The pioneering design of chimeric antigen receptor (CAR) T-cell therapy demonstrated the potential of reprogramming the immune system. Nonetheless, T-cell exhaustion, toxicity, and suppressive microenvironments limit their efficacy in solid tumors. We previously characterized a subset of tumor-infiltrating CD4+ T cells expressing the FcγRI receptor. Herein, we detail engineering of a receptor, based on the FcγRI structure, allowing T cells to target tumor cells using antibody intermediates. These T cells showed effective and specific cytotoxicity only when an appropriate antibody was added. Only target-bound antibodies activated these cells, while free antibodies were internalized without activation. Their cytotoxic activity was correlated to target protein density, therefore targeting tumor cells with high antigen density while sparing normal cells with low or no expression. This activation mechanism prevented premature exhaustion. Furthermore, during antibody-dependent cytotoxicity these cells secreted attenuated cytokine levels compared with CAR T cells, thereby enhancing their safety profile. These cells eradicated established melanomas, infiltrated the tumor microenvironment, and facilitated host immune cell recruitment in immunocompetent mice. In NOD/SCID gamma mice the cells infiltrate, persist, and eradicate tumors. As opposed to CAR T-cell therapies, which require changing the receptor across different types of cancer, our engineered T cells remain the same across tumor types, while only the injected antibody changes. Overall, we generated a highly flexible T-cell therapy capable of binding a wide range of tumor cells with high affinity, while preserving the cytotoxic specificity only to cells expressing high density of tumor-associated antigens and using a single manufacturing process.

Anticancer peptides (ACPs) offer a promising alternative to conventional chemotherapy but face challenges, including poor selectivity, limited tumor penetration, low cellular uptake, and rapid degradation in serum. To address these barriers, we developed synthetic mRNAs encoding chimeric ACPs designed for enhanced intracellular delivery and activity. mRNAs for constructs SAK6L9AS(1X), SAK6L9AS(4X), and WTAS-K6L9(4X) were transcribed in vitro and tested against 4T1 breast cancer cells. Cytotoxicity was assessed by cell confluence and MTT assays, while apoptosis was evaluated using caspase 3/7 activation, PI staining, and Annexin V flow cytometry. Our results demonstrate that all SAK6L9AS variants induced robust apoptosis and cellular toxicity in 4T1 cells. Importantly, this work provides the first demonstration of intracellular expression of an mRNA-encoded ACP fused to a cell-penetrating peptide, thereby validating a modular platform for RNA-based delivery of anticancer agents. This study highlights the feasibility of mRNA-encoded peptide therapeutics as a scalable and customizable strategy for cancer treatment. By combining the advantages of mRNA delivery with rational peptide design, ACP chimeras can be expressed directly inside tumor cells, overcoming the limitations of exogenous peptide administration. Our findings support further development of synthetic mRNA therapeutics to generate potent, selective anticancer peptides with reduced systemic toxicity and improved translational potential.

Background: Diffuse hemispheric glioma (DHG), H3 G34-mutant, is a highly aggressive and fatal pediatric brain tumor, with a median survival of only ∼18 months and no effective targeted therapies. While chimeric antigen receptor (CAR) T cell therapy has shown success in B-cell leukemia and promise in other pediatric central nervous system tumors, it has not yet been evaluated explicitly in preclinical or clinical models of DHG. B7-H3 (CD276), a tumor-associated antigen overexpressed in pediatric brain tumors, represents a promising target for immunotherapeutic intervention in DHG. Here, we present the first preclinical evaluation of B7-H3-directed CAR T cell therapy in DHG. Methods: We evaluated B7-H3 expression in specimens from DHG patients and patient-derived cell lines. Two B7-H3-targeted CAR constructs were generated and evaluated for antigen-specific activation, cytokine production, exhaustion, and cytotoxicity in vitro. Therapeutic efficacy was assessed in multiple orthotopic DHG xenograft models, followed by multiplex immunofluorescence and serum cytokine profiling. Results: B7-H3 was highly expressed in DHG tumors and cell lines, but at minimal levels in normal brain tissue. B7-H3 CAR T cells demonstrated potent, antigen-specific cytotoxicity against DHG cells, with negligible activity against B7-H3-knockout DHG cells. In vivo, the intratumoral administration of B7-H3 CAR T cells led to significant tumor regression and a substantial extension of survival in 3 DHG mouse models, with durable tumor eradication. Conclusion: This study provides preclinical evidence supporting B7-H3 CAR T cell therapy as a highly effective immunotherapeutic strategy for DHG. Our findings support B7-H3 as a compelling immunotherapeutic target for DHG, laying the groundwork for clinical translation.

Supplementary tables and figures

The pioneering design of chimeric antigen receptor (CAR) T-cell therapy demonstrated the potential of reprogramming the immune system. Nonetheless, T-cell exhaustion, toxicity, and suppressive microenvironments limit their efficacy in solid tumors. We previously characterized a subset of tumor-infiltrating CD4+ T cells expressing the FcγRI receptor. Herein, we detail engineering of a receptor, based on the FcγRI structure, allowing T cells to target tumor cells using antibody intermediates. These T cells showed effective and specific cytotoxicity only when an appropriate antibody was added. Only target-bound antibodies activated these cells, while free antibodies were internalized without activation. Their cytotoxic activity was correlated to target protein density, therefore targeting tumor cells with high antigen density while sparing normal cells with low or no expression. This activation mechanism prevented premature exhaustion. Furthermore, during antibody-dependent cytotoxicity these cells secreted attenuated cytokine levels compared with CAR T cells, thereby enhancing their safety profile. These cells eradicated established melanomas, infiltrated the tumor microenvironment, and facilitated host immune cell recruitment in immunocompetent mice. In NOD/SCID gamma mice the cells infiltrate, persist, and eradicate tumors. As opposed to CAR T-cell therapies, which require changing the receptor across different types of cancer, our engineered T cells remain the same across tumor types, while only the injected antibody changes. Overall, we generated a highly flexible T-cell therapy capable of binding a wide range of tumor cells with high affinity, while preserving the cytotoxic specificity only to cells expressing high density of tumor-associated antigens and using a single manufacturing process.

Supplementary tables and figures