Human hematopoietic stem/progenitor cells generate CD5+ B lymphoid cells in NOD/SCID mice

Advances in Human Immune System Mouse Models for Studying Human Hematopoiesis and Cancer Immunotherapy

Immunotherapy has established itself as a promising tool for cancer treatment. There are many challenges that remain including lack of targets and some patients across various cancers who have not shown robust clinical response. One of the major problems that have hindered the progress in the field is the dearth of appropriate mouse models that can reliably recapitulate the complexity of human immune-microenvironment as well as the malignancy itself. Immunodeficient mice reconstituted with human immune cells offer a unique opportunity to comprehensively evaluate immunotherapeutic strategies. These immunosuppressed and genetically modified mice, with some overexpressing human growth factors, have improved human hematopoietic engraftment as well as created more functional immune cell development in primary and secondary lymphoid tissues in these mice. In addition, several new approaches to modify or to add human niche elements to further humanize these immunodeficient mice have allowed a more precise characterization of human hematopoiesis. These important refinements have opened the possibility to evaluate not only human immune responses to different tumor cells but also to investigate how malignant cells interact with their niche and most importantly to test immunotherapies in a more preclinically relevant setting, which can ultimately lead to better success of these drugs in clinical trials.

Critical assessment of human antibody generation in humanized mouse models

Immunodeficient mice reconstituted with human hematopoietic stem cells provide a small-animal model for the study of development and function of human hematopoietic cells in vivo. However, in the current models, the immune response, and especially the humoral response by the human immune cells is far from optimal. The B cells found in these mice exhibit an immature and abnormal phenotype correlating with a reduced capacity to produce antigen-specific affinity matured antibodies upon infection or immunization. Herein, we review the current state of knowledge of development, function and antibody production of human B cells and discuss the obstacles for the improvement of these models.

Humoral immune responses in humanized BLT mice immunized with West Nile virus and HIV-1 envelope proteins are largely mediated via human CD5+ B cells

BLT mice, constructed by surgical implantation of human fetal thymus-liver tissues and intravenous delivery of autologous CD34+ haematopoietic stem cells into adult non-obese diabetic/severe combined immunodeficiency mice, were evaluated for vaccine-induced humoral immune responses. Following engraftment, these mice developed a human lymphoid system; however, the majority of the peripheral human B lymphocytes displayed an immature phenotype as evidenced by surface CD10 expression. Over 50% of the human B cells in the periphery but not in the bone marrow also expressed the CD5 antigen, which is found only infrequently on mature follicular B cells in humans. A single intramuscular immunization with recombinant viral envelope antigens, e.g., HIVgp140 and West Nile Virus envelope proteins, together with the immune stimulatory KLK/ODN1a composition) [corrected] adjuvant resulted in seroconversion characterized by antigen-specific human antibodies predominantly of the IgM isotype. However, repeated booster immunizations did not induce secondary immune responses as evidenced by the lack of class switching and specific IgM levels remaining relatively unchanged. Interestingly, the peripheral CD19+  CD5+ but not the CD19+  CD5- human B lymphocytes displayed a late developing CD27+  IgM+ memory phenotype, suggesting that the CD5+ B-cell subset, previously implicated in 'natural antibody' production, may play a role in the vaccine-induced antibody response. Furthermore, human T lymphocytes from these mice demonstrated suboptimal proliferative responses and loss of co-stimulatory surface proteins ex vivo that could be partially reversed with human interleukin-2 and interleukin-7. Therefore, vaccine-induced immune responses in BLT mice resemble a T-cell-independent pathway that can potentially be modulated in vivo by the exogenous delivery of human cytokines/growth factors.

Functional CD5+ B cells develop predominantly in the spleen of NOD/SCID/gammac(null) (NOG) mice transplanted either with human umbilical cord blood, bone marrow, or mobilized peripheral blood CD34+ cells

OBJECTIVE

Human CD5+ B cells are the major B cell subset in fetal spleen and umbilical cord blood (CB), and their number gradually diminishes in both spleen and peripheral blood from infancy through childhood while conventional B cells increase. In this study, we investigated whether CD5+ cells differentiate from adult hematopoietic stem cells (HSCs) as well as fetal ones in immunodeficient mice.

METHODS

In our system, NOD/SCID/gammac(null) (NOG) mice were transplanted with CD34+ cells from CB (hCB model), adult bone marrow (hBM model), and mobilized peripheral blood (hMPB model).

RESULTS

In these model mice, a high proportion of CD19+IgM+CD5+ mature B cells appeared in the spleen, regardless of the CD34+ cell origin, 4 to 8 weeks after transplantation, while the majority were CD19+IgM-CD5- immature B cells in BM. The CD19+CD5- BM cells showed to express CD5 after the coculture with NOG spleen cells. In the sera of immunized hCB model mice with DNP-KLH, antigen-specific IgM but not IgG was enhanced.

CONCLUSION

Our results show that adult CD34+ cells develop into functional CD5+ B cells in NOG spleen as much as fetal CD34+ cells do.

The NOD/SCID chimeric mouse model of human B cell development: studies on the VH4 family immunoglobulin repertoire and implications for SLE

The use of the NOD/SCID mouse as a transplant recipient for human cord blood B cell progenitors as a tool for investigations into the development of human B cells has become an exciting reality. The characteristics of the immunoglobulin repertoire in such a model is important to investigate, as it is possible that normal or skewed representations could be produced. Here we review our current work in which we describe a normal VH4 repertoire produced in this chimeric mouse model and describe the differences in combinatorial diversity between the human cells that were isolated from the bone marrow and spleen. The implications of this model for studies of systemic lupus erythematosus are also discussed.

Reconstitution of functional human B lymphocytes in NOD/SCID mice engrafted with ex vivo expanded CD34(+) cord blood cells

OBJECTIVE

Functional capacity of B cells developed from ex vivo expanded hematopoietic stem cells has not been fully evaluated. Therefore, we investigated the antigen-specific antibody production in human B cells maturated from ex vivo expanded cord blood (CB) CD34(+) cells in NOD/Shi-scid (NOD/SCID) mice.

MATERIALS AND METHODS

CB CD34(+) cells were cultured for 5 days in the presence of human cytokines and the murine stromal cell line HESS-5, and transplanted into irradiated NOD/SCID mice. These mice, reconstituted with human hematopoietic cells, were challenged with T-cell-independent (TI) or T-cell-dependent (TD) antigens after CD19(+) cells appeared at 6 weeks.

RESULTS

Three months later, anti-dinitrophenol (DNP)-specific antibody was detected in both mice immunized with DNP-Ficoll (TI) and those immunized with DNP-keyhole limpet hemocyanin or DNP-ovalbumin (TD). The anti-DNP antibody was mainly immunoglobulin M, but a small amount of immunoglobulin G also was detected. In the spleen, the majority of CD19(+) cells expressed mature B-cell markers such as CD40, immunoglobulin M, immunoglobulin D, cytoplasmic Cmu, and light chains kappa, and lambda.

CONCLUSIONS

These results indicate that human B cells develop from CD34(+) cells in NOD/SCID mice to produce antigen-specific antibody with in vivo primary stimulation. This system provides a powerful and versatile tool for studying the entire process of human B-lymphocyte development and producing specific human monoclonal antibodies.

Targeting transgene expression to antigen-presenting cells derived from lentivirus-transduced engrafting human hematopoietic stem/progenitor cells

Hematopoietic stem cells (HSCs) represent an important target for the treatment of various blood disorders. As the source of critical cells within the immune system, genetic modification of HSCs can also be used to modulate immune responses. The effectiveness of HSC-mediated gene therapy largely depends on efficient gene delivery into long-term repopulating progenitors and targeted transgene expression in an appropriate progeny of the transduced pluripotent HSCs. Self-inactivating (SIN) lentiviral vectors have been demonstrated to be capable of transducing mitotically inactive cells, including HSCs, and accommodating a nonviral promoter to control the transgene expression in transduced cells. In this study, we constructed 2 SIN lentiviral vectors, EF.GFP and DR.GFP, to express the green fluorescent protein (GFP) gene controlled solely by the promoter of either a housekeeping gene EF-1alpha or the human HLA-DRalpha gene, which is selectively expressed in antigen-presenting cells (APCs). We demonstrated that both vectors efficiently transduced human pluripotent CD34+ cells capable of engrafting nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice. When the EF.GFP vector was used, constitutive high-level GFP expression was obtained in all the human HSC progeny detectable in NOD/SCID mice and in subsequent in vitro differentiation assays, indicating that engrafting human HSCs have been transduced. In contrast, the DR.GFP vector mediated transgene expression specifically in human HLA-DR+ cells and highly in differentiated dendritic cells (DCs), which are critical in regulating immunity. Furthermore, human DCs derived from transduced and engrafted human cells potently stimulated allogeneic T-cell proliferation. This study demonstrated successful targeting of transgene expression to APCs/DCs after stable gene transduction of pluripotent HSCs.

A model of chronic lymphocytic leukemia with Ritcher's transformation in severe combined immunodeficiency mice

OBJECTIVE

The major aim of the study was to establish a murine model of chronic lymphocytic leukemia with B-1 cells derived from a New Zealand white mouse.

MATERIAL AND METHODS

Malignant B-1 cells (named CLL-RT cells) derived from a New Zealand white mouse were injected into the peritoneal cavity of severe combined immunodeficiency mice. Upon follow-up of recipient mice, the lymphomas showed characteristics similar to chronic lymphocytic leukemia (CLL) with Ritcher's transformation.

RESULTS

Blood samples from the recipient mice showed that CLL-RT cells increased rapidly in peripheral blood after 5 weeks. Serum interleukin-10 also increased significantly in recipient mice, as in human chronic lymphocytic leukemia patients. These CLL-RT cells showed a high nucleus-to-cytoplasm ratio. These cells could metastasize via circulation in the recipients and form diffuse lymphomas in various tissues. These aggressive and diffuse lymphomas were similar to Ritcher's transformation of human CLL. The cell surface antigens of the spleen and peritoneal resident cells were analyzed by flow cytometry. The CLL-RT cells constantly expressed surface immunoglobulins M and G, and CD5, CD19, B220, and CD40 molecules. They did not express any CD11b, CD3, MAC-3, CD23, NK1.1, or H-2K(d) molecules.

CONCLUSIONS

The characteristics of our animal model are very similar to human CLL. This animal system could be an ideal model for the human disease. We believe the animal model would be valuable in therapeutic studies and aid in the identification of the specific genetic alleles associated with the disease.

Relatively normal human lymphopoiesis but rapid turnover of newly formed B cells in transplanted nonobese diabetic/SCID mice

Human B lineage lymphocyte precursors in chimeric nonobese diabetic/SCID mice transplanted with umbilical cord blood cells were directly compared with those present in normal bone marrow. All precursor subsets were represented and in nearly normal proportions. Cell cycle activity and population dynamics were investigated by staining for the Ki-67 nuclear Ag as well as by incorporation experiments using 5-bromo-2'-deoxyuridine. Again, this revealed that human B lymphopoiesis in chimeras parallels that in normal marrow with respect to replication and progression through the lineage. Moreover, sequencing of Ig gene rearrangement products showed that a diverse repertoire of V(H) genes was utilized by the newly formed lymphocytes but there was no evidence for somatic hypermutation. The newly formed B cells frequently acquired the CD5 Ag and had a short life span in the periphery. Thus, all molecular requirements for normal B lymphocyte formation are present in nonobese diabetic/SCID mice, but additional factors are needed for recruitment of B cells into a fully mature, long-lived pool. The model can now be exploited to learn about species restricted and conserved environmental cues for human B lymphocyte production.

Transplanted long-term cultured pre-BI cells expressing calpastatin are resistant to B cell receptor-induced apoptosis

Long-term cultured pre-B cells are able to differentiate into immunoglobulin (Ig)M-positive B cells (IgM(+) cells) when transplanted into severe combined immunodeficient (SCID) mice. Based on previous studies, here we report the development of a reconstitution assay in nonobese diabetic/SCID (NOD/SCID) mice using pre-B cells, which allows us to study the role of calpains (calcium-activated endopeptidases) during B cell development as well as in B cell clonal deletion. Using this model, we show that calpastatin (the natural inhibitor of calpains) inhibits B cell receptor-induced apoptosis in IgM(+) cells derived from transplanted mice. We thus hypothesize an important function for calpain in sculpting the B cell repertoire.

Preconditioning with fetal cord blood facilitates engraftment of primary childhood T-cell acute lymphoblastic leukemia in immunodeficient mice

Childhood T-cell acute lymphoblastic leukemia (T-ALL) is one of the most common childhood cancers. It is reported that preconditioning sublethally irradiated immunodeficient NOD/SCID (nonobese diabetic/X-linked severe combined immunodeficient) mice with human cord blood mononuclear cells facilitates the engraftment, expansion, and dissemination in these mice of primary T-ALL cells obtained from patients at the time of diagnosis. Cells recovered from mouse bone marrow or spleen resembled the original leukemia cells from patients with respect to surface lineage markers and T-cell receptor Vbeta gene rearrangements. Moreover, the pattern of leukemia dissemination in mouse tissues, resulting in universally fatal leukemia, is reminiscent of the human clinical disease. In addition, the fidelity of the model to the human disease is documented with regard to the presence of morphologically identifiable human leukemia cells in mouse bone marrow and blood and the maintenance of leukemia-initiating capacity within the leukemia-engrafted mouse. Therefore, several lines of independent approaches are used to suggest that the engrafted cells are of human leukemia origin and are not derived from cord blood. The in vivo model described here should enable the study of the growth properties of primary T-ALL cells obtained from patients and should prove useful in evaluating the potential efficacy of therapeutic strategies directed toward T-ALL.