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Multiple myeloma (MM) is a heterogeneous malignant plasma cell disorder with complex molecular and genetic abnormalities. Clonal evolution in MM is a hallmark of treatment failure. The origin of clonal evolution seems to result from the pressure induced by treatment, microenvironmental factors and immune response. In this work we identified that ctDNA may reshape tumor genetic landscape by horizontal gene transfer similar to what is seen in prokaryotes and some Eukaryotes. Our work demonstrated that ctDNA from treatment resistant patients can transmit the phenotype to MM cell lines. Using in vitro microscopy assays and whole genome sequencing methods, we identified that ctDNA preferentially target cells that resemble their MM cell of origin compared to other cancer cell types. The tropism for MM ctDNA to target MM cells was validated in in vivo xenograft mouse models, where ctDNA targeted tumor cells and spared other tissues or other tumor xenografts. To further understand, whether cell targeting was produced via a direct interaction of ctDNA with a receptor protein, we treated ctDNA with anti-DNA antibodies derived from lupus patients prior adding it to cell culture. Our results showed a significant reduction of ctDNA incorporation. Then, we treated cells with trypsin after 30 minutes incubation with ctDNA and showed a significant reduction of CY5-ctDNA cellular signal suggesting that ctDNA incorporation is mediated by a direct interaction of ctDNA with a receptor protein. Based on these findings, we performed mass spectrometry on proteins pulled from coculture of biotin labelled ctDNA and cell lysates derived from 3 different tumor types. Results identified eight proteins bound to ctDNA that were enriched compared to biotin or a CMV-GFP linearized control vector (HLA-A, CD41, Cd97, Integrin αVβ5, P14K2A, TMEM and PTK7A). The role of these proteins in ctDNA incorporation was evaluated by culturing cells with antibodies against these proteins prior to adding ctDNA. Integrin αVβ5 followed by PTK7A, P14K2A, TMEM and HLA-A were able to reduce ctDNA cell incorporation. These results are being confirmed using shRNA methods and results will be available at the time for the meeting. In summary, we have identified a novel mechanism by which MM cells share genetic material altering their genetic landscape and elucidated potential receptors mediating ctDNA recognition. Disclosures Vardarajan: Kodikaz Therapeutic Solutions, LLC: Consultancy. El-Rayes: exelixis: Consultancy; erytotech: Research Funding; dicephera pharmaceutical: Consultancy; Astra Zeneca: Consultancy, Research Funding; Bristol Myers Squibb: Research Funding; Boston biomedical: Research Funding; Novartis: Research Funding; Merck: Research Funding; Pfizer: Research Funding; Bayer: Research Funding. Martinez-Medina: Kodikaz Therapeutic Solutions: Current Employment. Gries: Kodikaz Therapeutic Solutions: Current Employment; Feldan Therapeutics: Consultancy. Bernal-Mizrachi: Takeda Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bigene: Membership on an entity's Board of Directors or advisory committees; Kodikaz Therapeutic Solutions: Consultancy, Current holder of individual stocks in a privately-held company, Patents & Royalties; Winship Cancer Institute of Emory University: Current Employment.

Mutations on NOTCH1 gene are the most commonly found mutations in T-cell acute lymphoblastic leukemia (T-ALL) and they are reported to be favorable indicators for T-ALL patients' prognosis. However, the effects of activating NOTCH1 mutations on T-ALL's chemosensitivity have not been studied. We reported that NOTCH1 inhibition by γ-secretase inhibitors or shRNA knockdown in MOLT-3 cells could reduce the T-ALL cells' sensitivity to chemotherapeutic drugs. However, this effect was absent in Jurkat and CUTLL cells. We further demonstrated that NOTCH1 inhibition could activate the PI3K-AKT pathway in a cell specific pattern similar as their effects on chemosensitivity. RNA-seq revealed that Phosphatidylinositol-3,4,5-Trisphosphate Dependent Rac Exchange Factor 2 (PREX2) is a target gene of NOTCH1 and may mediate the effects of activating NOTCH1 mutations on chemosensitivity. Consistently, we proved that overexpression of PREX2 could mimic the effects of NOTCH1 inhibition on chemosensitivity. Our study has highlighted the effects of activating NOTCH1 mutations on T-ALL's chemosensitivity by altering PREX2-AKT pathway, which may explain the favorable effects of NOTCH1 mutations on T-ALL patients' prognosis, as well as provided potential targets to alter T-ALL cells' chemosensitivity. Disclosures No relevant conflicts of interest to declare.

Understanding hematologic cell types, their characteristics, and how they function physiologically and pathologically can be challenging to master, especially for first- or second-year medical students. The current mainstays of undergraduate medical education include lectures, PowerPoint, and supplemental textbook readings. Many learners retain information better when they feel connected to the content. Accordingly, we developed a hematology personality quiz as an innovative, fun, and memorable learning tool. Given that our intention was to focus on foundational hematology, we included thirteen common hematologic cell types as "results" for the quiz. These included erythrocyte, reticulocyte, platelet, neutrophil, eosinophil, basophil, mast cell, monocyte, natural killer cell, CD8+ T-cell, CD4+ T-cell, mature B-lymphocyte, and plasma cell. We generated personality traits that were complementary to each cell's form and function. Platelets, for example, are very sticky cells that rely on adhesion, activation, and aggregation to achieve primary hemostasis. We translated this function into a personality type that is outgoing/communicative, touchy-feely, and always trying to connect with others, noting that platelet personalities may get "stuck" on what others think. Erythrocytes, which deliver oxygen to tissues as they squeeze into and out of vessels, were matched with energetic and flexible personality types. Working backwards from the 13 cells/personality types, we generated 20 quiz questions whose results correlated with the cells' scientific properties and personality traits. Questions included "How long would you last in a zombie apocalypse?" as well as asking quiz takers whether they rely on "gut-feelings" or are more data driven when making decisions. The former corresponded to the average life span of the cell, the latter to the innate vs adaptive immune system. The number of questions was later reduced to 13 to eliminate redundancy. Our content was then integrated on a commercially available online quiz platform, using a frequency algorithm to generate results. Each answer corresponded to specific cell types. After answering the quiz questions, participants are paired with a single personality type that correlates with the majority of their selected responses. In addition to generating a complementary personality type, each result is coupled with information about the cell, an image of the cell under electron microscopy, as well as high yield clinical correlations. Faculty reviewed material for appropriate content. While the quiz generates one result, students have access to all thirteen results after completion. As part of our pilot phase, the quiz and a corresponding survey were sent to all first-year medical students during the hematology learning sequence as well as second-year medical students rotating on the internal medicine clerkship. Using a Likert scale, the participants were asked to rate their enjoyment of the quiz, how well their result matched their personality, whether it facilitated learning, whether they would use the comprehensive guide to study, and if it increased their interest in hematology. Our preliminary findings (tables 1 and 2) indicate that a hematology-based personality quiz can be a fun tool to promote learning. Disclosures Ahmed: Immunovant: Other: Institutional PI on industry initiated trial; Cadence: Other: Institutional PI on industry initiated trial.

Neutrophils act as the body’s first line of defense against infection and respond to diverse inflammatory cues, including cancer. Neutrophils display plasticity, with the ability to adapt their function in different inflammatory contexts. In the tumor microenvironment, neutrophils have varied functions and have been classified using different terms, including N1/N2 neutrophils, tumor-associated neutrophils, and polymorphonuclear neutrophil myeloid–derived suppressor cells (PMN-MDSCs). These populations of neutrophils are primarily defined by their functional phenotype, because few specific cell surface markers have been identified. In this review, we will discuss neutrophil polarization and plasticity and the function of proinflammatory/anti-inflammatory and protumor/antitumor neutrophils in the tumor microenvironment. We will also discuss how neutrophils with the ability to suppress T-cell activation, referred to by some as PMN-MDSCs, fit into this paradigm.

In this issue of Blood , a new study by Kiyasu et al used a double-staining technique to identify cell-specific programmed cell death ligand 1 (PD-L1) expression in 1253 diffuse large B-cell lymphoma (DLBCL) samples and analyzed the findings together with programmed death-1 (PD-1) expression in tumor-infiltrating lymphocytes (TILs) and clinical outcomes, providing new insights into the role of the PD-1/PD-L1 pathway in DLBCL. 1

The gene expression programs that establish and maintain specific cell states in humans are controlled by thousands of transcription factors, cofactors, and chromatin regulators. Our understanding of the DNA elements and regulators that control gene expression programs has advanced considerably in the last year. I will describe new insights into the roles that these elements and regulators play in global gene control during normal development and in various diseases. These insights provide opportunities for the development of novel diagnostics and therapeutics. Disclosures: Young: Syros Pharmaceuticals: Consultancy, Equity Ownership, Membership on an entity’s Board of Directors or advisory committees; Enzon Pharmaceuticals: Equity Ownership, Membership on an entity’s Board of Directors or advisory committees.

Comment on Underhill et al, page [3867][1] Leukocytes emigrate into inflamed tissues by binding to selectins on endothelial cells; while different leukocyte subsets traffic to different tissue sites, the mechanisms regulating selective expression of selectin ligands on specific cell subsets are

Graft CD34+ cell content based on ABW affects outcome after conventional allografts (Singhal et al. BMT 2000;26:489–96). Engraftment after autologous (Ali et al. BMT 2003;31:861–4) and allogeneic (Cilley et al. BMT 2004;33:161–4) HSCT correlates better with CD34+ cell dose based on IBW than ABW. 63 patients (27–66 y, median 52) underwent submyeloablative HSCT from HLA-matched sibling (n=37), 10/10 allele-matched unrelated (n=19), or 1-locus/allele mismatched (n=7) donors for hematologic malignancies after 100 mg/m2 melphalan with (n=42; no prior autograft) or without (n=21; prior autograft) 50 mg/kg cyclophosphamide. GVHD prophylaxis comprised cyclosporine-mycophenolate with HLA-matched sibs and tacrolimus-mycophenolate with the rest. G/GM-CSF were not used. Supportive care was uniform. ABW and IBW values were 45–147 kg (median 79) and 52–85 kg (median 67) respectively. The ABW-IBW difference was −24% to +133% (median +16%); 9 patients were >5% underweight and 41 were >5% overweight. Chemotherapy doses were based on ABW for underweight patients, and adjusted weight for overweight (IBW + 25% of the ABW-IBW difference). The target CD34+ cell dose was 2–8 x106/kg IBW; preferably >6 and ≤ 8 based on prior findings (Singhal et al. ASH 2004). The CD34+ cell dose infused was 1.4–11.8 (median 5) by IBW and 1.2–9.3 (median 4.5) by ABW. The CD3+ cell dose (108/kg) was 0.9–14.9 (median 3) by IBW and 0.7–19.7 (median 2.7) by ABW. The 2-y cumulative incidence of relapse and transplant-related mortality (TRM) was 55% and 24% respectively. The 2-y probabilities of overall (OS) and disease-free (DFS) survival were 35% and 21% respectively. | | CD34+ cell dose by IBW | CD34+ cell dose by ABW | |:----------- | ---------------------- | ---------------------- | ----- | | | >6 and ≤ 8 (n=11) | 6 or >8 (n=52) ≤ | P | >6 and ≤ 8 (n=8) | 6 or >8 (n=55) ≤ | P | | 3-y OS | 61% | 27% | 0.040 | 31% | 25% | 0.22 | | 3-y DFS | 41% | 13% | 0.043 | 0% | 14% | 0.53 | | 1-y TRM | 0% | 27% | 0.029 | 0% | 25% | 0.090 | | 1-y Relapse | 45% | 48% | 0.34 | 63% | 47% | 0.70 | | | CD3+ cell dose by IBW | | CD3+ cell dose by ABW | |:----------- | --------------------- | ---------- | --------------------- | --------- | |

The development of safe and effective gene therapy poses many formidable challenges. Some biomedical applications such as the hemoglobinopathies require that the gene product be expressed in a specific cell type, for example, erythroid progenitors. No such constraint pertains when the gene product

In the article by Shimada et al, entitled “Erythropoietin-Specific Cell Cycle Progression in Erythroid Subclones of the Interleukin-3-Dependent Cell Line 32D” which appeared in the February 15, 1993 issue (Vol 81, No 4, pp 935-941), an author name was incorrectly represented. The corrected listing of author names should read: Yoshihiro Shimada, Giovanni Migliaccio, Harold Ralph, and Anna Rita Migliaccio.

Contrary to the traditional concept, in many instances the leukemias are characterized by an essentially normal or slower individual leukocyte generation time, impaired maturation, altered cell release into the circulation, and prolonged survival of the "leukemic" cell, resulting in a progressive accretion of the potentially divisible cell population arrested in intermediary phases of development. We have come to a critical reorientation in our thinking of the leukemias and neoplasia in general. Continued expansion along conventional lines might be profitably complemented by another program aimed at correction of the leukemic process by encouraging maturation without cellular destruction. The significance of this moment is the inevitable realization that the dream of a cell specific "magic bullet" which would jam the metabolic machinery of the "leukemic cell" may instead correct that defective mechanism by aiding the leukocyte to mature properly. Efforts to accelerate or correct the altered maturation may offer additional approaches to the treatment of the leukemias with or without conventional chemotherapy. A reevaluation of the leukemias and possibly other neoplasms as disorders primarily of accumulation rather than proliferation may be a useful working hypothesis to encourage newer therapeutic approaches.