Florian O Losch
Research interests
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InterestsCancer Biology, Cancer Biomarkers, Stem Cell, Regenerative Medicine, Epigenetics, Gene Regulation, Chromatin, Gene Expression, Genomics, Computational Biology, Genetic Analysis, Human Genetics, Medical Genetics
Publications
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5.87Impact points
Therapeutic vaccination with recombinant adenovirus reduces splenic parasite burden in experimental visceral leishmaniasis.
The Journal of infectious diseases. 03/2012; 205(5):853-63.
Therapeutic vaccines, when used alone or in combination therapy with antileishmanial drugs, may have an important place in the control of a variety of forms of human leishmaniasis. Here, we describe the development of an adenovirus-based vaccine (Ad5-KH) comprising a synthetic haspb gene linked to a... [more] Therapeutic vaccines, when used alone or in combination therapy with antileishmanial drugs, may have an important place in the control of a variety of forms of human leishmaniasis. Here, we describe the development of an adenovirus-based vaccine (Ad5-KH) comprising a synthetic haspb gene linked to a kmp11 gene via a viral 2A sequence. In nonvaccinated Leishmania donovani-infected BALB/c mice, HASPB- and KMP11-specific CD8(+) T cell responses were undetectable, although IgG1 and IgG2a antibodies were evident. After therapeutic vaccination, antibody responses were boosted, and IFNγ(+)CD8(+) T cell responses, particularly to HASPB, became apparent. A single vaccination with Ad5-KH inhibited splenic parasite growth by ∼66%, a level of efficacy comparable to that observed in early stage testing of clinically approved antileishmanial drugs in this model. These studies indicate the usefulness of adenoviral vectors to deliver leishmanial antigens in a potent and host protective manner to animals with existing L. donovani infection.
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1.94Impact points
Therapeutic vaccination for cancer immunotherapy: antigen selection and clinical responses.
Human vaccines. 01/2011; 7 Suppl:115-9.
Because of its high specificity and low toxicity therapeutic vaccination is considered a desirable treatment for cancer. So far, however, the results of cancer vaccination trials have been disappointing, which is often attributed to the problem identifying appropriate vaccine antigens. Tumorassociat... [more] Because of its high specificity and low toxicity therapeutic vaccination is considered a desirable treatment for cancer. So far, however, the results of cancer vaccination trials have been disappointing, which is often attributed to the problem identifying appropriate vaccine antigens. Tumorassociated antigens are mostly autoantigens and therefore expected to be subject to immunosuppressive mechanisms. Cancer-testis antigens are the most prominent exception as, still being self, they are physiologically only expressed in immunopriviledged tissues and should therefore not induce autotolerance. This leads to the widely accepted hypothesis that cancer-testis antigens should be more efficient inducers of anti-tumor cellular immune responses than differentiation antigens. Aim of the study was to test this hypothesis by evaluating the published reports on clinical therapeutic vaccination trials for the objective clinical response rates to vaccination with cancer testis antigen vs. differentiation antigens. The results of vaccination clinical trials with cancer testis and/or differentiation antigens published in literature and databanks were analyzed for clinical outcome versus vaccine antigens. 21 publications on cancer testis antigen-based trials in which clinical outcome was reported according to WHO or RECIST were identified and analyzed. The rate of objective responses to cancer testis antigen vaccines in 239 patients was 3.8% and for the 235 patients vaccinated with cancer testis plus 3 differentiation antigens 4.3% compared to 2.6% for the 496 patients vaccinated with differentiation antigens alone. Cancer testis antigen-based vaccines seem slightly superior over vaccines based on differentiation antigens providing support for the hypothesis.
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Attractors in Sequence Space: Agent-Based Exploration of MHC I Binding Peptides
Molecular Informatics. 01/2010; 29(1-2-12):65-74.
Ant Colony Optimization (ACO) is a meta-heuristic that utilizes a computational analogue of ant trail pheromones to solve combinatorial optimization problems. The size of the ant colony and the representation of the ants’ pheromone trails is unique referring to the given optimization problem. In the... [more] Ant Colony Optimization (ACO) is a meta-heuristic that utilizes a computational analogue of ant trail pheromones to solve combinatorial optimization problems. The size of the ant colony and the representation of the ants’ pheromone trails is unique referring to the given optimization problem. In the present study, we employed ACO to generate novel peptides that stabilize MHC I protein on the plasma membrane of a murine lymphoma cell line. A jury of feedforward neural network classifiers served as fitness function for peptide design by ACO. Bioactive murine MHC I H-2Kb stabilizing as well as nonstabilizing octapeptides were designed, synthesized and tested. These peptides reveal residue motifs that are relevant for MHC I receptor binding. We demonstrate how the performance of the implemented ACO algorithm depends on the colony size and the size of the search space. The actual peptide design process by ACO constitutes a search path in sequence space that can be visualized as trajectories on a self-organizing map (SOM). By projecting the sequence space on a SOM we visualize the convergence of the different solutions that emerge during the optimization process in sequence space. The SOM representation reveals attractors in sequence space for MHC I binding peptides. The combination of ACO and SOM enables systematic peptide optimization. This technique allows for the rational design of various types of bioactive peptides with minimal experimental effort. Here, we demonstrate its successful application to the design of MHC-I binding and nonbinding peptides which exhibit substantial bioactivity in a cell-based assay.
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1.75Impact points
MHC I stabilizing potential of computer-designed octapeptides.
Journal of biomedicine & biotechnology. 01/2010; 2010:396847.
Experimental results are presented for 180 in silico designed octapeptide sequences and their stabilizing effects on the major histocompatibility class I molecule H-2K(b). Peptide sequence design was accomplished by a combination of an ant colony optimization algorithm with artificial neural network... [more] Experimental results are presented for 180 in silico designed octapeptide sequences and their stabilizing effects on the major histocompatibility class I molecule H-2K(b). Peptide sequence design was accomplished by a combination of an ant colony optimization algorithm with artificial neural network classifiers. Experimental tests yielded nine H-2K(b) stabilizing and 171 nonstabilizing peptides. 28 among the nonstabilizing octapeptides contain canonical motif residues known to be favorable for MHC I stabilization. For characterization of the area covered by stabilizing and non-stabilizing octapeptides in sequence space, we visualized the distribution of 100,603 octapeptides using a self-organizing map. The experimental results present evidence that the canonical sequence motives of the SYFPEITHI database on their own are insufficient for predicting MHC I protein stabilization.
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3.62Impact points
Immunosuppressive mechanisms in cancer: Consequences for the development of therapeutic vaccines.
Vaccine. 03/2009;
Recent investigations revealed strong immunosuppressive mechanisms in tumors that may block anti-tumor T cells and be responsible for failures of immunotherapies. Current attempts to overcome this immunosuppression include blockade of co-inhibitory factors on T cells. Reports from the respective tri... [more] Recent investigations revealed strong immunosuppressive mechanisms in tumors that may block anti-tumor T cells and be responsible for failures of immunotherapies. Current attempts to overcome this immunosuppression include blockade of co-inhibitory factors on T cells. Reports from the respective trials indicate that the strategy can improve efficacy of therapeutic vaccination, but at the cost of severe inflammatory and autoimmune reactions. We tried to circumvent tumor-associated immunosuppression by mimotope vaccination to broaden reactive anti-tumor T cell repertoires to include T cells that have not been rendered anergic by the tumor. Initial clinical observations suggest that this strategy bears considerable promise.
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Cancer Stem Cells in Melanoma
ecancermedicalscience. 12/2008; 2(114).
The identification of cancer stem cells in various malignancies led to the hypothesis that these cells have the exclusive ability of selfrenewal, contribute to the plasticity of the tumours and may be the cause for ineffective cancer therapies. Several markers of melanoma stem cells have been descr... [more] The identification of cancer stem cells in various malignancies led to the hypothesis that these cells have the exclusive ability of selfrenewal, contribute to the plasticity of the tumours and may be the cause for ineffective cancer therapies. Several markers of melanoma stem cells have been described in recent studies including CD133, CD166, Nestin and BMI-1. Further studies are necessary to identify, better define and understand the origin and function of cancer stem cells. If confirmed that cancer stem cells play an important role in malignancy, therapeutic strategies may need to be redirected towards these cells to circumvent the failure of conventional therapies.
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2.42Impact points
Coordinated expression of clustered cancer/testis genes encoded in a large inverted repeat DNA structure.
Gene. 06/2008; 415(1-2):68-73.
Cancer/testis antigens (CTA) are expressed in cancers and testis or placenta only and, therefore are considered promising targets for cancer immunotherapy and diagnosis. One family of CTA is the MAGEA family which comprises 13 members and was shown to be expressed synchronously with members from the... [more] Cancer/testis antigens (CTA) are expressed in cancers and testis or placenta only and, therefore are considered promising targets for cancer immunotherapy and diagnosis. One family of CTA is the MAGEA family which comprises 13 members and was shown to be expressed synchronously with members from the CSAG (TRAG-3) family of CTA. The MAGEA genes are arranged in 4 subclusters located on the X chromosome. Subcluster III exposes a remarkable gene organization with an inverted repeat (IR) DNA structure of a triplicated couplet of a MAGEA gene and a CSAG gene. Analyzing the mRNA expression pattern of all genes of the MAGEA and CSAG family of cancer/testis genes, we show that the MAGEA and CSAG genes encoded in the large IR are expressed coordinately and independent from the MAGEAs encoded outside the IR. These results reinforce our hypothesis that the large MAGEA/CSAG-IR DNA structure has an impact on the regulation of gene expression.
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4.52Impact points
Evidence for a large double-cruciform DNA structure on the X chromosome of human and chimpanzee.
Human genetics. 12/2007; 122(3-4):337-43.
The human X chromosome consists of a high number of large inverted repeat (IR) DNA sequences which fulfill all requirements for formation of cruciform DNA structures. Such alternative DNA structures are suggested to have a great impact in altering the chromatin architecture and function. Our compreh... [more] The human X chromosome consists of a high number of large inverted repeat (IR) DNA sequences which fulfill all requirements for formation of cruciform DNA structures. Such alternative DNA structures are suggested to have a great impact in altering the chromatin architecture and function. Our comprehensive analysis of the corresponding orthologous nucleotide sequences of an IR sequence from Homo sapiens and Pan troglodytes revealed that most of the nucleotide differences between the two species are symmetrical to the apex of the IR, and that the spacer region of the orthologous IRs are in reverse orientation. We provide evidence that this IR forms a large non-B DNA structure containing two Holliday junctions, allowing intrastrand nucleotide pairing of the arms and interstrand pairing of the spacer region of the IR. This structure would extrude into a large double-cruciform DNA structure providing the molecular basis of translocation events and regulation of gene expression.
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2.60Impact points
Design of MHC I stabilizing peptides by agent-based exploration of sequence space.
Protein engineering, design & selection : PEDS. 04/2007; 20(3):99-108.
Identification of molecular features that determine peptide interaction with major histocompatibility complex I (MHC I) is essential for vaccine development. We have developed a concept for peptide design by combining an agent-based artificial ant system with artificial neural networks. A jury of fe... [more] Identification of molecular features that determine peptide interaction with major histocompatibility complex I (MHC I) is essential for vaccine development. We have developed a concept for peptide design by combining an agent-based artificial ant system with artificial neural networks. A jury of feedforward networks classifies octapeptides that are recognized by mouse MHC I protein H-2K(b). Prediction accuracy yielded a correlation coefficient of 0.94. Peptides were designed in machina by the artificial ant system and tested in vitro for their MHC I stabilizing effect. The behavior of the search agents during the design process was controlled by the jury network. The experimentally determined prediction accuracy was 89% for the designed stabilizing and 95% for the non-stabilizing peptides. Novel H-2K(b) stabilizing peptides were conceived that reveal extensions of known residue motifs. The combined network-agent system recognized context dependencies of residue positions. A diverse set of novel sequences exhibiting substantial activity was generated.
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3.03Impact points
A Strategy for the Identification of Canonical and Non-canonical MHC I-binding Epitopes Using an ANN-based Epitope Prediction Algorithm.
QSAR & Combinatorial Science. 04/2006; 25(4):350–358.
Small peptides bound by Major Histocompatibility Complex (MHC) class I molecules and recognized in this context by the T-cell receptor of CD8+ T cells are known as T-cell epitopes and are of extraordinary importance for the development of new vaccines against cancer and viral infections. Several alg... [more] Small peptides bound by Major Histocompatibility Complex (MHC) class I molecules and recognized in this context by the T-cell receptor of CD8+ T cells are known as T-cell epitopes and are of extraordinary importance for the development of new vaccines against cancer and viral infections. Several algorithms predicting a peptide's binding capability to a given MHC class I molecule are currently available and have been successfully applied in the identification of new T-cell epitopes within proteins. Most of these newly identified epitopes obey to the empirically determined anchor residue patterns that are specific for the different MHC I alleles. However, in recent studies an increasing number of weakly binding T-cell epitopes could be identified that do not fit to these canonical amino acid patterns. Therefore there is a need for new prediction algorithms improving the prediction accuracy for weakly binding epitopes that are biologically relevant as they are presented by, e.g. antigen presenting cells.
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5.65Impact points
Identification of noncanonical melanoma-associated T cell epitopes for cancer immunotherapy.
Journal of immunology (Baltimore, Md. : 1950). 07/2005; 174(11):6716-24.
The identification of tumor-associated T cell epitopes has contributed significantly to the understanding of the interrelationship of tumor and immune system and is instrumental in the development of therapeutic vaccines for the treatment of cancer. Most of the known epitopes have been identified wi... [more] The identification of tumor-associated T cell epitopes has contributed significantly to the understanding of the interrelationship of tumor and immune system and is instrumental in the development of therapeutic vaccines for the treatment of cancer. Most of the known epitopes have been identified with prediction algorithms that compute the potential capacity of a peptide to bind to HLA class I molecules. However, naturally expressed T cell epitopes need not necessarily be strong HLA binders. To overcome this limitation of the available prediction algorithms we established a strategy for the identification of T cell epitopes that include suboptimal HLA binders. To this end, an artificial neural network was developed that predicts HLA-binding peptides in protein sequences by taking the entire sequence context into consideration rather than computing the sum of the contribution of the individual amino acids. Using this algorithm, we predicted seven HLA A*0201-restricted potential T cell epitopes from known melanoma-associated Ags that do not conform to the canonical anchor motif for this HLA molecule. All seven epitopes were validated as T cell epitopes and three as naturally processed by melanoma tumor cells. T cells for four of the new epitopes were found at elevated frequencies in the peripheral blood of melanoma patients. Modification of the peptides to the canonical sequence motifs led to improved HLA binding and to improved capacity to stimulate T cells.
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4.72Impact points
Activation of T cells via tumor antigen specific chimeric receptors: the role of the intracellular signaling domain.
International journal of cancer. Journal international du cancer. 02/2003; 103(3):399-407.
T cells engineered to express hybrid receptors with antibody defined specificity can successfully be targeted to tumor cells. In order to select intracellular domains of chimeric receptors capable of efficiently activate T cells in vitro and in vivo, we compared the function of receptors, which shar... [more] T cells engineered to express hybrid receptors with antibody defined specificity can successfully be targeted to tumor cells. In order to select intracellular domains of chimeric receptors capable of efficiently activate T cells in vitro and in vivo, we compared the function of receptors, which share the same extracellular antigen-binding part, joined to different intra-cellular signal transduction units. The antigen binding domain of the receptors was a single-chain fragment of a monoclonal antibody, which recognize a High Molecular Weight Melanoma-Associated Antigen with high affinity. The intracellular tails were derived from the T-cell receptor zeta chain (TCR-zeta), from the B-cell receptor Ig-alpha molecule and from a mutated Ig-alpha molecule able of stronger signal transduction. We compared the activity of the different chimeric receptors at a single-cell level by using a T-cell line that expressed an activation-dependent EGFP-reporter gene. Upon cross-linking with immobilized antibodies, all receptors were able to induce EGFP expression in the majority of the T cells. In contrast, EGFP expression was induced by contact to melanoma cells in vitro only in T cells that expressed the chimeric receptor that contained the TCR-zeta intracellular tail. In these T cells, the co-expression of chimeric receptors that contain a mutated Ig-alpha tail lowers the threshold of T-cell activation and facilitates tumor recognition in vitro and in vivo. Given their specificity and efficiency, T cells grafted with these type of receptors may represent potential candidates for cancer passive immunotherapy.
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Aktivierung von T-Lymphozyten durch melanomspezifische variante Antigen-Rezeptoren
Es wurde die Signalleitkapazität melanomspezifischer, varianter Antigen-Rezeptoren (vAgR) verglichen, mit dem Ziel, Rezeptoren oder Rezeptor-Kombinationen zu entwickeln, die nach Kontakt mit Melanomzellen, T-Zellen effektiv aktivieren können. Der extrazelluläre, antigenbindende Teil der vAgR stammt ... [more] Es wurde die Signalleitkapazität melanomspezifischer, varianter Antigen-Rezeptoren (vAgR) verglichen, mit dem Ziel, Rezeptoren oder Rezeptor-Kombinationen zu entwickeln, die nach Kontakt mit Melanomzellen, T-Zellen effektiv aktivieren können. Der extrazelluläre, antigenbindende Teil der vAgR stammt vom monoklonalen Antikörper 225.28S, der spezifisch für das High Molecular Weight-Melanoma Associated Antigen' ist. Die intrazellulären, signalleitenden Teile stammen von Signalkomponenten des T-Zell Rezeptors (CD3-z), des B-Zell Rezeptors (Ig-a) und einer mutierten Form des Ig-a. Die Signalleiteffizienz dieser vAgR wurde mit einer T-Helfer Linie analysiert, die aktivierungsabhängig das Enhanced Green Fluorescent Protein' (EGFP) exprimiert. Die vAgR-Transfektanten konnten somit am Fluorescense Aktivated Cell Scanner' (FACS) auf Einzell-Zell Ebene verglichen werden. Nach Stimulation mit immobilisierten Antikörpern waren alle vAgR in der Lage die EGFP Expression in der Mehrheit der T-Zellen zu induzieren. Wurde jedoch mit nativem Antigen auf Melanomzellen stimuliert, konnte die EGFP Expression nur durch den vAgR mit dem intrazellulären Teil des CD3-z induziert werden. Die Koexpression dieses vAgR und des vAgR mit dem mutierten Ig-a, senkte den Schwellenwert für die Aktivierung der T-Zellen und erleichterte damit die Melanomerkennung in vitro und in vivo. Biochemische Analysen zeigten, dass die vAgR mit den Ig-a Sequenzen effizienter als der vAgR mit der CD3-z Sequenz, im Kontext mit der Kinase Syk phosphoryliert werden. Zielgerichtete Mutationen der Aminosäuren um das zweite Immunorezeptor Tyrosine-based Activation Motif' des CD3-z erhöhte jedoch die Effizienz dieser Phosphorylierung. Des Weiteren konnten durch die Konstruktion eines induzierbaren Vektors für Perforin, T-Helfer Zellen mit zytotoxischen Eigenschaften ausgestattet werden. Diese Zellen können nach Aktivierung, die Membranen von kokultivierten Zellen permeabilisieren.
Following (3)
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Suresh Oncosuresh
Bharathidasan University -
Mandy Leist
Charité Universitätsmedizin Berlin -
Rita Carsetti
Ospedale Pediatrico Bambino Gesù
