Institut für Transfusionsmedizin
Medizinische Hochschule Hannover
Tel.: +49 (511) 532 9744
Fax: +49 (511) 532 9701
Our research examines various aspects of antigen recruitment and presentation through MHC class I molecules.
This includes techniques such as lentiviral transduction, flow cytometry, cellular assays, real-time PCR, protein purification, immunochemistry assays, mass spectrometric analysis, protein crystallography.
Major Research Projects
Peptide characterization to assess allogenicity
Immune recognition is mediated by the major histocompatibility complex class I (MHC I, HLA I) molecules, which scan the cell and carry small peptides of intracellular origin to the cell surface. Effector T-lymphocytes (CTL) survey MHC-peptide complexes and target cells displaying allogenic peptides. Since CTLs are capable to detect already single amino acid (AA) exchanges between peptides, the comparison of allelic peptide binding spectra may help to weight the importance of individual AA substitutions within the peptide binding region (PBR) of the HLA molecule.
We developed a technology for mass spectrometric analysis of individual allele specific ligands. These data provide the basis for assessment of subtypic allogenicity in the donor search before allogeneic stem cell transplantation.
Tapasin mediated antigen recruitment
Following proteasomal processing peptides are transported into the endoplasmatic reticulum (ER) and loaded onto HLA class I molecules with assistance of the Peptide Loading Complex (PLC). As part of the PLC, the transmembrane glycoprotein Tapasin (TPN) plays an important role in optimising potential ligands and thus in the immunorecognition of certain pathogens. Single polymorphism of HLA molecules can significantly alter their TPN-mediated interaction with the PLC. During infection, virally-encoded immune evasion proteins retain TPN-dependent HLA molecules within the ER thus preventing the presentation of allogeneic/immunogeneic epitopes to the immune system, whilst TPN-independent molecules remain unaffected.
We currently investigate a) the biophysical and cellular basis of HLA/TPN association to identify alternative pathways by which certain HLA molecules can acquire ligands and b) the structural involvement of single mismatches for HLA/TPN interaction/association.
Immune response by HLA-E T- and NK-cells
HLA-E molecules are targets for αβ T-cell-as well as for CD94/NKG2 receptors, expressed on T-or NK-lymphocytes. Those receptors discriminate between different HLA-E binding peptides.
Under healthy conditions HLA-E present signal peptides of self HLA molecules, displaying targets for the inhibitory receptor CD94/NKG2A. In a viral infection peptides of viral origin can be presented by HLA-E, being targets for the activatory receptor CD94/NKG2C. Under cellular stress (e.g. misfolded proteins in the lumen of the ER) heat shock protein fragments can act as ligands for HLA-E molecules and thus elicit CD8+ T-cell responses.
We aim to understand the a) recruitment of peptide antigens by HLA-E molecules, b) mechanism of effector cell inhibition/activation by certain HLA-E recruited peptides.
HLA class I structures
Biophysical characterization of selected HLA molecules by high resolution X-ray crystallography provides a basis for understanding HLA restriction and ranking of allelic variants according to their structural similarity.
Bioinformatical tools (POCKETCHECK)
There have been several attempts over the years to define which positions in the HLA binding groove (pockets) influence the specificity of bound amino acids at each position in the peptide. The structural determination of the HLA molecule by X-ray crystallography has provided valuable information for understanding how peptides bind to HLA.
To increase the precision of peptide prediction and support the characterization of individual weights for individual amino acids we aim to provide advanced prediction algorithm.
Several computational tools have been developed, HISTOCHECK (www.histocheck.org), PEPTIDECHECK (www.peptidecheck.org) and HAPLOCHECK (www.halpocheck.org). POCKETCHECK is a new and advanced bioinformatic tool spanning all available peptide-HLA structures and calculating mismatch permissivity.
Immune response to anti-cancer therapy
Immune-mediated tumor rejection relies on functional T-cell responses, however the balance between T cell receptor (TCR) stimulation and co stimulatory signals is frequently manipulated by the tumor microenvironment. Certain cancer patients undergoing peptide therapy do not respond to treatment and a subset of CD8+ T cells that are peptide-specific but that are non-tumor reactive are generated post-vaccination against tumor antigens.
Our aim is to investigate the role that certain co stimulatory signals have on the generation of CD8+ T cells with a non-tumor reactive phenotype.
Impact of HCMV immune evasions on the repertoire of presented antigenic peptides and the CMV-specific T cell repertoire
Viral immune escape mechanisms comprise the interference of the virus with the function of antigen presentation, resulting in poor or inappropriate activation of T cells. The immune evasion strategy of HCMV ensures that viral antigens are not presented on the cell surface during the early phase of HCMV infection. The intracellular peptides presented through HLA molecules are targets for the immune response, thus the retaining of HLA molecules by HCMV proteins is for a virus the most effective strategy of immune escape.
Since the expression kinetics of the HCMV HLA class I immune-evasion-genes is unknown, it is not yet well understood at what state of infection viral peptides are presented through HLA molecules.
The aim is to investigate the expression kinetics of HCMV HLA class I immune-evasion-genes and the peptide profile of certain HLA class I molecules with respect to different states of HCMV infection. Additionally, we aim to answer the question if ligands of viral origin would be preferentially selected and presented, hence raising the question of immune competence of T cells.