The Pragmatist roots of scientific medicine: Reassessing Abraham Flexner's report on medical education.

Abraham Flexner's 1910 report on medical education is widely regarded as a watershed moment in the history of modern medicine in the US and beyond. Most commentators focus on its administrative and managerial impact, despite Flexner dedicating a sizeable portion of his report to a theoretical account of the kind of medicine that he seeks to implement. Close attention to these sections reveals a surprisingly coherent account of medicine that, based on a Deweyan Pragmatist philosophy of science, unites scientific investigator and medical practitioner in a new experimental paradigm of science. Flexner can develop an account that goes beyond a mere epistemic redefinition of medicine, providing the profession with a social, cultural, and ethical identity that avails itself of the extremely wide purview that Dewey granted to modern science. Due to the subsequent narrowing of philosophy of science to a delimited academic subdiscipline, these broad Pragmatist philosophical commitments at the roots of Flexner's scientific medicine remained a largely unexplored intellectual legacy.

Transgenic angiotensin-converting enzyme 2 overexpression in the rat vasculature protects kidneys from ageing-induced injury.

Chronic kidney disease is one of the leading causes of morbidity and mortality especially among the aged population. A decline in kidney function with ageing comparable to ageing-related processes in human kidneys has also been described in Sprague-Dawley (SD) rats. The renin-angiotensin-system (RAS) plays a pivotal role in the pathophysiology of cardiovascular and kidney disease and is a successful therapeutic target. The discovery of angiotensin-(1-7) (Ang(1-7)), mainly produced by angiotensin-converting enzyme 2 (ACE2), and its receptor MAS offered a new view on the RAS. This ACE2/Ang(1-7)/MAS axis counteracts most deleterious actions of the RAS in the kidney. In order to evaluate if activation of this axis has a protective effect in ageing-induced kidney disease we generated a transgenic rat model (TGR(SM22hACE2)) overexpressing human ACE2 in vascular smooth muscle cells. These animals showed a specific transgene expression pattern and increased ACE2 activity in the kidney. Telemetric recording of cardiovascular parameters and evaluation of kidney function by histology and urine analysis revealed no alterations in blood pressure regulation and basal kidney function in young transgenic rats when compared to young SD rats. However, with ageing, SD rats developed a decline in kidney function characterized by severe albuminuria which was significantly less pronounced in TGR(SM22hACE2) rats. Concomitantly, we detected lower mRNA expression levels of kidney damage markers in aged transgenic animals. Thus, our results indicate that vascular ACE2-overexpression protects the kidney against ageing-induced decline in kidney function, supporting the kidney-protective role of the ACE2/Ang(1-7)/MAS axis.

Restored TDCA and valine levels imitate the effects of bariatric surgery.

Background: Obesity is widespread and linked to various co-morbidities. Bariatric surgery has been identified as the only effective treatment, promoting sustained weight loss and the remission of co-morbidities. Methods: Metabolic profiling was performed on diet-induced obese (DIO) mice, lean mice, and DIO mice that underwent sleeve gastrectomies (SGx). In addition, mice were subjected to intraperitoneal (i.p.) injections with taurodeoxycholic acid (TDCA) and valine. Indirect calorimetry was performed to assess food intake and energy expenditure. Expression of appetite-regulating hormones was assessed through quantification of isolated RNA from dissected hypothalamus tissue. Subsequently, i.p. injections with a melanin-concentrating hormone (MCH) antagonist and intrathecal administration of MCH were performed and weight loss was monitored. Results: Mass spectrometric metabolomic profiling revealed significantly reduced systemic levels of TDCA and L-valine in DIO mice. TDCA and L-valine levels were restored after SGx in both human and mice to levels comparable with lean controls. Systemic treatment with TDCA and valine induced a profound weight loss analogous to effects observed after SGx. Utilizing indirect calorimetry, we confirmed reduced food intake as causal for TDCA/valine-mediated weight loss via a central inhibition of the MCH. Conclusions: In summary, we identified restored TDCA/valine levels as an underlying mechanism of SGx-derived effects on weight loss. Of translational relevance, TDCA and L-valine are presented as novel agents promoting weight loss while reversing obesity-associated metabolic disorders. Funding: This work has been supported in part by a grant from NIH (UO-1 A1 132898 to S.G.T., DP and MA). M.Q. was supported by the IFB Integrated Research and Treatment Centre Adiposity Diseases (Leipzig, Germany) and the German Research Foundation (QU 420/1-1). J.I. was supported by the Biomedical Education Program (BMEP) of the German Academic Exchange Service (DAAD). T.H. (HE 7457/1-1) and F.K. (KR 4362/1-1) were supported by the German Research Foundation (DFG). H.R.C.B. was supported the Swiss Society of Cardiac Surgery. Y.N. was supported by the Chinese Scholarship Council (201606370196) and Central South University. H.U., T.M. and R.M. were supported by the Osaka Medical Foundation. C.S.F. was supported by the German Research Foundation (DFG, SFB738, B3).

Targeting age-specific changes in CD4+ T cell metabolism ameliorates alloimmune responses and prolongs graft survival.

Age impacts alloimmunity. Effects of aging on T-cell metabolism and the potential to interfere with immunosuppressants have not been explored yet. Here, we dissected metabolic pathways of CD4+ and CD8+ T cells in aging and offer novel immunosuppressive targets. Upon activation, CD4+ T cells from old mice failed to exhibit adequate metabolic reprogramming resulting into compromised metabolic pathways, including oxidative phosphorylation (OXPHOS) and glycolysis. Comparable results were also observed in elderly human patients. Although glutaminolysis remained the dominant and age-independent source of mitochondria for activated CD4+ T cells, old but not young CD4+ T cells relied heavily on glutaminolysis. Treating young and old murine and human CD4+ T cells with 6-diazo-5-oxo-l-norleucine (DON), a glutaminolysis inhibitor resulted in significantly reduced IFN-γ production and compromised proliferative capacities specifically of old CD4+ T cells. Of translational relevance, old and young mice that had been transplanted with fully mismatched skin grafts and treated with DON demonstrated dampened Th1- and Th17-driven alloimmune responses. Moreover, DON diminished cytokine production and proliferation of old CD4+ T cells in vivo leading to a significantly prolonged allograft survival specifically in old recipients. Graft prolongation in young animals, in contrast, was only achieved when DON was applied in combination with an inhibition of glycolysis (2-deoxy-d-glucose, 2-DG) and OXPHOS (metformin), two alternative metabolic pathways. Notably, metabolic treatment had not been linked to toxicities. Remarkably, immunosuppressive capacities of DON were specific to CD4+ T cells as adoptively transferred young CD4+ T cells prevented immunosuppressive capacities of DON on allograft survival in old recipients. Depletion of CD8+ T cells did not alter transplant outcomes in either young or old recipients. Taken together, our data introduce an age-specific metabolic reprogramming of CD4+ T cells. Targeting those pathways offers novel and age-specific approaches for immunosuppression.

CTLA4-Ig prolongs graft survival specifically in young but not old mice.

Elderly organ transplant recipients have remained underrepresented in clinical trials, despite representing a rapidly growing population. Here, we assessed age-specific effects of CTLA4-Ig (cytotoxic T-lymphocyte antigen 4-Ig), a fusion protein blocking costimulatory signaling between antigen-presenting cells and T cells through CD28. Cardiac allografts in young mice (2-3 months) treated with CTLA4-Ig survived indefinitely, whereas 80% of old recipients (18 months) had lost their graft after 100 days. CTLA4-Ig was also significantly less effective in older recipients of skin transplants. CTLA4-Ig reduced CD4+ central memory and effector memory T cells and diminished systemic interferon-gamma levels only in young recipients. These differences corresponded to a reduced expression of CD28 on antigen-experienced CD4+ T cells in old mice. In support, adoptive transfer of old CD4+ T cells that were transfected with a lentiviral vector inducing constant expression of CD28 accelerated the rejection of allogeneic skin grafts in young RAG2-/- recipient mice. Regulatory T cells (Tregs), in contrast, demonstrated an increased expression of CD28 with aging and CTLA4-Ig treatment in old recipients resulted in reduced frequencies, compromised proliferation, and diminished suppressive capacity of Tregs. These findings may prove to have unique clinical consequences for immunosuppression in the growing population of elderly transplant recipients.

Senolytics prevent mt-DNA-induced inflammation and promote the survival of aged organs following transplantation.

Older organs represent an untapped potential to close the gap between demand and supply in organ transplantation but are associated with age-specific responses to injury and increased immunogenicity, thereby aggravating transplant outcomes. Here we show that cell-free mitochondrial DNA (cf-mt-DNA) released by senescent cells accumulates with aging and augments immunogenicity. Ischemia reperfusion injury induces a systemic increase of cf-mt-DNA that promotes dendritic cell-mediated, age-specific inflammatory responses. Comparable events are observed clinically, with the levels of cf-mt-DNA elevated in older deceased organ donors, and with the isolated cf-mt-DNA capable of activating human dendritic cells. In experimental models, treatment of old donor animals with senolytics clear senescent cells and diminish cf-mt-DNA release, thereby dampening age-specific immune responses and prolonging the survival of old cardiac allografts comparable to young donor organs. Collectively, we identify accumulating cf-mt-DNA as a key factor in inflamm-aging and present senolytics as a potential approach to improve transplant outcomes and availability.

Mast cells regulate CD4+ T-cell differentiation in the absence of antigen presentation.

BACKGROUND: Given their unique capacity for antigen uptake, processing, and presentation, antigen-presenting cells (APCs) are critical for initiating and regulating innate and adaptive immune responses. We have previously shown the role of nicotinamide adenine dinucleotide (NAD+) in T-cell differentiation independently of the cytokine milieu, whereas the precise mechanisms remained unknown. OBJECTIVE: The objective of this study is to further dissect the mechanism of actions of NAD+ and determine the effect of APCs on NAD+-mediated T-cell activation. METHODS: Isolated dendritic cells and bone marrow-derived mast cells (MCs) were used to characterize the mechanisms of action of NAD+ on CD4+ T-cell fate in vitro. Furthermore, NAD+-mediated CD4+ T-cell differentiation was investigated in vivo by using wild-type C57BL/6, MC-/-, MHC class II-/-, Wiskott-Aldrich syndrome protein (WASP)-/-, 5C.C7 recombination-activating gene 2 (Rag2)-/-, and CD11b-DTR transgenic mice. Finally, we tested the physiologic effect of NAD+ on the systemic immune response in the context of Listeria monocytogenes infection. RESULTS: Our in vivo and in vitro findings indicate that after NAD+ administration, MCs exclusively promote CD4+ T-cell differentiation, both in the absence of antigen and independently of major APCs. Moreover, we found that MCs mediated CD4+ T-cell differentiation independently of MHC II and T-cell receptor signaling machinery. More importantly, although treatment with NAD+ resulted in decreased MHC II expression on CD11c+ cells, MC-mediated CD4+ T-cell differentiation rendered mice resistant to administration of lethal doses of L monocytogenes. CONCLUSIONS: Collectively, our study unravels a novel cellular and molecular pathway that regulates innate and adaptive immunity through MCs exclusively and underscores the therapeutic potential of NAD+ in the context of primary immunodeficiencies and antimicrobial resistance.

Rapamycin Prolongs Graft Survival and Induces CD4+IFN-γ+IL-10+ Regulatory Type 1 Cells in Old Recipient Mice.

BACKGROUND: Although the elderly represents a rapidly growing population among transplant recipients, age-specific aspects have not been considered sufficiently in clinical trials. Moreover, age-specific effects of immunosuppressive therapies remain poorly understood. METHODS: Here, we assessed the impact of rapamycin on alloimmune responses in old recipients using a fully major histocompatibility complex-mismatched murine transplantation model. RESULTS: Old untreated recipients displayed a prolonged skin graft survival compared to their young counterparts, an observation that confirmed data of our previous experiments. Rapamycin led to a significant prolongation of graft survival in both young and old recipients. However, graft survival was age-dependent and extended in old versus young recipients (19 days vs 12 days, P = 0.004). This age-specific effect was not linked to changes in frequencies or subset composition of either cluster of differentiation (CD)8 or CD4 T cells. Moreover, antiproliferative effects of rapamycin on CD8 and CD4 T cells as assessed by in vivo bromdesoxyuridine incorporation were comparable and age-independent. In contrast, the systemic production of IL-10 was markedly elevated in old recipients treated with rapamycin. In parallel to this shift in cytokine balance, IFN-γ/IL-10 double-positive regulatory type 1 cells emerged during T helper type 1 differentiation of old T helper cells in presence of rapamycin. Similarly, CD4IFN-γIL-10 cells expanded among Foxp3-negative cells after in vivo treatment of old recipients with rapamycin. CONCLUSIONS: Our results highlight novel aspects of age-dependent immunosuppressive effects of rapamycin, with relevance for age-specific immunosuppressive regimens.

Recall features and allorecognition in innate immunity.

Alloimmunity traditionally distinguishes short-lived, rapid and nonspecific innate immune responses from adaptive immune responses that are characterized by a highly specific response initiated in a delayed fashion. Key players of innate immunity such as natural killer (NK) cells and macrophages present the first-line defence of immunity. The concept of unspecific responses in innate immunity has recently been challenged. The discovery of pattern recognition receptors (PRRs) has demonstrated that innate immune cells respond in a semi-specific fashion through the recognition of pathogen-associated molecular patterns (PAMPs) representing conserved molecular structures shared by large groups of microorganisms. Although immunological memory has generally been considered as exclusive to adaptive immunity, recent studies have demonstrated that innate immune cells have the potential to acquire memory. Here, we discuss allospecific features of innate immunity and their relevance in transplantation.

NAD(+) regulates Treg cell fate and promotes allograft survival via a systemic IL-10 production that is CD4(+) CD25(+) Foxp3(+) T cells independent.

CD4(+) CD25(+) Foxp3(+) Tregs have been shown to play a central role in immune homeostasis while preventing from fatal inflammatory responses, while Th17 cells have traditionally been recognized as pro-inflammatory mediators implicated in a myriad of diseases. Studies have shown the potential of Tregs to convert into Th17 cells, and Th17 cells into Tregs. Increasing evidence have pointed out CD25 as a key molecule during this transdifferentiation process, however molecules that allow such development remain unknown. Here, we investigated the impact of NAD(+) on the fate of CD4(+) CD25(+) Foxp3(+) Tregs in-depth, dissected their transcriptional signature profile and explored mechanisms underlying their conversion into IL-17A producing cells. Our results demonstrate that NAD(+) promotes Treg conversion into Th17 cells in vitro and in vivo via CD25 cell surface marker. Despite the reduced number of Tregs, known to promote homeostasis, and an increased number of pro-inflammatory Th17 cells, NAD(+) was able to promote an impressive allograft survival through a robust systemic IL-10 production that was CD4(+) CD25(+) Foxp3(+) independent. Collectively, our study unravels a novel immunoregulatory mechanism of NAD(+) that regulates Tregs fate while promoting allograft survival that may have clinical applications in alloimmunity and in a wide spectrum of inflammatory conditions.

CD11c+ Dendritic Cells Accelerate the Rejection of Older Cardiac Transplants via Interleukin-17A.

BACKGROUND: Organ transplantation has seen an increased use of organs from older donors over the past decades in an attempt to meet the globally growing shortage of donor organs. However, inferior transplantation outcomes when older donor organs are used represent a growing challenge. METHODS AND RESULTS: Here, we characterize the impact of donor age on solid-organ transplantation using a murine cardiac transplantation model. We found a compromised graft survival when older hearts were used. Shorter graft survival of older hearts was independent of organ age per se, because chimeric young or old organs repopulated with young passenger leukocytes showed comparable survival times. Transplantation of older organs triggered more potent alloimmune responses via intragraft CD11c+ dendritic cells augmenting CD4+ and CD8+ T-cell proliferation and proinflammatory cytokine production, particularly that of interleukin-17A. Of note, depletion of donor CD11c+ dendritic cells before engraftment, neutralization of interleukin-17A, or transplantation of older hearts into IL-17A(-/-) mice delayed rejection and reduced alloimmune responses to levels observed when young hearts were transplanted. CONCLUSIONS: These results demonstrate a critical role of old donor CD11c+ dendritic cells in mounting age-dependent alloimmune responses with an augmented interleukin-17A response in recipient animals. Targeting interleukin-17A may serve as a novel therapeutic approach when older organs are transplanted.

Immunosenescence and organ transplantation.

Increasing numbers of elderly transplant recipients and a growing demand for organs from older donors impose pressing challenges on transplantation medicine. Continuous and complex modifications of the immune system in parallel to aging have a major impact on transplant outcome and organ quality. Both, altered alloimmune responses and increased immunogenicity of organs present risk factors for inferior patient and graft survival. Moreover, a growing body of knowledge on age-dependent modifications of allorecognition and alloimmune responses may require age-adapted immunosuppression and organ allocation. Here, we summarize relevant aspects of immunosenescence and their possible clinical impact on organ transplantation.

Obesity and its impact on transplantation and alloimmunity.

Obesity has become an increasing problem in healthcare worldwide with far-reaching consequences. More obese patients with irreversible end-stage organ failure undergo organ transplantation, and organs from obese donors are more frequently used. A growing body of evidence suggests more frequent postoperative complications and inferior patient and graft survival linked to obesity. More recently, adipose tissue has been linked to chronic inflammatory processes potentially impacting alloimmune responses and graft quality.

Impact of immunosenescence on transplant outcome.

Aging affects all compartments of the immune response and has a major impact on transplant outcome and organ quality. Although clinical trials in the aging transplant population remain rare, our current understanding of immunosenescence provides a basis for an age-adapted immunosuppression and organ allocation with the goal to optimize utilization and to improve outcomes in older recipients. From a more general perspective, understanding the mechanisms and consequences of immunosenescence will have a broad impact on immune therapies in and beyond transplantation.

Clinical experience with the ATS 3F stentless aortic bioprosthesis: five years' follow up.

BACKGROUND AND AIM OF THE STUDY: The ATS 3F aortic bioprosthesis is an equine pericardial stentless valve used for aortic valve replacement (AVR). The study aim was to determine the incidence of valve-related events during a five-year follow up period. METHODS: Between 2002 and 2003, a total of 35 patients (mean age 73 +/- 6 years; range 61-86 years) underwent AVR with the ATS 3F valve implanted in the subcoronary position, utilizing a single running suture technique. The mean valve size was 26.0 +/- 1.9 mm. Prior to surgery, all patients were in NYHA class III or IV. The hemodynamic performance of the valve was assessed after one, three, and five years by means of transthoracic echocardiography. Clinical outcome was evaluated by either physical examination or by telephone interviews with the primary care physicians. RESULTS: The total patient follow up was 123 patient-years. Four patients (11%) were lost to follow up. The overall survival was 86%, and none of the deaths was valve-related. Up to five years, no severe structural or non-structural valve dysfunction was identified in the followed patients. Freedom from severe adverse events (SAE) was 89%; the SAE included one permanent and three transient neuroembolic events, but echocardiographic examinations of these patients were unsuggestive for thrombotic depositions on the prosthetic valves. Freedom from endocarditis was 100%. Minimal paravalvular regurgitation was detected in four patients; this was of no clinical importance, and resulted in a 100% freedom from reoperation. The mean transvalvular pressure gradients were 12.9 +/- 6.3, 11.2 +/- 4.2, and 15.2 +/- 5.3 mmHg at one, three, and five years, respectively. The left ventricular mass and NHYA class were each improved significantly during the observation period. The left ventricular geometries showed also a trend towards improvement. CONCLUSION: The ATS 3F aortic valve prosthesis continues to perform with satisfactory hemodynamic results, comparable to those of other pericardial valves. With minimal SAE, the prosthesis demonstrated excellent intermediate-term clinical results and--to date--is proving to be durable.