On June 8, 2026 Lyell Immunopharma, Inc. (Nasdaq: LYEL), a late-stage clinical company advancing a pipeline of next-generation chimeric antigen receptor (CAR) T-cell therapies for patients with cancer, reported an update on the safety profile of LYL273 in its ongoing U.S. Phase 1 clinical trial in patients with relapsed or refractory metastatic colorectal cancer (mCRC), and announced the Phase 1 trial has been amended to enable seamless expansion into a potential pivotal single-arm Phase 2 trial pending regulatory alignment.

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LYL273 is a guanylyl cyclase C (GCC)-targeted CAR T-cell product candidate enhanced with CD19 CAR expression and controlled cytokine release designed to improve CAR T-cell expansion, immune cell infiltration and cancer cell killing in the hostile solid tumor microenvironment. A 50% overall response rate across Dose Levels 1 and 2 has been previously reported (data cutoff date of October 28, 2025) in third- or later-line (3L+) relapsed or refractory mCRC patients in the U.S. Phase 1 clinical trial. The FDA has granted LYL273 Fast Track designation for the treatment of mCRC.

"The substantial reduction of Grade 2 or higher diarrhea or colitis, and absence of Grade 3 or higher CRS and ICANS in patients treated under our gastrointestinal prophylaxis and standardized safety management plan suggest we can manage the safety profile of LYL273 in patients with relapsed or refractory metastatic colorectal cancer," said Lynn Seely, M.D., President and Chief Executive Officer of Lyell. "We are continuing to move forward to selection of the recommended Phase 2 dose and are on track for an End-of-Phase 1 meeting with the FDA by the end of the year."

Updated Safety Data from U.S. Phase 1 Clinical Trial Evaluating LYL273 in Patients with Relapsed or Refractory Third- or Later-Line mCRC

Nineteen patients have been enrolled in the U.S. Phase 1 clinical trial across Dose Levels 1 and 2 (1 and 2 x 106 CAR+ cells/kg) as of the data cutoff date of May 5, 2026. Ten of these patients were enrolled under the new gastrointestinal (GI) prophylaxis regimen including infliximab, vedolizumab and budesonide, along with a standardized safety management plan. Notably, the GI prophylaxis and standardized safety management plan reduced Grade > 2 diarrhea or colitis from 55% to 10% in patients without (N = 9) and with (N = 10) GI prophylaxis, respectively. These ten patients did not experience Grade ≥ 3 cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). No additional adverse events of interest have been identified. There was no difference observed in GCC-CAR+ cell expansion either in terms of maximum cell expansion or area under the curve in those patients who received GI prophylaxis and those who did not.

Dose escalation continues in the U.S. Phase 1 clinical trial; the maximum tolerated dose has not been determined.

Phase 1 Clinical Trial Amended to Phase 1/2 Design

The U.S. Phase 1 clinical trial evaluating LYL273 in relapsed or refractory 3L+ mCRC has been amended to a Phase 1/2 design (CARABINER). The amended design enables seamless expansion into a potential pivotal single-arm Phase 2 trial once the recommended Phase 2 dose has been determined, subject to discussions with the U.S. Food and Drug Administration (FDA). New centers are being added to the trial in preparation for initiating the dose expansion portion of the Phase 1/2 trial.

The Phase 1 portion of the clinical trial includes four dose-escalation cohorts at Dose Levels 1 through 4 (1, 2, 3, 4 x 106 CAR+ cells/kg). Each dose-escalation cohort is designed to include three or six patients, with up to twenty-four patients across the four dose-escalation cohorts.

In addition to the existing 3L+ cohorts, the amendment adds new cohorts, including a second-line cohort and a cohort evaluating a combination strategy with radiotherapy. Up to sixty patients are expected to be enrolled across the new cohorts. The Phase 2 portion will expand enrollment at the recommended Phase 2 dose in an open-label, single-arm cohort.

Upcoming LYL273 Milestones

In the second half of 2026, additional Phase 1 clinical data, including clinical outcomes, and an End-of-Phase 1 meeting with the FDA are expected.

(Press release, Lyell Immunopharma, JUN 8, 2026, View Source [SID1234666501])