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J M McCune

Publications and source records attributed to J M McCune.

At least 37 records · Page 2Linked to original sources
PubMed1999

Experimental transmission of Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) to SCID-hu Thy/Liv mice.

Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8) is a novel human lymphotropic herpesvirus linked to several human neoplasms. To date, no animal model for infection by this virus has been described. We have examined the susceptibility of C.B-17 scid/scid mice implanted with human fetal thymus and liver grafts (SCID-hu Thy/Liv mice) to KSHV infection. KSHV virions were inoculated directly into the implants, and viral DNA and mRNA production was assayed using real-time quantitative polymerase chain reaction. This revealed a biphasic infection, with an early phase of lytic replication accompanied and followed by sustained latency. Ultraviolet irradiation of the inoculum abolished all DNA- and mRNA-derived signals, and infection was inhibited by ganciclovir. Viral gene expression was most abundant in CD19(+) B lymphocytes, suggesting that this model faithfully mimics the natural tropism of this virus. Short-term coinfection with HIV-1 did not alter the course of KSHV replication, nor did KSHV alter levels of HIV-1 p24 during the acute phase of the infection. Although no disease was evident in infected animals, SCID-hu Thy/Liv mice should allow the detailed study of KSHV tropism, latency, and drug susceptibility.

Animals↗
PubMed1999

Direct evidence for thymic function in adult humans.

The understanding of human thymic function and evaluation of its contribution to T cell homeostasis are matters of great importance. Here we report the development of a novel assay to quantitate the frequency and diversity of recent thymic emigrants (RTEs) in the peripheral blood of humans. Such cells were defined by the presence of T cell receptor (TCR) rearrangement deletion circles (DCs), episomal byproducts of TCR-beta V(D)J rearrangement. DCs were detected in T cells in the thymus, cord blood, and adult peripheral blood. In the peripheral blood of adults aged 22 to 76 years, their frequency was highest in the CD4(+)CD45RA(+) CD62L(+) subpopulation of naive T cells. TCR DCs were also observed in other subpopulations of peripheral blood T cells, including those with the CD4(+)CD45RO(-)CD62L(+) and CD4(+)CD45RO(+)CD62L(+) phenotypes. RTEs were observed to have more than one Vbeta rearrangement, suggesting that replenishment of the repertoire in the adult is at least oligoclonal. These results demonstrate that the normal adult thymus continues to contribute, even in older individuals, a diverse set of new T cells to the peripheral circulation.

Adult↗
PubMed1999

Fas is expressed early in human thymocyte development but does not transmit an apoptotic signal.

We investigated the expression and function of Fas on human thymocytes prepared from fetal and pediatric tissue specimens and from SCID-hu Thy/Liv grafts. Unlike mouse thymocytes, human thymocytes exhibited a pattern of Fas expression skewed to immature cells, in that the highest expression was seen on double negative thymocytes and on intrathymic T progenitor cells. Fas expression was intermediate on double positive human thymocytes, and low or negative on mature single positive CD4 and CD8 medullary thymocytes. In spite of this relatively abundant surface expression, cross-linking of Fas with agonist mAb was incapable of triggering an apoptotic signal in human thymocytes. Apoptotic signaling was not enhanced by treatment with cycloheximide, nor by restoring a cosignaling milieu by addition of thymic stromal cells. Mouse thymocytes were induced to apoptosis by cross-linked recombinant soluble human Fas ligand both in vitro and in vivo, though human thymocytes were also resistant to this mode of receptor ligation. Membrane-bound Fas ligand also induced apoptotic death in murine thymocytes but not in human thymocytes. Human thymocytes were as sensitive as Jurkat cells, however, to apoptosis induced by TNF-alpha, suggesting that these cells have a signaling defect before activation of the earliest caspases. These data demonstrate a durable and specific resistance of human thymocytes to apoptosis induced through Fas receptor engagement, and reveal significant species-specific differences in the biology of thymocyte-programmed cell death.

Animals↗
PubMed1999

Human herpesvirus 6 (HHV-6) causes severe thymocyte depletion in SCID-hu Thy/Liv mice.

Human herpesvirus 6 (HHV-6) is a potentially immunosuppressive agent that may act as a cofactor in the progression of AIDS. Here, we describe the first small animal model of HHV-6 infection. HHV-6 subgroup A, strain GS, efficiently infected the human thymic tissue implanted in SCID-hu Thy/Liv mice, leading to the destruction of the graft. Viral DNA was detected in Thy/Liv implants by quantitative polymerase chain reaction (PCR) as early as 4 d after inoculation and peaked at day 14. The productive nature of the infection was confirmed by electron microscopy and immunohistochemical staining. Atypical thymocytes with prominent nuclear inclusions were detected by histopathology. HHV-6 replication was associated with severe, progressive thymocyte depletion involving all major cellular subsets. However, intrathymic T progenitor cells (ITTPs) appeared to be more severely depleted than the other subpopulations, and a preferred tropism of HHV-6 for ITTPs was demonstrated by quantitative PCR on purified thymocyte subsets. These findings suggest that thymocyte depletion by HHV-6 may be due to infection and destruction of these immature T cell precursors. Similar results were obtained with strain PL-1, a primary isolate belonging to subgroup B. The severity of the lesions observed in this animal model underscores the possibility that HHV-6 may indeed be immunosuppressive in humans.

Animals↗
PubMed1999

Induction of MHC class I expression on immature thymocytes in HIV-1-infected SCID-hu Thy/Liv mice: evidence of indirect mechanisms.

The SCID-hu Thy/Liv mouse and human fetal thymic organ culture (HF-TOC) models have been used to explore the pathophysiologic mechanisms of HIV-1 infection in the thymus. We report here that HIV-1 infection of the SCID-hu Thy/Liv mouse leads to the induction of MHC class I (MHCI) expression on CD4+CD8+ (DP) thymocytes, which normally express low levels of MHCI. Induction of MHCI on DP thymocytes in HIV-1-infected Thy/Liv organs precedes their depletion and correlates with the pathogenic activity of the HIV-1 isolates. Both MHCI protein and mRNA are induced in thymocytes from HIV-1-infected Thy/Liv organs, indicating induction of MHCI gene expression. Indirect mechanisms are involved, because only a fraction (<10%) of the DP thymocytes were directly infected by HIV-1, although the majority of DP thymocytes are induced to express high levels of MHCI. We further demonstrate that IL-10 is induced in HIV-1-infected thymus organs. Similar HIV-1-mediated induction of MHCI expression was observed in HF-TOC assays. Exogenous IL-10 in HF-TOC induces MHCI expression on DP thymocytes. Therefore, HIV-1 infection of the thymus organ leads to induction of MHCI expression on immature thymocytes via indirect mechanisms involving IL-10. Overexpression of MHCI on DP thymocytes can interfere with thymocyte maturation and may contribute to HIV-1-induced thymocyte depletion.

Animals↗
PubMed1999

Directly measured kinetics of circulating T lymphocytes in normal and HIV-1-infected humans.

The dynamic basis for T-cell depletion in late-stage HIV-1 disease remains controversial. Using a new, non-radioactive, endogenous labeling technique, we report direct measurements of circulating T-cell kinetics in normal and in HIV-1-infected humans. In healthy, HIV-1-seronegative subjects, CD4+ and CD8+ T cells had half-lives of 87 days and 77 days, respectively, with absolute production rates of 10 CD4+ T cells/microl per day and 6 CD8+ T cells/microl per day. In untreated HIV-1-infected subjects (with a mean CD4 level of 342 cells/microl), the half-life of each subpopulation was less than 1/3 as long as those of healthy, HIV-1-seronegative subjects but was not compensated by an increased absolute production rate of CD4+ T cells. After viral replication was suppressed by highly active antiretroviral therapy for 12 weeks, the production rates of circulating CD4+ and CD8+ T cells were considerably elevated; the kinetic basis of increased CD4 levels was greater production, not a longer half-life, of circulating cells. These direct measurements indicate that CD4+ T-cell lymphopenia is due to both a shortened survival time and a failure to increase the production of circulating CD4+ T cells. Our results focus attention on T-cell production systems in the pathogenesis of HIV-1 disease and the response to antiretroviral therapy.

CD4 Lymphocyte Count↗
PubMed1999

R5 strains of human immunodeficiency virus type 1 from rapid progressors lacking X4 strains do not possess X4-type pathogenicity in human thymus.

Some individuals infected with only R5 strains of human immunodeficiency virus type 1 progress to AIDS as quickly as individuals harboring X4 strains. We determined that three R5 viruses were much less pathogenic than an X4 virus in SCID-hu Thy/Liv mice, suggesting that R5 virus-mediated rapid disease progression is associated with host, not viral, factors.

Animals↗
PubMed1998

CXCR4 and CCR5 expression delineates targets for HIV-1 disruption of T cell differentiation.

HIV-1 disease is often associated with CD4+ T lymphopenia as well as quantitative reductions in naive CD8+ T cells and cytopenias involving nonlymphoid hemopoietic lineages. Studies in HIV-1-infected humans as well as in animal models of lenti-virus disease indicate that these effects may be secondary to infection and destruction of multilineage and lineage-restricted hemopoietic progenitor cells. To define the stages of T cell differentiation that might be susceptible to HIV-1, we performed flow cytometric analysis of the surface expression of CXCR4 and CCR5 on T cells and their progenitors from fetal tissue, cord blood, SCID-hu Thy/Liv mice, and adult peripheral blood. We found that CXCR4 is expressed at low levels on hemopoietic progenitors in the bone marrow, is highly expressed on immature (CD3-CD4+CD8-) T cell progenitors in the thymus, and then is down-regulated during thymocyte differentiation. As thymocytes leave the thymus and enter the peripheral circulation, the expression of CXCR4 is again up-regulated. In contrast, CCR5 is undetectable on most hemopoietic progenitors in the bone marrow and on intrathymic T progenitor cells. It is up-regulated when thymocytes coexpress CD4 and CD8, then down-regulated either in the thymus (CD4+ cells) or during exit from the thymus (CD8+ cells). These results indicate that discrete, lineage-related populations of T cell progenitors may vary widely in their potential to respond to chemokines and to be infected by HIV-1, and that T lymphoid differentiation is particularly vulnerable to CXCR4-using viruses.

Adult↗
PubMed1998

High prevalence of thymic tissue in adults with human immunodeficiency virus-1 infection.

The thymus in adults infected with the HIV-1 is generally thought to be inactive, both because of age-related involution and viral destruction. We have revisited the question of thymic function in adults, using chest-computed tomography (CT) to measure thymic tissue in HIV-1-seropositive (n = 99) or HIV-1-seronegative (n = 32) subjects, and correlating these results with the level of circulating CD4(+) and CD8(+) T cells that are phenotypically described as naive thymic emigrants. Abundant thymic tissue was detectable in many (47/99) HIV-1-seropositive adults, aged 20-59. Independent of age, radiographic demonstration of thymic tissue was significantly associated with both a higher CD4(+) T cell count (P = 0.02) and a higher percentage and absolute number of circulating naive (CD45RA+CD62L+) CD4(+) T cells (P < 0.04). The prevalence of an abundant thymus was especially high in younger HIV-1-seropositive adults (</= 39 yr) with CD4 counts in the range 300-500 cells/microl and in older subjects (> 40 yr) regardless of CD4 count (P = 0.03). These studies suggest that the thymus is functional in some but not all adults with HIV-1 disease.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Human immunodeficiency virus-1 infection interrupts thymopoiesis and multilineage hematopoiesis in vivo.

It is still uncertain whether multilineage hematopoietic progenitor cells are affected by human immunodeficiency virus-1 (HIV-1) infection in vivo. The SCID-hu Thy/Liv model is permissive of long-term multilineage human hematopoiesis, including T lymphopoiesis. This model was used to investigate the effects of HIV-1 infection on early hematopoietic progenitor function. We found that both lineage-restricted and multilineage hematopoietic progenitors were depleted from grafts infected with either a molecular clone or a primary isolate of HIV-1. Depletion of hematopoietic progenitors (including CD34(+) cells, colony-forming units in methylcellulose, and long-term culture-initiating cells) occurred several days before the onset of thymocyte depletion, indicating that the subsequent rapid decline in thymocyte numbers was due at least in part to loss of thymocyte progenitors. HIV-1 proviral genomes were not detected at high frequency in hematopoietic cells earlier than the intrathymic T-progenitor cell stage, despite the depletion of such cells in infected grafts. Proviral genomes were also not detected in colonies derived from progenitor cells from infected grafts. These data demonstrate that HIV-1 infection interrupts both lineage-restricted and multilineage hematopoiesis in vivo and suggest that depletion of early hematopoietic progenitor cells occurs in the absence of direct viral infection.

Animals↗
PubMed1998

Furry flasks?

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Animals↗
PubMed1998

Restoration of cytomegalovirus-specific CD4+ T-lymphocyte responses after ganciclovir and highly active antiretroviral therapy in individuals infected with HIV-1.

Recent studies of subjects infected with human immunodeficiency virus (HIV-1) have produced conflicting results about the extent of reconstitution possible in the CD4+ lymphocyte repertoire after highly active antiretroviral therapy (HAART). The effect of HAART on the incidence of opportunistic infections will probably depend on reconstitution of antigen-specific CD4+ lymphocyte responses to important pathogens, including cytomegalovirus (CMV), the leading cause of blindness in AIDS. Several studies have demonstrated an important role for CD4+ lymphocytes in controlling CMV replication in vitro and in clinical studies. It is now possible to quantitate antigen-specific CD4+ lymphocyte responses by flow cytometry. Using this method, we studied CMV-specific CD4+ lymphocyte responses in individuals infected with HIV-1 with and without a history of active CMV-associated end organ disease (EOD), and in those with quiescent CMV EOD after ganciclovir therapy and HAART. The presence of active CMV-associated EOD strongly correlated with loss of CMV-specific lymphocyte responses (P = 0.0004). In contrast, patients with no history of CMV-associated EOD and most patients with quiescent EOD after HAART demonstrated strong CMV-specific CD4+ lymphocyte responses. These data indicate that the loss of CMV-specific CD4+ lymphocyte responses in individuals infected with HIV-1 who have active CMV EOD may be restored after ganciclovir therapy and HAART, which provides evidence for functional immune reconstitution to an important pathogen.

AIDS-Related Opportunistic Infections↗
PubMed1998

Inhibition of human immunodeficiency virus type 1 infection in SCID-hu Thy/Liv mice by the G-quartet-forming oligonucleotide, ISIS 5320.

Viral replication was inhibited in a dose-dependent manner after administration of the phosphorothioate oligonucleotide TTGGGGTT (ISIS 5320) to human immunodeficiency virus type 1 (HIV-1)-infected SCID-hu Thy/Liv mice. Potent in vivo antiviral activity was observed against the T-cell-tropic molecular clone NL4-3; the agent was found to have weak activity against one primary HIV-1 isolate, and the agent was inactive against a second primary isolate.

Acquired Immunodeficiency Syndrome↗
PubMed1998

CCR5- and CXCR4-utilizing strains of human immunodeficiency virus type 1 exhibit differential tropism and pathogenesis in vivo.

CCR5-utilizing (R5) and CXCR4-utilizing (X4) strains of human immunodeficiency virus type 1 (HIV-1) have been studied intensively in vitro, but the pathologic correlates of such differential tropism in vivo remain incompletely defined. In this study, X4 and R5 strains of HIV-1 were compared for tropism and pathogenesis in SCID-hu Thy/Liv mice, an in vivo model of human thymopoiesis. The X4 strain NL4-3 replicates quickly and extensively in thymocytes in the cortex and medulla, causing significant depletion. In contrast, the R5 strain Ba-L initially infects stromal cells including macrophages in the thymic medulla, without any obvious pathologic consequence. After a period of 3 to 4 weeks, Ba-L infection slowly spreads through the thymocyte populations, occasionally culminating in thymocyte depletion after week 6 of infection. During the entire time of infection, Ba-L did not mutate into variants capable of utilizing CXCR4. Therefore, X4 strains are highly cytopathic after infection of the human thymus. In contrast, infection with R5 strains of HIV-1 can result in a two-phase process in vivo, involving apparently nonpathogenic replication in medullary stromal cells followed by cytopathic replication in thymocytes.

Animals↗
PubMed1997

Superantigen-mediated deletion of specific T cell receptor V beta subsets in the SCID-hu Thy/Liv mouse is induced by staphylococcal enterotoxin B, but not HIV-1.

Infection by HIV-1 has been associated with perturbations in the TCR V beta repertoire, suggesting the involvement of a superantigen. Among the hallmarks of superantigens is the capacity to delete T cells bearing specific TCR V beta families in the developing thymus. To verify the presence of a superantigen in HIV-1, we analyzed the SCID-hu Thy/Liv TCR V beta repertoire within CD4+CD8+, CD4+CD8-, or CD4-CD8+ thymocytes subsets by flow cytometry using a panel of Abs recognizing about 60% of the TCR repertoire following injection of SEB or infection by two different HIV-1 isolates. Seven days following SEB injection, thymocyte subsets bearing TCR V beta 3, V beta 12, V beta 17, and V beta 20, but not V beta 5 or V beta 8 , were deleted relative to mock-injected mice. In contrast, no changes were observed in the TCR V beta repertoire in CD4+CD8+, CD4+CD8-, or CD4-CD8+ thymocyte subsets after infection with HIV-1. The T cell depletion caused by HIV-1 infection is most likely not mediated by an HIV-encoded superantigen.

Animals↗
PubMed1997

Thymic function in HIV-1 disease.

The thymus involutes over time and is generally considered to be non-functional in adults. If this is the case, T-cell depletion in adult HIV-1 disease would in part be due to insufficient intrathymic production. This review summarizes information relevant to the structure and function of the thymus under normal conditions and in the setting of infection with HIV-1. The speculation is raised: could residual thymic reserve be present in some adults and be inducible during pathophysiological states of T-cell depletion? If so, the contribution of thymopoiesis during adult HIV-1 disease may be more significant than otherwise assumed.

Age Factors↗