Chimeric antigen receptor (CAR) T cells have shown great success in the treatment of CD19+ hematological malignancies, leading to their recent approval by the FDA as a new cancer treatment modality. However, their broad use is limited since a CAR targets a single tumor associated antigen (TAA), which is not effective against tumors with heterogeneous TAA expression or emerging antigen loss variants. Further, stably engineered CAR T cells can continually and uncontrollably proliferate and activate in response to antigen, potentially causing fatal on-target off-tumor toxicity, cytokine release syndrome, or neurotoxicity without a method of control or elimination. To address these issues, our lab and others have developed various universal immune receptors (UIRs) that allow for targeting of multiple TAAs by T cells expressing a single receptor. UIRs function through the binding of an extracellular adapter domain which acts as a bridge between intracellular T cell signaling domains and a soluble tumor antigen targeting ligand (TL). The dissociation of TAA targeting and T cell signaling confers many advantages over standard CAR therapy, such as dose control of T cell effector function, the ability to simultaneously or sequentially target multiple TAAs, and control of immunologic synapse geometry. There are currently four unique UIR platform types: ADCC-mediating Fc-binding immune receptors, bispecific protein engaging immune receptors, natural binding partner immune receptors, and anti-tag CARs. These UIRs all allow for potential benefits over standard CARs, but also bring unique engineering challenges that will have to be addressed to achieve maximal efficacy and safety in the clinic. Still, UIRs present an exciting new avenue for adoptive T cell transfer therapies and could lead to their expanded use in areas which current CAR therapies have failed. Here we review the development of each UIR platform and their unique functional benefits, and detail the potential hurdles that may need to be overcome for continued clinical translation.

Universal immune receptors represent a rapidly emerging form of adoptive T-cell therapy with the potential to overcome safety and antigen escape challenges faced by conventional chimeric antigen receptor (CAR) T-cell therapy. By decoupling antigen recognition and T-cell signaling domains via bifunctional antigen-specific targeting ligands, universal immune receptors can regulate T-cell effector function and target multiple antigens with a single receptor. Here, we describe the development of the SpyCatcher immune receptor, the first universal immune receptor that allows for the post-translational covalent attachment of targeting ligands at the T-cell surface through the application of SpyCatcher-SpyTag chemistry. The SpyCatcher immune receptor redirected primary human T cells against a variety of tumor antigens via the addition of SpyTag-labeled targeting ligands, both in vitro and in vivo. SpyCatcher T-cell activity relied upon the presence of both target antigen and SpyTag-labeled targeting ligand, allowing for dose-dependent control of function. The mutational disruption of covalent bond formation between the receptor and the targeting ligand still permitted redirected T-cell function but significantly compromised antitumor function. Thus, the SpyCatcher immune receptor allows for rapid antigen-specific receptor assembly, multiantigen targeting, and controllable T-cell activity.

Pancreatic ductal adenocarcinoma (PDAC) is currently the third leading cause of cancer-related death in the United States. The five-year survival rate of less than nine percent is attributed mainly to a difficulty in early detection and a lack of effective treatments. Tumor-associated glycans represent a potential anti-tumor target for two reasons: (i) protein glycosylation is known to play a role in tumor progression, and (ii) alternatively glycosylated proteins may function as tumor neoantigens. The glycosyltransferase MGAT5 catalyzes the formation of beta-1,6-N-acetylglucosamine branched glycans, and overexpression has been implicated in tumor growth and metastasis in multiple cancers. Using a panel of clonal cell lines that recapitulate the immune heterogeneity of PDAC, we found that knockout of MGAT5 in some clones (“T cell-inflamed" tumors) allows for complete clearance of tumors while in other clones (“non-T cell-inflamed”) MGAT5 deficiency led to a marked decrease in tumor growth. This phenotype was confirmed in orthotopic injection as well as subcutaneous injection into syngeneic mice. By contrast, MGAT5 loss had no impact on tumor cell growth in vitro. To probe immune system involvement in this robust rejection of tumor growth, the MGAT5 KO cells were injected into Nod/Scid mice, resulting in full rescue of the phenotype. Tumor eradication or growth inhibition in vivo was found to be dependent specifically on the presence of CD4/CD8 T cells and dendritic cells. Tumor challenge experiments, in which mice were immunized with MGAT5 KO cells and challenged with wild-type tumors four weeks later, revealed that tumor rejection was associated with a durable immunologic memory. Finally, therapeutic vaccination with the knockout line concomitantly with wild-type tumor cell injection led to decreased tumor growth. These results are consistent with a model in which MGAT5 loss results in the formation of new tumor antigens and/or enhances the immunogenicity of pre-existing antigens. Ongoing work seeks to determine the identity of the responsible antigens and further investigate the relationship between altered glycosylation and anti-tumor immunity. Citation Format: Erin Hollander, Ben Stanger. Loss of the MGAT5 glycosyltransferase sensitizes pancreatic tumor cells to immune clearance [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C006.