In a groundbreaking leap for cancer immunotherapy, researchers have successfully demonstrated the in vivo generation of chimeric antigen receptor (CAR) T cells through precise, site-specific genetic engineering directly within living hosts. This technological advance, recently detailed in a study published in Nature, represents a transformative shift from traditional ex vivo T cell manufacturing towards a streamlined, one-step treatment process. By employing dually optimized adeno-associated viral vectors (AAV) and engineered delivery vehicles (EDVs) targeting the T cell receptor alpha constant (TRAC) locus, scientists have established a robust platform for reprogramming T cells in situ, creating potent antitumour agents capable of combating both haematological cancers and notoriously difficult solid tumours.
The pioneering approach centers around the design and deployment of a TRAC-BCMA-CAR donor construct packaged within AAV-hT7 vectors. This vector system was delivered to immune-compromised NSG-MHC-I/II double-knockout mice harboring implanted multiple myeloma, specifically seeded with the OPM2 cell line. Following engraftment with human peripheral blood mononuclear cells (PBMCs), the mice received a combined treatment with anti-CD3-targeted EDVs—carrying Cas9 and sgRNAs specifically engineered to edit the TRAC locus—and HDR donor templates delivered by the AAV system. Remarkably, all treated animals exhibited complete tumour regression, as monitored by bioluminescence imaging, highlighting the powerful antitumour capacity of these in vivo generated CAR T cells.
Critically, the therapeutic effect demonstrated durable, long-lasting tumor control. Upon re-exposure to a high-dose OPM2 challenge thirty-five days post-treatment, a majority of the mice maintained tumour remission. This finding underscores the functional persistence of the TRAC-edited CAR T cells, mirroring the long-term efficacy sought in conventional ex vivo CAR T therapies but achieved through an innovative in vivo editing mechanism. The ability to induce sustained antitumour responses directly within the organism streamlines therapeutic delivery and potentially bypasses several cost and logistics barriers associated with cell manufacturing and reinfusion.
Extending beyond hematologic cancer models, the researchers addressed a long-standing challenge of CAR T therapy: efficacy against solid tumours. Employing a second-generation CAR construct targeting B7H3, an antigen found overexpressed in various solid malignancies, the team integrated a CD28ζ-1XX signaling domain within the TRAC locus using the EDV/AAV dual delivery strategy in immunodeficient mice implanted with MES-SA sarcoma cells. Echoing the successes in multiple myeloma models, this innovative approach achieved complete remission in the majority of treated mice, marking the first demonstration of effective in vivo CAR T cell generation against solid tumour xenografts.
The anti-B7H3 CAR construct, when expressed in vivo, not only mediated potent tumour clearance but also improved survival outcomes significantly compared to controls receiving PBMCs alone or tumours without any intervention. The survival benefit and tumor growth inhibition were consistent across multiple human PBMC donors, validating the reproducibility of this approach across donor variability. These tantalizing results open new avenues for tackling solid tumours, a realm where CAR T therapies have struggled due to immune suppression and physical barriers within the tumor microenvironment.
Fundamental to this platform is the precise and efficient targeting of the TRAC locus, which disrupts endogenous TCR signaling and enables uniform CAR expression regulated by native T cell transcriptional machinery. This targeted editing reduces the risk of graft-versus-host disease and enhances safety profiles by minimizing off-target effects commonly associated with random transgene integration. The synergy of CRISPR-Cas9 components, delivered via EDVs, with AAV-based homology-directed repair templates capitalizes on the high specificity and stability of gene editing in human T cells in situ.
The dual-vector system leverages the tissue-tropic selectivity of AAV and the immune-cell-targeting specificity of anti-CD3 EDVs, ensuring precise delivery of both CRISPR machinery and donor DNA to T cells circulating within the host. This sophisticated co-delivery circumvents several key bottlenecks faced by ex vivo manufacturing, such as T cell isolation, activation, expansion, and re-infusion, which demand specialized facilities and extended processing times. Instead, the engineering occurs within natural physiological contexts, potentiated by the in vivo microenvironment that facilitates cell viability and persistence.
Moreover, this approach may dramatically lower the barriers to CAR T accessibility worldwide by reducing manufacturing costs and expanding the eligible patient population, making advanced immunotherapies more scalable. The demonstrated durability and potency against both blood cancers and solid malignancies highlight the broad translational potential of this platform, promising a versatile therapeutic modality adaptable to diverse oncologic indications by simply altering the CAR construct encoded within the HDR donor templates.
The comprehensive preclinical validation included rigorous monitoring by bioluminescent imaging and caliper-measured tumor burden metrics, providing quantitative and temporal resolution of therapeutic responses. Importantly, the TRAC-CAR T cells generated in vivo demonstrated functional longevity, as evidenced by sustained tumor control upon rechallenge, a hallmark of effective immunological memory and resilience against cancer recurrence.
While challenges remain for clinical translation—including immunogenicity of delivery vectors, potential off-target genomic effects, and optimization of dosing regimens—the proof-of-concept established by this study paves the way for next-generation in vivo gene editing therapies. The integration of CRISPR technology with cell-specific delivery vehicles marks a paradigm shift, offering the first scalable model for direct immune modulation within patients, potentially transforming cancer treatment landscapes.
In summary, this study exemplifies a landmark advance in immuno-oncology, merging precision genome engineering with state-of-the-art viral vector technology to generate powerful, targeted CAR T cells without ex vivo manipulation. By demonstrating efficacy across both hematologic malignancies and solid tumour models, the research provides a compelling framework for future clinical applications, offering new hope for patients with refractory cancers and propelling the field towards truly accessible, off-the-shelf cellular therapies.
Subject of Research: In vivo site-specific genetic engineering for T cell reprogramming to generate CAR T cells targeting haematological and solid tumours.
Article Title: In vivo site-specific engineering to reprogram T cells.
Article References:
Nyberg, W.A., Bernard, P.L., Ngo, W. et al. In vivo site-specific engineering to reprogram T cells. Nature (2026). https://doi.org/10.1038/s41586-026-10235-x
