Main

Cellular senescence is a stress response program characterized by stable cell cycle arrest1,2 and the production of the senescence-associated secretory phenotype (SASP), which includes pro-inflammatory cytokines and matrix remodeling enzymes3. In physiological conditions in young individuals (for example, wound healing, tumor suppression), the SASP contributes to the recruitment of immune cells, whose role is to clear the senescent cells and facilitate restoration of tissue homeostasis3. However, during aging, the combination of increased tissue damage and decreased function of the immune system leads to the accumulation of senescent cells4,5, thereby generating a chronic pro-inflammatory milieu that leads to a range of age-related tissue pathologies6,7,8,9. As such, senolytic strategies to eliminate senescent cells from aged tissues have the potential to dramatically improve healthspan.

Most efforts to develop senolytic therapies have focused on the development of small-molecule drugs that target poorly defined molecular dependencies present in senescent cells and that must be administered repeatedly over time10. In contrast, CAR T cells are a form of cellular therapy that redirects T cell specificity toward cells expressing a specific cell-surface antigen11. Unlike small molecules, CAR T cells only require that the target antigen is differentially expressed on target cells compared to normal tissues; moreover, as ‘living drugs’, these therapeutics have the potential to persist and mediate their potent effects for years after single administration12. We have shown that CAR T cells targeting the cell-surface protein uPAR, which is upregulated on senescent cells, can efficiently deplete senescent cells in young animals and reverse liver fibrosis. Here, we explore whether CAR T cells could safely and effectively eliminate senescent cells in aged mice and modulate healthspan.

Results

uPAR is upregulated in physiological aging

uPAR promotes remodeling of the extracellular matrix during fibrinolysis, wound healing and tumorigenesis13. In physiological conditions, it is primarily expressed in certain subsets of myeloid cells and, at low levels, in the bronchial epithelium14. We recently described the upregulation of uPAR on senescent cells across different cell types and multiple triggers of senescence14 and showed that CAR T cells targeting this cell-surface protein could efficiently remove senescent cells from tissues in young mice without deleterious effects to normal tissues14. Given these results, we set out to test whether uPAR might serve as a target for senolytic CAR T cells in aged tissues.

Plasma levels of soluble uPAR positively correlate with the pace of aging in humans15,16 and Plaur (the gene encoding uPAR) is a component of the SenMayo gene signature recently reported to identify senescent cells in aged tissues17. To explore the association with uPAR expression in aged tissues further, we surveyed RNA-sequencing (RNA-seq) data from the Tabula Muris Senis project18. Expression of Plaur was upregulated in several organs in samples from 20-month-old mice compared to 3-month-old mice (Extended Data Fig. 1a). Because mRNA levels are not linearly related to surface protein levels19, we performed immunohistochemistry and indeed confirmed an age-associated increase in uPAR protein in liver, adipose tissue, skeletal muscle and pancreas (Fig. 1a and Extended Data Fig. 1b). This increase in the fraction of uPAR-positive cells was paralleled by an increase in the percentage of senescence-associated beta-galactosidase (SA-β-gal)-positive cells (Extended Data Fig. 1c–f). Co-immunofluorescence revealed that a large majority of these SA-β-gal-expressing cells were in fact uPAR positive, whereas only a minority of these cells were macrophages as evidenced by coexpression of F4/80 (Extended Data Fig. 1g–j).

Fig. 1: uPAR is upregulated on senescent cells in physiological aging.
figure 1

a, Immunohistochemical staining of mouse uPAR in liver, adipose tissue, muscle and pancreas from young (age 3 months) or old (age 20 months) mice (n = 3 per age). bm, Single-cell analysis of uPAR expression and senescence. uPAR-positive and uPAR-negative cells were sorted from the liver, adipose tissue and pancreas of 20-month-old mice and subjected to single-cell RNA-seq by 10x chromium protocol (n = the sequencing of four mice where two females were combined into one replicate and two males were combined into another replicate). b, Uniform manifold approximation and projection (UMAP) visualization of liver cell types. c, UMAP visualization of adipose tissue cell types. d, UMAP visualization of pancreas cell types. e, UMAP visualization of hepatic uPAR-negative and uPAR-positive cell types. f, UMAP visualization of adipose uPAR-negative and uPAR-positive cell types. g, UMAP visualization of pancreatic uPAR-negative and uPAR-positive cell types. h,j,l, UMAP visualizations with senescence signature scores24 in each cell indicated by the color scale. i,k,m, Quantification of the proportion of uPAR-positive and uPAR-negative cells contributing to the respective senescence signature. h,i, Liver; j,k, adipose tissue; l,m, pancreas. Results are from one independent experiment (am). DC, dendritic cell; NK, natural killer; pDC, plasmacytoid dendritic cell; ASPC, adipose progenitor and stem cells.

To add granularity to our understanding of the molecular characteristics of uPAR-positive cells in aged tissues, we performed single-cell RNA sequencing (scRNA-seq) on approximately 4,000–15,000 uPAR-positive and uPAR-negative cells sorted by fluorescence-activated cell sorting (FACS) from the liver, fat and pancreas (Fig. 1b–m and Extended Data Figs. 2 and 3). Using unsupervised clustering and marker-based cell labeling20,21, we identified the major uPAR-positive cell types and cell states present in each of the three organs (Fig. 1b–d and Extended Data Fig. 2). Of note, some minor cell types (for example, hepatic stellate cells in the liver, and beta cells in the pancreas) require specialized isolation procedures and were not captured using our protocol22,23.

Analysis of the different populations for uPAR expression indicated that endothelial and myeloid cells were the most prominent uPAR-expressing populations in the liver (Fig. 1e and Extended Data Fig. 2b), whereas in adipose tissue uPAR was expressed mainly in subsets of preadipocytes, dendritic cells and myeloid cells (Fig. 1f and Extended Data Fig. 2d). In the aged pancreas, uPAR expression was prominent in subsets of endothelial cells, fibroblasts, dendritic cells and myeloid cells (Fig. 1g and Extended Data Fig. 2f). Compared to uPAR-negative cells, uPAR-positive cells were significantly enriched in gene signatures linked to inflammation, the complement pathway and the coagulation cascade as well as transforming growth factor-beta signaling (Extended Data Fig. 3a–c).

Importantly, when senescent cells present in these tissues were identified using two independent transcriptomic signatures of senescence17,24, we observed that the main senescent cell types present in aged tissues were distinct: endothelial and myeloid cells in the liver (Fig. 1h and Extended Data Fig. 3d,g–i), dendritic cells, myeloid cells and preadipocytes in adipose tissue (Fig. 1j and Extended Data Fig. 3e,j–l) and endothelial cells, fibroblasts, dendritic cells and myeloid cells in the pancreas (Fig. 1l and Extended Data Fig. 3f,m–o). Thus, uPAR-positive cells constituted a significant fraction of the senescent cell burden in these tissues (67–90% in liver, 92–66% in adipose tissue and 76–63% in pancreas; Fig. 1i,k,m and Extended Data Fig. 3h,k,n). Note that while our analysis could not evaluate pancreatic beta cells, analysis of published data revealed that expression of Plaur was significantly upregulated in senescent beta cell populations isolated from aged animals and subjected to bulk RNA-seq25.

Finally, to ascertain whether uPAR was expressed in senescent cells that accumulate with age in human tissues, we analyzed available datasets of human pancreas collected from young (0- to 6-year-old) and aged (50- to 76-year-old) individuals26. While we were limited to an analysis of PLAUR transcript abundance in these settings, we found that the fraction of PLAUR-expressing cells was substantially greater in older individuals (Fig. 2).

Fig. 2: Upregulation of uPAR and senescence signatures in aged human pancreas.
figure 2

scRNA-seq data of human pancreas of different ages from ref. 26 were analyzed. a, UMAP visualization of Plaur expression across pancreas cell types in young humans (0–6 years old) and old humans (50–76 years old). b, UMAP visualization of senescence signature expression17 across pancreas cell types in young humans (0–6 years old) and old humans (50–76 years old). c, Quantification of the proportion of uPAR-positive and uPAR-negative cells by cell type and age. d, Quantification of the proportion of cells expressing senescence signature17 or not expressing senescence signature17 by cell type and age.

Overall, these results indicate that the levels of uPAR-positive senescent cells increase with age and that most senescent cells present in aged tissues express uPAR. The fact that we can identify settings in which an increased expression of uPAR protein expression does not correlate with Plaur mRNA levels indicates that the absence of an induction of Plaur transcript levels does not exclude the possibility of an increase in uPAR protein expression.

Effect of uPAR CAR T cells in naturally aged mice

To determine the tolerability and therapeutic activity of uPAR-targeting CAR T cells on physiologically aged mice, we intravenously infused aged C57BL/6 mice (18–20 months old) with our previously developed mouse second-generation CAR T cells targeting mouse uPAR14 (m.uPAR-m.28z). m.uPAR-m.28z CAR T cells contain an anti-mouse uPAR single-chain variable fragment (scFV) linked to mouse CD28 costimulatory and mouse CD3ζ signaling domains and are, therefore, fully mouse CAR T cells that allow for syngeneic studies14. Importantly, the CAR T cells were generated from CD45.1 mice and infused into C57BL/6 mice, which are CD45.2, thus allowing for CAR T cells to be differentiated from endogenous T cells and therefore monitored over time (Fig. 3a). As controls, parallel cohorts of sex- and aged-matched mice were infused with the same dose of either untransduced T (UT) cells or T cells expressing a mouse CAR targeting human CD19 (h.19-m.28z) that does not recognize the mouse CD19 protein but encompasses the exact same signaling structure thus controlling for nonspecific T cell cytotoxicity. We opted to test a dose of 0.5 × 106 CAR-positive cells, which we previously found to balance safety and senolytic efficacy in young animals14.

Fig. 3: uPAR CAR T cells eliminate senescent cells in old mice.
figure 3

a, Experimental scheme for Figs. 35. C57BL/6N mice (18 to 20 months old) were injected with 0.5 × 106 m.uPAR-m.28z CAR T cells, h.19-m.28z CAR T cells or UT cells generated from CD45.1 mice 16 h after administration of cyclophosphamide (200 mg per kg body weight). Mice were harvested 20 d later and/or monitored over time. Schematic created with BioRender.com. b, Representative SA-β-gal and uPAR staining 20 d after cell infusion. c, Heat map depicting fold change in the levels of SASP cytokines compared to UT-treated mice (n = 3 for UT cells; n = 3 for h.19-m.28z; n = 4 for m.uPAR-m.28z). Results are from one experiment (b and c).

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Mice infused with m.uPAR-m.28z CAR T cells, but not controls, showed a reduction in the proportions of SA-β-gal-positive and uPAR-positive cells throughout the tissues examined, most notably in the pancreas, liver and adipose tissue (Fig. 3b and Extended Data Fig. 4). As has been previously reported, our aged mouse cohort displayed elevated levels of pro-inflammatory cytokines linked to the SASP in the peripheral blood, a phenomenon often referred to as ‘inflammaging’27. Consistent with a reduction in senescent cell burden and/or improved organismal health, m.uPAR-m.28z CAR T cell-treated animals showed a decrease in the plasma levels of these factors (Fig. 3c).

Despite detectable expression of uPAR in some normal tissues, our previous work indicates that a dose of 0.5 × 106 m.uPAR-m.28z CAR T cells is well tolerated in young mice14. As was the case in young animals, the dose of 0.5 × 106 m.uPAR-m.28z CAR T cells was well tolerated in aged mice (18–20 months old), all of whom remained active without observable signs of morbidity, weight loss or relevant alterations in serum chemistry or complete blood counts (Fig. 4). In addition, microscopic evaluation of tissues did not reveal tissue damage secondary to toxicity in aged tissues obtained from whole-body necropsies of m.uPAR-m.28z CAR T cell-treated mice when compared to age-matched control-treated animals (Extended Data Fig. 5).

Fig. 4: Safety of uPAR CAR T cells in aged mice.
figure 4

Mice were treated with m.uPAR-m.28z CAR T cells, h.19-m.28z CAR T cells or UT cells as schematized in Fig. 3a. a, Body weight 24 h before and at various times after cell infusion (n = 12 mice for UT; n = 11 for h.19-m.28z; n = 12 for m.uPAR-m.28z). b, Triglyceride levels 20 d after cell infusion (n = 12 mice for UT; n = 11 for h.19-m.28z; n = 13 for m.uPAR-m.28z). c, Cholesterol levels 20 d after cell infusion (n = 12 for UT and for h.19-m.28z; n = 13 for m.uPAR-m.28z). d, Alanine transaminase (ALT) levels 20 d after cell infusion (sample sizes as in c). e, Aspartate aminotransferase (AST) levels 20 d after cell infusion (n = 12 for UT; n = 11 for h.19-m.28z; n = 13 for m.uPAR-m.28z). f, BUN/creatinine ratio 20 d after cell infusion (sample sizes as in c). g, Creatine kinase (CK) 20 d after cell infusion (n = 12 for UT; n = 9 for h.19-m.28z; n = 11 for m.uPAR-m.28z). h, Hemoglobin levels 20 d after cell infusion (n = 11 for UT; n = 11 for h.19-m.28z; n = 10 for m.uPAR-m.28z). i, Platelet numbers 20 d after cell infusion (n = 11 for UT; n = 11 for h.19-m.28z; n = 10 for m.uPAR-m.28z). j, Lymphocyte numbers 20 d after cell infusion (n = 11 for UT; n = 11 for h.19-m.28z; n = 10 for m.uPAR-m.28z). k, Monocyte numbers 20 d after cell infusion (n = 11 for UT; n = 11 for h.19-m.28z; n = 10 for m.uPAR-m.28z). l, Neutrophil numbers 20 d after cell infusion (n = 11 for UT; n = 10 for h.19-m.28z; n = 10 for m.uPAR-m.28z). m, Eosinophil numbers 20 d after cell infusion (n = 11 for UT; n = 11 for h.19-m.28z; n = 10 for m.uPAR-m.28z). Results are from two independent experiments. Data are the mean ± s.e.m.; P values from two-tailed unpaired Student’s t-test (bm).

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One prominent feature of aging in humans and mice is the emergence of age-related metabolic dysfunction, which is a collection of phenotypes linked to impaired glucose tolerance25,28 and decreased exercise capacity29,30. Interestingly, we observed that aged m.uPAR-m.28z CAR T cell-treated mice had significantly decreased fasting glucose levels compared with UT or h.19-m.28z-treated controls (Fig. 5a). Upon challenge with an intraperitoneal bolus of glucose (2 g per kg body weight), m.uPAR-m.28z CAR T cell-treated aged but not young mice presented significantly lower plasma glucose levels than controls for over 2 h after administration (Fig. 5b,c and Extended Data Fig. 6a,b). Furthermore, m.uPAR-m.28z CAR T cell-treated mice had lower basal insulin levels after fasting that was followed by a significant increase in insulin levels 15 min after the glucose load, indicative of improved pancreatic beta cell function (Fig. 5d). Of note, m.uPAR-m.28z CAR T cell-treated aged mice also presented improved peripheral insulin sensitivity, suggesting a coordinated multiorgan improvement in glucose homeostasis (Extended Data Fig. 6c,d). In addition, most aged mice with m.uPAR-m.28z CAR T cells showed improvements in their exercise capacity at 2.5 months after treatment compared to pretreatment levels (Fig. 5e,f).

Fig. 5: uPAR CAR T cells revert natural age-associated phenotypes.
figure 5

Mice were treated with m.uPAR-m.28z CAR T cells, h.19-m.28z CAR T cells or UT cells as schematized in Fig. 3a. a, Levels of basal glucose (mg ml−1) after starvation 2.5 months after cell infusion (n = 11 mice for UT; n = 12 for h.19-m.28z and for m.uPAR-m.28z). b, Levels of glucose before (0 min) and after intraperitoneal administration of glucose (2 g per kg body weight) 2.5 months after cell infusion (samples sizes as in a). c, Area under the curve (AUC) representing the results from b. Each point represents a single mouse. d, Levels of insulin before and 15 min after intraperitoneal glucose administration (2 g per kg body weight) 2.5 months after cell infusion (n = 6 for UT; n = 5 for h.19-m.28z; n = 6 for m.uPAR-m.28z). e, Fold change in time to exhaustion in exercise capacity testing before cell infusion and 2.5 months after it (n = 7 for UT; n = 8 for h.19-m.28z and n = 8 for m.uPAR-m.28z). f, Fold change in maximum speed in capacity testing before cell infusion and 2.5 months after it (sample sizes as in e). g,h, Percentage of CD45.1+ T cells in the spleen (g) or liver (h) of 4-month-old or 20-month-old mice 20 d after cell infusion (n = 3 mice per age group for UT and for h.19-m.28z; n = 4 for m.uPAR-m.28z). The corresponding flow cytometry gating is shown in Extended Data Fig. 10. Results are from two independent experiments (ac, e and f) or one experiment (d, g and h). Data are the mean ± s.e.m.; P values from two-tailed unpaired Student’s t-test (a, c, d, g and h) or two-tailed Mann–Whitney test (e and f).

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Importantly, the improvement in metabolic function noted in m.uPAR-m.28z CAR T cell-treated old mice was accompanied by an expansion of m.uPAR-m.28z CAR T cells and their trafficking to several organs such as liver and spleen as assessed by flow cytometry (Fig. 5g,h). These m.uPAR-m.28z CAR T cells were mostly cytotoxic CD8+T cells in the livers and CD4+T cells in the spleen and presented an effector phenotype indicative of their activated response (Extended Data Fig. 7a–d). Of note, this expansion did not occur in aged-matched UT or h.19-m.28z-treated controls and was lower in m.uPAR-m.28z CAR T cell-treated young mice, results that were consistent with the lower fraction of uPAR-positive cells in younger animals (Figs. 1a and 5g,h and Extended Data Fig. 1).

Collectively, these results show that uPAR CAR T cells can safely and effectively remove senescent uPAR-positive cells in the tissues of naturally aged mice and ameliorate age-dependent metabolic and physical dysfunction.

Persistence and prophylaxis by uPAR CAR T cells in aging

Unlike small molecules, CAR T cells can persist in the organism and exert their effects over time12. Indeed, in human cancer patients cured of disease, the presence of CAR T cells has been noted as much as 10 years after the initial infusion12. Such persistence raises the question of whether the administration of uPAR CAR T cells in young animals would prevent or delay the development of age-triggered phenotypes later in life. To explore this possibility, we infused young mice (3 months old) with one dose of 0.5 × 106 m.uPAR-m.28z CAR T, h.19-m.28z CAR T or UT cells and monitored the mice over their natural lifespan (Fig. 6). Despite the initially lower numbers of uPAR-positive cells compared to aged animals (see above), uPAR CAR T cells were detectable in the spleens and livers of treated mice 12 months after the initial single infusion at substantially higher levels than the low number of persisting UT or h.19 CAR T controls (Fig. 6a,b). Consistent with their persistent activity, flow cytometry of the spleen and livers of uPAR CAR T cell-treated mice indicated that the persisting cells were mostly cytotoxic CD8+ T cells harboring a memory and effector phenotype in the spleens (Extended Data Fig. 7e–h). Therefore, uPAR CAR T cells persist and expand over the lifespan of the animal, presumably owing to increased antigen stimulation as the frequency of target uPAR-positive cells increases over time.

Fig. 6: uPAR CAR T cells prevent natural age-associated phenotypes.
figure 6

Three- to four-month-old C57BL/6N mice were injected with 0.5 × 106 m.uPAR-m.28z CAR T cells, h.19-m.28z CAR T cells or UT cells generated from CD45.1 mice 16 h after administration of cyclophosphamide (200 mg per kg body weight). Mice were monitored over time and/or harvested at 15 months of age. a,b, Percentage of CD45.1+ T cells in the spleen (a) or liver (b) of 15-month-old mice 12 months after cell infusion (n = 3 mice per group). c, Levels of basal glucose after starvation 15–18 months after cell infusion (n = 11 mice for UT cells; n = 12 for h.19-m.28z and for m.uPAR-m.28z). d, Levels of glucose before (0 min) and after intraperitoneal administration of glucose (2 g per kg body weight) 15–18 months after cell infusion (sample sizes as in c). e, AUC representing the results from d. Each point represents a single mouse. f, Levels of insulin (ng ml−1) before and 15 min after intraperitoneal glucose (2 g per kg body weight) 15 months after cell infusion (n = 6 for UT cells; n = 6 for h.19-m.28z; n = 7 for m.uPAR-m.28z). g, Time to exhaustion in exercise capacity testing 6 months after cell infusion (n = 9 for UT cells; n = 7 for h.19-m.28z; n = 12 for m.uPAR-m.28z). h, Maximum speed (m min−1) in capacity testing 6 months after cell infusion (sample sizes as in g). i, Representative staining of SA-β-gal and uPAR 15 months after cell infusion. Results are from one independent experiment (a, b, f and i) or two independent experiments (ce, g and h). Data are the mean ± s.e.m.; P values from two-tailed unpaired Student’s t-test (ac, e and f) or two-tailed Mann–Whitney test (g and h).

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As was observed in aged animals upon therapeutic treatment, prophylactic uPAR CAR T cell administration in young mice limited metabolic decline in old age. Specifically, uPAR CAR T cell-treated mice had significantly lower fasting glucose levels (Fig. 6c), improved glucose tolerance (Fig. 6d,e) and enhanced pancreatic beta cell function as assessed by glucose-stimulated insulin secretion (Fig. 6f) than mice treated with either UT or h.19-m.28z. In terms of fitness, mice that in their youth had been treated with m.uPAR-m.28z CAR T cells, compared with control-treated mice, showed higher exercise capacity at 9 months of age (Fig. 6g,h), although this waned over time (Extended Data Fig. 7i,j). These phenotypes correlated with a significant decrease in both SA-β-gal-positive and uPAR-positive cells in pancreas, liver and adipose tissue (Fig. 6i and Extended Data Fig. 7k–p). Taken together, these results show that uPAR CAR T cells can not only treat, but also prevent, features of age-dependent metabolic decline.

uPAR CAR T cells to treat or prevent metabolic syndrome

Many of the features associated with metabolic syndrome in aged mice can be recapitulated in young animals given a high-fat diet (HFD)31 and, indeed, obesity has been described to accelerate the ‘aging clock’32. As in aged animals, such treatment leads to the accumulation of senescent cells25 (Extended Data Fig. 8a–d). To test the therapeutic potential of uPAR CAR T cells in this context, we modeled metabolic syndrome by feeding mice an HFD, which induces obesity and metabolic stress33. After 2 months on an HFD, mice were treated with 0.5 × 106 m.uPAR-m.28z CAR T or UT cells and continued on the diet (Fig. 7a). At 20 d after infusion, mice treated with uPAR CAR T cells displayed significantly lower body weight, better fasting blood glucose levels and improvements in both glucose and insulin tolerance compared to controls (Fig. 7b–g). This therapeutic effect persisted through the period of monitoring (2.5 m after cell infusion) and was accompanied by decreased senescent cell burden in pancreas, liver and adipose tissue as assessed by SA-β-gal (Fig. 7h,i and Extended Data Fig. 8e–h). Thus, uPAR CAR T cell therapy produced a similar improvement to metabolic dysfunction in the context of metabolic syndrome in young animals as was observed in naturally aged mice.

Fig. 7: uPAR CAR T cells are therapeutic and preventive in metabolic syndrome.
figure 7

a, Experimental scheme for bi. Three-month-old C57BL/6N mice were treated with an HFD for 2 months followed by intravenous infusion with 0.5 × 106 m.uPAR-m.28z or UT cells 16 h after administration of cyclophosphamide (200 mg per kg body weight). Mice were euthanized 1 month later or monitored over time. b, Body weight 1 month after cell infusion (n = 10 mice per group). c, Basal glucose levels after starvation at 1 month after cell infusion (n = 10 mice per group). d, Glucose levels before (0 min) and after intraperitoneal administration of glucose (1 g per kg body weight) 1 month after cell infusion (n = 10 mice per group). e, AUC representing the results from d. f, Glucose levels before (0 min) and after intraperitoneal administration of insulin (0.5 units per kg body weight) 1 month after cell infusion (n = 4 mice per group). g, AUC representing the results from f. Each point represents a single mouse. h, Glucose levels before (0 min) and after intraperitoneal glucose administration (1 g per kg body weight) 2.5 months after cell infusion (n = 3 mice per group). i, AUC representing the results from h. Each point represents a single mouse. j, Experimental scheme for kp. Three-month-old C57BL/6N mice were intravenously infused with 0.5 × 106 m.uPAR-m.28z or UT cells 16 h after administration of cyclophosphamide (200 mg per kg body weight). At 1.5 months after infusion, mice were placed on an HFD, then euthanized 2 months later or monitored over time. k, Body weight at 3.5 months after cell infusion (n = 20 mice per group). l, Basal glucose levels after starvation 3.5 months after cell infusion (n = 20 mice per group). m, Levels of glucose before (0 min) and after intraperitoneal administration of glucose (1 g per kg body weight) 1 month after cell infusion (n = 20 mice per group). n, AUC representing the results from m. o, Glucose levels before (0 min) and after intraperitoneal glucose administration (1 g per kg body weight) 5.5 months after cell infusion (n = 5 mice per group). p, AUC representing the results from o. Each point represents a single mouse (ap). Results are from two independent experiments (be and kn) or one independent experiment (fi, o and p). Data are the mean ± s.e.m.; P values derived from two-tailed unpaired Student’s t-test (b, c, e, g, i, k, l, n and p). Schematics were created with BioRender.com.

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To test whether prophylactic administration of uPAR CAR T cells could impede the development of metabolic disorders in young mice given an HFD, we administered 0.5 × 106 m.uPAR-m.28z CAR T cells 1.5 months before placement on an HFD (Fig. 7j). Remarkably, m.uPAR-m.28z CAR T cells (but not treatment with UT cells) acted prophylactically to blunt the accumulation of senescent cells over time, an effect that was also associated with decreased weight gain and glucose levels 3.5 months after infusion (Extended Data Fig. 8i–l and Fig. 7k–n). At this time, m.uPAR-m.28z CAR T cells were detectable and enriched in the spleens and livers of treated mice, where they again were composed mostly of CD8+ T cells with an effector phenotype (Extended Data Fig. 9). This preventive effect on metabolic dysfunction was sustained for at least 5.5 months after cell infusion despite continuous exposure to an HFD (Fig. 7o,p).

Overall, these data highlight the contribution of uPAR-positive cells to metabolic dysfunction in aged and obese mice and raise the possibility that targeting these cells through CAR T cells could have therapeutic benefit in humans.

Discussion

Our study provides proof-of-principle evidence that senolytic cell therapies can ameliorate symptoms associated with physiological aging. We previously showed that uPAR-targeting CAR T cells could safely and effectively eliminate senescent cells in the livers of young animals14. Here, focusing on metabolic dysfunction as one prominent age-related pathology, we show that: (i) the fraction of uPAR-positive cells increases with age; (ii) these cells significantly contribute to the senescence burden in aged tissues; (iii) uPAR-positive cells with senescence signatures consist of both immune and non-immune populations, the latter consisting of a range of cell types that are organ dependent; (iv) uPAR CAR T cells can be effective at eliminating uPAR-positive senescent cells; (v) their effect is not associated with pathology in tissues or alterations of hepatic and renal functional parameters in aged mice; and finally, (vi) the action of uPAR CAR T cells is associated with improved glucose homeostasis and metabolic fitness in both physiological aging and HFD feeding. Importantly, at doses used to produce these therapeutic benefits, we noted no overt toxicities of uPAR CAR T cells, which could persist and expand for over 15 months as mice progressed from a youthful to an aged state.

Perhaps the most striking observation of the current work was the ability of uPAR CAR T cells to act prophylactically to blunt age-induced and diet-induced metabolic decline. Unlike senolytic approaches based on small molecules, uPAR CAR T cells have long-lasting effects after the administration of a single low dose, causing a marked impairment in age-induced or HFD-induced metabolic syndrome when mice were treated during youth or administration of HFD, respectively. Our findings are consistent with those of an earlier study that explored vaccination against GPNMB on senescent cells to address age-related pathology34, although with our cellular therapy, both effect sizes and duration were substantially larger. In fact, our results demonstrate a protective effect for over a year in the context of physiological aging in the laboratory mouse, a species with an average lifespan of around 2 years.

Studies using genetic or pharmacological approaches to senolysis have been equivocal as to whether elimination of senescent cells will significantly extend longevity29,30,35. Our current studies are not sufficiently powered to draw conclusions on longevity at this stage. As senescent cells contribute to a range of age-related tissue pathologies, studying the impact of senolysis in aged animals provides an opportunity to interrogate multiple comorbidities under similar conditions. Future studies will evaluate the potential of uPAR CAR T cells (or other senolytic cell therapies) in additional aging and related tissue-damage pathologies, the latter disease contexts providing a more likely starting point for clinical implementation.

It remains to be determined which of the uPAR-positive cell populations targeted by uPAR CAR T cells are responsible for the improved metabolic function we observe. In other senolytic studies, the elimination of senescent pancreatic beta cells has been linked to improved glucose tolerance25. However, there are reports suggesting that targeting senescent cells in adipose tissue28 or even immune cell senescence36 may also play a role. In this regard, recent studies suggest that the elimination of macrophage populations with senescent features can also improve tissue decline in mice37,38. Whether or not these macrophages are truly ‘senescent’ or have an alternative cell state is a topic of debate; regardless, given that we observe a fraction of uPAR-expressing macrophages that also coexpress SA-β-gal and senescence-associated transcriptional signatures accumulating in aged tissues, it seems likely that their elimination contributes to the phenotypes we observe.

While the mechanism of action of most current small molecules is often inferred or poorly understood, senolytic CAR T cells have a clear underlying rationale based on the expression of a specific surface antigen. While toxicity issues are invariably a concern, cellular therapy harbors the versatility to simultaneously target several surface antigens through AND gate approaches11, modulate persistence through different CAR designs39 and/or incorporate safety switches40, all of which provide avenues to mitigate side effects that are not possible through vaccination strategies or small-molecule approaches40. Indeed, another recent report reveals that mice and primates tolerate CAR T cells that target a natural killer cell ligand that is upregulated on senescent cells and other cell types41. Taken together, these efforts could result in the identification of tissue-specific senolytic antigens that could be targeted with cellular therapy to treat different age-related phenotypes. The persistence of the uPAR-targeted CAR T cells and the durability of the effects after a single low-dose treatment highlight the clinical potential of the senolytic CAR T cell approach for the treatment of chronic pathologies.

Methods

Mice

All mouse experiments were approved by the MSKCC and/or CSHL Internal Animal Care and Use Committee (animal protocol 11-06-011 at MSKCC and 21-4 at CSHL). All relevant animal use guidelines and ethical regulations were followed. Mice were maintained under specific pathogen-free conditions. Housing was on a 12-h–12-h light–dark cycle under standard temperature and humidity of approximately 18–24 °C and 40–60%, respectively. The following mice were used: 3- to 4-month-old C57BL/6 mice (purchased from Charles River), 18-month-old C57BL/6 mice (obtained from the National Institute of Aging) and 6-week-old B6.SJL-Ptrca/BoyAiTac (CD45.1) mice (purchased from Taconic). Mice of both sexes were used at 8–12 weeks of age and 18–20 months of age for the aging experiments, males of 8–12 weeks old for the HFD experiments and females of 6–10 weeks old for T cell isolation. Mice were kept in group housing. Mice had free access to food and water except during the starvation period before glucose or insulin tolerance testing. Aging mice were fed a normal diet (PicoLab Rodent Diet 20, LabDiet), mice on the HFD experiments were fed an HFD (TD.06414, 60% of kcal from fat; Envigo).

Flow cytometry

For in vivo sample preparation, livers were dissociated using the MACS liver dissociation kit (Miltenyi Biotec, 130-1-5-807), filtered through a 100-μm strainer and washed with PBS, and red blood cells were lysed by an ammonium–chloride–potassium (ACK) lysing buffer (Lonza). Cells were washed with PBS, resuspended in FACS buffer and either used for immediate analysis or fixed with Fixation Buffer (BD Biosciences, 554655) according to the manufacturer’s instructions and used for later analysis. Spleens were mechanically disrupted with the back of a 5-ml syringe, filtered through a 40-μm strainer and washed with PBS and 2 mM EDTA; then red blood cells were lysed by ACK lysing buffer (Lonza). Gonadal adipose tissue was dissociated as described42. In short, adipose tissue was isolated and placed in a digestion solution consisting of 4 mg ml−1 collagenase, type II (Sigma) in DPBS (Life Technologies) supplemented with 0.5% BSA (Sigma) and 10 mM CaCl2 digested at 37 °C for 20 min in a rotational shaker. Afterwards, samples were mechanically dissociated with a 10-ml serological pipette, filtered through a 40-μm strainer and washed with PBS and 2 mM EDTA; then red blood cells were lysed by ACK lysing buffer (Lonza). Pancreata were placed into cold DMEM with 10% FBS and penicillin and streptomycin. The pancreata were minced in this media on ice into 2- to 4-mm fragments so that they would pass through the end of a 1-ml pipette tip with ease. The minced tissue was collected in a 15-ml Falcon tube and dissociated in 100 mg ml−1 Dispase (Life Technologies, 17105041), 20 mg ml−1 collagenase P (Roche, 11249002001) and 1 mM EDTA for 20 min on a heated rocker at 37 °C (Eppendorf). After 20 min, 5 ml of DMEM with 10% FBS was added to quench the reaction. The supernatant was removed and filtered through a 100-µm filter (VWR). Next, 5 ml of dissociation media consisting of 100 mg ml−1 Dispase (Life Technologies, 17105041), 20 mg ml−1 collagenase P (Roche, 11249002001) and 1 mM EDTA was added before replacing the 15-ml tube into the heated rocker for 20 min. The reaction was quenched again after 20 min with media and filtered via a 100-µm filter. The dissociated cells were spun at 500 r.c.f. for 10 min in a swinging-bucket centrifuge. The supernatant was discarded, and the cells were resuspended in ACK lysis buffer for 2–4 min in ice. Cells were washed with PBS, resuspended in FACS buffer and either used for immediate analysis or fixed with Fixation Buffer (BD Biosciences, 554655) and used for later analysis.

Fc receptors were blocked using FcR blocking reagent, mouse (Miltenyi Biotec). The following fluorophore-conjugated antibodies were used in the indicated dilutions: Myc-tag AF647 (clone 9B11, Cell Signaling Technology, 2233S, 25; 1:50 dilution), m.CD45.1 BV785 (clone A20, BioLegend, 110743, B347719; 1:100 dilution), m.CD45.2 BV785 (clone 104, BioLegend, 109839, B343292; 1:100 dilution), mCD3 AF488 (clone 17A2, BioLegend, 100210, B284975; 1:100 dilution), mCD4 BUV395 (clone GK1.5, BD, 563790, 1097734; 1:50 dilution), mCD8 PE-Cy7 (clone 53-6.7, BioLegend, 100722, B312604; 1:50 dilution), mCD62L BV421 (clone MEL-14, BioLegend, 104435, B283191; 1:50 dilution), mCD44 APC-Cy7 (clone IM7, BD Pharminogen, 560568, 1083068; 1:100 dilution), mCD3 BV650 (clone 17A2, BioLegend, 100229, B350667; 1:100 dilution), mCD19 BV650 (clone 1D3, BD Biosciences, 563235, 1354015; 1:100 dilution), mNKp46 BV650 (clone 29A1.4, BioLegend, 137635, B298809; 1:100 dilution), mCD11b BUV395 (clone M1/70, BD Biosciences, 563553, 0030272; 1:50 dilution), mLy-6C APC-Cy7 (clone HK1.4, BioLegend, 128026, B375238; 1:100 dilution), mly6G BV605 (clone 1A8, BD Biosciences, 563005, 2144780; 1:100 dilution), m.uPAR AF700 (R&D systems, FAB531N, 1656339; 1:50 dilution), m.uPAR PE (R&D systems, FAB531P, ABLH0722051; 1:50 dilution), mF4/80 PE-eFluor610 (clone BM8, Invitrogen, 61-4801-82, 2338698; 1:100 dilution), 7-AAD (BD, 559925, 9031655; 1:40 dilution) or Ghost UV 450 Viability Dye (13-0868-T100, Tonbo Biosciences, D0868083018133, 1 µl ml−1) was used as viability dye. Flow cytometry was performed on an LSRFortessa instrument (BD Biosciences), FACS was performed on a SONY SH800S cell sorter and data were analyzed using FlowJo (TreeStar).

Single-cell RNA-seq

Sequencing data was demultiplexed, mapped, and processed into gene/cell expression matrices using 10x Genomics’ Cell Ranger software v7.1.0 (https://support.10xgenomics.com/single-cell-gene-expression/software/pipelines/latest/what-is-cell-ranger/). Gene expression reads were aligned to the mouse reference genome version gex-mm10-2020-A, available from the 10x Genomics website. We kept cells using the following parameters: ‘min.cells > 10, nFeature_RNA > 500, nCount_RNA > 2,500, percent.mt < 15’. Gene expression count data were normalized using SCTransform to regress out the percentage of mitochondrial RNA. The R package BBKNN was used to remove batch effects between mouse samples, and 0.5 was used as expression cutoff to define uPAR High cell populations. Clusters were identified using a resolution of 0.8, and cell types were annotated using R packages celldex, SingleR, Azimuth and custom gene sets20,21. Known markers for each cell type were plotted using the DotPlot function in Seurat. Senescence gene sets from refs. 17,24 were used to calculate signature scores using the AddModuleScore function in Seurat, and a signature score cutoff of 0.05 was used to define Senescence High cell populations. Differential expression analysis and functional annotations of gene sets were analyzed in the following way: Differential gene expression analysis was performed by comparing all the uPAR-positive versus uPAR-negative cells using RunPresto in Seurat, and the differentially expressed genes (DEGs) were determined by >1.5-fold change in gene expression with adjusted P value < 0.1. Pathway enrichment analysis was performed using the msigDB Hallmark gene sets using enrichR43. Significance of the tests was assessed using combined score, described as c = log(P) × z, where c is the combined score, P is Fisher’s exact test P value, z is the z-score for deviation from expected rank, and adjusted P values defined by enrichR. A lollipop plot was generated by plotting the top enriched/depleted log2(combined.score) on the x axis (directional), and size and color of the dots represents by −log10(adjusted P value).

Isolation, expansion and transduction of mouse T cells

B6.SJL-Ptrca/BoyAiTac mice (CD45.1 mice) were euthanized and spleens were collected. After tissue dissection and red blood cell lysis, primary mouse T cells were purified using the mouse Pan T cell Isolation Kit (Miltenyi Biotec). Purified T cells were cultured in RPMI-1640 (Invitrogen) supplemented with 10% FBS (HyClone), 10 mM HEPES (Invitrogen), 2 mM l-glutamine (Invitrogen), MEM non-essential amino acids 1× (Invitrogen), 55 µM β-mercaptoethanol, 1 mM sodium pyruvate (Invitrogen), 100 IU ml−1 recombinant human IL-2 (Proleukin; Novartis) and mouse anti-CD3/28 Dynabeads (Gibco) at a bead:cell ratio of 1:2. T cells were spinoculated with retroviral supernatant collected from Phoenix-ECO cells 24 h after initial T cell activation as described in refs. 44,45 and used for functional analysis 3–4 d later.

Genetic modification of T cells

The mouse SFG γ-retroviral m.uPAR-m28z plasmid has been described14. The mouse SFG γ-retroviral h.19-m28z plasmid14 was constructed by stepwise Gibson assembly (New England BioLabs) using the amino acid sequence for the scFv specific for human CD19 of the SFG-1928z backbone46 and cloned into the backbone of the SFG γ-retroviral m.uPAR-m28z plasmid14. In both constructs, the anti-mouse uPAR scFv or anti-human CD19 scFv is preceded by a mouse CD8A leader peptide and followed by the Myc-tag sequence (EQKLISEEDL), mouse CD28 transmembrane and intracellular domain and mouse CD3z intracellular domain44,45. Plasmids encoding the SFGγ retroviral vectors were used to transfect gpg29 fibroblasts (H29) to generate VSV-G pseudotyped retroviral supernatants, which were used to construct stable retrovirus-producing cell lines as described44,46.

Glucose tolerance testing

Blood samples from mice fasted for 8–12 h were collected at 0, 15, 30, 60 and 120 min after intraperitoneal injections of glucose (Sigma-Aldrich; 2 g per kg body weight for aging experiments and 1 g per kg body weight for HFD experiments). Insulin was measured from serum collected at the 0-min and 15-min time points. Concentrations were determined using the UltraSensitive Mouse Insulin ELISA kit (Crystal Chem, 90080).

Insulin tolerance testing

Blood samples from mice fasted for 4 h were collected at 0, 15, 30 and 60 min after intraperitoneal injections of insulin (Humulin R; Eli Lilly; 0.5 units per kg body weight).

Histological analysis

Tissues were fixed overnight in 10% formalin, embedded in paraffin and cut into 5-μm sections. Sections were subjected to H&E staining. Immunohistochemical staining was performed following standard protocols. The following antibodies were used: anti-mouse uPAR (AF534, R&D, DCL0521042; 1:50 dilution) and horse anti-goat IgG (30116; Vector Laboratories, ZH0526). Three fields per section were counted per sample with Fiji-ImageJ and averaged to quantify the percentage of uPAR-positive area per field. SA-β-gal staining was performed as previously described47 at a pH of 5.5 for mouse tissues. Specifically, fresh frozen tissue sections were fixed with 0.5% glutaraldehyde in PBS for 15 min, washed with PBS supplemented with 1 mM MgCl2 and stained for 5–8 h in PBS containing 1 mM MgCl2, 1 mg ml−1 X-gal, 5 mM potassium ferricyanide and 5 mM potassium ferrocyanide. Tissue sections were counterstained with eosin. Three fields per section were counted with ImageJ and averaged to quantify the percentage of SA-β-gal-positive area per field.

Immunofluorescence analysis

For the fluorescent SA-β-gal labeling, tissue slides were exposed to the C12RG substrate at 37 °C according to manufacturer’s instructions (ImaGene Red C12RG lacZ Gene Expression Kit, Molecular Probes, I2906)48,49. Subsequently, for immunofluorescence analysis, slides were fixed with 4% paraformaldehyde for 10 min at room temperature and regular immunofluorescence was performed following standard protocols and those previously described14. The following antibodies were used: anti-mouse uPAR uPAR (AF534,R&D, DCL0521042; 1:50 dilution) and anti-mouse F4/80 (Bio-Rad, CI:A3-1, 155529; 1:100 dilution). For quantification, five high-power fields per section were counted and averaged to quantify the percentage of SA-β-gal+, uPAR+ and F4/80+ per DAPI-positive cells. For colocalization analysis, Pearson coefficient was calculated using ImageJ.

Exercise capacity testing

Exercise capacity was assessed using a motorized treadmill (model 1050 EXER 3/6; Columbus Instruments). For 3 d before testing, mice were acclimatized to the treadmill (the mice walked on the treadmill at 10 m min−1 for 10 to 15 min per day). Following acclimatization, all mice underwent exercise capacity tests on consecutive days. Tests began with mice walking at 10 m min−1 with speed increased by 2 m min−1 every 2 min until exhaustion (mice could no longer achieve treadmill running speed despite repeated encouragement). The primary end points were time to exhaustion and maximum speed.

Blood measurements

Complete blood counts with differentials were performed using an automated hematology analyzer (IDEXX Procyte DX). For serum chemistry, blood was collected in tubes containing a serum separator. The tubes were then centrifuged, and the serum was obtained for analysis. Serum chemistry was performed by the LCP on a Beckman Coulter AU680 analyzer (Beckman Coulter Life Sciences). For cytokine analysis, plasma was collected and samples were processed and measured by Eve Technologies.

Pathology

Mice submitted for postmortem examination were euthanized by CO2 asphyxiation and cardiac exsanguination. Complete necropsies were performed at the Laboratory of Comparative Pathology (MSK, the Rockefeller University, and Weill Cornell Medicine). Representative sections were taken from all organ systems including heart, thymus, lungs, esophagus, trachea, thyroid glands, spleen, pancreas, liver, gallbladder, kidneys, adrenal glands, stomach, duodenum, jejunum, ileum, cecum, colon, lymph nodes (mesenteric and submandibular), salivary glands, skin (trunk and head), urinary bladder, epididymides, testes, prostate, seminal vesicles, uterus, cervix, vagina, ovaries, oviducts, spinal cord, vertebrae, sternum, femur, tibia, stifle joint, skeletal muscle, nerves, skull, nasal cavity, oral cavity, teeth, ears, eyes, pituitary gland and brain. Sections were fixed in 10% neutral-buffered formalin, processed in alcohol and xylene, embedded in paraffin, sectioned (5 μm thick) and stained with H&E. The skull, spinal column, sternum and hindlimb were decalcified in a formic acid and formaldehyde solution (Surgipath Decalcifier I, Leica Biosystems) before processing. H&E-stained tissue sections were evaluated by a board-certified veterinary pathologist (S.E.C.). Representative images were captured using a brightfield BX45 microscope with a DP26 camera and cellSens (version 1.18) Dimension software (Olympus America).

Statistical analysis

Data are presented as the mean ± s.e.m. Statistical analysis was performed by Student’s t-test or Mann–Whitney test using Prism v9.3.1 (GraphPad software). No statistical methods were used to predetermine sample size in the mouse studies, and no randomization method was used to allocate mice to experimental groups. Mouse conditions were observed by an operator who was blinded to the treatment groups in addition to the main investigator who was not blind to group allocation. Pathological analysis and exercise testing studies were performed in a blinded fashion. Data analysis was not performed in a blinded fashion. Data analysis was based on objectively measurable data (cell count, blood tests). No data were excluded except for histological assessment of HFD experiments, where we excluded OCT cassettes of samples containing adipose tissue or pancreas that were folded and presented a morphology that did not allow for successful slide generation; these were not further processed. Data distribution was assumed to be normal, but this was not formally tested. No adjustment for multiple comparisons was performed. The rationale for this was that to increase the rigor of select analyses, two control groups were compared to the experimental group, but it could have been biologically possible to just have one control group. Thus, for any given endpoint, there were two pairwise comparisons: the experiment group separately compared to each control. While two tests were evaluated, we only considered the analysis statistically significant if both tests had a P value less than 0.05. If only one of the two tests was significant, we did not claim the groups were significantly different; instead, we considered the analysis inconclusive and reported a trend. Viewing the analysis as significant only if both P values were less than 0.05 preserves the family-wise error rate at less than 0.05. Figures were prepared using BioRender.com for scientific illustrations in Figs. 3a and 7a,j, GraphPad Prism v9.3.1, and Microsoft Excel v16.77 and Illustrator CC 2022 (Adobe).

Reporting summary

Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.