Simultaneous De-Repression Of Innate And Adaptive Immune Responses Through Dual Targeting Of Ilt4 And Pd(L)-1 With Bispecific Antibodies.

Abstract Activation of innate immunity using targeted therapies has become an attractive approach to stimulate antitumor responses. Dual inhibition of receptors that suppress myeloid and T cell compartments through the generation of bispecific antibodies (bsAbs) is a promising strategy to overcome resistance to checkpoint inhibition. Activation of the ITIM-bearing ILT4/LILRB2 receptor by its cognate ligands (HLA-G and HLA Class I) in myeloid cells induces a strong immunosuppressive response that may be leveraged by tumors to evade immune surveillance. Monoclonal antibodies (mAbs) that inhibit ILT4 activity have demonstrated promising preclinical and early clinical data in combination with PD-1 inhibitors, including in the checkpoint refractory setting. These findings provide a rationale to co-target ILT4 with PD(L)-1 using a single molecule. We describe the discovery and characterization of ILT4 inhibitory mAbs for engineering bsAbs that revert myeloid cell suppression by antagonizing ILT4 and activate T cell responses through PD(L)-1 inhibition. Humanized anti-ILT4 mAbs were generated that specifically bind human and macaque ILT4. These mAbs exhibit sub-nanomolar HLA-G binding to ILT4 expressing cells. Macrophages treated with ILT4 mAbs release inflammatory cytokines/chemokines and upregulate activation markers resulting in polarization to an M1 inflammatory phenotype. These activities are further potentiated in the presence of toll-like receptor activation with lipopolysaccharide (LPS). We engineered tetravalent bsAbs using an Fc-silenced IgG1 linked to scFv format from our anti-ILT4 and anti-PD-L1 mAbs in both orientations. The bsAbs have good biophysical characteristics and retain functional properties similar to the parental mAbs. Further in vitro and in vivo characterization efforts are ongoing to select the bsAb candidate to enter development activities and IND-enabling studies. Citation Format: Laura Vitale, Mike Murphy, Jeff Weidlick, Anna Wasiuk, Thomas O'Neill, Jenifer Widger, Laura Mills-Chen, Andrea Crocker, Colleen Patterson, James Boyer, Linda Crew, Edward J. Natoli, Jay S. Lillquist, Joel Goldstein, Lawrence J. Thomas, Henry C. Marsh, Diego Alvarado, Tibor Keler. Simultaneous de-repression of innate and adaptive immune responses through dual targeting of ILT4 and PD(L)-1 with bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1865.