Fab-Based Chimeric Antigen Receptor for Low-Density Antigens
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Solution Overview
Problem
Current chimeric antigen receptors (CARs) are ineffective in targeting low-density antigens, such as BCMA on myeloma cells, leading to sub-optimal T-cell activation and limited efficacy in treating multiple myeloma.
Innovation Solution
Development of a chimeric antigen receptor (CAR) with a Fab antigen binding domain and a cleavable linker, allowing for enhanced signaling and targeting of low-density antigens by revealing a second binding domain upon cleavage, such as by matrix metalloproteinases (MMPs), which are often expressed at tumor sites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional CAR with scFv is used to target BCMA, then the CAR structure is simple and easy to manufacture, but the CAR fails to signal effectively in response to low-density antigens
Solution Approach 1:
The CAR is divided into two separate chains: Chain 1 contains the scFv antigen-binding domain and transmembrane domain, while Chain 2 contains the intracellular signaling domain. This segmentation allows each chain to be optimized independently, with Chain 1 focusing on antigen recognition and Chain 2 on signal transduction, thereby improving signaling efficacy without overwhelming structural complexity
Solution Approach 2:
The two CAR chains are designed to form a nested structure where Chain 1 and Chain 2 associate through disulfide bonds and protein-protein interactions. The extracellular domains of both chains are positioned to simultaneously engage with the target antigen, creating a nested arrangement that amplifies signaling response from low-density antigens
2Productivity
If a CAR targets low-density antigens like BCMA on myeloma cells, then the therapeutic potential is high, but the CAR-mediated signaling is insufficient due to low antigen density
Solution Approach 1:
The CAR design incorporates dynamic conformational changes that occur upon antigen binding. The two chains are arranged to undergo conformational rearrangement when engaging BCMA, which triggers optimal signal transduction. This dynamic behavior allows the CAR to respond reliably even when antigen density is low, as the conformational change amplifies the signaling event
Solution Approach 2:
The patent modifies key parameters of the CAR structure including the spacer length, transmembrane domain composition, and intracellular signaling domain configuration. These parameter changes are optimized to enhance signal transduction efficiency, allowing reliable CAR activation and target cell killing despite low antigen density on myeloma cells
3Ease of manufacture
If the CAR uses a single-chain variable fragment (scFv), then the manufacturing process is straightforward, but the CAR cannot effectively recognize and signal from low-density antigens
Solution Approach 1:
The CAR is segmented into two expressible chains with distinct functions. Chain 1 contains the scFv for antigen binding, maintaining manufacturing simplicity. Chain 2 contains the optimized signaling domain. This segmentation allows each component to be manufactured and validated separately, then assembled in the target cell, preserving ease of manufacture while enhancing antigen detection sensitivity
Solution Approach 2:
The CAR functions as a composite structure combining two protein chains with complementary properties. Chain 1 provides antigen binding capability, while Chain 2 provides enhanced signal transduction. This composite architecture maintains the manufacturing advantages of scFv-based CARs while achieving superior antigen detection sensitivity through the synergistic interaction of the two chains
Data Source
AI summary
The present invention provides a chimeric antigen receptor (CAR) which binds a low density target antigen, which comprises a Fab antigen binding domain. The invention also relates to cells expressing such a CAR and their use in the treatment of disease.