Material Event (Form 8-K)

On April 13, 2026, Allogene Therapeutics, Inc. ("Allogene" or the "Company") announced interim futility analysis from its pivotal Phase 2 ALPHA3 trial of cemacabtagene ansegedleucel ("cema-cel")in first-line ("1L") consolidation for large B-celllymphoma ("LBCL").

The ALPHA3 trial is the first randomized study in LBCL designed to assess whether minimal residual disease ("MRD")-guided intervention with cema-celbefore relapse can eliminate residual disease and potentially prevent recurrence. The study identifies high-risk patients using Natera's investigational CLARITY^™ MRD assay which is powered by its phased variant MRD technology. Patients with LBCL who have completed curative-intent treatment in both front-line and later line settings, including autologous CAR T therapy, and who achieve MRD negative status by technology have demonstrated improved progression-free survival ("PFS") and event-free survival ("EFS") compared to those who do not attain MRD-negativestatus.

This interim futility analysis was based on the first 24 patients randomized in the two study arms still open to enrollment (12 in the cema-celarm and 12 in the observation arm) and followed for post-treatment MRD assessment. MRD is assessed on Day 45, Month 3, and every three months during the first year of follow-up.The primary endpoint of EFS, defined as starting new anti-lymphoma therapy, disease progression, or death, along with key secondary endpoints of PFS and overall survival ("OS"), remains blinded.

Summary of Efficacy Data

At the protocol-defined data cutoff date, 58.3% (7/12) of patients in the cema-celarm achieved MRD negativity compared to 16.7% (2/12) in the observation arm. This represents a 41.6% absolute difference in MRD clearance between the two arms. Based on literature, a difference in percentage points of 25-30%in MRD clearance could translate into meaningful clinical benefit at study completion. In these initial patients, the clearance of MRD occurred rapidly following cel-celtreatment. At the first MRD assessment (Day 45), plasma ctDNA levels decreased from baseline by a median of 97.7% in the cema-cel arm compared to a 26.6% median increase in the observation arm. The Company believes these interim data provide initial support for cema-cel'spotential as a novel strategy for treating high-risk patients at the end of first-line treatment.

Summary of Safety Data

Cema-celhas been generally well-tolerated as of the data cutoff with no serious adverse events related to treatment. There were no cases of cytokine release syndrome ("CRS"), immune effector cell-associated neurotoxicity syndrome ("ICANS") or graft-versus-host disease ("GvHD") in the Treatment Emergent Adverse Event ("TEAE") of Special Interest category, which captures adverse events associated with CAR T.

Ten of 12 patients who received cema-celwere managed entirely outpatient post-infusion. The remaining two patients were briefly hospitalized for events deemed unrelated to cema-celtreatment (atrial fibrillation and non-cardiacchest pain). One patient in the observation arm was hospitalized for febrile neutropenia. This contrasts with the broader CAR T experience where hospitalization for toxicity management remains common, even in outpatient programs, with approximately 70-90% of patients requiring admission and roughly 75% hospitalized for adverse events within 30 days.

Patient Characteristics

Both study arms consisted of patients with high-risk, aggressive lymphomas. Although limited by the small sample size, baseline characteristics show that a numerically greater number of patients in the cema-celarm had more aggressive disease features, specifically stage III-IVdisease and higher International Prognostic Index ("IPI") scores, compared to the observation arm.

A high-intensity variant of R-CHOP, DA-EPOCH-R,was the most commonly administered first-line therapy across both arms, with a slightly higher proportion of patients in the cema-celarm receiving this first line treatment regimen (58.3% vs. 41.7%). Twenty-five percent of patients in each arm entered the study after achieving a partial remission to 1L therapy.

Planned Activities

The ALPHA3 trial is enrolling across more than 60 sites, with additional sites coming online, and is expected to enroll approximately 220 patients. Study accrual is anticipated to be complete by the end of 2027. The study is powered to detect a 50% reduction in the risk of EFS events. The Company anticipates an interim EFS analysis in mid-2027and the primary EFS analysis in mid-2028.If positive, these results could support a Biologics License Application ("BLA") submission.