The use of plasma HIV RNA as a study endpoint in efficacy trials of antiretroviral drugs.

OBJECTIVES: To evaluate the utility of HIV RNA as an endpoint in antiretroviral efficacy studies. DESIGN: Data collected from antiretroviral efficacy trials were analyzed to explore relationships between clinical progression and the magnitude, nadir and duration of HIV RNA reductions. The proportion of patients suppressing HIV RNA below assay quantification, time to maximal virologic response, and loss of virologic response in relation to pretreatment characteristics were also analyzed. METHODS: Analyses were conducted using data from individual antiretoviral efficacy trials or groups of trials that studied similar types of drug regimens and used similar HIV RNA assays. Treatment regimens were pooled for most analyses. Clinical progression was defined as the occurrence of an AIDS-defining event (essentially Centers of Disease Control criteria) or death. RESULTS: Treatment-induced reductions in HIV RNA approximating total assay variability of about 0.5 log10 copies/ml were associated with decreases in the risk of clinical progression. Larger and more sustained reductions in HIV RNA were directly associated with lower risks for disease progression. Lower initial HIV RNA reductions were associated with more durable HIV RNA suppression. CONCLUSIONS: For antiretoviral efficacy studies, plasma HIV RNA is a suitable study endpoint that is likely to predict a decreased risk for AIDS progression and death. Because greater and more sustained reductions in HIV RNA appear to confer greater reductions in clinical risk, maintaining maximal suppression of plasma HIV RNA, particularly below the limits of assay quantification, appears to be a rigorous benchmark for assessing the efficacy of antiretroviral regimens.

Overexpression of nef as a marker for restricted HIV-1 infection of astrocytes in postmortem pediatric central nervous tissues.

In previous studies, using polymerase chain reaction amplification of HIV-1 genes directly from pathologic tissues of children who died with AIDS encephalopathy, we showed that the reading frame of the HIV-1 regulatory nef gene is open, suggesting that the nef protein was expressed. We now show, using immunocytochemistry and in situ hybridization with nef-specific probes in postmortem pediatric CNS tissues, that nef mRNA and protein are present in up to 20% of astrocytes in tissue sections selected for extensive histopathology. By contrast, HIV-1 structural proteins such as gag and their coding mRNAs are present in multinucleated giant cells that harbor productive infection and are the hallmark of HIV-1 infection in the CNS. These findings are consistent with the nonproductive infection of glial cells observed in vitro, and imply that HIV-1 infection of astrocytes is restricted to early regulatory gene products, of which nef is the best target as it is expressed at high levels and is membrane-anchored. In developing central nervous tissues of children, restricted and latent HIV-1 infection of astrocytes may be extensive and contribute significantly to HIV-1 neuropathogenesis.

Human neural xenografts: progress in developing an in-vivo model to study human immunodeficiency virus (HIV) and human cytomegalovirus (HCMV) infection.

Human immunodeficiency virus type 1 (HIV-1) infection is highly specific for its human host. In order to study HIV-1 infection of the human nervous system, we have established a small animal model in which second-trimester (11-17.5 weeks) human fetal brain or neural retina is transplanted into the anterior chamber of the eye of immunosuppressed adult rats (Epstein et al., 1992; Cvetkovich et al., 1992), and more recently in immunodeficient (SCID) mice. The human xenografts survive for many months, vascularize and form a blood-brain barrier. Immunohistochemistry with PGP 9.5 identified neuronal cell bodies and neuritic processes. Electron microscopy revealed axonal growth cones and synaptic junctions. Infection of these xenografts with cell-free HIV-1 proved difficult, however co-engraftment with HIV-1-infected human monocytes resulted in characteristic pathological changes, including the formation of syncytial giant cells, neuronal loss, and astroglial proliferation, supporting the hypothesis that these cells can mediate neurotoxicity. In other studies, xenografts of human fetal retinal tissue were readily infected with cell-free human cytomegalovirus (HCMV) strain AD169. These grafts contained cells with intracytoplasmic and intranuclear inclusions typical of HCMV infection. Productive infection within these grafts was demonstrated by the presence of immediate early, and late (capsid) HCMV antigens, by recovery of HCMV on human fibroblast cultures, and by serial passage of virus to additional retinal xenografts (DiLoreto et al., 1994).(ABSTRACT TRUNCATED AT 250 WORDS)

Human immunodeficiency virus type 1 infection of neural xenografts.

Human immunodeficiency virus type 1 (HIV-1) infection is highly specific for its human host. To study HIV-1 infection of the human nervous system, we have established a small animal model in which second-trimester (11 to 17.5 weeks) human fetal brain or neural retina is transplanted to the anterior chamber of the eye of immunosuppressed adult rats. The human xenografts vascularized, formed a blood-brain barrier, and differentiated, forming neurons and glia. The xenografts were infected with cell-free HIV-1 or with HIV-1-infected human monocytes. Analysis by polymerase chain reaction revealed HIV-1 sequences in DNA from xenograft tissue exposed to HIV-1 virions, and in situ hybridization demonstrated HIV-1 mRNA localized in macrophages and multinucleated giant cells. Pathological damage was observed only in neural xenografts containing HIV-1-infected human monocytes, supporting the hypothesis that these cells mediate neurotoxicity. This small animal model allows the study of direct and indirect effects of HIV-1 infection on developing human fetal neural tissues, and it should prove useful in evaluating antiviral therapies, which must ultimately target HIV-1 infection of the brain.

Successful xenografts of second trimester human fetal brain and retinal tissue in the anterior chamber of the eye of adult immunosuppressed rats.

Successful xenografting of first trimester human fetal CNS tissue and retina has been reported in the literature. We wished to test the feasibility of using the anterior chamber of the rat eye to support the development of more mature human fetal xenografts. Here we report on the successful outcome of human brain and retinal transplants. Adult host rats immunosuppressed with cyclosporin A accepted these xenografts and supported their further development. Periodic examination of the host eyes using a direct ophthalmoscope or an ophthalmic slit lamp permitted direct visual monitoring of the health and growth of the transplants. Histologically it was possible to identify neuronal, macroglial, and microglial (macrophage) cell types within the grafts. Mitotic activity and histogenetic differentiation took place. Blood vessels filled with hematic cells were commonly present within the grafts. The walls of these vessels prevented the leakage of horseradish peroxidase, suggesting the presence of a functional brain-blood barrier in the graft. These results indicate that it is possible to use a small animal model to study normal and pathological phenomena on late fetal human neural tissues. Our group has already taken advantage of the model to achieve HIV infectivity of fetal human brain outside the human body.