Limited B cell repertoire in severe combined immunodeficient mice engrafted with peripheral blood mononuclear cells derived from immunodeficient or normal humans

Characterization of novel, severely immunodeficient PrkdcΔex57/Δex57 mice

Severely immunodeficient mice are useful for understanding the pathogenesis of certain tumors and for developing therapeutic agents for such tumors. In addition, engraftment of these mice with human hematopoietic cells can yield information that helps us understand the in vivo molecular mechanisms underlying actual human viral infections. In our present research, we discovered a novel, severely immunodeficient strain of mice having a mutation in exon 57 of the Prkdc gene (PrkdcΔex57/Δex57) in an inbred colony of B10.S/SgSlc mice. Those PrkdcΔex57/Δex57 mice showed thymic hypoplasia and lack of mature T cells and B cells in peripheral lymphoid tissues, resulting in very low levels of production of serum immunoglobulins. In addition, those mice were highly susceptible to influenza viruses due to the lack of acquired immune cells. On the other hand, since they had sufficient numbers of NK cells, they rejected tumor transplants, similarly to Prkdc+/+ mice. Next, we generated Foxn1nu/nuPrkdcΔex57/Δex57Il2rg-/- (NPG) mice on the BALB/cSlc background, which lack all lymphocytes such as T cells, B cells and innate lymphoid cells, including NK cells. As expected, these mice were able to undergo engraftment of human tumor cell lines. These findings suggest that PrkdcΔex57/Δex57 mice will be useful as a novel model of immunodeficiency, while NPG mice will be useful for xenografting of various malignancies.

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.

Humanized mice for the development and testing of human vaccines

Mouse models of human disease form a link between genetics and biology. However, mice and humans differ in many aspects of immune system biology. These differences might explain, in part, why many successful preclinical immunotherapy studies in mice turn out to be unsuccessful when used in clinical trials in humans. Pioneering studies in the late 1980s demonstrated the reconstitution of human lympho-hematopoietic cells in immunodeficient mice. Since this time, immunodeficient mice are being tested as hosts for human hematopoietic organs or cells in an effort to create an in vivo model of the complete human immune system. Such Humouse models could permit us to generate and test novel human vaccines.

Highly active antiretroviral therapy potently suppresses HIV infection in humanized Rag2-/-gammac-/- mice

Humanized Rag2(-/-)gamma(c)(-/-) mice (Hu-DKO mice) become populated with functional human T cells, B cells, and dendritic cells following transplantation with human hematopoietic stem cells (HSC) and represent an improved model for studying HIV infection in vivo. In the current study we demonstrated that intrasplenic inoculation of hu-DKO mice with HIV-1 initiated a higher level of HIV infection than intravenous or intraperitoneal inoculation, associated with a reciprocal decrease in peripheral CD4(+) T cells and increase in peripheral CD8(+) T cells. HIV infection by intrasplenic injection increased serum levels of human IgG and IgM including human IgM and IgG specific for HIV-1 gp120. There was a significant inverse correlation between the level of HIV-1 infection and the extent of CD4(+) T cell depletion. Highly active antiretroviral therapy (HAART) initiated 1 week after HIV-1 inoculation markedly suppressed HIV-1 infection and prevented CD4(+) T cell depletion. Taken together, these findings demonstrate that intrasplenic injection of hu-DKO mice with HIV is a more efficient route of HIV infection than intravenous or intraperitoneal injection and generates increased infection associated with an increased anti-HIV humoral response. This animal model can serve as a valuable in vivo model to study the efficacy of anti-HIV therapies.

Novel humanized murine models for HIV research

There are few models in which HIV pathogenesis, particularly gut-associated lymphoid tissue CD4(+) T-cell depletion, can be studied and in which potential clinical interventions against HIV disease can be evaluated. HIV cannot be studied in normal mice due to the limited species tropism of the virus. Through the pioneering efforts of many investigators, humanized mice are now routinely used to rapidly advance HIV research. It is important to recognize that not all humanized murine models are equal, and their strengths and weaknesses must be taken into consideration to obtain information that is most relevant to the human condition. This review distinguishes the major humanization protocols and highlights each model's recent contributions to HIV research, including mucosal transmission, gut-associated lymphoid tissue pathogenesis, and the evaluation of novel therapeutic and prevention approaches to potentially treat HIV disease and prevent the further spread of AIDS.

Novel mouse models for understanding HIV-1 pathogenesis

Small animal models in which in vivo HIV-1 infection, pathogenesis, and immune responses can be studied would permit both basic research on the biology of the disease, as well as a system to rapidly screen developmental therapeutics and/or vaccines. To date, the most widely-used models have been the severe combined immunodeficient (SCID)-hu (also known as the thy/liv SCID-hu) and the huPBL-SCID mouse models. Recently three new models have emerged, i.e., the intrasplenic huPBL/SPL-SCID model, the NOD/SCID/IL2Rgamma(null) mouse model, and the Rag2(-/-)gamma(c) (-/-) mouse model. Details on the construction, maintenance and HIV-1 infection of these models are discussed.

Murine models for HIV vaccination and challenge

HIV-1 only infects humans and chimpanzees. SIV or SHIV are, therefore, used as models for HIV in rhesus, cynomologus and pigtail macaques. Since conducting experiments in primate models does not fully mimic infection or vaccination against HIV-1 and is expensive, there is a great need for small-animal models in which it is possible to study HIV-1 infection, immunity and vaccine efficacy. This review summarizes the available murine models for studying HIV-1 infection with an emphasis on our experience of the HIV-1-infected-cell challenge as a model for evaluating candidate HIV-1 vaccines. In the cell-based challenge model, several important factors that, hopefully, can be related to vaccine efficacy in humans were discovered: the efficiency of combining plasmid DNA representing several of the viral genes originating from multiple clades of HIV-1, the importance of adjuvants activating innate and induced immunity and the enhanced HIV eradication by drug-conjugated antibody.

Construction of human-SCID chimeric mice

Until recently, testing of new therapeutic agents has relied extensively upon the use of mice and nonhuman primates for in vivo preclinical studies. Unfortunately, these animal models do not always mimic the physiological and pathophysiological processes that occur in humans. The finding that C.B-17 severe combined immunodeficiency (SCID) mice lack a competent immune system, and therefore are unable to mount effective cellular and humoral responses to foreign antigens, has led to their use as recipients for xenografts of human tissues. This unit is focused on the construction of human-SCID chimeric through the surgical implantation of human fetal hematolymphoid tissues into SCID mice (SCID-hu mice). The Basic Protocol describes the surgical implantation of human fetal thymus and liver under the kidney capsules of SCID mice (SCID-hu Thy/Liv model). Subcutaneous transplantation of human fetal bone marrow and thymus (SCID-hu Bm/Thy mice) is described in the Alternate Protocol. Additional support protocols provide procedures to analyze human lymphocyte populations in the peripheral blood and grafted organs of SCID-hu mice. The advantages and disadvantages of each protocol and potential applications are discussed in the Commentary.

Comparison of the human immune response to conjugate and polysaccharide pneumococcal vaccination using a reconstituted SCID mouse model

The pneumococcal conjugate vaccine (CV), although highly immunogenic in infants and young children, does not consistently demonstrate an advantage over the pneumococcal polysaccharide vaccine (PPV) in older adults. To further elucidate the adult immune response to CV, we compared its response to PPV on a molecular level using a severe combined immunodeficient (SCID) mouse model. This model allowed us to analyze a single individual's response to two different forms of antigen and define differences in gene usage elicited by these vaccines. We reconstituted SCID mice with human lymphocytes derived from an unimmunized donor; the mice were divided into two groups and immunized with either the PPV or CV. Our results demonstrate significant differences in variable gene usage in SCID mice immunized with PPV versus CV and suggest that the nature of the immunizing agent has a significant impact on gene usage and therefore influences antibody function and vaccine efficacy.

Immunogenicity of Embryonic Stem Cells and Their Progeny

The ability of pluripotent human embryonic stem cells (hESCs) to differentiate into multiple cell types has led to great excitement about their potential use in the treatment of various degenerative and malignant human diseases. Before such a goal is attainable, however, it must be demonstrated that pure populations of specialized cell types can be isolated and transplanted while simultaneously avoiding possible immune-mediated rejection of these cells. In this chapter, I will discuss the utility of the humanized mouse Trimera model as an in vivo experimental system to study the immunological properties of hESCs and their differentiated derivatives.

Mouse models for HIV-1 infection

The generation of small animal models, which preserve the ability for the generation of primary and memory immune responses of the engrafted human immune cells and in which a robust HIV-1 infection may occur, may enable the rapid screening, development and evaluation of HIV-1 protective vaccines and adjuvants. This manuscript reviews the existing mouse HIV-1 models used to study virologic, immunologic and pathogenic aspects of HIV-1 infection and disease and discusses their limitations and advantages, especially in the context of vaccine development, with special focus on the recently developed Trimera-HIV-1 animal model.

Insight into Graves' hyperthyroidism from animal models

Graves' hyperthyroidism can be induced in mice or hamsters by novel approaches, namely injecting cells expressing the TSH receptor (TSHR) or vaccination with TSHR-DNA in plasmid or adenoviral vectors. These models provide unique insight into several aspects of Graves' disease: 1) manipulating immunity toward Th1 or Th2 cytokines enhances or suppresses hyperthyroidism in different models, perhaps reflecting human disease heterogeneity; 2) the role of TSHR cleavage and A subunit shedding in immunity leading to thyroid-stimulating antibodies (TSAbs); and 3) epitope spreading away from TSAbs and toward TSH-blocking antibodies in association with increased TSHR antibody titers (as in rare hypothyroid patients). Major developments from the models include the isolation of high-affinity monoclonal TSAbs and analysis of antigen presentation, T cells, and immune tolerance to the TSHR. Studies of inbred mouse strains emphasize the contribution of non-MHC vs. MHC genes, as in humans, supporting the relevance of the models to human disease. Moreover, other findings suggest that the development of Graves' disease is affected by environmental factors, including infectious pathogens, regardless of modifications in the Th1/Th2 balance. Finally, developing immunospecific forms of therapy for Graves' disease will require painstaking dissection of immune recognition and responses to the TSHR.

Engraftment of human T, B and NK cells in CB.17 SCID/beige mice by transfer of human spleen cells

Models of severe combined immuno-deficient (SCID) mice reconstituted with a competent human immune system represent a valuable tool for the study of human immune responses in vivo. Reconstitution with human cells can be achieved using large numbers of peripheral blood lymphocytes, but levels of engraftment are poor and graft versus host disease (GVHD) frequently occurs. SCID/beige mice are at the same time deficient for adaptive and innate immunity and the objective of this study was to develop a safe and efficient way to achieve human lymphocyte engraftment in these mice using human spleen cells. After institutional authorisations and informed consent of relatives, a piece of spleen was obtained from cadaveric organ donors and the splenocytes were isolated and cryopreserved for later use. Single intraperitoneal injections of 5-100 x10(6) splenocytes were performed into SCID/beige mice. Reconstitution of a human immune system was monitored weekly by the presence of human cells and IgG in peripheral blood. The mice were sacrificed 4 weeks after the injection and the engraftment in lymphoid organs was studied. A reproducible reconstitution was obtained with intraperitoneal injection of 30-40 x10(6) spleen cells. Human T, B and NK cells as well as human IgG were present in peripheral blood. In lymphoid tissues, the same lymphocytic subpopulations were detected and in addition some antigen presenting cells. The reconstitution was functional because graft rejection was observed after transplantation of human allogeneic tissues. When less than 30 x10(6) cells were injected, the reconstitution was variable. When more than 40 x10(6) cells were injected, GVHD occurred with increasing frequency. In conclusion, we show that intraperitoneal injection of 30-40 x10(6) human splenocytes into SCID/beige mice induces a quick and functional engraftment of human T, B and NK cells with no risk of GVHD. This model may be used to study human transplantation immunobiology in vivo.

A novel small animal model for HIV-1 infection

Lethally irradiated normal BALB/c mice, reconstituted with murine SCID bone marrow and engrafted with human PBMC (Trimera mice), were used to establish a novel murine model for HIV-1 infection. The Trimera mice were successfully infected with different clades and primary isolates of T- and M-tropic HIV-1, with the infection persisting in the animals for 4-6 wk. Rapid loss of the human CD4+ T cells, decrease in CD4/CD8 ratio, and increased T cell activation accompanied the viral infection. All HIV-1 infected animals were able to generate both primary and secondary immune responses, including HIV specific human humoral and cellular responses. In addition to testing the efficacy of new antiviral compounds, this new murine HIV-1 model may be used for studying host-virus interactions and, most importantly, for screening and developing potential HIV-1 protective vaccines and adjuvants (Ayash-Rashkovsky et al., http://www.fasebj.org/cgi/doi/10.1096/fj.04-3185fje; doi:10.1096/fj.04-3185fje.).

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.

Engraftment and dissemination of T lymphocytes from primary haemophagocytic lymphohistiocytosis in scid mice

Although primary haemophagocytic lymphohistiocytosis (HLH) is a genetic disorder of T lymphocytes, it remains unclear why T lymphocytes of primary HLH patients preferentially infiltrate the central nervous system and peripheral blood, in addition to the reticuloendothelial systems. We engrafted Herpesvirus saimiri (HVS)-immortalized T-lymphocyte lines established from primary HLH patients into severe combined immunodeficient (scid) mice and examined their capacity to infiltrate mouse organs. A diffuse infiltration of human T lymphocytes was detected in each organ of scid mice treated with 1 x 10(6) T lymphocytes from all four primary HLH patients assessed, whereas no infiltration of T lymphocytes from healthy individuals was observed in any organ. The infiltration of T lymphocytes was mainly observed in the lung, brain and peripheral blood, in association with haemophagocytosis. These cells were positive for HLA-DR, CD3 and either CD8 or CD4, but negative for CD68. Certain markers of proliferation and apoptotic activities were highly positive in these cells. There was no difference between the infiltration pattern of T lymphocytes of primary HLH patients with a perforin deficiency and those without. By Southern blot analysis, T lymphocytes infiltrating mouse organs were observed to be polyclonal. These findings suggest that our murine model implementing HVS-immortalized human T lymphocytes is suitable to clarify the pathogenesis of primary HLH.

Development and characterization of anti-idiotype based peptide and DNA vaccines which mimic the capsular polysaccharide of Neisseria meningitidis serogroup C

Anti-idiotypic antibodies and peptides which mimic antigens may offer an alternate strategy for converting a thymus-independent (TI) antigen to a thymus dependent (TD) antigen. We have developed an anti-idiotype based peptide mimic of the capsular polysaccharide of N. meningitidis serogroup C (MCPS) which induces a T-dependent protective immune response in mice. Subsequent studies have demonstrated that immunization of severe combined immunodeficient mice reconstituted with human B cells respond to immunization with the MCPS peptide mimic with bactericidal anti-polysaccharide directed antibody response. We hypothesized that administration of a DNA vaccine resulting in endogenous expression of this carbohydrate peptide mimic would induce anti-MCPS antibodies.

Functional human IgE specific for Dermatophagoides farinae antigen is produced in SCID mice reconstituted with peripheral mononuclear cells derived from healthy persons and patients with asthma

BACKGROUND

Whether normal peripheral blood mononuclear cells (PBMCs) transferred to severe combined immunodeficient (SCID) mice produce specific IgE remains unclear.

METHODS

Mice received injections of Dermatophagoides farinae antigen (Df)-stimulated PBMCs from healthy persons (IgE RAST score of 0).

RESULTS

High titers of Df-specific IgE were detected. The Df-specific IgE activity produced was comparable to or higher than that produced by cells from patients with asthma although the time to maximal production was longer. IgE derived from PMBCs of healthy persons or patients with asthma induced histamine release from cultured human basophils that had been stimulated with Df antigen or an anti-IgE antibody. Treatment of Df-stimulated PBMCs with a high dose, but not a low dose, of interleukin-4 stimulated production of Df-specific IgE by PMBCs from healthy persons or patients with asthma. In contrast, intravenous injection of IFN-gamma into reconstituted SCID mice decreased Df-specific IgE production by PBMCs from patients with asthma. In PMBCs from healthy persons, IgE class-switching may occur later and block the effects of treatment with IFN-gamma.

CONCLUSIONS

PBMCs from healthy persons and persons with asthma have clones reactive to allergen and produce functional IgE specific for relevant antigens in mite-sensitive bronchial asthma.

Induction of strong hepatitis B virus (HBV) specific T helper cell and cytotoxic T lymphocyte responses by therapeutic vaccination in the trimera mouse model of chronic HBV infection

Humanized BALB/c mice (termed trimera mice) conditioned by lethal total body irradiation and bone marrow transplantation from SCID mice have been described to support rapid engraftment of human peripheral blood mononuclear cells (PBMC) and the induction of strong B and T cell responses after immunization in vivo. Moreover, these mice can be infected with the hepatitis B and C viruses (HBV, HCV). The current study employed this model to study therapeutic vaccination approaches against the HBV. Thus, strong primary Th cell responses against the HBV core (HBc) and the Borrelia burgdorferi control antigen were induced by transfer of antigen-loaded dendritic cells together with autologous PBMC from HBV-naive donors as well as by vaccination with high doses of antigen or a DNA plasmid encoding for HBcAg. Moreover, primary peptide-specific CTL responses against the immunodominant epitope HBc(18 - 27) were induced by HBc particle or DNA vaccination of chimera engrafted with HBV-naive PBMC. Finally, strong HBc-specific Th cell and antibody responses were induced by HBc or DNA vaccination of mice reconstituted with PBMC from a chronic HBV patient. Thus, since HBc represents the immunodominant antigen in self-limited HBV infection, HBc particles or DNA vectors are good candidates for therapeutic vaccination, that will be further studied in our model and clinical studies.

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.

The novel human IgE epsilon heavy chain, epsilon tailpiece, is present in plasma as part of a covalent complex

Several splice variants of the secreted human epsilon heavy chain have previously been identified by reverse transcription-PCR. The heavy chain of one isoform, IgE tailpiece, differs from the originally identified IgE, IgE classic, by the replacement of the 2 carboxy-terminal amino acids by 8 novel amino acids including a carboxy-terminal cysteine residue. Recombinant human epsilon tailpiece and epsilon classic heavy chains were expressed and secreted as H2L2 monomers in Sp2/0 murine myeloma cells. We have investigated the in vitro function and in vivo occurrence of epsilon tailpiece heavy chains using receptor binding assays, granule release assays, flow cytometry, half-life studies, immunoprecipitation, SDS-PAGE, two-dimensional SDS-PAGE, and Western blotting. IgE tailpiece and IgE classic exhibited similar in vivo half-lives in BALB/c mice, bound the human high- and low-affinity IgE receptors with similar affinities and triggered equivalent levels of high affinity IgE receptor induced degranulation. In humans, IgE classic is present as a 190 kD circulating protein in vivo. In contrast, we found that in plasma epsilon tailpiece was primarily present as part of covalent complexes of approximately 300 and 338 kD. Dissociation of the complexes revealed that two species of epsilon tailpiece heavy chains were present therein and surprisingly, these in vivo derived epsilon tailpiece heavy chains were approximately 5 and 10 kD smaller than the recombinant expressed epsilon tailpiece or epsilon classic heavy chains. These results show that epsilon tailpiece is present in novel covalent complexes in humans.

Human adult tonsil xenotransplantation into SCID mice for studying human immune responses and B cell lymphomagenesis

OBJECTIVE

To generate a human-mouse xenochimeric model where human cells remain clustered in the animal to optimize their interactions and recovery.

MATERIALS AND METHODS

Severe combined immune deficient mice (SCID) were xenografted subcutaneously with human adult tonsil pieces (hu-ton-SCID mice). Such animals were: (a) compared with those receiving tonsil cells in suspension, and (b) immunized with de novo and recall antigens.

RESULTS

Human tonsil pieces survived a long period of time in SCID mice, while polyclonal human T- and B-lymphocytes persisted in close vicinity within the implantation area; however, little or no graft-versus-host disease was detectable. Not surprisingly, local development of lymphoproliferative disease was often observed in animals receiving lymphoid implants from donors previously infected by the Epstein-Barr virus. One month after surgery, higher serum levels of human IgG were found in SCID mice transplanted with tonsil pieces (2x10(7) cells/animal) than in animals injected with 5x10(7) tonsil cells in suspension (1.9 vs. 0.3 mg/mL, p < 0.002). Importantly, the production of human IgG in hu-ton-SCID mice remained polyclonal for at least 6 months and was linked to the presence of cells within the implants. Immunization of hu-ton-SCID mice with hepatitis B core, a de novo antigen, did not produce a significant IgG immune response; however immunization with tetanus toxoid (TT), a thymus-dependent recall antigen, yielded high (> 700-fold increase in anti-TT IgG levels) and long-lasting (> 6 months) secondary immune responses.

CONCLUSION

The hu-ton-SCID mouse xenochimeric model described in this report may improve our understanding of human lymphoid cell interactions, secondary immune responses, and lymphomagenesis.

Long term substitution and specific immune responses after transfer of bovine peripheral blood lymphocytes into severe combined immunodeficient mice

The long term immune responsiveness of bovine peripheral blood lymphocytes engrafted into severe combined immunodeficient mice (bovine PBL SCID mice) was analyzed. After intraperitoneal transfer (i.p.) of 2x10(7) bovine PBL into SCID mice, FACS analysis revealed successful engraftment of bovine CD4 and CD8+ T cells in the peritoneal cavity, the peripheral blood, spleen, lymph nodes, bone marrow, and thymus of reconstituted mice for up to 13 weeks. As shown by immunocytochemistry in sections of spleens from SCID mice 16 weeks after substitution, bovine T and B cells were localized perivasculary forming pseudofollicular structures. Nevertheless, histopathology of spleen and liver from bovine PBL SCID mice revealed pathological alterations indicating rejection of xenogenic cells or graft versus host disease (GVHD). On the functional level, i.p. transfer of bovine PBL into SCID mice induced increasing levels of bovine IgM and IgG in the sera of recipients. Bovine Ig could be detected up to 20 weeks. Immunization of SCID mice reconstituted with PBL of normal donors with dinitrophenol (DNP)-edestin induced a weak specific bovine antibody response in recipient mice. In contrast, a secondary specific bovine IgG response was observed after antigen restimulation of SCID mice reconstituted with PBL from calves preimmunized either with DNP-edestin or keyhole limpet hemocyanin (KLH) showing functional T cell-independent and -dependent antibody responses of bovine PBL SCID mice. Our data demonstrate that transfer of bovine PBL into SCID mice leads to a long term engraftment of bovine cells in lymphatic and non-lymphatic organs inducing a functional substitution of T and B cell immune response of SCID mice. Therefore, bovine PBL SCID chimera can serve as a small animal model for the analysis of bovine lymphopoiesis and infectious diseases of cattle.

Human immune response to a peptide mimic of Neisseria meningitidis serogroup C in hu-PBMC-SCID mice

An anti-idiotype-based peptide mimic vaccine for Neisseria meningitidis serogroup C polysaccharide (MCPS) has been developed and shown to induce a response in mice that is specific, functional, and T-dependent. In this study, the immunogenicity of the MCPS peptide mimic vaccine preparation, as a potential vaccine for use in humans, is shown using the hu-PBMC-SCID mouse model. The human antibody response to the MCPS peptide mimic vaccine is specific and functional as shown by inhibition enzyme-linked immunoadsorbent assay (ELISA) and bactericidal assay. These data support the usefulness of the peptide mimic vaccine strategy for humans.

Antigen-specific B and T cells in human/mouse radiation chimera following immunization in vivo

Adoptive transfer of human peripheral blood mononuclear cells (PBMC) into mice with severe combined immunodeficiency (SCID) or into lethally irradiated BALB/c mice radioprotected with SCID bone marrow, leads to marked engraftment of human T and B cells. In such chimeras, human serum antibody responses can be stimulated readily by vaccination with recall antigens, but the detection of antigen-specific functional T or B cells has been extremely difficult. In the present study, we were able to detect by Elispot analysis high frequencies of immunoglobulin G (IgG)-secreting B cells and mitogen-responsive interferon-gamma (IFN-gamma) or interleukin-4 (IL-4)-secreting T cells in peritoneum and spleen of human/BALB/c chimeric mice during the first 3 weeks after PBMC transfer. Moreover, specific memory responses were elicited by vaccination with tetanus toxoid (TT) or hepatitis B virus (HBV) surface (HBs) antigen of chimeric mice transplanted with PBMC derived from TT- or HBV-immune donors. Substantially higher TT-specific B-cell frequencies were found during the first 3 weeks after vaccination in mice challenged with the specific antigen compared to the levels found in control animals. High numbers of TT-specific IFN-gamma-secreting T cells persisted in the peritoneum of vaccinated, but not of unvaccinated, animals during the entire observation period, but only low numbers of specific IL-4-secreting T cells were found in vaccinated mice. Similar results were achieved following vaccination with HBs antigen of chimeric mice, transplanted with PBMC of HBV immunized donors. Thus, TT or HBsAg-specific antibody responses in our model correlate closely with the existence of specific IFN-gamma-secreting T helper 1/0 cells. Furthermore, these results show that adoptive transfer of human PBMC into lethally irradiated mice provides an efficient approach to generate specific B-cell fusion partners for the production of human monoclonal antibodies and specific T-cell lines for adoptive cell therapy of malignant or infectious diseases.

Clonal dissemination of T-lymphocytes in scid mice from familial hemophagocytic lymphohistiocytosis

BACKGROUND

Although familial hemophagocytic lymphohistiocytosis (FHL) has been considered a disorder of T-cell dysfunction, there is no evidence of the clonal origin of T-cells in this disease.

PROCEDURE

We engrafted mononuclear cells (MNCs) from five FHL patients into scid mice and examined the infiltration of human cells in mouse organs. The characterization of human cells that infiltrated in the mouse organs was then performed.

RESULTS

A diffuse infiltration of human lymphoid cells was detected in scid mice treated with 1 x 10(6) MNCs from one of the five patients. These cells were positive for HLA-DR and CD3, but negative for CD4, CD8, CD20, and CD68, suggesting the infiltration of double negative (DN) T-cells. The MNCs from the other four patients induced murine lymphoma-like disease; T-cell lymphoma in one and lymphoma of unknown origin in three. The characterization of these human DN T-cells was performed. The analysis of the Vbeta repertoire showed no preferential usage of the Vbeta family in MNCs, while the dominant expression of Vbeta13 was detected in T-cells infiltrating in the spleen and lung. A Jbeta analysis showed the restricted usage of Jbeta1.2 for Vbeta13 in these cells, and the clonality of Vbeta13-Jbeta1.2 fragment was confirmed by a single-strand confirmation polymorphism analysis. The analysis of the Valpha repertoire showed that Valpha24 was exclusively used in these DN T-cells, but no usage of JalphaQ for Valpha24 was observed.

CONCLUSIONS

A clonal expansion of T-cells was induced in scid mice by the engraftment of MNCs from an FHL patient. The infiltration of DN alphabeta T-cells bearing invariant Valpha24 T-cell receptor in mouse organs may provide a useful clue to the pathogenesis of FHL. In the patients whose MNCs induced murine lymphoma-like disease, some cytokines or unknown factors that stimulate the growth and the tumorigenicity of murine lymphocytes might be produced by the MNCs engrafted in scid mice. Further study is needed to confirm the validity of our experimental approach and the findings observed in scid mice by using more FHL samples.

Engraftment of myasthenia gravis thymocytes into severe combined immunodeficiency (SCID) mice

To study the human immune system, thymocytes from myasthenia gravis (MG) patients were transferred into the peritoneal cavity of severe combined immunodeficiency (SCID) mice, which caused the mice to produce human IgG and IgM. The injected thymocytes were then recovered from the peritoneal cavities of MG-SCID mice. The recovered thymocytes were CD3+ or CD20+ human cells expressing the MHC class II molecule. AChR-specific T cell lines were also recovered from peritoneal cells of the mice. These cells were made up of helper T (CD3+ CD4+ CD8- CD20- HLA-DR+), suppressor T (CD3+ CD4- CD8+ CD20- HLA-DR+), and probably NK cells (CD3- CD4- CD8- CD20- HLA-DR+). Therefore, the functional human T and B cells survived in the SCID mice for a long period. SCID mice may provide a unique tool in the study of human cell immunity by creating more congenial physiological conditions than conventional culture systems, and by providing an animal model of the human immune system.

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.

Primary Th1 Cell Immunization Against HIVgp160 in SCID-hu Mice Coengrafted with Peripheral Blood Lymphocytes and Skin

SCID-hu mouse models are of interest in the pathologic investigation of HIV infection, but obtaining a T cell response in SCID-hu-PBL mice is still controversial. We have developed a SCID model by engrafting human skin and autologous PBLs from HIV-seronegative individuals. The study describes the ability of this human-mouse chimera to generate in vivo a primary T lymphocyte response against HIV Ag. The injection of human autologous PBLs was performed 4 to 5 wk after the skin engraftment. Two weeks after injection of PBLs, chimeric mice were immunized with recombinant canary pox virus expressing HIV-1 LAIgp160 (vCP-LAIgp160) and supplemented or not with rIL-2. Intradermal vCP-LAIgp160 injection induced an intradermal perivascular human lymphocytic infiltrate and an epidermic network of CD1a+, CD80+, and CD86+ cells. We derived CD4+ T cell lines (STLs) from the human skin graft of immunized mice, showing that STLs mediated an MHC class II-restricted cytolytic activity directed against HIV-LAIgp160 Ags. Cytokine gene expression in both human skin cells and in STLs showed a predominance of IL-2, IFN-γ, and IL-12 transcripts. Finally, the T cell repertoire analysis using the immunoscope technique showed a very limited CDR3 length polymorphism in the skin infiltrating lymphocytes suggesting an Ag-specific repertoire. The ability to induce a primary Th1 cell response in vivo affords a useful preclinical model for testing vaccine strategies.

Human IgE production in hu-PBL-SCID mice injected with birch pollen and diesel exhaust particles

Mice with severe combined immunodeficiency were transplanted with human peripheral blood lymphocytes (hu-PBL-SCID mice). The response to immunisation with birch pollen was used to study possible effects of diesel exhaust particles (DEP) and aluminium hydroxide (Al(OH)3) on human IgE production in this human in vivo model. The adjuvants were well tolerated, as determined by the number of human cells in the peritoneal cavity at the end of the experiments. Total and birch pollen-specific IgE was detected in 76 and 41% of the mice, respectively. In the present experiments where the mice were stimulated early with birch pollen, a doubling in percentage of hu-PBL-SCID mice with production of specific IgE was observed, as compared to later stimulation used in previous experiments. Although a tendency to higher total IgE levels was observed after treatment with DEP, no statistically significant adjuvant effect of DEP or Al(OH)3 could be demonstrated. Electron microscopy analysis after immunogold labelling showed that the major birch pollen allergen Bet v I was released from the pollen grains and adsorbed to the surface of the DEP. Early stimulation with allergen appears to be important for optimal production of specific IgE in the hu-PBL-SCID model. However, our results show that further improvements are needed in order to demonstrate the expected effects from adjuvants and environmental pollutants.

Lymphoproliferative Disease in Human Peripheral Blood Mononuclear Cell-Injected SCID Mice. IV. Differential Activation of Human Th1 and Th2 Lymphocytes and Influence of the Atopic Status on Lymphoma Development

Intraperitoneal transfer of PBMC from EBV+ donors into SCID mice leads to high human Ig levels in mouse serum and B cell lymphoproliferative disease. As these events depend on the activation of coinjected human T cells, we addressed the behavior of the Th1 and Th2 subsets in this model. Production of IFN-γ, but not of Th2 cytokines such as IL-4, was detected in culture supernatants of PBMC stimulated in vitro with mouse splenocytes. Moreover, anti-CD3 stimulation of the human cells recovered from mice brought about IFN-γ, but not IL-4, synthesis; on the other hand, PCR and in situ hybridization analysis of ex vivo-recovered cells disclosed the presence of mRNA for both cytokines following in vitro restimulation, thus suggesting post-transcriptional regulation of IL-4 gene expression. When SCID mice were inoculated with PBMC from atopic donors, whose Th1/Th2 profile displays an imbalance toward Th2 cells, tumor development rates were lower, and tumor latency was higher, compared with those in mice injected with PBMC from normal donors. Isotypic analysis of human Ig in mouse serum showed the exclusive presence of IFN-γ-driven IgG subclasses; in addition, human IgE were low or undetectable in most cases. These findings indicate that following transfer into SCID mice, human Th1 lymphocytes undergo preferential activation, whereas Th2 function is down-regulated. Th1 lymphocytes probably are a major component in promoting EBV+ B cell expansion and tumor development; the individual Th1/Th2 profile could in part account for the as yet unexplained donor variability in tumor generation in this experimental model.

Human monoclonal antibodies specific to hepatitis B virus generated in a human/mouse radiation chimera: the Trimera system

An approach to develop fully human monoclonal antibodies in a human/mouse radiation chimera, the Trimera system, is described. In this system, functional human lymphocytes are engrafted in normal strains of mice which are rendered immuno-incompetent by lethal total body irradiation followed by radioprotection with severe combined immunodeficient (SCID) mouse bone marrow. Following transplantation, human lymphocytes colonize murine lymphatic organs and secrete human immunoglobulins. We have established this system as a tool to develop fully human monoclonal antibodies, and applied it for the generation of monoclonal antibodies specific for hepatitis B virus surface antigen. A strong memory response to hepatitis B surface antigen was elicited in Trimera engrafted with lymphocytes from human donors positive for antibodies to hepatitis B surface antigen. The human specific antibody fraction in the Trimera was 10(2)-10(3)-fold higher as compared with that found in the donors. Spleens were harvested from Trimera mice showing high specific-antibody titres and cells were fused to a human-mouse heteromyeloma fusion partner. Several stable hybridoma clones were isolated and characterized. These hybridomas produce high-affinity, IgG, anti-hepatitis B surface antigen antibodies demonstrating the potential of the Trimera system for generating fully human monoclonal antibodies. The biological function and the neutralizing activity of these antibodies are currently being tested.

Frequency of human anti-FVIII antibodies in humanized SCID mice elicited by recombinant deleted factor VIII and by a plasma derived factor VIII

SCID mice were grafted with human PBL (hu-PBL-SCID) from healthy or haemophilia A donors. Those containing human and no murine Ig in their plasma, were injected with 100 U VIII:Ag of a plasma derived (pd) FVIII or recombinant deleted Factor VIII (FVIII deltaII) and with 10 microg of tetanus toxoid as control immunogen. The frequency and the intensity of the humoral specific responses were measured in 253 mice humanized with PBL from 13 different donors. There was no significant difference in the frequency or intensity of the anti-FVIII immune responses to pd FVIII and FVIII deltaII. Neutralizing antibodies were only detected in the plasma of mice humanized with cells from haemophiliacs having FVIII inhibitors in their blood. The immune responses observed in hu-PBL-SCID mice correlated with the immune status of the corresponding human donor.

In vivo but not in vitro stimulations rescue of the defective class switching to IgG or IgA in B-cells of immunodeficiency with hyper IgM

In an X-linked immunodeficiency with hyper IgM (X-HIM), several mutations of genes coding for CD40 ligand are responsible for B-cell defects. However, it is controversial whether the defective class switching from IgM to IgG or IgA but not IgE is rescued by in vitro stimulations or not. In six X-HIM patients, signaling through CD40 induced IgE but not IgG or IgA secretion in vitro. When transferred into SCID mice, however, B-cells of X-HIM patients secreted as much IgG and IgA as those of healthy controls. Moreover, sIgG and sIgA expressions were also induced by the in vivo stimulation. These results support that B-cells of X-HIM patients are defective of in vitro class switching from IgM to IgG or IgA and show that the in vivo stimulations rescue the defective class switching and suggest that the class switching of IgE and that of IgG or IgA might be regulated quite differently.

Human peripheral blood leukocyte-reconstituted severe combined immunodeficient mouse: analysis of the human immune response against porcine islet transplantation

Human peripheral blood leukocyte (PBL)-reconstituted severe combined immunodeficient (SCID) mice (Hu-PBL-SCID) were used as a model to study xenograft rejection in humans. SCID mice were reconstituted with human PBL using a protocol that included a booster injection with anti-human CD3 antibody-primed cells. This protocol enhanced chimera establishment in SCID mice and resulted in the detection of higher levels of human Ig when compared with SCID mice receiving unprimed PBL alone. Human xenoreactive natural antibodies (XNA), both IgM and IgG subtypes, which recognized porcine islets (PI), were detected in sera of Hu-PBL-SCID by cytofluorometric analysis. Pretreatment of porcine cells with GS-IB4 lectin inhibited the XNA binding, demonstrating the specificity of the XNA from Hu-PBL-SCID. Western blot analysis showed that XNA from normal human serum and Hu-PBL-SCID serum recognized similar xenoantigens on PI, indicating that Hu-PBL-SCID contained a XNA repertoire representative of normal human serum. Immunofluorescent staining of the tissue sections revealed that both human IgG and IgM bound in vivo to the PI engrafted beneath the kidney capsule of Hu-PBL-SCID. In addition, mouse complement (C3) was detected on xenografted PI. The function of xenografted islets were monitored by measuring porcine insulin concentration using a radioimmunoassay. Porcine insulin concentration in the sera of both Hu-PBL-SCID and plain SCID xenografted with PI was similar for up to 14 days after transplantation, after which the insulin levels in Hu-PBL-SCID decreased, thereby indicating rejection. Therefore, PI transplanted into the Hu-PBL-SCID should be a useful model for the study of cellular as well as acquired humoral immune response against xenoislets.

A Model for Human B-Chronic Lymphocytic Leukemia in Human/Mouse Radiation Chimera: Evidence for Tumor-Mediated Suppression of Antibody Production in Low-Stage Disease

B-chronic lymphocytic leukemia (BCLL) is a lymphoproliferative disease that is characterized by clonal expansion of CD5+ B cells. BCLL is associated with secondary immunodeficiency and hypogammaglobulinemia. It has been suggested that T-cell dysregulation may play a role in the hypogammaglobulinemia and in the increased incidence of autoimmunity in BCLL patients. We attempted to transfer human peripheral blood mononuclear cells (PBMC) from BCLL patients in different stages of the disease into immunodeficient mice. PBMC from BCLL patients in stage 0, stages I to II, and stages III to IV were transplanted into the peritoneal cavity of lethally irradiated Balb/c or beige/nude/Xid (BNX) mice radioprotected with bone marrow (BM) from severe combined immunodeficiency (SCID) mice. Different engraftment profiles were found in the chimeric mice 2 weeks after transplantation of PBMC according to the disease stage of the BCLL donors. Infusion of PBMC from donors in stage 0 led to marked engraftment of human T cells, whereas the human tumor cells could hardly be detected. In contrast, chimeric mice receiving PBMC from patients in stage III to IV disease exhibited engraftment with a dominance of tumor cells, compared with a miniscule level of T cells. The ability of the engrafted cells to produce human Ig was also found to be correlated with the disease stage of the donor, although all donors had the same magnitude of hypogammaglobulinemia. Total human Ig production in the chimeric mice was normal in mice receiving PBMC from donors in stage 0, whereas in chimeric mice engrafted with PBMC from donors in stages III to IV almost no human Igs could be detected. This differential reconstitution of antibody production in the mouse model according to the stage of the patient's disease will allow further studies on possible cellular interactions between malignant and immune cells in BCLL.

Human peripheral blood lymphocyte-reconstituted, severe combined immunodeficient mice as a model for porcine islet xenograft rejection in humans

Previously we established human peripheral blood lymphocyte-reconstituted severe combined immunodeficiency (SCID) (hu-PBL-SCID) mice as a model for human islet allograft rejection. The function of xenografted hu-PBL was confirmed to reject human alloislets in hu-PBL-SCID mice. In this study, we modified this model as a porcine islet xenograft to study porcine islet rejection in humans. Chimeric mice were used as the recipients of porcine islets to reveal the mechanisms of xenograft rejection in humans. SCID mice were reconstituted with 30 x 10(6) of hu-PBL initially, and 10 x 10(6) of antihuman CD3-primed PBL was injected intraperitoneally 2 days later as a booster. An additional booster injection provided greater possibility (86.7%, n = 15) of chimera establishment as well as a higher human immunoglobulin concentration in SCID mice than the single injection group. In an in vitro assay, sera from hu-PBL-SCID mice were found to recognize porcine islets by FACS staining. In an in vivo study, immunofluorescent analysis of a frozen section showed that human immunoglobulins adhered to the xenografted porcine islet under the kidney capsule of hu-PBL-SCID mice. Although no mouse immunoglobulins were detected on sections, mouse complement (C3) was shown to adhere to the xenografted porcine islet. Thus, hu-PBL-SCID mice provide a useful model for investigating the real-life situation of porcine islet xenograft rejection in humans.

An in vivo model of allergic inflammation: pulmonary human cell infiltrate in allergen-challenged allergic Hu-SCID mice

CB.17 severe combined immunodeficient (SCID) mice were used to establish a model of allergic pulmonary inflammation. SCID mice were intraperitoneally reconstituted with 10(7) peripheral blood mononuclear cells (PBMC) from patients sensitive to Dermatophagoides pteronyssinus (Dpt) and 2 weeks later were exposed to Dpt aerosols. After Dpt nebulization, SCID mice engrafted with PBMC from Dpt-sensitive patients developed a specific human IgE response as well as an intense pulmonary infiltrate of human cells. In contrast, SCID mice reconstituted with PBMC from patients allergic to grass pollen or from non-allergic donors failed to produce IgE or to exhibit a similar inflammatory response. The level of the IgE production was dependent on the IgE level of the allergic donor. In the lungs of the same allergic SCID mice, 2 months after Dpt inhalation, the cell infiltrate contained CD45+, CD45RO+, CD20+ and HLA-DR+ human cells. They were located in perivascular and peribronchial areas and disseminated in the mouse lung parenchyma. Moreover, mRNA IL-5+ cells and eosinophils were found in peribronchial infiltrates. The observations indicate that humanized allergic SCID mice may develop, after nebulization with the relevant allergen, immune reactions similar to those observed in man and suggest that SCID mice may represent a useful model to analyze the regulatory mechanisms of IgE-associated allergic diseases.

Biochemical and functional characterization of xenoreactive natural antibodies in hu-PBL-SCID mice

An in vivo model system to understand the mechanism of xenograft rejection was established using human peripheral blood leukocyte-reconstituted SCID (hu-PBL-SCID) mice. Human xenoreactive natural antibodies (XNA), of IgM and IgG subtypes, capable of binding to pig aortic endothelial cells (PAEC) were detected in the sera of hu-PBL-SCID by ELISA and flowcytometric methods. Western blot analysis of PAEC lysates showed that IgM and IgG XNA from hu-PBL-SCID recognized xenoantigens with similar molecular mass as those recognized by XNA from normal human serum (NHS). This result demonstrated that hu-PBL-SCID contained XNA representing the same repertoire as that of the NHS. XNA from NHS and hu-PBL-SCID were also able to induce intracellular Ca2+ signals in cultured PAEC several fold above the basal level. This result revealed their functional similarity and demonstrated for the first time that XNA in the absence of C can activate PAEC, which may lead to the pathology of xenograft rejection. In vivo, PAEC transplanted under the kidney capsule of hu-PBL-SCID mice showed deposition of human IgM and mouse C. In summary, the present study demonstrates that hu-PBL-SCID can serve as a useful model to characterize innate immunity against xenograft.

Immune deficiency in SCID mice

Since the discovery of SCID mice in 1983, numerous studies utilizing these mice were carried out. These investigations can be classified into two major groups. First, the analysis of the immune defect has revealed defective V(D)J recombination and defective DNA double-strand break repair, and has lead to the identification of the candidate gene for SCID mice. Second, the use of SCID mice to explore ways to introduce a murine or xenogeneic immune system into SCID mice by taking advantage of the immune deficiency of the mice has provided an animal model to examine the in vivo function of transferred human or murine immune cells. In this review, we summarize the recent advances made in these two areas of SCID mouse research.

Human recombinant interleukin-4 (HurIL-4) improves SCID mouse reconstitution with human peripheral blood lymphocytes

The application of human-scid mouse chimera (hu-scid) technology has some limitations, because of the variable amounts and functional heterogeneity of human cells recovered from engrafted mice. Attempts to optimize the construction of hu-scid chimeras with human peripheral blood mononuclear cells (Hu-PBMC) by using in vivo anti-asialo GM1 antibody treatment in mice in order to eliminate natural killer cells have been published by other authors with interesting results. In this study, Hu-PBMC were incubated in vitro with human recombinant interleukin-4 (HurIL-4) or human recombinant interleukin-2 (HurIL-2) for two hours and were intraperitoneally transferred into scid mice. Total human IgM and IgG levels in hu-scid sera, human cell markers in the thymus and in the spleen of grafted mice were considered as parameters of successful engraftment. HurIL-4 significantly enhanced human immunoglobulin production while HurIL-2 did not show any obvious effect. Human cell markers (CD2 and CD19) were significantly higher in the group of HurIL-4 treated Hu-PBMC than in the other groups, despite the high variability in human cell proliferation in the recipients. Thus, HurIL-4 can be used as an adjuvant growth factor which improves successful engraftment of human peripheral blood lymphocytes in scid mice.

Engraftment and humoral immunity in SCID and RAG-2-deficient mice transplanted with human peripheral blood lymphocytes

SCID and RAG-2 deficient mice were transplanted intraperitoneally with human peripheral blood lymphocytes (hu-PBL-SCID and hu-PBL-RAG mice). Seven days after transplantation the mice were immunized with a pneumococcal polysaccharide vaccine. Flow cytometry analysis of cells from the peritoneal cavity and the spleen after 8-10 weeks revealed that human cells had more limited engraftment in RAG than in SCID recipient mice, and that more human cells were found in the spleen than in the peritoneal cavity. Functionality of the human cells recovered from these two locations was explored by the counting of human immunoglobulin secreting cells (hu-ISC). A total of 83% of the hu-PBL-SCID mice and 29% of the hu-PBL-RAG mice had detectable hu-ISC in the peritoneal cavity and/or the spleen. The kinetic profiles of human immunoglobulins in the mouse sera during the experiment showed donor dependency. More than 90% of the hu-PBL-SCID mice had detectable levels of human IgG, IgM and IgA, while 78% had detectable levels of IgE, whereas detectable levels of IgG, IgM, IgA and IgE were measured in 37%, 64%, 68% and 23% of the hu-PBL-RAG mice, respectively. Forty-seven per cent of immunized hu-PBL-SCID mice showed a human antipneumococcal IgG level that was significantly above the background level in non-immunized mice, while none of the hu-PBL-RAG mice produced any detectable levels of human antipneumococcal IgG. In short, human PBL showed a better engraftment and a better antibody response when transplanted into SCID mice than into RAG mice.

The human immune system in hu-PBL-SCID mice

Severe combined immunodeficiency (SCID) mice can be stably grafted with human peripheral blood lymphocytes, creating hu-PBL-SCID chimeras; essentially, these are mice with a human immune system. Here, Magdalena Tary-Lehmann, Andrew Saxon and Paul Lehmann discuss the immunobiology of these chimeras. The authors propose that hu-PBL-SCID chimerism evolves in two phases. During the first three weeks after grafting, many of the injected cells survive and the human immune system is functional. Subsequently, anti-mouse-reactive clones are selected and the immune system becomes nonfunctional. The implications of this scenario for the utilization of the hu-PBL-SCID model are discussed.

Enhancement of specific immunoglobulin production in SCID-hu-PBL mice after in vitro priming of human B cells with superantigen

Priming of human mature B cells in vitro with staphylococcal enterotoxin A (SEA) prior to transplantation of the B cells into severe combined immunodeficiency (SCID) mice, together with human T-helper cells, resulted in higher and more uniform concentrations of serum IgG in the mice. This indicated that a large number of B cells had become activated, which was supported by the finding that SEA priming resulted in production of immunoglobulin displaying a more normal kappa/lambda ratio than was obtained in the absence of SEA priming. However, IgM concentrations were not affected by SEA priming. Immunization of mice, transplanted with SEA-primed B cells, with both primary and secondary antigens resulted in a high specific IgG response to both types of antigen. The elevated levels of specific antibodies were not merely the consequence of an unspecific stimulation of B cells caused by SEA, as the ratio of specific antibody to total IgG was much higher in animals receiving SEA-primed B cells. Thus, a co-operative effect on immunoglobulin production of stimulating B cells via surface immunoglobulin and help delivered by SEA-activated T-helper cells was indicated. A specific antigen-dependent IgM response to a secondary antigen was observed as well, but was, in contrast to the IgG response, not influenced by SEA priming of B cells. No IgM antibodies with reactivities to the primary antigens were detected in the SCID sera at any time-point after immunization. The results thus indicate that SEA might replace T-cell epitopes in antigens and efficiently recruit an abundance of T-cell help to B cells, resulting in enhanced production of specific IgG antibodies.

A human monoclonal antibody to a human self-antigen, CD2 derived from human peripheral blood lymphocytes engrafted in SCID mice

To establish human hybridoma lines, production of human immunoglobulin (Ig) and behavior of the implanted human peripheral blood lymphocytes (PBL) were characterized in severe combined immunodeficiency (SCID) mice. Human PBL from healthy donors were injected into the peritoneal cavity of SCID mice, and they were immunized with self-antigen, CD2. CD45+ cells (human PBL) migrated to lymphoid tissues in the mice as early as 4 days, accounting for more than half the lymph node cells and thymocytes. The number of cells releasing human IgG specific to the antigen increased 3.5 weeks after immunization without the usual constraint that production of the IgG, an autoantibody, is prohibited by immunological tolerance in humans. Therefore, we established several human hybridomas secreting human IgG to CD2, since splenocytes and lymph node cells from the implanted SCID mice at 3.5 weeks were fused with a human B lymphoblastoid cell line. A human anti-CD2 monoclonal antibody (MAb) was confirmed to bind to natural CD2 on human T cells by flow cytometric analysis. The epitope for the MAb was identical with a portion that the ligand LFA-3 binded, so that the MAb might reduce the inflammatory reaction caused by preventing activation of human T cells. Here, we report that the human immune system could be reconstituted in SCID mice to develop human hybridomas producing human MAb to a human self-antigen.

Lol p I-specific IgE and IgG synthesis by peripheral blood mononuclear cells from atopic subjects in SCID mice

BACKGROUND

The development of an animal model representative of the in vivo situation of human atopic diseases is always of interest for a better understanding of IgE production and regulation. Along these lines, mice with severe combined immunodeficiency (SCID mice) engrafted with lymphocytes from atopic subjects might be a suitable model for such studies.

OBJECTIVE

This study aims to analyze the production of Lol p I-specific IgE and IgG antibodies in SCID mice after transplantation of human peripheral blood mononuclear cells from atopic patients sensitive to grass pollens and from nonatopic donors.

METHODS

Peripheral blood mononuclear cells were transplanted into SCID mice, which were then challenged with Lol p I, and antibody responses (IgG and IgE) were analyzed over a 6-week period.

RESULTS

Total IgG antibody was measured in each mouse serum after transplantation. Also, most mice (regardless of whether donors were atopic) that were challenged with Lol p I produced specific IgG antibody. Total IgE antibody production was observed only in mice grafted with cells from atopic patients. Lol p I-specific IgE antibodies were also produced after immunization with Lol p I. Although IgG antibody/response tended to plateau, the IgE antibody response increased until it peaked and declined thereafter. Interferon-gamma was detected in sera from mice producing IgE antibody, which supports a possible role of interferon-gamma in the decrease of IgE response.

CONCLUSION

This study suggests that the SCID mouse model could represent an interesting approach to studying specific, total IgG and IgE antibody production, and ultimately their regulation.