Bispecific Antibodies Enable Synthetic Agonistic Receptor-Transduced T Cells for Tumor Immunotherapy

Abstract

Purpose: Genetically engineered T cells are powerful anticancer treatments but are limited by safety and specificity issues. We herein describe an MHC-unrestricted modular platform combining autologous T cells, transduced with a targetable synthetic agonistic receptor (SAR), with bispecific antibodies (BiAb) that specifically recruit and activate T cells for tumor killing.Experimental Design: BiAbs of different formats were generated by recombinant expression. T cells were retrovirally transduced with SARs. T-cell activation, proliferation, differentiation, and T-cell-induced lysis were characterized in three murine and human tumor models in vitro and in vivo.Results: Murine T cells transduced with SAR composed of an extracellular domain EGFRvIII fused to CD28 and CD3z signaling domains could be specifically recruited toward murine tumor cells expressing EpCAM by anti-EGFRvIII Â anti-EpCAM BiAb. BiAb induced selective antigen-dependent activation, proliferation of SAR T cells, and redirected tumor cell lysis. Selectivity was dependent on the monovalency of the antibody for EGFRvIII. We identified FAS ligand as a major mediator of killing utilized by the T cells. Similarly, human SAR T cells could be specifically redirected toward mesothelin-expressing human pancreatic cancer cells. In vivo, treatment with SAR T cells and BiAb mediated antitumoral activity in three human pancreatic cancer cell xenograft models. Importantly, SAR activity, unlike CAR activity, was reversible in vitro and in vivo.Conclusions: We describe a novel ACT platform with antitumor activity in murine and human tumor models with a distinct mode of action that combines adoptive T-cell therapy with bispecific antibodies.

Versatile chimeric antigen receptor platform for controllable and combinatorial T cell therapy

“…Our data are in line with previously published findings showing that the killing mechanism of conventional CARs and the UniCAR system is mainly mediated via the granzyme/perforin pathway, whereas the Fas/FasL axis is also involved. 49,50 Surprisingly, Karches et al 19 published that tumor cell killing caused by their adaptor CAR platform termed SAR was independent from granzyme and perforin release but mainly mediated by FasL. Different killing mechanisms of RevCAR versus SAR that both trigger CD28 and CD3z signals, might maybe also be explained by differences between mice and humans.…”

“…Meanwhile, several adaptor CAR platforms have been developed. [11][12][13][14][15][16][17][18][19] However, some of them bear the risk for immunogenicity and cross-reactivity if the interacting components are not carefully selected with respect to species compatibility and natural expression pattern in the recipient. 3 Moreover, some of them are not flexible with respect to antigen targeting and guarantee no steering of T cell activity, when the adaptor molecules have a long-term pharmacokinetic half-life.…”

“…In order to improve the safety management of CAR T cell therapy, we and others have developed different adaptor CAR platforms allowing a repeatable on/off-switch and steering of CAR T cell activity. [11][12][13][14][15][16][17][18][19] The concept of these adaptor CAR technologies is basically that T cells modified with a universal receptor do not directly recognize a TAA but have to be redirected to tumor cells by separate adaptor molecules that are directed against a tumor target and simultaneously to the universal CAR. By dosing of the adaptor molecules, CAR T cell activity can be controlled.…”

Adaptor CAR Platforms—Next Generation of T Cell-Based Cancer Immunotherapy

“…In a fully murine B cell depletion model, Ma et al demonstrated that B cells repopulated within a short time frame after the termination of CD19-directed FITC adaptor infusion [44]. Several groups further confirmed the functional reversibility of adaptor CAR systems in immunodeficient or competent mouse models, underlining that therapeutic effects can be rapidly re-initiated to control tumor growth in case of tumor relapse (e.g., [44,72,74,80]). In a clinical setting, rapidly eliminated adaptors will facilitate a prompt intervention and fast manipulation of adaptor molecule doses.…”

“…Although this was the first in vitro data to verify the general functionality of the system, the lytic activity of the redirected FRα CAR T cells against B cell lines was low due to the poor quality of the bsAb adaptors [79]. Later, Karches et al presented alternative bsAb-binding adaptor CARs containing the ECD of human epidermal growth factor receptor variant III (EGFRvIII) or human Cripto-1 and termed them synthetic agonistic receptors (SARs) ( Figure 2i) [80]. In their studies, they explored both tetravalent (2 + 2) and trivalent (2 + 1) bispecific adaptors targeting EpCAM or mesothelin in murine and human mouse models.…”