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Jason M Brenchley

Publications and source records attributed to Jason M Brenchley.

At least 19 recordsLinked to original sources
PubMed2006

Acquisition of direct antiviral effector functions by CMV-specific CD4+ T lymphocytes with cellular maturation.

The role of CD4+ T cells in the control of persistent viral infections beyond the provision of cognate help remains unclear. We used polychromatic flow cytometry to evaluate the production of the cytokines interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-2, the chemokine macrophage inflammatory protein (MIP)-1beta, and surface mobilization of the degranulation marker CD107a by CD4+ T cells in response to stimulation with cytomegalovirus (CMV)-specific major histocompatibility complex class II peptide epitopes. Surface expression of CD45RO, CD27, and CD57 on responding cells was used to classify CD4+ T cell maturation. The functional profile of virus-specific CD4+ T cells in chronic CMV infection was unique compared with that observed in other viral infections. Salient features of this profile were: (a) the simultaneous production of MIP-1beta, TNF-alpha, and IFN-gamma in the absence of IL-2; and (b) direct cytolytic activity associated with surface mobilization of CD107a and intracellular expression of perforin and granzymes. This polyfunctional profile was associated with a terminally differentiated phenotype that was not characterized by a distinct clonotypic composition. Thus, mature CMV-specific CD4+ T cells exhibit distinct functional properties reminiscent of antiviral CD8+ T lymphocytes.

Adult↗
PubMed2006

Microbial translocation is a cause of systemic immune activation in chronic HIV infection.

Chronic activation of the immune system is a hallmark of progressive HIV infection and better predicts disease outcome than plasma viral load, yet its etiology remains obscure. Here we show that circulating microbial products, probably derived from the gastrointestinal tract, are a cause of HIV-related systemic immune activation. Circulating lipopolysaccharide, which we used as an indicator of microbial translocation, was significantly increased in chronically HIV-infected individuals and in simian immunodeficiency virus (SIV)-infected rhesus macaques (P <or= 0.002). We show that increased lipopolysaccharide is bioactive in vivo and correlates with measures of innate and adaptive immune activation. Effective antiretroviral therapy seemed to reduce microbial translocation partially. Furthermore, in nonpathogenic SIV infection of sooty mangabeys, microbial translocation did not seem to occur. These data establish a mechanism for chronic immune activation in the context of a compromised gastrointestinal mucosal surface and provide new directions for therapeutic interventions that modify the consequences of acute HIV infection.

Animals↗
PubMed2006

PD-1 is a regulator of virus-specific CD8+ T cell survival in HIV infection.

Here, we report on the expression of programmed death (PD)-1 on human virus-specific CD8(+) T cells and the effect of manipulating signaling through PD-1 on the survival, proliferation, and cytokine function of these cells. PD-1 expression was found to be low on naive CD8(+) T cells and increased on memory CD8(+) T cells according to antigen specificity. Memory CD8(+) T cells specific for poorly controlled chronic persistent virus (HIV) more frequently expressed PD-1 than memory CD8(+) T cells specific for well-controlled persistent virus (cytomegalovirus) or acute (vaccinia) viruses. PD-1 expression was independent of maturational markers on memory CD8(+) T cells and was not directly associated with an inability to produce cytokines. Importantly, the level of PD-1 surface expression was the primary determinant of apoptosis sensitivity of virus-specific CD8(+) T cells. Manipulation of PD-1 led to changes in the ability of the cells to survive and expand, which, over several days, affected the number of cells expressing cytokines. Therefore, PD-1 is a major regulator of apoptosis that can impact the frequency of antiviral T cells in chronic infections such as HIV, and could be manipulated to improve HIV-specific CD8(+) T cell numbers, but possibly not all functions in vivo.

Antigens, CD↗
PubMed2006

Degeneracy and repertoire of the human HIV-1 Gag p17(77-85) CTL response.

CD8+ CTL responses are important for the control of HIV-1 infection. The immunodominant HLA-A2-restricted Gag epitope, SLYNTVATL (SL9), is considered to be a poor immunogen because reactivity to it is rare in acute infection despite its paradoxical dominance in patients with chronic infection. We have previously reported SL9 to be a help-independent epitope in that it primes highly activated CTLs ex vivo from CD8+ T cells of seronegative healthy donors. These CTLs produce sufficient cytokines for extended autocrine proliferation but are sensitive to activation-induced cell death, which may cause them to be eliminated by a proinflammatory cytokine storm. Here we identified an agonist variant of the SL9 peptide, p41 (SLYNTVAAL), by screening a large synthetic combinatorial nonapeptide library with ex vivo-primed SL9-specific T cells. p41 invariably immunized SL9-cross-reactive CTLs from other donors ex vivo and H-2Db beta2m double knockout mice expressing a chimeric HLA-A*0201/H2-Db MHC class I molecule. Parallel human T cell cultures showed p41-specific CTLs to be less fastidious than SL9-CTLs in the level of costimulation required from APCs and the need for exogenous IL-2 to proliferate (help dependent). TCR sequencing revealed that the same clonotype can develop into either help-independent or help-dependent CTLs depending on the peptide used to activate the precursor CD8+ T cells. Although Ag-experienced SL9-T cells from two patients were also sensitive to IL-2-mediated cell death upon restimulation in vitro, the loss of SL9 T cells was minimized with p41. This study suggests that agonist sequences can replace aberrantly immunogenic native epitopes for the rational design of vaccines targeting HIV-1.

Amino Acid Sequence↗
PubMed2006

Maintenance of HIV-specific CD4+ T cell help distinguishes HIV-2 from HIV-1 infection.

Unlike HIV-1-infected people, most HIV-2-infected subjects maintain a healthy CD4+ T cell count and a strong HIV-specific CD4+ T cell response. To define the cellular immunological correlates of good prognosis in HIV-2 infection, we conducted a cross-sectional study of HIV Gag-specific T cell function in HIV-1- and HIV-2-infected Gambians. Using cytokine flow cytometry and lymphoproliferation assays, we show that HIV-specific CD4+ T cells from HIV-2-infected individuals maintained proliferative capacity, were not terminally differentiated (CD57-), and more frequently produced IFN-gamma or IL-2 than CD4+ T cells from HIV-1-infected donors. Polyfunctional (IFN-gamma+/IL-2+) HIV-specific CD4+ T cells were found exclusively in HIV-2+ donors. The disparity in CD4+ T cell responses between asymptomatic HIV-1- and HIV-2-infected subjects was not associated with differences in the proliferative capacity of HIV-specific CD8+ T cells. This study demonstrates that HIV-2-infected donors have a well-preserved and functionally heterogeneous HIV-specific memory CD4+ T cell response that is associated with delayed disease progression in the majority of infected people.

CD4 Lymphocyte Count↗
PubMed2006

HIV disease: fallout from a mucosal catastrophe?

The pathogenesis of human immunodeficiency virus has long been thought to center on a gradual depletion of CD4(+) T cells, with an average of 100 cells lost per microliter of blood per year. However, studies of macaques infected with simian immunodeficiency virus and humans infected with human immunodeficiency virus have shown that the infection rapidly kills most CD4(+) T cells at mucosal surfaces. Although most CD4(+) T cells reside at these sites, the magnitude of this assault on the immune system is not reflected in the peripheral blood. Here we consider models of human immunodeficiency virus disease pathogenesis given those findings and propose a hypothesis to account for particular aspects of the disease during the chronic phase of infection that can be directly attributed to early depletion of mucosal CD4(+) T cells.

Animals↗
PubMed2006

Lymphatic tissue fibrosis is associated with reduced numbers of naive CD4+ T cells in human immunodeficiency virus type 1 infection.

The organized structure of lymphatic tissues (LTs) constitutes a microenvironment referred to as a niche that plays a critical role in immune system homeostasis by promoting cellular interactions and providing access to cytokines and growth factors on which cells are dependent for survival, proliferation, and differentiation. In chronic human immunodeficiency virus type 1 (HIV-1) infection, immune activation and inflammation result in collagen deposition and disruption of this LT niche. We have previously shown that these fibrotic changes correlate with a reduction in the size of the total population of CD4+ T cells. We now show that this reduction is most substantial within the naïve CD4+ T-cell population and is in proportion to the extent of LT collagen deposition in HIV-1 infection. Thus, the previously documented depletion of naïve CD4+ T cells in LTs in HIV-1 infection may be a consequence not only of a decreased supply of thymic emigrants or chronic immune activation but also of the decreased ability of those cells to survive in a scarred LT niche. We speculate that LT collagen deposition might therefore limit repopulation of naïve CD4+ T cells with highly active antiretroviral therapy, and thus, additional treatments directed to limiting or reversing inflammatory damage to the LT niche could potentially improve immune reconstitution.

Adult↗
PubMed2006

Preferential infection shortens the life span of human immunodeficiency virus-specific CD4+ T cells in vivo.

CD4(+) T-cell help is essential for effective immune responses to viruses. In human immunodeficiency virus (HIV) infection, CD4(+) T cells specific for HIV are infected by the virus at higher frequencies than other memory CD4(+) T cells. Here, we demonstrate that HIV-specific CD4(+) T cells are barely detectable in most infected individuals and that the corresponding CD4(+) T cells exhibit an immature phenotype compared to both cytomegalovirus (CMV)-specific CD4(+) T cells and other memory CD4(+) T cells. However, in two individuals, we observed a rare and diametrically opposed pattern in which HIV-specific CD4(+) T-cell populations of large magnitude exhibited a terminally differentiated immunophenotype; these cells were not preferentially infected in vivo. Clonotypic analysis revealed that the HIV-specific CD4(+) T cells from these individuals were cross-reactive with CMV. Thus, preferential infection can be circumvented in the presence of cross-reactive CD4(+) T cells driven to maturity by coinfecting viral antigens, and this physical proximity rather than activation status per se is an important determinant of preferential infection based on antigen specificity. These data demonstrate that preferential infection reduces the life span of HIV-specific CD4(+) T cells in vivo and thereby compromises the generation of effective immune responses to the virus itself; further, this central feature in the pathophysiology of HIV infection can be influenced by the cross-reactivity of responding CD4(+) T cells.

CD4-Positive T-Lymphocytes↗
PubMed2005

T-cell responses directed against multiple HLA-A*0201-restricted epitopes derived from Wilms' tumor 1 protein in patients with leukemia and healthy donors: identification, quantification, and characterization.

PURPOSE: Antigens derived from the Wilms' tumor (WT1) protein, which is overexpressed in leukemias, are attractive targets for immunotherapy. Four HLA-A*0201-restricted WT1-derived epitopes have been identified: WT37, WT126, WT187, and WT235. We determined the natural immunogenecity of these antigens in patients with hematologic malignancies and healthy donor. EXPERIMENTAL DESIGN: To detect very low frequencies of WT1-specific CD8+ T cells, we used quantitative reverse transcription-PCR to measure IFN-gamma mRNA production by WT1 peptide-pulsed CD8+ T cells from 12 healthy donors, 8 patients with chronic myelogenous leukemia, 6 patients with acute myelogenous leukemia, and 8 patients with acute lymphoblastic leukemia. RESULTS: Responses were detected in 5 of 8 chronic myelogenous leukemia patients, 4 of 6 patients with acute myelogenous leukemia, and 7 of 12 healthy donors. No responses were detected in patients with acute lymphoblastic leukemia. The magnitude and extent of these CD8+ T-cell responses was greater in patients with myeloid leukemias than in healthy donors. Clonotypic analysis of WT1-specific CD8+ T cells directly ex vivo in one case showed that this naturally occurring population was oligoclonal. Using fluorescent peptide-MHC class I tetramers incorporating mutations in the alpha3 domain (D227K/T228A) that abrogate binding to the CD8 coreceptor, we were able to confirm the presence of high-avidity T-cell clones within the antigen-specific repertoire. CONCLUSION: The natural occurrence of high-avidity WT1-specific CD8+ T cells in the periphery could facilitate vaccination strategies to expand immune responses against myeloid leukemias.

Amino Acid Sequence↗
PubMed2005

Avidity for antigen shapes clonal dominance in CD8+ T cell populations specific for persistent DNA viruses.

The forces that govern clonal selection during the genesis and maintenance of specific T cell responses are complex, but amenable to decryption by interrogation of constituent clonotypes within the antigen-experienced T cell pools. Here, we used point-mutated peptide-major histocompatibility complex class I (pMHCI) antigens, unbiased TCRB gene usage analysis, and polychromatic flow cytometry to probe directly ex vivo the clonal architecture of antigen-specific CD8(+) T cell populations under conditions of persistent exposure to structurally stable virus-derived epitopes. During chronic infection with cytomegalovirus and Epstein-Barr virus, CD8(+) T cell responses to immunodominant viral antigens were oligoclonal, highly skewed, and exhibited diverse clonotypic configurations; TCRB CDR3 sequence analysis indicated positive selection at the protein level. Dominant clonotypes demonstrated high intrinsic antigen avidity, defined strictly as a physical parameter, and were preferentially driven toward terminal differentiation in phenotypically heterogeneous populations. In contrast, subdominant clonotypes were characterized by lower intrinsic avidities and proportionately greater dependency on the pMHCI-CD8 interaction for antigen uptake and functional sensitivity. These findings provide evidence that interclonal competition for antigen operates in human T cell populations, while preferential CD8 coreceptor compensation mitigates this process to maintain clonotypic diversity. Vaccine strategies that reconstruct these biological processes could generate T cell populations that mediate optimal delivery of antiviral effector function.

Amino Acid Sequence↗
PubMed2005

Interaction between the CD8 coreceptor and major histocompatibility complex class I stabilizes T cell receptor-antigen complexes at the cell surface.

The off-rate (k(off)) of the T cell receptor (TCR)/peptide-major histocompatibility complex class I (pMHCI) interaction, and hence its half-life, is the principal kinetic feature that determines the biological outcome of TCR ligation. However, it is unclear whether the CD8 coreceptor, which binds pMHCI at a distinct site, influences this parameter. Although biophysical studies with soluble proteins show that TCR and CD8 do not bind cooperatively to pMHCI, accumulating evidence suggests that TCR associates with CD8 on the T cell surface. Here, we titrated and quantified the contribution of CD8 to TCR/pMHCI dissociation in membrane-constrained interactions using a panel of engineered pMHCI mutants that retain faithful TCR interactions but exhibit a spectrum of affinities for CD8 of >1,000-fold. Data modeling generates a "stabilization factor" that preferentially increases the predicted TCR triggering rate for low affinity pMHCI ligands, thereby suggesting an important role for CD8 in the phenomenon of T cell cross-reactivity.

Antigens↗
PubMed2005

Immunologic pressure within class I-restricted cognate human immunodeficiency virus epitopes during highly active antiretroviral therapy.

Cytotoxic T lymphocytes (CTL) and highly active antiretroviral therapy (HAART) are known to exert strong evolutionary pressures on the virus population during human immunodeficiency virus (HIV) infection. However, it is not known whether CTL responses continue to substantially affect viral evolution during treatment. To study the effect of immunologic pressure on viral sequences during HAART, we identified 10 targeted HIV-specific CD8+-T-cell epitopes in five treatment-naive patients, sequenced each epitope in plasma-derived viruses, and then identified evidence of immunologic pressure at these epitopes by comparing the frequency of viral variants in plasma to the frequency of the CD8+-T-cell response for each variant identified. For one of the five patients, evidence of viral evolution was found during therapy. The sequence of the CTL-targeted epitope changed from an apparent escape variant prior to the initiation of therapy, to the sequence that is best recognized by the CTL response after the initiation of therapy, and then finally to a new escape variant during continued therapy. These data show that CTL-mediated pressure can continue to affect viral evolution after the initiation of HAART, even when treatment drives the viral load below detectable levels, and suggest that antiretroviral therapy may preferentially inhibit those virus variants that escape the CTL response.

Amino Acid Substitution↗
PubMed2004

CD4+ T cell depletion during all stages of HIV disease occurs predominantly in the gastrointestinal tract.

The mechanisms underlying CD4(+) T cell depletion in human immunodeficiency virus (HIV) infection are not well understood. Comparative studies of lymphoid tissues, where the vast majority of T cells reside, and peripheral blood can potentially illuminate the pathogenesis of HIV-associated disease. Here, we studied the effect of HIV infection on the activation and depletion of defined subsets of CD4(+) and CD8(+) T cells in the blood, gastrointestinal (GI) tract, and lymph node (LN). We also measured HIV-specific T cell frequencies in LNs and blood, and LN collagen deposition to define architectural changes associated with chronic inflammation. The major findings to emerge are the following: the GI tract has the most substantial CD4(+) T cell depletion at all stages of HIV disease; this depletion occurs preferentially within CCR5(+) CD4(+) T cells; HIV-associated immune activation results in abnormal accumulation of effector-type T cells within LNs; HIV-specific T cells in LNs do not account for all effector T cells; and T cell activation in LNs is associated with abnormal collagen deposition. Taken together, these findings define the nature and extent of CD4(+) T cell depletion in lymphoid tissue and point to mechanisms of profound depletion of specific T cell subsets related to elimination of CCR5(+) CD4(+) T cell targets and disruption of T cell homeostasis that accompanies chronic immune activation.

CD4-Positive T-Lymphocytes↗
PubMed2004

The functional profile of primary human antiviral CD8+ T cell effector activity is dictated by cognate peptide concentration.

Antiviral CD8(+) T cells can elaborate at least two effector functions, cytokine production and cytotoxicity. Which effector function is elaborated can determine whether the CD8(+) T cell response is primarily inflammatory (cytokine producing) or antiviral (cytotoxic). In this study we demonstrate that cytotoxicity can be triggered at peptide concentrations 10- to 100-fold less than those required for cytokine production in primary HIV- and CMV-specific human CD8(+) T cells. Cytolytic granule exocytosis occurs at peptide concentrations insufficient to cause substantial TCR down-regulation, providing a mechanism by which a CD8(+) T cell could engage and lyse multiple target cells. TCR sequence analysis of virus-specific cells shows that individual T cell clones can degranulate or degranulate and produce cytokine depending on the Ag concentration, indicating that response heterogeneity exists within individual CD8(+) T cell clonotypes. Thus, antiviral CD8(+) T cell effector function is determined primarily by Ag concentration and is not an inherent characteristic of a virus-specific CD8(+) T cell clonotype or the virus to which the response is generated. The inherent ability of viruses to induce high or low Ag states may be the primary determinant of the cytokine vs cytolytic nature of the virus-specific CD8(+) T cell response.

Antigens↗
PubMed2004

Flow cytometric analysis of vaccine responses: how many colors are enough?

The past 5 years have seen an explosion in technological advances related to measuring immunogenicity. Specifically, two distinct areas of development have led to considerably more detailed analysis of T cell responses: first, the ability to measure over a dozen distinct antigens expressed by individual cells simultaneously (12-color flow cytometry); and second, a host of assays that rapidly and viably identify antigen-specific T cells. Together, these technologies reveal the complex heterogeneity of an immune response generated during infection or after vaccine challenge. The next 5 years will see the determination of which underlying variables will be most important to quantifying vaccine efficacy. In this manuscript, we discuss these technologies, with a focus on assisting in the design and implementation of immunogenicity trials for future vaccine efforts.

Animals↗
PubMed2004

T cell receptor recognition motifs govern immune escape patterns in acute SIV infection.

Escape from adaptive T cell immunity through transmutation of viral antigenic structure is a cardinal feature in the pathogenesis of SIV/HIV infection and a major obstacle to antiretroviral vaccine development. However, the molecular determinants of this phenomenon at the T cell receptor (TCR)-antigen interface are unknown. Here, we show that mutational escape is intimately linked to the structural configuration of constituent TCR clonotypes within virus-specific CD8(+) T cell populations. Analysis of 3416 SIV-specific TCR sequences revealed that polyclonal T cell populations characterized by highly conserved TCRB CDR3 motifs were rendered ineffectual by single residue mutations in the cognate viral epitope. Conversely, diverse clonotypic repertoires without discernible motifs were not associated with viral escape. Thus, fundamental differences in the mode of antigen engagement direct the pattern of adaptive viral evolution. These findings have profound implications for the development of vaccines that elicit T cell immunity to combat pathogens with unstable genomes.

Acute Disease↗
PubMed2004

T-cell subsets that harbor human immunodeficiency virus (HIV) in vivo: implications for HIV pathogenesis.

Identification of T-cell subsets that are infected in vivo is essential to understanding the pathogenesis of human immunodeficiency virus (HIV) disease; however, this goal has been beset with technical challenges. Here, we used polychromatic flow cytometry to sort multiple T-cell subsets to 99.8% purity, followed by quantitative PCR to quantify HIV gag DNA directly ex vivo. We show that resting memory CD4(+) T cells are the predominantly infected cells but that terminally differentiated memory CD4(+) T cells contain 10-fold fewer copies of HIV DNA. Memory CD8(+) T cells can also be infected upon upregulation of CD4; however, this is infrequent and HIV-specific CD8(+) T cells are not infected preferentially. Naïve CD4(+) T-cell infection is rare and principally confined to those peripheral T cells that have proliferated. Furthermore, the virus is essentially absent from naïve CD8(+) T cells, suggesting that the thymus is not a major source of HIV-infected T cells in the periphery. These data illuminate the underlying mechanisms that distort T-cell homeostasis in HIV infection.

Adult↗