Common Wart (Verruca vulgaris)
HPV lesions are generally self-limited but can persist for several years. They eventually regress in most cases due to cell-mediated immunity. Regression is associated with basal cell degeneration, epidermal degeneration, and vascular thrombosis. After regression, the person is immune to further HPV infections. Patients with defective cell-mediated immunity (primary, iatrogenic, or HIV-induced) are particularly at risk for developing large crops of warts that don't regress spontaneously and are difficult to treat.
The image shows common wart arising on the trunk of an adult male.