From spheroids to organoids: next-generation models for CAR-T cell therapy research in solid tumors.

Chimeric Antigen Receptor T-cell (CAR-T) therapy is a revolutionary immunotherapy involving the genetic modification of T cells to express chimeric receptors targeting specific tumor antigens. Over the past decade, CAR-T therapy has significantly advanced with the development of five generations of CAR-T cells, each introducing modifications to enhance T cell efficacy, persistence, and the ability to overcome immune evasion mechanisms. The manufacturing of CAR-T cells has also evolved, employing techniques such as viral vector transduction or CRISPR-based gene editing, lipid nanoparticle, or transposon mediated approaches, to optimize their function. However, the development of CAR-T therapy for solid tumors faces significant challenges, primarily due to the hostile tumor microenvironment (TME), which traditional two-dimensional (2D) culture systems fail to accurately replicate. This review explores the potential of three-dimensional (3D) culture models, including spheroids and organoids, as tools for studying CAR-T cells in the context of solid tumors. Unlike 2D models, 3D systems offer a more physiologically relevant environment, better mimicking the TME, tumor heterogeneity, and immune interactions which CAR-T cells must encounter. We examine the advantages and limitations of 2D versus 3D models and discuss four key methods for generating spheroids/organoids: direct cell aggregation, scaffold-based, microfluidic, organs-on-chip and bioprinting, and patient-derived organotypic tumor approaches. Moreover, we explore the use of murine models in preclinical CAR-T research, highlighting their role in studying the dynamics of CAR-T cell trafficking, efficacy, and off-target effects. While CAR-T therapy has shown impressive success in some hematological malignancies, there is still a critical need for improved models to study CAR-T efficacy against solid tumors, particularly in relation to the TME. 2D models remain a valuable tool but should be combined with 3D models and