Interleukin-4 Diminishes CD8+ Respiratory Syncytial Virus-Specific Cytotoxic T-Lymphocyte Activity In Vivo

Although interleukin-4 (IL-4) has been implicated in respiratory syncytial virus (RSV)-enhanced disease, the mechanism by which it modulates immune responses to primary RSV infection remains unclear. We have developed a system to investigate the effect of IL-4 on RSV epitope-specific cytotoxic T-lymphocyte (CTL) effector function in vivo, using an H-2K(d)-restricted RSV M2 epitope. BALB/c mice were infected with recombinant vaccinia virus (rVV) constructed to express RSV M2 protein (vvM2) alone or coexpress M2 and IL-4 (vvM2/IL-4). Splenocytes were assessed for M2-specific CTL activity in a direct (51)Cr release assay and intracellular gamma interferon (IFN-gamma) production by fluorescence-activated cell sorting analysis. Mice infected with vvM2/IL-4 had less M2-specific primary CTL activity than those infected with vvM2. M2-specific CTL frequency, as measured by M2 peptide-induced intracellular IFN-gamma production, was diminished in the vvM2/IL-4 group, partially accounting for the reduction of CTL activity. Mice immunized with either construct were challenged intravenously with RSV 4 weeks postimmunization, and direct CTL were measured. These results demonstrate that local expression of IL-4, at the time of antigen presentation, diminishes the cytolytic activity of primary and memory CD8(+) RSV-specific CTL responses in vivo.     

Association between Virus-Specific Cytotoxic T-Lymphocyte and Helper Responses in Human Immunodeficiency Virus Type 1 Infection

Cellular immune responses are thought to be an important antiviral host defense, but the relationship between virus-specific T-helper and cytotoxic-T-lymphocyte (CTL) responses has not been defined. To investigate a potential link between these responses, we examined functional human immunodeficiency virus type 1 (HIV-1)-specific memory CTL precursor frequencies and p24-specific proliferative responses in a cohort of infected untreated persons with a wide range of viral loads and CD4 cell counts. Levels of p24-specific proliferative responses positively correlated with levels of Gag-specific CTL precursors and negatively correlated with levels of plasma HIV-1 RNA. These data linking the levels of HIV-specific CTL with virus-specific helper cell function during chronic viral infection provide cellular immunologic parameters to guide therapeutic and prophylactic vaccine development.     

CD40 Ligand-Mediated Interactions Are Involved in the Generation of Memory CD8+ Cytotoxic T Lymphocytes (CTL) but Are Not Required for the Maintenance of CTL Memory following Virus Infection

CD8⁺ cytotoxic T lymphocytes (CTL) play a key role in the control of many virus infections, and the need for vaccines to elicit strong CD8⁺ T-cell responses in order to provide optimal protection in such infections is increasingly apparent. However, the mechanisms involved in the induction and maintenance of CD8⁺ CTL memory are currently poorly understood. In this study, we investigated the involvement of CD40 ligand (CD40L)-mediated interactions in these processes by analyzing the memory CTL response of CD40L-deficient mice following infection with lymphocytic choriomeningitis virus (LCMV). The maintenance of memory CD8⁺ CTL precursors (CTLp) at stable frequencies over time was not impaired in CD40L-deficient mice. By contrast, the initial generation of memory CTLp was affected. CD40L-deficient mice produced lower levels of CD8⁺ CTLp during the primary immune response to LCMV than did wild-type controls, despite the fact that the LCMV-specific effector CTL response of CD40L-deficient mice was indistinguishable from that of control animals. The differentiation of naïve CD8⁺ T cells into effector and memory CTL thus involves pathways that can be discriminated from each other by their requirement for CD40L-mediated interactions. Expression of CD40L by CTLp themselves was not an essential step during their expansion and differentiation from naïve CD8⁺ cells into memory CTLp; instead, the reduction in memory CTLp generation in CD40L-deficient mice was likely a consequence of defects in the CD4⁺ T-cell response mounted by these animals. These results thus suggest a previously unappreciated role for CD40L in the generation of CD8⁺ memory CTLp, the probable nature of which is discussed.     

Immunogenicity of a Human Immunodeficiency Virus (HIV) Polytope Vaccine Containing Multiple HLA A2 HIV CD8+ Cytotoxic T-Cell Epitopes

Compelling evidence now suggests that alphabeta CD8 cytotoxic T lymphocytes (CTL) have an important role in preventing human immunodeficiency virus (HIV) infection and/or slowing progression to AIDS. Here, we describe an HIV type 1 CTL polyepitope, or polytope, vaccine comprising seven contiguous minimal HLA A2-restricted CD8 CTL epitopes conjoined in a single artificial construct. Epitope-specific CTL lines derived from HIV-infected individuals were able to recognize every epitope within the construct, and HLA A2-transgenic mice immunized with a recombinant virus vaccine coding for the HIV polytope also generated CTL specific for different epitopes. Each epitope in the polytope construct was therefore processed and presented, illustrating the feasibility of the polytope approach for HIV vaccine design. By simultaneously inducing CTL specific for different epitopes, an HIV polytope vaccine might generate activity against multiple challenge isolates and/or preempt the formation of CTL escape mutants.     

Functionally Heterogeneous CD8+ T-Cell Memory Is Induced by Sendai Virus Infection of Mice

It has recently been established that memory CD8(+) T cells induced by viral infection are maintained at unexpectedly high frequencies in the spleen. While it has been established that these memory cells are phenotypically heterogeneous, relatively little is known about the functional status of these cells. Here we investigated the proliferative potential of CD8(+) memory T cells induced by Sendai virus infection. High frequencies of CD8(+) T cells specific for both dominant and subdominant Sendai virus epitopes persisted for many weeks after primary infection, and these cells were heterogeneous with respect to CD62L expression (approximately 20% CD62L(hi) and 80% CD62L(lo)). Reactivation of these cells with the antigenic peptide in vitro induced strong proliferation of antigen-specific CD8(+) T cells. However, approximately 20% of the cells failed to proliferate in vitro in response to a cognate peptide but nevertheless differentiated into effector cells and acquired full cytotoxic potential. These cells also expressed high levels of CD62L (in marked contrast to the CD62L(lo) status of the proliferating cells in the culture). Direct isolation of CD62L(hi) and CD62L(lo) CD8(+) T cells from memory mice confirmed the correlation of this marker with proliferative potential. Taken together, these data demonstrate that Sendai virus infection induces high frequencies of memory CD8(+) T cells that are highly heterogeneous in terms of both their phenotype and their proliferative potential.     

How Does Cross-Reactive Stimulation Affect the Longevity of CD8+ T Cell Memory?

Immunological memory—the ability to “remember” previously encountered pathogens and respond faster upon re-exposure is a central feature of the immune response in vertebrates. The cross-reactive stimulation hypothesis for the maintenance of memory proposes that memory cells specific for a given pathogen are maintained by cross-reactive stimulation following infections with other (unrelated) pathogens. We use mathematical models to examine the cross-reactive stimulation hypothesis. We find that: (i) the direct boosting of cross-reactive lineages only provides a very small increase in the average longevity of immunological memory; (ii) the expansion of cross-reactive lineages can indirectly increase the longevity of memory by reducing the magnitude of expansion of new naive lineages which occupy space in the memory compartment and are responsible for the decline in memory; (iii) cross-reactive stimulation results in variation in the rates of decline of different lineages of memory cells and enrichment of memory cell population for cells that are cross-reactive for the pathogens to which the individual has been exposed.     

The Memory Cytotoxic T-Lymphocyte (CTL) Response to Human Cytomegalovirus Infection Contains Individual Peptide-Specific CTL Clones That Have Undergone Extensive Expansion In Vivo

Human cytomegalovirus (HCMV)-specific CD8⁺ cytotoxic T lymphocytes (CTL) appear to play an important role in the control of virus replication and in protection against HCMV-related disease. We have previously reported high frequencies of memory CTL precursors (CTLp) specific to the HCMV tegument protein pp65 in the peripheral blood of healthy virus carriers. In some individuals, the CTL response to this protein is focused on only a single epitope, whereas in other virus carriers CTL recognized multiple epitopes which we identified by using synthetic peptides. We have analyzed the clonal composition of the memory CTL response to four of these pp65 epitopes by sequencing the T-cell receptors (TCR) of multiple independently derived epitope-specific CTL clones, which were derived by formal single-cell cloning or from clonal CTL microcultures. In all cases, we have observed a high degree of clonal focusing: the majority of CTL clones specific to a defined pp65 peptide from any one virus carrier use only one or two different TCRs at the level of the nucleotide sequence. Among virus carriers who have the same major histocompatibility complex (MHC) class I allele, we observed that CTL from different donors that recognize the same peptide-MHC complex often used the same Vβ segment, although other TCR gene segments and CDR3 length were not in general conserved. We have also examined the clonal composition of CTL specific to pp65 peptides in asymptomatic human immunodeficiency virus-infected individuals. We have observed a similarly focused peptide-specific CTL response. Thus, the large population of circulating HCMV peptide-specific memory CTLp in virus carriers in fact contains individual CTL clones that have undergone extensive clonal expansion in vivo.

CD8⁺ cytotoxic T lymphocytes (CTL) recognize virus-infected cells via the T-cell receptor (TCR), an αβ heterodimer that has specificity for the peptide antigen presented by major histocompatibility complex (MHC) class I molecules. During T-cell development in the thymus, the TCR β-chain is constructed by rearrangement of variable (V), diversity (D), and joining (J) gene segments, and the α-chain by rearrangement of V and J segments. Additional diversity is generated by imperfect joining of these segments, exonucleotide nibbling at the joins, and addition of non-germ line-encoded N-region nucleotides (25). The regions spanning the V-D-J and V-J joins constitute the hypervariable CDR3 regions which are thought to interact with the middle of the bound peptide and to account for approximately 50% of the TCR’s interaction with peptide (14, 15, 20). The α- and β-chain complementarity determining regions CDR1, which reside within the TCR V segments, are thought to interact with the N and C termini of a peptide that is bound to MHC. By contrast, Vα and Vβ CDR2s are thought to interact predominantly with the MHC itself (14, 15).Human cytomegalovirus (HCMV) is a ubiquitous betaherpesvirus that infects between 60 and 90% of individuals, depending on the population studied. After primary HCMV infection, the virus persists lifelong in a latent state in cells of the myeloid lineage and under the control of the immune system (5). HCMV reactivation can, however, cause serious disease in immunocompromised individuals, such as patients with advanced human immunodeficiency virus (HIV) infection (30) and patients who have undergone bone marrow transplantation (33). Evidence from animal models (32) and from studies of immunosuppressed humans (39) indicates that virus-specific CD8⁺ CTL have a role in protection against CMV disease.We previously studied in detail the HCMV-specific CTL response in healthy virus carriers. All seropositive donors had high frequencies of MHC-restricted HCMV-specific memory CTL precursors in peripheral blood and strongly recognized one of the viral tegument proteins, pp65. In some donors, the CTL response to this protein was highly focused, recognizing only a single epitope within pp65, whereas in others the CTL recognized multiple pp65 peptides (41 and unpublished data).The aim of this study was to examine the clonal composition of the memory CTL response to HCMV pp65 by determining how many different CTL clones are involved in the recognition of a given pp65 peptide. In order to do this, we analyzed the TCR α- and β-chain usage of multiple independently derived peptide-specific CTL clones from healthy virus carriers.Previous studies have examined the heterogeneity of the CTL response to other human virus infections within single subjects (2, 8, 11, 18, 19, 22, 38) or between different donors (2, 6, 8, 11, 23, 38). In the most extreme cases, a very high degree of TCR focusing has been seen: in a study of one HIV-positive individual’s CTL response to an HLA-B14-restricted HIV env peptide, the same TCR was used by 9 of 10 peptide-specific CTL clones, each derived at different time points over the course of 36 months (22). Similarly, multiple independent CTL clones specific to an HLA-B8-restricted Epstein-Barr virus (EBV) peptide derived from one virus carrier at one time point all used the same TCR (2). The CTL response to different human T-lymphotropic virus type 1 (HTLV-1) peptides has been observed to be oligoclonal within individual donors (38). However, in a variety of other human and mouse viral infections within a given individual, the repertoire of CTL specific for a given peptide has been highly heterogeneous (8, 11, 18, 19).The TCRs of CTL obtained from different donors that recognize the same peptide-MHC complex often show some conservation of gene segment usage, although they differ in hypervariable sequence. For example, Vβ segments and certain β-chain CDR3 motifs were conserved between TCR that recognized an HLA-A2-restricted influenza virus peptide in CTL clones derived from different donors (23); the same phenomenon has been seen for an HLA-B27 restricted influenza virus peptide (6) and an HLA-A11-restricted EBV peptide (8). A much higher degree of TCR conservation has also been seen; the same TCR α- and β-chain protein sequences were used by CTL clones from four of five unrelated donors that recognized an HLA-B8 restricted EBV peptide (2). In the case of HTLV-1, CTL from different donors that were specific to the same peptide used largely unrelated TCR (38).For all of the human viruses so far studied, the clonal composition of virus-specific CTL has only been examined for a very few viral peptide-MHC combinations, sometimes in only one donor or at only one time point. In this study, we have therefore examined multiple CTL clones specific to a total of four pp65 peptides, all restricted by three different HLA alleles. We have derived these clones from six healthy virus carriers at one to four time points up to 18 months apart. To identify CTL clonotypes for longitudinal studies and to determine whether HIV infection modifies the clonal composition of HCMV-specific CTL, we have also examined pp65-specific memory CTL in two asymptomatic HIV-infected subjects who are HCMV seropositive. For any given individual, whether HIV seropositive or seronegative, our results indicate that the memory CTL response to individual HCMV pp65 epitopes is highly focused and contains CTL clones that have undergone extensive expansion in vivo.     

Predominance of HLA-Restricted Cytotoxic T-Lymphocyte Responses to Serotype-Cross-Reactive Epitopes on Nonstructural Proteins following Natural Secondary Dengue Virus Infection

We examined the memory cytotoxic T-lymphocytic (CTL) responses of peripheral blood mononuclear cells (PBMC) obtained from patients in Thailand 12 months after natural symptomatic secondary dengue virus infection. In all four patients analyzed, CTLs were detected in bulk culture PBMC against nonstructural dengue virus proteins. Numerous CD4⁺ and CD8⁺ CTL lines were generated from the bulk cultures of two patients, KPP94-037 and KPP94-024, which were specific for NS1.2a (NS1 and NS2a collectively) and NS3 proteins, respectively. All CTL lines derived from both patients were cross-reactive with other serotypes of dengue virus. The CD8⁺ NS1.2a-specific lines from patient KPP94-037 were HLA B57 restricted, and the CD8⁺ NS3-specific lines from patient KPP94-024 were HLA B7 restricted. The CD4⁺ CTL lines from patient KPP94-037 were HLA DR7 restricted. A majority of the CD8⁺ CTLs isolated from patient KPP94-024 were found to recognize amino acids 221 to 232 on NS3. These results demonstrate that in Thai patients after symptomatic secondary natural dengue infections, CTLs are mainly directed against nonstructural proteins and are broadly cross-reactive.     

Respiratory Mucosal Immunization with Reovirus Serotype 1/L Stimulates Virus-Specific Humoral and Cellular Immune Responses, Including Double-Positive (CD4+/CD8+) T Cells

Respiratory virus infections are a serious health challenge. A number of models that examine the nature of the respiratory immune response to particular pathogens exist. However, many pathogens that stimulate specific immunity in the lung are frequently not effective immunogens at other mucosal sites. A pathogen that is an effective respiratory as well as gastrointestinal immunogen would allow studies of the interaction between the mucosal sites. Reovirus (respiratory enteric orphan virus) serotype 1 is known to be an effective gut mucosal immunogen and provides a potential model for the relationship between the respiratory and the gut mucosal immune systems. In this study, we demonstrate that intratracheal immunization with reovirus 1/Lang (1/L) in C3H mice resulted in high titers of virus in the respiratory tract-associated lymphoid tissue (RALT). High levels of reovirus-specific immunoglobulin A were determined in the RALT fragment cultures. The major responding components of the bronchus-associated lymphoid tissue were the CD8(+) T lymphocytes. Cells from draining lymph nodes also exhibited lysis of reovirus-infected target cells after an in vitro culture. The present study also describes the distribution of transiently present CD4(+)/CD8(+) double-positive (DP) T cells in the mediastinal and tracheobronchial lymph nodes of RALT. CD4(+)/CD8(+) DP lymphocytes were able to proliferate in response to stimulation with viral antigen in culture. Furthermore, these cells exhibited lysis of reovirus-infected target cells after in vitro culture. These results establish reovirus 1/L as a viable model for future investigation of the mucosal immune response in the RALT and its relationship to the common mucosal immune system.     

CD4+ Cytotoxic T-Lymphocyte Activity against Macrophages Pulsed with Bovine Herpesvirus 1 Polypeptides

Bovine herpesvirus 1 (BHV-1) induces immune suppression, but the mechanisms for suppression are not well identified. We examined the induction and activity of BHV-1-specific cytolytic CD4⁺ T lymphocytes (CTL) by stimulating peripheral blood mononuclear cells (PBMC) of cattle immunized with attenuated live BHV-1. Cytolytic effector cells were primarily CD4⁺ T lymphocytes and lysed autologous, but not allogeneic, macrophages infected with BHV-1 or pulsed with BHV-1 polypeptides. Apoptosis of BHV-1-expressing target cells was observed in CD4⁺ CTL assays by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) analysis. To determine if apoptosis was mediated by a perforin- or Fas-mediated pathway, EGTA, a known selective inhibitor of the perforin pathway, was used. EGTA did not inhibit CD4⁺-T-cell-mediated cytotoxic activity, but it did limit the NK cell cytotoxicity of virus infected cells. These findings support the concept that CD4⁺ CTL lyse macrophages pulsed with BHV-1 polypeptides through a Fas-mediated lytic pathway by inducing apoptosis in the target cells. The prominent cytotoxicity mediated by CD4⁺ CTL suggests a mechanism of selective removal of viral antigen-associated antigen-presenting cells.     

Costimulation of Naive CD8+ Lymphocytes Induces CD4 Expression and Allows Human Immunodeficiency Virus Type 1 Infection

Human immunodeficiency virus type 1 (HIV-1) infection requires cell surface expression of CD4. Costimulation of CD8⁺/CD4⁻ T lymphocytes by anti-CD3 and anti-CD28 antibodies or by allogeneic dendritic cells induced expression of CD4 and rendered these CD8 cells susceptible to HIV-1 infection. Naive CD45RA⁺ cells responded with greater expression of CD4 than did CD45RO⁺ cells. CD8⁺ lymphocytes derived from fetal or newborn sources exhibited a greater tendency to express CD4, consistent with their naive states. This mechanism of infection suggests HIV-induced perturbation of the CD8 arm of the immune response and could explain the generally rapid disease progression seen in HIV-infected children.     

Establishment and Characterization of Japanese Encephalitis Virus-Specific, Human CD4+ T-Cell Clones: Flavivirus Cross-Reactivity, Protein Recognition, and Cytotoxic Activity

We analyzed the CD4⁺ T-lymphocyte responses of two donors who had received Japanese encephalitis virus (JEV) vaccine 6 or 12 months earlier. Bulk culture proliferation assays showed that peripheral blood mononuclear cells (PBMC) responded to JEV antigens (Ag) but also responded at lower levels to West Nile virus (WNV) and dengue virus type 1, 2, and 4 (D1V, D2V, and D4V, respectively) Ag. Five JEV-specific CD4⁺ human T-cell clones and one subclone were established from PBMC of these two donors. Two clones responded to WNV Ag as well as to JEV Ag, whereas the others responded only to JEV Ag. Three of five CD4⁺ T-cell clones had JEV-specific cytotoxic activity and recognized E protein. The HLA restriction of the JEV-specific T-cell clones was examined. Three clones were HLA-DR4 restricted, one was HLA-DQ3 restricted, and the HLA restriction of one clone was not determined. T-cell receptor analysis showed that these clones expressed different T-cell receptors, suggesting that they originated from different T lymphocytes. These results indicate that JEV vaccine induces JEV-specific and flavivirus-cross-reactive CD4⁺ T lymphocytes and that these T lymphocytes recognize E protein. The functions and HLA restriction patterns of these T lymphocytes are, however, heterogeneous.     

Protective Mechanisms Induced by a Japanese Encephalitis Virus DNA Vaccine: Requirement for Antibody but Not CD8+ Cytotoxic T-Cell Responses

We have previously shown that a plasmid (pE) encoding the Japanese encephalitis virus (JEV) envelope (E) protein conferred a high level of protection against a lethal viral challenge. In the present study, we used adoptive transfer experiments and gene knockout mice to demonstrate that the DNA-induced E-specific antibody alone can confer protection in the absence of cytotoxic T-lymphocyte (CTL) functions. Plasmid pE administered by either intramuscular or gene gun injection produced significant E-specific antibodies, helper T (Th)-cell proliferative responses, and CTL activities. Animals receiving suboptimal DNA vaccination produced low titers of anti-E antibodies and were only partially or not protected from viral challenge, indicating a strong correlation between anti-E antibodies and the protective capacity. This observation was confirmed by adoptive transfer experiments. Intravenous transfer of E-specific antisera but not crude or T-cell-enriched immune splenocytes to sublethally irradiated hosts conferred protection against a lethal JEV challenge. Furthermore, experiments with gene knockout mice showed that DNA vaccination did not induce anti-E titers and protective immunity in Igmu(-/-) and I-Abeta(-/-) mice, whereas in CD8alpha(-/-) mice the pE-induced antibody titers and protective rate were comparable to those produced in the wild-type mice. Taken together, these results demonstrate that the anti-E antibody is the most critical protective component in this JEV challenge model and that production of anti-E antibody by pE DNA vaccine is dependent on the presence of CD4(+) T cells but independent of CD8(+) T cells.     

Both Memory and CD45RA+/CD62L+ Naive CD4+ T Cells Are Infected in Human Immunodeficiency Virus Type 1-Infected Individuals

Cellular activation is critical for the propagation of human immunodeficiency virus type 1 (HIV-1) infection. It has been suggested that truly naive CD4(+) T cells are resistant to productive HIV-1 infection because of their constitutive resting state. Memory and naive CD4(+) T-cell subsets from 11 HIV-1-infected individuals were isolated ex vivo by a combination of magnetic bead depletion and fluorescence-activated cell sorting techniques with stringent criteria of combined expression of CD45RA and CD62L to identify naive CD4(+) T-cell subsets. In all patients HIV-1 provirus could be detected within naive CD45RA+/CD62L+ CD4(+) T cells; in addition, replication-competent HIV-1 was isolated from these cells upon CD4(+) T-cell stimulation in tissue cultures. Memory CD4(+) T cells had a median of fourfold more replication-competent virus and a median of sixfold more provirus than naive CD4(+) T cells. Overall, there was a median of 16-fold more integrated provirus identified in memory CD4(+) T cells than in naive CD4(+) T cells within a given patient. Interestingly, there was a trend toward equalization of viral loads in memory and naive CD4(+) T-cell subsets in those patients who harbored CXCR4-using (syncytium-inducing) viruses. Within any given patient, there was no selective usage of a particular coreceptor by virus isolated from memory versus naive CD4(+) T cells. Our findings suggest that naive CD4(+) T cells may be a significant viral reservoir for HIV, particularly in those patients harboring CXCR4-using viruses.     

The Nucleocapsid Protein of Rift Valley Fever Virus Is a Potent Human CD8+ T Cell Antigen and Elicits Memory Responses

There is no licensed human vaccine currently available for Rift Valley Fever Virus (RVFV), a Category A high priority pathogen and a serious zoonotic threat. While neutralizing antibodies targeting the viral glycoproteins are protective, they appear late in the course of infection, and may not be induced in time to prevent a natural or bioterrorism-induced outbreak. Here we examined the immunogenicity of RVFV nucleocapsid (N) protein as a CD8⁺ T cell antigen with the potential for inducing rapid protection after vaccination. HLA-A*0201 (A2)-restricted epitopic determinants were identified with N-specific CD8⁺ T cells from eight healthy donors that were primed with dendritic cells transduced to express N, and subsequently expanded in vitro by weekly re-stimulations with monocytes pulsed with 59 15mer overlapping peptides (OLPs) across N. Two immunodominant epitopes, VT9 (VLSEWLPVT, N_121–129) and IL9 (ILDAHSLYL, N_165–173), were defined. VT9- and IL9-specific CD8⁺ T cells identified by tetramer staining were cytotoxic and polyfunctional, characteristics deemed important for viral control in vivo. These peptides induced specific CD8⁺ T cell responses in A2-transgenic mice, and more importantly, potent N-specific CD8⁺ T cell reactivities, including VT9- and IL9-specific ones, were mounted by mice after a booster vaccination with the live attenuated RVF MP-12. Our data suggest that the RVFV N protein is a potent human T cell immunogen capable of eliciting broad, immunodominant CD8⁺ T cell responses that are potentially protective. Understanding the immune responses to the nucleocapsid is central to the design of an effective RVFV vaccine irrespective of whether this viral protein is effective as a stand-alone immunogen or only in combination with other RVFV antigens.     

Residual Viral Replication during Antiretroviral Therapy Boosts Human Immunodeficiency Virus Type 1-Specific CD8+ T-Cell Responses in Subjects Treated Early after Infection

Human immunodeficiency virus type 1 (HIV-1)-infected subjects treated early after infection have preserved HIV-1-specific CD4+ T-cell function. We studied the effect of highly active antiretroviral therapy (HAART) on the frequency of HIV-1-specific CD8+ T cells in patients treated during early (n = 31) or chronic (n = 23) infection. The degree of viral suppression and time of initiation of treatment influenced the magnitude of the CD8+ T-cell response. HIV-1-specific CD8+ T cells can increase in number after HAART in subjects treated early after infection who have episodes of transient viremia.     

CD4+-T-Cell and CD20+-B-Cell Changes Predict Rapid Disease Progression after Simian-Human Immunodeficiency Virus Infection in Macaques

Simian-human immunodeficiency virus 89.6PD (SHIV_89.6PD) was pathogenic after intrarectal inoculation of rhesus macaques. Infection was achieved with a minimum of 2,500 tissue culture infectious doses of cell-free virus stock, and there was no evidence for transient viremia in animals receiving subinfectious doses by the intrarectal route. Some animals experienced rapid progression of disease characterized by loss of greater than 90% of circulating CD4⁺ T cells, sustained decreases in CD20⁺ B cells, failure to elicit virus-binding antibodies in plasma, and high levels of antigenemia. Slower-progressing animals had moderate but varying losses of CD4⁺ T cells; showed increases in circulating CD20⁺ B cells; mounted vigorous responses to antibodies in plasma, including neutralizing antibodies; and had low or undetectable levels of antigenemia. Rapid progression led to death within 30 weeks after intrarectal inoculation. Plasma antigenemia at 2 weeks after inoculation (P ≤ 0.002), B- and T-cell losses (P ≤ 0.013), and failure to seroconvert (P ≤ 0.005) were correlated statistically with rapid progression. Correlations were evident by 2 to 4 weeks after intrarectal SHIV inoculation, indicating that early events in the host-pathogen interaction determined the clinical outcome.     

Influenza Virus-Infected Epithelial Cells Present Viral Antigens to Antigen-Specific CD8+ Cytotoxic T Lymphocytes

We have investigated the mechanisms involved in the clearance of viral infection at the epithelium level by analyzing the activity of influenza virus-specific cytotoxic T lymphocytes (CTL) against virus-infected CMT-93 intestinal epithelial cells. Epithelial cells infected with live influenza virus effectively present viral antigens and were lysed by both homotypic and heterotypic influenza virus-specific CD8⁺ T cells. These results shed new light on the control of viral infection through the elimination of virus-infected epithelial cells by virus-specific CTL and demonstrate that CMT-93 cells furnish an appropriate model for in vitro evaluation of CTL activity against virus-infected epithelial cells.