Infectious recombinant viruses

An important safety issue of viral vectors is whether or not the recombinant viruses are able to replicate in the infected cells. Replication of viral vectors is unwanted in most gene-therapy approaches. Therefore, replication-defective vectors have been designed, which are able to perform only one initial infectious cycle within the target cell. In addition, replication-competent vectors have been designed, which are able to productively infect the target cell and to spread in the target tissue. 

Rocha C D, Gaetano B C, Machado A V, et al. (2004). Recombinant viruses as tools to induce protective cellular immunity against infectious diseases. Int. Microbiol. 7 83-94. 

Mackett, M., Smith, G. L., and Moss, B. (1984) General method for production of infectious vaccinia virus recombinants expressing foreign genes. /. Virol. 49, 857-864. 

Ding L, Lu S, MunshiNC. In vitro packaging of an infectious recombinant adeno-associated virus 2. GeneTher 1997 4 1167-1172. 

Vaccination to induce an adaptive immune response is expected for a broad range of infectious diseases and cancers. Traditional vaccines are mainly composed of live attenuated viruses, whole inactivated pathogens, or inactivated bacterial toxins. In general, these approaches have been successful for developing vaccines that can induce an immune response based on antigen-specific antibody and cytotoxic T lymphocyte (CTL) responses, which kill host cells infected with intracellular organisms (Fig. 1) [1,2], One of the most important current issues in vaccinology is the need for new adjuvants (immunostimulants) and delivery systems. Many of the vaccines currently in development are based on purified subunits, recombinant... 

Ongoing clinical trials continue to assess the efficacy of recombinant interferon preparations in treating a variety of cancers. Some trials suggest that treatments are most effective when administered in the early stages of cancer development. rhIFN-as have also proven effective in the treatment of various viral conditions, most notably viral hepatitis. Hepatitis refers to an inflammation of the liver. It may be induced by toxic substances, immunological abnormalities, or by viruses (infectious hepatitis). The main viral causative agents are ... 

Members of the Caliciviridae family can hardly be examined in cell culture or animal models. Therefore, so-called virus-Hke particles (VLP) are employed in current experiments. These particles are expressed recombinantly in insect cells using a baculovirus system and do not carry infectious viral RNA [70-72]. It has been shown by single particle tracking studies that VLPs are internalized into the cells in a similar fashion to native viruses [73]. VLPs are believed to present identical molecular recognition elements to the outside world as do native viruses. 

The process of actually getting the recombinant DNA into a cell will depend on the type of vector used. If the vector is a plasmid, the DNA is now ready for transfection into the host cells. If the vector is a virus, it may be necessary to package the DNA into infectious virus particles before it can be introduced into the host cells. Infection is usually a fairly efficient means of introducing the recombinant DNA into the host, while transfection tends to be quite inefficient. Transfection involves special chemical and enzymatic treatment of the host cell to make its cell membrane permeable to the DNA, and such treatment tends to reduce the viability of the host. 

K., Summerford, C., Samulski, R. J. and Muzyczka, N. (1999). Recombinant adeno-associated virus purification using novel methods improves infectious titer and yield. Gene Ther. 6, 973-985. 

---