Heterologous transplantation of human neural tumors

Meningioma animal models: a systematic review and meta-analysis

BACKGROUND

Animal models are widely used to study pathological processes and drug (side) effects in a controlled environment. There is a wide variety of methods available for establishing animal models depending on the research question. Commonly used methods in tumor research include xenografting cells (established/commercially available or primary patient-derived) or whole tumor pieces either orthotopically or heterotopically and the more recent genetically engineered models-each type with their own advantages and disadvantages. The current systematic review aimed to investigate the meningioma model types used, perform a meta-analysis on tumor take rate (TTR), and perform critical appraisal of the included studies. The study also aimed to assess reproducibility, reliability, means of validation and verification of models, alongside pros and cons and uses of the model types.

METHODS

We searched Medline, Embase, and Web of Science for all in vivo meningioma models. The primary outcome was tumor take rate. Meta-analysis was performed on tumor take rate followed by subgroup analyses on the number of cells and duration of incubation. The validity of the tumor models was assessed qualitatively. We performed critical appraisal of the methodological quality and quality of reporting for all included studies.

RESULTS

We included 114 unique records (78 using established cell line models (ECLM), 21 using primary patient-derived tumor models (PTM), 10 using genetically engineered models (GEM), and 11 using uncategorized models). TTRs for ECLM were 94% (95% CI 92-96) for orthotopic and 95% (93-96) for heterotopic. PTM showed lower TTRs [orthotopic 53% (33-72) and heterotopic 82% (73-89)] and finally GEM revealed a TTR of 34% (26-43).

CONCLUSION

This systematic review shows high consistent TTRs in established cell line models and varying TTRs in primary patient-derived models and genetically engineered models. However, we identified several issues regarding the quality of reporting and the methodological approach that reduce the validity, transparency, and reproducibility of studies and suggest a high risk of publication bias. Finally, each tumor model type has specific roles in research based on their advantages (and disadvantages).

SYSTEMATIC REVIEW REGISTRATION

PROSPERO-ID CRD42022308833.

Engraftment of Human Glioblastoma Cells in Immunocompetent Rats through Acquired Immunosuppression

Transplantation of glioblastoma patient biopsy spheroids to the brain of T cell-compromised Rowett (nude) rats has been established as a representative animal model for human GBMs, with a tumor take rate close to 100%. In immunocompetent littermates however, primary human GBM tissue is invariably rejected. Here we show that after repeated passaging cycles in nude rats, human GBM spheroids are enabled to grow in the brain of immunocompetent rats. In case of engraftment, xenografts in immunocompetent rats grow progressively and host leukocytes fail to enter the tumor bed, similar to what is seen in nude animals. In contrast, rejection is associated with massive infiltration of the tumor bed by leukocytes, predominantly ED1+ microglia/macrophages, CD4+ T helper cells and CD8+ effector cells, and correlates with elevated serum levels of pro-inflammatory cytokines IL-1β, IL-18 and TNF-α. We observed that in nude rat brains, an adaptation to the host occurs after several in vivo passaging cycles, characterized by striking attenuation of microglial infiltration. Furthermore, tumor-derived chemokines that promote leukocyte migration and their entry into the CNS such as CXCL-10 and CXCL-12 are down-regulated, and the levels of TGF-β2 increase. We propose that through serial in vivo passaging in nude rats, human GBM cells learn to avoid and or/ suppress host immunity. Such adapted GBM cells are in turn able to engraft in immunocompetent rats without signs of an inflammatory response.

In vivo models of primary brain tumors: pitfalls and perspectives

Animal modeling for primary brain tumors has undergone constant development over the last 60 years, and significant improvements have been made recently with the establishment of highly invasive glioblastoma models. In this review we discuss the advantages and pitfalls of model development, focusing on chemically induced models, various xenogeneic grafts of human cell lines, including stem cell–like cell lines and biopsy spheroids. We then discuss the development of numerous genetically engineered models available to study mechanisms of tumor initiation and progression. At present it is clear that none of the current animal models fully reflects human gliomas. Yet, the various model systems have provided important insight into specific mechanisms of tumor development. In particular, it is anticipated that a combined comprehensive knowledge of the various models currently available will provide important new knowledge on target identification and the validation and development of new therapeutic strategies.

Transplantation of tissue grafts into the anterior eye chamber: a method to study intrinsic neurons

Intrinsic nerves play a crucial role in the regulation of body functions. It is therefore of paramount importance to be able to study the biology of intrinsic nerves in tissue grafts. The anterior eye chamber of rats has long been used to study different biological mechanisms, growth and differentiation of a variety of tissues, because of the transparency of the cornea, which also allows macroscopic changes to be seen. Despite its extended use, a detailed, easy to follow description of the technique of tissue and cell transplantation into the anterior eye chamber has not been presented. In this study, pancreatic tissue fragments were transplanted into the anterior eye chamber of rats alone or with brain tissue fragments to examine the survival and viability of intrinsic nerves in these tissue fragments, which have been detached from their original extrinsic nerves. The pancreatic transplants contained intact 5-HT and AChE-positive intrinsic neurons. The brain tissue grafts contained many AChE-enzyme reactive cells. The method is simple and can be used to study the morphology or physiology of intrinsic neurons in any tissue fragment. The grafts are easily vascularised and reinnervated because of the rich blood and nerve supply of the iris which forms the bed of the anterior eye chamber. The graft will also survive with ease because the anterior eye chamber is an immunologically privileged site. In conclusion, the intrinsic nerves of pancreatic and brain tissue fragments can survive after several weeks of transplantation into the anterior eye chamber of rats. In addition to this, these intrinsic nerves have the ability to produce and or store neurotransmitters and their enzymes.

Intracerebral transplantation of a human glioma line in immunosuppressed rats

A model was developed for in vivo study of the human glioma-derived D-54 MG cell line in the brains of immunosuppressed Fischer 344 rats. The rats were injected with horse anti-rat thymocyte serum before and after intracerebral inoculation with 5 or 10 microliters of a D-54 MG tumor cell suspension. Reproducible mortality distributions were obtained, with deaths occurring 18 to 34 days after intracerebral inoculation. Tumors grew as well circumscribed intracerebral masses with sheets of anaplastic cells, areas of necrosis bordered by concentrated nuclei, and minimal lymphocytic infiltration. Cytogenetic analysis revealed the same general chromosome distribution and markers in the heterotransplanted glioma cells as in the cultured line. Blood-brain barrier disruption was demonstrated by intracerebral tumor staining after intravenous injection of Evans blue dye. The in vivo growth of D-54 MG in immunosuppressed rats provides a reliable experimental model for the study of chemotherapy, immunodiagnosis, and immunotherapy of a human glioma-derived tumor in an animal sufficiently large to evaluate intracarotid or intratumoral injection of therapeutic agents.

Chorioallantoic membrane heterotransplantation of human brain tumors

Specimens of human tumors were taken from the operating room and directly heterotransplanted to chick chorioallantoic membranes. Seventy-one percent of the eggs survived the procedure and 41% of the tumors appeared viable after 1 week. Microscopically, the first-generation heterotransplants resembled the parent tumors. Many specimens showed evidence of growth, but in most of them there was also some degree of necrosis. The necrosis increased with serial heterotransplantation, so that tumor propagation usually was not possible beyond the second to third transplant generation; nevertheless, it was found that almost any histological type of intracranial tumor could be grown for short periods of time at least on the chick chorioallantoic membrane.

Morphological observations of dysplastic gliomas heterotransplanted to experimental animals

Observations concerning transplantation of 5 cases of malignant dysplastic gliomas to the anterior chamber of the guinea-pig eye have been presented. This type of gliomas, composed mainly of cytoplasm-abundant cells, show weak transplantability, slow rate of growth, and particular tendency to degeneration and necrosis. At the same time, in subsequent passages, an intensive proliferation of small-cell component occurs, comparing with cytoplasm-abundant cells.