Biomarkers in Pulmonary Arterial Hypertension Treated With Nilotinib

The investigators hypothesize that bone marrow progenitor cells are mobilized into the
circulation in PAH, home to the lungs and differentiate into mast cells, which promote
vascular remodeling and vasoconstriction through release of renin and chymase. As a
corollary to this, the investigators hypothesize that anti cKit tyrosine kinase inhibitor
(TKI), nilotinib, provides clinical benefit to patients through inhibition of mast cell
progenitor proliferation, mobilization and differentiation. To test this, the investigators
will determine if mast cell progenitors and mast cell biomarkers are related to nilotinib
clinical response. This will be an ancillary study, part of a placebo-controlled,
double-blind multi center clinical trial of nilotinib in pulmonary arterial hypertension.