OMAP-8: Organ Mapping Antibody Panel (OMAP) for Multiplexed Antibody-Based Imaging of Placenta with Imaging Mass Cytometry (IMC), v1.0

OMAP-8 was designed for Imaging Mass Cytometry (IMC) (https://pubmed.ncbi.nlm.nih.gov/24584193/) of formalin-fixed<br>paraffin-embedded (FFPE) human term-placenta samples. The tissue slides were prepared with a two-step antigen<br>retrieval process (pH 6 and pH 9, as described https://dx.doi.org/10.17504/protocols.io.bpwumpew). OMAP antibodies<br>validated by immunohistochemistry and IMC were conjugated to polymers containing metal isotopes. Conjugated antibodies<br>were used to stain processed human term-placenta tissue simultaneously. Regions of the processed tissue were then<br>acquired on the imaging mass cytometer (Hyperion; Standard BioTools) by laser ablation and visualized. The panel<br>contains 26 antibodies conjugated to unique metal isotopes and iridium marks the DNA. This OMAP provides a spatial<br>context for key placenta cell types in the [ASCT+B v.1.0<br>table](https://doi.org/10.48539/HBM446.WGLG.755). Single-cell RNA sequencing data were used to guide marker selection<br>for multiplexed tissue imaging. For example, ASCL2, HLA-G, PD-L1, CD68 and LYVE1 allow functionally specialized cell<br>types to be visualized and quantified in the placenta. Note that one of our core antibodies is to LYVE1 but, unlike in<br>other tissues where it is used to mark lymphatic vasculature, here we use it to mark the macrophage of the placenta<br>(Hofbauer cells) – there should be no lymphatics in the placenta.