Chapter 17 : Human Retroviruses in the Second Decade: Some Pathogenic Mechanisms and Approaches to Their Control

Phylogenetic tree of simian T-cell leukemia/lymphotropic virus type I (STLV-I), HTLV-I, and HTLV-II envelope nucleotide ( 30 ) DNA sequences (positions 6046 to 6567) are constructed on the outgroup HTLV-IIMO as calculated by the DNA Boot program (Phylip V.3:41), which implements the bootstrap method for placing confidence intervals, using parsimony for DNA sequences. The numbers located at the forks indicate the frequency of association of the various virus groups in the bootstrap analysis after 100 replications of the data. Agm, African green monkey.

Schematic representation of HTLV-I genomic organization. The open boxes in the pX region (located between the end of the envelope gene and the 3' viral LTR) include the open reading frames for the p27rex/p21rex proteins, p40tax and the proteins pl2I, pl3II, and p30II, recently demonstrated to be produced through alternative splicing ( 31 , 32 ). aa, amino acids.

Comparison of the putative amino acid sequences of the bovine papillomavirus type 1 (BPV-1) E5 and HTLV-I pl2I proteins. Single amino acid codes are used, and the lower part of the figure represents the hydrophage profile of both proteins ( 17 ).

Genome structure of HIV-1 with reading frames indicated. Gag and Pol products are translated from unspliced RNA, and Env is translated from singly spliced RNA. More complex, multiple splicing events lead to formation of mRNA for the regulatory proteins.

Experimental evidence indicating that HHV-7 uses CD4 as a component of its receptor: monoclonal antibodies (mAbs) to human CD4, the soluble form of human CD4 (sCD4), and the soluble form of HIV-1 gpl20 all inhibit infection of human CD4+ T cells by HHV-7.

Infection of primary human CD4+ T lymphocytes by different HIV-1 isolates is inhibited by preexposure of the cells to HHV-7 for 48 h. Isolates 571, 573, and BO are primary isolates passaged only in primary human peripheral blood mononuclear cells.

Time course of HIV-1 inhibition by hydroxyurea (HU) and/or by ddl in activated lymphocytes. Lymphocytes were obtained from an HIV-1-infected patient, isolated, and stimulated for 2 days with phytohemagglutinin and IL-2. Subsequently, hydroxyurea and ddl were added at the concentrations illustrated, and replication was analyzed as follows: every 3 to 4 days, supernatants were harvested for p24 analysis, and fresh supernatant and drugs were added. Partial inhibition was obtained when the drugs were used separately, and complete block of HIV-1 replication was achieved when hydroxyurea and ddl were used in combination. Hydroxyurea concentrations necessary to block HIV-1 (in combination with ddl) were not toxic and corresponded to the lower concentrations measured in the sera of cancer patients treated with hydroxyurea ( 4 ). (Reprinted with permission from Lori et al., Science 266:801-805, 1994.)

HIV-1 inhibitory genes. Indicated above are some of the HIV-1 inhibitory genes currently being developed by us for possible clinical use. Poly(TAR) is an oligomer containing 30 to 50 repeats of the Tat activation response (TAR) region ( 33 ). trans-dominant Gag is a mutant with a short deletion encompassing a Gag precursor cleavage site ( 56 , 58 ). trans-dominant rev is a mutant of rev which interferes with the activity of the wild-type gene product ( 45 ). Antisense oligonucleotides are antisense to the indicated genes and have phosphorothioate or phosphodiester backbones.

Inhibition of HIV-lmB replication in MOLT-3 cells by intracellular anti-RT antibody fragments. HIV-1 replication over 30 days in MOLT-3 cell cultures was derived after, minimally, 2 weeks of selection. Values are means of triplicate experiments (standard deviation, ≥15%); multiplicity of infection was 2.0.

(A) Schematic of Tat-Tat activation response (TAR) region interaction leading to transcriptional activation. Tat binds to the bulge of the stem-loop structure of the TAR element and also interacts with a cellular factor(s) (CF) which binds to the loop of the stem-loop. The diagram on the left assumes that Tat has an activation domain that interacts with the promoter element to activate transcription. The diagram on the right on the other band assumes that Tat does not have an activation domain and that its role is to recruit a cellular factor(s) which activates transcription. The lower diagram depicts a combination of the two possibilities. (B) Tat-mediated transcriptional activation. Tat is depicted to promote both transcriptional initiation and elongation. Its major effect may be to enhance the processivity of transcription.

Electron micrograph illustrating the ultrastructures of mature HHV-6 and HHV-7 virions.

Antisense phosphorothioate oligodeoxynucleotides directed against bFGF (AS bFGF) but not sense oligomers (S bFGF) block the growth of AIDS-KS cells derived from different patients (AIDS-KS3, -KS4, and -KS6) (A) but not the proliferation of normal endothelial cells (human umbilical-vein-derived endothelial cells [H-UVE]) grown under standard conditions (aFGF and heparin) (B). □, medium; ▪, AS bFGF; □-S bFGF. Reproduced from the Journal of Clinical Investigation, 1994, 94:1736-1746, by permission of The Society for Clinical Investigation.