Considered as an essential "metabolic organ", intestinal microbiota plays a key role in human health and the predisposition to diseases. It is an aggregate genome of trillions of microorganisms residing in the human gastrointestinal tract. Since the 20th century, researches have showed that intestinal microbiome possesses a variety of metabolic activities that are able to modulate the fate of more than 30 approved drugs and immune checkpoint inhibitors. These drugs are transformed to bioactive, inactive, or toxic metabolites by microbial direct action or host-microbial co-metabolism. These metabolites are responsible for therapeutic effects exerted by these drugs or side effects induced by these drugs, even for death. In view of the significant effect on the drugs metabolism by the gut microbiota, it is pivotal for personalized medicine to explore additional drugs affected by gut microbiota and their involved strains for further making mechanism clear through suitable animal models. This review mainly focus on specific mechanisms involved, with reference to the current literature about drugs metabolism by related bacteria or its enzymes available.

The skin is the largest defense organ and immune organ. Establishing immune memory in the skin is a key component of the acquired immune response. The skin harbors several subpopulations of memory T cells in the skin, including tissue resident memory T cells (TRMs). TRMs have a unique transcriptional profile, with the most significant features of long-term survival (lifespan) and long-term residence in skin lesions. Under physiological conditions, TRMs can respond quickly to the challenge of pathogen infection. However, increasing evidence supports their role in the recurrence of chronic inflammatory skin diseases under uncontrolled conditions. Elucidating the characteristics of skin TRMs will help to provide promising strategies for reducing the frequency and severity of skin inflammation recurrence. In this chapter, we plan to discuss the latest consensus on the biology of TRMs, and share our views on the roles of TRMs in the recurrence of inflammatory skin diseases.