Viral vectors and vaccines
Viral vector vaccines
(Priv. Doz. Dr. Ingo Drexler)
Research topics
Poxviruses engineered to express foreign genes are established tools for target protein synthesis and vaccine development in biomedical research. A large packaging capacity for recombinant DNA, precise virus-specific control of target gene expression, lack of persistence or genomic integration in the host, high immuno-genicity as vaccine, and ease of vector and vaccine production are important features. Modified vaccinia virus Ankara (MVA) was originally developed through attenuation by serial passage in primary chicken embryo cells to serve as a safer vaccine against smallpox. After more than 570 passages in tissue culture MVA had lost the broad cellular host range of vaccinia virus (VACV), being unable to productively grow in many cells of mammalian origin. MVA is a valuable tool for the expression of recombinant genes used for such purposes as the study of protein functions or characterization of innate or adaptive cellular and humoral immune responses. A major advantage of MVA is its clear safety record, and it can be handled under biosafety level 1 conditions. Despite its replication deficiency in human and most mammalian cells, MVA provides high-level gene expression and has proven to be immunogenic when delivering heterologous antigens in animals and humans.
· Viral vector design and vaccine development
The adoption of up-to-date methodology for convenient vector generation, vector quality control, and vector vaccine immune monitoring has increased the pace bringing recombinant MVA vaccines into clinical trials. By now, initial studies testing MVA vaccines for prophylaxis or immunotherapy of infectious diseases and cancer have been completed. First results are overall very encouraging confirming clinical safety, but importantly also demonstrating first clinical efficacy despite the intrinsic difficulties associated with these target diseases (for review see Drexler 2004). Moreover, MVA is reconsidered as prime candidate vaccine for safer protection against orthopoxvirus infections.
However, knowledge about the biological properties of target antigens or modalities of antigen delivery to efficiently induce or expand MVA-vaccine-mediated immunity in vivo is still sparse. Recently, we found that CTL responses against MVA-produced antigens were dominated by cross-priming in vivo, despite the ability of the virus to efficiently infect professional antigen-presenting cells (APC) such as dendritic cells (DC) (Gasteiger 2007). Moreover, stable mature protein was preferred to pre-processed antigen as the substrate for cross-priming. These findings demonstrate that MVA vaccine design can be essentially improved, as they point to the need for optimal adjustment of the target antigen properties to the intrinsic requirements of the delivering vector system. Therefore, we strongly focus on the identification of key mechanisms essential for the efficient generation (priming) and expansion (recall) of T cell responses. Next to the optimization of the vector backbone and expression of target genes, we aim to optimize protocols for generation, isolation and molecular characterization of MVA vector viruses.
· Immunoprophylaxis / immunotherapy of virus infections and cancer
We have established preclinical animal models to test MVA vaccine efficacy for viral diseases (e.g. HBV, HCMV) and cancer (malignant melanoma, breast cancer). The quality and quantity of induced immune responses is determined for humoral (ELISA, neutralization assays) and cellular (intracellular cytokine release, multimer binding) immunity with particular emphasis on functional and phenotypical characterization of antigen-specific MVA-mediated CD8+ and CD4+ T cell responses. Our target antigens are structural/non-structural viral proteins (e.g. S-Ag (HBV), nef (HIV), pp65 (HCMV) or so-called differentiation antigens (e.g. tyrosinase and TRP-2 (melanoma) and overexpressed tumorantigens (e.g. HER-2/neu (breast cancer)) for the tumor models. Our vaccines are evaluated in vaccination studies in a variety of transgenic or non-transgenic mouse models applying direct immunization as well as adoptive transfer protocols (Kastenmuller, Gasteiger 2009; Huster 2009; Nörder 2010).
· Poxvirus immunology
With more recombinant MVA used for antigen delivery in clinical research, there is increasing need to evaluate MVA-specific CD8+ and CD4+ T cell responses following immunization. Recently, we identified an immunodominant HLA-A*0201-restricted VACV-epitope which is highly conserved among orthopoxvirus species including variola virus and, for the first time has permitted comparative analysis and monitoring of epitope-specific CD8+ T cell responses elicited against both viral vector and recombinant antigens after immunization (Drexler 2003). Meanwhile, the number of T cell epitopes has been considerably extended in mice and men, and allowed us to elucidate some of the mechanisms which are relevant for the induction and maintenance of VACV-mediated T cell responses in vivo (Moutaftsi et al 2010). These include the requirement of cross-presentation of VACV-encoded antigens to efficiently prime naïve T cells (Gasteiger 2007) as well as the shaping of the immunodominance pattern in the recall by competing CTL (Kastenmuller 2007).
We will further investigate these issues including the role of regulatory T cells for poxviral immunity and the impact of viral gene expression on antigen presentation and processing (Meyer 2008). Additionally, we want to investigate which cellular receptors (e.g. TLRs) and pathways activate innate immunity to poxviruses and which viral ligands or specific molecular patterns are associated with this activation.
· Cellular and systemic poxvirus-host interactions
The interplay of viral and host mechanisms that regulate the outcome of an infection can result in quite distinct phenotypes for different VACV-strains. For instance, the MVA genome lacks functional copies of numerous genes interfering with host response to infection compared to replication-competent strains like the parental CVA strain. We want to use the genetic background information as a comparative basis to characterize the molecular mechanisms associated with these differential phenotypes e.g. distinct distribution patterns in vivo.
We recently demonstrated that various subsets of DC are efficiently infected by MVA in vitro (Kastenmuller 2006) and in vivo (Gasteiger 2007), but fail to induce T cell responses. In particular, late viral antigens are poorly or not processed by infected APC even in cell types which allow for late gene expression. We want to identify which APC are responsible for T cell induction and expansion in primary and secondary infections and in which compartments this interplay takes place in vivo.
Fundamental research in the lab aims to further the understanding of virus-host interactions in vitro and in vivo by characterizing the genetical basis of viral immune modulation and virulence and by identification of key mechanisms required for the efficient generation of innate and adaptive immune responses during poxviral infections.