Immunohistochemical staining of bladder from a patient undergoing treatment with vaccinia vector. Pretreatment biopsies (a, c, and e) and post-treatment cystectomy sections (b, d, and f) were stained for the T-cell marker CD3 (a and b); the CD45RO marker (c and d), which is found on activated T cells; and factor XIIIa (e and f), a dendritic cell marker. The presence of activated T cells and dendritic cells in the tumor infiltrates suggests that the treatment has induced a robust immunologic response.