AACR 2026 Oral Presentation: Abogen Presents Preliminary Results of ABO2203 (mRNA-Encoded CD3×CD19 TCE) from First-in-Human Clinical Study in R/R B-NHL

SAN DIEGO, April 20, 2026 /PRNewswire/ -- Abogen, a clinical-stage biotechnology company focused on RNA innovation, today announced preliminary clinical results from the first-in-human (FIH) study of ABO2203 in patients with relapsed/refractory B-cell non-Hodgkin lymphoma (R/R B-NHL). The data were presented in an oral session delivered at the AACR Annual Meeting 2026 in San Diego by Professor Li Wang of Ruijin Hospital Affiliated to Shanghai Jiao Tong University School of Medicine.

ABO2203 is a lipid nanoparticle (LNP)-formulated mRNA drug candidate encoding a CD3×CD19 bispecific T-cell engager (TCE). By enabling in vivo TCE expression via mRNA, ABO2203 is designed to mitigate cytokine release syndrome (CRS) while maintaining robust clinical efficacy.

The Key to TCE Therapies: Overcoming CRS Toxicity

Nearly all marketed protein-based TCEs carry black-box warnings for CRS, which remains a primary safety challenge in the development of such therapies. While step-up dosing strategies are commonly used to reduce CRS risk, their effectiveness remains limited: Grade 2 CRS still occurs on average in 13%-22% of patients, with some cases requiring hospitalization or even ICU admission. In addition, from the standpoint of drug development, 2-3 years are typically required for dose-finding to determine an appropriate step-up dosing regimen.

These challenges are further amplified when extending TCE therapies beyond oncology into autoimmune diseases. Patients with autoimmune conditions often exhibit heightened immune responsiveness and lower tolerance for adverse events, further raising the safety threshold. Moreover, given the chronic and generally non-life-threatening nature of these diseases, CRS-related risks present significant clinical barriers, particularly in outpatient settings. In autoimmune diseases where long-term disease stability depends on treatment safety, a favorable safety profile may represent a more meaningful competitive advantage than efficacy alone.

Initial Clinical Data: Proof of Concept Validated, with Unlimited Potential

The first‑in‑human trial of ABO2203 in R/R B‑NHL is a dose‑escalation and expansion study. The presentation included data from nine patients in the dose- escalation stage. Patients had received a median of four prior lines of therapy, and all had failed prior CD20‑targeted therapy. ABO2203 was administered subcutaneously across dose levels ranging from 3 μg to 1,920 μg. The maximum tolerated dose (MTD) has not yet been reached.

Exceptional Safety Profile: ABO2203 was well tolerated across all evaluated dose levels. No dose‑limiting toxicities (DLTs), CRS, or ICANS were observed. Elevations in liver enzyme elevations were limited to Grade 1 and occurred at low incidence. The most common adverse event was Grade 1–2 pyrexia, without clinically significant changes in oxygen saturation or blood pressure. Grade 3/4 events were infrequent and primarily hematologic, with no unexpected safety signals beyond those associated with the TCE class or NHL.

Favorable Pharmacokinetics and Pharmacodynamics: TCE expression was detected across all three dose cohorts. The time to peak concentration was gradual after each administration (T_max = 5.5 days), with a half‑life of 7.9 days. These findings support an initial once-weekly dosing regimen, with the potential to extend dosing intervals to every two weeks following response, and possibly every three to four weeks thereafter.

In contrast to the "pulse‑like" pharmacokinetic profile of protein‑based TCEs, the mRNA‑expressed TCE demonstrated a flatter and more sustained exposure profile. Compared with a protein TCE of identical amino acid sequence (P4107), which reached peak levels and was eliminated rapidly, ABO2203 exhibited a delayed peak TCE concentration and prolonged half-life. The lower peak concentration (C_max) may help mitigate cytokine release, while sustained mRNA expression may contribute to more durable anti-tumor efficacy than P4107.

Encouraging Efficacy Signals: Based on Lugano 2014 criteria, objective response rates (ORR) were dose-dependent across cohorts, reaching 33%, 67%, and 100% in the low-, medium-, and high-dose groups, respectively. Complete metabolic responses (CMRs) were observed in both the medium- and high-dose cohorts, with a 100%  complete response (CR) rate achieved in the high-dose cohort as updated by Professor Li Wang. Responses were seen across both aggressive (DLBCL) and indolent (FL, MCL, MZL) lymphomas, with a 100% ORR in follicular lymphoma.

Compelling Clinical Significance and Commercial Potential

These findings provide initial clinical proof of concept (PoC) for mRNA-encoded TCE therapeutics, demonstrating a superior safety profile, favorable pharmacodynamics, and encouraging efficacy in B-NHL. The data also suggest potential applications in autoimmune diseases. ABO2203's ability to effectively deplete B cells within lymph nodes may address a well-recognized limitation of conventional CD19/CD20 monoclonal antibodies and existing TCEs in these indications.

The results come amid growing momentum in the TCE field. Since late 2024, the sector has seen increased deal activity, including Merck's USD 1.3 billion acquisition of CN201 (CD3/CD19) and GSK's USD 300 million upfront licensing of Chimagen's trispecific TCE. More recently, Gilead announced a USD 1.675 billion upfront acquisition of Ouro Medicines and its CD3/BCMA bispecific asset, CM336/OM336 this March. With the global TCE market projected to reach USD 121 billion by 2035 (Frost & Sullivan), ABO2203 represents a promising asset in this rapidly expanding category.

About Abogen

Abogen is a clinical-stage biotechnology company dedicated to developing novel medicines based on RNA technologies. Founded in 2019, the company has established integrated in-house capabilities spanning the full mRNA development lifecycle, including protein engineering, mRNA sequence design and synthesis, lipid nanoparticle (LNP) delivery, formulation, and large-scale manufacturing.