CD25-expressing CD8+ T cells are potent memory cells in old age

We have recently described an IL-2/IL-4-producing CD8+CD25+ non-regulatory memory T cell population that occurs in a subgroup of healthy elderly persons who characteristically still have a good humoral response after vaccination. The present study addresses this specific T cell subset and investigates its origin, clonal composition, Ag specificity, and replicative history. We demonstrate that CD8+CD25+ memory T cells frequently exhibit a CD4+CD8+ double-positive phenotype. The expression of the CD8 alphabeta molecule and the occurrence of signal-joint TCR rearrangement excision circles suggest a thymic origin of these cells. They also have longer telomeres than their CD8+CD25- memory counterparts, thus indicating a shorter replicative history. CD8+CD25+ memory T cells display a polyclonal TCR repertoire and respond to IL-2 as well as to a panel of different Ags, whereas the CD8+CD25- memory T cell population has a more restricted TCR diversity, responds to fewer Ags, and does not proliferate in response to stimulation with IL-2. Molecular tracking of specific clones with clonotypic primers reveals that the same clones occur in CD8+CD25+ and CD8+CD25- memory T cell populations, demonstrating a lineage relationship between CD25+ and CD25- memory CD8+ T cells. Our results suggest that CD25-expressing memory T cells represent an early stage in the differentiation of CD8+ cells. Accumulation of these cells in elderly persons appears to be a prerequisite of intact immune responsiveness in the absence of naive T cells in old age.     

Activation-induced cytidine deaminase expression in CD4+ T cells is associated with a unique IL-10-producing subset that increases with age

Activation-induced cytidine deaminase (AID), produced by the Aicda gene, is essential for the immunoglobulin gene (Ig) alterations that form immune memory. Using a Cre-mediated genetic system, we unexpectedly found CD4(+) T cells that had expressed Aicda (exAID cells) as well as B cells. ExAID cells increased with age, reaching up to 25% of the CD4(+) and B220(+) cell populations. ExAID B cells remained IgM(+), suggesting that class-switched memory B cells do not accumulate in the spleen. In T cells, AID was expressed in a subset that produced IFN-γ and IL-10 but little IL-4 or IL-17, and showed no evidence of genetic mutation. Interestingly, the endogenous Aicda expression in T cells was enhanced in the absence of B cells, indicating that the process is independent from the germinal center reaction. These results suggest that in addition to its roles in B cells, AID may have previously unappreciated roles in T-cell function or tumorigenesis.     

CD8+ IL-17-producing T cells are important in effector functions for the elicitation of contact hypersensitivity responses

Allergen-induced contact hypersensitivity (CHS) is a T cell-mediated delayed-type immune response which has been considered to be primarily mediated by CD8+ T cytotoxic type I (Tc1) cells. IFN-gamma, the prototype Tc1 (Th1) cytokine, has been implicated as the primary inflammatory cytokine for CHS. In this study, we demonstrate that neutralization of IL-17 rather than IFN-gamma suppresses the elicitation of CHS. The suppression does not result from inhibition of the proliferation of allergen-activated T cells. Allergen sensitization induces the development of distinct CD8+ T cell subpopulations that produce IFN-gamma or IL-17. Although CD8+ IL-17-producing cells are stimulated by IL-23, they are inhibited by IL-12, a prototypical stimulator of IFN-gamma-producing Tc1 cells. This indicates that CD8+ IL-17-producing cells are distinct from Tc1 cells and are important in effector functions at the elicitation of CHS. These studies provide insights into a novel mechanism for CHS.     

Human bone marrow hosts polyfunctional memory CD4+ and CD8+ T cells with close contact to IL-15-producing cells

Recently, a key role in memory T cell homing and survival has been attributed to the bone marrow (BM) in mice. In the human BM, the repertoire, function, and survival niches of CD4(+) and CD8(+) T cells have not yet been elucidated. In this study, we demonstrate that CD4(+) and CD8(+) effector memory T cells accumulate in the human BM and are in a heightened activation state as revealed by CD69 expression. BM-resident memory T cells produce more IFN-γ and are frequently polyfunctional. Immunofluorescence analysis revealed that CD4(+) and CD8(+) T cells are in the immediate vicinity of IL-15-producing BM cells, suggesting a close interaction between these two cell types and a regulatory role of IL-15 on T cells. Accordingly, IL-15 induced an identical pattern of CD69 expression in peripheral blood CD4(+) and CD8(+) T cell subsets. Moreover, the IL-15-inducible molecules Bcl-x(L), MIP-1α, MIP-1β, and CCR5 were upregulated in the human BM. In summary, our results indicate that the human BM microenvironment, in particular IL-15-producing cells, is important for the maintenance of a polyfunctional memory CD4(+) and CD8(+) T cell pool.     

HIV-specific IL-10-positive CD8+ T cells are increased in advanced disease and are associated with decreased HIV-specific cytolysis

IL-10-producing T cells have been shown to inhibit Ag-specific CD8+ T cell responses, and may play a role in the immune dysregulation observed in HIV-1 infection. We characterized the Gag-specific IL-10 responses by CD8+ T cells in HIV-1-positive volunteers from Uganda. HIV-specific IL-10 responses were detected in 32 of 61 (52.4%) antiretroviral naive and 2 of 15 (13.3%) volunteers with a complete virologic response on antiretroviral therapy (< 400 copies/ml). The frequency of HIV-specific IL-10-positive cells was significantly higher in volunteers with advanced disease (CD4+ T cell count <200 cells/mm3; p = 0.0004), and correlated positively with plasma HIV RNA (r = 0.43, p = 0.0004). Interestingly, the frequency of Gag-specific CD107a/b-, but not IFN-gamma-, positive cells was significantly lower in individuals with detectable IL-10-positive CD8+ T cells (p = 0.004). Gag-specific IL-10-positive CD8+ T cells demonstrated a pattern of surface memory marker expression that is distinct compared with CD107a/b- and IFN-gamma-positive CD8+ T cell populations (p < 0.0001). Our study describes a distinct population of IL-10-positive CD8+ T cells that may play a role in HIV-associated immune dysfunction.     

Functional properties and lineage relationship of CD8+ T cell subsets identified by expression of IL-7 receptor alpha and CD62L

Three major subsets of Ag-experienced CD8+ T cells have been identified according to their expression of CD62L and CD127. These markers are associated with central memory T cells (CD62L+ CD127+), effector memory T cells (CD162L- CD127+), and effector T cells (CD62L- CD127-). In this study we characterized the development of these three populations during acute and chronic viral infections and after immunization with virus-like particles and determined their lineage relation and functional and protective properties. We found that the balance between the three subsets was critically regulated by the availability of Ag and time. After initial down-regulation of CD127, the responding CD8+ T cell population down-regulated CD62L and re-expressed CD127. Dependent on Ag availability, the cells then further differentiated into CD62L- CD127- effector cells or, in the absence of Ag, re-expressed CD62L to become central memory T cells. Although all three populations efficiently produced effector cytokines such as IFN-gamma, CD62L- CD127- effector cells exhibited the highest ex vivo lytic potential. In contrast, CD62L+ CD127+ central memory T cells most efficiently produced IL-2 and proliferated extensively in vitro and in vivo upon antigenic restimulation. Strikingly, only effector and effector memory, but not central memory, T cells were able to protect against peripheral infection with vaccinia virus, whereas central memory T cells were most potent at protecting against systemic infection with lymphocytic choriomeningitis virus, indicating that the antiviral protective capacities of specific CD8+ T cell subsets are closely related to the nature of the challenging pathogen.     

Selective killing of CD8+ cells with a 'memory' phenotype (CD62Llo) by the N-acetyl-D-galactosamine-specific lectin from Viscum album L

As reported previously by our group, among the toxic proteins from Viscum album L. only the mistletoe lectins (MLs) induce the apoptotic killing pathway in human lymphocytes. Although one may expect a homogenous distribution of carbohydrate domains on cell surface receptors for the carbohydrate binding B chains of the toxic protein, the sensitivity of cells to these B chains obviously differ. Here we report a selective killing of CD8+ CD62Llo cells from healthy individuals by the galNAc-specific ML III (and RCA60, which binds to gal and galNAc), while the gal-specific ML I was less effective. This selective killing is not sufficiently explained by protein synthesis inhibition alone, since this subset was not affected by other ribosome inhibiting proteins such as the lectin from Ricinus communis (RCA120), lectin from Abrus precatorus (APA), abrin A, and inhibitors of RNA, DNA and/or protein synthesis such as actinomycin D, mitomycin C, and cycloheximide. We conclude that CD8+ cells with 'memory' phenotype (CD62Llo) are more sensitive to the ML III-mediated killing than their CD8+ CD62Lhi counterparts, CD4+ T cells, and CD19+ B cells. These cells probably express a distinct receptor with galNAc domains that is missing or not active on CD8+ cells with a 'naive' phenotype.     

Herpesvirus-specific CD8 T cell immunity in old age: cytomegalovirus impairs the response to a coresident EBV infection

Aging in humans is associated with increased infections and the reduced proliferative capacity of T cells, part of the more global phenomenon termed immune senescence. The etiology of immune senescence is unknown but the accumulation of virus-specific memory T cells may be a contributory factor. We have examined CD8 T cell responses to two persistent herpesvirus infections, CMV and EBV, and to a recurrent virus infection, influenza, in different age cohorts of healthy donors using HLA-peptide tetramers and intracellular cytokine detection. Of these, CMV appears to be the most immunogenic, with the CD8 T cell response representing over 10% of the CD8 pool in many elderly donors. Interestingly, the effect of age upon EBV-specific responses depends upon donor CMV sero-status. In CMV seropositive donors, the magnitude of the EBV-specific immune response is stable with age, but in CMV seronegative donors, the response to EBV increases significantly with age. By contrast, the influenza-specific CD8 T cell immune response decreases with age, independent of CMV status. The functional activity of the herpesvirus-specific immune response decreases in elderly donors, although the characteristic phenotypes of CMV- and EBV-specific memory populations are retained. This demonstrates that aging is associated with a marked accumulation of CMV-specific CD8 T cells together with a decrease in immediate effector function. Moreover, infection with CMV can reduce prevailing levels of immunity to EBV, another persistent virus. These results suggest that carriage of CMV may be detrimental to the immunocompetent host by suppressing heterologous virus-specific immunity during aging.     

Progressive differentiation and commitment of CD8+ T cells to a poorly cytolytic CD8low phenotype in the presence of IL-4

Exposure to IL-4 during activation of naive murine CD8+ T cells leads to generation of IL-4-producing effector cells with reduced surface CD8, low perforin, granzyme B and granzyme C mRNA, and poor cytolytic function. We show in this study that maximal development of these cells depended on exposure to IL-4 for the first 5 days of activation. Although IL-4 was not required at later times, CD8 T cell clones continued to lose surface CD8 expression with prolonged culture, suggesting commitment to the CD8low phenotype. This state was reversible in early differentiation. When single CD8low cells from 4-day cultures were cultured without IL-4, 65% gave rise to clones that partly or wholly comprised CD8high cells; the proportion of reverted clones was reduced or increased when the cells were cloned in the presence of IL-4 or anti-IL-4 Ab, respectively. CD8 expression positively correlated with perforin and granzyme A, B, and C mRNA, and negatively correlated with IL-4 mRNA levels among these clones. By contrast, most CD8low cells isolated at later time points maintained their phenotype, produced IL-4, and exhibited poor cytolytic function after many weeks in the absence of exogenous IL-4. We conclude that IL-4-dependent down-regulation of CD8 is associated with progressive differentiation and commitment to yield IL-4-producing cells with little cytolytic activity. These data suggest that the CD4-CD8- cells identified in some disease states may be the product of a previously unrecognized pathway of effector differentiation from conventional CD8+ T cells.     

The CD8+ T cell population elicited by recombinant adenovirus displays a novel partially exhausted phenotype associated with prolonged antigen presentation that nonetheless provides long-term immunity

We have previously reported that the CD8+ T cell response elicited by recombinant adenovirus vaccination displayed a delayed contraction in the spleen. In our current study, we demonstrate that this unusual kinetic is a general phenomenon observed in multiple tissues. Phenotypic analysis of transgene-specific CD8+ T cells present 30 days postimmunization with recombinant adenovirus revealed a population with evidence of partial exhaustion, suggesting that the cells had been chronically exposed to Ag. Although Ag expression could no longer be detected 3 wk after immunization, examination of Ag presentation within the draining lymph nodes demonstrated that APCs were loaded with Ag peptide for at least 40 days postimmunization, suggesting that Ag remains available to the system for a prolonged period, although the exact source of this Ag remains to be determined. At 60 days postimmunization, the CD8+ T cell population continued to exhibit a phenotype consistent with partially exhausted effector memory cells. Nonetheless, these CD8+ T cells conferred sterilizing immunity against virus challenge 7-12 wk postimmunization, suggesting that robust protective immunity can be provided by CD8+ T cells with an exhausted phenotype. These data demonstrate that prolonged exposure to Ag may not necessarily impair protective immunity and prompt a re-evaluation of the impact of persistent exposure to Ag on T cell function.     

Increased tumor-infiltrating CD8+Foxp3+ T lymphocytes are associated with tumor progression in human gastric cancer

Background

CD8⁺Foxp3⁺ T lymphocytes have been detected in tumors. However, the distribution, phenotypic features, and regulation of these cells in gastric cancer remain unknown.

Methods

The levels of CD8⁺Foxp3⁺ T lymphocytes in the peripheral blood, tumor-draining lymph nodes, non-tumor tissues, and tumor tissues of patients with gastric cancer were detected by flow cytometry. Foxp3 induction in CD8⁺Foxp3^? T cells was investigated in vitro. The suppressive function of CD8⁺Foxp3⁺ T lymphocytes was analyzed by their effect on CD4⁺ T-cell proliferation and IFN-γ production. The percentages of CD8⁺Foxp3⁺ T lymphocytes were evaluated for the association with tumor stage.

Results

The frequency of CD8⁺Foxp3⁺ T lymphocytes in tumor tissues was significantly higher than that in non-tumor tissues, and similar results were also observed in tumor-draining lymph nodes compared with peripheral blood. Most intratumoral CD8⁺Foxp3⁺ T lymphocytes were activated effector cells (CD45RA^?CD27^?). TGF-β1 levels were positively correlated with the frequency of CD8⁺Foxp3⁺ T lymphocytes in tumor tissues, and in vitro TGF-β1 could induce the generation of CD8⁺Foxp3⁺ T lymphocytes in a dose-dependent manner. Furthermore, intratumoral CD8⁺Foxp3⁺ T lymphocytes suppressed the proliferation and IFN-γ production of CD4⁺ T cells. Finally, intratumoral CD8⁺Foxp3⁺ T lymphocytes were significantly increased with tumor progression in terms of tumor-node-metastasis (TNM) stage.

Conclusions

Our data have shown that increased intratumoral CD8⁺Foxp3⁺ T lymphocytes are associated with tumor stage and potentially influence CD4⁺ T-cell functions, which may provide insights for developing novel immunotherapy protocols against gastric cancer.     

Measles virus infection in adults induces production of IL-10 and is associated with increased CD4+ CD25+ regulatory T cells

Despite steady progress in elimination of measles virus globally, measles infection still causes 500,000 annual deaths, mostly in developing countries where endemic measles strains still circulate. Many adults are infected every year in China, with symptoms more severe than those observed in children. In this study, we have used blood samples from adult measles patients in Shanghai and age-matched healthy controls to gain an understanding of the immune status of adult measles patients. IFN-alpha mRNA was reduced in patient PBMC compared with healthy controls. In contrast, gene expression and plasma production of IL-2, IL-10, and IFN-gamma were elevated in patient blood. A similar cytokine profile was observed at early times when cultured PBMC were infected with a clinical isolate of measles virus. In contrast to previous studies in pediatric patients, we did not find a reduction in total CD4(+) and CD8(+) T cells in patient PBMC. Interestingly, we found that CD4(+)CD25(+)CD127(low) regulatory T cells were significantly increased in patient PBMC compared with controls. Using intracellular cytokine staining we also show that the measles virus induces IL-10-producing CD14(+) and CD4(+)CD25(+) cells in PBMC. Our results show that adult measles patients in the acute phase of the disease have a mixed Th1/Th2 type response, accompanied with severe immunosuppression of both innate and adaptive responses including suppression of type I IFN. Both regulatory T cells and plasma IL-10 may contribute to the immunosuppression.     

T cells with a CD4+CD25+ regulatory phenotype suppress in vitro proliferation of virus-specific CD8+ T cells during chronic hepatitis C virus infection

Chronic hepatitis C virus (HCV) infection is associated with impaired proliferative, cytokine, and cytotoxic effector functions of HCV-specific CD8(+) T cells that probably contribute significantly to viral persistence. Here, we investigated the potential role of T cells with a CD4(+)CD25(+) regulatory phenotype in suppressing virus-specific CD8(+) T-cell proliferation during chronic HCV infection. In vitro depletion studies and coculture experiments revealed that peptide specific proliferation as well as gamma interferon production of HCV-specific CD8(+) T cells were inhibited by CD4(+)CD25(+) T cells. This inhibition was dose dependent, required direct cell-cell contact, and was independent of interleukin-10 and transforming growth factor beta. Interestingly, the T-cell-mediated suppression in chronically HCV-infected patients was not restricted to HCV-specific CD8(+) T cells but also to influenza virus-specific CD8(+) T cells. Importantly, CD4(+)CD25(+) T cells from persons recovered from HCV infection and from healthy blood donors exhibited significantly less suppressor activity. Thus, the inhibition of virus-specific CD8(+) T-cell proliferation was enhanced in chronically HCV-infected patients. This was associated with a higher frequency of circulating CD4(+)CD25(+) cells observed in this patient group. Taken together, our results suggest that chronic HCV infection leads to the expansion of CD4(+)CD25(+) T cells that are able to suppress CD8(+) T-cell responses to different viral antigens. Our results further suggest that CD4(+)CD25(+) T cells may contribute to viral persistence in chronically HCV-infected patients and may be a target for immunotherapy of chronic hepatitis C.     

Expanded CD8+ T cells of murine and human CLL are driven into a senescent KLRG1+ effector memory phenotype

Altered numbers and functions of T cells have previously been demonstrated in chronic lymphocytic leukemia (CLL) patients. However, dynamics and specific T-cell subset alterations have not been studied in great detail. Therefore, we studied CLL blood lymphocyte subsets of individual patients in a longitudinal manner. Dynamic expansions of blood CD4 ⁺ and CD8 ⁺ T-cell numbers were consistently associated with a progressively increasing CLL leukemic compartment. Interestingly, the T-cell subset expansion over time was more pronounced in CD38 ⁺ CLL. Additionally, we performed gene expression profiling of CD3 ⁺ T cells of CLL patients and normal donors. Using gene set enrichment analysis, we found significant enrichment of genes with higher expression in CLL T cells within CD8⁺ effector memory and terminal effector T-cell gene signatures. In agreement with these data, we observed a marked expansion of phenotypic CD8 ⁺ effector memory T cells in CLL by flow cytometry. Moreover, we observed that increments of CD8 ⁺ effector memory T cells in human CLL and also mouse CLL (Eμ-TCL1 model) were due to an expansion of the inhibitory killer cell lectin-like receptor G1 (KLRG1) expressing cellular subset. Furthermore, higher plasma levels of the natural KLRG1 ligand E-cadherin were detected in CLL patients compared to normal donor controls. The predominance of KLRG1⁺ expression within CD8⁺ T cells in conjunction with increased systemic soluble E-cadherin might significantly contribute to CLL immune dysfunction and might additionally represent an important component of the CLL microenvironment.     

DNA vaccines,combining form of antigen and method of delivery to raise a spectrum of IFN-gamma and IL-4-producing CD4+ and CD8+ T cells

DNA-based immunizations have been used to determine the patterns of type 1 and type 2 cytokines that can be induced in vivo for Ag-specific CD4(+) and CD8(+) T cells. IL-4 was used as a signature cytokine for a type 2 T cell response and IFN-gamma as the signature cytokine for a type 1 response. Gene gun deliveries of secreted Ags were used to bias responses toward type 2 and saline injections of cell-associated Ags to bias responses toward type 1. The studies revealed that gene gun bombardments of DNAs expressing secreted Ags strongly biased responses toward type 2, inducing IL-4-producing CD8(+) as well as CD4(+) T cells. Saline injections of DNAs expressing cell-associated Ags strongly biased responses toward type 1, inducing IFN-gamma-producing CD8(+) and CD4(+) cells. A mixed type 1/type 2 response of IFN-gamma-producing CD8(+) T cells and IL-4-producing CD4(+) T cells was found for gene gun deliveries of cell-associated Ags. Saline injections of secreted Ags raised a weakly type 1-biased response characterized by only slightly higher frequencies of IFN-gamma- than IL-4-producing CD4(+) and CD8(+) T cells. Studies in B cell knockout and hen egg lysozyme Ig transgenic mice revealed that B cells were required for the generation of IL-4-producing CD8(+) T cells.     

IL-15 prolongs the duration of CD8+ T cell-mediated immunity in mice infected with a vaccine strain of Toxoplasma gondii.

Immunization of mice with a vaccine (ts-4) strain of Toxoplasma gondii is known to induce complete protection against subsequent lethal infection. Ts-4-mediated protection has been reported to be primarily dependent on IFN-gamma-producing CD8+ T cells. However, duration of CD8+ T cell-mediated immunity in the ts-4-vaccinated animals is not known. In the present study, the kinetics of the CD8+ T cell response in mice immunized with the ts-4 strain of T. gondii was evaluated. Optimal CD8+ T cell immunity persisted at least 6 mo after vaccination, and mice at this time point continued to overcome lethal challenge with a more virulent strain. However, at 9 mo postimmunization, CD8+ T cell immunity was severely diminished and the mice succumbed to Toxoplasma challenge. Pretreatment of animals, vaccinated 9 mo earlier, with rIL-15 prevented the mortality induced by Toxoplasma challenge. The protective effect of IL-15 treatment was due to a rise in the frequency of Ag-specific CD8+ T cells. CD8+ T cells from IL-15-administered animals showed increased proliferation and IFN-gamma production in response to antigenic restimulation. These findings suggest that rIL-15 can reverse the decline in the long-term CD8+ T cell immune response in mice immunized with vaccine strain of T. gondii.     

Mouse CD8+ CD122+ T cells with intermediate TCR increasing with age provide a source of early IFN-gamma production

Although CD8+ IL-2Rbeta (CD122)+ T cells with intermediate TCR reportedly develop extrathymically, their functions still remain largely unknown. In the present study, we characterized the function of CD8+ CD122+ T cells with intermediate TCR of C57BL/6 mice. The proportion of CD8+ CD122+ T cells in splenocytes gradually increased with age, whereas CD8+ IL-2Rbeta-negative or -low (CD122-) T cells conversely decreased. The IFN-gamma production from splenocytes stimulated with immobilized anti-CD3 Ab in vitro increased with age, whereas the IL-4 production decreased. When sorted CD8+ CD122+ T cells were stimulated in vitro by the anti-CD3 Ab, they promptly produced a much larger amount of IFN-gamma than did CD8+ CD122- T cells or CD4+ T cells, whereas only CD4+ T cells produced IL-4. The depletion of CD8+ CD122+ T cells from whole splenocytes greatly decreased the CD3-stimulated IFN-gamma production and increased the IL-4 production, whereas the addition of sorted CD8+ CD122+ T cells to CD8+ CD122+ T cell-depleted splenocytes restored the IFN-gamma production and partially decreased IL-4 production. It is of interest that CD8+ CD122+ T cells stimulated CD4+ T cells to produce IFN-gamma. The CD3-stimulated IFN-gamma production from each T cell subset was augmented by macrophages. Furthermore, CD3-stimulated CD8+ CD122+ T cells produced an even greater amount of IFN-gamma than did liver NK1.1+ T cells and also showed antitumor cytotoxicity. These results show that CD8+ CD122+ T cells may thus be an important source of early IFN-gamma production and are suggested to be involved in the immunological changes with aging.     

Human CD8+ EMRA T cells display a senescence‐associated secretory phenotype regulated by p38 MAPK

Cellular senescence is accompanied by a senescence‐associated secretory phenotype (SASP). We show here that primary human senescent CD8⁺ T cells also display a SASP comprising chemokines, cytokines and extracellular matrix remodelling proteases that are unique to this subset and contribute to age‐associated inflammation. We found the CD8⁺ CD45RA⁺CD27^? EMRA subset to be the most heterogeneous, with a population aligning with the naïve T cells and another with a closer association to the effector memory subset. However, despite the differing processes that give rise to these senescent CD8⁺ T cells once generated, they both adopt a unique secretory profile with no commonality to any other subset, aligning more closely with senescence than quiescence. Furthermore, we also show that the SASP observed in senescent CD8⁺ T cells is governed by p38 MAPK signalling.     

Rapid clonal expansion and prolonged maintenance of memory CD8+ T cells of the effector (CD44highCD62Llow) and central (CD44highCD62Lhigh) phenotype by an archaeosome adjuvant independent of TLR2

Vaccines capable of eliciting long-term T cell immunity are required for combating many diseases. Live vectors can be unsafe whereas subunit vaccines often lack potency. We previously reported induction of CD8(+) T cells to Ag entrapped in archaeal glycerolipid vesicles (archaeosomes). In this study, we evaluated the priming, phenotype, and functionality of the CD8(+) T cells induced after immunization of mice with OVA-Methanobrevibacter smithii archaeosomes (MS-OVA). A single injection of MS-OVA evoked a profound primary response but the numbers of H-2K(b)OVA(257-264)-specific CD8(+) T cells declined by 14-21 days, and <1% of primarily central phenotype (CD44(high)CD62L(high)) cells persisted. A booster injection of MS-OVA at 3-11 wk promoted massive clonal expansion and a peak effector response of approximately 20% splenic/blood OVA(257-264)-specific CD8(+) T cells. Furthermore, contraction was protracted and the memory pool (IL-7Ralpha(high)) of approximately 5% included effector (CD44(high)CD62L(low)) and central (CD44(high)CD62L(high)) phenotype cells. Recall response was observed even at >300 days. CFSE-labeled naive OT-1 (OVA(257-264) TCR transgenic) cells transferred into MS-OVA-immunized recipients cycled profoundly (>90%) within the first week of immunization indicating potent Ag presentation. Moreover, approximately 25% cycling of Ag-specific cells was seen for >50 days, suggesting an Ag depot. In vivo, CD8(+) T cells evoked by MS-OVA killed >80% of specific targets, even at day 180. MS-OVA induced responses similar in magnitude to Listeria monocytogenes-OVA, a potent live vector. Furthermore, protective CD8(+) T cells were induced in TLR2-deficient mice, suggesting nonengagement of TLR2 by archaeal lipids. Thus, an archaeosome adjuvant vaccine represents an alternative to live vectors for inducing CD8(+) T cell memory.     

IL-12 and NK cells are required for antigen-specific adaptive immunity against malaria initiated by CD8+ T cells in the Plasmodium yoelii model.

CD8+ T cells have been implicated as critical effector cells in protection against preerythrocytic stage malaria, including the potent protective immunity of mice and humans induced by immunization with radiation-attenuated Plasmodium spp. sporozoites. This immunity is directed against the Plasmodium spp. parasite developing within the host hepatocyte and for a number of years has been presumed to be mediated directly by CD8+ CTL or indirectly by IFN-gamma released from CD8+ T cells. In this paper, in BALB/c mice, we establish that after immunization with irradiated sporozoites or DNA vaccines parasite-specific CD8+ T cells trigger a novel mechanism of adaptive immunity that is dependent on T cell- and non-T cell-derived cytokines, in particular IFN-gamma and IL-12, and requires NK cells but not CD4+ T cells. The absolute requirement for CD8+ T cells to initiate such an effector mechanism, and the requirement for IL-12 and NK cells in such vaccine-induced protective immunity, are unique and underscore the complexity of the immune responses that protect against malaria and other intracellular pathogens.