Evidence for the Chronic in Vivo Production of Human T Cell Leukemia Virus Type I Rof and Tof Proteins from Cytotoxic T Lymphocytes Directed against Viral Peptides

Human T cell leukemia virus type I (HTLV-I) is a persistent virus that causes adult T cell leukemia and tropical spastic paraparesis/HTLV-I–associated myelopathy. Studies on rabbits have shown that viral proteins encoded by the open reading frames pX-I and pX-II are required for the establishment of the persistent infection. To examine the in vivo production of these proteins in humans, we have investigated whether cytotoxic T lymphocytes isolated from HTLV-I–infected individuals recognized pX-I and pX-II peptides. CD8⁺ T lymphocytes to pX-I and pX-II peptides were detected in HTLV-I–infected individuals, whatever their clinical status, and even in the absence of any antigenic restimulation. These findings indicate that the HTLV-I pX-I and pX-II proteins are chronically synthesized in vivo, and are targets of the natural immune response to the virus.