The first and the only cell-based adoptive cancer immunotherapy, sipuleucel-T, was approved in 2010 by the FDA to treat advanced prostate cancer (1). While this successful development clearly represents a milestone in the field, there remains much room to improve in terms of efficacy, technical flexibility, broader applicability, and cost (2-9). For example, sipuleucel-T treatment involves three cycles of enrichment of antigen presenting cells (APCs) from leukapheresis, activation of APCs ex vivo, and reinfusion of the resulting pheresis product to the patient, at a cost of ~$100,000 for a 4-month survival benefit (10). If there were an off-the-shelf artificial APC (aAPC) system capable of eliciting sustained and potent tumor-specific T-cell responses either in vivo or ex vivo, it would enable cancer immunotherapy to treat many different types of cancer, as well as other immune-modulating diseases. Therefore, development of such an aAPC system is critical to realize the therapeutic, and even the preventative potential, of cancer immunotherapy. On a fundamental level, T cell activation and its functional outcome depend on not only the recognition of the (tumor) antigen, but also the context in which the antigen is recognized. This context, termed immunological synapse (IS), at the APC-T-cell interface plus the soluble cytokine signals determine the specificity, activation, and function of the T cell (11-13). A productive IS formatio involves an array of receptor-ligand interactions that dynamically organize into a supramolecular structure (14, 15). Therefore, recapitulating the IS structure by the therapeutic aAPC system is important for eliciting an effective anti- tumor response. A majority, if not all, of the current aPC designs have focused on the identity and a homogeneous presentation of the proteins involved in the IS (16-18), which may be partly the reason why the induced anti-tumor activity is limited.
Aimi ng at better functional conditioning of tumor-specific T cells, the goal of this proposal is to develop an aAPC system that mimics the supramolecular structure of the IS. Specifically, a 2D protein scaffold will be constructed on a yeast cell surface using 6 different dock subunits, of which the number and the spatial arrangement can be precisely controlled via genetic engineering. In the meantime, T-cell-stimulating molecules (including peptide-MHC complex and costimulatory/adhesion proteins) will be fused to an anchor subunit, each of which binds a dock in the scaffold specifically with a high affinity (Kd ~10-9-10-12 M). Through the stable, orthogonal, and specific dock- anchor interactions, the T-cell-potentiating proteins are patterned in a similar way as found in the IS on our aAPC surface. Due to the modular nature of our aAPC system assembly, la carte formulation of these proteins is readily achieved without any protein purification or chemical conjugation required in other aAPC designs. Therefore, the success of the proposed aAPC system will enable us to understand, optimize, and achieve better functional conditioning of tumor-specific, and theoretically any antigen-specific, T cells.
Cancer is responsible for ~25% of all deaths in the US, mainly due to a high relapse rate (19), thus the idea of using a patient's own tumor-specific T cells to keep the malignancy in check is very compelling (20, 21). While this approach holds great promise, as recognized by the recent FDA approval of such a cellular cancer immunotherapy (1), the therapeutic efficacy is limited in part by the sub-optimal T-cell activation in vivo or ex vivo, which is a result of the lack of control of density and spatial arrangement of the T-cell- stimulating proteins in current antigen presenting system designs. To address these issues, we propose to display a 2D protein scaffold on yeast cell surface to enable presentation of supramolecular patterns mimicking those found in the natural immunological synapse, which determines the activation and function of antigen/tumor-specific T cells.
| Smith, Mason R; Khera, Eshita; Wen, Fei (2015) Engineering Novel and Improved Biocatalysts by Cell Surface Display. Ind Eng Chem Res 54:4021-4032 |
