BackgroundMesothelin (MSLN) is a classic tumor-associated antigen that is expressed in lung cancer and many other solid tumors. However, MSLN is also expressed in normal mesothelium which creates a significant risk of serious inflammation for MSLN-directed therapeutics. We have developed a dual-receptor (Tmod™) system that exploits the difference between tumor and normal tissue in a subset of patients with defined heterozygous gene loss (LOH) in their tumors.MethodsT cells engineered with the MSLN CAR Tmod construct described here contain (1) a novel MSLN-activated CAR and (2) an HLA-A*02-gated inhibitory receptor (blocker). A*02 binding is intended to override T-cell cytotoxicity, even in the presence of MSLN. The Tmod system is designed to treat heterozygous HLA class I patients, selected for HLA LOH. When A*02 is absent from tumors selected for LOH, the MSLN Tmod cells are predicted to mediate potent killing of the MSLN(+)A*02(−) malignant cells.ResultsThe sensitivity of the MSLN Tmod cells is comparable with a benchmark MSLN CAR-T that was active but toxic in the clinic. Unlike MSLN CAR-T cells, the Tmod system robustly protects surrogate “normal” cells even in mixed-cell populations in vitro and in a xenograft model. The MSLN CAR can also be paired with other HLA class I blockers, supporting extension of the approach to patients beyond A*02 heterozygotes.ConclusionsThe Tmod mechanism exemplified by the MSLN CAR Tmod construct provides an alternative route to leverage solid-tumor antigens such as MSLN in safer, more effective ways than previously possible.
Progress toward improved solid-tumor treatment has long been hindered by the lack of truly tumor-specific targets. We have developed an approach to T cell therapy based on a dual-receptor system called Tmod™ that addresses this problem. The Tmod system exploits one of the few common genetic differences between tumor and normal cells: loss of heterozygosity (LOH). It utilizes the basic mechanistic logic that evolved in early vertebrates to mediate self vs. non-self discrimination, where an activation stimulus is blocked by self-ligands. Tmod constructs employ a chimeric antigen receptor (CAR) or T cell receptor (TCR) as activator component and a modified LIR-1 inhibitory receptor (blocker) to achieve high selectivity based on expression of the blocker antigen (Ag). Here we explore the in vitro pharmacology of a blocker directed at the HLA-A*02 Ag paired with either a mesothelin CAR or an HLA-A*11-restricted KRAS peptide TCR. While more sensitive to receptor expression changes on effector cells, we show that Tmod response is well-buffered against variations in Ag levels on target cells. In addition, the data reveal at least two distinguishable pharmacologic mechanisms of Tmod blocker function: (1) reducing activator sensitivity and (2) decreasing activation magnitude.
We set out to examine the behavior in preclinical models of a dual-receptor cell therapy approach (Tmod࣪ system) designed to exploit instances of somatic LOH in cancer that can be readily identified through molecular diagnostics. We utilized quantitative pharmacologic assays in vitro and dual-flank efficacy/selectivity models in vivo to test the activity of a variety of constructs comprised of: (i) CAR “activators” that target tumor-associated antigens (TAAs) such as CEA, MSLN and others; and, (ii) LIR-1-based “blockers” that target HLA class I proteins. We generated substantial datasets around multiple targets, including well known tumor-associated antigens (TAAs). In the presence of the HLA class I blocker antigen, Tmod cells were OFF within a wide range of activator antigen expression levels on the “normal” target cells. They were ON when tumor cells expressed the TAA without the HLA blocker antigen, and killed tumor cells selectively even in mixed tumor-normal cell populations. The Tmod system transformed imperfect TAAs into true tumor-selective targets, where the activity of the engineered T cells is controlled by the presence/absence of the HLA blocker antigen. The system was sufficiently modular to use with autologous and allogeneic products. Several of these Tmod constructs are advancing to the clinic where a robust genetic selection tool is being used to screen patients for treatment and match them with a suitable Tmod therapy. In summary, Tmod is a robust system with quantitative pharmacologic behavior in preclinical models consistent with efficacy and safety across a range of targets. Citation Format: Han Xu, Agnes Hamburger, Yuta Ando, Grace Asuelime, Kristian Bolanos, Mark Daris, Breanna DiAndreth, Maria C. Imun, Wen-Hua Lee, Chuck Z. Li, Breanna Luna, Diane Manry, Aaron D. Martin, Michele E. McElvain, Jee-Young Mock, Martin Naradikian, Mark L. Sandberg, Julyun Oh, Sanam Shafaattalab, Shruti Sharma, Talar Tokatlian, Xueyin Wang, Lu Min Wong, Alexander Kamb. The modular Tmod dual_receptor system exploits tumor deletions to achieve robust tumor-selective cytotoxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2751.
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