HUMAN LYMPHOBLASTOID CD4(-CELLS BECOME PERMISSIVE TO MACROPHAGE-TROPIC STRAINS OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 AFTER PASSAGE INTO SEVERE COMBINED IMMUNODEFICIENT MICE THROUGH IN-VIVO UP-REGULATION OF CCR5 - IN-VIVO DYNAMICS OF CD4(+) T-CELL DIFFERENTIATION IN PATHOGENESISOF AIDS() T)

In this article, we show that passage in SCID mice rendered a human CD 4(+) T-cen line (CEM cells) highly susceptible to infection by macroph age-tropic (M-tropic) strains and primary clinical isolates of human i mmunodeficiency virus type 1 (HIV-I). This in vivo-acquired permissive ness of CEM cells was associated with the induction of a CD45RO(+) phe notype as well as of some beta-chemokine receptors. Regulated upon act ivation, normal T-cell expressed and secreted chemokine entirely inhib ited the ability of M-tropic HIV-1 strains to infect these cells. Thes e findings may lead to new approaches in investigating in vivo the cap acity of different HIV strains to exploit chemokine receptors in relat ion to the dynamics of the activation and/or differentiation state of human CD4(+) T cells.