Human herpesvirus 8 (HHV-8) is a recently discovered gammaherpesvirus that is the etiologic agent of Kaposi sarcoma (KS). IntroductionHuman herpesvirus 8 (HHV-8, also called Kaposi sarcomaassociated herpesvirus) is a recently discovered gammaherpesvirus that is the etiologic agent of Kaposi sarcoma (KS). 1 There is currently little knowledge of the clinical syndromes associated with primary HHV-8 infection or immune responses to the virus. Primary infection of adults with Epstein-Barr virus (EBV), the other human gammaherpesvirus, can commonly result in a prolonged, although self-limiting, symptomatic mononucleosis illness with long-term expansion of activated CD8 ϩ T cells and inhibition of T-cell reactivity to mitogens and viral antigens. [2][3][4][5][6][7][8] Recently, primary infection with HHV-8 was reported in one adult patient infected with human immunodeficiency virus-1 (HIV-1), which was associated with fever, arthralgia, and cervical lymphadenopathy. 9 It is not clear, however, whether these clinical signs and symptoms were related to the underlying HIV-1 infection in this patient.Virus-specific CD8 ϩ T cells are likely to be central in host control of primary HHV-8 infection. CD8 ϩ T cells specific for lytic cycle proteins of EBV, including structural, immediate-early (IE), and early proteins, 10-14 appear prominent in EBV mononucleosis. Thus, they may play a major role in limiting the primary phase of EBV infection. 3,11,15 Indeed, 0.5% to 6%, and as much as 44%, of circulating CD8 ϩ cells are specific for EBV lytic peptides by HLA tetramer staining during infectious mononucleosis. 16,17 It has also been shown that IE proteins are frequent targets for EBV-specific, CD8 ϩ T cells during persistent infection. 14,18 Similarly, infection of mice with murine herpesvirus 68 (MHV-68), another gammaherpesvirus, results in expansion of CD8 ϩ cytotoxic T-lymphocyte precursors (CTLp's) specific for MHV-68 lytic proteins. 19,20 These are detectable in both lymph nodes and at the site of local infection after primary infection in mice, 20 and could be involved in control of MHV-68 infection. 21,22 In contrast, only 2 studies to date have been able to detect CD8 ϩ T-cell reactivity specific for HHV-8. 23,24 Moreover, the levels of anti-HHV-8 CD8 ϩ T-cell responses measured by bulk CTL assays used in these cross-sectional studies were relatively low, with narrow specificity for different HHV-8 proteins.In this report, we conducted the first prospective study of HIV-1-negative adults with documented seroconversion to HHV-8 infection to identify clinical syndromes, potential immunosuppressive states and immune responses, and virologic markers related to this primary gammaherpesvirus infection. We used CTLp and single-cell interferon ␥ (IFN-␥) enumeration methods for more sensitive and quantitative assessment of anti-HHV-8 CD8 ϩ T-cell responses, and compared these for 5 lytic cycle proteins of HHV-8. The results show that primary HHV-8 infection is associated with nonspecific, mild symptoms and generates CD8 ϩ T-cell...

IntroductionHuman herpesvirus 8 (HHV-8; also termed Kaposi sarcomaassociated herpesvirus) is a gammaherpesvirus that is considered to be the causative agent of Kaposi sarcoma (KS), body cavity B-cell lymphoma, and multicentric Castleman disease. 1 T-cell immunity is thought to play an important role in control of HHV-8 infection and these associated diseases. [2][3][4][5] In this regard, we 2,3 and others 4 have demonstrated that major histocompatibility complex (MHC) class I-restricted, CD8 ϩ cytotoxic T lymphocytes (CTLs), and interferon ␥ (IFN-␥) responses are detectable in peripheral blood mononuclear cells (PBMCs) of HHV-8 ϩ individuals using recombinant vaccinia viruses expressing HHV-8 lytic and latent cycle proteins. These anti-HHV-8 T-cell responses are lower during human immunodeficiency virus type 1 (HIV-1) infection and may be involved in prevention of KS and other HHV-8-associated diseases.Support for the potential role of CD8 ϩ T-cell immunity in control of HHV-8 infection comes from several studies on immune control of acute and persistent infections with 2 other gammaherpesviruses, specifically, Epstein-Barr virus (EBV) and murine herpesvirus 68 (MHV-68). 6-10 Although EBV latency proteins can induce strong CD8 ϩ T-cell responses, 11 lytic cycle proteins are considered as major CD8 ϩ T-cell targets in both acute and persistent EBV infections. 12 Immunodominant epitopes restricted to different HLA class I alleles, which are important for our understanding of viral immunopathogenesis and development of appropriate vaccines, 13 have been determined for peptides derived from EBV structural proteins gp350 and gp85, and immediate-early (IE) and early proteins such as BZLF1, BRLF1, and BMLF1. [6][7][8][9] Compared to latency proteins, the frequency of CD8 ϩ T lymphocytes specific for peptides derived from lytic cycle proteins is higher in PBMCs of healthy virus carriers. 14 CD8 ϩ CTLs have also been demonstrated to secrete IFN-␥ in response to EBV lytic cycle antigens in seropositive individuals. 15 During primary EBV infectious mononucleosis, up to 60% of CD8 ϩ T cells circulating in blood are EBV-specific. 16 Furthermore, by use of a peptide-tetramer complex, Tan et al 17 have directly visualized from 0.5% to 6.6% of CD8 ϩ T blood cells in virus carriers that are specific for a single BMLF-1 epitope.In MHV-68 infection, lytic cycle proteins also induce CD8 ϩ T cell responses. 10,18,19 T cells specific for peptides derived from lytic cycle proteins dominate the acute phase of MHV-68 infection. 10,19 Moreover, vaccination with immunodominant CD8 ϩ T-cell epitopes derived from lytic cycle proteins of MHV-68 significantly reduces viral titers and the level of infected cells during acute infection. 20 We have tested CD8 ϩ T-cell reactivity to peptides derived from 5 HHV-8 lytic cycle proteins based on a prediction model for the HLA A*0201 motif in HHV-8-infected subjects to determine immunodominant epitopes to the virus. We chose HLA A*0201 because it is prevalent in a large percentage of the white populat...