With advances in DNA sequencing and various ’omics‘ technologies, it has become possible to capture changes in immune cells through the analysis of biologically active substances such as cytokines and chemokines, as well as T- and B- cell receptor sequence analysis in various pathological conditions and drug responses. Furthermore, technological advances in the single cell level have made it possible to understand the dynamic changes in immune cells in detail. In addition, it has been suggested that the immune responses activated through drug and HLA interaction play key roles in drug-induced skin hypersensitivity and hepatotoxicity. HLA class I molecules are associated with drug eruptions such as Stevens-Johnson syndrome, and class II molecules with hepatotoxicity. In cancer treatment, it is becoming clear that the immune environment within cancer tissues and throughout the body is important not only for cancer immunotherapy but also for the responsiveness of other anticancer drugs and radiation therapy. Changes in immune responses during the onset, remission, and progression processes of various diseases have not been completely analyzed until now, but development of immunopharmacogenomics will certainly help to elucidate these changes.