Aging Impairs Long-Term Hematopoietic Regeneration after Autologous Stem Cell Transplantation

A systematic review of lifespan studies in rodents using stem cell transplantations

Organismal aging involves the progressive decline in organ function and increased susceptibility to age-associated diseases. Regardless of its origin, cellular aging is consequently reflected at the level of organ and associated systems dysfunction. Aging of stem cell populations within the body and their decreased ability to self-renew, differentiate, and regenerate damaged tissues, is a key contributor to organismal decline. Based on this, supplementing young stem cells may delay tissue aging, improve frailty and extend health and lifespan. This review investigates studies in rodents using stem cell transplantation from either mice or human donors. The aim is to consolidate available information on the efficacy of stem cell therapies in rodent models and provide insights to guide further research efforts. Out of the 21 studies included in this review, the methodology varied significantly including the lifespan measurement. To enable comparison the median lifespan was calculated using WebPlotDigitizer 4.6 if not provided by the literature. A total of 18 out of 21 studies evidenced significant lifespan extension post stem cell transplant, with 7 studies demonstrating benefits in reduced frailty and other aging complications.

An iron rheostat controls hematopoietic stem cell fate

Mechanisms governing the maintenance of blood-producing hematopoietic stem and multipotent progenitor cells (HSPCs) are incompletely understood, particularly those regulating fate, ensuring long-term maintenance, and preventing aging-associated stem cell dysfunction. We uncovered a role for transitory free cytoplasmic iron as a rheostat for adult stem cell fate control. We found that HSPCs harbor comparatively small amounts of free iron and show the activation of a conserved molecular response to limited iron-particularly during mitosis. To study the functional and molecular consequences of iron restriction, we developed models allowing for transient iron bioavailability limitation and combined single-molecule RNA quantification, metabolomics, and single-cell transcriptomic analyses with functional studies. Our data reveal that the activation of the limited iron response triggers coordinated metabolic and epigenetic events, establishing stemness-conferring gene regulation. Notably, we find that aging-associated cytoplasmic iron loading reversibly attenuates iron-dependent cell fate control, explicating intervention strategies for dysfunctional aged stem cells.

Combatting ageing in dermal papilla cells and promoting hair follicle regeneration using exosomes from human hair follicle dermal sheath cup cells

Dermal papilla cells (DPCs) undergo premature ageing in androgenetic alopecia and senescent alopecia. As critical components of hair follicle reconstruction, DPCs are also prone to senescence in vitro, resulting in a diminished hair follicle inductivity capacity. Dermal sheath cup cells (DSCCs), a specific subset of hair follicle mesenchymal stem cells, intimately linked to the function of DPCs. The primary objective of this research is to investigate the anti-ageing effect of exosomes derived from DSCCs (ExoDSCCs ) on DPCs. Exosomes were utilized to treat H2 O2 -induced DPCs or long-generation DPCs(P10). Our findings demonstrate that ExoDSCCs(P3) promote the proliferation, viability and migration of senescent DPCs while inhibiting cell apoptosis. The expression of senescence marker SA-β-Gal were significantly downregulated in senescent DPCs. When treated with ExoDSCCs(P3) , expression of inducibility related markers alkaline phosphatase and Versican were significantly upregulated. Additionally, ExoDSCCs(P3) activated the Wnt/β-catenin signalling in vitro. In patch assay, ExoDSCCs(P3) significantly promoted hair follicle reconstruction in senescent DPCs. In summary, our work highlights that ExoDSCCs(P3) may restore the biological functions and improve the hair follicle induction ability of senescent DPCs. Therefore, ExoDSCCs(P3) may represent a new strategy for intervening in the ageing process of DPCs, contributing to the prevention of senile alopecia.

Patient Reported and Clinical Outcomes after High-Dose Chemotherapy and Autologous Stem Cell Transplantation in Primary Central Nervous System Lymphoma

Primary central nervous system lymphomas (PCNSL) are rare and associated with an adverse prognosis. High-dose chemotherapy followed by autologous stem cell transplantation (HDC/ASCT) improves progression free (PFS) and overall survival (OS) but neurocognition, performance status and quality of life (QoL) in patient-reported outcome (PRO) after HDC/ASCT remains underexplored. Especially elderly patients may insufficiently recover from this demanding therapy. Therefore, this single-center analysis investigated all PCNSL patients who received HDC/ASCT at the University Hospital Tübingen from 2006-2021 (n = 40, median age 60.5 years) in a retrospective manner. The 2-year PFS/OS was 78.7%/77.3%, respectively, without significant differences between the tested age-groups (≤60 vs. >60 years, p = 0.531/p = 0.334). Higher Thiotepa dosage was an independent predictor for better OS (p = 0.018). Additionally, a one-time prospective, cross-sectional analysis after HDC/ASCT in the same cohort was performed (n = 31; median follow-up 45 months). Here, the median ECOG improved by HDC/ASCT from 1 to 0 and mini-mental state examinations revealed unimpaired neurocognitive functioning (median 28 pts.). PRO data collected by EORTC QLQ-C30 showed a good QoL in both age groups with an average global health status (GHS) of 68.82% (≤60y: 64.72%, >60y: 74.14%). Together, our data indicate that HDC/ASCT is an effective therapy with respect to disease control, overall health status and quality of life, irrespective of patient age.

DNA damage and aging on hematopoietic stem cells: Impact of oxidative stress in ApoE-/- mice

The effects of aging on ROS production and DNA damage were assessed in hematopoietic stem cells (HSCs) from apolipoprotein E-deficient (ApoE^-/^-) mice (2-, 12- and 24-month-old), a traditional experimental model of atherogenic dyslipidemia. HSCs from aged ApoE^-/- mice were associated with increased ROS levels, leading to loss quiescence, DNA damage, apoptosis and telomere shortening. The concurrence of lack of ApoE and aging result in exhaustion and senescence of HSCs accompanied by increased oxidative stress and inflammation. Therefore, our data open avenues to a better understanding of age-related changes and genetic factors, which may synergistically compromise the efficacy of aged HSC recovery and/or transplantation.

Early onset of aging phenotype in vascular repair by Mas receptor deficiency

Aging is associated with impaired vascular repair following ischemic insult, largely due to reparative dysfunctions of progenitor cells. Activation of Mas receptor (MasR) was shown to reverse aging-associated vasoreparative dysfunction. This study tested the impact of MasR-deficiency on mobilization and vasoreparative functions with aging. Wild type (WT) or MasR-deficient mice (MasR^-/- or MasR^+/-) at 12-14 weeks (young) or middle age (11-12 months) (MA) were used in the study. Mobilization of lineage-negative, Sca-1-positive cKit-positive (LSK) cells in response to G-CSF or plerixafor was determined. Hindlimb ischemia (HLI) was induced by femoral artery ligation. Mobilization and blood flow recovery were monitored post-HLI. Radiation chimeras were made by lethal irradiation of WT or MasR^-/- mice followed by administration of bone marrow cells from MasR^-/- or WT mice, respectively. Nitric oxide (NO) generation by stromal-derived factor-1α (SDF) and mitochondrial reactive oxygen species (mitoROS) levels were determined by flow cytometry. Effect of A779 treatment on mobilization, blood flow recovery, and NO and ROS levels were determined in young WT and MasR^+/- mice. Circulating LSK cells in basal or in response to plerixafor or G-CSF or in response to ischemic injury were lower in MasR^-/- mice compared to the WT. Responses in MasR^+/- mice were similar to the WT at young age but at the middle age, impairments were observed. Impaired mobilization to ischemia or G-CSF was rescued in WT → MasR^-/- chimeras. NO levels were lower and mitoROS were higher in MasR^-/- LSK cells compared to WT cells. A779 precipitated dysfunctions in young-MasR^+/- mice similar to that observed in MA-MasR^+/-, and this accompanied decreased NO generation by SDF and enhanced mitoROS levels. This study shows that mice at MA do not exhibit vasoreparative dysfunction. Either partial or total loss of MasR precipitates advanced-aging phenotype likely due to lack of NO and oxidative stress.

IL-1 Mediates Microbiome-Induced Inflamm-Ageing of Hematopoietic Stem Cells in Mice

Ageing is associated with impaired hematopoietic and immune function. This is caused in part by decreased hematopoietic stem cell (HSC) population fitness and an increased myeloid differentiation bias. The reasons for this aging-associated HSC impairment are incompletely understood. We here demonstrate that aged specific pathogen free (SPF) wild-type mice in contrast to young SPF mice produce more IL-1a/b in steady-state bone marrow (BM), with most of IL-1a/b being derived from myeloid BM cells. Further, blood of steady-state aged SPF wild-type mice contains higher levels of microbe associated molecular patterns (MAMPs), specifically TLR4 and TLR8 ligands. Also, BM myeloid cells from aged mice produce more IL-1b in vitro, and aged mice show higher and more durable IL-1a/b responses upon LPS stimulation in vivo. To test if HSC ageing is driven via IL-1a/b, we evaluated HSCs from IL-1 receptor 1 (IL-1R1) knock-out mice. Indeed, aged HSCs from IL-1R1 knock-out mice show significantly mitigated ageing-associated inflammatory signatures. Moreover, HSCs from aged IL-1R1KO and also from germ-free mice maintain unbiased lympho-myeloid hematopoietic differentiation upon transplantation, thus resembling this functionality of young HSCs. Importantly, in vivo antibiotic suppression of microbiota or pharmacologic blockade of IL-1 signaling in aged wild-type mice was similarly sufficient to reverse myeloid biased output of their HSC populations. Collectively, our data defines the microbiome-IL-1/IL-1R1 axis as a key, self-sustaining, but also therapeutically partially reversible driver of HSC inflamm-ageing.

Inflammation as a regulator of hematopoietic stem cell function in disease, aging, and clonal selection

Inflammation is an evolutionarily selected defense response to infection or tissue damage that involves activation and consumption of immune cells in order to reestablish and maintain organismal integrity. In this process, hematopoietic stem cells (HSCs) are themselves exposed to inflammatory cues and via proliferation and differentiation, replace mature immune cells in a demand-adapted fashion. Here, we review how major sources of systemic inflammation act on and subsequently shape HSC fate and function. We highlight how lifelong inflammatory exposure contributes to HSC inflamm-aging and selection of premalignant HSC clones. Finally, we explore emerging areas of interest and open questions remaining in the field.

Clonal tracking of haematopoietic cells: insights and clinical implications

Recent advances in high-throughput genomics have enabled the direct tracking of outputs from many cell types, greatly accelerating the study of developmental processes and tissue regeneration. The capacity for long-term self-renewal with multilineage differentiation potential characterises the cellular dynamics of a special set of developmental states that are critical for maintaining homeostasis. In haematopoiesis, the archetypal model for development, lineage-tracing experiments have elucidated the roles of haematopoietic stem cells to ongoing blood production and the importance of long-lived immune cells to immunological memory. An understanding of the biology and clonal dynamics of these cellular fates and states can provide clues to the response of haematopoiesis to ageing, the process of malignant transformation, and are key to designing more efficacious and durable clinical gene and cellular therapies.

ACE2/ACE imbalance and impaired vasoreparative functions of stem/progenitor cells in aging

Aging increases risk for ischemic vascular diseases. Bone marrow–derived hematopoietic stem/progenitor cells (HSPCs) are known to stimulate vascular regeneration. Activation of either the Mas receptor (MasR) by angiotensin-(1-7) (Ang-(1-7)) or angiotensin-converting enzyme-2 (ACE2) stimulates vasoreparative functions in HSPCs. This study tested if aging is associated with decreased ACE2 expression in HSPCs and if Ang-(1-7) restores vasoreparative functions. Flow cytometric enumeration of Lin⁻CD45^lowCD34⁺ cells was carried out in peripheral blood of male or female individuals (22–83 years of age). Activity of ACE2 or the classical angiotensin-converting enzyme (ACE) was determined in lysates of HSPCs. Lin⁻Sca-1⁺cKit⁺ (LSK) cells were isolated from young (3–5 months) or old (20–22 months) mice, and migration and proliferation were evaluated. Old mice were treated with Ang-(1-7), and mobilization of HSPCs was determined following ischemia induced by femoral ligation. A laser Doppler blood flow meter was used to determine blood flow. Aging was associated with decreased number (Spearman r = − 0.598, P < 0.0001, n = 56), decreased ACE2 (r = − 0.677, P < 0.0004), and increased ACE activity (r = 0.872, P < 0.0001) (n = 23) in HSPCs. Migration or proliferation of LSK cells in basal or in response to stromal-derived factor-1α in old cells is attenuated compared to young, and these dysfunctions were reversed by Ang-(1-7). Ischemia increased the number of circulating LSK cells in young mice, and blood flow to ischemic areas was recovered. These responses were impaired in old mice but were restored by treatment with Ang-(1-7). These results suggest that activation of ACE2 or MasR would be a promising approach for enhancing ischemic vascular repair in aging.

Pregnancy as a model for aging

The process of aging can be defined as the sum accumulation of damages and changes in metabolism during the life of an organism, due to both genetic predisposition and stochastic damage. During the gestational period and following parturition, similar damage can be seen due to the strenuous effect on the maternal body, exhibited on both the physiological and cellular level. In this review, we will focus on the similar physiological and cellular characteristics exhibited during pregnancy and aging, including induction of and response to oxidative stress, inflammation, and degradation of telomeres. We will evaluate any similar processes between aging and pregnancy by comparing common biomarkers, pathologies, and genetic and epigenetic effects, to establish the pregnant body as a model for aging. This review will approach the connection both in respect to current theories on aging as a byproduct of natural selection, and regarding unrelated biochemical similarities between the two, drawing on existing studies and models in humans and other species where relevant alike. Furthermore, we will show the response of the pregnant body to these changes, and through that illuminate unique areas of potential study to advance our knowledge of the maladies relating to aging and pregnancy, and an avenue for solutions.

Exosomes derived from human umbilical cord MSCs rejuvenate aged MSCs and enhance their functions for myocardial repair

Background

Age and other cardiovascular risk factors have been reported to impair the activities of mesenchymal stem cells (MSCs), which will affect the efficacy of stem cell transplantation. The objective of the study is to investigate whether exosomes derived from human umbilical cord MSCs (UMSCs) could enhance the activities of bone marrow MSCs from old person (OMSCs), and improve their capacity for cardiac repair.

Methods

Exosomes extracted from conditioned medium of UMSCs were used to treat OMSCs to generate OMSCs^Exo. The key molecule in the exosomes that have potential to rejuvenate aged MSCs were screened, and the role of OMSC was tested in the mouse model of mycardial infarction (MI).

Results

We found the activity of senescence-associated β-galactosidase and the expression of aging-related factors such as p53, p21, and p16 were significantly higher in OMSCs than those in UMSCs. After treatment with UMSC exosomes, these senescence phenotypes of OMSCs were remarkably reduced. The proliferation, migration, differentiation, and anti-apoptotic and paracrine effect were increased in OMSCs^Exo. In vivo study, mice with cardiac infarction had significantly better cardiac function, less fibrosis, and more angiogenesis after they were injected with OMSCs^Exo as compared with those with OMSC. There was more miR-136 expression in UMSCs and OMSCs^Exo than in OMSCs. Upregulation of miR-136 by transfection of miR-136 mimic into OMSCs significantly attenuated the apoptosis and senescence of OMSCs. Apoptotic peptidase activating factor (Apaf1) was found to be the downstream gene that is negatively regulated by miR-136 via directly targeting at its 3′UTR.

Conclusion

Our data suggest that exosomes from young MSCs can improve activities of aged MSCs and enhance their function for myocardial repair by transferring exosomal miR-136 and downregulating Apaf1.

Aging and Hematopoiesis

In hematopoiesis, mature blood cells, granulocytes, erythrocytes, and megakaryocytes originate from hematopoietic stem cells. With age, changes in hematopoiesis may have clinical consequences: defective immune responses, cytopenias (most commonly anemia and lymphopenia), hematological malignancy, and effects mediated by hematopoietic cells in other organs. Clonal hematopoiesis is commonly seen with aging and has been associated with both blood concerns and atherosclerosis, but further study is required to determine a causative link.

The Instructive Role of the Bone Marrow Niche in Aging and Leukemia

Purpose of review

In this review, we aim to discuss the role of the bone marrow microenvironment in supporting hematopoiesis, with particular focus on the contribution of the endothelial niche in dictating hematopoietic stem cell (HSC) fate.

Recent findings

Evidence gathered in the past two decades revealed that specific cell types within the bone marrow niche influence the hematopoietic system. Endothelial cells have emerged as a key component of the HSC niche, directly affecting stem cell quiescence, self-renewal, and lineage differentiation. Physiological alterations of the bone marrow niche occurring in aging have been described to be sufficient to promote functional aging of young HSCs. Furthermore, a growing body of evidence suggests that aberrant activation of endothelial-derived signaling pathways can aid or trigger neoplastic transformation.

Summary

Several groups have contributed to the characterization of the different cell types that comprise the complex bone marrow environment, whose function was long perceived as an undiscernible sum of many parts. Further studies will need to uncover niche cell-type-specific pathways, in order to provide new targets and therapeutic options that aim at withdrawing the microenvironmental support to malignant cells while sparing normal HSCs.

The potential of non-myeloablative heterochronous autologous hematopoietic stem cell transplantation for extending a healthy life span

Aging is a complex multifactorial process, a prominent component being the senescence of the immune system. Consequently, immune-related diseases develop, including atherosclerosis, cancer, and life-threatening infections, which impact on health and longevity. Rejuvenating the aged immune system could mitigate these diseases, thereby contributing to longevity and health. Currently, an appealing option for rejuvenating the immune system is heterochronous autologous hematopoietic stem cell transplantation (haHSCT), where healthy autologous bone marrow/peripheral blood stem cells are collected during the youth of an individual, cryopreserved, and re-infused when he or she has reached an older age. After infusion, young hematopoietic stem cells can reconstitute the compromised immune system and improve immune function. Several studies using animal models have achieved substantial extension of the life span of animals treated with haHSCT. Therefore, haHSCT could be regarded as a potential procedure for preventing age-related immune defects and extending healthy longevity. In this review, the pros, cons, and future feasibility of this approach are discussed.

Replication stress in hematopoietic stem cells in mouse and man

Life-long blood regeneration relies on a rare population of self-renewing hematopoietic stem cells (HSCs). These cells' nearly unlimited self-renewal potential and lifetime persistence in the body signifies the need for tight control of their genome integrity. Their quiescent state, tightly linked with low metabolic activity, is one of the main strategies employed by HSCs to preserve an intact genome. On the other hand, HSCs need to be able to quickly respond to increased blood demands and rapidly increase their cellular output in order to fight infection-associated inflammation or extensive blood loss. This increase in proliferation rate, however, comes at the price of exposing HSCs to DNA damage inevitably associated with the process of DNA replication. Any interference with normal replication fork progression leads to a specialized molecular response termed replication stress (RS). Importantly, increased levels of RS are a hallmark feature of aged HSCs, where an accumulating body of evidence points to causative relationships between RS and the aging-associated impairment of the blood system's functional capacity. In this review, we present an overview of RS in HSCs focusing on its causes and consequences for the blood system of mice and men.

The impact of aging on primate hematopoiesis as interrogated by clonal tracking

Age-associated changes in hematopoietic stem and progenitor cells (HSPCs) have been carefully documented in mouse models but poorly characterized in primates and humans. To investigate clinically relevant aspects of hematopoietic aging, we compared the clonal output of thousands of genetically barcoded HSPCs in aged vs young macaques after autologous transplantation. Aged macaques showed delayed emergence of output from multipotent (MP) clones, with persistence of lineage-biased clones for many months after engraftment. In contrast to murine aging models reporting persistence of myeloid-biased HSPCs, aged macaques demonstrated persistent output from both B-cell and myeloid-biased clones. Clonal expansions of MP, myeloid-biased, and B-biased clones occurred in aged macaques, providing a potential model for human clonal hematopoiesis of indeterminate prognosis. These results suggest that long-term MP HSPC output is impaired in aged macaques, resulting in differences in the kinetics and lineage reconstitution patterns between young and aged primates in an autologous transplantation setting.

Intercellular Transfer of Microvesicles from Young Mesenchymal Stromal Cells Rejuvenates Aged Murine Hematopoietic Stem Cells

Donor age is one of the major concerns in bone marrow transplantation, as the aged hematopoietic stem cells (HSCs) fail to engraft efficiently. Here, using murine system, we show that a brief interaction of aged HSCs with young mesenchymal stromal cells (MSCs) rejuvenates them and restores their functionality via inter-cellular transfer of microvesicles (MVs) containing autophagy-related mRNAs. Importantly, we show that MSCs gain activated AKT signaling as a function of aging. Activated AKT reduces the levels of autophagy-related mRNAs in their MVs, and partitions miR-17 and miR-34a into their exosomes, which upon transfer into HSCs downregulate their autophagy-inducing mRNAs. Our data identify previously unknown mechanisms operative in the niche-mediated aging of HSCs. Inhibition of AKT in aged MSCs increases the levels of autophagy-related mRNAs in their MVs and reduces the levels of miR-17 and miR-34a in their exosomes. Interestingly, transplantation experiments showed that the rejuvenating power of these "rescued" MVs is even better than that of the young MVs. We demonstrate that such ex vivo rejuvenation of aged HSCs could expand donor cohort and improve transplantation efficacy. Stem Cells 2018;36:420-433.

Age-associated changes in human hematopoietic stem cells

Aging has a broad impact on the function of the human hematopoietic system. This review will focus primarily on the effect of aging on the human hematopoietic stem cell (HSC) population. With age, even though human HSCs increase in number, they have decreased self-renewal capacity and reconstitution potential upon transplantation. As a population, human HSCs become more myeloid-biased in their differentiation potential. This is likely due to the human HSC population becoming more clonal with age, selecting for myeloid-biased HSC clones. The HSC clones that come to predominate with age may also contain disease-causing genetic and epigenetic changes that confer an increased risk of developing into an age-associated clonal hematopoietic disease, such as myelodysplastic syndrome, myeloproliferative disorders, or leukemia. The selection of these aged human HSC clones may be in part due to changes in the aging bone marrow microenvironment. While there have been significant advances in the understanding of the effect of aging on mouse hematopoiesis and mouse HSCs, we have comparatively less detailed analyses of the effect of aging on human HSCs. Continued evaluation of human HSCs in the context of aging will be important to determine how applicable the findings in mice and other model organisms are to the human clinical setting.

Chemotherapy and Stem Cell Transplantation Increase p16INK4a Expression, a Biomarker of T-cell Aging

The expression of markers of cellular senescence increases exponentially in multiple tissues with aging. Age-related physiological changes may contribute to adverse outcomes in cancer survivors. To investigate the impact of high dose chemotherapy and stem cell transplantation on senescence markers in vivo, we collected blood and clinical data from a cohort of 63 patients undergoing hematopoietic cell transplantation. The expression of p16^INK4a, a well-established senescence marker, was determined in T-cells before and 6 months after transplant. RNA sequencing was performed on paired samples from 8 patients pre- and post-cancer therapy. In patients undergoing allogeneic transplant, higher pre-transplant p16^INK4a expression was associated with a greater number of prior cycles of chemotherapy received (p = 0.003), prior autologous transplantation (p = 0.01) and prior exposure to alkylating agents (p = 0.01). Transplantation was associated with a marked increase in p16^INK4a expression 6 months following transplantation. Patients receiving autologous transplant experienced a larger increase in p16^INK4a expression (3.1-fold increase, p = 0.002) than allogeneic transplant recipients (1.9-fold increase, p = 0.0004). RNA sequencing of T-cells pre- and post- autologous transplant or cytotoxic chemotherapy demonstrated increased expression of transcripts associated with cellular senescence and physiological aging. Cytotoxic chemotherapy, especially alkylating agents, and stem cell transplantation strongly accelerate expression of a biomarker of molecular aging in T-cells.

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Peripheral blood T-cell senescence, as measured by the marker p16^INK4a, increases following autologous or allogeneic HSCT.

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RNAseq of T-cells post- auto HSCT or chemotherapy show increased expression of transcripts associated with senescence.

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Autologous HCT in particular induces a stronger effect on Tcell p16^INK4a expression than any other environmental stimulus tested to date.

Human chronological aging is associated with increased expression of markers of cellular aging (senescence). Cancer chemotherapy can produce frailty syndromes – recipients of cancer treatment may experience physiological changes ordinarily seen in individuals of more advanced chronological age. In our study, we found that a well-known marker of cellular senescence, p16^INK4a, increased in patients following autologous or allogeneic hematopoietic cell transplantation. Expression of p16^INK4a was higher in patients exposed to greater amounts of chemotherapy before transplant and those exposed to specific types of chemotherapy. These findings may ultimately influence clinical decision-making for patients with diseases that are commonly treated with transplantation.

Human and Murine Hematopoietic Stem Cell Aging Is Associated with Functional Impairments and Intrinsic Megakaryocytic/Erythroid Bias

Aging within the human hematopoietic system associates with various deficiencies and disease states, including anemia, myeloid neoplasms and reduced adaptive immune responses. Similar phenotypes are observed in mice and have been linked to alterations arising at the hematopoietic stem cell (HSC) level. Such an association is, however, less established in human hematopoiesis and prompted us here to detail characteristics of the most primitive human hematopoietic compartments throughout ontogeny. In addition, we also attempted to interrogate similarities between aging human and murine hematopoiesis. Coupled to the transition from human cord blood (CB) to young and aged bone marrow (BM), we observed a gradual increase in frequency of candidate HSCs. This was accompanied by functional impairments, including decreased lymphoid output and reduced proliferative potential. Downstream of human HSCs, we observed decreasing levels of common lymphoid progenitors (CLPs), and increasing frequencies of megakaryocyte/erythrocyte progenitors (MEPs) with age, which could be linked to changes in lineage-affiliated gene expression patterns in aged human HSCs. These findings were paralleled in mice. Therefore, our data support the notion that age-related changes also in human hematopoiesis involve the HSC pool, with a prominent skewing towards the megakaryocytic/erythroid lineages, and suggests conserved mechanisms underlying aging of the blood cell system.

High-Dose Chemotherapy and Autologous Stem Cell Transplant in Older Patients with Lymphoma

High-dose chemotherapy followed by autologous hematopoietic stem cell transplant (HDT/ASCT) can improve survival in patients with lymphoma. Limited experience is available on the safety and efficacy of HDT/ASCT in elderly patients. In this article, we review the published data on the role of HDT/ASCT in management of lymphoma in older patients. Based on available data, evaluation of comorbidities, functional status, and comprehensive geriatric assessment (CGA) will help identify those who can benefit most from this intervention. Prospective clinical trials focusing on HDT/ASCT in older patients with lymphoma are needed to establish optimal management protocols in this select population.

Concise review: hematopoietic stem cell aging and the prospects for rejuvenation

Because of the continuous increases in lifetime expectancy, the incidence of age-related diseases will, unless counteracted, represent an increasing problem at both the individual and socioeconomic levels. Studies on the processes of blood cell formation have revealed several shortcomings as a consequence of chronological age. They include a reduced ability to mount adaptive immune responses and a blood cell composition skewed toward myeloid cells, with the latter coinciding with a dramatically increased incidence of myelogenous diseases, including cancer. Conversely, the dominant forms of acute leukemia affecting children associate with the lymphoid lineages. A growing body of evidence has suggested that aging of various organs and cellular systems, including the hematopoietic system, associates with a functional demise of tissue-resident stem cell populations. Mechanistically, DNA damage and/or altered transcriptional landscapes appear to be major drivers of the hematopoietic stem cell aging state, with recent data proposing that stem cell aging phenotypes are characterized by at least some degree of reversibility. These findings suggest the possibility of rejuvenating, or at least dampening, stem cell aging phenotypes in the elderly for therapeutic benefit.