With as many as 13% of adolescents diagnosed with depressive disorders each year, prevention of depressive disorders has become a key priority for the National Institute of Mental Health (NIMH). Currently, we have no widely available interventions to prevent these disorders. To address this need, we developed a multi-health system collaboration to develop and evaluate the primary care based technology “behavioral vaccine,” Competent Adulthood Transition with Cognitive-Behavioral Humanistic and Interpersonal Therapy (CATCH-IT). The full CATCH-IT program demonstrated evidence of efficacy in prevention of depressive episodes in clinical trials. However, CATCH-IT became larger and more complex across trials, creating issues with adherence and scalability.We will use a multiphase optimization strategy approach to optimize CATCH-IT. The theoretically grounded components of CATCH-IT include: behavioral activation, cognitive-behavioral therapy, interpersonal psychotherapy, and parent program. We will use a 4-factor (2x2x2x2) fully crossed factorial design with N = 16 cells (25 per cell, after allowing 15% dropout) to evaluate the contribution of each component. Eligible at-risk youth will be high school students 13 through 18 years old, with subsyndromal symptoms of depression. The study design will enable us to eliminate non-contributing components while preserving efficacy and to optimize CATCH-IT by strengthening tolerability and scalability by reducing resource use. By reducing resource use, we anticipate satisfaction and acceptability will also increase, preparing the way for an implementation trial.