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Biomedical subjects

Mark B Feinberg

Publications and source records attributed to Mark B Feinberg.

At least 19 recordsLinked to original sources
PubMed2006

Adaptation of a diverse simian immunodeficiency virus population to a new host is revealed through a systematic approach to identify amino acid sites under selection.

Simian immunodeficiency viruses (SIV) have had considerable success at crossing species barriers; both human immunodeficiency virus (HIV)-1 and HIV-2 have been transmitted on multiple occasions from SIV-infected natural host species. However, the precise evolutionary and ecological mechanisms characterizing a successful cross-species transmission event remain to be elucidated. Here, in addition to expanding and clarifying our previous description of the adaptation of a diverse, naturally occurring SIVsm inoculum to a new rhesus macaque host, we present an analytical framework for understanding the selective forces driving viral adaptation to a new host. A preliminary analysis of large-scale changes in virus population structure revealed that viruses replicating in the macaques were subject to increasing levels of selection through day 70 postinfection (p.i.), whereas contemporaneous viruses in the mangabeys remained similar to the source inoculum. Three different site-by-site methods were employed to identify the amino acid sites responsible for this macaque-specific selection. Of 124 amino acid sites analyzed, 3 codons in V2, a 2-amino acid shift in an N-linked glycosylation site, and variation at 2 sites in the highly charged region were consistently evolving under either directional or diversifying selection at days 40 and 70 p.i. This strong macaque-specific selection on the V2 loop underscores the importance of this region in the adaptation of SIVsm to rhesus macaques. Due to the extreme viral diversity already extant in the naturally occurring viral inoculum, we employed a broad range of phylogenetic and numerical tools in order to distinguish the signatures of past episodes of selection in viral sequences from more recent selection pressures.

Adaptation, Biological↗
PubMed2006

The AIDS resistance of naturally SIV-infected sooty mangabeys is independent of cellular immunity to the virus.

In contrast to human immunodeficiency virus (HIV)-infected humans, natural hosts for simian immunodeficiency virus (SIV) very rarely progress to acquired immunodeficiency syndrome (AIDS). While the mechanisms underlying this disease resistance are still poorly understood, a consistent feature of natural SIV infection is the absence of the generalized immune activation associated with HIV infection. To investigate the immunologic mechanisms underlying the absence of AIDS in SIV-infected sooty mangabeys (SMs), a natural host species, we performed a detailed analysis of the SIV-specific cellular immune responses in 110 SIV-infected SMs. We found that while SIV-specific T-cell responses are detectable in the majority of animals, their magnitude and breadth are, in fact, lower than what has been described in HIV-infected humans, both in terms of cytokine production (ie, IFN-gamma, TNF-alpha, and IL-2) and degranulation (ie, CD107a expression). Of importance, SIV-specific T-cell responses were similarly low when either SIVmac239-derived peptides or autologous SIVsmm peptides were used as stimuli. No correlation was found between SIV-specific T-cell responses and either viral load or CD4+ T-cell count, or between these responses and markers of T-cell activation and proliferation. These findings indicate that the absence of AIDS in naturally SIV-infected sooty mangabeys is independent of a strong cellular immune response to the virus.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Differences and similarities in viral life cycle progression and host cell physiology after infection of human dendritic cells with modified vaccinia virus Ankara and vaccinia virus.

Modified vaccinia virus Ankara (MVA) is an attenuated strain of vaccinia virus (VV) that has attracted significant attention as a candidate viral vector vaccine for immunization against infectious diseases and treatment of malignancies. Although MVA is unable to replicate in most nonavian cells, vaccination with MVA elicits immune responses that approximate those seen after the administration of replication-competent strains of VV. However, the mechanisms by which these viruses elicit immune responses and the determinants of their relative immunogenicity are incompletely understood. Studying the interactions of VV and MVA with cells of the human immune system may elucidate these mechanisms, as well as provide a rational basis for the further enhancement of the immunogenicity of recombinant MVA vectors. Toward this end, we investigated the consequences of MVA or VV infection of human dendritic cells (DCs), key professional antigen-presenting cells essential for the generation of immune responses. We determined that a block to the formation of intracellular viral replication centers results in abortive infection of DCs with both VV and MVA. MVA inhibited cellular protein synthesis more rapidly than VV and displayed a distinct pattern of viral protein expression in infected DCs. MVA also induced apoptosis in DCs more rapidly than VV, and DC apoptosis after MVA infection was associated with an accelerated decline in the levels of intracellular Bcl-2 and Bcl-X(L). These findings suggest that antigen presentation pathways may contribute differentially to the immunogenicity of VV and MVA and that targeted modifications of virus-induced DC apoptosis may further increase the immunogenicity of MVA-vectored vaccines.

Apoptosis↗
PubMed2005

SIVsm quasispecies adaptation to a new simian host.

Despite the potential for infectious agents harbored by other species to become emerging human pathogens, little is known about why some agents establish successful cross-species transmission, while others do not. The simian immunodeficiency viruses (SIVs), certain variants of which gave rise to the human HIV-1 and HIV-2 epidemics, have demonstrated tremendous success in infecting new host species, both simian and human. SIVsm from sooty mangabeys appears to have infected humans on several occasions, and was readily transmitted to nonnatural Asian macaque species, providing animal models of AIDS. Here we describe the first in-depth analysis of the tremendous SIVsm quasispecies sequence variation harbored by individual sooty mangabeys, and how this diverse quasispecies adapts to two different host species-new nonnatural rhesus macaque hosts and natural sooty mangabey hosts. Viral adaptation to rhesus macaques was associated with the immediate amplification of a phylogenetically related subset of envelope (env) variants. These variants contained a shorter variable region 1 loop and lacked two specific glycosylation sites, which may be selected for during acute infection. In contrast, transfer of SIVsm to its natural host did not subject the quasispecies to any significant selective pressures or bottleneck. After 100 d postinfection, variants more closely representative of the source inoculum reemerged in the macaques. This study describes an approach for elucidating how pathogens adapt to new host species, and highlights the particular importance of SIVsm env diversity in enabling cross-species transmission. The replicative advantage of a subset of SIVsm variants in macaques may be related to features of target cells or receptors that are specific to the new host environment, and may involve CD4-independent engagement of a viral coreceptor conserved among primates.

Journal Article↗
PubMed2005

Preclinical assessment of HIV vaccines and microbicides by repeated low-dose virus challenges.

BACKGROUND: Trials in macaque models play an essential role in the evaluation of biomedical interventions that aim to prevent HIV infection, such as vaccines, microbicides, and systemic chemoprophylaxis. These trials are usually conducted with very high virus challenge doses that result in infection with certainty. However, these high challenge doses do not realistically reflect the low probability of HIV transmission in humans, and thus may rule out preventive interventions that could protect against "real life" exposures. The belief that experiments involving realistically low challenge doses require large numbers of animals has so far prevented the development of alternatives to using high challenge doses. METHODS AND FINDINGS: Using statistical power analysis, we investigate how many animals would be needed to conduct preclinical trials using low virus challenge doses. We show that experimental designs in which animals are repeatedly challenged with low doses do not require unfeasibly large numbers of animals to assess vaccine or microbicide success. CONCLUSION: Preclinical trials using repeated low-dose challenges represent a promising alternative approach to identify potential preventive interventions.

AIDS Vaccines↗
PubMed2005

Disabling poxvirus pathogenesis by inhibition of Abl-family tyrosine kinases.

The Poxviridae family members vaccinia and variola virus enter mammalian cells, replicate outside the nucleus and produce virions that travel to the cell surface along microtubules, fuse with the plasma membrane and egress from infected cells toward apposing cells on actin-filled membranous protrusions. We show that cell-associated enveloped virions (CEV) use Abl- and Src-family tyrosine kinases for actin motility, and that these kinases act in a redundant fashion, perhaps permitting motility in a greater range of cell types. Additionally, release of CEV from the cell requires Abl- but not Src-family tyrosine kinases, and is blocked by STI-571 (Gleevec), an Abl-family kinase inhibitor used to treat chronic myelogenous leukemia in humans. Finally, we show that STI-571 reduces viral dissemination by five orders of magnitude and promotes survival in infected mice, suggesting possible use for this drug in treating smallpox or complications associated with vaccination. This therapeutic approach may prove generally efficacious in treating microbial infections that rely on host tyrosine kinases, and, because the drug targets host but not viral molecules, this strategy is much less likely to engender resistance compared to conventional antimicrobial therapies.

Actins↗
PubMed2005

Loss of CD127 expression defines an expansion of effector CD8+ T cells in HIV-infected individuals.

The immunodeficiency that follows HIV infection is related to the virus-mediated killing of infected CD4(+) T cells, the chronic activation of the immune system, and the impairment of T cell production. In this study we show that in HIV-infected individuals the loss of IL-7R (CD127) expression defines the expansion of a subset of CD8(+) T cells, specific for HIV as well as other Ags, that show phenotypic (i.e., loss of CCR7 and CD62 ligand expression with enrichment in activated and/or proliferating cells) as well as functional (i.e., production of IFN-gamma, but not IL-2, decreased ex vivo proliferative potential and increased susceptibility to apoptosis) features of effector T cells. Importantly, in HIV-infected individuals the levels of CD8(+)CD127(-) T cells are directly correlated with the main markers of disease progression (i.e., plasma viremia and CD4(+) T cell depletion) as well as with the indices of overall T cell activation. In all, these results identify the expansion of CD8(+)CD127(-) effector-like T cells as a novel feature of the HIV-associated immune perturbation. Further studies are thus warranted to determine whether measurements of CD127 expression on CD8(+) T cells may be useful in the clinical management of HIV-infected individuals.

Adult↗
PubMed2005

Vaccinia virus tropism for primary hematolymphoid cells is determined by restricted expression of a unique virus receptor.

The presumed broad tropism of poxviruses has stymied attempts to identify both the cellular receptor(s) and the viral determinant(s) for binding. Detailed studies of poxvirus binding to and infection of primary human cells have not been conducted. In particular, the determinants of target cell infection and the consequences of infection for cells involved in the generation of antiviral immune responses are incompletely understood. In this report, we show that vaccinia virus (VV) exhibits a more restricted tropism for primary hematolymphoid human cells than has been previously recognized. We demonstrate that vaccinia virus preferentially infects antigen-presenting cells (dendritic cells, monocytes/macrophages, and B cells) and activated T cells, but not resting T cells. The infection of activated T cells is permissive, with active viral replication and production of infectious progeny. Susceptibility to infection is determined by restricted expression of a cellular receptor that is induced de novo upon T-cell activation and can be removed from the cell surface by either trypsin or pronase treatment. The VV receptor expressed on activated T cells displays unique characteristics that distinguish it from the receptor used to infect cell lines in culture. The observed restricted tropism of VV may have significant consequences for the understanding of natural poxvirus infection and immunity and for poxvirus-based vaccine development.

Animals↗
PubMed2005

Divergent host responses during primary simian immunodeficiency virus SIVsm infection of natural sooty mangabey and nonnatural rhesus macaque hosts.

To understand how natural sooty mangabey hosts avoid AIDS despite high levels of simian immunodeficiency virus (SIV) SIVsm replication, we inoculated mangabeys and nonnatural rhesus macaque hosts with an identical inoculum of uncloned SIVsm. The unpassaged virus established infection with high-level viral replication in both macaques and mangabeys. A species-specific, divergent immune response to SIV was evident from the first days of infection and maintained in the chronic phase, with macaques showing immediate and persistent T-cell proliferation, whereas mangabeys displayed little T-cell proliferation, suggesting subdued cellular immune responses to SIV. Importantly, only macaques developed (CD4+)-T-cell depletion and AIDS, thus indicating that in mangabeys limited immune activation is a key mechanism to avoid immunodeficiency despite high levels of SIVsm replication. These studies demonstrate that it is the host response to infection, rather than properties inherent to the virus itself, that causes immunodeficiency in SIV-infected nonhuman primates.

Animals↗
PubMed2004

Enhanced SIV replication and accelerated progression to AIDS in macaques primed to mount a CD4 T cell response to the SIV envelope protein.

Given the dual role of CD4 T cells as both immune effectors and targets for HIV infection, the balance of CD4 versus CD8 T cell-mediated responses induced by candidate AIDS vaccines may be critical in determining postvaccination infection outcomes. An attenuated recombinant varicella-zoster virus vaccine expressing the simian immunodeficiency virus (SIV) envelope (Env) elicited nonneutralizing Env-binding antibodies and little if any cytotoxic T lymphocyte responses in rhesus macaques (Macaca mulatta). After challenge with SIV, Env vaccinees manifested increased levels of SIV replication, more rapid CD4 depletion, and accelerated progression to AIDS compared with controls. Enhanced SIV replication correlated with increased CD4 T cell proliferation soon after SIV challenge, apparently the result of an anamnestic response to SIV antigens. Thus activation of virus-specific CD4 T cells at the time of exposure to a CD4 T cell-tropic lentivirus, in the absence of an effective CD8 response, may enhance virus replication and disease. These data suggest suggest that candidate AIDS vaccines may not simply be either efficacious or neutral; they may also have the potential to be harmful.

Animals↗
PubMed2004

Prospects for an AIDS vaccine: three big questions, no easy answers.

The unremitting devastation created by the AIDS pandemic will probably only be controlled when a vaccine is developed that is safe, effective, affordable, and simple enough to permit implementation in developing countries where the impact of AIDS is most severe. Although formidable practical, political, economic, social, and ethical challenges face the AIDS vaccine development effort, the most fundamental challenges now reside at the level of the basic biology of HIV-1 infection and pathogenesis. Of these biological considerations, three questions loom especially large: can we design immunogens that will elicit neutralising antibodies that are reactive against a wide variety of primary HIV isolates; will vaccine-elicited cytotoxic T cells be fundamentally better at controlling HIV-1 replication and ameliorating disease progression than those responses that arise during natural HIV infection; and to what extent will the tremendous global genetic diversity of HIV-1 compromise the breadth of vaccine-elicited protective immunity and the overall effectiveness of an AIDS vaccine? Although these are three exceptionally challenging questions, they are now being approached with clear hypotheses whose testing is being facilitated by an ever-improving array of technologies for vaccine design and immunological characterisation. The extent to which the field of AIDS vaccine research can now come together to answer these questions in the best coordinated, most efficient manner will probably be an important determinant of how and when an effective AIDS vaccine will be developed.

AIDS Vaccines↗
PubMed2004

Roles of target cells and virus-specific cellular immunity in primary simian immunodeficiency virus infection.

There is an ongoing debate on whether acute human immunodeficiency virus infection is controlled by target cell limitation or by virus-specific cellular immunity. To resolve this question, we developed a novel mathematical modeling scheme which allows us to incorporate measurements of virus load, target cells, and virus-specific immunity and applied it to a comprehensive data set generated in an experiment involving rhesus macaques infected with simian immunodeficiency virus. Half of the macaques studied were treated during the primary infection period with reagents which block T-cell costimulation and as a result displayed severely impaired virus-specific immune responses. Our results show that early viral replication in normal infection is controlled to a large extent by virus-specific CD8(+) T cells and not by target cell limitation.

Abatacept↗
PubMed2004

Blockade of T cell costimulation reveals interrelated actions of CD4+ and CD8+ T cells in control of SIV replication.

In vivo blockade of CD28 and CD40 T cell costimulation pathways during acute simian immunodeficiency virus (SIV) infection of rhesus macaques was performed to assess the relative contributions of CD4+ T cells, CD8+ T cells, and Ab responses in modulating SIV replication and disease progression. Transient administration of CTLA4-Ig and anti-CD40L mAb to SIV-infected rhesus macaques resulted in dramatic inhibition of the generation of both SIV-specific cellular and humoral immune responses. Acute levels of proliferating CD8+ T cells were associated with early control of SIV viremia but did not predict ensuing set point viremia or survival. The level of in vivo CD4+ T cell proliferation during acute SIV infection correlated with concomitant peak levels of SIV plasma viremia, whereas measures of in vivo CD4+ T cell proliferation that extended into chronic infection correlated with lower SIV viral load and increased survival. These results suggest that proliferating CD4+ T cells function both as sources of virus production and as antiviral effectors and that increased levels of CD4+ T cell proliferation during SIV infections reflect antigen-driven antiviral responses rather than a compensatory homeostatic response. These results highlight the interrelated actions of CD4+ and CD8+ T cell responses in vivo that modulate SIV replication and pathogenesis.

Animals↗
PubMed2004

Assessment of lymphocyte-mediated cytotoxicity using flow cytometry.

Cytotoxic lymphocytes, including cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, kill target cells by releasing granules containing perforin and granzymes, and/or via Fas-Fas ligand interactions. Both pathways lead to prompt activation within target cells of caspase cascades responsible for apoptosis induction and cell death. We have utilized cell-permeable fluorogenic caspase substrates and multiparameter flow cytometry to detect caspase activation in target cells, and applied these tools to quantify and visualize cytotoxic lymphocyte activities. This novel assay, referred to as the flow cytometric cytotoxicity (FCC) assay, is a nonradioactive single-cell-based assay that provides a more rapid, biologically informative, and sensitive approach to measure cytotoxic lymphocyte activity when compared to other assays such as the 51chromium (51Cr) release assay. In addition, the FCC assay can be used to study CTL-mediated killing of primary target cells of different cell lineages that are frequently not amenable to study by the 51Cr release assay. Furthermore, the FCC assay enables evaluation of the phenotype and fate of both target and effector cells, and as such, provides a useful new approach to illuminate the biology of cytotoxic lymphocytes.

Apoptosis↗
PubMed2004

The roles of nonhuman primates in the preclinical evaluation of candidate AIDS vaccines.

Preclinical studies in nonhuman primates (NHP) play key roles in AIDS vaccine development efforts. In addition to their traditional utilization to gauge vaccine safety and immunogenicity, NHP models are currently employed to an unprecedented extent and in unprecedented ways in contemporary basic and applied vaccine development efforts. Current studies employ NHP models to probe fundamental mechanisms of primate immune system regulation, to investigate pathogenic mechanisms of AIDS, and to optimize immunization strategies involving novel vaccine vectors. The use of experimental challenges of immunized NHPs with either simian immunodeficiency virus or chimeric simian/human immunodeficiency virus to generate preclinical vaccine efficacy data has emerged as an important criterion for facilitating entry of a given vaccine candidate into early phase clinical evaluation in humans. However, for studies of the biology of AIDS virus transmission, AIDS virus disease pathogenesis and AIDS virus vaccine efficacy that are predicated on experimental viral challenge to be most valuable, additional efforts need to be devoted to generating challenge models that more closely recapitulate HIV-1 infection in humans. Towards this end, improved communication between clinical and preclinical investigators, to promote a bidirectional flow of information focusing on individual research needs and shared goals should enable the NHP models to most effectively expedite progress toward the development of a safe and effective AIDS vaccine.

AIDS Vaccines↗
PubMed2003

Suppression of cerebrospinal fluid HIV burden in antiretroviral naive patients on a potent four-drug antiretroviral regimen.

OBJECTIVE: To determine the longitudinal response of HIV in the cerebrospinal fluid (CSF) to highly active antiretroviral therapy (HAART) and to investigate the levels of indinavir penetrating into the CSF. DESIGN: Open study of HIV-infected subjects naive to therapy with protease inhibitors. SETTING: Tertiary care referral center. SUBJECTS: Twenty-five participants were begun on indinavir, nevirapine, zidovudine, and lamivudine. INTERVENTIONS: Lumbar punctures were performed prior to therapy and 2 and 6 months after beginning therapy. Plasma and CSF were assayed for routine cell counts, chemistries, HIV load and indinavir levels. RESULTS: Twenty-two subjects had CSF HIV RNA level data available at all three time points, three others at baseline and 2 months. At month 2 of therapy, nine of 25 (36%) subjects had CSF HIV RNA levels > 50 HIV RNA copies/ml. By 6 months, all 22 subjects had CSF HIV RNA levels < 50 HIV RNA copies/ml. CSF white blood cell counts fell from a baseline mean of 5.3 x 10(6)/l to 1.9 x 10(6)/l (P = 0.013) at 6 months. Plasma indinavir levels declined rapidly while CSF levels remained stable throughout the 8-h dosing interval. The median CSF indinavir level was 71 ng/ml, approximating the upper limit of the 95% inhibitory concentration for indinavir against HIV-1. CONCLUSIONS: CSF HIV RNA levels cannot be expected to fall below 50 HIV RNA copies/ml even after 2 months of therapy on HAART. Prolonged therapy may be required to suppress HIV levels within the central nervous system.

Adult↗