Characterization of a HTLV-I-infected cell line derived from a patient with adult T-cell leukemia with stable co-expression of CD4 and CD8

A long-term T-cell line, termed SP⁺, was developed from a human T-cell leukemia virus type I (HTLV-I)-infected patient with adult T-cell leukemia that is dependent on exogenous IL-2 for growth. The SP⁺ expresses a full complimentation of HTLV-I-specifrc viral proteins, and contains replication competent viral particles. Restriction enzyme digestion followed by Southern blot analysis demonstrated the presence of a single integrated proviral copy and limiting dilution analysis confirmed the clonality of the cell line. Interestingly, phenotypically, the SP⁺ cell line is CD2⁺, CD3⁺ and coexpresses CD4 and CD8, yet lacks TCRαβ and TCRτδ expression. Further ontogenetic characterization of the SP⁺ cell line demonstrated the lack of thymic T-cell precursor markers, including absence of cell surface expression of CD1, intracellular thymic terminal deoxynucleotidyl transferase (TdT) enzyme, as well as message expression for V(D)J recombinase activating gene-1 (RAG-1). Furthermore, the SP⁺ cell did express the message for the CD3δ chain. Taken together, these data suggest that the SP⁺ cell line resulted from HTLV-I infection of a mature CD4⁺/CDB⁺ lymphocyte. This cell line can be potentially useful as a model, both for regulation of cellular functions by HTLV-I and for immunologic functions of mature dual CD4/CD8 positive T-cells.