Multiple integrations of human T-lymphotropic virus type 1 proviruses in the engrafted cells from the asymptomatic carriers in NOD/SCID/gammacnull mice.

OBJECTIVES Successful engraftment of human T-lymphotropic virus type 1 (HTLV-1)-infected cells and a marked increase of proviral DNA loads (PVLs) in non-obese diabetic/severe combined immunodeficient (NOD/SCID)/gammac(null) (NOG) mice have been reported. Whether the increased PVL in transplanted mice is due to the new infection of HTLV-1 was examined. METHODS Mononuclear cells from 3 NOG mice with primary engraftment from asymptomatic HTLV-1 carriers were transplanted into a second group of NOG mice. HTLV-1 PVL, proviral integration by fluorescence in situ hybridization assay, expression of viral antigen, and T-cell clonality were analyzed. RESULTS The PVLs in the secondarily transplanted NOG mice were significantly higher than those of primarily transplanted NOG mice. Multiple signals of HTLV-1 proviruses in the nucleus of the infected cells were revealed by fluorescence in situ hybridization analysis. Expression of HTLV-1 tax/rex mRNA and antigen was observed. The variety of T-cell clones was limited in the transplanted NOG mice. CONCLUSIONS Multiple proviral integrations were considered to be due to the new infection from HTLV-1-infected cells to the other cells. Only a certain fraction of T cells seemed to have selectively survived in NOG mice after engraftment.