Polymer “stealthing” can prevent unwanted binding of Ad5 to human erythrocytes. (A) Representation of HPMA-EGF used to modify Ad5. (B) Comparison of normal and EGF-mediated infection in neutralizing plasma. Ad5 or EGF-P-Ad5 was incubated with dilutions of neutralizing antisera and then added to a monolayer of A431 cells; after 90 minutes, media was removed and washing performed in PBS; and after 24 hours, luciferase expression was analyzed. (C) Ad5 or EGF-P-Ad5 was incubated with washed erythrocytes suspended in PBS/1% BSA or whole fresh human plasma. After incubation, erythrocyte and liquid fractions were separated and assayed for Ad5 genome content as described in “Quantitation of Ad5 binding to erythrocytes by real-time (quantitative) PCR” (□ represents liquid fraction; ■, cell fraction). (D) Comparison of normal and EGF-mediated infection in presence of human erythrocytes. A431 cells were infected with Ad5 or EGF-P-Ad5 in the presence of a 1 in 5 dilution of erythrocytes suspended in PBS or plasma. After 90 minutes, media was removed and thorough washing in PBS performed; 24 hours later, luciferase expression was analyzed. ■ represent Ad5; □, EGF-P-Ad. (B-D) N = 4, SEM shown. **P < .005.