Mechanism of action of a T cell-dependent bispecific antibody as a breakthrough immunotherapy against refractory colorectal cancer with an oncogenic mutation

Abstract

T cell-dependent bispecific antibody (TDB)-induced T cell activation, which can eliminate tumor cells independent of MHC engagement, is expected to be a novel breakthrough immunotherapy against refractory cancer. However, the mechanism of action of TDBs has not been fully elucidated thus far. We focused on TDB-induced T cell-tumor cell contact as an important initial step in direct T cell-mediated tumor cell killing via transport of cytotoxic cell proteases (e.g., granzymes) with or without immunological synapse formation. Using an anti-EGFR/CD3 TDB, hEx3, we visualized and quantified T cell-tumor cell contact and demonstrated a correlation between the degree of cell contact and TDB efficacy. We also found that cytokines, including interferon-gamma (IFNγ) and tumor necrosis factor-alpha (TNFα) secreted by activated T cells, damaged tumor cells in a cell contact-independent manner. Moreover, therapeutic experiences clearly indicated that hEx3, unlike conventional anti-EGFR antibodies, was effective against colorectal cancer (CRC) cells with mutant KRAS, BRAF, or PIK3CA. In a pharmacokinetic analysis, T cells spread gradually in accordance with the hEx3 distribution within tumor tissue. Accordingly, we propose that TDBs should have four action steps: 1st, passive targeting via size-dependent tumor accumulation; 2nd, active targeting via specific binding to tumor cells; 3rd, T cell redirection toward tumor cells; and 4th, TDB-induced cell contact-dependent (direct) or-independent (indirect) tumor cell killing. Finally, our TDB hEx3 may be a promising reagent against refractory CRC with an oncogenic mutation associated with a poor prognosis. Keywords Antibody therapeutics • Bispecific antibody (BsAb) • T cell-dependent bispecific antibody (TDB) • Immunological synapse • Immunotherapy • Colorectal cancer Abbreviations BsAb Bispecific antibody CRC Colorectal cancer EPR Enhanced permeability and retention IS Immunological synapse MTA Molecular targeted agent TDB T cell-dependent bispecific antibody Electronic supplementary material The online version of this article (

T Cell Bispecific Antibodies: An Antibody-Based Delivery System for Inducing Antitumor Immunity

“…In an inhibition assay, Gruen and colleagues found that other death ligands in addition to the Fas-FasL pathway, including TRAIL and TNFα, also failed to cause T-BsAb-induced lysis of B-cell lines from leukemia and lymphoma [90]. Recently, however, we demonstrated that secreted cytokines from T-BsAb-activated T cells damaged target cells in a cell contact-independent manner, although cell contact-dependent tumor cell killing, which was presumably attributed to perforin and granzyme activity, showed stronger cytotoxicity [82]. This discrepancy might be explained by target cells having differing sensitivity to various ligands and cytokines.…”

“…Further, these markers have been commonly detected in three types of ISs induced by T-BsAbs with different configurations, indicating that this might be a general pattern among T-BsAbs. Many studies have visualized T-BsAb-induced ISs in vitro [80][81][82]. Recently, IS formation was successfully evaluated by Cremasco et al in an in vivo humanized mouse model involving transfer of human hematopoietic stem cells [75].…”

Redirecting Polyclonal T Cells against Cancer with Soluble T-Cell Receptors

“…In vitro , tebentafusp induced cell killing that led to cross-presentation of tumor antigen that could stimulate epitope spreading ( 5 ). In addition, T cells activated by TCE may release cytokines that kill adjacent, antigen negative tumor cells ( 6 ).…”

“…One potential explanation is that tebentafusp, with in vitro sensitivity to very low pHLA/cell, may outstrip the sensitivity of IHC, requiring >10 3 molecules per cell. Alternatively, even a small percentage of gp100 + cells may be sufficient for tebentafusp to trigger an initial immune response that could result in IFN-induced upregulation ( 43 ), cytokine-mediated tumor stasis or killing ( 6 ), or epitope spreading ( 5 ). Finally, even a low percentage of positive tumor cells may be sufficient for tebentafusp to slow tumor growth kinetics.…”

“…As soluble proteins, TCEs have more predictable and tunable serum kinetics that is reflected in a more predictable adverse event profile. Finally, the TCE mechanism favors polyclonal T cells activation and recruitment ( 4 ) that could trigger a secondary natural response, including antigen spreading ( 5 ) or even cytokine-mediated cell killing ( 6 ) of adjacent tumor cells that do not express the target of the TCE.…”