An orthotopic organoid-based model to track CD8⁺ T cell exhaustion dynamics in colorectal cancer.

A deeper understanding of CD8⁺ T cell exhaustion and its contribution to immune checkpoint inhibitor (ICI) responsiveness is essential for the development of more effective therapeutic strategies. Here, we established a syngeneic organoid-based orthotopic CRC mouse model by transplanting quadruple mutant Apc⁻/⁻KrasG12D/+Trp53R172H/⁻Smad4⁻/⁻ (AKPS) intestinal organoids into the rectal submucosa of immunocompetent mice.

Single-cell transcriptomic profiling revealed that tumor-infiltrating CD8⁺ T cell phenotypes span a continuum of differentiation states, ranging from precursor exhausted (Tpex) to terminally exhausted (Tex) CD8+ cell subsets. In contrast, subcutaneous implants of AKPS were infiltrated by mixed CD4⁺ and CD8⁺ cell subsets, with CD8⁺ T cells exhibiting a markedly lower exhaustion profile, highlighting the limitations of heterotopic tumor models for studying antitumor immune responses.