A recent single-cell transcriptomics study from Huang et al.16 identified the presence of peripheral CD38+ HLA-DR+ cycling lymphocytes, comprised of CD4+ T cells, CD8+ T cells, and cNK cells, in patients with macrophage activation syndrome (MAS), a cytokine storm syndrome which develops in the context of rheumatic disorders. The gene discussed is CD38; the disease is macrophage activation syndrome.