Immunogenicity.
The ADA response was monitored in both CSF and serum during the course of Study 250-201 Part 2 (The only 3 patients with ADA in serum at week 1 were those who had already received tralesinidase alfa treatment in Study 250-201 Part 1 (The largest drop in plasma drug exposure occurred between week 1 and week 5 of Study 250-201 Part 2 (h2B), when the median ADA titer in serum was only 1:405 at week 4. In vitro cell-based studies suggested that antibodies detected in ADA-positive CSF samples were not able to neutralize the uptake of tralesinidase alfa (titers of neutralizing antibodies were <1:100 in ADA-positive CSF samples).