In vitro selection of strain-selective siRNAs. (A) HEK293 cells were transfected with 5 nM candidate siVwf, siVwf.B6, siVwf.129S, or scrambled siControl together with plasmids expressing VWF-B6-MYC (blue bars) and VWF-129S-HA (red bars). Seventy-two hours after transfection, VWF-MYC and VWF-HA were measured in conditioned medium. For both B6 and 129S, siRNAs are ranked based on highest inhibitory effect in their corresponding strain relative to siControl. (B) HEK293 cells transfected with VWF-B6-MYC and VWF-129S-HA were cotransfected with siVwf (black squares), siVwf.B6-2 (blue circles), or siVwf.129S-3 (red triangles) at a concentration range of 0.0125 to 40 nM and MYC (VWF-B6, upper panel) and HA (VWF-129S, lower panel) were determined. Data are represented as the mean ± standard deviation (SD) of an n = 6.