Cell therapies, including chimeric antigen receptor (CAR) T-cell therapy, are emerging as promising treatments, especially for hematological malignancies. However, many challenges remain in developing this emerging class of therapeutics, from deepening responses in blood-based tumors to expanding efficacy in solid tumors. To face these challenges, understanding the mechanisms behind response, resistance, and toxicity to cell therapies is key. Tools with the resolution and scalability to reveal intra- and inter-patient heterogeneity across cancer types will enable researchers to identify key biomarkers and optimize therapeutic products. Explore how 10x Genomics single-cell solutions can help uncover molecular insights into cell therapeutic efficacy and toxicity, transforming the way we approach immune cell therapies for cancer.