TanCAR: A Novel Bispecific Chimeric Antigen Receptor for Cancer Immunotherapy

Abstract

Targeted T cells are emerging as effective non-toxic therapies for cancer. Multiple elements, however, contribute to the overall pathogenesis of cancer through both distinct and redundant mechanisms. Hence, targeting multiple cancer-specific markers simultaneously could result in better therapeutic efficacy. We created a functional chimeric antigen receptor-the TanCAR, a novel artificial molecule that mediates bispecific activation and targeting of T cells. We demonstrate the feasibility of cumulative integration of structure and docking simulation data using computational tools to interrogate the design and predict the functionality of such a complex bispecific molecule. Our prototype TanCAR induced distinct T cell reactivity against each of two tumor restricted antigens, and produced synergistic enhancement of effector functions when both antigens were simultaneously encountered. Furthermore, the TanCAR preserved the cytolytic ability of T cells upon loss of one of the target molecules and better controlled established experimental tumors by recognition of both targets in an animal disease model. This proof-of-concept approach can be used to increase the specificity of effector cells for malignant versus normal target cells, to offset antigen escape or to allow for targeting the tumor and its microenvironment.Molecular Therapy-Nucleic Acids (2013) 2, e105; doi:10.1038/mtna.2013.32; published online 9 July 2013.

Figure 1

Designing a bispecific tandem chimeric antigen receptor (TanCAR) molecule. representation of the proposed chimeric antigen receptor molecule extracellular domains engaging the two targets; HER2 and CD19.

Figure 2

Docking platforms predict favorable binding potential of TanCAR to target molecules. Compilation of structure and docking data of (a) hypothetical structure of both FRP5-derived scFv and the CD19-specific scFv joined with a 20 amino acid Gly-Ser linker; (b) most favorable docking models of FRP5-derived scFv and the distal 200 amino acid residues of the extracellular domain of HER2; (c) most favorable docking models of CD19-scFv and the extracellular domain of CD19, and combined docking of (d) HER2 and (e) CD19 and the whole TanCAR exodomain, individually.

Figure 3

Construction and surface expression of the TanCAR molecule. (a) pSFG vector construct encoding the TanCAR; (b) detection of the surface expression of the TanCAR using a Fab-specific antibody and FRP5-specific HER2-Fc protein on 293T cells; and (c) on T cells. See Supplementary Figure S2 for description of the labeling strategy.

Figure 4

The TanCAR T cells distinctly recognize individual target molecules. (a) Flow cytometric analysis of the surface expression of the target antigens, HER2 and CD19, on a panel of human cancer cell lines used for functional testing; (b) cytotoxicity assay showing recognition and killing of HER2-positive Daoy cells and efficient blocking of this lysis using a soluble HER2 fragment; (c) similarly, TanCAR T cells recognized CD19-positive Raji cells and this lysis was blocked using the CD19 Ab 4G7; (d) in cocultures, TanCAR T cells secreted IFN-γ as well as IL-2 upon encounter of HER2- and CD19-positive target cell above the non-transduced T-cell control (NT). No cytokines were secreted in coculture with the HER2- and CD19-null target cell MDA-MB-468. (b–d) Shown are representative plots of three or more experiments done in triplicates.

Figure 5

Enhanced cytolytic function upon simultaneous recognition of two antigens and preserved TanCAR T cell-induced cytolysis in a model of antigen loss. (a) Collective modeling of the simultaneous docking of the TanCAR to both HER2 and CD19. (b) In cytotoxicity assays, we saw consistently higher killing after the induction of CD19 at various tumor to T cell ratios. This was synergistic; with an exponential trend following a higher order equation; and was more prominent in higher tumor to T cell ratios (right panel). (c) Similarly, induction of CD19 (DOX⁺) in Daoy.TET.CD19 and T cell cocultures resulted in a more than fourfold increase in IFN-γ release as detected by ELISA (P < 0.01). (d) We modeled the scenario in which tumor cells downregulate the target antigen, by blocking HER2 in CD19-induced (DOX⁺) and CD19 null (DOX⁻) Daoy.TET.CD19 cells using a soluble HER2 fragment (s.HER2). Although soluble HER2 successfully induced substantial blocking of HER2-mediated killing in DOX⁻ cells at various tumor to T cell ratios, it resulted only in a partial decrease in the cytolytic effect of TanCAR T cells in DOX⁺. P values were significant at T cell to tumor cell ratios of 1:20, 1:10, and 1:5. Shown are representative plots of three experiments done in triplicates.

Figure 6

Simultaneous targeting of two antigens enhances the in vivo antitumor activity of adoptively transferred TanCAR T cells. (a) Daoy.TET.CD19 xenografts were established for 3 weeks in the flanks of SCID mice, and then animals were randomized into four groups. Administration of PBS into the tumor and/or systemic doxycycline induced minimal or no alteration of the tumor growth pattern. By contrast, treatment with TanCAR T cells resulted in a significant delay in tumor progression that was further enhanced by induction of CD19 expression in the DOX⁺ group. (b) Kaplan–Meier survival curve: analysis performed 60 days after PBS or T-cells injection. Mice treated with TanCAR T cells had a significantly longer survival probability in comparison with control mice. Furthermore, induction of CD19 by the administration of doxycycline resulted in enhanced antitumor activity of adoptively transferred TanCAR T cells.