Study on the Extrapolability of Current Tumorgenicity Test With Mice by Comparing the Syngeneic or Allogeneic Mouse Transplantation Model

The extrapolability of the current tumorigenicity test performed by transplanting human cell product into immunodeficient (NOG) mice was investigated. For this purpose, the susceptibility to form teratomas of NOG mice was assessed by transplanting undifferentiated human-induced pluripotent stem cells (hiPSCs) as positive control cells via the liver, striatum, or tail vein and evaluating the TPD50 value (dose required to form teratomas in half of the transplanted mice). This was then compared to the TPD50 of syngeneic or allogeneic mouse models. The TPD50 of C57/BL/6(B6)-iPSC or 129/Ola(129)-embryonic stem cell (ESC) transplanted into the liver of syngeneic mice was 4.08 × 105 and 4.64 × 104 cells, respectively, while the TPD50 of hiPSC administered into the liver of NOG mice was 4.64 × 104 cells. The TPD50 of B6-miPSC-synergic, 129-mESC-synergic, or 129-cell/B6 allogeneic transplantation into the striatum was 5.09 × 102, 1.0 × 104, and 3.73 × 104 cells, respectively, while that of hiPSC/NOG mice was 1.0 × 103 cells. The TPD50 for B6-miPSC or 129-mESC syngeneic tail vein infusion was 3.16 × 106 or 5.62 × 106 cells, respectively, while no incidence was observed from 1 × 107 B6-miPSCs in 129 mice or hiPSCs in NOG mice infusion study. Although the number of data sets was limited, these data indicate that the teratoma formation from transplanted undifferentiated hiPSCs via the liver or striatum in NOG mice is comparable to that in syngeneic or allogeneic mouse transplantation model, suggesting that the result of the current tumorigenicity test in NOG mice would provide useful information to infer the incidence of teratoma from residual undifferentiated hPSCs in hPSC-derived products after transplantation.

Clinicopathological characteristics associated with the engraftment of patient lymphoma cells in NOG mice

Patient-derived xenograft (PDX) mouse models are useful for deepening our understanding of the biology of malignant lymphoma; however, factors associated with the success of the PDX lymphoma model are largely unknown. We retrospectively analyzed the characteristics of 66 xenotransplantations from 65 patients. In all, 43 (65%) specimens were obtained from patients aged > 60 years, and 42 (64%) specimens were obtained at diagnosis. Specimens were obtained from patients with the following diseases: diffuse large B-cell lymphoma (n = 30), intravascular large B-cell lymphoma (n = 12), follicular lymphoma (n = 8), peripheral T-cell lymphoma (n = 7), mantle cell lymphoma (n = 2), and other (n = 7). The specimens were sourced mainly from bone marrow (n = 31, 47%) and extranodal tumors (n = 13, 20%). Engraftment was successful in 33/66 (50%) xenotransplantations. The median age of patients who provided successful specimens was significantly higher than that for unsuccessful specimens (p = 0.013). Specimens with a high proportion of tumor cells in the graft and those obtained from patients with relapsed/refractory disease showed higher tendencies toward successful engraftment. Taken together, these data suggest that tumor cells with a highly malignant potential might have a high likelihood of engraftment.

High Incidence of Lymph-node Metastasis in a Pancreatic-cancer Patient-derived Orthotopic Xenograft (PDOX) NOG-Mouse Model

BACKGROUND/AIM

Our laboratory pioneered the patient-derived orthotopic xenograft (PDOX) model. An important goal of PDOX-model development is facile visualization of metastasis in live mice. In the present report we evaluated tumor growth and metastasis in pancreatic cancer PDOX NOG [Non-obese diabetes (NOD)/Scid/IL2Rγnull]-and nude-mouse models using red fluorescent protein (RFP)-expressing tumor stroma to visualize the primary tumor and metastasis.

MATERIALS AND METHODS

A patient-derived pancreatic cancer was initially implanted in transgenic RFP-expressing nude mice. Then, tumor fragments, which acquired RFP expressing stroma while growing in RFP-expressing nude mice were orthotopically implanted in nude and NOG mice. The primary pancreatic tumor and metastasis were observed 8 weeks after implantation.

RESULTS

Lymph-node metastases expressing red fluorescence were detected only in NOG mice. Significantly faster growth of primary pancreatic tumors and a higher incidence of lymph-node metastasis occurred in NOG mice compared to nude mice.

CONCLUSION

RFP-expressing tumor stroma, which traffics together with cancer cells to lymph nodes, is useful to observe tumor behavior, such as lymph-node metastasis in a PDOX NOG-mouse model which can be used for evaluation of novel anti-metastatic agents, as well as personalized therapy to identify effective drugs.

Spontaneous granulocytic leukemia in a NOD/Shi-scid IL-2Rγnull mouse

Here, we report a case of spontaneous granulocytic leukemia in a 51-week-old male NOD/Shi-scid IL-2Rγ ^null (NOG) mouse. The mouse showed progressive anemia and rough respiratory movement. Macroscopically, the spleen was discolored and enlarged. Histologically, the bone marrow of the sternum and femur was highly cellular and almost exclusively filled with neoplastic cells. The nuclei of neoplastic cells were large, oval to slightly irregular in shape, and a small number of cells had kidney- or ring-shaped nuclei. Neoplastic cells extensively infiltrated the organs, and the spleen and liver were prominently involved. Immunohistochemically, a large population of neoplastic cells in the red pulp of the spleen and sinusoid of the liver was positive for myeloperoxidase. Based on the histological features, this case was diagnosed with granulocytic leukemia. This novel information on spontaneous tumors may be helpful for the appropriate use of this mouse strain in further research.

Evaluation of domain of unknown function 1220 (DUF1220) for detection of human genome by quantitative polymerase chain reaction: Potential use in assessing the biodistribution of transplanted therapeutic human cells

The biodistribution profile of cell-based therapy products in animal models is important for evaluation of their safety and efficacy. Because of its quantitative nature and sensitivity, the quantitative polymerase chain reaction (qPCR) is a useful method for detecting and quantifying xenogeneic cell-derived DNA in animal models, thereby allowing a biodistribution profile to be established. Although the restriction endonuclease family from Arthrobacter luteus (Alu) of repetitive elements in human genome sequences has been used to assess the biodistribution of human cells, high background signals are detected. In the present study, we evaluate the potential of domain of unknown function 1220 (DUF1220), which is a human lineage-specific, multiple-copy gene similar to Alu sequences, for such analysis. Using qPCR analysis for DUF1220, human genome could be detected against a mouse genome background at a level comparable to that of Alu sequences with no detectable background signals. Moreover, using this approach, the human genome could be distinguished from the cynomolgus monkey genome. Further investigation of the quantitative aspects of this DUF1220-based qPCR assay might prove its usefulness for biodistribution studies of human cells transplanted into animals in the future.

Patient-derived xenograft (PDX) models: characteristics and points to consider for the process of establishment

Tumor research has largely relied on xenograft models created by the engraftment of cultured cell lines derived from tumor tissues into immunodeficient mice for in vivo studies. Like in vitro models, such models retain the ability of tumor cells to continuously proliferate, so they have been used to predict the clinical relevance of studies on proliferating cells. However, these models are composed of a limited population of tumor cells, which include only those tumor cells that are able to adapt to culture conditions, and thus they do not reflect the diversity and heterogeneity of tumors. This, at least in part, explains the poor predictivity of non-clinical data in the research and development of molecularly targeted drugs. Recently, research focus has been directed towards patient-derived xenograft (PDX) models created by directly engrafting tumor tissues, which have not been cultured in vitro, into immunodeficient mice. PDX models reflect the diversity and heterogeneity of tumors, and the evidence they provide can be verified in the patient tissues from which they were derived originally. PDX models are anticipated to efficiently bridge non-clinical and clinical data in translational research. Based on the evidence obtained from our research experience, this review describes the characteristics of PDX models for acting as tumor models, and elucidates the points to consider when attempting to establish these models.

Incidence of spontaneous lymphomas in non-experimental NOD/Shi-scid, IL-2Rγnull (NOG) mice

Severely immunodeficient NOD/Shi-scid, IL-2Rγ^null (NOG) mice provide an in vivo model for human cell/tissue transplantation studies. NOG mice were established by combining interleukin-2 receptor-γ chain knockout mice and NOD/Shi-scid mice. They exhibit a high incidence of thymic lymphomas and immunoglobulin (Ig) leakiness. In this study, we assessed the incidence of malignant lymphomas and the occurrence of leakiness in 2,184 non-experimental NOG retired breeder mice aged 16-40 weeks. We established that the total incidence of lymphomas was only 0.60% (13/2,184). Most lymphomas (10/13) occurred in female mice by the age of around 25 weeks. No mice developed Ig leakiness. All lymphomas were derived from the thymus, and consisted mainly of CD3-positive and CD45R-negative lymphoblastic-like cells. Therefore, based on the absence of Ig leakiness and a very low incidence of lymphomas, including thymic lymphomas, NOG mice may be useful in regeneration medicine for xenotransplantation of human embryonic stem (ES) cells or induced pluripotent stem (iPS) cells, and in transplantation experiments involving tumor cells.

Antitumor effects of minodronate, a third-generation nitrogen-containing bisphosphonate, in synergy with γδT cells in human glioblastoma in vitro and in vivo

Nitrogen-containing bisphosphonates (N-BPs), which prevent bone resorption, exert direct and γδT cell (GDT)-mediated antitumor effects against several tumor cell types, including glioblastoma (GBM). However, limited information is available regarding the antitumor effects of N-BPs in GBM. Specifically, the antitumor effects of minodronate (MDA), a third-generation N-BP, in GBM are yet unclear. This study aimed to investigate the antitumor effects of MDA in GBM in vitro and in vivo. We performed growth inhibition and apoptosis detection assays using the GBM cell lines U87MG and U138MG. Apoptosis inhibition assays were also conducted. In vivo xenograft assays were performed in highly immunodeficient NOD.Cg-Prkdc(scid) Il2rg(tm1Sug)/Jic mice subcutaneously implanted with U87MG and U138MG cells. Growth inhibition and apoptosis detection assays demonstrated that MDA inhibited GBM cell growth via apoptosis, which was markedly enhanced by ex vivo expanded GDT. A pan-caspase inhibitor, z-VAD-fmk, inhibited MDA-induced U138MG apoptosis and MDA/GDT-induced U87MG and U138MG apoptosis. But z-VAD-fmk increased MDA-induced U87MG apoptosis. MDA/GDT-mediated apoptosis was blocked by the anti-T cell receptor (TCR) Vγ9, mevalonate pathway inhibitor, granzyme B inhibitor, and antitumor necrosis factor (TNF)-α. In vivo xenograft assays showed that combined intraperitoneal administration of MDA/GDT induced antitumor effects on unestablished U87MG-derived subcutaneous tumors. MDA exerted direct and GDT-mediated anti-GBM apoptotic effects in a caspase-dependent manner. GDT recognized MDA-exposed GBM cells via TCRVγ9 and induced apoptosis via granzyme B and TNF-α release. Because MDA elicited anti-GBM effects in synergy with GDT in vivo, a combination of MDA and ex vivo-generated GDT could be an effective treatment in patients with GBM.

Histopathological characteristics of human non-tumor thyroid tissues in a long-term model of adenomatous goiter xenografts in the NOD/Shi-scid, IL-2Rγ(null) mouse

There is a growing need for modeling the human thyroid to link data obtained from animals to humans because of its sensitivity to radiation exposure and endocrine disruption chemicals. In a scid mouse model produced by transplanting human thyroid tissues, leakiness and thymic lymphoma that occurs spontaneously in the scid mouse can complicate the interpretation of experimental results. Considering that the NOD.Cg-Prkdc(scid)Il2rg(tm1Sug)/Jic mouse (NOD/Shi-scid, IL-2Rγ(null) or NOG mouse) may be a better host because this strain has low incidence of leakiness and thymic lymphoma, we have evaluated the potential of a model that allows long-term observation of non-tumor human thyroid tissues in this mouse. We transplanted tissues of human adenomatous goiter into NOG mice and examined the tissues histopathologically. The morphology of human adenomatous goiter tissues was maintained from 24 to 44 weeks after transplantation in NOG mice with no noted differences between donor-matched tissues or the weeks after transplantation. The tissues expressed thyroglobulin protein and mRNA as well as thyroperoxidase. Endothelial cells originating from human were found in the transplanted tissues and were thought to be a characteristic of this model. The intactness of the tissues before transplantation was found to affect the rate of tissue engraftment. From the present results we have concluded that transplanted thyroid tissues in NOG mice maintain the histopathological characteristics of their origin for long terms. Therefore this model was thought feasible for toxicity evaluation.