Transplantation of normal and leukemic human bone marrow into immune-deficient mice: development of animal models for human hematopoiesis

Efficacy of Engraftment and Safety of Human Umbilical Di-Chimeric Cell (HUDC) Therapy after Systemic Intraosseous Administration in an Experimental Model

Cell-based therapies hold promise for novel therapeutic strategies in regenerative medicine. We previously characterized in vitro human umbilical di-chimeric cells (HUDCs) created via the ex vivo fusion of human umbilical cord blood (UCB) cells derived from two unrelated donors. In this in vivo study, we assessed HUDC safety and biodistribution in the NOD SCID mouse model at 90 days following the systemic intraosseous administration of HUDCs. Twelve NOD SCID mice (n = 6/group) received intraosseous injection of donor UCB cells (3.0 × 106) in Group 1, or HUDCs (3.0 × 106) in Group 2, without immunosuppression. Flow cytometry assessed hematopoietic cell surface markers in peripheral blood and the presence of HLA-ABC class I antigens in lymphoid and non-lymphoid organs. HUDC safety was assessed by weekly evaluations, magnetic resonance imaging (MRI), and at autopsy for tumorigenicity. At 90 days after intraosseous cell administration, the comparable expression of HLA-ABC class I antigens in selected organs was found in UCB control and HUDC therapy groups. MRI and autopsy confirmed safety by no signs of tumor growth. This study confirmed HUDC biodistribution to selected lymphoid organs following intraosseous administration, without immunosuppression. These data introduce HUDCs as a novel promising approach for immunomodulation in transplantation.

Phenotypic characterization of disease-initiating stem cells in JAK2- or CALR-mutated myeloproliferative neoplasms

Myeloproliferative neoplasms (MPN) are characterized by uncontrolled expansion of myeloid cells, disease-related mutations in certain driver-genes including JAK2, CALR, and MPL, and a substantial risk to progress to secondary acute myeloid leukemia (sAML). Although behaving as stem cell neoplasms, little is known about disease-initiating stem cells in MPN. We established the phenotype of putative CD34+ /CD38- stem cells and CD34+ /CD38+ progenitor cells in MPN. A total of 111 patients with MPN suffering from polycythemia vera, essential thrombocythemia, or primary myelofibrosis (PMF) were examined. In almost all patients tested, CD34+ /CD38- stem cells expressed CD33, CD44, CD47, CD52, CD97, CD99, CD105, CD117, CD123, CD133, CD184, CD243, and CD274 (PD-L1). In patients with PMF, MPN stem cells often expressed CD25 and sometimes also CD26 in an aberrant manner. MPN stem cells did not exhibit substantial amounts of CD90, CD273 (PD-L2), CD279 (PD-1), CD366 (TIM-3), CD371 (CLL-1), or IL-1RAP. The phenotype of CD34+ /CD38- stem cells did not change profoundly during progression to sAML. The disease-initiating capacity of putative MPN stem cells was confirmed in NSGS mice. Whereas CD34+ /CD38- MPN cells engrafted in NSGS mice, no substantial engraftment was produced by CD34+ /CD38+ or CD34- cells. The JAK2-targeting drug fedratinib and the BRD4 degrader dBET6 induced apoptosis and suppressed proliferation in MPN stem cells. Together, MPN stem cells display a unique phenotype, including cytokine receptors, immune checkpoint molecules, and other clinically relevant target antigens. Phenotypic characterization of neoplastic stem cells in MPN and sAML should facilitate their enrichment and the development of stem cell-eradicating (curative) therapies.

The Coming of Age of Preclinical Models of MDS

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal bone-marrow diseases with ineffective hematopoiesis resulting in cytopenias and morphologic dysplasia of hematopoietic cells. MDS carry a wide spectrum of genetic abnormalities, ranging from chromosomal abnormalities such as deletions/additions, to recurrent mutations affecting the spliceosome, epigenetic modifiers, or transcription factors. As opposed to AML, research in MDS has been hindered by the lack of preclinical models that faithfully replicate the complexity of the disease and capture the heterogeneity. The complex molecular landscape of the disease poses a unique challenge when creating transgenic mouse-models. In addition, primary MDS cells are difficult to manipulate ex vivo limiting in vitro studies and resulting in a paucity of cell lines and patient derived xenograft models. In recent years, progress has been made in the development of both transgenic and xenograft murine models advancing our understanding of individual contributors to MDS pathology as well as the complex primary interplay of genetic and microenvironment aberrations. We here present a comprehensive review of these transgenic and xenograft models for MDS and future directions.

Phenotypic characterization of leukemia-initiating stem cells in chronic myelomonocytic leukemia

Chronic myelomonocytic leukemia (CMML) is a stem cell-derived neoplasm characterized by dysplasia, uncontrolled expansion of monocytes, and substantial risk to transform to secondary acute myeloid leukemia (sAML). So far, little is known about CMML-initiating cells. We found that leukemic stem cells (LSC) in CMML reside in a CD34+/CD38- fraction of the malignant clone. Whereas CD34+/CD38- cells engrafted NSGS mice with overt CMML, no CMML was produced by CD34+/CD38+ progenitors or the bulk of CD34- monocytes. CMML LSC invariably expressed CD33, CD117, CD123 and CD133. In a subset of patients, CMML LSC also displayed CD52, IL-1RAP and/or CLL-1. CMML LSC did not express CD25 or CD26. However, in sAML following CMML, the LSC also expressed CD25 and high levels of CD114, CD123 and IL-1RAP. No correlations between LSC phenotypes, CMML-variant, mutation-profiles, or clinical course were identified. Pre-incubation of CMML LSC with gemtuzumab-ozogamicin or venetoclax resulted in decreased growth and impaired engraftment in NSGS mice. Together, CMML LSC are CD34+/CD38- cells that express a distinct profile of surface markers and target-antigens. During progression to sAML, LSC acquire or upregulate certain cytokine receptors, including CD25, CD114 and CD123. Characterization of CMML LSC should facilitate their enrichment and the development of LSC-eradicating therapies.

Inhibition of PRDM14 expression in pancreatic cancer suppresses cancer stem-like properties and liver metastasis in mice

Pancreatic cancer is one of the most lethal types of cancer, with aggressive properties characterized by metastasis, recurrence and drug resistance. Cancer stem cells are considered to be responsible for these properties. PRDM14, a transcriptional regulator that maintains pluripotency in embryonic stem cells, is overexpressed in some cancers. Here, we assessed PRDM14 expression and the effects of PRDM14 knockdown on cancer stem-like phenotypes in pancreatic cancer. We observed that PRDM14 protein was overexpressed in pancreatic cancer tissues compared with normal pancreatic tissues. Using lentiviral shRNA-transduced pancreatic cancer cells, we found that PRDM14 knockdown decreased sphere formation, number of side population and cell surface marker-positive cells and subcutaneous xenograft tumors and liver metastasis in mice. This was accompanied by upregulation of some microRNAs (miRNAs), including miR-125a-3p. miR-125a-3p, a tumor suppressor that is down-regulated in pancreatic cancer, has been suggested to regulate the expression of the Src-family kinase, Fyn. In PRDM14-knockdown cells, Fyn was expressed at lower levels and downstream proteins were less activated. These changes were considered to cause suppression of the above cancer phenotypes. In addition, we used small interfering RNA (siRNA)-based therapy targeting PRDM14 in a mouse model of liver metastasis induced using MIA-PaCa2 cells, and this treatment significantly decreased metastasis and in vitro migration. Taken together, these results suggest that targeting the overexpression of PRDM14 suppresses cancer stem-like phenotypes, including liver metastasis, via miRNA regulation and siRNA-based therapy targeting it shows promise as a treatment for patients with pancreatic cancer.

Humanized mice for HIV and AIDS research

HIV has a very limited species tropism that prevents the use of most conventional small animal models for AIDS research. The in vivo analysis of HIV/AIDS has benefited extensively from novel chimeric animal models that accurately recapitulate key aspects of the human condition. Specifically, immunodeficient mice that are systemically repopulated with human hematolymphoid cells offer a viable alternative for the study of a multitude of highly relevant aspects of HIV replication, pathogenesis, therapy, transmission, prevention, and eradication. This article summarizes some of the multiple contributions that humanized mouse models of HIV infection have made to the field of AIDS research. These models have proven to be highly informative and hold great potential for accelerating multiple aspects of HIV research in the future.

In vivo platforms for analysis of HIV persistence and eradication

HIV persistence in patients undergoing antiretroviral therapy is a major impediment to the cure of HIV/AIDS. The molecular and cellular mechanisms underlying HIV persistence in vivo have not been fully elucidated. This lack of basic knowledge has hindered progress in this area. The in vivo analysis of HIV persistence and the implementation of curative strategies would benefit from animal models that accurately recapitulate key aspects of the human condition. This Review summarizes the contribution that humanized mouse models of HIV infection have made to the field of HIV cure research. Even though these models have been shown to be highly informative in many specific areas, their great potential to serve as excellent platforms for discovery in HIV pathogenesis and treatment has yet to be fully developed.

Evolution of the cancer stem cell model

Genetic analyses have shaped much of our understanding of cancer. However, it is becoming increasingly clear that cancer cells display features of normal tissue organization, where cancer stem cells (CSCs) can drive tumor growth. Although often considered as mutually exclusive models to describe tumor heterogeneity, we propose that the genetic and CSC models of cancer can be harmonized by considering the role of genetic diversity and nongenetic influences in contributing to tumor heterogeneity. We offer an approach to integrating CSCs and cancer genetic data that will guide the field in interpreting past observations and designing future studies.

The use of BLT humanized mice to investigate the immune reconstitution of the gastrointestinal tract

The gastrointestinal (GI) track represents an important battlefield where pathogens first try to gain entry into a host. It is also a universe where highly diverse and ever changing inhabitants co-exist in an exceptional equilibrium without parallel in any other organ system of the body. The gut as an organ has its own well-developed and fully functional immune organization that is similar and yet different in many important ways to the rest of the immune system. Both a compromised and an overactive immune system in the gut can have dire and severe consequences to human health. It has therefore been of great interest to develop animal models that recapitulate key aspects of the human condition to better understand the interplay of the host immune system with its friends and its foes. However, reconstitution of the GI tract in humanized mice has been difficult and highly variable in different systems. A better molecular understanding of the development of the gut immune system in mice has provided critical cues that have been recently used to develop novel humanized mouse models that fully recapitulate the genesis and key functions of the gut immune system of humans. Of particular interest is the presence of human gut-associated lymphoid tissue (GALT) aggregates in the gut of NOD/SCID BLT humanized mice that demonstrate the faithful development of bona fide human plasma cells capable of migrating to the lamina propria and producing human IgA1 and IgA2.

Cancer mouse models: past, present and future

The development and advances in gene targeting technology over the past three decades has facilitated the generation of cancer mouse models that recapitulate features of human malignancies. These models have been and still remain instrumental in revealing the complexities of human cancer biology. However, they will need to evolve in the post-genomic era of cancer research. In this review we will highlight some of the key developments over the past decades and will discuss the new possibilities of cancer mouse models in the light of emerging powerful gene manipulating tools.

Leukemia stem cells: Old concepts and new perspectives

Myeloid leukemias are heterogeneous malignancies in morphology, immunophenotype, genetic and epigenetic alterations, and response to therapy. This heterogeneity is thought to depend on the accumulation of secondary mutations enhancing proliferation/survival and/or blocking differentiation in a small subset of leukemia-initiating cells capable of self-renewal. This model of clonal evolution is based on xenotransplantation studies demonstrating that leukemia can be initiated and maintained in immunodeficient mice by a small subset of purified leukemic cells immunophenotypically similar to normal hematopoietic stem cells and is known as the leukemia stem cell model. Since its original formulation, many studies have validated the main conclusion of this model. However, recent data from xenotransplantation studies in more severely immunodeficient mice suggest that imunophenotype and behavior of leukemic stem cells is more heterogeneous and "plastic" than originally thought. We will discuss here the evolution of the leukemia stem cell model and its impact for the therapy of patients with myeloid malignancies.

Leukemia stem cells in 2010: current understanding and future directions

Myeloid leukemias are clonal disorders originating in a primitive multipotential hematopoietic cell and characterized by aberrant proliferation, differentiation and maturation of leukemic progenitors and precursor cells. These diseases are the result of multiple genetic and epigenetic events, although the nature and number of events vary widely among patients. For over four decades, studies have identified sub-populations of leukemic cells possessing different functional capabilities. Investigators have struggled to understand the origin and significance of this heterogeneity. The stem cell model for myeloid malignancies has offered one potential explanation. Since 1994, experimental data supporting the presence of leukemia stem cells has been reported and validated in numerous studies. We will review the history of the model, data from the past decade supporting the stem cell model for myeloid malignancies, more recent data regarding patient specific variability in leukemic stem cell surface antigen phenotype and the impact the stem cell model has on the care of patients with myeloid malignancies.

In utero transplantation of human bone marrow-derived multipotent mesenchymal stem cells in mice

Mesenchymal stem cells (MSCs) are multipotent cells that can be isolated from human bone marrow and possess the potential to differentiate into progenies of embryonic mesoderm. However, current evidence is based predominantly on in vitro experiments. We used a murine model of in utero transplantation (IUT) to study the engraftment capabilities of human MSCs. MSCs were obtained from bone marrow by negative immunoselection and limiting dilution, and were characterized by flow cytometry and by in vitro differentiation into osteoblasts, chondrocytes, and adipocytes. MSCs were transplanted into fetal mice at a gestational age of 14 days. Engraftment of human MSCs was determined by flow cytometry, polymerase chain reaction, and fluorescence in situ hybridization (FISH). MSCs engrafted into tissues originating from all three germ layers and persisted for up to 4 months or more after delivery, as evidenced by the expression of the human-specific beta-2 microglobulin gene and by FISH for donor-derived cells. Donor-derived CD45+ cells were detectable in the peripheral blood of recipients, suggesting the participation of MSCs in hematopoiesis at the fetal stage. This model can further serve to evaluate possible applications of MSCs.

Monitoring the effect of gene silencing by RNA interference in human CD34+ cells injected into newborn RAG2-/- gammac-/- mice: functional inactivation of p53 in developing T cells

Tumor suppressor p53 plays an important role in regulating cell cycle progression and apoptosis. Here we applied RNA interference to study the role of p53 in human hematopoietic development in vivo. An siRNA construct specifically targeting the human tumor-suppressor gene p53 was introduced into human CD34(+) progenitor cells by lentivirus-mediated gene transfer, which resulted in more than 95% knockdown of p53. We adapted the human-SCID mouse model to optimize the development of hematopoietic cells, particularly of T cells. This was achieved by the intraperitoneal injection of CD34(+) precursor cells into newborn Rag2(-/-) gammac(-/-) mice that lack T, B, and NK cells. Robust development of T cells was observed in these mice, with peripheral T-cell repopulation 8 weeks after injection of the precursor cells. Other lymphocyte and myeloid subsets also developed in these mice. Injecting p53 siRNA-transduced CD34(+) cells resulted in stable expression and down-modulation of p53 in the mature T-cell offspring. Inactivating p53 did not affect the development of CD34(+) cells into various mature leukocyte subsets, including T cells, but it conferred resistance to gamma-irradiation and other p53-dependent apoptotic stimuli to the T cells.

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.

Thrombopoietin is a major limiting factor for selective outgrowth of human umbilical cord blood cells in non-obese diabetic/severe combined immunodeficient recipient mice

A single dose (0.3 microg) of recombinant human thrombopoietin (TPO) was injected into sublethal irradiated non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice immediately after transplantation of 1.5 x 10(5) purified CD34+ umbilical cord blood (UCB) cells. Bone marrow (BM) was analysed for human cells by immunophenotyping and colony culture at d 35. TPO treatment produced a two- to sixfold increase in the frequency and number of human CD45+ cells. The lineage distributions among the human cells were similar irrespective of TPO treatment; however, a prominent increase was observed in CD71+GpA- cells, reflecting the proliferative stimulus provided by TPO. The frequency of immature CD34+ cells and human granulocyte-macrophage colony-forming units and erythroid burst-forming units in TPO-treated mice was similar to that of untreated mice, but their absolute numbers had increased proportionally to the increase in human cells. The results demonstrate that human TPO is a major limiting factor for multilineage outgrowth of human UCB cells in NOD/SCID mice and can be conveniently supplemented by single-dose treatment immediately after transplantation. TPO did not affect the survival of mice after transplantation and did not significantly increase the number of immature CD34+CD38- cells; secondary transplantation revealed that TPO administration also had no significant effect on long-term repopulation. The findings demonstrate that human TPO is required for proper outgrowth of human haematopoietic stem cells after transplantation. In addition, a single administration of TPO may improve the efficiency and reproducibility of the NOD/SCID mouse assay for human immature transplantable progenitor cells.

Lineage-negative side-population (SP) cells with restricted hematopoietic capacity circulate in normal human adult blood: immunophenotypic and functional characterization

Side-population (SP) cells are a recently described rare cell population detected in selected tissues of various mammalian species, but not yet described in the peripheral circulation. In the present study, we have identified for the first time SP cells in lineage-negative adult human blood and have provided an extensive functional and immunophenotypic characterization of these cells. Adult peripheral blood was depleted of mature leukocyte cell types by density gradient and immunomagnetic separation. The SP cell population was identified by its characteristic Hoechst 33342 profile. Immunophenotypic analysis revealed that blood SP cells expressed high levels of CD45, CD59, CD43, CD49d, CD31, and integrin markers and lacked CD34. Highly purified SP cells were put into cobblestone area-forming cell (CAFC), long-term culture-initiating cell (LTC-IC), and liquid cell culture assays; repopulating assays were performed utilizing nonobese diabetic/severe combined immunodeficient mice. Circulating SP cells were shown to exhibit verapamil sensitivity and a low growth rate. LTC-IC, CAFC, and engraftment assays indicated that circulating SP cells had lost the multipotentiality described in murine bone marrow SP cells. However, outgrowth of mature cell types from liquid cell culture suggests the presence of common lymphoid (T and natural killer) and dendritic cell precursor(s) within circulating SP cell populations. The absence of SP cell growth in the LTC-IC, CAFC, and repopulating assays might be intrinsic to the tissue source (marrow versus blood) or species (mouse versus human) tested. Thus, human blood SP cells, although rare, may serve as a source of selected leukocyte progenitor cells. The immunophenotype of circulating SP cells may provide clues to their seeding and homing capacity.

Elimination of porcine hemopoietic cells by macrophages in mice

The difficulty in achieving donor hemopoietic engraftment across highly disparate xenogeneic species barriers poses a major obstacle to exploring xenograft tolerance induction by mixed chimerism. In this study, we observed that macrophages mediate strong rejection of porcine hemopoietic cells in mice. Depletion of macrophages with medronate-encapsulated liposomes (M-liposomes) markedly improved porcine chimerism, and early chimerism in particular, in sublethally irradiated immunodeficient and lethally irradiated immunocompetent mice. Although porcine chimerism in the peripheral blood and spleen of M-liposome-treated mice rapidly declined after macrophages had recovered and became indistinguishable from controls by wk 5 post-transplant, the levels of chimerism in the marrow of these mice remained higher than those in control recipients at 8 wks after transplant. These results suggest that macrophages that developed in the presence of porcine chimerism were not adapted to the porcine donor and that marrow-resident macrophages did not phagocytose porcine cells. Moreover, M-liposome treatment had no effect on the survival of porcine PBMC injected into the recipient peritoneal cavity, but was essential for the migration and relocation of these cells into other tissues/organs, such as spleen, bone marrow, and peripheral blood. Together, our results suggest that murine reticuloendothelial macrophages, but not those in the bone marrow and peritoneal cavity, play a significant role in the clearance of porcine hemopoietic cells in vivo. Because injection of M-liposomes i.v. mainly depletes splenic macrophages and liver Kupffer cells, the spleen and/or liver are likely the primary sites of porcine cell clearance in vivo.

Characterization of a novel human anaplastic large cell lymphoma cell line tumorigenic in SCID mice

L82, a novel anaplastic large cell lymphoma (ALCL) cell line was established from the pleural effusion of a 24-year-old patient with recurrent ALCL. L82 cells showed the typical morphologic features of ALCL cells with irregular, often indented, nuclear profiles, prominent nucleoli, and abundant cytoplasm. The immunoprofile of L82 corresponds to that seen typically in primary ALCL cells, with positivity for CD30, EMA, CD3, CD4, CD25, CD71, TIA1, and granzyme B; the cells were negative for EBV-related antigens. Cytogenetic analysis showed a complex, near triploid karyotype with 72-77 chromosomes, including the ALCL specific translocation t(2;5)(p23;q35). Chromosomal analysis revealed a number of secondary structural alterations including amplification of 7q21-31, 1q, and 6p, and gain of chromosomal material in 8q (affecting the c-myc gene). The rearrangement of the T-cell receptor-gamma locus shows that L82 is clonally derived from T-lineage lymphoid cells. mRNAs for interleukin 7 (IL-7), IL-8, IL-9, IL-10, TNF-beta, and for the IL-7 and IL-9 receptor were found. These data show that the T-helper cell (Th)1/Th2 balance was polarized to Th2. L82 were inoculated intraperitoneally into 4 week-old SCID mice and produced a disseminated tumor within 4-6 weeks. Morphological, immunohistochemical, and molecular genetic investigation confirmed that the xenograft and the original ALCL tumor were identical. SCID mice xenografted with the human ALCL cell line, L82, provide a useful model system for the investigation of the biology of ALCL and of new therapeutic approaches, such as specific immunotherapy.

The generation of immunocompetent dendritic cells from CD34+ acute myeloid or lymphoid leukemia cells

The ability of CD34+ leukemic cells to differentiate to dendritic cells (DCs) was investigated in 18 acute myeloid leukemia (AML) and 4 lymphoid leukemia (ALL) patients. The generation of DCs was determined by the expression of DC-associated CD1a or CD83 (more than 30%) with costimulatory molecules, by CD80 antigens (>20%), and by the exhibition of allostimulatory activity. In the AML patients, allostimulatory mature DCs were generated from 3 of 9 M0 or M1, 2 of 5 M2,2 of 4 M4 or M5, and 3 of 4 ALL (L2) cases. In total, DCs were more efficiently induced from cases expressing over 75% of CD34+ among whole bone marrow mononuclear cells (8 of 12), compared with those under 75% (2 of 10; P < .05). B-cell (CD19), natural killer (NK)-cell (CD56), or T-cell (CD7) lineage markers, which were aberrantly expressed on the blasts, were rarely found on leukemic DCs at the end of the culture period, and myeloid (CD13, CD33), not lymphoid (CD10), markers were shown on ALL-derived DCs. In Philadelphia chromosome-positive ALL or AML patients with t (8;21), DCs were confirmed to be of leukemic origin by fluorescence in situ hybridization analysis.

Detection and clinical significance of human acute myeloid leukaemia progenitors capable of long-term proliferation in vitro

Acute myeloid leukaemia (AML) blasts within individual patients are heterogeneous in their surface antigen expression and proliferative ability suggesting that, subsequent to transformation, differentiation occurs creating a hierarchy of progenitors in AML. Cells that can produce AML colonies (colony forming units, CFU) in growth factor containing suspension cultures (SC) over 4-8 weeks have a phenotype similar to AML progenitors that engraft non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice, but different from bulk AML blasts, suggesting that these AML SC-initiating cells (SC-IC) may be early progenitors. In this study, we evaluated culture conditions that provide for optimal growth of AML progenitors capable of long-term proliferation. The frequency of CFU, both initially and after 2-4 weeks of SC, varied over four logs between individual patients and was not related to French-American-British subtype. Using limiting dilution, the proliferative potential of individual SC-IC varied from 1 to 480 CFU. The frequency of CFU from SC after > 4 weeks was prognostic for patient survival, and correlated with NOD/SCID engrafting ability. These results suggest the use of long-term culture as an assay for AML cells with leukaemia sustaining potential.

Neopterin production in SCID mice injected with human peripheral blood mononuclear cells

Intraperitoneal transfer of peripheral blood mononuclear cells (PBMC) from human EBV+ donors into severe combined immunodeficiency (SCID) mice is a suitable model for studying some aspects of lymphomagenesis and immune activation. Neopterin is a soluble immune marker which was found to be a useful indicator for immune activation processes in humans, e.g. to monitor immunological complications in allograft recipients or to predict prognosis in HIV-infected individuals. In contrast, this pteridine compound is normally synthesized in murine organism in only very low amounts. The measurement of neopterin concentrations in serum and urine should be feasible in SCID mice reconstituted with human PBMC. In this study, we examined the usability of this experimental model for monitoring human T cell activation by neopterin measurements. The production of neopterin by SCID mice after injection of freshly isolated human PBMC, purified B or T cells and cultured Epstein-Barr virus (EBV)+ lymphoblastoid cells (LCL) was determined. It was found that neopterin can be detected early after injecting SCID mice with PBMC, whereas injection of purified human T or B cells did not result in neopterin production. Highest neopterin levels were detected in mice treated with LCL cells when developing lymphoma. We discuss the possible sources of neopterin along this process and its usefulness in this model.

Monitoring of engraftment and progression of acute lymphoblastic leukemia in individual NOD/SCID mice

OBJECTIVE

The aim of this study was to develop an animal model for human acute lymphoblastic leukemia (ALL) in which the kinetics and characteristics of leukemia can be sequentially monitored in individual mice.

MATERIALS AND METHODS

NOD/SCID mice were inoculated intravenously with primary ALL. Progression of leukemia was monitored throughout the development of disease by determination of absolute leukemic cell counts (LCC) in peripheral blood.

RESULTS

LCC as low as 10(4) leukemic cells/mL blood could be detected. ALL cells from 5 of 5 patients engrafted, and after identification of the first leukemic cells in peripheral blood, LCC increased exponentially. Leukemic cells showed specificity of homing to spleen and bone marrow, and LCC strongly correlated with the level of leukemic engraftment in these organs throughout disease progression, demonstrating that LCC are representative for overall leukemic burden. Cytogenetic analysis of leukemic cells recovered after six successive in vivo transfers revealed no major karyotypic changes as compared to primary cells, and selection of the dominant clones was observed. This selection process was reflected by an increase in the rate of leukemic progression as compared to the first inoculation, demonstrating the accuracy with which kinetics of leukemic progression can be studied by determination of LCC.

CONCLUSIONS

This model is suitable for detailed studies of kinetics and characteristics of ALL in vivo, and it may be useful for monitoring effects of novel therapeutic regimens.

An animal model for anaplastic large cell lymphoma in the immunocompetent syngeneic C57Bl/6 mouse

We report on the analysis of a murine anaplastic lymphoid cell line TS1G6, established recently by interleukin (IL)-9 transfection. TS1G6 revealed a highly characteristic pattern of large anaplastic cells with mononuclear, binuclear, or multinuclear cells resembling Hodgkin (H) or Sternberg-Reed (SR) cells. This cell line is tumorigenous after injection of as few as 10(4) lymphoma cells into nude or immunocompetent C57Bl/6 mice and leads to death from progressive disease of all treated animals within a few weeks. The histological analysis of these tumors revealed a diffuse large cell malignant lymphoma that is morphologically almost identical to human anaplastic large cell lymphoma (ALCL). The lymphoma cells did not show overexpression of the anaplastic lymphoma kinase (ALK) gene, which is found in about 50% of the cases of human ALCL. Thus, this model may be an animal model for an important subset of human ALCL. The cytokine profile, which is of the T helper 2 type, showed strong parallels to the human lymphoma counterpart. Mice suffering from such lymphomas could not be cured with a regimen using high dose cyclophosphamide similar to many ALCL patients. Such an animal model for ALCL has not yet been recognized, but may provide the basis for investigating new antitumor immunotherapies in a fully immunocompetent host.

Porcine stem cell engraftment and seeding of murine thymus with class II+ cells in mice expressing porcine cytokines: toward tolerance induction across discordant xenogeneic barriers

BACKGROUND

Mixed hematopoietic chimerism is a reliable means of tolerance induction, but its utility has not been demonstrated in discordant xenogeneic combinations because of the difficulty in achieving lasting hematopoietic engraftment. Miniature swine are likely to be suitable organ donors for humans. To evaluate the ability of mixed chimerism to induce swine-specific tolerance in widely disparate xenogeneic recipients, this study aimed to achieve long-lasting chimerism in a pig to mouse combination.

METHODS

Immunodeficient transgenic mice were developed by crossing transgenic founders carrying porcine interleukin-3, granulocyte macrophage-colony stimulating factor, and stem cell factor genes with severe combined immunodeficient mice or non-obese diabetic/severe combined immunodeficient mice. Swine bone marrow transplantation was performed in these mice, and porcine chimerism was followed for 20 weeks.

RESULTS

Whereas swine cells became undetectable in all non-Tg littermates by 7 weeks, high levels of porcine hematopoietic chimerism, including the presence of porcine class II+ cells in the host thymus were maintained in Tg mice for >20 weeks. Colony-forming assays revealed the presence of large numbers of swine hematopoietic progenitor cells in the marrow of these mice at 20 weeks after bone marrow transplantation.

CONCLUSIONS

These transgenic mice demonstrate for the first time that spontaneous migration of marrow donor antigen-presenting cells to an intact recipient thymus can occur and that porcine stem cells can persist in this highly disparate species combination. These data therefore support the feasibility of the eventual goal of tolerance induction by mixed chimerism in discordant xenogeneic combinations.

Conditions that enable human hematopoietic stem cell engraftment in all NOD-SCID mice

BACKGROUND

Transplantation of human hematopoietic stem cells is the only true test of their long-term repopulation potential. Models are readily available to evaluate murine hematopoietic stem cells, but few exist that allow reliable quantification of human stem cells. The non-obese diabetic-severe combined immunodeficient (NOD-SCID) mouse model enables quantification of human hematopoietic stem cells, but the conditions that permit human engraftment in all animals have yet to be defined. The aims of the project were, therefore, to describe the variables that allow human engraftment in the NOD-SCID mouse model and the techniques that accurately quantify this engraftment.

METHODS

NOD-SCID mice that had or had not received 250, 325, or 400 cGy irradiation received cord blood (CB) mononuclear or CD34+ cells i.v. or i.p. Mice were killed 6 weeks after transplantation, and the bone marrow, spleen, and thymus were harvested. Four-color flow cytometric analysis, semi-quantitative PCR, myeloid and erythroid progenitor, and stem cell assays were used to monitor human engraftment.

RESULTS

A 250 or 325 cGy and i.v. injection of CB mononuclear or CD34+ cells is required to detect multilineage human engraftment in the bone marrow, spleen, or thymus of NOD-SCID mice. Four-color flow cytometric analysis and semi-quantitative PCR enable accurate detection of 0.1% human cells. Progenitor and stem cell assays provide functional information about the engrafted cells.

CONCLUSIONS

Successful development of the NOD-SCID mouse model and techniques to assess human engraftment now allow it to be used reliably to analyze the effects of short-term cytokine exposure on the long-term repopulating capacity of CB stem cells.

Development and analysis of transgenic mice expressing porcine hematopoietic cytokines: a model for achieving durable porcine hematopoietic chimerism across an extensive xenogeneic barrier

The capacity of mixed hematopoietic chimerism to induce tolerance has not been demonstrated in discordant xenogeneic species combinations because of the difficulty in achieving lasting hematopoietic engraftment. In an effort to create a model of long-lasting disparate xenogeneic hematopoietic chimerism, we have developed transgenic (Tg) mice carrying porcine cytokines. Three lines of Tg mice were generated: one carrying porcine IL-3 and GM-CSF genes only (termed IL/GM) and the remaining two lines carrying in addition, the soluble SCF gene (termed IL/GM/sS) or membrane-bound SCF gene (termed IL/GM/mS). Sera from mice with IL/GM and IL/GM/sS transgenes markedly stimulated the proliferation of swine marrow cells in vitro. However, proliferation of swine marrow cells was not induced in cultures containing IL/GM/mS sera. Consistent with these observations, ELISA assays revealed detectable levels of porcine cytokines in the sera of IL/ GM and IL/GM/sS, but not in sera of IL/GM/mS Tg mice. Marrow stromal cells prepared from all three kinds of Tg mice, but not those from non-Tg littermates, were capable of supporting the growth of porcine hematopoietic cells in vitro. Immunodeficient Tg mice were generated by crossing Tg founders with C.B-17 SCID mice for five generations. All Tg immunodeficient mice showed improved porcine hematopoietic engraftment compared with non-Tg controls. These Tg mice provide a useful model system for studying porcine hematopoietic stem cells, and for evaluating the feasibility of donor-specific tolerance induction by mixed chimerism across highly disparate xenogeneic barriers.

Enhancement of swine progenitor chimerism in mixed swine/human bone marrow cultures with swine cytokines

OBJECTIVE

The induction of transplantation tolerance across xenogeneic barriers by bone marrow transplantation holds great promise, but engraftment of xenogeneic stem cells has been difficult to achieve. Part of this difficulty is due to species-specific differences in regulatory cytokines and elements of the stromal microenvironment, which we studied here.

MATERIALS AND METHODS

We developed a system where fresh bone marrow cells from swine and human are cultured on human bone marrow stroma in order to study these limiting factors in a clinically relevant species combination.

RESULTS

We report here the ability of recombinant swine interleukin (IL)-3 and c-kit ligand (KL) to specifically enhance swine hematopoietic chimerism in this system. In the absence of exogenous swine cytokines, there were about half as many swine progenitors as human progenitors at 1, 2, and 4 weeks of culture. When used alone, swine IL-3 led to a notable but transient increase in the relative ratio of swine progenitors, while addition of swine KL increased the ratio of swine progenitors only modestly and only at later time points. In contrast, when swine IL-3 and KL were added together, there was a two- to fourfold increase in the ratio of swine to human progenitors at all times tested.

CONCLUSION

These data demonstrate that both swine IL-3 and KL are needed for prolonged enhancement of swine progenitor chimerism under these conditions, and suggest that the species specificity of either one or both of these cytokines may represent an important barrier to prolonged engraftment of swine bone marrow in humans.

Purification of hematopoietic stem cells for further biological study

For many years, the hematopoietic system has provided a convenient and fascinating model for studies of the molecular processes regulating cell growth and differentiation. However, this system also poses considerable challenges because the most primitive "stem" cells as well as their initial differentiating progeny are normally present in hematopoietic tissues at extremely low frequencies and no unique, stable phenotype has yet been identified to allow hematopoietic cells with specific stem and progenitor functions to be measured directly. Rather, this requires the use of functional assays that detect their developmental properties and take several weeks to complete. Accordingly, many investigations of primitive hematopoietic cell behavior and their responses to molecular cues in the environment have relied on the development of cell separation techniques specifically designed for obtaining highly enriched populations of primitive hematopoietic cells. Key to these procedures is the use of a preenrichment step(s) in which differences in cell density, size, or sensitivity to pharmacological agents or surface phenotype are exploited to first "debulk" the sample. This step can then be followed by a more selective antibody-mediated procedure to generate useful numbers of highly purified cells. Batchwise immunoadsorption techniques offer many advantages for obtaining enriched populations of hematopoietic progenitors because they avoid the nonspecific toxicity seen with antibody-mediated cell killing and are suitable for rapidly processing large samples. For any cell separation procedure, a balance must be struck between the purity and the recovery of the desired cells because steps to increase cell purity usually reduce yields. Both the negative and the positive selection techniques are useful strategies but negative selection usually requires one less manipulation step and circumvents potential effects incurred by the presence of antibody on the surface of the cell being isolated. Specific details for the use and results obtained with an immunomagnetic negative column selection technique are then presented.

Prognostic significance of T-lineage leukemic cell growth in SCID mice: a Children's Cancer Group study

Contemporary intensive therapies are effective for the majority of pediatric T-lineage acute lymphoblastic leukemia (ALL) patients, thus current challenge is to identify patients who may benefit from alternative treatment modalities. Previously, we demonstrated that human leukemic cell growth in the severe combined immunodeficiency (SCID) mouse was a significant prognostic factor for very high risk B-lineage ALL patients. In the current report we show that primary leukemic cells from 24 of 88 (27%) T-lineage ALL patients (SCID+) caused histopathologically detectable leukemia in SCID mice. These SCID+ patients were similar to SCID- (n = 64) patients with respect to virtually all presenting features, including age, sex, race, and leukocyte count. Growth of primary leukemic cells in SCID mice was not a significant predictor of outcome for the aggregate population of T-lineage ALL patients. Two-year event-free survival (EFS) outcomes for SCID+ patient and SCID- patients were 76.2% (SD = 5.6%) and a 64.0% (SD = 10.4%; p = 0.20). Overall survival also was similar between the two groups (p = 0.36). Among the subset of patients with M1 or M2 marrow status by day 7 of induction chemotherapy (rapid early responders), those who were SCID+ had poorer outcomes than those who were SCID-, with a 2-year EFS of 68.4% (SD = 11.9%) vs. 85.7% (SD = 6.0%) and relative hazard rate of 3.06 (p = 0.06). These data suggest that leukemic cell growth in SCID mice may identify a subset of T-lineage ALL patients who are at higher risk for relapse despite achieving a rapid early response to induction chemotherapy.

Distinct in vivo engraftment and growth patterns of t(1;19)+/E2A-PBX1+ and t(9;22)+/BCR-ABL+ human leukemia cells in SCID mice

The SCID mouse represents a valuable tool for assessing growth characteristics and drug sensitivity of human leukemic cells. We have examined differences in the engraftment patterns in SCID mice of primary human leukemic cells isolated from children (< 21 years old) with either t(1;19)+/E2A-PBX1+ or t(9;22)+/BCR-ABL+ acute lymphoblastic leukemia. Leukemic cells from 13/24 t(1;19)+/E2A-PBX1+ patients caused overt leukemia in SCID mice. Macroscopic lesions were evident in 6/13 cases, with multiple sites involved in some mice: hepatomegaly,(3) splenomegaly(4), thymic enlargement; liver tumors(1), kidney tumors(1), abdominal tumors(1). Microscopic lesions in SCID mouse organs were present in all 13 cases and involved the bone marrow, brain, heart, gut, liver, kidney, lung, ovary, pancreas, skeletal muscle, spleen, and thymus. Leukemic cells from 5/20 t(9;22)+/BCR-ABL+ patients caused overt leukemia in SCID mice. Notably, macroscopic lesions (splenomegaly; leukemic bones; hepatic tumors) were observed in only 1 case. In all 5 cases, microscopic lesions were found in the mouse bone marrow. Additional microscopic lesions were restricted to skeletal muscle, spleen, and mesentery (1 case) or thymus (1 case). These findings differ markedly from those of t(1;19)+/E2A-PBX1+ leukemic cells due to the lack of involvement of major organs such as liver, pancreas, kidney, skin, or brain. These data illustrate the biological heterogeneity of childhood ALL and suggest that the differential risks associated with t(1;19)+/E2A-PBX1+ and t(9;22)+/BCR-ABL ALL might arise from unique engraftment and proliferation capabilities of the respective leukemic cell populations.

Enhanced human cell engraftment in mice deficient in RAG2 and the common cytokine receptor gamma chain

Xenotransplantation of human cells into immunodeficient mice has been used to develop models of human haemopoiesis and lymphoid cell function. However, the utility of existing mouse strains can be limited by shortened life-spans, spontaneous production of functional lymphocytes with ageing, and residual innate immunity leading to variable levels of engraftment. Mice with a deletion of the common cytokine receptor gamma chain (gamma c) gene have reduced numbers of peripheral T and B lymphocytes, and absent natural killer cell (NK) activity. A genetic cross with a recombinase activating gene 2 (RAG2)-deficient strain produced mice doubly homozygous for the gamma c and RAG2 null alleles (gamma c-/RAG2-). These mice have a stable phenotype characterized by the absence of all T lymphocyte. B lymphocyte and NK cell function. Injection of human B-lymphoblastoid cells resulted in earlier fatal metastatic lymphoproliferative disease than in NOD/LtSz-scid controls. This was particularly evident in animals injected intravenously, possibly because of residual NK activity in NOD/LtSz-scid mice. Levels of engraftment with peripheral-blood-derived human lymphocytes were also increased and associated with higher CD4/CD8 ratios. These findings demonstrate that this new strain of immunodeficient mice has significant advantages over existing strains for engraftment of human cells, and may be useful for study of adoptive immunotherapy and novel therapies for GvHD and HIV infection.

Prognostic significance of B-lineage leukemic cell growth in SCID mice: a Children's Cancer Group Study

Primary leukemic cells isolated from children (N = 681 ) with newly diagnosed B-lineage ALL enrolled on risk-adjusted treatment protocols of the Children's Cancer Group (CCG) were injected via the tail vein into 7-10 week old SCID mice. Leukemic cells from 104 of 681 patients (15.3%) were able to engraft and proliferate in one or more SCID mouse organs. These SCID+ patients were somewhat more likely than SCID patients to be older than 10 years of age (p = 0.03) and have WBC counts >20,000/microL (p = 0.04), but the groups were similar with respect to all other presenting features. Event-free survival (EFS) outcome at 3 years of follow-up was similar for SCID+ patients compared with SCID- patients (79.2%, SD = 5. 1% vs. 84.8%, SD = 2.8%; p = 0.20). Overall survival also was similar between the two groups (p = 0.93). This result was maintained within the subgroups of lower risk (N = 448) and higher risk (N = 233) patients. However, there were trends for poorer outcome among patients whose cells caused overt leukemia in SCID mice and infiltrated either 6 or more organs (p = 0.03), skeletal muscle (p = 0.0003), kidney (p = 0.05), or spleen (p = 0.06). Thus, engraftment of primary leukemic cells in SCID mice was not a significant predictor of outcome for the aggregate population of B-lineage ALL patients, the majority of whom were low risk, treated according to contemporary intensive chemotherapy programs of the CCG. However, development of disseminated overt leukemia and infiltration of SCID mouse skeletal muscle by primary leukemic cells from adjacent bone marrow may reflect a biologically more aggressive disease and identify patients at higher risk for treatment failure.

Primary blasts from infants with acute lymphoblastic leukemia cause overt leukemia in SCID mice

The establishment of an in vivo animal model system for infant acute lymphoblastic leukemia (ALL) would allow the testing of new agents against primary leukemic cells from infant ALL patients. We have demonstrated previously that growth of B-lineage leukemic cells in mice with severe combined immunodeficiency (SCID) was a significant prognostic factor for children with high risk ALL. We now have examined the significance of this prognostic variable for 13 infants with newly diagnosed ALL treated at participating institutions of the Children's Cancer Group (CCG). Chromosomal translocations were detected in 10/12 evaluated cases, including five with t(4;11), one each with t(7;9) and t(7;11), t(1;19), and t(9;22), and two with t(11;19). Twelve of the thirteen infants with ALL achieved remissions following induction chemotherapy. Primary leukemic cells from 8 of the 13 infants caused overt leukemia in SCID mice. Among these 8 SCID+ infants, 7 were CD10- and seven had cytogenetic or molecular evidence of an 11q23 rearrangement. Six of the 8 SCID+ infants have relapsed; only 2 remain in remission following chemotherapy or bone marrow transplant. However, among the 5 SCID- infants there were also two relapses. These data are suggestive of a poorer outcome for SCID+ infants, but larger numbers of patients must be analyzed to assess their statistical significance. In summary, we have established a SCID mouse model for human infant ALL that will be useful for 1) predicting short-term and long-term outcome of patients, 2) testing pharmacokinetics, efficacy, and toxicity of new agents, and 3) elucidating the in vivo mechanisms of chemotherapeutic drug resistance in infant ALL.

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.

Assay of human stem cells by repopulation of NOD/SCID mice

The only conclusive method to assay stem cells is to follow their ability to repopulate conditioned recipients, making it difficult to study human stem cells. The development of systems to transplant human hematopoietic cells into immune-deficient mice lays the foundation for such an experimental repopulation assay for primitive human cells. Cell purification and gene marking studies have shown that the repopulating cells, termed severe-combined immunodeficiency (SCID) mouse-repopulating cells (SRC), are primitive and distinct from most of the progenitors that are detected using short and long-term in vitro culture assays. The SRC are exclusively CD34+CD38- and poorly infected with retrovirus vectors. These gene marking data are reminiscent of the human clinical trials establishing that the SRC assay is a good surrogate to develop improved transduction methods. Limiting dilution analysis has been used to establish a quantitative assay for SRC that can be used to precisely determine the effect of various cytokine cocktails on the proliferation and differentiation of SRC during in vitro culture.

Severe Combined Immunodeficiency Mice Engrafted With Human T Cells, B Cells, and Myeloid Cells After Transplantation With Human Fetal Bone Marrow or Liver Cells and Implanted With Human Fetal Thymus: A Model for Studying Human Gene Therapy

To develop an in vivo model wherein human hematopoiesis occurs, we transplanted severe combined immunodeficiency (SCID) mice with either human fetal bone marrow (HFBM) or human fetal liver (HFL). After transplantation of SCID mice with cultured HFBM (BM-SCID-hu mice) or HFL cells (Liv-SCID-hu mice), significant engraftment of the mouse bone marrow (BM) and population of the peripheral blood with human leukocytes was detected. Human colony-forming unit–granulocyte macrophage and burst forming unit-erythroid were detected in the BM of the BM-SCID-hu and Liv-SCID-hu mice up to 8 months after transplantation. When the HFBM or HFL cells were transduced with a retroviral vector before transplantation, integrated retroviral sequences were detected in human precursor cells present in the SCID mouse BM and in leukocytes circulating in the peripheral blood (PB) up to 7 months after transplantation. The PB of the BM-SCID-hu mice also became populated with human T cells after implantation with human thymic tissue, which provided a human microenvironment wherein human pre-T cells from the BM could mature. When the HFBM was retrovirally transduced before transplantation, integrated retrovirus was detected in sorted CD4+CD8+ double positive and CD4+ single positive cells from the thymic implant and CD4+ cells from the PB. Taken together, these data indicated that the BM of our BM-SCID-hu and Liv-SCID-hu mice became engrafted with retrovirally transduced human hematopoietic precursors that undergo the normal human hematopoietic program and populate the mouse PB with human cells containing integrated retroviral sequences. In addition to being a model for studying in vivo human hematopoiesis, these mice should also prove to be a useful model for investigating in vivo gene therapy using human stem/precursor cells.

Severe Combined Immunodeficiency Mice Engrafted With Human T Cells, B Cells, and Myeloid Cells After Transplantation With Human Fetal Bone Marrow or Liver Cells and Implanted With Human Fetal Thymus: A Model for Studying Human Gene Therapy

To develop an in vivo model wherein human hematopoiesis occurs, we transplanted severe combined immunodeficiency (SCID) mice with either human fetal bone marrow (HFBM) or human fetal liver (HFL). After transplantation of SCID mice with cultured HFBM (BM-SCID-hu mice) or HFL cells (Liv-SCID-hu mice), significant engraftment of the mouse bone marrow (BM) and population of the peripheral blood with human leukocytes was detected. Human colony-forming unit–granulocyte macrophage and burst forming unit-erythroid were detected in the BM of the BM-SCID-hu and Liv-SCID-hu mice up to 8 months after transplantation. When the HFBM or HFL cells were transduced with a retroviral vector before transplantation, integrated retroviral sequences were detected in human precursor cells present in the SCID mouse BM and in leukocytes circulating in the peripheral blood (PB) up to 7 months after transplantation. The PB of the BM-SCID-hu mice also became populated with human T cells after implantation with human thymic tissue, which provided a human microenvironment wherein human pre-T cells from the BM could mature. When the HFBM was retrovirally transduced before transplantation, integrated retrovirus was detected in sorted CD4+CD8+ double positive and CD4+ single positive cells from the thymic implant and CD4+ cells from the PB. Taken together, these data indicated that the BM of our BM-SCID-hu and Liv-SCID-hu mice became engrafted with retrovirally transduced human hematopoietic precursors that undergo the normal human hematopoietic program and populate the mouse PB with human cells containing integrated retroviral sequences. In addition to being a model for studying in vivo human hematopoiesis, these mice should also prove to be a useful model for investigating in vivo gene therapy using human stem/precursor cells.

The contribution of animal models to the development of treatments for hematologic recovery following myeloablative therapy: a review

This review describes the role that animal models have played in the development of clinical procedures for growth factor and hematopoietic cell therapies following high-dose cancer chemotherapy, radiotherapy or both. Data are discussed describing animal models that add to the understanding of human hematopoiesis, including myeloid and lymphoid lineage localization and in vivo maturation. Finally, current animal models of cytokine and cell therapies are presented in the context of their contributions to early clinical trials and future therapies. These studies underscore the past and current contributions animal investigations have made to improving clinical therapies.

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.

Offspring of xenogeneically-reconstituted scid/scid mice are capable of a primary xenogeneic immune response to DNP-KLH

Human peripheral blood leukocyte (PBL) reconstitution of severe combined immunodeficient (SCID) mice has provided a small animal model system (hu-PBL-SCID) useful for the study of the human immune system and disease pathogenesis. Transfer of xenogeneic PBL from donors other than humans has also been successful; however, the controversy remains regarding the capability of xenogeneically engrafted lymphocytes to mount a primary immune response. Human cells have been identified in offspring from hu-PBL-SCID but were not evaluated for a primary immune response. In the present study, offspring of bovine PBL-reconstituted SCID mice (F1-PBL-SCID-bo) were assessed for specific immune function. Sera from all of the F1-PBL-SCID-bo contained relatively low levels of bovine IgG 5 weeks after birth but bovine Ig became undetectable by 14 or 18 weeks. Eight F1-PBL-SCID-bo (23 or 27 weeks of age) were immunized with a single dose of 100 mu g dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH). Individual cells secreting bovine antibody were enumerated using the ELISA-plaque assay. One week after immunization, bovine cells secreting bovine immunoglobulin (IgG) specific for DNP-KLH were identified in the spleens from three of the F1-PBL-SCID-bo at a frequency of one antibody-secreting cell per 9 x 10(3) to 1 x 10(6) spleen cells. Thus, xenogeneic lymphocytes, passed from the mother to her offspring, retain the capacity for a primary immune response to DNP-KLH.

Improved engraftment of human hematopoietic cells in severe combined immunodeficient (SCID) mice carrying human cytokine transgenes

We have generated immunodeficient scid-/scid- (SCID)-transgenic mice expressing the genes for human interleukin 3, granulocyte/macrophage-colony stimulating factor, and stem cell factor. We have compared engraftment and differentiation of human hematopoietic cells in transgenic SCID mice with two strains of nontransgenic SCID mice. Human bone marrow cells carrying the CD34 antigen or human umbilical cord blood were injected into sublethally irradiated recipients. Human DNA was detected by polymerase chain reaction in peripheral blood and bone marrow of 14 of 28 transgenic SCID mice after transplantation, but in only 2 of 15 nontransgenic SCID littermates at a 10-fold lower level. Bone marrow cultures 8 wk after transplantation of cord blood gave rise to human burst-forming unit erythroid, colony-forming unit granulocyte/macrophage, or granulocyte/erythroid/macrophage/megakaryocyte colonies. Engraftment was observed for up to 6 mo in transgenic SCID mice, twice as long as nontransgenic littermates or previous studies in which transplanted SCID mice were given daily injections of growth factors. We conclude that the level and duration of engraftment of human cells in SCID mice can be improved by expression of human cytokine transgenes and that transgenic SCID mice are an efficient model system for the study of human hematopoiesis.

Alternative signals to RAS for hematopoietic transformation by the BCR-ABL oncogene

Biological function of the BCR-ABL oncogene is dependent on its activated tyrosine kinase. Mutations that inactivate the SRC homology 2 (SH2) domain, the GRB2-binding site in BCR, or the major autophosphorylation site of the kinase domain selectively disrupt downstream signaling but not tyrosine kinase activity. Despite a loss of fibroblast transformation activity, all three mutants retain the ability to render hematopoietic cell lines growth factor independent and transform primary bone marrow cells in vitro. In vivo tests of malignant potential reveal a most critical role for signals dependent on the BCR-ABL SH2 domain. The efficiency of both fibroblast and hematopoietic transformation by BCR-ABL is strongly affected by increased dosage of the SHC adapter protein, which can connect tyrosine kinase signals to RAS. The BCR-ABL oncogene activates multiple alternative pathways to RAS for hematopoietic transformation.

Reconstitution of SCID mice with human lymphoid and myeloid cells after transplantation with human fetal bone marrow without the requirement for exogenous human cytokines

Investigation of human hematopoietic maturation has been hampered by the lack of in vivo models. Although engraftment of irradiated C.B-17 scid/scid (SCID) mice with human progenitor cells occurred after infusion with human pediatric bone marrow cells, significant engraftment of the mouse bone marrow with human cells was dependent upon continuous treatment with exogenous human cytokines. Furthermore, despite cytokine treatment, only minimal peripheral engraftment of these mice with human cells was observed. In the present study, after infusion of irradiated SCID mice with pre-cultured human fetal bone marrow cells (BM-SCID-hu mice), their bone marrow became significantly engrafted with human precursor cells and their peripheral lymphoid compartment became populated with human B cells and monocytes independently of the administration of extraneous human cytokines. Examination of the bone marrow of the BM-SCID-hu mice for human cytokine mRNA gene expression demonstrated human leukemia inhibitory factor mRNA and interleukin 7 mRNA in nine of nine BM-SCID-hu mice and macrophage-colony-stimulating factor mRNA in seven of eight BM-SCID-hu mice. This was an intriguing observation because these cytokines regulate different stages of human hematopoiesis. Since engraftment occurs in the absence of exogenous cytokine treatment, the BM-SCID-hu mouse model described should provide a useful in vivo system for studying factors important in the maturation of human myeloid and lymphoid cells in the bone marrow and the behavior of the mature human cells after dissemination into the peripheral lymphoid tissue.

Human hematolymphoid cells in SCID mice

The severe combined immunodeficient C.B.-17 scid/scid (SCID) mouse has been widely used to study the normal processes of murine lymphoid differentiation. To create an in vivo model of the human hematolymphoid system, this mouse strain has been engrafted with human organ systems (the SCID-hu mouse) or with human peripheral blood mononuclear cells (the hu-PBL-SCID mouse). These mouse models have now been characterized and used to analyze human infectious diseases, hematopoiesis, malignancies and vaccines.

A cell initiating human acute myeloid leukaemia after transplantation into SCID mice

Most human acute myeloid leukaemia (AML) cells have limited proliferative capacity, suggesting that the leukaemic clone may be maintained by a rare population of stem cells. This putative leukaemic stem cell has not been characterized because the available in vitro assays can only detect progenitors with limited proliferative and replating potential. We have now identified an AML-initiating cell by transplantation into severe combined immune-deficient (SCID) mice. These cells homed to the bone marrow and proliferated extensively in response to in vivo cytokine treatment, resulting in a pattern of dissemination and leukaemic cell morphology similar to that seen in the original patients. Limiting dilution analysis showed that the frequency of these leukaemia-initiating cells in the peripheral blood of AML patients was one engraftment unit in 250,000 cells. We fractionated AML cells on the basis of cell-surface-marker expression and found that the leukaemia-initiating cells that could engraft SCID mice to produce large numbers of colony-forming progenitors were CD34+ CD38-; however, the CD34+ CD38+ and CD34- fractions contained no cells with these properties. This in vivo model replicates many aspects of human AML and defines a new leukaemia-initiating cell which is less mature than colony-forming cells.

A study on the engraftment and trafficking of bovine peripheral blood leukocytes in severe combined immunodeficient mice

Bovine lymphoid cells were engrafted into untreated and into sublethally irradiated scid/scid mice, following intraperitoneal (i.p.) injection of bovine peripheral blood leukocytes (PBL). To distinguish bovine from murine cells, bovine PBL were stained prior to i.p. injection with a fluorescent cell linker compound, PKH26-GL and, after cell recovery, labelled with a monoclonal antibody (mAb) reactive with the bovine pan leukocyte cell surface marker, CD45, and analyzed by flow cytometry. This dual labelling system was used to monitor tissue localization and migration of bovine cells within PBL-SCID-bo from 30 min to 64 days after bovine PBL injection. Inoculated bovine PBL were rapidly cleared from the peritoneal cavity of PBL-SCID-bo over the first 24 h after injection, then bovine cell numbers within the peritoneal cavity increased gradually over the next 35 days. No bovine cells were observed in the peritoneal wash from either non-irradiated or irradiated mice after Day 56. Bovine cells were detected in the spleens of both non-irradiated and irradiated mice 12-14 days after inoculation, but were undetectable in non-irradiated and irradiated mice after Day 56, and in irradiated mice after Day 35. This decrease coincided with a significant reduction in both the numbers of bovine cells in the peritoneal cavity, and in the levels of bovine Ig detected in the sera. Bovine IgG and bovine IgM were detected in both normal and irradiated PBL-SCID-bo by 4 days after PBL injection, and remained detectable to 8 weeks after inoculation. T-cells appeared to be the predominant bovine cell population in the spleens. In a small proportion of both normal and irradiated PBL-SCID-bo, spleens three to 20 times the size of a normal SCID mouse spleen were observed. Relatively high levels of bovine cells were detected in the thymuses of some irradiated PBL-SCID-bo. Sporadic, low levels of bovine cells were observed in the mesenteric lymph nodes, peripheral blood, and kidneys of normal and irradiated mice, and in the lungs and livers of non-irradiated but not irradiated PBL-SCID-bo. Sublethal gamma irradiation of SCID recipients appeared to enhance engraftment of bovine cells into the murine spleen and thymus.