This RFA invites R01 applications for mechanistic studies in clinical trials of: immunomodulatory interventions for immune system mediated diseases, including, but not limited to: asthma and allergic diseases; graft failure in solid organ, cell, tissue and stem cell transplantation; and chronic inflammatory, autoimmune, and immunodeficiency diseases; preventative and therapeutic, vaccines for non-HIV/AIDS infectious diseases, including NIAID Category A, B, and C agents of bioterrorism and emerging/re-emerging infectious diseases.