CAR-T Meeting 2026 | The selective targeting of T-cell malignancies using a TRBC1-directed CAR T-cell therapy

T-cell malignancies are hard to target because malignant and healthy T-cells share most surface antigens, so conventional CARs target risk fratricide during manufacturing and profound T-cell aplasia in patients. The key to selective targeting is to exploit clonality. Major T-cells express one of two mutually exclusive TCR beta constant regions, TRBC1 or TRBC2, and the malignant T-cell clone is restricted to only one. A TRBC1-directed CAR therefore recognizes and eliminates TRBC1-positive malignant cells, while leaving TRBC2-positive healthy T-cell compartment intact. That is the core of the selectivity: it’s not “pan–T-cell targeting,” it’s clonotype-restricted targeting within the T-cell lineage. In our preclinical work, this translated into robust killing of TRBC1-positive targets with the preservation of TRBC2 T-cells and single-cell imaging confirmed that the cytotoxicity was strictly TRBC1-dependent. The practical insight is that TRBC1 provides a therapeutic window in which meaningful antitumor activity can be achieved while preserving a functional T-cell compartment. 

The rationale for developing this therapy is based on biological T-cell receptor rearrangement. During thymic development, T-cells undergo allelic exclusion at the TCR beta locus, meaning that each mature T-cell expresses only one functional beta chain constant region, either TRBC1 or TRBC2, and this choice is irreversible and stable over time. In T-cell malignancies, because the disease is clonal, the entire tumor population uniformly retains the same TRBC isoform. These makes a TRBC1 lineage-intrinsic and clonotype-stable marker. What makes TRBC1 particularly promising is that it is not only merely overexpressed; it is structurally encoded within the TCR complex. At the same time, targeting TRBC1 preserves the TRBC2-positive healthy T-cell repertoire, thereby maintaining a proportion of the adaptive immune compartment. The rationale is not selectivity, but also biological stability, reduced escape potential, and immune preservation within the same strategy. 

We tested the CAR-T One T-cells for fitness during manufacturing, for in vitro efficacy and specificity at single-cell and also bulk culture levels, for safety against the inadvertent tumor cell transduction, and finally, for in vivo anti-leukemia performance. First, we asked whether CAR-T-One engineering impacts the TRBC2 compartment. CAR-T-One efficiently transduces beta 2 T-cells and preserves their fitness with a stem cell memory rich phenotype and minimal exhaustion during manufacturing. We then evaluated the in vitro potency and the specificity using Jurkat T-cell ALL and the H9 T-cell lymphoma models. In both cases, we achieved nearly complete tumor killing by 72 hours, while TRBC1-negative SUDHL-1 cells were unaffected, demonstrating antigen specificity. We then tested the effect of the expected on-target off-tumor toxicity on normal TRBC1 T-lymphocytes in vitro. When CAR-T-One T-cells were challenged against the bulk T-lymphocytes, so expressing not only TRBC1 but also TRBC2 antigens, we observed an early but transient reduction in both populations, so beta1 and beta2 T-cells. Similarly, when we challenged CAR-T-One T-cells against the TRBC1 compartment alone, we observed a reduction in both populations, but also we observed a limited persistence of CAR-T-One effector cells with CAR down-modulation, suggesting a limited persistence of this type of effector cell in this specific setting. 

A key safety question in T-cell malignancies is accidental tumor cell transduction during manufacturing. We modeled it by transducing TRBC1-positive tumor cells in the absence of the effector cell and observed progressive loss of CAR-positive tumor cells with a decrease of CAR expression with reduced viability, consistent with auto-killing rather than clonal expansion. Importantly, CAR expression on tumor cells did not mask TRBC1 from CAR-T-One effector cell recognition, suggesting that the risks associated with this event are negligible. We then conducted the single-cell tracking experiment, which confirmed a rapid TRBC1-dependent killing. TRBC2 healthy T-cells were completely spared, and the cytotoxicity was driven by specific antigen recognition rather than the contact duration between effector and target cell. 

Finally, in vivo, we tested the efficacy of CAR-T-One in both minimal residual disease and high-tumor-burden settings. In the MRD, CAR-T-One achieved rapid, durable eradication with 80% long-term overall survival, while in the high-tumor burden experiment, we saw a transient but significant complete remission at early times, which resulted in significant disease-free survival benefit, suggesting CAR-T-One could be a bridge to transplant option for relapse/refractory T-ALL and TCL patients. Finally, to enable a first-in-human CAR-T-One trial, we successfully produced a GMP-compliant lentiviral vector batch using an industrially scalable, closed process in collaboration with IDIBAPS Hospital Clinic in Barcelona. 

The logical next step is to transfer the process to our recently approved in-house cell factory to proceed with the clinical testing of the CAR-T-One therapeutic strategy in patients with T-cell malignancies. However, these types of trials are very expensive, so we will need to first raise funds to cover the cost before proceeding with the first in-human trial of CAR-T-One.

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