SCID mice in the study of human autoimmune diseases

The use of animal models in rheumatoid arthritis research

The pathological hallmark of rheumatoid arthritis (RA) is a synovial pannus that comprises proliferating and invasive fibroblast-like synoviocytes, infiltrating inflammatory cells, and an associated neoangiogenic response. Animal models have been established to study these pathological features of human RA. Spontaneous and induced animal models of RA primarily reflect inflammatory aspects of the disease. Among various induced animal models, collagen-induced arthritis (CIA) and collagen antibody-induced arthritis (CAIA) models are widely used to study the pathogenesis of RA. Improved transplantation techniques for severe combined immunodeficiency (SCID) mouse models of RA can be used to evaluate the effectiveness of potential therapeutics in human tissues and cells. This review provides basic information on various animal models of RA, including CIA and CAIA. In addition, we describe a SCID mouse coimplantation model that can measure the long-distance migration of human RA synoviocytes and cartilage destruction induced by these cells.

Humanized Mouse Models of Systemic Lupus Erythematosus: Opportunities and Challenges

Animal models have played a crucial role in the understanding of the mechanisms and treatments of human diseases; however, owing to the large differences in genetic background and disease-specific characteristics, animal models cannot fully simulate the occurrence and progression of human diseases. Recently, humanized immune system mice, based on immunodeficient mice, have been developed that allow for the partial reconstruction of the human immune system and mimic the human in vivo microenvironment. Systemic lupus erythematosus (SLE) is a complex disease characterized by the loss of tolerance to autoantigens, overproduction of autoantibodies, and inflammation in multiple organ systems. The detailed immunological events that trigger the onset of clinical manifestations in patients with SLE are still not well known. Two methods have been adopted for the development of humanized SLE mice. They include transferring peripheral blood mononuclear cells from patients with SLE to immunodeficient mice or transferring human hematopoietic stem cells to immunodeficient mice followed by intraperitoneal injection with pristane to induce lupus. However, there are still several challenges to be overcome, such as how to improve the efficiency of reconstruction of the human B cell immune response, how to extend the lifespan and improve the survival rate of mice to extend the observation period, and how to improve the development of standardized commercialized models and use them. In summary, there are opportunities and challenges for the development of humanized mouse models of SLE, which will provide novel strategies for understanding the mechanisms and treatments of SLE.

Human tonsil implants xenotransplanted in SCID mice display broad lymphocytic diversity and cellular activation profile similar to those in the original lymphoid organ

BACKGROUND

Models consisting of human immune cells in suspension transferred to severe combined immune deficient (SCID) mice have been invaluable for studying immune response, autoimmunity, and lymphomagenesis. The dissemination of human cells within the mouse body hampers immune functionality with time and favorites the development of human graft vs. mouse host (GvH) disease. To circumvent these limitations we surgically implanted tonsil pieces subcutaneously in SCID animals (hu-ton-SCID mice). Recall humoral responses was elicited and animals did not suffer from signs of GvH disease. A detailed cell subset and cell activation analysis of implants has not yet been reported.

METHODS

Implants from 86 hu-ton-SCID mice were evaluated by immunohistochemistry and flow cytometry analyses to assess human lymphoid cell subpopulation surviving with time after implantation, and to evaluate status of human cell activation.

RESULTS

B cells persist over 3 months in implants. The proportion of class and type-specific Ig+ cells varied between implants, but as a whole IgG+ cells were more abundant than IgA+, and IgM+ cells, and kappa+ cells predominated over lambda+ cells. The mean proportions of these cells resemble those in the original tonsil. Fine analysis of CD19+ B cells demonstrated no expansion of activated (CD5+, CD23+, CD69+) B cells in implants compared with tonsils, and a decrease of CD19+CD77+ B cells corresponding to a centroblastic phenotype, which is consistent with the disappearance of follicular structure in implants. Double positive CD20+CD27+ memory B cells were detected in implants by immunohistochemistry. T cell CD4+CD8-/CD4-CD8+ ratios were about 4 in implants, that is similar to those in tonsils, and there was no expansion of CD3+CD4+CD8+ and of CD3+CD4-CD8- T-cell subpopulations. T cells activation markers (CD25, CD69) were similarly expressed in implants and tonsils, and implants contained cells with a memory T cell phenotype (CD45RO). Finally cells within implants depicted a low rate of proliferation when assessed by Ki-67 expression levels.

CONCLUSIONS

Compared with original tonsils, tonsil implants in hu-ton-SCID mice lose the germinal center architecture, which is correlated with the decrease of CD77+ B cells, but conserve T and B cell subpopulation diversity, notably memory cells. In addition, implant T and B cells are not differently activated when compared with those in original tonsils and do not proliferate extensively. These observations indicate indirectly absence of GvH reaction at the cellular level in this model. Collectively, the detailed implant cellular characterization in the hu-ton-SCID model provides a strong rationale for the use of this model in the study of human recall antibody response.

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.

Tetanus toxoid-specific T cell responses in severe combined immunodeficiency (SCID) mice reconstituted with human peripheral blood lymphocytes

SCID mice reconstituted with human peripheral blood lymphocytes (PBL) have repeatedly been shown to produce antigen-specific B cell responses. We have derived tetanus toxoid (TT)-specific human T cell lines from cells of the peritoneal cavity, spleen and lymph nodes of SCID mice reconstituted with human PBL and boosted with TT. Establishment of these cell lines was dependent on the time interval between reconstitution of the mice with human PBL and initiation of lymphocyte cultures in vitro. When lymphocytes were collected from the mice 8 weeks after reconstitution, human lymphocytes with TT-specific proliferative activity in vitro were isolated from the peritoneal cavity and spleen, but long-term cell lines could not be established after repeated lymphocyte stimulation with TT, IL-2 and autologous Epstein-Barr virus-transformed B cells. In contrast, three long-term (> 10 months) TT-specific human T cell lines were established from lymphocytes collected from two of the eight mice in the group 4 weeks after reconstitution. The T cell lines were either CD4+ (two lines derived from peritoneal cavity and lymph node, respectively) or CD8+ (one line derived from spleen) and all expressed CD3, T cell receptor alpha/beta, and human histocompatibility leucocyte class I antigen. The T cell lines, however, lacked cytotoxic, helper and suppressor activities. Thus, SCID mice can support human T cells that actively migrate to various organs and respond to antigenic stimuli both in vivo and in vitro, but these T cells lack characteristic functions.

Limitations of the severe combined immunodeficiency (SCID) mouse model for study of human B-cell responses

Mice lacking functional T and B lymphocytes offer an in vivo animal model for the study of human immune functions. We have attempted to optimize the reconstitution of severe combined immunodeficiency (SCID) mice with human peripheral blood lymphocytes (PBL) using radiation, anti-asialo GM1 antibody or cyclophosphamide (Cy) treatment of the mice and in vitro stimulation of human PBL with interleukin (IL)-2 prior to their transfer to the mice. Total human IgG and tetanus-toxoid (TT)-specific human IgG responses of the mice were used as parameters of successful reconstitution. Treatment of the mice with anti-asialo GM1 antibody significantly enhanced total human IgG levels, but not TT-specific antibody responses, whereas irradiation or Cy treatment of the mice had no effect on human antibody production. In vitro treatment of human PBL with IL-2 prior to engraftment significantly decreased total human IgG responses of human PBL-grafted SCID mice. The immune responses of individual mice within a group were highly variable, which constitutes a major disadvantage of this model.

A new model for rheumatoid arthritis generated by engraftment of rheumatoid synovial tissue and normal human cartilage into SCID mice

OBJECTIVE

A new animal model was used to study the interaction between rheumatoid synovial cells and cartilage and to explore the cellular basis of rheumatoid joint destruction.

METHODS

Fresh synovial tissue derived from patients with rheumatoid arthritis was implanted with normal human cartilage into SCID mice, either subcutaneously or under the renal capsule, for up to 304 days. The implants were analyzed by light and electron microscopy, as well as by immunohistochemistry and in situ hybridization.

RESULTS

Human synovial tissue and cartilage implanted in SCID mice are maintained by the animals for up to 304 days. After 35 days, focal erosions occur at the site of attachment of synovial lining cells to the cartilage. After 105 days, a pannus-like formation, consisting of proliferating synovial fibroblast-like cells invading the cartilage, is observed. The fibroblast nature of these cells was supported by observation of only focal expression of the macrophage markers CD14 and CD68. Cells at the immediate site of cartilage destruction express messenger RNA for cathepsin L, whereas cathepsin D messenger RNA was detected in subsynovial regions away from the site of destruction. The human origin of the tissue involved in cartilage destruction was demonstrated using monoclonal antibodies to HLA-ABC and human type IV collagen.

CONCLUSION

The present approach introduces a novel in vivo model of rheumatoid arthritis for the study of the molecular and cellular mechanisms of rheumatoid joint destruction at sites of synovial attachment to cartilage. In this model, the SCID mouse acts as a useful host for studying the properties of rheumatoid synovium in the absence of circulating human blood components.