In multicellular organisms, each cell has a distinct identity characterized by unique transcriptional and chromatin-accessibility profiles. The introduction of single-cell RNA sequencing has revolutionized the ability to analyse each individual cell. However, cells do not operate in isolation; they exist within an intricate network, engaging in continuous communication with neighbouring cells to sustain the organism as a whole. It is through these interactions that cells share information, shaping each other’s function. Thus, overlaying transcriptional data with information on a cell’s ‘interactome’ is regarded as the next phase in deciphering the biological role of a cell1.

In 2018, our group introduced LIPSTIC (labelling immune partnerships by Sor-tagging intercellular contacts), a tool that uses enzymatic transfer of a labelled peptide tag from a donor cell expressing the bacterial transpeptidase Sortase A (SrtA) to an acceptor cell expressing a protein with an N-terminal pentaglycine (G5) to label interacting cells in vivo2. This first version of LIPSTIC was restricted to cells expressing CD40 and CD40L, as SrtA and G5 were fused to this receptor–ligand pair. Our more recent work reengineered this tool to eliminate such dependence; this resulted in the development of universal (u)LIPSTIC, which allows the recording of interactions between a broader spectrum of cell types3. In uLIPSTIC, SrtA and G5 are anchored non-specifically to the cell membrane at high density; the enzymatic reaction is allowed to proceed when apposing membranes come into close contact, which can be driven by interactions between any receptor–ligand pair of the appropriate dimensions. Using the appropriate Cre drivers, we and our collaborators were able to record the interactomes of a wide range of cells within the immune system and beyond, both in homeostasis and infection.