Functional heterogeneity of vaccine-induced CD8(+) T cells

The functional status of circulating vaccine-induced, tumor-specific T cells has been questioned to explain their paradoxical inability to inhibit tumor growth. We enumerated with HLA-A*0201/peptide tetramers (tHLA) vaccine-elicited CD8(+) T cell precursor frequency among PBMC in 13 patients with melanoma undergoing vaccination with the HLA-A*0201-associated gp100:209-217(210 M) epitope. T cell precursor frequency increased from undetectable to 12,400 +/- 3,600 x 10(6) CD8(+) T cells after vaccination and appeared heterogeneous according to previously described functional subtypes: CD45RA(+)CD27(+) (14 +/- 2.6% of tHLA-staining T cells), naive; CD45RA(-)CD27(+) (14 +/- 3.2%), memory; CD45RA(+)CD27(-) (43 +/- 6%), effector; and CD45RA(-)CD27(-) (30 +/- 4.1%), memory/effector. The majority of tHLA(+)CD8(+) T cells displayed an effector, CD27(-) phenotype (73%). However, few expressed perforin (17%). Epitope-specific in vitro stimulation (IVS) followed by 10-day expansion in IL-2 reversed this phenotype by increasing the number of perforin(+) (84 +/- 3.6%; by paired t test, p < 0.001) and CD27(+) (from 28 to 67%; by paired t test, p = 0.01) tHLA(+) T cells. This conversion probably represented a change in the functional status of tHLA(+) T cells rather than a preferential expansion of a CD27(+) (naive and/or memory) PBMC, because it was reproduced after IVS of a T cell clone bearing a classic effector phenotype (CD45RA(+)CD27(-)). These findings suggest that circulating vaccine-elicited T cells are not as functionally active as inferred by characterization of IVS-induced CTL. In addition, CD45RA/CD27 expression may be more informative about the status of activation of circulating T cells than their status of differentiation.     

Effect of ageing on CMV-specific CD8 T cells from CMV seropositive healthy donors

Background  

Ageing is associated with changes in the immune system with substantial alterations in T-lymphocyte subsets. Cytomegalovirus (CMV) is one of the factors that affect functionality of T cells and the differentiation and large expansions of CMV pp65-specific T cells have been associated with impaired responses to other immune challenges. Moreover, the presence of clonal expansions of CMV-specific T cells may shrink the available repertoire for other antigens and contribute to the increased incidence of infectious diseases in the elderly. In this study, we analyse the effect of ageing on the phenotype and frequency of CMV pp65-specific CD8 T cell subsets according to the expression of CCR7, CD45RA, CD27, CD28, CD244 and CD85j.     

Functional heterogeneity of cytokines and cytolytic effector molecules in human CD8+ T lymphocytes.

CD8(+) T cells use a number of effector mechanisms to protect the host against infection. We have studied human CD8(+) T cells specific for CMV pp65(495-503) epitope, or for staphylococcal enterotoxin B, for the expression patterns of five cytokines and cytolytic effector molecules before and after antigenic stimulation. Ex vivo, the cytolytic molecule granzyme B was detected in a majority of circulating CMV-specific CD8(+) T cells, whereas perforin was rarely expressed. Both were highly expressed after Ag-specific activation accompanied by CD45RO up-regulation. TNF-alpha, IFN gamma, and IL-2 were sequentially acquired on recognition of Ag, but surprisingly, only around half of the CMV-specific CD8(+) T cells responded to antigenic stimuli with production of any cytokine measured. A dominant population coexpressed TNF-alpha and IFN-gamma, and cells expressing TNF-alpha only, IFN-gamma only, or all three cytokines together also occurred at lower but clearly detectable frequencies. Interestingly, perforin expression and production of IFN-gamma and TNF-alpha in CD8(+) T cells responding to staphylococcal enterotoxin B appeared to be largely segregated, and no IL-2 was detected in perforin-positive cells. Together, these data indicate that human CD8(+) T cells can be functionally segregated in vivo and have implications for the understanding of human CD8(+) T cell differentiation and specialization and regulation of effector mechanisms.     

Polyomavirus-infected dendritic cells induce antiviral CD8(+) T lymphocytes

CD8(+) T cells are critical for the clearance of acute polyomavirus infection and the prevention of polyomavirus-induced tumors, but the antigen-presenting cell(s) involved in generating polyomavirus-specific CD8(+) T cells have not been defined. We investigated whether dendritic cells and macrophages are permissive for polyomavirus infection and examined their potential for inducing antiviral CD8(+) T cells. Although dendritic cells and macrophages both supported productive polyomavirus infection, dendritic cells were markedly more efficient at presenting the immunodominant viral epitope to CD8(+) T cells. Additionally, infected dendritic cells, but not infected macrophages, primed anti-polyomavirus CD8(+) T cells in vivo. Treatment with Flt3 ligand, a hematopoietic growth factor that dramatically expands the number of dendritic cells, markedly enhanced the magnitude of virus-specific CD8(+) T-cell responses during acute infection and the pool of memory anti-polyomavirus CD8(+) T cells. These findings suggest that virus-infected dendritic cells induce polyomavirus-specific CD8(+) T cells in vivo and raise the potential for their use as cellular adjuvants to promote CD8(+) T cell surveillance against polyomavirus-induced tumors.     

Identification of naive or antigen-experienced human CD8(+) T cells by expression of costimulation and chemokine receptors: analysis of the human cytomegalovirus-specific CD8(+) T cell response

Human CMV (HCMV) infection provides an informative model of how long term human CD8(+) T cell memory is maintained in the presence of Ag. To clarify the phenotypic identity of Ag-experienced human CD8(+) T cells in vivo, we determined the expression of costimulation and chemokine receptors on Ag-specific CD8(+) T cells by quantifying individual virus-specific clones in different cell populations using TCR clonotypic probing. In healthy HCMV carriers, expanded CD8(+) clones specific for either HCMV tegument protein pp65 or immediate-early protein IE72 are found in both CD45RO(high) cells and the subpopulation of CD45RA(high) cells that lack the costimulatory molecule CD28. In contrast to previous suggested models of CD8(+) T cell memory, we found that in healthy virus carriers highly purified CD28(-)CD45RA(high)CCR7(-) cells are not terminally differentiated, because following stimulation in vitro with specific HCMV peptide these cells underwent sustained clonal proliferation, up-regulated CD45RO and CCR5, and showed strong peptide-specific cytotoxic activity. In an individual with acute primary HCMV infection, HCMV pp65-specific CD8(+) T cells are predominantly CD28(-)CD45RO(high)CCR7(-). During convalescence, an increasing proportion of pp65-specific CD8(+) T cells were CD28(-)CD45RA(high)CCR7(-). We conclude that naive human CD8(+) T cells are CD28(+)CD45RA(high), express CCR7 but not CCR6, and are predominantly CD27(+) and L-selectin CD62 ligand-positive. The phenotype CD27(+)CD45RA(high) should not be used to identify naive human CD8(+) T cells, because CD27(+)CD45RA(high) cells also contain a significant subpopulation of CD28(-)CD27(+) Ag-experienced expanded clones. Thus CD8(+) T cell memory to HCMV is maintained by cells of expanded HCMV-specific clones that show heterogeneity of activation state and costimulation molecular expression within both CD45RO(high) and CD28(-)CD45RA(high) T cell pools.     

Decline of influenza-specific CD8+ T cell repertoire in healthy geriatric donors

Background

While influenza vaccination results in protective antibodies against primary infections, clearance of infection is primarily mediated through CD8⁺ T cells. Studying the CD8⁺ T cell response to influenza epitopes is crucial in understanding the disease associated morbidity and mortality especially in at risk populations such as the elderly. We compared the CD8⁺ T cell response to immunodominant and subdominant influenza epitopes in HLA-A2⁺ control, adult donors, aged 21-42, and in geriatric donors, aged 65 and older.

Results

We used a novel artificial Antigen Presenting Cell (aAPC) based stimulation assay to reveal responses that could not be detected by enzyme-linked immunosorbent spot (ELISpot). 14 younger control donors and 12 geriatric donors were enrolled in this study. The mean number of influenza-specific subdominant epitopes per control donor detected by ELISpot was only 1.4 while the mean detected by aAPC assay was 3.3 (p = 0.0096). Using the aAPC assay, 92% of the control donors responded to at least one subdominant epitopes, while 71% of control donors responded to more than one subdominant influenza-specific response. 66% of geriatric donors lacked a subdominant influenza-specific response and 33% of geriatric donors responded to only 1 subdominant epitope. The difference in subdominant response between age groups is statistically significant (p = 0.0003).

Conclusion

Geriatric donors lacked the broad, multi-specific response to subdominant epitopes seen in the control donors. Thus, we conclude that aging leads to a decrease in the subdominant influenza-specific CTL responses which may contribute to the increased morbidity and mortality in older individuals.     

Valpha24-JalphaQ-independent,CD1d-restricted recognition of alpha-galactosylceramide by human CD4(+) and CD8alphabeta(+) T lymphocytes

Human CD1d molecules present an unknown ligand, mimicked by the synthetic glycosphingolipid alpha-galactosylceramide (alphaGC), to a highly conserved NKT cell subset expressing an invariant TCR Valpha24-JalphaQ paired with Vbeta11 chain (Valpha24(+)Vbeta11(+) invariant NK T cell (NKT(inv))). The developmental pathway of Valpha24(+)Vbeta11(+)NKT(inv) is still unclear, but recent studies in mice were consistent with a TCR instructive, rather than a stochastic, model of differentiation. Using CD1d-alphaGC-tetramers, we demonstrate that in humans, TCR variable domains other than Valpha24 and Vbeta11 can mediate specific recognition of CD1d-alphaGC. In contrast to Valpha24(+)Vbeta11(+)NKT(inv) cells, Valpha24(-)/CD1d-alphaGC-specific T cells express either CD8alphabeta or CD4 molecules, but they are never CD4 CD8 double negative. We show that CD8alphabeta(+)Valpha24(-)/CD1d-alphaGC-specific T cells exhibit CD8-dependent specific cytotoxicity and have lower affinity TCRs than Valpha24(+)/CD1d-alphaGC-specific T cells. In conclusion, our results demonstrate that, contrary to the currently held view, recognition of CD1d-alphaGC complex in humans is not uniformly restricted to the Valpha24-JalphaQ/Vbeta11 NKT cell subset, but can be mediated by a diverse range of Valpha and Vbeta domains. The existence of a diverse repertoire of CD1d-alphaGC-specific T cells in humans strongly supports their Ag-driven selection.     

Induction of polyomavirus-specific CD8(+) T lymphocytes by distinct dendritic cell subpopulations

Dendritic cells are pivotal antigen-presenting cells for generating adaptive T-cell responses. Here, we show that dendritic cells belonging to either the myeloid-related or lymphoid-related subset are permissive for infection by mouse polyomavirus and, when loaded with a peptide corresponding to the immunodominant anti-polyomavirus CD8(+) T-cell epitope or infected by polyomavirus, are each capable of driving expansion of primary polyomavirus-specific CD8(+) T-cell responses in vivo.     

CD8(+) T lymphocytes mediate Borna disease virus-induced immunopathology independently of perforin

Perforin-mediated lysis of target cells is the major antiviral effector mechanism of CD8(+) T lymphocytes. We have analyzed the role of perforin in a mouse model for CD8(+) T-cell-mediated central nervous system (CNS) immunopathology induced by Borna disease virus. When a defective perforin gene was introduced into the genetic background of the Borna disease-susceptible mouse strain MRL, the resulting perforin-deficient mice developed strong neurological disease in response to infection indistinguishable from that of their perforin-expressing littermates. The onset of disease was slightly delayed. Brains of diseased perforin-deficient mice showed similar amounts and a similar distribution of CD8(+) T cells as wild-type animals. Perforin deficiency had no impact on the kinetics of viral spread through the CNS. Unlike brain lymphocytes from diseased wild-type mice, lymphocytes from perforin-deficient MRL mice showed no in vitro cytolytic activity towards target cells expressing the nucleoprotein of Borna disease virus. Taken together, these results demonstrate that CD8(+) T cells mediate Borna disease independent of perforin. They further suggest that the pathogenic potential of CNS-infiltrating CD8(+) T cells does not primarily reside in their lytic activity but rather in other functions.     

Rapamycin enriches for CD4(+) CD25(+) CD27(+) Foxp3(+) regulatory T cells in ex vivo-expanded CD25-enriched products from healthy donors and patients with multiple sclerosis

BACKGROUND: CD4(+) CD25(bright+) regulatory T cells (Treg) can be expanded to clinical doses using CD3/CD28 Ab-coated beads plus IL-2. However, this method requires high purity of the starting population to prevent overgrowth by non-regulatory T cells. Rapamycin, an agent that inhibits T-cell proliferation but selectively spares Treg, may be a means to expand Treg from less pure CD25-enriched cells. METHODS: CD25-enriched cells were prepared by a single-step immunomagnetic-selection using anti-CD25 microbeads. The cells were activated with a single addition of anti-CD3/CD28 beads and expanded in ex vivo 15-5% HS and autologous CD4(+) CD25(-) feeder cells,+/-rapamycin (0.01-20 ng/mL). IL-2 was added on day 3. Cells were rested for 2 days in ex vivo 15-5% HS and tested for phenotype, intracellular Foxp3 protein and suppressor activity. RESULTS: In the absence of rapamycin, CD25-enriched fractions expanded >17 000-fold by 21 days. Although suppressor activity was detected to day 14, it declined significantly by 21 days as non-regulatory cells expanded. The addition of rapamycin inhibited expansion of non-regulatory T cells at doses > or =1 ng/mL while increasing suppressor activity and the percentage of CD4(+) CD25(+) CD27(+) Foxp3(+) cells. Rapamycin did not enrich for Foxp3(+) cells in expanded cultures of CD4(+) CD25(-) cells. Treg were also readily expanded in cultures of CD25-enriched cells obtained from patients with multiple sclerosis in the presence of rapamycin. DISCUSSION: The addition of 1-20 ng/mL rapamycin to CD25-enriched cultures increased the purity of cells with the phenotype and function of Treg. This approach may alleviate the need for rigorous enrichment of Treg prior to activation and expansion for potential clinical use.     

Human immunodeficiency virus type 1- and cytomegalovirus-specific cytotoxic T lymphocytes can persist at high frequency for prolonged periods in the absence of circulating peripheral CD4(+) T cells

CD4(+) T cells are thought to be critical in the maintenance of virus-specific CD8(+) cytotoxic T-cell (CTL) responses. In human immunodeficiency virus type 1 (HIV-1) infection, a selective decline in HIV-1-specific CTL as the CD4(+) T-cell count decreases has been reported. Using HLA-peptide tetrameric complexes, we show the presence at high frequency of HIV-1- and cytomegalovirus-specific CD8(+) T cells when the peripheral CD4(+) T-cell count was low or zero in three HIV-1-infected patients. No direct virus-specific CD8(+)-mediated effector activity was seen in these subjects, suggesting antigen unresponsiveness, although tetramer-sorted cells could be expanded in vitro in the presence of interleukin-2 into responsive effector cells. Thus, virus-specific CD8(+) T cells can be maintained in the peripheral circulation at high frequency in the absence of circulating peripheral CD4(+) T cells, but these cells may lack direct effector activity. Strategies designed to overcome this antigen unresponsiveness may be of value in therapies for the treatment of AIDS.     

Frequencies of virus-specific CD4(+) and CD8(+) T lymphocytes secreting gamma interferon after acute natural rotavirus infection in children and adults

Human rotavirus-specific CD4(+) and CD8(+) T-cell responses in peripheral blood lymphocytes were studied using a flow cytometric assay that detects the intracellular accumulation of cytokines after short-term in vitro antigen stimulation. The frequencies of virus-specific T cells that secrete gamma interferon and interleukin-13 (IL-13) were determined in adults and children during the acute or convalescent phase of rotavirus-induced diarrhea, in asymptomatically infected adults and laboratory workers who worked with human stool samples containing rotavirus, and in healthy adults. Significantly higher frequencies of rotavirus-specific interferon gamma-secreting CD8(+) and CD4(+) T cells, but not IL-13-secreting T cells, were detected in symptomatically infected adults and exposed laboratory workers than in healthy adults and children with acute rotavirus diarrhea. The levels of rotavirus-specific T cells returned to levels found in healthy adults by 32 days after the onset of rotavirus diarrhea in most adult subjects. Children with rotavirus diarrhea had undetectable or very low levels of CD4(+) and CD8(+) T cells that secrete gamma interferon. Adult cytomegalovirus-seropositive individuals had frequencies of cytomegalovirus-specific T cells that secrete gamma interferon that were approximately 20 times the level of rotavirus-specific T cells. This result suggests that rotavirus is a relatively poor inducer of circulating memory T cells that secrete gamma interferon. The frequencies of gamma interferon-secreting CD4(+) and CD8(+) T cells and the frequencies of IL-13-secreting CD4(+) T cells responding to the T-cell superantigen staphylococcal enterotoxin B (SEB) were lower in children than in adults. In both adults and children, the frequencies of CD4(+) cells secreting gamma interferon in response to SEB were higher than the frequencies of cells secreting IL-13.     

Proliferation requirements of cytomegalovirus-specific,effector-type human CD8+ T cells

Two prototypic types of virus-specific CD8(+) T cells can be found in latently infected individuals: CD45R0(+)CD27(+)CCR7(-) effector-memory, and CD45RA(+)CD27(-)CCR7(-) effector-type cells. It has recently been implied that CD45RA(+)CD27(-)CCR7(-) T cells are terminally differentiated effector cells and as such have lost all proliferative capacity. We show in this study, however, that stimulation of CMV-specific CD45RA(+)CD27(-)CCR7(-) T cells with their cognate peptide in concert with either CD4(+) help or IL-2, IL-15, or IL-21 in fact induces massive clonal expansion. Concurrently, these stimulated effector T cells change cell surface phenotype from CD45RA to CD45R0 and regain CCR7, while effector functions are maintained. Our data imply that CD45RA(+)CD27(-)CCR7(-) effector-type T cells contribute to immunity not only by direct execution of effector functions, but also by yielding progeny in situations of viral reinfection or reactivation.     

Increased frequencies of micronuclei in T8 lymphocytes of smokers

Micronucleus frequencies and mitotic indices were analyzed in B, T4, and T8 lymphocytes from 40 smokers and 42 non-smoking referents. The highest level of micronuclei was found in T4 cells followed by T8 and B cells. These differences were statistically significant. There were statistically significant linear correlations between the micronucleus frequencies of all three subsets. There was a statistically significant effect of smoking only in the T8 cells. Smoking also increased the number of neutrophilic granulocytes and lymphocytes in the peripheral blood. There was a statistically significant effect of age on the micronucleus frequencies in T4 and T8 lymphocytes. The mitotic indices did not have any effect on the micronucleus frequencies and they were not influenced by smoking, age or sex.     

Cross-linking of 4-1BB up-regulates IL-13 expression in CD8(+) T lymphocytes

4-1BB, one of co-stimulatory molecules, is a member of TNF receptor superfamily and expressed on T cells upon TCR ligation. We have shown that 4-1BB is a co-stimulatory molecule enhancing cell cycle progression and inhibiting activation-induced cell death of CD8+ T cells by enhancing TCR signaling pathways. Here, we first report that the cross-linking of 4-1BB increased the expression of IL-13 mRNA and protein, and its secretion apparently via calcineurin, a Ca2+/calmodulin-dependent phosphatase. Ligation of 4-1BB with p815-m-4-1BBL evoked intracellular Ca2+ level in CD8+ T cells. CD8+ T cells express IL-13 receptor alpha1 mRNA. Incubation with anti-IL-13 blocking mAb reduced proliferation of CD8+ T cells enhanced by 4-1BB, and the treatment of CD3/4-1BB-ligated CD8+ T cells with recombinant IL-13 enhances cell proliferation, indicating that 4-1BB-induced IL-13 expression is partially responsible for the CD8+ T cell expansion in an autocrine or paracrine manner.     

Induction of mucosal homing virus-specific CD8(+) T lymphocytes by attenuated simian immunodeficiency virus

Induction of virus-specific T-cell responses in mucosal as well as systemic compartments of the immune system is likely to be a critical feature of an effective AIDS vaccine. We investigated whether virus-specific CD8(+) lymphocytes induced in rhesus macaques by immunization with attenuated simian immunodeficiency virus (SIV), an approach that is highly effective in eliciting protection against mucosal challenge, express the mucosa-homing receptor alpha4beta7 and traffic to the intestinal mucosa. SIV-specific CD8(+) T cells expressing alpha4beta7 were detected in peripheral blood and intestine of macaques infected with attenuated SIV. In contrast, virus-specific T cells in blood of animals immunized cutaneously by a combined DNA-modified vaccinia virus Ankara regimen did not express alpha4beta7. These results demonstrate the selective induction of SIV-specific CD8(+) T lymphocytes expressing alpha4beta7 by a vaccine approach that replicates in mucosal tissue and suggest that induction of virus-specific lymphocytes that are able to home to mucosal sites may be an important characteristic of a successful AIDS vaccine.     

Functional heterogeneity among CD4+ encephalitogenic T cells in recruitment of CD8+ T cells in experimental autoimmune encephalomyelitis

Inoculation of Lewis rats with live or attenuated (irradiated or paraformaldehyde-fixed) CD4+ encephalitogenic T cells (S1 line) protects the recipients from transferred experimental autoimmune encephalomyelitis (tEAE) induced by S1 cells. A CD8+ T lymphocyte population specifically activated against the EAE-inducing S1 cells can be readily isolated from the lymphoid organs of pretreated animals. We show, in the present study, that encephalitogenic T cell lines derived from Lewis rats differ in their ability to induce resistance against tEAE in vivo and to stimulate CD8+ cell proliferation in vitro. We also demonstrate that the S19 line of encephalitogenic T cells, in combination with myelin basic protein (MBP), can stimulate CD8+ cell proliferation in vitro. The CD8+ cells generated in this way strongly suppress MBP-specific T cell proliferation in vitro. This combined effect of T cells and MBP was also evident in vivo. Neither S19 cells nor MBP alone induced resistance against S19-mediated tEAE, rather coinjection of these cells and MBP was required. Our results suggest that resistance to EAE is mediated by distinct populations of encephalitogenic T cells that activate Ts cells through different mechanisms. In some instances, both autoreactive T cells and their relevant autoantigen(s) may be needed to activate Ts cells in vivo.     

Presence of effector CD8+ T cells in hepatitis C virus-exposed healthy seronegative donors.

CTL responses against multiple hepatitis C virus (HCV) epitopes were detected in 7 of 29 (24.1%) healthy family members (HFM) persistently exposed to chronically HCV-infected patients (HCV-HFM). These precursor CTL were at very low or undetectable frequencies, as determined by limiting dilution analysis. However, when HCV-specific effector CD8+ T cells, freshly isolated from PBMC of HCV-HFM, were assessed by a sensitive enzyme-linked immunospot assay, their frequencies were severalfold higher than those of precursor CTL. These results indicate that the two assays detect two functionally distinct T cell populations and that the effector cells are not assayed by the 51Cr-release assay. Furthermore, the combination of cell depletion and enzyme-linked immunospot analyses showed that the effector cells were confined into a CD8+ CD45RO+ CD28- population. The persistence of effector CD8+ T cells specific for both the structural and nonstructural viral proteins in uninfected HCV-HFM, suggest that: 1) an immunological memory is established upon a subclinical infection without any evidence of hepatitis, in a large cohort of HCV-exposed individuals; 2) because these cells required neither restimulation nor the addition of particular cytokines in vitro for differentiating in effectors, they should be capable of prompt HCV-specific effector function in vivo, possibly providing antiviral protection; and 3) the maintenance of effector T cell responses may be sustained by persisting low-level stimulation induced by inapparent infections.