Pseudocowpox virus, a novel vector to enhance the therapeutic efficacy of antitumor vaccination.

Objective: Antitumor viral vaccines, and more particularly poxviral vaccines, represent an active field for clinical development and translational research. To improve the efficacy and treatment outcome, new viral vectors are sought, with emphasis on their abilities to stimulate innate immunity, to display tumor antigens and to induce a specific T-cell response. Methods: We screened for a new poxviral backbone with improved innate and adaptive immune stimulation using IFN-α secretion levels in infected PBMC cultures as selection criteria. Assessment of virus effectiveness was made in vitro and in vivo. Results: The bovine pseudocowpox virus (PCPV) stood out among several poxviruses for its ability to induce significant secretion of IFN-α. PCPV produced efficient activation of human monocytes and dendritic cells, degranulation of NK cells and reversed MDSC-induced T-cell suppression, without being offensive to activated T cells. A PCPV-based vaccine, encoding the HPV16 E7 protein (PCPV-E7), stimulated strong antigen-specific T-cell responses in TC1 tumor-bearing mice. Complete regression of tumors was obtained in a CD8+ T-cell-dependent manner after intratumoral injection of PCPV-E7, followed by intravenous injection of the cancer vaccine MVA-E7. PCPV also proved active when injected repeatedly intratumorally in MC38 tumor-bearing mice, generating tumor-specific T-cell responses without encoding a specific MC38 antigen. From a translational perspective, we demonstrated that PCPV-E7 effectively stimulated IFN-γ production by T cells from tumor-draining lymph nodes of HPV+-infected cancer patients. Conclusion: We propose PCPV as a viral vector suitable for vaccination in the field of personalised cancer vaccines, in particular for heterologous prime-boost regimens.

Oncolytic properties of non-vaccinia poxviruses.

Vaccinia virus, a member of the Poxviridae family, has been extensively used as an oncolytic agent and has entered late stage clinical development. In this study, we evaluated the potential oncolytic properties of other members of the Poxviridae family. Numerous tumor cell lines were infected with ten non-vaccinia poxviruses to identify which virus displayed the most potential as an oncolytic agent. Cell viability indicated that tumor cell lines were differentially susceptible to each virus. Raccoonpox virus was the most potent of the tested poxviruses and was highly effective in controlling cell growth in all tumor cell lines. To investigate further the oncolytic capacity of the Raccoonpox virus, we have generated a thymidine kinase (TK)-deleted recombinant Raccoonpox virus expressing the suicide gene FCU1. This TK-deleted Raccoonpox virus was notably attenuated in normal primary cells but replicated efficiently in numerous tumor cell lines. In human colon cancer xenograft model, a single intratumoral inoculation of the recombinant Raccoonpox virus, in combination with 5-fluorocytosine administration, produced relevant tumor growth control. The results demonstrated significant antitumoral activity of this new modified Raccoonpox virus armed with FCU1 and this virus could be considered to be included into the growing armamentarium of oncolytic virotherapy for cancer.

Viral based vaccine TG4010 induces broadening of specific immune response and improves outcome in advanced NSCLC.

BACKGROUND: Advanced non-small cell lung cancer patients receiving TG4010, a therapeutic viral vaccine encoding human Mucin 1 and interleukin-2 in addition to standard chemotherapy, displayed longer overall survival in comparison to that of patients treated with standard chemotherapy alone. Our study intended to establish the association between overall survival and vaccine-induced T cell responses against tumor associated antigens (TAA) targeted by the vaccine. METHOD: The TIME trial was a placebo-controlled, randomized phase II study aimed at assessing efficacy of TG4010 with chemotherapy in NSCLC. 78 patients from the TIME study carrying the HLA-A02*01 haplotype were analyzed using combinatorial encoding of MHC multimers to detect low frequencies of cellular immune responses to TG4010 and other unrelated TAA. RESULTS: We report that improvement of survival under TG4010 treatment correlated with development of T cell responses against MUC1. Interestingly, responses against MUC1 were associated with broadening of CD8 responses against non-targeted TAA, thus demonstrating induction of epitope spreading. CONCLUSION: Our results support the causality of specific T-cell response in improved survival in NSCLC. Additionally, vaccine induced epitope spreading to other TAA participates to the enrichment of the diversity of the anti-tumor response. Hence, TG4010 appears as a useful therapeutic option to maximize response rate and clinical benefit in association with other targeted immuno-modulators. TRIAL REGISTRATION: Registered on ClinicalTrials.gov under identifier NCT01383148 on June 23rd, 2011.

Cowpox Virus: A New and Armed Oncolytic Poxvirus.

Oncolytic virus therapy has recently been recognized as a promising new therapeutic approach for cancer treatment. In this study, we are proposing for the first time to evaluate the in vitro and in vivo oncolytic capacities of the Cowpox virus (CPXV). To improve the tumor selectivity and oncolytic activity, we developed a thymidine kinase (TK)-deleted CPXV expressing the suicide gene FCU1, which converts the non-toxic prodrug 5-fluorocytosine (5-FC) into cytotoxic 5-fluorouracil (5-FU) and 5-fluorouridine-5'-monophosphate (5-FUMP). This TK-deleted virus replicated efficiently in human tumor cell lines; however, it was notably attenuated in normal primary cells, thus displaying a good therapeutic index. Furthermore, this new recombinant poxvirus rendered cells sensitive to 5-FC. In vivo, after systemic injection in mice, the TK-deleted variant caused significantly less mortality than the wild-type strain. A biodistribution study demonstrated high tumor selectivity and low accumulation in normal tissues. In human xenograft models of solid tumors, the recombinant CPXV also displayed high replication, inducing relevant tumor growth inhibition. This anti-tumor effect was improved by 5-FC co-administration. These results demonstrated that CPXV is a promising oncolytic vector capable of expressing functional therapeutic transgenes.

Identification of new MUC1 epitopes using HLA-transgenic animals: implication for immunomonitoring.

BACKGROUND: The success of immunotherapeutics in oncology and the search for further improvements has prompted revisiting the use of cancer vaccines. In this context, knowledge of the immunogenic epitopes and the monitoring of the immune response cancer vaccines generate are essential. MUC1 has been considered one of the most important tumor associated antigen for decades. METHODS: To identify HLA-restricted MUC1 peptides we used eight human MHC class I transgenic mouse lines, together covering more than 80% of the human population. MUC1 peptides were identified by vaccinating each line with full length MUC1 coding sequences and using an IFNγ ELIspot restimulation assay. Relevant peptides were tested in a flow cytometry-based tetramer assay and for their capacity to serve as target in an in vivo killing assay. RESULTS: Four previously identified MUC1 peptides were confirmed and five are described here for the first time. These nine peptide-MHC combinations were further characterized. Six gave above-background tetramer staining of splenocytes from immunized animals and three peptides were induced more than 5% specific in vivo killing. CONCLUSIONS: These data describe for the first time five new HLA class I-restricted peptides and revisit some that were previously described. They also emphasize the importance of using in vivo/ex vivo models to screen for immunogenic peptides and define the functions for individual peptide-HLA combinations.

Yeast virus-derived stimulator of the innate immune system augments the efficacy of virus vector-based immunotherapy.

UNLABELLED: To identify novel stimulators of the innate immune system, we constructed a panel of eight HEK293 cell lines double positive for human Toll-like receptors (TLRs) and an NF-κB-inducible reporter gene. Screening of a large variety of compounds and cellular extracts detected a TLR3-activating compound in a microsomal yeast extract. Fractionation of this extract identified an RNA molecule of 4.6 kb, named nucleic acid band 2 (NAB2), that was sufficient to confer the activation of TLR3. Digests with single- and double-strand-specific RNases showed the double-strand nature of this RNA, and its sequence was found to be identical to that of the genome of the double-stranded RNA (dsRNA) L-BC virus of Saccharomyces cerevisiae. A large-scale process of production and purification of this RNA was established on the basis of chemical cell lysis and dsRNA-specific chromatography. NAB2 complexed with the cationic lipid Lipofectin but neither NAB2 nor Lipofectin alone induced the secretion of interleukin-12(p70) [IL-12(p70)], alpha interferon, gamma interferon-induced protein 10, macrophage inflammatory protein 1ß, or IL-6 in human monocyte-derived dendritic cells. While NAB2 activated TLR3, Lipofectin-stabilized NAB2 also signaled via the cytoplasmic sensor for RNA recognition MDA-5. A significant increase of RMA-MUC1 tumor rejection and survival was observed in C57BL/6 mice after prophylactic vaccination with MUC1-encoding modified vaccinia virus Ankara (MVA) and NAB2-Lipofectin. This combination of immunotherapies strongly increased at the injection sites the percentage of infiltrating natural killer (NK) cells and plasmacytoid dendritic cells (pDCs), cell types which can modulate innate and adaptive immune responses. IMPORTANCE: Virus-based cancer vaccines offer a good alternative to the treatment of cancer but could be improved. Starting from a screening approach, we have identified and characterized an unexplored biological molecule with immunomodulatory characteristics which augments the efficacy of an MVA-based immunotherapeutic agent. The immune modulator consists of the purified dsRNA genome isolated from a commercially used yeast strain, NAB2, mixed with a cationic lipid, Lipofectin. NAB2-Lipofectin stimulates the immune system via TLR3 and MDA-5. When it was injected at the MVA vaccination site, the immune modulator increased survival in a preclinical tumor model. We could demonstrate that NAB2-Lipofectin augments the MVA-induced infiltration of natural killer and plasmacytoid dendritic cells. We suggest indirect mechanisms of activation of these cell types by the influence of NAB2-Lipofectin on innate and adaptive immunity. Detailed analysis of cell migration at the vaccine injection site and the appropriate choice of an immune modulator should be considered to achieve the rational improvement of virus vector-based vaccination by immune modulators.