Human pluripotent stem cells (PSCs) provide a unique entry to study species-specific aspects of human disorders such as Alzheimer's disease (AD). However, in vitro culture of neurons deprives them of their natural environment. Here we transplanted human PSC-derived cortical neuronal precursors into the brain of a murine AD model. Human neurons differentiate and integrate into the brain, express 3R/4R Tau splice forms, show abnormal phosphorylation and conformational Tau changes, and undergo neurodegeneration. Remarkably, cell death was dissociated from tangle formation in this natural 3D model of AD. Using genome-wide expression analysis, we observed upregulation of genes involved in myelination and downregulation of genes related to memory and cognition, synaptic transmission, and neuron projection. This novel chimeric model for AD displays human-specific pathological features and allows the analysis of different genetic backgrounds and mutations during the course of the disease.

Infiltration of the central nervous system is a severe trait of T cell acute lymphoblastic leukemia. Inhibition of CXC chemokine receptor 4 significantly ameliorates T cell acute lymphoblastic leukemia in murine models of the disease; however, signaling by CXC chemokine receptor 4 is important in limiting the divagation of peripheral blood mononuclear cells out of the perivascular space into the central nervous system parenchyma. Therefore, Inhibition of CXC chemokine receptor 4 potentially may untangle T cell acute lymphoblastic leukemia cells from retention outside the brain. Here, we show that leukemic lymphoblasts massively infiltrate cranial bone marrow, with diffusion to the meninges without invasion of the brain parenchyma, in mice that underwent xenotransplantation with human T cell acute lymphoblastic leukemia cells or that developed leukemia from transformed hematopoietic progenitors. We tested the hypothesis that T cell acute lymphoblastic leukemia neuropathology results from meningeal infiltration through CXC chemokine receptor 4-mediated bone marrow colonization. Inhibition of leukemia engraftment in the bone marrow by pharmacologic CXC chemokine receptor 4 antagonism significantly ameliorated neuropathologic aspects of the disease. Genetic deletion of CXCR4 in murine hematopoietic progenitors abrogated leukemogenesis induced by constitutively active Notch1, whereas lack of CCR6 and CCR7, which have been shown to be involved in T cell and leukemia extravasation into the central nervous system, respectively, did not influence T cell acute lymphoblastic leukemia development. We hypothesize that lymphoblastic meningeal infiltration as a result of bone marrow colonization is responsible for the degenerative alterations of the neuroparenchyma as well as the alteration of cerebrospinal fluid drainage in T cell acute lymphoblastic leukemia xenografts. Therefore, CXC chemokine receptor 4 may constitute a pharmacologic target for T cell acute lymphoblastic leukemia neuropathology.

Patient-derived tumor xenograft (PDTX) approach is nowadays considered a reliable preclinical model to study in vivo cancer biology and therapeutic response. NOD scid and Il2rg-deficient mice represent the “gold standard” host for the generation of PDTXs. Compared to other immunocompromised murine lines, these mice offers several advantages including higher engraftment rate, longer lifespan and improved morphological and molecular preservation of patient-derived neoplasms. Here we describe a spectrum of previously uncharacterized post-transplant disorders affecting 14/116 (12%) NOD.Cg- Prkdcscid Il2rgtm1Sug/JicTac (NOG) mice subcutaneously engrafted with patient-derived metastatic melanomas. Affected mice exhibited extensive scaling/crusting dermatitis (13/14) associated with emaciation (13/14) and poor/unsuccessful tumor engraftment (14/14). In this context, the following pathological conditions have been recognized and characterized in details: (i) immunoinflammatory disorders with features of graft versus host disease (14/14); (ii) reactive lymphoid infiltrates effacing xenografted tumors (8/14); (iii) post-transplant B cell lymphomas associated with Epstein-Barr virus reactivation (2/14). We demonstrate that all these entities are driven by co-transplanted human immune cells populating patient-derived tumor samples. Since the exploding interest in the utilization of NOD scid and Il2rg-deficient mice for the establishment of PDTX platforms, it is of uppermost importance to raise the awareness of the limitations associated with this model. The disorders here described adversely impact tumor engraftment rate and animal lifespan, potentially representing a major confounding factor in the context of efficacy and personalized therapy studies. The occurrence of these conditions in the NOG model reflects the ability of this mouse line to promote efficient engraftment of human immune cells. Co-transplanted human lymphoid cells have indeed the potential to colonize the recipient mouse initiating the post-transplant conditions here reported. On the other hand, the evidence of an immune response of human origin against the xenotransplanted melanoma opens intriguing perspectives for the establishment of suitable preclinical models of anti-melanoma immunotherapy.

Genetically engineered mouse lines on a C57BL/6J background are widely employed as preclinical models to study neurodegenerative human disorders and brain tumors. However, because of the lack of comprehensive data on the spontaneous background neuropathology of the C57BL/6J strain, discriminating between naturally occurring changes and lesions caused by experimental mutations can be challenging. In this context, this study aims at defining the spectrum and frequency of spontaneous brain changes in a large cohort of C57BL/6J mice and their association with specific biological variables, including age and sex. Brains from 203 experimentally naive and clinically unremarkable C57BL/6J mice were collected and analyzed by means of histopathology and immunohistochemistry. Mice ranged in age from 3 to 110 weeks with 89 females, 111 males, and 3 unknowns. Sixteen different spontaneous lesion categories were described in this cohort. Age-related neurodegenerative and/or neuroinflammatory findings represented the most common pathologic changes and included (1) Hirano-like inclusions in the thalamic neurons, (2) neuroaxonal dystrophy in the medulla oblongata, (3) periodic acid–Schiff–positive granular deposits in the neuropil of the hippocampus, and (4) progressive neuroinflammation characterized by microgliosis and astrogliosis. Neoplastic conditions, developmental abnormalities, and circulatory disorders were rarely observed incidental findings. In conclusion, this study describes spontaneous age-related brain lesions of the C57BL/6J mouse and provides a reference for evaluating and interpreting the neuropathological phenotype in genetically engineered mouse models developed and maintained on this congenic background.