Abstract LB344: A novel approach to limit off-tumor toxicity of CAR-T cells targeting solid cancers
Authors: Bartlett Alex , Mcwhorter Matthew , Collier Camille , Jenkins Chelsea , Eil Robert 
Published: April 2024

T cells genetically engineered to express a chimeric antigen receptor (CAR) specific for the molecule CD19 have achieved significant gains in the treatment of chemotherapy-resistant leukemia and lymphoma. Despite evidence of long-lived cures in patients with metastatic solid cancer after receiving tumor-specific T cells, no CAR-T cell treatment is currently approved for use against any solid cancer. A large majority of solid cancers express one of many tumor-associated antigens (TAAs) that are vulnerable to CAR T cell recognition. However, in nearly all cases those same TAAs are present in healthy tissues. Since CAR T cells cannot differentiate between cancer and normal cells, CAR T cell recognition of TAAs on healthy tissues provokes dose-limiting ‘on-target off-tumor’ toxicities at sites of endogenous expression (lung, intestine).

Thus, there remains a pressing need to develop strategies to mitigate off-tumor toxicity of CAR T cells. To this end, we develop two immunocompetent models of CAR T cell transfer targeting TAAs abundant in metastatic colorectal cancer and pancreatic cancer. TAA-specific CAR T cells affected tumor shrinkage along with infiltrating and damaging sites of endogenous expression (primarily lung, pancreas, & colon). In both of our models, off-tumor toxicities were antigen-dependent and resulted in tissue damage, systemic inflammation, and host death that was titratable to CAR-T cell dose.

TAA-specific CAR T cells infiltrated sites of endogenous expression such as the intestine, pancreas, and lungs. Notably, the respiratory system was the site of greatest pathology in both of our models, with massive CAR T cell accumulation and tissue destruction that resulted in systemic wasting and rapid weight loss. Remarkably, we found that the presence of an antigen-bearing tumor in the liver, but not other sites, greatly exacerbated CAR-T cell pulmonary infiltration, tissue destruction, and host mortality.The liver is the most common site of metastasis in patients with colorectal and pancreatic adenocarcinoma and the only site of metastasis in one-third of colorectal cancers. Our models indicated that TAA-specific CAR-T cells given for the treatment of liver metastasis result in dose-limiting pulmonary toxicity due to the presence of the TAA in the healthy lung.

To address this translational barrier, we designed and validated a multiparameter genetic reprogramming targeting T cell trafficking and tissue residency introduced with the CAR to imbue CAR-T cells with liver tropism. In multiple models, CAR T cells programmed with liver-specific tropism augmented CAR T cell liver trafficking, decreased lung infiltration and toxicity, and effectively treated TAA+ liver metastasis. We aim to initiate a pilot clinical trial using tissue resident-programmed CAR T cells to treat colorectal liver metastasis.

Citation Format: Alex Bartlett, Matthew Mcwhorter, Camille Collier, Chelsea Jenkins, Robert Eil. A novel approach to limit off-tumor toxicity of CAR-T cells targeting solid cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB344.