Titration of in vitro inhibition of GCR enzymatic activity by sera of seroconverted Gaucher patients. (A) Representative patient sera showing <50% in vitro inhibitory activity. Transient inhibition was detected when pretreatment, 13, 15, and 18 months posttreatment sera were compared. (B) Patient sera showing >50% inhibition, comparison to normal human serum (NHS) and different time points in therapy.