sentence: HEK 293T cells were transfected with 15 μ g of pLenti-X1-puro-PI3K C2A shRNA , 15 μ g of pMDLg / pRRE ( Addgene plasmid 12251 ) , 6 μ g of pRSV-Rev ( Addgene plasmid 12253 ) , and 3 μ g of pMD2.G ( Addgene plasmid 12259 ) as per Campeau et al. ( 2009 ) .