![](/_userfiles/pages/images/gene_therapy/sourceofaavstartingmaterial_1080x532.png)
Left: Despite giving a higher initial yield (column 3, blue) than the helper free system (column 5, grey), when that rAAV seed stock is used to co-infect HEK293 cells with a second TESSA vector, the resulting rAAV2 yields are comparable (columns 1 and 2, blue). Right: However, while still higher than with helper free production (grey), infectious AAV2 yields are slightly lower after a second round of rAAV2 production (columns 1 and 2, vs column 3).