Sialic acid removal from dendritic cells improves antigen cross-presentation and boosts anti-tumor immune responses

Objectives: Reduced expression of adhesion molecules in tumor vasculature can limit infiltration of effector T cells. To improve T cell adhesion to tumor endothelial cell (EC) antigens and enhance transendothelial migration, we developed bispecific, T-cell engaging antibodies (bsAb) that activate T cells after cross-linking with EC cell surface antigens. Methods: Recombinant T-cell stimulatory anti-VEGFR2–anti-CD3 and costimulatory anti-TIE2–anti-CD28 or anti-PD-L1–anti-CD28 bsAb were engineered and expressed. Primary lines of human umbilical vein endothelial cells (HUVEC) that constitutively express VEGFR2 and TIE2 growth factor receptors and PD-L1, but very low levels of adhesion molecules, served as models for anergic tumor EC. Results: In cocultures with HUVEC, anti-VEGFR2–anti-CD3 bsAb increased T cell binding and elicited rapid T cell activation. The release of proinflammatory cytokines TNF-α, IFN-γ, and IL-6 was greatly augmented by the addition of anti-TIE2–anti-CD28 or anti-PD-L1–anti-CD28 costimulatory bsAb. Concomitantly, T cell-released cytokines upregulated E-selectin, ICAM1, and VCAM1 adhesion molecules on HUVEC. HUVEC cultured in breast cancer cell-conditioned medium to mimic the influence of tumor-secreted factors were similarly activated by T cell-engaging bsAb. Migration of T cells in transwell assays was significantly increased by anti-VEGFR2–anti-CD3 bsAb. The combination with costimulatory anti-TIE2–anti-CD28 bsAb augmented activation and proliferation of migrated T cells and their cytotoxic capacity against spheroids of the MCF-7 breast cancer cell line seeded in the lower transwell chamber. Conclusions: T cells activated by anti-VEGFR2–anti-CD3 and costimulatory EC-targeting bsAb can reverse the energy of quiescent EC in vitro, resulting in improved T cell migration through an EC layer.

Soluble variants of recombinant T cell receptors (TCRs) have become attractive tools for the retargeting of cytotoxic T cells toward intracellular tumor or viral antigens by combining them with CD3-binding antibodies in bispecific T cell engagers; however, TCR-based NK cell engagers have not been studied so far. Here, we developed TCR-based bispecific agents for the redirection of NK cells utilizing a bivalent IgG1-like format. Trifunctional NK engagers included an Fc part with enhanced binding to FcγRIII/CD16A and single-chain (scFv) antibodies recognizing either NKp46 or CD16A, activating NK cell receptors. HCMV pp65/HLA-A2 reactive TCR-scFv-Fc fusion proteins incorporating an affinity-matured TCR and anti-NKp46 scFv activated peripheral blood NK cells and induced cytotoxicity in an antigen-specific manner. For T cell redirection, TCR-scFv-Fc fusion proteins included an scFv antibody recognizing CD3ε. Compared with NK cell engagers, T cell engagers showed similar sensitivity but lower peptide selectivity. For two TCRs recognizing melanoma-associated peptides, affinity-matured TCR-scFv-Fc fusion proteins enabled NK and T cell redirection and activation, and killing of tumor target cells loaded with exogenous peptides. Our results expand the versatility of the soluble TCR technology to NK cell engagers; however, they still require improvement in sensitivity to target tumor cells with low peptide/MHC-I complex densities.