CD38, also known as cyclic ADP ribose hydrolase, is a multifunctional transmembrane glycoprotein expressed on various immune cells such as T lymphocytes, B cells, and plasma cells. It functions as both a receptor and an enzyme, playing a crucial role in cell adhesion, signal transduction, and the regulation of intracellular calcium levels. CD38 catalyzes the metabolism of nicotinamide adenine dinucleotide (NAD+), generating molecules like cyclic ADP-ribose (cADPR) and ADP-ribose (ADPR), which are involved in calcium signaling and immune responses. It is highly expressed on myeloma cells and is used as a therapeutic target for multiple myeloma and other hematological malignancies. Additionally, CD38 is implicated in various physiological processes, including inflammation, phagocytosis, and antigen presentation, making it a subject of interest in both immunology and oncology.