NOD-SCID IL2R Research Articles

A mouse model for ulcerative colitis based on NOD-scid IL2R γnull mice reconstituted with peripheral blood mononuclear cells from affected individuals.

ABSTRACTAnimal models reflective of ulcerative colitis (UC) remain a major challenge, and yet are crucial to understand mechanisms underlying the onset of disease and inflammatory characteristics of relapses and remission. Mouse models in which colitis-like symptoms are induced through challenge with toxins such as oxazolone, dextran sodium sulfate (DSS) or 2,4,6-trinitrobenzenesulfonic acid (TNBS) have been instrumental in understanding the inflammatory processes of UC. However, these neither reflect the heterogeneous symptoms observed in the UC-affected population nor can they be used to test the efficacy of inhibitors developed against human targets where high sequence and structural similarity of the respective ligands is lacking. In an attempt to overcome these problems, we have developed a mouse model that relies on NOD-scid IL2R γnull mice reconstituted with peripheral blood mononuclear cells derived from UC-affected individuals. Upon challenge with ethanol, mice developed colitis-like symptoms and changes in the colon architecture, characterized by influx of inflammatory cells, edema, crypt loss, crypt abscesses and epithelial hyperplasia, as previously observed in immune-competent mice. TARC, TGFβ1 and HGF expression increased in distal parts of the colon. Analysis of human leucocytes isolated from mouse spleen revealed an increase in frequencies of CD1a+, CD64+, CD163+ and TSLPR+ CD14+ monocytes, and antigen-experienced CD44+ CD4+ and CD8+ T-cells in response to ethanol. Analysis of human leucocytes from the colon of challenged mice identified CD14+ monocytes and CD11b+ monocytes as the predominant populations. Quantitative real-time PCR (RT-PCR) analysis from distal parts of the colon indicated that IFNγ might be one of the cytokines driving inflammation. Treatment with infliximab ameliorated symptoms and pathological manifestations, whereas pitrakinra had no therapeutic benefit. Thus, this model is partially reflective of the human disease and might help to increase the translation of animal and clinical studies.

Therapeutic Targeting of CD163 on Hematopoietic Progenitor Cells By Novel Monoclonal Antibody TBI 304H Demonstrates an Increase in Erythropoiesis in Humanized Mice

▪Hemoglobin (Hb) is known to stimulate erythropoiesis, a process that may be mediated by CD163. CD163 is a receptor for the hemoglobin-haptoglobin (Hb-Hp) complex expressed on monocyte/macrophages as well as a subpopulation of human CD34+ hematopoietic progenitor cells (HPCs). We have demonstrated that administration of ligands to the CD163 receptor can measurably stimulate erythropoiesis in human CD34+ cell-engrafted severe-combined immunodeficiency (SCID) mice. To better elucidate the role of CD163 in hematopoiesis, we investigated the effects of the natural ligand to CD163 (Hb-Hp) as well as a stimulatory antibody, TBI 304H, on HPCs in vivo. SCID mice engrafted with human CD34+ cells were used as a model system were used to investigate the effect of Hb and anti-CD163 monoclonal antibodies (TBI 304 and TBI 304H) on human hematopoiesis in vivo. In an initial study, NOD-SCID IL2R gammanull (NSG) mice were engrafted with human CD34+ cells and animals with < 30% human CD45+ cells in the peripheral blood were administered 2 mg Hb/mouse, or 100 or 500 µg/mouse TBI 304 every 4 days for a total of four doses. At study termination on day 14, bone marrow cells (BMCs) were examined by flow cytometry and CD34+ cells were recovered from the BMCs for enumeration in colony-forming assays. Hemoglobin administration resulted in an increase of human CD34+ cells ranging from 4% to 7% of BMCs and a corresponding 57% increase in colony-forming cells (CFCs) over control animals. In contrast, the monoclonal antibody (mAb), TBI 304, produced a dose-dependent decrease in CD34+ and colonies, possibly reflecting a depletion of CD34+/CD163+ cells as a result of overstimulation due to the much longer circulating half-life of the mAb compared to Hb.. To confirm this hypothesis, human CD34+ cell engrafted animals were given only a single dose of 10 or 100 µg/mouse of TBI 304 and BMCs were examined earlier on day 7. TBI 304 provided a 3.5-fold increase in human CD34+ cells as well as a 1.8 to 6.7-fold increase in bone marrow erythroid lineage engraftment (huGlyA+, huCD36+ and huCD71+) and a 2-fold increase in colony-forming cells. The ability of TBI 304 to stimulate erythropoiesis in preclinical models led to the creation of an anti-CD163 mAb suitable for human clinical use. TBI 304H was generated by grafting the complementarity-determining regions derived from TBI 304 onto a humanized IgG4 framework without altering antigen specificity. An IgG4 framework, as an antibody without Fc effector function, was deemed the most suitable for an agonistic mAb. In the single dose, 7 day Hu-SCID model human CD34+ cells were mobilized from the mouse bone marrow by TBI 304H, as reflected by dose dependent decreases in huCD34+, huCD71+, and huGlyA+ cells in the mouse marrow. At the highest dose tested (500 µg/mouse) the decrease in human HPCs was similar to that found in animals administered Hb (2 mg/mouse). In this model, human hematopoiesis derived from the engrafted human CD34+ cells is not sustained and these date may reflect a mobilization of human HPCs through stimulation by an anti-CD163 antibody. Therapure has received U.S. FDA approval to conduct a Phase I trial of the novel therapeutic antibody TBI 304H. The Phase I clinical trial is a single-center, open-label, intra-subject escalating dose study, which will evaluate the safety, tolerability and pharmacokinetics of TBI 304H following administration to subjects experiencing chemotherapy-induced anemia. DisclosuresMatthews:Therapure Biopharma: Employment. Eberle-Ayres:Therapure Biopharma: Employment. Lu:Therapure Biopharma: Employment. Singh:Therapure Biopharma: Employment. Cutler:Therapure Biopharma: Employment. Bell:Therapure Biopharma: Employment.

Abstract A193: Fully human bispecific antibodies induce potent anti-tumor effects against prostate tumors in mice

Abstract Despite multiple new treatment options for patients with castrate-resistant prostate cancer (CRPC), this is still an area of un-met need. Prostate specific membrane antigen (PSMA) is highly expressed in prostate cancer and expression is maintained in CRPC, making it an attractive target for late stage prostate cancer. We have developed a novel full-length human IgG bispecific antibody that binds to human and monkey PSMA and CD3 and results in T cell activation via the CD3 complex in the presence of PSMA-expressing tumors. In cell-based assays, our PSMAxCD3 bispecific resulted in target cell-dependent activation and cytokine release by human T cells, and efficient redirected T cell lysis of prostate tumor cells. Of note, in the absence of PSMA-expressing tumor cells, no T cell activation was seen. Our bispecific antibody also resulted in redirected killing by cynomolgus monkey T cells, enabling pre-clinical toxicity studies. To examine bispecific anti-tumor efficacy in vivo, we developed xenogenic and syngeneic tumor models. In studies with human tumor cells, NOD SCID IL2R gamma deficient (NSG) mice were co-implanted with human peripheral blood mononuclear (PBMC) cells plus human prostate tumor cells (22Rv1 or C4-2), and the mice treated immediately with PSMAxCD3 i.p. Significant inhibition of tumor growth was observed against both human prostate tumors with dose levels as low as 0.004mg/kg. Importantly, PSMAxCD3 bispecific antibodies could also suppress growth of established C4-2 tumors when PBMCs were transferred i.p.. Our PSMAxCD3 bispecific was also tested in mice engrafted with human hematopoietic CD34+ stem cells. Newborn SIRPα BALB/c-Rag2null IL2rγnull (BRG) pups were engrafted with hCD34+ fetal liver cells as hematopoietic progenitor cells, which gave rise to human T, B, and NK cells, as well as granulocytes, monocytes, and DCs. Once engraftment was achieved (3 months later), mice were given C4-2 tumor cells subcutaneously. Eight days after tumor implantation, mice were treated with PSMAxCD3 (0.4mg/kg) followed by twice weekly doses. The PSMAxCD3 bispecific reduced tumor growth in this model. To examine the effects of our lead-candidate bispecifics in an immune-competent model, we engineered mice to express both human CD3 and PSMA in the corresponding murine loci. T cells from these mice were efficiently activated by antibodies to human CD3, and the expression of human PSMA allowed assessment of effects on normal tissues that may express PSMA. T cell activation, proliferation and cytokine production in response to our bispecific antibodies were examined in the absence of tumor as well as the absence of target. To assess anti-tumor efficacy in this model, a murine prostate cancer line expressing human PSMA was generated and tumors cells were implanted s.c. into these mice. Our bispecific antibodies significantly suppressed tumor growth when mice were treated at the time of implantation and also when treatment was delayed until tumors were established. Moreover, T cells were still present at normal levels in the spleen of mice treated with our bispecific at the end of the experiment and the treatment was well-tolerated. Taken together, these studies show potent anti-tumor activity of our PSMAxCD3 bispecific in several different tumor models and also demonstrate that treatment was well-tolerated in mice expressing human PSMA and human CD3. Citation Format: Alison Crawford, Kristin Vazzana, Jeffrey VanValkenburgh, Lauric Haber, Jennifer Principio, Cagan Gurer, Kara Olson, Eric Smith, Gavin Thurston, Jessica R. Kirshner. Fully human bispecific antibodies induce potent anti-tumor effects against prostate tumors in mice. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A193.

Abstract P6-06-02: Molecular characterization of a patient-derived xenograft (PDX) resource for triple negative breast cancer

Abstract The Jackson Laboratory (JAX) has developed a resource of human tumors implanted into immune deficient mice (patient derived xenografts; PDX) as a platform for testing standard of care and novel therapeutic options for Triple Negative Breast Cancer. PDX models provide an advantage over cell culture based models for testing therapeutic interventions because they retain properties such as tumor cell heterogeneity that are critical to the biological properties of a patient’s tumor and response to treatment. Tumor material acquired from biopsy or surgical resection was implanted subcutaneously into the flank of immune deficient NOD-scid IL2r gamma-chain null (NSG) mice. The PDX resource currently contains 21 established breast cancer PDX models (12 TNBC) with 24 additional models currently in development. Two of the established TNBC PDX models have BRCA1 mutations. The median age of the patients from whom tumor material was obtained for all breast models is 53 (45-89). Tumors that successfully engrafted were characterized for somatic mutations using the new JAX Clinical Cancer Panel, Copy Number Variants using the Affymetrix human 6.0 SNP array, and gene expression using both Affymetrix U133 plus v2 and RNA-Seq. Normalized gene expression was analyzed for characteristic patterns in a pan-cancer approach across all PDX models and further compared with the previously identified TNBC molecular subtypes (Lehmann et al. 2011. JCI 121:2750-2767). The combination of principal components analysis and classification via expression pattern resulted in putative matches of models to most of the known molecularly defined subtypes of TNBC tumors. Tumor bearing mice for the TNBC PDX models have been treated with docetaxel, cisplatin, cyclophosphamide and doxorubicin. Preliminary studies of tumor response to these treatment regimes revealed systematic differences that can be correlated with features of the genomic analysis, including expression subtype characterization. The JAX collection of TNBC cancer PDX models is a well-annotated, publically available resource of models with deep genomic characterization and standard of care therapy response data for use in the development of advanced therapeutic options. Genomically defined subgroups within the collection suggest strategies to refine patient selection and treatment algorithms. Information about the models along with summarized genomic data is publicly available at the Mouse Tumor Biology database PDX web portal (http://tumor.informatics.jax.org). Citation Format: Joel H Graber, James G Keck, Susan D Airhart, Carol J Bult, Edison T Liu. Molecular characterization of a patient-derived xenograft (PDX) resource for triple negative breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-06-02.

A Novel CD20xCD3 Bispecific Fully Human Antibody Induces Potent Anti-Tumor Effects Against B Cell Lymphoma in Mice

Bispecific antibodies that redirect effector T cells to kill tumor cells have shown considerable promise in both pre-clinical and clinical studies. However, these bispecific formats can have short half-lives necessitating constant infusion of the molecules into patients. We report here on a novel full-length human IgG CD20xCD3 bispecific antibody (REGN1979) that targets CD20 expressed on normal and malignant B cells and CD3 expressed on T cells in humans and cynomolgus monkeys. Our results demonstrate CD20-target cell-dependent activation and cytokine release by T cells, and efficient redirected T cell lysis of target tumor cells. Raji B cell lymphomas grown as tumors in NOD SCID IL2R gamma deficient (NSG) mice and co-implanted with human peripheral blood mononuclear (PBMC) cells were completely inhibited when treated at the time of implantation with a low dose (0.004 mg/kg; 2x/week) of REGN1979. As expected, T cells were required for this tumor inhibition, since treatment in the absence of human T cells was not effective. REGN1979 bispecific antibody also demonstrated potent activity against other tumor cells expressing CD20, as it significantly delayed CD20-transduced B16F10.9 tumor growth in immune-competent mice. Most importantly, REGN1979 induced dramatic tumor regression in large advanced (500-900 mm3) Raji tumors, associated with long-lasting tumor control. The tumor-infiltrating lymphocytes (TILs) in B cell lymphomas in these untreated NSG mice were found to express the inhibitory receptors Tim-3 and PD-1 and were the predominant fraction of T cells in the tumors and in the circulation. T cells in mice treated with REGN1979 showed decreased Tim-3 and PD-1 expression in the circulation accompanied by complete tumor regression. In further studies, REGN1979 (dosed at 0.4 mg/kg; 2x/week) was superior to rituximab therapy (dosed at 8 mg/kg; 5x/week) and comparable to the CD19xCD3 BiTE (dosed at 0.5 mg/kg; 5x/week) in suppressing established Raji tumors (200-400mm3). Pre-clinical studies in cynomolgus monkeys to assess activity of the bispecific antibody for depleting B cells in circulation and various lymphoid organs showed that a single injection of REGN1979 (0.1 mg/kg) was more potent at depleting CD20+ B cells in the mesenteric lymph nodes than a high dose of rituximab (30 mg/kg). In separate studies, REGN1979 was also found to have a long half-life (>14 days) in the circulation of monkeys following depletion of B cells. These studies show potent activity of a new class of fully human bispecific antibodies for treating tumors, and support clinical testing of REGN1979 in patients with CD20+ cancers. [Display omitted] DisclosuresVarghese:Regeneron Pharmaceuticals: Employment, Equity Ownership. Menon:Regeneron Pharmaceuticals: Employment, Equity Ownership. Rodriguez:Regeneron Pharmaceuticals: Employment, Equity Ownership. Haber:Regeneron Pharmaceuticals: Employment, Equity Ownership. Olson:Regeneron Pharmaceuticals: Employment, Equity Ownership. Duramad:Regeneron Pharmaceuticals: Employment, Equity Ownership. Oyejide:Regeneron Pharmaceuticals: Employment, Equity Ownership. Smith:Regeneron Pharmaceuticals: Employment, Equity Ownership. Thurston:Regeneron Pharmaceuticals: Employment, Equity Ownership. Kirshner:Regeneron Pharmaceuticals: Employment, Equity Ownership.

AG-221, an Oral, Selective, First-in-Class, Potent IDH2-R140Q Mutant Inhibitor, Induces Differentiation in a Xenotransplant Model

Somatic point mutations in the active site of IDH (isocitrate dehydrogenase) 1 and IDH2 genes are observed in acute myeloid leukemia (AML). These mutations lead to the production and accumulation of R-2-hydroxyglutarate (2-HG) in the tumor blast cells as well as in the plasma of patients. High levels of 2-HG have been shown to inhibit alpha-ketoglutarate-dependent dioxygenases, including epigenetic regulators (i.e. histone or DNA demethylases), resulting in altered cellular differentiation. Ex vivo experiments in primary cells from AML IDH2 mutant patients have demonstrated that IDH2 mutant inhibitors are able to revert this phenotype. In order to test the biological activity of AG-221, an oral, reversible and selective inhibitor of mutated IDH2 currently in phase I trials, we developed primary human AML xenograft models.Primary blast cells from 3 AML patients with normal karyotype (n=3), NPM1 mutation (n=3) and FLT3ITD (n=1) were injected into immunodeficient NOD SCID IL2R gamma null (NSG) mice by intrafemoral injection after sub-lethal irradiation. Medullar and peripheral tumoral engraftment was monitored by flow cytometry (using species-specific antibodies) and serum 2-HG measurements. Engraftment of IDH2-R140Q human blast cells was not lethal, but these AML cells persisted over time. Twelve months after injection, IDH2-R140Q blast cell-engrafted mice were randomized into two groups, for treatment with AG-221 (30 mpk) or vehicle (0.5% methylcellulose / 0.2% Tween 80, in water) (n=10 mice; 5 mice per condition). Treatments were administered by oral gavage for 38 days twice per day (BID). Peripheral blood was collected at multiple time points for the determination of pharmacokinetics (PK) and pharmacodynamics (PD), and the assessment of the differentiation effects by AG-221 on human tumor cells.PK/PD analyses showed good plasma exposure of AG-221 and reduction of 2-HG. Furthermore, AG-221 administration also induced a burst of proliferation of human blasts followed by myeloid differentiation starting at day 20 in peripheral blood as measured by the expression of CD11b, CD14, CD15, CD24 and cell morphology. No effects on proliferation or differentiation were seen in the absence of AG-221 administration. Histological analyses of hematopoietic organs in treated animals showed a decrease of infiltrating human cells, as well as obvious morphological changes in the human cell population in AG-221-treated animals compared with vehicle-treated animals. Flow cytometry confirmed the differentiation of the human cells in the spleen and bone marrow of the AG-221-treated mice. Furthermore, cells undergoing differentiation retained the R140Q mutation, demonstrating the differentiating effect of the compound.In conclusion, AG-221 reduced serum 2-HG levels and triggered differentiation of leukemic blast cells engrafted in NSG mice. These results are consistent with what has been observed clinically in IDH2 mutant AML patients treated with AG-221 in a phase I dose escalation trial. DisclosuresQuivoron:Institut National de la Santé Et de la Recherche Médicale (INSERM): Grant Other; Association Laurette Fugain: Grant, Grant Other; Institut National du Cancer (INCa): Grant, Grant Other; Association pour la recherche contre le Cancer (ARC): Grant, Grant Other; AGIOS: Grant Other. David:Institut National de la Santé Et de la Recherche Médicale (INSERM): Grant Other; Institut National du Cancer (INCa): Grant, Grant Other; Association pour la Recherche contre le Cancer (ARC): Grant, Grant Other; Association Laurette Fugain: Grant, Grant Other; AGIOS: Grant Other. Straley:Agios Pharmaceuticals: Employment, Stockholder Other. Travins:Agios Pharmaceuticals: Employment, Stockholder Other. Kim:Agios Pharmaceuticals: Employment, Stockholder Other. Chen:Agios Pharmaceuticals: Employment, Stockholder Other. Zhu:Agios Pharmaceuticals: Employment, Stockholder Other. Bawa:AGIOS: Grant Other. Bernard:Institut National de la Santé Et de la Recherche Médicale (INSERM): Grant Other; Association Laurette Fugain: Grant, Grant Other; Institut National du Cancer (INCa): Grant, Grant Other; Ligue Nationale contre le cancer (LNCC): Grant, Grant Other; AGIOS: Grant Other. Yang:Agios Pharmaceuticals: Employment, Stockholder Other. Agresta:Agios Pharmaceuticals: Employment, Stockholder Other. de Botton:AGIOS: Grant Other. Yen:Agios: Employment. Penard-Lacronique:Institut National de la Santé Et de la Recherche Médicale (INSERM): Grant Other; Association Laurette Fugain: Grant, Grant Other; Institut National du Cancer (INCa): Grant, Grant Other; Association pour la recherche contre le Cancer (ARC): Grant, Grant Other; AGIOS: Grant Other.

Functional Analysis of Kinase-Activating Fusions in Ph-like Acute Lymphoblastic Leukemia

Introduction: Ph-like or BCR-ABL1-like B-progenitor acute lymphoblastic leukemia (ALL) is a high-risk subtype characterized by a gene expression profile similar to BCR-ABL1 ALL. The prevalence of Ph-like ALL rises from 10% in standard risk childhood ALL to over 25% in young adults. Next-generation sequencing of Ph-like ALL identified a variety of alterations involving kinase or cytokine receptor genes, including rearrangement, sequence mutation and copy number alterations. Chromosomal rearrangements in about one-third of Ph-like ALL cases create fusion genes of a variety of 5’ partners that involve ABL1-class genes (ABL1, ABL2, CSF1R and PDGFRB) or activate JAK family members (JAK2, TYK2, IL2RB) that are potentially amenable to treatment with ABL1-class or JAK-class tyrosine kinase inhibitors (TKIs). Notably, ABL2 (Abelson-related gene, ARG), a homolog of ABL1, has rarely been identified as a rearrangement partner in ALL. CSF1R (encoding the macrophage colony stimulating receptor) regulates the differentiation of macrophages, and is not normally expressed in lymphocytes. Likewise, rearrangements involving the JAK family member TYK2, the beta chain of the interleukin 2 cytokine receptor (IL2RB), and the neurotrophic tyrosine kinase receptor type 3 (NTRK3), have not been previously described in leukemia. The goals of this study were to assess the role of these kinase alterations in leukemogenesis, to determine the activation of signaling pathways, and to investigate the efficacy of TKIs.Methods: Kinase fusions were expressed in interleukin-3 dependent Ba/F3 cells, and co-expressed with the dominant negative isoform of IKAROS (IK6) in interleukin-7 dependent Arf-/- mouse pre-B cells. Xenograft models of 10 Ph-like ALL tumors - ETV6-ABL1, RANBP2-ABL1, PAG1-ABL2, RCSD1-ABL2, SSBP2-CSF1R, IGH-EPOR, ETV6-NTRK3, ATF7IP-JAK2, PAX5-JAK2 and ZEB2-PDGFRB - were generated by engrafting primary human leukemia cells into NOD-SCID IL2R gamma null (NSG) mice. Activation of kinase signaling was performed using phosphoflow cytometry analysis, and sensitivity to TKIs was assessed ex vivo and in vivo.Results: All kinase fusions (PAG1-ABL2, MYH9-IL2RB, ATF7IP-JAK2, ETV6-NTRK3 or MYB-TYK2) induced cytokine-independent proliferation of Ba/F3 cells. Mice transplanted with Arf-/- pre-B cells co-expressing IK6 and either RCSD1-ABL2 or SSBP2-CSF1R developed pre-B ALL (CD43+, B220+, CD19+, BP-1+ and IgM-) with a median latency of 36 and 40 days respectively, providing evidence that ABL2 and CSF1R fusions contribute to leukemogenesis.In human leukemic cells harvested from xenograft mice we observed distinct patterns of kinase signaling activation and TKI sensitivity for the different fusions. Xenograft cells expressing ABL1-class kinase fusions showed activation of STAT5 that was inhibited with imatinib or dasatinib. Phosphorylation of CRKL, a known target of ABL1 and ABL2, was only observed in cells expressing ABL1/2 fusions. Cells harboring ATF7IP-JAK2, PAX5-JAK2 or IGH-EPOR showed phosphorylation of STAT5 that was attenuated with the JAK2 inhibitor, ruxolitinib. In contrast, cells expressing ETV6-NTRK3 signaled through the MAPK pathway with constitutive pERK1/2 that was inhibited with the ALK-inhibitor, crizotinib. This TKI response profile was confirmed by cytotoxicity assays in xenograft cells, with ABL1-class fusions being sensitive to dasatinib (IC50 range 1-2nM), whilst cases harboring ATF7IP-JAK2 or EPOR rearrangement uniquely responded to ruxolitinib with IC50 values of 500nM and 850nM respectively. Interestingly, in human leukemic cells harboring the ETV6-NTRK3 fusion we observed selective inhibition with both crizotinib and the FLT3 inhibitor, lestaurtinib. Pre-clinical studies on three xenograft models of Ph-like ALL - ETV6-ABL1, RCSD1-ABL2 and SSBP2-CSF1R – showed significantly reduced leukemic burden in dasatinib treated mice (20mg/kg/day p.o) compared to vehicle treated mice.Conclusions: These data provide important insight on new targets of rearrangement in ALL and describe the first engineered mouse models of Ph-like B-ALL. Functional modeling of these alterations is essential to improve the clinical management of Ph-like ALL by identifying patients with specific genomic lesions at diagnosis and directing them to treatment with appropriate TKIs combined with chemotherapy, analogous to current treatment for BCR-ABL1 B-ALL. DisclosuresHunger:Bristol Myers Squibb: Consultancy.

Tu1693 DCLK1 Enhances Epithelial Pluripotency and Oncogenic Signaling During Intestinal Tumor Progression

Objective(s): HIV infection is a risk factor for the tumorigenesis including non-AIDS defining cancers like those of the gastrointestinal tract. However, the mechanisms underlying such cancer outgrowth are still unknown. Further, combined HIV/cancer studies are difficult to evaluate using primatemodels or in the clinical patient setting. To understand themechanisms of tumor outgrowth in the context of HIV infection, we adopted a humanized mouse model permissive to infection and cancer. Design: In vivo humanized mouse challenge with colon cancer in the context of HIV infection. Methods: Immunodeficient NOD SCID IL-2R-/mice were immunologically reconstituted by adoptive transfer of HIV-negative donor peripheral blood leukocytes and challenged with HCT116 human colon cancer cells. A group of mice was treated with antiretroviral therapy. Tumor microenvironment and epithelial tissues in the context of HIV infection were analyzed using immunohistochemistry. Results: We demonstrate that HIV-infected humanized mice develop significantly larger tumors than uninfected mice (P<0.05). Epithelial cell proliferation in HIV-infected mice is significantly enhanced in comparison to proliferation in uninfected mice (P<0.01). Moreover, the activation of β-catenin, an important step in intestinal epithelial cell proliferation and tumorigenesis, is elevated in the tumors of HIV-infected mice (P<0.0001). Importantly, antiretroviral therapy reverses these pathological processes independently of CD4+ T cell return. Conclusions: These findings model the ability of HIV infection to result in tumor outgrowth that is evident in HIV-positive patients and lend insight into previously unrecognized mechanisms that may underlie this pathology.

Tu1692 HIV Infection Accelerates Gastrointestinal Tumor Outgrowth in Humanized NSG-HuPBL Mice

Objective(s): HIV infection is a risk factor for the tumorigenesis including non-AIDS defining cancers like those of the gastrointestinal tract. However, the mechanisms underlying such cancer outgrowth are still unknown. Further, combined HIV/cancer studies are difficult to evaluate using primatemodels or in the clinical patient setting. To understand themechanisms of tumor outgrowth in the context of HIV infection, we adopted a humanized mouse model permissive to infection and cancer. Design: In vivo humanized mouse challenge with colon cancer in the context of HIV infection. Methods: Immunodeficient NOD SCID IL-2R-/mice were immunologically reconstituted by adoptive transfer of HIV-negative donor peripheral blood leukocytes and challenged with HCT116 human colon cancer cells. A group of mice was treated with antiretroviral therapy. Tumor microenvironment and epithelial tissues in the context of HIV infection were analyzed using immunohistochemistry. Results: We demonstrate that HIV-infected humanized mice develop significantly larger tumors than uninfected mice (P<0.05). Epithelial cell proliferation in HIV-infected mice is significantly enhanced in comparison to proliferation in uninfected mice (P<0.01). Moreover, the activation of β-catenin, an important step in intestinal epithelial cell proliferation and tumorigenesis, is elevated in the tumors of HIV-infected mice (P<0.0001). Importantly, antiretroviral therapy reverses these pathological processes independently of CD4+ T cell return. Conclusions: These findings model the ability of HIV infection to result in tumor outgrowth that is evident in HIV-positive patients and lend insight into previously unrecognized mechanisms that may underlie this pathology.

HIV Infection Accelerates Gastrointestinal Tumor Outgrowth in NSG-HuPBL Mice

HIV infection is a risk factor for the tumorigenesis including non-AIDS-defining cancers such as those of the gastrointestinal tract. However, the mechanisms underlying such cancer outgrowth are still unknown. Furthermore, combined HIV/cancer studies are difficult to evaluate using primate models or in the clinical patient setting. To understand the mechanisms of tumor outgrowth in the context of HIV infection, we adopted a humanized mouse model permissive to infection and cancer as well as an in vivo humanized mouse challenge with colon cancer in the context of HIV infection. Immunodeficient NOD SCID IL-2R(-/-) mice were immunologically reconstituted by adoptive transfer of 10(7) HIV-negative donor peripheral blood leukocytes and challenged with 10(6) HCT116 human colon cancer cells. A group of mice was treated with antiretroviral therapy. Tumor microenvironment and epithelial tissues in the context of HIV infection were analyzed using immunohistochemistry. We demonstrate that HIV-infected humanized mice develop significantly larger tumors than uninfected mice (p<0.05). Epithelial cell proliferation in HIV-infected mice is significantly enhanced in comparison to proliferation in uninfected mice (p<0.01). Moreover, the activation of β-catenin, an important step in intestinal epithelial cell proliferation and tumorigenesis, is elevated in the tumors of HIV-infected mice (p<0.0001). Importantly, antiretroviral therapy reverses these pathological processes independently of CD4(+) T cell return. These findings model the ability of HIV infection to result in tumor outgrowth that is evident in HIV-positive patients and lend insight into previously unrecognized mechanisms that may underlie this pathology.

Engraftment of canine peripheral blood lymphocytes into nonobese diabetic-severe combined immune deficient IL-2R common gamma chain null mice

To study the canine immune system we generated a mouse model engrafted with canine lymphocytes using NOD SCID IL2R common gamma chain −/− (NSG) mice as recipients (Ca-PBL-SCID). Engraftment of canine peripheral blood lymphocytes (PBLs) was determined post-injection with 107 peripheral blood mononuclear cells (PBMCs) into irradiated NSG mice using flow cytometry and fluorescently labeled antibodies specific to canine helper T cells (CD45+ CD4+), cytotoxic lymphocytes (CD45+ CD8+), regulatory T cells (CD45+ CD4+ Foxp3+), and B cells (CD45+ Ig+ CD21lo). Canine CD45+ lymphocytes were detectable as early as day 1 in the peritoneal cavity, and beginning at 9 days in the blood, bone marrow, and spleen. CD4+ T cells, of which Foxp-3+ CD25hi cells constituted a minor percentage, were the predominant lymphocyte population at 9 days post engraftment contrasting with increasing proportions of CD8+ CTL's and Ig+ B cells beginning at 16 days. Canine immunoglobulin was initially detected in the serum of Ca-PBL-SCID mice at 9 days post-engraftment and peaked in concentration at day 36. From day 28 to 52 post-engraftment 30% of the Ca-PBL-SCID mice became markedly anemic and thrombocytopenic, yet gross and histopathologic examination of bone marrow, kidneys, spleen, liver, and intestine revealed no obvious lesions. Blood smear evaluation revealed agglutination of mature red blood cells, reticulocytes and a regenerative anemia. These findings demonstrate that NSG mice are capable of engraftment of canine PBLs yet develop graft versus host disease similar to Hu-PBL-SCID mice.

Improved function and proliferation of adult human beta cells engrafted in diabetic immunodeficient NOD-scid IL2r&amp;gamma;null mice treated with alogliptin

PurposeDipeptidyl-peptidase-4 (DPP-4) inhibitors are known to increase insulin secretion and beta cell proliferation in rodents. To investigate the effects on human beta cells in vivo, we utilize immunodeficient mice transplanted with human islets. The study goal was to determine the efficacy of alogliptin, a DPP-4 inhibitor, to enhance human beta cell function and proliferation in an in vivo context using diabetic immunodeficient mice engrafted with human pancreatic islets.MethodsStreptozotocin-induced diabetic NOD-scid IL2rγnull (NSG) mice were transplanted with adult human islets in three separate trials. Transplanted mice were treated daily by gavage with alogliptin (30 mg/kg/day) or vehicle control. Islet graft function was compared using glucose tolerance tests and non-fasting plasma levels of human insulin and C-peptide; beta cell proliferation was determined by bromodeoxyuridine (BrdU) incorporation.ResultsGlucose tolerance tests were significantly improved by alogliptin treatment for mice transplanted with islets from two of the three human islet donors. Islet-engrafted mice treated with alogliptin also had significantly higher plasma levels of human insulin and C-peptide compared to vehicle controls. The percentage of insulin+BrdU+ cells in human islet grafts from alogliptin-treated mice was approximately 10-fold more than from vehicle control mice, consistent with a significant increase in human beta cell proliferation.ConclusionHuman islet-engrafted immunodeficient mice treated with alogliptin show improved human insulin secretion and beta cell proliferation compared to control mice engrafted with the same donor islets. Immunodeficient mice transplanted with human islets provide a useful model to interrogate potential therapies to improve human islet function and survival in vivo.

Gene Therapy With a High-Affinity Single-Chain p53-Specific TCR Mediates Potent Anti-Tumor Response Without Inducing Gvhd In Vivo

The adoptive transfer of tumor-reactive cells is a promising approach in the treatment of human malignancies, but the challenge of isolating T cells with high-avidity for tumor antigens in each patient has limited its widespread application. Using HLA-A2.1 transgenic mice, we have demonstrated the feasibility of T-cell receptor (TCR) gene transfer into T cells to circumvent self-tolerance to the widely expressed human p53(264-272) tumor-associated antigen and developed approaches to generate high-affinity CD8-independent TCR. However, a safety concern of TCR gene transfer is the risk of pairing between introduced and the naturally expressed endogenous TCR chains, resulting in the generation of self-reactive T cells (off-target autoimmunity). We first genetically modified p53TCR constructs to minimize mispairing and improve correct pairing of the introduced TCR. We and others have shown that, cysteine modifications are able to increase the expression of the introduced TCR but fail to prevent mispairing formation in mouse and human T cells. To further enhance preferential TCR pairing, cell surface expression and TCR function, we introduced additional cysteine residues into the TCR α and β chain constant domains along with codon-optimization of the TCR sequences and cloning of the TCR constructs into one single 2A-based retroviral vector. To overcome TCR mispairing formation, we designed a single chain (sc) TCR by connecting the variable TCRa domain to the TCRb chain via a short peptide linker co-expressed with a truncated constant TCR a domain. Beside off-target toxicity, adoptive transfer of high-avidity T cells may potentially cause severe on-target toxicity for normal cells expressing low level of antigens. In this respect, pre-clinical in vivo studies are still missing.Here, we evaluated the safety issues raised by the risk of p53TCR gene transfer-associated on/off-target toxicities in relevant mouse models of adoptive transfer.In vitro studies showed that, scTCR-modified CD4+ and CD8+ T cells displayed similar high-avidity compared to the full-length TCR, as determined by peptide titration in cytotoxicity assays and were able to mediate specific lysis of p53 mutant A2.1+ tumor cells. Though, genetic modifications preserved the antigen specificity of these TCRs, the full-length version of the TCR could not prevent mispairing-mediated lethal off-target autoimmunity in vivo. In sharp contrast, T cells engrafted with the modified scTCR did not induce graft-versus-host disease (GVHD) following adoptive transfer. We next assessed the potential of scTCR-modified T cells to cause on-target autoimmunity in vivo, using mice which express the human wild type p53 and A2.1Kb (Hupki-A2.1Kb). We found that lymphodepleting preconditioning regimens plus vaccination-induced expansion of transferred TCR-specific T cells did not result in a depletion of hematopoietic cells, as mice recovered normal white blood cell counts, including lymphocytes and monocytes and survived without any sign of toxicity. Importantly, our study demonstrated that high-avidity scTCR-engineered human T cells were able to eradicate established tumors and persist for more than 6 months after infusion without inducing xeno-GVHD in NodScid IL-2R gamma chain-null mice.Taken together, our study provided evidence that an optimized high-affinity scTCR-specific for the broadly expressed tumor-associated antigen p53(264-272) can eradicate p53+A2.1+ tumor cells in vivo without inducing off-target or self-directed toxicities in humanized mouse models of adoptive T-cell transfer. These data strongly support the improved safety and therapeutic efficacy of high-affinity scp53TCR for TCR-based immunotherapy of p53-associated malignancies. Disclosures:No relevant conflicts of interest to declare.

P53 and c-Myc Are Critical Signaling Hubs That Maintain Chronic Myeloid Leukemia

Abstract Chronic myeloid leukemia (CML) is a clonal disorder of the hematopoietic system, leading to increased production of mature and progenitor myeloid cells. Although protein tyrosine kinase inhibitors (TKI) have been successful in managing the disease, there are exceptions where drug resistance and onset of blast crisis occur. Furthermore TKIs are ineffective against leukemic stem cells (LSC) that are responsible for disease initiation and maintenance. We have shown mRNA changes in primitive hematopoietic cells do not correlate directly to protein changes. Therefore to elucidate fundamental cellular differences between CML and normal cells we employed a proteomic approach (mass spectrometry with isobaric tagging for relative quantification). This approach permits unbiased analyses using direct comparative quantification of peptides and thus proteins from chronic phase CML and normal CD34+ human samples. Systematic data analysis identified that the majority of deregulated proteins are connected and regulated by two oncogenes with well defined roles in human disease, p53 and c-myc. The direction of regulation inferred suppression of p53 and up-regulation of c-myc. Altered expression of key proteins was validated using western blotting and immuno-fluorescence approaches. All (6/6) candidate/hub proteins identified using mass spectrometry were confirmed using these orthogonal approaches. Based on our systematic analysis, we targeted the candidate hubs using the drugs RITA (activates p53) and CPI-203 (inhibits c-myc expression; provided by Constellation Pharmaceuticals). In CML CD34+ cells, RITA reduced cell expansion in a concentration-dependent manner and induced significant levels of apoptosis as confirmed by positive staining of Annexin V and 4',6-diamidino-2-phenylindole (DAPI) using flow cytometry. CPI-203 also reduced cell expansion, but importantly induced differentiation in addition to apoptosis, as supported by flow cytometric monitoring of levels of carboxyfluorescein succinimidyl ester (CFSE) and CD34. Overlays of CFSE plots for untreated control vs. CPI-203 demonstrated that as cells divided in the presence of CPI-203, there was clear and rapid loss of CD34 expression which was not seen with RITA treatment. By measuring the dose-effect relationship of each drug alone and in combination, we demonstrated potent synergy with combination index (CI) values ranging from 0.034-0.286 based on loss of cell viability. Using flow cytometry we gated on CD34+38- CML cells to enable quantification of the differential effects of each drug alone and in combination against the most primitive and quiescent 1-5% of total CD34+ cells. Critically the apoptotic effect was inclusive of primitive CD34+38- cells and quiescent CFSEmax populations. In addition, experiments combining RITA and CPI-203 demonstrated undetectable colony forming cell units at the highest concentrations of drug used. Importantly, it appears that combining these two drugs has negligible effects on normal CD34+ cell counts, apoptosis and CFSE profiles. Currently NOD-SCID IL2R gamma null (NSG) repopulation assays are underway to determine if these drugs affect stem cells capable of engrafting immunocompromised mice. Our systems biology approach suggests that altered c-myc and p53 function underlie the most significant cellular differences within CML CD34+ cells, which has not been previously demonstrated. We confirm that in CML, p53 and c-myc hub proteins have the ability to modulate downstream defined target proteins thereby enhancing survival and proliferation and thus allowing maintenance of disease. Disclosures: No relevant conflicts of interest to declare.

NOD-scid IL2R γnull mice engrafted with human peripheral blood mononuclear cells as a model to test therapeutics targeting human signaling pathways

BackgroundAnimal models of human inflammatory diseases have limited predictive quality for human clinical trials for various reasons including species specific activation mechanisms and the immunological background of the animals which markedly differs from the genetically heterogeneous and often aged patient population.ObjectiveDevelopment of an animal model allowing for testing therapeutics targeting pathways involved in the development of Atopic Dermatitis (AD) with better translatability to the patient.MethodsNOD-scid IL2R γnull mice engrafted with human peripheral blood mononuclear cells (hPBMC) derived from patients suffering from AD and healthy volunteers were treated with IL-4 and the antagonistic IL-4 variant R121/Y124D (Pitrakinra). Levels of human (h)IgE, amount of B-, T- and plasma- cells and ratio of CD4 : CD8 positive cells served as read out for induction and inhibition of cell proliferation and hIgE secretion. Results were compared to in vitro analysis.ResultshIgE secretion was induced by IL-4 and inhibited by the IL-4 antagonist Pitrakinra in vivo when formulated with methylcellulose. B-cells proliferated in response to IL-4 in vivo; the effect was abrogated by Pitrakinra. IL-4 shifted CD4 : CD8 ratios in vitro and in vivo when hPBMC derived from healthy volunteers were used. Pitrakinra reversed the effect. Human PBMC derived from patients with AD remained inert and engrafted mice reflected the individual responses observed in vitro.ConclusionNOD-scid IL2R γnull mice engrafted with human PBMC reflect the immunological history of the donors and provide a complementary tool to in vitro studies. Thus, studies in this model might provide data with better translatability from bench to bedside.

The Hemoglobin-Haptoglobin Receptor (CD163) Is Expressed by a Subpopulation of Erythroid and Granulo-Macrophagic Progenitors and Can Be Stimulated in Vitro and in Vivo by Physiological and Pharmacological Ligands to Stimulate Hematopoiesis

AbstractAbstract 1221The receptor for the hemoglobin (Hb)-haptoglobin (Hp) complex, CD163, is expressed on the surface of a subpopulation of hematopoietic stem/progenitor cells (HPCs) (Matthews et al, 2006). The purpose of the studies presented here were two-fold – to demonstrate that the CD34+CD163+ double positive population could be isolated from normal adult bone marrow cells and these cells were functional as HPCs and, in addition, that these cells could be stimulated in vivo by ligands to CD163 to affect hematopoiesis. To investigate the clonogenic potential of CD34+/CD163+ HPCs, bone marrow CD34+ cells were examined for CD163 co-expression, sorted by fluorescence activated cell sorting (FACS) and plated into colony-forming assays (CFAs). 4.2% ± 1.4% (n=4) of CD34+ cells were found to co-express CD163 and this population consisted of two distinct sub-populations, CD34++ (hi)CD163+ and CD34+(lo)CD163+, each of which represented approximately half of the total CD34+CD163+ population. All three sorted populations (CD34+(all)CD163−, CD34++(hi) CD163+, CD34+(lo)CD163+) were plated into CFAs (n=4) and were assessed for erythroid and myeloid colony formation. The clonogenic efficiency of CD34++(hi)CD163+ had a 2.5-fold increase in the number CFU-E and CFU-GM when compared to both CD34+ (total) CD163− and CD34+(lo) CD163+ cells. In contrast, CD34+(hi an low)CD163+cells produced fewer BFU-E.To determine how the expression of CD163 expression on progenitor cells may play a role in hematopoiesis, we investigated the effects of the natural ligand to CD163 (Hb/Hp) as well as an agonistic antibody to CD163 (TBI 304) on HPCs in vivo. NOD-scid IL2R gammanull (NSG) mice (HuMurine Technologies) were engrafted with human CD34+cells and animals with < 30% human CD45+ cells in the peripheral blood were administered either 2 mg Hb/mouse, or 100 or 500 μg/mouse TBI 304 every 4 days. At study termination (day 14), bone marrow cells (BMC) were examined by flow cytometry and enriched for CD34+ cells for enumeration in CFAs. Hb administration resulted in an increase of human CD34+cells ranging from 4% to 7% of BMC and a corresponding 57% increase in colony-forming cells (CFC) when compared to control (PBS-administered) animals. In contrast, TBI 304 produced a dose dependent decrease in CD34+ and CFC, possibly reflecting a depletion of CD34+/CD163+ cells from overstimulation due to the longer circulating antibody. To investigate this, human CD34+ cell engrafted animals were given a single dose of 10 or 100 μg/mouse of TBI 304 and bone marrow cells were examined on day 7. TBI 304 provided a 3.5-fold increase in human CD34+ cells as well as a 1.8 to 6.7-fold increase in bone marrow erythroid lineage engraftment (huGlyA+, huCD36+ and huCD71+) and a 2-fold increase in erythroid and myeloid colony-forming cells. No overall toxicities were observed with the administration of TBI 304 or Hb.We have demonstrated that CD163 is expressed on a population of CD34+ hematopoietic progenitor cells, these cells have increased hematopoietic progenitor activity in vitro and that administration of physiological or pharmacological agonists of the CD163 receptor can measurably stimulate hematopoiesis in vivo. Disclosures:Matthews:Therapure Biopharma: Employment. Bell:Therapure Biopharma: Employment.

Properties of TNFR2, PDL-1 dependent human CD8+ regulatory cells generated ex-vivo that can be strongly protective in vivo (116.4)

Abstract In addition to CD4+CD25+Foxp3+ Tregs, natural and induced CD8+ Tregs have been described. Here we report our progress in generating human CD8+ Tregs ex-vivo. Naïve CD8+ cells were activated with anti-CD3/28 beads with IL-2 ± TGF-β for 1 to 9 days. As with CD4+ cells, TGF-β markedly enhanced expression of Foxp3. TGF-β also enhanced CD122, CD103, and PD-1, but decreased granzymes, HLA-DR, CD80 and CD86 expression. Sustained Foxp3 expression and suppressive function was IL-2 dependent. Secondarily stimulated CD8+ cells proliferated weakly, and suppressed activation, proliferation and cytokine production by CD4+ cells in vitro. In vivo functional activity was assessed in NOD SCID IL-2R cγ chain-/- mice injected with allogeneic human PBMC. While human CD4+Foxp3+ Tregs doubled survival from GVHD, CD8 Regs, remarkably, quadrupled survival. Only previously activated CD8+ cells had suppressive activity and protection was unrelated to Foxp3 expression. Adding retinoic acid or rapamycin to TGF-β did not improve survival. By contrast, these activated CD8+ cells rapidly expressed TNFR2 and PDL-1 within one day, and at all time points studied only cells expressing these markers had suppressive activity. Suppressive activity in vivo was IL-10 dependent and partially TGF-β dependent. Thus, in agreement with functional CD8regs described in lupus, diabetes and multiple sclerosis, protective CD8 regs can be induced ex-vivo, and the therapeutic potential of TNFR2, PDL-1+ cells should be carefully explored.

Induction of oxazolone mediated features of atopic dermatitis in NOD-scid IL2R γnull mice engrafted with human peripheral blood mononuclear cells

SUMMARYAnimal models mimicking human diseases have been used extensively to study the pathogenesis of autoimmune diseases and the efficacy of potential therapeutics. They are, however, limited with regard to their similarity to the human disease and cannot be used if the antagonist and its cognate receptor require high similarity in structure or binding. Here, we examine the induction of oxazolone-mediated features of atopic dermatitis (AD) in NOD-scid IL2Rγnull mice engrafted with human peripheral blood mononuclear cells (PBMC). The mice developed the same symptoms as immunocompetent BALB/c mice. Histological alterations induced by oxazolone were characterized by keratosis, epithelial hyperplasia and influx of inflammatory cells into the dermis and epidermis. The cellular infiltrate was identified as human leukocytes, with T cells being the major constituent. In addition, oxazolone increased human serum IgE levels. The response, however, required the engraftment of PBMC derived from patients suffering from AD, which suggests that this model reflects the immunological status of the donor. Taken together, the model described here has the potential to evaluate the efficacy of therapeutics targeting human lymphocytes in vivo and, in addition, might be developed further to elucidate molecular mechanisms inducing and sustaining flares of the disease.

The CXCR4 Inhibitor Plerixafor Effectively Mobilizes Primary AML in NODscid IL2Rγc−/− Xenografts and Markedly Reduces but Does Not Eradicate Leukemia in Combination with Cytarabine +/− Clofarabine Chemotherapy

Abstract 1432 Background:The origin of relapse in AML is believed to be related to persistence of resistant “leukemia stem cells.” in the bone marrow microenvironment where adhesion confers drug resistance. Engraftment of human AML in immunodeficient mice is dependent on CXCR4 (Tavor et al 2004). CXCR4 inhibitors, such as AMD3100 (plexiglass,hereafter P), overcome adhesion mediated chemotherapy resistance (Zeng et al 2006) and mobilize human leukemia engrafted in immunodeficient mice (Zeng et al 2009). P also mobilized leukemia in an APL murine model and in combination with chemotherapy reduced tumor burden (Nervi et al 2009). Methods:We studied the combination of P 5mg/kg daily sc X 3, cytarabine (araC=A) 300mg/kg IP X 3 and clofarabine (C), 20mg/kg IP X 3 in the NODscid IL2R γc−/− mouse engrafted with primary patient AML CD34+ cells after 350 cGy total body irradiation. We could first detect circulating human CD45+ or human CD34+ cells, denoting engraftment, by flow cytometry as early as 5–13 weeks. We then injected plerixafor to assess mobilization capability at 8–16 weeks, followed by the combination of plerixafor and chemotherapy. Animals were sacrificed by 14–38 days after chemotherapy, and assessed for AML in blood, marrow, and spleen. Results:A single 5mg/kg dose of P, produced a 2.26 ± 0.94 (SD) fold increase in peak mobilization (at 2 hours) compared to saline control, p=0.026. P-induced mobilization was directly related to expression of CXCR4, with a patient exhibiting 10.3% CXCR4 showing 0.86× baseline, as compared to a patient with 24.7% CXCR4 exhibiting a 2.2-fold increase, and 84.9% CXCR4, a 3-fold increase. Chemotherapy,described above, was given 2 hours after plerixafor. For animals that received P/A vs. P/A/C, there was no statistically significant difference in leukemic burden (in millions of human CD34+ AML cells ± SD) of the animals sacrificed 14 days after initiation of treatment: bone marrow six bones 116.3 ± 33.7 vs. 111.7 ± 29.2 (p=0.86), spleen 50.8 ± 10 vs. 43.7 ± 19.1 (p=0.59), blood 10.9 ± 9.6 vs. 3.1 ± 1.4 (p=0.16), or estimated total body burden 178.0 ± 45.3 vs. 158.5 ± 30 (p=0.52). A comparison of 4 groups of animals, P/A/C vs. P/A vs. A/C vs. A demonstrated a statistically significant difference between certain groups, at certain time points. For example, on day 10, P/A/C treated animals had a lower human PB CD34+ count than P/A, 0.07 vs. 0.24 × 109/L (p=0.034). On day 14, P/A/C had a lower CD34+ count than A/C, 0.08 vs. 0.16 (p=0.047). But at day 38, the leukemia had already recurred, and there was no statistically significant difference in the organ or total body involvement by the leukemia. There was a very low white blood count days 5–24 post chemotherapy, with only minimal residual disease detectable by flow cytometry (analogous to a period of remission in humans), but by day 38, the leukemia had recurred (Figure 1), and there was no statistically significant difference in the organ or total body involvement by the leukemia amongst the groups (Figure 2). Conclusion:This model demonstrates the efficacy of chemotherapy in reducing circulating leukemia, but resistant cells appear to remain sheltered and give rise to relapse. Despite the beneficial effects of CXCR4 inhibitors in vitro and in vivo in a murine APL model, the combination of plerixafor with chemotherapy did not prevent or postpone leukemic relapse. These results could be attributed to either inefficient scheduling of plerixafor (for example, continuous infusion may have worked better), or non-cycling cells may be preferentially mobilized (Bonig H et al., 2009), and thus less susceptible to cytarabine treatment. These concepts are currently being explored. Alternatively, concomitant inhibition of other adhesion receptors may be necessary to prevent leukemia from homing back to the marrow. Precise timing and degree of mobilization in combination with chemotherapy may be required to optimize this approach in the clinic. [Display omitted] [Display omitted] Disclosures:Becker:Sanofi-Oncology (Genzyme): Research Funding.

A large-scale method for the selective depletion of αβ T lymphocytes from PBSC for allogeneic transplantation

We sought to develop a method for the clinical large-scale depletion of alphabeta T lymphocytes from mobilized peripheral stem cells, which would allow the allogeneic transplantation of a graft enriched for stem cells, natural killer (NK) cells and gammadelta T lymphocytes. Therefore, we obtained mononuclear cells from either mobilized or non-mobilized healthy adult volunteer donors and incubated the cells with a biotinylated anti-alphabeta T-cell Ab and subsequently with an anti-biotin Ab conjugated with magnetic microbeads. The depletion was then performed using a CliniMACS device. The median T-cell depletion was 3.9 log (range 3.5-4.1 log). The recovery of the gammadelta and NK cells was 92% and 80%, respectively. The recovery of CD34+ stem cells from the mobilized donors was 66%. This method had no negative influence on the in vitro colony formation of stem cells, and transplantation of alphabeta-depleted cells into NOD-SCID IL-2 common gamma chain knockout (NOD-scid IL2r (null)) mice resulted in a rapid engraftment of human myeloid and lymphoid cells. This method will allow large-scale depletion of alphabeta T cells from mobilized peripheral blood in clinical trials.