Viral Vectors and Transgenes

All vectors are not the same. More importantly, the class of gene insert can change the Biosafety level of the construct. It is also important to realize that obtaining a cloning/expression vector from a commercial source does not mean it is automatically exempt or a BSL-1. Table 3 lists many of the more common viral vectors in combination with different classes of inserts and their associated BSL level.

     ^aRefers to the parental or wild-type virus and some of the common deletions used in viral vectors. MMLV, Moloney murine leukemia virus; SIV, simian immunodeficiency virus.

     ^bRefers to ability of vector to infect cells from a range of species. Ecotropic generally means able to infect only cells of the species originally isolated from or identified in. Please note that the ecotropic host for HIV and HSV would be human cells, but the ecotropic host for MMLV would be murine cells. Amphotropic and VSV-G-pseudotyped virus host range includes human cells.

     ^cShown are general categories of cellular genes and functions. Please note that there are differences in the containment level for the same class depending on whether the viral vector integrates into the recipient genome at a high rate. The general categories are as follows: S, structural proteins (actin, myosin, etc.); E, enzymatic proteins (serum proteases, transferases, oxidases, phosphatases, etc.); M, metabolic enzymes (amino acid metabolism, nucleotide synthesis, etc.); G, cell growth, housekeeping; CC, cell cycle, cell division; DR, DNA replication, chromosome segregation, mitosis and meiosis; MP, membrane proteins, ion channels, G-coupled protein receptors, transporters, etc.; T, tracking genes such as those for green fluorescent proteins and luciferases and photoreactive genes; TX, active subunit genes for toxins such as ricin, botulinum toxin and Shiga and Shiga-like toxins; R, regulatory genes for transcription and cell activators such as cytokines, lymphokines and tumor suppressors; Ov and Oc, oncogenes identified via transforming potential of viral and cellular analogs, or mutations in tumor suppressor genes resulting in a protein that inhibits/moderates the normal cellular wild-type proteins. This does not include SV40 T antigen. SV40 T-antigen-containing cells should not be considered more hazardous than the intact virus. SV40 is considered a risk level 1 agent (the lowest level) according to the NIH Guidelines. The prevalence of SV40 infection in the U.S. population due to contaminated polio vaccine does not seem to have caused a statistically significant increase in the rate of cancers. However, the data from the various studies on SV40 association with cancer are equivocal (Strickler et al. 1998; Butel and Lednicky, 1999; Dang-Tan et al., 2004).

     ^dThis is a general assessment of containment levels for laboratory construction and use of these vectors for nonproduction quantities only based on the 4th edition of BMBL. This table cannot cover every potential use within a research or laboratory settings; as information is gained, risk assessments and containment levels may be changed. Local IBCs should use all available information and their best judgment to determine appropriate containment levels. BSL-1* refers to the containment level based on parent virus risk group. However, most procedures involving the handling and manipulation of the viral vectors are done at BSL-2 to protect cell cultures and viral stocks from contamination.

     ^eCertain specific strains of poxviruses, such as MVA, NYVAC, ALVAC and TROVAC, are considered low-risk agents and can be handled at BSL-1 in certain cases. From Biological Safety Principles and Practices, 4th ed., pg. 524, D.O. Fleming and D.L. Hunt, Ed, ASM Press, 2006.