Combination therapy with bispecific antibodies and PD-1 blockade enhances the antitumor potency of T cells

The DOCK-AND-LOCK (DNL®) method is a platform technology that combines recombinant engineering and site-specific conjugation to create multispecific, multivalent antibodies of defined composition with retained bioactivity. We have applied DNL® to generate a novel class of trivalent bispecific antibodies (bsAbs), each comprising an anti-CD3 scFv covalently conjugated to a stabilized dimer of different anti-tumor Fabs. Here we report the further characterization of two such constructs, (E1)-3s and (14)-3s, which activate T cells and target Trop-2- and CEACAM5-expressing cancer cells, respectively. (E1)-3s and (14)-3s, in the presence of human T cells, killed target cells grown as monolayers at subnanomolar concentrations, with a similar potency observed for drug-resistant cells. Antitumor efficacy was demonstrated for (E1)-3s co-administered with human peripheral blood mononuclear cells (PBMC) in NOD/SCID mice harboring xenografts of MDA-MB-231, a triple-negative breast cancer line constitutively expressing Trop-2 and PD-L1. Growth inhibition was observed following treatment with (E1)-3s or (14)-3s combined with human PBMC in 3D spheroids generated from target cell lines to mimic the in vivo behavior and microenvironment of these tumors. Moreover, addition of an antagonistic anti-PD-1 antibody increased cell death in 3D spheroids and extended survival of MDA-MB-231-bearing mice. These preclinical results emphasize the potential of combining T cell-redirecting bsAbs with antagonists or agonists that mitigate T cell inhibition within the tumor microenvironment to improve immunotherapy of solid cancers in patients. They also support the use of 3D spheroids as a predictive alternative to in vivo models for evaluating T cell functions.

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