(A) Upon resting status, dephosphorylated SAMHD1 binds to 3’ UTR of Foxp3 and Helios mRNAs in nucleus, and then transfer those to cytoplasm to process 3’ UTR of mRNAs. After the processing, SAMHD1 is shuttled back to nucleus. (B) However, if ODNps25 is added in the cells, ODNps25 preferentially binds to SAMHD1–3’UTR complex in cytoplasm. The binding inhibits dNTPase activity of SAMHD1 and subsequent processing of 3’ UTRs, resulting of accumulation of the complex and enhancement of stability of Foxp3 and Helios mRNAs. (C) In TCR stimulation, CDK2-mediated Thr592 phosphorylation of SAMHD1 inhibits dNTPase activity, resulting of the induction of Foxp3 and Helios expression as well.