Efficient transduction of nondividing human cells by feline immunodeficiency virus lentiviral vectors.

The molecular bases for species barriers to lentiviral replication are not well understood, but are of interest for explaining lentiviral pathogenesis, devising therapeutic strategies, and adapting lentiviruses to gene therapy. HIV-1-based lentiviral vectors efficiently transduce nondividing cells, but present complex safety concerns. Nonprimate (ungulate or feline) lentiviruses might provide safer alternatives, but these viruses display highly restricted tropisms, and their potential for adaptation as replication-defective vectors capable of transducing human cells is unknown. Feline immunodeficiency virus (FIV) does not infect humans or other non-Felidae despite prevalent natural exposure. Although long terminal repeat (LTR)-directed FIV expression was found to be negligible in human cells, promoter substitution enabled an env-deleted, three-plasmid, human cell-FIV lentiviral vector system to express high levels of FIV proteins and FIV vectors in human cells, thus bypassing the hazards of feline vector producer cells. Pseudotyped FIV vectors efficiently transduced dividing, growth-arrested, and postmitotic human targets. The experiments delineate mechanisms involved in species-restricted replication of this lentivirus and show that human cells support both productive- and infective-phase mechanisms of the FIV life cycle needed for efficient lentiviral vector transduction. Nonprimate lentiviral vectors may offer safety advantages, and FIV vectors provide unique experimental opportunities.

Dextran sulfate suppression of viruses in the HIV family: inhibition of virion binding to CD4+ cells.

The first step in the infection of human T lymphocytes by human immunodeficiency virus type 1 (HIV-1) is attachment to the target cell receptor, the CD4 antigen. This step may be vulnerable to attack by antibodies, chemicals, or small peptides. Dextran sulfate (molecular weight approximately 8000), which has been given to patients as an anticoagulant or antilipemic agent for more than two decades, was found to block the binding of virions to various target T lymphocytes, inhibit syncytia formation, and exert a potent inhibitory effect against HIV-1 in vitro at concentrations that may be clinically attainable in human beings. This drug also suppressed the replication of HIV-2 in vitro. These observations could have theoretical and clinical implications in the strategy to develop drugs against HIV types 1 and 2.

Type-restricted neutralization of molecular clones of human immunodeficiency virus.

In a study of the immunologic significance of the genetic diversity present within single isolates of human immunodeficiency virus type 1 (HIV-1), the neutralization of viruses derived from molecular clones of the HIV-1 strain HTLV-IIIB by an extensive panel of sera was compared. Sera from HIV-1-infected patients and from goats immunized with polyacrylamide gel-purified HIV-1 envelope glycoprotein (gp120), native gp120, or gp120-derived recombinant peptides, showed marked heterogeneity in neutralizing activity against these closely related viruses. The change of a single amino acid residue in gp120 may account for such "clonal restriction" of neutralizing activity.

Long-term high-titer neutralizing activity induced by octameric synthetic HIV-1 antigen.

A titer for homologous viral neutralization activity (greater than 1:19,683) was observed after a 3.5-year immunization period with an octameric, branching peptide representing the principal neutralizing determinant (PND) of the human immunodeficiency virus-1IIIB envelope protein. Booster immunizations elicited persistent and potent antibodies in guinea pigs, exceeding responses produced by a conventional bovine serum albumin conjugate by 100-fold. Peptide length, central presentation of a conserved sequence, and inclusion of an upstream sequence contributed to immunogenicity. Titers (greater than 1:1,000) of heterotypic neutralizing antibodies also developed. Octameric PND peptides are a promising approach for an acquired immunodeficiency syndrome (AIDS) vaccine.

Antiproliferative effect of retinoid compounds on Kaposi's sarcoma cells.

A panel of retinoid compounds (tretinoin, isotretinoin, acitretin, and RO13-1470) were tested for inhibitory activity against Kaposi's sarcoma cell (KSC) cultures in vitro. Tretinoin was found to be the most effective retinoid tested, inhibiting the growth of KSC in vitro while having no effect on the expression of interleukin-6 and basic fibroblast growth factor, two important cytokines involved in KSC growth. Tretinoin also did not appear to downregulate the expression of receptors for these two cytokines. At low concentrations (10(-9) M), acitretin and tretinoin selectively inhibited growth of early passage KSC. At higher concentrations (10(-6)-10(-5) M), retinoid treatment induced a pattern of DNA degradation and morphological changes in KSC characteristic of apoptosis (programmed cell death). The inhibitory activity of tretinoin on KSC growth was decreased if human serum (but not fetal calf serum) was present in the growth medium, and partially restored by removal of serum lipids. These data suggest that retinoids possess potential as therapeutic agents in Kaposi's sarcoma.

Antiproliferative effects of enediynes on AIDS-derived Kaposi's sarcoma cells.

We have investigated the antiproliferative and cytotoxic effects of selected enediynes against three Kaposi's sarcoma (KS) cell lines. The enediynes tested were found to be very potent in inhibiting the growth of KS cells. Treatment with concentrations of 10(-10) M or less were capable of producing 50% inhibition of growth. Furthermore, treatment of KS cells with enediynes induced apoptosis in up to 80% of the cells. This unique class of antitumor agents has therapeutic potential for the treatment of KS.

Kaposi sarcoma-associated herpesvirus promotes tumorigenesis by modulating the Hippo pathway.

Kaposi sarcoma-associated herpesvirus (KSHV) is an oncogenic virus and the culprit behind the human disease Kaposi sarcoma (KS), an AIDS-defining malignancy. KSHV encodes a viral G-protein-coupled receptor (vGPCR) critical for the initiation and progression of KS. In this study, we identified that YAP/TAZ, two homologous oncoproteins inhibited by the Hippo tumor suppressor pathway, are activated in KSHV-infected cells in vitro, KS-like mouse tumors and clinical human KS specimens. The KSHV-encoded vGPCR acts through Gq/11 and G12/13 to inhibit the Hippo pathway kinases Lats1/2, promoting the activation of YAP/TAZ. Furthermore, depletion of YAP/TAZ blocks vGPCR-induced cell proliferation and tumorigenesis in a xenograft mouse model. The vGPCR-transformed cells are sensitive to pharmacologic inhibition of YAP. Our study establishes a pivotal role of the Hippo pathway in mediating the oncogenic activity of KSHV and development of KS, and also suggests a potential of using YAP inhibitors for KS intervention.

A controlled, Phase 1 clinical trial to evaluate the safety and effects in HIV-1 infected humans of autologous lymphocytes transduced with a ribozyme that cleaves HIV-1 RNA.

This Phase I study, "Ribozyme Gene Therapy of HIV-1 Infection" (UCSD HSC #971072, FDA BB-IND 6405), is a prospective, open-label trial of infusion of autologous gene-altered cells into asymptomatic HIV-1 seropositive individuals. The objectives of this trial are to test the safety, feasibility, and potential efficacy of T-cell ribozyme gene therapy of HIV-1 infection. To accomplish this, autologous CD8-depleted mononuclear cells are transduced with ribozyme expressing or control murine retroviral vectors, expanded ex vivo, and and infused. Subjects are monitored intensively to determine effects of infusion on HIV burden and replication. In addition, in vivo survival of control and ribozyme transduced cells is followed in an effort to obtain evidence of proof of concept. A unique strategy of sample blinding is introduced in this protocol, wherein both subject and control specimens are supplied to the research laboratory as coded samples, spiking blood from HIV seropositive volunteers matched for CD4 lymphocyte count with known but varying numbers of cells transduced with each vector. While this study is still in progress, preliminary results indicate that infusion of gene-altered, activated T-cells in HIV infected patients is safe, and that transduced cells can persist for long intervals in HIV-infected subjects. Results also suggest ribozyme transduced cells may possess a survival advantage in vivo.

Differences in the interaction of HIV-1 and HIV-2 with CD4.

Inhibition of infectivity, cytopathicity, and binding by soluble CD4 was determined for several human immunodeficiency virus (HIV)-1 and HIV-2 strains. Although infectivity and binding of both groups were blocked equally well by OKT4A, HIV-2 viruses were more refractory to inhibition by soluble CD4. Rates of envelope shedding, as determined by thermal stability, did not differ between HIV-1 and HIV-2; however, Scatchard plot analysis of radiolabeled virus binding revealed that fewer HIV-2 virions were bound to CD4+ cells under saturating conditions. The HIV-2 viruses also possessed consistently greater infectivity, whereas greater concentrations of gp120 were found in supernatants of HIV-1-infected cells and in HIV-2 virus pellets, suggesting that more envelope glycoprotein remains associated with HIV-2 virions. This factor may contribute to the observed in-vitro resistance of HIV-2 viruses to soluble CD4.

A recombinant clone of HIV-1 preferentially transmitted in normal peripheral blood mononuclear cells.

To study biologic properties associated with specific regions of HIV-1, a chimera, pHX-JY1, was constructed by exchanging the vif-env region of a Zairian molecular clone (JY1) with that of pHXB2gpt, a full-length biologically active proviral clone of North American origin. Virus was produced by transfection of permissive cells with parental and recombinant clones, and the biologic and molecular properties of these viruses were compared. Virus derived from pHXB2gpt infected phytohemagglutinin (PHA)-activated normal peripheral blood mononuclear cells (PBMC) and CD4+ leukemic T cell lines equally well. In contrast, virus derived from pHX-JY1 was transmitted slowly to both PBMC and cell lines, and the infectivity of pHX-JY1 virus was two orders of magnitude greater for PBMC than for T cell lines. All essential viral genes in the exchanged JY1 vif-env region were intact and functioned comparably to those of the parent clone in transfected COS-1 cells. The findings suggest differences in these regions of the HIV-1 genome may play an important role in differential cell tropism.

Molecular cloning and characterization of a TAR-binding nuclear factor from T cells.

The TAt protein of the human immunodeficiency virus type 1 (HIV-1) activates the expression of viral mRNA through a cis-acting element in the LTR termed TAR. TAR RNA forms a stable stem-loop structure. Mutagenesis studies indicate that the stem structure, the primary sequence of the loop, and three unpaired bases in the stem (bulge) are important for Tat activation. Using the in vitro-transcribed TAR RNA as a probe, we have cloned a gene (TARBP-b) that encodes a TAR-binding protein from a cDNA expression library derived from Hut-78 cells. Expression of the 1.4-kb TARBP-b mRNA was observed in all mammalian cell lines tested. TARBP-b binds specifically to the bulge region of TAR RNA and trans-activates the HIV-1 long terminal repeat in the presence of ptat and prev expression plasmids. These results suggest that TARBP-b contributes to tat-mediated trans-activation.

Role of the carboxy-terminal portion of the HIV-1 transmembrane protein in viral transmission and cytopathogenicity.

The transmembrane glycoprotein (gp41) of human immunodeficiency virus type-1 (HIV-1) has a long cytoplasmic domain of unknown functional significance. To investigate the role of the carboxy-terminal (C-terminal) portion of the HIV-1 envelope protein in viral replication, infectivity, and cytopathogenicity, we examined the properties of a panel of mutants with variable deletions in the 3'-env region. Deletion of the C-terminal 76 amino acids did not abolish production of reverse transcriptase upon transfection of COS-1 cells. Deletion of the C-terminal 6-14 amino acids appeared sufficient to alter the replication pattern, infectivity, and cytopathogenicity of some clones. The data suggest that conformational determinants or specific sequences are responsible for the observed changes, rather than simply the length of the gp41 cytoplasmic tail.

Retroviral vectors expressing soluble CD4: a potential gene therapy for AIDS.

Retroviral vectors have been developed which produce a secreted form of the helper/inducer T-cell antigen, CD4. Amphotropically packaged vectors were used to transduce cells, and these cells were shown to express the secreted CD4 (sCD4) gene product. The sCD4 produced by the viral vectors is immunoprecipitated by monoclonal antibodies against CD4, which specifically block human immunodeficiency virus (HIV) infection of helper/inducer T cells. A direct physical interaction of vector-produced sCD4 and HIV-1 gp120 was demonstrated by coprecipitation of sCD4/gp120 with antiserum directed against HIV gp120. Furthermore, transduced cells producing sCD4 can protect HIV-susceptible cells from infection by HIV. These data suggest that gene therapy is a potential approach for the treatment of AIDS.

Alteration of HIV-1 infectivity and neutralization by a single amino acid replacement in the V3 loop domain.

The V3 loop (residues 303-338) of the human immunodeficiency virus type 1 (HIV-1) gp120 envelope protein represents a principal neutralizing determinant for the virus. An HIV-1 proviral clone containing a mutation in the V3 loop was constructed in which the proline residue at position 313 was changed to an alanine (P313-A). This mutation alters the conserved GPGR sequence that is found in the V3 loop sequences of different HIV-1 isolates. The P313-A clone produced virus particles, which were infectious for a number of T-cell lines including MOLT-4, CEM, and SupT1, but demonstrated a relatively low infectivity on the AA5 B-cell line when compared with wild-type viruses, HTLV-IIIB, HXB2/10 (a chimeric molecular clone), and another mutant virus (Q290-T). V3 loop-specific neutralizing polyclonal sera and the 9284 monoclonal antibody, which recognizes the amino side of the V3 loop sequence, effectively blocked infectivity and syncytia formation of all viruses tested. In contrast, the 0.5 beta monoclonal antibody, which is biologically more potent than 9284 and recognizes a different V3 loop determinant, failed to neutralize the P313-A virus. These results suggest that the proline residue in the relatively conserved GPGR "turn" region of the V3 loop is crucial for recognition by the 0.5 beta antibody. The observed variation in sensitivity of the B-cell line to the P313-A virus may reflect the presence of cell-specific factors which could be important in establishing an HIV-1 infection.

Characterization of a molecular clone of HIV type 2 infectious for Macaca nemestrina.

A lambda phage clone containing a full-length HIV-2 provirus, designated HIV-2KR, was obtained from the genomic DNA of Molt4 clone 8 (Molt4/8) lymphoblastic cells infected with the HIV-2PEI2 strain. HIV-2KR is genetically distinct from known HIV-2 isolates, possessing both a unique deletion in the LTR promoter region, and a long rev reading frame. It is replication competent in vitro after transfection into Molt4/8 cells, replicates in a variety of established human T lymphoblastic (Molt-3, Molt4/8, SupT1, H9, C8166) and myelomonocytic (U937) cell lines, and displays prominent cytopathic effects on infection of Molt4/8 cells, reflecting usage of both CCR5 and CXCR4 coreceptors. In addition, HIV-2KR was found to be infectious for human and Macaca nemestrina peripheral blood lymphocytes, and primary human monocyte-macrophage cultures. Intravenous inoculation of cell-free virus into M. nemestrina resulted in infection characterized by transient, low-level viremia and modest temporary decline in CD4 lymphocyte numbers, making HIV-2KR the first HIV-2 molecular clone reported to be infectious for this primate species.

Topical treatment of cutaneous lesions of acquired immunodeficiency syndrome-related Kaposi sarcoma using alitretinoin gel: results of phase 1 and 2 trials.

OBJECTIVE: To evaluate the efficacy and safety of topical alitretinoin gel (9-cis-retinoic acid [LGD1057], Panretin gel; Ligand Pharmaceuticals, Inc, San Diego, Calif) in cutaneous Kaposi sarcoma (KS). DESIGN: Open-label, within-patient, controlled, dose-escalating phase 1 and 2 clinical trials. In all patients, 1 or more cutaneous KS lesions were treated with alitretinoin gel, and at least 2 other lesions served as untreated controls for up to 16 weeks. Alitretinoin (0.05% or 0.1% gel) was applied twice daily for the first 2 weeks and up to 4 times daily thereafter, if tolerated. SETTING: Nine academic clinical centers. PATIENTS: One hundred fifteen patients with biopsy-proven acquired immunodeficiency syndrome (AIDS)-related KS. MAIN OUTCOME MEASURES: AIDS Clinical Trials Group response criteria. RESULTS: Statistically significant clinical responses were observed in 31 (27%) of 115 patients for the group of treated index lesions compared with 13 (11%) for the group of untreated control lesions (P<.001). Responses occurred with low CD4(+) lymphocyte counts (<200 cells/microL) and in some patients with refractory response to previous systemic anti-KS therapy. The incidence of disease progression was significantly lower for treated index lesions compared with untreated control lesions (39/115 [34%] vs 53/115 [46%]; P =.02). Alitretinoin gel generally was well tolerated, with 90% of treatment-related adverse events confined to the application site and only mild or moderate in severity. CONCLUSIONS: Alitretinoin gel has significant antitumor activity as a topical treatment for AIDS-related KS lesions, substantially reduces the incidence of disease progression in treated lesions, and is generally well tolerated.

CXCR4 is required by a nonprimate lentivirus: heterologous expression of feline immunodeficiency virus in human, rodent, and feline cells.

A heterologous feline immunodeficiency virus (FIV) expression system permitted high-level expression of FIV proteins and efficient production of infectious FIV in human cells. These results identify the FIV U3 element as the sole restriction to the productive phase of replication in nonfeline cells. Heterologous FIV expression in a variety of human cell lines resulted in profuse syncytial lysis that was FIV env specific, CD4 independent, and restricted to cells that express CXCR4, the coreceptor for T-cell-line-adapted strains of human immunodeficiency virus. Stable expression of human CXCR4 in CXCR4-negative human and rodent cell lines resulted in extensive FIV Env-mediated, CXCR4-dependent cell fusion and infection. In feline cells, stable overexpression of human CXCR4 resulted in increased FIV infectivity and marked syncytium formation during FIV replication or after infection with FIV Env-expressing vectors. The use of CXCR4 is a fundamental feature of lentivirus biology independent of CD4 and a shared cellular link to infection and cytopathicity for distantly related lentiviruses that cause AIDS. Their conserved use implicates chemokine receptors as primordial lentivirus receptors.