates that Listeria monocytogenes (Lm)-LLO immunotherapies effect on the suppressive ability of MDSC and Treg in the tumor microenvironment (TME), resulting in a loss in the ability of these cells to suppress T cells. This alteration of immunosuppression in the TME was an inherent property of all Lm-LLO immunotherapies tested and was independent of the tumor model. The virtually total loss in the suppressive ability of these cells in the TME was linked to the reduction in the expression of arginase I in MDSC and IL-10 in Treg. The results presented here provide insight into a novel mechanism of Lm-LLO immunotherapies that potentially contributes to therapeutic antitumor responses.

Control of Gene Expression at a Bacterial Leader RNA, the agn43 Gene Encoding Outer Membrane Protein Ag43 of Escherichia coli

The family of agn alleles in Escherichia coli pathovars encodes autotransporters that have been implicated in biofilm formation, autoaggregation, and attachment to cells. The alleles all have long leader RNAs preceding the Ag43 translation initiation codon. Here we present an analysis of the agn43 leader RNA from E. coli K-12. We demonstrate the presence of a rho-independent transcription terminator just 28 bp upstream of the main translation start codon and show that it is functional in vitro. Our data indicate that an as-yet-unknown mechanism of antitermination of transcription must be operative in earlier phases of growth. However, as bacterial cell cultures mature, progressively fewer transcripts are able to bypass this terminator. In the K-12 leader sequence, two in-frame translation initiation codons have been identified, one upstream and the other downstream of the transcription terminator. For optimal agn43 expression, both codons need to be present. Translation from the upstream start codon leads to increased downstream agn43 expression. Our findings have revealed two novel modes of regulation of agn43 expression in the leader RNA in addition to the previously well-characterized regulation of phase variation at the agn43 promoter.

Abstract LB-229: Agonistic antibodies to costimulatory molecules, OX40 and GITR, significantly enhance the antitumor efficacy of Listeria monocytogenes (Lm-LLO)-based immunotherapy

Combinational anti-cancer immune therapies that target multiple tumor-mediated suppressive mechanisms or enhance effector immunity are emerging as promising strategies for cancer treatment. Recently, we demonstrated that the combination of Listeria monocytogenes (Lm-LLO)-based immunotherapy (ADXS11-001) and anti-PD-1 antibody results in improved anti-tumor therapeutic and immune efficacy. Interestingly, regardless of the presence of an antigen or treatment with anti-PD-1 antibody, treatment with the Lm-LLO alone significantly inhibited the suppressive arm of the immune system, including regulatory T cells and myeloid-derived suppressor cells. We therefore hypothesized that combination of ADXS11-001 with agonistic antibodies against co-stimulatory molecules will lead to further improvement of immune and therapeutic efficacy as a result of the combined down-regulation of the suppressive arm and the enhancement of the effector arm. Here we demonstrate that combining Lm-LLO-based immunotherapy with anti-OX40 or anti-GITR antibodies lead to significant inhibition of tumor growth and prolonged survival of animals. The complete regression of established TC-1 tumors occurs in 40% and 60% of animals treated with ADXS11-001 in combination with anti-OX40 and anti-GITR antibodies, respectively. We show that this therapeutic potency enhancement is due to a significant increase in antigen-specific immune responses along with ADXS11-001-mediated inhibition of suppressor cells. Thus, we believe that simultaneous stimulation of T cells while inhibiting the suppressor cells, specifically using Lm-LLO-based immunotherapy combination with agonistic anti-co-stimulatory molecule antibody is a feasible and translatable approach that can lead to overall enhancement of the efficacy of an anti-tumor immunotherapy. Citation Format: Mikayel Mkrtichyan, Rajeev Shrimali, Shamim Ahmad, Rasha Abu Eid, Zuzana Berrong, Anu Wallecha, Robert Petit, Samir N. Khleif. Agonistic antibodies to costimulatory molecules, OX40 and GITR, significantly enhance the antitumor efficacy of Listeria monocytogenes (Lm-LLO)-based immunotherapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-229. doi:10.1158/1538-7445.AM2015-LB-229