Intra-and Intergenerational Persistence of an Insect Nucleopolyhedrovirus: Adverse Effects of Sublethal Disease on Host Development, Reproduction, and Susceptibility to Superinfection ᰔ

Sublethal infections by qPCR analysis indicated a consistently higher prevalence of sublethal infection than RT-PCR. Sublethal infection was associated with significant reductions in pupal weight, adult emergence, fecundity, and fertility (egg hatch) and significant increases in larval development time and duration of the preoviposition period. Insects taken from a persistently infected experimental population were significantly more susceptible to the OB inoculum than control insects that originated from the same virus-free colony as the persistently infected insects. We conclude that OB treatment results in rapid establishment of sublethal infections that persist between generations and which incur costs in the development and reproductive capacity of the host insect

Potentiation of therapeutic immune responses against malignancies with monoclonal antibodies

Immunotherapeutic monoclonal antibodies (mAbs) can be defined as those that exert their functions by tampering with immune system cell molecules, causing an enhancement of antitumor immune responses. Some of these antibodies are agonistic ligands for surface receptors involved in the activation of lymphocytes and/or antigen-presenting cells, whereas others are antagonists of mechanisms that normally limit the intensity of immune reactions. Several mAbs of this category have been described to display in vivo antitumor activity in mouse models. Only anti–CTLA-4 (CD152) mAb has entered clinical trials, but the preclinical effects described for anti- CD40, anti-CD137 (4-1BB), anti-CD102 (intercellular adhesion molecule-2), and regulatory T cell-depleting mAbs should lead to their prompt clinical development. Their use in combination with immunizations against tumor antigens has been reported to be endowed with synergistic properties. This new group of antitumor agents holds promise for at least additive effects with conventional therapies of cancer and deserves intensive translational research

The immunotherapy potential of agonistic anti-CD137 (4-1BB) monoclonal antibodies for malignancies and chronic viral diseases

Pharmacological intervention on the immune system to achieve more intense lymphocyte responses has potential application in tumour immunology and in the treatment of chronic viral diseases. Immunostimulating monoclonal antibodies are defined as a new family of drugs that augment cellular immune responses. They interact as artificial ligands with functional proteins of the immune system, either activating or inhibiting their functions. There are humanized monoclonal antibodies directed to the inhibitory receptor CD152 (CTLA-4) that are being tested in clinical trials with evidence of antitumoural activity. As a drawback, anti-CTLA-4 monoclonal antibodies induce severe autoimmunity reactions in a fraction of the patients. Anti-CD137 monoclonal antibodies have the ability to induce potent immune responses mainly mediated by cytotoxic lymphocytes with the result of frequent complete tumour eradications in mice. Comparative studies in experimental models indicate that the antitumour activity of anti-CD137 monoclonal antibodies is superior to that of anti-CD152. CD137 (4-1BB) is a leukocyte differentiation antigen selectively expressed on the surface of activated T and NK lymphocytes, as well as on dendritic cells. Monoclonal antibodies acting as artificial stimulatory ligands of this receptor (anti-CD137 agonist antibodies) enhance cellular antitumoural and antiviral immunity in a variety of mouse models. Paradoxically, anti-CD137 monoclonal antibodies are therapeutic or preventive in the course of model autoimmune diseases in mice. In light of these experimental results, a number of research groups have humanized antibodies against human CD137 and early clinical trials are about to start

Low surface expression of B7-1 (CD80) is an immunoescape mechanism of colon carcinoma

Artificially enforced expression of CD80 (B7-1) and CD86 (B7-2) on tumor cells renders them more immunogenic by triggering the CD28 receptor on T cells. The enigma is that such B7s interact with much higher affinity with CTLA-4 (CD152), an inhibitory receptor expressed by activated T cells. We show that unmutated CD80 is spontaneously expressed at low levels by mouse colon carcinoma cell lines and other transplantable tumor cell lines of various tissue origins. Silencing of CD80 by interfering RNA led to loss of tumorigenicity of CT26 colon carcinoma in immunocompetent mice, but not in immunodeficient Rag-/- mice. CT26 tumor cells bind CTLA-4Ig, but much more faintly with a similar CD28Ig chimeric protein, thus providing an explanation for the dominant inhibitory effects on tumor immunity displayed by CD80 at that expression level. Interestingly, CD80-negative tumor cell lines such as MC38 colon carcinoma and B16 melanoma express CD80 at dim levels during in vivo growth in syngeneic mice. Therefore, low CD80 surface expression seems to give an advantage to cancer cells against the immune system. Our findings are similar with the inhibitory role described for the dim CD80 expression on immature dendritic cells, providing an explanation for the low levels of CD80 expression described in various human malignancies

Dendritic cells delivered inside human carcinomas are sequestered by interleukin-8

In the course of a clinical trial consisting of intratumoral injections of dendritic cells (DCs) transfected to produce interleukin-12, the use of (111)In-labeled tracing doses of DCs showed that most DCs remained inside tumor tissue, instead of migrating out. In search for factors that could explain this retention, it was found that tumors from patients suffering hepatocellular carcinoma, colorectal or pancreatic cancer were producing IL-8 and that this chemokine attracted monocyte-derived dendritic cells that uniformly express both IL-8 receptors CXCR1 and CXCR2. Accordingly, neutralizing antihuman IL-8 monoclonal antibodies blocked the chemotactic attraction of DCs by recombinant IL-8, as well as by the serum of the patients or culture supernatants of human colorectal carcinomas. In addition, tissue culture supernatants of colon carcinoma cells inhibited DC migration induced by MIP-3beta in an IL-8-dependent fashion. IL-8 production in malignant tissue and the responsiveness of DCs to IL-8 are a likely explanation of the clinical images, which suggest retention of DCs inside human malignant lesions. Impairment of DC migration toward lymphoid tissue could be involved in cancer immune evasion

Recombinant adenoviral vectors turn on the type I interferon system without inhibition of transgene expression and viral replication

Recombinant adenovirus administration gives rise to transgene-independent effects caused by the ability of the vector to activate innate immunity mechanisms. We show that recombinant adenoviruses encoding reporter genes trigger IFN-alpha and IFN-beta transcription from both plasmacytoid and myeloid mouse dendritic cells. Interestingly, IFN-beta and IFN-alpha5 are the predominant transcribed type I IFN genes both in vitro and in vivo. In human peripheral blood leukocytes type I IFNs are induced by adenoviral vectors, with a preponderance of IFN-beta together with IFN-alpha1 and IFN-alpha5 subtypes. Accordingly, functional type I IFN is readily detected in serum samples from human cancer patients who have been treated intratumorally with a recombinant adenovirus encoding thymidine kinase. Despite inducing functional IFN-alpha release in both mice and humans, gene transfer by recombinant adenoviruses is not interfered with by type I IFNs either in vitro or in vivo. Moreover, IFN-alpha does not impair replication of wild-type adenovirus. As a consequence, cancer gene therapy strategies with defective or replicative-competent adenoviruses are not expected to be hampered by the effect of the type I IFNs induced by the vector itself. However, type I IFN might modulate antitumor and antiadenoviral immune responses and thus influence the outcome of gene immunotherapy

Transmission strategy is correlated with pathogenicity and disparate virulence and productivity traits in an insect nucleopolyhedrovirus

Trabajo presentado en la 43rd Annual Meeting of the Society for Invertebrate Pathology y 10th International Colloquium on Invertebrate Pathology, celebrado en Trabzon (Turquía) del 11 al 15 de julio de 2010. The Final Meeting of COST862 Action: Bacterial Toxins for Insect Control.The prevalence of sublethal infections of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) was quantified in natural populations of S. exigua in Almeria, Spain, during 2006 and 2007. Of 1045 adults collected, 16% proved positive for viral polyhedrin gene transcripts by RT-PCR. The prevalence of covert infection varied significantly according to sex and sample date. Of 1660 progeny of field-collected insects, lethal disease was observed in 10-33% of offspring of transcript-positive females and 9-49% of offspring of transcript-negative females. Isolates associated with vertically-transmitted infections were characterized by restriction endonuclease analysis using BglII and compared with isolates believed to be horizontally-transmitted. Insects from a sublethally-infected Almerian colony were ~3.4-fold more susceptible to infection than healthy insects from a Swiss colony. Horizontally-transmitted isolates were significantly more pathogenic than vertically-transmitted isolates in insects from both colonies. Mean speed of kill varied between isolates by >20 h, whereas mean occlusion body (OB) production varied by 3.8-fold among isolates. Intriguingly, all three horizontally transmitted isolates were very similar in speed of kill and OB production, whereas all three vertically transmitted isolates differed significantly from one another in both variables, and also differed significantly from the group of horizontally-transmitted isolates in one or both variables. We conclude that key pathogenicity and virulence traits of SeMNPV isolates vary according to their principal transmission strategy.Peer Reviewe

Do persistent NPV infections in Spodoptera exigua affect host fitness?

Trabajo presentado en la 43rd Annual Meeting of the Society for Invertebrate Pathology y 10th International Colloquium on Invertebrate Pathology, celebrado en Trabzon (Turquía) del 11 al 15 de julio de 2010. The Final Meeting of COST862 Action: Bacterial Toxins for Insect Control.Vertical transmission of covert NPV infections is a common phenomenon in field populations of the beet armyworm (Spodoptera exigua, Huber) in the horticultural region of Almería (Spain). The genotypic diversity of the Spodoptera exigua nucleopolyhedrovirus population in this region has proved to be extremely high. A recent study suggests that some of these genotypic variants are involved in vertically-transmitted infections whereas other genotypes are involed in horizontally-transmitted infections. These findings led us to examine whether host-pathogen interactions are associated with a range of fitness correlates or tradeoffs in either the insect or the virus. First, we demonstrated that S. exigua adults that survived a virus challenge (9 x 103 OB/ml) presented a persistent sublethal infection detected by RT-PCR (85 - 100% of insects were positive for viral transcripts of the DNA-polymerase gene) following inoculation by vertically transmitted genotypes. A vertically transmitted genotype was then selected to examine the effects of larval age at inoculation and the dose of virus ingested on the prevalence of persistent virus infections in adults. Larvae of four different larval instars (L2, L3, L4, and L5) were dosed with four different concentrations that resulted in 20 to 80% of NPV-mortality. A similar trend was observed for each larval stage, the higher the dose of inoculum, the higher the proportion of adults that proved positive for viral transcripts. Finally, we observed that persistent infections reduce the fitness of individuals which survive the infection in terms of host developmental parameters (larval developmental time, pupal weight, adult fecundity, fertility, and longevity) in an insect colony in which a persistent infection had been induced compared to mocked-infected insects. On-going experiments are being performed to examine the biological costs of harbouring covert infections.Peer Reviewe

Occlusion body pathogenicity, virulence and productivity traits vary with transmission strategy in a nucleopolyhedrovirus

9 p., 4 figures, 1 table and referencesThe prevalence of sublethal infections of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) was quantified in natural populations of S. exigua in Almería, Spain, during 2006 and 2007. Of 1045 adults collected, 167 (16.1%) proved positive for viral polyhedrin gene transcripts by RT-PCR. The prevalence of covert infection varied significantly according to sex and sample date. Of 1660 progeny of field-collected insects, lethal disease was observed in 10–33% of offspring of transcript-positive females and 9–49% of offspring of transcript-negative females. Isolates associated with vertically transmitted infections were characterized by restriction endonuclease analysis using BglII or EcoRV and compared with isolates originating from greenhouse soil-substrate believed to be horizontally transmitted. Insects from a sublethally infected Almerian colony were between 2.3-fold and 4.6-fold more susceptible to infection than healthy insects from a Swiss colony, depending on isolate. Horizontally transmitted isolates were significantly more pathogenic than vertically transmitted isolates in insects from both colonies. Mean speed of kill in second instars (Swiss colony) varied between isolates by >20 h, whereas mean occlusion body (OB) production in fourth instars (Swiss colony) varied by 3.8-fold among isolates. Intriguingly, all three horizontally transmitted isolates were very similar in speed of kill and OB production, whereas all three vertically transmitted isolates differed significantly from one another in both variables, and also differed significantly from the group of horizontally transmitted isolates in speed of kill (one isolate) or both variables (two isolates). We conclude that key pathogenicity and virulence traits of SeMNPV isolates vary according to their principal transmission strategy.This study received financial support from the Spanish Ministry for Science and Technology (AGL2005-07909-CO3-01, AGL2008-05456-C03-01). O.C. received a predoctoral fellowship from the Spanish Ministry of Education and Culture.Peer reviewe