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N L Letvin

Publications and source records attributed to N L Letvin.

At least 127 records · Page 7Linked to original sources
PubMed1995

A human recombinant Fab identifies a human immunodeficiency virus type 1-induced conformational change in cell surface-expressed CD4.

To explore the role of the CD4 molecule in human immunodeficiency virus (HIV) infection following initial virus-CD4 binding, we have characterized CD4-specific antibodies raised by immunizing an HIV-1-infected human with human recombinant soluble CD4 (rsCD4). Fabs were selected from a human recombinant Fab library constructed from the bone marrow of this immunized individual. Here, we describe a human rsCD4-specific recombinant Fab clone selected by panning the library over complexes of human rsCD4 and recombinant HIV-1 envelope protein. While this Fab does not bind to CD4-positive T-cell lines or to human T lymphocytes, it recognizes cell surface-expressed CD4 following the incubation of these cells with a recombinant form of HIV-1 gp120 or with HIV-1 virions. The Fab is not HIV-1 envelope specific, since it does not bind to recombinant gp120 or to native cell surface-expressed HIV-1 envelope proteins. As confirmation of its CD4 specificity, we show that this Fab immunoprecipitates a 55-kDa protein, corresponding to the molecular mass of cellular CD4, from an H9 cell lysate. The specificity of this human Fab provides evidence for a virus-induced conformational change in cell surface-expressed on CD4. The characterization of this altered CD4 conformation and its effects on the host cell will be important in defining postbinding events in HIV infection.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Antibody facilitation of multiple sclerosis-like lesions in a nonhuman primate.

In the human disease multiple sclerosis (MS), the immune mechanisms responsible for selective destruction of central nervous system myelin are unknown. In the common marmoset Callithrix jacchus, a unique demyelinating form of experimental allergic encephalomyelitis resembling MS can be induced by immunization with whole myelin. Here we show that the MS-like lesion can be reproduced by immunization against the extracellular domain of a single myelin protein, myelin/oligodendrocyte glycoprotein (MOG). By contrast, immunization against the quantitatively major myelin proteins myelin basic protein or proteolipid protein results in inflammation but little or no demyelination. Furthermore, in the presence of encephalitogenic (e.g., disease-inducing) T cells, the fully demyelinated lesion is reconstructed by systemic administration of IgG purified from whole myelin-, or MOG-immunized animals, and equally by a monoclonal antibody against MOG, but not by control IgG. Encephalitogenic T cells may contribute to the MS-like lesion through disruption of the blood-brain barrier that permits access of demyelinating antibody into the nervous system. The identification of MOG as a major target antigen for autoimmune demyelination in a nonhuman primate should facilitate development of specific immunotherapies for human MS.

Animals↗
PubMed1994

The repertoire of cytotoxic T lymphocytes in the recognition of mutant simian immunodeficiency virus variants.

The importance of the repertoire of a primed, AIDS virus-specific population of CTL in the recognition of emerging mutant viruses was assessed in simian immunodeficiency virus (SIV)-infected rhesus monkeys. These studies were done by using the well-characterized CTL recognition of the SIVmac Gag peptide 11C (p11C) epitope in rhesus monkeys expressing the MHC class I molecule Mamu-A*01. Lysis of peptide-pulsed targets by bulk PBL effector cells from SIVmac-infected, Mamu-A*01+ monkeys was significantly decreased by mutations at residues 2, 3, and 5 of the nine-amino-acid Gag p11C epitope. However, effector cell lysis of targets pulsed with p11C containing substitutions at residues 3 or 5 was substantially increased by in vitro incubation of the monkeys' PBL with these mutant peptides. This suggested that expandable populations of cells exist in the primed CTL of infected monkeys capable of recognizing mutant peptide sequences. In fact, without in vitro exposure of PBL to mutant peptides, SIVmac Gag-specific CTL could be cloned from PBL of infected monkeys that lysed targets pulsed with mutant peptides. These observations suggest that clones of effector cells capable of recognizing many viral mutants may be able to expand in vivo to control the spread of emerging variant AIDS viruses.

Amino Acid Sequence↗
PubMed1994

Role of CD26/dipeptidyl peptidase IV in human immunodeficiency virus type 1 infection and apoptosis.

To examine the role of CD26/dipeptidyl peptidase IV (DPPIV; EC 3.4.14.5) in infection by human immunodeficiency virus type 1 (HIV-1), we utilized CD26 cDNA-transfected Jurkat T-cell lines. Both CD26- parental Jurkat cells and mutant CD26+ (DPPIV-) transfected Jurkat cells were readily infected with HIV-1, whereas wild-type CD26+ (DPPIV+) transfected Jurkat cells were more resistant to HIV-1 infection. Our results suggest that CD26 is not essential for HIV-1 infectivity as suggested by others but that DPPIV enzyme activity may decrease the efficiency of HIV-1 infection. Of great interest, we found that mutant CD26+ (DPPIV-) transfectants and CD26- parental Jurkat cells strongly expressed CD95 (Fas/Apo-1) and were more sensitive than wild-type CD26+ (DPPIV+) transfectants to the induction of apoptosis by anti-CD95 monoclonal antibody. These results suggest that CD26 may play a role in HIV-1-associated loss of -CD4+ cells through the process of programmed cell death.

Antigens, CD↗
PubMed1994

Use of human leukocyte-specific monoclonal antibodies for clinically immunophenotyping lymphocytes of rhesus monkeys.

The rhesus monkey (Macaca mulatta) is an important experimental animal frequently utilized for studies of infectious diseases, immunity, hematopoiesis, and transplantation. Since the structure of cell surface molecules is phylogenetically conserved, monoclonal antibodies raised against human leukocyte antigens can sometimes recognize the homologous determinant on monkey leukocytes. To facilitate better utilization of this animal model, we tested 89 commercially available monoclonal antibodies which define 27 human cell surface antigens for reactivity with rhesus monkey PBL. Certain antigens which delineate clinical useful lymphocyte subsets such as CD2, CD4, CD8, CD14, CD16, CD20, and MHC class II are apparently well conserved since most human cell-specific antibodies identified the homologous cell subset in monkeys. However, other antigens such as CD3, CD19, CD45, and CD56 were identified infrequently by human cell-specific antibodies. FITC-modification of antibodies which had no effect on their binding to human cells occasionally inhibited antibody binding to monkey cells. Nevertheless, an adequate number of cross-reactive monoclonal antibodies was identified to allow gating of lymphocytes for accurate flow cytometric analysis and quantitation of the major lymphocyte subsets of the rhesus monkey. The T lymphocyte subset distribution in blood and lymphoid tissue of rhesus monkeys was similar to man. However, the B subset was significantly larger in monkeys. The daily variation in absolute PBL subset size was marked and found to be due mainly to daily fluctuations in total lymphocyte number.

Animals↗
PubMed1994

An acutely lethal simian immunodeficiency virus stimulates expansion of V beta 7- and V beta 14-expressing T lymphocytes.

SIVsmmPBj14, a variant simian immunodeficiency virus isolated from a pig-tailed macaque, stimulates the proliferation of macaque T lymphocytes in vitro and induces an acutely lethal disease in macaques characterized, in part, by lymphadenopathy and splenomegaly. To determine whether SIVsmmPBj14 exhibits superantigen-like activity, in vitro and in vivo studies of T-cell receptor V beta repertoire were undertaken using PCR-based quantitative methods. Whereas in vitro phytohemagglutinin stimulation of macaque peripheral blood lymphocytes did not cause a perturbation of T-cell receptor V beta repertoire, SIVsmmPBj14 stimulated the expansion of both CD4+ and CD8+ T-lymphocyte subpopulations expressing the V beta 7 and V beta 14 gene families. Such V beta 7 and V beta 14 expansions could be confirmed by a multiple RNase protection assay. Furthermore, the expansion of the same lymphocyte subpopulations was also detected in peripheral blood lymphocytes and lymph node cells of virus-infected macaques. These observations suggest that SIVsmmPBj14-mediated V beta expansion may contribute to the induction of an acutely lethal disease in macaques.

Acute Disease↗
PubMed1994

A simian immunodeficiency virus envelope V3 cytotoxic T-lymphocyte epitope in rhesus monkeys and its restricting major histocompatibility complex class I molecule Mamu-A*02.

The use of the simian immunodeficiency virus (SIV) macaque model for assessing human immunodeficiency virus vaccine strategies will be facilitated by the characterization of predominant SIV cytotoxic T-lymphocyte (CTL) epitopes and their restricting major histocompatibility complex (MHC) class I molecules in macaque species. We now define a rhesus monkey SIVmac CTL epitope in the third hypervariable region of the envelope glycoprotein of the virus. This epitope, YNLTMKCR, contains the first two amino acids of a cysteine-cysteine loop which is the SIVmac analog of the human immunodeficiency virus type 1 V3 loop. We also employed one-dimensional isoelectric focusing to characterize the MHC class I molecule of the rhesus monkey that binds this SIVmac envelope peptide fragment. Cloning and sequencing the cDNA encoding this rhesus monkey MHC class I molecule demonstrates that it is a newly described HLA-A homolog, Mamu-A*02. This viral CTL epitope and its restricting MHC class I molecule will facilitate the use of the SIVmac rhesus monkey model for studies of envelope-based vaccine strategies and for exploring AIDS immunopathogenesis.

Amino Acid Sequence↗
PubMed1994

Immunopathogenic events in acute infection of rhesus monkeys with simian immunodeficiency virus of macaques.

Infection of the rhesus monkey with simian immunodeficiency virus of macaques (SIVmax) was employed to explore the early immune events associated with the initial containment of an acute AIDS virus infection. In nine rhesus monkeys infected intravenously with uncloned SIVmac strain 251, high-level p27 plasma antigenemia was usually detected transiently from approximately day 7 through day 21 following virus inoculation. SIVmac replication in lymph nodes measured by in situ RNA hybridization closely paralleled the time course and magnitude of viremia. The containment of SIVmac spread by 3 to 4 weeks following infection suggests an efficient, early immune control of this virus infection. Anti-SIVmac antibodies were first detected in the blood at approximately day 14. At the time antigenemia was decreased or cleared, SIVmac neutralizing antibodies were present. A rise in circulating and lymph node CD8+ T cells also occurred coincident with the clearance of antigenemia and persisted thereafter. These CD8+ lymphocytes in lymph nodes had increased expression of both major histocompatibility complex class II and the adhesion molecule LFA-1; they also demonstrated decreased expression of the naive T-cell-associated CD45RA molecule. SIVmac-specific cytotoxic T-lymphocyte precursors were detected in both blood and lymph node by 7 days post-virus inoculation. These studies indicate that both virus-specific humoral and cellular immune mechanisms in blood and lymph node are associated with the clearance of viremia that occurs within the first month of infection of rhesus monkeys with SIVmac.

Animals↗
PubMed1994

In healthy primates, circulating autoreactive T cells mediate autoimmune disease.

A T cell response against myelin basic protein (MBP) is thought to contribute to the central nervous system (CNS) inflammation that occurs in the human demyelinating disease multiple sclerosis. To test whether MBP-reactive T cells that are normally retrieved from the circulation are capable of inducing CNS disease, MBP-reactive T cell clones were isolated from the peripheral blood of healthy, unimmunized Callithrix jacchus (C. jacchus) marmosets. This primate species is characterized by a natural chimerism of bone marrow elements between siblings that should make possible adoptive transfer of MBP-reactive T cells. We report that MBP-reactive T cell clones efficiently and reproducibly transfer CNS inflammatory disease between members of C. jacchus chimeric sets. The demyelination that is characteristic of experimental allergic encephalomyelitis induced in C. jacchus by immunization against human white matter did not occur after adoptive transfer of the MBP-reactive clones. It was noteworthy that encephalitogenic T cell clones were diverse in terms of their recognition of different epitopes of MBP, distinguishing the response in C. jacchus from that in some inbred rodents in which restricted recognition of MBP occurs. These findings are the first direct evidence that natural populations of circulating T cells directed against a CNS antigen can mediate an inflammatory autoimmune disease.

Animals↗
PubMed1993

Synthetic peptide in mineral oil adjuvant elicits simian immunodeficiency virus-specific CD8+ cytotoxic T lymphocytes in rhesus monkeys.

In view of the importance of cell-associated virus in AIDS virus transmission, an HIV vaccine should be able to induce a virus-specific CTL response. Traditional subunit vaccines have not elicited virus-specific CD8+ MHC class I-restricted CTL. We have used the simian immunodeficiency virus of macaques (SIVmac)/rhesus monkey model to explore the use of CTL epitope peptide-helper peptide conjugates for the vaccine elicitation of AIDS virus-specific CTL. We found that both the CTL epitope peptide-helper peptide conjugate and the CTL epitope peptide alone, when delivered in an emulsion with IFA, induced CTL epitope-specific CD8+ MHC class I-restricted CTL. These effector cells recognized processed viral protein and were readily cloned from PBL of the immunized monkeys. Moreover, the cloned effector cells inhibited SIVmac replication in PBL. Immunization with the CTL epitope peptide used in this study also elicited a CD4+ PBL proliferative response, suggesting that the peptide also contained a helper epitope. These studies provide further evidence for the potential usefulness of peptide-based AIDS virus vaccines.

AIDS Vaccines↗
PubMed1993

Conserved T-cell receptor repertoire in simian immunodeficiency virus-infected rhesus monkeys.

Studies to assess the possibility that the HIV may encode a superantigen that plays a role in the depletion of functional CD4+ lymphocytes in the infected individual have yielded discrepant results. The problem in performing conclusive examinations of this issue may be attributed, at least in part, to the difficulty of prospectively studying individuals from before their infection until the time of profound CD4+ lymphocyte loss. To determine whether the AIDS virus deletes particular subpopulations of V beta-expressing lymphocytes, we have employed an animal model of AIDS, the simian immunodeficiency virus (SIV)-infected macaque monkey. Rhesus monkeys were experimentally infected with SIVmac and studied prospectively. A PCR-based quantitative method for assessing TCR repertoire was employed to analyze the expression of 24 V beta and 30 V alpha gene families in the monkeys. Although circulating PBL were increased in number by 3 wk after SIVmac infection, the expanded lymphocyte populations exhibited no significant perturbation in their TCR V beta repertoires. PBL obtained from monkeys before and 0.5 to 3 years after infection displayed no significant change in V beta and V alpha gene family expression. Finally, no deletion of V beta-expressing cell subpopulations could be demonstrated in purified CD4+ lymphocytes from infected monkeys. This was true even for monkeys whose blood contained less than 200 CD4+ lymphocytes/microliters. These results indicate that the TCR repertoire is conserved in SIVmac-infected rhesus monkeys and suggests that mechanisms other than superantigen-induced deletion must be responsible for CD4+ lymphocyte loss in these animals.

Animals↗
PubMed1993

Immunization with recombinant BCG-SIV elicits SIV-specific cytotoxic T lymphocytes in rhesus monkeys.

Because the transmission of HIV is likely to occur through cell-associated virus, an effective HIV vaccine should be capable of eliciting HIV-specific CTL. We have employed the simian immunodeficiency virus (SIV)/rhesus monkey model to explore the use of the attenuated tuberculosis bacillus, Calmette Guérin bacillus (BCG), as a vaccine vehicle to elicit AIDS virus-specific CTL. BCG was engineered to express SIVmac gag under the control of hsp70 regulatory sequences. Immunization with this rBCG-SIVmac gag elicited MHC class I-restricted, CD8+ SIVmac gag-specific CTL in rhesus monkeys. In fact, SIVmac gag-specific CTL could be cloned readily from peripheral blood lymphocytes of these immunized monkeys. These findings provide further evidence for the power of BCG as a vaccine vector and its continued exploration as a vehicle for eliciting HIV-specific immunity.

Amino Acid Sequence↗
PubMed1993

Simian immunodeficiency virus-specific cytotoxic T lymphocytes in rhesus monkeys: characterization and vaccine induction.

An effective HIV vaccine should be capable of eliciting virus-specific cytotoxic T lymphocytes (CTL). We have characterized the cellular and molecular features of a simian immunodeficiency virus of macaques (SIVmac) gag-specific CTL response in rhesus monkeys. We have shown that SIVmac-infected rhesus monkeys expressing the major histocompatibility complex (MHC) class I molecule Mamu-A*01 develop a SIVmac gag-specific CTL response which recognizes a 9 amino acid fragment of the gag protein in association with Mamu-A*01. Moreover, this peptide/MHC class I recognition is mediated by T cell receptors (TCR) employing a predominant V beta gene family and J beta gene. Using this understanding of a SIVmac-specific CTL response, we have shown that SIVmac-specific CTL can be elicited through three novel approaches to vaccination: a recombinant viral vector, a recombinant bacterial vector and a peptide vaccine. These studies illustrate the utility of the SIV/macaque model in AIDS vaccine research.

Animals↗
PubMed1993

Sequence and evolution of cattle MHC class I cDNAs: concerted evolution has not taken place in cattle.

To explore genetic mechanisms responsible for major histocompatibility complex (MHC) class I evolution in the artiodactyls, we cloned and sequenced MHC class I cDNAs from a Bos taurus bull heterozygous for cattle MHC (BoLA) class I serological specificities w2 and w30. Four unique cDNAs were found, indicating the presence of at least two MHC class I loci. Analysis of these four cDNAs and all previously published BoLA cDNA sequences suggested that there may be three cattle MHC class I loci. Additionally, comparison of all of the BoLA class I cDNAs to MHC class I cDNAs of other artiodactyls showed that some of the BoLA class I cDNAs were more similar to certain sheep cDNAs than they were to other cattle cDNAs. These data indicate that each BoLA class I locus has evolved independently after an ancestral gene duplication event and that inter-locus segmental exchange or concerted evolution has not occurred rapidly enough to cause extensive divergence between the orthologous MHC class I loci of sheep and cattle.

Amino Acid Sequence↗
PubMed1993

Immunization with lentivirus-like particles elicits a potent SIV-specific recall cytotoxic T-lymphocyte response in rhesus monkeys.

An effective acquired immunodeficiency syndrome (AIDS) vaccine should be capable of eliciting human immunodeficiency virus (HIV)-specific cytotoxic T-lymphocyte (CTL) responses. We have explored the use of lentivirus-like particles produced in mammalian cells infected with a recombinant vaccinia virus to immunize for the induction of CTL in the simian immunodeficiency virus (SIV)/rhesus monkey model for AIDS. SIV-like particles in a threonyl-MDP-based adjuvant did not elicit a high frequency of SIV gag-specific effector cells in naive rhesus monkeys. However, immunization with these particles elicited a potent recall CTL response in monkeys previously vaccinated with a recombinant vaccinia-SIV virus. These observations suggest that poxvirus-produced virus-like particles may represent a safe immunogen for use in periodic boosting to maintain viable cell-mediated immunity to the AIDS virus.

Animals↗