OMAP-8: Organ Mapping Antibody Panel (OMAP) for Multiplexed Antibody-Based Imaging of Placenta with Imaging Mass Cytometry (IMC), v1.2

OMAP-8 was designed for Imaging Mass Cytometry (IMC) (Giesen et al. 2014) of formalin fixed paraffin embedded (FFPE)<br>human term-placenta samples. The tissue slides were prepared with a two-step antigen retrieval process (pH 6 and pH 9)<br>as described (McDonough et al. 2020). OMAP antibodies validated by immunohistochemistry and IMC were conjugated to<br>polymers containing metal isotopes. Conjugated antibodies were used to stain processed human term-placenta tissue<br>simultaneously. Regions of the processed tissue were then acquired on the imaging mass cytometer (Hyperion, Standard<br>BioTools) by laser ablation and visualized. The panel contains 26 antibodies conjugated to unique metal isotopes and<br>iridium marks the DNA. This OMAP provides a spatial context for key placenta cell types in the ASCT+B v1.0 table<br>(Laurent, Parast, and Fisch 2022). Single-cell RNA sequencing data were used to guide marker selection for multiplexed<br>tissue imaging. For example, ASCL2, HLA-G, PD-L1, CD68, and LYVE1 allow functionally specialized cell types to be<br>visualized and quantified in the placenta. Note that one of the core antibodies is to LYVE1 but, unlike in other<br>tissues where it marks lymphatic vasculature, here it is used to mark Hofbauer cells (placental macrophages), as there<br>are no lymphatics in the placenta. A representative dataset using this OMAP can be found here: (Robson, Ramasamy, and<br>Sivajothi 2023).<br><br>**Bibliography:**<br><br>* Giesen, Charlotte, Hao A. O. Wang, Denis Schapiro, Nevena Zivanovic, Andrea Jacobs, Bodo Hattendorf, Peter J. Schüffler, et al. 2014. “Highly Multiplexed Imaging of Tumor Tissues with Subcellular Resolution by Mass Cytometry.” *Nature Methods* 11 (4): 417–22. https://doi.org/10.1038/nmeth.2869.<br>* Laurent, Louise, Mana Parast, and Kathleen Fisch. 2022. “Placenta-Full-Term (v1.0) Graph Data, v1.0.” https://lod.humanatlas.io/asct-b/placenta-full-term/v1.0/.<br>* McDonough, Liz, Chrystal Chadwick, Fiona Ginty, Christine Surrette, and Anup Sood. 2020. “Cell DIVE™ Platform | Slide Clearing and Antigen Retrieval.” December. https://doi.org/10.17504/protocols.io.bpwumpew.<br>* Robson, Paul, Ramalakshmi Ramasamy, and Santhosh Sivajothi. 2023. “OMAP-8: Multiplexed Antibody-Based Imaging of Placenta with Imaging Mass Cytometry (IMC), v1.0.” Zenodo. https://zenodo.org/records/10406597.