Number Of Memory CD8 Research Articles

IL-27 mediates immune response of pneumococcal vaccine SPY1 through Th17 and memory CD4+T cells

Vaccination is an effective means of preventing pneumococcal disease and SPY1 is a live attenuated pneumococcal vaccine we obtained earlier. We found IL-27 and its specific receptor (WSX-1) were increased in SPY1 vaccinated mice. Bacterial clearance and survival rates were decreased in SPY1 vaccinated IL-27Rα-/- mice. The vaccine-induced Th17 cell response and IgA secretion were also suppressed in IL-27Rα-/- mice. STAT3 and NF-κB signaling and expression of the Th17 cell polarization-related cytokines were also decreased in IL-27Rα-/- bone-marrow-derived dendritic cells(BMDC) stimulated with inactivated SPY1. The numbers of memory CD4+T cells were also decreased in SPY1 vaccinated IL-27Rα-/- mice. These results suggested that IL-27 plays a protective role in SPY1 vaccine by promoting Th17 polarization through STAT3 and NF-κB signaling pathways and memory CD4+T cells production in the SPY1 vaccine. In addition, we found that the immune protection of SPY1 vaccine was independent of aerobic glycolysis.

Sepsis-induced changes in differentiation, maintenance, and function of memory CD8 T cell subsets.

Formation of long-lasting memory lymphocytes is one of the foundational characteristics of adaptive immunity and the basis of many vaccination strategies. Following the rapid expansion and contraction of effector CD8 T cells, the surviving antigen (Ag)-specific cells give rise to the memory CD8 T cells that persist for a long time and are phenotypically and functionally distinct from their naïve counterparts. Significant heterogeneity exists within the memory CD8 T cell pool, as different subsets display distinct tissue localization preferences, cytotoxic ability, and proliferative capacity, but all memory CD8 T cells are equipped to mount an enhanced immune response upon Ag re-encounter. Memory CD8 T cells demonstrate numerical stability under homeostatic conditions, but sepsis causes a significant decline in the number of memory CD8 T cells and diminishes their Ag-dependent and -independent functions. Sepsis also rewires the transcriptional profile of memory CD8 T cells, which profoundly impacts memory CD8 T cell differentiation and, ultimately, the protective capacity of memory CD8 T cells upon subsequent stimulation. This review delves into different aspects of memory CD8 T cell subsets as well as the immediate and long-term impact of sepsis on memory CD8 T cell biology.

Protective Effect against Neosporosis Induced by Intranasal Immunization with Neospora caninum Membrane Antigens Plus Carbomer-Based Adjuvant.

Neospora caninum is an obligate intracellular protozoan responsible for abortion and stillbirths in cattle. We previously developed a mucosal vaccination approach using N. caninum membrane proteins and CpG adjuvant that conferred long-term protection against neosporosis in mice. Here, we have extended this approach by alternatively using the carbomer-based adjuvant Carbigen™ in the immunizing preparation. Immunized mice presented higher proportions and numbers of memory CD4+ and CD8+ T cells. Stimulation of spleen, lungs and liver leukocytes with parasite antigens induced a marked production of IFN-γ and IL-17A and, less markedly, IL-4. This balanced response was also evident in that both parasite-specific IgG1 and IgG2c were raised by immunization, together with specific intestinal IgA. Upon intraperitoneal infection with N. caninum, immunized mice presented lower parasitic burdens than sham-immunized controls. In the infected immunized mice, memory CD4+ T cells predominantly expressed T-bet and RORγt, and CD8+ T cells expressing T-bet were found increased. While spleen, lungs and liver leukocytes of both immunized and sham-immunized infected animals produced high amounts of IFN-γ, only the cells from immunized mice responded with high IL-17A production. Since in cattle both IFN-γ and IL-17A have been associated with protective mechanisms against N. caninum infection, the elicited cytokine profile obtained using CarbigenTM as adjuvant indicates that it could be worth exploring for bovine neosporosis vaccination.

Combined immunodeficiency caused by a novel homozygous NFKB1 mutation

Genetic faults in several components of the nuclear factor-κB pathway cause immunodeficiency. Most defects lead to combined immunodeficiency with a range of severity. Heterozygous mutations in NFKB1 were associated with common variable immunodeficiency, however, homozygous mutations have not been described. We studied the molecular basis of combined immunodeficiency in a patient who presented with failure to thrive, persistent EBV viremia and hepatitis, pneumocystis jirovecii pneumonitis, and generalized lymphadenopathy. Whole genome and exome sequencing followed by Sanger confirmation were performed to identify the genetic defect. Molecular and cellular techniques were used to assess the variant impact on the nuclear factor-κB pathway and lymphocyte function. Genetic analysis revealed a novel homozygous mutation in NFKB1, c.2878G>A, p.Gly960Arg (G960R). This affected p105 phosphorylation and p50 formation on antigen and cytokine stimulation, as well as attenuating nuclear signal transmission. As a result, both T- and B-cell maturation and function were perturbed. The number of memory CD4+ T cells were reduced, while CD8+ T cells consisted predominately of expanded differentiated populations. The function of T cells were diminished as shown by reduced responses to mitogens as well as diminished cytokine secretion. B-cell maturation was also affected, with decreased IgD+CD27+ memory B cells while transitional B cells were increased, likely contributing to the reduced ability to produce specific antibodies. Homozygous G960R mutation in NFKB1 leads to a severe clinical presentation of combined immunodeficiency. This was associated with blockade of nuclear factor-κB pathway signaling, resulting in aberrations in T- and B-cell maturation and function.

Abstract 486: Chronic Periodontitis Induces Adverse Post-myocardial Wound Healing Through Activation of CD8+ T-cells

Increased risk of adverse cardiac remodeling post-myocardial infarction (MI) has been observed in patients with periodontal disease. Previously, we demonstrated that chronic inflammation induced by periodontal pathogen Porphyromonas gingivalis lipopolysaccharide (LPS) resets cardiac homeostasis, causing acceleration and exacerbation of the macrophage response post-MI. We hypothesize that chronic LPS activates a memory T-cell response resulting in adverse cardiac remodeling post-MI. Analysis of the mouse heart attack research tool (mHART) 1.0 identified 135 mice (5.4 ± 0.1 months of age) associated with the LPS study that had both echo and plasma data collected. Of these 26 mice also had tissue blocks in the mHART tissue bank. Mice were grouped as follows: 1) Saline day 0 unoperated mice (D0), 2) 28 day LPS day 0 unoperated mice (LPS), 3) Saline day 1 MI (MI), and 4) 28 day LPS day 1 MI (LPS+MI). Immunofluorescence of the left ventricle (LV) demonstrated that chronic LPS increased the number of memory CD8+ T-cells (CD3+CD8+CD27+) in the LV and remained elevated in the LPS+MI group compared to D0 and MI controls. Similar to chronic LPS, ligature-induced periodontitis (21 days) also showed upregulation of CD8+ T-cells in the LV along with changes in plasma proteins associated with interleukin, cytokine, chemokine receptor binding, peptide ligand-binding, inflammasome pathway, class A/1 rhodopsin-like receptors, G-protein coupled receptor ligand binding, and RUNX1 and FOXP3 control of Treg development and signaling. To dissect T-cell mediated signaling pathways, we constantly infused an MHC-I blocking antibody (MHCi; 0.2 μg/day; n=3) by osmotic mini-pumps implanted subcutaneously 7 days before (21 days after LPS infusion) and after MI surgery. Interestingly, MHCi attenuated the effector CD8+ T-cell response (CD3+CD8+CD44+) without affecting the memory response. MHCi also attenuated macrophage numbers within the infarct, thereby improving cardiac function at post-MI day 1. Our data showed the recruitment of effector but not memory CD8+ T-cells is regulating macrophage-mediated adverse post-MI remodeling in the setting of chronic periodontitis.

The inoculation of α-Galactosylceramide and HPV18-E1 protein promote a cytokines profile involved in the generation of central memory CD8 + T cells

Abstract CD8+ mediated immune response plays a major role in the clearance of Human Papillomavirus (HPV) infected cells. In the natural history of an HPV infection, the expression of HPV-E1 helicase during viral replication makes it a potential immunological target. Currently, there are no therapeutic vaccines that eliminate the lesions caused by HPV. Nevertheless, there are many studies on developing therapeutic vaccines against HPV. Vaccines and immunological therapies mostly use adjuvants, particularly α-galactocilceramide (α-GalCer) is an adjuvant that promotes a CD8+ T lymphocyte response mainly. We demonstrate in previous work, that immunization of HPV type 18 E1 protein along with α-GalCer adjuvant elicited CD8 T cell-immune response, able to eliminate tumor cells expressing HPV18 E1 protein. In this study, we analyzed the effect of α-GalCer in the generation of memory T CD8+ populations. We evaluated the serum levels of IL-15, IL-7, IL-4, IL-31, IL-2, TNF-α and the number of memory CD8+ T cells. The serum levels of IL-15, IL-7, IL-4 and TNF- α are increase in mice inoculated with α-GalCer plus HPV18-E1 with respect to mice inoculated with α-GalCer or HPV18-E1 protein. These data correlate with the increase of central memory T CD8+ population in mice inoculated with α-GalCer plus HPV18-E1. These data indicate that the administration of α-GalCer along with HPV18-E1 protein helps the generation of central memory CD8 + T lymphocytes. This adjuvant could be useful in the development of new therapeutic strategies to clearance HPV established infections. INCAN: (017/076/17) (CEI/1076/17)

Abstract 591: Efficacy of ALKS 4230, a novel immunotherapeutic agent, in murine syngeneic tumor models alone and in combination with immune checkpoint inhibitors

Abstract ALKS 4230 is a novel immunotherapeutic agent being tested in an ongoing phase 1 study to evaluate safety and tolerability in the treatment of patients with refractory solid tumors. ALKS 4230 is a selective agonist of the intermediate-affinity interleukin 2 (IL-2) receptor that when administered to mice results in a significant increase in numbers of memory CD8+ T cells and NK cells with no expansion of CD4+ regulatory T cells (Tregs). The selectivity achieved by ALKS 4230 is due to the fact that the molecule is a fusion of circularly permuted IL-2 to the extracellular portion of the IL-2 receptor α, and the resulting fusion protein is sterically prevented from binding to the high-affinity IL-2 receptor expressed on Tregs. The efficacy of ALKS 4230 was compared to recombinant human IL-2 in a B16F10 lung tumor metastasis model. ALKS 4230 treatment resulted in dose-dependent reduction of lung tumor colonization, with 100% inhibition at the highest dose tested. In contrast, while IL-2 was able to reduce lung tumor colonization, the maximal level of inhibition achieved was 60-70% at multiple dose levels such that increasing doses did not result in greater inhibition. Thus, the activation and expansion of effector cells without expansion of Tregs in response to ALKS 4230 treatment correlates with its improved efficacy over IL-2, which non-selectively expands both effector cells and Tregs. The antitumor efficacy mediated by ALKS 4230 was further evaluated in several murine subcutaneous syngeneic tumor models, including B16F10, MC38 and EMT6. Treatment with ALKS 4230 or its murine ortholog resulted in inhibition of tumor growth and improved survival in multiple models. When dosed in combination with anti-CTLA-4 or anti-PD-1 antibodies, ALKS 4230 resulted in further improvement of tumor growth inhibition and survival. These results demonstrate the murine antitumor efficacy of ALKS 4230 alone and in combination with immune checkpoint inhibitors and support the ongoing clinical evaluation of ALKS 4230 as an immunotherapy for cancer. Citation Format: Heather C. Losey, Jared E. Lopes, Reginald L. Dean, Michael R. Huff, Rosemarie A. Moroso, Juan C. Alvarez. Efficacy of ALKS 4230, a novel immunotherapeutic agent, in murine syngeneic tumor models alone and in combination with immune checkpoint inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 591. doi:10.1158/1538-7445.AM2017-591

MTOR Promotes Antiviral Humoral Immunity by Differentially Regulating CD4 Helper T Cell and B Cell Responses.

mTOR is a serine/threonine kinase involved in a variety of cellular activities. Although its specific inhibitor, rapamycin, is currently used as an immunosuppressive drug in transplant patients, it has been reported that rapamycin can also stimulate pathogen-specific cellular immunity in certain circumstances. However, whether and how mTOR regulates humoral immunity are not well understood. Here we found that rapamycin treatment predominantly inhibited GC B cell responses during viral infection and that this led to biased helper CD4 T cell differentiation as well as impaired antibody responses. These findings suggest that inhibition of B cell responses by rapamycin may play an important role in regulation of allograft-specific antibody responses to prevent organ rejection in transplant recipients. Our results also show that consideration of antibody responses is required in cases where rapamycin is used to stimulate vaccine-induced immunity.

Mcl-1 regulates effector and memory CD8 T-cell differentiation during acute viral infection

Mcl-1, an anti-apoptotic member of Bcl-2 family maintains cell viability during clonal expansion of CD8 T cells, but the cell intrinsic role of Mcl-1 in contraction of effectors or the number of memory CD8 T cells is unknown. Mcl-1 levels decline during the contraction phase but rebound to high levels in memory CD8 T cells. Therefore, by overexpressing Mcl-1 in CD8 T cells we asked whether limiting levels of Mcl-1 promote contraction of effectors and constrain CD8 T-cell memory. Mcl-1 overexpression failed to affect CD8 T-cell expansion, contraction or the magnitude of CD8 T-cell memory. Strikingly, high Mcl-1 levels enhanced mTOR phosphorylation and augmented the differentiation of terminal effector cells and effector memory CD8 T cells to the detriment of poly-cytokine-producing central memory CD8 T cells. Taken together, these findings provided unexpected insights into the role of Mcl-1 in the differentiation of effector and memory CD8 T cells.

Abstract 1346: Immunotherapy against breast cancer based on Stat3 blockade

Abstract The signal transducer and activator of transcription 3 (Stat3) is constitutively active in breast cancer (BC) and contributes to malignant transformation by promoting cell cycle progression, inhibiting apoptosis and mediating tumor immune evasion. Stat3 inhibition induces expression of proinflammatory cytokines and chemokines. On the other hand, it has been shown that oncogene inactivation induces cellular senescence and the secretion of senescence-associated secretome (SAS) in diverse tumor types. We recently described that Stat3 blockade leads to a senescence program in murine BC cells, which is accompanied by the secretion of proinflammatory cytokines. In addition, we demonstrated that immunization of mice with syngeneic Stat3 blocked BC cells induces an antitumoral immune response that involves the participation of CD4+ Th cells and cytotoxic NK cells. In this study our objectives were to study whether immunization with supernatants (SN) produced by Stat3-blocked cells induces an antitumor immune response and to explore the contribution of senescence phenotype in this response. For that purpose we used BC models of ErbB-2-positive, JIMT-1 and KPL-4 cells (human) and C4HD cells (murine), and of triple negative, MDA-MB231 cells (human) and 4T1 cell (murine). Knockdown of Stat3 with siRNA in these cells, induced senescence (assessed by acidic β-galactosidase staining). In human BC cells the senescent phenotype was accompanied by up-regulation of p21cip1 and downregulation of Rb expressions. In mouse BC cells we observed an increased expression of p16ink4a. In addition, simultaneous transfection with siRNAs targeting Stat3 and p16ink4a reverted the senescent phenotype. Then, we used a pre-clinical model in which we embedded the SN of C4HD cells in a slow-delivery depot as an adjuvant of a cellular immunotherapy. We immunized the animals with irradiated C4HD cells together with a depot containing lyophilized SN of C4HD cells transfected in vitro either with Stat3 siRNA (senescent) and Stat3 and p16ink4a siRNA (non-senescent), or a control siRNA. After 3 immunizations, with 15 d of interval between them, animals were challenged with C4HD tumor and tumor growth was monitored for 40 d. We observed that immunization with SN of cells with Stat3 siRNA decreased tumor growth vs. control siRNA group. Interestingly, there was no difference between tumor growth of animals immunized with SN of cells with Stat3 siRNA vs Stat3 and p16ink4a siRNA. We observed in these two groups greater cytotoxic activity of NK cells and an increase in the number of memory CD4+ T cells vs. control. These results suggest that Stat3 blockade drives a senescence program also in human BC cells. The secretome of Stat3-blocked BC cells is an effective adjuvant and could be formulated for immunotherapies independently of the SAS. Defining the protein, peptide, cytokine, chemokine composition of this supernatant opens up new avenues for immunotherapy in cancer patients. Citation Format: Mara De Martino, María Florencia Mercogliano, Mercedes Tkach, Leandro Venturutti, Patricia Virginia Elizalde, Roxana Schillaci. Immunotherapy against breast cancer based on Stat3 blockade. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1346. doi:10.1158/1538-7445.AM2015-1346

Epstein–Barr virus effect on frequency of functionally distinct T cell subsets in children with infectious mononucleosis

PurposeEpstein–Barr virus is a common human pathogen which infects the great majority of population worldwide. A striking proliferation of CD8+ T cells is an immune response to EBV invasion of B lymphocytes during infectious mononucleosis. The aim of the study was to analyze frequencies of CD28+CD95−, CD28+CD95+, CD28−CD95+ T cell subsets putative naïve (TN), central (TCM) and effector memory (TEM) T cells in children with infectious mononucleosis. Material/methodsMultiparameter flow cytometric analysis of CD4+ and CD8+ T cell subsets was performed in 19 children with acute infectious mononucleosis. ResultsThe CD4+/CD8+ ratio was found to be decreased (0.53) in children with infectious mononucleosis. Median TN, TCM, TEM frequencies were estimated to be 3.7, 4.5, 15.1% of CD8+ and 23, 59.3, 5.5% of CD4+ T cells, respectively. In the present study we demonstrated negative correlations between CD8+CD28+CD95+ and CD8+CD28−CD95+ T cells and both VCA IgM antibody titers and disease duration. However, no such correlation was found when subset of CD4+ T cells or CD8+CD28+CD95− cells was compared. ConclusionsWe conclude that there is a rapid decrease in the number of memory CD8+ T cells in early acute stage of infectious mononucleosis.

Virus-specific CD4 and CD8 T cell responses in the absence of Th1-associated transcription factors (P6052)

Abstract The eradication of various types of pathogens is mediated by the coordinated efforts of both effector CD4 and CD8 T cells. Following pathogen control, the majority of CD4 and CD8 T cell effector populations undergo apoptosis, but a subset of these cells persists, giving rise to the memory T cell pool. The requirements for the generation of T cell memory have not been completely elucidated, hence we were interested in understanding importance of the Th1 transcription factors Tbet and STAT4 in this process. To interrogate this, we utilized lymphocytic choriomeningitis virus infection of BALB/c mice. Not surprisingly, we observed that in the absence of Tbet, the virus-specific CD4 T cell IFNγ response was ablated but the IL-2 response remained unperturbed. In contrast, we found that STAT4 was not required for IFNγ production by virus-specific CD4 T cells. Conversely, the functional virus-specific CD8 T cell response was intact in the absence of Tbet, STAT4, or both, although increases in the proportion of effector cells competent for IL-2 production were noted in mice that lacked Tbet expression. We did detect marked differences in the expression of CD127 and KLRG1 on virus-specific effector CD8 T cells, however this did not translate into alterations in the numbers of memory CD8 T cells after the resolution of the infection. Collectively, we discovered distinct roles for Tbet and STAT4 in shaping the phenotype and function of virus-specific T cell responses.

FOXO3 Regulates CD8 T Cell Memory by T Cell-Intrinsic Mechanisms

CD8 T cell responses have three phases: expansion, contraction, and memory. Dynamic alterations in proliferation and apoptotic rates control CD8 T cell numbers at each phase, which in turn dictate the magnitude of CD8 T cell memory. Identification of signaling pathways that control CD8 T cell memory is incomplete. The PI3K/Akt signaling pathway controls cell growth in many cell types by modulating the activity of FOXO transcription factors. But the role of FOXOs in regulating CD8 T cell memory remains unknown. We show that phosphorylation of Akt, FOXO and mTOR in CD8 T cells occurs in a dynamic fashion in vivo during an acute viral infection. To elucidate the potentially dynamic role for FOXO3 in regulating homeostasis of activated CD8 T cells in lymphoid and non-lymphoid organs, we infected global and T cell-specific FOXO3-deficient mice with Lymphocytic Choriomeningitis Virus (LCMV). We found that FOXO3 deficiency induced a marked increase in the expansion of effector CD8 T cells, preferentially in the spleen, by T cell-intrinsic mechanisms. Mechanistically, the enhanced accumulation of proliferating CD8 T cells in FOXO3-deficient mice was not attributed to an augmented rate of cell division, but instead was linked to a reduction in cellular apoptosis. These data suggested that FOXO3 might inhibit accumulation of growth factor-deprived proliferating CD8 T cells by reducing their viability. By virtue of greater accumulation of memory precursor effector cells during expansion, the numbers of memory CD8 T cells were strikingly increased in the spleens of both global and T cell-specific FOXO3-deficient mice. The augmented CD8 T cell memory was durable, and FOXO3 deficiency did not perturb any of the qualitative attributes of memory T cells. In summary, we have identified FOXO3 as a critical regulator of CD8 T cell memory, and therapeutic modulation of FOXO3 might enhance vaccine-induced protective immunity against intracellular pathogens.

Dendritic Cells Prevent Rather Than Promote Immunity Conferred by a Helicobacter Vaccine Using a Mycobacterial Adjuvant

Immunization against the gastric bacterium Helicobacter pylori could prevent many gastric cancers and other disorders. Most vaccination protocols used in preclinical models are not suitable for humans. New adjuvants and a better understanding of the correlates and requirements for vaccine-induced protection are needed to accelerate development of vaccines for H pylori. Vaccine-induced protection against H pylori infection and its local and systemic immunological correlates were assessed in animal models, using cholera toxin or CAF01 as adjuvants. The contribution of B cells, T-helper (Th)-cell subsets, and dendritic cells to H pylori-specific protection were analyzed in mice. Parenteral administration of a whole-cell sonicate, combined with the mycobacterial cell-wall-derived adjuvant CAF01, protected against infection with H pylori and required cell-mediated, but not humoral, immunity. The vaccine-induced control of H pylori was accompanied by Th1 and Th17 responses in the gastric mucosa and in the gut-draining mesenteric lymph nodes; both Th subsets were required for protective immunity against H pylori. The numbers of memory CD4+ T cells and neutrophils in gastric tissue were identified as the best correlates of protection. Systemic depletion of dendritic cells or regulatory T cells during challenge infection significantly increased protection by overriding immunological tolerance mechanisms activated by live H pylori. Parenteral immunization with a Helicobacter vaccine using a novel mycobacterial adjuvant induces protective immunity against H pylori that is mediated by Th1 and Th17 cells. Tolerance mechanisms mediated by dendritic cells and regulatory T cells impair H pylori clearance and must be overcome to improve immunity.

Exploiting cross-priming to generate protective CD8 T-cell immunity rapidly

The number of memory CD8 T cells generated by infection or vaccination correlates strongly with the degree of protection observed in infection and tumor models. Therefore, rapid induction of protective numbers of effector and memory CD8 T cells may be crucial in the case of malignancy, pandemic infection, or bioterrorism. Many studies have shown that amplifying T-cell numbers by prime-boost vaccination is most effective with a substantial time interval between immunizations. In contrast, immunization with peptide-coated mature dendritic cells (DCs) results in a CD8 T-cell response exhibiting accelerated acquisition of memory characteristics, including the ability to respond to booster immunization within days of initial priming. However, personalized DC immunization is too costly, labor intensive, and time-consuming for large-scale vaccination. Here, we demonstrate that in vivo cross-priming with cell-associated antigens or antigen-coated, biodegradable microspheres in the absence of adjuvant quickly generates CD8 T cells that display the phenotype and function of long-term memory populations. Importantly, cross-primed CD8 T cells can respond to booster immunization within days of the initial immunization to generate rapidly large numbers of effector and memory T cells that can protect against bacterial, viral, and parasitic infections, including lethal influenza and malaria-causing Plasmodium infection. Thus, accelerated CD8 T-cell memory after in vivo cross-priming in the absence of adjuvant is generalizable and can be exploited to generate protective immunity rapidly.

Cell-Intrinsic Defects in the Proliferative Response of Antiviral Memory CD8 T Cells in Aged Mice upon Secondary Infection

Although previous studies have demonstrated delayed viral clearance and blunted effector T cell responses in aged mice during infection, memory CD8 T cells and especially secondary responses have received less attention. In this study, we show that modest differences in the number of memory CD8 T cells formed in aged versus young animals were associated with altered memory CD8 T cell differentiation. Aged immune mice had increased morbidity and mortality upon secondary viral challenge, suggesting changes in T cell immunity. Indeed, virus-specific memory CD8 T cells from aged mice showed substantially reduced proliferative expansion upon secondary infection using multiple challenge models. In addition, this defect in recall capacity of aged memory CD8 T cells was cell-intrinsic and persisted upon adoptive transfer into young mice. Thus, the poor proliferative potential of memory T cells and altered memory CD8 T cell differentiation could underlie age-related defects in antiviral immunity.

Characterization of neutralizing anti-mouse IL-15 antibodies (96.15)

Abstract IL-15 is believed to play a central role in the pathogenesis of a wide variety of disease states. We have developed neutralizing anti-mouse IL-15 antibodies from IL-15-null mice immunized with E.coli-derived recombinant mIL-15. Monoclonal antibodies M96 and M95 blocked the mIL-15-induced proliferation of CTLL-2 cells in vitro. In a mouse acute GVHD model, M96 inhibited donor CTL expansion and limited donor anti-host cytotoxic activity. In normal mice M96 induced a profound loss of NK cells and, though the total number of CD8 T cells, CD4 T cells, and B cells was not affected by M96, there was a slight reduction in the number of memory CD8 T cells in M96-treated mice. During time course studies, mice treated with 10μg of M96 lost about 50% of NK cells from the spleens within the first day and 95% of NK cells were eliminated by day 4. By day 14 the mice had recovered about 75-80% of their splenic NK cells, and by day 28 splenic NK cell levels were indistinguishable from untreated controls. We believe that M96 will be a useful tool for dissecting the roles of IL15 in normal homeostasis and inflammatory diseases.

Poor anti-viral immunity in aged mice is associated with defects in CD8 T cell recall responses (44.5)

Abstract Aging leads to an increased susceptibility to infectious diseases. To investigate the age-related changes in T cell memory we compared anti-viral CD8 T cell immunity in young versus aged mice following systemic (lymphocytic choriomeningitis virus; LCMV) or local (influenza virus) viral infections. The number of memory CD8 T cells formed was similar or only modestly different between aged and young animals, though in some cases changes in immunodominance and cytokine production were apparent. Both influenza virus-specific and LCMV-specific memory CD8 T cells from aged mice, however, had major substantially reduced proliferative capacity upon secondary infection. As a result, aged mice displayed increased morbidity and mortality upon viral rechallenge. The studies described herein demonstrate that the defects intrinsic to aged CD8 T cells are at least partially responsible for diminished immunity of aged mice. Thus, the strategies that accelerate the induction of T cell responses or that overcome proliferative deficiencies may prove beneficial. These studies were funded by grants from AHA, NIH (HHSN266200500030C) and the Ellison Medical Foundation.

Memory CD8 T-cell compartment grows in size with immunological experience

Memory CD8 T cells, generated by natural pathogen exposure or intentional vaccination, protect the host against specific viral infections. It has long been proposed that the number of memory CD8 T cells in the host is inflexible, and that individual cells are constantly competing for limited space. Consequently, vaccines that introduce over-abundant quantities of memory CD8 T cells specific for an agent of interest could have catastrophic consequences for the host by displacing memory CD8 T cells specific for all previous infections. To test this paradigm, we developed a vaccination regimen in mice that introduced as many new long-lived memory CD8 T cells specific for a single vaccine antigen as there were memory CD8 T cells in the host before vaccination. Here we show that, in contrast to expectations, the size of the memory CD8 T-cell compartment doubled to accommodate these new cells, a change due solely to the addition of effector memory CD8 T cells. This increase did not affect the number of CD4 T cells, B cells or naive CD8 T cells, and pre-existing memory CD8 T cells specific for a previously encountered infection were largely preserved. Thus, the number of effector memory CD8 T cells in the mammalian host adapts according to immunological experience. Developing vaccines that abundantly introduce new memory CD8 T cells should not necessarily ablate pre-existing immunity to other infections.

Bmi1 regulates memory CD4 T cell survival via repression of the Noxa gene

The maintenance of memory T cells is central to the establishment of immunological memory, although molecular details of the process are poorly understood. In the absence of the polycomb group (PcG) gene Bmi1, the number of memory CD4+ T helper (Th)1/Th2 cells was reduced significantly. Enhanced cell death of Bmi1−/− memory Th2 cells was observed both in vivo and in vitro. Among various proapoptotic genes that are regulated by Bmi1, the expression of proapoptotic BH3-only protein Noxa was increased in Bmi1−/− effector Th1/Th2 cells. The generation of memory Th2 cells was restored by the deletion of Noxa, but not by Ink4a and Arf. Direct binding of Bmi1 to the Noxa gene locus was accompanied by histone H3-K27 methylation. The recruitment of other PcG gene products and Dnmt1 to the Noxa gene was highly dependent on the expression of Bmi1. In addition, Bmi1 was required for DNA CpG methylation of the Noxa gene. Moreover, memory Th2-dependent airway inflammation was attenuated substantially in the absence of Bmi1. Thus, Bmi1 controls memory CD4+ Th1/Th2 cell survival and function through the direct repression of the Noxa gene.