Effector CD8 T cell development: a balancing act between memory cell potential and terminal differentiation

Characterization of abscopal effects of intratumoral electroporation-mediated IL-12 gene therapy

Intratumoral electroporation-mediated IL-12 gene therapy (IT-pIL12/EP) has been shown to be safe and effective in clinical trials, demonstrating systemic antitumor effects with local delivery of this potent cytokine. We recently optimized our IL-12 gene delivery platform to increase transgene expression and efficacy in preclinical models. Here we analyze the immunological changes induced with the new IT-pIL12/EP platform in both electroporated and distant, non-electroporated lesions. IT-pIL12/EP-treated tumors demonstrated rapid induction of IL-12-regulated pathways, as well as other cytokines and chemokines pathways, and upregulation of antigen presentation machinery. The distant tumors showed an increase in infiltrating lymphocytes and gene expression changes indicative of a de novo immune response in these untreated lesions. Flow cytometric analyses revealed a KLRG1hi CD8+ effector T-cell population uniquely present in mice treated with IT-pIL12/EP. Despite being highly activated, this population expressed diminished levels of PD-1 when re-exposed to antigen in the PD-L1-rich tumor. Other T-cell exhaustion markers appeared to be downregulated in concert, suggesting an orchestrated "armoring" of these effector T cells against T-cell checkpoints when primed in the presence of IL-12 in situ. These cells may represent an important mechanism by which local IL-12 gene therapy can induce a systemic antitumor immune response without the associated toxicity of systemic IL-12 exposure.

Expression of the DNA-Binding Factor TOX Promotes the Encephalitogenic Potential of Microbe-Induced Autoreactive CD8+ T Cells

Infections are thought to trigger CD8⁺ cytotoxic T lymphocyte (CTL) responses during autoimmunity. However, the transcriptional programs governing the tissue-destructive potential of CTLs remain poorly defined. In a model of central nervous system (CNS) inflammation, we found that infection with lymphocytic choriomeningitis virus (LCMV), but not Listeria monocytogenes (Lm), drove autoimmunity. The DNA-binding factor TOX was induced in CTLs during LCMV infection and was essential for their encephalitogenic properties, and its expression was inhibited by interleukin-12 during Lm infection. TOX repressed the activity of several transcription factors (including Id2, TCF-1, and Notch) that are known to drive CTL differentiation. TOX also reduced immune checkpoint sensitivity by restraining the expression of the inhibitory checkpoint receptor CD244 on the surface of CTLs, leading to increased CTL-mediated damage in the CNS. Our results identify TOX as a transcriptional regulator of tissue-destructive CTLs in autoimmunity, offering a potential mechanistic link to microbial triggers.

Paracrine costimulation of IFN-γ signaling by integrins modulates CD8 T cell differentiation

The cytokine IFN-γ is a critical regulator of immune system development and function. Almost all leukocytes express the receptor for IFN-γ, yet each cell type elicits a different response to this cytokine. Cell type-specific effects of IFN-γ make it difficult to predict the outcomes of the systemic IFN-γ blockade and limit its clinical application, despite many years of research. To better understand the cell-cell interactions and cofactors that specify IFN-γ functions, we focused on the function of IFN-γ on CD8 T cell differentiation. We demonstrated that during bacterial infection, IFN-γ is a dominant paracrine trigger that skews CD8 T cell differentiation toward memory. This skewing is preferentially driven by contact-dependent T cell-T cell (T-T) interactions and the localized IFN-γ secretion among activated CD8 T cells in a unique splenic microenvironment, and is less sensitive to concurrent IFN-γ production by other immune cell populations such as natural killer (NK) cells. Modulation of CD8 T cell differentiation by IFN-γ relies on a nonconventional IFN-γ outcome that occurs specifically within 24 hours following infection. This is driven by IFN-γ costimulation by integrins at T-T synapses, and leads to synergistic phosphorylation of the proximal STAT1 molecule and accelerated IL-2 receptor down-regulation. This study provides evidence of the importance of context-dependent cytokine signaling and gives another example of how cell clusters and the microenvironment drive unique biology.

Class-B CpG-ODN Formulated With a Nanostructure Induces Type I Interferons-Dependent and CD4+ T Cell-Independent CD8+ T-Cell Response Against Unconjugated Protein Antigen

There is a need for new vaccine adjuvant strategies that offer both vigorous antibody and T-cell mediated protection to combat difficult intracellular pathogens and cancer. To this aim, we formulated class-B synthetic oligodeoxynucleotide containing unmethylated cytosine-guanine motifs (CpG-ODN) with a nanostructure (Coa-ASC16 or coagel) formed by self-assembly of 6-0-ascorbyl palmitate ester. Our previous results demonstrated that mice immunized with ovalbumin (OVA) and CpG-ODN formulated with Coa-ASC16 (OVA/CpG-ODN/Coa-ASC16) elicited strong antibodies (IgG1 and IgG2a) and Th1/Th17 cellular responses without toxic systemic effects. These responses were superior to those induced by a solution of OVA with CpG-ODN or OVA/CpG-ODN formulated with aluminum salts. In this study, we investigated the capacity of this adjuvant strategy (CpG-ODN/Coa-ASC16) to elicit CD8+ T-cell response and some of the underlying cellular and molecular mechanisms involved in adaptive response. We also analyzed whether this adjuvant strategy allows a switch from an immunization scheme of three-doses to one of single-dose. Our results demonstrated that vaccination with OVA/CpG-ODN/Coa-ASC16 elicited an antigen-specific long-lasting humoral response and importantly-high quality CD8+ T-cell immunity with a single-dose immunization. Moreover, Coa-ASC16 promoted co-uptake of OVA and CpG-ODN by dendritic cells. The CD8+ T-cell response induced by OVA/CpG-ODN/Coa-ASC16 was dependent of type I interferons and independent of CD4+ T-cells, and showed polyfunctionality and efficiency against an intracellular pathogen. Furthermore, the cellular and humoral responses elicited by the nanostructured formulation were IL-6-independent. This system provides a simple and inexpensive adjuvant strategy with great potential for future rationally designed vaccines.

Phenotypic and Functional Signatures of Herpes Simplex Virus-Specific Effector Memory CD73+CD45RAhighCCR7lowCD8+ TEMRA and CD73+CD45RAlowCCR7lowCD8+ TEM Cells Are Associated with Asymptomatic Ocular Herpes

HSV type 1 (HSV-1)-specific CD8⁺ T cells protect from herpes infection and disease. However, the nature of protective CD8⁺ T cells in HSV-1 seropositive healthy asymptomatic (ASYMP) individuals (with no history of clinical herpes disease) remains to be determined. In this study, we compared the phenotype and function of HSV-specific CD8⁺ T cells from HLA-A*02:01-positive ASYMP and symptomatic (SYMP) individuals (with a documented history of numerous episodes of recurrent ocular herpetic disease). We report that although SYMP and ASYMP individuals have similar frequencies of HSV-specific CD8⁺ T cells, the "naturally" protected ASYMP individuals have a significantly higher proportion of multifunctional HSV-specific effector memory CD8⁺ T cells (CD73⁺CD45RA^highCCR7^lowCD8⁺ effector memory RA (T_EMRA) and CD73⁺CD45RA^lowCCR7^lowCD8⁺ effector memory (T_EM) as compared with SYMP individuals. Similar to humans, HSV-1-infected ASYMP B6 mice had frequent multifunctional HSV-specific CD73⁺CD8⁺ T cells in the cornea, as compared with SYMP mice. Moreover, in contrast to wild type B6, CD73^-/- deficient mice infected ocularly with HSV-1 developed more recurrent corneal herpetic infection and disease. This was associated with less functional CD8⁺ T cells in the cornea and trigeminal ganglia, the sites of acute and latent infection. The phenotypic and functional characteristics of HSV-specific circulating and in situ CD73⁺CD8⁺ T cells, demonstrated in both ASYMP humans and mice, suggest a positive role for effector memory CD8⁺ T cells expressing the CD73 costimulatory molecule in the protection against ocular herpes infection and disease. These findings are important for the development of safe and effective T cell-based herpes immunotherapy.

The Transcription Factor Runx2 Is Required for Long-Term Persistence of Antiviral CD8+ Memory T Cells

During acute lymphocytic choriomeningitis virus infection, pathogen-specific CD8⁺ cytotoxic T lymphocytes undergo clonal expansion leading to viral clearance. Following this, the majority of pathogen-specific CD8⁺ T cells undergo apoptosis, leaving a small number of memory CD8⁺ T cells that persist long-term and provide rapid protection upon secondary infection. Whereas much is known about the cytokines and transcription factors that regulate the early effector phase of the antiviral CD8⁺ T cell response, the factors regulating memory T cell homeostasis and survival are not well understood. In this article, we show that the Runt-related transcription factor Runx2 is important for long-term memory CD8⁺ T cell persistence following acute lymphocytic choriomeningitis virus-Armstrong infection in mice. Loss of Runx2 in T cells led to a reduction in KLRG1^lo CD127^hi memory precursor cell numbers with no effect on KLRG1^hi CD127^lo terminal effector cell populations. Runx2 expression levels were transcriptionally regulated by TCR signal strength via IRF4, TLR4/7, and selected cytokines. These data demonstrate a CD8⁺ T cell–intrinsic role for Runx2 in the long-term maintenance of antiviral memory CD8⁺ T cell populations.

Foxo transcription factors in T cell biology and tumor immunity

The evolutionally conserved forkhead box O (Foxo) family of transcription factors is pivotal in the control of nutrient sensing and stress responses. Recent studies have revealed that the Foxo proteins have been rewired to regulate highly specialized T cell activities. Here, we review the latest advances in the understanding of how Foxo transcription factors control T cell biology, including T cell trafficking, naive T cell homeostasis, effector and memory responses, as well as the differentiation and function of regulatory T cells. We also discuss the emerging evidence on Foxo-mediated regulation in antitumor immunity. Future work will further explore how the Foxo-dependent programs in T cells can be exploited for cancer immunotherapy.

PD-1 deficiency augments bone marrow failure in a minor-histocompatibility antigen mismatch lymphocyte infusion model

Although PD-1 blockade has revolutionized cancer immunotherapy, immune-related adverse events (irAEs) present life-threatening complications. Recent reports of aplastic anemia (AA) as irAEs implicate PD-1/PD-L1 as important in preventing immune-mediated destruction of the hematopoietic niche. Infusion of PD-1-deficient (PD-1 knockout [KO]) lymph node (LN) cells into minor-antigen mismatched mice resulted in early mortality, as well as more severe bone marrow (BM) hypoplasia, anemia, and BM microarchitecture disruption in PD-1 KO LN-infused mice relative to mice that received B6 LN cell infusion. Mice that received PD-1 KO LN cells had more CD8⁺ T-cell infiltration of the BM and greater expansion of H60-specific CD8⁺ T cells than did their B6 LN-infused counterparts. In the spleen, CD8⁺ T cells were skewed to an effector memory phenotype, suggesting accelerated differentiation of PD-1 KO T cells. Our data suggest that PD-1 dysregulation has a role in murine BM failure and vigilance in irAE monitoring may be desirable to treat early AA and related cytopenias.

Cytokine- and TCR-Mediated Regulation of T Cell Expression of Ly6C and Sca-1

Ly6C and Sca-1 (Ly6A/E) are Ly6 family GPI-anchored surface molecules that are differentially expressed by multiple immune populations. Ly6C expression has been used to distinguish short-lived effector CD4⁺ T cells from memory precursor effector cells, whereas Sca-1 has been used in the identification of CD8⁺ memory stem cells. This study examines the expression patterns of these molecules and establishes that, in vitro, IL-27, type I IFN, and IFN-γ are potent inducers of Ly6C and Sca-1 in naive mouse CD4⁺ and CD8⁺ T cells, whereas TGF-β limits their expression. The induction of Ly6C and Sca-1 by IL-27 and IFN-γ is dependent on STAT1, but not STAT3 or T-bet. In mouse splenocytes, at homeostasis, Ly6C and Sca-1 expression was not restricted to effector cells, but was also found at various levels on naive and memory populations. However, in response to infection with Toxoplasma gondii, pathogen-specific T cells expressed high levels of these molecules and in this context, endogenous IL-27 and IFN-γ were required for the expression of Ly6C but not Sca-1. Together, these findings highlight the TCR-dependent and cytokine-mediated signals that modulate T cell expression of Ly6C and Sca-1 in vitro and in vivo during infection.

Multifaceted Role of Neuropilins in the Immune System: Potential Targets for Immunotherapy

Neuropilins (NRPs) are non-tyrosine kinase cell surface glycoproteins expressed in all vertebrates and widely conserved across species. The two isoforms, such as neuropilin-1 (NRP1) and neuropilin-2 (NRP2), mainly act as coreceptors for class III Semaphorins and for members of the vascular endothelial growth factor family of molecules and are widely known for their role in a wide array of physiological processes, such as cardiovascular, neuronal development and patterning, angiogenesis, lymphangiogenesis, as well as various clinical disorders. Intriguingly, additional roles for NRPs occur with myeloid and lymphoid cells, in normal physiological as well as different pathological conditions, including cancer, immunological disorders, and bone diseases. However, little is known concerning the molecular pathways that govern these functions. In addition, NRP1 expression has been characterized in different immune cellular phenotypes including macrophages, dendritic cells, and T cell subsets, especially regulatory T cell populations. By contrast, the functions of NRP2 in immune cells are less well known. In this review, we briefly summarize the genomic organization, structure, and binding partners of the NRPs and extensively discuss the recent advances in their role and function in different immune cell subsets and their clinical implications.

The Antitumor Effects of Vaccine-Activated CD8+ T Cells Associate with Weak TCR Signaling and Induction of Stem-Like Memory T Cells

To understand why vaccine-activated tumor-specific T cells often fail to generate antitumor effects, we studied two α-fetoprotein-specific CD8⁺ T cells (Tet₄₉₉ and Tet₂₁₂) that had different antitumor effects. We found that Tet₄₉₉ required high antigen doses for reactivation, but could survive persistent antigen stimulation and maintain their effector functions. In contrast, Tet₂₁₂ had a low threshold of reactivation, but underwent exhaustion and apoptosis in the presence of persistent antigen. In vivo, Tet₄₉₉ cells expanded more than Tet₂₁₂ upon reencountering antigen and generated stronger antitumor effects. The different antigen responsiveness and antitumor effects of Tet₂₁₂ and Tet₄₉₉ cells correlated with their activation and differentiation states. Compared with Tet₂₁₂, the population of Tet₄₉₉ cells was less activated and contained more stem-like memory T cells (Tscm) that could undergo expansion in vivo The TCR signaling strength on Tet₄₉₉ was weaker than Tet₂₁₂, correlating with more severe Tet₄₉₉ TCR downregulation. Weak TCR signaling may halt T-cell differentiation at the Tscm stage during immune priming and also explains why Tet₄₉₉ reactivation requires a high antigen dose. Weak TCR signaling of Tet₄₉₉ cells in the effector stage will also protect them from exhaustion and apoptosis when they reencounter persistent antigen in tumor lesion, which generates antitumor effects. Further investigation of TCR downregulation and manipulation of TCR signaling strength may help design cancer vaccines to elicit a mix of tumor-specific CD8⁺ T cells, including Tscm, capable of surviving antigen restimulation to generate antitumor effects. Cancer Immunol Res; 5(10); 908-19. ©2017 AACR.

Elevated expression of miR-155 is associated with the differentiation of CD8+ T cells in patients with HIV-1

The differentiation and response ofCD8+ T cells is vital in host defense against human immunodeficiency virus type 1 (HIV-1). MicroRNA (miR)‑155 is an important regulator of T cell differentiation. However, the profile of miR-155 in HIV‑1 infected individuals and its association with CD8+ T cell differentiation remain to be fully elucidated. The present cross‑sectional study was performed involving 63 HIV‑1‑infected patients undergoing highly active antiretroviral therapy (HAART), 31 HAART‑naïve patients and 35 healthy controls. The levels of miR‑155 in CD8+ T cells were detected using reverse transcription‑quantitative polymerase chain reaction analysis. Subsets of CD8+ T cell differentiation were detected using flow cytometry. The results revealed that the discord controllers and HAART‑naïve patients showed higher percentages of effector and effector memory cells, and lower percentages of naïve cells (P<0.05). The levels of miR‑155 in CD8+ T cells from the HIV‑1‑infected patients were higher, particularly in the discord controllers and HAART naïve patients (P<0.01). The expression levels of miR‑155 were positively correlated with the percentages of effector and effector memory CD8+ T cells, and negatively correlated with the percentages of naïve and central memory CD8+ T cells (P<0.01). Taken together, these findings suggested that the levels of miR‑155 in CD8+ T cells of patients with HIV-1 were increased and asso-ciated with CD8+ T cell differentiation.

Antifungal Tc17 cells are durable and stable, persisting as long-lasting vaccine memory without plasticity towards IFNγ cells

Our understanding of persistence and plasticity of IL-17A⁺ memory T cells is clouded by conflicting results in models analyzing T helper 17 cells. We studied memory IL-17A⁺ CD8⁺ T-cell (Tc17) homeostasis, persistence and plasticity during fungal vaccine immunity. We report that vaccine-induced memory Tc17 cells persist with high fidelity to the type 17 phenotype. Tc17 cells persisted durably for a year as functional IL-17A⁺ memory cells without converting to IFNγ⁺ (Tc1) cells, although they produced multiple type I cytokines in the absence of residual vaccine antigen. Memory Tc17 cells were canonical CD8⁺ T cells with phenotypic features distinct from Tc1 cells, and were Ror(γ)t^hi, TCF-1^hi, T-bet^lo and EOMES^lo. In investigating the bases of Tc17 persistence, we observed that memory Tc17 cells had much higher levels of basal homeostatic proliferation than did Tc1 cells. Conversely, memory Tc17 cells displayed lower levels of anti-apoptotic molecules Bcl-2 and Bcl-xL than Tc1 cells, yet were resistant to apoptosis. Tc1 cells required Bcl-2 for their survival, but Bcl-2 was dispensable for the maintenance of Tc17 cells. Tc17 and Tc1 cells displayed different requirements for HIF-1α during effector differentiation and sustenance and memory persistence. Thus, antifungal vaccination induces durable and stable memory Tc17 cells with distinct requirements for long-term persistence that distinguish them from memory Tc1 cells.

CD4⁺ T-cell deficient patients such as those with AIDS and idiopathic CD4⁺ T-cell lymphopenia are vulnerable to systemic fungal infections. We previously showed that CD8⁺ T cells can be exploited in CD4⁺ T cell deficient hosts for vaccine immunity against lethal fungal pneumonia in mice and that IL-17A production by these cells (Tc17) is essential. Existing dogma holds that IL-17A producing CD4⁺ T cells (Th17) are highly plastic, unstable, and convert into IFNγ producing cells, losing the capacity to produce IL-17A, which is the signature feature of Tc17 cells. Here, we show that vaccine-elicited antifungal Tc17 cells are maintained as stable and long-lasting memory cells that resist conversion into IFNγ cells (Tc1) and protect CD4⁺ T cell deficient hosts against lethal pulmonary fungal infection. Antifungal Tc17 cells displayed features that define classical memory cells. However, memory Tc17 exhibited different requirements than Tc1 cells in the factors that promote T cell survival, including anti-apoptotic molecules Bcl-2 and Bcl-xl, and HIF-1α, which aids survival of cells in lower oxygen conditions found during inflammation. Thus, our study reveals that fungal vaccination elicits a durable, stable population of Tc17 cells with distinct features of survival needed for preventing infection in immunocompromised hosts.

Expansion of T Cells with Interleukin-21 for Adoptive Immunotherapy of Murine Mammary Carcinoma

We previously demonstrated that culturing antigen-sensitized draining lymph node (DLN) lymphocytes from BALB/c mice in interleukin (IL)-7/15 after activation with bryostatin/ionomycin (B/I) is superior to culture in IL-2 for expansion, differentiation to cluster of differentiation (CD)8+ cells and anti-tumor activity. We sought to determine whether the substitution or addition of IL-21 to culture had a similar effect. DLN lymphocytes were antigen-sensitized with 4T1 mammary carcinoma 10 days prior to harvest, activated with B/I, and expanded in culture for 7 days with either IL-2, IL-21, IL-2/21, IL-7/15, or IL-7/15/21. Cellular expansion, phenotype, interferon (IFN)-γ responses, and in vivo anti-tumor activity were compared. We found that T cells grown in IL7/15/21 demonstrated significantly greater lymphocyte expansion than IL-2, IL-21, IL-2/21, and IL-7/15 (38.4-fold vs. 5.5, 6.6, 9.5, and 23.9-fold, respectively). Of these expanded cells, IL-7/15/21 significantly expanded the greatest percentage of CD8+ cells (67.1% vs. 22.2%, 47.2%, 47.4%, and 55.3%, respectively), and the greatest number of T central memory cells (T_CM) compared to IL-2, IL-21 and IL-2/21 (45.8% vs. 11.1%, 7.7%, and 12.1%, respectively). IL-21 and IL-2/21-expanded T cells preferentially differentiated into T naïve cells (T_N) vs. those expanded in IL-2, IL-7/15 and IL-7/15/21 (27.6% and 23.2% vs. 1.7%, 4.5%, and 10.4%, respectively), and demonstrated the highest IFN-γ levels in vitro. In vivo adoptive immunotherapy (AIT) experiments demonstrated anti-tumor efficacy was equally effective using IL-2, IL-21, IL-2/21, IL-7/15 and IL-7/15/21-cultured lymphocytes vs. control or cyclophosphamide alone, even at lower doses or with greater initial size of tumor prior to treatment.

Human Asymptomatic Epitopes Identified from the Herpes Simplex Virus Tegument Protein VP13/14 (UL47) Preferentially Recall Polyfunctional Effector Memory CD44high CD62Llow CD8+ TEM Cells and Protect Humanized HLA-A*02:01 Transgenic Mice against Ocular Herpesvirus Infection

Herpes simplex virus 1 (HSV-1) infection is widespread among humans. The HSV-1 virion protein 13/14 (VP13/14), also known as UL47, is a tegument antigen targeted by CD8⁺ T cells from HSV-seropositive individuals. However, whether VP13/14-specific CD8⁺ T cells play a role in the natural protection seen in asymptomatic (ASYMP) individuals (individuals who have never had a clinical herpetic disease) has not been elucidated. Using predictive computer-assisted algorithms, we identified 10 potential HLA-A*02:01-restricted CD8⁺ T-cell epitopes from the 693-amino-acid sequence of the VP13/14 protein. Three out of 10 epitopes exhibited a high to moderate affinity of binding to soluble HLA-A*02:01 molecules. The phenotype and function of CD8⁺ T cells specific for each epitope were compared in HLA-A*02:01-positive ASYMP individuals and symptomatic (SYMP) individuals (individuals who have frequent clinical herpetic diseases) using determination of a combination of tetramer frequency and the levels of granzyme B, granzyme K, perforin, gamma interferon, tumor necrosis factor alpha, and interleukin-2 production and CD107^a/b cytotoxic degranulation. High frequencies of multifunctional CD8⁺ T cells directed against three epitopes, VP13/14 from amino acids 286 to 294 (VP13/14_286-294), VP13/14 from amino acids 504 to 512 (VP13/14_504-512), and VP13/14 from amino acids 544 to 552 (VP13/14_544-552), were detected in ASYMP individuals, while only low frequencies were detected in SYMP individuals. The three epitopes also predominantly recalled more CD45RA^low CD44^high CCR7^low CD62L^low CD8⁺ effector memory T cells (T_EM cells) in ASYMP individuals than SYMP individuals. Moreover, immunization of HLA-A*02:01 transgenic mice with the three CD8⁺ T_EM-cell epitopes from ASYMP individuals induced robust and polyfunctional HSV-specific CD8⁺ T_EM cells associated with strong protective immunity against ocular herpesvirus infection and disease. Our findings outline the phenotypic and functional features of protective HSV-specific CD8⁺ T cells that should guide the development of a safe and effective T-cell-based herpes simplex vaccine.

IMPORTANCE

Although most herpes simplex virus 1 (HSV-1)-infected individuals shed the virus in their body fluids following reactivation from latently infected sensory ganglia, the majority never develop a recurrent herpetic disease and remain asymptomatic (ASYMP). In contrast, small proportions of individuals are symptomatic (SYMP) and develop frequent bouts of recurrent disease. The present study demonstrates that naturally protected ASYMP individuals have a higher frequency of effector memory CD8⁺ T cells (CD8⁺ T_EM cells) specific to three epitopes derived from the HSV-1 tegument protein VP13/14 (VP13/14_286-294,VP13/14_504-512, and VP13/14_544-552) than SYMP patients. Moreover, immunization of humanized HLA-A*02:01 transgenic mice with the three CD8⁺ T_EM-cell epitopes from ASYMP individuals induced robust and polyfunctional HSV-specific CD8⁺ T cells associated with strong protective immunity against ocular herpesvirus infection and disease. The findings support the emerging concept of the development of a safe and effective asymptomatic herpes simplex vaccine that is selectively based on CD8⁺ T-cell epitopes from ASYMP individuals.

Manipulating Memory CD8 T Cell Numbers by Timed Enhancement of IL-2 Signals

As a result of the growing burden of tumors and chronic infections, manipulating CD8 T cell responses for clinical use has become an important goal for immunologists. In this article, we show that dendritic cell (DC) immunization coupled with relatively early (days 1-3) or late (days 4-6) administration of enhanced IL-2 signals increase peak effector CD8 T cell numbers, but only early IL-2 signals enhance memory numbers. IL-2 signals delivered at relatively late time points drive terminal differentiation and marked Bim-mediated contraction and do not increase memory T cell numbers. In contrast, early IL-2 signals induce effector cell metabolic profiles that are more conducive to memory formation. Of note, downregulation of CD80 and CD86 was observed on DCs in vivo following early IL-2 treatment. Mechanistically, early IL-2 treatment enhanced CTLA-4 expression on regulatory T cells, and CTLA-4 blockade alongside IL-2 treatment in vivo prevented the decrease in CD80 and CD86, supporting a cell-extrinsic role for CTLA-4 in downregulating B7 ligand expression on DCs. Finally, DC immunization followed by early IL-2 treatment and anti-CTLA-4 blockade resulted in lower memory CD8 T cell numbers compared with the DC+early IL-2 treatment group. These data suggest that curtailed signaling through the B7-CD28 costimulatory axis during CD8 T cell activation limits terminal differentiation and preserves memory CD8 T cell formation; thus, it should be considered in future T cell-vaccination strategies.

An imbalance between innate and adaptive immune cells at the maternal-fetal interface occurs prior to endotoxin-induced preterm birth

Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality worldwide. A transition from an anti-inflammatory state to a pro-inflammatory state in the mother and at the maternal-fetal interface has been implicated in the pathophysiology of microbial-induced preterm labor. However, it is unclear which immune cells mediate this transition. We hypothesized that an imbalance between innate and adaptive immune cells at the maternal-fetal interface will occur prior to microbial-induced preterm labor. Using an established murine model of endotoxin-induced PTB, our results demonstrate that prior to delivery there is a reduction of CD4+ regulatory T cells (Tregs) in the uterine tissues. This reduction is neither linked to a diminished number of Tregs in the spleen, nor to an impaired production of IL10, CCL17, or CCL22 by the uterine tissues. Endotoxin administration to pregnant mice does not alter effector CD4+ T cells at the maternal-fetal interface. However, it causes an imbalance between Tregs (CD4+ and CD8+), effector CD8+ T cells, and Th17 cells in the spleen. In addition, endotoxin administration to pregnant mice leads to an excessive production of CCL2, CCL3, CCL17, and CCL22 by the uterine tissues as well as abundant neutrophils. This imbalance in the uterine microenvironment is accompanied by scarce APC-like cells such as macrophages and MHC II+ neutrophils. Collectively, these results demonstrate that endotoxin administration to pregnant mice causes an imbalance between innate and adaptive immune cells at the maternal-fetal interface.

The Role of Lymphatic Niches in T Cell Differentiation

Long-term immunity to many viral and bacterial pathogens requires CD8(+) memory T cell development, and the induction of long-lasting CD8(+) memory T cells from a naïve, undifferentiated state is a major goal of vaccine design. Formation of the memory CD8(+) T cell compartment is highly dependent on the early activation cues received by naïve CD8(+) T cells during primary infection. This review aims to highlight the cellularity of various niches within the lymph node and emphasize recent evidence suggesting that distinct types of T cell activation and differentiation occur within different immune contexts in lymphoid organs.

Latent Cytomegalovirus Infection in Rheumatoid Arthritis and Increased Frequencies of Cytolytic LIR-1+CD8+ T Cells

Objective

Leukocyte immunoglobulin‐like receptor 1 (LIR‐1) is up‐regulated by cytomegalovirus (CMV), which in turn, has been associated with premature aging and more severe joint disease in patients with rheumatoid arthritis (RA). The aim of this study was to investigate the expression and functional significance of LIR‐1 in CMV‐positive RA patients.

Methods

We determined the phenotype, cytolytic potential, CMV‐specific proliferation, and HLA–G–triggered, LIR‐1–mediated inhibition of interferon‐γ secretion of LIR‐1+ T cells in RA patients and healthy controls.

Results

We found increased frequencies of CD8+ T cells with CMV pp65–specific T cell receptors in CMV‐positive RA patients as compared to CMV‐positive healthy controls. CMV‐specific CD8+ T cells in these patients were preferentially LIR‐1+ and exhibited a terminally differentiated polyfunctional phenotype. The numbers of LIR‐1+CD8+ T cells increased with age and disease activity, and showed high levels of reactivity to CMV antigens. Ligation of LIR‐1 with soluble HLA–G molecules in vitro confirmed an inhibitory role of the molecule when expressed on CD8+ T cells in RA patients.

Conclusion

We propose that latent CMV infection in the context of a chronic autoimmune response induces the recently described “chronic infection phenotype” in CD8+ T cells, which retains anti‐infectious effector features while exhibiting autoreactive cytolytic potential. This response is likely dampened by LIR‐1 to avoid overwhelming immunopathologic changes in the setting of the autoimmune disease RA. The known deficiency of soluble HLA–G in RA and the observed association of LIR‐1 expression with disease activity suggest, however, that LIR‐1+ T cells are insufficiently controlled in RA and are still likely to be involved in the pathogenesis of the disease.

Attrition of memory CD8 T cells during sepsis requires LFA-1

CD8 T cell loss and dysfunction have been implicated in the increased susceptibility to opportunistic infections during the later immunosuppressive phase of sepsis, but CD8 T cell activation and attrition in early sepsis remain incompletely understood. With the use of a CLP model, we assessed CD8 T cell activation at 5 consecutive time points and found that activation after sepsis results in a distinct phenotype (CD69⁺CD25^intCD62L^HI) independent of cognate antigen recognition and TCR engagement and likely through bystander-mediated cytokine effects. Additionally, we observed that sepsis concurrently results in the preferential depletion of a subset of memory-phenotype CD8 T cells that remain "unactivated" (i.e., fail to up-regulate activation markers) by apoptosis. Unactivated CD44^HI OT-I cells were spared from sepsis-induced attrition, as were memory-phenotype CD8 T cells of mice treated with anti-LFA-1 mAb, 1 h after CLP. Perhaps most importantly, we demonstrate that attrition of memory phenotype cells may have a pathologic significance, as elevated IL-6 levels were associated with decreased numbers of memory-phenotype CD8 T cells in septic mice, and preservation of this subset after administration of anti-LFA-1 mAb conferred improved survival at 7 d. Taken together, these data identify potentially modifiable responses of memory-phenotype CD8 T cells in early sepsis and may be particularly important in the application of immunomodulatory therapies in sepsis.

Nanoparticle-Based Modulation of the Immune System

The immune system is an incredibly complex biological network that plays a significant role in almost all disease pathogenesis. With an increased understanding of how this vital system operates, there has been a great emphasis on leveraging, manipulating, and/or supplementing endogenous immunity to better prevent or treat different disease states. More recently, the advent of nanotechnology has ushered in a plethora of new nanoparticle-based platforms that can be used to improve existing immunomodulation modalities. As the ability to engineer at the nanoscale becomes increasingly sophisticated, nanoparticles can be finely tuned to effect the desired immune responses, leading to exciting new avenues for addressing pressing issues in public health. In this review, we give an overview of the different areas in which nanoparticle technology has been applied toward modulating the immune system and highlight the recent advances within each.

Type 1 interferon licenses naïve CD8 T cells to mediate anti-viral cytotoxicity

Naïve T cells, unlike memory T cells, exhibit very limited effector function in response to cognate antigen, but exposure to type 1 interferon (IFN) prior to cognate antigen allows for rapid manifestation of effector functions. A full assessment of the functions of these IFN-sensitized otherwise naïve T cells has not been made, nor has their capacity to be effector cells in vivo. We describe here that IFN-sensitized naïve T cells in the absence of cognate antigen adopt a partial activated phenotype distinguished by the upregulation of the surface activation marker CD69, effector-associated transcription factors Eomes and IRF4, and cytotoxicity effector molecule granzyme B. IFN-sensitized naive T cells lysed target cells in vivo and responded to low concentrations and affinities of cognate ligands. We suggest that this rapid and sensitive effector function of IFN-conditioned naïve CD8 T cells may play a role in pathogen control and help ward off superinfections.

Characterization of Diabetogenic CD8+ T Cells: IMMUNE THERAPY WITH METABOLIC BLOCKADE

Type 1 diabetes mellitus is caused by the killing of insulin-producing β cells by CD8+T cells. The disease progression, which is chronic, does not follow a course like responses to conventional antigens such as viruses, but accelerates as glucose tolerance deteriorates. To identify the unique features of the autoimmune effectors that may explain this behavior, we analyzed diabetogenic CD8+ T cells that recognize a peptide from the diabetes antigen IGRP (NRP-V7-reactive) in prediabetic NOD mice and compared them to others that shared their phenotype (CD44(+)CD62L(lo)PD-1(+)CXCR3(+)) but negative for diabetes antigen tetramers and to LCMV (lymphocytic choriomeningitis)-reactive CD8+ T cells. There was an increase in the frequency of the NRP-V7-reactive cells coinciding with the time of glucose intolerance. The T cells persisted in hyperglycemic NOD mice maintained with an insulin pellet despite destruction of β cells. We compared gene expression in the three groups of cells compared with the other two subsets of cells, and the NRP-V7-reactive cells exhibited gene expression of memory precursor effector cells. They had reduced cellular proliferation and were less dependent on oxidative phosphorylation. When prediabetic NOD mice were treated with 2-deoxyglucose to block aerobic glycolysis, there was a reduction in the diabetes antigen versus other cells of similar phenotype and loss of lymphoid cells infiltrating the islets. In addition, treatment of NOD mice with 2-deoxyglucose resulted in improved β cell granularity. These findings identify a link between metabolic disturbances and autoreactive T cells that promotes development of autoimmune diabetes.

Role of memory T cell subsets for adoptive immunotherapy

Adoptive transfer of primary (unmodified) or genetically engineered antigen-specific T cells has demonstrated astonishing clinical results in the treatment of infections and some malignancies. Besides the definition of optimal targets and antigen receptors, the differentiation status of transferred T cells is emerging as a crucial parameter for generating cell products with optimal efficacy and safety profiles. Long-living memory T cells subdivide into phenotypically as well as functionally different subsets (e.g. central memory, effector memory, tissue-resident memory T cells). This diversification process is crucial for effective immune protection, with probably distinct dependencies on the presence of individual subsets dependent on the disease to which the immune response is directed as well as its organ location. Adoptive T cell therapy intends to therapeutically transfer defined T cell immunity into patients. Efficacy of this approach often requires long-term maintenance of transferred cells, which depends on the presence and persistence of memory T cells. However, engraftment and survival of highly differentiated memory T cell subsets upon adoptive transfer is still difficult to achieve. Therefore, the recent observation that a distinct subset of weakly differentiated memory T cells shows all characteristics of adult tissue stem cells and can reconstitute all types of effector and memory T cell subsets, became highly relevant. We here review our current understanding of memory subset formation and T cell subset purification, and its implications for adoptive immunotherapy.

Retrogenic ICOS Expression Increases Differentiation of KLRG-1hiCD127loCD8+ T Cells during Listeria Infection and Diminishes Recall Responses

Following T cell encounter with Ag, multiple signals are integrated to collectively induce distinct differentiation programs within Ag-specific CD8(+) T cell populations. Several factors contribute to these cell fate decisions, including the amount and duration of Ag, exposure to inflammatory cytokines, and degree of ligation of cosignaling molecules. The ICOS is not expressed on resting T cells but is rapidly upregulated upon encounter with Ag. However, the impact of ICOS signaling on programmed differentiation is not well understood. In this study, we therefore sought to determine the role of ICOS signaling on CD8(+) T cell programmed differentiation. Through the creation of novel ICOS retrogenic Ag-specific TCR-transgenic CD8(+) T cells, we interrogated the phenotype, functionality, and recall potential of CD8(+) T cells that receive early and sustained ICOS signaling during Ag exposure. Our results reveal that these ICOS signals critically impacted cell fate decisions of Ag-specific CD8(+) T cells, resulting in increased frequencies of KLRG-1(hi)CD127(lo) cells, altered BLIMP-1, T-bet, and eomesodermin expression, and increased cytolytic capacity as compared with empty vector controls. Interestingly, however, ICOS retrogenic CD8(+) T cells also preferentially homed to nonlymphoid organs and exhibited reduced multicytokine functionality and reduced ability to mount secondary recall responses upon challenge in vivo. In sum, our results suggest that an altered differentiation program is induced following early and sustained ICOS expression, resulting in the generation of more cytolyticly potent, terminally differentiated effectors that possess limited capacity for recall response.

Adaptive immune response to therapy in hmgcr autoantibody myopathy

INTRODUCTION

We evaluated the response to immunosuppression in a case of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR)-autoantibody myopathy.

METHODS

T- and B-cell subsets were determined by flow cytometry pre- and posttherapy.

RESULTS

Baseline immune profiling demonstrated strikingly elevated T-follicular helper (Tfh) cells and plasmablasts. Immunosuppression resulted in clinical improvement and decreased Tfh cells, plasmablasts, and autoantibodies.

CONCLUSIONS

Immune profiling in HMGCR-autoantibody myopathy suggests a B-cell-mediated disease. Tfh cells and plasmablasts may be therapeutic biomarkers.

Regulation of effector and memory CD8(+) T cell function by inflammatory cytokines

Cells communicate with each other through the production and secretion of cytokines, which are integral to the host response to infection. Once recognized by specific cytokine receptors expressed on the cell surface, these exogenous signals direct the biological function of a cell in order to adapt to their microenvironment. CD8(+) T cells are critical immune cells that play an important role in the control and elimination of intracellular pathogens. Current findings have demonstrated that cytokines influence all aspects of the CD8(+) T cell response to infection or immunization. The cytokine milieu induced at the time of activation impacts the overall magnitude and function of the effector CD8(+) T cell response and the generation of functional memory CD8(+) T cells. This review will focus on the impact of inflammatory cytokines on different aspects of CD8(+) T cell biology.

CD70 and IFN-1 selectively induce eomesodermin or T-bet and synergize to promote CD8+ T-cell responses

CD70-mediated stimulation of CD27 is an important cofactor of CD4(+) T-cell licensed dendritic cells (DCs). However, it is unclear how CD70-mediated stimulation of T cells is integrated with signals that emanate from signal 3 pathways, such as type-1 interferon (IFN-1) and IL-12. We find that while stimulation of CD27 in isolation drives weak Eomesodermin(hi) T-bet(lo) CD8(+) T-cell responses to OVA immunization, profound synergistic expansion is achieved by cotargeting TLR. This cooperativity can substantially boost antiviral CD8(+) T-cell responses during acute infection. Concomitant stimulation of TLR significantly increases per cell IFN-γ production and the proportion of the population with characteristics of short-lived effector cells, yet also promotes the ability to form long-lived memory. Notably, while IFN-1 contributes to the expression of CD70 on DCs, the synergy between CD27 and TLR stimulation is dependent upon IFN-1's effect directly on CD8(+) T cells, and is associated with the increased expression of T-bet in T cells. Surprisingly, we find that IL-12 fails to synergize with CD27 stimulation to promote CD8(+) T-cell expansion, despite its capacity to drive effector CD8(+) T-cell differentiation. Together, these data identify complex interactions between signal 3 and costimulatory pathways, and identify opportunities to influence the differentiation of CD8(+) T-cell responses.

MicroRNAs and Their Targets Are Differentially Regulated in Adult and Neonatal Mouse CD8+ T Cells

Immunological memory, which protects organisms from re-infection, is a hallmark of the mammalian adaptive immune system and the underlying principle of vaccination. In early life, however, mice and other mammals are deficient at generating memory CD8+ T cells, which protect organisms from intracellular pathogens. The molecular basis that differentiates adult and neonatal CD8+ T cells is unknown. MicroRNAs (miRNAs) are both developmentally regulated and required for normal adult CD8+ T cell functions. We used next-generation sequencing to identify mouse miRNAs that are differentially regulated in adult and neonatal CD8+ T cells, which may contribute to the impaired development of neonatal memory cells. The miRNA profiles of adult and neonatal cells were surprisingly similar during infection; however, we observed large differences prior to infection. In particular, miR-29 and miR-130 have significant differential expression between adult and neonatal cells before infection. Importantly, using RNA-Seq, we detected reciprocal changes in expression of messenger RNA targets for both miR-29 and miR-130. Moreover, targets that we validated include Eomes and Tbx21, key genes that regulate the formation of memory CD8+ T cells. Notably, age-dependent changes in miR-29 and miR-130 are conserved in human CD8+ T cells, further suggesting that these developmental differences are biologically relevant. Together, these results demonstrate that miR-29 and miR-130 are likely important regulators of memory CD8+ T cell formation and suggest that neonatal cells are committed to a short-lived effector cell fate prior to infection.

Development and Function of Protective and Pathologic Memory CD4 T Cells

Immunological memory is one of the defining features of the adaptive immune system. As key orchestrators and mediators of immunity, CD4 T cells are central to the vast majority of adaptive immune responses. Generated following an immune response, memory CD4 T cells retain pertinent information about their activation environment enabling them to make rapid effector responses upon reactivation. These responses can either benefit the host by hastening the control of pathogens or cause damaging immunopathology. Here, we will discuss the diversity of the memory CD4 T cell pool, the signals that influence the transition of activated T cells into that pool, and highlight how activation requirements differ between naïve and memory CD4 T cells. A greater understanding of these factors has the potential to aid the design of more effective vaccines and to improve regulation of pathologic CD4 T cells, such as in the context of autoimmunity and allergy.

Patient-derived glioblastoma stem cells are killed by CD133-specific CAR T cells but induce the T cell aging marker CD57

The AC133 epitope of CD133 is a cancer stem cell (CSC) marker for many tumor entities, including the highly malignant glioblastoma multiforme (GBM). We have developed an AC133-specific chimeric antigen receptor (CAR) and show that AC133-CAR T cells kill AC133+ GBM stem cells (GBM-SCs) both in vitro and in an orthotopic tumor model in vivo. Direct contact with patient-derived GBM-SCs caused rapid upregulation of CD57 on the CAR T cells, a molecule known to mark terminally or near-terminally differentiated T cells. However, other changes associated with terminal T cell differentiation could not be readily detected. CD57 is also expressed on tumor cells of neural crest origin and has been preferentially found on highly aggressive, undifferentiated, multipotent CSC-like cells. We found that CD57 was upregulated on activated T cells only upon contact with CD57+ patient-derived GBM-SCs, but not with conventional CD57-negative glioma lines. However, CD57 was not downregulated on the GBM-SCs upon their differentiation, indicating that this molecule is not a bona fide CSC marker for GBM. Differentiated GBM cells still induced CD57 on CAR T cells and other activated T cells. Therefore, CD57 can apparently be upregulated on activated human T cells by mere contact with CD57+ target cells.

Methamphetamine mediates immune dysregulation in a murine model of chronic viral infection

Methamphetamine (METH) is a highly addictive psychostimulant that not only affects the brain and cognitive functions but also greatly impacts the host immune system, rendering the body susceptible to infections and exacerbating the severity of disease. Although there is gathering evidence about METH abuse and increased incidence of HIV and other viral infections, not much is known about the effects on the immune system in a chronic viral infection setting. We have used the lymphocytic choriomeningitis virus (LCMV) chronic mouse model of viral infection in a chronic METH environment and demonstrate that METH significantly increases CD3 marker on splenocytes and programmed death-1 (PD-1) expression on T cells, a cell surface signaling molecule known to inhibit T cell function and cause exhaustion in a lymphoid organ. Many of these METH effects were more pronounced during early stage of infection, which are gradually attenuated during later stages of infection. An essential cytokine for T-lymphocyte homeostasis, Interleukin-2 (IL-2) in serum was prominently reduced in METH-exposed infected mice. In addition, the serum pro-inflammatory (TNF, IL12 p70, IL1β, IL-6, and KC-GRO) and Th2 (IL-2, IL-10, and IL-4) cytokine profiles were also altered in the presence of METH. Interestingly CXCR3, an inflammatory chemokine receptor, showed significant increase in the METH treated LCMV infected mice. Similarly, compared to only infected mice, epidermal growth factor receptor (EGFR) in METH exposed LCMV infected mice were up regulated. Collectively, our data suggest that METH alters systemic, peripheral immune responses and modulates key markers on T cells involved in pathogenesis of chronic viral infection.

An Excess of the Proinflammatory Cytokines IFN-γ and IL-12 Impairs the Development of the Memory CD8+ T Cell Response to Chlamydia trachomatis

The obligate intracellular bacterium Chlamydia trachomatis is the most common cause of bacterial sexually transmitted disease in the United States and the leading cause of preventable blindness worldwide. Transfer of cultured Chlamydia-specific CD8(+) T cells or vaccination with recombinant virus expressing an MHC I-restricted Chlamydia Ag confers protection, yet surprisingly a protective CD8(+) T cell response is not stimulated following natural infection. In this study, we demonstrate that the presence of excess IL-12 and IFN-γ contributes to poor memory CD8(+) T cell development during C. trachomatis infection of mice. IL-12 is required for CD8(+) T cell expansion but drives effector CD8(+) T cells into a short-lived fate, whereas IFN-γ signaling impairs the development of effector memory cells. We show that transient blockade of IL-12 and IFN-γ during priming promotes the development of memory precursor effector CD8(+) T cells and increases the number of memory T cells that participate in the recall protection against subsequent infection. Overall, this study identifies key factors shaping memory development of Chlamydia-specific CD8(+) T cells that will inform future vaccine development against this and other pathogens.

Combination of inflammation-related cytokines promotes long-term muscle stem cell expansion

Muscle stem cells (MuSCs, satellite cells) are the major contributor to muscle regeneration. Like most adult stem cells, long-term expansion of MuSCs in vitro is difficult. The in vivo muscle regeneration abilities of MuSCs are quickly lost after culturing in vitro, which prevents the potential applications of MuSCs in cell-based therapies. Here, we establish a system to serially expand MuSCs in vitro for over 20 passages by mimicking the endogenous microenvironment. We identified that the combination of four pro-inflammatory cytokines, IL-1α, IL-13, TNF-α, and IFN-γ, secreted by T cells was able to stimulate MuSC proliferation in vivo upon injury and promote serial expansion of MuSCs in vitro. The expanded MuSCs can replenish the endogenous stem cell pool and are capable of repairing multiple rounds of muscle injuries in vivo after a single transplantation. The establishment of the in vitro system provides us a powerful method to expand functional MuSCs to repair muscle injuries.

Genetically modified T cells in cancer therapy: opportunities and challenges

Tumours use many strategies to evade the host immune response, including downregulation or weak immunogenicity of target antigens and creation of an immune-suppressive tumour environment. T cells play a key role in cell-mediated immunity and, recently, strategies to genetically modify T cells either through altering the specificity of the T cell receptor (TCR) or through introducing antibody-like recognition in chimeric antigen receptors (CARs) have made substantial advances. The potential of these approaches has been demonstrated in particular by the successful use of genetically modified T cells to treat B cell haematological malignancies in clinical trials. This clinical success is reflected in the growing number of strategic partnerships in this area that have attracted a high level of investment and involve large pharmaceutical organisations. Although our understanding of the factors that influence the safety and efficacy of these therapies has increased, challenges for bringing genetically modified T-cell immunotherapy to many patients with different tumour types remain. These challenges range from the selection of antigen targets and dealing with regulatory and safety issues to successfully navigating the routes to commercial development. However, the encouraging clinical data, the progress in the scientific understanding of tumour immunology and the improvements in the manufacture of cell products are all advancing the clinical translation of these important cellular immunotherapies.

CD8 T cell persistence in treated HIV infection

PURPOSE OF REVIEW

Many treated HIV-infected persons maintain persistently high circulating CD8 T cell numbers, even after many years of therapy. Recent reports have suggested that persistent CD8 T cell expansion is associated with higher risk of morbid non-AIDS events. Thus, assessing the mechanisms of CD8 T cell expansion and persistence may give insights into a feature of HIV disease that is clinically important.

RECENT FINDINGS

Acute HIV infection is associated with activation and expansion of the CD8 T cell compartment. Expanded CD8 T cells persist throughout the disease course, and in contrast to the plasticity that typically characterizes immune responses to most other pathogens, circulating CD8 T cell numbers do not normalize in many patients despite pharmacologic suppression of HIV replication. We suspect that residual inflammation in treated HIV infection contributes to antigen-independent CD8 T cell expansion and persistence as most of these cells are not HIV-reactive.

SUMMARY

Circulating CD8 T cell numbers remain abnormally elevated in many treated HIV-infected patients and this elevation is associated with adverse clinical events. Future studies will be needed to assess the mechanisms of CD8 T cell expansion and to define the role of CD8 lymphocytosis in the clinical course of treated HIV disease.

HLA-A02:01-restricted epitopes identified from the herpes simplex virus tegument protein VP11/12 preferentially recall polyfunctional effector memory CD8+ T cells from seropositive asymptomatic individuals and protect humanized HLA-A*02:01 transgenic mice against ocular herpes

The HSV type 1 tegument virion phosphoprotein (VP) 11/12 (VP11/12) is a major Ag targeted by CD8(+) T cells from HSV-seropositive individuals. However, whether and which VP11/12 epitope-specific CD8(+) T cells play a role in the "natural" protection seen in seropositive healthy asymptomatic (ASYMP) individuals (who have never had clinical herpes disease) remain to be determined. In this study, we used multiple prediction computer-assisted algorithms to identify 10 potential HLA-A*02:01-restricted CD8(+) T cell epitopes from the 718-aa sequence of VP11/12. Three of 10 epitopes exhibited high-to-moderate binding affinity to HLA-A*02:01 molecules. In 10 sequentially studied HLA-A*02:01-positive and HSV-1-seropositive ASYMP individuals, the most frequent, robust, and polyfunctional effector CD8(+) T cell responses, as assessed by a combination of tetramer frequency, granzyme B, granzyme K, perforin, CD107(a/b) cytotoxic degranulation, IFN-γ, and multiplex cytokines assays, were predominantly directed against three epitopes: VP11/1266-74, VP11/12220-228, and VP11/12702-710. Interestingly, ASYMP individuals had a significantly higher proportion of CD45RA(low)CCR7(low)CD44(high)CD62L(low)CD27(low)CD28(low)CD8(+) effector memory CD8(+) T cells (TEMs) specific to the three epitopes, compared with symptomatic individuals (with a history of numerous episodes of recurrent ocular herpetic disease). Moreover, immunization of HLA-A*02:01 transgenic mice with the three ASYMP CD8(+) TEM cell epitopes induced robust and polyfunctional epitope-specific CD8(+) TEM cells that were associated with a strong protective immunity against ocular herpes infection and disease. Our findings outline phenotypic and functional features of protective HSV-specific CD8(+) T cells that should guide the development of an effective T cell-based herpes vaccine.

Phenotypic and functional characterization of herpes simplex virus glycoprotein B epitope-specific effector and memory CD8+ T cells from symptomatic and asymptomatic individuals with ocular herpes

Herpes simplex virus 1 (HSV-1) glycoprotein B (gB)-specific CD8(+) T cells protect mice from herpes infection and disease. However, whether and which HSV-1 gB-specific CD8(+) T cells play a key role in the "natural" protection seen in HSV-1-seropositive healthy asymptomatic (ASYMP) individuals (who have never had clinical herpes disease) remain to be determined. In this study, we have dissected the phenotypes and the functions of HSV-1 gB-specific CD8(+) T cells from HLA-A*02:01 positive, HSV-1 seropositive ASYMP and symptomatic (SYMP) individuals (with a history of numerous episodes of recurrent ocular herpes disease). We found the following. (i) Healthy ASYMP individuals maintained a significantly higher proportion of differentiated HSV-1 gB-specific effector memory CD8(+) T cells (TEM cells) (CD45RA(low) CCR7(low) CD44(high) CD62L(low)). In contrast, SYMP patients had frequent less-differentiated central memory CD8(+) T cells (TCM cells) (CD45RA(low) CCR7(high) CD44(low) CD62L(high)). (ii) ASYMP individuals had significantly higher proportions of multifunctional effector CD8(+) T cells which responded mainly to gB342-350 and gB561-569 "ASYMP" epitopes, and simultaneously produced IFN-γ, CD107(a/b), granzyme B, and perforin. In contrast, effector CD8(+) T cells from SYMP individuals were mostly monofunctional and were directed mainly against nonoverlapping gB17-25 and gB183-191 "SYMP" epitopes. (iii) Immunization of an HLA-A*02:01 transgenic mouse model of ocular herpes with "ASYMP" CD8(+) TEM cell epitopes, but not with "SYMP" CD8(+) TCM cell epitopes, induced a strong CD8(+) T cell-dependent protective immunity against ocular herpes infection and disease. Our findings provide insights into the role of HSV-specific CD8(+) TEM cells in protection against herpes and should be considered in the development of an effective vaccine.

IMPORTANCE

A significantly higher proportion of differentiated and multifunctional HSV-1 gB-specific effector memory CD8(+) T cells (TEM cells) (CD45RA(low) CCR7(low) CD44(high) CD62L(low)) were found in healthy ASYMP individuals who are seropositive for HSV-1 but never had any recurrent herpetic disease, while there were frequent less-differentiated and monofunctional central memory CD8(+) T cells (TCM cells) (CD45RA(low) CCR7(high) CD44(low) CD62L(high)) in SYMP patients. Immunization with "ASYMP" CD8(+) TEM cell epitopes, but not with "SYMP" CD8(+) TCM cell epitopes, induced a strong protective HSV-specific CD8(+) T cell response in HLA-A*02:01 transgenic mice. These findings are important for the development of a safe and effective T cell-based herpes vaccine.

Serine protease inhibitor-6 differentially affects the survival of effector and memory alloreactive CD8-T cells

The clonal expansion of effector T cells and subsequent generation of memory T cells are critical in determining the outcome of transplantation. While cytotoxic T lymphocytes induce direct cytolysis of target cells through secretion of Granzyme-B (GrB), they also express cytoplasmic serine protease inhibitor-6 (Spi6) to protect themselves from GrB that has leaked from granules. Here, we studied the role of GrB/Spi6 axis in determining clonal expansion of alloreactive CD8-T cells and subsequent generation of memory CD8-T cells in transplantation. CD8-T cells from Spi6(-/-) mice underwent more GrB mediated apoptosis upon alloantigen stimulation in vitro and in vivo following adoptive transfer into an allogeneic host. Interestingly, while OT1.Spi6(-/-) CD8 T cells showed significantly lower clonal expansion following skin transplants from OVA mice, there was no difference in the size of the effector memory CD8-T cells long after transplantation. Furthermore, lack of Spi6 resulted in a decrease of short-lived-effector-CD8-cells but did not impact the pool of memory-precursor-effector-CD8-cells. Similar results were found in heart transplant models. Our findings suggest that the final alloreactive CD8-memory-pool-size is independent from the initial clonal-proliferation as memory precursors express low levels of GrB and therefore are independent of Spi6 for survival. These data advance our understanding of memory T cells generation in transplantation and provide basis for Spi6 based strategies to target effector T cells.

AMPK in lymphocyte metabolism and function

Adenosine monophosphate-activated protein kinase (AMPK) is a serine/threonine kinase that is crucial for cellular energy metabolism homeostasis. AMPK monitors cellular energy status in response to nutritional variations and, once activated by low energy status, switches on ATP-producing catabolic pathways and switches off ATP-consuming anabolic pathways to restore cellular energy homeostasis. When T lymphocytes encounter foreign antigens, they initiate a program of differentiation leading to the rapid generation of effector and memory cells that clear the pathogen and prevent future infection, respectively. Differentiation of naïve T cells in effector or long term memory cells is tightly associated with changes in their energy metabolic activity and recent data have revealed that fine-tuning of metabolism could modulate T cell functions. Here, we will review recent data about the regulation of T cell metabolism by AMPK and discuss its influence on T cell function.

Agonistic anti-CD40 enhances the CD8+ T cell response during vesicular stomatitis virus infection

Intracellular pathogens are capable of inducing vigorous CD8⁺ T cell responses. However, we do not entirely understand the factors driving the generation of large pools of highly protective memory CD8⁺ T cells. Here, we studied the generation of endogenous ovalbumin-specific memory CD8⁺ T cells following infection with recombinant vesicular stomatitis virus (VSV) and Listeria monocytogenes (LM). VSV infection resulted in the generation of a large ovalbumin-specific memory CD8⁺ T cell population, which provided minimal protective immunity that waned with time. In contrast, the CD8⁺ T cell population of LM-ova provided protective immunity and remained stable with time. Agonistic CD40 stimulation during CD8⁺ T cell priming in response to VSV infection enabled the resultant memory CD8⁺ T cell population to provide strong protective immunity against secondary infection. Enhanced protective immunity by agonistic anti-CD40 was dependent on CD70. Agonistic anti-CD40 not only enhanced the size of the resultant memory CD8⁺ T cell population, but enhanced their polyfunctionality and sensitivity to antigen. Our data suggest that immunomodulation of CD40 signaling may be a key adjuvant to enhance CD8⁺ T cell response during development of VSV vaccine strategies.

An animated landscape representation of CD4+ T-cell differentiation, variability, and plasticity: insights into the behavior of populations versus cells

Recent advances in understanding CD4(+) T-cell differentiation suggest that previous models of a few distinct, stable effector phenotypes were too simplistic. Although several well-characterized phenotypes are still recognized, some states display plasticity, and intermediate phenotypes exist. As a framework for reexamining these concepts, we use Waddington's landscape paradigm, augmented with explicit consideration of stochastic variations. Our animation program "LAVA" visualizes T-cell differentiation as cells moving across a landscape of hills and valleys, leading to attractor basins representing stable or semistable differentiation states. The model illustrates several principles, including: (i) cell populations may behave more predictably than individual cells; (ii) analogous to reticulate evolution, differentiation may proceed through a network of interconnected states, rather than a single well-defined pathway; (iii) relatively minor changes in the barriers between attractor basins can change the stability or plasticity of a population; (iv) intrapopulation variability of gene expression may be an important regulator of differentiation, rather than inconsequential noise; (v) the behavior of some populations may be defined mainly by the behavior of outlier cells. While not a quantitative representation of actual differentiation, our model is intended to provoke discussion of T-cell differentiation pathways, particularly highlighting a probabilistic view of transitions between states.

Exploiting differential expression of the IL-7 receptor on memory T cells to modulate immune responses

Interleukin-7 is a non-redundant growth, differentiation and survival factor for human T lymphocytes. Most circulating, mature T cells express the receptor for IL-7, but not all. Importantly, CD4 Tregs express greatly reduced levels of IL-7R compared to conventional CD4 T cells, presenting an opportunity to selectively target the latter cells with either more IL-7 to boost responses, or to block IL-7 signalling to limit responses. This article reviews what is known about regulation of IL-7R expression, and recent progress in therapeutic approaches related to IL-7 and its receptor.

Regulation of tissue-dependent differences in CD8+ T cell apoptosis during viral infection

Virus-specific CD8+ T cells in the lymphoid organs contract at the resolution of virus infections by apoptosis or by dissemination into peripheral tissues, and those residing in nonlymphoid organs, including the peritoneal cavity and fat pads, are more resistant to apoptosis than those in the spleen and lymph nodes. This stability of memory T cells in the nonlymphoid tissues may enhance protection to secondary challenges. Here, we show that lymphocytic choriomeningitis virus (LCMV)-specific CD8+ T cells in nonlymphoid tissues were enriched for memory precursors (expressing high levels of interleukin-7 receptor and low levels of killer cell lectin-like receptor G1 [IL-7Rhi KLRG1lo]) and had higher expression of CD27, CXCR3, and T cell factor-1 (TCF-1), each a marker that is individually correlated with decreased apoptosis. CD8+ T cells in the peritoneal cavity of TCF-1-deficient mice had decreased survival, suggesting a role for TCF-1 in promoting survival in the nonlymphoid tissues. CXCR3+ CD8+ T cells resisted apoptosis and accumulated in the lymph nodes of mice treated with FTY720, which blocks the export of lymph node cells into peripheral tissue. The peritoneal exudate cells (PEC) expressed increased amounts of CXCR3 ligands, CXCL9 and CXCL10, which may normally recruit these nonapoptotic cells from the lymph nodes. In addition, adoptive transfer of splenic CD8+ T cells into PEC or spleen environments showed that the peritoneal environment promoted survival of CD8+ T cells. Thus, intrinsic stability of T cells which are present in the nonlymphoid tissues along with preferential migration of apoptosis-resistant CD8+ T cells into peripheral sites and the availability of tissue-specific factors that enhance memory cell survival may collectively account for the tissue-dependent apoptotic differences.

IMPORTANCE

Most infections are initiated at nonlymphoid tissue sites, and the presence of memory T cells in nonlymphoid tissues is critical for protective immunity in various viral infection models. Virus-specific CD8+ T cells in the nonlymphoid tissues are more resistant to apoptosis than those in lymphoid organs during the resolution and memory phase of the immune response to acute LCMV infection. Here, we investigated the mechanisms promoting stability of T cells in the nonlymphoid tissues. This increased resistance to apoptosis of virus-specific CD8+ T cells in nonlymphoid tissues was due to several factors. Nonlymphoid tissues were enriched in memory phenotype CD8+ T cells, which were intrinsically resistant to apoptosis irrespective of the tissue environment. Furthermore, apoptosis-resistant CD8+ T cells preferentially migrated into the nonlymphoid tissues, where the availability of tissue-specific factors may enhance memory cell survival. Our findings are relevant for the generation of long-lasting vaccines providing protection at peripheral infection sites.

Loss of the death receptor CD95 (Fas) expression by dendritic cells protects from a chronic viral infection

Chronic viral infections incapacitate adaptive immune responses by "exhausting" virus-specific T cells, inducing their deletion and reducing productive T-cell memory. Viral infection rapidly induces death receptor CD95 (Fas) expression by dendritic cells (DCs), making them susceptible to elimination by the immune response. Lymphocytic choriomeningitis virus (LCMV) clone 13, which normally establishes a chronic infection, is rapidly cleared in C57Black6/J mice with conditional deletion of Fas in DCs. The immune response to LCMV is characterized by an extended survival of virus-specific effector T cells. Moreover, transfer of Fas-negative DCs from noninfected mice to preinfected animals results in either complete clearance of the virus or a significant reduction of viral titers. Thus, DC-specific Fas expression plays a role in regulation of antiviral responses and suggests a strategy for stimulation of T cells in chronically infected animals and humans to achieve the clearance of persistent viruses.

TLR4 ligands lipopolysaccharide and monophosphoryl lipid a differentially regulate effector and memory CD8+ T Cell differentiation

Vaccines formulated with nonreplicating pathogens require adjuvants to help bolster immunogenicity. The role of adjuvants in Ab production has been well studied, but how they influence memory CD8(+) T cell differentiation remains poorly defined. In this study we implemented dendritic cell-mediated immunization to study the effects of commonly used adjuvants, TLR ligands, on effector and memory CD8(+) T cell differentiation in mice. Intriguingly, we found that the TLR4 ligand LPS was far more superior to other TLR ligands in generating memory CD8(+) T cells upon immunization. LPS boosted clonal expansion similar to the other adjuvants, but fewer of the activated CD8(+) T cells died during contraction, generating a larger pool of memory cells. Surprisingly, monophosphoryl lipid A (MPLA), another TLR4 ligand, enhanced clonal expansion of effector CD8(+) T cells, but it also promoted their terminal differentiation and contraction; thus, fewer memory CD8(+) T cells formed, and MPLA-primed animals were less protected against secondary infection compared with those primed with LPS. Furthermore, gene expression profiling revealed that LPS-primed effector cells displayed a stronger pro-memory gene expression signature, whereas the gene expression profile of MPLA-primed effector cells aligned closer with terminal effector CD8(+) T cells. Lastly, we demonstrated that the LPS-TLR4-derived "pro-memory" signals were MyD88, but not Toll/IL-1R domain-containing adapter inducing IFN-β, dependent. This study reveals the influential power of adjuvants on the quantity and quality of CD8(+) T cell memory, and that attention to adjuvant selection is crucial because boosting effector cell expansion may not always equate with more memory T cells or greater protection.

Maturation and migration of murine CD4 single positive thymocytes and thymic emigrants

T lymphopoiesis in the thymus was thought to be completed once they reach the single positive (SP) stage, when they are “fully mature” and wait to be exported at random or follow a “first in-first out” manner. Recently, accumulating evidence has revealed that newly generated SP thymocytes undergo further maturation in the thymic medulla before they follow a tightly regulated emigrating process to become recent thymic emigrants (RTEs). RTEs in the periphery then experience a post-thymic maturation and peripheral tolerance and eventually become licensed as mature naïve T cells. This review summarizes the recent progress in the late stage T cell development in and outside of the thymus. The regulation of this developmental process is also discussed.

Sprouty-2 regulates HIV-specific T cell polyfunctionality

The ability of individual T cells to perform multiple effector functions is crucial for protective immunity against viruses and cancer. This polyfunctionality is frequently lost during chronic infections; however, the molecular mechanisms driving T cell polyfunctionality are poorly understood. We found that human T cells stimulated by a high concentration of antigen lacked polyfunctionality and expressed a transcription profile similar to that of exhausted T cells. One specific pathway implicated by the transcription profile in control of T cell polyfunctionality was the MAPK/ERK pathway. This pathway was altered in response to different antigen concentrations, and polyfunctionality correlated with upregulation of phosphorylated ERK. T cells that were stimulated with a high concentration of antigen upregulated sprouty-2 (SPRY2), a negative regulator of the MAPK/ERK pathway. The clinical relevance of SPRY2 was confirmed by examining SPRY2 expression in HIV-specific T cells, where high levels of SPRY2 were seen in HIV-specific T cells and inhibition of SPRY2 expression enhanced the HIV-specific polyfunctional response independently of the PD-1 pathway. Our findings indicate that increased SPRY2 expression during chronic viral infection reduces T cell polyfunctionality and identify SPRY2 as a potential target for immunotherapy.