 Participants who are on alpha-1 replacement therapy who have had fewer than 2 exacerbations in the last year will be asked whether they are interested in a withdrawal study. For this second part of the study, eligible and willing participants will be asked to stop their alpha-1 replacement therapy for 5 weeks and come in for a 4th study visit. This will allow AAT levels to drop briefly to those seen in the absence of AAT augmentation. 