Celldex Therapeutics, Inc./Biosion, Inc. Poster Presentation at SITC, November 12-13, 2021

Abstract to be published in Journal of Immunotherapy of Cancer (JITC)

CDX-585, A bispecific antibody with dual targeting of ILT4 and PD-1 checkpoint pathways

Laura Vitale2, Mike Murphy1, Collin Xia4, Zeyu Peng4, Thomas O’Neill2, Ed Natoli1, Jay Lillquist1, Linda Crew1, Anna Wasiuk2, Jeff Weidlick2, Jenifer Widger2, Laura Mills-Chen2, Andrea Crocker2, Colleen Patterson2, James Boyer3, April R. Baronas3, Russell A. Hammond3, Mingjiu Chen4, Hugh M. Davis5, Mark Ma4, Joel Goldstein2, Lawrence J. Thomas3, , Diego Alvarado1, Henry C. Marsh3 and Tibor Keler2

1Celldex Therapeutics, Inc., New Haven, CT 06511, 2Hampton, NJ 08827 and 3Fall River, MA 02723

4Biosion, Inc., Nanjing, China and 5Biosion USA, Inc., Newark, DE 19711

Background: Activation of the ITIM-bearing ILT4/LILRB2 receptor by its cognate ligands (HLA-G and HLA Class I) has been postulated as a resistance mechanism for checkpoint blockade of PD-1 and CTLA-4. Dual inhibition of receptors that suppress myeloid and T cell compartments through the generation of bispecific antibodies (bsAbs) is a promising strategy to improve outcomes for patients whose tumors are resistant to checkpoint inhibition.

Methods: We describe the discovery and characterization of novel ILT4 (7B1) and PD-1 (V8-3) inhibitory mAbs for engineering bsAbs that revert myeloid cell suppression by antagonizing ILT4 and activate T-cell responses through PD-1 inhibition. Humanized 7B1 and V8-3 mAbs were generated that specifically bind human ILT4 and PD-1, with sub-nanomolar affinity. Additionally, using these highly specific parental mAbs, we engineered a tetravalent bsAb (CDX-585) using the PD-1 IgG1 mAb (Fc null, enhanced PK) linked to scFv of the ILT4 mAb at the C-terminus of the heavy chain. CDX-585 has good biophysical characteristics and retains functional properties similar to or better than the parental mAbs.

Results: CDX-585 has high affinity binding to ILT4 and PD-1 and is a potent competitor of their respective ligands. Primary cultures of human macrophages and dendritic cells treated with CDX-585 enhanced production of inflammatory cytokines/chemokines, which was further potentiated in the presence of toll like receptor activation with lipopolysaccharide (LPS).  CDX-585 was particularly effective in promoting T cell activation as measured by mixed lymphocyte reactions, and in polarizing macrophages towards M1 based on their cytokine profile. Pilot studies in mice and cynomolgus macaques confirmed a favorable pharmacokinetic profile without adverse effects of treatment noted in clinical observations or clinical chemistry.

Conclusions: CDX-585 effectively combines ILT4 and PD-1 blockade into one molecule with favorable biophysical and functional characteristics supporting the initiation of development activities including manufacturing and IND-enabling studies.