GSK3772847, an anti-interleukin (IL)33 receptor monoclonal antibody, is a novel treatment for asthma. This is a phase 2a study which aims to evaluate efficacy, safety, tolerability, pharmacokinetic (PK) and pharmacodynamic (PD) profiles of GSK3772847 in subjects with moderately severe asthma. The study will be conducted in 4 phases including screening, run-in phase, treatment phase and follow-up. In treatment phase, eligible subjects will be randomized to receive either GSK3772847 or placebo administered via intravenous (IV) route every 4 weeks in addition to open-label background therapy of fluticasone propionate/ salmeterol (FP/Sal) 500/50 micrograms (mcg) twice daily. During the treatment phase, the background therapy will be switched to FP 500 mcg for 2 weeks and the dose of FP will be reduced by approximately 50 percent at every 2 weeks until complete FP discontinuation. The total duration of study will be approximately 33 weeks and approximately 148 subjects with moderately severe asthma who are maintained on high-dose of inhaled corticosteroids/ Long-Acting Beta-2-Agonists (ICS/LABA) will be randomized.