Role of human T-cell leukemia virus type 1 X region proteins in immortalization of primary human lymphocytes in culture.

Human T-cell leukemia virus type 1 (HTLV-1) immortalizes human CD4+ T lymphocytes in culture. Previous studies show that in the context of a herpesvirus saimiri vector, the sequence of the X region at the 3' end of the HTLV-1 genome is also capable of immortalizing CD4+ lymphocytes in the absence of HTLV-1 structural proteins. The X region of HTLV-1 encodes two trans-acting viral proteins, the 42-kDa Tax protein and the 27-kDa Rex protein. Infection of human cord blood cells with herpesvirus saimiri recombinants which contain HTLV-1 X region sequences defective for expression of tax, rex, or both tax and rex demonstrates that tax function is necessary and sufficient for immortalization of primary human CD4+ cord blood lymphocytes in culture in the context of the herpesvirus saimiri vector.