Assessing the applicability and outcomes of the COMPASS trial a large cohort of atherosclerotic disease patients

Background

Atherosclerotic Cardiovascular disease (ASCVD) is the leading cause of morbidity and mortality worldwide with substantial impact on health care resources. Rivaroxaban 2.5 mg twice daily with low dose ASA reduced death, myocardial infarction and stroke compared to ASA alone in stable ASCVD patients studied in the COMPASS trial.

Purpose

To assess the applicability and potential outcomes of applying the COMPASS antithrombotic strategy in a population-based cohort of patients with ASCVD.

Methods

All patients with a new diagnosis of ASCVD identified during hospital admission or outpatient medical encounters using validated case definitions from 2008–2019 were included. We determined the proportion who met COMPASS eligibility criteria (Eligible), the proportion who met inclusion criteria but had exclusion criteria (Excluded), and the proportion who did not meet inclusion criteria (Ineligible). Primary outcomes of interest were CV death, myocardial infarction, and stroke (MACE), with secondary outcomes all cause death, CV hospitalization, PAD intervention, amputation, and all bleeding which were followed to end of study.

Results

Of 226,446 new ASCVD patients in the 11 years studied, 73% had coronary artery disease, 17% had peripheral artery disease including cerebral and peripheral vascular disease (PAD), and 10% had both. Of the 364,442 prevalent cases, 27% met COMPASS eligibility criteria, another 42% met inclusion criteria but would have been excluded and 31% were Ineligible. The main reasons for exclusion were high bleeding risk characteristics in 69% and concomitant medical therapy (CYP3A4 inducers 30%, oral anticoagulants 28%, and dual antiplatelet therapy 7%). The MACE event rates were approximately twice as high in the excluded group as those deemed COMPASS eligible (figures 1). COMPASS eligible patients in our cohort exhibited event rates similar to the ASA arm of COMPASS (figure 2). The other event rates per 100 person-years for Eligible, Excluded, and Ineligible patients respectively were: all-cause death 4.6, 10.6, 1.2,; CV hospitalization 4.8, 8.8, 3.0; PAD intervention 0.6, 0.6, 0.1; and all bleeding 1.9, 4.3, 1.1. If the COMPASS antithrombotic strategy of Rivaroxaban 2.5 twice daily with low dose ASA was given to patients deemed eligible in this population, there would have been a potential reduction of 87 MACE events, 34 CV death, 25 MI, 24 stroke, and 12 amputations per 10,000 patient years of treatment.

Conclusion

In a population of 4.4 million persons, there are approximately 20,000 incident ASCVD patients diagnosed yearly. Approximately 70% of patients with ASCVD in the real-world met COMPASS inclusion criteria, although more than half would be excluded due to high-bleed risk characteristics or concomitant medical therapy. Implementing the COMPASS antithrombotic strategy would result in substantial reduction in CV death and MACE events.

Funding Acknowledgement

Type of funding sources: Private company. Main funding source(s): Bayer MACE by COMPASS eligibilityEvent rates compared to COMPASS ASA

Real-world evidence on short- and long-term outcomes for acute coronary syndrome patients with a prior history of atrial fibrillation

Background

Acute coronary syndromes (ACS) are often complicated by new-onset atrial fibrillation (AF), which is associated with higher short-term mortality. It is unknown whether a prior history of AF affects outcomes beyond in-hospital mortality in a real-world setting.

Purpose

To assess (i) the prevalence of prior AF in patients with ACS, including unstable angina (UA), non-ST-segment elevation myocardial infarction (NSTEMI) and ST-segment elevation myocardial infarction (STEMI); (ii) clinical characteristics of ACS patients with and without AF; and (iii) in-hospital mortality and long-term outcomes in the presence of prior AF.

Methods

We used linked administrative health databases to identify patients hospitalized with a primary diagnosis of ACS and prior history of non-valvular AF (ICD-9 code 427.3 and ICD-10 code 148), which was defined as 1 hospitalization or 1 emergency department visit or 2 outpatient visits at least 30 days apart in 1 year in any position, between April 2002 and March 2016 in Alberta, Canada. Outcomes included in-hospital mortality, long-term mortality and a composite of all-cause mortality, hospitalisation for myocardial infarction (MI) or stroke over 3 years. Kaplan-Meier curves were constructed for mortality and the composite outcome according to presence of prior AF and ACS type.

Results

Of 31,056 presenting with an ACS, 4,173 (13.4%) had a prior history of AF. Compared to patients without prior AF, patients with AF were older (75.7 versus 64.7 years), female (35.5% versus 29.9%), with a higher comorbidity burden (Charlson Comorbidity Index 1.7 versus 1.1). Patient with AF more often presented with NSTEMI (57.7% versus 48.2%) and UA (17.1% versus 16.4%) compared to STEMI (25.2% versus 35.4%). In-hospital mortality was higher for ACS patients in the presence of prior AF (8.1% versus 3.3%; p<0.0001). Mortality and the composite endpoint were also significantly higher in patients with prior AF compared to those without AF (Panel A and B) over the 3-year period. A worse prognosis was observed for STEMI and NSTEMI patients with prior AF compared to any other group (panel C and D).

Conclusion

In this large, population-based study, we found that a history of AF is common in patients presenting with an ACS. In the presence of AF, short- and long-term prognosis is poor particularly for STEMI and NSTEMI patients. Aggressive modification of shared risk factors and use of evidence-based therapies to improve outcomes is needed in this high-risk population.

Outcomes by presence of AF and ACS type

Funding Acknowledgement

Type of funding source: None

4071Early changes in quality of life after transcatheter aortic valve replacement: One-year results from the 3M TAVR Study

Background

In patients with severe calcific aortic stenosis, transcatheter aortic valve replacement (TAVR) has been shown to significantly improve quality of life (QOL). However, changes in QOL at early follow-up (<1 month), and following next-day discharge are poorly understood.

Methods

A total of 411 patients at 13 centers were enrolled in the Multimodality, Multidisciplinary but Minimalist TAVR (3M TAVR) study in 2015–2017. QOL was evaluated using the Kansas City Cardiomyopathy Questionnaire (KCCQ-12) in participants with a baseline score and at least one score at 2 weeks, 30 days and 1 year. Study endpoints were change in (1) KCCQ-Overall Summary Score (KCCQ-OS) and (2) minimal clinically important differences (MCID). Mixed effects models were used to explore patterns of change from baseline, with fixed terms for time, status at 1-year and their interaction terms, and a random intercept for subject to account for within subject correlation. Descriptive statistics were used to report MCID.

Results

Data were available for 358 (87.1%) participants. 216 (60.3%) were men with a median age 84.0 and STS 5.0 There was significant increase in QOL 2 weeks after TAVR (p≤0.01), and further significant improvement at the 1-month timepoint (p<0.01) for participants who were alive at 1 year. Sex, age category, and STS score category did not have a significant effect on the change in QOL (p>0.05). In the first 2 weeks, moderate (10–20 points) and large (>20 points) improvements were observed in 19.9% and 49.0% of the surviving patients, respectively; at 1-year, similar MCID were seen in 14.6% and 64.0% respectively.

Figure 1

Conclusion

This is the first study to report significant increase in QOL 2 weeks after TAVR, with sustained improvement during the first year in patients treated with the Vancouver TAVR Clinical Pathway with a goal of next-day discharge. Further studies are necessary to determine whether alternative TAVR clinical pathways yield similar findings.

Acknowledgement/Funding

Investigator-initiated unrestricted research grant, Edwards

Investigation of the First Seven Reported Cases of Candida auris, a Globally Emerging Invasive, Multidrug-Resistant Fungus-United States, May 2013-August 2016

November 11, 2016/65(44);1234-1237. What is already known about this topic? Candida auris is an emerging pathogenic fungus that has been reported from at least a dozen countries on four continents during 2009-2015. The organism is difficult to identify using traditional biochemical methods, some isolates have been found to be resistant to all three major classes of antifungal medications, and C. auris has caused health care-associated outbreaks. What is added by this report? This is the first description of C. auris cases in the United States. C. auris appears to have emerged in the United States only in the last few years, and U.S. isolates are related to isolates from South America and South Asia. Evidence from U.S. case investigations suggests likely transmission of the organism occurred in health care settings. What are the implications for public health practice? It is important that U.S. laboratories accurately identify C. auris and for health care facilities to implement recommended infection control practices to prevent the spread of C. auris. Local and state health departments and CDC should be notified of possible cases of C. auris and of isolates of C. haemulonii and Candida spp. that cannot be identified after routine testing.

Type 1 interferon primes naïve CD8 T cells to respond to lower concentrations and affinities of cognate ligands (VIR6P.1178)

During an acute virus infection, antigen-specific CD8 T cells undergo clonal expansion and differentiation into effector cells in order to control the infection. Studies have shown that CD8 T cells need to divide at least once before they acquire specific effector functions, including the ability to directly lyse target cells and produce certain cytokines. However, recently we have shown that pre-exposure of the host to type I interferon (IFN) sensitizes CD8 T cells to rapidly acquire effector function without the need to divide. The IFN-primed naïve CD8 T cells produced IFNγ, enhanced TNF and degranulated upon stimulation with high affinity cognate antigen. The threshold required for IFN-induced sensitized CD8 T cells to become activated and produce effector functions was reduced, as primed CD8 T cells produced cytokines in response to lower affinity ligands and lower concentrations of cognate ligands. In addition, an in vivo cytotoxicity assay showed that primed naïve CD8 T cells specifically lysed target cells. The reduced requirement of naïve CD8 T cells to produce effector functions if pre-exposed to IFN-induced environments may increase the overall number of naïve T cells able to respond to any given antigen. IFN-primed increased numbers and response of naïve T cells may help to control antigen load during an acute infection.

IRF4 regulates the ratio of T-bet to eomesodermin in CD8+ T cells responding to persistent LCMV infection (IRM14P.447)

CD8+ T cell exhaustion commonly occurs in chronic infections and cancers. During T cell exhaustion there is a progressive and hierarchical loss of effector cytokine production, up-regulation of inhibitory co-stimulatory molecules, and eventual deletion of antigen specific cells by apoptosis. A key factor that regulates T cell exhaustion is persistent TCR stimulation. Loss of this interaction results in restoration of CD8+ T cell effector functions in previously exhausted CD8+ T cells. TCR stimulation is also important for the differentiation of Eomeshi CD8+ effector T cells from T-bethi precursors, both of which are required for optimal viral control. However, the molecular mechanisms regulating the differentiation of these two cell subsets and the relative ratios required for viral clearance have not been described. We show that TCR signal strength regulates the relative expression of T-bet and Eomes in antigen-specific CD8+ T cells by modulating levels of IRF4. Reduced IRF4 expression results in lower proportions and numbers of T-bet+ Eomes- precursors and poor control of LCMV Clone 13 infection. Altering the ratio of T-bet to Eomes by generating compound heterozygotes of Irf4 and Eomes restores the differentiation of T-bet+ Eomes- precursors and leads to efficient viral control. These data highlight a critical role for IRF4 in regulating CD8+ T cell responses by ensuring a protective ratio of T-bet to Eomes, leading to the ultimate control of this chronic viral infection.

NK cells and virus-related cancers

Natural killer (NK) cells become activated during viral infections and can play roles in such infections by attacking virus-infected cells or by regulating adaptive immune responses. Experimental models suggest that NK cells may also have the capacity to restrain virus-induced cancers. Here, we discuss the seven viruses linked to human cancers and the evidence of NK cell involvement in these systems.

Differential requirement for IRF4 in CD8+ T cell responses to acute versus chronic LCMV infection (IRM4P.498)

The magnitude of the CD8+ T cell response to acute infection is regulated by the strength of TCR signaling. A key component to this is the level of expression of the transcription factor IRF4, which controls CD8+ T cell expansion in a dose-dependent manner. During an acute response to LCMV-Armstrong, a modest reduction in IRF4 levels, such as that achieved by a haplo-deficiency at the irf4 locus, leads to a 2-4 fold reduction in the number of LCMV specific CD8+ T cells without impacting viral clearance (RN manuscript submitted). These data indicate that acute LCMV infections are associated with an expansion of cognate CD8+ T cells that is in excess of that needed to clear the virus. In contrast, during LCMV-clone 13 infection, the modestly-reduced CD8+ T cell response of irf4+/- T cells fails to control the infection, resulting in long-term viral persistence. In this system, loss of one allele of irf4 results in reduced CD8+ T cell function, increased exhaustion due to loss of PD1 low Tbet high precursors, and less weight loss than in LCMV-clone 13-infected WT mice. These data indicate differential requirements for high levels of IRF4 in generating functional CD8+ T cell responses capable of clearing acute versus chronic virus infections.

Natural killer cells suppress humoral immunity and development of neutralizing antibodies (VIR1P.962)

Pathogen-specific neutralizing antibodies (nAbs) are a key component of protective immunity after infection or vaccination. However, broadly-specific nAbs that can prevent infections with highly mutable viruses like HIV are rarely seen in infected patients and are poorly elicited by current vaccines. Therefore, new vaccine strategies are needed to enhance the induction of nAbs, potentially by augmenting the germinal center (GC) reactions that facilitate somatic hypermutation, affinity maturation and development of high-affinity nAbs. Here, we demonstrate that natural killer (NK) cells impair humoral immunity by contributing to a weak GC response and subdued generation of virus-specific nAbs after acute lymphocytic choriomeningitis virus (LCMV) infection of mice. The magnitude and duration of the LCMV-induced GC response was substantially reduced by NK cells, which constricted the number of both follicular helper T cells (Tfh) and GC B cells present in lymphoid tissues. NK cell-mediated suppression of GC responses was also observed in different stains of mice and after infection with a variety of dissimilar pathogens, suggesting that NK cell suppression of humoral immunity is a universal feature of infection. Notably, NK cell inhibition of the GC response during LCMV infection resulted in a markedly delayed and relatively weak nAb response. Thus, targeting of immunosuppressive NK cells could represent a revolutionary method to enhance the efficacy of future vaccine regimens.

Mechanisms underlying specificity of natural killer cell regulation of adaptive immunity (IRC8P.485)

Viral persistence is determined in part by the regulatory activities of murine natural killer (NK) cells, including the lysis of activated CD4 T cells. We now find that NK cells also impair virus-specific memory T cell responses [and repress humoral immunity (separate abstract)] after acute Pichinde or lymphocytic choriomeningitis virus infections. Hence, limiting NK cell inhibition of adaptive immunity during vaccination could enhance long-lived protective immunity. To enable selective targeting of this NK cell activity in a vaccine, the molecular mechanisms of such suppression must be ascertained. Thus, we have explored changes in the expression of NK cell receptors (NKR) and their ligands (NKRL) on both NK cells and target T cells after infection. This analysis revealed that: 1) suppression of adaptive immunity corresponded with reduced inhibitory NKR expression on NK cells; 2) archetypical activating NKR such as NKG2D were dispensable in our system; and 3) susceptibility of activated CD4 T cells to NK cell lysis correlated with reduced expression of inhibitory NKRL (e.g. CD48) and corresponding higher levels of activating NKRL (e.g. Ly108), than were present on NK cell-resistant CD8 T cells. Further, the selectivity of NK cell killing of different T cells could be deregulated by altering NKR/NKRL expression. Our findings may facilitate development of innovative strategies to harness or inhibit NK cell lysis of T cells in the context of vaccination or immune therapy.

The transcription factor ZBTB32 negatively regulates CD8+ T cell responses during acute and chronic viral infection (VIR4P.1010)

The transcription factor, ZBTB32, is not expressed in resting naïve CD8+ T cells, but is upregulated following TCR stimulation in the presence of cytokines IFNγ, IL-12 or IL-2. To investigate the role of ZBTB32 in the development of anti-viral CD8+ T cells, Zbtb32-/- mice were infected with LCMV-Armstrong or LCMV-Clone 13. Following infection with LCMV-Armstrong, Zbtb32-/- mice exhibited normal viral clearance, but generated increased numbers of virus-specific CD8+ T cells, relative to wild-type mice, resulting in an increased memory cell population. The Zbtb32-/- CD8+ memory T cell population showed rapid proliferation and enhanced protective memory potential to secondary challenge. In contrast, upon infection with LCMV-Clone 13, 70% of Zbtb32-/- mice succumbed to a fatal disease starting at day 9 post-infection, and exhibited severe immune pathology in the lung compared to WT mice. Examination of the surviving mice indicated reduced LCMV-clone 13 viral titers in Zbtb32-/- mice. Gene expression analysis showed up-regulation of Eomes, Cd27, Pvr and Cd7 in virus-specific Zbtb32-/- CD8+ T cells. ChIP assays confirmed that ZBTB32 bound to the regulatory regions of these genes and recruited HDAC1 and HDAC2 to promote repressive histone modifications. These data indicate that ZBTB32 acts an epigenetic regulator and negatively regulates T cell responses and memory generation during acute and chronic LCMV infection.

Properties of virus-induced NK cells correlating with their ability to kill activated CD4 T cells (IRM7P.489)

Activated natural killer (NK) cells induced during viral infections of mice can regulate adaptive immunity by lysing activated CD4 T cells. This seems to be a general property of interferon-inducing viruses, but the efficiency of this process is in part dependent on the nature of the instigating virus. Here we examined the differential expression of activating and inhibitory receptors on NK cells from lymphocytic choriomeningitis virus (LCMV) and vaccinia virus (VACV)-infected mice, because NK cells from VACV-infected mice were far less efficient at killing activated CD4 T cells than those from LCMV-infected mice. Relative to expression levels on LCMV-activated NK cells, NKG2A expression was higher in VACV-induced NK cells while NKG2D was lower. NK cells activated by infections with LCMV, Pichinde virus (PV), mouse hepatitis virus (MHV), and murine cytomegalovirus (MCMV) displayed similar expression patterns for all of the examined receptors, whereas VACV-induced cells had a distinct expression pattern. Another major difference between VACV-induced NK cells and NK cells activated by the other viruses was in the expression of granzyme B, an essential component of NK cell-mediated cytolysis. VACV-induced NK cells expressed granzyme B at lower levels than NK cells from mice infected with LCMV, PV, MHV A59, or MCMV. These results indicate that the NK cell receptor expression and the cytolytic activity of NK cells can vary with the infecting virus.

Out-of-sequence signal 3 as a mechanism for virus-induced immune suppression of CD8 T cell proliferation (VIR1P.960)

Virus infections are known to induce a transient state of immune suppression often associated with an inhibition of T cell proliferation in response to mitogen or cognate-antigen stimulation. Recently, virus-induced immune suppression has been linked to responses to type 1 IFN, a signal 3 cytokine that normally can augment the proliferation and differentiation of T cells exposed to antigen (signal 1) and co-stimulation (signal 2). However, pre-exposure of CD8 T cells to IFN-inducers such as viruses or poly(I:C) prior to antigen signaling is inhibitory, indicating that the timing of IFN exposure is of essence. Studies with T cells lacking IFN receptors implicated a direct role for type 1 IFN in this process. CD8 T cells pretreated with poly(I:C) down-regulated the IFN receptor, up-regulated SOCS1, and were refractory to IFNβ-induced STAT phosphorylation. When exposed to a viral infection these CD8 T cells behaved more like 2-signal than 3-signal T cells, showing defects in short lived effector cell differentiation, reduced effector function, delayed cell division, and reduced levels of survival proteins. This suggests that IFN-pretreated CD8 T cells are unable to receive the positive effects that type 1 IFN provides as a signal 3 cytokine when delivered later in the signaling process. This desensitization mechanism may partially explain why vaccines function poorly in virus-infected individuals.

TCR signal strength via IRF4 influences CD8 T cell responses to acute LCMV infections (P6096)

CD8+ T cells undergo rapid proliferation, differentiation and contraction following acute infections. One of the key factors influencing these CD8+ T cell responses is the strength of TCR-ligand interactions. We have previously shown that the transcription factor Interferon Regulatory Factor 4 (IRF4) is important in the differentiation of CD8 T cells. IRF4 is not expressed in naïve CD8 T cells, but is rapidly up-regulated upon T cell activation. Further, this up-regulation is directly regulated by the strength of TCR signaling, such that stronger signaling leads to higher levels of IRF4 expression. To test the function of IRF4 in vivo, we have utilized the acute LCMV infection model together with mice expressing graded levels of IRF4. These studies indicated that CD8 T cell proliferation and differentiation into effector and memory populations is regulated by IRF4. Further, we found that IRF4 was impacting the expression of major downstream transcription factors, Eomes, TBet, and TCF1, that are critical for effector responses and memory differentiation. Together these data establish a transcription factor network that is highly responsive to the strength of TCR-ligand interactions during infection.

Out of sequence “signal 3” suppresses CD8 T cell proliferation (P6040)

Type 1 interferons (IFN), the first cytokines to be discovered, have been shown to regulate many aspects of the immune system. Type 1 IFN can act directly on CD8 T cells as a “signal 3” cytokine, which augments proliferation and differentiation of T cells into effectors in response to antigen. Exposure of CD8 T cells to IFN-inducers at the same time as antigen had stimulatory effects, whereas pre-exposure to IFN-inducers was inhibitory, indicating that the timing of IFN exposure was of essence. Pre-exposure of CD8 T cells to the type 1 IFN inducer and TLR agonist poly(I:C) had transient inhibitory effects on CD8 T cell proliferation. CD8 T cells lacking type 1 IFN receptors were resistant to the suppressive effects of poly(I:C), indicating a direct involvement of IFN. Poly(I:C)-pretreated CD8 T cells were refractory to further IFNβ stimulation, as measured by phosphorylation of STAT molecules, including STAT1, 3, 4, and 5. Reduced phospho-STAT levels were not due to a decrease in total STAT protein. Poly(I:C)-pretreated CD8 T cells phosphorylated STAT molecules in response to other cytokines, including IL-6 and IL-15. A decrease in type 1 IFN receptors and increased expression of SOCS1 likely contribute to the unresponsiveness to IFNβ stimulation. These data suggest that IFN-pretreated CD8 T cells are unable to get the positive effects that type 1 IFN provides as a “signal 3” cytokine, and this may partially explain why vaccines function poorly in virus-infected individuals.

The intrinsic role of ROG in CD8+ T cell development has an impact on protective immunity against viral infection (P1452)

Repressor of GATA3 (ROG) is a member of the poxviruses and zinc finger family of transcriptional repressors, and is also known as ZBTB32. Several studies have suggested that ROG may regulate the activation and differentiation CD4+ and CD8+ T cells, and further, may also play a role in plasma cell differentiation. We have investigated the role of ROG in the development of anti-viral memory T cells. Upon acute infection with LCMV Armstrong, Rog-/- mouse accumulated higher proportions and numbers of virus-specific CD8+ T cells, resulting in an increased number of memory cells. Rog-/- mouse exhibited normal viral clearance, but as a consequence of the elevated primary response, the Rog-/- CD8+ T cell population contains enhanced protective memory potential. We also examined the response of Rog-/- mice to infection with a high dose of LCMV-clone 13, which causes a chronic infection leading to exhaustion of the CD8+ T cells. We found that approximately one-half of Rog-/- mice infected with high dose LCMV-clone 13 succumbed to this infection as early as day 9 post-infection and also exhibited severe immune pathology in the lung compared to WT mice. The higher frequency of IFNg-producing virus-specific CD8+ T cells in Rog-/- mice also resulted in enhanced viral control following LCMV-clone 13 infection. These data indicate that ROG plays a unique non-redundant role during acute and chronic LCMV infection, and is an important regulator of CD8+ effector and memory T cell generation.

Immune regulation by natural killer cells through lysis of activated T cells (168.4)

We have previously shown that natural killer (NK) cells can influence viral pathogenesis either by directly lysing virus-infected cells or through lysis of activated CD4 T cells. The latter phenomenon contributed to an inhibition of anti-viral T cells that favored viral persistence and host survival rather than lethal pathology during lymphocytic choriomeningitis virus (LCMV) infection. Infections with unrelated viruses, including Pichinde virus (PV), or inoculation with the type I IFN inducer, polyI:C, also triggered NK cell lysis of activated CD4 T cells. This lysis was coincident with poor control of PV infection and diminished PV-specific memory T cell responses, suggesting that such NK cell immunoregulation is a general principle of virus infection. LCMV infection was unable to induce NK cell lysis of activated T cells in IFN receptor (IFNAR)-deficient mice, implicating type I IFN in stimulation of this NK cell activity. Expression of the CD48, the ligand for the inhibitory NK cell receptor 2B4/CD244, was greater on NK cell-resistant CD8 T cells than their CD4 counterparts. However, genetic deletion of 2B4 facilitated lysis of activated CD8 T cells, and was associated with impaired clearance of both acute and chronic virus infections. Thus, type I IFN expression during virus infection or vaccination stimulates a 2B4/CD48-regulated, NK cell-mediated lysis of anti-viral T cells which impairs viral control and immune memory.

IL-2 regulates tissue-dependent differences in CD8 T cell apoptosis during and after- viral Infection. (110.19)

Virus-specific CD8 T cell populations in lymphoid organs contract by apoptosis or by dissemination into peripheral tissues, and those residing in non-lymphoid organs, including the peritoneal cavity (PEC: peritoneal exudate cells), are more resistant to apoptosis than those in the lymphoid organs, including the spleen. We questioned whether tissue-dependent apoptotic differences in LCMV-specific T cells were due to environment factors or intrinsic stability of the CD8 T cells. The PEC environment conferred an anti-apoptotic effect, as shown by mixing PEC with excess splenic leukocytes or vice versa. This anti-apoptotic effect correlated with Stat5 phosphorylation induced by IL-2 spontaneously secreted by CD4 T cells. Spontaneous IL-2 production by CD4 T cells occurred in vivo during the contraction and the long term memory stage after LCMV infection in PEC and Fat pads, but much less so in spleen and lymph nodes. Virus-specific CD8 T cells in the PEC were also intrinsically more stable, as most had a memory precursor effector cell (MPEC) phenotype and higher expression of CD27, both correlating with decreased apoptosis. However, regardless of their phenotype, PEC CD8 T cells remained less apoptotic than their spleen cell counterparts. We conclude that long after the resolution of viral infections, IL-2-producing CD4 T cells linger in peripheral sites and locally contribute to the stability of memory CD8 T cells, thereby enhancing resistance to re-infection.

Interferon-mediated inhibition of T cell proliferation contributes to virus-induced transient immune suppression (105.1)

Vaccine-induced memory is required for protective immunity to pathogens, but many viruses induce a transient state of immune suppression that may contribute to the reduction of vaccine efficacy. We demonstrate here that the production of type I interferon (IFN) during an acute virus infection contributes to this transient immune suppression. Exposure of T cells to IFN-inducers at the same time as antigen had stimulatory effects, whereas pre-exposure to IFN-inducers was inhibitory, indicating that the timing of type I IFN exposure was of essence. Suppression of transgenic T cell proliferation was validated in two models of virus infection, where CD8 T cell proliferation in response to cognate antigen was inhibited 3-9 days after virus infection. Pre-exposure of T cells to the type I IFN inducer and TLR agonist poly(I:C) also had inhibitory effects on CD8 T cell proliferation, as shown by competition between poly(I:C)-pre-treated and control-treated P14 CD8 T cells during a LCMV infection. Poly(I:C)-induced inhibition of CD8 T cell proliferation was transient. T cells lacking type I IFN receptors were resistant to the suppressive effects of poly(I:C), indicating a direct involvement of IFN. Detection of IFN receptor and phosphorylated STAT molecules was reduced in poly(I:C)-pre-treated naive CD8 T cells. Inhibition of CD8 T cell proliferation by exposure to type I IFN prior to antigen stimulation may thus contribute to virus-induced immune suppression.

Blimp-1 regulates CD8 T cell effector/memory development via regulation of cytokine receptor expression (110.20)

During infections, the pathogen-induced cytokine milieu has been shown to determine T cell fate decisions between effector cells and memory precursor cells. However, how changes in cytokine receptor expression contribute to this process is poorly understood. Blimp-1 is known to be an important transcriptional repressor involved in the differentiation of short-lived CD8+ effector T cells following LCMV infection. Using a genome-wide ChIP-sequencing technique, we found that Blimp-1 directly controls cytokine receptor expression during the contraction phase of CD8+ T cells. During the expansion phase at day 5 post-infection (p.i.), CD8+ T cells are highly responsive to several cytokines, whereas at day 7 or 9 p.i. their responses are significantly decreased. In contrast, Blimp-1-/- CD8+ T cells maintain their cytokine responsiveness, and have increased cytokine receptor expression and increased formation of memory CD8+ T cells. Furthermore, Blimp-1 recruits histone modifying enzymes, HDAC2 and G9a to the genomic loci of cytokine receptors IL-2Rα and CD27. This study defines the mechanism by which Blimp-1 association with histone modifying enzymes controls cytokine receptor expression during the expansion and contraction phases of CD8+ T cells following LCMV infection, and thereby contributes to the generation of CD8+ effector and memory T cells.

The role of immunoproteasomes in antigen presentation and thymic selection (100.7)

Proteasomes, multisubunit complexes that degrade cellular proteins, are instrumental in forming epitopes for MHC class I antigen presentation. An alternate set of catalytic proteasome beta subunits are induced by IFN-gamma and expressed constitutively in dendritic cells, T-cells and B-cells. Immunoproteasomes containing these inducible subunits have increased chymotryptic and tryptic activities and decreased caspase-like activity, and are hypothesized to produce more peptides suitable for binding to MHC class I. To date mutant mice lacking one or two of the immunoproteasome subunits have been generated and have revealed some changes in MHC class I antigen presentation. However, the overall role of the immunoproteasome is unclear because mice that completely lack all three subunits have not been produced up until now. We have generated mice that completely lack immunoproteasomes. These animals have reduced presentation of MHC class I-presented peptides, and the peptides that are presented appear to be substantially different than those on cells from wild type mice. Moreover, the phenotype of these animals is distinct from mice lacking any individual immunoproteasome subunit. The loss of immunoproteasomes also affects T cell development in the thymus. The phenotype of these animals will be discussed.

Viral persistence and fatal CD8 T cell-associated pathology are consequences of NK cell-mediated killing of activated CD4 T cells (105.6)

Natural killer (NK) cells directly control virus replication during some infections and are postulated to indirectly regulate antiviral immunity during other infections through modulation of antiviral T cell responses, but the consequences and mechanisms of this regulation remain largely unexplored. Using the relatively NK cell-resistant lymphocytic choriomeningitis virus (LCMV), we identified a crucial role for NK cells in repression of antiviral T cell responses to a degree that alters the balance between virus clearance and immune pathology. Depletion of NK cells prior to infection of mice with a LCMV clone 13 dose (2 x 105 PFU) normally associated with fatal T cell-mediated immunopathology completely prevented virus-associated morbidity and promoted rapid viral clearance. In contrast, mice depleted of NK cells succumbed to a higher viral dose (2 x 106 PFU) normally associated with non-lethal persistent infection and clonal exhaustion of T cells. During the first three days of infection, NK cells eliminated activated CD4 T cells in a perforin-dependent manner. This early NK cell-mediated decrease in CD4 T cells resulted in lower numbers and diminished cytokine-producing capacity of LCMV-specific CD8 T cells. Thus, NK cells can dramatically alter viral clearance and infection-associated immunopathology by reducing the ability of CD4 T cells to support antiviral CD8 T cell responses in the context of high viral loads and disseminated infection.

Bi-specific MHC heterodimers for the characterization of cross-reactive T cells (67.13)

T cell cross-reactivity describes the phenomenon whereby a single T cell can recognize two or more different peptide antigens presented in complex withMHCproteins. Cross-reactive T cells have previously been characterized at the population level by cytokine secretion and MHC tetramer staining assays, but single-cell analysis is difficult or impossible using these methods. In this study, we describe development of a novel peptide-MHC heterodimer specific for cross-reactive T cells. MHC-peptide monomers were independently conjugated to hydrazide or aldehyde-containing cross-linkers using thiol-maleimide coupling at cysteine residues introduced into recombinant MHC heavy chain proteins. Hydrazone formation provided bi-specific MHC heterodimers carrying two different peptides. Using this approach we prepared heterodimers of the murine class I MHC protein H-2Kb carrying peptides from lymphocytic choriomeningitis virus and vaccinia virus, and used these to identify crossreactive CD8[|#1#|] T cells recognizing both lymphocytic choriomeningitis virus and vaccinia virus antigens. A similar strategy could be used to develop reagents to analyze cross-reactive T cell responses in humans.

Memory T cell stability in the wake of heterologous viral infections (105.35)

CD8 T cell memory is generally stable but can be reduced by heterologous infections. CD44hi CD8 and CD4 T cells undergo attrition early during infection with type I IFN-inducing pathogens or after exposure to toll receptor agonists. This attrition coincides with the early reduction of bona fide virus-specific CD8 and CD4 memory T cells and can explain the long-term loss in memory T cells that occurs after heterologous infection. An increase in the percentage of apoptotic cells was detected by TUNEL assay in both CD44hi CD8 and CD44hi CD4 T cells at day 3 post-infection with lymphocytic choriomeningitis virus (LCMV), a strong type I IFN inducer. Infection with LCMV significantly reduced vaccinia (VV)-specific CD8 memory T cells, which were further reduced by heterologous infection with murine cytomegalovirus (MCMV). MCMV also reduced LCMV-specific CD8 and CD4 memory T cells, but LCMV memory was not further eroded by persistent MCMV infection over a 48-week period, even though MCMV-specific memory cells increased in number due to memory inflation. This argued that the early IFN-dependent attrition had a greater effect on memory loss than did competition later on by inflating memory cells. A caveat, however, is that MCMV memory inflation was somewhat impaired by a prior LCMV infection, possibly due to reduced latent MCMV load caused by heterologous immunity. These results illustrate the dynamic nature of T cell memory in the wake of acute and persistent viral infections.

Licensing of naïve T cells for rapid TNF production (138.14)

TNF is a potent inflammatory cytokine with numerous immunological functions, including the ability to limit the magnitude of virus-specific T cell responses during infection. Naïve T cells in secondary lymphoid organs (SLOs) exhibit a unique ability to produce TNF rapidly after activation and prior to acquiring other effector functions. Peripheral T cells are a heterogeneous population of cells at various stages of post-thymic development. To determine how maturation influences the licensing of T cells to produce TNF, we compared cytokine profiles of single positive thymic T cells, recent thymic emigrants (RTEs) and matured-naïve T cells during TCR activation. Thymic T cells exhibited a poor ability to produce TNF when compared to splenic T cells, despite possessing a similar potential for activation. Moreover, thymic T cells had significantly reduced levels of TNF message and phosphorylated MAPK (Erk1/2) when compared to their splenic counterparts. Stimulation of thymic T cells in the presence of splenic B cells and APCs partially licensed the T cells to produce TNF but not to the same extent as peripheral T cells. RTEs had a significantly enhanced ability to produce TNF as compared to thymic T cells, but fully matured naïve T cells were the most efficient TNF producers. Together, these findings suggest that TNF expression by naïve T cells is regulated via a gradual licensing process that requires functional maturation in peripheral lymphoid organs.

Modulation of the RIG-I/MDA5-MAVS-dependent signaling pathway by distinct LCMV components shapes type I interferon responses (136.12)

Early and efficient induction of type I IFN and other interferon-stimulated genes following virus infection is essential for the control of the viral infection, and this induction is mostly controlled by the innate immune system via pattern-recognition receptors (PRRs), including the endosomal Toll-like receptors and the retinoic acid inducible gene-I like RNA helicases RIG-I and MDA5. The prototypic arenavirus, Lymphocytic choriomeningitis virus (LCMV), is an excellent system to study the impact of virus-host interactions on viral pathogenesis. Although most aspects of LCMV model have been extensively studied and the findings obtained from this model have been used to interpret the pathogenesis of human viral diseases, the molecular mechanisms by which LCMV modulates type I IFN responses are not clear. Better understanding of these mechanisms is critical for the development of novel vaccines and effective antiviral therapeutic strategies against arenavirus infection. In the present study, we demonstrate that LCMV genomic RNA activates the RIG-I/MDA5-MAVS-dependent signaling pathway to induce type I IFN responses. We further demonstrate that LCMV nucleoprotein inhibits LCMV RNA induced type I IFN responses by physically interacting with both RIG-I and MDA5 signaling molecules. These results indicate that interactions between LCMV viral proteins and viral genomic RNA and the host signaling molecules are critical to regulate the virus induced innate immune response.

Outcomes after stereotactic lung radiotherapy or wedge resection for stage I non-small cell lung cancer (NSCLC)

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Background: To compare clinical outcomes between lung stereotactic radiotherapy (SBRT) and wedge resection for stage I NSCLC. Methods: 112 cases of T1–2N0 NSCLC were treated with wedge resection (n=69) or image-guided lung SBRT (n=43) from 2/2003–8/2008. SBRT patients were treated on a phase II trial. All patients were ineligible for anatomic lobectomy; 93% undergoing SBRT were medically inoperable; 7% refused surgery. Mean FEV1 and DLCO were 1.58L and 13.9ml/min/mmHg for wedge cases vs 1.29L and 10.1ml for SBRT (p<0.01, p<0.01). Mean Charlson Co-morbidity Index and median age were 3 and 74y for wedge vs 4 and 77y for SBRT (p<0.01, p=0.04). Patients were staged using CT, 18FDG PET-CT, pulmonary function testing, and chemistries. SBRT patients had bone scan and brain MRI. Mediastinoscopies were performed for 28% of wedge cases vs.16% for SBRT (p=NS). SBRT was prescribed as 48 (T1) or 60 (T2) Gy in 4–5 fractions to the edge of the target volume. Adjuvant chemotherapy was given to 22% of SBRT vs12% of wedge patients (p=NS). Results: Median potential follow-up=2.3y. No significant differences were identified in local (LR), regional (RR), or locoregional recurrence (LRR), distant metastasis (DM), freedom from any failure (FFF), overall survival, or cause-specific survival between the two groups (Table); however, trends toward reduced LR and improved FFF were found with SBRT. Results excluding cases of synchronous primary tumors or pathologicalT4 (satellite lesion at wedge) are also shown, with FFF significantly better for SBRT. Multivariate analysis showed tumor grade to predict LR; LR to predict DM; LR and angiolymphatic invasion to predict RR and RR, (+)margin, FEV1, and pathologic diameter OS (p=0.06, p=0.08, p=0.01, p=0.04) in wedge cases. Conclusions: Both lung SBRT and wedge resection are reasonable treatment options for Stage I NSCLC patients ineligible for anatomic lobectomy. SBRT showed trends toward reduced LR and failure. Additional follow-up will be needed to verify durability of these findings.

[Table: see text]

No significant financial relationships to disclose.