Endogenous IL-27 during toxoplasmosis limits early monocyte responses and their inflammatory activation by pathological T cells

Mice that lack the genes for IL-27, or the IL-27 receptor, and infected with Toxoplasma gondii develop T cell-mediated pathology. Here, studies were performed to determine the impact of endogenous IL-27 on the immune response to T. gondii in wild-type (WT) mice. Analysis of infected mice revealed the early production of IL-27p28 by a subset of Ly6Chi, inflammatory monocytes, and sustained IL-27p28 production at sites of acute and chronic infection. Administration of anti-IL-27p28 prior to infection resulted in an early (day 5) increase in levels of macrophage and granulocyte activation, as well as enhanced effector T cell responses, as measured by both cellularity, cytokine production, and transcriptional profiling. This enhanced acute response led to immune pathology, while blockade during the chronic phase of infection resulted in enhanced T cell responses but no systemic pathology. In the absence of IL-27, the enhanced monocyte responses observed at day 10 were a secondary consequence of activated CD4+ T cells. Thus, in WT mice, IL-27 has distinct suppressive effects that impact innate and adaptive immunity during different phases of this infection.

IMPORTANCE

The molecule IL-27 is critical in limiting the immune response to the parasite Toxoplasma gondii. In the absence of IL-27, a lethal, overactive immune response develops during infection. However, when exactly in the course of infection this molecule is needed was unclear. By selectively inhibiting IL-27 during this parasitic infection, we discovered that IL-27 was only needed during, but not prior to, infection. Additionally, IL-27 is only needed in the active areas in which the parasite is replicating. Finally, our work found that a previously unstudied cell type, monocytes, was regulated by IL-27, which contributes further to our understanding of the regulatory networks established by this molecule.

Innate and Adaptive Cell-Mediated Immune Responses to a COVID-19 mRNA Vaccine in Young Children

Background

There is little information on cell-mediated immunity (CMI) to COVID-19 mRNA vaccines in children. We studied adaptive and innate CMI in vaccinated children aged 6 to 60 months.

Methods

Blood obtained from participants in a randomized placebo-controlled trial of an mRNA vaccine before and 1 month after the first dose was used for antibody measurements and CMI (flow cytometry).

Results

We enrolled 29 children with a mean age of 28.5 months (SD, 15.7). Antibody studies revealed that 10 participants were infected with SARS-CoV-2 prevaccination. Ex vivo stimulation of peripheral blood mononuclear cells with SARS-CoV-2 spike peptides showed significant increases pre- to postimmunization of activated conventional CD4+ and γδ T cells, natural killer cells, monocytes, and conventional dendritic cells but not mucosa-associated innate T cells. Conventional T-cell, monocyte, and conventional dendritic cell responses in children were higher immediately after vaccination than after SARS-CoV-2 infection. The fold increase in CMI pre- to postvaccination did not differ between children previously infected with SARS-CoV-2 and those uninfected.

Conclusions

Children aged 6 to 60 months who were vaccinated with a COVID-19 mRNA vaccine developed robust CMI responses, including adaptive and innate immunity.

An Observational Study on the Humoral and Cellular Immune Response to SARS-CoV-2 mRNA Vaccination in Multiple Sclerosis and Other Autoimmune Neurological Disorders Treated With Anti-CD20 Therapies

Objective

To assess adaptive immunity to SARS-CoV-2 in anti-CD20 treated individuals with mRNA vaccination.

Background

Anti-CD20 therapies attenuate humoral responses to vaccines. However, their effect on T cell responses is less clear. We examined B and T cell responses following COVID-19 vaccination in patients receiving anti-CD20 therapy for multiple sclerosis (MS) and other autoimmune inflammatory neurologic diseases (AINDs, e.g., autoimmune encephalitis, stiff person syndrome, etc.).

Design/Methods

MS and AIND patients on anti-CD20 therapies were prospectively enrolled for longitudinal analysis of antibody and T cell responses after a 3rd COVID-19 vaccination. Serum antibodies against the receptor-binding domain of the S1 spike protein (RBD-S1 IgG), neutralizing antibodies, and SARS-CoV-2 CD8 T cell responses, using activation-induced markers (AIM) and INF-γ release assays (EUROIMMUN, Germany), were measured at various time points including pre-vaccination, post initial vaccination series, and 4 and 12 weeks after 3rd dose.

Results

Thirty-four MS and AIND participants are enrolled. Results for these patients (mean age 52 years-old, 79% female, 21 Pfizer, 13 Moderna) demonstrated attenuated RBD IgG antibody responses. However, a robust CD8 T cell response was observed, following a two-dose series, compared to non-immunosuppressed, age-matched vaccinated controls or unvaccinated with severe SARS-CoV-2 infection (p = 0.01). T cell response was sustained long-term (>12 weeks post 3rd dose) in all 11 anti-CD20 patients analyzed thus far. Collections are completed for all participants at 12 weeks and analysis to be completed by 05/15/22. Further analysis includes correlation of the INF- γ release assay compared to RBD-CD8 T cell response detected by AIM assay.

Conclusions

Results suggest that patients treated with anti-CD20 therapy generate a robust CD8 T cell response to SARS-CoV-2 mRNA after three doses but remain with attenuated humoral immune responses. Our observational study will provide important data to guide vaccine management in patients on or anticipating anti-CD20 therapy.

Harmonization of Multiple SARS-CoV-2 Reference Materials Using the WHO IS (NIBSC 20/136): Results and Implications

Background

There is an urgent need for harmonization between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serology platforms and assays prior to defining appropriate correlates of protection and as well inform the development of new rapid diagnostic tests that can be used for serosurveillance as new variants of concern (VOC) emerge. We compared multiple SARS-CoV-2 serology reference materials to the WHO International Standard (WHO IS) to determine their utility as secondary standards, using an international network of laboratories with high-throughput quantitative serology assays. This enabled the comparison of quantitative results between multiple serology platforms.

Methods

Between April and December 2020, 13 well-characterized and validated SARS-CoV-2 serology reference materials were recruited from six different providers to qualify as secondary standards to the WHO IS. All the samples were tested in parallel with the National Institute for Biological Standards and Control (NIBSC) 20/136 and parallel-line assays were used to calculate the relevant potency and binding antibody units.

Results

All the samples saw varying levels of concordance between diagnostic methods at specific antigen–antibody combinations. Seven of the 12 candidate materials had high concordance for the spike-immunoglobulin G (IgG) analyte [percent coefficient of variation (%CV) between 5 and 44%].

Conclusion

Despite some concordance between laboratories, qualification of secondary materials to the WHO IS using arbitrary international units or binding antibody units per milliliter (BAU/ml) does not provide any benefit to the reference materials overall, due to the lack of consistent agreeable international unit (IU) or BAU/ml conversions between laboratories. Secondary standards should be qualified to well-characterized reference materials, such as the WHO IS, using serology assays that are similar to the ones used for the original characterization of the WHO IS.

Antibody-Dependent Complement Responses toward SARS-CoV-2 Receptor-Binding Domain Immobilized on "Pseudovirus-like" Nanoparticles

Many aspects of innate immune responses to SARS viruses remain unclear. Of particular interest is the role of emerging neutralizing antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 in complement activation and opsonization. To overcome challenges with purified virions, here we introduce "pseudovirus-like" nanoparticles with ∼70 copies of functional recombinant RBD to map complement responses. Nanoparticles fix complement in an RBD-dependent manner in sera of all vaccinated, convalescent, and naı̈ve donors, but vaccinated and convalescent donors with the highest levels of anti-RBD antibodies show significantly higher IgG binding and higher deposition of the third complement protein (C3). The opsonization via anti-RBD antibodies is not an efficient process: on average, each bound antibody promotes binding of less than one C3 molecule. C3 deposition is exclusively through the alternative pathway. C3 molecules bind to protein deposits, but not IgG, on the nanoparticle surface. Lastly, "pseudovirus-like" nanoparticles promote complement-dependent uptake by granulocytes and monocytes in the blood of vaccinated donors with high anti-RBD titers. Using nanoparticles displaying SARS-CoV-2 proteins, we demonstrate subject-dependent differences in complement opsonization and immune recognition.

Dissecting the effect of a novel hypomorphic IL2RB mutation on immune dysregulation

Human inborn errors of immunity (IEIs) are a class of genetic disorders caused by monogenic germline mutations that impair the function of the encoded protein. We recently described a novel IEI due to an IL2RB homozygous mutation (p.Pro222_Gln225Del) in two siblings who suffered from multi-organ autoimmunity and CMV susceptibility. This mutation resulted in decreased cell surface protein expression and increased serum IL-2/15 levels, with concomitant increased baseline STAT5 phosphorylation (pSTAT5) but poor pSTAT5 response to IL-2 and IL-15 stimulation. Counterintuitively, this IL-2Rβ hypomorphic mutation led to an expansion of memory CD8+ T and immature CD56bright NK cells, which express the highest levels of IL-2Rβ and require IL-2/15 signaling for survival and differentiation. Yet, their maturation and function appeared impaired, suggesting that both intrinsic (hypomorphic receptor) and extrinsic (serum cytokine milieu) mechanisms were at play. To further interrogate these receptor instrinsic/extrinsic mechanisms we developed a mouse model that harbors the homolog mutation (Il2rbMut/Mut). When mutant bone marrow cells reconstituted a WT host, serum IL-2/15 levels and IL-2Rβ protein surface expression partially normalized, though IL-2/15-induced signaling remained hypofunctional. Additionally, the dysregulated mutant IL-2Rβ-driven CD8+ T cell immunophenotype normalized but the NK phenotype did not. These data highlight the asymmetrical effect that a partial IL-2Rβ defect has on CD8 T and NK cell IL-2/15-dependent signaling and downstream cellular processes. These results imply that strategies to modify serum IL-2/15 levels may serve as a therapeutic approach to treating IL-2/15 signaling defects.

 Supported by grants from NIH (T32 AI074491, K23 AR070897)

Inflammation suppresses elevated TCF1 and FOXO1 expression in vaccine-elicited T cells

T cells that express TCF1 display self-renewing capacity and are essential for the long-term T cell response during chronic infections and cancer. Due to their increased responsiveness to checkpoint blockade, TCF1+ T cells are recognized as promising targets for immunotherapies. We found that, in contrast to T cells responding to infections (Tinf), the majority of adjuvanted subunit vaccine-elicited T cells (Tvac) rapidly acquired a memory phenotype (CD127hi) and were TCF1hi. This suggests that Tvacs could be programmed by TCF1 to commit to a memory cell fate. We found that Tvac peak and memory responses were more compromised in the absence of TCF1 than those of Tinf. However, TCF1 KO Tvacs still developed memory, suggesting that additional factors were involved. FOXO1 is important for T cell memory after infections. We found that Tvacs expressed more FOXO1 than Tinfs. In contrast to Tinf, FOXO1 was required for both the peak and memory Tvac responses. Moreover, even though FOXO1 drives TCF1 in Tinfs, Tvacs expressed TCF1 independently of FOXO1. To explore the cause for such high expression of TCF1 and FOXO1 in Tvacs, we next examined the role of inflammatory mediators in their regulation. Tvac TCF1 and FOXO1 inversely correlated with adjuvant-elicited pro-inflammatory signals. Moreover, addition of pro-inflammatory TLR9 ligand CpG reduced Tvac TCF1, FOXO1 and memory. In contrast to prior reports, anti-IL-12 failed to reverse the effect of CpG on Tvacs. Anti-IFNγ, however, restored the Tvac memory phenotype even as CpG drove additional inflammatory mediators. Our data highlight the differences in the transcriptional regulation of vaccine- and infection-elicited T cells and provide insights into the mechanisms regulating TCF1 and FOXO1.

Supported by grants from NIH (T32 AI074491, R01 AI066121)

The transcription factor T cell factor 1 (TCF1) expression is elevated in vaccine-elicited CD8+ T cells and negatively regulated by T-bet

T cells that express high levels of TCF1 display stem cell-like properties and give rise to effector-like cells that protect during chronic infections and cancer. Due to their increased responsiveness to checkpoint blockade, TCF1hi T cells are now recognized as promising targets for immunotherapies. We found that adjuvanted subunit vaccine-elicited T cells (Tvac) express significantly higher levels of TCF1 than T cells responding to infections (Tinf). In exploring the underlying causes for such high expression of TCF1 in Tvac, we examined the role of sustained TCR and inflammatory mediators in Tvac TCF1 regulation. Using Nr4a3-Tocky reporter mice and pMHCI antibody blockade, we found that TCR mediated signals regulate Tvac TCF1 to a limited degree. In line with previous reports, TCF1 expression in Tvac inversely correlated with adjuvant-elicited pro-inflammatory signals, increasing concomitantly with the rapid decline of cytokines after adjuvant administration. Further, the addition of TLR9 ligand CpG increased inflammatory cytokine production as it reduced TCF1 expression. However, in contrast to previous work, anti-IL-12 or anti-IFNγ treatment failed to reverse the lower TCF1 expression induced by CpG. More surprisingly, we found that Tvac TCF1 is regulated independently of Foxo1 even while Foxo1 plays its canonical role in facilitating TCF1 expression under inflammatory conditions. Inflammation does however negatively regulate TCF1 in a T-bet dependent manner, such that T-bet KO Tvac maintained high TCF1 expression even when inflammation was increased. Our data highlight differences in the transcriptional regulation of vaccine- and infection-elicited T cells and provide insights into the mechanism of TCF1 regulation.

Vaccine-elicited T cells adopt an early memory-like transcriptional phenotype distinct from infection-elicited T cells

Protection from pathogens relies on both humoral (antibody-mediated) and cellular (T cell-mediated) responses. While infections robustly elicit both of these types of immunity, currently approved vaccine adjuvants largely fail to induce significant T cell responses. However, recent work by our lab and others suggests that the mechanisms governing vaccine-elicited T cells (Tvac) may be substantially different than those governing infection-elicited T cells (Tinf). We have recently demonstrated that optimal subunit vaccine-elicited T cell responses rely on different cytokine signals (IL-27 and 15) and metabolic function (oxidative phosphorylation vs. aerobic glycolysis) leading to phenotypically and functionally different outcomes (memory vs. effector). Our goal was to investigate the transcriptional programming that drives Tvac formation and function from immunization to memory timepoints. Using a single-cell RNA-seq approach along with functional assays, we compared Tvac and Tinf at various time points post-immunization or infectious challenge. Our data indicate that the gene expression of Tvac markedly diverges from Tinf at early and peak time points. Remarkably, while capable of being highly proliferative, Tvac adopt a distinct transcriptional phenotype with similarities to recently identified self-renewing stem cell memory T cells, such as TCF1 expression. This transcriptional program likely enables the persistence of Tvac in substantially greater abundance at memory time points conferring overall greater protection. Taken together, our data have identified a novel transcriptional program that supports a robust vaccine-elicited T cell response with implications for future therapeutic vaccine design.

Chemokine Signatures of Pathogen-Specific T Cells I: Effector T Cells

The choreography of complex immune responses, including the priming, differentiation, and modulation of specific effector T cell populations generated in the immediate wake of an acute pathogen challenge, is in part controlled by chemokines, a large family of mostly secreted molecules involved in chemotaxis and other patho/physiological processes. T cells are both responsive to various chemokine cues and a relevant source for certain chemokines themselves; yet, the actual range, regulation, and role of effector T cell-derived chemokines remains incompletely understood. In this study, using different in vivo mouse models of viral and bacterial infection as well as protective vaccination, we have defined the entire spectrum of chemokines produced by pathogen-specific CD8⁺ and CD4⁺T effector cells and delineated several unique properties pertaining to the temporospatial organization of chemokine expression patterns, synthesis and secretion kinetics, and cooperative regulation. Collectively, our results position the "T cell chemokine response" as a notably prominent, largely invariant, yet distinctive force at the forefront of pathogen-specific effector T cell activities and establish novel practical and conceptual approaches that may serve as a foundation for future investigations into the role of T cell-produced chemokines in infectious and other diseases.

Chemokine Signatures of Pathogen-Specific T Cells II: Memory T Cells in Acute and Chronic Infection

Pathogen-specific memory T cells (T_M) contribute to enhanced immune protection under conditions of reinfection, and their effective recruitment into a recall response relies, in part, on cues imparted by chemokines that coordinate their spatiotemporal positioning. An integrated perspective, however, needs to consider T_M as a potentially relevant chemokine source themselves. In this study, we employed a comprehensive transcriptional/translational profiling strategy to delineate the identities, expression patterns, and dynamic regulation of chemokines produced by murine pathogen-specific T_M CD8⁺T_M, and to a lesser extent CD4⁺T_M, are a prodigious source for six select chemokines (CCL1/3/4/5, CCL9/10, and XCL1) that collectively constitute a prominent and largely invariant signature across acute and chronic infections. Notably, constitutive CCL5 expression by CD8⁺T_M serves as a unique functional imprint of prior antigenic experience; induced CCL1 production identifies highly polyfunctional CD8⁺ and CD4⁺T_M subsets; long-term CD8⁺T_M maintenance is associated with a pronounced increase of XCL1 production capacity; chemokines dominate the earliest stages of the CD8⁺T_M recall response because of expeditious synthesis/secretion kinetics (CCL3/4/5) and low activation thresholds (CCL1/3/4/5/XCL1); and T_M chemokine profiles modulated by persisting viral Ags exhibit both discrete functional deficits and a notable surplus. Nevertheless, recall responses and partial virus control in chronic infection appear little affected by the absence of major T_M chemokines. Although specific contributions of T_M-derived chemokines to enhanced immune protection therefore remain to be elucidated in other experimental scenarios, the ready visualization of T_M chemokine-expression patterns permits a detailed stratification of T_M functionalities that may be correlated with differentiation status, protective capacities, and potential fates.

Abstract NG12: Mechanisms governing efficacy of combination CD40 agonist and anti-PD-L1 in pancreatic ductal adenocarcinoma

Background: Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy that is resistant to conventional therapies including monotherapy using PD-1 or PD-L1 inhibition. Combination agonistic anti-CD40 and PD-1/PD-L1 blockade have clinical promise in advanced cancer patients including PDA. The underlying mechanism(s) driving the therapeutic effects of this combination are ill-defined. Here, we create a syngeneic PDA animal model and utilize various genetic tools to assess how CD40 agonist, PD-L1 blockade or the combination impact tumor antigen-specific T cells using fluorescently-labeled peptide:MHC tetramers and cells in the tumor microenvironment. Molecular analyses of tumor cell escape variants is also performed.

Methods: We recently developed a high-throughput orthotopic syngeneic KPC pancreatic cancer mouse model that expresses a novel model neoantigen in B6 mice described in Burrack et al., Cell Reports, 2019. We create fluorescently labeled peptide:H-2Db tetramers to track the fate of endogenous pancreatic tumor-antigen specific CD8+ T cells over time. Here, we use this model alone or mixed at a 1:1 ratio of KPC tumor cells that do not express the neoantigen to examine how agnostic anti-CD40 (a single dose, clone FGK145), anti-PDL1 (3 doses, clone 10F.932), or the combination impact tumor growth in the pancreas over time using bioluminescent imaging and high-resolution ultrasound. We use multiparameter flow cytometry to investigate how anti-CD40 +/- PD-L1 blockade impacts the phenotype, longevity and functionality of tetramer-binding T cells over time. We assess how other immune cell lineages are altered systemically and in the tumor microenvironment by quantifying myeloid subpopulations, B cells, NK cells and regulatory T cells following therapy. We use Batf3-/- mice and XCR1VenusDTR mice to assess the role of conventional type I dendritic cells (cDC1s) on therapeutic efficacy. We employ both cytokine and chemokine reporter strains to identify how anti-CD40 +/- PD-L1 blockade impacts inflammatory gene expression in immune cells enriched the tumor microenvironment. We examine the persistence and location of tetramer-binding T cells in the pancreas, lung and liver of mice following tumor eradication. Additionally, we re-derive resistant tumor cells from mice and evaluate the integrity of MHC class I antigen processing and presentation pathways. Finally, single cell sequencing is performed to assess the traits of subpopulations of tumor-antigen specific T cells that correlate with enhanced antitumor activity following therapy.

Results: We show that anti-CD40 or anti-PD-L1 monotherapy have significant yet transient antitumor effects in mice with neoantigen+ PDA with distinct effects on tumor specific T cells. Objective responses occur in 100% of the monotherapy treated mice and survival is significantly prolonged. However, tumors recur in 100% of these animals. Tumor escape variants defective in MHC class I protein and Tap1 gene expression following IFN-gamma treatment ultimately emerge. In contrast, combination agonistic anti-CD40 + PD-L1 blockade synergize therapeutically resulting in cures in 60% of the animals and formation of pancreas resident memory T cells that specifically bind tetramer and express CD49a and CD103 following tumor eradication. Mechanistically, the combination selectively expands conventional type 1 dendritic cells (cDC1s) in the spleens and tumors of tumor-bearing animals. cDC1s in PDA are CD11c+MHCII+ and express CD8, CD103 and Xcr1. Using Batf3-/- mice or an Xcr1venusDTR transient cDC1 depletion model, we demonstrate a striking dependency on cDC1s for therapeutic benefit with anti-CD40 or PD-L1 blockade. Unexpectedly, we find that the expansion of cDC1s in pancreatic tumor-bearing animals is partially dependent on Xcr1 expression by DCs. Anti-CD40+PD-L1 blockade significantly expand the number of tetramer-binding T cells that express KLRG1 in PDA. The tetramer-binding T cells remain PD-1+ yet have lower expression of Lag3 and have heightened polyfunctionality as measured by cytokine production. Further studies using chemokine and cytokine reporter models, we uncover key differences in how anti-CD40 and anti-PD-L1 impact inflammatory gene expression by antigen presenting cells in PDA. Finally, we demonstrate the requirement for tumor neoantigen expression for efficacy because in mice that have tumors containing a 50:50 mixture of neoantigen+ pancreatic tumor cells with neoantigen- pancreatic tumor cells, combination anti-CD40 + PD-L1 blockade results in elimination of predominantly those tumor cells that express the neoantigen. Further single cell sequencing data on how this combination impacts tumor-antigen specific T cell subpopulations as well as epitope spreading will be discussed.

Conclusions: These findings reveal for the first time to our knowledge that anti-CD40 + PD-L1 blockade synergize via the expansion of cDC1s in pancreatic tumor-bearing animals. Instead of anti-CD40 promoting priming of neoantigen-specific T cells, we find that this combination promotes the systemic expansion and intratumoral accumulation of KLRG1+ tumor-specific T cells that eradicate PDA and form pancreas resident CD49a+CD103+ memory T cells.

Citation Format: Adam L. Burrack, Meagan R. Rollins, Ellen J. Spartz, Jackson F. Raynor, Iris Wang, Jason Mitchell, Tsuneyasu Kaisho, Brian Fife, Ross Kedl, Stephen Shen, Ingunn M. Stromnes. Mechanisms governing efficacy of combination CD40 agonist and anti-PD-L1 in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr NG12.

The regulation of transcription factor T cell factor 1 (TCF1) in vaccine-elicited CD8+ T cells

Our lab has developed a subunit vaccination regimen that induces a highly robust T cell response. These vaccine-elicited CD8+ T cells (Tvac) are phenotypically, functionally and metabolically distinct from infection-elicited CD8+ T cells (Tinf). In contrast to Tinf, almost all Tvac rapidly acquire a memory phenotype (CD127hi, KLRG1lo). This suggests that Tvac could be differentially transcriptionally programmed to commit to a memory, rather than effector, cell fate. The transcription factor TCF1 (encoded by tcf7) is essential for CD8+ T cell memory in response to infection. Since high TCF1 expression is also important for the generation of stem-like T cells with long-term survival capacity and anti-tumor properties, it is now recognized as a promising target for immunotherapies. However, little is known about how TCF1 is regulated in response to subunit vaccination. We find that, in striking contrast to Tinf, TCF1 expression is actually increased in Tvac after vaccination. As others have shown, we also find that increasing inflammation during vaccination by the addition of TLR9 agonist CpG reduces TCF1 expression in Tvac, skewing their memory phenotype towards the effector phenotype (CD127lo, KLRG1hi) and compromising their long-term memory. While the loss of TCF1 in this context has conventionally been ascribed to inflammatory receptors, utilizing reporter Nur77GFP mice, we also observe an altered duration and frequency of TCR triggering in the context of inflammation. Our data indicates a complex, previously unappreciated interplay between inflammatory and TCR-mediated signals in the regulation of TCF1.

IL-27-producing B cells synergize with IFNγ to promote IgG2a and IgG1 antibody responses

How B cells integrate innate receptor and adaptive T cell signals in the class-switched antibody response needs be better understood. By using cytokine gene knockout and reporter mice, in vitro B cell cultures and single-cell analyses, we have identified a subset of B cells that produces IL-27 as signature cytokine upon priming by TLR ligands, which up-regulate CD40 expression, and exposure to Tfh cell stimuli CD154 and IL-21. B cell IL-27 induction depends on NF-kB activated by linear ubiquitin assembly complexes and up-regulated Baft3 transcription factor, which are recruited to the Il27p28 locus, as made accessible by CD154 and IL-21 stimulation. IL-27-producing B cells are bystander B cells that are inefficient in secreting antibodies, but express high levels of adhesion molecules which engage other activated B cells. Together with IFNg, they boost proliferation, survival and class-switching to IgG2a of B cells stimulated with CD154 and IL-21. Accordingly, mice with B cell-specific ablation of IL-27 and IFNg receptors display severe defects in germinal center B cell and plasma cell differentiation, leading to abrogation of IgG2a and markedly reduced IgG1 responses. Thus, IL-27-producing B cells function as “helper” cells to promote differentiation of antigen-specific B cells for optimal IgG responses. As such, they play a critical role in the production of effective anti-viral antibodies and, possibly, modulation of anti-tumoral immunity.

B lymphocytes are a major source of IL-27 that drives class-switched antibody responses and anti-viral immunity through paracrinic targeting of B cells and T follicular helper cells

In addition to generating antibodies against infections, B lymphocytes produce cytokines to regulate immune functions. Here, we have identified B cells as a major source of cytokine IL-27 (the heterodimer of IL-27p28 and EBI3) by using B cell-deficient mMT and JH mice, mice with B cell-specific deficiency in Ebi3 and NSG mice transplanted with highly purified B cells. IL-27 in turn targets B cells to undergo class-switching to IgG2a, as shown by decreased antigen-specific IgG2a in mice with B cell-specific deficiency IL-27 receptor signaling, leading to defective clearance of vaccinia virus infection. The paracrinic function of IL-27 is recapitulated in vitro by B cell production of IL-27 upon stimulation by a TLR ligand together with CD154 (CD40 ligand) and IL-21, two hallmark stimuli of TFH cells, and IL-27 induction of T-bet and a gene signature similar to that induced by IFNγ, IL-27 collaboration with IFNγ in inducing T-bet and IgG2a, and, finally, selective switching to IgG2a in primed B cells when mixed with IL-27-producing B cells, which display a metabolic program distinct from that in IL-27-responding B cells, i.e., heightened TCA cycle activities and enhanced lactate generation and glutaminolysis. B cell-produced IL-27 also promotes differentiation of TFH cells, as shown by reduced number of TFH cells and defective IL-21 expression in residual TFH cells in mice with B cell-specific deficiency in Ebi3 and, consequently, severe impairments in the germinal center development, class-switching to all Ig isotypes and protective antibody responses to vaccinia virus infection in these mice. Overall, B cell production of IL-27 is a previously unrecognized important regulatory mechanism in the antibody response and anti-viral immunity.

A role for apoptotic and scavenger receptors in mediating antigen exchange between lymphatic endothelial cells and migratory dendritic cells

Antigen persistence following viral infection or vaccination occurs for several weeks after resolution of the inflammatory response. Lymphatic endothelial cells (LECs) capture and archive antigen, which is then transferred to migratory dendritic cells (DCs) and ultimately cross-presented to circulating memory T cells. Following vaccination, both BatF3-dependent and BatF3-independent DCs are needed for antigen exchange, while virus-associated antigen exchange is mediated only by BatF3-dependent DCs. Here, we explore the role of apoptotic and scavenger receptors in mediating this antigen capture and exchange between LECs and DCs. Cross-presentation of the DC-associated antigen to circulating T cells results in a memory pool with increased effector function and enhanced protective capacity. Overall, this work furthers our understanding of how persisting antigen impacts the CD8+ memory T cell response in both vaccine and infectious settings.

Natural IgM initiates the immunological cascade against minor antigen-mismatched cells, illustrating the dependency and unique role of APC subtypes

In organ transplantation a major obstacle is the immunological response against mismatches of major and minor histocompatibility antigen (Ags). Even when MHC Ags are matched between donor and recipient, minor Ags can elicit graft rejection. To date, it is unclear how endogenous antigen-presenting cells (APCs) recognize, coordinate and induce immunological responses against minor Ag-mismatched cells, particularly in the absence of pathogen-associated molecular patterns (PAMPs). We hypothesized that each APC subtype is dependent on each other to complete an immunological response against mismatches of minor Ags. Using a well-established minor Agmismatch model, we demonstrated that the elimination of any one APC subtype (Batf3+ DCs, Irf4+ DCs, Ly6C+ monocytes or B cells) resulted in a diminished or abolished immune response against minor Ag-mismatches. Specifically, we demonstrated that this immunological response began with the recognition of minor Ag-mismatched cells by natural IgM, which resulted in an immune complex formation. This cellular immune complex was then acquired by MHC II presenting APCs, of which one was MHC II expressing Ly6C+ monocytes. Subsequently, Ly6C+ monocyte induced Ag-specific CD4+ T cells licensed Batf3+ DCs via CD40 to present mismatches of minor antigen to Ag-specific CD8+T cells, which were required for the cytotoxic elimination of minor-Ag mismatched cells. Overall, our in vivo findings suggest a sequential, coordinated immunological event is required for the rejection of minor Ag-mismatched cells.

Aging promotes acquisition of naive-like CD8+ memory T cell traits and enhanced functionalities

Protective T cell memory is an acquired trait that is contingent upon the preservation of its constituents and therefore vulnerable to the potentially deleterious effects of organismal aging. Here, however, we have found that long-term T cell memory in a natural murine host-pathogen system can substantially improve over time. Comprehensive molecular, phenotypic, and functional profiling of aging antiviral CD8+ memory T cells (CD8+ TM) revealed a pervasive remodeling process that promotes the gradual acquisition of distinct molecular signatures, of increasingly homogeneous phenotypes, and of diversified functionalities that combine to confer a CD8+ TM-autonomous capacity for enhanced recall responses and immune protection. Notably, the process of CD8+ TM aging is characterized by a progressive harmonization of memory and naive T cell traits, is broadly amenable to experimental acceleration or retardation, and serves as a constitutional component for the "rebound model" of memory T cell maturation. By casting CD8+ TM populations within the temporal framework of their slowly evolving properties, this model establishes a simple ontogenetic perspective on the principal organization of CD8+ T cell memory that may directly inform the development of improved diagnostic, prophylactic, and therapeutic modalities.

Double-edged sword: self-acquiring Batf3-dependent dendritic cell required for anti-tumor immunity and graft rejection (APP3P.104)

One of the major obstacles for the graft acceptance of tissue and organs is the mismatch of major and minor histocompatibility (H) antigens. Minor H antigens are peptides derived from polymorphic proteins and presented by antigen-presenting cells on major histocompatibility complex (MHC) molecules. Here we hypothesized that the self-acquiring, cross-presenting Batf3-dependent dendritic cell (DC) is responsible for minor-antigen graft rejection. Using three models of minor-antigen graft rejection: 1) male antigen 2) non-sex complex minor antigen and 3) skin organ transplant, we demonstrate that Batf3-dependent DCs are responsible for minor-antigen graft rejection. However, in the presence of a TLR7 ligand, the requirement for Batf3-dependent DCs is bypassed by shifting the functionality of Batf3-independent DCs to elicit minor-antigen graft rejection. Overall our study identifies the DC subtype responsible for minor-antigen graft rejection.

Virtual memory cells: a consequence of self-affinity-linked naïve CD8 T cell heterogeneity (LYM5P.703)

Memory phenotype (MP), CD44hi CD49dlo CD8 T cells are found in nearly all mice—lymphoreplete, pathogen naïve, and even TCR transgenics. The presence of MP was long thought to be due to environmental pathogen exposure (or, in the case of transgenics, heterologous immunity to same), but studies establishing the presence of these cells in germ-free mice suggested that this was not the case. These cells, dubbed Virtual Memory (VM), are of special relevance due to their increased effector functioning, and, in contrast to other MP CD8 T cells, develop in the periphery with a dependence on IL-15. Our recent studies have determined that VM cells develop in a manner reminiscent of lymphopenic homeostatic expansion, whereby the highest self-affinity T cells (as measured by CD5) interact with available IL-15 to turn into VM cells. This indicates that the naïve CD8 T cell pool is not as homogeneous as usually assumed, and RNA sequencing has further confirmed the heterogeneity of the CD8 naïve T cell pool (separated on CD5). The sequencing has further implicated VM cells in mediating CD8 bystander protection, and ongoing studies suggest that this is indeed the case, with the VM bystander effects being IL-15 dependent.

Follicular CD8+ T cells: a novel subset in immune protection and antibody responses. (VAC3P.1062)

Endogenous antigen-specific CD8 T cells have been detected within B cell zones of the splenic white pulp during the primary response to multiple infections. The physiologic implications of CD8 T cell recruitment to B cell zones are unknown. However, such CD8 T cell localization may be beneficial for immunity in multiple ways, including, but not limited to: 1) direct CD8 T cell-mediated costimulation of B cells, 2) CD8 T cell-derived signals lowering the threshold of help required from CD4 follicular helper T cells (Tfh) for B cell maturation, and/or 3) direct CD8 T cell-mediated support of Tfh cells. We show here that after a combined TLR agonist and anti-CD40 antibody immunization (TLR/CD40) the follicular-homing CD8 T cell population is increased compared to infection, particularly at 2-3 days post-immunization. Concurrently, CD8 T cells upregulate Tfh cell-associated markers including CXCR5, PD-1, and ICOS. IL-21 is secreted robustly by CD8 T cells at this time point, which could help support B cell germinal center maintenance, class-switching, and Tfh cell differentiation. Indeed, in the context of TLR/CD40 immunization, the absence of CD8 T cells does not affect the IgM response, but reduces an isotype thought to be directed by IL-21, IgG2c, to levels seen in CD4 T cell-depleted animals. Our data indicates that CD8 T cells can assume a Tfh-like phenotype, we call follicular cytotoxic T cells (Tfc), early after challenge and direct antibody responses.

Antigen archiving and management by lymphatic endothelial cells. (INC1P.363)

Antigen derived from virus infections such as influenza and Vesicular Stomatitis Virus (VSV) can persist well beyond the natural rise and fall of the adaptive immune response against the infection. Antigen can similarly persist following both viral Vaccinia challenge and subunit vaccination. Surprisingly, persisting antigen from either Vaccinia or subunit vaccination is captured and maintained by a stromal cell subset: Lymphatic Endothelial Cells (LECs). The duration of antigen persistence is directly correlated with antigen dose and pattern recognition receptor (PRR) activation. PRR induced inflammation leads to LEC proliferation followed by antigen persistence in the lymph node. The coupling of LEC proliferation and antigen capture identifies a novel mechanism by which the secondary lymphoid stroma stores, or “archives”, antigens for extended periods of time after antigen challenge. Consistent with the idea that viral antigen persistence impacts the function of circulating memory T cells, we find that vaccine elicited antigen archiving on LECs has a significant impact on the fate of circulating memory T cells. As such, antigen archiving on LECs leads to increased production of interferon gamma and interleukin 2 by antigen specific CD8 T cells and protection against secondary infection. These findings may broadly impact our understanding of how lymph node stroma, specifically LECs, are involved in i) managing antigen and ii) protecting against re-infection.

Pulmonary dendritic cells require cis-activation to cross-prime T cells (APP4P.117)

Dendritic cells (DCs) are required for the induction of cytotoxic T cells (CTL). In most tissues, including the lung, the resident migratory DC fall into two types, respectively expressing the integrin markers, CD103 and CD11b. The current supposition is that DC function is predetermined by lineage, designating the CD103+ DC as the major cross-presenting DC able to induce CTL. Here we proposed that DC function might also be determined by the nature of the pathogen associated molecular pattern (PAMP) that stimulates it and to which it is able to respond. Thus, in the presence of a TLR3 (CD103+) or a TLR7 (CD11b+) agonist respectively we demonstrated in vivo that both DC subtypes did exhibit the capacity to orchestrate a CTL response. This selectivity did not extend to antigen cross-presentation for T cell proliferation but was required for induction of cytotoxicity and protection in a model of tumor metastasis.

Peripheral blood mononuclear cell gene expression in chronic obstructive pulmonary disease

Although most cases of chronic obstructive pulmonary disease (COPD) occur in smokers, only a fraction of smokers develop the disease. We hypothesized distinct molecular signatures for COPD and emphysema in the peripheral blood mononuclear cells (PBMCs) of current and former smokers. To test this hypothesis, we identified and validated PBMC gene expression profiles in smokers with and without COPD. We generated expression data on 136 subjects from the COPDGene study, using Affymetrix U133 2.0 microarrays (Affymetrix, Santa Clara, CA). Multiple linear regression with adjustment for covariates (gender, age, body mass index, family history, smoking status, and pack-years) was used to identify candidate genes, and ingenuity pathway analysis was used to identify candidate pathways. Candidate genes were validated in 149 subjects according to multiplex quantitative real-time polymerase chain reaction, which included 75 subjects not previously profiled. Pathways that were differentially expressed in subjects with COPD and emphysema included those that play a role in the immune system, inflammatory responses, and sphingolipid (ceramide) metabolism. Twenty-six of the 46 candidate genes (e.g., FOXP1, TCF7, and ASAH1) were validated in the independent cohort. Plasma metabolomics was used to identify a novel glycoceramide (galabiosylceramide) as a biomarker of emphysema, supporting the genomic association between acid ceramidase (ASAH1) and emphysema. COPD is a systemic disease whose gene expression signatures in PBMCs could serve as novel diagnostic or therapeutic targets.

IL-27Rα is required for shaping the magnitude and repertoire of T cells responses to subunit immunization (P4500)

A goal of cellular immune vaccines is the generation of large numbers of antigen specific T cells in response to subunit immunization. A broad spectrum of cytokine and cell surface costimulatory molecules are known to shape the magnitude and repertoire of T cells responding to vaccination. We show here the majority of TLR agonist-based vaccine adjuvants unexpectedly depend on IL-27 for eliciting CD4 and CD8 T cells responses. This is in sharp contrast to infectious challenge which generates T cell responses that are IL-27 independent. Mixed bone marrow chimera experiments demonstrate that IL-27 dependency is T cell intrinsic, requiring T cell expression of IL-27Rα. Further, we show that IL-27 dependency is not only necessary for the maximal expression of vaccine elicited T cell responses, but also critical for representation of high affinity T cells in the responding T cell pool. This observation complements the biology from other reports demonstrating dependence of low affinity T cells on the TNFR family member CD27. Collectively our data highlight the unexpected central importance of IL-27 in the generation of robust, high affinity cellular immune response to subunit immunization.

CD8+ DC trans-presentation of IL-15 to naïve CD8+ T cells produces antigen inexperienced T cells in the periphery with memory phenotype and function (P1315)

Various populations of memory phenotype CD8+ T cells have been described over the last 15-20 years, all of which possess elevated effector functions relative to naïve phenotype cells. Using a technique for isolating antigen specific cells from unprimed hosts, we recently identified a new subset of cells, specific for nominal antigen, but phenotypically and functionally similar to memory cells arising as a result of homeostatic proliferation (HP). We show here that these “Virtual Memory” cells are independent of previously identified “innate memory” cells, arising as a result of their response to IL-15 trans-presentation by lymphoid tissue-resident CD8α+ DCs in the periphery. The absence of IL-15, CD8+ T cell expression of either CD122 or Eomes, or of CD8a+ DCs all lead to the loss of Virtual Memory cells in the host. Our results show that CD8+ T cell homeostatic expansion is an active process within the non-lymphopenic environment, is mediated by IL-15, and produces antigen inexperienced memory cells which retain the capacity to respond to nominal antigen with memory-like function. Preferential engagement of these “Virtual Memory” T cells into a vaccine response could dramatically enhance the rate by which immune protection develops.

Vaccine induced antigen persistence mediated by dendritic cells and lymphatic endothelial cells influences immune memory (P4508)

Numerous studies have established that antigen persists for extended periods of time following infection. However, little is known about the functional significance of this persisting antigen. Herein, we demonstrate that antigen can persist in a mouse following infection with both vaccinia virus and listeria monocytogenes far longer than the peak of the immune response and clearance of the infection. Furthermore, using a TLR/CD40 protein combination vaccine as a model we are able to show persistence of antigen for more than 20 days beyond the peak of the primary immune response. Antigen persistence following TLR/CD40 immunization is dependent on the TLR stimulatory component of the vaccine as well as antigen dose. Surprisingly, we find that antigen persists, not on follicular dendritic cells, but on lymphatic endothelial cells, and requires the participation of conventional dendritic cells but not B cells. Expansion of the LECs in the lymph node is required for antigen persistence and this expansion is a direct result of T cell expansion in the lymph node. Taken together, these studies demonstrate that 1) antigen from subunit vaccination can persist for extended periods after immunization, 2) antigen persists on LECs, a cell type not previously known for its capacity to capture and hold antigen for extended periods of time, and requires LEC expansion, and 3) this persistence correlates directly to the induction of protective immunity after vaccination.

Regulation of TNFR:TNFRL interactions mediates CD8+ T cell clonal competiton (P1013)

The ability to respond to self and foreign antigens requires a network of signals between antigen presenting cells (APCs) and responding T lymphocytes. In our studies, we demonstrate that access to TNF-ligands confer a competitive advantage to CD8+ T cells in response to foreign antigen. Previous work has demonstrated that immunization of mice deficient in CD27, the receptor for CD70, results in a severely restricted antigen-specific CD8 T cell repertoire. We show that adoptively transferred CD8+ T cells are able to compete against endogenous antigen-specific CD8+ T cells more effectively than CD27-deficient CD8+ T cells. To dissect the mechanism by which CD27 expression confers a competitive advantage to CD8+ T cells, we were able to demonstrate that upon engagement of CD27 by CD70, CD27 is lost from the surface of CD8+ T cells and captured by CD70 expressing dendritic cells, effectively blocking access to CD70. These data demonstrate a novel mechanism by which CD8+ T cells of the same specificity can compete against one another by regulating access to TNF-ligands on APCs. Furthermore, multiphoton microscopy revealed CD27 expression is critical to maintain stable T cell:APC interactions. Collectively, our data demonstrate that T cells compete against each other for access to the TNF-ligands, an interaction which affects the duration and potency of T cell:DC interactions and thus influences the repertoire of responding CD8+ T cells to self or foreign antigens.

Combined TLR/CD40 vaccination produces robust T lymphocyte memory by suppressing mTOR. (P4498)

A long-sought goal of vaccine development is to produce robust cytotoxic T cell responses to prevent future infection. This can be accomplished via live-attenuated vaccines, with the caveat of poor stability and pathogenic reversion concerns. However, a combined TLR agonist/CD40 agonist adjuvant mix (TLR/CD40 vaccination) pioneered by our lab produces potent and protective CD8+/CD4+ T cell memory. However, the mechanistic underpinnings of the protective memory are unknown. Recent work suggests that the metabolic state of a T cell plays a crucial role in the cell fate, effector or memory, realized. While glycolysis is primarily utilized in effector T cells, FAO and catabolic processes are extensively used in naïve and memory T cells. Rapamycin and metformin treatment skews T cell fate decision toward memory by inhibiting mTOR and the respiratory chain complex 1 respectively. Interestingly, CD8+ T cells induced in the presence of these agents have a phenotype identical to that generated by TLR/CD40 vaccination suggesting that our vaccination may influence the metabolic pathways utilized by the responding T cells. Consistent with this, phospho-mTOR levels are suppressed in T cells generated by TLR/CD40 vaccination as compared to those responding to Listeria monocytogenes infection. Ongoing work is establishing the means by which TLR/CD40 vaccination and related costimulatory molecules and cytokines (IL-27 and CD27) influence the metabolic processes in T cells post vaccination.

Varying frequencies of T cells exhibiting CMV peptide-specific reactivity to allo-MHC are present in cord blood transplant units (P2228)

Cord blood transplants are a desirable treatment option for a number of hematopoietic diseases due partly to the increased tolerance of HLA mismatches between transplant donor and recipient, manifest in the decreased occurrence of GVHD. Unfortunately, these patients also have an increased risk of reactivating latent infections (e.g. CMV) post-transplant which will ultimately be fatal; likely due to the same decreased T cell functioning that results in HLA mismatch tolerance. Viral reactivation is by no means universal after transplant, however, and while certain factors are known to increase a patient’s risk (e.g. GVHD or in-vivo t cell depletion), there remains no good method for predicting susceptibility. Using MHC tetramers, our lab has found a population of T cells specific to the HLA-A2 CMV peptide in not only A2, but also non-A2 cord blood samples. The frequency of these cells varies widely between cord blood units, which could be a potential signifier of a unit’s efficacy in fighting viral reactivation. Further, preliminary studies suggest that these cells have a specificity and functionality that would make them therapeutically useful.

Treatment with N-acetyl-seryl-aspartyl-lysyl-proline prevents experimental autoimmune myocarditis in rats

Myocarditis is commonly associated with cardiotropic infections and has been linked to development of autoimmunity. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a naturally occurring tetrapeptide that prevents inflammation and fibrosis in hypertension and other cardiovascular diseases; however, its effect on autoimmune-mediated cardiac diseases remains unknown. We studied the effects of Ac-SDKP in experimental autoimmune myocarditis (EAM), a model of T cell-mediated autoimmune disease. This study was conducted to test the hypothesis that Ac-SDKP prevents autoimmune myocardial injury by modulating the immune responses. Lewis rats were immunized with porcine cardiac myosin and treated with Ac-SDKP or vehicle. In EAM, Ac-SDKP prevented both systolic and diastolic cardiac dysfunction, remodeling as shown by hypertrophy and fibrosis, and cell-mediated immune responses without affecting myosin-specific autoantibodies or antigen-specific T cell responses. In addition, Ac-SDKP reduced cardiac infiltration by macrophages, dendritic cells, and T cells, pro-inflammatory cytokines [interleukin (IL)-1α, tumor necrosis factor-α, IL-2, IL-17] and chemokines (cytokine-induced neutrophil chemoattractant-1, interferon-γ-induced protein 10), cell adhesion molecules (intercellular adhesion molecule-1, L-selectin), and matrix metalloproteinases (MMP). Ac-SDKP prevents autoimmune cardiac dysfunction and remodeling without reducing the production of autoantibodies or T cell responses to cardiac myosin. The protective effects of Ac-SDKP in autoimmune myocardial injury are most likely mediated by inhibition of 1) innate and adaptive immune cell infiltration and 2) expression of proinflammatory mediators such as cytokines, chemokines, adhesion molecules, and MMPs.

Depletion of macrophages and dendritic cells in ischemic acute kidney injury

BACKGROUND

Inflammation is thought to play a role in ischemic acute kidney injury (AKI). We have demonstrated that macrophage and dendritic cell depletion, using liposome-encapsulated clodronate (LEC), is protective against ischemic AKI.

METHODS

To determine whether macrophages or dendritic cells or both play a role in ischemic AKI, we performed ischemic AKI in CD11b-DTR mice that have a diphtheria toxin (DT)-induced depletion of CD11b cells (macrophages) and CD11c-DTR mice that have a DT-induced depletion of CD11c cells (dendritic cells).

RESULTS

While LEC-treated animals had a significant functional protection from AKI, CD11b-DTR and CD11c-DTR mice were not protected against AKI despite a similar degree of renal macrophage and dendritic cell depletion. Proinflammatory cytokines are known to play a role in ischemic AKI. To determine the possible reasons for the lack of protection in CD11b-DTR and CD11c-DTR mice compared to LEC-treated mice, 32 cytokines/chemokines were measured in these mice. Of the cytokines/chemokines measured, IL-6, MCP-1, GMCSF, IL-1β and CXCL1 (also known as IL-8 in humans or KC in mice) showed significant differences in the LEC-treated, CD11b-DTR and CD11c-DTR mice. MCP-1 and CXCL1 (known mediators of AKI), and also GMCSF and IL-1β were increased in AKI and decreased in LEC-treated AKI but not AKI in CD11b-DTR or CD11c-DTR mice.

CONCLUSIONS

These findings suggest that LEC-mediated protection from AKI is not simply mediated by depletion of renal macrophage or dendritic cell subpopulations. Protection against AKI in LEC-treated compared to CD11b-DTR or CD11c-DTR mice may be partially explained by differences in proinflammatory cytokine profiles.

Polyethylenimine-based siRNA nanocomplexes reprogram tumor-associated dendritic cells via TLR5 to elicit therapeutic antitumor immunity

The success of clinically relevant immunotherapies requires reversing tumor-induced immunosuppression. Here we demonstrated that linear polyethylenimine-based (PEI-based) nanoparticles encapsulating siRNA were preferentially and avidly engulfed by regulatory DCs expressing CD11c and programmed cell death 1-ligand 1 (PD-L1) at ovarian cancer locations in mice. PEI-siRNA uptake transformed these DCs from immunosuppressive cells to efficient antigen-presenting cells that activated tumor-reactive lymphocytes and exerted direct tumoricidal activity, both in vivo and in situ. PEI triggered robust and selective TLR5 activation in vitro and elicited the production of hallmark TLR5-inducible cytokines in WT mice, but not in Tlr5-/- littermates. Thus, PEI is a TLR5 agonist that, to our knowledge, was not previously recognized. In addition, PEI-complexed nontargeting siRNA oligonucleotides stimulated TLR3 and TLR7. The nonspecific activation of multiple TLRs (specifically, TLR5 and TLR7) reversed the tolerogenic phenotype of human and mouse ovarian tumor-associated DCs. In ovarian carcinoma-bearing mice, this induced T cell-mediated tumor regression and prolonged survival in a manner dependent upon myeloid differentiation primary response gene 88 (MyD88; i.e., independent of TLR3). Furthermore, gene-specific siRNA-PEI nanocomplexes that silenced immunosuppressive molecules on mouse tumor-associated DCs elicited discernibly superior antitumor immunity and enhanced therapeutic effects compared with nontargeting siRNA-PEI nanocomplexes. Our results demonstrate that the intrinsic TLR5 and TLR7 stimulation of siRNA-PEI nanoparticles synergizes with the gene-specific silencing activity of siRNA to transform tumor-infiltrating regulatory DCs into DCs capable of promoting therapeutic antitumor immunity.

Vaccination with liposome--DNA complexes elicits enhanced antitumor immunity

Cationic liposomes have been shown to potentiate markedly the ability of plasmid DNA to activate innate immune responses. We reasoned therefore that liposome-DNA complexes (LDC) could be used to produce more effective plasmid DNA vaccines for cancer. To test this hypothesis, tumor-bearing mice were vaccinated with conventional plasmid DNA vaccines or with LDC vaccines encoding model tumor antigens and CD8(+) T-cell responses and antitumor activity were assessed. We found that although plasmid DNA vaccines generated large increases in antigen-specific CD8(+) T cells, they failed to elicit significant antitumor immunity. In contrast, LDC vaccines elicited large numbers of antigen-specific CD8(+) T cells and also generated significant antitumor activity against established tumors. The antitumor activity elicited by immunization with LDC vaccines was mediated primarily by CD8(+) T cells. Studies of the interaction of LDC with antigen-presenting cells found that LDC triggered dendritic cell production of interleukin-12 and interferon (IFN)-gamma production by natural killer cells in vivo. Activation by LDC was also accompanied by upregulation of costimulatory molecule expression. These findings suggest that by concurrently activating strong systemic innate immune responses and generating cytotoxic T-lymphocyte responses, LDC may be used to increase the effectiveness of therapeutic plasmid DNA vaccination for cancer.

Efficient Immunization and Cross-Priming by Vaccine Adjuvants Containing TLR3 or TLR9 Agonists Complexed to Cationic Liposomes

Complexing TLR9 agonists such as plasmid DNA to cationic liposomes markedly potentiates their ability to activate innate immunity. We therefore reasoned that liposomes complexed with DNA or other TLR agonists could be used as effective vaccine adjuvants. To test this hypothesis, the vaccine adjuvant effects of liposomes complexed to TLR agonists were assessed in mice. We found that liposomes complexed to nucleic acids (liposome-Ag-nucleic acid complexes; LANAC) were particularly effective adjuvants for eliciting CD4(+) and CD8(+) T cell responses against peptide and protein Ags. Notably, LANAC containing TLR3 or TLR9 agonists effectively cross-primed CD8(+) T cell responses against even low doses of protein Ags, and this effect was independent of CD4(+) T cell help. Ag-specific CD8(+) T cells elicited by LANAC adjuvants were functionally active and persisted for long periods of time in tissues. In a therapeutic tumor vaccine model, immunization with the melanoma peptide trp2 and LANAC adjuvant controlled the growth of established B16 melanoma tumors. In a prophylactic vaccine model, immunization with the Mycobacterium tuberculosis protein ESAT-6 with LANAC adjuvant elicited significant protective immunity against aerosol challenge with virulent M. tuberculosis. These results suggest that certain TLR agonists can be combined with cationic liposomes to produce uniquely effective vaccine adjuvants capable of eliciting strong T cell responses against protein and peptide Ags.

Genomic-scale analysis of gene expression in resting and activated T cells

Recent advances in gene array technology and isolation of lymphocytes now allow comprehensive analysis of gene expression in many different types of T cells. So far only a few sets of results have been published. However it is already clear that these analyses provide accurate measurements of gene expression in T cells. This technology offers the first opportunity to examine global and subtle changes in gene expression in response to specific stimuli.

T-cell survival

Like other cells, T cells are dependent on signals from their environment for their survival. Resting T cells are supported in vitro by cytokines such as interleukin (IL)-4, IL-6 and IL-7. The latter two cytokines are made constitutively in animals and hence might affect the lifetimes of their resting T cells. Resting T cells are also kept alive by interaction with an as yet unidentified molecule on the surface of other cells. Activated T cells are also supported in vitro by members of two families of these proteins, the IL-2 family and the interferon-alpha beta family. Members of the latter family may have effects on activated cells in vivo. Thus although both resting and activated T cells require signals to keep themselves alive, the signals are different for the two types of cells. This perhaps allows the immune response to control the numbers of activated cells during infections without compromising its pool of precursor, resting T cells.

Comparative sequence analysis of the reovirus S4 genes from 13 serotype 1 and serotype 3 field isolates

The reovirus sigma 3 protein is a major outer capsid protein that may function to regulate translation within infected cells. To facilitate the understanding of sigma 3 structure and functions and the evolution of mammalian reoviruses, we sequenced cDNA copies of the S4 genes from 10 serotype 3 and 3 serotype 1 reovirus field isolates and compared these sequences with sequences of prototypic strains of the three reovirus serotypes. We found that the sigma 3 proteins are highly conserved: the two longest conserved regions contain motifs proposed to function in binding zinc and double-stranded RNA. We used the 16 viral isolates to investigate the hypothesis that structural interactions between sigma 3 and the cell attachment protein, sigma 1, constrain their evolution and to identify a determinant within sigma 3 that is in close proximity to the sigma 1 hemagglutination site.