Immune senescence: relative contributions of age and cytomegalovirus infection

Cytomegalovirus generates long-lived antigen-specific NK cells with diminished bystander activation to heterologous infection

Gundula Min-Oo and Lewis Lanier show that memory NK cells generated during MCMV infection respond poorly to cytokines generated during heterologous viral or bacterial infection, as compared with naïve NK cells.

Natural killer (NK) cells play a key role in the host response to cytomegalovirus (CMV) and can mediate an enhanced response to secondary challenge with CMV. We assessed the ability of mouse CMV (MCMV)–induced memory Ly49H⁺ NK cells to respond to challenges with influenza, an acute viral infection localized to the lung, and Listeria monocytogenes, a systemic bacterial infection. MCMV-memory NK cells did not display enhanced activation or proliferation after infection with influenza or Listeria, as compared with naive Ly49H⁺ or Ly49H⁻ NK cells. Memory NK cells also showed impaired activation compared with naive cells when challenged with a mutant MCMV lacking m157, highlighting their antigen-specific response. Ex vivo, MCMV-memory NK cells displayed reduced phosphorylation of STAT4 and STAT1 in response to stimulation by IL-12 and type I interferon (IFN), respectively, and IFN-γ production was reduced in response to IL-12 + IL-18 compared with naive NK cells. However, costimulation of MCMV-memory NK cells with IL-12 and m157 antigen rescues their impaired response compared with cytokines alone. These findings reveal that MCMV-primed memory NK cells are diminished in their response to cytokine-driven bystander responses to heterologous infections as they become specialized and antigen-specific for the control of MCMV upon rechallenge.

Acute bacterial infection negatively impacts cancer specific survival of colorectal cancer patients

AIM: To assess the impact of bacterial infections on cancer-specific survival in patients with colorectal cancer.

METHODS: This was a retrospective cohort study of colorectal cancer patients treated at the A.C. Camargo Cancer Center between January 2006 and April 2010. The presence of bacterial infection during cancer treatment, or up to one year after, was confirmed by laboratory tests or by the physician. Infections of the urinary, respiratory or digestive tracts, bloodstream, skin or surgical site were defined by testing within a single laboratory. Criteria for exclusion from the study were: chronically immunosuppressed patients; transplant patients (due to chronic immunosuppression); human immunodeficiency virus carriers; chronic use of corticosteroids or other immunosuppressive drugs; patients with autoimmune disease or primary immunodeficiency; known viral or parasitic infections. Patients with infections that did not require hospitalization were not included in the study because of the difficulty of collecting and tracking data related to infectious processes. In addition, patients hospitalized for pulmonary thromboembolism, stroke, acute myocardial infarction, uncontrolled diabetes, malignant hypercalcemia or other serious non-infectious complications not directly related to infection were also excluded. Survival curves were plotted using the Kaplan-Meier method, and log-rank tests (univariate analysis) and a Cox test assuming a proportional hazards model (multivariate analysis) were performed to examine associations between clinical history and characteristics of infection with cancer-specific survival.

RESULTS: One-hundred and six patients with colorectal cancer were divided into two groups based on the presence or absence of bacterial infection. Patient ages ranged from 23 to 91 years, with a median of 55 years. The majority of patients were male (57/106, 53.77%) with stage III colorectal cancer (45/106, 44.11%). A total of 86 bacteriologic events were recorded. Results indicate that the presence and number of infections during or after the end of treatment were associated with poorer-cancer specific survivals (P = 0.02). Elevated neutrophil counts were also associated with poorer cancer-specific survival (P = 0.02). Analysis of patient age revealed that patients > 65 years of age had a poorer cancer-specific survival (P = 0.04). A multivariate analysis demonstrated that infection was an independent predictor of poor survival (HR = 2.62, 95%CI: 1.26-5.45; P = 0.01) along with advanced clinical staging (HR = 2.63, 95%CI: 1.08-6.39; P = 0.03).

CONCLUSION: Infection and high neutrophil counts are associated with a poorer cancer-specific survival in colorectal cancer patients.

TTV DNA plasma load and its association with age, gender, and HCMV IgG serostatus in healthy adults

Understanding immunosenescence and changes in antimicrobial immune response with age is of high importance. The association of immunosenescence with gender and persistent infection with human cytomegalovirus (HCMV) is a matter of intensive research. We determined whether replication of another persistent and highly prevalent virus, Torque teno virus (TTV), is related to age, gender, and HCMV IgG serostatus of the host. TTV DNA load in plasma was assessed by real-time PCR in 313 healthy persons: 20-30 years old (young, n = 104), 50-60 years old (middle-aged, n = 101), or >80 years old (elderly, n = 108). TTV DNA loads were further associated with age-groups, gender, and HCMV IgG serostatus. TTV load was significantly higher in the elderly compared to the young group (p < 0.001; Tukey's honest significant difference (HSD)), and the higher TTV DNA levels over age were found to be gender-specific (p = 0.002; ANOVA), with young women showing the lowest TTV load compared to young men (p = 0.009, t test) and compared to the other female age-groups (middle-aged p = 0.005; elderly p < 0.001; Tukey's HSD). TTV load of HCMV IgG-seropositive persons was significantly higher than that of the HCMV IgG seronegative in the young (p = 0.005; t test) and middle-aged (p = 0.016; t test) groups. These results indicate that the host's immune control of TTV replication decreases with age and is gender-specific. Persistent HCMV infection is significantly related to higher TTV DNA loads, especially at a younger age. Therefore, the influence of gender and HCMV on immunosenescence earlier in life should be further explored.

IFNγ⁻TNFα⁻IL2⁻MIP1α⁻CD107a⁺PRF1⁺ CD8 pp65-Specific T-Cell Response Is Independently Associated With Time to Death in Elderly Humans

Persistent cytomegalovirus (CMV) infection has been suggested to be a major driving force in the immune deterioration and an underlying source of age-related diseases in the elderly. CMV antibody titers are associated with lower responses to vaccination, cardiovascular diseases, frailty, and mortality. CMV infection is also associated with shorter T-cell telomeres and replicative senescence. Although an age-related deregulation of CMV-specific T-cell responses could be an underlying cause of the relationship between CMV and immune defects, strong and polyfunctional responses are observed in elderly individuals, casting uncertainty on their direct role in age-related immune frailty. In this study, we longitudinally followed a cohort of healthy donors aged over 50 years, assessing their mortality rates and time to death during a 2-year period. Specific T-cell responses to the immunodominant antigen pp65 (IFNγ, TNFα, IL2, MIP1α, CD107a, and perforin production) were analyzed at the beginning of the 2-year observation period. A cytotoxic CD8 pp65-specific T-cell response, without cytokine or chemokine coexpression, was independently associated with all-cause mortality in these elderly individuals. This pp65-specific CD8 T-cell response could be a useful tool to identify individuals with depressed immune function and a higher risk of death.

Aging of the T cell compartment in mice and humans: from no naive expectations to foggy memories

Until the mid-20th century, infectious diseases were the major cause of morbidity and mortality in humans. Massive vaccination campaigns, antibiotics, antivirals, and advanced public health measures drastically reduced sickness and death from infections in children and younger adults. However, older adults (>65 y of age) remain vulnerable to infections, and infectious diseases remain among the top 5-10 causes of death in this population. The aging of the immune system, often referred to as immune senescence, is the key phenomenon underlying this vulnerability. This review centers on age-related changes in T cells, which are dramatically and reproducibly altered with aging. I discuss changes in T cell production, maintenance, function, and response to latent persistent infection, particularly against CMV, which exerts a profound influence on the aging T cell pool, concluding with a brief list of measures to improve immune function in older adults.

Latent infection with cytomegalovirus is associated with poor memory CD4 responses to influenza A core proteins in the elderly

Influenza remains a major pathogen in older people. Infection with CMV and the accumulation of late-differentiated T cells associated with it have been implicated in poor Ab responsiveness to influenza vaccination in the elderly, most of whom are CMV positive. However, whether CMV infection also affects memory T cell responses to influenza remains unknown. To investigate this, we assessed T cell responses to influenza A matrix protein and nucleoprotein ex vivo in 166 Dutch individuals (mean age 62.2 y, range 42-82) and validated the results in a second cohort from North America (mean age 73.1 y, range 65-81, n = 28). We found that less than half of the CMV-infected older subjects mounted a CD4 T cell response to influenza Ags, whereas ∼80% of uninfected elderly did so. A similar proportion of younger subjects possessed influenza A virus-responsive CD4 T cells, and, interestingly, this was the case whether they were CMV-infected. Thus, the effect of CMV was only seen in the older donors, who may have been exposed to the virus for decades. The percentage of donors with CD8 responses to influenza A virus was lower than those with CD4; this was not influenced by whether the subjects were CMV seropositive or seronegative. CMV-seropositive responders had significantly higher frequencies of late-differentiated CD4 T-cells (CD45RA(+/-)CCR7(-)CD27(-)CD28(-)) compared with CMV-infected nonresponders. These data add to the accumulating evidence that infection with CMV has profound but heterogeneous effects on responses to the products of other viruses and have implications for the design of influenza vaccines, especially in the elderly.

Gammaherpesvirus latency differentially impacts the generation of primary versus secondary memory CD8+ T cells during subsequent infection

Unlike laboratory animals, humans are infected with multiple pathogens, including the highly prevalent herpesviruses. The purpose of these studies was to determine the effect of gammaherpesvirus latency on T cell number and differentiation during subsequent heterologous viral infections. Mice were first infected with murine gammaherpesvirus 68 (MHV68), a model of Epstein-Barr virus (EBV) infection, and then after latency was established, they were challenged with the Armstrong strain of lymphocytic choriomeningitis virus (LCMV). The initial replication of LCMV was lower in latently infected mice, and the maturation of dendritic cells was abated. Although the number of LCMV-specific effector CD8(+) T cells was not altered, they were skewed to a memory phenotype. In contrast, LCMV-specific effector CD4(+) T cells were increased in latently infected mice compared to those in mice infected solely with LCMV. When the memory phase was reached, latently infected mice had an LCMV-specific memory T cell pool that was increased relative to that found in singly infected mice. Importantly, LCMV-specific memory CD8(+) T cells had decreased CD27 and increased killer cell lectin-like receptor G1 (KLRG1) expression. Upon secondary challenge, LCMV-specific secondary effector CD8(+) T cells expanded and cleared the infection. However, the LCMV-specific secondary memory CD8(+) T cell pool was decreased in latently infected animals, abrogating the boosting effect normally observed following rechallenge. Taken together, these results demonstrate that ongoing gammaherpesvirus latency affects the number and phenotype of primary versus secondary memory CD8(+) T cells during acute infection.

IMPORTANCE

CD8(+) T cells are critical for the clearance of intracellular pathogens, including viruses, certain bacteria, and tumors. However, current models for memory CD8(+) T cell differentiation are derived from pathogen-free laboratory mice challenged with a single pathogen or vaccine vector. Unlike laboratory animals, all humans are infected with multiple acute and chronic pathogens, including the highly prevalent herpesviruses Epstein-Barr virus (EBV), cytomegalovirus (CMV), herpes simplex viruses (HSV), and varicella-zoster virus (VZV). The purpose of these studies was to determine the effect of gammaherpesvirus latency on T cell number and differentiation during subsequent heterologous viral infections. We observed that ongoing gammaherpesvirus latency affects the number and phenotype of primary versus secondary memory CD8(+) T cells during acute infection. These results suggest that unlike pathogen-free laboratory mice, infection or immunization of latently infected humans may result in the generation of T cells with limited potential for long-term protection.

New advances in CMV and immunosenescence

Immunosenescence, defined as the age-associated dysregulation and dysfunction of the immune system, is characterized by impaired protective immunity and decreased efficacy of vaccines. An increasing number of immunological, clinical and epidemiological studies suggest that persistent Cytomegalovirus (CMV) infection is associated with accelerated aging of the immune system and with several age-related diseases. However, current evidence on whether and how human CMV (HCMV) infection is implicated in immunosenescence and in age-related diseases remains incomplete and many aspects of CMV involvement in immune aging remain controversial. The attendees of the 4th International Workshop on "CMV & Immunosenescence", held in Parma, Italy, 25-27th March, 2013, presented and discussed data related to these open questions, which are reported in this commentary.

Independent skewing of the T cell and NK cell compartments associated with cytomegalovirus infection suggests division of labor between innate and adaptive immunity

Cytomegalovirus (CMV) infection induces profound changes in different subsets of the cellular immune system. We have previously identified an immune risk profile (IRP) where CMV-associated changes in the T cell compartment, defined as a CD4/CD8 ratio < 1, are associated with increased mortality in elderly people. Since natural killer (NK) cells have an important role in the defense against viral infections, we examined whether the expansion of CD8 + T cells seen in individuals with CD4/CD8 ratio < 1 is coupled to a parallel skewing of the NK cell compartment. A number of 151 subjects were examined with CMV serology and a flow cytometry panel for assessment of T cell and NK cell subsets. CMV-seropositive individuals had higher frequencies of CD57 + and NKG2C + NK cells and lower frequencies of NKG2A + NK cells, in line with a more differentiated NK cell compartment. Intriguingly, however, there was no correlation between CD4/CD8 ratio and NK cell repertoires among CMV-seropositive donors, despite the profound skewing of the T cell compartment in the group with CD4/CD8 ratio < 1. Conversely, donors with profound expansion of NK cells, defined as NKG2C + NK cells with high expression of CD57 and ILT-2, did not display more common changes in their T cell repertoire, suggesting that NK cell expansion is independent of the T cell-defined IRP. Altogether, these results indicate that the effect of CMV on CD8 T cells and NK cells is largely nonoverlapping and independent.

The influence of intrinsic and extrinsic factors on immune system aging

Sex and age-matched wild-type and TCR transgenic mice were infected with cytomegalovirus (CMV) at 6 months of age and followed for 12 additional months to examine aging of the immune system. It was found that viral infection of C57Bl/6 mice resulted in accelerated aging of the immune system as shown by a loss of CD8(+)28(+) cells and an accumulation of KLRG1(+) T cells. CMV infection of OT-1 transgenic mice had no influence on immune aging of these mice which nonetheless demonstrated an accumulation of CD8(+)28(-) and KLRG1(+) T cells with time. CD4(+) T cells were unaffected in either strain of mice. Thus, immunological aging was found to be due to both cell-intrinsic and cell-extrinsic factors. Persistent viral infections may accelerate immunological aging but consideration must be given to individual variation in the aging process.

CMV latent infection improves CD8+ T response to SEB due to expansion of polyfunctional CD57+ cells in young individuals

Cytomegalovirus (CMV) latent infection has a deleterious effect on the efficacy of influenza vaccination in the elderly, suggesting that CMV restricts immunological diversity impairing the immune system functionality in old age. Polyfunctional T cells produce multiple cytokines and higher amounts than mono-functional T cells. High number of polyfunctional T cells correlates with better prognosis during infection. Thus, the efficiency of T cell response associates with quality (polyfunctionality) rather than with quantity (percentage of T cells). We analyze the effect of CMV infection on CD8+ T cells polyfunctionality ―degranulation (CD107a), IFN-gamma and TNF-alpha production―, from young CMV-seropositive and CMV-seronegative individuals and in middle age CMV-seropositive donors, in response to Staphylococcal Enterotoxin B (SEB). Our results show a higher percentage of polyfunctional CD8+ T cells in young CMV-seropositive individuals compared to CMV-seronegative. Also, we find an expansion of CD8+CD57+ T cells in CMV-seropositive individuals, which are more polyfunctional than CD8+CD57− cells. In middle age individuals there is a higher frequency of SEB-responding CD8+ T cells, mainly TNF-alpha or TNF-alpha/IFN-gamma producers, whereas the percentage of polyfunctional cells (IFN-gamma/TNF-alpha/CD107a) is similar to the percentages found in young CMV-seropositive. Therefore, whereas it has been shown that CMV latent infection can be detrimental for immune response in old individuals, our results indicate that CMV-seropositivity is associated to higher levels of polyfunctional CD8+ T cells in young and middle age donors. This increase in polyfunctionality, which can provide an immunological advantage in the response to other pathogens, is due to a CD8+CD57+ T cell expansion in CMV-seropositive individuals and it is independent of age. Conversely, age could contribute to the inflammation found in old individuals by increasing the percentage of cells producing pro-inflammatory cytokines. These findings highlight the necessity of further studies on the benefits/detrimental effects of CMV infection in the response to vaccination and other infections.

Aging and cytomegalovirus infection differentially and jointly affect distinct circulating T cell subsets in humans

The impact of intrinsic aging upon human peripheral blood T cell subsets remains incompletely quantified and understood. This impact must be distinguished from the influence of latent persistent microorganisms, particularly CMV, which has been associated with age-related changes in the T cell pool. In a cross-sectional cohort of 152 CMV-negative individuals, aged 21-101 y, we found that aging correlated strictly to an absolute loss of naive CD8, but not CD4, T cells but, contrary to many reports, did not lead to an increase in memory T cell numbers. The loss of naive CD8 T cells was not altered by CMV in 239 subjects (range 21-96 y), but the decline in CD4(+) naive cells showed significance in CMV(+) individuals. These individuals also exhibited an absolute increase in the effector/effector memory CD4(+) and CD8(+) cells with age. That increase was seen mainly, if not exclusively, in older subjects with elevated anti-CMV Ab titers, suggesting that efficacy of viral control over time may determine the magnitude of CMV impact upon T cell memory, and perhaps upon immune defense. These findings provide important new insights into the age-related changes in the peripheral blood pool of older adults, demonstrating that aging and CMV exert both distinct and joint influence upon blood T cell homeostasis in humans.

Mouse CMV infection delays antibody class switch upon an unrelated virus challenge

Poor immune protection upon vaccination is a critical determinant of immunosenescence. Latent Cytomegalovirus (CMV) infection has been associated with poor antibody responses to vaccination, but a causative role for CMV in the poor immune response requires experimental evidence and thus could not be confirmed in clinical studies. To test the hypothesis that latent CMV infection causes poor antibody responses, we infected young or adult mice with mouse CMV and challenged them with Vesicular stomatitis virus (VSV) at 15 or 18months of age. Latent, but not primary infection with mouse CMV resulted in diminished neutralizing titers of the serum IgG fraction at day 7 post challenge, which recovered by day 14 post challenge. This phenomenon was specific for mice infected with mouse CMV, but not mice infected with other herpesviruses, like murine herpesvirus-68 or herpes simplex virus type 1, or mice infected with non-persistent viruses, such as influenza or Vaccinia virus. Hence, our data indicate a delay in IgG class-switch that was specific for the CMV infection. Herpesviral infections did not change the B-cell memory compartment, and increased the size of the effector-memory subset of blood CD4 T-cells only when administered in combination. Furthermore, CD4 T-cell response to VSV infection was maintained in latently infected mice. Therefore, our results argue that latent CMV infection impairs B-cell, but not T-cell responses to a challenge with VSV and delays antibody class-switch by a mechanism which may be independent of T-cell help.

Human T cell aging and the impact of persistent viral infections

Aging is associated with a dysregulation of the immune response, loosely termed “immunosenescence.” Each part of the immune system is influenced to some extent by the aging process. However, adaptive immunity seems more extensively affected and among all participating cells it is the T cells that are most altered. There is a large body of experimental work devoted to the investigation of age-associated differences in T cell phenotypes and functions in young and old individuals, but few longitudinal studies in humans actually delineating changes at the level of the individual. In most studies, the number and proportion of late-differentiated T cells, especially CD8+ T cells, is reported to be higher in the elderly than in the young. Limited longitudinal studies suggest that accumulation of these cells is a dynamic process and does indeed represent an age-associated change. Accumulations of such late-stage cells may contribute to the enhanced systemic pro-inflammatory milieu commonly seen in older people. We do not know exactly what causes these observed changes, but an understanding of the possible causes is now beginning to emerge. A favored hypothesis is that these events are at least partly due to the effects of the maintenance of essential immune surveillance against persistent viral infections, notably Cytomegalovirus (CMV), which may exhaust the immune system over time. It is still a matter of debate as to whether these changes are compensatory and beneficial or pathological and detrimental to the proper functioning of the immune system and whether they impact longevity. Here, we will review present knowledge of T cell changes with aging and their relation to chronic viral and possibly other persistent infections.

Circulating antibody and memory B-Cell responses to C. difficile toxins A and B in patients with C. difficile-associated diarrhoea, inflammatory bowel disease and cystic fibrosis

C. difficile infection (CDI) is rarely reported in cystic fibrosis (CF) patients despite frequent hospitalisations and antibiotic usage. Conversely, the prevalence of CDI in inflammatory bowel disease (IBD) has received increased attention. We investigated components of the IgG-specific humoral immune response to C. difficile toxins A and B in patients with C. difficile-associated diarrhoea (CDAD), IBD patients with CDI, CF patients and healthy controls. Serum anti-toxin IgG was determined by ELISA. Circulating antigen-activated B-cells were investigated using Alexa Fluor 488-labelled toxin A and assessed by flow cytometry. Following induction of differentiation of memory B-cells, toxin A- and B-specific antibody secreting cells (ASCs) were quantified using ELISpot. We present the first data showing levels of serum anti-toxin A and B antibodies were significantly higher in patients with CF (without a history of CDI) than in CDAD patients and were stably maintained over time. Notably, the CDAD patients were significantly older than the CF patients. We also show that circulating toxin A-specific memory B-cells (IgD-negative) can be detected in CDAD patients [0.92 (0.09–1.78)%], and were prominent (5.64%, 1.14%) in two CF patients who were asymptomatic carriers of C. difficile. There was correlation between toxin A- and B-specific ASCs, with significantly higher proportions of the latter seen. In some with CDAD, high serum antibody levels were seen to only one of the two toxins. Mucosal secretion of toxin-specific IgG was detected in an additional group of IBD patients with no history of CDI. We conclude that enhanced and stable humoral immune responses to toxins A and B may protect CF and some IBD patients against CDI. The impaired ability to generate strong and/or sustained toxin-specific antibody and memory B-cell responses may increase susceptibility of older patients to CDI and highlight the need to investigate the role of immune senescence in future studies.

An attenuated temperature-sensitive strain of cytomegalovirus (tsm5) establishes immunity without development of CD8(+) T cell memory inflation

Cytomegalovirus (CMV) is a widely prevalent herpesvirus that is well tolerated by an immune competent host yet establishes a state of chronic infection. The virus is thought to undergo frequent subclinical episodes of reactivation which leads to an unusually large accumulation of CMV-specific CD8(+) T lymphocytes in the peripheral blood, a phenomenon termed "memory inflation." The high magnitude of the CMV T cell response has been implicated in impaired immunity to heterologous pathogens such as EBV, influenza and West Nile virus. Here, using murine CMV (MCMV), we show that memory inflation of virus-specific CD8(+) T cells is avoided if mice are infected with a replication defective virus called temperature-sensitive mutant 5 (tsm5), which carries an attenuating mutation within the DNA primase gene. Mice infected with tsm5 do generate primary T cell responses towards viral proteins but these do not amass to skew the memory repertoire of CD8(+) T cells. Therefore, attenuation of the virus replication machinery may be valuable in future CMV vaccine designs because the virus remains immunogenic but does not contribute to CMV associated T cell immune senescence.

NK cells improve control of friend virus infection in mice persistently infected with murine cytomegalovirus

Background

Co-infection of HIV patients with cytomegalovirus (CMV) is associated with enhanced AIDS progression and CMV end-organ diseases. On the other hand, persistent CMV infection has recently been shown to decrease tumor relapse and protect against lethal bacterial infection. The influence of persistent CMV on the outcome of an acute retroviral superinfection is still unknown.

Results

Here we show that a persistent murine CMV (mCMV) infection surprisingly confers higher resistance to a primary Friend retrovirus infection (FV) of mice. Decreased FV titers and augmented FV-specific CD8 T-cell responses were found in mCMV infected mice during primary FV superinfection. NK cells produced higher amounts of IFNgamma after FV infection of persistently mCMV infected mice suggesting that these cells were involved in the ‘protective’ effect. Depletion of NK1.1⁺ cells or neutralization of IFNgamma during FV superinfection abrogated the mCMV-mediated effect.

Conclusion

Our data demonstrate for the first time that a persistent CMV infection induces long-lasting NK cell responses that can enhance immunity to primary retroviral infections. To our knowledge, studies investigating primary HIV infection have not analyzed the role of the CMV seropositivity in these patients. Our observations suggest that NK cells in CMV seropositive individuals might contribute to the control of primary HIV infection.

Understanding immunosenescence to improve responses to vaccines

In the older adult, the benefits of vaccination to prevent infectious disease are limited, mainly because of the adaptive immune system's inability to generate protective immunity. The age-dependent decrease in immunological competence, often referred to as 'immunosenescence', results from the progressive deterioration of innate and adaptive immune responses. Most insights into mechanisms of immunological aging have been derived from studies of mouse models. In this Review, we explore how well such models are applicable to understanding the aging process throughout the 80-100 years of human life and discuss recent advances in identifying and characterizing the mechanisms that underlie age-associated defective adaptive immunity in humans.

Cytomegalovirus disease in nonimmunocompromised, human immunodeficiency virus-negative adults with chronic kidney disease

BACKGROUND/PURPOSE(S)

To identify the clinical characteristics of cytomegalovirus (CMV) disease in chronic kidney disease (CKD) patients.

METHODS

Patients from two sources were reviewed: (1) a retrospective study of hospitalized patients admitted between January 1990 and February 2009 was performed at a tertiary hospital in Taiwan; (2) the English literature from 1990 to 2009 was reviewed for additional cases, and adults with CKD and histopathologically documented cytomegalovirus disease were included.

RESULTS

Seven CKD patients from our hospital and seven from the literature were included. Nine (64.3%) patients were males, and the mean age was 66 years. Histopathologically proven CMV disease was present in the gastrointestinal (GI) tract of 13 (92.9%) and in the skin of one (7.1%) patient. GI symptoms included bleeding (78.6%), abdominal pain (35.7%), and diarrhea (28.6%).The most common comorbidities were diabetes mellitus (7, 50%) and hypertension (8, 57.1%). Thirteen patients had CMV GI disease. The endoscopic gross features of the GI tract lesions included single or multiple ulcers and a large polypoid or uneven surface mass. Of the seven cases with available data, a low body mass index (22.3 ± 1.3 kg/m(2)) and hypoalbuminemia (25 ± 7.0 g/L) were noted. Twelve patients had received ganciclovir or valganciclovir therapy. Five (35.7%) patients died, and the death of two patients was directly related to bowel perforation caused by CMV colitis.

CONCLUSION

CMV disease may occur in CKD patients without the presence of overt immunodeficiency. The gastrointestinal tract is the most common site of involvement. Clinicians should be aware of this possibility in CKD patients who have GI symptoms.

Lifelong persistent viral infection alters the naive T cell pool, impairing CD8 T cell immunity in late life

Persistent CMV infection has been associated with immune senescence. To address the causal impact of lifelong persistent viral infection on immune homeostasis and defense, we infected young mice systemically with HSV-1, murine CMV, or both viruses and studied their T cell homeostasis and function. Herpesvirus(+) mice exhibited increased all-cause mortality compared with controls. Upon Listeria-OVA infection, 23-mo-old animals that had experienced lifelong herpesvirus infections showed impaired bacterial control and CD8 T cell function, along with distinct alterations in the T cell repertoire both before and after Listeria challenge, compared with age-matched, herpesvirus-free controls. Herpesvirus infection was associated with reduced naive CD8 T cell precursors above the loss attributable to aging. Moreover, the OVA-specific CD8 T cell repertoire recruited after Listeria challenge was entirely nonoverlapping between control and herpesvirus(+) mice. To our knowledge, this study for the first time causally links lifelong herpesvirus infection to all-cause mortality in mice and to disturbances in the T cell repertoire, which themselves correspond to impaired immunity to a new infection in aging.

Self-boosting vaccines and their implications for herd immunity

Advances in vaccine technology over the past two centuries have facilitated far-reaching impact in the control of many infections, and today's emerging vaccines could likewise open new opportunities in the control of several diseases. Here we consider the potential, population-level effects of a particular class of emerging vaccines that use specific viral vectors to establish long-term, intermittent antigen presentation within a vaccinated host: in essence, "self-boosting" vaccines. In particular, we use mathematical models to explore the potential role of such vaccines in situations where current immunization raises only relatively short-lived protection. Vaccination programs in such cases are generally limited in their ability to raise lasting herd immunity. Moreover, in certain cases mass vaccination can have the counterproductive effect of allowing an increase in severe disease, through reducing opportunities for immunity to be boosted through natural exposure to infection. Such dynamics have been proposed, for example, in relation to pertussis and varicella-zoster virus. In this context we show how self-boosting vaccines could open qualitatively new opportunities, for example by broadening the effective duration of herd immunity that can be achieved with currently used immunogens. At intermediate rates of self-boosting, these vaccines also alleviate the potential counterproductive effects of mass vaccination, through compensating for losses in natural boosting. Importantly, however, we also show how sufficiently high boosting rates may introduce a new regime of unintended consequences, wherein the unvaccinated bear an increased disease burden. Finally, we discuss important caveats and data needs arising from this work.

Antiviral therapy can reverse the development of immune senescence in elderly mice with latent cytomegalovirus infection

Cytomegalovirus (CMV) infection leads to the development of adaptive and humoral immune responses that are among the largest for any pathogen, and intriguingly, the magnitude of the immune response increases with age, a phenomenon termed "memory inflation." Elevated CMV-specific immunity has been correlated with an increased mortality rate in elderly individuals and with impaired vaccination responses. The latent phase of CMV infection is characterized by intermittent episodes of subclinical viral reactivation and the production of immunogenic transcripts that may maintain memory inflation of virus-specific cytotoxic lymphocytes. However, the relative importance of CMV reactivation in the development of memory inflation is uncertain, as is the potential for antiviral treatment to reverse this effect. Here, we administered valaciclovir for up to 12 months in mice with established murine CMV (MCMV) infection. Treatment reduced the magnitude of the MCMV-specific CD8(+) T-lymphocyte response by 80%, and the residual MCMV tetramer-specific lymphocytes exhibited a less differentiated phenotype. In addition, latent MCMV infection suppressed the proportion of naïve CD8(+) T cells by 60% compared to antiviral-treated mice or MCMV-negative animals. Furthermore, treatment led to a reduction in influenza A viral loads following a challenge in elderly MCMV-infected animals and also reduced the differentiation of influenza virus-specific cytotoxic lymphocytes. These observations demonstrate that MCMV-specific memory inflation is maintained by viral replication and that therapeutic intervention could lead to improved immune function.