Kristine Buch Uldahl:
Hyperthermophilic archaeal viruses as novel nanoplatforms

Date: 15-11-2015    Supervisor: Xu Peng

Viruses are the most abundant biological entities on earth, and with an estimated 1031 virus-like particles in the biosphere, viruses are virtually everywhere. Traditionally, the study of viruses has focused on their roles as infectious agents. However, over the last decades with the development of a broad range of genetic and chemical engineering methods, viral research has expanded. Viruses are now emerging as nanoplatforms with applications in materials science and medicine. A great challenge in biomedicine is the targeting of therapeutics to specific locations in the body in order to increase therapeutic benefit and minimize adverse effects. Virus-based nanoplatforms take advantage of the natural circulatory and targeting properties of viruses, to design therapeutics that specifically target tissues of interest in vivo. Plant-based viruses and bacteriophages are typically considered safer nanoplatforms than mammalian viruses because they cannot proliferate in humans and hence are less likely to trigger adverse effects. Another group of viruses that fits this criterion is archaeal viruses yet their potential remains untapped. As a group, archaeal viruses offer distinct advantages such as unique morphotypes and inherent stability under extreme conditions. This thesis presents the first in depth investigation of any archaeal virus, SMV1, as a potential nanoplatform for applications in nanomedicine.

In order to provide a strong foundation for downstream experiments and future applications, Chapter I presents an in depth investigation of the hyperthermophilic archaeal virus SMV. Decisive steps in the viral life-cycle are studied with focus on the early stages of infection. TEM observations suggest that SMV1 virions enter into host cells via a fusion entry mechanism, involving three distinct stages; attachment, alignment, and fusion. Upon infection, the intracellular replication cycle lasts 8 h at which point the virus particles are released as spindle-shaped tailless particles. Chapter II builds on the replication and purification methods in Chapter I to study the interaction between the two hyperthermophilic archaeal viruses, SMV1 and SSV2 and cells of human origin. This chapter provides the first results demonstrating that archaeal viruses can be taken up and internalized by human cells, thus indicating a potential as intracellular delivery agents. Chapter III investigates SMV1 particles as potential nanocarriers targeting the gut microbiome. Stability experiments proved SMV1 to be highly stable in both simulated conditions of the human gastrointesinal tract (in vitro) and when passaged orally in mice (in vivo). In general, high doses of SMV1 elicited a nearly undetectable murine inflammatory response and challenged mice showed no observable signs of pain or distress. The stability of SMV1 was compared to that of the traditionally used Inovirus, M13KE. SMV1 outperformed this state-of-the-art vector as measured by in vitro and in vivo survival. Chapter III provides strong evidence that SMV1 in particular and archaeal viruses in general have intrinsically favorable in vivo characteristics for bioengineering applications, such as drug delivery in the gastrointestinal tract. Chapter IV presents an overview of all known archaeal viruses and discusses the application potential of archaeal viruses.