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Articles by Norman L. Letvin
Total Records ( 7 ) for Norman L. Letvin
  Ralf Geiben-Lynn , John R. Greenland , Kwesi Frimpong-Boateng and Norman L. Letvin
  While a new generation of vaccine vectors has been developed for eliciting cellular immune responses, little is known about the optimal routes for their administration or about the ramifications of the kinetics of in vivo vaccine antigen expression for immunogenicity. We evaluated the kinetics of vaccine antigen expression by real-time in vivo photon imaging and showed dramatic differences in these kinetics using different vectors and different routes of administration. Further, using a gamma interferon enzyme-linked immunospot assay to measure T-lymphocyte immune responses, we observed an association between the kinetics of vaccine antigen expression in vivo and the magnitude of vaccine-elicited memory T-lymphocyte responses. These results highlight the utility of the real-time in vivo photon-imaging technology in evaluating novel immunization strategies and suggest an association between the kinetics of vaccine antigen clearance and the magnitude of vaccine-elicited T-lymphocyte memory immune responses.
  Dan Huang , Yun Shen , Liyou Qiu , Crystal Y. Chen , Ling Shen , Jim Estep , Robert Hunt , Daphne Vasconcelos , George Du , Pyone Aye , Andrew A. Lackner , Michelle H. Larsen , William R. Jacobs Jr. , Barton F. Haynes , Norman L. Letvin and Zheng W. Chen
  Little is known about the immune distribution and localization of antigen-specific T cells in mucosal interfaces of tissues/organs during infection of humans. In this study, we made use of a macaque model of Mycobacterium tuberculosis infection to assess phosphoantigen-specific Vγ2Vδ2 T cells regarding their tissue distribution, anatomical localization, and correlation with the presence or absence of tuberculosis (TB) lesions in lymphoid and nonlymphoid organs/tissues in the progression of severe pulmonary TB. Progression of pulmonary M. tuberculosis infection generated diverse distribution patterns of Vγ2Vδ2 T cells, with remarkable accumulation of these cells in lungs, bronchial lymph nodes, spleens, and remote nonlymphoid organs but not in blood. Increased numbers of Vγ2Vδ2 T cells in tissues were associated with M. tuberculosis infection but were independent of the severity of TB lesions. In lungs with apparent TB lesions, Vγ2Vδ2 T cells were present within TB granulomas. In extrathoracic organs, Vγ2Vδ2 T cells were localized in the interstitial compartment of nonlymphoid tissues, and the interstitial localization was present despite the absence of detectable TB lesions. Finally, Vγ2Vδ2 T cells accumulated in tissues appeared to possess cytokine production function, since granzyme B was detectable in the γδ T cells present within granulomas. Thus, clonally expanded Vγ2Vδ2 T cells appeared to undergo trans-endothelial migration, interstitial localization, and granuloma infiltration as immune responses to M. tuberculosis infection.
  Pritha Sen , William A. Charini , Ramu A. Subbramanian , Edwin R. Manuel , Marcelo J. Kuroda , Patrick A. Autissier and Norman L. Letvin
  To afford the greatest possible immune protection, candidate human immunodeficiency virus (HIV) vaccines must generate diverse and long-lasting CD8+ T lymphocyte responses. In the present study, we evaluate T-cell receptor Vβ (variable region beta) gene usage and a CDR3 (complementarity-determining region 3) sequence to assess the clonality of epitope-specific CD8+ T lymphocytes generated in rhesus monkeys following vaccination and simian-human immunodeficiency virus (SHIV) challenge. We found that vaccine-elicited epitope-specific CD8+ T lymphocytes have a clonal diversity comparable to those cells generated in response to SHIV infection. Moreover, we show that the clonal diversity of vaccine-elicited CD8+ T-lymphocyte responses is dictated by the epitope sequence and is not affected by the mode of antigen delivery to the immune system. Clonal CD8+ T-lymphocyte populations persisted following boosting with different vectors, and these clonal cell populations could be detected for as long as 4 years after SHIV challenge. Finally, we show that the breadth of these epitope-specific T lymphocytes transiently focuses in response to intense SHIV replication. These observations demonstrate the importance of the initial immune response to SHIV, induced by vaccination or generated during primary infection, in determining the clonal diversity of cell-mediated immune responses and highlight the focusing of this clonal diversity in the setting of high viral loads. Circumventing this restricted CD8+ T-lymphocyte clonal diversity may present a significant challenge in the development of an effective HIV vaccine strategy.
  Eun-Young Kim , Ronald S. Veazey , Roland Zahn , Kimberly J. McEvers , Susanne H. C. Baumeister , Gabriel J. Foster , Melisa D. Rett , Michael H. Newberg , Marcelo J. Kuroda , E. Peter Rieber , Michael Piatak , Jeffrey D. Lifson , Norman L. Letvin , Steven M. Wolinsky and Jorn E. Schmitz
  Here, we investigated the containment of virus replication in simian immunodeficiency virus (SIV) infection by CD8+ lymphocytes. Escape mutations in Mamu-A*01 epitopes appeared first in SIV Tat TL8 and then in SIV Gag p11C. The appearance of escape mutations in SIV Gag p11C was coincident with compensatory changes outside of the epitope. Eliminating CD8+ lymphocytes from rhesus monkeys during primary infection resulted in more rapid disease progression that was associated with preservation of canonical epitopes. These results confirm the importance of cytotoxic T cells in controlling viremia and the constraint on epitope sequences that require compensatory changes to go to fixation.
  Elisa I. Choi , Keith A. Reimann and Norman L. Letvin
  The contribution of natural killer (NK) cells to the immune containment of human immunodeficiency virus infection remains undefined. To directly assess the role of NK cells in an AIDS animal model, we depleted rhesus monkeys of >88% of CD3 CD16+ CD159a+ NK cells at the time of primary simian immunodeficiency virus (SIV) infection by using anti-CD16 antibody. During the first 11 days following SIV inoculation, when NK cell depletion was most profound, a trend toward higher levels of SIV replication was noted in NK cell-depleted monkeys compared to those in control monkeys. However, this treatment did not result in significant changes in the overall levels or kinetics of plasma viral RNA or affect the SIV-induced central memory CD4+ T-lymphocyte loss. These findings are consistent with a limited role for cytotoxic CD16+ NK cells in the control of primary SIV viremia.
  Yue Sun , Sampa Santra , Jorn E. Schmitz , Mario Roederer and Norman L. Letvin
  While a diversity of immunogens that elicit qualitatively different cellular immune responses are being assessed in clinical human immunodeficiency virus vaccine trials, the consequences of those varied responses for viral control remain poorly understood. In the present study, we evaluated the induction of virus-specific T-cell responses in rhesus monkeys using a series of diverse vaccine vectors. We assessed both the magnitude and the functional profile of the virus-specific CD8+ T cells by measuring gamma interferon, interleukin-2, and tumor necrosis factor alpha production. We found that the different vectors generated virus-specific T-cell responses of different magnitudes and with different functional profiles. Heterologous prime-boost vaccine regimens induced particularly high-frequency virus-specific T-cell responses with polyfunctional repertoires. Yet, immediately after a pathogenic simian-human immunodeficiency virus (SHIV) challenge, no significant differences were observed between these cohorts of vaccinated monkeys in the magnitudes or the functional profiles of their virus-specific CD8+ T cells. This finding suggests that the high viral load shapes the functional repertoire of the cellular immune response during primary infection. Nevertheless, in all vaccination regimens, higher frequency and more polyfunctional vaccine-elicited virus-specific CD8+ T-cell responses were associated with better viral control after SHIV challenge. These observations highlight the contributions of both the quality and the magnitude of vaccine-elicited cellular immune responses in the control of immunodeficiency virus replication.
  Roland C. Zahn , Melisa D. Rett , Birgit Korioth-Schmitz , Yue Sun , Adam P. Buzby , Simoy Goldstein , Charles R. Brown , Russell A. Byrum , Gordon J. Freeman , Norman L. Letvin , Vanessa M. Hirsch and Jorn E. Schmitz
  African green monkeys (AGM) do not develop overt signs of disease following simian immunodeficiency virus (SIV) infection. While it is still unknown how natural hosts like AGM can cope with this lentivirus infection, a large number of investigations have shown that CD8+ T-cell responses are critical for the containment of AIDS viruses in humans and Asian nonhuman primates. Here we have compared the phenotypes of T-cell subsets and magnitudes of SIV-specific CD8+ T-cell responses in vervet AGM chronically infected with SIVagm and rhesus monkeys (RM) infected with SIVmac. In comparison to RM, vervet AGM exhibited weaker signs of immune activation and associated proliferation of CD8+ T cells as detected by granzyme B, Ki-67, and programmed death 1 staining. By gamma interferon enzyme-linked immunospot assay and intracellular cytokine staining, SIV Gag- and Env-specific immune responses were detectable at variable but lower levels in vervet AGM than in RM. These observations demonstrate that natural hosts like SIV-infected vervet AGM develop SIV-specific T-cell responses, but the disease-free course of infection does not depend on the generation of robust CD8+ T-cell responses.
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