A phase 1, first-in-human (FIH), dose-escalation and dose-optimization study to evaluate the safety, tolerability, pharmacokinetics, and anti-tumor activity of CBI-1214 T-cell engager in participants with advanced or metastatic microsatellite-stable (MSS)/microsatellite instability–low (MSI-L) colorectal cancer (CRC).

TPS3678 Background: Advanced and metastatic colorectal cancer (CRC) remains an area of significant unmet clinical need, particularly for patients with MSS/MSI-L tumors. In recent years, there have been several advancements in the treatment of solid tumors with T cell engagers. Our ATLAS scRNA-seq based discovery platform identified LY6G6D as a highly-specific tumor-associated antigen in advanced and metastatic CRC. CBI-1214, a CD3 bispecific T cell engager targeting LY6G6D with potent in vitro and in vivo activity even at low LY6G6D expression levels of ~300 copies/cell ( Yigit B et al, AACR 2025 ), is being developed for the treatment of patients with advanced or metastatic MSS/MSI-L CRC. Methods: This ongoing, open-label FIH study (CBI-1214-001) is being conducted to evaluate the safety, tolerability, pharmacokinetics (PK), and anti-tumor activity of CBI-1214 and to determine the maximum tolerated dose (MTD) and/or optimal biological dose (OBD) in participants with advanced or metastatic MSS/MSI-L CRC who have exhausted at least one prior line of systemic treatment and do not qualify for available targeted treatment options for actionable genomic alterations. Additional eligibility criteria include: at least 18 years of age, measurable disease (as defined by RECIST v1.1), available archival tumor tissue sample or a fresh tumor sample, ECOG PS 0 or 1, as well as adequate hematologic and organ functions. Patients whose CRC tumor tissues have been identified as dMMR or MSI-H are excluded. The study is conducted in two parts: Part 1 dose escalation, which starts with Part 1a as accelerated dose escalation, followed by Part 1b escalation, which is based on a modified toxicity probability interval (mTPI-2) design, and Part 2, which is designed as a randomized dose optimization study to select the final recommended phase 2 dose (RP2D). For both parts of the study, the study intervention is administered as monotherapy, given as an intravenous (IV) infusion, in 21-day treatment cycles, with a step-up option. After an up-to-28-day screening period, eligible patients receive study medication and are followed for their entire treatment period plus a follow-up period of approximately 90 days. The study is open for recruitment in the United States (NCT07321106). Clinical trial information: NCT07321106 .