protein-engineering-by-yeast-surface-display

Protein Engineering by Yeast Surface Display

Protein engineering enables the improvement of existing functions of a given protein or the generation of novel functions. One of the most widely used and ...

BOKU University

CD Laboratory for Next Generation CAR T Cells

Molecular ON-switches in which a chemical compound induces protein-protein interactions can allow cellular function to be controlled with small molecules. ON-switches based on clinically applicable compounds and human proteins would greatly facilitate their therapeutic use. Here, we developed an ON-switch system in which the human retinol binding protein 4 (hRBP4) of the lipocalin family interacts with engineered hRBP4 binders in a small molecule-dependent manner. Two different protein scaffolds were engineered to bind to hRBP4 when loaded with the orally available small molecule A1120. The crystal structure of an assembled ON-switch shows that the engineered binder specifically recognizes the conformational changes induced by A1120 in two loop regions of hRBP4. We demonstrate that this conformation-specific ON-switch is highly dependent on the presence of A1120, as demonstrated by an ∼500-fold increase in affinity upon addition of the small molecule drug. Furthermore, the ON-switch successfully regulated the activity of primary human CAR T cells in vitro. We anticipate that lipocalin-based ON-switches have the potential to be broadly applied for the safe pharmacological control of cellular therapeutics.

A conformation-specific ON-switch for controlling CAR T cells with an orally available drug.

T cells that are genetically engineered to express chimeric antigen receptors (CAR T cells) have shown impressive clinical efficacy against B-cell malignancies. In contrast to these highly potent CD19-targeting CAR T cells, many of those directed against other tumor entities and antigens currently suffer from several limitations. For example, it has been demonstrated that many scFvs used as antigen-binding domains in CARs show some degree of oligomerization, which leads to tonic signaling, T cell exhaustion, and poor performance in vivo. Therefore, in many cases alternatives to scFvs would be beneficial. Fortunately, due to the development of powerful protein engineering technologies, also non-immunoglobulin-based scaffolds can be engineered to specifically recognize antigens, thus eliminating the historical dependence on antibody-based binding domains. Here, we discuss the advantages and disadvantages of such engineered binding scaffolds, in particular with respect to their application in CARs. We review recent studies, collectively showing that there is no functional or biochemical aspect that necessitates the use of scFvs in CARs. Instead, antigen recognition can also be mediated efficiently by engineered binding scaffolds, as well as natural ligands or receptors fused to the CAR backbone. Finally, we critically discuss the risk of immunogenicity and show that the extent of nonhuman amino acid stretches in engineered scaffolds-even in those based on nonhuman proteins-is more similar to humanized scFvs than might be anticipated. Together, we expect that engineered binding scaffolds and natural ligands and receptors will be increasingly used for the design of CAR T cells.

Driving CARs with alternative navigation tools - the potential of engineered binding scaffolds.

Chimeric antigen receptor (CAR) T cells have shown remarkable response rates in hematological malignancies. In contrast, CAR T cell treatment of solid tumors is associated with several challenges, in particular the expression of most tumor-associated antigens at lower levels in vital organs, resulting in on-target/off-tumor toxicities. Thus, innovative approaches to improve the tumor specificity of CAR T cells are urgently needed. Based on the observation that many human solid tumors activate epidermal growth factor receptor (EGFR) on their surface through secretion of EGFR ligands, we developed an engineering strategy for CAR-binding domains specifically directed against the ligand-activated conformation of EGFR. We show, in several experimental systems, that the generated binding domains indeed enable CAR T cells to distinguish between active and inactive EGFR. We anticipate that this engineering concept will be an important step forward to improve the tumor specificity of CAR T cells directed against EGFR-positive solid cancers.

An engineering strategy to target activated EGFR with CAR T cells.

CAR T cells have generated great excitement due to their remarkable clinical response rates in selected hematologic malignancies. However, these engineered immune cells are living drugs which are hard to control after administration.

Small molecule-regulated switches to provide functional control of CAR T cells within the patient.

Yeast surface display is a versatile protein engineering technology, enabling precise control of the applied selection pressure. We present a yeast-surface-display-based protocol for the enrichment of binders specifically recognizing ligand-bound receptors. We describe steps for magnetic bead selections, random mutagenesis, and flow cytometric sorting, followed by library sequencing and detailed analysis of enriched clones. While this approach is exemplified with rcSso7d-based libraries and epidermal growth factor (EGF)-epidermal growth factor receptor (EGFR) complexes, it can also be adapted to other binder scaffolds and ligand-receptor systems. For complete details on the use and execution of this protocol, please refer to Dobersberger et al..

Charlotte U. Zajc

Department of Chemistry,
Institute of Biochemistry,
Department of Chemistry, Institute of Biochemistry

BOKU University

Protein Engineering by Yeast Surface Display

Charlotte U. Zajc

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Chemistry,Institute of Biochemistry,Department of Chemistry, Institute of Biochemistry

BOKU University

Protein Engineering by Yeast Surface Display

Department of Chemistry,
Institute of Biochemistry,
Department of Chemistry, Institute of Biochemistry