Stem cell aging and autoimmunity in rheumatoid arthritis

Cartilage organoids for cartilage development and cartilage-associated disease modeling

Cartilage organoids have emerged as powerful modelling technology for recapitulation of joint embryonic events, and cartilage regeneration, as well as pathophysiology of cartilage-associated diseases. Recent breakthroughs have uncovered "mini-joint" models comprising of multicellular components and extracellular matrices of joint cartilage for development of novel disease-modifying strategies for personalized therapeutics of cartilage-associated diseases. Here, we hypothesized that LGR5-expressing embryonic joint chondroprogenitor cells are ideal stem cells for the generation of cartilage organoids as "mini-joints" ex vivo "in a dish" for embryonic joint development, cartilage repair, and cartilage-associated disease modelling as essential research models of drug screening for further personalized regenerative therapy. The pilot research data suggested that LGR5-GFP-expressing embryonic joint progenitor cells are promising for generation of cartilage organoids through gel embedding method, which may exert various preclinical and clinical applications for realization of personalized regenerative therapy in the future.

Type I IFNs Act upon Hematopoietic Progenitors To Protect and Maintain Hematopoiesis during Pneumocystis Lung Infection in Mice

Although acquired bone marrow failure (BMF) is considered a T cell-mediated autoimmune disease, few studies have considered contributing roles of innate immune deviations following otherwise innocuous infections as a cause underlying the immune defects that lead to BMF. Type I IFN signaling plays an important role in protecting hematopoiesis during systemic stress responses to the opportunistic fungal pathogen Pneumocystis. During Pneumocystis lung infection, mice deficient in both lymphocytes and type I IFN receptor (IFrag(-/-)) develop rapidly progressing BMF associated with accelerated hematopoietic cell apoptosis. However, the communication pathway eliciting the induction of BMF in response to this strictly pulmonary infection has been unclear. We developed a conditional-null allele of Ifnar1 and used tissue-specific induction of the IFrag(-/-) state and found that, following Pneumocystis lung infection, type I IFNs act not only in the lung to prevent systemic immune deviations, but also within the progenitor compartment of the bone marrow to protect hematopoiesis. In addition, transfer of sterile-filtered serum from Pneumocystis-infected mice as well as i.p. injection of Pneumocystis into uninfected IFrag(-/-) mice induced BMF. Although specific cytokine deviations contribute to induction of BMF, immune-suppressive treatment of infected IFrag(-/-) mice ameliorated its progression but did not prevent loss of hematopoietic progenitor functions. This suggested that additional, noncytokine factors also target and impair progenitor functions; and interestingly, fungal β-glucans were also detected in serum. In conclusion, our data demonstrate that type 1 IFN signaling protects hematopoiesis within the bone marrow compartment from the damaging effects of proinflammatory cytokines elicited by Pneumocystis in the lung and possibly at extrapulmonary sites via circulating fungal components.

B cells modulate systemic responses to Pneumocystis murina lung infection and protect on-demand hematopoiesis via T cell-independent innate mechanisms when type I interferon signaling is absent

HIV infection results in a complex immunodeficiency due to loss of CD4(+) T cells, impaired type I interferon (IFN) responses, and B cell dysfunctions causing susceptibility to opportunistic infections such as Pneumocystis murina pneumonia and unexplained comorbidities, including bone marrow dysfunctions. Type I IFNs and B cells critically contribute to immunity to Pneumocystis lung infection. We recently also identified B cells as supporters of on-demand hematopoiesis following Pneumocystis infection that would otherwise be hampered due to systemic immune effects initiated in the context of a defective type I IFN system. While studying the role of type I IFNs in immunity to Pneumocystis infection, we discovered that mice lacking both lymphocytes and type I IFN receptor (IFrag(-/-)) developed progressive bone marrow failure following infection, while lymphocyte-competent type I IFN receptor-deficient mice (IFNAR(-/-)) showed transient bone marrow depression and extramedullary hematopoiesis. Lymphocyte reconstitution of lymphocyte-deficient IFrag(-/-) mice pointed to B cells as a key player in bone marrow protection. Here we define how B cells protect on-demand hematopoiesis following Pneumocystis lung infection in our model. We demonstrate that adoptive transfer of B cells into IFrag(-/-) mice protects early hematopoietic progenitor activity during systemic responses to Pneumocystis infection, thus promoting replenishment of depleted bone marrow cells. This activity is independent of CD4(+) T cell help and B cell receptor specificity and does not require B cell migration to bone marrow. Furthermore, we show that B cells protect on-demand hematopoiesis in part by induction of interleukin-10 (IL-10)- and IL-27-mediated mechanisms. Thus, our data demonstrate an important immune modulatory role of B cells during Pneumocystis lung infection that complement the modulatory role of type I IFNs to prevent systemic complications.

Chondrogenic differentiation increases antidonor immune response to allogeneic mesenchymal stem cell transplantation

Allogeneic mesenchymal stem cells (allo-MSCs) have potent regenerative and immunosuppressive potential and are being investigated as a therapy for osteoarthritis; however, little is known about the immunological changes that occur in allo-MSCs after ex vivo induced or in vivo differentiation. Three-dimensional chondrogenic differentiation was induced in an alginate matrix, which served to immobilize and potentially protect MSCs at the site of implantation. We show that allogeneic differentiated MSCs lost the ability to inhibit T-cell proliferation in vitro, in association with reduced nitric oxide and prostaglandin E2 secretion. Differentiation altered immunogenicity as evidenced by induced proliferation of allogeneic T cells and increased susceptibility to cytotoxic lysis by allo-specific T cells. Undifferentiated or differentiated allo-MSCs were implanted subcutaneously, with and without alginate encapsulation. Increased CD3(+) and CD68(+) infiltration was evident in differentiated and splenocyte encapsulated implants only. Without encapsulation, increased local memory T-cell responses were detectable in recipients of undifferentiated and differentiated MSCs; however, only differentiated MSCs induced systemic memory T-cell responses. In recipients of encapsulated allogeneic cells, only differentiated allo-MSCs induced memory T-cell responses locally and systemically. Systemic alloimmune responses to differentiated MSCs indicate immunogenicity regardless of alginate encapsulation and may require immunosuppressive therapy for therapeutic use.

Immunosenescence, aging, and systemic lupus erythematous

Senescence is a normal biological process that occurs in all organisms and involves a decline in cell functions. This process is caused by molecular regulatory machinery alterations, and it is closely related to telomere erosion in chromosomes. In the context of the immune system, this phenomenon is known as immunosenescence and refers to the immune function deregulation. Therefore, functions of several cells involved in the innate and adaptive immune responses are severely compromised with age progression (e.g., changes in lymphocyte subsets, decreased proliferative responses, chronic inflammatory states, etc.). These alterations make elderly individuals prone to not only infectious diseases but also to malignancy and autoimmunity. This review will explore the molecular aspects of processes related to cell aging, their importance in the context of the immune system, and their participation in elderly SLE patients.

Long-term culture in vitro impairs the immunosuppressive activity of mesenchymal stem cells on T cells

Improved knowledge of the immunological properties of mesenchymal stem cells (MSCs) creates a potential cell-mediated immunotherapeutic approach for arthritic diseases. The low frequency of MSCs necessitates their in vitro expansion prior to clinical use. As sequential passage has been used as the most popular strategy for expansion of MSCs, the effect of long-term culture on the immunological properties of MSCs is not clear. In this study, we observed that the morphology of MSCs showed the typical characteristics of the Hayflick model of cellular aging during sequential expansion. The growth kinetics of MSCs decreased while the number of MSCs staining positive for SA β-gal (senescence marker) increased in long-term culture. Although long-term culture exerts less of an effect on the immunophenotype of MSCs, the immunosuppressive effects of MSCs on the allogeneic T-cell proliferation, activation-antigen expression (CD69 and CD25) and cytokine production (IFN-γ, TNF-α, IL-10) were significantly impaired following stimulation with phytohemagglutinin (PHA).

Mechanisms of immunosenescence: lessons from models of accelerated immune aging

With increasing age, the ability of the adaptive immune system to respond to vaccines and to protect from infection declines. In parallel, the production of inflammatory mediators increases. While cross-sectional studies have been successful in defining age-dependent immunological phenotypes, studies of accelerated immune aging in human subpopulations have been instrumental in obtaining mechanistic insights. The immune system depends on its regenerative capacity; however, the T cell repertoire, once established, is relatively robust to aging and only decompensates when additionally stressed. Such stressors include chronic infections such as CMV and HIV, even when viral replication is controlled, and autoimmune diseases. Reduced regenerative capacity, chronic immune activation in the absence of cell exhaustion, T cell memory inflation, and accumulation of highly potent effector T cells in these patients synergize to develop an immune phenotype that is characteristic of the elderly. Studies of accelerated immune aging in autoimmune diseases have identified an unexpected link to chronic DNA damage responses that are known to be important in aging, but so far had not been implicated in immune aging.

The number of elevated cytokines and chemokines in preclinical seropositive rheumatoid arthritis predicts time to diagnosis in an age-dependent manner

OBJECTIVE

To evaluate levels of biomarkers in preclinical rheumatoid arthritis (RA) and to use elevated biomarkers to develop a model for the prediction of time to future diagnosis of seropositive RA.

METHODS

Stored samples obtained from 73 military cases with seropositive RA prior to RA diagnosis and from controls (mean 2.9 samples per case; samples collected a mean of 6.6 years prior to diagnosis) were tested for rheumatoid factor (RF) isotypes, anti-cyclic citrullinated peptide (anti-CCP) antibodies, 14 cytokines and chemokines (by bead-based assay), and C-reactive protein (CRP).

RESULTS

Preclinical positivity for anti-CCP and/or ≥2 RF isotypes was >96% specific for future RA. In preclinical RA, levels of the following were positive in a significantly greater proportion of RA cases versus controls: interleukin-1α (IL-1α), IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, IL-15, fibroblast growth factor 2, flt-3 ligand, tumor necrosis factor α, interferon-γ-inducible 10-kd protein, granulocyte-macrophage colony-stimulating factor, and CRP. Also, increasing numbers of elevated cytokines/chemokines were present in cases nearer to the time of diagnosis. RA patients who were ≥40 years old at diagnosis had a higher proportion of samples positive for cytokines/chemokines 5-10 years prior to diagnosis than did patients who were <40 years old at diagnosis (P < 0.01). In regression modeling using only case samples positive for autoantibodies highly specific for future RA, increasing numbers of cytokines/chemokines were predictive of decreased time to diagnosis, and the predicted time to diagnosis based on cytokines/chemokines was longer in older compared with younger cases.

CONCLUSION

Levels of autoantibodies, cytokines/chemokines, and CRP are elevated in the preclinical period of RA development. In preclinical autoantibody-positive cases, the number of elevated cytokines/chemokines is predictive of the time of diagnosis of future RA in an age-dependent manner.

Rejuvenating the immune system in rheumatoid arthritis

In rheumatoid arthritis (RA), the aging process of the immune system is accelerated. Formerly, this phenomenon was suspected to be a consequence of chronic inflammatory activity. However, newer data strongly suggest that deficiencies in maintaining telomeres and overall DNA stability cause excessive apoptosis of RA T cells, imposing proliferative pressure and premature aging on the system. Already during the early stages of their life cycle, and long before they participate in the inflammatory process, RA T cells are lost owing to increased apoptotic susceptibility. A search for underlying mechanisms has led to the discovery of defective pathways of repairing broken DNA and elongating and protecting telomeric sequences at the chromosomal ends. Two enzymatic machineries devoted to DNA repair and maintenance have been implicated. RA T cells fail to induce sufficient amounts of the telomeric repair enzyme telomerase, leaving telomeric ends uncapped and thus susceptible to damage. Of equal importance, RA T cells produce low levels of the DNA repair enzyme ataxia telangiectasia mutated and the complex of nucleoproteins that sense and fix DNA double-strand breaks. The inability to repair damaged DNA renders naive T cells vulnerable to apoptosis, exhausts T-cell regeneration and reshapes the T cell repertoire. Therapeutic attempts to reset the immune systems of patients with RA and prevent premature immunosenescence should include restoration of DNA repair capability.

Deficiency of the DNA repair enzyme ATM in rheumatoid arthritis

In rheumatoid arthritis (RA), dysfunctional T cells sustain chronic inflammatory immune responses in the synovium. Even unprimed T cells are under excessive replication pressure, suggesting an intrinsic defect in T cell regeneration. In naive CD4 CD45RA⁺ T cells from RA patients, DNA damage load and apoptosis rates were markedly higher than in controls; repair of radiation-induced DNA breaks was blunted and delayed. DNA damage was highest in newly diagnosed untreated patients. RA T cells failed to produce sufficient transcripts and protein of the DNA repair kinase ataxia telangiectasia (AT) mutated (ATM). NBS1, RAD50, MRE11, and p53 were also repressed. ATM knockdown mimicked the biological effects characteristic for RA T cells. Conversely, ATM overexpression reconstituted DNA repair capabilities, response patterns to genotoxic stress, and production of MRE11 complex components and rescued RA T cells from apoptotic death. In conclusion, ATM deficiency in RA disrupts DNA repair and renders T cells sensitive to apoptosis. Apoptotic attrition of naive T cells imposes lymphopenia-induced proliferation, leading to premature immunosenescence and an autoimmune-biased T cell repertoire. Restoration of DNA repair mechanisms emerges as an important therapeutic target in RA.

Defective proliferative capacity and accelerated telomeric loss of hematopoietic progenitor cells in rheumatoid arthritis

OBJECTIVE

In rheumatoid arthritis (RA), telomeres of lymphoid and myeloid cells are age-inappropriately shortened, suggesting excessive turnover of hematopoietic precursor cells (HPCs). The purpose of this study was to examine the functional competence (proliferative capacity, maintenance of telomeric reserve) of CD34+ HPCs in RA.

METHODS

Frequencies of peripheral blood CD34+,CD45+ HPCs from 63 rheumatoid factor-positive RA patients and 48 controls matched for age, sex, and ethnicity were measured by flow cytometry. Proliferative burst, cell cycle dynamics, and induction of lineage-restricted receptors were tested in purified CD34+ HPCs after stimulation with early hematopoietins. Telomere sequences were quantified by real-time polymerase chain reaction. HPC functions were correlated with the duration, activity, and severity of RA as well as its treatment.

RESULTS

In healthy donors, CD34+ HPCs accounted for 0.05% of nucleated cells; their numbers were strictly age dependent and declined at a rate of 1.3% per year. In RA patients, CD34+ HPC frequencies were age-independently reduced to 0.03%. Upon growth factor stimulation, control HPCs passed through 5 replication cycles over 4 days. In contrast, RA-derived HPCs completed only 3 generations. Telomeres of RA CD34+ HPCs were age-inappropriately shortened by 1,600 bp. All HPC defects were independent of disease duration, disease activity, and smoking status, and were present to the same degree in untreated patients.

CONCLUSION

In RA, circulating bone marrow-derived progenitor cells were diminished, and concentrations stagnated at levels typical of those in old control subjects. HPCs from RA patients displayed growth factor nonresponsiveness and sluggish cell cycle progression; marked telomere shortening indicated proliferative stress-induced senescence. Defective HPC function independent of disease activity markers suggests bone marrow failure as a potential pathogenic factor in RA.

Duration of preclinical rheumatoid arthritis-related autoantibody positivity increases in subjects with older age at time of disease diagnosis

OBJECTIVES

To investigate factors that may influence the prevalence and timing of appearance of rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies during the preclinical phase of rheumatoid arthritis (RA) development.

METHODS

243 serial prediagnosis serum samples from 83 subjects with RA were examined for the presence of RF and anti-CCP antibodies.

RESULTS

Of the 83 cases, 47 (57%) and 51 (61%) subjects had at least one prediagnosis sample positive for RF or anti-CCP, respectively. Gender and race were not significantly associated with the prevalence or timing of preclinical antibody appearance. Preclinical anti-CCP positivity was strongly associated with the development of erosive RA (odds ratio = 4.64; 95% confidence interval 1.71 to 12.63; p<0.01), but RF was not (p = 0.60). Additionally, as age at the time of diagnosis of RA increased the duration of prediagnosis antibody positivity for RF and anti-CCP increased, with the longest duration of preclinical antibody positivity seen in patients diagnosed with RA over the age of 40. In no subjects did symptom onset precede the appearance of RF or anti-CCP antibodies.

CONCLUSIONS

The period of time that RF and anti-CCP are present before diagnosis lengthens as the age at the time of diagnosis of RA increases. This finding suggests that factors such as genetic risk or environmental exposure influencing the temporal relationship between the development of RA-related autoantibodies and clinically apparent disease onset may differ with age.

The use of stem cells for the treatment of autoimmune diseases

Autoimmune diseases constitute a heterogeneous group of conditions commonly treated with anti-inflammatory, immunosuppressant and immunomodulating drugs, with satisfactory results in most cases. Nevertheless, some patients become resistant to conventional therapy. The use of high doses of drugs in such cases results in the need for bone marrow reconstitution, a situation which has stimulated research into the use of hematopoietic stem cells in autoimmune disease therapy. Stem cell transplantation in such diseases aims to destroy the self-reacting immune cells and produce a new functional immune system, as well as substitute cells for tissue damaged in the course of the disease. Significant results, such as the reestablishment of tolerance and a decrease in the recurrence of autoimmune disease, have been reported following stem cell transplantation in patients with autoimmune disease in Brazil and throughout the world. These results suggest that stem cell transplantation has the potential to become an important therapeutic approach to the treatment of various autoimmune diseases including rheumatoid arthritis, juvenile idiopathic arthritis, systemic lupus erythematosus, multiple sclerosis, systemic sclerosis, Crohn's disease, autoimmune blood cytopenias, and type I diabetes mellitus.

Humanized mouse models for organ-specific autoimmune diseases

Murine models for human autoimmune diseases are an essential tool for studying pathogenesis and for identifying new therapeutic targets. Mice are not the natural disease host, and conventional models have proved to be poor predictors of efficacy and safety in recent trials aiming to translate drug and biologic treatments to humans. Evidently, further steps towards recapitulating human diseases are urgently needed, for example using transgenic predisposing human HLA allele(s) plus T-cell receptor(s) implicated in a representative patient's autoimmune disease. The latest development - humanizing most of the immune system by transplanting human hematopoietic stem cells into severely immunodeficient mice - should lead to even better modeling.

Rheumatoid arthritis

Therapeutic efficacy of depleting B cells or blocking T-cell costimulation in rheumatoid arthritis (RA) has confirmed the critical pathogenic role of adaptive immune responses. Yet, RA preferentially affects elderly individuals, in whom adaptive immunity to exogenous antigens begins to fail. Here, we propose that senescence of the immune system is a risk factor for RA, with chronic inflammation resulting from the accumulation of degenerate T cells that have a low threshold for activation and utilize a spectrum of novel receptors to respond to microenvironmental cues. The process of immunosenescence is accelerated in RA and precedes the onset of disease, the acceleration, in part, being conferred by the HLA-DR4 haplotype. Naive CD4(+) T cells in RA are contracted in diversity and restricted in clonal burst. Senescence of effector CD4(+) T cells is associated with the loss of CD28 and the de novo expression of KIR2DS2, NKG2D, and CX(3)CR1, all of which function as costimulatory molecules and reduce the threshold for T-cell activation. The synovial microenvironment promotes chronic persistent immune responses by facilitating ectopic lymphoid neogenesis, such as the formation of aberrant germinal centers. With the propensity to develop complex lymphoid architectures and to provide optimal activation conditions for senescent CD4(+) T cells, the synovium becomes a natural target for pathogenic immune responses in prematurely aged individuals.

T cell costimulation by fractalkine-expressing synoviocytes in rheumatoid arthritis

OBJECTIVE

Patients with rheumatoid arthritis (RA) accumulate prematurely aged T cells that have acquired a new profile of regulatory receptors. Many of the de novo-expressed receptors are typically found on natural killer cells, including CX(3)CR1, the receptor for the chemokine fractalkine (FKN). This study explored whether interactions between CX(3)CR1 and FKN are relevant for T cell functions in rheumatoid synovitis.

METHODS

FKN expression was examined by real-time polymerase chain reaction and immunohistochemistry. CX(3)CR1 expression on peripheral blood T cells was analyzed by flow cytometry. T cell activation was quantified by determining proliferative responses, interferon-gamma (IFNgamma) secretion, and granule release. Fibroblast-like synoviocyte (FLS)/T cell adhesion was measured by the retention of 5-carboxyfluorescein diacetate succinimidyl ester-labeled T cells on FLS monolayers.

RESULTS

FKN was expressed on cultured synovial fibroblasts and hyperplastic synoviocytes in the rheumatoid tissue. Among CD4+ T cells, only senescent CD28- T cells were positive for CX(3)CR1 (P < 0.001). Such CD4+,CD28-,CX(3)CR1+ T cells strongly adhered to FLS, with soluble FKN blocking the interaction. FKN expressed on FLS costimulated T cell-activating signals and amplified proliferation, IFNgamma production, and expulsion of cytoplasmic granules.

CONCLUSION

Senescent CD4+ T cells that accumulate in rheumatoid arthritis aberrantly express CX(3)CR1. FKN, which is membrane-anchored on synoviocytes, enhances CD4+ T cell adhesion, provides survival signals, and costimulates the production of proinflammatory cytokines as well as the release of granules. By virtue of their altered receptor profile, senescent CD4+ T cells receive strong stimulatory signals from nonprofessional antigen-presenting cells in the synovial microenvironment.