Question: What is the purpose of the Tissue Adhesion Test, and how should it be performed?
Answer: The Tissue Adhesion Test is an optional test that can be used to screen candidate FFPE tissue blocks for their adhesive properties to aid in selecting which blocks may be more ideal for the Visium for FFPE assay. Please note that the Tissue Adhesion Test is not an optimization experiment where protocol steps can be modified to improve attachment, as our protocols are already optimized to maximize tissue adhesion.
An overview of the Tissue Adhesion Test:
The Tissue Adhesion Test utilizes Visium Tissue Section Test Slides. The Tissue Section Test Slides have similar surface properties as the Visium Spatial Gene Expression Slides. It has 8 Capture Areas (8 x 8 mm) etched on the surface. An image of the Tissue Section Test Slide is shown below.
The Tissue Adhesion Test involves sectioning and placement onto the Tissue Section Test Slide, drying, deparaffinizing, and H&E staining. After staining, a visual inspection of the tissue will determine how well tissue remained adhered to the Tissue Section Test Slide.
How to perform the Tissue Adhesion Test:
Tissue adhesion to slides is impacted by tissue processing (fixation and embedding) and other factors such as sample handling. Given that sample handling can impact Tissue Adhesion Test performance, it is critical to use sample handling best practices (as described in the Visium for FFPE Tissue Preparation Guide and Visium for FFPE H&E Staining Demonstrated Protocol). General steps in how to perform the Tissue Adhesion Test are listed below:
- Section and place four 5 µm sections per tissue block for testing (following instructions as described in the Visium for FFPE Tissue Preparation Guide), whereby up to two candidate blocks can be tested per slide. When placing sections, start at the topmost two Capture Areas (A1 and A2) and proceed downward (B1 and B2, C1 and C2, then D1 and D2). The two sections should be placed simultaneously to ensure that sections are not re-submerged in the water bath.
- Incubate the Tissue Section Test Slide for 3 hours in an oven (or equivalent equipment such as a thermal cycler with the Thermocycler Adapter) at 42°C.
- Transfer the Tissue Section Test Slide to a room temperature desiccator for at least 12 hours to ensure proper drying.
- Perform Deparaffinization and H&E staining as per the Visium for FFPE H&E Staining Demonstrated Protocol.
- After H&E staining, visually inspect the tissue sections on the Tissue Section Test Slides.
Please note: Tissue Adhesion Test results should be interpreted by the naked eye, and imaging isn't required. If taking an image of the slide to record your results, do not coverslip the slide. It should be noted that not coverslipping can compromise the H&E staining, but this is not relevant to Tissue Adhesion Test interpretation.
How to interpret the Tissue Adhesion Test results:
During the Tissue Adhesion Test, sections can experience no detachment (minor, major, and complete). These phenotypes, and next steps, are shown in the graphic below.
If all sections from a block experience no detachment or minor detachment, sections from the block will likely adhere well to the Gene Expression Slide and can be used for the Visium Spatial Gene Expression for FFPE assay.
If best practices are followed and any number of sections from a block experience major or complete detachment, this indicates that the block may be more prone to detachment on Visium Slides and may be less ideal for the Visium Spatial Gene Expression for FFPE assay. If there are no other blocks of interest, it may be possible to use such blocks for the Visium Spatial Gene Expression for FFPE assay by using more sections (up to four) on the Gene Expression Slide.
Products: Visium for FFPE