Abstract 7534: Tobemstomig, a novel bispecific checkpoint inhibitory antibody to preferentially block PD-1 and LAG-3 on CD8 TILs over Tregs

Abstract Checkpoint inhibitors targeting PD-1 have shown unprecedented clinical efficacy in several cancer indications and therefore have, revolutionized the standard of care. However, despite this advancement, only ~20-30% of the patients derive durable benefit from such a treatment. One of the suggested reasons for this limited success is the expression/activation of compensatory inhibitory pathways such as LAG-3 on tumor-reactive T cells. Therefore, it is envisioned that simultaneous antagonism of PD-1 and LAG-3 receptors would overcome this adaptive resistance mechanism and allow a more profound reinvigoration of tumor-reactive T cells. LAG-3 is constitutively expressed by regulatory T cells (on Tregs) and it has been reported that its blockade increases Treg suppressive function which could potentially off-sets the benefit of blocking LAG-3 on tumor-reactive CD8 T cells. We therefore developed a 1+1 PD1-LAG3 bispecific antibody, Tobemstomig, with a unique PD-1 binder recognizing a glycoepitope and more than 20 fold higher affinity than the LAG-3 binder which recognizes a novel and differentiated binding epitope (E3). This difference in affinities allows for an avidity driven selectivity gain to PD-1 and LAG-3 double positive T cells over and the following advantages over monospecific and other bispecific aPD-1/-L1 and aLAG-3 antibodies: 1. improved targeting to tumor-reactive T cells rather than Tregs due to the selectivity gain and different expression patterns of PD-1 and LAG-3 on these two T cell types, 2. reduced internalization, 3. resistance to drug-shaving by macrophages due to Fc -silencing via P329G LALA, 4. increased in vitro T cell effector functions even in the presence of Tregs, 5. in-vivo targeting and expansion of CD8 TILs, including stem-like T cells, and increase in T cell effector functions and6. superior in vivo tumor control/eradication compared to combination of monospecific anti-PD1 and anti-LAG3 antibodies, in several mouse models including Panc02 in syngeneic huPD-1xhuLAG3 dtg mice and BXPC3, WSU, OCI-Ly18 and BC004 in humanized mice Tobemstomig has completed dose escalation and is currently tested in a composite proof of concept Ph2 trial in several solid tumor indications. Citation Format: Laura Codarri-Deak, Patrick Aaron Weber, Valeria Nicolini, Christian Klein, Pablo Umana, Stefan Seeber, Mario Perro, Stephane Leclair. Tobemstomig, a novel bispecific checkpoint inhibitory antibody to preferentially block PD-1 and LAG-3 on CD8 TILs over Tregs abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 7534.