Transfection reagent for AAV packaging: How can the transfection efficiency of the three-plasmid system in HEK293T be improved?

I used PEIpro for AAV9. At 80% confluency, the T75 flask is on the high side; it is recommended to lower it to around 70% before transfection. Use a total plasmid amount of 25 μg per T75, with a three-plasmid mass ratio of 1:1:2 (pAAV-pHelper-RepCap), and a reagent-to-DNA volume ratio of about 3:1. On the day of transfection, replace the medium with Opti-MEM in advance, and add the complex dropwise slowly after 15 min. If the titer is low, 10 mM sodium butyrate or chloroquine can also be added, and at 48 h collect cells and supernatant separately for measurement. If the supplier requires technical support, it is recommended to choose brands with distributors in South China, such as Polyplus and Yeasen, so that they can provide batch reports and AAV case protocols; do not only ask about stock availability.

Low titer is not necessarily a reagent issue; it is commonly due to too high serum/antibiotic levels in the medium during transfection. We use TransIT-VirusGEN to package AAV9, with 25 μg total DNA per T75, 60 μL reagent, medium replenishment 18–24 h after transfection, and sample collection at 72 h. For enhancers, you can try chloroquine (final concentration 25 μM) or caffeine, but watch for cytotoxicity and run a test first. In South China, the Polyplus distributor or Dakewe provide better technical support; they can give an optimization table based on total plasmid amount and vessel, and Guangzhou generally has stock. If within budget, domestic alternatives can be considered, but ask clearly whether they have been validated for the three AAV plasmids.

For low triple-plasmid AAV titer, first check the total DNA amount. At 80% density in a T75 flask, I usually use 25-30 μg total DNA (equimolar ratio of pAAV:pHelper:pRepCap at about 1:1:1), with PEI MAX 40k at a mass ratio of 3:1 (PEI:DNA), rather than simply using a 1:3 volume ratio. One hour before transfection, switch to serum-free DMEM; allow the complex to form for 15 min; 6 h after addition, switch to complete medium. For reagents, you can try Polyplus PEIpro or the domestic Yeasen PEI. For in-stock items in South China, contact Guangzhou Dakewe or a local distributor, and ask clearly about lead time.

Cell density and plasmid ratio have a significant impact; after optimization, we increased the titer by more than twofold.

I suggest trying PEIpro, which is cheaper than liposomes, but pay attention to pH and mixing method.