CAMBRIDGE, Mass. — September 9, 2026

Crossbow Therapeutics, Inc. announced dosing of the first participant in the Phase 1 TelOscope-001 clinical trial of CBX-663, a first-in-class T-cell engager (TCE) being developed for multiple hematologic and solid malignancies. The open-label, dose-escalation study will evaluate the safety, tolerability and clinical activity of CBX-663 in patients with relapsed or refractory myeloid malignancies, advanced solid tumors and recurrent or progressive glioblastoma multiforme (GBM). The clinical milestone moves Crossbow’s second TCE candidate into human testing and expands the company’s efforts to develop antibody therapies against cancer targets that have historically been difficult to address. Crossbow expects to report initial clinical data from TelOscope-001 around the end of 2027, providing an early assessment of CBX-663’s therapeutic potential and safety profile.

CBX-663 Targets TERT Across Multiple Cancer Types

CBX-663 is designed to target telomerase reverse transcriptase (TERT), a protein overexpressed in approximately 90% of cancers. The molecule uses Crossbow’s T-Bolt™ platform to recognize a TERT-derived peptide-human leukocyte antigen (pHLA) complex displayed on the surface of tumor cells. CBX-663 is an engineered bispecific antibody that combines TERT-directed binding with a CD3-binding arm, enabling it to recruit and activate T cells against tumor cells. The candidate incorporates two binding domains for TERT, which Crossbow designed to strengthen tumor-cell engagement and immune activation. By targeting an intracellular tumor protein through its pHLA presentation rather than requiring a conventional surface antigen, the approach is intended to expand the range of cancer proteins accessible to antibody-based therapies. The company believes TERT’s broad expression across hematologic and solid malignancies provides an opportunity for a potentially broad pan-cancer development strategy.

TelOscope-001 Evaluates Safety and Antitumor Activity

The Phase 1 TelOscope-001 study is designed to establish the clinical profile of CBX-663 through a fixed step-up dosing schedule. Participants with relapsed or refractory myeloid malignancies, advanced solid tumors or recurrent/progressive GBM will be evaluated during dose escalation, with safety and tolerability representing primary development priorities alongside assessments of preliminary clinical activity. The trial follows preclinical studies in which CBX-663 demonstrated potent, antigen-specific tumor killing across multiple TERT-positive cancer models. Crossbow reported minimal activity against TERT-negative or HLA-mismatched cells, supporting the intended specificity of the TERT/pHLA targeting strategy. The company also reported a favorable preclinical safety profile and pharmacokinetic characteristics comparable to conventional antibody therapies. As the first human study of CBX-663, TelOscope-001 will provide critical information on dosing, pharmacokinetics, tolerability and early evidence of antitumor activity across multiple cancer settings.

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Crossbow Expands Its T-Bolt TCE Pipeline

The advancement of CBX-663 strengthens Crossbow Therapeutics’ broader T-Bolt™ platform and its strategy to develop TCR-mimetic antibody therapies. The platform combines optimized antibody libraries with precision screening technologies to identify high-affinity binders against intracellular tumor antigens presented as pHLA complexes. Crossbow developed CBX-663 internally and is conducting the TelOscope-001 study, maintaining control over both the therapeutic candidate and its clinical development strategy. As the company’s second TCE candidate, CBX-663 demonstrates the potential of the T-Bolt approach to generate therapies directed at cancer proteins that are not readily accessible through traditional antibody targeting. The first patient dosing milestone marks a transition from platform and preclinical validation toward clinical proof-of-concept, with the upcoming Phase 1 data expected to determine the next development steps for CBX-663 across hematologic malignancies, solid tumors and GBM.

Source: Crossbow Therapeutics press release