Isolation and characterization of human immunodeficiency virus type 1 variants infectious to brain-derived cells: detection of common point mutations in the V3 region of the env gene of the variants

T-cell-line-tropic human immunodeficiency virus type 1 cannot infect CD4-positive, brain-derived cells. We isolated several new variants that readily infected brain-derived cells. Mutation of proline to serine, to alanine, or to threonine in the well-conserved GPGR sequence in the V3 region of the envelope glycoprotein was found in all these variants. This indicates the importance of amino acid sequences at the tip of the V3 region for brain cell tropism of human immunodeficiency virus type 1.