CD4 and systemic lupus erythematosus: Conversely, recent research has demonstrated that an elevated histone H3 lysine 27 trimethylation enrichment at the promoter of haematopoietic progenitor kinase 1 (HPK1) in SLE CD4+ T cells (in comparison to controls) suppresses HPK1 expression and has a role in promoting autoimmunity in SLE [40].