4-Hydroperoxy cyclophosphamide is the active metabolite form of the precursor Cyclophosphamide. 4-Hydroperoxy cyclophosphamide cross-links DNA to induce T cell apoptosis independent of caspase receptor activation, and can activate the mitochondrial death pathway by producing reactive oxygen species (ROS). 4-Hydroperoxy cyclophosphamide can be used in the study of rheumatoid arthritis and autoimmune diseases.