Enhanced engraftment of human cells in RAG2/gammac double-knockout mice after treatment with CL2MDP liposomes

Lack of lymphocytes impairs macrophage polarization and angiogenesis in diabetic wound healing

AIMS

This study aimed to investigate the effect of lymphocytes in wound healing and the underlying mechanisms, in diabetic and non-diabetic mice, using Balb/c recombination activating gene (Rag)-2 and interleukin 2 receptor gamma (IL-2Rγ) double knockout (KO) (RAG2^-/- IL-2Rγ^-/-) mice.

MAIN METHODS

Wound healing in vivo was performed in control and STZ-induced diabetic mice, in both KO and WT mice. Inflammation and ROS production were evaluated by immunofluorescence microscopy analysis, antioxidant enzymes and angiogenesis were evaluated by quantitative PCR and immunofluorescence microscopy analysis, and wound closure kinetics evolution was evaluated by measurement of acetate tracing of the wound area.

KEY FINDINGS

Wound closure was significantly delayed in KO mice, where the M1/M2 macrophage ratio and basal ROS levels were significantly increased, while antioxidant defenses and angiogenesis were significantly decreased. Moreover, the expected increase in matrix metallopeptidase (MMP)-9 protein levels in diabetic conditions was not observed in KO mice, suggesting that the mechanisms leading to the increase in MMP-9 observed in diabetic wounds may in part be lymphocyte-dependent.

SIGNIFICANCE

Our results indicate that lack of lymphocytes compromises wound healing independent of diabetes. The lack of these cells, even in non-diabetic mice, mimics the phenotype observed in wounds under diabetic conditions. Moreover, the combination of diabetes and the lack of lymphocytes, further impair the wound healing conditions, indicating that when the innate regulatory function is lost in these KO mice, excessive M1 polarization, poor angiogenesis and impaired wound healing are worsen.

Creation of an immunodeficient HLA-transgenic mouse (HUMAMICE) and functional validation of human immunity after transfer of HLA-matched human cells

Research on human immunology has been hindered by the lack of optimal small animal models, given that the protective immune responses of human and non-human species show significant differences. However, due to ethical constraints[1] and the high cost of clinical trials, it is urgent to improve the current animal models that can mimic faithfully human physiology, particularly the human immune system (HIS). HIS mice had been generated recently by engrafting human hematopoietic stem cells (hHSCs) or human peripheral mononuclear cells (hPBMCs) into highly immuno-deficient mice such as NSG, NOG or NRG mice. However, a major experimental drawback for studies using these models is the rapid onset of Graft-versus-Host Disease (GvHD). In the present study, we overcome this limitation by generating new immuno-deficient mice named "HUMAMICE" (HLA-A2^+/+/DR1^+/+/H-2-β₂m^-/-/IAβ^-/-/Rag2^-/-/IL2rγ^-/-/Perf^-/- mice), which expressed human HLA molecules instead of mouse MHC molecules (H-2), and whose immuno-deficient status was reversed by transferring functional HLA-matched PBMCs thus producing mice with an immuno-competent status with a functional human immune system. We showed that in this HLA-matched context, the hPBMC-transfer led to high lymphocytes engraftment rates without GvHD over three months in this novel mouse model. Furthermore, to evaluate the utility of the hPBMC-HUMAMICE, we immunized them with commercial vaccine of Hepatitis B virus (HBsAg, Hepvac@) which resulted in robust and reproducible production of high levels of HBsAg-specific antibodies, implying that both transferred T and B lymphocytes were functional in HUMAMICE. These responses are comparable to those observed in human clinical trials with this identical vaccine. In conclusion, these findings indicated that the HLA-matched-hPBMC-HUMAMICE represents a promising model for dissecting human immune responses in various human diseases, including infectious diseases, cancers and tumors, and to facilitate the development of novel vaccines and cellular therapies.

Reversion to an embryonic alternative splicing program enhances leukemia stem cell self-renewal

Formative research suggests that a human embryonic stem cell-specific alternative splicing gene regulatory network, which is repressed by Muscleblind-like (MBNL) RNA binding proteins, is involved in cell reprogramming. In this study, RNA sequencing, splice isoform-specific quantitative RT-PCR, lentiviral transduction, and in vivo humanized mouse model studies demonstrated that malignant reprogramming of progenitors into self-renewing blast crisis chronic myeloid leukemia stem cells (BC LSCs) was partially driven by decreased MBNL3. Lentiviral knockdown of MBNL3 resulted in reversion to an embryonic alternative splice isoform program typified by overexpression of CD44 transcript variant 3, containing variant exons 8-10, and BC LSC proliferation. Although isoform-specific lentiviral CD44v3 overexpression enhanced chronic phase chronic myeloid leukemia (CML) progenitor replating capacity, lentiviral shRNA knockdown abrogated these effects. Combined treatment with a humanized pan-CD44 monoclonal antibody and a breakpoint cluster region - ABL proto-oncogene 1, nonreceptor tyrosine kinase (BCR-ABL1) antagonist inhibited LSC maintenance in a niche-dependent manner. In summary, MBNL3 down-regulation-related reversion to an embryonic alternative splicing program, typified by CD44v3 overexpression, represents a previously unidentified mechanism governing malignant progenitor reprogramming in malignant microenvironments and provides a pivotal opportunity for selective BC LSC detection and therapeutic elimination.

Development of a realistic in vivo bone metastasis model of human renal cell carcinoma

About one-third of patients with advanced renal cell carcinoma (RCC) have bone metastases. The incidence of RCC is increasing and bone metastatic RCC merits greater focus. Realistic preclinical bone metastasis models of RCC are lacking, hampering the development of effective therapies. We developed a realistic in vivo bone metastasis model of human RCC by implanting precision-cut tissue slices under the renal capsule of immunodeficient mice. The presence of disseminated cells in bone marrow of tissue slice graft (TSG)-bearing mice was screened by human-specific polymerase chain reaction and confirmed by immunohistology using human-specific antibody. Disseminated tumor cells in bone marrow of TSG-bearing mice derived from three of seven RCC patients were detected as early as 1 month after tissue implantation at a high frequency with close resemblance to parent tumors (e.g., CAIX expression and high vascularity). The metastatic patterns of TSGs correlated with disease progression in patients. In addition, TSGs retained capacity to metastasize to bone at high frequency after serial passaging and cryopreservation. Moreover, bone metastases in mice responded to Temsirolimus treatment. Intratibial injections of single cells generated from TSGs showed 100 % engraftment and produced X-ray-visible tumors as early as 3 weeks after cancer cell inoculation. Micro-computed tomography (μCT) and histological analysis revealed osteolytic characteristics of these lesions. Our results demonstrated that orthotopic RCC TSGs have potential to develop bone metastases that respond to standard therapy. This first reported primary RCC bone metastasis model provides a realistic setting to test therapeutics to prevent or treat bone metastases in RCC.

Comparison of three humanized mouse models for adoptive T cell transfer

BACKGROUND

Humanized mouse models for adoptive T cell transfer are important for preclinical efficacy and toxicity studies. However, common xenograft models using immunodeficient mice have so far failed to efficiently support the homing of human T cells to secondary lymphoid tissues.

METHODS

We established a new mouse model for the adoptive transfer of genetically-modified (gm) T cells using conditioned BALB/c mice. Conditioning involved cyclophosphamide injections, lethal irradiation and radioprotection with bone marrow from immunodeficient mice. We compared repopulation kinetics and the quality of grafts in these modified Trimera (mT3) mice with immunodeficient BALB/c Rag2(-/-) interleukin (IL)2 receptor gamma (rg) knockout (DKO) and NOD/LtSz-scid IL2rg(-/-) (NSG) recipient mouse strains.

RESULTS

DKO mice showed only marginal engraftment until onset of graft-versus-host disease, whereas mT3 and NSG were repopulated with comparable kinetics. However, T cell repertoire and human cytokine profiles suggest a xenoreactivity-driven gm T cell expansion in mT3 mice, whereas NSG mice were characterized by an initial homeostatic proliferation. Morphological analysis revealed high levels of human gm T cell infiltration in the spleen and liver of all three mouse strains. However, mT3 mice provided the strongest homing of human gm T cells to mucosal sites. Additionally, mT3 mice were the only model with macroscopically visible superficial inguinal lymph nodes. These lymph nodes strongly supported the homing of gm T cells.

CONCLUSIONS

In the present study, we give proof-of-concept that wild-type mice can accept gm T cell grafts while providing secondary lymphoid structures. Despite limitations, mT3 mice are a valid alternative for applications that specifically rely on improved secondary lymphoid structures.

Production and characterization of humanized Rag2-/-γc -/- mice

Mice reconstituted with human immune cells represent a model to study the development and functionality of the human immune system. Recent improvements in humanized mice have resulted in multi-lineage hematopoiesis, prolonged human cell engraftment that is detectable in many mouse organs, and the ability to generate de novo human innate and adaptive immune responses. Here, we describe the methods used to produce and characterize humanized Rag2(-/-)γc(-/-) mice.

Humanized mice for immune system investigation: progress, promise and challenges

Significant advances in our understanding of the in vivo functions of human cells and tissues and the human immune system have resulted from the development of 'humanized' mouse strains that are based on severely immunodeficient mice with mutations in the interleukin-2 receptor common γ-chain locus. These mouse strains support the engraftment of a functional human immune system and permit detailed analyses of human immune biology, development and functions. In this Review, we discuss recent advances in the development and utilization of humanized mice, the lessons learnt, the remaining challenges and the promise of using humanized mice for the in vivo study of human immunology.

Intrahepatic transplantation of CD34+ cord blood stem cells into newborn and adult NOD/SCID mice induce differential organ engraftment

In vivo studies concerning the function of human hematopoietic stem cells (HSC) are limited by relatively low levels of engraftment and the failure of the engrafted HSC preparations to differentiate into functional immune cells after systemic application. In the present paper we describe the effect of intrahepatically transplanted CD34(+) cells from cord blood into the liver of newborn or adult NOD/SCID mice on organ engraftment and differentiation. Analyzing the short and long term time dependency of human cell recruitment into mouse organs after cell transplantation in the liver of newborn and adult NOD/SCID mice by RT-PCR and FACS analysis, a significantly high engraftment was found after transplantation into liver of newborn NOD/SCID mice compared to adult mice, with the highest level of 35% human cells in bone marrow and 4.9% human cells in spleen at day 70. These human cells showed CD19 B-cell, CD34 and CD38 hematopoietic and CD33 myeloid cell differentiation, but lacked any T-cell differentiation. HSC transplantation into liver of adult NOD/SCID mice resulted in minor recruitment of human cells from mouse liver to other mouse organs. The results indicate the usefulness of the intrahepatic application route into the liver of newborn NOD/SCID mice for the investigation of hematopoietic differentiation potential of CD34(+) cord blood stem cell preparations.

Contribution of classic and alternative effector pathways in peanut-induced anaphylactic responses

Food allergy affects approximately 5% of children and is the leading cause of hospitalization for anaphylactic reactions in westernized countries. However, the pathways of anaphylaxis in food allergy are still relatively unknown. We investigated the effector pathways of allergic and anaphylactic responses of different strains of mice in a clinical relevant model of peanut allergy. C3H/HeOuJ, C57BL/6 and BALB/c mice were sensitized by intragastric peanut extract and challenged by intragastric or intraperitoneal injection of peanut. Peanut-specific T cell responses, IgE, IgG1 and IgG2a and mucosal mast cell degranulation were induced to different extent in C3H/HeOuJ, C57BL/6 and BALB/c mice. Interestingly, anaphylactic symptoms after systemic challenge were highest in C3H/HeOuJ followed by C57BL/6 but were absent in BALB/c mice. Mechanistic studies showed that the food allergic systemic anaphylaxis was dependent on platelets, FcRγ and mast cells, and partially dependent on platelet activating factor and monocytes/macrophages, depending on mouse strain. These data demonstrate that in three mouse strains, components of the classic and alternative anaphylactic cascade are differently expressed, leading to differential outcomes in parameters of allergic disease and food induced systemic anaphylaxis.

Transgenic expression of human signal regulatory protein alpha in Rag2-/-gamma(c)-/- mice improves engraftment of human hematopoietic cells in humanized mice

Transplantation of human hematopoietic stem cells into severely immunocompromised newborn mice allows the development of a human hematopoietic and immune system in vivo. NOD/scid/γ(c)(-/-) (NSG) and BALB/c Rag2(-/-)γ(c)(-/-) mice are the most commonly used mouse strains for this purpose and a number of studies have demonstrated the high value of these model systems in areas spanning from basic to translational research. However, limited cross-reactivity of many murine cytokines on human cells and residual host immune function against the xenogeneic grafts results in defective development and maintenance of human cells in vivo. Whereas NSG mice have higher levels of absolute human engraftment than similar mice on a BALB/c background, they have a shorter lifespan and NOD ES cells are unsuitable for the complex genetic engineering that is required to improve human hematopoiesis and immune responses by transgenesis or knockin of human genes. We have generated mice that faithfully express a transgene of human signal regulatory protein alpha (SIRPa), a receptor that negatively regulates phagocytosis, in Rag2(-/-)γ(c)(-/-) mice on a mixed 129/BALB/c background, which can easily be genetically engineered. These mice allow significantly increased engraftment and maintenance of human hematopoietic cells reaching levels comparable to NSG mice. Furthermore, we found improved functionality of the human immune system in these mice. In summary, hSIRPa-transgenic Rag2(-/-)γ(c)(-/-) mice represent a unique mouse strain supporting high levels of human cell engraftment, which can easily be genetically manipulated.

Pretransplant CSF-1 therapy expands recipient macrophages and ameliorates GVHD after allogeneic hematopoietic cell transplantation

Host macrophages protect against graft-versus-host disease in part by engulfing donor T cells and inhibiting their proliferation.

Acute graft-versus-host disease (GVHD) results from the attack of host tissues by donor allogeneic T cells and is the most serious limitation of allogeneic hematopoietic cell transplantation (allo-HCT). Host antigen-presenting cells are thought to control the priming of alloreactive T cells and the induction of acute GVHD after allo-HCT. However, whereas the role of host DC in GVHD has been established, the contribution of host macrophages to GVHD has not been clearly addressed. We show that, in contrast to DC, reducing of the host macrophage pool in recipient mice increased donor T cell expansion and aggravated GVHD mortality after allo-HCT. We also show that host macrophages that persist after allo-HCT engulf donor allogeneic T cells and inhibit their proliferation. Conversely, administration of the cytokine CSF-1 before transplant expanded the host macrophage pool, reduced donor T cell expansion, and improved GVHD morbidity and mortality after allo-HCT. This study establishes the unexpected key role of host macrophages in inhibiting GVHD and identifies CSF-1 as a potential prophylactic therapy to limit acute GVHD after allo-HCT in the clinic.

Human thrombopoietin knockin mice efficiently support human hematopoiesis in vivo

Hematopoietic stem cells (HSCs) both self-renew and give rise to all blood cells for the lifetime of an individual. Xenogeneic mouse models are broadly used to study human hematopoietic stem and progenitor cell biology in vivo. However, maintenance, differentiation, and function of human hematopoietic cells are suboptimal in these hosts. Thrombopoietin (TPO) has been demonstrated as a crucial cytokine supporting maintenance and self-renewal of HSCs. We generated RAG2(-/-)γ(c)(-/-) mice in which we replaced the gene encoding mouse TPO by its human homolog. Homozygous humanization of TPO led to increased levels of human engraftment in the bone marrow of the hosts, and multilineage differentiation of hematopoietic cells was improved, with an increased ratio of myelomonocytic verus lymphoid lineages. Moreover, maintenance of human stem and progenitor cells was improved, as demonstrated by serial transplantation. Therefore, RAG2(-/-)γ(c)(-/-) TPO-humanized mice represent a useful model to study human hematopoiesis in vivo.

HuMab-7D8, a monoclonal antibody directed against the membrane-proximal small loop epitope of CD20 can effectively eliminate CD20 low expressing tumor cells that resist rituximab-mediated lysis

BACKGROUND

Incorporation of the chimeric CD20 monoclonal antibody rituximab in the treatment schedule of patients with non-Hodgkin's lymphoma has significantly improved outcome. Despite this success, about half of the patients do not respond to treatment or suffer from a relapse and additional therapy is required. A low CD20-expression level may in part be responsible for resistance against rituximab. We therefore investigated whether the CD20-expression level related resistance to rituximab could be overcome by a new group of CD20 mAbs (HuMab-7D8 and ofatumumab) targeting a unique membrane-proximal epitope on the CD20 molecule.

DESIGN AND METHODS

By retroviral transduction of the CD20 gene into CD20-negative cells and clonal selection of transduced cells a system was developed in which the CD20-expression level is the only variable. These CD20 transduced cells were used to study the impact of rituximab and HuMab-7D8 mediated complement-dependent cytotoxicity. To study the in vivo efficacy of these mAbs an in vivo imaging system was generated by retroviral expression of the luciferase gene in the CD20-positive cells.

RESULTS

We show that HuMab-7D8 efficiently killed CD20(low) cells that are not susceptible to rituximab-induced killing in vitro. In a mouse xenograft model, we observed a comparable increase in survival time between HuMab-7D8 and rituximab-treated mice. Most significantly, however, HuMab-7D8 eradicated all CD20-expressing cells both in the periphery as well as in the bone marrow whereas after rituximab treatment CD20(low) cells survived.

CONCLUSIONS

Cells that are insensitive to in vitro and in vivo killing by rituximab as the result of their low CD20-expression profile may be efficiently killed by an antibody against the membrane-proximal epitope on CD20. Such antibodies should, therefore, be explored to overcome rituximab resistance in the clinic.

Luciferase labeling for multipotent stromal cell tracking in spinal fusion versus ectopic bone tissue engineering in mice and rats

Tissue engineering of bone, by combining multipotent stromal cells (MSCs) with osteoconductive scaffolds, has not yet yielded any clinically useful applications so far. The fate and contribution of the seeded cells are not sufficiently clarified, especially at clinically relevant locations. Therefore, we investigated cell proliferation around the spine and at ectopic sites using noninvasive in vivo bioluminescence imaging (BLI) in relation to new bone formation. Goat MSCs were lentivirally transduced to express luciferase. After showing both correlation between MSC viability and BLI signal as well as survival and osteogenic capacity of these cells ectopically in mice, they were seeded on ceramic scaffolds and implanted in immunodeficient rats at two levels in the spine for spinal fusion as well as subcutaneously. Nontransduced MSCs were used as a control group. All rats were monitored at day 1 and after that weekly until termination at week 7. In mice a BLI signal was observed during the whole observation period, indicating survival of the seeded MSCs, which was accompanied by osteogenic differentiation in vivo. However, these same MSCs showed a different response in the rat model, where the BLI signal was present until day 14, both in the spine and ectopically, indicating that MSCs were able to survive at least 2 weeks of implantation. Only when the signal was still present after the total implantation period ectopically, which only occurred in one rat, new bone was formed extensively and the implanted MSCs were responsible for this bone formation. Ectopically, neither a reduced proliferative group (irradiated) nor a group in which the cells were devitalized by liquid nitrogen and the produced extracellular matrix remained (matrix group) resulted in bone formation. This suggests that the release of soluble factors or the presence of an extracellular matrix is not enough to induce bone formation. For the spinal location, the question remains whether the implanted MSCs contribute to the bone regeneration or that the principal mechanism of MSC activity is through the release of soluble mediators.

Parameters for establishing humanized mouse models to study human immunity: analysis of human hematopoietic stem cell engraftment in three immunodeficient strains of mice bearing the IL2rgamma(null) mutation

"Humanized" mouse models created by engraftment of immunodeficient mice with human hematolymphoid cells or tissues are an emerging technology with broad appeal across multiple biomedical disciplines. However, investigators wishing to utilize humanized mice with engrafted functional human immune systems are faced with a myriad of variables to consider. In this study, we analyze HSC engraftment methodologies using three immunodeficient mouse strains harboring the IL2rgamma(null) mutation; NOD-scid IL2rgamma(null), NOD-Rag1(null) IL2rgamma(null), and BALB/c-Rag1(null) IL2rgamma(null) mice. Strategies compared engraftment of human HSC derived from umbilical cord blood following intravenous injection into adult mice and intracardiac and intrahepatic injection into newborn mice. We observed that newborn recipients exhibited enhanced engraftment as compared to adult recipients. Irrespective of the protocol or age of recipient, both immunodeficient NOD strains support enhanced hematopoietic cell engraftment as compared to the BALB/c strain. Our data define key parameters for establishing humanized mouse models to study human immunity.

Correlation of high-resolution X-ray micro-computed tomography with bioluminescence imaging of multiple myeloma growth in a xenograft mouse model

Multiple myeloma (MM) is an incurable B-cell neoplasia in which progressive skeletal lesions are a characteristic feature. Earlier we established an animal model for human MM in the immune-deficient RAG2(-/-)gammac(-/-) mouse, in which the growth of luciferase-transduced MM cells was visualized using noninvasive bioluminescence imaging (BLI). This model appeared well suited to study disease progression and response to therapy by identifying the location of various foci of MM tumor growth scattered throughout the skeleton and at subsequent time points the quantitative assessment of the tumor load by using BLI. We report here on the corresponding high-resolution X-ray micro-computed tomographic (micro-CT) analysis to study skeletal defects in the mice with full-blown MM. Several anatomical derangements were observed, including abnormalities in geometry and morphology, asymmetrical bone structures, decreased overall density in the remaining bone, loss of trabecular bone mass, destruction of the inner microarchitecture, as well as cortical perforations. Using the combination of BLI, micro-CT imaging, and immune-histopathological techniques, we found a high correlation between the micro-CT-identified lesions, exact tumor location, and infiltration leading to structural lesions and local bone deformation. This confirms that this animal model strongly resembles human MM and has the potential for studying the biology of MM growth and for preclinical testing of novel therapies for MM and for repair of MM-induced bone lesions.

Investigation into the role of tumor-associated macrophages in the antitumor activity of Doxil

PURPOSE

Our recent studies show specific localization of long-circulating liposomes (LCL) within the endosomal/lysosomal compartment of tumor-associated macrophages (TAM). Based on this finding, the present study aims to investigate whether clinically applied LCL formulations such as Doxil (LCL-encapsulated doxorubicin), have alternative mechanisms of action additionally to direct drug-mediated cytotoxicity towards tumor cells.

METHODS

The antitumor activity of Doxil was evaluated in B16.F10 melanoma-bearing mice, in the presence and in the absence of TAM. To suppress TAM functions, liposomal clodronate (Lip-CLOD) was injected 24 h before the actual treatment. The effect of Doxil on the levels of angiogenic factors was determined using an angiogenic protein array. As positive control, the same experiments were conducted with LCL-encapsulated prednisolone phosphate (LCL-PLP), a tumor-targeted formulation with known strong anti-angiogenic/anti-inflammatory effects on TAM.

RESULTS

Our results show that the antitumor efficacy of Doxil was only partially attributed to the inhibition of TAM-mediated angiogenesis whereas LCL-PLP inhibited tumor growth through strong suppressive effects on pro-angiogenic functions of TAM. As described previously, the main mechanism of Doxil might be a cytotoxic effect on tumor cells.

CONCLUSIONS

Our findings suggest that the antitumor activity of Doxil does not depend mainly on the presence of functional TAM in tumors.

Innate immune 'self' recognition: a role for CD47-SIRPalpha interactions in hematopoietic stem cell transplantation

Self-nonself discrimination is a central property of the immune system. This paradigm was originally established in the context of tissue transplantation, leading to the discovery of major histocompatibility complex molecules as signals of 'self'. However, accumulating evidence has shown that innate immune cells are regulated in a similar fashion. Recent evidence has suggested that interactions between the 'self' molecule CD47 and the innate inhibitory receptor signal regulatory protein-alpha expressed on macrophages may be a critical determinant of transplant engraftment, supporting the concept that 'self'-awareness is a general property of all immune cells.

Antitumor activity of liposomal prednisolone phosphate depends on the presence of functional tumor-associated macrophages in tumor tissue

Prednisolone phosphate (PLP) encapsulated in long-circulating liposomes (LCLs) (LCL-PLP) exerts antitumor activity through the inhibition of tumor angiogenesis. It is known that tumor-associated macrophages (TAMs) play a crucial role in tumor growth as they are actively involved in promoting and maintaining tumor angiogenesis. To gain more insight into the antiangiogenic mechanisms of LCL-PLP, this study aimed to investigate the role of TAM in the antitumor mode of action of LCL-PLP in B16.F10 melanoma-bearing mice. Our results show that TAMs have a pivotal function in the growth of B16.F10 melanoma through the production of pro-angiogenic/pro-inflammatory factors. One of the major inhibitory actions of LCL-PLP on tumor growth is the reduction of the TAM-mediated production of pro-angiogenic factors, whereas production of anti-angiogenic factors by these cells is hardly affected.

Humanized SCID mouse models for biomedical research

There is a growing need for effective animal models to carry out experimental studies on human hematopoietic and immune systems without putting individuals at risk. Progress in development of small animal models for the in vivo investigation of human hematopoiesis and immunity has seen three major breakthroughs over the last three decades. First, CB 17-Prkdc(scid) (abbreviated CB 17-scid) mice were discovered in 1983, and engraftment of these mice with human fetal tissues (SCID-Hu model) and peripheral blood mononuclear cells (Hu-PBL-SCID model) was reported in 1988. Second, NOD-scid mice were developed and their enhanced ability to engraft with human hematolymphoid tissues as compared with CB17-scid mice was reported in 1995. NOD-scid mice have been the "gold standard" for studies of human hematolymphoid engraftment in small animal models over the last 10 years. Third, immunodeficient mice bearing a targeted mutation in the IL-2 receptor common gamma chain (IL2rgamma(null)) were developed independently by four groups between 2002 and 2005, and a major increase in the engraftment and function of human hematolymphoid cells as compared with NOD-scid mice has been reported. These new strains of immunodeficient IL2rgamma(null) mice are now being used for studies in human hematopoiesis, innate and adaptive immunity, autoimmunity, infectious diseases, cancer biology, and regenerative medicine. In this chapter, we discuss the current state of development of these strains of mice, the remaining deficiencies, and how approaches used to increase the engraftment and function of human hematolymphoid cells in CB 17-scid mice and in previous models based on NOD-scid mice may enhance human hematolymphoid engraftment and function in NOD-scid IL2rgamma(null) mice.

Human immunodeficiency virus type 1 pathobiology studied in humanized BALB/c-Rag2-/-gammac-/- mice

The specificity of human immunodeficiency virus type 1 (HIV-1) for human cells precludes virus infection in most mammalian species and limits the utility of small animal models for studies of disease pathogenesis, therapy, and vaccine development. One way to overcome this limitation is by human cell xenotransplantation in immune-deficient mice. However, this has proved inadequate, as engraftment of human immune cells is limited (both functionally and quantitatively) following transplantation of mature human lymphocytes or fetal thymus/liver. To this end, a human immune system was generated from umbilical cord blood-derived CD34(+) hematopoietic stem cells in BALB/c-Rag2(-/-)gamma(c)(-/-) mice. Intrapartum busulfan administration followed by irradiation of newborn pups resulted in uniform engraftment characterized by human T-cell development in thymus, B-cell maturation in bone marrow, lymph node development, immunoglobulin M (IgM)/IgG production, and humoral immune responses following ActHIB vaccination. Infection of reconstituted mice by CCR5-coreceptor utilizing HIV-1(ADA) and subtype C 1157 viral strains elicited productive viral replication and lymphadenopathy in a dose-dependent fashion. We conclude that humanized BALB/c-Rag2(-/-)gamma(c)(-/-) mice represent a unique and valuable resource for HIV-1 pathobiology studies.

Accelerated macrophage apoptosis induces autoantibody formation and organ damage in systemic lupus erythematosus

Increased monocyte/macrophage (Mphi) apoptosis occurs in patients with systemic lupus erythematosus (SLE) and is mediated, at least in part, by an autoreactive CD4(+) T cell subset. Furthermore, autoreactive murine CD4(+) T cells that kill syngeneic Mphi in vitro induce a lupus-like disease in vivo. However, it is unclear whether increased Mphi apoptosis in SLE per se is sufficient to accelerate/promote autoimmunity. We have investigated whether increased Mphi apoptosis in vivo, induced by the administration of clodronate liposomes, can exacerbate the autoimmune phenotype in NZB x SWR (SNF(1)) lupus-prone mice, and induce autoantibody production in haplotype-matched BALB/c x DBA1 (DBF(1)) non-lupus-prone mice. Lupus-prone mice SNF(1) mice that were treated with clodronate liposomes, but not mice treated with vehicle, developed significant increases in autoantibodies to dsDNA, nucleosomes, and the idiotypically related family of nephritic Abs Id(LN)F(1), when compared with untreated SNF(1) mice. Furthermore, clodronate treatment hastened the onset of proteinuria and worsened SNF(1) lupus nephritis. When compared with vehicle-treated controls, clodronate-treated non-lupus-prone DBF(1) mice developed significantly higher levels of anti-nucleosome and Id(LN)F(1) Abs but did not develop lupus nephritis. We propose that Mphi apoptosis contributes to the pathogenesis of autoantibody formation and organ damage through both an increase in the apoptotic load and impairment in the clearance of apoptotic material. This study suggests that mechanisms that induce scavenger cell apoptosis, such as death induced by autoreactive cytotoxic T cells observed in SLE, could play a pathogenic role and contribute to the severity of the disease.

Experimental Models to Study Development and Function of the Human Immune System In Vivo

The study of development and function of the immune system in vivo has made intensive use of animal models, but performing such work in humans is difficult for experimental, practical, and ethical reasons. Confronted with this scientific challenge, several pioneering groups have developed in the late 1980s mouse models of human immune system development. Although these experimental approaches were proven successful and useful, they were suffering from limitations due to xenograft transplantation barriers. By reviewing the characteristics of the successive models over the last 20 years, it becomes apparent that screening of potentially interesting mouse strains and usage of combinations of genetic deficiencies has led to major advances. This is particularly true for human T cell development in the murine thymus. This review will focus on these advances and the potential future improvements that remain to be accomplished.

An assay for human hematopoietic stem cells based on transplantation into nonobese diabetic recombination activating gene-null perforin-null mice

Abstract Nonobese diabetic recombination activating gene-null perforin-null (NOD- Rag1 null Prf1 null ) mice, which totally lack mature T and B cells and natural killer cell cytotoxic function, survive longer and are easier to breed than NOD-severe combined immunodeficiency ( scid ) or NOD- scid /beta 2 -microglobulin null mice. We have tested the use of NOD- Rag1 null Prf1 null mice as recipients in a long-term xenograft assay for human hematopoietic stem cells (HSCs) by adopting Yoder and colleagues' method of conditioned newborn mice, with minor modifications. Pregnant NOD- Rag1 null Prf1 null dams were treated with busulfan 22.5 mg/kg. On the day of delivery, the busulfan-exposed pups underwent transplantation with 4 to 5 million T cell--depleted human cord blood mononuclear cells via the facial vein. At 2 months after transplantation, all 11 transplanted mice showed human hematopoietic engraftment in the peripheral blood. At 6 months after transplantation, human cells were detected in 5 mice, which showed higher than 0.9% human cell engraftment at 2 months. The mean percentage of human CD45 + cells in the bone marrow of engrafted mice was 43.9% +/- 36.5% (range, 2.0%-79.9%). Next, we tested the usefulness of conditioned newborn NOD- Rag1 null Prf1 null mice for applications to characterize the dye efflux capability and phenotypic features of human HSCs. Given that cord blood HSCs have the ability to efflux rhodamine 123 (Rho), we attempted transplantations of sorted cells that retained a low level (Rho low ) or high level (Rho high ) of Rho. Six-month engraftment was found only with the Rho low cells, which contained high percentages of CD34 + CD38 - cells and side population cells with Hoechst 33324 efflux activity. These observations suggest that Rho low cells are highly enriched for primitive hematopoietic cells. Accordingly, conditioned newborn NOD- Rag1 null Prf1 null mice provide a desirable model for an assay of long-term transplantable human HSCs.