Cell lines are often immortalised by artificial expression of proteins which specifically cause the knockout of important cancer suppression genes or the activation of proto-oncogenes.
Cellular immortality happens upon impairment of cell-cycle checkpoint pathways (p53/p16/pRb), reactivation or up-regulation of telomerase enzyme, or upregulation of some oncogenes or oncoproteins leading to a higher rate of cell division.
However, this would appear to fall under the purview of Biosafety Level 3 since the protein expression vectors are capable of causing cancer in the researcher when they infect the researcher. Cancer can certainly be considered a serious or lethal disease, and aerosolisation of the vectors, while rare, is not impossible (for example during a spill).
According to the biosafety definitions of Columbia University,
Agents: serious or lethal diseases transmissible via aerosols, e.g., M. tuberculosis, SARS. Recombinant DNA activities using genetic material from BSL-3 organisms or such organisms as host cells.
Why then, does the CDC classify cell line work, including work with viral production cells, as a BSL-2 activity requiring only BSL-2 containment levels, when the act of immortalising the cells would involve working with viral agents that can cause cancer?
Cells immortalized with viral agents such as SV-40, EBV adenovirus or HPV, as well as cells carrying viral genomic material also present potential hazards to laboratory workers. Tumorigenic human cells also are potential hazards as a result of self-inoculation.[...]
Human and other primate cells should be handled using BSL-2 practices and containment. All work should be performed in a BSC, and all material decontaminated by autoclaving or disinfection before discarding. BSL-2 recommendations for personnel protective equipment such as laboratory coats, gloves and eye protection should be rigorously followed.
Are the transformation cells (eg the 293T viral cells containing the transformant viruses) considered Level 3 biosafety risk, and if not, why not?