Hobit and Blimp1 instruct a universal transcriptional program of tissue-residency in lymphocytes

Tissue-resident memory T cells (Trm) are non-circulating memory T cells that localize to portals of pathogen entry such as the skin, gut and lung where they provide efficient early protection against reinfection. Trm are characterized by a molecular profile that actively prevents egress from peripheral sites including the constitutive expression of the lectin CD69 and down-regulation of the chemokine receptor (CCR)7 and sphingosine-1-phosphate receptor 1 (S1PR1). This program is partially mediated by down-regulation of the transcription factor KLF2; however, to date no transcriptional regulator specific to Trm has been identified. Here we show that the Blimp1 related transcription factor Hobit is specifically upregulated in Trm and together with Blimp1, mediates the development and maintenance of Trm in various tissues including skin, gut, liver and kidney. Importantly, we found that the Hobit/Blimp1 transcriptional module is also required for other tissue-resident lymphocytes including Natural Killer T (NKT) cells and liver tissue-resident NK cells (trNK). We show that these populations share a universal transcriptional program with Trm instructed by Hobit and Blimp1 that includes the repression of CCR7, S1PR1 and KLF2 thereby enforcing tissue retention. Our results identify Hobit and Blimp1 as major common regulators that drive the differentiation of distinct populations of tissue-resident lymphocytes.