Internalization of MORAb-009-mesothelin complex. (A) Mesothelin positive, FRa-negative cells were reacted with MORAb-009 alone, MORAb-009 complexed with saporin-conjugated anti-human mAb (toxin), anti-FRa mAb alone, or anti-FRa mAb complexed with toxin. Cell killing, and thus internalization, of MORAb-009-mesothelin complex was only seen with MORAb-009 complexed with toxin. (B) Same as in A using mesothelin-negative, FRa-positive cells. Internalization was only seen with anti-FRa mAb complexed with toxin.