Single-cell spatial transcriptomic analysis of PAH lungs further revealed complement-rich adventitial fibroblasts, granzyme K (GZMK)<sup>+</sup> CD8 T cells, and activated macrophages forming proinflammatory niches within the pulmonary artery adventitia in the different pulmonary vascular lesions in PAH. The gene discussed is GZMK; the disease is pulmonary arterial hypertension.