Cell culture systems and methods provide improved immunotherapeutic product manufacturing with greater scalability, flexibility, and automation. Cell culture systems are configured with interchangeable cartridges, allowing versatility and scalability. Systems are configured to have multiple connected cell culture chambers, which allows parallel processing of different types of cells. Gas-impermeable cell culture chambers and methods for generating cells in closed systems prevent contamination and user error. Methods for recycling cell culture medium provide additional efficiencies.