Lentiviral media - HEPES buffered DMEM - do I titrate? - (Oct/31/2012 )

Hello,

I have been attempting to produce lentivirus in 293FT cells, I have been using normal DMEM + 10%FBS as my regular culture, transfection, and viral production medium.

I've noticed that after I transfect the 293FT's and replace the transfection media with fresh media for viral production, the media becomes acidic much more rapidly than usual. I have read that this acidic pH can be harmful for viral infectivity, do others have this problem with the viral production media becoming acidic too rapidly? Have you noticed this affecting your titers or infectivity?

I recently tried supplementing the culture medium by adding HEPES to a concentration of 25 mM in order to buffer against the acidity, however I noticed that after adding the HEPES to the DMEM it becomes more orange-ish than it is normally, meaning it is starting at a more acidic pH than the DMEM without HEPES. Do I need to re-titrate the media after adding HEPES? I was under the impression that it would inherently balance itself based off its pKa, however this doesn't seem to be happening.

Thanks for your time!
-dkc

Are you still using bicarbonate in the medium when you are adding HEPES? If so, the buffering may be out because of this.

Can't answer the first part of your question- no lentiviral experience...