I am a little concerned with 293T cell lines, I have been working with this cell line for a few years with less frequency. However there were times that i extracted the proteins from these cell lines outside the hood. I never work with virus, i have only transfected plasmid DNA. can someone help me if there are any chance o exposure, if yes, how dangerous is it.
293T cells do incorporate partial virus genomes, consisting of about 4000 bases (about 11%, if I remember right) of the adenovirus type 5 genome (Cloning and Sequencing of the Cellular–Viral Junctions from the Human Adenovirus Type 5 Transformed 293 Cell Line).
This amount of DNA is not enough to make a viable virus; it lacks all the structural components of the capsid, for example.
293T cells also include the SV40 Large T antigen, another viral gene. Again, this is not enough to make a replicating virus.
Therefore these cells don't pose any human health hazard aside from the normal almost entirely theoretical risk associated with any transformed human cell line (actually considerably less, since these were never tumor cells but were transformed in the lab, so they have no intrinsic adaptations to replication in humans, unlike say HeLa cells -- which are also demonstrably safe).
293 cells have been continuously cultured in thousands or tens of thousands of labs for over 40 years, and I'm not aware of any safety incidents associated with them. Of course, you should always handle cultured cells with appropriate precautions and protective wear, but these are not a specific concern.
Washington State has a nice risk assessment out of their biosafety department that outlines the risks associated with 293 cell lines (downloads a docx). The risk in itself is predicated upon poor work practices and the potential for the generation of a live virus in the technician, or the cell line itself (see the special hazard notes in the risk assessment report). However common these events may be I don't know, but in the US, OSHA 29CFR1910.1030 (The Bloodborne Pathogens Standard) sets us up for risk management regardless of the incidence (or frequency) of such events.
The 293 cell line is considered BSL-II, requiring work done in a BSC with a carefully selected PPE ensemble and training for the manipulations being performed. This isn't at the discretion of the lab personnel but rather at the discretion of the EH&S or Biosafety department. OSHA levies heavy fines against institutions for non-compliance and thus decisions regarding compliance are left up to administrative professionals. I would recommend checking out Biosafety in Microbiological and Biomedical Laboratories (BMBL) 5th Edition (link) for guidance.
Ideally, though, check out your institutions written Exposure Control plan, which you're given access to by law for instruction and assessment performed by your own institution with the goal of mitigating exposure events.