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Abstract 2673 Introduction: Follicular Lymphoma International Prognostic Index 2 (FLIPI-2) is a widely accepted tool for risk assessment of follicular lymphoma (FL), which is based on age, hemoglobin level, presence of bone marrow (BM) invasion, tumor size, and b2-microgloblin levels. Although it is easy to evaluate in clinical practice, it is a combination of tumor burden and patient physical condition, and a simple and powerful biomarker reflecting the tumor burden and its character is still not established. LR11 (also called SorLA or SORL1) was identified and characterized as a regulator of uPAR function through complex formation with uPAR. We have identified that serum soluble LR11 (sLR11) levels are significantly elevated in patients with acute leukemia and B cell lymphomas, and are associated with tumor burden and BM invasion (Sakai et al 2012). We have also found that high sLR11 levels had a significant negative prognostic impact on progression-free survival (PFS) in FL. Therefore, we have retrospectively evaluated the clinical characteristics of sLR11 and its prognostic impact on FL, in a larger patient cohort. Patients and Methods: Sixty-one patients with FL treated at Chiba University Hospital and affiliated hospitals from 2002 to 2012 were evaluated. The majority of patients were treated by the R-CHOP regimen (rituximab 375 mg/m2 on day 1; cyclophosphamide, 750 mg/m2 on day 1; adriamycin, 50 mg/m2 on day 1; vincristine, 1.4 mg/m2 on day 1; and prednisolone, 100 mg/body on day 1–5). Serum sLR11 levels were measured by ELISA method. Patient laboratory data and treatment outcome were obtained retrospectively. Results: Serum sLR11 levels of patients with lymphoma were significantly increased (mean ± SD: 19.4 ± 17.1 ng/ml) compared with those of normal control subjects (8.8 ± 1.79 ng/ml, P15.4 ng/ml at diagnosis compared with those with ≤15.4 ng/ml (Figure 1, 9.7 % vs 100 %, P15.4 ng/ml at diagnosis was a significant prognostic factor for PFS (hazard ratio: 2.65 × 107, 95% CI: NA). Conclusions: Serum sLR11 levels in FL patients were associated with BM invasion, lower Hb levels and elevated b2-microglobulin, which are 3 of 5 variables in FLIPI-2. This suggests that serum sLR11 is a useful tool to predict “high” FLIPI-2 score, especially highlighting those with high tumor burden by simple serum evaluation and can be a promising biomarker in patients with FL. Disclosures: No relevant conflicts of interest to declare.

Abstract 2416 TET2 mutations are frequently observed in myeloid malignancies including myelodysplastic syndrome (MDS), myeloproliferative neoplasm (MPN) and MDS/MPN. Several groups have already reported that deletion of Tet2 in mice leads to dysregulated hematopoietic stem cell self-renewal and subsequent development of myeloid malignancies. Of note, mice hypomorphic or heterozygous for the Tet2 allele have been reported to show similar phenotypes as those of Tet2-null mice, suggesting that haploinsufficiency of Tet2 plays a role in the development of myeloid malignancies. However, little is known about long-term cell autonomous effects of Tet2 loss in hematopoietic cells: most of the reports were based on relatively short-term observations or did not exclude the influence of Tet2 loss in the niche cells. To study long-term cell autonomous effect of Tet2 loss in hematopoietic cells, we analyzed the hematopoiesis of wild-type recipient mice reconstituted with fetal liver cells from Tet2 hypomorphic mice for a longer period up to 1 year. Tet2 gene trap mice (Tet2trap/trap), in which the gene trap vector was inserted into the exon 2 of Tet2 just before the first coding exon, express Tet2 mRNA at the level approximately 20% of that of the wild-type (WT) mice (Shide et al. Leukemia 2012). We transplanted fetal liver cells from E14.5 WT or Tet2trap/trap mice into lethally irradiated recipient mice. At 4 months after transplantation, the recipient mice reconstituted with Tet2trap/trap cells showed a significantly increased proportion of monocytes in peripheral blood (PB) compared with those with WT cells (WT=5.59±2.57%, Tet2trap/trap=12.67±7.45%, p=0.01). While there were no significant differences between the two groups in the bone marrow (BM) compartments including the numbers of Lineage−Sca-1+c-Kit+ (LSK) hematopoietic stem/progenitor cells, extramedullary hematopoiesis in the spleen was markedly enhanced in the recipients with Tet2trap/trap cells. The proportion of LSK, granulocyte/macrophage progenitors (GMPs) and megakaryocyte/erythroid progenitors (MEPs) in the spleen of recipient mice reconstituted with WT and Tet2trap/trap cells were 0.002±0.001% vs 0.006±0.001% (p Of note, after a long observation period, particularly after 9 months post-transplantation, mice reconstituted with Tet2trap/trap cells developed advanced hematological disease and 53.3% (8 of 15) died or were killed because of their moribund condition by 11 months after transplantation. Detailed analysis on moribund as well as surviving mice reconstituted with Tet2trap/trap cells (n=3 each) revealed that the 2/3 of the mice developed CMML-like disease with monocytosis in PB and evident extramedullary hematopoiesis harboring increased number of LSK and GMPs in spleen, whereas the remaining 1/3 of mice developed MDS/MPN-like disease with severe anemia. The latter mice did not show monocytosis in PB and BM, but displayed dyserythropoiesis accompanied by massive extramedullary erythropoiesis, as we saw increased number of LSK and MEPs, but not GMPs, in spleen. The proportion of Annexin V+ cells in Ter119highCD71higherythroblasts in the BM of WT mice, CMML-like disease-carrying mice and MDS/MPN-like disease-carrying mice were 9.46±0.53%, 10.71±0.36%, and 19.04±0%, respectively, suggesting that the enhanced apoptosis led to the severe anemia seen in the MDS/MPN-like disease-carrying mice. Thus, decreased expression of Tet2 is sufficient to promote not only CMML-like disease, but also an MDS/MPN-like disease as well. Our findings confirmed a long-term cell autonomous effect from insufficient function of Tet2 in the development of hematological diseases. Interested in the molecular mechanism of disease progression, we have identified 1,642 differentially methylated regions (DMRs) in Tet2trap/trap GMPs compared with WT GMPs by ChIP-sequencing. We are now working to understand how these DMRs are involved in the development of the two distinct diseases associated with hypomorphic Tet2. Disclosures: No relevant conflicts of interest to declare.

Abstract 5104 Introduction: Intravascular large B-cell lymphoma (IVLBCL) is a rare disease entity of malignant lymphoma, characterized by the selective growth of lymphoma cells within the lumina of vessels in various organs. Although recent reports showed that prompt and accurate diagnosis lead to better outcomes, absence of typical clinical manifestations and its aggressive behavior frequently makes it difficult. LR11 (also called SorLA or SORL1) is a type I membrane protein, from which a soluble form (sLR11) is released by proteolytic shedding. sLR11 is originally known to be a biomarker of carotid intima-media thickness. We have recently found that LR11 is expressed on human leukemia cell lines, and sLR11 is released in its culture medium. Serum sLR11 levels are significantly elevated in patient serum samples with acute leukemia and B cell lymphomas, and are associated with tumor burden and bone marrow invasion. Based on these findings, we hypothesized that LR11 may be also expressed and released from IVLBCL cells; therefore we evaluated its clinical importance in IVLBCL. Materials and methods: Serum samples and paraffin embedded tumor specimens were obtained from 6 patients who were histologically diagnosed as IVLBCL from 2009 to 2012. Specimens were subjected to immunostaining using anti-LR11 antibody, and serum sLR11 levels were measured by ELISA method. Patient laboratory and clinical data were collected retrospectively. Also, serum samples from 75 healthy volunteers, and 10 patients with collagen diseases presenting similar clinical manifestations as IVLBCL were analyzed. Results: Tissue samples of IVLBCL were obtained by bone marrow biopsy (N=2), transbronchial lung biopsy (N=2), and random skin biopsy (N=2). Biopsy specimens showed that cytoplasm of IVLBCL cells were specifically immunoreacted against the anti-LR11 antibody (Figure 1). Median serum sLR11 level of IVLBCL patients was 86. 0 ng/ml (mean ± SD: 201. 8 ± 260. 0 ng/ml), which was significantly elevated than those of healthy volunteers (median: 8. 4 ng/ml, mean±SD: 8. 8 ± 1. 8 ng/ml, p Conclusions: We have identified LR11 as a novel molecule which was proven to be expressed in IVLBCL cells and circulated in patients' serum. LR11 immunostaining clearly highlights the tumor cells and sLR11 enables to distinguish IVLBCL from other differential diagnosis by serum evaluation. These findings suggest that LR11 is a useful diagnostic tool for IVLBCL, and serum sLR11 is a sensitive biomarker for diagnosis and disease monitoring of this challenging disease. Disclosures: No relevant conflicts of interest to declare.