Abstract
BackgroundRedirection of T lymphocytes against tumor antigens can induce dramatic regression of advanced stage malignancy. The use of bispecific antibodies (BsAbs) that bind both the T-cell receptor (TCR) and a target antigen is one promising approach to T-cell redirection. However, BsAbs indiscriminately bind all CD3+ T-cells and trigger TCR activation in the absence of parallel costimulatory signals required to overcome T-cell unresponsiveness or anergy.MethodsTo address these limitations, a combination platform was designed wherein a unique BsAb referred to as frBsAb exclusively engages T-cells engineered to express a novel chimeric receptor comprised of extracellular folate receptor fused to intracellular TCR and CD28 costimulatory signaling domains in tandem; a BsAb-binding immune receptor (BsAb-IR). As a surrogate TCR, the BsAb-IR allows for concomitant TCR and costimulatory signaling exclusively in transduced T-cells upon engagement with specific frBsAbs, and can therefore redirect T-cells on command to desired antigen. Human primary T-cells were transduced with lentiviral vector and expanded for 14–18 days. BsAb-IRs were harvested and armed with frBsAbs to test for redirected cytotoxicity against CD20 positive cancer cell lines.ResultsUsing frBsAbs specific for CD20 or HER2, the lytic activity of primary human T-cells expressing the BsAb-IR was specifically redirected against CD20+ leukemic cells or HER2+ epithelial cancer cells, respectively, while non-engineered T-cells were not activated. Notably, elimination of the CD28 costimulatory domain from the BsAb-IR construct significantly reduced frBsAb-redirected antitumor responses, confirming that frBsAbs are capable of delivering simultaneous TCR activation and costimulatory signals to BsAb-IR T-cells.ConclusionIn summary, our results establish the proof of concept that the combination of BsAbs with optimized gene-engineered T-cells provides the opportunity to specify and augment tumor antigen-specific T-cell activation and may improve upon the early success of conventional BsAbs in cancer immunotherapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12967-014-0347-2) contains supplementary material, which is available to authorized users.
Highlights
Antigen-specific monoclonal antibodies are established as immunotherapeutic agents for the treatment of human malignancies such as non-Hodgkin lymphoma (NHL), CD30-positive lymphoma [1,2], EGFR-expressing advanced bowel cancer, metastatic colorectal carcinoma [3,4,5,6]
Using frBsAbs of diverse antigen specificities, we show that tumor antigen-specific frBsAbs bind target antigen on human tumor cells and, upon co-engagement of the Bispecific antibody (BsAb)-binding immune receptor (BsAb-IR) on engineered T-cells, delivers simultaneous T-cell receptor (TCR) CD3 activation and CD28 costimulation signals in a target dependent manner, resulting in the selective augmentation of activation, proliferation and antitumor activity of BsAb-IR T-cell subset
In line with the known role of costimulatory signals in T-cell function [33], we found that BsAb-IR-28z T-cells produced at least three Th1 type cytokines, IFN-g, IL-2 and TNF-a, as well as Macrophage inhibitory protein (MIP-1a), at levels that were significantly higher than those produced by BsAb-IR-z T-cells, following the engagement by frBsAb
Summary
Antigen-specific monoclonal antibodies (mAbs) are established as immunotherapeutic agents for the treatment of human malignancies such as non-Hodgkin lymphoma (NHL), CD30-positive lymphoma [1,2], EGFR-expressing advanced bowel cancer, metastatic colorectal carcinoma [3,4,5,6]. While a mAb recognizes a single antigen target and closely resembles a naturally-occurring antibody, a BsAb is a synthetic construct that aligns two antigen-specific binding potentials within one molecule enabling the linking of two distinct antigens [9]. Cancer cells are killed when cytotoxic T lymphocytes are engaged to antigen-expressing tumor cells and simultaneously activated by the arm of the BsAb that triggers TCR activation [10,11]. Most BsAbs rely on re-direction of cytotoxic T-cells, the most powerful effector cells of the immune system [12], where the BsAb indiscriminately engages all available TCR CD3 molecules and overrides the natural antigen-specificity of T-cells. The use of bispecific antibodies (BsAbs) that bind both the T-cell receptor (TCR) and a target antigen is one promising approach to T-cell redirection. BsAbs indiscriminately bind all CD3+ T-cells and trigger TCR activation in the absence of parallel costimulatory signals required to overcome T-cell unresponsiveness or anergy
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