The AP13CP02 study is a phase 2, open-label, dose escalation trial to determine how safe and tolerable multiple subcutaneous (SC) injections of APL-9796 are for patients with PH. The study will also assess how effective APL-9796 could be for treating patients with PH and whether the body produces antibodies working against APL-9796.

The trial will be conducted in two parts:

• Part A: Up to 36 adults with WHO Group 1 Pulmonary arterial hypertension (PAH).
• Part B (optional): Up to 12 adults with WHO Group 3 - PH associated with ILD (PH-ILD).

Inclusion Criteria:

1. Participant must be 18 to 80 years of age inclusive
2. Participants who are diagnosed with pulmonary hypertension via right heart catheterisation (RHC), documented at any time prior to Screening.
3. WHO Functional Class II or III
4. Participant has the CardioMEMS PA Sensor implanted.

Exclusion Criteria:

1. Hospital admission related to PH within 3 months prior to Screening.
2. Major surgical procedure within 3 months prior to Screening, unless participant is assessed as completely recovered by the Investigator
3. Diagnosis of PH due to human immunodeficiency virus, portal hypertension, schistosomiasis, or uncorrected congenital heart disease
4. History of left-sided heart disease and/or clinically significant cardiac disease
5. History of uncontrolled systemic hypertension
6. eGFR ≤30 ml/min/1.73m2
7. Life expectancy of < 12 months, as assessed by the Investigator
8. Diagnosed with a malignancy within 5 years of enrolment
9. Contraindications to protocol-required imaging (MRI), diagnostic, or sampling methods