The recent development of high-throughput DNA sequencing technologies has driven the rapid progress in genomics research and enabled us to address a multitude of biological questions. It is clear that our immune system plays a critical role in various biological and pathological conditions， such as cancer， autoimmune diseases， and drug-induced toxicities. The recent development of cancer immunotherapies clearly demonstrates the importance of host immune cells， particularly drugs modulating the immune checkpoint molecules， in the fight against cancer. However， the molecular mechanisms by which these new therapies kill tumor cells still remain unclear.  Hence， we have explored the roll of newly-developed tools such as next generation sequencing in characterization of the immune system， which has been referred to as immunopharmacogenomics. This new field has enormous potential to help us better understand the changes/alterations to our immune responses during the course of cancer treatment. I here report the deep sequencing of T-cell receptors that will enable us to capture the molecular contribution of the immune system， including the immune microenvironment in tumors and its application for personalized TCR (T cell receptor)-engineered T cell treatment.