Depletion of LAG‐3(+) T Cells Translated to Pharmacology and Improvement in Psoriasis Disease Activity: A Phase I Randomized Study of mAb GSK2831781

Activated T cells drive a range of immune‐mediated inflammatory diseases. LAG‐3 is transiently expressed on recently activated CD4(+) and CD8(+) T cells. We describe the engineering and first‐in‐human clinical study (NCT02195349) of GSK2831781 (an afucosylated humanized IgG1 monoclonal antibody enhanced with high affinity for Fc receptors and LAG‐3 and antibody‐dependent cellular cytotoxicity capabilities), which depletes LAG‐3 expressing cells. GSK2831781 was tested in a phase I/Ib, double‐blind, placebo‐controlled clinical study, which randomized 40 healthy participants (part A) and 27 patients with psoriasis (part B) to single doses of GSK2831781 (up to 0.15 and 5 mg/kg, respectively) or placebo. Adverse events were generally balanced across groups, with no safety or tolerability concern identified. LAG‐3(+) cell depletion in peripheral blood was observed at doses ≥ 0.15 mg/kg and was dose‐dependent. In biopsies of psoriasis plaques, a reduction in mean group LAG‐3(+) and CD3(+) T‐cell counts was observed following treatment. Downregulation of proinflammatory genes (IL‐17A, IL‐17F, IFNγ, and S100A12) and upregulation of the epithelial barrier integrity gene, CDHR1, was observed with the 5 mg/kg dose of GSK2831781. Psoriasis disease activity improved up to day 43 at all GSK2831781 doses (0.5, 1.5, and 5 mg/kg) compared with placebo. Depletion of LAG‐3‐expressing activated T cells is a novel approach, and this first clinical study shows that GSK2831781 is pharmacologically active and provides encouraging early evidence of clinical effects in psoriasis, which warrants further investigation in T‐cell‐mediated inflammatory diseases.