This protocol will use leukapheresis to collect lymphocytes to study immune responses following vaccination with BCG in BCG-naïve participants. These studies will include, but not necessarily be limited to: anti-T-cell and anti-Natural Killer (NK) T-cell responses, anti-lipid responses, and antibody responses to BCG following re-vaccination. These responses will provide a detailed framework characterizing the immune responses that are induced and responses that are not induced in humans by BCG, a partially protective TB vaccine. This framework will allow new hypotheses to be formulated and tested regarding what new and more effective TB vaccines should target for optimal protective immunity.