CD4 and systemic lupus erythematosus: By chromatin immunoprecipitation (ChIP) microarray data, Zhang et al. has identified significantly increased level of histone H3 lysine 27 trimethylation (H3K27me3) enrichment at the hematopoietic progenitor kinase 1 (HPK1), a negative regulator of T cell-mediated immune responses, promoter of SLE CD4+ T cells relative to controls.