Gene Knock-in by CRISPR/Cas9 and Cell Sorting in Macrophage and T Cell Lines
November 13th, 2021
10.8K views
This protocol uses fluorescent reporters and cell sorting to simplify knock-in experiments in macrophage and T cell lines. Two plasmids are used for these simplified knock-in experiments, namely a CRISPR/Cas9- and DsRed2-expressing plasmid and a homologous recombination donor plasmid expressing EBFP2, which is permanently integrated at the Rosa26 locus in immune cells.
Overview
This article presents a streamlined protocol for CRISPR/Cas9-mediated gene knock-in in immune cell lines, specifically T cells and macrophages, using transient expression of fluorescent reporters and cell sorting. The method enables efficient insertion of genes, such as human ACE2, into the Rosa26 locus without relying on drug-resistance selection or viral vectors, overcoming common challenges in genetic manipulation of immune cells.
Key Study Components
Area of Science
- Functional genomics
- Immunology
- Genetic engineering
Background
- Genetic manipulation of immune cells is essential for functional genomics studies.
- Traditional methods for gene knock-in in T cells and macrophages are inefficient due to low transfection rates and reliance on drug selection or viral vectors.
- The Rosa26 locus is a well-established genomic safe harbor for transgene insertion.
- Fluorescent reporters can facilitate identification and sorting of successfully modified cells.
Purpose of Study
- To develop a protocol for efficient CRISPR/Cas9-mediated gene knock-in in immune cell lines without drug-resistance selection or viral vectors.
- To demonstrate the feasibility of this approach by expressing human ACE2 in RAW264.7 macrophages.
- To provide a method applicable for mechanistic studies in immune cells.
Methods Used
- Design and construction of sgRNAs targeting the mouse Rosa26 locus using bioinformatics tools.
- Preparation of donor plasmids containing the gene of interest flanked by homologous arms for recombination.
- Electroporation of immune cell lines with CRISPR/Cas9 and donor plasmids.
- Transient expression of dual fluorescent reporters to identify successfully transfected cells.
- Fluorescence-activated cell sorting (FACS) to isolate putative knock-in cells.
- Screening and validation of knock-in events by PCR, Sanger sequencing, flow cytometry, and immunoblotting.
Main Results
- Efficient gene knock-in at the Rosa26 locus was achieved in both T cells and macrophages.
- Human ACE2 was successfully expressed in RAW264.7 macrophages as a proof-of-concept.
- Fluorescent reporters enabled rapid identification and sorting of modified cells without drug selection.
- Knock-in cells were validated at the DNA and protein levels, confirming correct integration and expression.
Conclusions
- This protocol enables efficient CRISPR/Cas9-mediated gene knock-in in immune cell lines without drug-resistance or viral vectors.
- The method is broadly applicable for mechanistic studies and protein interaction analyses in immune cells.
- It facilitates the generation of stable knock-in cell lines for functional genomics research.
Frequently Asked Questions
What is the main advantage of this CRISPR/Cas9 knock-in protocol for immune cells?
The protocol enables efficient gene knock-in in T cells and macrophages without the need for drug-resistance selection or viral vectors, using transient fluorescent reporters and cell sorting instead.
Why is the Rosa26 locus used for gene knock-in?
The Rosa26 locus is considered a genomic safe harbor, allowing stable and consistent expression of inserted transgenes without disrupting endogenous gene function.
How are successfully modified cells identified in this protocol?
Cells transiently expressing dual fluorescent reporters after electroporation are identified and isolated using fluorescence-activated cell sorting (FACS).
What validation steps are performed to confirm successful gene knock-in?
Validation includes PCR and Sanger sequencing of genomic DNA, flow cytometry for reporter expression, and immunoblotting to confirm protein expression.
Can this method be used for genes other than ACE2?
Yes, the protocol is adaptable for inserting various genes of interest into immune cell lines for mechanistic and functional studies.
What are the potential applications of knock-in immune cell lines generated by this method?
These cell lines can be used for mechanistic studies, protein-protein interaction analyses, and functional genomics research in immunology.
Is this protocol suitable for primary immune cells?
While demonstrated in cell lines, the principles may be adapted for primary cells, but optimization may be required due to differences in transfection efficiency and viability.
Executive Industry Relevance
Efficient gene knock-in in immune cell lines is a critical bottleneck for functional genomics and mechanistic de-risking in immunology drug discovery. This protocol enables precise genetic modification in T cells and macrophages without drug-resistance selection or viral vectors, supporting robust target validation and pathway interrogation. The approach enhances predictive confidence at the early discovery and lead identification stages, directly impacting portfolio triage and translational research continuity.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables interrogation of gene function and pathway roles in disease-relevant immune cell models.
- Supports mechanistic de-risking by allowing controlled addition of protein tags or functional domains.
- Facilitates functional target validation through stable, precise genomic integration at the Rosa26 locus.
- Improves predictive confidence for downstream screening and biomarker development.
Screening & Assay Development
- Generates validated cell lines with stable expression of transgenes for reproducible assay development.
- Eliminates confounding effects of drug selection or viral integration, supporting assay standardization.
- Enables rapid identification and isolation of modified cells using transient fluorescent reporters and FACS.
- Prepares robust platforms for reliable compound evaluation and screening scalability.
Translational & Preclinical Research
- Provides disease-relevant immune cell models for mechanistic and protein interaction studies.
- Ensures continuity from discovery through preclinical validation by enabling stable genetic modifications.
- Supports risk-adjusted advancement decisions by reducing biological ambiguity in immune cell systems.
Pipeline & Workflow Integration
This method integrates into the discovery continuum from early hypothesis testing and target validation through assay development and preclinical research in immune cell models.
- Discovery Biology: Facilitates hypothesis testing and pathway clarification in genetically engineered immune cells.
- Screening: Delivers reproducible, quantitative outputs via stable knock-in cell lines for assay readiness.
- Analytics: Provides robust readouts through PCR, sequencing, and flow cytometry for condition comparison.
- Translational Research: Aligns with biomarker and mechanistic studies in disease-relevant systems.
- Enterprise Reuse: Establishes a reusable platform for diverse gene knock-in applications across immune cell lines.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in immune cell research.
- Operational Value: Standardizes genetic modification workflows and enhances reproducibility without drug or viral confounders.
- Strategic Value: Enables better go/no-go decisions and capital efficiency by providing validated, scalable cell models.
- Portfolio Impact: Supports risk-adjusted prioritization and advancement of immune-targeted programs.
Implementation Considerations
- Requires expertise in CRISPR/Cas9 design, plasmid construction, and cell sorting techniques.
- Needs access to electroporation equipment, FACS instrumentation, and molecular validation tools.
- Demands cross-team standardization for reproducibility and data comparability.
- May require adaptation for different immune cell types or primary cells due to transfection variability.
- Efficiency and viability may be limited in quiescent or hard-to-transfect cell lines.
Biopharma FAQs
Why does null hypothesis testing matter for CRISPR/Cas9 knock-in target validation?
Null hypothesis testing in knock-in cell lines enables rigorous assessment of gene function by comparing modified and wild-type cells, supporting confident target validation and mechanistic de-risking in immune models.
How does independent variable isolation fit the cell sorting workflow?
Cell sorting based on transient fluorescent reporter expression isolates cells that have received both CRISPR/Cas9 and donor constructs, ensuring that observed phenotypes are attributable to the intended genetic modification.
What do quantitative dependent variable measurements enable in knock-in validation?
Quantitative measurements such as flow cytometry, PCR, and sequencing provide objective confirmation of knock-in efficiency and integration fidelity, enabling robust comparison across experimental conditions.
Why are replication requirements critical for cross-functional immune cell studies?
Replication ensures that knock-in results are reproducible across cell lines and experiments, facilitating cross-team collaboration and reliable data for downstream screening or mechanistic studies.
What statistical analysis capabilities are required before implementing knock-in cell lines?
Statistical analysis of knock-in efficiency, reporter expression, and validation assays is essential to confirm integration success and to support data-driven decisions in immune cell research pipelines.
Chapters in this video
0:05
Introduction
0:32
Design and Plasmid Construction of sgRNAs Targeting Rosa26 Locus
2:28
Design and Construction of Targeting Vector as Homologous Recombination Template
3:46
Electroporation of Macrophage and T Cell Lines
7:19
Cell Sorting to Isolate Putative Knock-in Cells
8:58
Screening and Validation of Positive Knock-in Cells
10:16
Representative Results
10:52
Conclusion
