Availability of a diversely avid CD8+ T cell repertoire specific for the subdominant HLA-A2-restricted HIV-1 Gag p2419-27 epitope

Interleukin-36gamma Mediates the In Vitro Activation of CD8+ T Cells from Patients Living with Chronic Human Immunodeficiency Virus-1 Infection

Interleukin-36 (IL-36) signaling plays an important role in promoting CD8+ T cell-mediated antitumor immune responses. The role of IL-36 signaling in CD8+ T cells that are involved in host immune responses during human immunodeficiency virus-1 (HIV-1) infection has not been characterized. Sixty-one patients living with chronic HIV-1 infection and 23 controls were enrolled in this study. The levels of IL-36 cytokine family members were measured by enzyme-linked immunosorbent assay. Purified CD8+ T cells were stimulated with recombinant IL-36gamma (1 or 10 ng/mL). The expression of inhibitory receptors, the secretion of cytotoxic molecules and interferon-gamma, and the mRNA levels of apoptosis-related ligands were assessed to evaluate the effect of IL-36gamma on CD8+ T cell function in vitro. There were no significant differences in IL-36alpha, IL-36beta, or IL-36 receptor antagonist levels between patients living with chronic HIV-1 infection and controls. Plasma IL-36gamma levels were reduced in patients living with chronic HIV-1 infection. Perforin, granzyme B, and granulysin secretion, as well as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL) mRNA expression, but not programmed death-1 (PD-1) or cytotoxic T lymphocyte-associated protein-4 (CTLA-4) expression was downregulated in CD8+ T cells from patients living with chronic HIV-1 infection. The addition of both 1 and 10 ng/mL IL-36gamma enhanced perforin, granzyme B, granulysin, and interferon-gamma secretion by CD8+ T cells without affecting PD-1/CTLA-4 or TRAIL/FasL mRNA expression in CD8+ T cells from patients living with chronic HIV-1 infection. The addition of 1 ng/mL IL-36gamma also promoted perforin and granzyme B secretion by HIV-1-specific CD8+ T cells from patients living with chronic HIV-1 infection. The reduced IL-36gamma levels in patients living with chronic HIV-1 infection might be insufficient for the activation of CD8+ T cells, leading to CD8+ T cell exhaustion.

Chimeric antigen receptors enable superior control of HIV replication by rapidly killing infected cells

Engineered T cells hold great promise to become part of an effective HIV cure strategy, but it is currently unclear how best to redirect T cells to target HIV. To gain insight, we generated engineered T cells using lentiviral vectors encoding one of three distinct HIV-specific T cell receptors (TCRs) or a previously optimized HIV-targeting chimeric antigen receptor (CAR) and compared their functional capabilities. All engineered T cells had robust, antigen-specific polyfunctional cytokine profiles when mixed with artificial antigen-presenting cells. However, only the CAR T cells could potently control HIV replication. TCR affinity enhancement did not augment HIV control but did allow TCR T cells to recognize common HIV escape variants. Interestingly, either altering Nef activity or adding additional target epitopes into the HIV genome bolstered TCR T cell anti-HIV activity, but CAR T cells remained superior in their ability to control HIV replication. To better understand why CAR T cells control HIV replication better than TCR T cells, we performed a time course to determine when HIV-specific T cells were first able to activate Caspase 3 in HIV-infected targets. We demonstrated that CAR T cells recognized and killed HIV-infected targets more rapidly than TCR T cells, which correlates with their ability to control HIV replication. These studies suggest that the speed of target recognition and killing is a key determinant of whether engineered T cell therapies will be effective against infectious diseases.

Persistent memory despite rapid contraction of circulating T Cell responses to SARS-CoV-2 mRNA vaccination

Introduction

While antibodies raised by SARS-CoV-2 mRNA vaccines have had compromised efficacy to prevent breakthrough infections due to both limited durability and spike sequence variation, the vaccines have remained highly protective against severe illness. This protection is mediated through cellular immunity, particularly CD8+ T cells, and lasts at least a few months. Although several studies have documented rapidly waning levels of vaccine-elicited antibodies, the kinetics of T cell responses have not been well defined.

Methods

Interferon (IFN)-γ enzyme-linked immunosorbent spot (ELISpot) assay and intracellular cytokine staining (ICS) were utilized to assess cellular immune responses (in isolated CD8+ T cells or whole peripheral blood mononuclear cells, PBMCs) to pooled peptides spanning spike. ELISA was performed to quantitate serum antibodies against the spike receptor binding domain (RBD).

Results

In two persons receiving primary vaccination, tightly serially evaluated frequencies of anti-spike CD8+ T cells using ELISpot assays revealed strikingly short-lived responses, peaking after about 10 days and becoming undetectable by about 20 days after each dose. This pattern was also observed in cross-sectional analyses of persons after the first and second doses during primary vaccination with mRNA vaccines. In contrast, cross-sectional analysis of COVID-19-recovered persons using the same assay showed persisting responses in most persons through 45 days after symptom onset. Cross-sectional analysis using IFN-γ ICS of PBMCs from persons 13 to 235 days after mRNA vaccination also demonstrated undetectable CD8+ T cells against spike soon after vaccination, and extended the observation to include CD4+ T cells. However, ICS analyses of the same PBMCs after culturing with the mRNA-1273 vaccine in vitro showed CD4+ and CD8+ T cell responses that were readily detectable in most persons out to 235 days after vaccination.

Discussion

Overall, we find that detection of spike-targeted responses from mRNA vaccines using typical IFN-γ assays is remarkably transient, which may be a function of the mRNA vaccine platform and an intrinsic property of the spike protein as an immune target. However, robust memory, as demonstrated by capacity for rapid expansion of T cells responding to spike, is maintained at least several months after vaccination. This is consistent with the clinical observation of vaccine protection from severe illness lasting months. The level of such memory responsiveness required for clinical protection remains to be defined.

Therapeutic Vaccines for the Treatment of HIV

Despite the success of anti-retroviral therapy (ART) in transforming HIV into a manageable disease, it has become evident that long-term ART will not eliminate the HIV reservoir and cure the infection. Alternative strategies to eradicate HIV infection, or at least induce a state of viral control and drug-free remission are therefore needed. Therapeutic vaccination aims to induce or enhance immunity to alter the course of a disease. In this review we provide an overview of the current state of therapeutic HIV vaccine research and summarize the obstacles that the field faces while highlighting potential ways forward for a strategy to cure HIV infection.

Role of CD8+ T Cells in the Selection of HIV-1 Immune Escape Mutations

Human immunodeficiency virus type-1 (HIV-1) infection represents one of the biggest public health problems worldwide. The immune response, mainly the effector mechanisms mediated by CD8⁺ T cells, induces the selection of mutations that allows the virus to escape the immune control. These mutations are generally selected within CD8⁺ T cell epitopes restricted to human leukocyte antigen class I (HLA-I), leading to a decrease in the presentation and recognition of the epitope, decreasing the activation of CD8⁺ T cells. However, these mutations may also affect cellular processing of the peptide or recognition by the T cell receptor. Escape mutations often carry a negative impact in viral fitness that is partially or totally compensated by the selection of compensatory mutations. The selection of either escape mutations or compensatory mutations may negatively affect the course of the infection. In addition, these mutations are a major barrier for the development of new therapeutic strategies focused on the induction of specific CD8⁺ T cell responses.

Identification and translational validation of novel mammaglobin-A CD8 T cell epitopes

Mammaglobin-A (MAM-A) is a secretory protein that is overexpressed in 80 % of human breast cancers. Its near-universal expression in breast cancer as well as its exquisite tissue specificity makes it an attractive target for a breast cancer prevention vaccine, and we recently initiated a phase 1 clinical trial of a MAM-A DNA vaccine. Previously, we have identified multiple MAM-A CD8 T cell epitopes using a reverse immunology candidate epitope approach based on predicted binding, but to date no attempt has been made to identify epitopes using an unbiased approach. In this study, we used human T cells primed in vitro with autologous dendritic cells expressing MAM-A to systematically identify MAM-A CD8 T cell epitopes. Using this unbiased approach, we identified three novel HLA-A2-restricted MAM-A epitopes. CD8 T cells specific for these epitopes are able to recognize and lyse human breast cancer cells in a MAM-A-specific, HLA-A2-dependent fashion. HLA-A2(+)/MAM-A(+) breast cancer patients have an increased prevalence of CD8 T cells specific for these novel MAM-A epitopes, and vaccination with a MAM-A DNA vaccine significantly increases the number of these CD8 T cells. The identification and translational validation of novel MAM-A epitopes has important implications for the ongoing clinical development of vaccine strategies targeting MAM-A. The novel MAM-A epitopes represent attractive targets for epitope-based vaccination strategies, and can also be used to monitor immune responses. Taken together these studies provide additional support for MAM-A as an important therapeutic target for the prevention and treatment of breast cancer.

HIV-Specific CD8(+) T Lymphocytes in Blood of Long-Term HIV-Infected Hemophilia Patients

Hemophilia patients infected with human immunodeficiency virus (HIV) 30 years ago show increased proportions of activated CD8⁺DR⁺ blood lymphocytes. We hypothesized that this might indicate a cellular immune response directed against HIV and might be the reason for long-term clinical stability of these patients. CD8⁺ peripheral blood lymphocytes (PBL) reactive with six HIV and two cytomegalovirus (CMV) pentamers were determined in heparinized whole blood. Additional lymphocyte subsets as well as plasma cytokines and HIV-1 load were studied. Long-term HIV-infected hemophilia patients with (n=15) or without (n=33) currently detectable HIV-1 load in the plasma showed higher proportions of CD8⁺ lymphocytes reactive with HIV (p<0.001) and CMV pentamers (p=0.010) than healthy individuals. The cellular anti-HIV response tended to be stronger and more polyclonal in patients during periods of viral replication than in patients with retroviral quiescence (p=0.077). Anti-HIV CD8⁺ lymphocyte responses were strongest in patients with high counts of activated CD8⁺DR⁺ T (r=0.353; p=0.014) and low CD19⁺ B lymphocyte counts (r=−0.472; p=0.001). Patients with or without HIV-1 viral load showed normal Th1 and Th2 plasma cytokine levels and high plasma interleukin-6 (versus healthy controls, p=0.001) and tumor necrosis factor-α (p=0.020). Hemophilia patients who have been living with HIV for more than 30 years showed a polyclonal CD8⁺ T-cell response against HIV and CMV. This cellular antiviral immune response was strongest during periods of HIV-1 replication and remained detectable during periods of HIV-1 quiescence. We hypothesize that the consistent cellular anti-HIV-1 response in combination with highly active antiretroviral therapy ensures stability and survival of these chronically HIV-1–infected hemophilia patients.

HLA-A*68:02-restricted Gag-specific cytotoxic T lymphocyte responses can drive selection pressure on HIV but are subdominant and ineffective

BACKGROUND

Human leukocyte allele (HLA) class I polymorphism has the greatest impact of human genetic variation on viral load set point. A substantial part of this effect is due to the action of HLA-B and HLA-C alleles. With few exceptions the role of HLA-A molecules in immune control of HIV is unclear.

METHODS

We here study HLA-A*68:02, one of the most highly prevalent HLA-A alleles in C-clade infected sub-Saharan African populations, and one that plays a prominent role in the HIV-specific CD8 T-cell responses made against the virus.

RESULTS

We define eight epitopes restricted by this allele and propose the peptide binding motif for HLA-A*68:02. Although one of these epitopes almost exactly overlaps an HLA-B*57-restricted epitope in Gag linked with immune control of HIV, this HLA-A*68:02-restricted Gag-TA10 response imposed only weak selection pressure on the virus and was not associated with significantly lower viral setpoint. The only HLA-A*68:02-restricted responses imposing strong selection pressure on HIV were in the flanking regions of Pol-EA8 and Pol-EA11 and within the Vpr-EV10 epitope (P  =  8 × 10). However, targeting of this latter epitope was associated with significantly higher viral loads (P  =  0.003), suggesting lack of efficacy.

CONCLUSION

This study is consistent with previous data showing that HLA-A-restricted Gag-specific responses can impose selection pressure on HIV. In the case of HLA-A*68:02 the Gag response is subdominant, and apparently has little impact in natural infection. However, these data suggest the potential for high frequency vaccine-induced Gag responses restricted by this allele to have significant antiviral efficacy in vaccine recipients.

Rapid perturbation in viremia levels drives increases in functional avidity of HIV-specific CD8 T cells

The factors determining the functional avidity and its relationship with the broad heterogeneity of antiviral T cell responses remain partially understood. We investigated HIV-specific CD8 T cell responses in 85 patients with primary HIV infection (PHI) or chronic (progressive and non-progressive) infection. The functional avidity of HIV-specific CD8 T cells was not different between patients with progressive and non-progressive chronic infection. However, it was significantly lower in PHI patients at the time of diagnosis of acute infection and after control of virus replication following one year of successful antiretroviral therapy. High-avidity HIV-specific CD8 T cells expressed lower levels of CD27 and CD28 and were enriched in cells with an exhausted phenotype, i.e. co-expressing PD-1/2B4/CD160. Of note, a significant increase in the functional avidity of HIV-specific CD8 T cells occurred in early-treated PHI patients experiencing a virus rebound after spontaneous treatment interruption. This increase in functional avidity was associated with the accumulation of PD-1/2B4/CD160 positive cells, loss of polyfunctionality and increased TCR renewal. The increased TCR renewal may provide the mechanistic basis for the generation of high-avidity HIV-specific CD8 T cells. These results provide insights on the relationships between functional avidity, viremia, T-cell exhaustion and TCR renewal of antiviral CD8 T cell responses.

CD8 T cells directed against virus are complex and functionally heterogeneous. One relevant component of CD8 T cells is their functional avidity which reflects their sensitivity to cognate antigens, i.e. how prone T cells are to respond when they encounter low doses of antigens. In patients with chronic and established HIV infection, we observed that the sensitivity of HIV-specific CD8 T cells was not different between patients with progressive or non-progressive disease. In contrast, the sensitivity of HIV-specific CD8 T cells was significantly lower in patients with early and recent HIV infection. Furthermore, CD8 T cells of high avidity were preferentially associated with a state of functional impairment known as exhaustion. Of interest, some patients treated with antiretroviral therapy during acute infection spontaneously interrupted their treatment and experienced a rebound of virus. In these patients, the avidity of HIV-specific CD8 T cells increased and this increase was associated to stronger cell exhaustion and greater renewal of the population of antiviral CD8 T cells, thus potentially providing the mechanistic basis for the generation of high-avidity CD8 T cells. Overall, our data suggest that rapid perturbation in viremia levels drove increases in the functional avidity of HIV-specific CD8 T cells.

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, N165-173), 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.

Functional avidity: a measure to predict the efficacy of effector T cells?

The functional avidity is determined by exposing T-cell populations in vitro to different amounts of cognate antigen. T-cells with high functional avidity respond to low antigen doses. This in vitro measure is thought to correlate well with the in vivo effector capacity of T-cells. We here present the multifaceted factors determining and influencing the functional avidity of T-cells. We outline how changes in the functional avidity can occur over the course of an infection. This process, known as avidity maturation, can occur despite the fact that T-cells express a fixed TCR. Furthermore, examples are provided illustrating the importance of generating T-cell populations that exhibit a high functional avidity when responding to an infection or tumors. Furthermore, we discuss whether criteria based on which we evaluate an effective T-cell response to acute infections can also be applied to chronic infections such as HIV. Finally, we also focus on observations that high-avidity T-cells show higher signs of exhaustion and facilitate the emergence of virus escape variants. The review summarizes our current understanding of how this may occur as well as how T-cells of different functional avidity contribute to antiviral and anti-tumor immunity. Enhancing our knowledge in this field is relevant for tumor immunotherapy and vaccines design.

Autologous HIV-1 clade-B Nef peptides elicit increased frequency, breadth and function of CD8+ T-cells compared to consensus peptides

OBJECTIVE

To determine the function and phenotype of CD8(+) T-cells targeting consensus and autologous sequences of entire HIV-1 Nef protein.

METHODS

Multiparameter flow cytometry-based analysis was used to evaluate the responses of two treatment naïve HIV-infected individuals, during primary and the chronic phases of infection.

RESULTS

A greater breadth and magnitude of CD8 IFN-γ responses to autologous compared to clade-B consensus peptides was observed in both subjects. Cross recognition between autologous and consensus peptides decreased in both subjects during progression from primary to chronic infection. The frequencies of TEMRA and TEM CD8(+) T-cells targeting autologous peptides were higher than those targeting consensus peptides and were more polyfunctional (IFN-γ(+) Gr-B(+) CD107a(+)).

CONCLUSIONS

Our data indicate superior sensitivity and specificity of autologous peptides. The functional and maturational aspects of "real" versus "cross-recognized" responses were also found to differ, highlighting the importance of a sequence-specific approach towards understanding HIV immune response.

Conservation of HIV-1 T cell epitopes across time and clades: validation of immunogenic HLA-A2 epitopes selected for the GAIA HIV vaccine

HIV genomic sequence variability has complicated efforts to generate an effective globally relevant vaccine. Regions of the viral genome conserved in sequence and across time may represent the "Achilles' heel" of HIV. In this study, highly conserved T-cell epitopes were selected using immunoinformatics tools combining HLA-A2 supertype binding predictions with relative global conservation. Analysis performed in 2002 on 10,803 HIV-1 sequences, and again in 2009, on 43,822 sequences, yielded 38 HLA-A2 epitopes. These epitopes were experimentally validated for HLA binding and immunogenicity with PBMCs from HIV-infected patients in Providence, Rhode Island, and/or Bamako, Mali. Thirty-five (92%) stimulated an IFNγ response in PBMCs from at least one subject. Eleven of fourteen peptides (79%) were confirmed as HLA-A2 epitopes in both locations. Validation of these HLA-A2 epitopes conserved across time, clades, and geography supports the hypothesis that such epitopes could provide effective coverage of virus diversity and would be appropriate for inclusion in a globally relevant HIV vaccine.

The influence of HLA on HIV-associated neurocognitive impairment in Anhui, China

Background

HLA-DR*04 was identified as a predictor of HIV-Associated neurocognitive disorder (HAND), low CD4 T-cell responses to HIV, and low plasma HIV RNA levels in a U.S. cohort. We hypothesized that low CD4 T-cell activation leads to poor immune control of HIV in the CNS, predisposing to HAND, but also provided fewer target (activated CD4 T-cells) for HIV replication. To assess the consistency of these HLA Class II associations in a new cohort and extend analysis to HLA Class I, HLA types, neurocognitive, and virologic status were examined in a cohort of former plasma donors in China.

Methods

178 HIV infected individuals in Anhui China, were HLA typed and underwent neurocognitive evaluations (using locally standardized norms), neuromedical, treatment and virologic assessments at baseline and at 12 months.

Results

HLA DR*04 was associated with a higher rate of baseline neurocognitive impairment (p = 0.04), neurocognitive decline (p = 0.04), and lower levels of HIV RNA in plasma (p = 0.05). HLA Class I alleles (B*27,57,58,A*03,33) that specify a CD8 T-cell response to conserved HIV sequences were neuroprotective, associated with less impairment at baseline (p = 0.037), at month 012 (p = 0.013) and less neurocognitive decline (p = 0.023) in the interval. Consistent with the theory that effective CD8 T-cell responses require CD4 T-cell support, the HLA DR*04 allele reduced the neuroprotective effect of the Class I alleles. The presence of HLA-DR*04 and the Alzheimer associated allele ApoE4 in the same individual had a synergistic negative effect on cognition (p = 0.003).

Conclusions

Despite major background differences between U.S. and Anhui China cohorts, HLA DR*04 predicted neurocognitive impairment and lower plasma HIV RNA levels in both populations. HLA Class I alleles associated with CD8 T-cell control of HIV were associated with protection from HAND, but protection was reduced in the presence of HLA-DR*04.

A high-throughput single-cell analysis of human CD8⁺ T cell functions reveals discordance for cytokine secretion and cytolysis

CD8+ T cells are a key component of the adaptive immune response to viral infection. An inadequate CD8+ T cell response is thought to be partly responsible for the persistent chronic infection that arises following infection with HIV. It is therefore critical to identify ways to define what constitutes an adequate or inadequate response. IFN-γ production has been used as a measure of T cell function, but the relationship between cytokine production and the ability of a cell to lyse virus-infected cells is not clear. Moreover, the ability to assess multiple CD8+ T cell functions with single-cell resolution using freshly isolated blood samples, and subsequently to recover these cells for further functional analyses, has not been achieved. As described here, to address this need, we have developed a high-throughput, automated assay in 125-pl microwells to simultaneously evaluate the ability of thousands of individual CD8+ T cells from HIV-infected patients to mediate lysis and to produce cytokines. This concurrent, direct analysis enabled us to investigate the correlation between immediate cytotoxic activity and short-term cytokine secretion. The majority of in vivo primed, circulating HIV-specific CD8+ T cells were discordant for cytolysis and cytokine secretion, notably IFN-γ, when encountering cognate antigen presented on defined numbers of cells. Our approach should facilitate determination of signatures of functional variance among individual effector CD8+ T cells, including those from mucosal samples and those induced by vaccines.

HLA-A*7401-mediated control of HIV viremia is independent of its linkage disequilibrium with HLA-B*5703

The potential contribution of HLA-A alleles to viremic control in chronic HIV type 1 (HIV-1) infection has been relatively understudied compared with HLA-B. In these studies, we show that HLA-A*7401 is associated with favorable viremic control in extended southern African cohorts of >2100 C-clade-infected subjects. We present evidence that HLA-A*7401 operates an effect that is independent of HLA-B*5703, with which it is in linkage disequilibrium in some populations, to mediate lowered viremia. We describe a novel statistical approach to detecting additive effects between class I alleles in control of HIV-1 disease, highlighting improved viremic control in subjects with HLA-A*7401 combined with HLA-B*57. In common with HLA-B alleles that are associated with effective control of viremia, HLA-A*7401 presents highly targeted epitopes in several proteins, including Gag, Pol, Rev, and Nef, of which the Gag epitopes appear immunodominant. We identify eight novel putative HLA-A*7401-restricted epitopes, of which three have been defined to the optimal epitope. In common with HLA-B alleles linked with slow progression, viremic control through an HLA-A*7401-restricted response appears to be associated with the selection of escape mutants within Gag epitopes that reduce viral replicative capacity. These studies highlight the potentially important contribution of an HLA-A allele to immune control of HIV infection, which may have been concealed by a stronger effect mediated by an HLA-B allele with which it is in linkage disequilibrium. In addition, these studies identify a factor contributing to different HIV disease outcomes in individuals expressing HLA-B*5703.

Mycobacterium tuberculosis directs immunofocusing of CD8+ T cell responses despite vaccination

Vaccines that elicit T cell responses try to mimic protective memory T cell immunity after infection by increasing the frequency of Ag-specific T cells in the immune repertoire. However, the factors that determine immunodominance during infection and after vaccination and the relation between immunodominance and protection are incompletely understood. We previously identified TB10.4(20-28) as an immunodominant epitope recognized by H2-K(d)-restricted CD8(+) T cells after M. tuberculosis infection. Here we report a second epitope, EspA(150-158), that is recognized by a substantial number of pulmonary CD8(+) T cells. The relative abundance of these T cells in the naive repertoire only partially predicts their relative frequency after M. tuberculosis infection. Furthermore, although vaccination with recombinant vaccinia virus expressing these epitopes changes their relative immunodominance in the preinfection T cell repertoire, this change is transient after challenge with M. tuberculosis. We speculate that factors intrinsic to the chronic nature of M. tuberculosis infection establishes the hierarchy of immunodominance and may explain the failure of some vaccines to provide protection.

Profile of a serial killer: cellular and molecular approaches to study individual cytotoxic T-cells following therapeutic vaccination

T-cell vaccination may prevent or treat cancer and infectious diseases, but further progress is required to increase clinical efficacy. Step-by-step improvements of T-cell vaccination in phase I/II clinical studies combined with very detailed analysis of T-cell responses at the single cell level are the strategy of choice for the identification of the most promising vaccine candidates for testing in subsequent large-scale phase III clinical trials. Major aims are to fully identify the most efficient T-cells in anticancer therapy, to characterize their TCRs, and to pinpoint the mechanisms of T-cell recruitment and function in well-defined clinical situations. Here we discuss novel strategies for the assessment of human T-cell responses, revealing in part unprecedented insight into T-cell biology and novel structural principles that govern TCR-pMHC recognition. Together, the described approaches advance our knowledge of T-cell mediated-protection from human diseases.

Enhanced induction of HIV-specific cytotoxic T lymphocytes by dendritic cell-targeted delivery of SOCS-1 siRNA

Dendritic cells (DCs) are potent antigen-presenting cells that play a critical role in the activation of T cells. RNA interference (RNAi)-mediated silencing of negative immunoregulatory molecules expressed by DCs may provide a strategy to enhance the potency of DC-based vaccines and immunotherapy. Ablation of suppressor of cytokine signaling-1 (SOCS-1) in antigen-presenting cells has been shown to enhance cellular immune response in mice. Here, we used a previously reported DC-targeting approach to deliver small interfering RNA (siRNA) against SOCS-1 to human myeloid-derived DCs (MDDCs). SOCS1-silencing in MDDCs resulted in enhanced cytokine responses to lipopolysaccharide (LPS) and a strong mixed-lymphocyte reaction. Moreover, only DCs treated with SOCS-1 siRNA, and not controls, elicited strong primary in vitro responses to well-characterized HLA-A*0201-restricted Melan-A/MART-1 and human immunodeficiency virus (HIV) Gag epitopes in naive CD8(+) T cells from healthy donors. Finally, stimulation of CD8(+) T cells from HIV-seropositive subjects with SOCS1-silenced DCs resulted in an augmented polyfunctional cytotoxic T-lymphocyte (CTL) response, suggesting that SOCS-1 silencing can restore functionally compromised T cells in HIV infection. Collectively, these results demonstrate the feasibility of DC3-9dR-mediated manipulation of DC function to enhance DC immunogenicity for potential vaccine or immunotherapeutic applications.

Generation of robust CD8+ T-cell responses against subdominant epitopes in conserved regions of HIV-1 by repertoire mining with mimotopes

HLA-A 0201-restricted virus-specific CD8(+) CTL do not appear to control HIV effectively in vivo. To enhance the immunogenicity of a highly conserved subdominant epitope, TV9 (TLNAWVKVV, p24 Gag(19-27)), mimotopes were designed by screening a large combinatorial nonapeptide library with TV9-specific CTL primed in vitro from healthy donors. A mimic peptide with a low binding affinity to HLA-A 0201, TV9p6 (KINAWIKVV), was studied further. Parallel cultures of in vitro-primed CTL showed that TV9p6 consistently activated cross-reactive and equally functional CTL as measured by cytotoxicity, cytokine production and suppression of HIV replication in vitro. Comparison of TCRB gene usage between CTL primed from the same donors with TV9 or TV9p6 revealed a degree of clonal overlap in some cases and an example of a conserved TCRB sequence encoded distinctly at the nucleotide level between individuals (a "public" TCR); however, in the main, distinct clonotypes were recruited by each peptide antigen. These findings indicate that mimotopes can mobilize functional cross-reactive clonotypes that are less readily recruited from the naïve T-cell pool by the corresponding WT epitope. Mimotope-induced repertoire diversification could potentially override subdominance under certain circumstances and enhance vaccine-induced responses to conserved but poorly immunogenic determinants within the HIV proteome.

Epitope mapping of HIV-specific CD8+ T cells in a cohort dominated by clade A1 infection

BACKGROUND

CD8+ T cell responses are often detected at large magnitudes in HIV-infected subjects, and eliciting these responses is the central aim of many HIV-1 vaccine strategies. Population differences in CD8+ T cell epitope specificity will need to be understood if vaccines are to be effective in multiple geographic regions.

METHODOLOGY/PRINCIPAL FINDINGS

In a large Kenyan cohort, we compared responsive CD8+ T cell HIV-1 Env overlapping peptides (OLPs) to Best Defined Epitopes (BDEs), many of which have been defined in clade B infection. While the majority of BDEs (69%) were recognized in this population, nearly half of responsive OLPs (47%) did not contain described epitopes. Recognition frequencies of BDEs were inversely correlated to epitopic sequence differences between clade A1 and BDE (P = 0.019), and positively selected residues were more frequent in "new" OLPs (without BDEs). We assessed the impact of HLA and TAP binding on epitope recognition frequencies, focusing on predicted and actual epitopes in the HLA B7 supertype.

CONCLUSIONS/SIGNIFICANCE

Although many previously described CD8 epitopes were recognized, several novel CD8 epitopes were defined in this population, implying that epitope mapping efforts have not been completely exhausted. Expansion of these studies will be critical to understand population differences in CD8 epitope recognition.

Primary human immunodeficiency virus type 1-specific CD8+ T-cell responses induced by myeloid dendritic cells

Induction of an antigenically broad and vigorous primary T-cell immune response by myeloid dendritic cells (DC) in blood and tissues could be important for an effective prophylactic or therapeutic vaccine to human immunodeficiency virus type 1 (HIV-1). Here we show that a primary CD8(+) T-cell response can be induced by HIV-1 peptide-loaded DC derived from blood monocytes of HIV-1-negative adults and neonates (moDC) and by Langerhans cells (LC) and interstitial, dermal-intestinal DC (idDC) derived from CD34(+) stem cells of neonatal cord blood. Optimal priming of single-cell gamma interferon (IFN-gamma) production by CD8(+) T cells required CD4(+) T cells and was broadly directed to multiple regions of Gag, Env, and Nef that corresponded to known and predicted major histocompatibility complex class I epitopes. Polyfunctional CD8(+) T-cell responses, defined as single-cell production of more than one cytokine (IFN-gamma, interleukin 2, or tumor necrosis factor alpha), chemokine (macrophage inhibitory factor 1beta), or cytotoxic degranulation marker CD107a, were primed by moDC, LC, and idDC to HIV-1 Gag and reverse transcriptase epitopes, as well as to Epstein-Barr virus and influenza A virus epitopes. Thus, three major types of blood and tissue myeloid DC targeted by HIV-1, i.e., moDC, LC, and idDC, can prime multispecific, polyfunctional CD8(+) T-cell responses to HIV-1 and other viral antigens.