There is a membrane bound version of eGFP that can be used. Here is one company that sells the lenti prep:

Membrane eGFP Lentivirus

You can also use a lenti vector that encodes any membrane protein that is not present in the cell line that you are using. Of course, you would need to detect it via Ab staining.

My link didn't work but the company is BPS Bioscience and search for membrane eGFP lentivirus

Thank you, Michael. Presumably restricting GFP expression to the membrane will minimize toxicity?

I'm not sure. I don't have any experience with cells reacting poorly to GFP expression. There are other fluorescent markers that you could try, such as RFP, DsRed, mCherry, etc., if GFP is the only fluorescent protein giving you problems.

Your question suggested that cytoplasmic expression of GFP is the problem. Membrane localization of the GFP may solve your problem.

Just curious, but how did you determine that GFP was causing toxicity? As opposed to transduction conditions, etc. Have you used other lenti vectors expressing other transgenes without issue?

In short, we didn't. I am guilty of simplifying the story a little in order to get the basic point across, but suffice it to say, the cells appear to have a strong selective pressure to suppress GFP expression, as there is substantial 'drift' over time. Our assumption was that this was due to some deleterious/toxic effect of the GFP in these cells. The vector has an E1FA promoter, so it is unlikely that it is being silenced, supported by the fact that Puro resistance that is contained on the same lentivector is maintained by the cells.