Alexander Kroemer

Universität Regensburg, Ratisbon, Bavaria, Germany

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Publications (20)68.09 Total impact

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    ABSTRACT: We studied the developmental and functional mechanisms behind NK cell-mediated antitumor responses against metastatic colorectal carcinoma (CRC) in mice. In particular, we focused on investigating the significance of T-box transcription factors and the immunotherapeutic relevance of IL-15 in the development and function of tumor-reactive NK cells. Pulmonary CRC metastases were experimentally seeded via an adoptive i.v. transfer of luciferase-expressing CT26 CRC cells that form viewable masses via an in vivo imaging device; genetically deficient mice were used to dissect the antitumor effects of developmentally different NK cell subsets. IL-15 precomplexed to IL-15 receptor-α was used in immunotherapy experiments. We found that mice deficient for the T-box transcription factor T-bet lack terminally differentiated antitumor CD27(low)KLRG1(+) NK cells, leading to a terminal course of rapid-onset pulmonary CRC metastases. The importance of this NK cell subset for effective antitumor immunity was shown by adoptively transferring purified CD27(low)KLRG1(+) NK cells into T-bet-deficient mice and, thereby, restoring immunity against lung metastasis formation. Importantly, immunity to metastasis formation could also be restored in T-bet-deficient recipients by treating mice with IL-15 precomplexed to IL-15 receptor-α, which induced the development of eomesodermin(+)KLRG1(+) NK cells from existing NK cell populations. Thus, contingent upon their T-bet-dependent development and activation status, NK cells can control metastatic CRC in mice, which is highly relevant for the development of immunotherapeutic approaches in the clinic.
    The Journal of Immunology 01/2014; · 5.52 Impact Factor
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    ABSTRACT: Natural killer cells (NK cells) play a key role in cancer immunosurveillance. However, their activity is highly dependent upon their maturation stage, which in turn relates to organ distribution. Here, we discuss the role of intrinsic master transcription factors and extrinsic IL-15 signaling on NK cell-mediated immune protection against murine pulmonary metastasis.
    Oncoimmunology. 01/2014; 3:e28328.
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    ABSTRACT: Although Th1, Th2, and Th17 cells are thought to be major effector cells in adaptive alloimmune responses, their respective contribution to allograft rejection remains unclear. To precisely address this, we used mice genetically modified for the Th1 and Th17 hallmark transcription factors T-bet and RORγt, respectively, which allowed us to study the alloreactive role of each subset in an experimental transplant setting. We found that in a fully mismatched heterotopic mouse heart transplantation model, T cells deficient for T-bet (prone to Th17 differentiation) versus RORγt (prone to Th1 differentiation) rejected allografts at a more accelerated rate, indicating a predominance of Th17- over Th1-driven alloimmunity. Importantly, T cells doubly deficient for both T-bet and RORγt differentiated into alloreactive GATA-3-expressing Th2 cells, which promptly induced allograft rejection characterized by a Th2-type intragraft expression profile and eosinophilic infiltration. Mechanistically, Th2-mediated allograft rejection was contingent on IL-4, as its neutralization significantly prolonged allograft survival by reducing intragraft expression of Th2 effector molecules and eosinophilic allograft infiltration. Moreover, under IL-4 neutralizing conditions, alloreactive double-deficient T cells upregulated Eomesodermin (Eomes) and IFN-γ, but not GATA-3. Thus, in the absence of T-bet and RORγt, Eomes may salvage Th1-mediated alloimmunity that underlies IL-4 neutralization-resistant allograft rejection. We summarize that, whereas Th17 cells predictably promote allograft rejection, IL-4-producing GATA-3(+) Th2 cells, which are generally thought to protect allogeneic transplants, may actually be potent facilitators of organ transplant rejection in the absence of T-bet and RORγt. Moreover, Eomes may rescue Th1-mediated allograft rejection in the absence of IL-4, T-bet, and RORγt.
    The Journal of Immunology 09/2013; · 5.52 Impact Factor
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    ABSTRACT: An emerging body of evidence suggests a pivotal role of CD3(+) T cells in mediating early ischemia reperfusion injury (IRI). However, the precise phenotype of T cells involved and the mechanisms underlying such T cell-mediated immune responses in IRI, as well as their clinical relevance, are poorly understood. In this study, we investigated early immunological events in a model of partial warm hepatic IRI in genetically targeted mice to study the precise pathomechanistic role of RORγt(+) T cells. We found that unconventional CD27(-)γδTCR(+) and CD4(-)CD8(-) double-negative T cells are the major RORγt-expressing effector cells in hepatic IRI that play a mechanistic role by being the main source of IRI-mediating IL-17A. We further show that unconventional IRI-mediating T cells are contingent on RORγt, as highlighted by the fact that a genetic deficiency for RORγt, or its therapeutic antagonization via digoxin, is protective against hepatic IRI. Therefore, identification of CD27(-)γδTCR(+) and CD4(-)CD8(-) double-negative T cells as the major source of IL-17A via RORγt in hepatic IRI opens new therapeutic options to improve liver transplantation outcomes.
    The Journal of Immunology 06/2013; · 5.52 Impact Factor
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    ABSTRACT: BACKGROUND: Mammalian target of rapamycin (mTOR) inhibitors possess anticancer properties potentially useful in reducing posttransplantation malignancy. Besides controlling tumor-sensitive proliferative and angiogenic effects, mTOR influences transcription factors T-bet and Eomesodermin (Eomes) in CD8 cytotoxic T cells (Tc), which are key in rejecting tumors, and allografts. METHODS: To study the role of mTOR in tumor and transplant immunity in an antigen-specific way, we used T-cell receptor transgenic B6.OTI recipients, B6.OVA.TG donors, and OVA-B16F10 melanoma cells. For tracking color-coded OTI-Tc cells associated with antitumor and alloimmunity in vivo, CD8-OTI transgenic reporter mice were created by crossbreeding DsRed-expressing B6.Nagy mice with B6.OTI mice. RESULTS: The role of mTOR in regulating the differentiation and function of alloreactive Tc cells in vitro was explored by stimulating OTI-Tc cells with ovalbumin-transgenic antigen-presenting cells in the presence of rapamycin or tacrolimus. Rapamycin, but not tacrolimus, induced a pro-antitumor phenotypic shift from CD62LCD44 effector memory Tc cells to CD62LCD44 central memory Tc cells, which featured up-regulated levels of T-bet and Eomes and preserved levels of interferon-γ and perforin. For future investigations, an in vivo model was established whereby DsRedOTI-Tc cells adoptively transferred into B6 mice bearing either a ovalbumin-transgenic mouse skin transplant or OVA-B16F10 tumor could be traced by fluorescence-activated cell sorting analysis as effector or memory Tc cells in transplant and tumor tissues. CONCLUSION: mTOR, but not calcineurin, inhibition spares antitumoral memory Tc cells by distinctively regulating T-bet and Eomes. This finding is now testable in a new tumor transplant model, which incorporates DsRedOTI-Tc cell tracing, opening the way to study the differential effects of immunosuppressants in posttransplantation malignancy.
    Transplantation 12/2012; · 3.78 Impact Factor
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    ABSTRACT: The prognosis of patients suffering from pancreatic cancer is still poor and novel therapeutic options are urgently needed. Recently, the transcription factor signal transducer and activator of transcription 5b (STAT5b) was associated with tumor progression in human solid cancer. Hence, we assessed whether STAT5b might serve as an anticancer target in ductal pancreatic adenocarcinoma (DPAC). We found that nuclear expression of STAT5b can be detected in approximately 50% of DPAC. Blockade of STAT5b by stable shRNA-mediated knockdown showed no effects on tumor cell growth in vitro. However, inhibition of tumor cell motility was found even in response to stimulation with epidermal growth factor or interleukin-6. These findings were paralleled by a reduction of prometastatic and proangiogenic factors in vitro. Subsequent in vivo experiments revealed a strong growth inhibition on STAT5b blockade in subcutaneous and orthotopic models. These findings were paralleled by impaired tumor angiogenesis in vivo. In contrast to the subcutaneous model, the orthotopic model revealed a strong reduction of tumor cell proliferation that emphasizes the meaning of assessing targets in an appropriate microenvironment. Taken together, our results suggest that STAT5b might be a potential novel target for human DPAC.
    Neoplasia (New York, N.Y.) 10/2012; 14(10):915-25. · 5.48 Impact Factor
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    ABSTRACT: Purpose: In this study we investigated the sensitivity of high resolution ultrasound (HRU) in the detection of small liver tumors and its microcirculation in a humanized tumor mouse model (HTM). These mice develop a complete human immune system and human breast cancer growth in the liver which allows the investigation of antibody based immunotherapies under human like conditions. Method: HTM were generated by the co-transplantation of human breast cancer cells and human hematopoietic stem cells. HRU, Doppler sonography (CCDS), contrast enhanced ultrasound (CEUS) and color-coded elastography were performed on all HTM and confirmed by histopathological assessment. Results: Using HRU and CEUS, noncystic solid liver lesions between 2 and 11 mm (mean 3.5 mm) size were detectable in HTM. Granulomatous areas were identified by B-scan imaging, showing areas of higher stiffness in elastography and areas without contrast media uptake in the late phase (CEUS). In addition, CEUS detected capillary microcirculation of benign and malignant liver lesions smaller than 10 mm. Conclusion: Beyond human breast cancer HTM additionally developed small parenchymal liver lesions, which could be characterized by HRU in combination with CEUS and elastography in-vivo. Nevertheless, the defined diagnoses of solid liver lesions less than 5 mm require confirmation by histopathology.
    Clinical hemorheology and microcirculation 09/2012; · 3.40 Impact Factor
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    ABSTRACT: Eosinophilic cholangitis is a rare clinical entity characterised by transmural eosinophilic infiltration of the biliary system. The aetiology of this disease is still unclear. We report on a 49-year-old male patient who presented with symptoms of obstructive jaundice and imaging suggestive for periampullary carcinoma. After partial pancreatoduodenectomy for suspected pancreatic cancer, pathology revealed massive eosinophilic cholecystitis as well as intra- and extrahepatic eosinophilic cholangitis with pseudopolypoid papillary lesions. Our case illustrates the diagnostic pitfalls in eosinophilic cholangitis as careful imaging procedures - optimally interdisciplinary - should be considered and performed in such patients. In conclusion, eosinophilic cholangitis is an uncommon, inflammatory condition that needs to be considered as a differential diagnosis for periampullary malignancies.
    Zeitschrift für Gastroenterologie 08/2012; 50(8):766-70. · 1.41 Impact Factor
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    ABSTRACT: To evaluate a new 2-step technique for obtaining adequate but short-term parenchymal hypertrophy in oncologic patients requiring extended right hepatic resection with limited functional reserve. Patients presenting with primary or metastatic liver tumors often face the dilemma that the remaining liver tissue may not be sufficient. Preoperative portal vein embolization has thus far been established as the standard procedure for achieving resectability. Two-staged hepatectomy was performed in patients who preoperatively appeared to be marginally resectable but had a tumor-free left lateral lobe. Marginal respectability was defined as a left lateral lobe to body weight ratio of less than 0.5. In the first step, surgical exploration, right portal vein ligation (PVL), and in situ splitting (ISS) of the liver parenchyma along the falciform ligament were performed. Computed tomographic volumetry was performed before ISS and before completion surgery. The study included 25 patients with primary liver tumors (hepatocellular carcinoma: n = 3, intrahepatic cholangiocarcinoma: n = 2, extrahepatic cholangiocarcinoma: n = 2, malignant epithelioid hemangioendothelioma: n = 1, gallbladder cancer: n = 1 or metastatic disease [colorectal liver metastasis]: n = 14, ovarian cancer: n = 1, gastric cancer: n = 1). Preoperative CT volumetry of the left lateral lobe showed 310 mL in median (range = 197-444 mL). After a median waiting period of 9 days (range = 5-28 days), the volume of the left lateral lobe had increased to 536 mL (range = 273-881 mL), representing a median volume increase of 74% (range = 21%-192%) (P < 0.001). The median left lateral liver lobe to body weight ratio was increased from 0.38% (range = 0.25%-0.49%) to 0.61% (range = 0.35-0.95). Ten of 25 patients (40%) required biliary reconstruction with hepaticojejunostomy. Rapid perioperative recovery was reflected by normalization of International normalized ratio (INR) (80% of patients), creatinine (84% of patients), nearly normal bilirubin (56% of patients), and albumin (64% of patients) values by day 14 after completion surgery. Perioperative morbidity was classified according to the Dindo-Clavien classification of surgical complications: grade I (12 events), grade II (13 events), grade III (14 events, III a: 6 events, III b: 8 events), grade IV (8 events, IV a: 3 events, IV b: 5 events), and grade V (3 events). Sixteen patients (68%) experienced perioperative complications. Follow-up was 180 days in median (range: 60-776 days) with an estimated overall survival of 86% at 6 months after resection. Two-step hepatic resection performing surgical exploration, PVL, and ISS results in a marked and rapid hypertrophy of functional liver tissue and enables curative resection of marginally resectable liver tumors or metastases in patients that might otherwise be regarded as palliative.
    Annals of surgery 03/2012; 255(3):405-14. · 7.90 Impact Factor
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    ABSTRACT: Mesenchymal stem cells (MSC) are under investigation as a therapy for a variety of disorders. Although animal models show long term regenerative and immunomodulatory effects of MSC, the fate of MSC after infusion remains to be elucidated. In the present study the localization and viability of MSC was examined by isolation and re-culture of intravenously infused MSC. C57BL/6 MSC (500,000) constitutively expressing DsRed-fluorescent protein and radioactively labeled with Cr-51 were infused via the tail vein in wild-type C57BL/6 mice. After 5 min, 1, 24, or 72 h, mice were sacrificed and blood, lungs, liver, spleen, kidneys, and bone marrow removed. One hour after MSC infusion the majority of Cr-51 was found in the lungs, whereas after 24 h Cr-51 was mainly found in the liver. Tissue cultures demonstrated that viable donor MSC were present in the lungs up to 24 h after infusion, after which they disappeared. No viable MSC were found in the other organs examined at any time. The induction of ischemia-reperfusion injury in the liver did not trigger the migration of viable MSC to the liver. These results demonstrate that MSC are short-lived after i.v. infusion and that viable MSC do not pass the lungs. Cell debris may be transported to the liver. Long term immunomodulatory and regenerative effects of infused MSC must therefore be mediated via other cell types.
    Frontiers in Immunology 01/2012; 3:297.
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    ABSTRACT: The immunological impact on antibody-based anticancer therapies remains incompletely understood due to the lack of appropriate animal models for in vivo analysis. Here, we present a novel humanized tumor mouse (HTM) model, generated by concurrent transplantation of human hematopoietic stem cells (HSCs) and human breast cancer cells in neonatal NOD-scid IL2Rγnull mice. Five weeks after intrahepatic transplantation, a functional human immune system was developed in all organs, and, in addition, tumor cells were detectable in lung and bone marrow (early dissemination). After 3 months posttransplant, tumor-cell effusions and macroscopic tumors associated with liver or spleen were found. Furthermore, disseminated cells in different lymphoid and nonlymphoid organs were measurable. Tumor growth was accompanied by specific T-cell maturation and tumor cell-specific T-cell activation. In addition, Natural–Killer cell accumulation and activation were observed in HTM, which was further enhanced upon IL-15 treatment facilitating the possibility of immune cell modulation in, e.g., antibody-dependent cellular cytotoxicity-based immunotherapeutic approaches. This novel mouse model makes it possible to combine transfer of MHC mismatched tumor cells together with human HSCs resulting in a solid coexistence and interaction without evidence for rejection. Overall, humanized tumor mice represent a powerful in vivo model that for the first time permits the investigation of human immune system-related target cancer therapy and resistance.
    International Journal of Cancer 07/2011; 129(9):2194 - 2206. · 6.20 Impact Factor
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    ABSTRACT: Successful liver gene therapy depends on efficient gene transfer techniques and long-lasting gene expression after successful transfer. Over the last decades, important progress has been made with the introduction of viral vectors using animal models, although their use is hampered by a complex and costly preparation compared to the simple and cost-effective preparation of plasmid DNA. These problems become even more critical when considering the application of viral vectors in human gene therapy and gene therapy trials. In a previous study, we were able to show that the hydrodynamics-based gene transfer of plasmid-DNA, containing the adeno-associated-virus specific inverted terminal repeats (AAV-ITR), prolongs gene expression in the liver, although it remained unclear whether plasmid gene transfer could achieve similar expression levels compared to viral-vector gene transfer. Rat livers were transfected in-vivo with AAV-ITR-containing plasmid-DNA using a modified hydrodynamics-based procedure. Expression levels were monitored thereafter and compared with expression levels after viral-vector gene transfer. A high and stable long-term expression was achieved after in vivo transfection of rat livers with AAV-ITR-containing plasmids. The expression course resembled that after AAV-mediated gene transfer, and the expression was at least as high, and lasted as long, compared to recombinant AAV-mediated gene transfer. We consider AAV-ITR-containing plasmids as a simple and cost-effective alternative to recombinant viral vectors, especially for liver-directed gene therapy in rodents. With ongoing progress in gene transfer methods for naked DNA, these plasmids may also become a successful alternative to recombinant viral vectors in human gene therapy.
    The Journal of Gene Medicine 10/2010; 12(10):810-7. · 2.16 Impact Factor
  • Zeitschrift Fur Gastroenterologie - Z GASTROENTEROL. 01/2010; 48(08).
  • Transplantation 01/2010; 90. · 3.78 Impact Factor
  • Journal of Hepatology - J HEPATOL. 01/2008; 48.
  • Transplantation 01/2008; 86. · 3.78 Impact Factor
  • Transplantation 01/2008; 86. · 3.78 Impact Factor
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    ABSTRACT: Cancer is an increasingly recognized problem associated with immunosuppression. Recent reports, however, suggest that the immunosuppressive agent rapamycin has anti-cancer properties that could address this problem. Thus far, rapamycin's effects on immunity and cancer have been studied separately. Here we tested the effects of rapamycin, versus cyclosporine A (CsA), on established tumors in mice simultaneously bearing a heart allograft. In one tumor-transplant model, BALB/c mice received subcutaneous syngenic CT26 colon adenocarcinoma cells 7 days before C3H ear-heart transplantation. Rapamycin or CsA treatment was initiated with transplantation. In a second model system, a B16 melanoma was established in C57BL/6 mice that received a primary vascularized C3H heart allograft. In vitro angiogenic effects of rapamycin and CsA were tested in an aortic ring assay. Results show that CT26 tumors grew for 2 weeks before tumor complications occurred. However, rapamycin protected allografts, inhibited tumor growth, and permitted animal survival. In contrast, CsA-treated mice succumbed to advancing tumors, albeit with a functioning allograft. Rapamycin's antitumor effect also functioned in severe combined immunodeficient BALB/c mice. Similar effects of the drugs occurred with B16 melanomas and primary vascularized C3H allografts in C57BL/6 mice. Furthermore, in this model, rapamycin inhibited the tumor growth-enhancing effects of CsA. Moreover, in vitro experiments showed that CsA promotes angiogenesis by a transforming growth factor-beta-related mechanism, and that this effect is abrogated by rapamycin. This study demonstrates that rapamycin simultaneously protects allografts from rejection and attacks tumors in a complex transplant-tumor situation. Notably, CsA protects allografts from rejection, but cancer progression is promoted in transplant recipients.
    Transplantation 06/2004; 77(9):1319-26. · 3.78 Impact Factor
  • Transplantation 01/2004; 78. · 3.78 Impact Factor
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    ABSTRACT: Sensitized organ transplant recipients face an increased risk of hyperacute rejection (HAR) due to donor major histocompatibility complex (MHC) class I antigen (Ag) preexposure. We recently reported a novel donor-specific strategy to address this problem, whereby soluble donor MHC class I Ag gene therapy prevented HAR of heart allografts in passively sensitized rats. Here, we tested this same approach in presensitized rat recipients with a fully preactivated humoral and cellular immune response. Our gene therapy method involved liposomal transfection of cultured recipient (Lewis-RT1.A(1)) hepatocytes with DNA encoding secretable donor MHC class I Ag, RT1.A(a). Control-transfected or RT1.A(a)-transfected hepatocytes were implanted intrasplenically into Lewis rats presensitized with three skin transplants. Subsequently, antidonor antibody, cytotoxic T lymphocyte (CTL), and helper T lymphocyte (HTL) assays were performed. Additionally, the effectiveness of our gene therapy on the prevention of ACI (RT1(a)) heart HAR was evaluated. Results indicated that soluble MHC not only decreased cytotoxic antibody levels, but also suppressed antidonor CTL and HTL responses; furthermore, HAR of heart allografts was prevented in all recipients. Therefore, soluble donor MHC class I gene therapy can inhibit multiple aspects of the primed antidonor immune response in actively presensitized rats. Development of this strategy in presensitized humans could improve organ transplant outcome.
    Human Immunology 11/2002; 63(10):948-54. · 2.30 Impact Factor

Publication Stats

243 Citations
68.09 Total Impact Points

Institutions

  • 2002–2014
    • Universität Regensburg
      • Department of Surgery
      Ratisbon, Bavaria, Germany
  • 2010–2011
    • University Hospital Regensburg
      • Klinik für Chirurgie
      Ratisbon, Bavaria, Germany