Ichiro Taniuchi, Group Director of the Laboratory for Transcriptional Regulation, received the 16th Japanese Society for Immunology Award for his elucidation of how T cell development is regulated at the transcriptional level. Taniuchi discovered that Runx transcription factor complexes are essential to activate a silencer in the CD4 gene for its lineage-specific expression. Following identification of a Thpok as a master transcription factor for CD4 T cell development, he indicated that Runx play an essential role in repression of Thpok gene expression, which is an essential process for differentiation into cytotoxic-lineage T cells. By generating series of gene manipulated mice and cutting edge molecular biology technique, he demonstrated that antagonistic interplay between ThPOK and Runx factors is a key mechanism for an helper/cytotoxic dichotomy, and provided insight into how cell fate decision to become helper or killer T cells is controlled in nucleus. It is noteworthy that he recently uncovered the hidden plasticity in CD4 T cells, which allow them to acquire cytotoxic features upon exposure to the gut environment. This finding of retained flexibility in CD4 T cells gave a big impact in the field of developmental immunology. His expanding research is not only focusing on a molecular link between TCR signals with transcriptional regulation, but also addressing how balance of stability and flexibility is conferred to T cells during thymocyte differentiation. Award is given to a researcher, age 50 or below, whose contribution to the advancement of immunology was original and extraordinary and who is able to further expand research to provide a new paradigm in the Immunology.