Abstract A170: The mode of action of Orf virus – a novel viral vector for therapeutic cancer vaccines
Authors: Mueller Melanie , Amann Ralf , Feger Thomas , Rammensee Hans-Georg 
Published: May 2016

Viral vector vaccines still represent most excellent inducers of cell-mediated and humoral immune responses. Therefore, intensive investigations are performed to improve the use of several virus families as safe and efficient viral vectors, not only against diverse infectious diseases but also against tumors. During the last decade we developed a novel vector virus platform using Orf virus (ORFV), a member of the genus Parapoxvirus of Poxviridae. The attractiveness of an ORFV vector rely on the following advantages: (i) a very restricted host range, (ii) no evidence for viral systemic spread, (iii) the fast induction of humoral and cellular immune responses, especially also in non-permissive hosts that do not support vector replication, (iv) a short-term vector-specific immunity allowing multiple re-immunizations, and (v) the possibility to generate recombinants by targeted deletion of ORFV virulence genes on the basis of the highly attenuated, apathogenic ORFV strain D1701-V.

Recently, we were able to demonstrate the excellent immune stimulating (humoral and cellular) and prophylactic capacity of ORFV-based recombinants against numerous different viral diseases manifold. Obviously, it would be of great interest, if ORFV might serve as a platform for the development of therapeutic tumor vaccines for humans. Hence, we would like to investigate the so far poorly understood mechanism of immune stimulation and -induction as well as the possibilities to further manipulate/trigger the induced immune response by co-expression of immune regulating factors more precise.

With the aid of a recombinant ORFV expressing the fluorescent marker protein mCherry, the mode of action and the immune cells involved in this immune activation is investigated. In a first step, freshly isolated human PBMC subpopulations were infected at different time points and with different MOIs (multiplicity of infections) and the infection rate and cell viability were measured. Thereby we observed that professional antigen presenting cells (APC) were most susceptible for infection/uptake of virus. Next we wanted to investigate the activation status of the APCs. Therefore we analyzed the effect of ORFV on the expression of surface markerswhich are important for antigen-presentation and co-stimulation of T-cells (e.g. HLA DR, CD40, CD80 and CD86). In a further step we examined the cytokine release to elucidate the effects of ORFV infection on the immune stimulatory capacity of APCs.

The capability to cause T-cell priming, as an integral part of the immune activation, will be studied more precisely using the model antigens Melan A and pp65 (hCMV). Further optimization of the immune stimulatory capabilities of ORFV shall be achieved by co-expression of adequate cytokines together with the integrated model antigen.

Citation Format: Melanie Mueller, Ralf Amann, Thomas Feger, Hans-Georg Rammensee. The mode of action of Orf virus – a novel viral vector for therapeutic cancer vaccines. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A170.