AUTHOR=Nguyen Duy T. , Schaller Matthew A. , Terracina Krista P. , Xu Xia , Pedro Diego I. , Pepe Alfonso , Urueña Juan M. , Dupee Zadia , Diodati Nickolas , Smolchek Ryan A. , Famiglietti Jack E. , Nguyen Nhi Tran Yen , Tushoski-Alemán Gerik W. , Cheng Kuoyuan , Chen Lan , Linn Doug , Vidimar Vania , Fatima Aquila , Kwon Soon Woo , Sun Dongyu , Chen Hongmin , Xu Haiyan , Long Brian , Moy Lily Y. , Howell Bonnie J. , Addona George H. , Sawyer W. Gregory 

TITLE=Patient-derived colorectal microtumors predict response to anti-PD-1 therapy

JOURNAL=Frontiers in Immunology

VOLUME=Volume 16 - 2025

YEAR=2025

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2025.1640500

DOI=10.3389/fimmu.2025.1640500

ISSN=1664-3224

ABSTRACT=Immune checkpoint inhibitors have made remarkable impacts in treating various cancers, including colorectal cancer (CRC). However, CRC still remains a leading cause of cancer-related deaths. While microsatellite instability (MSI) CRC has shown positive responses to anti-PD-1 therapy, this subgroup represents a minority of all CRC patients. Extensive research has focused on identifying predictive biomarkers to understand treatment response in CRC. Interestingly, a growing number of clinical cases have reported favorable outcomes from a subtype of supposedly non-responder microsatellite stable (MSS) CRC, characterized by DNA polymerase ϵ (POLE) proofreading domain mutations with high tumor mutational burden (TMB). This subtype has shown a notable response, either partial or complete, to pembrolizumab as salvage treatment, often following significant disease progression. To improve efficiency, cost-effectiveness, and clinical outcomes, there is an essential need for a testing platform capable of promptly identifying evidence of anti-PD-1 response to inform treatment strategies. Here, we established a novel 3D ex vivo immunotherapy model using patient-derived tumor microexplants (or microtumors <1 mm) co-cultured with autologous peripheral blood mononuclear cells (PBMCs) from treatment-naïve CRC patients. We demonstrate that long-term ex vivo treatment with pembrolizumab induced a heterogeneous but appreciable interferon-gamma (IFN-γ) secretion, accompanied by infiltrating PBMCs. Intriguingly, a case study involving an MSS CRC phenotype harboring POLE mutation and associated ultrahigh TMB demonstrated a response to PD-1 blockade, potentially from the intratumoral immune cell population. Ultimately, this novel model could serve as a valuable tool in complementing clinical diagnostics and guiding personalized treatment plans for CRC patients, particularly those with specific phenotypes and mutational profiles.