Cancer immunotherapy with CAR T cells: well-trodden paths and journey along lesser-known routes.

BACKGROUND: Chimeric antigen receptor (CAR) T cell therapy is a clinically approved cancer immunotherapy approach using genetically engineered T cells. The success of CAR T cells has been met with challenges regarding efficacy and safety. Although a broad spectrum of CAR T cell variants and applications is emerging, this review focuses on CAR T cells for the treatment of cancer. In the first part, the general principles of adoptive cell transfer, the architecture of the CAR molecule, and the effects of design on function are presented. The second part describes five conceptual challenges that hinder the success of CAR T cells; immunosuppressive tumour microenvironment, T cell intrinsic properties, tumour targeting, manufacturing cellular product, and immune-related adverse events. Throughout the review, selected current approaches to address these issues are presented. CONCLUSIONS: Cancer immunotherapy with CAR T cells represents a paradigm shift in the treatment of certain blood cancers that do not respond to other available treatment options. Well-trodden paths taken by pioneers led to the first clinical approval, and now the journey continues down lesser-known paths to treat a variety of cancers and other serious diseases with CAR T cells.

Expression of inducible factors reprograms CAR-T cells for enhanced function and safety.

Despite the success of CAR-T cell cancer immunotherapy, challenges in efficacy and safety remain. Investigators have begun to enhance CAR-T cells with the expression of accessory molecules to address these challenges. Current systems rely on constitutive transgene expression or multiple viral vectors, resulting in unregulated response and product heterogeneity. Here, we develop a genetic platform that combines autonomous antigen-induced production of an accessory molecule with constitutive CAR expression in a single lentiviral vector called Uni-Vect. The broad therapeutic application of Uni-Vect is demonstrated in vivo by activation-dependent expression of (1) an immunostimulatory cytokine that improves efficacy, (2) an antibody that ameliorates cytokine-release syndrome, and (3) transcription factors that modulate T cell biology. Uni-Vect is also implemented as a platform to characterize immune receptors. Overall, we demonstrate that Uni-Vect provides a foundation for a more clinically actionable next-generation cellular immunotherapy.

Biochemical and functional characterization of mutant KRAS epitopes validates this oncoprotein for immunological targeting.

Activating RAS missense mutations are among the most prevalent genomic alterations observed in human cancers and drive oncogenesis in the three most lethal tumor types. Emerging evidence suggests mutant KRAS (mKRAS) may be targeted immunologically, but mKRAS epitopes remain poorly defined. Here we employ a multi-omics approach to characterize HLA class I-restricted mKRAS epitopes. We provide proteomic evidence of mKRAS epitope processing and presentation by high prevalence HLA class I alleles. Select epitopes are immunogenic enabling mKRAS-specific TCRαß isolation. TCR transfer to primary CD8+ T cells confers cytotoxicity against mKRAS tumor cell lines independent of histologic origin, and the kinetics of lytic activity correlates with mKRAS peptide-HLA class I complex abundance. Adoptive transfer of mKRAS-TCR engineered CD8+ T cells leads to tumor eradication in a xenograft model of metastatic lung cancer. This study validates mKRAS peptides as bona fide epitopes facilitating the development of immune therapies targeting this oncoprotein.

Quantitative Control of Gene-Engineered T-Cell Activity through the Covalent Attachment of Targeting Ligands to a Universal Immune Receptor.

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.

Delivery system for the enhanced efficiency of immunostimulatory nucleic acids.

Toll-like receptors (TLRs) play a key role in the recognition of pathogen-associated molecular patterns, including immunostimulatory nucleic acids (INAs). INAs are recognized by TLRs in endosomes, leading to the activation of signalling pathways that activate the innate immune response. This feature makes INAs and their synthetic analogues useful as adjuvants in vaccines and in cancer treatment. We tested a delivery system for the improvement of the therapeutic effect of INAs which consists of a conjugate between transferrin (Tf) and poly-L-lysine (PLL). Tf is a ligand of the transferrin receptor (TfR) and is internalized via receptor-mediated endocytosis, while PLL binds negatively charged INAs. The TfPLL conjugate protected TLR3 ligand polyinosinic:polycytidylic acid [poly(I:C)] from RNase degradation and enhanced the uptake of poly(I:C) in HeLa cells. Co-localization between TfPLL-bound poly(I:C) and lysosomes demonstrated delivery into the endosomal pathway. Time dependence of the production of IL-6 in the primary cell line showed that TfPLL conjugate enabled a gradual release of poly(I:C) and stronger activation of TLR3 receptor in comparison with poly(I:C) alone. Only 3 h of stimulation by poly(I:C) + TfPLL complexes initiated a strong immune response in contrast to poly(I:C) alone. The poly(I:C) + TfPLL complexes have potential use for development of advanced vaccine adjuvants and targeted cancer immune therapy in cells that express higher levels of TfR.