ABSTRACT
BCG vaccine is one of the most widely used vaccines in human history, with tens of billions of doses administered annually over the past century as an important means of preventing tuberculosis. However, BCG is also used for non-traditional purposes of prevention and treatment, such as bladder cancer immunotherapy. In addition to cancer immunotherapy, BCG is increasingly found to be helpful for a variety of immune diseases, including multiple sclerosis, typeⅠdiabetes, and some atopic diseases. It also can protect against non-tuberculous mycobacterium infections, viral infections and even COVID-19. This allogenic protective effect lies in the BCG vaccine's ability to alter immune set points through allogenic T cell immunity, as well as in the epigenetic and immunological effects of metabolomic changes in innate immune cells, a process known as “training immunity”. This paper summarizes the anti-TB effect of BCG and focuses on its heterologous protection and related mechanism.