During normal fetal ontogeny, one of the first organs to harbour CD4-positive cells is the thymus. This organ could therefore be one of the earliest targets infected by human immunodeficiency virus type 1 (HIV-1) in utero. HIV-1-infected cells and pathological abnormalities of the thymus have been seen in HIV-1-infected adults and children, and in some fetuses aborted from infected women. Studies of HIV-1 pathogenesis have been hampered by lack of a suitable animal model system. Here we use the SCID-hu mouse as a model to investigate the effect of virus infection on human tissue. The mouse is homozygous for the severe combined immunodeficiency (SCID) defect. The model is constructed by implanting human fetal liver and thymus under the mouse kidney capsule. A conjoint human organ develops, which allows normal maturation of human thymocytes. After direct inoculation of HIV-1 into these implants, we observed severe depletion of human CD4-bearing cells within a few weeks of infection. This correlated with increasing virus load in the implants. Thus the SCID-hu mouse may be a useful in vivo system for the study of HIV-1-induced pathology.

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Although natural killer (NK) cell-mediated control of viral infections is well documented, very little is known

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The survival of viral mediated lymphomas depends upon constitutive nuclear factor kappa B (NF-B) activity. AIDS-related human herpesvirus type 8-associated primary effusion lymphoma (PEL) responds poorly to chemotherapy and is almost invariably fatal. We have previously demonstrated that the antiviral combination of interferon alpha (IFN-␣) and azidothymidine (AZT) induces apoptosis in PEL cell lines. We therefore used these agents as therapy for an AIDS patient with PEL.

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Human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 are highly related viruses that differ in disease manifestation. HTLV-1 is the etiologic agent of adult T-cell leukemia and lymphoma, an aggressive clonal malignancy of human CD4-bearing T lymphocytes. Infection with HTLV-2 has not been conclusively linked to lymphoproliferative disorders. We previously showed that human hematopoietic progenitor (CD34 ؉ ) cells can be infected by HTLV-1 and that proviral sequences were maintained after differentiation of infected CD34