Ectopic mineralized cartilage formation in human undifferentiated pancreatic adenocarcinoma explants grown in nude mice

Pericyte stem cells induce Ly6G+ cell accumulation and immunotherapy resistance in pancreatic cancer

We report the identification of a cell population that shares pericyte, stromal and stemness features, does not harbor the Kras^G12D mutation and drives tumoral growth in vitro and in vivo. We term these cells pericyte stem cells (PeSCs) and define them as CD45^- EPCAM^- CD29⁺ CD106⁺ CD24⁺ CD44⁺ cells. We perform studies with p48-Cre;Kras^G12D (KC), pdx1-Cre;Kras^G12D ;Ink4a/Arf^fl/fl (KIC) and pdx1-Cre;Kras^G12D ;p53^R172H (KPC) and tumor tissues from PDAC and chronic pancreatitis patients. We also perform single-cell RNAseq analysis and reveal a unique signature of PeSC. Under steady-state conditions, PeSCs are barely detectable in the pancreas but present in the neoplastic microenvironment both in humans and mice. The coinjection of PeSCs and tumor epithelial cells leads to increased tumor growth, differentiation of Ly6G⁺ myeloid-derived suppressor cells, and a decreased amount of F4/80⁺ macrophages and CD11c⁺ dendritic cells. This population induces resistance to anti-PD-1 immunotherapy when coinjected with epithelial tumor cells. Our data reveal the existence of a cell population that instructs immunosuppressive myeloid cell responses to bypass PD-1 targeting and thus suggest potential new approaches for overcoming resistance to immunotherapy in clinical settings.

Rapid combined light and electron microscopy on large frozen biological samples

The use of large unfixed frozen tissue samples (10 x 10 x 5 mm(3)) for combined light microscopy (LM) and electron microscopy (EM) is described. First, cryostat sections are applied for various LM histochemical approaches including in situ hybridization, immunohistochemistry and metabolic mapping (enzyme histochemistry). When EM inspection is needed, the tissue blocks that were used for cryostat sectioning and are stored at -80 degrees C, are then fixed at 4 degrees C with glutaraldehyde/paraformaldehyde and prepared for EM according to standard procedures. Ultrastructurally, most morphological aspects of normal and pathological tissue are retained whereas cryostat sectioning at -25 degrees C does not have serious damaging effects on the ultrastructure. This approach allows simple and rapid combined LM and EM of relatively large tissue specimens with acceptable ultrastructure. Its use is demonstrated with the elucidation of transdifferentiated mouse stromal elements in human pancreatic adenocarcinoma explants grown subcutaneously in nude mice. Combined LM and EM analysis revealed that these elements resemble cartilage showing enchondral mineralization and aberrant muscle fibres with characteristics of skeletal muscle cells.

Culture of cells gained from temporomandibular joint cartilage on non-absorbable scaffolds

The objective of this study was to investigate the adhesion, spreading and extracellular matrix synthesis of temporomandibular joint (TMJ) derived cells on non-absorbable scaffold materials to ultimately provide a durable stress-absorbent framework within tissue-engineered disc transplants. Scaffolds were prepared by polyamide monofilaments, expanded polytetrafluoroethylene (ePTFE) monofilaments, polyglycolic acid monofilaments (control) or natural bone mineral blocks (control). These scaffolds were incubated for 2, 4 and 8 weeks under common culture conditions with cells (human and porcine) harvested from the TMJ-disc or the articular eminence. The specimens were examined by scanning electron microscopy and transmission electron microscopy. The type of collagen synthesized was analyzed by SDS-PAGE. The cells were strongly adherent to all of the materials. Independent of their origin the cells became confluent on all scaffolds within four weeks. They filled recesses loosely and covered the constructs by an envelope of dense stratified cell layers. Moreover, the cells expressed collagen type II, which is specific for chondrocytes. Thus, it could be demonstrated, that ePTFE, polyamide, polyglycolic acid and natural bone mineral have an excellent compatibility in a three-dimensional cell culture system. ePTFE and polyamide scaffolds may be well suited for the development of tissue-engineered stress-resistant articular disc transplants.

Molecular markers predictive of the capacity of expanded human articular chondrocytes to form stable cartilage in vivo

OBJECTIVE

To establish a model and associated molecular markers for monitoring the capacity of in vitro-expanded chondrocytes to generate stable cartilage in vivo.

METHODS

Adult human articular chondrocytes (AHAC) were prepared by collagenase digestion of samples obtained postmortem and were expanded in monolayer. Upon passaging, aliquots of chondrocyte suspensions were either injected intramuscularly into nude mice, cultured in agarose, or used for gene expression analysis. Cartilage formation in vivo was documented by histology, histochemistry, immunofluorescence for type II collagen, and proteoglycan analysis by 35S-sulfate incorporation and molecular sieve chromatography of the radiolabeled macromolecules. In situ hybridization for species-specific genomic repeats was used to discriminate human-derived from mouse-derived cells. Gene expression dynamics were analyzed by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

Intramuscular injection of freshly isolated AHAC into nude mice resulted in stable cartilage implants that were resistant to mineralization, vascular invasion, and replacement by bone. In vitro expansion of AHAC resulted in the loss of in vivo cartilage formation. This capacity was positively associated with the expression of fibroblast growth factor receptor 3, bone morphogenetic protein 2, and alpha1(II) collagen (COL2A1), and its loss was marked by the up-regulation of activin receptor-like kinase 1 messenger RNA. Anchorage-independent growth and the reexpression of COL2A1 in agarose culture were insufficient to predict cartilage formation in vivo.

CONCLUSION

AHAC have a finite capacity to form stable cartilage in vivo; this capacity is lost throughout passaging and can be monitored using a nude mouse model and associated molecular markers. This cartilage-forming ability in vivo may be pivotal for successful cell-based joint surface defect repair protocols.

In vivo inhibition of cysteine proteinases delays the onset of growth of human pancreatic cancer explants

An animal model was used to study the effects of oral treatment with a small molecular selective inhibitor of cysteine proteinases, Z-Phe-Arg-fluoromethylketone (Z-Phe-Arg-FMK) on primary tumour development. Poorly differentiated rapidly growing and moderately differentiated slowly growing human pancreatic tumours were implanted in the neck of nude mice that were orally treated or not with the inhibitor. Growth rates of the tumours were determined during 38 days after implantation. The poorly differentiated tumours were not affected by treatment with the inhibitor. Development of the moderately differentiated tumours was inhibited significantly by Z-Phe-Arg-FMK treatment. Moreover, the amount of stroma was increased and the volume of cancer cells was reduced in the moderately differentiated tumours that had grown in the treated animals. Reduction in size of the tumours was not achieved by reduction in growth rate but in a delay of the onset of growth. It is concluded that cysteine proteinases play a transient role at the start of tumour development only when cancer cells are surrounded by stroma as was the case in the moderately differentiated but not in the poorly differentiated pancreatic tumours. However, this role of cysteine proteinases can easily be taken over by other proteinases.

Mechanical compression of a fibrous membrane surrounding bone causes bone resorption

Early micromovement and migration of a prosthesis of a hip or knee predicts late clinical loosening of the prosthesis. Such migration is likely to be associated with mechanical compression of the fibrous membrane interpositioned between bone and prosthesis during movement. Compression of the fibrous membrane by loading may lead to locally high fluid pressures reaching the underlying bone tissue. It has been established that high fluid pressures can lead to bone resorption. This resorption may eventually lead to clinical loosening of the prosthesis. We developed an experimental model to study the effects of compression of a soft tissue layer located between a titanium implant and cortical bone. In twelve rabbits, this device was implanted in the proximal tibia and allowed to osseointegrate. Next, a layer of soft tissue was allowed to form between titanium and bone. Subsequently, in six rabbits a cyclic load of 60 times in 2 min per day during 2 weeks was applied, leading to compression of the interpositioned soft tissue layer only. In the other six rabbits no load was applied. In all six loaded specimens, osteocyte death and bone resorption was observed underneath the area where compression of the fibrous membrane was exerted to a depth exceeding the amplitude of the loading device. Furthermore, formation of fibrocartilage was observed in the loaded areas. Formation of fibrocartilage, osteocyte death or bone resorption did not occur in the controls. Our results indicate that compression of a fibrous membrane surrounding bone can lead to resorption of the underlying bone primarily because of osteocyte death and subsequent resorption of dead bone tissue. This may explain the observation that early migration of a hip or knee prosthesis is predictive of clinical loosening of the prosthesis.