The immune system is being investigated as a potential therapeutic target in pulmonary arterial hypertension (PAH). (A) Current clinical trials investigating PAH therapies. A search was performed on ClinicalTrials.gov for “pulmonary hypertension” from January 1, 2015, to the January 1, 2019. Limits were set to “interventional study,” and adult patients only. Trial status classifications included were not yet recruiting, recruiting, enrolling by invitation, active not recruiting, and unknown status. A total of 170 studies were identified, and inclusion and exclusion categories are depicted in the flow chart. Of the 70 interventional trials included, half (54%) are investigating vasodilator therapy, 20% focus on immunological targets, and 21% are targeting metabolism and nutrition. (B) Specific examples of immune targets and therapies currently under clinical study in PAH. NCT refers to the registered Clinical Trial number, with study information available at ClinicalTrials.gov.