Peritoneal macrophages play an important role in eliminating human cells from severe combined immunodeficient mice transplanted with human peripheral blood lymphocytes

Developmental role of macrophages modeled in human pluripotent stem cell-derived intestinal tissue

Macrophages populate the embryo early in gestation, but their role in development is not well defined. In particular, specification and function of macrophages in intestinal development remain little explored. To study this event in the human developmental context, we derived and combined human intestinal organoid and macrophages from pluripotent stem cells. Macrophages migrate into the organoid, proliferate, and occupy the emerging microanatomical niches of epithelial crypts and ganglia. They also acquire a transcriptomic profile similar to that of fetal intestinal macrophages and display tissue macrophage behaviors, such as recruitment to tissue injury. Using this model, we show that macrophages reduce glycolysis in mesenchymal cells and limit tissue growth without affecting tissue architecture, in contrast to the pro-growth effect of enteric neurons. In short, we engineered an intestinal tissue model populated with macrophages, and we suggest that resident macrophages contribute to the regulation of metabolism and growth of the developing intestine.

Intestinal epithelial glucocorticoid receptor promotes chronic inflammation-associated colorectal cancer

Synthetic immunosuppressive glucocorticoids (GCs) are widely used to control inflammatory bowel disease (IBD). However, the impact of GC signaling on intestinal tumorigenesis remains controversial. Here, we report that intestinal epithelial GC receptor (GR), but not whole intestinal tissue GR, promoted chronic intestinal inflammation-associated colorectal cancer in both humans and mice. In patients with colorectal cancer, GR was enriched in intestinal epithelial cells and high epithelial cell GR levels were associated with poor prognosis. Consistently, intestinal epithelium–specific deletion of GR (GR iKO) in mice increased macrophage infiltration, improved tissue recovery, and enhanced antitumor response in a chronic inflammation–associated colorectal cancer model. Consequently, GR iKO mice developed fewer and less advanced tumors than control mice. Furthermore, oral GC administration in the early phase of tissue injury delayed recovery and accelerated the formation of aggressive colorectal cancers. Our study reveals that intestinal epithelial GR signaling repressed acute colitis but promoted chronic inflammation–associated colorectal cancer. Our study suggests that colorectal epithelial GR could serve as a predictive marker for colorectal cancer risk and prognosis. Our findings further suggest that, although synthetic GC treatment for IBD should be used with caution, there is a therapeutic window for GC therapy during colorectal cancer development in immunocompetent patients.

Anti-inflammatory and anti-insulin resistance activities of aqueous extract from Anoectochilus burmannicus

This study investigated biological activities including antioxidative stress, anti‐inflammation, and anti‐insulin resistance of Anoectochilus burmannicus aqueous extract (ABE). The results showed abilities of ABE to scavenging DPPH and ABTS free radicals in a dose‐dependent manner. Besides, ABE significantly reduced nitric oxide (NO) production in the lipopolysaccharide (LPS)‐treated RAW 264.7 via inhibition of mRNA and protein expressions of nitric oxide synthase (iNOS). The LPS‐induced mRNA expressions of cyclooxygenase‐2 (COX‐2) and interleukin 1β (IL‐1β) were suppressed by ABE. Moreover, ABE exerted anti‐insulin resistance activity as it significantly improved the glucose uptake in tumor necrosis factor (TNF)‐α treated 3T3‐L1 adipocytes. In addition, ABE at the concentration of up to 200 μg/mL was not toxic to human peripheral blood mononuclear cells (PBMCs) and did not induce mutations. Finally, the results of our study suggest the potential use of A. burmannicus as anti‐inflammatory, anti‐insulin resistance agents, or food supplement for prevention of chronic diseases.

Humanized Mice as Preclinical Models in Transplantation

Animal models have been instrumental in our understanding of the mechanisms of rejection and the testing of novel treatment options in the context of transplantation. We have now entered an exciting era with research on humanized mice driving advances in translational studies and in our understanding of the function of human cells in response to pathogens and cancer as well as the recognition of human allogeneic tissues in vivo. In this chapter we provide a historical overview of humanized mouse models of transplantation to date, outlining the distinct strains and share our experiences in the study of human transplantation immunology.

Human muscle-derived stem/progenitor cells promote functional murine peripheral nerve regeneration

Peripheral nerve injuries and neuropathies lead to profound functional deficits. Here, we have demonstrated that muscle-derived stem/progenitor cells (MDSPCs) isolated from adult human skeletal muscle (hMDSPCs) can adopt neuronal and glial phenotypes in vitro and ameliorate a critical-sized sciatic nerve injury and its associated defects in a murine model. Transplanted hMDSPCs surrounded the axonal growth cone, while hMDSPCs infiltrating the regenerating nerve differentiated into myelinating Schwann cells. Engraftment of hMDSPCs into the area of the damaged nerve promoted axonal regeneration, which led to functional recovery as measured by sustained gait improvement. Furthermore, no adverse effects were observed in these animals up to 18 months after transplantation. Following hMDSPC therapy, gastrocnemius muscles from mice exhibited substantially less muscle atrophy, an increase in muscle mass after denervation, and reorganization of motor endplates at the postsynaptic sites compared with those from PBS-treated mice. Evaluation of nerve defects in animals transplanted with vehicle-only or myoblast-like cells did not reveal histological or functional recovery. These data demonstrate the efficacy of hMDSPC-based therapy for peripheral nerve injury and suggest that hMDSPC transplantation has potential to be translated for use in human neuropathies.

Humanized mouse models in transplantation research

The interest in the use of humanized mouse models for research topics like Graft versus Host Disease (GvHD), allograft studies and other studies to the human immune system is growing. The design of these models is still improving and enables even more complicated studies to these topics. For researchers it can be difficult to choose the best option from the current pool of available models. The decision will depend on which hypothesis needs to be tested, in which field of interest, and therefore 'the best model' will differ from one to another. In this review, we provide a guide to the most common available humanized mouse models, with regards to different mouse strains, transplantation material, transplantation techniques, pre- and post-conditioning and references to advantages and disadvantages. Also, an evaluation of experiences with humanized mouse models in studies on GvHD and allograft rejection is provided.

Mouse models with human immunity and their application in biomedical research

Biomedical research in human beings is largely restricted to in vitro studies that lack complexity of a living organism. To overcome this limitation, humanized mouse models are developed based on immunodeficient characteristics of severe combined immunodeficiency (SCID) or recombination activating gene (Rag)(null) mice, which can accept xenografts. Peripheral constitution of human immunity in SCID or Rag(null) mice has been achieved by transplantation of mature human immune cells, foetal human thymus, bone marrow, liver tissues, lymph nodes or a combination of these, although efficiency needs to be improved. These mouse models with constituted human immunity (defined as humanized mice in the present text) have been widely used to investigate the basic principles of human immunobiology as well as complex pathomechanisms and potential therapies of human diseases. Here, elements of an ideal humanized mouse model are highlighted including genetic and non-genetic modification of recipient mice, transplantation strategies and proposals to improve engraftments. The applications of the humanized mice to study the development and response of human immune cells, human autoimmune diseases, virus infections, transplantation biology and tumour biology are reviewed as well.

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.

Reconstitution of a human immune system in immunodeficient mice: models of human alloreaction in vivo

Rodents have been widely used for studies in transplantation immunology because of their short reproduction period and the relative ease of generating inbred mutant or transgenic strains. However, although many biological mechanisms are similar between rodents and humans, several features clearly distinguish the immune system in these species. Consequently, it is rarely possible to extrapolate observations from rodent models directly into clinical practice. In vitro studies with human cells are useful for elucidation of basic mechanisms, but in order to study complex biological phenomena, in vivo studies are indispensable. In later years, a number of interesting models have been described where immunodeficient mice have been reconstituted with human cells, so-called humanized mice, in order to study human immune responses in vivo. This has opened a new field of experimental immunology that has been applied to areas such as cancer, autoimmunity, allergy, infections, and transplantation biology. In this review, we shall concentrate on the use of severe combined immunodeficient mice reconstituted with human immune or stem cells for studies of human alloreaction in vivo.

A new xenograft model for graft-versus-host disease by intravenous transfer of human peripheral blood mononuclear cells in RAG2-/- gammac-/- double-mutant mice

The safe application of new strategies for the treatment of graft-versus-host disease (GVHD) is hampered by the lack of a clinically relevant model for preclinical testing. Current models are based on intraperitoneal transfer of human peripheral blood mononuclear cells (huPBMCs) into NOD-SCID (nonobese diabetic-severe combined immunodeficient)/SCID mice. Intravenous transfer would be preferred but this has always been ineffective. We developed a new model for xenogeneic GVHD (X-GVHD) by intravenous transfer of huPBMCs into RAG2-/- gammac-/-mice. Our results show a high human T-cell chimerism of more than 20% (up to 98%) in more than 90% of mice, associated with a consistent development of XGVHD within 14 to 28 days and a total mortality rate of 85% shorter than 2 months. After murine macrophage depletion, engraftment was earlier and equally high with lower doses of huPBMCs. Human macrophages were also absent in these mice. Purified huCD3+ cells showed a similar X-GVH effect with contribution of both CD4 and CD8 phenotypes. Human immunoglobulins and cytokines were produced in diseased mice. One of 30 mice developed chronic X-GVHD with skin histology similar to human GVHD. In conclusion, we present a new model for X-GVHD by intravenous transfer of huPBMCs in RAG2-/- gammac-/- mice. Murine and human macrophages do not seem to be necessary for acute X-GVHD in this model.

Erythrocyte-replaced mouse model for Haemoparasite studies: comparison of NOD/shi-scid and C.B-17/Jcl-scid mouse upon acceptability of human erythrocytes

The erythrocyte-exchanged chimera mouse model has become to be a significant tool for studying animal and human (hu) protozoan haemoparasites, though the usefulness of this model varies depending primarily on the acceptability of xenogeneic red blood cells (RBC). To find a superior recipient in comparison with C.B-17/Jcl mouse with severe combined immuno-deficiency (scid) mutation, we examined in this report the non-obese diabetes (NOD)/shi-scid mouse, a recently available strain of SCID. When 2.5 x 10(8) of fluorescent dye-labeled hu-RBCs were transfused, C.B-17scid mouse eliminated them logarithmically by a simple linear regression, while NOD-scid mouse eradicated hu-RBCs by a unique two-step fashion, i.e., a potent but only briefly functioning RBC eradication followed by a weak steadily functioning step. The means of regression line constance +/- their standard deviations (SD) of 205 C.B-17scid and of 213 NOD-scid mice for their short- and long-lasting steps were -0.73 +/- 0.63, -0.53 +/- 0.25 and -0.16 +/- 0.10, respectively. Hu-RBC half-lives determined from these means of C.B-17scid mice and of NOD-scid mice for the short- and long-living steps were 3.6, 4.9 and 16.3 hr, respectively. Higher hu-RBC acceptability of NOD-scid mouse, especially at their long-lasting step, was also demonstrated under at an activated state of mouse innate immunity. Treatment with 1.0 mg heat-killed Candida cells caused an acceleration of hu-RBC elimination in both mouse strains but the magnitudes for the short- and long-living steps of NOD-scid mice evaluated by "stimulation index" were only 1/2.6 and 1/7.6 of C.B-17scid mice, respectively.

Gene delivery using human cord blood-derived CD34+cells into inflamed glomeruli in NOD/SCID mice

BACKGROUND

Bone marrow reconstitution using genetically-modified hematopoietic stem cells has been reported to confer resistance to inflammation and prevent renal injury in glomerulonephritis. Although this strategy has potentials for clinical use, taking hematopoietic stem cells from bone marrow is highly stressful for patients. In this regard, umbilical cord blood may be a useful alternative and, therefore, we focused on their suitability as a source of hematopoietic stem cells for transplantation-based therapy for glomerulonephritis.

METHODS

CD34+ cells were obtained from human umbilical cord blood, retrovirally transduced with human beta-glucuronidase (HBG) gene, and transplanted into nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. After confirming the successful chimerism, these mice were treated with lipopolysaccharide (LPS), and local HBG expression in glomeruli was examined using immunohistochemical analysis, HBG bioassay, and Western blot analysis.

RESULTS

Clonogenic assay showed that 88.4 +/- 5.9% burst-forming unit-erythroid (BFU-E), 79.7 +/- 11.4% in colony-forming unit-macrophage (CFU-M), and 81.1 +/- 14.1% in colony-forming unit-granulocyte (CFU-G), respectively, possessed the transgene after transfection, suggesting that precommited cells were susceptible to retroviral infection. Flow cytometric analysis revealed that 24.1 +/- 14.5% of bone marrow cells in these chimera mice expressed human lymphocyte antigen (HLA) 8 weeks after transplantation. Also, clonogenic assay showed that a sustained engraftment of human hematopoietic cells expressed HBG. CD14-positive cells were recruited into the glomeruli upon LPS treatment and they secreted bioactive HBG, suggesting that cord blood-derived CD34+cells may differentiate into monocyte lineage while maintaining the expression of the transgene.

CONCLUSION

These data indicate that umbilical cord blood cells can be utilized as a source of hematopoietic stem cells for the transplantation-based therapy of glomerulonephritis.

Promotion of xenogeneic hematopoietic chimerism in rodents by mononuclear phagocyte depletion

The successful establishment of tolerance toward pig tissues in primates through hematopoietic progenitor cell engraftment is restricted by the rapid disappearance of these cells in the recipient following infusion. We developed and tested the hypothesis that phagocytes of the reticuloendothelial system are responsible for the rapid clearance of infused pig hematopoietic cells using a mouse model. Mice received non-myeloablative conditioning and, on various days, were injected with medronate-encapsulated liposomes (M-L) or control blank liposomes, followed by the intravenous infusion of miniature swine hematopoietic cells. M-L were well-tolerated in mice (n=100) at levels that deplete mononuclear phagocytes. Depletion of mononuclear phagocytes in normal Balb/c mice as well as in severe combined immune deficient mice increased the accumulation of pig hematopoietic cells in the bone marrow (BM) by 10-fold when measured 24 h after the infusion of the cells. Colony-forming unit analysis showed an increased accumulation of pig hematopoietic progenitors in the BM of mice that were infused with medronate-liposomes. We conclude that depletion of mononuclear phagocytes by M-L has the potential to lower the barrier to the establishment of mixed chimerism and tolerance induction in xenotransplantation.

Patterns of engraftment in different strains of immunodeficient mice reconstituted with human peripheral blood lymphocytes

BACKGROUND

Models of immunodeficient mice reconstituted with a competent human immune system would represent an invaluable tool for the study of transplantation immunobiology allergy, autoimmunity, and infectious diseases. Severe combined immune deficiency (scid) mice can be successfully reconstituted with human peripheral blood lymphocytes (PBLs), but rates and levels of engraftment are poor. New strains of mice with diverse immunodeficiencies have been recently characterized or developed, which might prove to be advantageous for in vivo studies of human immune reactivity.

METHODS

We have compared rates and patterns of human PBL engraftment in four available immunodeficient murine strains; scid-beige, nonobese diabetic (NOD)-scid, NOD-scid-beta2 m- and rag-. T- and B-lymphocyte engraftment, phenotype of engrafted cells, and occurrence of graft-versus-host disease (GVHD) were studied and compared.

RESULTS

Successful engraftment of human PBL was readily obtained in the majority of scid-beige, NOD-scid, and NOD-scid-beta2 m- with a single i.p. administration of human PBLs, whereas it was seldom achieved in rag- animals. Human Ig levels were accordingly remarkably low in rag- recipients but, interestingly also in NOD-scid-beta2 m- mice. Engraftment was readily observed not only in peripheral blood but also in spleen and bone marrow of successfully reconstituted animals. Phenotypic analysis of engrafted human cells showed preserved CD4/CD8 ratios and a clear skewing toward an activated phenotype. GVHD was invariably observed in successfully reconstituted animals.

CONCLUSIONS

Our data indicate that a high rate of reconstitution with human lymphocytes can be achieved in scid-beige, NOD-scid, and NOD-scid-beta2 m- mice. Human Ig are produced at high levels, except in NOD-scid-beta2 m-, including xenoreactive natural antibodies. Scid-beige and NOD-scid appear therefore better suited than NOD-scid-beta2 m- or rag- for analysis of human immunoreactivity in vivo. An important caveat is the invariable occurrence of GVHD that precludes long-term studies in this model system.

Human peripheral blood leukocyte engraftment into SCID mice: critical role of CD4(+) T cells

We examined the influence of donor T lymphocytes on human peripheral blood leukocytes (PBL) engraftment into severe combined immune deficient (SCID) mice. Mice were injected with unfractionated or subset-depleted human PBL, and treated at various times with OKT3, a cytotoxic monoclonal antibody against human CD3(+) T lymphocytes. PBL engraftment, high levels of human Ig, and high incidence of lymphoproliferative disease (lpd) were found in mice transplanted with unfractionated PBL and CD8- or CD14-depleted PBL, and in mice treated with OKT3 at distance from PBL transfer. Animals xenografted with CD3- or CD4-depleted PBL, or treated at transplantation time with OKT3, had very low levels of human Ig and did not develop lpd. PBL engraftment was minimal or absent in these animals, as determined by immunohistochemistry, dot-blot, and RT-PCR analyses. These results demonstrate that the presence of donor CD4(+) T lymphocytes at transplantation time is necessary for observing human PBL engraftment into SCID mice, an essential condition for human Ig production and lpd development.

Human-SCID mouse chimeric models for the evaluation of anti-cancer therapies

The ability to engraft human tumors and human immunocompetent cells successfully in severe combined immunodeficient (SCID) mice has spawned the development and use of human-mouse chimeric models to evaluate anti-cancer therapies. The lack of standardization and many other potential pitfalls have contributed to the current controversy surrounding the reliability of these different models. Five frequently used SCID mouse models and their specific applications are summarized with the specific aim of providing an objective discussion of the strengths and limitations of each model, together with suggestions for overcoming some of the variabilities and for improving the design and use of future models.

Human B cell growth and differentiation in the spleen of immunodeficient mice

Human mAbs (HumAbs) have therapeutic potential against infectious diseases and cancer. Heretofore, their production has been hampered by ethical constraints preventing the isolation of Ag-specific activated B cells by in vivo immunization. Alternatively, severe combined immune deficient (SCID) mice, transplanted i.p. with human (Hu)-PBLs, allow the in vivo stimulation of human Ab responses without the usual constraints. Unfortunately, human B cells only represent a minor fraction of the surviving graft, they are scattered all over the animal body, and thus are hard to isolate for subsequent immortalization procedures. To prevent this dispersion and to provide the human B cells with a niche for expansion and maturation, SCID mice were engrafted with Hu-PBL directly into the spleen. Simultaneously endogenous murine NK cell activity was depleted by treatment with an anti-mouse IL-2 receptor beta-chain Ab. During engraftment, human B lymphocytes became activated, divided intensely, and differentiated into plasmacytoid cells. In vivo exposure to a recall Ag after cell transfer induced expansion of Ag-specific B cell clones. One week after inoculation, human B cells were abundant in the spleen and could easily be recovered for fusion with a heteromyeloma line. This resulted in the formation of stable hybridoma cell lines that secreted Ag-specific HumAbs. Thus transplantation of human lymphoid cells in the spleens of immune deficient mice represents a model for the study of human T cell-dependent B cell activation and proves to be an excellent tool for the successful production of HumAbs.

Human peripheral blood lymphocyte severe combined immunodeficiency (hu-PBL SCID) models of toxoplasmosis

Toxoplasmosis is a potentially fatal opportunistic infection of immunocompromised hosts. Improved animal models of toxoplasmosis are needed to more nearly approximate conditions that occur in immunocompromised humans. The development of models of toxoplasmosis using human peripheral blood lymphocytes (hu-PBL) transplanted into severe combined immunodeficiency (SCID) mice is described here. Transplantation of hu-PBL into SCID mice without prior conditioning of the mice resulted in detectable differences in quantitative histological scores of brain inflammation due to Toxoplasma gondii infection, but did not alter mortality when compared to SCID mouse controls. The lack of detectable differences in survival were due to inadequate engraftment of hu-PBL, as assessed by flow cytometry. Unconditioned hu-PBL SCID mice had low titre T. gondii-specific antibody detectable after infection. When pretransplantation conditioning with irradiation and antiasialo GM 1 (n-glucolyl neuraminic acid) antibody was used, prolonged hu-PBL engraftment was observed in SCID mice, which was associated with worsened histopathology and usually impaired survival when compared with SCID mouse controls. When pretransplantation conditioning with irradiation, antiasialo GM antibody and polyethylene glycol-conjugated IL-2 was used, prolonged hu-PBL engraftment was also documented, but this did not affect survival from T. gondii infection when compared with similarly conditioned SCID mouse controls. The latter conditioning protocol resulted in hu-PBL SCID mice producing high titre T. gondii-specific antibody after infection. Conditioned hu-PBL SCID mice had evidence of increased T. gondii-induced inflammatory scores when compared with conditioned SCID mice. These models show promise for the study of the pathogenesis of toxoplasmosis and conditioned hu-PBL SCID mice may have applications for the evaluation of novel therapies for toxoplasmosis in immunocompromised humans.

Islet xenograft destruction in the hu-PBL-severe combined immunodeficient (SCID) mouse necessitates anti-CD3 preactivation of human immune cells

Introduction of the hu-PBL-SCID mouse model has yielded a potentially useful tool for research in transplantation. The aim of this study was to define the conditions necessary for a reconstituted human immune system to destroy in a consistent manner rat islet xenografts in the alloxan-diabetic hu-PBL-SCID mouse. We examined different time points of hu-PBL reconstitution, different transplantation sites of the islets and several hu-PBL reconstitution protocols. Major differences in graft destruction were observed between the different hu-PBL reconstitution protocols, irrespective of timing of hu-PBL reconstitution or site of transplantation. Although preactivation of hu-PBL did not improve the level of hu-PBL chimerism, histological and immunohistochemical analysis of the grafts revealed a severe human lymphocytic infiltration and beta cell destruction only in the grafts of mice receiving preactivated hu-PBL. This beta cell injury resulted in impaired glucose tolerance, with in some animals recurrence of hyperglycaemia, and decreased insulin and C-peptide levels after glucose stimulation. Therefore, we conclude that activation of hu-PBL prior to transfer is essential in achieving xenograft infiltration and destruction in hu-PBL-SCID mice. The need for immune manipulation suggests that interactions between hu-PBL and xenografts in this model may be hampered by incompatibilities in cross-species adhesion and/or activation signals.

Mouse strain and conditioning regimen determine survival and function of human leucocytes in immunodeficient mice

The innate immune system of severe combined immunodeficient (SCID) mice represents an important barrier to the successful engraftment of human cells. Different genetic and pharmacological strategies improve the graft survival. Non-obese diabetic (NOD)-SCID mice are better hosts for reconstitution with human peripheral blood leucocytes (Hu-PBL) because of their reduced natural killer cell and macrophage activity next to defective T and B cell functions. We investigated effects of TM-beta1, a rat monoclonal antibody recognizing the mouse IL-2 receptor beta-chain, on Hu-PBL survival and function in NOD-SCID and SCID mice. Relative to untreated littermates, TM-beta1 improved Hu-PBL survival in SCID and NOD-SCID mice. Moreover, TM-beta1-pretreated NOD-SCID mice displayed significantly better Hu-PBL survival and tissue distribution than TM-beta1-pretreated SCID mice. Irradiation of NOD-SCID mice further enhanced the effects of TM-beta1. However, these animals died within 3 weeks post-grafting due to graft-versus-host disease. Secondary immune responses were evaluated with Hu-PBL from a donor immune to hepatitis B surface antigen (HBsAg). In TM-beta1-pretreated NOD-SCID mice, human HBsAg-specific memory B cells produced high titres of anti-HBsAg immunoglobulin irrespective of the administration of a secondary antigen booster dose. This contrasts with secondary immune responses in TM-beta1-pretreated SCID mice where high titred antigen-specific immunoglobulins were produced when the appropriate antigen booster was given. In conclusion, reducing the function of the innate immune system in immunodeficient mice improves survival of the human graft and can result in an activation of the memory B cells without the need for recall antigen exposure.

Murine IL-2 receptor beta chain blockade improves human leukocyte engraftment in SCID mice

Severe combined immunodeficient (SCID) mice accept human xenografts and can act as a model for human immune functions. Murine natural killer cells (NK), however, represent an important barrier for the reconstitution of SCID mice with human peripheral blood leukocytes (Hu-PBL). We investigated the effect on Hu-PBL survival of pretreatment with TM-beta1, a rat monoclonal antibody for the mouse IL-2 receptor beta chain. TM-beta1 greatly improved the survival of Hu-PBL. Human lymphocytes, predominantly T cells, survived in the peritoneum and infiltrated spleen and lungs already 1 week after engraftment and liver and thymus from 2 weeks on. Secondary humoral responses were evaluated with Hu-PBL from a donor immune to hepatitis-B surface Ag (HBsAg) and tetanus toxoid (TT). TM-beta1 pretreatment enhanced the recall Ig response to HBsAg and did not affect the baseline anti-TT Ig production. In conclusion, TM-beta1 pretreatment of SCID mice significantly improves the survival and functionality of the Hu-PBL graft.

Enhanced engraftment of human peripheral blood lymphocytes into anti-murine interferon-gamma monoclonal antibody-treated C.B.-17-scid mice

To improve the engraftment of human peripheral blood lymphocytes (PBL) to severe combined immunodeficient (SCID) mice, and to elucidate the factors which prevent the PBL's survival, we treated SCID mice with mAb, which neutralizes murine IFN-gamma's ability to activate cell-mediated immunity. Compared with untreated mice, mAb-treated mice retained significantly higher numbers and ratios of human PBL in the peritoneal cavity and spleen, as well as significantly higher serum titers of human IgG and IgM. Histologically, host versus graft reaction (HVGR) was less severe in the mAb-treated mice. Moreover, these phenomena were completely abrogated when mice were also treated with murine recombinant IFN-gamma. These results suggest that murine IFN-gamma plays an important role in the rejection of human cells in SCID mice and that its depletion by means of mAb treatment can significantly reduce HVGR and improve the engraftment of human PBL.