Epitope selection overcomes antigen shedding to enable effective CAR-M therapy in solid tumors.
- 1Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
- 2Evotec International GmbH, Marie-Curie-Str. 7, 37079 Goettingen, Germany.
Abstract
Chimeric antigen receptor-macrophages (CAR-Ms) represent a promising platform for solid tumors, but barriers limiting durable responses remain incompletely defined. Antigen shedding may be a key barrier because, unlike T cells, macrophages require sustained antigen engagement for effective phagocytosis. However, whether shed antigen directly impairs CAR-M function has not been established. Using mesothelin (MSLN) as a model target, we generated CAR-Ms targeting either an N-terminal epitope (SS1) or a membrane-proximal, non-shed epitope (15B6). Shed MSLN markedly impaired the phagocytic and cytotoxic activity of SS1 CAR-Ms, establishing antigen shedding as a direct functional barrier. In contrast, 15B6 CAR-Ms remained largely resistant and showed stronger antigen-specific activity across multiple MSLN⁺ tumor cells, demonstrating that rational epitope selection can overcome this barrier. In immunocompetent, MSLN-tolerant transgenic mouse models of colorectal and pancreatic cancer, 15B6 CAR-Ms demonstrated superior anti-tumor activity. In colorectal tumor-bearing mice, a single infusion of 15B6 CAR-Ms significantly prolonged survival, with 35% achieving complete tumor regression. Rechallenge of cured mice with MSLN⁻ tumor cells resulted in complete tumor rejection, suggesting the development of durable systemic anti-tumor immunity. Together, these findings identify antigen shedding as a critical barrier and support epitope selection as an important design strategy for CAR-M therapies targeting shed tumor antigens.
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BibTeX
@article{liu2026epitope,
title = {{Epitope selection overcomes antigen shedding to enable effective CAR-M therapy in solid tumors.}},
author = {Wenlong Liu and Xiufen Liu and Seraphim Kozlov and Qi Zhou and Masanori Onda and Nadja Wagner and Ira Pastan},
journal = {Molecular therapy. Oncology},
year = {2026},
month = sep,
doi = {10.1016/j.omton.2026.201354},
url = {https://europepmc.org/article/MED/42920992},
note = {CC BY},
}
RIS
TY - JOUR
TI - Epitope selection overcomes antigen shedding to enable effective CAR-M therapy in solid tumors.
AU - Wenlong Liu
AU - Xiufen Liu
AU - Seraphim Kozlov
AU - Qi Zhou
AU - Masanori Onda
AU - Nadja Wagner
AU - Ira Pastan
PY - 2026
DA - 2026/09/30
JO - Molecular therapy. Oncology
DO - 10.1016/j.omton.2026.201354
UR - https://europepmc.org/article/MED/42920992
AB - Chimeric antigen receptor-macrophages (CAR-Ms) represent a promising platform for solid tumors, but barriers limiting durable responses remain incompletely defined. Antigen shedding may be a key barrier because, unlike T cells, macrophages require sustained antigen engagement for effective phagocytosis. However, whether shed antigen directly impairs CAR-M function has not been established. Using mesothelin (MSLN) as a model target, we generated CAR-Ms targeting either an N-terminal epitope (SS1) or a membrane-proximal, non-shed epitope (15B6). Shed MSLN markedly impaired the phagocytic and cytotoxic activity of SS1 CAR-Ms, establishing antigen shedding as a direct functional barrier. In contrast, 15B6 CAR-Ms remained largely resistant and showed stronger antigen-specific activity across multiple MSLN⁺ tumor cells, demonstrating that rational epitope selection can overcome this barrier. In immunocompetent, MSLN-tolerant transgenic mouse models of colorectal and pancreatic cancer, 15B6 CAR-Ms demonstrated superior anti-tumor activity. In colorectal tumor-bearing mice, a single infusion of 15B6 CAR-Ms significantly prolonged survival, with 35% achieving complete tumor regression. Rechallenge of cured mice with MSLN⁻ tumor cells resulted in complete tumor rejection, suggesting the development of durable systemic anti-tumor immunity. Together, these findings identify antigen shedding as a critical barrier and support epitope selection as an important design strategy for CAR-M therapies targeting shed tumor antigens.
SN - 2950-3299
ER -