This innovative serum replacement is a new chemically defined composition formulated for culturing cells. In specific, this serum is the first of its kind to optimized for mouse CD4+ and CD8+ T cells, allowing reproducible ex vivo expansion and functional activation without animal derived serums, leading to a controllability and consistency for preclinical research and immune cell studies. The serum replacement also supports human T cell viability and proliferation, allowing cross-species applicability and translational potential.