Here, we present a protocol for combining iterative protein staining (IBEX) with RNAscope in situ hybridization technology for the deep spatial phenotyping of intact fixed frozen tissues for high-resolution spatial profiling applications.
Method Article
Here, we present a protocol for combining iterative protein staining (IBEX) with RNAscope in situ hybridization technology for the deep spatial phenotyping of intact fixed frozen tissues for high-resolution spatial profiling applications.
Here, we present a protocol to enable simultaneous spatial profiling of protein and ribonucleic acid (RNA) markers at single-cell resolution in intact tissues. One of the core issues surrounding solid tumor cancers is the inability to predict patient responsiveness to therapeutic intervention. Deciphering these complexities requires quantitative measurement of cellular behaviors, interactions, and phenotypes within intact tissues. Specifically, the proteome and transcriptome provide overlapping but nonredundant information that can be critical to designing rational immunotherapeutics. However, there is not currently a straightforward and cost-effective way to deeply profile both the transcriptional and functional state of all cells in the tumor microenvironment while retaining their critical spatial localization information. To this end, we have successfully combined the IBEX (iterative bleaching extends multiplexity) platform with HiPlex RNAscope to simultaneously visualize high-plex protein markers and high-plex ribonucleic acid (RNA) transcripts with single-cell resolution. This approach incorporates a modified RNA target retrieval step to preserve nuclear morphology and enable accurate image alignment across cycles. “Bex-Plex” enables us to perform an unmodified IBEX protocol on fixed frozen tissues followed by the HiPlex RNAscope protocol, in which we use a modified RNA target retrieval to ensure nuclear-level alignment with IBEX cycles. This protocol is optimized for fixed frozen tissues and enables integrated spatial analysis of transcriptional and functional cellular states. The power to profile at this single-cell level not only provides a deep well of information about the tissue itself but can also empower predictions about the nuanced cellular interactions that drive therapeutic responsiveness, providing a framework for studying spatial biology in tumor microenvironments and related systems.
Since their introduction in 2011, cancer immunotherapies that decrease the suppression of cytotoxic T cells by blocking inhibitory immune checkpoint molecules such as PDL-1 and CTLA-4 have emerged as the gold standard for solid tumor treatment1. However, despite large-scale use in patients, the clinical efficacies of these drugs vary widely because many solid tumor cancers either intrinsically present with or eventually generate resistance to these therapies2. In many cases this is due to the extremely heterogeneous nature of solid tumors, even among the same cancer type3. A more in depth understanding of the cell relationships that occur in solid tumors is key to generating improved treatment modalities. Thus, identifying the exact mechanisms and interactions that mount and sustain this resistance is at the forefront of cancer research. Here, we aim to develop a method that enables integrated spatial analysis of protein and RNA expression within intact tissues to better characterize these complex cellular interactions.
The tumor microenvironment (TME) is composed of the non-cancerous cellular and structural components that shape tumor growth and immune response, including cancer associated fibroblasts, infiltrating immune cells, vascular components, and the extracellular matrix4. Recently, it has become evident that the composition and organization of the TME strongly influence whether tumors are permissive or resistant to immune infiltration, one of the main factors dictating responsiveness to immunotherapy5. In many cancers, an “immune desert” phenotype, characterized by low numbers of T cells and the presence of highly immunosuppressive myeloid populations, correlates with poor responsiveness to checkpoint blockade therapies6,7. Chemokine signaling governs many of these recruitment dynamics. For example, CXCL1 and CCL2 attract immunosuppressive myeloid cells, while the CXCR3-CXCL9/CXCl10 axis recruits both cytotoxic and regulatory T cells into the tumor8. Consequently, the niche-specific signaling environment can potently influence cell phenotype and function. For instance, in colorectal cancer patients, the CCL5-CCR5 axis controls the suppressive function of tumor associated macrophages (TAMs) and blocking this signal skews TAM toward an anti-tumorigenic phenotype and correlates with improved clinical responses9. Furthermore, direct interactions between immune cells, cancer associated fibroblasts, and/or tumor cells via ICAM and PDL-1 can induce immune exhaustion and blunt antitumor immunity10. Together, these findings underscore the importance of spatially resolved analyses to understand how the TME influences therapeutic efficacy.
Immunofluorescent (IF) imaging remains a foundational approach for visualizing protein expression and cell-cell interactions in tissue. The field has advanced from conventional 3-4 color IF to high-content imaging workflows that rely on iterative staining and imaging. In these methods, large datasets are generated via repeated cycles of antibody labeling, imaging, and fluorophore inactivation or removal so that additional markers can be stained and imaged11. Iterative Bleaching Extends Multiplexity (IBEX) was recently introduced as a user-friendly and cost-effective iterative imaging platform12. Compatible with the use of commercial antibodies and conventional microscopes, IBEX utilizes lithium borohydride (LiBH4) to quench the fluorescence of most commonly used dyes without damaging tissue epitopes, allowing for the acquisition of up to 75 parameters for a single tissue13. The images obtained from this cyclic staining are aligned using the SimpleITK open-source software to produce composite datasets suitable for high-dimensional spatial analyses.
Complementary to protein-level phenotyping, spatial transcriptomic methods can provide valuable information about the transcriptional state of cells within their native environment. Notably, in-situ hybridization (ISH) is a popular technique to identify the localization of DNA or RNA sequences in a specific tissue11. RNAscope is a well-established ISH approach that uses probes with a unique Z chemistry to specifically amplify RNA transcripts at single-molecule resolution and is compatible with many different sample types14. As a widely adopted and commercially available platform through Advanced Cell Diagnostics (ACD), RNAscope offers validated probes against a wide variety of targets, simplifying experimental design for diverse applications.
A more complete view of cell identity and functions can be gained by combining protein and RNA detection within the same tissue. Short-lived secreted proteins, such as cytokines and chemokines, traditionally lack reliable antibody staining by IHC, but information about their expression can be gained through the quantification of their mRNA transcripts. Previous attempts to co-detect RNA and protein, such as conventional chromogenic IHC or TSA-OPAL, have been limited by nonlinear signal amplification and time- consuming antigen retrieval protocols15. Compared to these approaches, the Bex-Plex method enables simultaneous high-plex protein and RNA detection while preserving spatial context and nuclear morphology for accurate image registration.
Here we present “Bex-Plex”, a protocol that integrates the IBEX and RNAscope platforms for simultaneous, quantifiable characterization of the transcriptional and translational states of cells within their native tissues. In Bex-Plex, fixed OCT embedded tissues undergo the standard IBEX protocol followed by a slightly modified RNAscope HiPlex workflow, wherein target retrieval is performed at 60°C with a 1 h incubation time as compared to the original 99°C incubation for 5 min. This preserves the architecture of the nuclei, allowing for an accurate alignment of fiducial markers when registering the separate images from the IF and ISH cycles into one. This protocol is best suited for studies requiring simultaneous spatial analysis of protein and RNA expression in intact tissues, particularly when tissue availability is limited or when preserving spatial architecture is critical, such as in tumor microenvironment analysis or immune profiling studies.
Using widely available reagents and compatible with most imaging platforms, Bex-Plex can be carried out by any technically trained research personnel familiar with fluorescent imaging and with access to a conventional microscope. The protocol presented here is optimized for fixed frozen samples. At present, the protocol has been validated in fixed frozen tissues, and further optimization may be required for application to other sample types such as FFPE or human clinical specimens.
This workflow will be invaluable for any context where tissue is limited or precious, such as tissue biopsies or animal experiments that have a limited sample size, as well as for the phenotyping of cells that may be difficult to extract using dissociative techniques. Bex-Plex provides simultaneous, quantifiable information about the transcriptional and translational profiles of single cells while retaining their spatial context, data that is uniquely poised to answer questions about the relationships and crosstalk between cells in their original environment.
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The procedures outlined in this protocol were approved by the Institutional Animal Care and Use Committee of the University of California, San Diego (protocol number S24049). Male and female mice 7-12 weeks of age on a C57BL/6 genetic background and housed under specific pathogen-free conditions were used for these experiments.
1. Tissue preparation
2. Tissue sectioning
Note: All reagents and lab materials used for this protocol must be RNase free. Take care to prevent contamination when handling slides.
3. Protein staining
4. Fluorophore bleaching and iterative protein staining
5. Slide preparation for RNAscope HiPlex
6. RNAscope reagent preparation and probe hybridization
7. Probe amplification
Note: Ensure that all reagents are equilibrated to RT before applying to slides.
8. Cleaving the fluorophores and iterative RNA hybridization
9. Image processing
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Figure 1 : Overview of Bex-Plex workflow.
Fixed frozen tissues sectioned onto chrome alum-coated slides undergo up to 3 cycles of standard IBEX followed by up to three cycles of RNAScope HiPlex wherein the initial target retrieval step is performed at 60°C for 1 h. Images ...
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The Bex-Plex workflow integrates the iterative protein staining platform, IBEX, with RNAscope in situ hybridization to enable simultaneous detection of proteins and RNA transcripts at single-cell resolution. The primary goal of this protocol is to provide a reproducible method for integrated spatial analysis of protein and RNA expression within intact tissues. The ability to measure both protein and RNA expression in the same tissue has previously presented technical challenges: high costs, complex antigen retri...
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The authors declare no competing financial interests. No AI-based tools were used in the preparation of this manuscript.
Author contributions:
SK contributed to data curation, data analysis, investigation, and writing. CM contributed to data curation. PH contributed to data analysis. AV contributed to data curation. VM contributed to conceptualization, data curation, data analysis, supervision, and writing.
This work was supported by the University of California San Diego Department of Pediatrics, Division of Allergy, Immunology, and Rheumatology and NIH NIGMS grant R00GM147841 (MOSAIC K99/R00) and NCI U54CA272220 (UC San Diego FIRST grant). The authors would additionally like to thank Andrea Radtke for establishing the original IBEX method, without which we would have been unable to create Bex-Plex.
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| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| 1.5 ml microcentrifuge tubes | Biopioneer | MCNT-1.5F | |
| 200 proof EtOH | Fisher Scientific | BP28184 | |
| 20X SSC buffer | Invitrogen | AM9765 | |
| 24 well plates | |||
| Alexa Fluor 488 anti-mouse CD11b Antibody | Biolegend | 101217 | |
| Alexa Fluor 523 anti-mouse CD3e Antibody | Invitrogen | 58-0032-82 | |
| Alexa Fluor 647 anti-mouse Ly6G Antibody | Biolegend | 127610 | |
| Alexa Fluor 700 anti-mouse CD68 Antibody | Biolegend | 137025 | |
| BD Cytofix/Cytoperm fixation and permeablization solution | BD | 554722 | |
| Chrome alum gelatin | Fisher | NC1692262 | |
| Confocal microscope (e.g Leica Stellaris) | |||
| Cryomolds | VWR | 25608-922 | |
| Cryostat (e.g CryoStar NX50 Cryostat) | Thermofisher Scientific | 957100 | |
| Cryostat blades (e.g Leica Low Profile Disposable Blades DB80LX) | Leica Biosystems | 14035843496 | |
| DAPI | Thermofisher Scientific | 62248 | |
| Dissection microscope (e.g Zeiss SteREO Discovery.V8) | |||
| Dissection tools | |||
| Dry Ice | |||
| Dunk tank for slide staining (e.g Simport Scientific EasyDip Slide Staining Jars) | Fisher Scientific | 22-038-489 | |
| Fluoromount-G | Fisher | OB10001 | |
| Heated water bath | |||
| Histology brushes (e.g. Ted Pella Camel Hair Brushes) | Fisher Scientific | NC2023341 | |
| Hybridization oven (e.g. HybEZ II Hybridization System) | ACD | 321710 | |
| Image analysis software of choice | |||
| ImmEdge Hydrophobic Barrier PAP Pen | Vector Laboratories | H-4000 | |
| Kimwipes | VWR | 21905-026 | |
| Lithium borohydride | STREM Chemicals | 93-0397 | |
| Micropipettes (P-10, P-20, P-200, P-1000) | |||
| Mini Microcentrifuge (e.g. Corning LSE Mini Microcentrifuge) | Corning | 6770 | |
| Mouse BD Fc Block | BD | 553142 | |
| No 1.5 Coverglass | VWR | 48393-241 | |
| Pipette tips (P-10, P-20, P-200, P-1000) | |||
| RNAscope HiPlex Probe, mm-CD274-T7 | ACD | 420501-T7 | |
| RNAscope HiPlex Probe, mm-IL-10-T6 | ACD | 317261-T6 | |
| RNAscope HiPlex12 Reagents Kit v2 (includes detection kit, cleaving stock solution, protease reagents, target retreival reagents, and wash buffer) | ACD | 324409 | |
| RNAscope Protease III | ACD | 322337 | |
| RNase ZAP | Millipore Sigma | R2020-250 | |
| Simple ITK software: https://github.com/niaid/sitk-ibex | |||
| Slide staining tray/humidity chamber | |||
| Sucrose Bioxtra | Sigma | S7903-1KG | |
| Superfrost Plus Microscope slides | VWR | 48311-703 | |
| Tissue-Tek OCT | VWR | 25608-930 | |
| Tween-20, Molecular Biology grade | Promega | H5152 | |
| UltraPure DNase/RNase free water | Fisher Scientific | 10977023 |
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