Blood Disorders in the Elderly - part 3 pdf

88 Rita B. Effros of dying from infectious causes compared to those individuals with the longest telomeres [57]. It should be emphasized that such correlative studies do not in any way suggest that it is telomere shortening per se that is the cause of mortality. Rather, it is more likely that the reduced telomere length is a biomarker of other physiological changes [58]. For example, in the case of shorter telomeres being associated with increased death from infec- tious causes, one possible mechanism that might be operating is that the T cells were working over- time (and eventually failing) to control a particular infection, and in the process undergoing extensive cell division and concomitant telomere shortening. Studies on HIV-infected persons are consistent with this notion, since over many years the chronic acti- vation and proliferation of CD8 T cells does eventu- ally lead to high proportions of CD8 T cells that lack CD28 expression and have shortened telomeres. An alternative possibility to explain the short-telomere/ infection association relates to the observation that telomere length is a heritable trait [59–61], and may be linked to other genetic factors that are the true cause of the increased death risk from infections. Given that infections are a major cause of mor- bidity and mortality in the elderly, vaccination is an important prophylactic strategy. Infl uenza, in particular, has been shown to be the fourth leading cause of death in elderly persons, so that this age group is a priority target population for infl uenza vaccination. Thus, it is highly relevant that two stud- ies have shown a signifi cant correlation between poor response to infl uenza vaccination and high proportions of senescent CD8 T cells. The under- lying mechanism for this association has not been identifi ed, but in other contexts, CD8 T cells that lack CD28 expression have been shown to have sup- pressor cell functions, leading to downregulation of antigen presentation as well as other T-cell activi- ties [62]. CD8ϩCD28– T cells also accumulate and mediate liver damage in hepatitis C infection [63]. Suppressor functions have also been attributed to CD8 T cells that are CD57-positive, a phenotype associated with loss of CD28 expression. These putatively senescent CD8 T cells exert suppressive infl uences on effector functions of HIV-specifi c CTL [64]. Another interesting correlation that has emerged from clinical studies is the association between high proportions of senescent CD8 T cells and oste- oporotic fractures in a group of elderly women [65]. Although this was a small-scale study, increasing evidence suggests that chronic immune activation is, in fact, associated with bone loss [66]. Moreover, the profi le of cytokines produced by senescent T cells (e.g., increased IL-6 and reduced IFN-γ) would be predicted to favor maturation and activation of osteoclasts, the bone-resorbing cells. Further research in the relatively new fi eld of osteoimmunol- ogy will undoubtedly uncover new and important mechanisms that link the immune system of the eld- erly with some of the well-documented age-related skeletal changes. Senescent T cells and cancer One of the fundamental questions spanning the fi elds of both cancer biology and immunology is whether immune surveillance plays a role in tumor initiation and progression. Although for cancers in general this issue has not been resolved, there is accumulating evidence suggesting that in certain virally related cancers, exhaustion of immune con- trol over the virus may play a role in tumor initiation [67]. Immune defi ciency is, in fact, closely correlated with several types of tumors that have viral etiologies. For example, in immunosuppressed individuals, vir- tually all lymphomas are EBV in origin, presumably resulting from the ultimate failure of T cells to effec- tively control EBV infection [68,69]. Another latent herpesvirus-associated tumor, Kaposi’s sarcoma, is increased in HIV-infected persons, and cervical cancer, which also increases during immune sup- pression, is associated with certain strains of human papillomavirus. Viruses that are able to establish latency develop a complex relationship with the host’s immune sys- tem. Evasion of immune recognition as well as spe- cifi c physiological effects on the T cells themselves Replicative senescence, aging, and cancer 89 are probably involved [70]. It is clear that the initial primary infection with these viruses does elicit an immune response. During the acute phase of infec- tious mononucleosis (EBV infection), for example, high levels of telomerase activity and activation markers can be detected on the antigen-specifi c CD8 T cells. Nevertheless, one year after infection, when presumably the virus has become latent, these same T cells show evidence of having experienced chronic antigenic stimulation, as indicated by telomere shortening of the tetramer-binding CD8 T cells [17]. These data suggest that, at least in the case of EBV, latency is associated with prolonged antigen-specifi c proliferation in vivo. Since EBV is involved not only in lymphomas, but also in invasive breast cancer and in some tumors of the prostate and of the liver [68], it is possible that immune exhaustion caused by replicative senescence of virus-specifi c CD8 T cells plays a role in the development of a broad spectrum of tumor types. Persons with virally associated tumors do, in fact, have increased proportions of CD8 T cells with char- acteristics reminiscent of T cells that reach replicative senescence in cell culture, suggesting an association between loss of control over the virus and transfor- mation of the latently infected cells [4]. Indeed, it has been shown that antigen-specifi c CD8 T cells in sev- eral chronic viral infections, such as HIV, CMV, and EBV, eventually lose their antiviral cytolytic function once the infection becomes chronic [71]. Interesting, in patients with certain EBV-associated nasopha- ryngeal tumors, such fundamental CD8-T-cell pro- tective functions as secretion of IFN-γ and perforin expression by CD8 T cells are also impaired [72]. Moreover, in many of these cancer patients, reduced EBV-specifi c CTL precursor frequency has also been documented and, importantly, the defi cit correlated with plasma viral burden [73]. Since the limiting dilution assay used to detect precursor frequency is critically dependent on proliferation, the above observation is consistent with a role for proliferative exhaustion. In addition, EBV-associated lymphomas are correlated with high tumor necrosis factor α lev- els, reminiscent of senescent T-cell cultures [74]. In sum, there is increasing evidence lending support to the hypothesis that chronic exposure to antigens of latent viruses (e.g., EBV, HPV) may facilitate tumor progression and metastasis by driving the relevant antigen-specifi c T cells to senescence. The potential to generate senescent antigen- reactive T cells may not be restricted to situations involving latent infections. Certain non-viral tumor- associated antigens may also be a source of chronic immune stimulation. For example, prostate-specifi c antigen (PSA), the blood levels of which increase in persons with prostate cancer, is also present in nor- mal prostate tissue, and is thus an antigen to which T cells have had prolonged exposure [75]. CD8 T cells from patients with prostate cancer do, in fact, show reactivity to PSA peptides immediately ex vivo [76], consistent with the notion that they were previously primed in vivo to this antigen. Similarly, melanoma- specifi c antigens, which cause chronic activation of T cells, have been suggested to play a role in the loss of CD28 expression in some melanoma patients [77]. Thus, like antigens of viruses that establish latency, tumor-associated antigens also have the potential to cause chronic T-cell activation, possibly driving some antigen-specifi c cells to senescence. As noted above, loss of CD28 expression is the signature change of CD8 T-cell senescence in cell culture. It is thus relevant to note that altered expres- sion of CD28, and by implication replicative senes- cence, has also been associated with the clinical outcome of certain non-viral cancers. In advanced renal carcinoma, for example, the proportion of CD8 T cells that are CD57ϩ (a marker present on a majority of CD28– T cells) has predictive value with respect to patient survival [78]. Further, in patients with head and neck tumors, it has been shown that tumor resection is associated with a reduction in the CD8ϩCD28– T-cell subset, which had undergone expansion during the period of tumor growth [37]. Thus, replicative senescence of CD8 T cells, already implicated in defective immunity to chronic viral infections [44], may also play a role in the failed immune surveillance that may facilitate the devel- opment or metastasis of certain types of cancer. In addition to possibly facilitating the develop- ment of some tumors, the process of CD8-T-cell 90 Rita B. Effros replicative senescence also has an impact on adop- tive immunotherapy for cancer, since sustained control over the tumor requires extensive T-cell pro- liferation and maintenance of functional integrity. The impediment of replicative senescence has, in fact, been documented in the case of EBV, where in- vitro expansion of EBV-specifi c CD8 T cells for the purpose of cancer immunotherapy is associated with loss of cytolytic function [79, 80]. This change is con- sistent with observations from cell culture studies on replicative senescence [81]. Thus, prevention or retardation of the process of replicative senescence will lead to improvement in immunotherapy directed at cancer, one of the major diseases of old age. Solutions to the problem of T-cell replicative senescence Given the spectrum of deleterious effects associated with senescent T cells, investigators are actively pursuing strategies to reverse, prevent or retard the process of replicative senescence. Based on the cen- tral role of telomere shortening in signaling the cell- cycle arrest, one of the major approaches has been manipulation of the enzyme telomerase, either by genetic or by pharmacologic methods. Gene trans- duction with the catalytic component of human telomerase (hTERT) has been extensively analyzed in human fi broblasts, epithelial cells, and keratino- cytes. These studies have documented that the transduced cells show unlimited proliferation, tel- omere length stabilization, normalization of func- tion, and, importantly, no evidence of altered growth or tumorogenesis in immunodefi cient (SCID) mice. In CD8 T cells, gene transduction with hTERT is able to reverse some, but not all, of the components of the replicative senescence program. CD8 T cells that are specifi c for tumors and for HIV have both been shown to acquire unlimited proliferative capac- ity following transduction with hTERT. Nevertheless, the ultimate loss of CD28 expression is not prevented by this strategy [81,82]. The importance of retaining CD28 expression has been documented in several studies of cancer immunotherapy and anti-tumor vaccines, in which incorporation of the CD28 ligand, B7, enhanced treatment effi cacy [34,83–85]. Genetic modulation of telomerase activity also fails to pre- vent the ultimate collapse of antigen-specifi c cyto- lytic function in virus-specifi c cultures [86]. Ongoing research is addressing whether combinations of hTERT and CD28 gene therapies will result in more comprehensive correction of the features of CD8- T-cell replicative senescence. Because of the complexity and impractical aspects of gene-therapy approaches, efforts are also directed at identifying pharmacologic agents that might accomplish the same goals. It has been known for some time that cells of the immune sys- tem contain estrogen receptors; the original radio- active estrogen binding studies suggested that CD8 T cells, in particular, bind estrogen with high affi nity [87]. Although little is known about the spectrum of T-cell genes that are modulated by estrogen, an estrogen-responsive element has been documented in the promoter region of IFN-γ [88], a cytokine that is often monitored in evaluating immune responses to viruses and cancer [89]. Interestingly, IFN-γ has also been recently shown to upregulate the enzyme telomerase in T cells [90]. Estrogen can also directly modulate telomerase activity; there is an estrogen-responsive element in the promoter of the hTERT gene in a variety of reproductive tissues [91]. Estrogen also affects cal- cium mobilization in T cells. Thus, evidence from a variety of systems suggests that estrogen has the potential to modulate several T-cell functions that are altered in senescent cells, and may therefore constitute a novel type of non-genetic strategy to modulate senescence. Clearly, application of these hormone-based approaches to cancer immuno- therapy or to modulation of antiviral immunity will require identifying designer estrogens that specifi - cally affect T cells, but not estrogen-sensitive tumor cells. Finally, research on non-hormonal modulators of T-cell telomerase activity may provide additional approaches to modulating replicative senescence, thereby expanding the effi cacy of cancer immuno- therapy and effective control over viral infections in the elderly [92]. Replicative senescence, aging, and cancer 91 ACKNOWLEDGEMENTS The research described in this chapter has been supported in part by the NIH and the UCLA Center on Aging. 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Telomerase activa- tors increase HIV-specifi c CD8ϩ T cell function: a novel approach to prevent or delay immune exhaustion and progression to AIDS. In Cold Spring Harbor Symposium on Telomeres and Telomerase 2005, 197. Introduction This chapter explores the association of aging and qualitative abnormalities of hematopoiesis. While incidence and prevalence of benign and malignant hematologic conditions increase with age, it is not clear whether quantitative or qualitative abnormali- ties of hematopoiesis underlie these changes. A defi - nition of the mechanisms by which older individuals are more vulnerable to hematologic diseases is nec- essary for their prevention and treatment. A common example of a hematologic abnormality in the elderly is unexplained anemia [1–8]. Contro- versy lingers over whether hematopoietic exhaustion, erythropoietic abnormalities due to genomic dam- age, increased vulnerability to environmental stress, or a combination of these factors may lead to ane- mia. Likewise, changes in lymphocytic phenotype, a decline in immune function (immunosenescence), and reduced chemotaxis and bactericidal capacity of neutrophils have been reported in older individuals [9–15]. Despite these changes, hematopoiesis appears adequate to maintain the homeostasis of the periph- eral blood elements both in healthy elderly persons and in aging experimental animals, in the absence of hematopoietic stress [11–19]. Aging may be considered a condition of enhanced vulnerability to stress due to loss in functional reserve of multiple organ systems and simultaneous decline in personal and social resources [20–23]. Both envi- ronmental and genomic changes may conspire to restrict the functional reserve of the aged. Of the envi- ronmental changes the best defi ned is a condition of 8 Qualitative changes of hematopoiesis France Laurencet progressive infl ammation, associated with increased concentration of pro-infl ammatory cytokines in the circulation, that may hamper immune response, alter the ratio of various subpopulations of B and T cells in the circulation, promote apoptosis of hematopoi- etic progenitors, and reduce their responsiveness to growth factors [9,24,25]. At the same time, genomic alteration of these progenitors may prevent their dif- ferentiation and also reduce their responsiveness to growth factors [23,26]. Environmental and genomic alterations appear to converge in the pathogenesis of myelodysplastic syndromes (MDS), a group of common hematologic malignancies after age 60, characterized by clonal hematopoiesis and dysmorphic changes in the bone marrow (Fig. 8.1) and peripheral blood (Fig. 8.2), due to increased proliferation, increased apoptosis, and reduced maturation (Fig. 8.3) [27]. In the following discussion we will explore the mechanisms of MDS as the best-established manifestation of qualita- tively defi cient hematopoiesis in the elderly. Incidence of qualitative hematopoietic abnormalities Most industrialized countries have experienced an increase in the elderly population due to more pro- longed life expectancy and reduced birth rates [28]. In 2000, more than 20% of the people were older than 60 years, and this percentage is projected to increase in the foreseeable future [29,30]. Accumulation of oxidative damage to various organs and tissues is 95 8 Qualitative changes of hematopoiesis France Laurencet Blood Disorders in the Elderly, ed. Lodovico Balducci, William Ershler, Giovanni de Gaetano. Published by Cambridge University Press. © Cambridge University Press 2008. Figure 8.1 Aspirate smear showing hyperplastic and dysplastic features. See color plate section. Figure 8.2 Blood smear from a patient with myelodysplastic syndrome, showing an abnormal monocyte. See color plate section. Figure 8.3 (a and b) Aspirate smear: myelodysplastic dyserythropoiesis and mitosis. See color plate section. (a) (b) 96 Qualitative changes of hematopoiesis 97 partly responsible for age-related molecular changes [31,32]. In the hematopoietic system this damage may be manifested in minor dysplastic changes frequently observed in the bone marrow (BM) of elderly patients, the signifi cance of which is still not understood. In particular it is not clear whether these changes signal the development of MDS or are benign and self-lim- iting [33–35]. The incidence of hematopoietic neo- plasia [36–40] increases with age, but the incidence of MDS is diffi cult to defi ne precisely, because of the heterogeneity of the disease. The more benign sub- types might be under-diagnosed and under-reported [39–41]. MDSs are rarely seen before the age of 50, and the median age is about 70 years [42,43]. The overall disease incidence is about 3–4 per 100 000, but this may rise to 20–30 per 100 000 in the over-70s and up to 89 per 100 000 in the over-80s [44,45]. In Germany the incidence of MDS appears to have increased in recent decades, though this fi nding is con- troversial [46–49]. In a French analysis of 100 patients in a geriatric hospital with a median age of 86 years, the prevalence of macrocytosis was 21% [50,51]. Some of these cases may certainly be ascribed to B 12 and folate defi ciency, or to drugs interfering with nuclear metab- olisms. It is not farfetched to assume that at least in part these cases of macrocytosis represent early MDS or another form of qualitative hematopoietic defect. In conclusion, the incidence and prevalence of MDS, one example of a qualitative defect of hemato poiesis, increases with age. This fi nding suggests that the gen- eral prevalence of qualitative defects of hematopoiesis also increases with age. What is not yet clear is whether all forms of qualitative defects, and particularly mac- rocytosis, may end up as MDS. Risk factors The association of age and hematopoietic neopla- sias may be accounted for by both constitutional and environmental factors [36,37,52]. The occurrence of qualitative abnormalities of hematopoiesis may represent a likely step toward neoplasia [27,39,40]. Risk factors for MDS are shown in Table 8.1. Genetic factors Many karyotypic abnormalities, inherited mutations, polymorphism of several genes, and chromosomal instabilities are associated with disturbance of nor- mal hematopoiesis. Both gender and ethnic origin are important risk factors [53,54]. Of special interest in understanding the mechanism of hematopoietic abnormalities are the reports of familial MDS [55–61]. Inherited abnormalities as well as chromosomal instability may provide the initial genetic hit that predisposes to other hematopoietic abnormalities, including neoplasia [62,63]. Aging itself is associated Table 8.1. Risk factors for MDS. Age Environmental factors Drugs INH, anti-tuberculosis drugs, chloramphenicol, Cycloserine, penicillamine, immunosuppressors Toxins, drinking water Ethanol, zinc, arsenic, cadmium, chloroform, halomethanes Nutritional (malnutrition) Copper and pyridoxine defi ciency; phenols and hydroquinone Occupational Asbestos, paint products, benzene and organic solvents, ammonia, diesel fuel, or other petrochemicals Chronic exposure Pesticides, tobacco, agricultural chemicals, free radicals Infections Viruses Genetic factors Inherited mutations, karyotypic abnormalities, gene mutations, chromosomal instabilities, gender Immunological factors Lymphocytes and cytokines dysregulation Others Depression, obesity and endocrine status [...]... may be involved in the progression of MDS The 5q-minus syndrome consists of refractory anemia (RA), thrombocytosis, and abnormal megakaryocyte morphology with a relatively good prognosis [ 234 – 237 ] The deleted region of chromosome 5 contains the genes for several hematopoietic growth factors and is of particular interest regarding the maturation defect in MDS IL -3 , IL-4, IL-5, IL-9, GMCSF, the M-CSF receptor,... reduces the stress-coping ability of aged individuals In this chapter we explore the in uence of aging on response to hematopoietic stress and the potential mechanisms by which this response may be impaired The peripheral blood counts do not appear significantly reduced in the aged [1 3] , at least up to age 90, indicating that homeostasis is preserved even in the oldest old, in the absence of stress In the. .. (CFU-E) were less responsive to erythropoietin (EPO) It was then established in the mouse model that basal hematopoiesis was not altered in aging, but that the reserve capacity was compromised when mice were submitted to stress [10,11,91] During the last two decades there has been much progress in understanding the role of the immune system, pro -in ammatory cytokines [ 13] , gene interactions [92], point... progenitors in the circulation by stimulating their proliferation Chatta et al [39 ] studied the granulocyte reserve of younger ( 30 ) and older (у 70) individuals following hydrocortisone, epinephrine, and filgrastim, and found that the increment of neutrophils following epinephrine and filgrastim was unaffected by age, while the neutrophilic response to hydrocortisone was blunted in the elderly They concluded... Heijmans-Antonissen C, et al Reduced hematopoietic reserves in DNA interstrand 233 234 235 236 237 238 239 240 241 242 2 43 244 245 crosslink repair-deficient Ercc 1-/ - mice EMBO J 2005; 24: 861–71 Ueda M, Ota J, Yamashita Y, et al DNA microarray analysis of stage progression mechanism in myelodysplastic syndrome Br J Haematol 20 03; 1 23: 288–96 Van den Berghe H, Cassiman JJ, David G, Fryns JP Distinct haematological... unable to maintain a self-renewal capacity TGF-β activity, which inhibits proliferation, declines [181] Dendritic cells (DC) are the most powerful antigen-presenting cells able to activate T cells and partially regulate the adaptive and innate immune system Age does not seem to affect the function of DC in healthy older individuals [ 130 ], but it is compromised in the frail elderly [182] Another cause... and G-CSF [258] Thus, growth-promoting cytokines such as EPO, IL -3 , IL-6, and TPO, which are usually increased in MDS patients, may try to counterbalance the pro-apototic stimuli The role of the immune system One mechanism underlying the marrow failure in MDS is immunologic attack on the HSCs, which may also be found in aplastic anemia and paroxysmal nocturnal hemoglobinuria (PNH) T lymphocytes may inhibit... Following bleeding for blood donation the reticulocyte response was lower in older than in younger individuals, suggesting that the reconstitution of the red blood cell mass may take longer in the elderly [47,48] The mechanism for this reduced erythropoietic response to bleeding is disputed Some authors found that the production of erythropoietin may be blunted with aging [47,48,62], while others found... disease Clin Lab Haematol 2001; 23: 297 30 0 34 Malaguarnera M, Di Fazio I, Vinci E, et al Haematologic pattern in healthy subjects Panminerva Med 1999; 41: 227 31 35 Fernandez-Ferrero S, Ramos F Dyshaemopoietic bone marrow features in healthy subjects are related to age Leuk Res 2001; 25: 187–9 36 Nagura E, Minami S, Nagara K, et al Acute myeloid leukemia in the elderly: 159 Nagoya case studies 37 38 39 40... Am J Med Sci 2000; 31 9: 34 3–52 Mahmoud MY, Lugon M, Anderson CC Unexplained macrocytosis in elderly patients Age Ageing 1996; 25: 31 0–12 Gilleece MH, Dexter TM The biological ageing in bone marrow Rev Clin Gerontol 19 93; 3: 31 7–25 Sharp A, Zipori D, Toledo J, Tal S, Resnitzky P , Globerson A Age-related changes in hemopoietic capacity of bone marrow Mech Ageing Dev 1989; 48: 91–9 Pinto A, De Filippi . [10,11,91]. During the last two dec- ades there has been much progress in understanding the role of the immune system, pro -in ammatory cytokines [ 13] , gene interactions [92], point muta- tions,. [227– 231 ]. Spontaneous chro- mosomal instability and interstrand crosslink dam- age may contribute to the functional decline of the hematopoietic system associated with aging [ 232 , 233 ]. There. in older individuals [9–15]. Despite these changes, hematopoiesis appears adequate to maintain the homeostasis of the periph- eral blood elements both in healthy elderly persons and in aging