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

Chimeric Antigen Receptor (CAR-T) cell therapy has achieved remarkable success in treating hematological malignancies. However, translating this success to solid tumors remains a significant hurdle. Unlike blood cancers, solid tumors present a hostile tumor microenvironment (TME) characterized by physical barriers, nutrient and oxygen gradients, and immunosuppressive cell populations that hinder CAR-T cell infiltration, persistence, and activity. Traditional 2D co-culture systems, while useful for initial mechanistic studies, fail to capture these complex spatial and biochemical features, often leading to overly optimistic predictions of therapeutic efficacy.

To bridge the gap between simple in vitro assays and complex in vivo studies, researchers are increasingly adopting 3D culture systems. Spheroids and organoids offer a more physiologically relevant architecture, allowing for the study of cell-cell interactions, extracellular matrix (ECM) penetration, and the impact of the TME on CAR-T function. These models provide a more accurate platform to test advanced CAR designs, such as fourth-generation (TRUCKs) and fifth-generation constructs, which are engineered to modulate the TME upon activation.

Several methodologies are currently employed to generate these 3D structures:

• Direct Cell Aggregation: Utilizing low-attachment plates or hanging-drop techniques to encourage spontaneous sphere formation.
• Matrix-Based Scaffolds: Incorporating hydrogels, collagen, or Matrigel to mimic the structural support of the ECM.
• Advanced Technologies: Integrating microfluidics, organs-on-chip, and bioprinting to introduce dynamic perfusion, nutrient gradients, and vascular-like barriers.
• Patient-Derived Organotypic Cultures: Using actual tumor biopsies or slices to maintain the native heterogeneity of the patient's disease.