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Robert C Gallo

Publications and source records attributed to Robert C Gallo.

At least 19 recordsLinked to original sources
PubMed2006

HIV-1 transgenic rat CD4+ T cells develop decreased CD28 responsiveness and suboptimal Lck tyrosine dephosphorylation following activation.

Impaired CD4+ T cell responses, resulting in dysregulated T-helper 1 (Th1) effector and memory responses, are a common result of HIV-1 infection. These defects are often preceded by decreased expression and function of the alpha/beta T cell receptor (TCR)-CD3 complex and of co-stimulatory molecules including CD28, resulting in altered T cell proliferation, cytokine secretion and cell survival. We have previously shown that HIV Tg rats have defective development of T cell effector function and generation of specific effector/memory T cell subsets. Here we identify abnormalities in activated HIV-1 Tg rat CD4+ T cells that include decreased pY505 dephosphorylation of Lck (required for Lck activation), decreased CD28 function, reduced expression of the anti-apoptotic molecule Bcl-xL, decreased secretion of the mitogenic lympokine interleukin-2 (IL-2) and increased activation induced apoptosis. These events likely lead to defects in antigen-specific signaling and may help explain the disruption of Th1 responses and the generation of specific effector/memory subsets in transgenic CD4+ T cells.

Animals↗
PubMed2006

Preclinical evaluation of synthetic -2 RANTES as a candidate vaginal microbicide to target CCR5.

A potential strategy that can be used to combat the worldwide AIDS epidemic is the development of a vaginal microbicide that prevents the sexual transmission of human immunodeficiency virus type 1 (HIV-1). Certain CC chemokines, including RANTES, MIP-1alpha, and MIP-1beta, might facilitate the development of such microbicides since they potently suppress HIV-1 infection by binding to CCR5, the viral coreceptor used by most sexually transmitted strains of HIV-1 to enter host cells. In this study, we evaluated whether a CCR5-specific fragment of RANTES that lacks two N-terminal residues (-2 RANTES) and possesses especially potent HIV-1 suppressive activity has toxicity profiles conducive to the advancement of testing in candidate microbicide formulations. Analyses were carried out with a synthetic version of the chemokine, which was formulated with either Novasomes 7474, a nonphospholipid liposome, or methylcellulose gel. Dialysis studies demonstrated that the formulated -2 RANTES was released from both vehicles and retained anti-HIV-1 activity. Preclinical toxicity studies carried out with Swiss Webster mouse and New Zealand White rabbit vaginal irritation models demonstrated minimal inflammation and minimal adverse changes in cervicovaginal tissue integrity after short-term (10 min) and long-term (24 h) exposure to formulations containing up to 1 mg/ml of -2 RANTES. Similarly, no toxicity was observed with formulations of bioactive murine RANTES in the Swiss Webster mouse vaginal irritation model. Overall, these preclinical studies suggest that -2 RANTES is suitable for further testing as a candidate anti-HIV-1 microbicide.

Administration, Intravaginal↗
PubMed2005

Indirubin-3'-monoxime, a derivative of a Chinese antileukemia medicine, inhibits P-TEFb function and HIV-1 replication.

OBJECTIVE: To evaluate the effects of the cyclin dependent kinase (CDK) inhibitor Indirubin-3'-monoxime (IM) on Tat-mediated transactivation function, a step of the HIV-1 cycle that is not currently targeted in antiviral therapy. METHODS: The effects of IM on CDK implicated in HIV-1 Tat transactivation function were evaluated by kinase assays, transfection experiments, RNase protection assay and RT-PCR analysis of viral transcripts. The antiviral effect of IM was investigated in cells from HIV-1 infected individuals as well as in cell lines, primary lymphocytes and monocyte-derived macrophages. The antiviral activity of IM was also tested against drug-resistant HIV-1. RESULTS: IM inhibits the kinase activity of CDK9 [50% inhibitory concentration (IC50) of 0.05 microM], the catalytic subunit of Positive transcription elongation factor b (P-TEFb). Inhibition of CDK9 activity by IM results in abrogation of Tat-induced expression of HIV-1 RNA in cell lines. In addition, IM inhibits the replication of HIV-1 in both peripheral blood mononuclear cells (IC50 of 1 microM) and macrophages (IC50 of 0.5 microM). IM is effective against primary and drug-resistant strains of HIV-1. Importantly, the antiviral effects of the drug were seen at concentrations that did not affect cell proliferation. CONCLUSIONS: Non-toxic concentrations of IM inhibit HIV-1 by blocking viral gene expression mediated by the cellular factor P-TEFb. The drug is effective against wild-type and drug-resistant strains of HIV-1. IM may help control replication of HIV-1 in patients by disrupting a step of the HIV-1 cycle that is not being targeted in current antiretroviral treatments.

Cyclin-Dependent Kinases↗
PubMed2005

Persistence of HIV-1 structural proteins and glycoproteins in lymph nodes of patients under highly active antiretroviral therapy.

Here we report a long-term persistence of HIV-1 structural proteins and glycoproteins in germinal centers (GCs) of lymph nodes (LNs) in the absence of detectable virus replication in patients under highly active antiretroviral therapy (HAART). The persistence of viral structural proteins and glycoproteins in GCs was accompanied by specific antibody responses to HIV-1. Seven patients during the chronic phase of HIV-1 infection were analyzed for the presence of the capsid protein (HIV-1p24), matrix protein (HIV-1p17), and envelope glycoproteins (HIV-1gp120/gp41), as well as for viral RNA (vRNA) in biopsy specimens from LNs obtained before initiation of therapy and during HAART that lasted from 5 to 13 months. In parallel, these patients were also monitored for viremia and specific anti-HIV-1 antibody responses to structural proteins and glycoproteins both before and during treatment. Before-therapy viral levels, as determined by RT-PCR, ranged from 3 x 10(3) to 6.3 x 10(5) copies of vRNA per ml, whereas during treatment, vRNA was under detectable levels (<25 copies per ml). The pattern of vRNA detection in peripheral blood was concordant with in situ hybridization results of LN specimens. Before treatment, vRNA associated with follicular dendritic cells (FDCs) was readily detected in GCs of LNs of the patients, whereas during therapy, vRNA was consistently absent in the GCs of LN biopsies of treated patients. In contrast to vRNA hybridization results, viral structural proteins and glycoproteins, evaluated by immunohistochemical staining, were present and persisted in the GC light zone of LNs in abundant amounts not only before initiation of therapy but also during HAART, when no vRNA was detected in GCs. Consistent with immunohistochemical findings, specific antibody responses to HIV-1p17, -p24, and -gp120/gp41, as evaluated by ELISA and virus neutralization, persisted in patients under therapy for up to 13 months of follow-up. The implications of these findings are discussed in relation to HIV-1 persistence in infected individuals and the potential role of chronic antigenic stimulation by the deposited structural proteins in GCs for AIDS-associated B cell malignancies.

Antiretroviral Therapy, Highly Active↗
PubMed2005

History of the discoveries of the first human retroviruses: HTLV-1 and HTLV-2.

HTLV-1 was discovered in the US in 1979, and published in 1980. This was rapidly followed by four additional reports in early 1981 describing additional isolates, characterization of some of the HTLV-1 proteins, serological assays for specific antibodies indicative of HTLV-1 infection, and evidence for integrated DNA proviruses in infected cells. None of this early work was dependent upon or influenced by the subclassification of some T-cell malignancies as ATL (in Japan). Instead, I was stimulated by prior work from many investigators in the US and Europe on retroviruses which caused leukemia in animals and our discoveries were made possible by our technical approaches developed in the 1970s involving especially sensitive assays for RT as a surrogate marker for a retrovirus and our discovery of Il-2 which made it possible to culture human T cells. However, following our reports the same virus was isolated in Japan, and both groups provided evidence that HTLV-1 caused ATL, a subclassification of T-cell malignancies first recognized in Japan.

Animals↗
PubMed2005

The discovery of the first human retrovirus: HTLV-1 and HTLV-2.

I describe here the history leading up to and including my laboratory's discovery of the first human retrovirus, HTLV-I, and its close relative, HTLV-II. My efforts were inspired by early work showing a retroviral etiology for leukemias in various animals, including non-human primates. My two main approaches were to develop criteria for and methods for detection of viral reverse transcriptase and to identify growth factors that could support the growth of hematopoietic cells. These efforts finally yielded success following the discovery of IL-2 and its use to culture adult T cell lymphoma/leukemia cells.

Animals↗
PubMed2004

Differential polarization of immune responses by co-administration of antigens with chemokines.

Chemokines are key players in the elicitation of immune response, by selectively attracting subpopulations of immune cells to the site of antigen presentation. Therefore, they are natural candidates for modulating immune responses to antigens qualitatively and quantitatively. We have selected chemokines associated with different arms of the immune response, i.e. RANTES/CCL5, B-lymphocyte chemoattractant/CXCL13, and monocyte chemoattractant protein-1/CCL2, and co-injected DNA expression constructs encoding these chemokines with constructs encoding two HIV antigens, gp120 and gp160, in mice. We subsequently measured markers of both cellular and humoral immune responses, and found that these chemokines qualitatively influenced the outcome of immune responses to both antigens, essentially according to their predicted association to Th profiles. These results are relevant towards the engineering of novel vaccine and immune-based therapies, and point to chemokines as candidate adjuvant and immunomodulatory molecules.

Animals↗
PubMed2004

Total chemical synthesis of N-myristoylated HIV-1 matrix protein p17: structural and mechanistic implications of p17 myristoylation.

The HIV-1 matrix protein p17, excised proteolytically from the N terminus of the Gag polyprotein, forms a protective shell attached to the inner surface of the plasma membrane of the virus. During the late stages of the HIV-1 replication cycle, the N-terminally myristoylated p17 domain targets the Gag polyprotein to the host-cell membrane for particle assembly. In the early stages of HIV-1 replication, however, some p17 molecules dissociate from the viral membrane to direct the preintegration complex to the host-cell nucleus. These two opposing targeting functions of p17 require that the protein be capable of reversible membrane interaction. It is postulated that a significant structural change in p17 triggered by proteolytic cleavage of the Gag polyprotein sequesters the N-terminal myristoyl group, resulting in a weaker membrane binding by the matrix protein than the Gag precursor. To test this "myristoyl switch" hypothesis, we obtained highly purified synthetic HIV-1 p17 of 131 amino acid residues and its N-myristoylated form in large quantity. Both forms of p17 were characterized by circular dichroism spectroscopy, protein chemical denaturation, and analytical centrifugal sedimentation. Our results indicate that although N-myristoylation causes no spectroscopically discernible conformational change in p17, it stabilizes the protein by 1 kcal/mol and promotes protein trimerization in solution. These findings support the premise that the myristoyl switch in p17 is triggered not by a structural change associated with proteolysis, but rather by the destabilization of oligomeric structures of membrane-bound p17 in the absence of downstream Gag subdomains.

Cell Membrane↗
PubMed2004

HIV-1 transgenic rats develop T cell abnormalities.

HIV-1 infection leads to impaired antigen-specific T cell proliferation, increased susceptibility of T cells to apoptosis, progressive impairment of T-helper 1 (Th1) responses, and altered maturation of HIV-1-specific memory cells. We have identified similar impairments in HIV-1 transgenic (Tg) rats. Tg rats developed an absolute reduction in CD4+ and CD8+ T cells able to produce IFN-gamma following activation and an increased susceptibility of T cells to activation-induced apoptosis. CD4+ and CD8+ effector/memory (CD45RC- CD62L-) pools were significantly smaller in Tg rats compared to non-Tg controls, although the converse was true for the naïve (CD45RC+ CD62L+) T cell pool. Our interpretation is that the HIV transgene causes defects in the development of T cell effector function and generation of specific effector/memory T cell subsets, and that activation-induced apoptosis may be an essential factor in this process.

Animals↗
PubMed2004

Anti-cytokine Ab immune therapy: present status and perspectives.

Allergy, autoimmunity and the pathogenesis of some chronic diseases are dependent on host innate and adaptative immune responses. Both responses are associated with abnormal cytokine production within pathologic tissues. Over the past two decades, the availability of purified cytokines and cytokine antibodies (Abs) has prompted a therapeutic approach that aims to supply neutralizing Abs against deleterious cytokines, through either passive immunization (administration of large quantities of high affinity Abs, prepared ex vivo) or active immunization (induction of specific Abs, using immunogenic cytokine derivatives). Both passive and active immunization can safely, transiently and effectively be used, as has been documented by animal experimentation and confirmed by clinical trials. Novel anti-cytokine therapeutic compounds, based on passive Ab immunization, are now available to treat rheumatoid arthritis (RA) and have been shown to help control neoangiogenesis in cancer patients. Clinical trials using Abs to treat allergic disorders are also underway. However, the induction of anti-idiotypic Abs may restrict the long-term use of anti-cytokine immunotherapy using allogenic or humanized/chimeric Abs. We propose that greater consideration should be given to active immunization protocols.

Angiogenesis Inhibitors↗
PubMed2004

Sequence variation within the dominant amino terminus epitope affects antibody binding and neutralization of human immunodeficiency virus type 1 Tat protein.

Tat is among the required regulatory genes of human immunodeficiency virus type 1 (HIV-1). Tat functions both within infected cells as a transcription factor and as an extracellular factor that binds and alters bystander cells. Some functions of extracellular Tat can be neutralized by immune serum or monoclonal antibodies. In order to understand the antibody response to Tat, we are defining antibody epitopes and the effects of natural Tat sequence variation on antibody recognition. The dominant Tat epitope in macaque sera is within the first 15 amino acids of the protein amino terminus. Together with a subdominant response to amino acids 57 to 60, these two regions account for most of the macaque response to linear Tat epitopes and both regions are also sites for the binding of neutralizing antibodies. However, the dominant and subdominant epitope sequences differ among virus strains, and this natural variation can preclude antibody binding and Tat neutralization. We also examined serum samples from 31 HIV-positive individuals that contained Tat binding antibodies; 23 of the 31 sera recognized the amino terminus peptide. Similar to binding in macaques, human antibody binding to the amino terminus was affected by variations at positions 7 and 12, sequences that are distinct for clade B compared to other viral clades. Tat-neutralizing antibodies to the dominant amino terminus epitope are affected by HIV clade variation.

Amino Acid Sequence↗