Proliferation of double‐negative (CD4−CD8−) T cells bearing T‐cell receptor‐αβ in a haemophiliac with human immunodeficiency virus type 1 infection and factor VIII inhibitor: functional properties of double‐negative T‐cell receptor‐αβ+ T cells

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Abstract
We present a patient with haemophilia A showing human immunodeficiency virus type 1 (HIV‐1) infection and factor VIII inhibitor in whom a novel T‐cell subpopulation, double‐negative (CD4−CD8−) T cells bearing T‐cell receptor (TCR)αβ, proliferated polyclonally in the peripheral blood. An interleukin‐2‐dependent T‐cell line with a CD4−CD8−TCR‐αβ+ phenotype was established from the peripheral blood lymphocytes of the patient, and its biological functions were studied. It was found that the CD4−CD8−TCR‐αβ+ T cells possessed both HLA‐unrestricted cytotoxicity and helper function for immunoglobulin production by B cells. In addition, these T cells were found to produce interferon‐γ and interleukin‐2 following activation via CD3‐TCR complexes. These data demonstrating the multifunction of these newly defined CD4−CD8−TCR‐αβ+ T cells thus suggest that these cells play an important role in protection against HIV infection. The mechanism of production of factor VIII inhibitor in the present case is also discussed focusing on the CD4−CD8−TCR‐αβ+ T cells.