Detailed analysis of the effects of a NOT gate on activation and growth of T cells.

Background aims: Dual-receptor NOT gates provide a mechanism to target effector cells to antigens that are absent in specific tissues, a situation that occurs frequently in cancer. For example, loss of heterozygosity (LOH) is a genetic event that removes large segments of one or the other homologous chromosome. Roughly 20% of the genes in an average solid tumor undergo LOH by the time of clonal neoplastic expansion, such that these irreversible genetic lesions are present in every cell of the tumor. To exploit this opportunity for selective targeting and other situations that arise in disease, a version of a NOT gate called Tmod^TM technology has been developed. The Tmod platform incorporates two receptors: an activator based on a CAR or TCR, and a blocker based on the LIR-1 inhibitory receptor.

Methods: MHC class-I-regulated constructs display robust modularity, functioning well with a variety of activators-both CARs and TCRs-and blocker antigens encoded by different HLA class I alleles. We explore the details of activation, proliferation and cytotoxicity of the Tmod technology, focusing on a HER2 construct, but generalizing the conclusions by experiments with other Tmod constructs.

Results: We show that Tmod cells exhibit potent, selective tumor-killing even when surrounded by class-I-expressing cells in 3-dimensional spheroids in vitro and in the mouse body. This behavior is largely ligand-dependent, though there are small ligand-independent effects which are mainly ascribed to mechanisms other than the ITIM sequences of the LIR-1 blocker.

Conclusions: These detailed studies demonstrate that most of Tmod regulation is ligand dependent. Expression levels of the CAR affect activation/proliferation in a LIR-1 NOT gate, but the ITIM signaling module plays only a minor role in ligand-independent activity.