Need of comparative pathologists
Type | Comment | Main application | ||
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Cell line- based | Xenograft (CDX) | Subcutaneous or orthotopic | Also as patient-derived xenograft (PDX) | Cell biology, therapy |
Humanized preclinical models | Immunological research | |||
Syngraft (CDS) | Subcutaneous or orthotopic | Derived from spontaneously grown, toxically induced or genetically generated endogenous tumors | Cell biology, therapy | |
Complex, biologically/genetically engineered | Metabolically/toxically induced | Systemic | Mostly based on genetic alterations (targeted induction of a promotor for carcinogen), often organ-specific | Toxicology |
Mutagenesis- screen | Chemical or transposon-mutagenesis | Forward-genetic approaches | Basic cancer research (identification of gene functions) | |
Genetically Engineered Models (GEM) | Systemic | Knock-in/knock-out | Translational research (reverse-genetic approaches) | |
Organ-specific | Transgenic animals with organ-/cell type-specific promotor | |||
Conditional/inducible | Transgenic animals with localized or time-limited genetic alterations | |||
Targeted genetically modified animals by genome editing | ||||
Complex humanized preclinical models |
The CEP unit
Imaging and co-localization
Scientific step | Coordinator | Challenges/solutions | Benefit for researchers |
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Project management | Researcher | Definition of question, aim of the study, study and experimental design | |
Pathologist | Experimental design with focus on appropriate mouse models and histopathological evaluation with focus on co-localization | Choosing a suitable animal model for the research question, appropriate/realistic time table | |
In vivo imaging | Researcher | Performance, coordination of procedure and time table in consultation with pathologist | |
Pathologist | Coordination of histopathological tissue processing after in vivo imaging according to time table of researcher | Fast and correct tissue sampling and processing | |
Submission of tissue/animals | Researcher | Inform pathologist before necropsy, planning of necropsy in consultation with pathologist | |
Pathologist | Feedback to researcher about time table, fixation, tissue processing with focus on co-localization, provide appropriate protocols for necropsy | Fast and correct tissue sampling and processing | |
Co-localization | |||
- Basic co-localization | Researcher | Definition of question and aim of co-localization approach | |
Planning of necropsy with focus on special orientation | |||
Pathologist | Planning and consulting of necropsy and tissue processing - Flagging by ink - Embedding in the right plane - Consecutive slides | Ensure the correct orientation of tissues for later co-localization | |
- Complex co-localization | Researcher | Definition of question and aim of co-localization approach | |
Planning of necropsy with focus on special orientation | |||
Pathologist | Planning/consulting of necropsy/tissue processing with focus on orientation - Removement of tissue with adjacent organ structures - Flagging by ink - Embedding in the right plane - Consecutive slides | Ensure the correct orientation of tissues for later co-localization | |
Tissue processing | Researcher | In consultation with pathologist | |
Pathologist | Time table and coordination with the pathology laboratory (e.g. CEP) - Fixation - Embedding in the right plane, special orientation - Cutting: number and type of slides, consecutive slides - Staining: H&E, additional special stainings | Fast and appropriate tissue processing | |
- Immunohistochemistry | Selection of the right target antigen, antibody, protocol | ||
- Scanning | Simplification of co-localization and co-registration | ||
Histopathological evaluation | Researcher | In consultation with pathologist | |
Pathologist | Evaluation of H&E stains, special stainings, immunohistochemistry | Correct histopathological diagnosis because of - Classification of lesions in a comparative way - Standardized vocabulary in description - Knowledge of strain-specific background lesions - Knowledge of differential diagnoses (non-expected alterations) | |
Co-registration | Researcher | Combining in vivo imaging with histopathological findings, in consultation with pathologist | |
Pathologist | Consulting researcher with focus on co-localization of histomorphological findings to in vivo imaging | Use of correct histopathological terms and localization for description of findings | |
Summary | Interdisciplinary cooperation | Accuracy and reproducibility of results |
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Basic co-localization (cell line based xenograft model): solid growing subcutaneous tumors:For example, basic co-localization was done for a murine xenograft model of human myeloid sarcoma aiming at monitoring of human central memory T-cells by Immuno-Positron Emission Tomography (Immuno-PET) imaging [16]. Positron Emission Tomography/Computed Tomography (PET/CT) imaging showed diverse T-cell distribution patterns. Co-localized immunohistochemistry and semiquantitative evaluation of T-cell-infiltration within the tumor was done corresponding to the PET/CT images, which included exact orientation (for example ventral or dorsal), flagging by ink and correct embedding in the right plane (for example downward orientation of the axial cutting site) (Fig. 2). The cutting of consecutive slides is also a useful tool for co-localization. Semiquantitative evaluation of defined markers in predefined regions can be depicted by color codes. Co-localization of imaging and histologic slices can be performed by calculating the sum of total sections, including a variation factor of tissue modification due to the technical procedure.
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Complex co-localization (genetically modified conditional model): tissue-specific tumors:For tissue-/organ-specific tumors, we developed a workflow for identification of tumor imaging parameters of mouse pancreatic ductal adenocarcinomas (PDACs) and analysis of their applicability for translation to human settings. The study was performed using genetically engineered mouse models that develop an endogenous pancreatic ductal adenocarcinoma [17]. Neoplasms were removed from the abdominal cavity with adjacent organ structures (liver, spleen, gut, kidneys) to prevent change in orientation and to facilitate exact correlation of imaging plane and histology based on additional anatomical landmarks. After proper formalin fixation and paraffin embedding of the whole organ bulk in tissue cassettes, axial histologic slices through mouse abdomen with 4 mm distance could be correlated with in vivo imaging (Fig. 3). Figure 3 demonstrates how pathological examination after exact correlation can complement and improve the readout of the imaging data. By using the technique mentioned above, we were able to correlate areas with different growth patterns (ductal, mixed or solid) or even different types (cystic papillary neoplasm (CPN) vs. PDAC) of neoplasms to certain areas of the invivo imaging slice.For complex co-localization of endogenous or orthotopic tumors, we additionally developed different other approaches with respect to the specific research question:
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Light Sheet Fluorescence Microscopy (LSFM):