Work

811 AR166, a novel tri-specific immunocytokine, overcomes anti-PD-1 resistance by delivering cis-acting IL-2v via dual PD-1 and LAG-3 targeting

Year: 2026

Type: conference-abstract

Abstract: Background Immunocytokines fusing anti-PD-1 antibody with interleukin-2 (IL-2) show clinical potential in overcoming resistance to PD-(L)1 inhibitors. However, varied response rates highlight the need for improved efficacy, particularly in tumors with primary and acquired resistance to PD-1 blockade expressing high levels of LAG-3. Emerging evidence indicates LAG-3 acts synergistically with PD-1 to promote T cell exhaustion, while dual blockade can reprogram CD8 + T cells to enhance antitumor immunity. Here, we present AR166, a novel tri-specific immunocytokine engineered with Fc-silencing, delivering dual PD-1/LAG-3 blockade while inducing targeted CD8+ T cell activation via an optimized cis-acting IL-2 variant (IL-2v).Methods Patient-derived tumor samples, including colorectal cancer (CRC), were profiled by flow cytometry and IHC to confirm PD-1 and LAG-3 expression. PD-1×LAG-3 activity and cis-acting IL-2v were assessed via blockade and pSTAT5 activation assays. Fc-silencing was evaluated via ADCC, ADCP, and CDC. Exhausted T cells induced by repeated stimulation were co-cultured with tumor cells to determine T cell cytotoxicity in the presence of AR166. The ex vivo tumor patient-derived TILs were evaluated to characterize AR166-mediated immune activation. Antitumor efficacy was evaluated in anti-PD-1 drug-resistant tumor models using humanized PD-1/LAG-3/PD-L1 triple knock-in (KI) mice, and complete responders were rechallenged with tumor cells to assess immune memory. Tumor infiltrating lymphocytes (TILs) were profiled using the same mouse model. Safety and PK profiles were analyzed in cynomolgus monkeys.Results PD-1 and LAG-3 expression in CD8 T cells was confirmed in tumor patient-derived samples. AR166 effectively inhibited PD-1/PD-L1 and LAG-3/MHC II pathways, with IL-2v showing strictly cis-activity upon anchoring. Assessment of Fc-silencing showed no detectable effector functions. AR166 elicited robust T cell responses compared to bi-specific counterpart in an in vitro exhaustion model, with similar results observed in the ex vivo tumor patient-derived TILs.AR166 showed remarkable tumor growth inhibition in triple KI models recapitulating acquired resistance to anti-PD-1 therapy, expanding stem-like and effector T cells. Furthermore, tumor-specific immune memory was confirmed upon rechallenge with tumor cells. AR166 achieved favorable safety and PK profiles in cynomolgus monkeys.Conclusions Our findings demonstrate that AR166 represents an optimized tri-specific immunocytokine, establishing that dual PD-1 and LAG-3 targeting is essential to maximize the therapeutic efficacy of cis-acting IL-2v, thereby outperforming individual controls with a favorable safety profile and highlighting its therapeutic potential to overcome PD-1 resistance.

Source: Journal for ImmunoTherapy of Cancer

DOI: 10.1136/jitc-2026-sitc2026.0811