To better understand the spatial context and interactions of the two cell types most characteristic of photosensitive disease lesions, CD14+ myeloid cells and cytotoxic CD4+ T cells, we turned to spatial transcriptomics using Sequential fluorescence in situ hybridization (seqFISH), which enable the simultaneous detection of hundreds of gene transcripts with subcellular resolution3. The gene discussed is CD4; the disease is photosensitivity disease.