He received his medical degree at the University of California at San Francisco, and pursued pediatric residency training at the institution and the University of Washington, Seattle, WA. He completed a fellowship in Pediatric Infectious Diseases at the University of Washington, where he remained as a faculty member until 1997, when he joined the Stanford University faculty. Dr. Lewis has a long-standing interest in developmental and genetic limitations in T-cell immunity, including in humans. He is particularly interested in limitations in immunity mediated by CD4 T cells and how this compromises host defenses against intracellular pathogens. As part of his activities with the Modell Center, Dr. Lewis spends about 25% of his time seeing patients with primary immunodeficiencies.