A T cell receptor β chain–directed antibody fusion molecule activates and expands subsets of T cells to promote antitumor activity.

Despite the success of programmed cell death-1 (PD-1) and PD-1 ligand (PD-L1) inhibitors in treating solid tumors, only a proportion of patients respond. Here, we describe a first-in-class bifunctional therapeutic molecule, STAR0602, that comprises an antibody targeting germline Vβ6 and Vβ10 T cell receptors (TCRs) fused to human interleukin-2 (IL-2) and simultaneously engages a nonclonal mode of TCR activation with costimulation to promote activation and expansion of αβ T cell subsets expressing distinct variable β (Vβ) TCR chains. In solution, STAR0602 binds IL-2 receptors in cis with Vβ6/Vβ10 TCRs on the same T cell, promoting expansion of human Vβ6 and Vβ10 CD4⁺ and CD8⁺ T cells that acquire an atypical central memory phenotype. Monotherapy with a mouse surrogate molecule induced durable tumor regression across six murine solid tumor models, including several refractory to anti–PD-1. Analysis of murine tumor-infiltrating lymphocyte (TIL) transcriptomes revealed that expanded Vβ T cells acquired a distinct effector memory phenotype with suppression of genes associated with T cell exhaustion and TCR signaling repression. Sequencing of TIL TCRs also revealed an increased T cell repertoire diversity within targeted Vβ T cell subsets, suggesting clonal revival of tumor T cell responses. These immunological and antitumor effects in mice were recapitulated in studies of STAR0602 in nonhuman primates and human ex vivo models, wherein STAR0602 boosted human antigen-specific T cell responses and killing of tumor organoids. Thus, STAR0602 represents a distinct class of T cell–activating molecules with the potential to deliver enhanced antitumor activity in checkpoint inhibitor–refractory settings. Editor's summary: Activating T cells by targeting T cell receptors (TCRs), costimulatory receptors, or cytokine receptors represents an attractive approach to improving antitumor T cell responses; however, these approaches often do not sufficiently stimulate T cell responses and can cause severe toxicities that have impeded their translation into the clinic. To address this, Hsu et al. developed a bifunctional therapeutic molecule called STAR0602, comprising an antibody specific to human TCR Vβ6 and Vβ10 chains fused to a human interleukin-2 (IL-2) molecule, which selectively activates a subset of T cells through both the TCR and IL-2 receptor signaling pathways. STAR0602 promoted specific expansion of human Vβ6- and Vβ10-expressing T cells and promoted killing of human tumor organoids in vitro. In vivo studies showed that a murine surrogate molecule promoted durable control of tumor burden in six solid tumor models. These data, along with favorable safety data, support further development of STAR0602 and similar TCR-targeting antibody fusion molecules. —Courtney Malo [ABSTRACT FROM AUTHOR]