mRNA transfection is an efficient method for antigen delivery to APCs. (A) Greater than 75% transfection efficiency of DCs electroporated with GFP mRNA. MDDCs were transfected with 10 μg GFP mRNA (filled histogram) or mock transfected (open histogram). The degree of GFP expression was measured by FACS 24 hours after transfection. (B) mRNA transfection primes APCs for lysis by specific CTLs. Lysis of HLA-B57⁺ BLCLs by a CTL clone specific for the B57-ISW9 epitope (ISPRTLNAW) of HIV p24 was determined with a ⁵¹Cr-release assay at an effector-target ratio of 3:1. BLCLs were transfected with 10 μg of mRNA encoding p24 or irrelevant control mRNA. The transfected cells were loaded with ISW9 peptide as positive control or left untreated as a negative control. Results shown are the average of duplicate wells. By comparing the percent specific lysis of p24-transfected targets (68%) to percent specific lysis of targets loaded with 2 μg/mL peptide (78%), we estimate that the transfection efficiency of BLCLs electroporated with p24 mRNA approaches 90%. Dose titration showed that 10 μg mRNA was optimal for this assay (not shown).