Search PubMed⌕ Search

Biomedical subjects

J M McCune

Publications and source records attributed to J M McCune.

At least 73 records · Page 4Linked to original sources
PubMed1991

Lymphoid reconstitution of the human fetal thymus in SCID mice with CD34+ precursor cells.

The search for human hematopoietic stem cells has been hampered by the lack of appropriate assay systems. Demonstration of the ability of precursor cell candidates to give rise to T cells is of significant difficulty since dissociated in vitro cultured thymus stroma cells lose their ability to sustain thymocyte maturation. To define further the differentiative capacities of the rare human fetal liver and bone marrow cells that express the CD34 surface antigen and exhibit in vitro myeloid and pre-B cell activities, we have microinjected them into HLA-mismatched fetal thymus fragments, partially depleted of hematopoietic cells by low temperature culture. In vitro colonized thymuses have then been allowed to develop upon engraftment into immunodeficient SCID mice. Using this modification of the SCID-hu system, we show that low numbers of fetal CD34+ progenitor cells can repopulate the lymphoid compartment in the human thymus.

Animals↗
PubMed1991

Clonal analysis of the peripheral T cell compartment of the SCID-hu mouse.

Severe combined immunodeficiency (SCID) mice can be transplanted successfully with human fetal liver and thymus (SCID-hu mice). Precursor cells derived from the fetal liver differentiate in the thymus and migrate into the blood as mature T cells. In the present paper, the peripheral T cell compartment of such mice was studied. Peripheral WBC were activated by PHA and cultured in the presence of irradiated human feeder cells. The resultant cell population consisted exclusively of human CD1- CD2+ CD3+ CD7+ T lymphocytes; up to 4% of the T cells expressed the TCR gamma delta, whereas 95 to 100% were TCR alpha beta +. The CD4bright (42 to 66%) and CD8bright (30 to 54%) populations coexpressed variable but low levels of CD8 and CD4, respectively. The T cell cultures from the SCID-hu mice did not display reactivity towards the autologous human EBV-transformed B cell lines (B-LCL). On the other hand, these human T cells proliferated and were cytotoxic against allogeneic human B-LCL. T cell clones were established from cultured SCID-hu T cells. All T cell clones were TCR alpha beta + CD3+ CD2+; 61% of the clones were CD4+ CD8-, 27% were CD8+ CD4-, 11% were CD8+ CD4lo, and 2% were CD4+ CD8lo. None of these clones recognized the autologous B-LCL established from the fetal human donor. Fourteen of 100 T cell clones had specific alloreactivity, as tested on a panel of five B-LCL. Of these 14, two CD8+ CD4lo and two CD8+ CD4- clones were cytotoxic and did not proliferate in response to specific stimulator cells. Furthermore, two CD4+ CD8lo and eight CD4+ CD8- clones proliferated specifically in response to alloantigens. In conclusion, the peripheral human T cells of SCID-hu animals are functional and their TCR repertoire is polyclonal, alloreactive, and devoid of self-reactive cells. Therefore, the SCID-hu mouse can be a suitable model for the study of alloreactivity and allotolerance in vivo, as well as for the study of negative selection in the human thymus.

Animals↗
PubMed1991

Human T cells in the SCID-hu mouse are phenotypically normal and functionally competent.

SCID-hu mice are heterochimeric animals that are constructed by transplanting human fetal thymus (Thy), liver (Liv), and/or lymph nodes into congenitally immunodeficient C.B-17 scid/scid (SCID) mice. Sensitive and specific two-color flow cytometric assays were used to evaluate human lymphocytes from peripheral blood of SCID-hu mice. Kinetic studies presented in this report show long term T lymphopoiesis in SCID-hu mice. Approximately one-half of SCID-hu mice constructed with Thy and Liv tissue develop detectable levels of circulating human T cells by 4 mo after transplantation. The average level of circulating human cells in SCID-hu mice is generally less than 2% of the total lymphoid cells in the peripheral blood of these mice. Some SCID-hu mice with as high as 13% human lymphocytes, however, have been detected. Nearly all human cells in the peripheral blood of SCID-hu mice are CD3+ cells that express TCR-alpha beta. The percentages of gamma delta+, CD4+, CD8+, CD25+, CD69+, and Leu-8+ cells among CD45+ cells in SCID-hu blood are similar to the levels found in adult peripheral blood. On average, 74% of SCID-hu T cells express CD45RA and 18% express CD29. Functional studies demonstrate that cells from SCID-hu Thy/Liv grafts or human T cells from SCID-hu peripheral blood are functionally competent to respond to mitogens or allogeneic human cells in vitro. They are similar to fetal thymocytes or adult T cells, respectively, in these responses. These studies demonstrate that the SCID-hu mouse is a useful model for the analysis of human immune differentiation and function in vivo.

Animals↗
PubMed1991

Human immunodeficiency virus infection of human lymph nodes in the SCID-hu mouse.

The SCID-hu mouse is a small animal in which human hematolymphoid organs can be engrafted and maintained in vivo. In this study, parameters are described for reproducible infection of SCID-hu mice after i.v. inoculation. Infection was found to be dependent upon the time after inoculation, the virus isolate, the titer of virus, and the human target organ implanted into the mouse. Ten to 14 days after the i.v. administration of HIV isolates derived freshly from patients (e.g., JR-CSF, JR-FL, SM), 100% of engrafted human lymph nodes in SCID-hu mice were infected; greater than 95% of these animals were also viremic. Implants of human thymus or connective tissue, as well as the endogenous murine hematolymphoid organs, were not infected. As demonstrated by a combination of in situ hybridization and immunohistochemistry, both T-lymphoid and myelomonocytic lineage cells were infected in this system. HIV isolates that have been adapted to growth in vitro (e.g., HTLV-IIIb) were not infectious. When either 3'-azido-3'-deoxythymidine (AZT) or 2',3'-dideoxyinosine (ddIno) was administered to SCID-hu mice before HIV infection, the animals were protected in dose ranges similar to those used in man. This animal model may now be used as an efficient intermediate step between the lab and the clinic to study the infectious process in vivo and to best select efficacious antiviral compounds against HIV.

Animals↗
PubMed1991

SCID mice as immune system models.

C.B-17 scid/scid mice are born with severe combined immunodeficiency. This defect in the maturation of T and B cells has provided a novel experimental system in which to study normal lymphoid differentiation and function in mouse and man.

Animals↗
PubMed1991

Postexposure prophylaxis with zidovudine suppresses human immunodeficiency virus type 1 infection in SCID-hu mice in a time-dependent manner.

Occupational exposure to the human immunodeficiency virus (HIV) has led to a low but finite incidence of infection among health care providers. In such circumstances, postexposure administration of 3'-azido-3'-deoxythymidine (zidovudine; AZT) might be beneficial. To test this possibility, the SCID-hu mouse (the immunodeficient C.B-17 scid/scid mouse engrafted with human hematolymphoid organs) was treated with AZT at different times after intravenous infection with a standard dose of HIV (known to infect 100% of animals). If given within 2 h, AZT suppressed infection in all animals; if given after 2 days, no suppression was observed. At least in some animals, an AZT-sensitive phase lasted for as long as 36 h. These data support the hypothesis that prompt administration of AZT might be efficacious in suppressing acute HIV infection in humans. Further studies in the SCID-hu mouse might provide insight into treatment protocols of even greater efficacy.

Animals↗
PubMed1991

Preclinical evaluation of human hematolymphoid function in the SCID-hu mouse.

Work in the SCID-hu system has progressed significantly over the past 3-4 years. Reliable SCID-hu constructs can now be created for the evaluation of long-term multilineage human hematopoiesis, human immune function, and HIV infection of human hematolymphoid organs in vivo. Given these constructs, a variety of therapeutically important modalities can now be discovered and developed with a relevant in vivo model, prior to the time that they are moved into the clinic. With further progress in this and other preclinical models, useful therapies for important human disease states will hopefully be forthcoming at an even faster pace.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Long-term human hematopoiesis in the SCID-hu mouse.

Coimplantation of small fragments of human fetal thymus and fetal liver into immunodeficient SCID mice resulted in the formation of a unique structure (Thy/Liv). Thereafter, the SCID-hu mice showed reproducible and long-term reconstitution of human hematopoietic activity. For periods lasting 5-11 mo after transplantation, active T lymphopoiesis was observed inside the grafts and cells that were negative for T cell markers were found to have colony-forming units for granulocyte/macrophage (CFU-GM) and erythroid burst-forming unit (BFU-E) activity in the methylcellulose colony assay. In addition, structures similar to normal human bone marrow were observed inside the Thy/Liv grafts, consisting of blast cells, mature and immature forms of myelomonocytic cells, and megakaryocytes. These data indicate long-term maintenance, in vivo, of human progenitor cells for the T lymphoid, myelomonocytic, erythroid, and megakaryocytic lineages. The role of the implanted fetal liver fragments was analyzed using HLA-mismatched Thy/Liv implants. The HLA type of the liver donor was found on T cells and macrophages in the graft. In addition, cells grown in the methylcellulose colony assay and cells in a bone marrow-like structure, the "thymic isle," expressed the HLA type of the liver donor. Thus, the Thy/Liv implants provided a microenvironment in which to follow human hematopoietic progenitor cells for multiple lineages. The formation of the Thy/Liv structures also results in a continuous source of human T cells in the peripheral circulation of the SCID-hu mouse. Though present for 5-11 mo, these cells did not engage in a xenograft (graft-versus-host) reaction. This animal model, the first in which multilineage human hematopoietic activity is maintained for long periods of time, should be useful for the analysis of human hematopoiesis in vivo.

Animals↗
PubMed1990

Suppression of HIV infection in AZT-treated SCID-hu mice.

The SCID-hu mouse, engrafted with human hematolymphoid organs, is permissive for infection with the human immunodeficiency virus (HIV). This mouse model was used to test compounds for antiviral efficacy. Two weeks after infection with HIV, 100 percent (40/40) of SCID-hu mice were positive for HIV by the polymerase chain reaction. When first treated with 3'-azido-3'-deoxythymidine (AZT), none (0/17) were HIV-positive by this assay. However, AZT-treated SCID-hu mice did have a few infected cells; after AZT treatment was stopped, viral spread was detected by polymerase chain reaction in such mice. Thus, the SCID-hu mouse provides a means to directly compare new antiviral compounds with AZT and to further improve antiviral efficacy.

Animals↗
PubMed1988

Infection of the SCID-hu mouse by HIV-1.

SCID-hu mice with human fetal thymic or lymph node implants were inoculated with the cloned human immunodeficiency virus-1 isolate, HIV-1JR-CSF. In a time- and dose-dependent fashion, viral replication spread within the human lymphoid organs. Combination immunohistochemistry and in situ hybridization revealed only viral RNA transcripts in most infected cells, but some cells had both detectable viral transcripts and viral protein. Infected cells were always more apparent in the medulla than in the cortex of the thymus. These studies demonstrate that an acute infection of human lymphoid organs with HIV-1 can be followed in the SCID-hu mouse.

Acquired Immunodeficiency Syndrome↗
PubMed1988

The SCID-hu mouse: murine model for the analysis of human hematolymphoid differentiation and function.

The study of human hematopoietic cells and the human immune system is hampered by the lack of a suitable experimental model. Experimental data are presented showing that human fetal liver hematopoietic cells, human fetal thymus, and human fetal lymph node support the differentiation of mature human T cells and B cells after engraftment into mice with genetically determined severe combined immunodeficiency. The resultant SCID-hu mice are found to have a transient wave of human CD4+ and CD8+ T cells and human IgG (immunoglobulin G) in the peripheral circulation. The functional status of the human immune system within this mouse model is not yet known.

Animals↗
PubMed1988

Endoproteolytic cleavage of gp160 is required for the activation of human immunodeficiency virus.

The envelope protein of human immunodeficiency virus (HIV) is synthesized as a polyprotein (gp160) and cleaved intracellularly to a gp120-gp41 heterodimer. In this study, the tryptic-like endoproteolytic cleavage site was removed by site-directed mutagenesis and replaced with a chymotryptic-like site. The resultant mutant, RIP7/mut10, was found to be indistinguishable from wild-type HIV when analyzed at the level of proviral replication, RNA processing, protein expression, and viral assembly. However, the gp160 polyprotein was not cleaved and the mutated virions were biologically inactive, until and unless they were exposed to limiting concentrations of chymotrypsin. As is the case for other enveloped mammalian viruses, endoproteolytic cleavage of the HIV envelope protein and release of a unique hydrophobic domain appear to be necessary for the full expression of viral infectivity.

Amino Acid Sequence↗