This is a double-blind, placebo-controlled, randomized, parallel group, two-part study where single IV doses of GSK2831781 will be administered to healthy Japanese and Caucasian subjects in part A and SC doses will be administered to healthy Caucasian subjects in part B. GSK2831781 is a humanized, antibody-dependent cell cytotoxicity (ADCC) enhanced depleting monoclonal antibody that is specific to the lymphocyte activation gene-3 (LAG3) protein. LAG3 is a transmembrane receptor, which is upregulated on T cells following activation. The objective of the study is to assess the safety, tolerability, PK, PD and immunogenicity post administration of GSK2831781 in healthy subjects. The duration of the study is approximately 147 days for each subject enrolled. Approximately 36 subjects will be enrolled in the study, 16 subjects in Part A and 20 subjects in Part B.