To go or not to go? Biological logic gating engineered T cells

Abstract

Genetically engineered T cells have been successfully used in the treatment of hematological malignancies, greatly increasing both progression-free and overall survival in patients. However, the outcomes of patients treated with Chimeric Antigen Receptor (CAR) T cells targeting solid tumors have been disappointing. There is an unmet clinical need for therapies which are specifically designed to overcome the challenges associated with solid tumors such as tumor heterogeneity and antigen escape. Genetic engineering employing the use of biological logic gating in T cells is an emerging and cutting-edge field that may address these issues. The advantages of logic gating include localized secretion of anti-tumor proteins into the tumor microenvironment, multi antigen targeting of tumors and a potential increase in safety when targeting tumor antigens which may not be exclusively tumor specific. In this review, we introduce the concept of biological logic gating and how this technology addresses some of the challenges of current CAR T treatment. We outline the types of logic gating circuits and finally discuss the application of this new technology to engineered T cells, in the treatment of cancer.

Keywords: cell engineering; cytotoxicity, immunologic; immunotherapy; receptors, chimeric antigen.

Figure 1

Employment of logic gating strategies may address some of the considerations associated with current CAR T cell therapy for solid tumors. Localized production of antitumor molecules via logic gating systems reduces systemic adverse effects in patients and directly delivers these molecules where they are needed. Multiantigen targeting with logic gating has the potential to address both tumor heterogeneity and tumor antigen escape by targeting more of the tumor cells with a single treatment, with the goal of more complete elimination of tumor cells to protect against relapse. Immune responses such as CRS or off tumor toxicity could potentially be managed with logic gated production of anti-inflammatory or immune modulating molecules within the tumor microenvironment, inhibiting CAR function against healthy tissues. Tumor microenvironment gated expression of functional molecules such as cars is a method to enhance discrimination capabilities between healthy and malignant tissue. CAR, chimeric antigen receptor.

Figure 2

Logic gating technology has been applied to genetically engineered T cells. Chimeric Antigen Receptor (CAR) T cells bind to their target antigen and induce cell death. Using AND gating, genetic circuits are created where the ligation of the receptor induces cleavage of the transcription factor and induction of a second CAR targeting antigen B. CAR T cells created with an OR gate will kill the target cell in the presence of antigen A or B. Inhibitory cars use a NOT gating system and are designed with inhibitory signaling domains which if ligated, will not kill the target cell.

Figure 3

CAR modality effects anti-tumor function. Chimeric Antigen Receptor (CAR) T cells expressing a CAR specific for a single antigen demonstrate the lowest anti-tumor efficacy. Pooled CAR T cells are more efficacious than single specific CAR T cells and are generated by pooling two populations of single specific CAR T cells. Dual CAR T cells express multiple CARs on the one T cell. The most effective CAR modality is TanCAR T cells, with each T cell expressing one CAR engineered with multiple antigen recognition domains (scFvs). scFv, short-chain variable fragment.