Murine models of human development and disease

Abstract

The present disclosure relates to murine models of human cancer and autoimmunity and methods of use.

Description

[0001]MURINE MODELS OF HUMAN DEVELOPMENT AND DISEASE RELATED APPLICATIONS This application claims the benefit under 35 U.S.C. § 119(e) of U.S. provisional application number 63 / 520,593, filed August 18, 2023, U.S. provisional application number 63 / 599,800, filed November 16, 2023, and U.S. provisional application number 63 / 664,237, filed June 26, 2024, each of which is incorporated by reference herein in its entirety. GOVERNMENT LICENSE RIGHTS This invention was made with government support under AI132963 awarded by National Institutes of Health. The government has certain rights in the invention. REFERENCE TO AN ELECTRONIC SEQUENCE LISTING The contents of the electronic sequence listing (J022770141WO00-SEQ-HJD.xml; Size: 3,573 bytes; and Date of Creation: August 14, 2024) is herein incorporated by reference in its entirety. BACKGROUND Humanize mouse models, such as peripheral blood mononuclear cell (PBMC)- humanized and hematopoietic stem cell (HSC)-humanized mouse models, can effectively mimic human immune responses within a biological context, offering a robust platform for studying human development and pathologies as well as evaluating the safety and efficacy of novel therapeutics, including immunotherapeutics. SUMMARY Mouse models of the disclosure, in some embodiments, are humanized, immunodeficient, and have been genomically modified to express human interleukin 34. Interleukin-34 is a cytokine known to regulate macrophages and other cells by binding to its receptor colony-stimulating factor 1 receptor. It is involved in various physiological and pathological processes, including immune responses and inflammation. Interleukin 34 (IL34), Colony stimulating factor 1 (CSF1), and colony stimulating factor 1 receptor (CSF1R) are critical in macrophage development and persistence. Both CSF1 And IL34 are cytokines that interact with CSF1R to promote macrophage development and persistence. Macrophages are immune cells that exist throughout the body, including microglia in the central nervous system. The roles of CSF1, IL34, and CSF1R are conserved in mammals including, but not limited to, humans, mice, dogs, cats, and primates. Although the transgenic expression of human CSF1 and human IL34 in vivo may induce human microglia development and persistence in animal models (e.g., mice) following human cell engraftment, the presence of host (e.g., mouse) microglial cells will be a confounding factor because while mouse CSF1 and IL34 will only support mouse microglial cell development, human CSF1 and IL34 will support mouse as well as human microglial cell development through interaction with mouse CSF1R. The solution to this problem is to block the development of mouse microglial cells by reducing or eliminating mouse CSF1R activity while developing human microglial cells in humanized immunodeficient mice. Thus, some aspects of the present disclosure advance the field by providing a humanized immunodeficient mouse model that supports long-term engraftment and function of human microglial cells and other human immune cell types, with reduced levels or the absence mouse microglial cells. The humanized immunodeficient mouse models provided herein have a robust human (adaptive and innate) immune system, in part because they have little to no residual endogenous innate immunity, in addition to lacking endogenous CSF1R activity. This lack of endogenous CSF1R activity results in a decrease in or absence of mouse microglial cells. These humanized immunodeficient mouse models, in some embodiments, transgenically express human-CSF1, IL34, or both CSF1 and IL34, resulting in engraftment and persistence of human microglia and other human immune cells without endogenous levels of mouse microglia. Thus, the immunodeficient mouse models contemplated herein are particularly suited for the engraftment of human microglia and other human immune cell types, which provides much needed platforms in which to study human diseases associated with microglia, such as Alzheimer’s Disease and HIV-1 infection, as well as autoimmunity, such as Multiple Sclerosis and Lupus. Furthermore, in some aspects, the humanized mouse models herein can be used for assessing immunotherapy-induced toxicity, for example, toxicities resembling cytokine activation-related hemophagocytic lymphohistiocytosis (carHLH). Humanization, in some embodiments, is achieved using human peripheral blood mononuclear cell (hPBMC) engraftment. Following engraftment in mice, hPBMCs can develop into cells of the human immune system that secrete human cytokines, for example. Hematopoietic stem cell (HSC) engraftment may also, or alternatively, be used to humanize a mouse model herein. Humanized (PBMC and / or HSC) mouse models are valuable clinically relevant models, particularly for testing the efficacy and safety of new therapeutics, and to study pathogenesis of human diseases. In irradiated then PBMC-humanized mouse experiments, for example, it has been possible to replicate many of the clinical findings of 4-1BB agonists, including liver toxicity, increased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and increased IFN–induced cytokines. Mice engrafted with PBMC from one of two donors and treated with urelumab showed significant liver toxicity and elevated serum AST and ALT. Conversely, utomilumab-treated mice did not exhibit these adverse effects. This model's capacity to reflect urelemab’s toxicity profile was validated in further studies with five additional PBMC donors. Just as in clinical trials, donor variability was also observed –three donors exhibited severe liver damage and cytokine elevation post-urelumab treatment. One donor showed no toxicity and another moderate toxicity. The irradiated then PBMC-humanized mouse model’s utility extends to various immunotherapeutics, including blinatumomab, rituximab, EGFRxCD3 BiTE®, and CAR-T therapies. These evaluations demonstrate that this model replicates outcomes seen in human disease, such as cytokine release, body weight loss, clinical symptoms, and survival rates. Importantly, irradiated PBMC-humanized mice also exhibit reproducible donor variability in immune responses, highlighting its relevance in assessing population-wide safety and individual patient responses. Considering the limitations of traditional animal models and in vitro assays, there is a critical need for more reliable preclinical models. The current models often fall short in accurately predicting human responses, emphasizing the necessity for more sophisticated systems. The experimental data provided herein has demonstrated that a humanized (e.g., PBMC-humanized) mouse model can effectively mimic human immune responses within a biological context, offering a robust platform for evaluating the safety and efficacy of novel immunotherapeutics. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1A shows human IL34 serum levels in serum from an NSG-Eno2-huIL34 mouse and an NSG-huIL34 KI mouse. FIG.1B shows heightened human IL34 in brains and spinal cords of 7-12-month-old NSG-Eno2-Hu-IL34 mice. FIGs.2A-2C show that human hematopoietic stem cell (HSC) engrafted NSG-huIL34 mice support high levels of human myeloid engraftment in the blood. FIG.2A shows data from HSC-engrafted NSG® mice; FIG.2B shows data from HSC-engrafted NSG-Eno2-huIL34 mice; and FIG.2C shows a comparison of the human immune cell subsets. FIG.3A shows data from flow cytometry analyses demonstrating that by ~7 weeks post engraftment, the human HSC-engrafted NSG-Eno2-huIL34 mice exhibited poor survival. FIG. 3B shows that human HSC-engrafted NSG-huIL34 KI mice exhibited 100% survival, while NSG-Eno2-huIL34 mice died by 4 weeks post engraftment. FIG.4 shows flow cytometry data demonstrating that disaggregated brains exhibited much higher levels of human microglia in the NSG- huIL34 KI mice than in the NSG-huCSF1 mice. FIGs.5A-5C show data from flow cytometry analyses of peripheral blood cells (PBL), bone marrow (BM) cells and splenocytes from naïve NSG®mice, NSG-Eno2huIL34-APP / PS1 mice, and NSG-huCSF1-APP / PS1 mice, demonstrating that there were no significant differences in percentages of B220+ pre-B cells, CD3+ T cells, MHC class I+ cells, MHC class II + cells, DX5+ cells, (Mac1 Gr1) double positive myeloid cells, or Ter 119+ erythroid cells). FIG.6 shows that NSG-Eno2-huIL34-APP / PS1 mice had increased numbers of IBAl+ microglia and GFAP+ astrocytes compared with NSG®mice. Mean + / -SEM of microglia and astrocytes. FIG.7 shows survival data from 3 of the 6 NSG-FIRE KO lines generated. FIG.8 shows numbers of F4 / 80+ macrophages per area in tissues of individual NSG- Fire knockout (KO) mice, heterozygotes (HET) and + / + (WT) controls. FIG.9 shows data generated by flow cytometry analysis of brain macrophages following enzymatic disassociation of brain demonstrating that NSG-FIRE KO mice exhibit a 98% depletion of brain macrophages. FIG.10 shows data demonstrating that NSG-FIRE KO mice exhibit abnormalities in liver chemistry profiles. FIG.11. NSG mice transgenic for h-IL34KI / KI or hCSF1Tg / Tg mice were engrafted with human CD34+ HSCs as newborns. As 8 weeks (h-IL34KI) or 12 weeks (h-CSF1Tg) of age, mice were perfused with PBS and half the brains and whole spinal cords were harvested and processed for flow cytometry. Cells were stained with antibodies specific for human CD45, mouse CD45, and a panel of antibodies against human and mouse variants of CD45 and microglia markers. We define hMG and mMG as CD45+CX3CR1+P2RY12+ cells. In mouse cells, this population is identical to the classical CD45intCD11b+ microglia population. The left panels compare hMG and mMG in the brain, while the right panels examines microglia in the spinal cord (SC). n=3-4. FIG.12. Protein expression of HLA-DR in human cells (left plots and graphs) and MHC class II in mouse cells (right plots) were assessed in CD45+ populations identified in FIG.11. Representative flow cytometry plots are shown above. The left plots demonstrate a heat map of HLA-DR expression in human CD45+ cells. Populations of P2RY12hiCX3CR1hicells (green), P2RY12lowCX3CR1lowcells (pink), and P2RY12-CX3CR1- cells (blue) were overlayed on a plot measuring HLA-DR expression. The percentages of HLA-DR+ cells in each population were compared between IL34KIand CSF1Tgmice. n=3-4. FIG.13 shows that in mouse bone marrow cells, CD44 is expressed highly within both h-IL34KIand h-CSF1Tgexpressing mice, but not expressed highly in brain-resident cells, suggesting that CD44 may be a plausible marker for bone marrow derived cells. FIG.14. IL34, CSF1 and DKO mice were engrafted with human PBMCs from a healthy donor. Serum levels of human cytokines in PBMC-humanized mice from the three strains were measured 8, 11 (or 12), 14, and 16 days after PBMC engraftment. IL18 is representatively shown, and the data are plotted by each strain, with varied y-axis scales. The complete list of human cytokines measured is as follows: IFNγ, GM-CSF, MIP-1α, MIP-1β, TNFα, IP-10, MIG / CXCL9, MCP-1, MDC, RANTES, sCD40L, IL-1b, IL-2, IL-3, IL-4, IL-5, IL-6, IL-8, IL-9, IL-10, IL-13, IL-15, IL-17A, IL-17F, IL-18, and FLT-3L. FIG.15A. IL34 mice were engrafted with 8 million (8M) or 4 million (4M) of human PBMCs from one of five healthy donors. Serum levels of human cytokines in PBMC-humanized IL34 mice were measured 8, 11, 14, and 16 days after PBMC engraftment. Mean level of human IL18 for each PBMC donor and dose is representatively shown. The data are plotted by each donor, with varied y-axis scales. FIG.15B. Using flow cytometry, the number of human CD45- positive cells per 1 µl of peripheral blood was measured at 8, 11, 14, and 16 days after PBMC engraftment. FIG.15C. Body weight change was measured and survival monitored until Study Day 38. FIG.16. IL34 mice were engrafted with 4M of human PBMCs from the two of five healthy donors and treated with PBS or CAR T cells were used to obtain the data presented in FIGS.3A-3C. We measured human ferritin from serum collected on Study Day 17 (17 days post PBMC engraftment). The data is shown in median fluorescent intensity level obtained using Luminex assay. The data are plotted by each donor, with varied y-axis scales. FIG.17 shows data demonstrating that NSG-IL34 mice humanized with different PBMC donors have different survival curves after CAR-T treatment. FIGs.18A-18C show data demonstrating that CAR-T treatment in NSG-IL34 mice humanized with two PBMC donors generated different kinetics of HLH-like protein and cytokines. DETAILED DESCRIPTION Tissue resident macrophages derived from embryonic yolk sac progenitors, develop prior to birth, are long-lived and radioresistant, and have critical functions in maintaining tissue homeostasis and in the pathogenesis of many human diseases that are of broad interest in the field of neurodegenerative diseases. The present disclosure provides cutting-edge humanized mouse models that support the efficient development of human tissue resident macrophages in disease relevant conditions. There has been a paucity of translational animal models that are readily available to the research community to study human tissue resident macrophages in vivo and to evaluate their role in human diseases. While several humanized platforms expressing human cytokines have been reported to improve development of human macrophage populations, many of these models are not available to basic research programs. Moreover, these models are often focused on engraftment of single macrophage populations and thus lack components of the adaptive immune system and other innate immune cells. An additional limitation for humanized models is that the mouse resident macrophage populations occupy the "niches" available for tissue specific macrophages and resist replacement with human hematopoietic stem cell (HSC)-derived macrophages. Provided herein, in some embodiments, are mouse models in which the Fms-intronic regulatory element (FIRE) enhancer in the CSF1 receptor gene has been knocked out in immunodeficient mice, which impairs the development of mouse tissue resident macrophages. Crossing these mice with immunodeficient mice expressing certain relevant human cytokines, such as human IL-34 and / or human CSF1 promotes the development of human myeloid cells. Genetic modification of immunodeficient mice, such as NSG®mice, to express species-specific, myeloid-promoting cytokines and to reduce mouse tissue resident macrophage populations enhances the development of functional human tissue resident macrophages and provide a robust small animal model for the study of inflammatory immune responses mediated by human macrophage populations. These new mouse models also allow for the in vivo investigation of human tissue resident macrophages in multiple diseases and accelerate the development of human specific therapies. This disclosure also describes, in some aspects a human peripheral blood mononuclear cell (PBMC)-humanized immunodeficient mouse expressing human interleukin 34 from a locus in its genome. In some embodiments, the mouse model is a hPBMC-humanized non-diabetic (NOD) scid gamma mouse expressing human IL34 from the mouse IL34 promoter (genotype Mouse models of the disclosure hold important potential for advancing the field’s understanding of immunotherapy-induced toxicity, for example, adoptive cell toxicities, such a chimeric antigen receptor (CAR) T-cell toxicities, resembling cytokine activation-related hemophagocytic lymphohistiocytosis (carHLH). In one model, the human IL34 gene was knocked into the mouse Il34 locus (thus, under control of the mouse Il34 promoter) to provide physiological (normal) levels of human IL34 in the mouse. These “huIL34 knockin mice” have relatively high levels of serum huIL34 (e.g., 950 pg / ml). Mouse models of the disclosure show spontaneous induction of myeloid-derived human cytokines in vivo. Further, the data provided herein show that the human ferritin level in the mouse model is elevated following adoptive cell therapy (e.g., CAR-T cell therapy), recapitulating clinical data of carHLH. Thus, mouse model provided herein exhibit distinctive characteristics that set them apart from existing PBMC-humanized mouse strains, making them an invaluable tool for identifying potential toxicities associated with adoptive cell therapies. These mouse models closely resemble patient cytokine profile and immunophenotype and serves as in vivo system to test the potential toxicity of immunotherapies. Many therapeutics on the market and in development engage myeloid cells directly or indirectly, as a byproduct of downstream signaling from its intended target. Further, accumulating evidence suggests that CAR-T-associated toxicity such as immune effector cell-associated neurotoxicity syndrome (ICANS) resulting from abnormal myeloid-T cell signaling. Modeling Human Disease Murine models, such as mouse models, are commonly used as models to study human diseases due to their genetic, biological, and behavioral similarities to humans. Genetic manipulation techniques can be used, for example, to create knockout mice, where specific genes are inactivated to study their roles in health and disease. Transgenic mice, which carry genes not naturally found in their species, often human genes, help in understanding the effects of these genes. Knock-in mice have specific genes inserted into their genome to observe their impacts, while CRISPR / Cas9 gene editing allows for precise genetic changes to model specific human genetic disorders. Mice are invaluable for modeling a wide range of diseases. Cancer models, such as those provided herein, where mice are engineered to develop tumors mimicking human cancers, facilitate the study of cancer progression and treatment testing. Likewise, Autoimmune disease models in mice mimic conditions such as rheumatoid arthritis, multiple sclerosis, and lupus. Neurological disease models can be used to study conditions like Alzheimer’s, Parkinson’s, and Huntington’s by introducing human-associated genetic mutations. Cardiovascular disease models help in understanding heart diseases, hypertension, and atherosclerosis, while metabolic disease models, created by manipulating diet or genes, are essential for studying diabetes, obesity, and metabolic syndrome. Infectious disease models allow researchers to study immune responses to various pathogens, including bacteria, viruses, and parasites. Physiological and behavioral studies in mice are crucial for understanding neurological and psychiatric disorders through behavioral tests. The mouse models provided herein can also play a significant role in drug testing, assessing the efficacy and safety of new drugs before they are used in humans. Immunological studies benefit from humanized mice, which are engrafted with human cells or tissues, such as immune cells, to study human immune responses and diseases. Developmental studies using mouse embryos help researchers understand human developmental processes and congenital defects. The advantages of using mice include their genetic similarity to humans, with about 95% shared genes, a short lifespan allowing for rapid generation studies, and reproducibility due to inbred mouse strains providing a consistent genetic background. Additionally, ethical and practical considerations make mice more feasible for large-scale studies compared to larger mammals. Tissue Resident Macrophages Development Most of the organs in the body contain tissue resident macrophages. These macrophages encompass a heterogeneous group of immune cells that carry out tissue- and system-specific functions. Tissue resident macrophages include microglial cells in the brain, spinal cord and retina, epidermal Langerhans cells, Kuppfer cells in the liver, as well as fixed macrophage populations in the lung, intestine, peritoneum, adipose tissue and other organs. It has been difficult to study the role of human tissue resident macrophages in immunodeficient mice. Engraftment of these human tissue resident macrophages requires reducing the populations of mouse tissue resident macrophages, expressing growth factors needed for development of human tissue resident macrophages from hematopoietic stem cells (HSC), and engrafting the mice with human HSC. Provided herein are immunodeficient mouse models that express human cytokines (e.g., human IL34, human CSF1, or a combination thereof) that enable the mouse to develop and maintain human microglia. Microglia are macrophages in the brain that play a major role in maintaining brain homeostasis. They constitute 5-10% of total brain cells and are responsible for surveying the brain for foreign matter, phagocytosis of debris (e.g., foreign particles, dead cells), maintaining neuronal plasticity, trophic support to neurons, and enabling neuronal synapse homeostasis. Microglia become activated during inflammation, and activated microglia cause reactive oxygen species release, excessive synaptic pruning of neurons, reduced trophic support to neurons, and eventually a compromised blood brain barrier. The immunodeficient mouse models provided herein, in some embodiments, express several exogenous nucleic acids (e.g., transgenes), each encoding a human gene or chimeric gene. A transgene is a segment of DNA containing a gene sequence that has been introduced into an organism. Unless stated otherwise herein, a transgene is integrated into the genome of a recipient organism (e.g., mouse genome). In some embodiments, an immunodeficient mouse comprises a human interleukin-34 (IL34) transgene, optionally wherein the human IL34 transgene is expressed to produce functional human IL34 protein. In some embodiments, an immunodeficient mouse comprises a human colony stimulating factor 1 (CSF1) transgene, optionally wherein the human CSF1 transgene is expressed to produce functional human CSF1 protein. In some embodiments, an immunodeficient mouse provided herein expresses human interleukin 34 (huIL34). Interleukin 34 (IL34) is a cytokine produced by various cell types, and its expression is particularly elevated in the skin, liver, secondary lymphoid organs, and brain. IL34 signals via colony stimulating factor 1 receptor (CSF1R) and is critical for the differentiation, proliferation, and survival of monocytes and macrophages. Additionally, IL34 is essential for the development and persistence of microglia. During embryonic development, IL34 guides the differentiation of microglia precursors in the yolk sac, from which they migrate to the central nervous system to serve as tissue resident macrophages. Throughout life, IL34 also promotes the survival of microglia. IL34 is expressed in a wide variety of organisms including, but not limited to: humans, mice, rats, cows, Rhesus monkeys, frogs, dogs, chickens, fish, birds, pigs, cats, and horses. In some embodiments, an immunodeficient mouse model herein expresses a transgene encoding human IL34. A human IL34 sequence may be any human IL34 sequence known in the art (see, e.g., Gene ID: 146433). In some embodiments, a human IL34 sequence is codon- optimized for expression in a non-human host (e.g., an immunodeficient mouse). A human IL34 sequence may be expressed (e.g., in a mouse) by any method provided herein. Endogenous IL34 protein is expressed in mice to regulate macrophage development in the central nervous system and skin during development through the CSF1 receptor (CSF1R). Mouse IL34 also interacts with receptor protein tyrosine phosphatase-z on neural progenitor cells. IL34 plays an important role in the maintenance and differentiation of microglia and Langerhans cells (LCs). Mouse IL34 (Gene ID: 76527) is produced from a mouse IL34 gene. A mouse IL34 gene may be any mouse IL34 gene known in the art including, but not limited to: NM_001135100.2 and NM_029646.3. In some embodiments, an immunodeficient mouse provided herein has an endogenous (e.g., mouse) IL34nullmutation. An IL34nullmutation results in mouse IL34 protein whose function is reduced by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) compared to wildtype mouse IL34 protein. Non-limiting examples of mouse IL34nullmutations include: Il34em1Sz, Il34em1Adiuj, Il34em1Gpt, Il34em1Smoc, Il34em2Gpt, Il34tm1c(EUCOMM)Wtsi, Il34tm1Smoc, Il34Gt(298C10)Cmhd, Il34Gt(IST12345E9T)Tigm, Il34Gt(IST12579H11)Tigm, Il34Gt(IST13358D11)Tigm, Il34Gt(IST14082F1)Tigm, Il34Gt(IST14425H11)Tigm, Il34Gt(IST14835D5)Tigm, Il34Gt(OST149556)Lex, Il34Gt(OST315345)Lex, Il34Gt(OST415275)Lex, Il34Gt(OST447311)Lex, Il34Gt(PST10227)Mfgc, and Il34tm1e(EUCOMM)Wtsi. In some embodiments, an immunodeficient mouse provided herein comprises an IL34nullallele, optionally an Il34em1Szallele. In some embodiments, an immunodeficient mouse provided herein expresses human colony stimulating factor 1 (CSF1, also called macrophage colony stimulating factor, M-CSF). CSF1 is a cytokine produced by stromal cells, fibroblasts, and immune cells, and it acts as a growth factor that stimulates the proliferation and differentiation of hematopoietic progenitors in the bone marrow, leading to the generation of monocytes. Monocytes that egress from the bone marrow can populate peripheral tissues and differentiate into macrophages. Like IL34, CSF1 is critical to embryonic development of microglia in the yolk sac and the maintenance of microglia throughout life. CSF1 is also a ligand for CSF1R. CSF1 is expressed in a variety of organisms including, but not limited to: humans, mouse, rat, cows, pigs, Rhesus monkey, chimpanzee, dogs, cats, chickens, birds, frogs, and birds. A human CSF1 sequence may be any human CSF1 sequence known in the art (see, e.g., Gene ID: 1435). In some embodiments, a human IL34 sequence is codon-optimized for expression in a non-human host (e.g., an immunodeficient mouse). A human IL34 sequence may be expressed (e.g., in a mouse) by any method provided herein. In some embodiments, an immunodeficient mouse provided herein expresses a modified endogenous Csf1R allele. Colony stimulating factor 1 receptor (CSF1R) protein is expressed in mice to regulate macrophage development and maintenance throughout the body by interacting with CSF1 and IL34. Mouse CSF1R (Gene ID: 12978) is produced from a mouse CSF1R gene. A mouse CSF1R gene may be any mouse CSF1R gene known in the art including, but not limited to: NM_001037859.2. In some embodiments, an immunodeficient mouse provided herein has an endogenous (e.g., mouse) CSF1Rnullmutation. A CSF1Rnullmutation results in mouse CSF1R protein whose function is reduced by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) compared to wildtype mouse CSF1R protein. Non-limiting examples of mouse CSF1Rnullmutations include: Csf1rem1(cre / ERT2)Gpt, Csf1rem1(icre)Gpt, Csf1rem1Gpt, Csf1rem1H, In some embodiments, an immunodeficient mouse provided herein comprises an engineered genomic variant of an endogenous mouse colony stimulating factor 1 receptor (Csf1r) gene. An endogenous gene refers to a gene that originates from within an organism, cell, or system, as opposed to a gene that is introduced from the outside (exogenous). Thus, an endogenous gene is one that is naturally present and active within the organism. In mouse models, an endogenous gene is a mouse gene from the mouse (Mus Musculus) genome. An engineered genomic variant may be in any intron in a mouse Csf1r gene (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, and 22). The mammalian Csf1r locus contains a highly conserved super-enhancer, the Fms-intronic regulatory element (FIRE) in intron 2 that is bound by numerous transcription factors involved in microglia and macrophage development. Knocking out the FIRE enhancer is expected to reduce macrophage and microglia development and maintenance in vivo. In some embodiments, an engineered genomic variant is in intron 2 of a mouse Csf1r gene (e.g., comprising the FIRE enhancer). Non-limiting examples of engineered genomic variants in intron 2 include: Csf1rem2zand Csf1r∆FIRE. In some embodiments, an immunodeficient mouse provided herein comprises an engineered genomic variant that encodes Csf1rem2z. As described above, mouse CSF1R is critical in macrophage and microglia development and maintenance. In embodiments where an immunodeficient mouse expresses a Csf1rnullgene or an engineered genomic variant of endogenous Csf1r, the number of mouse macrophage cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. In some embodiments, the number of mouse macrophages is lower by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. In embodiments where an immunodeficient mouse expresses a Csf1rnullgene or an engineered genomic variant of endogenous Csf1r, the number of mouse microglia cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. In some embodiments, the number of mouse microglia is lower by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. Immunotherapy Induced Toxicity Hemophagocytic lymphohistiocytosis (HLH) is a severe and potentially fatal hyperinflammatory syndrome that results from uncontrolled activation and proliferation of T lymphocytes and macrophages. This leads to excessive cytokine production, known as a “cytokine storm,” which can cause multi-organ failure. HLH can be either primary (genetic) or secondary. The secondary form is often triggered by infections, malignancies, or autoimmune diseases and is sometimes referred to as secondary HLH or acquired HLH. When the secondary HLH is associated with a specific cause, it might also be termed as carHLH, denoting “cytokine activation-related HLH”. Aspects of the disclosure provide methods of assessing immunotherapy induced toxicity. Immunotherapy induced toxicity includes side effects resulting from the administration of an immunotherapy, such as an adoptive cell therapy, a cancer vaccine, or an immune checkpoint inhibitor. Such side effects can arise due to stimulation or alteration of the immune system, for example. Toxicities in humans include, among others, dermatologic, gastrointestinal, endocrine, pulmonary, cardiac, neurologic, renal, liver, musculoskeletal, hematologic, and ocular toxicities, any of which may be assessed using a mouse model provided herein. Immunotherapy induced toxicity is assessed herein using a mouse model, particularly an immunodeficient mouse model expressing human IL34. Different routes of administration may be used to deliver the immunotherapy, depending on the type of therapy – for example, by oral gavage, intravenous (e.g., tail vein injection), or subcutaneous. Doses of an immunotherapy administered to a mouse may range, for example, from sub-therapeutic to super-therapeutic to establish a dose-response curve and determine the maximum tolerated dose. In some embodiments, a mouse is administered a single dose, while in other embodiments, multiple doses are administered. Acute toxicity is typically assessed over a short period (e.g., 24 hours), while chronic toxicity can be assessed over an extended period (e.g., weeks to months). As discussed elsewhere herein, immunodeficient mice of the disclosure (e.g., expressing human IL34) are unexpectedly capable of serving as a model of cytokine activation-related hemophagocytic lymphohistiocytosis (carHLH). Following human PBMC engraftment, the cells, primarily including lymphocytes (e.g., T cells, B cells, and NK cells) and monocytes secrete human cytokines. In immunodeficient mice expressing a genomically integrated human IL34, the engrafted human PBMCs surprisingly secrete high (e.g., over 1000-2000 pg / ml) circulating levels of human pro-cancer and myeloid-derived cytokines such as IL8, IL18, MCP-1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ. IL18, for example, is elevated in patients with various cancer types. Currently, there is no available PBMC-humanized mouse model that induces human IL18 levels higher than 100 pg / ml, even after immunotherapy treatment. Thus, in some embodiments, assessing immunotherapy induced toxicity includes measuring a circulating level of a human pro-cancer and / or human myeloid derived cytokine. In some embodiments, assessing immunotherapy induced toxicity includes measuring a circulating level of one or more of IL8, IL18, MCP-1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ. In some embodiments, immunotherapy induced toxicity includes measuring a circulating level of two or more of IL8, IL18, MCP-1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ. In some embodiments, assessing immunotherapy induced toxicity includes measuring a circulating level of three or more of IL8, IL18, MCP-1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ. In some embodiments, assessing immunotherapy induced toxicity includes measuring a circulating level of IL18. In some embodiments, a PBMC-humanized immunodeficient mouse expressing human IL34 produces circulating human IL18 at serum levels higher than 100 pg / ml. For example, a PBMC-humanized immunodeficient mouse expressing human IL34 may produce circulating human IL18 at serum levels higher than 500 pg / ml, 1000 pg / ml, or 2000 pg / ml by 11-16 days following human PBMC engraftment. In some embodiments, a PBMC-humanized immunodeficient mouse expressing human IL34 produces circulating human IL18 at serum levels higher than 100 pg / ml at about 11 days following human PBMC engraftment. In some embodiments, a PBMC-humanized immunodeficient mouse expressing human IL34 produces circulating human IL18 at serum levels higher than 500 pg / ml at about 14 days following human PBMC engraftment. In some embodiments, a PBMC-humanized immunodeficient mouse expressing human IL34 produces circulating human IL18 at serum levels higher than 1000 pg / ml at about 16 days following human PBMC engraftment. In some embodiments, a PBMC- humanized immunodeficient mouse expressing human IL34 produces circulating human IL18 at serum levels higher than 2000 pg / ml at about 16 days following human PBMC engraftment. PBMC-humanized immunodeficient mouse models expressing human IL34 were also shown to have elevated human ferritin levels following immunotherapy, which can be a predictor of poor survival in the context of HLH-like toxicities induced by immunotherapies, such as CAR T therapy. Thus, in some embodiments, assessing immunotherapy induced toxicity includes measuring human ferritin. In some embodiments, assessing immunotherapy induced toxicity includes measuring human IL18 and human ferritin. In some embodiments, assessing immunotherapy induced toxicity includes measuring one, two, three or more of IL8, IL18, MCP- 1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ and measuring human ferritin. Multiple Sclerosis In some embodiments, the mice described herein model an autoimmune disease, such as multiple sclerosis. The most common model of multiple sclerosis (MS) in mice is Experimental Autoimmune Encephalomyelitis (EAE). MS is a chronic autoimmune disease that targets the central nervous system, causing inflammation and damage to the myelin sheath that surrounds neurons. As a non-limiting example of how the model is prepared, rather than using whole myelin, specific peptides derived from myelin proteins are often used, such as myelin oligodendrocyte glycoprotein (MOG), proteolipid protein (PLP), or myelin basic protein (MBP). These peptides are dissolved in an appropriate buffer. The myelin peptide solution is emulsified with an adjuvant, often Complete Freund's Adjuvant (CFA), which contains killed bacteria (typically Mycobacterium tuberculosis). The purpose of the adjuvant is to boost the immune response. Sometimes, an additional immune stimulant, such as pertussis toxin, is administered. Mice are then immunized by injecting the emulsified peptide solution subcutaneously or intradermally. This injection causes the immune system to recognize the myelin peptides as foreign. Over the following days and weeks, the mice develop a condition similar to MS, with the immune system attacking the myelin in the central nervous system. This leads to inflammation and damage, resulting in clinical signs such as weakness and paralysis. The progression of EAE is then monitored over time, typically by observing the clinical signs and scoring the severity of the disease. At the end of the experiment, tissues can be analyzed to understand the immune response and assess the extent of the damage. Lupus In some embodiments, the mice described herein model lupus. Pristane is a naturally occurring hydrocarbon found in mineral oil. It has been used in scientific research to induce a model of lupus in mice, known as pristane-induced lupus (PIL). Pristane is believed to trigger an autoimmune response in susceptible strains of mice, leading to the development of lupus-like symptoms. In the pristane-induced lupus model, researchers inject pristane into mice, typically intraperitoneally (into the abdominal cavity). The injection of pristane stimulates the immune system and causes the production of autoantibodies, which are antibodies that mistakenly target the body's own cells and tissues. As a non-limiting example of how the model is prepared, pristane is obtained in a pure form and doesn't require much preparation. The mice receive a single intraperitoneal (IP) injection of pristane. The dosage can vary, but it's usually around 0.5 mL. Over the following weeks and months, the mice develop a lupus-like syndrome. The pristane stimulates the production of various autoantibodies, similar to those seen in human lupus. It also causes chronic inflammation in the peritoneum (the lining of the abdominal cavity), which mimics some of the inflammatory processes seen in lupus. The mice are monitored over time for signs of lupus, such as the production of autoantibodies and the development of immune complex deposits in the kidneys (glomerulonephritis). Other signs of lupus, like skin lesions, are typically not seen in this model. Rheumatoid Arthritis In some embodiments, the mice described herein model rheumatoid arthritis. Type II collagen can be administered to mice, for example, to produce a model of human rheumatoid arthritis. Collagen-induced arthritis (CIA) is a commonly used animal model to study rheumatoid arthritis. This model has proven to be highly valuable in investigating the pathophysiological processes of arthritis and in evaluating potential therapeutic interventions. As a non-limiting example of how the model is prepared, Type II collagen, typically bovine or chicken, is dissolved in an acidic solution (often acetic acid) to create the collagen solution. The collagen solution is then emulsified with an adjuvant, often Complete Freund's Adjuvant (CFA), which contains killed bacteria (typically Mycobacterium tuberculosis). The purpose of the adjuvant is to boost the immune response. Mice are then immunized by injecting the emulsified collagen solution, usually into the base of the tail or into the flank. The injection causes the immune system to react against the collagen, which is similar to the mouse's own type II collagen. After about 21 days, a booster shot is often given to strengthen the immune response. This usually involves the same emulsified collagen solution, but sometimes without the adjuvant. After another couple of weeks, the mice typically start to develop signs of arthritis, such as swelling and redness in the joints, particularly in the hind paws. This is due to the immune system attacking the body's own collagen in the joints, which is seen as foreign due to the earlier exposure to the collagen solution. The progression of arthritis is then monitored over time, and the mice can be analyzed to understand the immune response and disease progression. Alzheimer’s Disease In some embodiments, an immunodeficient mouse model provided herein may be used to study a disease associated with microglial dysfunction. Microglial dysfunction refers to reduced or absent microglia function (e.g., supporting neurons, phagocytosis of foreign matter, maintaining neuronal plasticity). Non-limiting examples of disease associated with microglial dysfunction include Alzheimer’s Disease (AD), Parkinson’s disease, prion diseases, frontotemporal dementia, multiple sclerosis, and amyotrophic lateral sclerosis. In some embodiments, an immunodeficient mouse model provided herein may be used to study AD. Alzheimer’s Disease is the most common form of dementia and a growing public health concern worldwide. From 1990 to 2019, the incidence and prevalence of AD increased by nearly 150%. Li et al., Front. Aging Neurosci.2022.12:937486. AD primarily impacts adults aged 65 and older, though there are cases of early-onset Alzheimer's that can affect individuals in their 40s or 50s. On a physiological level, AD is characterized by the accumulation of abnormal protein aggregates in the brain. The two main types of protein deposits associated with AD are amyloid plaques, made up of beta-amyloid protein fragments that accumulate between neurons, and neurofibrillary tangles composed of the protein tau, which accumulates within neurons, causing neural malfunction and death. The neural degeneration in AD is associated with cognitive impairments, including memory loss, language difficulties, mood changes, disorientation, and a decline in the ability to perform complex tasks. Multiple mouse models have been developed to elucidate the molecular underpinnings of the development and progression of AD. Such models target various aspects of AD pathology, including the accumulation of amyloid-beta plaques and tau tangles, in addition to the cognitive impairments associated with AD. One mouse model commonly used in the field of AD research is the PWK.Cg-Tg(APPswe,PSEN1dE9)85Dbo (APP / PS1) mouse line (JAX Strain No. 025971). APP / PS1 mice are engineered to express a chimeric mouse / human amyloid precursor protein (APP) (Mo / HuAPP695swe) and a mutant human presenilin 1 (PS1) (PS1-dE9) in central nervous system (CNS) neurons. PS1 is a component of the gamma (γ)-secretase complex, which processes APP into smaller peptides. It is believed that malfunction of PS1 can lead to the aggregation of beta-amyloid fragments. The mutations employed in the APP / PS1 mouse model are both associated with early-onset AD in humans, and in APP / PS1 mice, a majority of plaques has seeded and are in the exponential growth phase by 6 months of age. While amyloid-beta plaques and tau tangles have long been associated with AD pathology, the role of microglia – the tissue resident macrophages of the CNS – in the development and progression of AD has become increasingly appreciated in recent years. For example, microglia are actively involved in the clearance of amyloid-beta fragments, and defects in this function can lead to aggregation of amyloid-beta into plaques. When microglia are activated, they can release factors that influence tau aggregation and dissemination, which can drive AD progression. Similarly, activated microglia release inflammatory factors that, when properly regulated, can promote the clearance of protein aggregates, but can drive tissue damage and exacerbate disease progression when regulatory processes go awry. To recapitulate the development and progression in human AD, it is ideal to study the function of human microglia in an APP / PS1 mouse model. However, a major drawback of this model is that, while the role of endogenous microglia can be studied, APP / PS1 mice do not support the engraftment of human microglia, as they do not produce the human cytokines necessary for their survival, such as colony stimulating factor 1 (CSF1) and interleukin 34 (IL34). Thus, there exists a need to develop APP / PS1 mice that support the engraftment of human microglia in the central nervous system. Accordingly, in some embodiments, the present disclosure provides an immunodeficient mouse comprising a Mo / HuAPP695swe transgene, optionally wherein the Mo / HuAPP695swe transgene is expressed to produce a modified humanized mouse amyloid beta (A4) precursor protein. In some embodiments, the immunodeficient mouse may also comprise a CSF1 transgene, optionally expressed to produce functional human CSF1 protein; an IL34 transgene, optionally expressed to produce functional human IL34 protein; or a CSF1 transgene and an IL34 transgene, optionally expressed to produce functional human CSF1 protein and human IL34 protein, respectively. In some embodiments, an immunodeficient mouse comprises a PS1-dE9 transgene, optionally wherein the PS1-dE9 transgene is expressed to produce a mutant human PS1 protein. In some embodiments, the immunodeficient mouse may also comprise a Mo / HuAPP695swe transgene; a CSF1 transgene; an IL34 transgene; or a Mo / HuAPP695swe transgene, a CSF1 transgene, and an IL34 transgene. The expression of human CSF1 and IL34 in an immunodeficient APP / PS1 mouse supports the engraftment of human microglia and enable the study of their role in the development and progression of AD, for example. HIV-1 Microglia are the principal innate immune defense cells of the central nervous system (CNS) and are also the target of the human immunodeficiency virus type one (HIV-1). A complete understanding of human microglial biology and function requires the cell’s presence in a brain microenvironment. Lack of relevant animal models thus far has also precluded studies of HIV-1 infection. Productive viral infection in brain occurs only in human myeloid linage microglia and perivascular macrophages and requires cells present throughout the brain. Once infected, however, microglia become immune competent serving as sources of cellular neurotoxic factors leading to disrupted brain homeostasis and neurodegeneration. Thus, in some embodiments, an immunodeficient mouse model provided herein may be used to study HIV-1 infection. Murine Models As is understood in the art, the term “murine” refers to mice and / or rats, particularly those belonging to the family Muridae. Herein, for simplicity, reference is made to “mouse” and “mouse models” (e.g., surrogates for human conditions); however, these terms, unless otherwise stated, may be interchanged throughout the specification with the terms “murine” and “murine models.” It should also be understood that standard genetic nomenclature used herein provides unique identification for different murine strains, and the strain symbol conveys basic information about the type of strain or stock used and the genetic content of that strain. Rules for symbolizing strains and stocks have been promulgated by the International Committee on Standardized Genetic Nomenclature for Mice. The rules are available on-line from the Mouse Genome Database (MGD; informatics.jax.org) and were published in print copy (Lyon et al. 1996). Strain symbols typically include a Laboratory Registration Code (Lab Code). The first Lab Code appended to a strain symbol identifies and credits the creator of the strain. The Lab Code at the end of a strain symbol indicates the current source for obtaining mice of that strain. Different Lab Codes appended to the same strain symbol distinguish sublines and alert the user that there may be genetic divergence between the different sublines. Lab Codes are assigned from a central registry to assure that each is unique. The registry is maintained at the Institute for Laboratory Animal Research (ILAR) at the National Academy of Sciences, Washington, D.C. Lab Codes may be obtained electronically at ILAR's web site (nas.edu / cls / ilarhome.nsf). See also Davisson MT, Genetic and Phenotypic Definition of Laboratory Mice and Rats / What Constitutes an Acceptable Genetic-Phenotypic Definition, National Research Council (US) International Committee of the Institute for Laboratory Animal Research. Washington (DC): National Academies Press (US); 1999. A murine (e.g., mouse) model of disease may be modified to enable the assessment of a disease. Any system (e.g., immune, respiratory, nervous, or circulatory), organ (e.g., blood, heart, blood vessels, spleen, thymus, lymph nodes, or lungs), tissue (e.g., epithelial, connective, muscle, and nervous), or cell type (e.g., lymphocytes or macrophages) may be modified, either independently or in combination, to enable studying disease in the models provided herein. Three conventional methods used for the production of genome-modified mice (e.g., knockout mice, transgenic mice), for example, include DNA microinjection (Gordon and Ruddle, Science 1981: 214: 1244-124, incorporated herein by reference), embryonic stem cell- mediated gene transfer (Gossler et al., Proc. Natl. Acad. Sci.1986, 83: 9065-9069, incorporated herein by reference) and retrovirus-mediated gene transfer (Jaenisch, Proc. Natl. Acad. Sci. 1976, 73: 1260-1264, incorporated herein by reference), any of which may be used as provided herein. Genomic editing methods using, for example, clustered regularly interspace palindromic repeats (CRISPR / Cas) nucleases, transcription activator-like effector nucleases (TALENs), or zinc finger nucleases (ZFNs) are described elsewhere herein. Following delivery of nucleic acids to a fertilized embryo (e.g., a single-cell embryo (e.g., a zygote) or a multi-cell embryo (e.g., a developmental stage following a zygote, such as a blastocyst), the fertilized embryo is transferred to a pseudopregnant female, which subsequently gives birth to offspring. New murine (e.g., mouse) models can also be created by breeding parental lines. With the variety of available mutant, knockout, knockin, transgenic, Cre-lox, Tet-inducible system, and other murine strains, multiple mutations and transgenes may be combined to generate new murine models. Multiple murine (e.g., mouse)strains may be bred together to generate double, triple, or even quadruple and higher multiple mutant / transgenic animals. In some embodiments, parental mice are bred to produce offspring, also referred to as progeny mice. A parental mouse may be, for example, homozygous, heterozygous, hemizygous, or homozygous null at a particular allele. An allele is one of two or more alternative forms of a gene that arise by mutation and are found at the same location on a chromosome. Homozygous describes a genotype of two identical alleles at a given locus, heterozygous describes a genotype of two different alleles at a locus, hemizygous describes a genotype consisting of only a single copy of a particular gene in an otherwise diploid organism, and homozygous null refers to an otherwise diploid organism in which both copies of the gene are missing. The mice described herein may by homozygous, heterozygous, hemizygous, or homozygous null for any one or more of the alleles described herein. A progeny mouse, in some embodiments, is an F1 mouse. F1 mice are the first- generation offspring resulting from a cross between two genetically distinct inbred strains. These mice are heterozygous, meaning they inherit one allele from each parent for each gene. All F1 offspring from a specific cross are genetically identical to each other because they inherit the same combination of alleles from their parents. A progeny mouse, in some embodiments, is an F2 mouse. F2 mice are the second-generation offspring resulting from the interbreeding of F1 mice. Unlike F1 mice, F2 mice exhibit significant genetic diversity. This diversity arises because each F2 mouse inherits a different combination of alleles from the F1 parents. The genetic makeup of F2 mice is more variable than that of F1 mice. Immunodeficient Murine Models Provided herein, in some embodiments, are immunodeficient murine (e.g., mouse) strains. Immunodeficient mouse strains, for example, are genetically engineered mice that have impaired or disrupted immune systems, making them useful models for studying human diseases and / or developing new therapies. These mice lack one or more key components of the immune system, such as T cells, B cells, and / or natural killer cells, which makes them unable to mount a proper immune response to infections or foreign substances. These mouse strains are commonly used in preclinical research to study cancer, infectious diseases, autoimmune disorders, and transplant rejection. For example, human tumor cells (e.g., patient-derived xenograft (PDX) cells) can be transplanted into immunodeficient mice to study cancer biology and test new cancer therapies. Immunodeficient mice can also be used to study infectious diseases by infecting the mice or engrafted human cells with human pathogens, such as viruses or bacteria. Some immunodeficient mice have specific deficiencies in MHC class I and / or II or defects in the production and / or function of cells selected from B cells, T cells, natural killer (NK) cells, myeloid cells (e.g., granulocytes and / or monocytes), macrophage cells, and dendritic cell. Some immunodeficient mice also, or alternatively, have immunodeficiency due to knockdown of certain genes coding for cytokines, cytokine receptors, TLR receptors, and / or a variety of transducers and / or transcription factors of signaling pathways. Examples of immunodeficiency mouse models include the single- and multi-gene mutation models such as nude-mice (nu) strains, the severe combined immunodeficiency (scid) strains, non-obese diabetic (NOD) immunodeficient strains, RAG-1 or RAG-2 (recombination activating gene 1 or 2) strains and a variety of hybrids originated by crossing doubly and triple mutation mice strains with additional defects in innate and adaptive immunity. Immunodeficient mice of the disclosure can include multiple alleles that render the mice immunodeficient. In some embodiments, an immunodeficient mouse comprises an interleukin-2 receptor gamma null (IL-2Rɣnull) allele. An IL-2Rɣnullallele is a null mutation in the gene encoding the interleukin 2 receptor gamma chain (IL2Rγ, homologous to IL2RG in humans), which blocks natural killer (NK) cell differentiation, thereby removing an obstacle that prevents the efficient engraftment of primary human cells (Cao et al., 1995; Greiner et al., 1998; and Shultz et al., 2005, each of which is incorporated herein by reference). In some embodiments, an immunodeficient mouse is homozygous for an IL-2Rɣnullallele. In some embodiments, an immunodeficient mouse comprises a severe combined immunodeficiency (scid) mutation, also referred to as a Prkdcscidallele. The Prkdcscidmutation is a loss-of-function (null) mutation in the mouse homolog of the human PRKDC (Protein Kinase, DNA-Activated, Catalytic Subunit) gene – this mutation essentially eliminates adaptive immunity (see, e.g., Blunt et al., 1995; Greiner, Hesselton, & Shultz, 1998), each of which is incorporated herein by reference). In some embodiments, an immunodeficient mouse is homozygous for a Prkdcscidallele. In some embodiments, an immunodeficient mouse comprises a Recombination Activating Gene 1 null (Rag1null) allele. The Rag1nullmutation renders the mice B and T cell deficient. In some embodiments, an immunodeficient mouse is homozygous for a Rag1nullallele. In some embodiments, an immunodeficient mouse comprises a Recombination Activating Gene 2 null (Rag2null) allele. The Rag2nullmutation also renders the mice B and T cell deficient. In some embodiments, an immunodeficient mouse is homozygous for a Rag2nullallele. Both Rag1nulland Rag2nullmice lack functional B and T cells due to defects in V(D)J recombination. However, the specific inactivation of either Rag1 or Rag2 allows researchers to study the distinct roles of these genes in immune system development. Non-limiting examples of spontaneous and transgenic immunodeficient mouse models include the following mouse strains: • NOD [Kikutani H et al. Adv Immunol 1992; 51: 285-322; and Anderson MS et al. Ann Rev Immunol 2005; 23: 447-85]; • Nude (nu) [Flanagan SP. Genet Res 1966; 8: 295-309; and Nehls M et al. Nature 1994; 372: 103-7]; • Scid (scid) [Bosma GC et al. Nature 1983; 301:527-30; Mosier DE et al. Nature 1988; 335: 256-9; and Greiner DL et al. Stem Cells 1998; 16: 166-77]; • RAG1 and RAG2 (rag) [Mombaerts P et al. Cell 1992; 68: 869-77; Shinkai U et al. Cell 1992; 68: 855-67]; • NOD-scid [Greiner DL et al.1998; Shultz LD et al. J Immunol 1995; 154: 180-91; Melkus MW et al. Nature Med 2006; 12: 1316-22; and Denton PW et al. PLoS Med 2008; 4(12): e357]; • IL2rgnull [DiSanto JP et al. Proc Natl Acad Sci USA 1995; 92: 377-81]; • B2mnull [Christianson SW et al. J Immunol 1997; 158: 3578-86]; • NSG®mice (NOD-scid IL2rγnull) [Shultz LD et al. Nat Rev Immunol 2007; 7: 118-30; Ito M et al. Blood 2002; 100: 3175-82; Ishikawa I et al. Blood 2005; 106: 1565-73; and Macchiarini F et al. J Exp Med 2005; 202: 1307-11]; • NRG mice (NOD.Cg-Rag1tm1MomIl2rgtm1Wjl / SzJ) [Pearson T et al. Clin Exp Immunol 2008 Nov;154(2):270-84] • NOG mice (NOD.cg-PrkdcscidIl2rgtm1Sug) [Shultz LD et al. Nat Rev Immunol 2007; 7: 118-30]; • NCG mice (NOD-Prkdcem26Cd52Il2rgem26Cd22 / NjuCrl); • NOD-scid B2mnull [Shultz et al.2007; Shultz LD et al. Transplantation 2003; 76: 1036- 42; Islas-Ohlmayer MA et al. J Virol 2004; 78:13891-900; and Macchiarini et al.2005]; • HLA transgenic mice [Grusby MJ et al. Proc Natl Acad Sci USA 1993; 90(9): 3913-7; and Roy CJ et al. Infect Immun 2005; 73(4): 2452-60]. See, e.g., Belizario JE The Open Immunology Journal, 2009; 2:79-85; • BRG mice (BALB / cA-Rag2nullIl2rγnull) [Goldman JP et al. Br J Haematol. 1998;103:335–342]; and • MISTRG mice (C;129S4-Rag2tm1.1FlvCsf1tm1(CSF1)FlvCsf2 / Il3tm1.1(CSF2,IL3)FlvThpotm1.1(TPO)FlvIl2rgtm1.1FlvTg(SIRPA)1Flv / J) [Rongvaux A et al. Nat Biotechnol.2014 Apr;32(4):364- 72]. Provided herein, in some embodiments, are immunodeficient mouse models having the non-obese diabetic (NOD) mouse genotype. The NOD mouse (e.g., Jackson Labs Strain #001976, NOD-ShiLtJ) is a polygenic mouse model of autoimmune (e.g., Type 1) diabetes, characterized by hyperglycemia and insulitis, a leukocytic infiltration of the pancreatic islet cells. The NOD mice are hypoinsulinemic and hyperglucagonemic, indicating a selective destruction of pancreatic islet beta cells. The major component of diabetes susceptibility in NOD mice is the unique MHC haplotype. NOD mice also exhibit multiple aberrant immunophenotypes including defective antigen presenting cell immunoregulatory functions, defects in the regulation of the T lymphocyte repertoire, defective NK cell function, defective cytokine production from macrophages (Fan et al., 2004) and impaired wound healing. They also lack hemolytic complement C5. NOD mice also are severely hard-of-hearing. A variety of mutations causing immunodeficiencies, targeted mutations in cytokine genes, as well as transgenes affecting immune functions, have been backcrossed into the NOD inbred strain background. In some aspects of the present disclosure, an immunodeficient mouse provided herein based on the NOD background has a genetic background (“background”) selected from NOD- . Other immunodeficient mouse strains are contemplated herein. The “genetic background” (referred to simply as the “background”) of an animal refers to the complete genetic composition of the mouse, excluding the specific gene or genes being studied or manipulated. The genetic background includes all other genes and their variants (alleles) that are present in the animal’s genome. In mice, for example, the genetic background is often associated with a specific mouse strain. Common laboratory strains include C57BL / 6, BALB / c, and 129 / Sv, each with its unique genetic makeup. These strains have been inbred to ensure genetic uniformity within the strain. Thus, an NSG® mouse engineered to express a human transgene or an NSG® mouse in which an endogenous gene of interest has been knocked out is considered a genetically engineered mouse having an NSG® background. In some embodiments, an immunodeficient mouse model based on the NOD genetic background has an NOD-Cg.-PrkdcscidIL2rgtm1wJl / SzJ (NSG®) background. The NSG®mouse (e.g., Jackson Labs Strain No.: #005557) is an immunodeficient mouse that lacks mature T cells, B cells, and NK cells, is deficient in multiple cytokine signaling pathways, and has many defects in innate immune immunity (see, e.g., Shultz, Ishikawa, & Greiner, 2007; Shultz et al., 2005; and Shultz et al., 1995, each of which is incorporated herein by reference). The NSG® mouse, derived from the NOD mouse strain NOD / ShiLtJ (see, e.g., Makino et al., 1980, which is incorporated herein by reference), includes the Prkdcscidmutation (also referred to as the “severe combined immunodeficiency” mutation or the “scid” mutation) and the Il2rgtm1Wjltargeted mutation. The Il2rgtm1Wjlmutation is a null mutation in the gene encoding the interleukin 2 receptor gamma chain (IL2Rγ, homologous to IL2RG in humans), which blocks NK cell differentiation, thereby removing an obstacle that prevents the efficient engraftment of primary human cells (Cao et al., 1995; Greiner et al., 1998; and Shultz et al., 2005, each of which is incorporated herein by reference). In some embodiments, an immunodeficient mouse model has an NSG.RosaBxb-GT / GA background, also referred to herein simply as NSG-ROSA26 (e.g., Jackson Labs Strain #036151). An NSG-ROSA26 mouse has the following genotype: NOD.Cg- Gt(ROSA)26Sorem5MvwPrkdcscidIl2rgtm1Wjl / MvwJ. NSG-ROSA26 mice are a resource for the rapid creation of vector-free targeted alleles in the Gt(ROSA)26Sor locus on the NSG® background. The dual Bxb1 attP-site "safe harbor landing pad" in the first intron of Gt(ROSA)26Sor enables efficient and precise integration of a donor DNA sequence by recombinase mediated cassette exchange (RMCE), and the vector backbone sequence is simultaneously excluded. In some embodiments, an immunodeficient mouse model has an NRG background. The NRG mouse (e.g., Jackson Labs Strain #007799) is extremely immunodeficient. This mouse comprises two mutations on the NOD / ShiLtJ genetic background; a targeted knockout mutation in recombination activating gene 1 (Rag1) and a complete null allele of the IL2 receptor common gamma chain (IL2rgnull). The extreme immunodeficiency of NRG allows the mice to be humanized by engraftment of human CD34+hematopoietic stem cells (HSC), human peripheral blood mononuclear cells, (PBMCs), and patient derived xenografts (PDXs) at high efficiency. The immunodeficient NRG mice are more resistant to irradiation and genotoxic drugs than mice with a scid mutation in the DNA repair enzyme Prkdc. In some embodiments, an immunodeficient mouse model has an NOG background. The NOG mouse (Ito M et al., Blood 2002) is an extremely severe combined immunodeficient (scid) mouse established by combining the NOD / scid mouse and the IL-2 receptor-γ chain knockout (IL2rγKO) mouse (Ohbo K. et al., Blood 1996). The NOG mouse lacks T and B cells, lacks natural killer (NK) cells, exhibits reduced dendritic cell function and reduced macrophage function, and lacks complement activity. In some embodiments, an immunodeficient mouse model has an NCG background. The NCG mouse (e.g., Charles River Strain #572) was created by sequential CRISPR / Cas9 editing of the Prkdc and Il2rg loci in the NOD / Nju mouse, generating a mouse coisogenic to the NOD / Nju. The NOD / Nju carries a mutation in the Sirpa (SIRPα) gene that allows for engrafting of foreign hematopoietic stem cells. The Prkdc knockout generates a SCID-like phenotype lacking proper T-cell and B-cell formation. The knockout of the Il2rg gene further exacerbates the SCID-like phenotype while additionally resulting in a decrease of NK cell production. Provided herein, in some embodiments, are immunodeficient mouse models that are deficient in MHC Class I, MHC Class II, or MHC Class I and MHC Class II. A mouse that is deficient in MHC Class I and / or MHC Class II does not express the same level of MHC Class I proteins (e.g., α-microglobulin and β2-microglobulin (B2M)) and / or MHC Class II proteins (e.g., α chain and β chain) or does not have the same level of MHC Class I and / or MHC Class II protein activity as a non-immunodeficient (e.g., MHC Class I / II wild-type) mouse. In some embodiments, the expression or activity of MHC Class I and / or MHC Class II proteins is reduced (e.g., by at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90% or more), relative to a non-immunodeficient mouse. Immunodeficient mice that are deficient in MHC Class I, MHC Class II, and MHC Class I and MHC Class II are described in International Publication No. WO 2018 / 209344, the contents of which are incorporated by reference herein. Thus, in some embodiments, a mouse an background (e.g., Jackson Laboratory Strain No.: 025216) also referred to as an NSG-MHC I / II DKO background, described in Brehm et al.2019 FASEB J [PMID:30383447]. In other embodiments, a mouse has an NOD.Cg- Rag2em8LutzyH2-K1b-tm1BpeH2-Ab1g7-em1MvwH2-D1b-tm1BpeIl2rgtm1Wjl / J background (e.g., Jackson Laboratory Strain No.: 037275) also referred to as an NRG-MHC I / II DKO background. In some embodiments, an immunodeficient mouse has an NOD.Cg-PrkdcscidIl2rgtm1WjlTg(CMV-IL3,CSF2,KITLG)1Eav / MloySzJ background (e.g., Jackson Laboratory Strain No.: 013062) also referred to as an NSG-SGM3 background. The transgenic NSG-SGM3 mice express three human cytokines: human Interleukin-3 (IL-3), human Granulocyte / Macrophage- colony stimulating factor 2 (GM-CSF), and human Stem Cell Factor (SCF). NSG-SGM3 mice combine the features of the highly immunodeficient NSG mouse with expression of human cytokines IL-3, GM-CSF, and SCF that support stable engraftment of myeloid lineages (e.g., monocytes, dendritic cells) and regulatory T cell populations. In some embodiments, an immunodeficient mouse has an NOD.Cg PrkdcscidIl2rgtm1WjlTg(CMV-IL3,CSF2,KITLG)1Eav Tg(CSF1)3Sz / J background (e.g., Jackson Laboratory Strain No.: 028657) also referred to as an NSG-QUAD background. The transgenic NSG-QUAD mice express the human cytokines CSF1 [colony stimulating factor 1 (macrophage)], interleukin-3 (IL3; IL-3), granulocyte / macrophage-stimulating factor (CSF2; GM-CSF), and Steel factor (KITLG; SCF or SF) on the immunodeficient NSG background. In humanized NSG QUAD mice, the human cytokines can be used to support the survival of human induced pluripotent stem cells (hiPSCs). Assessing an impaired immune system in mice can involve various methods and techniques, often depending on the specific type of immune impairment suspected or the specific research question at hand. Non-limiting examples of such methods include complete blood count (CBC), flow cytometry, cytokine analysis, immune challenge, histology and immunohistochemistry, T-cell proliferation assays, and serum antibody level analysis. CBC is a basic test that measures different components of the blood, including red blood cells, white blood cells, and platelets. Changes in these counts can indicate an immune response or immune deficiency. Flow cytometry can be used to analyze specific populations of immune cells in the blood, spleen, lymph nodes, or other tissues. By using antibodies tagged with fluorescent markers that bind to specific proteins on the surface of immune cells (known as cell markers or cluster of differentiation (CD) markers), researchers can identify and quantify different types of immune cells (e.g., T cells, B cells, macrophages, neutrophils). By measuring the levels of specific cytokines in the blood or tissues (using techniques like ELISA or multiplex assays), one can gain insights into the immune response. In immune challenge tests, mice are exposed to a specific antigen or pathogen, and the immune response is measured. This could involve measuring the response to a vaccine, the ability to clear a bacterial or viral infection, or the reaction to an inflammatory stimulus. Tissue samples from the mouse can be examined under a microscope to look for signs of inflammation or immune cell infiltration. With immunohistochemistry, specific types of immune cells can be labeled and visualized. T-cell proliferation assays measure the ability of T cells to proliferate in response to stimulation, which can be a key indicator of immune function. Measurement of specific antibodies in response to an antigen can indicate the functionality of the humoral immune response. Assessing cell signaling deficiencies typically involves a combination of molecular biology techniques, cellular assays, and sometimes in vivo animal studies, for example. Non- limiting examples of methods for assessing cell signaling deficiencies include Western blot, flow cytometry, immunofluorescence, quantitative PCR (qPCR), reporter gene assays, RNA sequencing (RNA-Seq), protein arrays and mass spectrometry. Western blotting is commonly used to measure the levels of specific proteins, including those involved in cell signaling. It can be used to detect the presence of a signaling protein and to assess changes in protein level or modifications (like phosphorylation) that may indicate activation or inhibition of a signaling pathway. Flow cytometry can be used to assess cell surface markers or intracellular signaling proteins, enabling the identification and quantification of cell populations with specific signaling characteristics. It can also be used to measure changes in signaling proteins following stimulation or inhibition of cells. Immunofluorescence can be used to visualize the location and expression level of signaling proteins within cells using fluorescently labeled antibodies. Quantitative PCR can be used to measure changes in gene expression levels, which can be indicative of changes in cell signaling pathways. This can be particularly useful when studying transcription factors or other signaling molecules that regulate gene expression. Reporter gene assays involve engineering cells to express a reporter gene (like luciferase or green fluorescent protein) under the control of a promoter that is responsive to a specific signaling pathway. Activation or inhibition of the pathway can then be assessed by measuring the output of the reporter gene. RNA Sequencing can be used to look at global changes in gene expression, which can provide a broad view of the activation or inhibition of cell signaling pathways. Protein arrays and mass spectrometry can be used to look at changes in protein-protein interactions or post-translational modifications that can indicate changes in cell signaling. In some embodiments, engineered nucleotide sequences are inserted into the “safe harbor” ROSA26 gene locus, which is constitutively expressed in a wide range of cell types and developmental stages. The ROSA26 gene locus is a genomic location in mice that is commonly used as a site for targeted gene insertion or knock-in experiments. The name “ROSA26” stands for “reverse orientation splice acceptor at position 26”, which refers to the specific sequence features of the locus. In alternative embodiments, an engineered nucleotide sequences may be inserted into other “safe harbor” loci. Myeloablation In some embodiments, immunodeficient mice are treated to deplete and / or suppress any remaining murine immune cells (e.g., chemically and / or with radiation). In some embodiments, immunodeficient mice are treated only chemically or only with radiation. In other embodiments, immunodeficient mice are treated both chemically and with radiation. In some embodiments, immunodeficient mice are administered a myeloablative agent, that is, a chemical agent that suppresses or depletes murine immune cells. Examples of myeloablative agents include busulfan, treosulfan, dimethyl mileran, melphalan, and thiotepa. In some embodiments, immunodeficient mice are irradiated prior to engraftment with human cells, such as human HSCs and / or PMBCs. It is thought that irradiation of an immunodeficient mouse destroys mouse immune cells in peripheral blood, spleen, and bone marrow, which facilitates engraftment of human cells, such as human PMBCs (e.g., by increasing human cell survival factors), as well as expansion of other immune cells. Irradiation also shortens the time it takes to accumulate the required number of human immune cells to “humanize” the mouse models. For immunodeficient mice (e.g., NSG® mice), this preparation is commonly accomplished through whole-body gamma irradiation. Irradiators may vary in size depending on their intended use. Animals are generally irradiated for short periods of time (less than 15 min). The amount of time spent inside the irradiator varies depending on the radioisotope decay charts, amount of irradiation needed, and source of ionizing energy (that is, X-rays versus gamma rays, for which a cesium or cobalt source is needed). A myeloablative irradiation dose is usually 200 to 1300 cGy, though in some embodiments, lower doses such as 1-100 cGy (e.g., about 2, 5, or 10 cGy), or 300-700 cGy may be used. As an example, the mouse may be irradiated with 100 cGy X-ray (or 75 cGy - 125 cGy X-ray). In some embodiments, the dose is about 1, 2, 3, 4, 5, 10, 20, 100, 125, 150, 175, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, or 1300 cGy, or between any of the two recited doses herein, such as 100-300 cGy, 200-500 cGy, 600-1000 cGy, or 700-1300 cGy. Humanization In some embodiments, the immunodeficient mice are engrafted with human peripheral blood mononuclear cells (PBMCs) and / or hematopoietic stem cells (HSCs), thereby humanizing the mice. Engraftment refers to the process of the human cells migrating to, and incorporating into, an existing tissue of interest in vivo. The human PBMCs and / or HSCs may be engrafted after irradiation and before engraftment of other human cells (e.g., human diseased cells), after irradiation and concurrently with engraftment of other human cells, or after irradiation and after engraftment of other human cells. Peripheral blood mononuclear cells are a type of white blood cell that is found in the bloodstream and have a round nucleus. These mononuclear blood cells recirculate between tissues and blood and are a critical component in the immune system to fight infection and adapt to intruders. There are two main types of PBMCs: lymphocytes and monocytes. The majority (~70-90%) of an enriched human PBMC sample is composed of lymphocytes (white blood cells), which include CD4+ helper T cells, CD8+ killer T cells, B cells, and Natural Killer (NK) cells. Monocytes make up a smaller portion (~10-30%) of the enriched human PBMC sample. Monocytes, when stimulated, can differentiate into macrophages or dendritic cells. Hematopoietic stem cells are a type of stem cell that are responsible for the production of all blood cells in the body. HSCs are found primarily in the bone marrow, but they can also be found in small numbers in peripheral blood and cord blood. HSCs can self-renew and differentiate into all the different types of blood cells, including red blood cells, white blood cells, and platelets. The process by which HSCs differentiate into different blood cell types is tightly regulated by various growth factors and cytokines. HSCs are critical for maintaining the health of the immune system and are essential for the treatment of various blood disorders, such as leukemia and aplastic anemia. HSCs can be harvested from bone marrow, peripheral blood, or umbilical cord blood and used for autologous or allogeneic transplantation. Human PBMCs and / or HSCs may be isolated from whole blood samples, for example (e.g., Ficoll gradient). In some embodiments, PBMCs and / or HSCs from a human subject with a current or previous diagnosis of cancer or an autoimmune disease may be used. In some embodiments, PBMCs and / or HSCs from a human subject with a current or previous diagnosis of cancer or an autoimmune disease may be used. Methods of engrafting immunodeficient mice with human PBMCs and / or HSCs to yield a humanized mouse model include but are not limited to intraperitoneal or intravenous injection (Shultz et al., J Immunol, 2015, 174:6477-6489; Pearson et al., Curr Protoc Immunol.2008; 15- 21; Kim et al., AIDS Res Hum Retrovirus, 2016, 32(2): 194-2020; Yaguchi et al., Cell & Mol Immunol, 2018, 15:953-962). In some embodiments, an immunodeficient mouse is administered (e.g., engrafted with) 0.5x106– 50x106human PBMCs and / or HSCs. For example, an immunodeficient mouse may be administered (e.g., engrafted with) 0.5x106– 50x106, 1x106– 50x106, 2x106– 50x106, 5x106– 50x106, 10x106– 50x106, 15x106– 50x106, 20x106– 50x106, 0.5x106– 20x106, 1x106– 20x106, 2x106– 20x106, 5x106– 20x106, 10x106– 20x106, 15x106– 20x106, 0.5x106– 15x106, 1x106– 15x106, 2x106– 15x106, 5x106– 15x106, 10x106– 15x106, 0.5x106– 10x106, 1x106– 10x106, 2x106– 10x106, 5x106– 10x106, 0.5x106– 5x106, 1x106– 5x106, 2x106– 10x106, 0.5x106– 2x106, 1x106– 2x106, or 0.5x106– 1x106human PBMCs and / or HSCs. In some embodiments, an immunodeficient mouse is administered (e.g., engrafted with) about 0.1x106, about 0.5 x106, about 1x106, about 1.5x106, about 2x106, about 2.5x106, about 3x106, about 3.5x106, about 4x106, about 4.5x106, about 5x106, about 5.5x106, about 6x106, about 6.5x106, about 7x106, about 7.5x106, about 8x106, about 8.5x106, about 9x106, about 9.5x106, or about 10x106human PBMCs and / or HSCs. In some embodiments, an immunodeficient mouse is administered (e.g., engrafted with) human PBMCs and / or HSCs, for example, following a myeloablative treatment, such as sublethal irradiation or chemical ablation. In some embodiments, an immunodeficient mouse is administered (e.g., engrafted with) human PBMCs and / or HSCs about 15 minutes, 30 minutes, 45 minutes, 1 hour, or more following the myeloablative treatment. In some embodiments, an immunodeficient mouse is administered (e.g., engrafted with) human PBMCs and / or HSCs about 1 to 5 days, about 1 to 10 days, or about 1 to 20 days, e.g., about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 days following the myeloablative treatment. Engrafted human cells may express and / or secrete cell signaling molecules, such as cytokines, for example. Cytokines are a broad category of small proteins that are important in cell signaling. They are released by cells and affect the behavior of other cells. Cytokines include chemokines, interferons, interleukins, lymphokines, and tumor necrosis factors, among others. They are produced by a broad range of cells, including immune cells like macrophages, B lymphocytes, T lymphocytes and mast cells, as well as endothelial cells, fibroblasts, and various stromal cells. Cytokines play a crucial role in the body's response to disease and infection, as well as in the regulation of immune responses, inflammation, and the formation of blood cells (hematopoiesis). They can be either pro-inflammatory (promoting inflammation) or anti-inflammatory (reducing inflammation). Non-limiting example of human serum cytokines include interleukins (ILs), interferons (IFNs), tumor necrosis factors (TNFs), growth factors, and chemokines. Interleukins are a group of cytokines that were first seen to be expressed by white blood cells (leukocytes). Examples include IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-10, IL-12, IL-17, etc. Each has specific effects on the interactions and communications between cells. Interferons are a group of signaling proteins that are released by host cells in response to the presence of several pathogens, such as viruses, bacteria, parasites, and tumor cells. Examples include IFN-alpha, IFN-beta, and IFN-gamma. Tumor necrosis factors are a group of cytokines that can cause cell death (apoptosis). An example is TNF-alpha, which plays a role in systemic inflammation and is involved in the acute phase reaction. Growth Factors are proteins that stimulate cell growth, proliferation, and differentiation. Examples include Epidermal Growth Factor (EGF), Fibroblast Growth Factor (FGF), and Vascular Endothelial Growth Factor (VEGF). Chemokines are a family of small cytokines, or signaling proteins secreted by cells. They induce chemotaxis in nearby responsive cells, guiding the migration of cells. Examples include CXCL8 (IL-8), CCL2 (MCP-1), and CXCL10 (IP-10). Peripheral Blood Mononuclear Cell Humanization An initial step of assessing immunotherapy induced toxicity in accordance with the disclosure can include administering human peripheral blood mononuclear cells (hPBMCs) to an immunodeficient mouse. Peripheral blood mononuclear cells are a type of white blood cell that is found in the bloodstream and have a round nucleus. These mononuclear blood cells recirculate between tissues and blood and are a critical component in the immune system to fight infection and adapt to intruders. There are two main types of PBMCs: lymphocytes and monocytes. The majority (~70-90%) of an enriched human PBMC sample is composed of lymphocytes (white blood cells), which include CD4+ helper T cells, CD8+ killer T cells, B cells, and Natural Killer (NK) cells. Monocytes make up a smaller portion (~10-30%) of the enriched human PBMC sample. Monocytes, when stimulated, can differentiate into macrophages or dendritic cells. Human PBMCs may be isolated from whole blood samples, for example (e.g., Ficoll gradient). In some embodiments, PBMCs from a human subject with a current or previous diagnosis of a neurodegenerative disease, cancer, or an autoimmune disease may be used. Methods of engrafting immunodeficient mice with human PBMCs to yield a humanized mouse model include but are not limited to intraperitoneal or intravenous injection. In some embodiments, about 1x106to 1x107human PBMCs are administered to an immunodeficient mouse. For example, about 4x106to about 8x106human PBMCs may be administered to an immunodeficient mouse to humanize the mouse. In some embodiments, an immunodeficient mouse is administered (e.g., engrafted with) 0.5x106– 50x106, 1x106– 50x106, 2x106– 50x106, 5x106– 50x106, 10x106– 50x106, 15x106– 50x106, 20x106– 50x106, 0.5x106– 20x106, 1x106– 20x106, 2x106– 20x106, 5x106– 20x106, 10x106– 20x106, 15x106– 20x106, 0.5x106– 15x106, 1x106– 15x106, 2x106– 15x106, 5x106– 15x106, 10x106– 15x106, 0.5x106– 10x106, 1x106– 10x106, 2x106– 10x106, 5x106– 10x106, 0.5x106– 5x106, 1x106– 5x106, 2x106– 10x106, 0.5x106– 2x106, 1x106– 2x106, or 0.5x106– 1x106human PBMCs. In some embodiments, (e.g., engrafted with) 0.1x106, about 0.5 x106, about 1x106, about 1.5x106, about 2x106, about 2.5x106, about 3x106, about 3.5x106, about 4x106, about 4.5x106, about 5x106, about 5.5x106, about 6x106, about 6.5x106, about 7x106, about 7.5x106, about 8x106, about 8.5x106, about 9x106, about 9.5x106, or about 10x106human PBMCs are administered to an immunodeficient mouse. In some embodiments, human PBMCs are administered to an immunodeficient mouse following a myeloablative treatment, such as sublethal irradiation or chemical ablation. In some embodiments, human PBMCs are administered to an immunodeficient mouse about 15 minutes, 30 minutes, 45 minutes, 1 hour, or more following the myeloablative treatment. In some embodiments, human PBMCs are administered to an immunodeficient mouse about 1 to 7 days, e.g., about 1, 2, 3, 4, 5, 6, or 7 days following the myeloablative treatment. Nucleic Acids: Engineering and Delivery The mouse models described herein comprise, in some embodiments, a nucleic acid comprising an open reading frame encoding a protein of interest, for example, a murine protein and / or a human protein, typically integrated into the genome of a mouse. The nucleic acids provided herein, in some embodiments, are engineered. An engineered nucleic acid includes a nucleic acid (e.g., at least two nucleotides covalently linked together, and in some instances, containing phosphodiester bonds, referred to as a phosphodiester backbone) that does not occur in nature. Engineered nucleic acids include recombinant nucleic acids and synthetic nucleic acids. A recombinant nucleic acid includes a molecule that is constructed by joining nucleic acids (e.g., isolated nucleic acids, synthetic nucleic acids or a combination thereof) from two different organisms (e.g., human and mouse). A synthetic nucleic acid includes a molecule that is amplified or chemically, or by other means, synthesized. A synthetic nucleic acid includes those that are chemically modified, or otherwise modified, but can base pair with (bind to) naturally occurring nucleic acid molecules. Recombinant and synthetic nucleic acids can also include those molecules that result from the replication of either of the foregoing. An engineered nucleic acid can comprise DNA (e.g., genomic DNA, cDNA or a combination of genomic DNA and cDNA), RNA or a hybrid molecule, for example, where the nucleic acid contains any combination of deoxyribonucleotides and ribonucleotides (e.g., artificial or natural), and any combination of two or more bases, including uracil, adenine, thymine, cytosine, guanine, inosine, xanthine, hypoxanthine, isocytosine and isoguanine. In some embodiments, a nucleic acid is a complementary DNA (cDNA). cDNA is synthesized from a single-stranded RNA (e.g., messenger RNA (mRNA) or microRNA (miRNA)) template in a reaction catalyzed by reverse transcriptase. Engineered nucleic acids of the present disclosure can be produced using standard molecular biology methods. A gene includes a distinct sequence of nucleotides, the order of which determines the order of monomers in a polynucleotide or polypeptide. A gene typically encodes a protein. A gene may be endogenous (occurring naturally in a host organism) or exogenous (transferred, naturally or through genetic engineering, to a host organism). An allele includes one of two or more alternative forms of a gene that arise by mutation and are found at the same locus on a chromosome. A gene, in some embodiments, includes a promoter sequence, coding regions (e.g., exons), non-coding regions (e.g., introns), and regulatory regions (also referred to as regulatory sequences). A mouse comprising a human gene is considered to comprise a human transgene. A transgene includes a gene exogenous to a host organism. That is, a transgene includes a gene that has been transferred, naturally or through genetic engineering, to a host organism. A transgene does not occur naturally in the host organism (the organism, e.g., mouse, comprising the transgene). A promoter includes a nucleotide sequence to which RNA polymerase binds to initial transcription (e.g., ATG). Promoters are typically located directly upstream from (at the 5' end of) a transcription initiation site. In some embodiments, a promoter is an endogenous promoter. An endogenous promoter includes a promoter that naturally occurs in that host animal. An open reading frame includes a continuous stretch of codons that begins with a start codon (e.g., ATG), ends with a stop codon (e.g., TAA, TAG, or TGA), and encodes a polypeptide, for example, a protein. An open reading frame is considered operably linked to a promoter if that promoter regulates transcription of the open reading frame. An exon includes a region of a gene that codes for amino acids. An intron (and other non-coding DNA) includes a region of a gene that does not code for amino acids. A nucleotide sequence encoding a product (e.g., protein), in some embodiments, has a length of 200 base pairs (bp) to 100 kilobases (kb). The nucleotide sequence, in some embodiments, has a length of at least 10 kb. For example, the nucleotide sequence may have a length of at least 15 kb, at least 20 kb, at least 25 kb, at least 30 kb, or at least 35 kb. In some embodiments, the nucleotide sequence has a length of 10 to 100 kb, 10 to 75 kb, 10 to 50 kb, 10 to 30 kb, 20 to 100 kb, 20 to 75 kb, 20 to 50 kb, 20 to 30 kb, 30 to 100 kb, 30 to 75 kb, or 30 to 50 kb. Any one of the nucleic acids provided herein can have a length of 200 bp to 500 kb, 200 bp to 250 kb, or 200 bp to 100 kb. A nucleic acid, in some embodiments, has a length of at least 10 kb. For example, a nucleic acid may have a length of at least 15 kb, at least 20 kb, at least 25 kb, at least 30 kb, at least 35 kb, at least 50 kb, at least 100 kb, at least 200 kb, at least 300 kb, at least 400 kb, or at least 500 kb. In some embodiments, a nucleic acid has a length of 10 to 500 kb, 20 to 400 kb, 10 to 300 kb, 10 to 200 kb, or 10 to 100 kb. In some embodiments, a nucleic acid has a length of 10 to 100 kb, 10 to 75 kb, 10 to 50 kb, 10 to 30 kb, 20 to 100 kb, 20 to 75 kb, 20 to 50 kb, 20 to 30 kb, 30 to 100 kb, 30 to 75 kb, or 30 to 50 kb. A nucleic acid may be circular or linear. The nucleic acids described herein, in some embodiments, include a modification. A modification, with respect to a nucleic acid, includes any manipulation of the nucleic acid, relative to the corresponding wild-type nucleic acid (e.g., the naturally-occurring nucleic acid). Thus, a genomic modification includes any manipulation of a nucleic acid in a genome (e.g., in a coding region, non-coding region, and / or regulatory region), relative to the corresponding wild- type nucleic acid (e.g., the naturally-occurring (unmodified) nucleic acid) in the genome. Non- limiting examples of nucleic acid (e.g., genomic) modifications include deletions, insertions, “indels” (deletion and insertion), and substitutions (e.g., point mutations). In some embodiments, a deletion, insertion, indel, or other modification in a gene results in a frameshift mutation such that the gene no longer encodes a functional product (e.g., protein). Modifications can also include chemical modifications, for example, chemical modifications of at least one nucleobase. Methods of nucleic acid modification, for example, those that result in gene inactivation, are known and include, without limitation, RNA interference, chemical modification, and gene editing (e.g., using recombinases or other programmable nuclease systems, e.g., CRISPR / Cas, TALENs, and / or ZFNs). A loss-of-function mutation, as is known in the art, results in a gene product with little or no function. A null mutation, which is a type of loss-of-function mutation, results in a gene product with no function. In some embodiments, an inactivated allele is a null allele. Other examples of loss-of-function mutations includes missense mutations and frameshift mutations. A nucleic acid, such as an allele or alleles of a gene, can be modified such that it does not produce a detectable level of a functional gene product (e.g., a functional protein). Thus, an inactivated allele includes allele that does not produce a detectable level of a functional gene product (e.g., a functional protein). A detectable level of a protein includes any level of protein detected using a standard protein detection assay, such as flow cytometry and / or an ELISA. In some embodiments, an inactivated allele is not transcribed. In some embodiments, an inactivated allele does not encode a functional protein. Vectors used for delivery of a nucleic acid include minicircles, plasmids, bacterial artificial chromosomes (BACs), and yeast artificial chromosomes. It should be understood, however, that a vector may not be needed. For example, a circularized or linearized nucleic acid may be delivered to an embryo without its vector backbone. Vector backbones are small (~ 4 kb), while donor DNA to be circularized can range from >100 bp to 50 kb, for example. Methods for delivering nucleic acids to mouse embryos for the production of transgenic mice include, but are not limited to, electroporation (see, e.g., Wang W et al. J Genet Genomics 2016;43(5):319-27; WO 2016 / 054032; and WO 2017 / 124086, each of which is incorporated herein by reference), DNA microinjection (see, e.g., Gordon and Ruddle, Science 1981: 214: 1244-124, incorporated herein by reference), embryonic stem cell-mediated gene transfer (see, e.g., Gossler et al., Proc. Natl. Acad. Sci.1986; 83: 9065-9069, incorporated herein by reference), and retrovirus-mediated gene transfer (see, e.g., Jaenisch, Proc. Natl. Acad. Sci. 1976; 73: 1260-1264, incorporated herein by reference), any of which may be used as provided herein. Human Interleukin-34 (IL-34) Transgene In some embodiments, an immunodeficient mouse provided herein expresses human interleukin 34 (huIL-34). Interleukin 34 (IL-34) is a cytokine produced by various cell types, and its expression is particularly elevated in the skin, liver, secondary lymphoid organs, and brain. IL-34 signals via colony stimulating factor 1 receptor (CSF1R) and is critical for the differentiation, proliferation, and survival of monocytes and macrophages. Additionally, IL-34 is essential for the development and persistence of microglia. During embryonic development, IL- 34 guides the differentiation of microglia precursors in the yolk sac, from which they migrate to the central nervous system to serve as tissue resident macrophages. Throughout life, IL-34 also promotes the survival of microglia. IL-34 is expressed in a wide variety of organisms including, but not limited to: humans, mice, rats, cows, Rhesus monkeys, frogs, dogs, chickens, fish, birds, pigs, cats, and horses. In some embodiments, an immunodeficient mouse model herein expresses a transgene encoding human IL-34. A human IL-34 sequence may be any human IL-34 sequence known in the art (see, e.g., Gene ID: 146433). In some embodiments, a human IL-34 sequence is codon- optimized for expression in a non-human host (e.g., an immunodeficient mouse). A human IL-34 sequence may be expressed (e.g., in a mouse) by any method provided herein. Mouse models of the disclosure express human interleukin 34 (IL34). It should be understood that unless stated otherwise an immunodeficient mouse that expresses human IL34 has been genomically modified to include a human IL34 coding sequence. Expression of human IL34, in some embodiments, is under the control of an endogenous mouse Il34 gene promoter. Thus, in some embodiments, a mouse model used in a method provided herein is considered a “knockin” model in which a human IL34 open reading frame sequence has been knocked into the mouse Il34 promoter in such a way that the mouse Il34 promoter drives expression of (is operably linked to) the human IL34 gene to produce human IL34 protein in the mouse. Human IL34 is a cytokine (a type of protein involved in cell signaling and regulation in the immune system) that is thought to stimulates the proliferation and differentiation of monocytes and macrophages through its receptor, colony-stimulating factor-1 receptor (CSF-1R). The CSF-1R is also a receptor for another cytokine, colony-stimulating factor-1 (CSF-1), which has similar but distinct functions. IL34 expression in humans is seen in various tissues, including the brain, heart, liver, kidney, spleen, thymus, testes, ovary, intestine, lung, bone marrow, stomach, and skin, and is believed to plays a role in the survival, differentiation, and function of monocytes and macrophages. An exemplary human IL34 mRNA sequence is provided: agcagctgca gtcggaaaaa tcagagaaag cgtcacccag ccccagattc cgaggggcct gccagggact ctctcctcct gctccttgga aaggaagacc ccgaaagacc cccaagccac cggctcagac ctgcttctgg gctgccatgg gacttgcggc caccgccccc cggctgtcct ccacgctgcc gggcagataa gggcagctgc tgcccttggg gcacctgctc actcccgcag cccagccact cctccagggc cagcccttcc ctgactgagt gaccacctct gctgccccga ggccatgtag gccgtgctta ggcctctgtg gacacactgc tggggacggc gcctgagctc tcagggggac gaggaacacc accatgcccc ggggcttcac ctggctgcgc tatcttggga tcttccttgg cgtggccttg gggaatgagc ctttggagat gtggcccttg acgcagaatg aggagtgcac tgtcacgggt tttctgcggg acaagctgca gtacaggagc cgacttcagt acatgaaaca ctacttcccc atcaactaca agatcagtgt gccttacgag ggggtgttca gaatcgccaa cgtcaccagg ctgcagaggg cccaggtgag cgagcgggag ctgcggtatc tgtgggtctt ggtgagcctc agtgccactg agtcggtgca ggacgtgctg ctcgagggcc acccatcctg gaagtacctg caggaggtgc agacgctgct gctgaatgtc cagcagggcc tcacggatgt ggaggtcagc cccaaggtgg aatccgtgtt gtccctcttg aatgccccag ggccaaacct gaagctggtg cggcccaaag ccctgctgga caactgcttc cgggtcatgg agctgctgta ctgctcctgc tgtaaacaaa gctccgtcct aaactggcag gactgtgagg tgccaagtcc tcagtcttgc agcccagagc cctcattgca gtatgcggcc acccagctgt accctccgcc cccgtggtcc cccagctccc cgcctcactc cacgggctcg gtgaggccgg tcagggcaca gggcgagggc ctcttgccct gagcaccctg gatggtgact gcggataggg gcagccagac cagctcccac aggagttcaa ctgggtctga gacttcaagg ggtggtggtg ggagcccccc ttgggagagg acccctggga agggtgtttt tcctttgagg gggattctgt gccacagcag ggctcagctt cctgccttcc atagctgtca tggcctcacc tggagcggag gggacctggg gacctgaagg tggatgggga cacagctcct ggcttctcct ggtgctgccc tcactgtccc cccgcctaaa gggggtactg agcctcctgt ggcccgcagc agtgagggca cagctgtggg ttgcagggga gacagccagc acggcgtggc cattctatga ccccccagcc tggcagactg gggagctggg ggcagagggc ggtgccaagt gccacatctt gccatagtgg atgctcttcc agtttctttt ttctattaaa caccccactt cctttgaaaa aaaaaaaaaa aaaaaaaaaa aaaaaaaaaa aaaaaaaaaa aa (SEQ ID NO: 1) Mouse Interleukin-34 (IL-34) Null Endogenous IL-34 protein is expressed in mice to regulate macrophage development in the central nervous system and skin during development through the CSF1 receptor (CSF1R). Mouse IL-34 also interacts with receptor protein tyrosine phosphatase-z on neural progenitor cells. IL-34 plays an important role in the maintenance and differentiation of microglia and Langerhans cells (LCs). Mouse IL-34 (Gene ID: 76527) is produced from a mouse IL-34 gene. A mouse IL-34 gene may be any mouse IL-34 gene known in the art including, but not limited to: NM_001135100.2 and NM_029646.3. In some embodiments, an immunodeficient mouse provided herein has an endogenous (e.g., mouse) IL-34nullmutation. An IL-34nullmutation results in mouse IL-34 protein whose function is reduced by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) compared to wildtype mouse IL-34 protein. Non- limiting examples of mouse IL-34nullmutations include: IL-34em1Sz, IL-34em1Adiuj, IL-34em1Gpt, IL- 34Gt(OST447311)Lex, IL-34Gt(PST10227)Mfgc, and IL-34tm1e(EUCOMM)Wtsi. In some embodiments, an immunodeficient mouse provided herein comprises an IL-34nullallele, optionally an IL-34em1Szallele. Human Colony Stimulating Factor 1 (CSF1) Transgene In some embodiments, an immunodeficient mouse provided herein expresses human colony stimulating factor 1 (CSF1, also called macrophage colony stimulating factor, M-CSF). CSF1 is a cytokine produced by stromal cells, fibroblasts, and immune cells, and it acts as a growth factor that stimulates the proliferation and differentiation of hematopoietic progenitors in the bone marrow, leading to the generation of monocytes. Monocytes that egress from the bone marrow can populate peripheral tissues and differentiate into macrophages. Like IL-34, CSF1 is critical to embryonic development of microglia in the yolk sac and the maintenance of microglia throughout life. CSF1 is also a ligand for CSF1R. CSF1 is expressed in a variety of organisms including, but not limited to: humans, mouse, rat, cows, pigs, Rhesus monkey, chimpanzee, dogs, cats, chickens, birds, frogs, and birds. A human CSF1 sequence may be any human CSF1 sequence known in the art (see, e.g., Gene ID: 1435). In some embodiments, a human IL-34 sequence is codon-optimized for expression in a non-human host (e.g., an immunodeficient mouse). A human IL-34 sequence may be expressed (e.g., in a mouse) by any method provided herein. In some embodiments, an immunodeficient mouse provided herein expresses a modified endogenous Csf1R allele. Colony stimulating factor 1 receptor (CSF1R) protein is expressed in mice to regulate macrophage development and maintenance throughout the body by interacting with CSF1 and IL-34. Mouse CSF1R (Gene ID: 12978) is produced from a mouse CSF1R gene. A mouse CSF1R gene may be any mouse CSF1R gene known in the art including, but not limited to: NM_001037859.2. In some embodiments, an immunodeficient mouse provided herein has an endogenous (e.g., mouse) CSF1Rnullmutation. A CSF1Rnullmutation results in mouse CSF1R protein whose function is reduced by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) compared to wildtype mouse CSF1R protein. Non-limiting examples of mouse CSF1Rnullmutations include: Csf1rem1(cre / ERT2)Gpt, Csf1rem1(icre)Gpt, Csf1rem1Gpt, Csf1rem1H, Endogenous Mouse Colony Stimulating Factor 1 Receptor (Csf1r) Variant In some embodiments, an immunodeficient mouse provided herein comprises an engineered genomic variant of an endogenous mouse colony stimulating factor 1 receptor (Csf1r) gene. An endogenous gene refers to a gene that originates from within an organism, cell, or system, as opposed to a gene that is introduced from the outside (exogenous). Thus, an endogenous gene is one that is naturally present and active within the organism. In mouse models, an endogenous gene is a mouse gene from the mouse (Mus Musculus) genome. An engineered genomic variant may be in any intron in a mouse Csf1r gene (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, and 22). The mammalian Csf1r locus contains a highly conserved super-enhancer, the Fms-intronic regulatory element (FIRE) in intron 2 that is bound by numerous transcription factors involved in microglia and macrophage development. Knocking out the FIRE enhancer is expected to reduce macrophage and microglia development and maintenance in vivo. In some embodiments, an engineered genomic variant is in intron 2 of a mouse Csf1r gene (e.g., comprising the FIRE enhancer). Non-limiting examples of engineered genomic variants in intron 2 include: Csf1rem2zand Csf1r∆FIRE. In some embodiments, an immunodeficient mouse provided herein comprises an engineered genomic variant that encodes Csf1rem2z. As described above, mouse CSF1R is critical in macrophage and microglia development and maintenance. In embodiments where an immunodeficient mouse expresses a Csf1rnullgene or an engineered genomic variant of endogenous Csf1r, the number of mouse macrophage cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. In some embodiments, the number of mouse macrophages is lower by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. In embodiments where an immunodeficient mouse expresses a Csf1rnullgene or an engineered genomic variant of endogenous Csf1r, the number of mouse microglia cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. In some embodiments, the number of mouse microglia is lower by 50% - 100% (e.g., 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or more) relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. Genomic Editing Methods Engineered nucleic acids, such as guide RNAs, donor polynucleotides, and other nucleic acid coding sequences, for example, can be introduced to a genome of an embryo or cell (e.g., stem cell) using any suitable method. The present application contemplates the use of a variety of gene editing technologies, for example, to introduce nucleic acids into the genome of an embryo or cell to produce a transgenic rodent. Non-limiting examples include programmable nuclease-based systems, such as clustered regularly interspaced short palindromic repeat (CRISPR) systems, zinc‐finger nucleases (ZFNs), and transcription activator‐like effector nucleases (TALENs). See, e.g., Carroll D Genetics.2011; 188(4): 773–782; Joung JK et al. Nat Rev Mol Cell Biol.2013; 14(1): 49–55; and Gaj T et al. Trends Biotechnol.2013 Jul; 31(7): 397–405, each of which is incorporated by reference herein. In some embodiments, a CRISPR system is used to edit the genome of mouse embryos provided herein. See, e.g., Harms DW et al., Curr Protoc Hum Genet.2014; 83: 15.7.1–15.7.27; and Inui M et al., Sci Rep.2014; 4: 5396, each of which are incorporated by reference herein). For example, Cas9 mRNA or protein, one or multiple guide RNAs (gRNAs), and / or a donor nucleic acid can be delivered, e.g., injected or electroporated, directly into mouse embryos at the one-cell (zygote) stage or a later stage to facilitate homology directed repair (HDR), for example, to introduce an engineered nucleic acid (e.g., donor nucleic acid) into the genome. The CRISPR / Cas system is a naturally occurring defense mechanism in prokaryotes that has been repurposed as an RNA-guided-DNA-targeting platform for gene editing. Engineered CRISPR systems contain two main components: a guide RNA (gRNA) and a CRISPR- associated endonuclease (e.g., Cas protein). The gRNA is a short synthetic RNA composed of a scaffold sequence for nuclease-binding and a user-defined nucleotide spacer (e.g., ~15-25 nucleotides, or ~20 nucleotides) that defines the genomic target (e.g., gene) to be modified. Thus, one can change the genomic target of the Cas protein by simply changing the target sequence present in the gRNA. In some embodiments, the Cas9 endonuclease is from Streptococcus pyogenes (NGG PAM) or Staphylococcus aureus (NNGRRT or NNGRR(N) PAM), although other Cas9 homologs, orthologs, and / or variants (e.g., evolved versions of Cas9) may be used, as provided herein. Additional non-limiting examples of RNA-guided nucleases that may be used as provided herein include Cpf1 (TTN PAM); SpCas9 D1135E variant (NGG (reduced NAG binding) PAM); SpCas9 VRER variant (NGCG PAM); SpCas9 EQR variant (NGAG PAM); SpCas9 VQR variant (NGAN or NGNG PAM); Neisseria meningitidis (NM) Cas9 (NNNNGATT PAM); Streptococcus thermophilus (ST) Cas9 (NNAGAAW PAM); and Treponema denticola (TD) Cas9 (NAAAAC). In some embodiments, the CRISPR-associated endonuclease is selected from Cas9, Cpf1, C2c1, and C2c3. In some embodiments, the Cas nuclease is Cas9. A guide RNA comprises at least a spacer sequence that hybridizes to (binds to) a target nucleic acid sequence and a CRISPR repeat sequence that binds the endonuclease and guides the endonuclease to the target nucleic acid sequence. As is understood by the person of ordinary skill in the art, each gRNA is designed to include a spacer sequence complementary to its genomic target sequence. See, e.g., Jinek et al., Science, 2012; 337: 816-821 and Deltcheva et al., Nature, 2011; 471: 602-607, each of which is incorporated by reference herein. In some embodiments, an RNA-guided nuclease and a gRNA are complexed to form a ribonucleoprotein (RNP), prior to delivery to an embryo. The concentration of RNA-guided nuclease or nucleic acid encoding a RNA-guided nuclease may vary. In some embodiments, the concentration is 100 ng / µl to 1000 ng / µl. For example, the concentration can be 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 ng / µl. In some embodiments, the concentration is 100 ng / µl to 500 ng / µl, or 200 ng / µl to 500 ng / µl. The concentration of gRNA may also vary. In some embodiments, the concentration is 200 ng / µl to 2000 ng / µl. For example, the concentration may be 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1700, 1900, or 2000 ng / µl. In some embodiments, the concentration is 500 ng / µl to 1000 ng / µl. In some embodiments, the concentration is 100 ng / µl to 1000 ng / µl. For example, the concentration may be 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 ng / µl. In some embodiments, the ratio of concentration of RNA-guided nuclease or nucleic acid encoding the RNA-guided nuclease to the concentration of gRNA is 2:1. In other embodiments, the ratio of concentration of RNA-guided nuclease or nucleic acid encoding the RNA-guided nuclease to the concentration of gRNA is 1:1. In yet other embodiments, the ratio of concentration of RNA-guided nuclease or nucleic acid encoding the RNA-guided nuclease to the concentration of gRNA is 1:1.5. In other embodiments, the ratio of concentration of RNA- guided nuclease or nucleic acid encoding the RNA-guided nuclease to the concentration of gRNA is 1:2. A donor nucleic acid typically includes a sequence of interest flanked by homology arms. Homology arms are regions of the ssDNA that are homologous to regions of genomic DNA located in a genomic locus. One homology arm is located to the left (5′) of a genomic region of interest (into which a sequence of interest is introduced) (the left homology arm) and another homology arm is located to the right (3′) of the genomic region of interest (the right homology arm). These homology arms enable homologous recombination between the ssDNA donor and the genomic locus, resulting in insertion of the sequence of interest into the genomic locus of interest (e.g., via CRISPR / Cas9-mediated homology directed repair (HDR)). The homology arms can vary in length. For example, each homology arm (the left arm and the right homology arm) can have a length of 20 nucleotide bases to 1000 nucleotide bases. In some embodiments, each homology arm has a length of 20 to 200, 20 to 300, 20 to 400, 20 to 500, 20 to 600, 20 to 700, 20 to 800, or 20 to 900 nucleotide bases. In some embodiments, each homology arm has a length of 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 nucleotide bases. In some embodiments, the length of one homology arm differs from the length of the other homology arm. For example, one homology arm can have a length of 20 nucleotide bases, and the other homology arm can have a length of 50 nucleotide bases. In some embodiments, the donor DNA is single stranded. In some embodiments, the donor DNA is double stranded. In some embodiments, the donor DNA is modified, e.g., via phosphorothioation. Other modifications can be made. Methods of Use A critical roadblock for the study of human microglia is the need for robust preclinical animal models for evaluation of the efficacy, safety and importantly, immunogenicity of potential therapies (e.g., such as human stem cell-based and immune cell-based therapy). Because of the cross-signaling between human and animal (e.g., mouse) proteins that regulated microglia, it has been challenging to test these therapies in vivo using other species. One approach to evaluating potential therapies for human diseases associated with microglial dysfunction without putting human patients at risk is to use humanized mice - immunodeficient mice engrafted with functional human cells, tissues, and immune system. Humanized mice can provide a critically needed preclinical bridge for evaluation of the safety, efficacy, and immunogenicity of potential therapies for diseases associated with microglial dysfunction. Thus, the humanized immunodeficient mouse models of the present disclosure may be used, in some embodiments, to evaluate the clinical efficacy of potential therapies for diseases associated with microglial dysfunction. Non-limiting examples of potential therapies include recombinant proteins, gene editing therapies, and autologous or allogeneic cells for certain therapeutic indications, including hematopoietic stem cells and adult and embryonic stem cells. Recombinant proteins may be any proteins produced outside the humanized immunodeficient mouse including, but not limited to, antibodies and antigen binding fragments. Thus, in some embodiments, a method provided herein comprises administering a potential therapy for a disease associated with microglial dysfunction to a humanized immunodeficient mouse described herein. In some embodiments, a humanized immunodeficient mouse has been engrafted with HSCs. In some embodiments, a humanized immunodeficient mouse has been engrafted with PBMCs. In some embodiments, a humanized immunodeficient mouse has been engrafted with human umbilical cord blood cells. In some embodiments, a humanized immunodeficient mouse has been engrafted with human mesenchymal stem cells. In some embodiments, a humanized immunodeficient mouse has been engrafted with embryonic stem cells. In some embodiments, a humanized immunodeficient mouse has been engrafted with induced pluripotent stem cells. In some embodiments, a potential therapy for a disease associated with microglial dysfunction is designed to treat (e.g., alleviate one or more symptom of) the disease. Non- limiting examples of diseases associated with microglial dysfunction include Alzheimer’s Disease, Parkinson’s Disease, prion disease (e.g., mad cow disease, kuru, Cruetzfeldt-Jakob disease), multiple sclerosis, amyotrophic lateral sclerosis, and AIDS dementia complex. Non- limiting examples of symptoms that may be alleviated by a potential therapeutic product include: confusion, irritability, mood swings, anxiety, wandering, difficulty walking, hallucination, fatigue, difficulty speaking, tremor, and decrease or loss of motor function, The methods may further comprise assessing one or more clinically-relevant characteristics of the potential therapy or one or more clinically-relevant effect on the engrafted human immune system. Clinically relevant characteristics may include, for example, a resolution of confusion, irritability, and anxiety. Diseased Cell Types Immunodeficient mouse models, in some embodiments, are engrafted with diseased (non-healthy) cells, for example, human (xenograft) diseased cells. Thus, in some embodiments, the disclosure provides methods of administering human diseased cells to an immunodeficient mouse, resulting in an immunodeficient mouse that has been engrafted with the human diseased cells. There are numerous cell types that can become diseased in the human body. For instance, cancerous cells are a type of diseased cell that divide uncontrollably and can invade nearby tissues. Other examples include infected cells such as those infected with viruses, bacteria, or fungi, which can cause diseases such as influenza, tuberculosis, or meningitis. In autoimmune diseases such as rheumatoid arthritis, the body's immune system mistakenly attacks healthy cells, leading to inflammation and tissue damage. Additionally, in genetic disorders like sickle cell anemia, red blood cells become misshapen and unable to carry oxygen effectively, leading to a host of health problems. In neurological diseases such as Alzheimer's, neurons in the brain become damaged and die, leading to cognitive decline and memory loss. In some embodiments, the diseased human cells are cancerous cells. Cancerous cells are cells that divide uncontrollably and can invade nearby tissues. In some embodiments, the diseased human cells are infected cells. Infected cells are cells that are infected with viruses, bacteria, fungi, or parasites that cause diseases such as influenza, tuberculosis, meningitis, and HIV. In some embodiments, the diseased human cells are autoimmune cells. Autoimmune cells are cells in the immune system that mistakenly attack healthy cells and tissues, leading to autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, and lupus. In some embodiments, the diseased human cells are red blood cells. Red blood cells are cells in the blood that carry oxygen throughout the body, which can be affected in conditions such as sickle cell anemia, hemophilia, and thalassemia. In some embodiments, the diseased human cells are white blood cells. White blood cells are cells in the immune system that help fight infections and diseases, which can be affected in conditions such as leukemia, lymphoma, and myeloma. In some embodiments, the diseased human cells are platelets. Platelets are cells in the blood that help with blood clotting, which can be affected in conditions such as thrombocytopenia and hemophilia. In some embodiments, the diseased human cells are neurons. Neurons are cells in the brain and nervous system that transmit information, which can be affected in conditions such as Alzheimer's, Parkinson's, and multiple sclerosis. In some embodiments, the diseased human cells are cardiac cells. Cardiac cells are cells in the heart that control its function, which can be affected in conditions such as heart failure, arrhythmia, and cardiomyopathy. In some embodiments, the diseased human cells are lung cells. Lung cells are cells in the lungs that help with breathing, which can be affected in conditions such as asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. In some embodiments, the diseased human cells are liver cells. Liver cells are cells in the liver that help with detoxification and metabolism, which can be affected in conditions such as hepatitis, cirrhosis, and liver cancer. There are many different types of cancer, each of which originates from different types of cells in the body. Non-limiting examples of cancerous (cancer) cells include breast cancer, lung cancer, prostate cancer, colorectal cancer, skin cancer, stomach cancer, leukemia, lymphoma, brain cancer, pancreatic cancer, and ovarian cancer cells. In some embodiments, the cancer cells are breast cancer cells. In other embodiments, the cancer cells are melanoma cells. In yet other embodiments, the cancer cells are colon cancer cells. Cancer antigens are proteins that are expressed by cancer cells and are recognized by the immune system as foreign. These antigens can be targeted by the immune system to help identify and destroy cancer cells. Non-limiting examples of cancer antigens include: Carcinoembryonic antigen (CEA), which is found in high levels in some types of cancer, including colorectal, pancreatic, and lung cancer; Cancer-testis antigens (CTAs), which are expressed in various types of cancer, including melanoma and ovarian cancer, and are also found in normal testis tissue; Prostate-specific antigen (PSA), which is found in high levels in prostate cancer and is used as a biomarker for disease detection and monitoring; Melanoma-associated antigens (MAGEs), which are expressed in melanoma and other types of cancer and are recognized by the immune system as foreign; Human epidermal growth factor receptor 2 (HER2), which is overexpressed in some types of breast cancer and can be targeted by monoclonal antibodies, such as trastuzumab; Mucin antigens, which are found in high levels in some types of cancer, including ovarian and pancreatic cancer, and can be targeted by monoclonal antibodies; Wilms' tumor antigen (WT1), which is expressed in various types of cancer, including leukemia, and is being studied as a potential target for cancer immunotherapy; Programmed cell death protein 1 (PD-1), which is expressed on immune cells and can be targeted by monoclonal antibodies, such as pembrolizumab and nivolumab, to help activate the immune system to attack cancer cells; B-cell lymphoma-2 (BCL-2), which is overexpressed in some types of lymphoma and can be targeted by small molecule inhibitors, such as venetoclax; and Cluster of differentiation 19 (CD19), which is expressed on the surface of some types of blood cancer cells and can be targeted by CAR T-cell therapy. In some embodiments, the diseased human cells are immortalized cells, i.e., from a cell line. Immortalized cells are cells that has been manipulated, either through genetic modification or via exposure to specific viruses or chemicals, to proliferate indefinitely. Thus, they do not undergo the normal process of senescence (cellular aging) and cell death (apoptosis) that would naturally limit their lifespan. Non-limiting examples of immortalized cell lines include HeLa cells, MCF-7 cells, PC-3 cells, A549 cells, HepG2 cells, Jurkat cells, U87 cells, and MDA-MB- 231 cells. In some embodiments, a patient-derived xenograft (PDX) or cells of a PDX are delivered to a mouse model provided herein. A PDX includes a tissue, such as a cancerous tissue, from a patient, which can be implanted into an immunodeficient mouse. A PDX is used, in some embodiments, to maintain the heterogeneity and architecture of the original tumor, enabling researchers to study cancer in a more natural and clinically relevant environment compared to traditional in vitro methods. Because PDX models preserve the complexity of the cancer, including its unique genetics and the interactions between the cancer cells and their microenvironment, they can provide more accurate predictions about how the tumor may respond to various therapies. The number of diseased human cells administered to an immunodeficient mouse to establish a tumor, for example, can vary widely depending on the type of cells, the mouse strain, and the specific experimental design. In some embodiments, 10^5 to 10^7 (100,000 to 10,000,000) cells are administered to the mouse. In other embodiments, a lower number of cells may be administered to see if they can establish a tumor, and then an increased number of cells may be administered if needed. In other embodiments, for example, if the cancer cells are very aggressive and form tumors easily, fewer cells are administered. The method of injection can influence the number of cells needed. For example, cells injected directly into the tissue (orthotopic injection) might establish a tumor with fewer cells compared to cells injected into the bloodstream (intravenous injection) or under the skin (subcutaneous injection). Diseased cells, in some embodiments, are administered systemically, as described elsewhere herein. When cells are introduced into a mouse via intravenous injection through the tail vein, they often first accumulate in the lungs. This happens because the pulmonary capillary system acts as a filter for the cells, trapping them in the lungs due to the narrow and complex network of blood vessels. Whether these cells engraft and integrate into the lung tissue depends on several factors including the type of cell, the status of the recipient mouse (e.g., any pre- conditioning like irradiation or chemotherapy), and whether the injected cells have the appropriate receptors for adhesion and interaction with lung tissue. The use of intravenous tail vein injection, for example, in mice is a common method for assessing the metastatic potential of cancer cells. This is because cancer cells often can invade, migrate, and establish new tumors (metastases) in distant organs like the lungs. In some embodiments, the diseased cells are labeled with a detectable marker, such as a detectable protein. A detectable marker refers to a molecule (e.g., protein) that can be identified and measured in biological samples using specific detection methods or techniques. Non- limiting examples of detectable markers include fluorescent proteins, enzymes, luminescent proteins, radioactive markers, and magnetic markers. In some embodiments, the detectable marker is a fluorescent protein, such as green fluorescent protein (GFP). In some embodiments, the detectable marker is an enzyme, such as horseradish peroxidase (HRP) or alkaline phosphatase (AP). In some embodiments, the detectable marker is a luminescent protein, such as luciferase. ). In some embodiments, the detectable marker is a radioactive marker (e.g., radioactive isotope), such as ^32P (phosphorus-32) or ^35S (sulfur-35). In some embodiments, the detectable marker is a magnetic marker, such as a magnetic marker protein engineered to contain paramagnetic or superparamagnetic properties. Therapeutic Modalities The murine models provided herein, in some embodiments, are used to assess therapeutic modalities (e.g., assess toxicity, efficacy, pharmacodynamics / pharmacokinetics, etc.). They can offer a range of advantages that help understand disease mechanisms, evaluate the efficacy and safety of new treatments, and refine therapeutic approaches before they are tested in humans. In some embodiments, a mouse model provided herein is used to model a human disease, such as cancer, an autoimmune disease, an infectious disease, or a neurological disorder. Other disease models are contemplated herein. Such mouse models, in some embodiments, are used to are used to evaluate the therapeutic efficacy of new drugs and biological agents, providing preliminary data on their potential benefits. Mouse models of the disclosure may also be used to assess the toxicity and / or safety profile of new (or old) treatments to help identify adverse effects and determine safe dosage ranges. In some embodiments, a mouse model of the disclosure is used to test the delivery and / or efficacy of gene therapy vectors, such as viral vectors carrying therapeutic genes. In some embodiments, a mouse model of the disclosure is used to evaluate the potential of cell-based therapies, for example, for regenerative medicine. In some embodiments, a mouse model of the disclosure is used to test the effectiveness or other characteristic of regulatory T cell (Treg) therapy. In some embodiments, a mouse model of the disclosure is used to test the effectiveness or other characteristic of chimeric antigen receptor (CAR) T cell therapy. Therapeutic modalities include the different approaches and strategies used in the treatment of various diseases and health conditions in a subject. Herein, the terms “subject,” “patient,” and “individual” are used interchangeably. In some embodiments, a subject is a human subject. Other animal subjects are also contemplated herein. Some of the most common therapeutic modalities include pharmacotherapy, which involves the use of drugs to treat diseases and manage symptoms. Other therapeutic modalities include gene therapy and immunotherapy, which use genetic manipulation and the immune system, respectively, to treat diseases such as cancer and genetic disorders. There are many therapeutic modalities available, and the choice of treatment depends on the patient's condition, medical history, and the expertise of the healthcare provider. The therapeutic modality, in some embodiments, is a targeted therapeutic. Targeted therapy includes a type of treatment, for example, cancer, anti-inflammatory, or infection disease treatment, that uses drugs or other substances to identify and attack cells more precisely than standard therapies. Unlike chemotherapy, for example, which can affect healthy cells as well as cancer cells, targeted therapy is designed to interfere with specific molecules (e.g., cancer antigens) or pathways involved in cancer cell growth and survival. Targeted therapy is based on the principle that diseased cells often have certain genetic or molecular abnormalities that distinguish them from normal cells. By targeting these specific abnormalities, targeted therapies can be more effective and less toxic than traditional therapies, such as chemotherapy. Non- limiting examples of targeted therapies include drugs that block the activity of specific enzymes or growth factor receptors, as well as immunotherapies that stimulate the immune system to recognize and attack cancer cells. In some embodiments, the mouse models provided herein are used to assess the on-target (e.g., on tumor) and off-target (e.g., off-tumor) effects of a therapeutic modality. Non-limiting examples of therapeutic modalities that may be used as provided herein include antibodies, small molecule drugs, gene therapies, cell therapies, vaccines, hormones, enzyme replacement therapies, and nucleic acid-based therapies. Antibodies include proteins produced by the immune system that can specifically recognize and bind to foreign substances, such as viruses and bacteria, and help neutralize or eliminate them from the body. Antibodies can also be designed and produced in the laboratory and used as therapeutics to target specific proteins or cells in the body. A therapeutic antibody used herein may be a full-length antibody or an antibody fragment. Antibody fragments are smaller fragments of a full-length antibody that have antigen-binding capacity. Some of the most used antibody fragments include Fab (fragment antigen-binding) fragments, F(ab')2 (fragment antigen-binding dimer) fragments, single-chain variable fragment (scFv), nanobodies, bispecific antibodies, diabodies, triabodies, and domain antibodies (dAbs). Fab fragments are the variable regions of the antibody that contain the antigen-binding site. Fab fragments can be produced by enzymatic cleavage of the antibody molecule and are often used in diagnostic applications, for example. F(ab')2 fragments are the Fab fragments joined together by a disulfide bond, resulting in a fragment that can bind two antigen molecules simultaneously. Single-chain variable fragments are recombinant antibody fragments that include the variable regions of the heavy and light chains of an antibody connected by a short linker peptide. Single-chain variable fragments can be produced in bacteria or yeast and are often used for targeting tumors or other disease- related antigens, for example. Nanobodies are single-domain antibody fragments derived from camelid or shark antibodies that have a small size and high stability. Nanobodies can be produced by genetic engineering, for example. Bispecific antibodies are antibodies that can bind to two different antigens simultaneously. Bispecific antibodies can be produced by fusing two different Fab or scFv fragments together or by engineering a single antibody molecule to contain two different antigen-binding sites. Diabodies are artificially engineered antibodies consisting of two different single-chain variable fragments (scFv) joined together. Diabodies have a small size and can bind to two different antigens simultaneously. Triabodies are artificially engineered antibodies consisting of three different single-chain variable fragments (scFv) joined together. Triabodies have a small size and can bind to three different antigens simultaneously. Domain antibodies are antibody fragments consisting of a single variable domain of the antibody that can be produced in bacteria or yeast. dAbs have a small size and high stability. In some embodiments, the therapeutic modality is a therapeutic antibody, such as a monoclonal antibody. Non-limiting examples of therapeutic antibodies include Trastuzumab (HERCEPTIN®): Rituximab (RITUXAN®), Bevacizumab (AVASTIN®), Pembrolizumab (KEYTRUDA®), Nivolumab (OPDIVO®), Atezolizumab (TECENTRIQ®), Durvalumab (IMFINZI®), Cetuximab (ERBITUX®), Panitumumab (VECTIBIX®), and Daratumumab (DARZALEX®). Trastuzumab is a monoclonal antibody that targets HER2, a protein that is overexpressed in some types of breast cancer and is used to treat HER2-positive breast cancer. Rituximab is a monoclonal antibody that targets CD20, a protein found on the surface of B cells, and is used to treat B-cell non-Hodgkin lymphoma, chronic lymphocytic leukemia, and other B- cell malignancies. Bevacizumab is a monoclonal antibody that targets vascular endothelial growth factor (VEGF) and is used to treat certain types of cancer, including colorectal, lung, and kidney cancer. Pembrolizumab is a monoclonal antibody that targets programmed death receptor-1 (PD-1) and is used to treat certain types of cancer, including melanoma, lung cancer, and head and neck cancer. Nivolumab is a monoclonal antibody that also targets PD-1 and is used to treat certain types of cancer, including melanoma, lung cancer, and renal cell carcinoma. Atezolizumab is a monoclonal antibody that targets programmed death-ligand 1 (PD-L1) and is used to treat certain types of cancer, including bladder cancer and non-small cell lung cancer. Durvalumab is a monoclonal antibody that also targets PD-L1 and is used to treat certain types of cancer, including bladder cancer and non-small cell lung cancer. Cetuximab is a monoclonal antibody that targets the epidermal growth factor receptor (EGFR) and is used to treat certain types of cancer, including head and neck cancer and colorectal cancer. Panitumumab is a monoclonal antibody that also targets EGFR and is used to treat colorectal cancer. Daratumumab is a monoclonal antibody that targets CD38, a protein found on the surface of multiple myeloma cells and is used to treat multiple myeloma. Small molecule drugs include low molecular weight (e.g., less than 10kDa) compounds that can bind to and modify the activity of specific proteins in the body. Small molecule drugs are often used to treat diseases such as cancer, hypertension, and diabetes, for example. Non- limiting examples of small molecule drugs that may be used as a therapeutic modality include Imatinib (GLEEVEC®), Erlotinib (TARCEVA®), Sorafenib (NEXAVAR®), Everolimus (AFINITOR®), Crizotinib (XALKORI®), Venetoclax (VENCLEXTA®), Olaparib (LYNPARZA®), Enzalutamide (XTANDI®), Ibrutinib (IMBRUVICA®), and Palbociclib (IBRANCE®). Imatinib is a tyrosine kinase inhibitor that is used to treat chronic myeloid leukemia (CML) and some types of gastrointestinal stromal tumors (GIST). Erlotinib is a tyrosine kinase inhibitor that is used to treat non-small cell lung cancer (NSCLC) that has a specific mutation in the epidermal growth factor receptor (EGFR). Sorafenib is a tyrosine kinase inhibitor that is used to treat advanced renal cell carcinoma (RCC) and some types of liver cancer. Everolimus is a mammalian target of rapamycin (mTOR) inhibitor that is used to treat advanced RCC and some types of breast cancer. Crizotinib is a tyrosine kinase inhibitor that is used to treat NSCLC that has a specific mutation in the anaplastic lymphoma kinase (ALK) gene. Venetoclax is a B-cell lymphoma-2 (BCL-2) inhibitor that is used to treat chronic lymphocytic leukemia (CLL) and some types of lymphoma. Olaparib is a poly ADP-ribose polymerase (PARP) inhibitor that is used to treat some types of ovarian and breast cancer that have specific mutations in the BRCA genes. Enzalutamide is an androgen receptor inhibitor that is used to treat advanced prostate cancer. Ibrutinib is a Bruton's tyrosine kinase (BTK) inhibitor that is used to treat some types of leukemia and lymphoma. Palbociclib is a cyclin-dependent kinase (CDK) 4 / 6 inhibitor that is used to treat some types of breast cancer. Gene therapies involve the delivery of genetic material, such as DNA or RNA, to cells in the body to correct genetic defects or modify cellular function, for example. In cancer, gene therapy can be used to modify cancer cells or immune cells to help them better target and destroy cancer cells. Non-limiting examples of some of the most studied gene therapies used to treat cancer include CAR T-cell therapy, oncolytic virus therapy, tumor suppressor gene therapy, suicide gene therapy, gene editing therapy, RNA interference (RNAi) therapy, T-cell receptor (TCR) gene therapy, NK cell therapy, and immune checkpoint inhibitor gene therapy. CAR T- cell therapy is a type of gene therapy that involves modifying a patient's own T cells to express a chimeric antigen receptor (CAR) that can recognize and attack cancer cells. CAR T-cell therapy has been approved for the treatment of certain types of leukemia and lymphoma. Oncolytic virus therapy is a type of gene therapy that involves using viruses that have been modified to selectively infect and kill cancer cells. Oncolytic viruses can also be engineered to express genes that stimulate the immune system to attack cancer cells. Tumor suppressor gene therapy involves introducing genes that encode tumor suppressor proteins, such as p53, into cancer cells to help inhibit their growth and survival. Suicide gene therapy involves introducing genes that can cause cancer cells to self-destruct, such as the herpes simplex virus thymidine kinase (HSV-TK) gene, which can be activated by a prodrug called ganciclovir. Gene editing therapy involves using technologies such as CRISPR / Cas9 to selectively modify the genes in cancer cells to help inhibit their growth and survival. RNA interference (RNAi) therapy involves using small RNA molecules to selectively silence specific genes that are involved in cancer growth and progression. T-cell receptor (TCR) gene therapy involves modifying a patient's own T cells to express a TCR that can recognize and attack cancer cells. NK cell therapy involves using natural killer (NK) cells, a type of immune cell, that have been genetically modified to express chimeric antigen receptors (CARs) or other genes that enhance their ability to recognize and attack cancer cells. Immune checkpoint inhibitor gene therapy involves introducing genes that encode immune checkpoint inhibitors, such as PD-1 or CTLA-4, into immune cells to help enhance their ability to attack cancer cells. Cell therapies involve the transplantation or modification of cells in the body to replace damaged or diseased cells or tissues, for example. Non-limiting examples of cell therapies include stem cell therapy, CAR T-cell therapy, gene editing using CRISPR / Cas9, mesenchymal stem cell therapy, retinal pigment epithelial cell therapy, natural killer cell therapy, tumor- infiltrating lymphocyte (TIL) therapy, regulatory T (Treg) cell therapy, dendritic cell therapy, cord blood stem cell therapy, and tissue engineering. Stem cell therapy involves the transplantation of stem cells, which can differentiate into various cell types in the body, to replace or regenerate damaged or diseased tissues. CAR T-cell therapy involves the modification of a patient's own T cells to express chimeric antigen receptors (CARs) that can recognize and eliminate cancer cells. Gene editing using CRISPR / Cas9 and other endonuclease-based system that involve the modification of the DNA sequence of cells to correct genetic defects or modify cellular function, for example. Mesenchymal stem cell therapy involves the use of mesenchymal stem cells, which have anti-inflammatory and immunomodulatory properties, to treat inflammatory and autoimmune disorders. Retinal pigment epithelial cell therapy involves the use of retinal pigment epithelial cells to treat age-related macular degeneration. Natural killer cell therapy involves the use of natural killer cells, which can recognize and kill cancer cells and infected cells, to treat cancer and viral infections. Tumor-infiltrating lymphocyte (TIL) therapy involves the isolation and expansion of tumor-infiltrating lymphocytes, which are immune cells that have infiltrated a tumor, and their reinfusion into the patient to enhance the anti-tumor immune response. Treg therapy aims to restore immune tolerance and reduce inflammation in autoimmune conditions such as type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and lupus. Dendritic cell therapy involves the isolation and activation of dendritic cells, which are immune cells that can stimulate an immune response, and their use as a cancer vaccine. Cord blood stem cell therapy involves the use of stem cells isolated from umbilical cord blood, which can differentiate into various cell types in the body, to treat diseases such as leukemia and sickle cell anemia. Tissue engineering involves the use of cells, biomaterials, and growth factors to create functional tissues or organs in the laboratory for transplantation into the patient. Vaccines include biological preparations that stimulate the immune system to produce a protective immune response against a specific infectious agent, such as a virus or bacteria. There are several types of vaccines, each of which uses a different method to stimulate the immune response. Some of the most common types of vaccines include inactivated vaccines, live attenuated vaccines, subunit, recombinant, and conjugate vaccines, mRNA vaccines, viral vector vaccines, and DNA vaccines. Inactivated vaccines contain killed or inactivated pathogens that cannot cause disease but can still stimulate the immune system to produce an immune response. Examples of inactivated vaccines include the polio vaccine and the hepatitis A vaccine. Live attenuated vaccines contain weakened, but still live, pathogens that can stimulate the immune system to produce a strong and long-lasting immune response. Examples of live attenuated vaccines include the measles, mumps, and rubella (MMR) vaccine and the yellow fever vaccine. Subunit, recombinant, and conjugate vaccines contain specific parts of the pathogen, such as proteins or sugars, that can stimulate the immune system to produce an immune response. Examples of subunit vaccines include the human papillomavirus vaccine and the hepatitis B vaccine. Recombinant vaccines use genetically engineered proteins or particles to stimulate an immune response, while conjugate vaccines combine bacterial proteins with sugars to stimulate an immune response. mRNA vaccines use fragments of messenger RNA (mRNA) to instruct cells to produce a specific protein (e.g., antigen) from the pathogen, which can then stimulate the immune system to produce an immune response. Examples of mRNA vaccines include the Moderna COVID-19 vaccine and the Pfizer-BioNTech COVID-19 vaccine. Viral vector vaccines use a harmless virus, such as an adenovirus or a poxvirus, to deliver genetic material from the pathogen into cells, which can then produce a specific protein from the pathogen and stimulate an immune response. Examples of viral vector vaccines include the Johnson & Johnson COVID-19 vaccine and the Ebola vaccine. DNA vaccines use fragments of DNA from the pathogen to stimulate an immune response. The DNA is usually delivered using a harmless virus or by direct injection. Hormones include chemical messengers produced by the endocrine system that regulate various physiological functions in the body. Hormones can be used as therapeutics to treat a variety if conditions such as diabetes, thyroid disorders, and growth hormone deficiency. Non- limiting examples of therapeutic hormones include insulin, thyroid hormone, growth hormone, adrenocorticotropic hormone (ACTH), gonadotropins, estrogen and progesterone, androgens, cortisol, parathyroid hormone, and vasopressin. Enzyme replacement therapies involve the administration of enzymes to replace or supplement enzymes that are deficient or missing in the body. Enzyme replacement therapy is often used to treat lysosomal storage disorders, such as Gaucher disease and Fabry disease. Nucleic acid-based therapies involve the delivery of nucleic acids, such as DNA or RNA, to cells in the body to modify gene expression or cellular function. Nucleic acid-based therapies include antisense oligonucleotide therapy and RNA interference therapy. RNA interference (RNAi) therapy is a type of gene therapy that involves the use of small RNA molecules to silence or "knock down" the expression of specific genes in the body. Examples of types of RNAi molecules include short interfering RNA (siRNA), microRNA (miRNA), short hairpin RNA (shRNA), ribozymes, aptamers, antisense RNA, and CRISPR RNA (crRNA). Short interfering RNA is a double-stranded RNA molecule that is typically 21-23 nucleotides in length. siRNA molecules are used to silence specific genes by targeting their mRNA for degradation. MicroRNAs are small, single-stranded RNA molecules that are typically 20-24 nucleotides in length. miRNA molecules are involved in regulating the expression of multiple genes by targeting their mRNAs for degradation or translation inhibition. Short hairpin RNA is a single-stranded RNA molecule that is typically 19-29 nucleotides in length and folds back on itself to form a hairpin structure. shRNA molecules are used to silence specific genes by targeting their mRNA for degradation. Ribozymes are RNA molecules that have enzymatic activity and can cleave specific RNA molecules, including mRNA. Aptamers are RNA molecules that can bind to specific targets, such as proteins or other molecules, with high affinity and specificity. Antisense RNA is a single-stranded RNA molecule that is complementary to a specific mRNA molecule. Antisense RNA molecules are used to inhibit translation of the target mRNA by forming a double-stranded RNA molecule that is degraded by the cell. CRISPR RNA is a RNA molecule that is part of the CRISPR-Cas9 system, a genome editing tool that can be used to target specific genes for deletion or modification. Some of the most studied RNAi therapies include Patisiran (ONPATTRO®), Inclisiran (LEQVIO®), Lumasiran (OXLUMO®), Givosiran (GIVLAARI®), Fitusiran, ALN-TTRsc02, RG6346, Danvatirsen, QPI-1007, and IONIS-TTR-LRx. Patisiran is an RNAi therapeutic approved by the FDA for the treatment of hereditary transthyretin-mediated (hATTR) amyloidosis, a rare and progressive genetic disorder that causes the accumulation of amyloid fibrils in various organs. Inclisiran is an RNAi therapeutic approved by the FDA for the treatment of high cholesterol. It targets PCSK9, a protein that regulates the levels of low-density lipoprotein (LDL) cholesterol in the blood. Lumasiran is an RNAi therapeutic approved by the FDA for the treatment of primary hyperoxaluria type 1 (PH1), a rare genetic disorder that causes the buildup of oxalate in the kidneys and other organs. Givosiran is an RNAi therapeutic approved by the FDA for the treatment of acute hepatic porphyria (AHP), a group of rare genetic disorders that affect the production of heme, a component of hemoglobin. Fitusiran is an RNAi therapeutic currently in clinical trials for the treatment of hemophilia A and B, rare bleeding disorders caused by deficiencies in clotting factors. ALN-TTRsc02 is an RNAi therapeutic currently in clinical trials for the treatment of hATTR amyloidosis. RG6346 is an RNAi therapeutic currently in clinical trials for the treatment of age-related macular degeneration, a leading cause of blindness in older adults. Danvatirsen is an RNAi therapeutic currently in clinical trials for the treatment of cancer, specifically non-small cell lung cancer and multiple myeloma. QPI-1007 is an RNAi therapeutic currently in clinical trials for the treatment of rare inherited eye diseases, including Leber hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (ADOA). IONIS-TTR-LRx is an RNAi therapeutic currently in clinical trials for the treatment of hATTR amyloidosis. Immunotherapies Some methods of the disclosure comprise administering a immunotherapy (e.g., a human immunotherapy intended to for treatment in a human) to an immunodeficient mouse, such as a PBMC-humanized immunodeficient mouse, and assessing immunotherapy induced toxicity in the mouse (representative of possible toxicity should the immunotherapy be administered in a human, for example, a human from which the PBMCs are obtained). Immunotherapy, also referred to as biological therapy, includes a type of cancer treatment designed to boost the body's natural defenses to fight the cancer. Immunotherapy uses substances made by the body or in a laboratory, for example, to improve or restore immune system function in an individual. Herein, the terms “subject,” “patient,” and “individual” are used interchangeably. In some embodiments, a subject is a human subject. Other animal subjects are also contemplated herein. Non-limiting examples of immunotherapies that may be administered to a mouse model of the disclosure include monoclonal antibodies, vaccines (e.g., cancer vaccines and / or infections disease vaccines), RNA analogues, check point inhibitors, non-specific immunotherapies such as interferons and interleukins, virus-based (e.g., oncolytic virus-based) therapies, and cell therapies, such as T cell therapies, including adoptive cell (e.g., T cell) therapies. Primary types of cell immunotherapies that may be tested in accordance with the disclosure include, for example, T cell transfer therapies (e.g., chimeric antigen receptor (CAR) T cell therapies and / or tumor infiltrating lymphocyte (TIL) therapies), natural killer (NK) cell therapies, dendritic cell therapies, monocyte cell therapies, gamma delta T cell therapies, and T cell receptor (TCR) therapies. In some aspects, a cell therapy is administered to an immunodeficient mouse that expresses human IL34. In some embodiments, the cell therapy is a T cell therapy. In some embodiments, the T cell therapy is a CAR T cell therapy. Non-limiting examples of CAR T cell therapies include Tisagenlecleucel (KYMRIAH®), Axicabtagene ciloleucel (YESCARTA®), Brexucabtagene autoleucel (TECARTUS®), Lisocabtagene maraleucel (BREYANZI®), and Idecabtagene vicleucel (ABECMA®). An immunotherapy may be administered to an immunodeficient mouse, such as a PBMC-humanized immunodeficient mouse expressing human IL34, within 15 days of administering the human PBMCs to the immunodeficient mouse. In some embodiments, an immunotherapy is administered within 10 days or within 5 days of administering human PBMCs to the immunodeficient mouse. In some embodiments, an immunotherapy is administered within 6 hours, within 12 hours, within 18 hours, or within 24 hours of administering human PBMCs to the immunodeficient mouse. In some embodiments, an immunotherapy is administered to the immunodeficient mouse on the same day (or at about the same time) that human PBMCs are administered. The dose of cell therapy, for example, that may be administered to an immunodeficient mouse, such as a PBMC-humanized immunodeficient mouse expressing human IL34, may range from about 1x106to 1x107cells, for example. In some embodiments, about 1x106, about 2x106, about 3x106, about 4x106, about 5x106, about 6x106, about 7x106, about 8x106, about 9x106, or about 1x107cells (e.g., T cells) are administered to an immunodeficient mouse. In some embodiments, about 0.1 million to about 0.5 million cells are administered to an immunodeficient mouse. In some embodiments, about 0.1 million to about 1.0 million cells are administered to an immunodeficient mouse. In some embodiments, about 0.5 million to about 1.0 million cells are administered to an immunodeficient mouse. In some embodiments, about 5x106T cells are administered to an immunodeficient mouse. Following administration of the immunotherapy, the level of one or more human cytokines circulating in a PBMC-humanized may be assess. In some embodiments, an assessment (e.g., an appropriate assay) is performed within 15 days of administering a human immunotherapy to the immunodeficient mouse. In some embodiments, an assessment is within 10 days or within 5 days of administering a human immunotherapy to the immunodeficient mouse. In some embodiments, an assessment is within 6 hours, within 12 hours, within 18 hours, or within 24 hours of administering a human immunotherapy to the immunodeficient mouse. In some embodiments, an assessment (e.g., an appropriate assay) is performed within 15 days of administering human PBMCs to the immunodeficient mouse. In some embodiments, an assessment is within 10 days or within 5 days of administering human PBMCs to the immunodeficient mouse. In some embodiments, an assessment is within 6 hours, within 12 hours, within 18 hours, or within 24 hours of administering human PBMCs to the immunodeficient mouse. Also contemplated here is the administration of human diseased cells, such as human tumor cells, to an immunodeficient mouse to test the efficacy of an immunotherapy, for example. A human tumor cell may be any tumor cell of interest obtained from a human tumor. Other human diseased cells are described herein. The therapeutic modalities described herein can be administered to a human (e.g., used to treat a disease) following assessment of the modality using a mouse model of the present disclosure. Routes of Administration Cells (e.g., human cells) and / or therapeutic modalities (or other substances / agents) of the present disclosure can be administered to an immunodeficient mouse (or other animal, such as human) via systemic administration or via local administration, for example. In some embodiments, a cell or therapeutic modality is administered via systemic administration. Systemic routes of administration in mice involve the methods by which drugs or therapeutic modalities are introduced into the body of mice to achieve systemic distribution and desired effects. Intravenous (IV) injection is a commonly used route in mice, involving the direct delivery of drugs or therapeutic modalities into veins such as the tail vein, lateral tail vein, retro- orbital sinus, or jugular vein. IV injection provides rapid and direct access to the systemic circulation, ensuring immediate distribution throughout the body. This route is suitable for substances requiring quick systemic effects. Intraperitoneal (IP) injection involves the delivery of drugs or therapeutic modalities into the peritoneal cavity of mice. The substance is absorbed through the peritoneal membrane and enters the systemic circulation. This route provides widespread distribution of the drug within the abdominal cavity and systemic circulation, making it suitable for drugs requiring extensive contact with abdominal organs. Subcutaneous (SC) injection involves the delivery of drugs or therapeutic modalities into the subcutaneous tissue, typically in the dorsal region or behind the neck of mice. The substance is absorbed into the systemic circulation through the capillaries in the subcutaneous tissue. SC injection provides slower but sustained release of the drug into the systemic circulation, making it suitable for substances requiring a longer duration of action. Intramuscular (IM) injection entails the delivery of drugs or therapeutic modalities directly into the muscle tissue of mice, such as the quadriceps or gastrocnemius muscle. The substance is absorbed through the capillaries within the muscle and enters the systemic circulation. IM injection allows for sustained release and longer duration of action compared to other routes, making it suitable for substances requiring a sustained effect. Oral gavage involves the administration of drugs or therapeutic modalities directly into the stomach of mice using a feeding needle or oral gavage needle. This route is commonly used for substances that are orally bioavailable and stable in the gastrointestinal tract. Oral gavage allows for systemic distribution through absorption in the gastrointestinal tract, making it suitable for substances that can be administered orally. Inhalation involves the administration of drugs or therapeutic modalities through inhalation of aerosolized substances. Inhalation chambers or specialized devices are used to deliver the substance to the respiratory system of mice. Inhalation allows for targeted delivery to the lungs and systemic distribution through absorption in the respiratory tract. This route is suitable for substances targeting the respiratory system or requiring direct delivery to the lungs. In some embodiments, a cell or therapeutic modality is administered via local administration. Local routes of administration in mice involve delivering drugs or therapeutic modalities directly to specific target tissues or regions of interest within the mouse body. These routes focus on localized delivery for localized effects, as opposed to systemic routes that aim for widespread distribution. Various local routes of administration are commonly used in mice for specific research objectives. Intradermal (ID) injection is a local route that delivers drugs or therapeutic modalities into the dermis, the layer of skin directly beneath the epidermis. This route is suitable for substances targeting the skin or requiring localized effects in the skin tissue. Subcutaneous (SC) injection, traditionally associated with systemic administration, can also be employed for local administration in mice. By targeting specific subcutaneous regions or anatomical sites, drugs or therapeutic modalities can be delivered directly to the desired local area. Intramuscular (IM) injection serves as both a systemic and local route of administration. In the context of local administration, the drug or therapeutic modality is injected directly into the muscle tissue at the specific site of interest. Intraperitoneal (IP) injection, primarily considered a systemic route, can also be utilized for local administration within the abdominal cavity. By delivering the drug or therapeutic modality into the peritoneal cavity, localized effects can be achieved in organs or tissues within the abdominal region. Intra-articular injection involves delivering drugs or therapeutic modalities directly into the joint space. Intranasal administration entails delivering drugs or therapeutic modalities through the nasal cavity. This local route allows for targeted effects in the nasal passages or the potential to target the central nervous system through the olfactory route. Topical administration involves the application of drugs or therapeutic modalities directly onto the skin or mucous membranes. This local route allows for localized effects on the skin or mucosal surfaces, such as the eyes, ears, or genitals. In some embodiments, cells and / or agents are administered orthotopically. Orthotopic administration refers to the delivery of drugs or therapeutic modalities directly to the anatomically correct or appropriate location within an organism, mimicking the natural or original site of the disease or condition being studied. In the context of animal research, particularly in mice, orthotopic administration aims to reproduce the physiological and anatomical characteristics of a specific organ or tissue to study disease progression, treatment response, or other relevant biological processes. Orthotopic administration in mice involves various techniques to target specific organs or tissues. One commonly used approach is orthotopic tumor implantation, where tumor cells or tissues are injected or surgically placed directly into the corresponding anatomical site of interest. This method allows researchers to study tumor growth, metastasis, and treatment response in a manner that closely resembles the natural environment of the tumor. Another approach is organ-specific injection, where drugs or therapeutic modalities are delivered directly into a specific organ or tissue of interest. By injecting cells or other substances into organs like the liver, lungs, brain, or other organs, researchers can investigate organ-specific effects, disease models, or therapeutic interventions. Orthotopic transplantation is another technique used in mice, involving the surgical transfer or transplantation of tissues or cells to their anatomically correct location within the recipient mouse. This method is commonly used in transplantation studies to assess graft survival, integration, and functionality. Orthotopic infusion or instillation involves the direct introduction of substances into organs or cavities through a catheter or needle. For example, instilling drugs into the bladder or bronchi can mimic the physiological conditions of urinary or respiratory diseases, enabling researchers to study localized effects or treatment approaches. In some embodiments, cells of the disclosure (e.g., human cells) are administered to a mammary fat pad of an immunodeficient mouse. The mammary fat pad of a mouse model refers to a specialized region of adipose (fat) tissue located within the mammary gland area of female mice. In female mice, the mammary glands are situated in pairs along the abdominal region. Each mammary gland is composed of multiple lobes and ductal structures embedded within the surrounding mammary fat pad. In some embodiments, cells of the disclosure (e.g., human cells) are administered to a renal capsule of an immunodeficient mouse. The renal capsule of a mouse refers to the outer layer or covering that encapsulates the kidneys. It is a fibrous layer composed of connective tissue that surrounds and protects the kidneys, providing structural support. The renal capsule acts as a barrier, separating the kidneys from the surrounding tissues and organs. The renal capsule is often utilized for various procedures, including transplantation or implantation of cells, tissues, or therapeutic modalities into the kidney. This can involve making an incision in the renal capsule to access the kidney and perform the desired manipulation. Assays In some embodiments, the methods further comprise assaying one or more characteristics (e.g., efficacy, toxicity, and / or pharmacodynamics / pharmacokinetics, etc.) of a therapeutic modality and / or effect(s) of a therapeutic modality on the human cells. In some embodiments, assaying comprises assaying for cell death (e.g., necrosis and / or apoptosis), inflammation, oxidative stress, alterations in cell morphology, alterations in cell function, accumulation of toxic substances, and changes in enzyme activity. In some embodiments, methods comprise assaying for cell death, which can lead to tissue damage and dysfunction. Cell death assays are used to measure and quantify different forms of cell death, such as apoptosis, necrosis, and autophagy. These assays help one understand the mechanisms and extent of cell death in various biological processes. Several commonly used cell death assays include the Annexin V / Propidium Iodide (PI) Assay, TUNEL Assay, Caspase Activity Assay, LDH Release Assay, MTT Assay, PI Exclusion Assay, and Caspase-Glo® Assays. The Annexin V / PI Assay distinguishes between early apoptotic and late- stage apoptotic or necrotic cells. Annexin V, labeled with a fluorescent marker, binds to phosphatidylserine, a marker for early apoptosis. Propidium iodide (PI) stains cells with compromised membranes, indicating late-stage apoptosis or necrosis. Flow cytometry is typically used to analyze the distribution of stained cells. The TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end labeling) Assay detects DNA fragmentation, a characteristic of apoptosis. It involves labeling DNA strand breaks using a modified nucleotide that can be visualized using fluorescence microscopy or flow cytometry. This assay allows for the quantification of apoptotic cells within a population. Caspase Activity Assays measure the activity of specific caspases, enzymes involved in apoptosis. Using fluorescent or colorimetric substrates, these assays detect the cleavage of substrates by active caspases, generating a measurable signal. Caspase-3, -8, or -9 activity can be measured, indicating the activation of apoptotic pathways. The LDH (Lactate Dehydrogenase) Release Assay measures the release of LDH, an enzyme, into the culture medium upon cell membrane damage or disruption, which is characteristic of necrotic cell death. This assay quantifies the amount of LDH in the culture supernatant using a colorimetric or fluorometric assay, indicating compromised membrane integrity and cell death. The MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide) Assay measures cell viability based on the ability of living cells to reduce MTT, a yellow tetrazolium salt, to a purple formazan product. The formazan can be quantified spectrophotometrically, and a decrease in formazan production indicates reduced cell viability. The PI Exclusion Assay uses propidium iodide (PI), a DNA-intercalating fluorescent dye, to distinguish viable cells from non-viable ones. PI cannot penetrate intact cell membranes, so it only stains cells with compromised membrane integrity, such as necrotic cells. Flow cytometry or fluorescence microscopy can be used to analyze the stained cells. Caspase-Glo® Assays are luminescent assays that utilize a luminogenic caspase substrate. Upon caspase cleavage, the substrate emits a light signal. These assays can be specific to different caspases, such as caspase- 3 / 7 or caspase-8, providing a sensitive and quantitative measurement of caspase activity, indicating apoptotic cell death. In some embodiments, methods comprise assaying for inflammation, which can lead to swelling, redness, and pain. Inflammation assays are widely used to study and measure the presence and extent of inflammation, a complex immune response that occurs in various tissues and organs. These assays help one understand the underlying mechanisms of inflammation, identify potential therapeutic targets, and evaluate the efficacy of anti-inflammatory treatments. Several commonly used inflammation assays include cytokine analysis, cell migration assays, leukocyte adhesion assays, nitric oxide assays, myeloperoxidase assays, histological staining, reactive oxygen species assays, and inflammatory gene expression analysis. Cytokine analysis is a key approach to quantify inflammation. This assay involves measuring the levels of specific cytokines, such as interleukins (IL), tumor necrosis factor-alpha (TNF-α), and interferons (IFN), in biological samples using techniques like ELISA, multiplex immunoassays, or protein arrays. By assessing cytokine profiles, one can gain insights into the inflammatory processes occurring in different tissues. Cell migration assays are utilized to study the migratory capacity of immune cells, such as neutrophils or monocytes, in response to inflammatory stimuli. Transwell assays or scratch assays provide valuable information about immune cell migration and infiltration into inflamed tissues. Leukocyte adhesion assays focus on measuring the adhesion of leukocytes (white blood cells) to endothelial cells, which is a critical step in the inflammatory response. By employing flow chamber assays or static adhesion assays, one can evaluate the adhesion properties of leukocytes under inflammatory conditions, contributing to our understanding of leukocyte-endothelial interactions. Nitric oxide (NO) assays are employed to measure the production of nitric oxide, a signaling molecule involved in inflammation. Griess reagent-based assays or fluorescent probes allow one to assess the levels of nitric oxide, which serves as an indicator of inflammatory activity. Myeloperoxidase (MPO) assays are used to quantify the presence of neutrophils or the extent of inflammation in tissues. MPO is an enzyme released by activated neutrophils and macrophages during inflammation, and measuring MPO activity provides insights into the level of neutrophil infiltration and inflammatory activity. Histological staining techniques, such as hematoxylin and eosin (H&E) staining, play a crucial role in visualizing and assessing inflammatory changes in tissue samples. By examining cellular and tissue alterations, including immune cell infiltration, tissue damage, and edema, one can identify and characterize inflammatory responses. Reactive oxygen species (ROS) assays detect the presence of reactive oxygen species generated during inflammation. Fluorescent probes, such as dichlorofluorescein diacetate (DCFDA), enable the measurement of ROS production in cells or tissues, indicating the presence and extent of inflammation. Inflammatory gene expression analysis involves quantifying the expression levels of specific inflammatory genes, including cytokines, chemokines, and adhesion molecules. Techniques such as quantitative real-time polymerase chain reaction (qPCR) or gene expression microarrays allow one to assess gene expression patterns, providing insights into the molecular aspects of the inflammatory response. In some embodiments, methods comprise assaying for oxidative stress, which can damage cellular components and cause tissue dysfunction. Oxidative stress assays are valuable tools used to measure and assess the levels of reactive oxygen species (ROS) and oxidative damage within cells and tissues. These assays provide insights into the oxidative stress status, which is implicated in various physiological and pathological conditions. Several commonly used oxidative stress assays include the DCFDA assay, NBT assay, total antioxidant capacity assay, lipid peroxidation assay, protein carbonyl assay, glutathione assay, DNA oxidation assay, and mitochondrial membrane potential assay. The DCFDA assay is a widely used fluorometric assay that measures intracellular ROS levels. DCFDA, a non-fluorescent probe, is oxidized by ROS to form the fluorescent compound dichlorofluorescein (DCF). The fluorescence intensity of DCF is proportional to the level of ROS within the cells and can be quantified using fluorescence microscopy or flow cytometry. The NBT assay detects superoxide anions, a type of ROS, by their ability to reduce NBT to formazan crystals. The intensity of the resulting blue formazan precipitate is proportional to the level of superoxide anions generated. This assay is commonly used in histochemical analysis to visualize and quantify superoxide production in tissues. Total antioxidant capacity assays measure the overall antioxidant capacity of biological samples, encompassing both enzymatic and non-enzymatic antioxidants. These assays evaluate the sample's ability to scavenge free radicals or prevent oxidative damage. Methods such as the Trolox equivalent antioxidant capacity (TEAC) assay and the ferric reducing antioxidant power (FRAP) assay are employed to determine the total antioxidant capacity. Lipid peroxidation assays assess the levels of lipid peroxidation products, such as malondialdehyde (MDA), as an indicator of oxidative damage to lipids. The thiobarbituric acid reactive substances (TBARS) assay or MDA assay is commonly used to measure lipid peroxidation, a common consequence of oxidative stress. Protein carbonyl assays detect the presence of carbonylated proteins, which result from protein oxidation due to oxidative stress. These assays derivatize the carbonyl groups with 2,4-dinitrophenylhydrazine (DNPH) and quantify the protein-bound DNPH, providing a measurement of protein oxidation using spectrophotometry. Glutathione assays evaluate the levels of reduced (GSH) and oxidized (GSSG) forms of glutathione, an important intracellular antioxidant. These assays, such as the enzymatic recycling method or Ellman's reagent-based assay, provide insights into the cellular antioxidant capacity and redox balance. DNA oxidation assays detect and quantify DNA damage resulting from oxidative stress. The comet assay (single-cell gel electrophoresis) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) assay are commonly used to assess DNA damage, including oxidized bases and DNA strand breaks caused by oxidative stress. Mitochondrial membrane potential assays measure changes in mitochondrial function resulting from oxidative stress. Fluorescent dyes such as JC-1 or TMRE (tetramethylrhodamine ethyl ester) are employed to evaluate alterations in mitochondrial membrane potential using fluorescence microscopy or flow cytometry. In some embodiments, methods comprise assaying for alterations in cell morphology, for example, changes in the size, shape, and structure of cells, which can lead to tissue dysfunction. Assaying for alterations in cell morphology is an approach to study cellular changes associated with various biological processes or pathological conditions. By examining the structural characteristics and shape of cells, one can gain insights into cellular function, differentiation, disease progression, and response to treatments. Several commonly used methods enable the assessment of alterations in cell morphology. Light microscopy is a fundamental technique for visualizing and assessing cell morphology. Brightfield microscopy provides high-resolution images that allow one to examine overall cell shape, size, and features such as organelles and cytoplasmic structures. Phase contrast microscopy and differential interference contrast (DIC) microscopy enhance contrast and improve the visualization of cellular details, especially for transparent or unstained cells. Fluorescence microscopy utilizes fluorescent dyes or genetically encoded fluorescent proteins to label specific cellular components or structures. By targeting specific molecules, one can visualize and study alterations in cell morphology, such as changes in cytoskeletal organization, organelle distribution, or nuclear morphology. Techniques like immunofluorescence staining and live cell imaging provide valuable information about cellular dynamics and structural changes. Electron microscopy (EM) offers high-resolution imaging of cellular structures at the ultrastructural level. Transmission electron microscopy (TEM) provides detailed views of cellular organelles, membranes, and cytoplasmic components. Scanning electron microscopy (SEM) enables three-dimensional visualization of cell surfaces and can reveal alterations in cell shape, surface morphology, or the presence of cellular protrusions. Cytospin and cell smear techniques involve spreading cells onto glass slides, followed by fixation and staining. These methods allow one to examine cell morphology under a microscope and assess features such as cell size, shape, nuclear characteristics, and the presence of cellular inclusions or abnormalities. Staining techniques like Giemsa, Wright-Giemsa, or Papanicolaou stains can be employed to enhance cellular details and facilitate the identification of specific cell types. High-content imaging combines automated microscopy with image analysis software to quantitatively assess alterations in cell morphology and subcellular structures. This approach enables large-scale screening of cellular phenotypes, measuring parameters such as cell shape, size, texture, or fluorescent intensity. High-content imaging is particularly useful for studying cellular responses to treatments, genetic perturbations, or disease-related processes. Advanced image analysis software tools are available to quantify alterations in cell morphology from microscopy images. These tools allow one to measure parameters such as cell area, perimeter, circularity, aspect ratio, and intensity distribution. By comparing these morphological parameters between different experimental conditions or cell populations, one can identify and quantify changes in cell shape or structure. In some embodiments, methods comprise assaying for alterations in cell function, which can lead to tissue dysfunction and organ failure. Assaying for alterations in cell function is crucial for understanding cellular processes, evaluating the effects of treatments or genetic modifications, and investigating disease mechanisms. Various techniques and assays are available to assess changes in cellular function. These methods provide valuable insights into cellular behavior, signaling pathways, metabolism, and overall cellular health. Enzyme activity assays measure the activity levels of specific enzymes involved in various cellular processes. By employing specific substrates that undergo measurable changes upon enzymatic reactions, one can assess alterations in metabolic pathways, signal transduction, or other enzymatic processes. Calcium imaging techniques enable the monitoring of intracellular calcium levels, which play a critical role in cellular signaling and the regulation of various cellular functions. Fluorescence microscopy using calcium-sensitive dyes allows one to assess alterations in calcium dynamics, providing insights into processes such as neuronal signaling, muscle contraction, or cell communication. Electrophysiological techniques, such as patch-clamp recordings, measure the electrical activity of cells. These techniques assess alterations in membrane potential, ion channel activity, action potentials, synaptic transmission, or other electrical properties of cells. Electrophysiology is widely used in neuroscience and cardiac research to study cellular excitability and function. Metabolic assays measure various aspects of cellular metabolism, such as glucose uptake, ATP production, or oxygen consumption. By utilizing specific substrates or indicators, these assays allow one to quantify alterations in cellular energy metabolism or metabolic pathways. Cell proliferation and viability assays evaluate changes in cell growth, division, or survival. Techniques like MTT assays, cell counting, or live / dead staining provide quantitative or qualitative measurements of alterations in cell proliferation or viability in response to treatments, genetic modifications, or environmental conditions. Analyzing cell signaling pathways reveals changes in cellular responses or signaling cascades. Techniques such as Western blotting, immunofluorescence staining, or ELISA can be used to analyze protein expression, phosphorylation levels, or activation states of specific signaling molecules. These methods elucidate alterations in signaling pathways involved in processes like cell growth, differentiation, or immune responses. Functional imaging techniques, such as fMRI or PET, are used to study alterations in cell function in living organisms or tissues. These non-invasive imaging methods provide insights into functional changes in organs, tissues, or specific cell types and are commonly used in neuroscience, cardiovascular research, or oncology. Flow cytometry allows for the simultaneous analysis of multiple cellular parameters. By using fluorescently labeled antibodies or dyes, flow cytometry assesses alterations in cell surface markers, intracellular protein expression, cell cycle distribution, or apoptosis. It provides quantitative information on alterations in various cellular functions within complex cell populations. In some embodiments, methods comprise assaying for accumulation of toxic substances, which can lead to tissue damage and dysfunction. Assaying for the accumulation of toxic substances is essential for studying the impact of various chemicals, pollutants, or drugs on cells and organisms. These assays provide valuable insights into toxicological mechanisms, the potential adverse effects of substances, and the efficacy of detoxification or protective interventions. Several commonly used methods enable the assessment of toxic substance accumulation. Analytical techniques such as HPLC (High-Performance Liquid Chromatography) and GC-MS (Gas Chromatography-Mass Spectrometry) allow for the identification and quantification of toxic substances. HPLC separates and quantifies a wide range of compounds, providing information about their accumulation levels. GC-MS combines gas chromatography and mass spectrometry to detect and characterize toxic substances based on their mass-to-charge ratio, particularly for volatile or semi-volatile compounds. Fluorescence spectroscopy measures the emission of fluorescent light from a sample upon excitation with specific wavelengths. By using fluorescent probes or dyes, fluorescence spectroscopy can assess the accumulation of toxic substances by monitoring changes in fluorescence intensity or emission spectra. These probes selectively bind to or react with specific toxic compounds, offering a direct readout of their accumulation. Enzyme activity assays evaluate alterations in enzyme function caused by toxic substances. These assays employ specific substrates and indicators to measure enzyme activity, providing insights into the impact of toxic substances on cellular processes. Some toxic compounds can interfere with cellular enzymes, inhibiting their activity or leading to abnormal enzymatic reactions. Immunohistochemistry and immunofluorescence techniques use specific antibodies to detect and visualize the accumulation of toxic substances in tissues or cells. By targeting specific antigens or epitopes related to toxic compounds, these techniques allow for the spatial identification and localization of accumulated toxic substances. Cell-based assays utilize specific fluorescent dyes or probes to assess the accumulation of toxic substances in cultured cells. These assays employ fluorescence microscopy or flow cytometry to quantify the accumulation of toxic compounds, offering insights into their cellular uptake, distribution, and metabolism. Tissue analysis can be employed to study the accumulation of toxic substances in vivo. Tissue analysis involves the extraction and quantification of toxic compounds from organs or biological fluids, enabling one to evaluate their accumulation levels and distribution patterns in different tissues or body compartments. Indirect assays target specific physiological or biochemical changes caused by toxic substances. Assays measuring oxidative stress markers, DNA damage, or metabolic alterations can indirectly infer the presence and accumulation of toxic compounds. These changes serve as indicators of the effects of toxic substances on cells or organisms. In some embodiments, methods comprise assaying for changes in enzyme activity, which can lead to tissue dysfunction and organ failure. Assaying for changes in enzyme activity can be used for studying enzymatic processes, assessing the impact of various factors on enzyme function, and identifying potential disease-related alterations. Several commonly used methods allow one to quantitatively measure the catalytic activity of enzymes and detect changes in their function. Spectrophotometric assays utilize the measurement of absorbance or color change to quantify enzyme activity. These assays often involve enzymatic reactions that produce or consume specific substrates, resulting in changes in light absorption. By monitoring the absorbance or color intensity, one can determine the rate of enzymatic activity. Examples include the use of substrates such as NADH or NADPH, which exhibit changes in absorbance upon enzymatic reactions. Fluorometric assays rely on the detection of fluorescence emitted by a substrate or product of an enzymatic reaction. Fluorescent molecules can be designed to interact specifically with certain enzymes, generating fluorescence signals upon enzymatic activity. By measuring the fluorescence intensity, one can quantify enzyme activity. Fluorometric assays are highly sensitive and often used in high-throughput screening. Radiometric assays involve the use of radioactive isotopes to track enzymatic reactions. Radioactive substrates or cofactors are used in the enzymatic reaction, and the radioactivity of the reaction products is measured using techniques such as liquid scintillation counting. These assays provide high sensitivity but require special precautions due to the use of radioactive materials. Enzyme-Linked Immunosorbent Assay (ELISA) utilizes the specificity of antibodies to detect and quantify enzyme activity. In these assays, enzymes are conjugated to antibodies or antigens, and their activity is measured through the detection of an enzymatic reaction product. ELISA is widely used for the quantification of various enzymes or enzyme activities in biological samples. Gel electrophoresis techniques, such as zymography or native gel electrophoresis, are used to assess changes in enzyme activity based on their mobility in a gel matrix. Enzymes are separated based on their size, charge, or activity, and subsequent staining or activity-based detection methods reveal alterations in enzyme activity. Kinetic assays measure the rate of enzyme-catalyzed reactions under varying substrate concentrations or reaction conditions. These assays determine key kinetic parameters such as the Michaelis-Menten constant (Km) and maximum reaction velocity (Vmax), providing insights into enzyme-substrate interactions and the impact of factors on enzyme activity. Common kinetic assays include the Lineweaver-Burk plot and steady-state kinetic analysis. Mass spectrometry can be utilized to quantify enzyme activity by measuring the consumption or production of metabolites involved in enzymatic reactions. Isotope-labeled substrates or reactants can be introduced, and the change in isotopic ratio is detected using mass spectrometry. This approach allows for precise measurements of enzyme activity and can be applied to complex enzymatic pathways. Activity-based probes are small molecules that selectively react with active enzyme sites. These probes covalently modify active enzymes, allowing for their subsequent detection or isolation. Activity-based probes provide a powerful method for profiling enzyme activity in complex biological systems. In some embodiments, assaying comprises assaying for reduced tumor volume, tumor necrosis, changes in tumor density, decreased tumor markers, and slowed tumor growth. In some embodiments, methods comprise assaying for reduced tumor volume. One of the primary goals of cancer treatment is to shrink the tumor size, and a reduction in tumor volume is often considered a sign of treatment success. Assaying for reduced tumor volume is a critical aspect of evaluating the effectiveness of anti-cancer therapies and monitoring the progression of cancer treatment. Several methods are used to assess changes in tumor size and volume, providing valuable information about treatment response and disease progression. Imaging techniques, including computed tomography (CT), magnetic resonance imaging (MRI), or ultrasound, are commonly employed to visualize and measure tumor size and volume. These non-invasive imaging modalities generate detailed images of the tumor and surrounding tissues, enabling accurate measurements of tumor dimensions and volume changes over time. Tumor biopsy and histopathological assessment play a crucial role in evaluating tumor size reduction. Tumor biopsy involves the removal of a tissue sample from the tumor for microscopic examination. Histopathological analysis allows for the evaluation of tumor size, growth patterns, and cellular characteristics. Reduction in tumor size and changes in cellular features observed through histopathology can indicate response to treatment. Caliper measurements are frequently used in preclinical models, where tumors are directly accessible and measurable. This method involves manually measuring tumor size using calipers or rulers. By measuring the longest diameter (length) and the perpendicular diameter (width) of the tumor, the volume can be estimated using mathematical formulas. Tumor weight serves as an indirect measure of tumor volume reduction. Tumors can be surgically excised and weighed before and after treatment, allowing for the determination of changes in tumor mass. Reduction in tumor weight indicates a decrease in tumor volume. Positron Emission Tomography (PET) imaging utilizes radiolabeled tracers that are selectively taken up by metabolically active tissues, including tumors. PET scans provide functional information on tumor metabolism and can be used to assess changes in tumor size and metabolic activity following treatment. The Response Evaluation Criteria in Solid Tumors (RECIST) is a standardized method for assessing tumor response in clinical trials. RECIST defines specific criteria based on changes in tumor size to categorize treatment response as complete response, partial response, stable disease, or progressive disease. It considers the longest diameter of target lesions to evaluate changes in tumor size. Advanced imaging software allows for 3D reconstruction and volumetric analysis of tumors. By segmenting the tumor region in imaging data, volumetric analysis provides a more precise and comprehensive assessment of tumor volume changes over time. Tumor markers are specific proteins or substances produced by tumor cells that can be measured in blood samples. Monitoring changes in tumor marker levels, such as PSA for prostate cancer or CEA for colorectal cancer, can provide indirect information about tumor response to treatment. In some embodiments, methods comprise assaying for tumor necrosis, which occurs when cancer cells die due to treatment, and can be seen as dark, dead tissue within the tumor on imaging studies. Assaying for tumor necrosis is an important aspect of evaluating the response to cancer treatments and understanding the pathological characteristics of tumors. Several methods are used to assess tumor necrosis and its extent, providing valuable information about treatment response and the nature of the tumor microenvironment. Histopathological examination of tumor tissue sections is a primary method for assessing tumor necrosis. Hematoxylin and eosin (H&E) staining allows pathologists to visualize tissue morphology and identify areas of necrosis within the tumor. Necrotic areas appear as pink amorphous material within the tumor sections. Analyzing the extent and patterns of necrosis provides important insights into the response to treatment. Immunohistochemistry (IHC) utilizes specific antibodies to detect and characterize proteins or markers associated with necrotic tissue. Antibodies against markers such as cleaved caspase-3, involved in the apoptosis pathway, can be used to identify apoptotic cells within necrotic areas. Other markers, such as hypoxia-inducible factor-1 alpha (HIF-1α), may indicate areas of tumor hypoxia, which can contribute to necrosis. Imaging techniques, including CT, MRI, or PET, provide non-invasive visualization of necrotic regions within tumors. Imaging features such as decreased enhancement, areas of low signal intensity, or reduced metabolic activity can indicate tumor necrosis. These techniques allow for the assessment of necrotic changes over time and can be useful for monitoring treatment response. Tumor markers, such as lactate dehydrogenase (LDH), can provide indirect information about tumor necrosis. Elevated levels of LDH in blood samples can indicate extensive tumor cell death, including necrosis. Monitoring changes in tumor marker levels can provide insights into the extent of tumor necrosis and treatment response. The analysis of circulating tumor DNA (ctDNA) in blood samples can also provide information about tumor necrosis. As tumor cells die, fragments of their DNA are released into the bloodstream. Detecting and quantifying ctDNA can be used to assess the presence of necrotic tumor cells and monitor their response to treatment. Molecular profiling techniques, such as gene expression analysis or genomic sequencing, can be employed to identify specific molecular signatures associated with tumor necrosis. These techniques provide insights into the molecular pathways and cellular processes underlying necrotic changes in tumors. Molecular profiling contributes to a better understanding of the mechanisms involved in tumor necrosis and can guide treatment strategies. In some embodiments, methods comprise assaying for changes in tumor density. Imaging studies such as CT or MRI can show changes in the density of the tumor after treatment, indicating the tumor is responding to treatment. Assaying for changes in tumor density is important for evaluating tumor characteristics, monitoring treatment response, and assessing disease progression. Tumor density refers to the composition and structural properties of the tumor mass, including the distribution of cells, extracellular matrix, blood vessels, and other components. Several methods are used to assess changes in tumor density, providing valuable insights into tumor biology. Computed Tomography (CT) imaging is commonly used to assess tumor density. It provides cross-sectional images of the tumor, allowing for the visualization and quantification of tissue density based on X-ray attenuation. CT scans can differentiate between different tissue densities, such as solid tumor regions, areas of necrosis, or cystic components. By analyzing the density distribution within the tumor, changes in tumor density can be identified. Magnetic Resonance Imaging (MRI) techniques can also provide information about tumor density. MRI utilizes magnetic fields and radio waves to generate detailed images of tissues. Different MRI sequences, such as T1-weighted or T2-weighted images, can provide insights into tissue composition and density. Areas of high cellularity, hemorrhage, or edema can be identified, contributing to the assessment of tumor density. Positron Emission Tomography (PET) imaging, combined with radiolabeled tracers, can assess tumor density by measuring metabolic activity. PET scans detect the distribution and concentration of radiotracers, which are taken up by metabolically active cells. Areas of high metabolic activity can indicate regions of increased cellularity and higher tumor density. PET scans often provide functional and metabolic information in conjunction with anatomical imaging modalities. Histopathological examination of tumor tissue sections is crucial for assessing tumor density at the cellular level. Hematoxylin and eosin (H&E) staining allows for the visualization of tumor architecture and cellularity. Pathologists examine the tissue sections under a microscope to identify areas of high cell density or stromal components, providing insights into tumor density and composition. Image analysis software can be used to quantitatively analyze tumor density based on imaging data. These tools can segment the tumor region and calculate parameters such as the fraction of high-density regions, low-density regions, or overall tumor density. Automated image analysis allows for standardized and objective assessments of tumor density. Radiomics, the extraction and analysis of quantitative features from medical images, can also provide information about tumor density. Texture analysis, a subset of radiomics, focuses on quantifying spatial variations in pixel intensities. Texture analysis can provide insights into tumor heterogeneity and density patterns, helping to characterize tumor density and its changes over time. In some embodiments, methods comprise assaying for decreased tumor markers. Some types of cancer produce specific biomarkers that can be measured in the blood, and a reduction in these markers after treatment can indicate a positive response. Assaying for decreased tumor markers is an important aspect of cancer diagnosis, monitoring treatment response, and assessing disease progression. Tumor markers are substances produced by tumor cells or the body in response to cancer. Elevated levels of specific tumor markers in blood or other biological samples can indicate the presence of cancer. Monitoring changes in tumor marker levels, particularly a decrease in their concentration, can provide valuable insights into treatment effectiveness and disease status. Blood tests are commonly used to measure tumor marker levels. Techniques such as ELISA or radioimmunoassay (RIA) allow for the quantification of specific tumor markers in the bloodstream. A decrease in tumor marker concentration over time can indicate a positive response to treatment. These blood tests provide a non-invasive and accessible method for assessing tumor marker levels. In addition to individual tumor markers, panels of multiple biomarkers may be assessed to provide a comprehensive assessment of cancer status. These panels can include various tumor markers that are associated with a specific type of cancer or provide complementary information. By monitoring the levels of multiple tumor markers within a panel, a decrease in their concentrations can provide a more robust assessment of treatment response. Imaging modalities, such as CT, MRI, or PET, can be used to visualize tumors and assess changes in tumor size or metabolic activity. A decrease in tumor size or metabolic activity observed through imaging can be correlated with a decrease in tumor marker levels. Combining imaging techniques with tumor marker assays offers a multi-dimensional assessment of treatment response and disease progression. Tumor marker levels can also be assessed through biopsy and histopathological analysis of tumor tissue. Tissue samples obtained through biopsy can be analyzed using techniques such as immunohistochemistry or in situ hybridization to detect and quantify tumor marker expression. A decrease in tumor marker staining intensity or extent can indicate treatment response at the tissue level. Molecular testing techniques, such as polymerase chain reaction (PCR) or next-generation sequencing (NGS), can be employed to assess tumor marker expression at the genetic or molecular level. These techniques allow for the quantification of specific genetic alterations or gene expression changes associated with tumor markers. A decrease in the expression or presence of these markers can indicate treatment response at the molecular level. In some embodiments, methods comprise assaying for slowed tumor growth. In some cases, cancer treatments may not shrink the tumor but can slow its growth, which can still be considered a positive response to treatment. Assaying for slowed tumor growth is a key component of assessing treatment efficacy and monitoring the progression of cancer. Various methods are employed to assay for slowed tumor growth, providing valuable insights into treatment effectiveness and disease management. Imaging techniques, such as CT, MRI, or PET, play a crucial role in visualizing tumors and assessing changes in their size over time. By comparing tumor measurements taken at different time points, the rate of tumor growth can be evaluated. Imaging also allows for the identification of new lesions or the absence of tumor progression, indicating successful treatment and slowed tumor growth. Tumor volume measurements provide quantitative assessments of tumor size using manual or automated methods. This can be done through caliper measurements, 3D reconstruction of imaging data, or volumetric analysis. Tracking changes in tumor volume over time enables the evaluation of tumor growth rate and identification of any deceleration or stabilization, indicating slowed tumor growth. Monitoring specific biomarkers associated with tumor growth can provide additional insights into treatment response. Tumor markers, such as PSA or carbohydrate antigen 125 (CA- 125), can be measured in blood samples. A decrease or stabilization in the levels of these markers suggests a reduced rate of tumor growth, indicating a positive response to therapy. Histopathological analysis of tumor tissue obtained through biopsies or surgical resections allows for direct examination of tumor characteristics. Pathologists assess the size and cellular features of tumor cells under a microscope. Decreased cellular proliferation, reduced mitotic activity, or a decrease in tumor grade can indicate a slowing of tumor growth, providing evidence of treatment effectiveness. Immunohistochemical staining for proliferation markers, such as Ki-67, provides insights into the rate of cell division within tumors. A decrease in the proportion of proliferating cells indicates slowed tumor growth. This approach allows for the assessment of treatment response at the cellular level and provides valuable information about the biological activity of the tumor. Molecular profiling techniques, such as gene expression analysis or genomic sequencing, offer insights into alterations in gene expression patterns associated with tumor growth. Decreased expression of genes associated with cell proliferation or tumor progression suggests a reduction in tumor growth rate, indicating a positive response to treatment. In some embodiments, methods comprise assaying for elimination of metastases. Some treatments, such as radiation therapy or targeted therapies, may be able to eliminate cancer that has spread to other parts of the body. Assaying for the elimination of metastases is a crucial aspect of cancer management and monitoring the effectiveness of treatments. Metastases, which refer to the spread of cancer cells from the primary tumor to distant sites in the body, pose significant challenges in cancer treatment. Detecting and assessing the elimination of metastases are essential for evaluating treatment response and determining disease progression. Imaging techniques, such as CT, MRI, or PET, play a key role in visualizing metastatic lesions in various organs. Regular imaging scans allow for the assessment of the size, number, and location of metastatic lesions. The elimination of metastases is indicated by the disappearance or significant reduction in the size and number of lesions over time, providing evidence of successful treatment response. Monitoring specific tumor markers associated with metastatic disease is another valuable approach. Tumor markers, such as CEA or PSA, can be measured in blood samples. A decrease or normalization of tumor marker levels indicates the elimination or effective control of metastatic disease. Tracking changes in tumor marker concentrations provides insights into treatment response and the elimination of metastatic lesions. Biopsy or surgical removal of metastatic lesions allows for direct examination of the tissue to confirm the absence of cancer cells. Histopathological analysis of the biopsy samples helps determine if the metastatic lesions have been eliminated. The absence of malignant cells in the biopsy specimen indicates successful treatment and elimination of metastases, providing definitive evidence of treatment efficacy. Molecular testing techniques, such as circulating tumor DNA (ctDNA) analysis or next-generation sequencing (NGS), can be employed to detect the presence or absence of specific genetic alterations associated with metastatic disease. The absence of genetic mutations or alterations previously detected in metastatic lesions indicates the elimination of those metastatic clones, further supporting the notion of treatment success. In some embodiments, methods comprise assaying for increased survival. In some embodiments, the methods comprise assaying for improved symptoms. If cancer is causing symptoms, such as pain or difficulty breathing, successful treatment can lead to an improvement in these symptoms. In some embodiments, the methods comprise assaying for improved overall health. Cancer treatments can improve overall health, such as improving blood counts or reducing inflammation, even if the tumor size remains stable. Additional Embodiments 1. An immunodeficient mouse comprising an engineered genomic variant of an endogenous mouse colony stimulating factor 1 receptor (Csf1r) gene. 2. The immunodeficient mouse of paragraph 1, wherein intron 2 of the endogenous Csf1r gene comprises the genomic variant. 3. The immunodeficient mouse of paragraph 2, wherein the Fms-intronic super enhancer (Fms-intronic regulatory element (FIRE) of intron 2 of the endogenous Csf1r gene comprises the genomic variant. 4. The immunodeficient mouse of any one of the preceding paragraphs, wherein the genomic variant is a deletion. 5. The immunodeficient mouse of any one of the preceding paragraphs, wherein the immunodeficient mouse has a non-obese diabetic (NOD) genetic background. 6. The immunodeficient mouse of paragraph A5, wherein the immunodeficient mouse comprises a Il2rgnullallele. 7. The immunodeficient mouse of paragraph 6, wherein the immunodeficient mouse is homozygous for the Il2rgnullallele, optionally a Il2rgtm1Wjlallele. 8. The immunodeficient mouse of any one of the preceding paragraphs, wherein the immunodeficient mouse comprises a Prkdcnullallele. 9. The immunodeficient mouse of paragraph 8, wherein the immunodeficient mouse is homozygous for the Prkdcnullallele, optionally a Prkdcscidallele. 10. The immunodeficient mouse of any one of the preceding paragraphs, wherein the number of tissue resident mouse macrophage cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene. 11. The immunodeficient mouse of paragraph 10, wherein the number of microglia is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene, optionally wherein the immunodeficient mouse does not comprise mouse microglia. 12. The immunodeficient mouse of any one of the preceding paragraphs, further comprising a human CSF1 transgene, optionally wherein the human CSF1 transgene is expressed to produce functional human CSF1 protein. 13. The immunodeficient mouse of any one of the preceding paragraphs, further comprising a human interleukin 34 (IL34) transgene, optionally wherein the human IL34 transgene is expressed to produce functional human IL34 protein. 14. The immunodeficient mouse of paragraph 13, wherein the human transgene comprises a rat enolase 2 promoter operably linked to a human IL34 coding sequence. 15. The immunodeficient mouse of paragraph 13, wherein the human transgene comprises the endogenous mouse IL34 promoter operably linked to a human IL34 coding sequence. 16. The immunodeficient mouse of any one of the preceding paragraphs, further comprising a chimeric mouse / human amyloid precursor protein (Mo / HuAPP695swe) transgene, optionally wherein the chimeric Mo / HuAPP695swe transgene is expressed to produce a modified humanized mouse amyloid beta (A4) precursor protein. 17. The immunodeficient mouse of any one of the preceding paragraphs, further comprising a mutant human presenilin 1 (PS1-dE9) transgene, optionally wherein the PS1-dE9 transgene is expressed to produce a mutant human presenilin 1 protein. 18. The immunodeficient mouse of any one of the preceding paragraphs, further engrafted with human cells. 19. The immunodeficient mouse of paragraph 18, wherein the human cells are selected from human stem cells or human progenitor cells. 20. The immunodeficient mouse of paragraph 19, wherein the human cells are selected from hematopoietic stem cells (HSCs), peripheral blood mononuclear cells (PBMCs), umbilical cord cells (UCs), embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), and induced pluripotent stem cells (iPSCs). 21. The immunodeficient mouse of paragraph 18, wherein the human cells are selected from human immune cells. 22. The immunodeficient mouse of paragraph 18, wherein the human cells are selected from human neural cells. 23. An immunodeficient mouse comprising a null colony stimulating factor 1 receptor allele. 24. The immunodeficient mouse of paragraph 23, wherein the immunodeficient mouse is homozygous for Csf1rnullallele. 25. The immunodeficient mouse of 23 or 24, wherein the immunodeficient mouse has a non- obese diabetic (NOD) genetic background. 26. The immunodeficient mouse of paragraph 25, wherein the immunodeficient mouse comprises a Il2rgnullallele. 27. The immunodeficient mouse of paragraph 26, wherein the immunodeficient mouse is homozygous for the Il2rgnullallele, optionally a Il2rgtm1Wjlallele. 28. The immunodeficient mouse of any one of paragraphs 23-27, wherein the immunodeficient mouse comprises a Prkdcnullallele. 29. The immunodeficient mouse of paragraph 28, wherein the immunodeficient mouse is homozygous for the Prkdcnullallele, optionally a Prkdcscidallele. 30. The immunodeficient mouse of any one of the preceding paragraphs, wherein the number of mouse macrophage cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene, optionally wherein the immunodeficient mouse does not comprise mouse macrophage cells. 31. The immunodeficient mouse of any one of the preceding paragraphs, further engrafted with human cells. 32. The immunodeficient mouse of paragraph 31, wherein the human cells are selected from human stem cells or human progenitor cells. 33. The immunodeficient mouse of paragraph 32, wherein the human cells are selected from hematopoietic stem cells (HSCs), peripheral blood mononuclear cells (PBMCs), umbilical cord cells (UCs), and mesenchymal stem cells (MSCs). 34. The immunodeficient mouse of paragraph 31, wherein the human cells are selected from human immune cells. 35. The immunodeficient mouse of paragraph 31, wherein the human cells are selected from human neural cells. 36. An immunodeficient mouse comprising a rat enolase 2 promoter operably linked to a human interleukin 34 (IL34) coding sequence, optionally wherein the human IL34 coding sequence is expressed to produce functional human IL34 protein. 37. An immunodeficient mouse comprising a human interleukin 34 (IL34) transgene in the mouse IL34 locus. 38. An immunodeficient mouse comprising an IL34nullallele. 39. The immunodeficient mouse of paragraph 38, wherein the immunodeficient mouse is homozygous for IL34nullallele. 40. The immunodeficient mouse of any one of the preceding paragraphs, wherein the immunodeficient mouse has a non-obese diabetic (NOD) genetic background. 41. The immunodeficient mouse of paragraph 40, wherein the immunodeficient mouse comprises a Il2rgnullallele. 42. The immunodeficient mouse of paragraph 41, wherein the immunodeficient mouse is homozygous for the Il2rgnullallele, optionally a Il2rgtm1Wjlallele. 43. The immunodeficient mouse of any one of the preceding paragraphs, wherein the immunodeficient mouse comprises a Prkdcnullallele. 44. The immunodeficient mouse of paragraph 43, wherein the immunodeficient mouse is homozygous for the Prkdcnullallele, optionally a Prkdcscidallele. 45. The immunodeficient mouse of any one of the preceding paragraphs, further engrafted with human cells. 46. The immunodeficient mouse of paragraph 45, wherein the human cells are selected from human stem cells or human progenitor cells. 47. The immunodeficient mouse of paragraph 46, wherein the human cells are selected from hematopoietic stem cells (HSCs), peripheral blood mononuclear cells (PBMCs), umbilical cord cells (UCs), embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), and induced pluripotent stem cells (iPSCs). 48. The immunodeficient mouse of paragraph 45, wherein the human cells are selected from human immune cells. 49. The immunodeficient mouse of paragraph 45, wherein the human cells are selected from human neural cells. 50. A method of producing an F1 mouse comprising breeding any two of the preceding immunodeficient mice. 51. A method comprising administering a therapeutic modality to the immunodeficient mouse of any one of the preceding paragraphs. 52. The method of paragraph 51 further comprising assaying the immunodeficient mouse or cells of the mouse for a phenotypic change, relative to a control. 53. A method of assessing immunotherapy induced toxicity, the method comprising: (a) administering human peripheral blood mononuclear cells, and optionally human diseased cells, to an immunodeficient mouse, wherein the genome of the immunodeficient mouse comprises an open reading frame encoding human interleukin-34 (IL34); (b) administering a human immunotherapy (e.g., an adoptive immune cell therapy) to the immunodeficient mouse; and (c) assaying a biological sample of the mouse for (i) a level of a human cytokine (e.g., expression or activity), optionally selected from IL8, IL18, MCP-1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ, (ii) a level of human ferritin (e.g., expression or activity), or (iii) a combination of a level of the human cytokine and the level of ferritin, thereby assessing immunotherapy induced toxicity. 54. The method of paragraph 53, wherein about 1x106to 1x107, optionally about 4x106or about 8x106, human peripheral blood mononuclear cells are administered to the immunodeficient mouse. 55. The method of paragraph 53 or 54, wherein the human immunotherapy is administered within 5 days, within 10 days, or within 15 days of administering the human peripheral blood mononuclear cells to the immunodeficient mouse. 56. The method of any one of the preceding paragraphs, wherein the human immunotherapy is a human cell therapy. 57. The method of paragraph 56, wherein the human T cell therapy is a human chimeric antigen receptor (CAR) T cell therapy. 58. The method of paragraph 56 or 57, wherein the human cell therapy comprises about 1x106to 1x107, optionally about 5x106, human cells. 59. The method of any one of the preceding paragraphs, wherein the assaying is within 5 days, within 10 days, or within 15 days of administering the human immunotherapy. 60. The method of any one of the preceding paragraphs, wherein the assaying is within 5 days, within 10 days, or within 15 days of administering the human peripheral blood mononuclear cells. 61. The method of any one of the preceding paragraphs, comprising administering human diseased cells, optionally human tumor cells, further optionally human cancer cells, to the immunodeficient mouse, and optionally assaying for efficacy of the human immunotherapy. 62. The method of any one of the preceding paragraphs, wherein the open reading frame encoding human IL34 is operably linked to the mouse IL34 promoter. 63. The method of any one of the preceding paragraphs, wherein the immunodeficient mouse has a non-obese diabetic (NOD) genetic background. 64. The method of paragraph 63, wherein the immunodeficient mouse comprises a Il2rgnullallele. 65. The method of paragraph 64, wherein the immunodeficient mouse is homozygous for the Il2rgnullallele. 66. The method of paragraph 64 or 65, wherein the Il2rgnullallele is the Il2rgtm1Wjlallele. 67. The method of any one of the preceding paragraphs, wherein the immunodeficient mouse comprises a Prkdcnullallele. 68. The method of paragraph 67, wherein the immunodeficient mouse is homozygous for the Prkdcnullallele. 69. The method of paragraph 68, wherein the Prkdcnullallele is the Prkdcscidallele. 70. An immunodeficient non-obese diabetic (NOD) mouse comprising: a genome comprising a mouse IL34 promoter operably linked to an open reading frame encoding human IL34, a Il2rgtm1Wjlallele, and a Prkdcnullallele, wherein the mouse is engrafted with human peripheral blood mononuclear cells, expresses human IL18 serum levels, optionally higher than 100 pg / ml, optionally expresses human ferritin, and optionally wherein the mouse has been administered a human immunotherapy. 71. The mouse of paragraph 70, wherein the human immunotherapy is a human cell therapy. 72. The mouse of paragraph 71, wherein the human T cell therapy is a human chimeric antigen receptor (CAR) T cell therapy. 73. An immunodeficient mouse whose genome comprises a nucleic acid comprising an open reading frame encoding human IL-34, wherein the immunodeficient mouse has an MHC Class I molecule deficiency and / or an MHC Class II molecule deficiency. 74. An immunodeficient mouse whose genome comprises a nucleic acid comprising an open reading frame encoding human colony stimulating factor 1 (CSF1), wherein the immunodeficient mouse has an MHC Class I molecule deficiency and / or an MHC Class II molecule deficiency 75. The immunodeficient mouse of paragraph 73 or 74, wherein the genome of the immunodeficient mouse comprises a null mutation in an endogenous gene selected from H2-K1, H2-Ab1, and H2-D1. 76. The immunodeficient mouse of any one of the preceding paragraphs, wherein the immunodeficient mouse has a MHC Class I molecule deficiency and an MHC Class II molecule deficiency. 77. The immunodeficient mouse of paragraph 76, wherein the genome of the mouse comprises a null mutation in an endogenous H2-K1 gene, an endogenous H2-Ab1 gene, and an endogenous H2-D1 gene. 78. The immunodeficient mouse of any one of the preceding paragraphs, wherein the genetic background of the mouse comprises a non-obese diabetic (NOD) genetic background. 79. The immunodeficient mouse of any one of the preceding paragraphs, wherein the genome of the mouse further comprises a null mutation in an endogenous Il-2Rγ gene. 80. The immunodeficient mouse of any one of the preceding paragraphs, wherein the genome of the mouse further comprises a severe combined immunodeficiency (Prkdcscid) mutation. 81. The immunodeficient mouse of any one of the preceding paragraphs, wherein the genetic background of the mouse comprises a NOD-Cg.-PrkdcscidIL2rgtm1wJl / SzJ genetic background and / or a NOD.Cg-PrkdcscidH2-K1b-tm1BpeH2-Ab1g7-em1MvwH2-D1b-tm1BpeIl2rgtm1Wjl / SzJ genetic background. 82. The immunodeficient mouse of any one of the preceding paragraphs engrafted with human cells, preferably human immune cells, optionally human hematopoietic stem cells, human peripheral blood mononuclear cells, or human immune cells selected from innate immune cells (e.g., phagocytes, granulocytes, natural killer cells, mast cells), adaptive immune cells (e.g., T cells, B cells), and other immune cell types (e.g., monocytes, megakaryocytes), further optionally obtained from a human subject (e.g., having a cancer such as a solid cancer, or an autoimmune disease such as multiple sclerosis or lupus). 83. A mouse embryo obtained from the immunodeficient mouse of any one of the preceding paragraphs. 84. An isolated mouse embryo whose genome comprises a nucleic acid comprising an open reading frame encoding human IL-34, wherein the immunodeficient mouse has an MHC Class I molecule deficiency and / or an MHC Class II molecule deficiency. 85. An isolated mouse embryo whose genome comprises a nucleic acid comprising an open reading frame encoding human colony stimulating factor 1 (CSF1), wherein the immunodeficient mouse has an MHC Class I molecule deficiency and / or an MHC Class II molecule deficiency 86. The isolated mouse embryo of paragraph 84 or 85, wherein the genome of the isolated mouse embryo comprises a null mutation in an endogenous gene selected from H2-K1, H2-Ab1, and H2-D1. 87. The isolated mouse embryo of any one of the preceding paragraphs, wherein the isolated mouse embryo has an MHC Class I molecule deficiency and an MHC Class II molecule deficiency. 88. The isolated mouse embryo of paragraph 87, wherein the genome of the isolated mouse embryo comprises a null mutation in an endogenous H2-K1 gene, an endogenous H2-Ab1 gene, and an endogenous H2-D1 gene. 89. The isolated mouse embryo of any one of the preceding paragraphs, wherein the genetic background of the isolated mouse embryo comprises a non-obese diabetic (NOD) genetic background. 90. The isolated mouse embryo of any one of the preceding paragraphs, wherein the genome of the isolated mouse embryo further comprises a null mutation in an endogenous Il-2Rγ gene. 91. The isolated mouse embryo of any one of the preceding paragraphs, wherein the genome of the isolated mouse embryo further comprises a severe combined immunodeficiency (Prkdcscid) mutation. 92. The isolated mouse embryo of any one of the preceding paragraphs, wherein the genetic background of the isolated mouse embryo comprises a NOD-Cg.-PrkdcscidIL2rgtm1wJl / SzJ genetic background and / or a NOD.Cg-PrkdcscidH2-K1b-tm1BpeH2-Ab1g7-em1MvwH2-D1b-tm1Bpe Il2rgtm1Wjl / SzJ genetic background. 93. A progeny mouse of the immunodeficient mouse of any one of the preceding paragraphs. 94. The progeny mouse of paragraph 93, wherein the progeny mouse is an F1 hybrid mouse. 95. A method of producing the immunodeficient mouse of any one of the preceding paragraphs. 96. A method of using the immunodeficient mouse of any one of the preceding paragraphs. 97. A method comprising: optionally irradiating the immunodeficient mouse of any one of paragraphs the preceding paragraphs; and administering a therapeutic agent to the immunodeficient mouse; and optionally assaying for an effect of the therapeutic agent on the immunodeficient mouse or a biological sample from the immunodeficient mouse. 98. The method of paragraph 97, wherein the therapeutic agent is an mRNA vaccine comprising an mRNA and a lipid nanoparticle. 99. A method comprising: administering a composition comprising an mRNA and a lipid nanoparticle to the immunodeficient mouse of any one of the preceding paragraphs; and assaying for an effect of the composition on the immunodeficient mouse or a biological sample from the immunodeficient mouse. EXAMPLES The mouse strains provided herein, such as those described in Table 1, can be used to model human disease, such as cancer and / or autoimmunity, for example, for testing efficacy, toxicity, and / or pharmacokinetics / pharmacodynamics of therapeutic agents, such as immunotherapeutic agents (e.g., including without limitation cellular and gene therapeutics). Table 1. NSG®Mouse Strains Tg: transgene / transgenic Example 1. Development NSG® Mouse Models Expressing Human Interleukin-34 NOD.Cg-PrkdcscidIl2rgtm1Wjl-Tg(Eno2-huIL34)1Sz / Sz mouse (also referred to as NSG-Eno2-huIL34) We first created a strain of NSG®mice transgenically expressing human IL34 using the rat enolase 2 gamma neuronal (Eno2) promoter to drive human IL34 cDNA for high expression in neurons (e.g., in the brain). Levels of serum IL34 were determined in offspring of two founder lines. While one of these lines did not produce detectable IL34, line 1 showed high levels of human serum IL34 (2800 pg / ml). Levels of IL34 in healthy humans are ~ 60pg / ml. Increased IL34 levels are associated with inflammatory diseases. This founder line was maintained in a hemizygous state as homozygosity of the transgene in females results in poor breeding, while male homozygotes are productive breeders. NOD.Cg-PrkdcscidIl2rgtm1WjlIL34em1(IL34*)1Szmouse (also referred to as NSG-huIL34 KI) We also created a strain of NSG®mice transgenically expressing human IL34 using the mouse promoter. A human IL34 transgene was knocked into the mouse locus to provide physiological levels of human IL34. Mouse IL34 is normally expressed in several structures, including alimentary system, brain, skin, genitourinary system, hemolymphoid system and mammary gland. Unexpectedly, these IL34 knockin mice had relatively high levels of serum IL34 (950 pg / ml), albeit lower than the levels seen in the IL34 transgenic that was driven by the enolase promoter. FIG.1A shows human IL34 serum levels in serum from an NSG-Eno2-huIL34 mouse and an NSG-huIL34 KI mouse. FIG.1B shows heightened human IL34 in brains and spinal cords of 7-12 month old NSG-Eno2-Hu-IL34 mice. Humanization Studies NSG-Eno2-huIL34 and NSG® control mice were engrafted with human CD34+ cord blood cells, then stained for human CD3, CD19, and Cd33 at 6 weeks post engraftment. FIGs. 2A-2C show that human hematopoietic stem cell (HSC) engrafted NSG-huIL34 mice support high levels of human myeloid engraftment in the blood. FIG.2A shows data from HSC- engrafted NSG® mice; FIG.2B shows data from HSC-engrafted NSG-Eno2-huIL34 mice; and FIG.2C shows a comparison of the human immune cell subsets. Survival Studies Next, mice (6-8 wk old) were irradiated with 100 cGy and injected intravenously with 105human HSC from human umbilical cord blood. Flow cytometry analyses showed that by ~7 weeks post engraftment, the human HSC-engrafted NSG-Eno2-huIL34 mice exhibited poor survival (FIG.3A). By contrast, human HSC-engrafted NSG-huIL34 KI mice exhibited 100% survival. In this study, NSG-huIL34 KI mice were HSC-engrafted as newborn (nb) or as adults. NSG-Eno2-huIL34 mice died by 4 weeks post engraftment. The presence of the SGM3 transgenes (huIL3, huCM-CSF, and huSCF) reduced survival of NSG-huIL34 KI mice. See FIG. 3B. Characterization of Human Microglial Cell Development We next compared human microglial cell development in the NSG-huIL34 KI mouse and in the NSG-huCSF1 mouse (NOD.Cg-PrkdcscidIl2rgtm1WjlTg(CSF1)3Sz / SzJ), an NSG® mouse expressing a human CSF1 transgene. Following low dose whole body irradiation (200 cGy), we engrafted 6-8 week old NSG-Eno2-huIL34 and NSG-huCSF1 mice with 5x104human CD34+HSCs derived from CD3-depleted umbilical cord blood, harvested the brains after perfusion, disaggregated the brains, and carried out flow cytometry for microglial cell markers. Flow cytometry of the disaggregated brains exhibited much higher levels of human microglia in the NSG- huIL34 KI mice than in the NSG-huCSF1 mice (FIG.4). This correlated with the heightened levels of human IL34 compared to human CSF1 in the transgenic mouse strains. Confocal images of the cortex, hippocampus, and thalamus of the NSG-huCSF1 mice showed a resting phenotype based on expression of human and mouse Iba1 (microglia marker that is upregulated in active microglia) and mouse p2RY12 (microglia marker that is involved in cell motility) (images not shown). By contrast, images of the cortex, hippocampus, and thalamus of the NSG-huIL34 KI mice showed an active phenotype. NOD.Cg-PrkdcscidIl2rgtm1Wjl-IL34em1Szmouse (also referred to as NSG-huIL34 KO) We also targeted the mouse IL34 gene by CRISPR Cas9. The absence of mouse IL34 will prevent the development of IL34-dependent resident microglia and other IL34-dependent macrophage populations. This mouse model is currently undergoing characterization studies. NOD.Cg-PrkdcscidIl2rgtm1Wjl-Tg(huIL34) Tg(APPswe,PSEN1dE9)85Dbo / Sz mouse (also referred to as NSG-Eno2-huIL34-APP / PS1) NSG-APP / PS1 are double transgenic mice that express a chimeric mouse / human amyloid precursor protein (Mo / HuAPP695swe) and a mutant human presenilin 1 (PS1-dE9), both directed to neurons. The NSG-APP / PS1 mice express high levels of amyloid plaques, microglial cell activation, and cognitive defects. Next, we crossed NSG-Eno2-huIL34 homozygous females with NSG-APP / PS1 hemizygous males to produce doubly hemizygous offspring and controls. The NSG-Eno2-huIL34-APP / PS1 transgenic line was maintained by breeding female NSG-Eno2-huIL34hemizygotes with male NSG-APP / PS1 hemizygotes. These stocks have been expanded to create cohorts of NSG-Tg (APP / PS1 Hu-IL34) mice along with NSG-APP / PS1 and NSG-Eno2-huIL34) controls. These mice were aged and cohorts euthanized at various ages to determine the effects of the human IL34 transgenes on mouse microglial cell populations and on progression of Alzheimer's disease. Male NSG-Eno2-IL34-APP / PS1 mice euthanized at 6 months of age exhibited increased microglia in the hippocampus as well as plaque formation (images not shown). NOD.Cg-PrkdcscidIl2rgtm1Wjl-Tg(huCSF1) Tg(APPswe,PSEN1dE9)85Dbo / Sz mouse (also referred to as NSG-huCSF1-APP / PS1) We then crossed NSG-huCSF1 homozygous females with NSG-APP / PS1 hemizygous males. The NSG-huCSF1-APP / PS1 strain was maintained by breeding female NSG-huCSF1 hemizygotes with male NSG-APP / PS1 hemizygotes. The human CSF1 hemizygous control offspring that don't express the APP / PS1 transgene serve as internal controls. The human CSF1 transgene supported microglial cell development in NSG® mice and supports both human microglial cell development and amyloid plaques in NSG-APP / PSEN mice. Thus, NSG- huCSF1-APP / PS1 mice have increased numbers or altered distribution of microglial cells compared with NSG-APP / PS1 controls. These stocks have been expanded to create cohorts of NSG-huCSFl-APP / PSEN mice along with NSG-APP / PSEN and NSG-huCSF1 controls. Flow cytometry analyses of peripheral blood cells (PBL), bone marrow (BM) cells and splenocytes from naïve NSG®, NSG-Eno2huIL34-APP / PS1 and NSG-huCSF1-APP / PS1 mice showed no significant differences in percentages of B220+ pre-B cells, CD3+ T cells, MHC class I+ cells, MHC class II + cells, DX5+ cells, (Mac1 Gr1) double positive myeloid cells, or Ter 119+ erythroid cells) (FIGs.5A-5C). Confocal imaging focused on the hippocampus of NSG-Eno2-huIL34-APP / PS1 and NSG®control mice at 6 months of age. NSG-Eno2-huIL34-APP / PS1 mice had increased numbers of IBAl+ microglia and GFAP+ astrocytes compared with NSG®mice (FIG.6). IBA1 (ionized calcium binding adaptor molecule) is specifically expressed in macrophages / microglia of mice and humans and is upregulated during the activation of these cells. GFAP (glial fibrillary acidic protein) is expressed by astrocytes. NSG-Eno2-huIL34-APP / PS1 mice showed dense accumulation of microglia with clumps of microglia forming plaques as well as increased numbers of astrocytes. We next examined development of human microglia following injection of human HSC. NSG-huCSF1 and NSG-Eno2-huIL34 mice were injected with human HSC and engraftment of human microglia was evaluated. The NSG-Eno2-huIL34 mice showed dense accumulations of human as well as mouse microglia while the. NSG-huCSF1 mice showed more physiological levels of human as well as mouse microglia (images not shown). Analyses of peripheral blood leukocytes, erythrocytes and platelets showed no major changes among the five different strains shown in Table 1. Table 1. Flow cytometry results NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2z / Sz mouse (also referred to as NSG-FIRE-KO) Lastly, CRISPR Cas9 deletion of intron 2 in the Csf1r gene of NSG mice was carried out to develop a strain of NSG mice lacking the FIRE enhancer. NSG-Csf1rem2z / Csf1rem2z(FIRE KO) founders were identified by sequencing and fixed to homozygosity. Initial breeding of NSG FIRE homozygotes was not successful. Male infertility appeared to be associated with impaired spermatogenesis. The testes resident macrophages appear to play an important role in spermatogenesis. The basis of NSG-FIRE KO female infertility is under investigation. We subsequently used In Vitro Fertilization (IVF) to impregnate NSG + / Fire knockout eggs with NSG FIRE / FIRE homozygous KO sperm and were successful in expanding the stock. Thus, the NSG- FIRE / FIRE males are fertile and IVF can be used for rapid stock expansion. The NSG FIRE KO lines were maintained by intercrossing NSG + / FIRE heterozygotes. Data presented in FIG.7 shows survival data from 3 of the 6 NSG-FIRE KO lines generated. FIG.8 shows numbers of F4 / 80+ macrophages per area in tissues of individual NSG- Fire knockout (KO) mice, heterozygotes (HET) and + / + (WT) controls. These mice show severely reduced numbers of F4 / 80+ macrophage populations at one week of age in multiple tissues. Similarly, data generated by flow cytometry analysis of brain macrophages following enzymatic disassociation of brain shows that NSG-FIRE KO mice exhibit a 98% depletion of brain macrophages (FIG.9, mouse CD45+ CD11+ cells are shown). These mice also show abnormalities in liver chemistry profiles (FIG.10). Immunohistochemical staining was also carried out to determine the effect of the FIRE knockout on populations of resident tissue macrophages. Severe resident macrophage depletion was observed in the brain (images not shown). Also, at 13 weeks of age, immunoperoxidase staining for f4 / 80 (pan mouse macrophage antigen) shows a loss of microglia in cerebellum and a loss of macrophages in the heart and kidneys of NSG-FORE KO mice (images not shown). As the NSG-FIRE mice age, some develop paralysis by 2 months of age initially observed by hind limb dragging. We observed demyelination in the spinal cord suggesting a possible model for multiple sclerosis (MS). Macrophages are known to play a dual role in MS. They can contribute to tissue damage by production of inflammatory mediators and can also mediate neuroprotection. The inability of NSG-FIRE mice to generate resident macrophages in the central nervous system before birth may help elucidate the role of these resident macrophages in human MS. Example 2. Diverging Phenotypes and Regional Accumulation of Human Microglia in Engrafted hCSF1- and hIL-34-expressing Mice h-IL34KImice have a higher percentage of human cells In CD45+ brain cells from h-IL34KI mice, there was a significantly higher percentage (88.66%) of human cells than mouse cells (11.56%) (FIG.11). Though h-CSF1Tg mice also had more human cells in the brain (58.06%), the overall percentage of human cells was less than in h- IL34KImice. Three distinct populations were found within human and mouse CD45+ population in both strains based on P2Ry12 and CX3CR1 expression (P2Ry12-CX3CR1-, P2Ry12lowCX3CR1low, P2Ry12highCX3CR1high). P2Ry12 or CX3CR1 are two common microglia markers, thus cells that do not express these markers may represent a population that of human cells that do not acquire microglia characteristics. Human CD45+ cells within the brain of h-Il34KI mice are largely P2RY12lowCX3CR1low. A smaller percentage are P2RY12highCX3CR1high. This is in contrast with cells within h-CSF1Tg brains, which were equally comprised of P2RY12highCX3CR1high cells and P2RY12lowCX3CR1low cells. Human cell composition in the brain of h-CSF1Tg mice more closely resembled the composition of endogenous mouse CD45+ populations, which were largely P2RY12highCX3CR1high but also had a population of P2RY12lowCX3CR1low cells. Based on our understanding that the large majority of mouse cells in the brain are microglia, the mouse expression profile, we postulate that high expression of P2RY12 and CX3CR1 represents the phenotypic profile of microglia in the mouse brain. Both h-IL34KI and h-CSF1Tg spinal cord tissue (SC) had a lower percentage of human cells as compared to mouse cells. However, more human cells accumulated in the spinal cords of h- IL34KI mice (48.62%) as compared to human cells within h-CSF1Tg mice (10.28%). Using HLA- DR and CD44 markers, three distinct cell populations were also found in mouse and human SC tissue in both mouse groups. Composition of human cell populations in h-IL34KI expressing mice did not differ greatly from composition of human cells within the h-CSF1Tg mouse group. h-IL34KIand h-CSF1Tgmice display different microglia localization Visually, coronal sections of h-IL34KI expressing mice appeared to support a larger population of hMG as compared to h-CSF1Tg mice. hMG were found largely within the cortex of h-IL34KI mice, while the majority of the hMG within h-CSF1Tg mice accumulated within the fiber tracts ventral to the hippocampus (images not shown). As expected from the lower numbers of hMG found in the cortex, the cortex of engrafted h-CSF1Tg mice resembled unengrafted NSG controls. However, hMG within the cortex of h-IL34KI brains assumed a reactive morphology. The hMG found within the fiber tracks in h-CSF1Tg mice had a ramified morphology, similar to that of endogenous mouse microglia. h-IL34KIMice Accumulate hMG in Specific Isocortex Regions Brain of h-IL34KI expressing mice were coronally sectioned at various regions and the distribution of hMG was assessed (images not shown). hMG were found to be unequally distributed between functional areas of the cortex, demonstrating hMG proliferation within the somatomotor and auditory regions, but little to no hMG in the somatosensory region in sections from the anterior portion of the hippocampus. HLA-DR is more highly expressed in P2Ry12lowCX3CR1low hMG in h-IL34KI mice P2Ry12-CX3CR1- populations in both h-IL34KI and h-CSF1Tg mice had higher HLA- DR expression as compared to the other two populations (FIG.12). A higher percentage of P2Ry12lowCX3CR1low cells expressed HLA-DR in h-IL34KI mice than h-CSF1Tg mice. The profile of MHCII expression in endogenous mouse P2Ry12lowCX3CR1low cells and P2RY12highCX3CR1high cells were more similar to HLA-DR expression profiles in h-IL34KI mice, though there was still significantly more expression in mouse cells. Expression of CD44 in h-CSF1Tg CD45+ cells more closely resemble mouse microglia In mouse bone marrow cells, CD44 is expressed highly within both h-IL34KI and h- CSF1Tg expressing mice, but not expressed highly in brain-resident cells, suggesting that CD44 may be a plausible marker for bone marrow derived cells (FIG.13). In both groups, P2RY12- CX3CR1- cells expressed levels of CD44 comparable to the same human cell population in the bone marrow, which further supports the hypothesis that P2RY12-CX3CR1- cells are a population of non-microglia cells. In contrast, P2RY12highCX3CR1high cells in each mouse strain, which we suspect to be most microglia-like, expressed lower levels of CD44 than the same population in the bone marrow. In P2Ry12lowCX3CR1low cells, h-IL34KI mice express CD44 at similar levels to P2RY12highCX3CR1high cells, while expression on this population in hCSF1Tg mice was less than that of P2RY12highCX3CR1high cells. Lower overall expression of CD44 in the P2Ry12lowCX3CR1low in h-CSF1Tg expressing mice resembles CD44 expression profiles in endogenous mouse microglia. Interestingly, in the bone marrow, P2RY12lowCX3CR1low cells expressed CD44 very highly, in stark contrast to P2Ry12lowCX3CR1low cells in either mouse group. Discussion Following injection of CD34+ HSCs into newborn mice, there is a significant difference in the number, location, and phenotype of engrafted hMG between NSG-hIL34KI and NSG- hCSF1Tg mice. HSC-engrafted h-IL34KI mice have a greater percentage of human cells compared to h-CSF1Tg mice, confirming the significance of IL34 in differentiation and proliferation of hMG. Engraftment efficiency of human cells in the spinal cord was significantly lower for bout h-IL34KI and h-CSF1Tg mice. Differences in expression of factors that regulate the development, cellular phenotype, and biological functions between brain and spinal cord microglia may explain this difference in engraftment efficacy between the two tissues. In both mouse groups, hMG can be separated into three distinct populations by the expression of microglia markers P2Ry12 and CX3CR1. P2RY12lowCX3CR1low cells are the most common cell population in h-IL34KI mice and expresses higher levels of HLA-DR than the comparable population in h-CSF1Tg mice, and therefore more closely resemble endogenous mouse microglia. However, expression patterns of CD44 suggests that phenotypic differences between hMG and mouse MG still exist in h-IL34KI mice, either due to activation status or cell origin. Regional accumulation of hMG varies between the two mice groups. hMG in h-IL34KI mice notably accumulate in distinct areas of the isocortex, with the somatosensory region clearly lacking hMG. In previous studies, mouse IL34 transcripts were found to be more highly expressed in the cortex of mice as compared to other regions of the brain, but no regional variation was noted. In contrast, hMG present in h-CSF1Tg expressing mice aggregated within the thalamus and fiber track areas ventral to the hippocampus. A similar distribution was found in mouse microglia depletion studies, where mice lacked microglia within the hippocampus of anti-CSF1 dosed mice. The relationship between hippocampal CSF1 expression and expression in the ventral fiber tracks is not known. hMG engrafted into mice expressing h-IL34 display morphology indicative of an activated phenotype, while hMG in h-CSF1Tg mice display a more ramified morphology similar to that of resting, endogenous mouse microglia. Interestingly, IL34 has previously been shown to be critical for phagocytosis and survival of mouse microglia, which indicates IL34 may cause a difference in functionality that leads to differences in morphology. Our results support the findings of other studies regarding the existence of different microglia populations, with distinct phenotypes across CNS regions. Ongoing studies focus on engrafting hMG in mice co- expressing h-IL34 and h-CSF1. We will characterize the phenotype, localization, and function of hMG in the presence of both CSF1R ligands. Additional Mouse Models Currently Under Development • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2zTg(huCSF1) / Sz mice o NSG-FIRE KO-huCSF1 • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2zTg(Eno2-huIL34) / Sz mice o NSG-FIRE KO-Eno2-huIL34 • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2zIL34em1(IL34*)1Szmice o NSG-FIRE KO-huIL34 KI • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2zTg(APPswe,PSEN1dE9)85Dbo) / Sz mice o NSG-FIRE KO-APP / PS1 • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2zTg(huCSF1) / Sz Tg(APPswe,PSEN1dE9)85Dbo / Sz mice o NSG-FIRE KO-huCSF1-APP / PS1 • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2zTg(Eno2-huIL34) / Sz Tg(APPswe,PSEN1dE9)85Dbo / How mice o NSG-FIRE KO-Eno2-huIL34-APP / PS1 • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rem2z / Csf1rem2zIL34em1(IL34*)1SzTg(APPswe,PSEN1dE9)85Dbo / Sz mice o NSG-FIRE KO-huIL34 KI-APP / PS1 • NOD.Cg-PrkdcscidIl2rgtm1Wjl-Csf1rnull / Csf1rnullmice o NSG-Csf1r KO Example 3. Development of a PBMC-Humanized NSG-huIL34 KI Mouse Model for Investigating Chimeric antigen receptor T-cell toxicities resembling hemophagocytic lymphohistiocytosis (car-HLH) Experiment 1 The NSG-huIL34 KI and NSG-huCSF1 strains were then humanized with human PBMCs (Donor 9534) aiming for high myeloid cell engraftment in the initial experiment. We used PBMC-humanized NOD.Cg-PrkdcscidH2-K1b-tm1BpeH2-Ab1g7-em1MvwH2-D1b- (DKO herein) strain as a comparison. Surprisingly, we did not observe significant difference in myeloid cell percentage in circulating blood from PBMC-humanized NSG-huIL34 KI strain or NSG-huCSF1 strain compared to the DKO strain when measured 14- and 16-days post PBMC engraftment. While this result was unexpected, we hypothesize that the engrafted myeloid cells have preferentially homed to organs within the NSG-IL34 mice. This hypothesis gains support from our remarkable finding regarding human cytokine induction in PBMC-humanized NSG- IL34 mice. We discovered surprisingly that PBMC-humanized NSG-IL34 mice show high circulating levels of human pro-cancer and myeloid-derived cytokines such as IL8, IL18, MCP- 1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ. This spontaneous cytokine induction is only observed in the PBMC-humanized NSG-IL34 strain compared to the other PBMC-humanized DKO or NSG-CSF1 strains (FIG.14). As previous reported, human IL18 is elevated in patients with various cancer types. Currently, there is no available PBMC-humanized mouse model that induces human IL18 levels higher than 100 pg / ml, even after immunotherapy treatment. This puts the PBMC-humanized NSG-IL34 mice in a unique niche standing as a significant asset due to their direct relevance to the cytokine milieu observed in cancer patients. It is known that the patient's immune status before the therapy might play a role in treatment response and side effects. Assessing a patient's immune characteristics before CAR-T therapy could help in predicting therapy success and identifying new treatment strategies. Experiment 2 Spurred by the initial surprising result, we designed a subsequent experiment to test if whether the NSG-huIL34 KI strain extends an advantageous feature of PBMC-humanized mouse model. Compared to HSC-humanized mouse models, PBMC-humanized mice readily capture the diverse variations between different PBMC donors, highlighting its suitability for studying donor-to-donor variability. This characteristic adds an immense advantage to the use of the model as a pre-screening tool for toxicity and efficacy resulting from immunotherapy, in addition to enabling insights into the nuanced responses of the human immune system across various individuals. If there is a donor variability of PBMC donors in cytokine induction, we can use this PBMC-humanized NSG-huIL34 KI model to recapitulate different baseline levels of myeloid-derived cytokines. Therefore, we engrafted each NSG-huIL34 KI mouse with one of the five PBMCs from healthy human donors either with 8M / mouse or 4M / mouse, aiming to see individual variability in cytokine induction 8, 11, 14, and 16 days post-engraftment, and we measured human cytokines. First, we found that the spontaneous human cytokine is repeatable; Donor 9534 was used for Experiment 1 and 2 and the cytokine induction level was replicated. Further, we found that the degree of spontaneous cytokine induction varies by PBMC donor and PBMC doses (FIG.15A). For instance, mice engrafted with Donor 9534 showed human IL18 levels significantly increased starting 11 days post-engraftment and reached higher than 1,000 pg / ml 16 days post-engraftment whereas mice engrafted with Donor 0877 had lower than 10 pg / ml of IL18 induced. It is noteworthy that mice engrafted with Donor 0877 had a significant level of huCD45+ cells in peripheral blood (FIG.15B), even higher than mice engrafted with Donor 9534. This data further supports that PBMC-humanized NSG-IL34 mice is a valuable platform to explore individual patient’s immune characteristics in vivo. Studies have shown that subsets of B-ALL patients show elevation of IL18 from already aberrantly high baseline level in response to CAR-T treatment and exhibit HLH-like toxicity (carHLH). The data on carHLH is limited as carHLH is newly recognized CAR-T related toxicity. Recent studies report that the patients with carHLH symptoms show very poor response to CAR-T therapy and abysmal overall survival rate. One major criterion currently in consensus in the field is having a ferritin level as high as 10,000 ng / ml, whereas normal ferritin levels range from 12 to 300 ng / ml in healthy human. The PBMC-humanized NSG-huIL34 KI model provided herein can be used to induce CAR-T associated toxicity such as carHLH because PBMC-humanized NSG-huIL34 KI mice have pathological cytokine signaling profiles mimicking that of cancer patients. Experiment 3 In this experiment, we selected two PBMC donors from Experiment 2 (Donor 9408 and Donor 9348) and engrafted with 4M / mouse (Study Day 0). We chose these two donors because in the Experiment 2 the two PBMC donors at 4M / mouse concentration induced significant human IL18 and other myeloid-derived cytokines while the mice did not show significant body weight loss stemming from PBMC engraftment (FIG.15C). Then we treated the mice with CD19 CAR-Ts (5M / mouse) either 9 days or 15 days after the PBMC engraftment. In serum collected from mice engrafted with Donor 9408 on Study Day 17 (FIG.16), human ferritin levels were significantly upregulated in CAR-T treated mice compared to control (PBS treated) group (FIG.16). In mice engrafted with Donor 9348, we observed a trend of elevated ferritin level in CAR-T treated mice. This elevation observed in one of the two PBMC donors aligns with the clinical diagnostic criterion of carHLH and reinforces the direct link between PBMC- humanized NSG-huIL34 KI mouse model and the clinical trajectory observed in carHLH patients. Notably, we found a trend that mice showing higher ferritin levels measured 2 days post CAR-T treatment reached endpoint earlier than those with lower ferritin levels. This affirms the prognostic relevance of heightened ferritin levels as a predictor of poor survival in the context of HLH-like toxicities induced by CAR-T treatment. Experiment 4 The data provided in the following set of experiments show that peak induction of Ferritin, IL18, and IL8 in NSG-IL34 mice humanized with PBMC donor 9408 correlates with the onset of mouse deaths after CAR-T treatment, reflecting markers for HLH toxicity in human. On study day 0, NSG-IL34 mice were irradiated and intravenously injected with 2x106PBMC / mouse. On study day 16, PBMC-humanized mice were i.v injected with 5x106CAR-T cells / mouse. Mice reaching endpoints early (≥ 20% BWL, CRS score ≥ 3, body score ≤ 2) were euthanized and survival rate was recorded until study terminus, study day 36 (FIG.17, left graph). There is higher mortality in CAR-T treated group compared to PBS-treated group in NSG-IL34 mice humanized with PBMC 9408, but no difference observed between treatment groups in NSG-IL34 mice humanized with PBMC 2406 (FIG.17, right graph). Blood was also collected by retro-orbital bleeding (at study days 18, 21, and 36) and processed to plasma to measure Ferritin (FIG.18A), IL18 (FIG.18B), and IL-8 (FIG.18C) protein level by 48-plex Luminex. Around study days 18-21, expression levels of Ferritin, IL18 and IL8 are significantly higher in CAR-T treated group compared to PBS treated group in NSG-IL34 mice humanized with PBMC 9408, but little difference observed between treatment groups in NSG-IL34 mice humanized with PBMC 2406. Data shown as Mean ± SEM. Example 5 The mouse recognized preclinical model for multiple sclerosis (MS) research is the Experimental Autoimmune Encephalomyelitis (EAE) model. While the current EAE model is a useful tool for MS research, it has limitations as a preclinical model, such as limited human correlation because the EAE model has a mouse immune system and does not fully capture all aspects of the human condition. To create a more clinically relevant EAE model, we obtain PBMCs (peripheral blood mononuclear cells) from MS patients, which likely include autoreactive CD4+ T cells, to reconstitute the MS patient’s immune system in the mouse. We induce EAE by administering myelin oligodendrocyte glycoprotein (MOG) and Freud’s adjuvant with or without the co-adjuvant for the immunization. Mice engrafted with PBMCs from a healthy population areused as control models. Systemic lupus erythematosus (SLE) is a complex autoimmune disease where T and B cells become overactive. This can lead to overproduction of autoantibodies and proinflammatory cytokines that ultimately cause organ damage including kidney dysfunction. Two methods for generating humanized SLE models have been published involving transferring human PBMC from SLE patients into immunodeficient mice or inducing SLE in CD34 humanized mice using Pristane. However, several challenges exist in to improve B cell immune response within these humanized mice. To improve on these early models, we utilize new strains of NSG® mice that have enhanced engraftment and expansion of B cells after PBMC engraftment. In all of the model development work, mice strains deficient in MHC class I / II are utilized to minimize the potential of graft-versus-host disease (GvHD) after engraftment with PBMCs. These mice allow longer term studies that are not possible in PBMC engrafted mice with intact MHC class I / II. In addition, irradiation of the mice prior to engraftment with PBMC enhances humanization of the mice with PBMCs and leads to the expansion of human T and B cells and depending on the model, NK and monocyte cells. For Multiple Sclerosis model development, we utilize highly reliable immunodeficient mouse strains, specifically NOD scid gamma (NSG) variants, NSG-CSF1, and / or NSG-IL34. These strains, with a reconstituted human immune system, support the infiltration of human immune cells into the central nervous system, presenting a unique opportunity to mimic and analyze patient-specific immune responses. Another advantage of utilizing mice engrafted with PBMCs from MS patients is that it provides the opportunity to identify the relevant MS-specific profiles of the T cell library, as the T cells can be expanded in PBMC-humanized mice. This is important because it has been challenging to detect autoreactive T cells in MS patients and clarify the MS-T cell profiles due to their low frequency. Multiple sclerosis model development: 1. Generate NSG-CSF1 and NSG-IL34 mice crossed with NSG-MHC class I / II knockout mice (DKO) to generate NSG-CSF1xDKO and NSG-IL34xDKO mice. 2. Confirm engraftment with 3 separate MS patient PBMC donors. Readouts is the lack of GvHD, engraftment of human CD45 cells and numbers and type of immune subsets. Histology isperformed to evaluate infiltration of the mouse brains with human immune cells. 3. Examine the listed endpoints for MS in comparison with normal healthy PBMC donor engrafted mice. As MS patients experience two types of disease progression patters, a relapsing-remitting (RR) or chronic progressive (CP) disease course, we establish an EAE model for both RR-EAE and CP-EAE in mice engrafted with PBMCs from the same MS patients to better understand the difference between RR- and CP-EAE. The model establishment is done by inducing the disease using different strengths of MOG peptides or applying different antigens, such as MOG for RR-EAE and proteolipid protein for CP-EAE. The mice are monitored using the following grading system: Grade 0: Normal / Grade 1: Flaccid tail / Grade 2: Mild hind-limb weakness (fast righting reflex) / Grade 3: Severe hind-limb weakness (slow righting reflex) / Grade 4: Hind-limb paralysis / Grade 5: Hind-limb paralysis and partial fore-limb weakness or moribund (Kalyvas 2004). At the stages of the disease corresponding to the initial onset (Grade 1), peak severity (Grade 4), and remission in RR-EAE, we euthanize the mice and proceed with further analysis. In cerebrospinal fluid (CSF) and blood collected from the mice, we observe oligoclonal bands, which is the most common laboratory test used to diagnose MS, and other potential biomarkers such as CNS NFL, GFAP, myelin basic protein, S100B, tau, NCAM, NGF, CNTF, and ferritin expression by ELISA or RT-PCR. Various cytokines, including pro-inflammatory (e.g., IFNγ and IL-17), anti-inflammatory (e.g., IL-10), and chemokines (e.g., CXCL13 and CCL2), are analyzed in the peripheral blood and CSF. The cellular profiles, including T cell subtypes (e.g., Th1, Th17, γδ, CD8+, and regulatory T cells), B cells, monocytes, and other immune cells in the peripheral blood, spleen, brain, and spinal cord, re analyzed by flow cytometry. We perform histological analysis of the brain and spinal cord to assess inflammation, demyelination, and apoptosis, and utilize quantification imaging methods (e.g., G-ratio) for quantifying the demyelination (Cruz-Martinez 2016; Parandavar 2024). 4. Determine if the MS patient model for MS is enhanced by addition of MOG peptide as seen in the EAE model for MS. Once we establish and characterize the model, we investigate the efficacy of potential therapeutics, such as peripheral BTK inhibitors and anti- VLA4, in inhibiting microgliosis induced by MOG in this platform. The proposed PBMC- humanized EAE model herein enables a more detailed examination of the clinical relevance in disease progression and treatment responses, thereby enhancing our understanding of MS. SLE model development: 1. SLE patients are often lymphopenic, which can be a challenge for obtaining enough PBMCs for successfully engrafting mice in studies. PBMC engrafted NSG- FLT3LxDKO or NSG-SGM3xIL15xDKO mice show more robust humanization including B cells and plasma cells, when compared to PBMC engrafted DKO mice. Our preliminary data also suggests these new transgenic DKO strains exhibit higher IgG levels and antibody production after antigen stimulation. 2. We use these advanced strains, NSG-FLT3xDKO and NSG-SGM3xIL15xDKO to engraft PBMC from healthy or SLE patients to address limitations caused by patient PBMCs and B cell responses. We investigate the effect of repeatedly stimulating B cell activation directly by anti-BCR antibody or indirectly by OKT3 or both. 3. The impact of Pristane stimulation on accelerating SLE in humanized mice is also evaluated. We assess the human immune cell engraftment time course with / without Pristane induction and examine the SLE clinical parameters including proinflammatory cytokines, autoantibody production, proteinuria, and nephritis. Ovarian cancer model development: 1. Up to 5 ovarian PDX cancer cells lines expressing luciferase are selected and screened for growth in non-humanized NSG-SGM3xIL15xDKO mice. Two cell lines are selected for next steps. 2. These two cell lines reused for growth curves in the presence of PBMC humanized NSG-SGM3xIL15xDKO mice. Up to 5 healthy PBMC donors are used to examine any unexpected early onset of GvHD, tumor cell line engraftment kinetics and the effects of tumor engraftment on PBMC humanization. 3. One cell line and up to three PBMC donors are used to test for efficacy using carboplatin, bevacizumab and / or additional ovarian cancer therapies based on availability. Furthermore, we generate murine MHC class I / II-double knockout (DKO) versions of these strains, CSF1xDKO and IL34xDKO, which have less GvHD occurrence and a longer lifespan in PBMC-humanized mice to improve the study design and extend the study duration. We also use whole-brain irradiation to increase blood-brain barrier permeability and enhance immune cell infiltration into the brain. For the SLE model development, our preliminary data using CD34 humanized mice induced with Pristane have shown some key SLE features such as lymphopenia, mild kidney glomerular pathology, proinflammatory cytokine release (IFNγ, IL-6, IL-8, and MCP-1), and increased serum level of anti-dsDNA antibody titer but we did not find proteinuria. Regular immunodeficient mice humanized with PBMC have a shorter lifespan, limiting their usefulness for studying the disease and testing potential treatment due to GVHD. Our DKO mice, which lack mouse MHC class I and II, address this limitation. All references, patents and patent applications disclosed herein are incorporated by reference with respect to the subject matter for which each is cited, which in some cases may encompass the entirety of the document. The indefinite articles “a” and “an,” as used herein the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited. In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03. The terms “about” and “substantially” preceding a numerical value mean ±10% of the recited numerical value. Where a range of values is provided, each value between the upper and lower ends of the range are specifically contemplated and described herein.

Claims

What is claimed is: CLAIMS 1. A method of assessing immunotherapy induced toxicity, the method comprising: (a) administering human peripheral blood mononuclear cells, and optionally human diseased cells, to an immunodeficient mouse, wherein the genome of the immunodeficient mouse comprises an open reading frame encoding human interleukin-34 (IL34); (b) administering a human immunotherapy to the immunodeficient mouse; and (c) assaying a biological sample of the mouse for (i) a level of a human cytokine selected from IL8, IL18, MCP-1, TNF-a, MIP-1A, MIP-1B, RANTES, MIG, IP-10, IL6, IL10, and IFNγ, (ii) a level of human ferritin, or (iii) a combination of a level of the human cytokine and the level of ferritin, thereby assessing immunotherapy induced toxicity.

2. The method of claim 1, wherein about 1x106to 1x107, optionally about 4x106or about 8x106, human peripheral blood mononuclear cells are administered to the immunodeficient mouse.

3. The method of claim 1 or 2, wherein the human immunotherapy is administered within 5 days, within 10 days, or within 15 days of administering the human peripheral blood mononuclear cells to the immunodeficient mouse.

4. The method of any one of the preceding claims, wherein the human immunotherapy is a human cell therapy.

5. The method of claim 4, wherein the human T cell therapy is a human chimeric antigen receptor (CAR) T cell therapy.

6. The method of claim 4 or 5, wherein the human cell therapy comprises about 1x106to 1x107, optionally about 5x106, human cells.

7. The method of any one of the preceding claims, wherein the assaying is within 5 days, within 10 days, or within 15 days of administering the human immunotherapy.

8. The method of any one of the preceding claims, wherein the assaying is within 5 days, within 10 days, or within 15 days of administering the human peripheral blood mononuclear cells.

9. The method of any one of the preceding claims, comprising administering human diseased cells, optionally human tumor cells, further optionally human cancer cells, to the immunodeficient mouse, and optionally assaying for efficacy of the human immunotherapy.

10. The method of any one of the preceding claims, wherein the open reading frame encoding human IL34 is operably linked to the mouse IL34 promoter.

11. The method of any one of the preceding claims, wherein the immunodeficient mouse has a non-obese diabetic (NOD) genetic background.

12. The method of claim 11, wherein the immunodeficient mouse comprises a Il2rgnullallele.

13. The method of claim 12, wherein the immunodeficient mouse is homozygous for the Il2rgnullallele.

14. The method of claim 12 or 13, wherein the Il2rgnullallele is the Il2rgtm1Wjlallele.

15. The method of any one of the preceding claims, wherein the immunodeficient mouse comprises a Prkdcnullallele.

16. The method of claim 15, wherein the immunodeficient mouse is homozygous for the Prkdcnullallele.

17. The method of claim 16, wherein the Prkdcnullallele is the Prkdcscidallele.

18. An immunodeficient mouse comprising: a genome comprising a mouse IL34 promoter operably linked to an open reading frame encoding human IL34, a Il2rgnullallele, and a Prkdcnullallele, wherein the mouse is engrafted with human peripheral blood mononuclear cells, expresses human IL18 serum levels higher than 100 pg / ml, expresses human ferritin, and optionally wherein the mouse has been administered a human immunotherapy.

19. The mouse of claim 18, wherein the human immunotherapy is a human cell therapy.

20. The mouse of claim 19, wherein the human T cell therapy is a human chimeric antigen receptor (CAR) T cell therapy.

21. An immunodeficient mouse whose genome comprise a Prkdcscidallele, a Il2rgtm1Wjlallele and a coding sequence encoding human interleukin 34, wherein the coding sequence is operably linked to an endogenous mouse IL34 promoter.

22. The immunodeficient mouse of claim 21 whose genome further comprises a H2-K1b-23. An immunodeficient mouse whose genome comprise a Prkdcscidallele, a Il2rgtm1Wjlallele, and a Csf1rnullallele, optionally a Csf1rem2zallele.

24. An immunodeficient mouse comprising an engineered genomic variant of an endogenous mouse colony stimulating factor 1 receptor (Csf1r) gene.

25. The immunodeficient mouse of claim 24, wherein intron 2 of the endogenous Csf1r gene comprises the genomic variant.

26. The immunodeficient mouse of claim 25, wherein the Fms-intronic super enhancer (Fms- intronic regulatory element (FIRE) of intron 2 of the endogenous Csf1r gene comprises the genomic variant.

27. The immunodeficient mouse of any one of the preceding claims, wherein the genomic variant is a deletion.

28. The immunodeficient mouse of any one of the preceding claims, wherein the immunodeficient mouse has a non-obese diabetic (NOD) genetic background.

29. The immunodeficient mouse of claim 28, wherein the immunodeficient mouse comprises a Il2rgnullallele, optionally wherein the immunodeficient mouse is homozygous for the Il2rgnullallele, optionally a Il2rgtm1Wjlallele; and or wherein the immunodeficient mouse comprises a Prkdcnullallele, optionally wherein the immunodeficient mouse is homozygous for the Prkdcnullallele, optionally a Prkdcscidallele.

30. The immunodeficient mouse of any one of the preceding claims, wherein the number of tissue resident mouse macrophage cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene, optionally wherein the number of microglia is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene, optionally wherein the immunodeficient mouse does not comprise mouse microglia.

31. The immunodeficient mouse of any one of the preceding claims, further comprising a human CSF1 transgene, optionally wherein the human CSF1 transgene is expressed to produce functional human CSF1 protein.

32. The immunodeficient mouse of any one of the preceding claims, further comprising a human interleukin 34 (IL34) transgene, optionally wherein the human IL34 transgene is expressed to produce functional human IL34 protein, optionally wherein the human transgene comprises a rat enolase 2 promoter operably linked to a human IL34 coding sequence.

33. The immunodeficient mouse of claim 32, wherein the human interleukin 34 (IL34) transgene comprises the endogenous mouse IL34 promoter operably linked to a human IL34 coding sequence.

34. The immunodeficient mouse of any one of the preceding claims, further comprising a chimeric mouse / human amyloid precursor protein (Mo / HuAPP695swe) transgene, optionally wherein the chimeric Mo / HuAPP695swe transgene is expressed to produce a modified humanized mouse amyloid beta (A4) precursor protein.

35. The immunodeficient mouse of any one of the preceding claims, further comprising a mutant human presenilin 1 (PS1-dE9) transgene, optionally wherein the PS1-dE9 transgene is expressed to produce a mutant human presenilin 1 protein.

36. The immunodeficient mouse of any one of the preceding claims, further engrafted with human cells, optionally wherein the human cells are selected from human stem cells or human progenitor cells, further optionally wherein the human cells are selected from hematopoietic stem cells (HSCs), peripheral blood mononuclear cells (PBMCs), umbilical cord cells (UCs), embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), and induced pluripotent stem cells (iPSCs); or wherein the human cells are selected from human immune cells and human neural cells.

37. An immunodeficient mouse comprising a null colony stimulating factor 1 receptor (Csf1rnull) allele, optionally wherein the immunodeficient mouse is homozygous for Csf1rnullallele.

38. The immunodeficient mouse of claim 37, wherein the immunodeficient mouse has a non- obese diabetic (NOD) genetic background, optionally wherein the immunodeficient mouse comprises a Il2rgnullallele, optionally wherein the immunodeficient mouse is homozygous for the Il2rgnullallele, optionally a Il2rgtm1Wjlallele; and / or wherein the immunodeficient mouse comprises a Prkdcnullallele, optionally wherein the immunodeficient mouse is homozygous for the Prkdcnullallele, optionally a Prkdcscidallele.

39. The immunodeficient mouse of claim 37 or 38, wherein the number of mouse macrophage cells is lower relative to an immunodeficient mouse comprising an unmodified endogenous Csf1r gene, optionally wherein the immunodeficient mouse does not comprise mouse macrophage cells.

40. The immunodeficient mouse of any one of claims 37-39, further engrafted with human cells, optionally wherein the human cells are selected from human stem cells or human progenitor cells. or optionally wherein the human cells are selected from hematopoietic stem cells (HSCs), peripheral blood mononuclear cells (PBMCs), umbilical cord cells (UCs), and mesenchymal stem cells (MSCs), or optionally wherein the human cells are selected from human immune cells and human neural cells.

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