Optimization of a peptide-based protocol employing IL-7 for in vitro restimulation of human cytotoxic T lymphocyte precursors

Substantial differences in specificity of HIV-specific cytotoxic T cells in acute and chronic HIV infection

Cytotoxic T lymphocytes (CTLs) play a vital part in controlling viral replication during human viral infections. Most studies in human infections have focused on CTL specificities in chronic infection and few data exist regarding the specificity of the initial CTL response induced in acute infection. In this study, HIV-1 infection in persons expressing human histocompatibility leukocyte antigen (HLA)-A*0201 was used as a means of addressing this issue. In chronic infection, the dominant HLA-A*0201-restricted CTL response is directed towards the epitope SLYNTVATL ("SL9") in p17 Gag (residues 77-85). This epitope is targeted by 75% of HLA-A*0201-positive adults, and the magnitude of this A*0201-SL9 response shows a strong negative association with viral load in progressive infection. Despite using the highly sensitive peptide-major histocompatibility complex tetramer and intracellular cytokine assays, responses to the SL9 epitope were not detectable in any of 11 HLA-A*0201-positive subjects with acute HIV-1 infection (P = 2 x 10(-6)), even when assays were repeated using the SL9 peptide variant that was encoded by their autologous virus. In contrast, multiple responses (median 3) to other epitopes were evident in 7 of the 11 A*0201-positive subjects. Longitudinal study of two subjects confirmed that the A*0201-SL9 response emerged later than other CTL responses, and after viral set point had been reached. Together, these data show that the CTL responses that are present and that even may dominate in chronic infection may differ substantially from those that constitute the initial antiviral CTL response. This finding is an important consideration in vaccine design and in the evaluation of vaccine candidates.

Changing patterns of dominant TCR usage with maturation of an EBV-specific cytotoxic T cell response

Infection with EBV provides a unique opportunity to follow the human CD8(+) T cell response to a persistent, genetically stable agent from the primary phase, as seen in infectious mononucleosis (IM) patients, into long-term memory. This study focuses on the response to an immunodominant HLA-A2.01-restricted epitope, GLCTLVAML, from the EBV-lytic cycle Ag BMLF1. TCR analysis of the highly amplified primary response to this epitope revealed markedly oligoclonal receptor usage among in vitro-derived clones, with similar clonotypes dominant in all three IM patients studied. Direct staining of IM T cell preparations with the A2.01/GLCTLVAML tetramer linked this oligoclonal epitope-specific response with appropriate Vbeta subset expansions in the patients' blood. These patients were studied again >2 years later, at which time TCR analysis of in vitro-reactivated clones suggested that rare clonotypes within the primary response had now come to dominate memory. Five additional A2. 01-positive IM patients were studied prospectively for Vbeta subset representation within primary and memory epitope-specific populations as identified by tetramer staining. In each case, the primary response contained large Vbeta2, Vbeta16, or Vbeta22 components, and in three of five cases the originally dominant Vbeta was represented very poorly, if at all, in memory. We conclude 1) that an EBV epitope-specific primary response large enough to account for up to 10% CD8(+) T cells in IM blood may nevertheless be dominated by just a few highly expanded clonotypes, and 2) that with persistent viral challenge such dominant T cell clonotypes may be lost and replaced by others in memory.

Recombinant modified vaccinia virus Ankara efficiently restimulates human cytotoxic T lymphocytes in vitro

The immunogenicity of recombinant modified vaccinia Ankara, a highly attenuated vaccinia virus, expressing influenza nucleoprotein (MVA-NP) and HIV-1 gag (MVA-gag) was investigated. Restimulation of peripheral blood lymphocytes of healthy subjects with MVA-NP led to expansion of CTL with specificity for known NP epitopes. These CTL efficiently lysed NP peptide-pulsed targets and released interferon-gamma (IFN-gamma) on contact with epitope peptide. MVA-NP-stimulated CTL specific for the HLA-B8 epitope, NP380-88, stained with a tetrameric complex of HLA-B8 refolded with the NP380-88 peptide and anti-CD8 antibody on flow cytometry. CTL were also elicited from two HIV-1 seropositive donors by restimulation with MVA-HIV-1 gag and showed specificity for immunodominant gag epitopes. These data indicate that restimulation of human CTL with recombinant MVA is effective and suggest that MVA will elicit CTL responses in humans in vivo.

T lymphocyte responses in HIV-1 infection: implications for vaccine development

Substantial progress has been made over the past year in understanding the cellular immune response in HIV pathogenesis. Cytotoxic T lymphocytes play a critical role in establishing the level of viremia and virus-specific Th cell responses appear to affect the in vivo efficacy of cytotoxic T lymphocytes. Together, these new data provide important insights to refocus efforts aimed at immunotherapeutic interventions and vaccine development.

Frequency of Class I HLA-Restricted Anti-HIV CD8+ T Cells in Individuals Receiving Highly Active Antiretroviral Therapy (HAART)

Peptide/MHC tetrameric complexes were used to enumerate the frequency of HLA class I-restricted epitope-specific CD8+ T cells in 18 HLA-A*0201 HIV type 1-infected asymptomatic patients. HLA-A*0201 molecules were complexed to HIV Gag p17 (amino acids 77–85) and reverse transcriptase (amino acids 464–472) peptides, biotinylated, and bound to streptavidin-phycoerythrin to form tetramers. We show in this study that 17 of 18 HIV-1-infected asymptomatic patients have circulating frequencies of 1/50–1/1000 CD8+ T cells that recognize both Gag and Pol CTL epitopes or either epitope alone. The functional nature of these cells is open to interpretation, as we show that despite relatively high frequencies of fresh epitope-specific CD8+ T cells, variant epitope sequences in viral plasma progeny were rare. In addition, the majority of tetramer-positive cells did not display discernible fresh CTL activity; only after restimulation with specific peptide in culture was there an expansion of epitope-specific CD8+ cells, correlating with high CTL activity. These data suggest that fresh tetramer-stained cells probably represent memory precursors; we demonstrate, with the application of highly active antiretroviral therapy, that the interruption of chronic antigenic stimulation causes significant reductions in the frequency of these cells in five of six patients. In conclusion, this study provides evidence that persistently replicating viral populations are probably required to maintain high frequencies of HIV-1 epitope-specific CD8+ T cells in asymptomatic chronically infected individuals

Distinct recognition of non-clade B human immunodeficiency virus type 1 epitopes by cytotoxic T lymphocytes generated from donors infected in Africa

We present detailed studies of human immunodeficiency virus (HIV)-specific cytotoxic T-lymphocyte (CTL) responses to clade A or C HIV type 1 in three donors infected in East Africa. We define several novel non-clade B CTL epitopes, including some restricted by HLA alleles common in Africans. Although cross-clade CTL recognition of these epitopes does occur, recognition can also be highly clade specific.

Cytotoxic T cell responses to multiple conserved HIV epitopes in HIV-resistant prostitutes in Nairobi

Many people who remain persistently seronegative despite frequent HIV exposure have HIV-specific immune responses. The study of these may provide information about mechanisms of natural protective immunity to HIV-1. We describe the specificity of cytotoxic T lymphocyte responses to HIV in seronegative prostitutes in Nairobi who are apparently resistant to HIV infection. These women have had frequent exposure to a range of African HIV-1 variants, primarily clades A, C, and D, for up to 12 yr without becoming infected. Nearly half of them have CTL directed towards epitopes previously defined for B clade virus, which are largely conserved in the A and D clade sequences. Stronger responses are frequently elicited using the A or D clade version of an epitope to stimulate CTL, suggesting that they were originally primed by exposure to these virus strains. CTL responses have been defined to novel epitopes presented by HLA class I molecules associated with resistance to infection in the cohort, HLA-A*6802 and HLA-B18. Estimates using a modified interferon-gamma Elispot assay indicate a circulating frequency of CTL to individual epitopes of between 1:3,200 and 1:50,000. Thus, HIV-specific immune responses-particularly cross-clade CTL activity- may be responsible for protection against persistent HIV infection in these African women.

High frequency of skin-homing melanocyte-specific cytotoxic T lymphocytes in autoimmune vitiligo

Vitiligo is an autoimmune condition characterized by loss of epidermal melanocytes. Using tetrameric complexes of human histocompatibility leukocyte antigen (HLA) class I to identify antigen-specific T cells ex vivo, we observed high frequencies of circulating MelanA-specific, A*0201-restricted cytotoxic T lymphocytes (A2-MelanA tetramer+ CTLs) in seven of nine HLA-A*0201-positive individuals with vitiligo. Isolated A2-MelanA tetramer+ CTLs were able to lyse A*0201-matched melanoma cells in vitro and their frequency ex vivo correlated with extent of disease. In contrast, no A2-MelanA tetramer+ CTL could be identified ex vivo in all four A*0201-negative vitiligo patients or five of six A*0201-positive asymptomatic controls. Finally, we observed that the A2-MelanA tetramer+ CTLs isolated from vitiligo patients expressed high levels of the skin homing receptor, cutaneous lymphocyte-associated antigen, which was absent from the CTLs seen in the single A*0201-positive normal control. These data are consistent with a role of skin-homing autoreactive melanocyte-specific CTLs in causing the destruction of melanocytes seen in autoimmune vitiligo. Lack of homing receptors on the surface of autoreactive CTLs could be a mechanism to control peripheral tolerance in vivo.