Synthetic Cell Death Switch for Precise Phagocytosis Assays
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Solution Overview
Problem
Current phagocytosis assays face high experimental variability due to inefficient and non-specific generation of apoptotic cells, modification of substrates through labeling, and lack of flexibility in timing, especially in complex multicellular models.
Innovation Solution
A recombinant expression vector encoding an inducible cell death switch and a combination of pH-stable and pH-sensitive fluorophores, allowing for on-demand apoptosis and precise phagocytosis detection using Caspase9 dimerization and fluorescent reporters like mCherry and Superecliptic pHluorin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If commonly used substrates (opsonized red blood cells, yeast particles, E. coli bioparticles) are labeled with pH-sensitive dyes to indicate phagocytosis, then phagocytosis can be detected, but the surface of the substrate is modified which may impact substrate recognition by the phagocyte and lead to variable labeling efficiencies
Solution Approach 1:
The substrate cells are engineered to autonomously produce and display the pH-sensitive fluorophore on their own surface without requiring external labeling. This self-labeling approach eliminates modification artifacts and ensures consistent substrate recognition by phagocytes while maintaining reliable phagocytosis detection through pH-dependent fluorescence changes.
2Productivity
If apoptotic cells are generated using chemical inducers (e.g., staurosporine), then cell death can be induced, but the efficiency is variable and other forms of cellular debris (necrotic cells, leaked DNA) are produced
Solution Approach 1:
An inducible caspase 9 system is used as an intermediary mechanism to trigger apoptosis. The exogenous chemical inducer (AP20187) binds to caspase 9, which then activates the endogenous apoptotic pathway in a controlled manner. This intermediary approach ensures high efficiency and specificity of apoptosis induction while avoiding the production of necrotic debris and leaked DNA associated with direct chemical induction.
Solution Approach 2:
The invention changes the parameter of cell death induction from non-specific chemical exposure to targeted caspase activation. By using the inducible caspase 9 system with specific small molecule inducers, the apoptosis process is precisely controlled, achieving high efficiency and purity of apoptotic cells without confounding necrotic components.
3Ease of operation
If the assay starts when all components are mixed, then the procedure is simple, but there is no flexibility in timing which is not desirable in complex multicellular in vitro models
Solution Approach 1:
The substrate cells are pre-engineered with the inducible caspase 9 system and pH-sensitive fluorophore before the assay begins. This preliminary preparation allows the cells to be ready for immediate apoptosis induction at any desired time point by simply adding the small molecule inducer, providing timing flexibility without complicating the overall assay procedure.
Solution Approach 2:
The invention introduces dynamic control to the assay timing through the inducible caspase 9 system. The apoptosis process can be dynamically initiated at any time point by adding the chemical inducer, allowing the assay to adapt to different experimental timelines and complex multicellular model requirements while maintaining procedural simplicity.
4Measurement precision
If pHrodo dyes are used to label substrates, then fluorescence intensity increases upon pH drop in phagolysosomes indicating phagocytosis, but the signal is variable between experiments and the threshold between high and low signal needs to be adjusted for each experiment
Solution Approach 1:
The substrate cells self-produce and display the pH-sensitive fluorophore on their surface through engineered expression systems. This eliminates the variability associated with external dye labeling, as the fluorophore is intrinsically part of the substrate cell membrane. The consistent expression levels and pH-responsive properties provide reliable and reproducible phagocytosis detection without requiring experiment-specific threshold adjustments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables consistent, reproducible, and flexible phagocytosis assays in 2D or 3D models, with high precision in distinguishing phagocytosed from non-phagocytosed cells, suitable for various cell types and complex in vitro systems.
Implementation Method 1
a pH-sensitive fluorophore... which increases its fluorescence intensity upon a drop in pH that occurs in phagolysosomes
Implementation Method 2
a pH-stable fluorophore... emit a constant signal regardless of pH changes
Implementation Method 3
Caspase9 dimerization... allowing for on-demand apoptosis
Data Source
AI summary
The present invention relates to a recombinant expression vector encoding an inducible cell death switch, a pH-stable fluorophore and a pH-sensitive fluorophore. Moreover, the invention relates to cells comprising said recombinant expression vector as well as their use in an in vitro phagocytosis assay.