B1 lymphocytes and myeloid dendritic cells in lymphoid organs are preferential extratumoral sites of parvovirus minute virus of mice prototype strain expression

Parvoviruses-tools to fine-tune anticancer immune responses

Oncolytic virotherapy represents a recent approach to anticancer therapy. Rodent autonomous parvoviruses (PVs) represent naturally oncolytic viruses that are non-pathogenic for humans but possess and extended tropism, being capable of infecting transformed cells of both rodent and human origin. Recent work from our group demonstrate that PVs can act as direct lytic agents and adjuvants, stimulating antitumor immune responses against glioma and pancreatic ductal adenocarcinoma (PDAC).

Immune System Stimulation by Oncolytic Rodent Protoparvoviruses

Rodent protoparvoviruses (PVs), parvovirus H-1 (H-1PV) in particular, are naturally endowed with oncolytic properties. While being historically described as agents that selectively replicate in and kill cancer cells, recent yet growing evidence demonstrates that these viruses are able to reverse tumor-driven immune suppression through induction of immunogenic tumor cell death, and the establishment of antitumorigenic, proinflammatory milieu within the tumor microenvironment. This review summarizes the most important preclinical proofs of the interplay and the cooperation between PVs and the host immune system. The molecular mechanisms of PV-induced immunostimulation are also discussed. Furthermore, initial encouraging in-human observations from clinical trials and compassionate virus uses are presented, and speak in favor of further H-1PV clinical development as partner drug in combined immunotherapeutic protocols.

Distinct host cell fates for human malignant melanoma targeted by oncolytic rodent parvoviruses

The rodent parvoviruses are known to be oncoselective, and lytically infect many transformed human cells. Because current therapeutic regimens for metastatic melanoma have low response rates and have little effect on improving survival, this disease is a prime candidate for novel approaches to therapy, including oncolytic parvoviruses. Screening of low-passage, patient-derived melanoma cell lines for multiplicity-dependent killing by a panel of five rodent parvoviruses identified LuIII as the most melanoma-lytic. This property was mapped to the LuIII capsid gene, and an efficiently melanoma tropic chimeric virus shown to undergo three types of interaction with primary human melanoma cells: (1) complete lysis of cultures infected at very low multiplicities; (2) acute killing resulting from viral protein synthesis and DNA replication, without concomitant expansion of the infection, due to failure to export progeny virions efficiently; or (3) complete resistance that operates at an intracellular step following virion uptake, but preceding viral transcription.

Toll-like receptor 9 in plasmacytoid dendritic cells fails to detect parvoviruses

Toll-like receptor 9 (TLR9) recognizes genomes of double-stranded DNA (dsDNA) viruses in the endosome to stimulate plasmacytoid dendritic cells (pDCs). However, how and if viruses with single-stranded DNA (ssDNA) genomes are detected by pDCs remain unclear. Here we have shown that despite the ability of purified genomic DNA to stimulate TLR9 and despite the ability to enter TLR9 endosomes, ssDNA viruses of the Parvoviridae family failed to elicit an interferon (IFN) response in pDCs.

"Up-dating the monograph." [corrected] Cytolytic immune lymphocytes in the armamentarium of the human host

The author of the monograph "Cytolytic Immune Lymphocytes..." (published in 2008 by Schenk Buchverlag Campus Dialog, Budapest, Passau, Pécs) proposed several research projects and described certain clinical events that require further elaboration and documentation. In this article the author provides what is required and has since become available. The first subject matter in question concerns the fusogenic viruses. The ancient fusogenic viruses might have created the first eukaryotic cell(s) by uniting archaeabacterial and prokaryotic/protobacterial protospheroplasts. Extant fusogenic viruses either produce tumor cell syncytia and lyse them, thus practicing viral oncolysis. Or, create chimaeric fusion products, the so-called "natural hybridomas", of lymphoma cells exhibiting transmembrane budding of retrovirus particles or envelope proteins, and anti-viral specific antibody-producing plasma cells. The second topic concerns the horizontal-lateral mode of acquisition of those genes, which were "present in the waiting" in the amphioxus, sea urchin, and the agnathans, and met in the primitive gnatostomata sharks to encode in unison the entire adaptive immune system. The consensus of opinion is such that these genes derived from newly acquired transposons/retrotransposons. The author points out that the extant Epstein-Barr virus harbors genes displaying sequence homology with those genes from the sharks up to mammals that regulate the somatic hypermutation of specific antibody production. The author proposes that an ancient herpesvirus might have propagated the V(D)J and RAG genes from sea urchins to sharks. The third area is that of lymphocytes cytotoxic/cytolytic to virally infected or malignantly transformed host cells. This discovery led to the adoptive immune lymphocyte therapy of tumors. Installed in the adaptive immune system are regulatory T cells and myeloid-derived suppressor cells for he protection of "self". Tumor cells masquerading as "self" are protected by these cells from attacks launched by immune T cells. The author supports the replacement of IL-2 by IL-15, inasmuch as IL-2 stimulates not only immune T cells, but also regulatory T cells expressing the CD25 IL-2 receptor. The administration of low dose whole body radiotherapy prior to immune lymphocyte therapy increases the efficacy of immune lymphocyte therapy. The author observed this phenomenon in the mid-1960s. The explanation of this phenomenon revealed itself just recently. In pre-irradiated hosts the intestinal wall becomes permeable to the gut flora; the intestinal bacteria activate the entire innate immune system in the mesenteric lymph nodes and a rapid activation of the adaptive immune faculties follows.

Induction of an antitumoral immune response by wild-type adeno-associated virus type 2 in an in vivo model of pancreatic carcinoma

We analyzed the immunologic impact of adeno-associated virus type 2 (AAV-2), a small single-stranded parvovirus with tumorsuppressive properties, on DSL6A pancreatic carcinoma in syngeneic rats. Established tumors of animals treated with AAV-2 or mock infected were resected (Ro), and DSL6A cells were rechallenged on the different site. Eleven (92%) of 12 mock-infected animals but only 3 (25%) of 12 AAV-2-treated animals redeveloped tumors. Adeno-associated virus type 2 infection provoked systemic raises in monocytes and neutrophils numbers and in levels of the proinflammatory monocyte chemoattractant protein 1 and interleukin 10. Adeno-associated virus type 2-treated tumors were infiltrated with monocytes, macrophages, natural killer cells, CD4+ T cells, and especially CD8+ T cells. In cytotoxicity assays, AAV-2-infected DSL6A tumor cells were recognized by lymphocytes from AAV-2-treated animals and from controls. Yet, uninfected DSL6A cells were exclusively killed by lymphocytes from AAV-2-treated animals. Additionally, those lymphocytes displayed high natural killer cell activity but failed to attack unrelated tumor targets. Taken together, these results suggest that the antiviral response toward AAV-2 cross-activates the immune system toward simultaneously present tumor disease. This and the known potential to significantly reduce toxic side effects of chemotherapy make nonpathogenic viruses such as AAV-2 as "1-agent combination therapy" to an interesting treatment option of residual tumor disease.

Humoral immune responses against minute virus of mice vectors

BACKGROUND

Owing to their oncolytic properties, autonomous rodent parvoviruses and derived vectors constitute potential anti-tumor agents.

METHODS

Humoral immune responses to minute virus of mice (MVMp) were characterized. In particular, the generation of neutralizing antibodies on subsequent therapeutic virus applications was evaluated in a mouse melanoma model. Mice bearing subcutaneous melanomas were injected intratumorally with virus and re-injected 10 days later in a second tumor on the other flank. Four days after the first or second injection, the tumors and lymph nodes were analyzed by RT-PCR for gene expression.

RESULTS

Injection of MVMp in tumor-bearing B6 mice resulted in viral gene expression in tumors and draining lymph nodes. A repeated virus administration did not lead to detectable viral transcription if it was preceded by a virus infection 10 days earlier. This protection correlated with the induction of virus-neutralizing antibodies following the first virus application. The restrictions on viral gene expression after a consecutive MVMp injection could be alleviated in subsequent applications by the use of viruses consisting of MVMp genomes packaged into capsids of a related parvovirus. Neutralizing antibody induction was irrespective of the route of administration and of the presence of a tumor and persisted at significant levels at least up to 26 weeks after the viral infection. MVMp infection of B6 mice stimulated the generation of IgM and IgG anti-viral antibodies, the latter mainly of the T-helper (Th) 1-dependent IgG2, and the T-cell-independent IgG3 subclasses.

CONCLUSIONS

Neutralizing antibodies impede the effectiveness of a subsequent virus administration, but can be overcome by pseudotyping.