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Epidemiological studies have demonstrated an increased incidence of MDS in patients with plasma cell disorder (PCD) i.e. multiple myeloma (MM) or MGUS and several case reports / series of co-occurring MDS and PCD have been published. The underlying pathogenesis for this condition, and if the two diseases share a common genetic lesion remains unknown. Here, we describe a cohort of 27 consecutive patients with co-occurring MDS and MM (n=6), MGUS (n=20) or plasmocytoma (n=1), diagnosed at the Karolinska University Hospital. In 5 patients, the diagnosis of MGUS preceded the diagnosis of MDS , in one patient the MDS diagnosis preceded PCD, and in 21 patients MDS and PCD were diagnosed at the same time. There was a preponderance for lower-risk MDS subgroups with only 3 patients belonging to the IPSS-R high / very high risk groups. Median overall survival for the whole cohort was 44 months. The most common mutations were TET2, SRSF2 and SF3B1. To identify potential common founder clones, we performed whole exome sequencing on isolated bone marrow myeloid-, plasma- and T-cells from 9 patients. In none of the patients, we could detect a common founder mutation and the two diseases have likely emerged from separate clones.

Introduction: Immunotherapies are gaining more and more importance in the treatment of multiple myeloma (MM). Antibodies directed against MM antigens like CD38, SLAMF7 or BCMA are used either in their natural form, conjugated to drugs, or in the form of bispecific T-cell engagers. Cellular therapies make use of cytotoxic lymphocytes, i.e. T cells or NK cells that can also be modified to express chimeric antigen receptors to target MM cells. Combinations of antibody and cellular therapies could further improve the outcome as, for example, NK cells can mediate antibody dependent cellular cytotoxicity (ADCC). However, NK cells also express CD38 and SLAMF7 and would be targeted by the therapeutic antibodies against these antigens. We have recently reported our clinical study infusing multiple doses of ex vivo activated and expanded autologous NK cells in six patients with MM post autologous stem-cell transplantation (EudraCT 2010-022330-83). Here, we report results of a phenotypic analysis of the ex vivo expanded NK cells and peripheral blood NK cells before and after infusion with implications for possible combination therapies. Methods: Ex vivo activated and expanded NK cells and NK cells in peripheral blood of the patients were analyzed by multiparameter flow cytometry. Peripheral blood cells were taken from the non-NK cell infusion arm before and at three different timepoints after infusion. NK-cell sub-populations within these samples were analyzed using t-SNE clustering. Results: Upon ex vivo activation and expansion, we observed that the NK cells gained a unique activated phenotype including populations of CD56 brightCD16 +Ki67 +HLA-DR + NK cells. Interestingly, these NK cells showed a reduced expression of CD38 compared to peripheral blood NK cells. Clustering analyses of data from peripheral blood samples revealed the gradual appearance of a new NK cell population with a similar phenotype in a dose-dependent fashion over four hours following infusion of the NK cell product. Infused NK cells could be detected in circulation up to four weeks after the last infusion. Like the NK cell infusion product, these cells expressed little to none CD38, high levels of NKG2D, 2B4, TIM-3, and TIGIT and similar levels of SLAMF7 compared to peripheral blood NK cells. Conclusions: The persistent high expression of CD16 and the low expression of CD38 in infused NK cells offers the choice to combine ex vivo activated and expanded NK cells with anti-CD38 antibody therapy without concern for antibody-mediated NK-cell death. Based on these findings, we have started a clinical trial testing this combined therapy (NCT04558931). Disclosures Nahi: XNK Therapeutics AB: Consultancy. Chrobook: XNK Therapeutics AB: Consultancy. Meinke: XNK Therapeutics AB: Consultancy, Current holder of stock options in a privately-held company. Gilljam: XNK Therapeutics AB: Current holder of individual stocks in a privately-held company. Stellan: XNK Therapeutics AB: Current holder of individual stocks in a privately-held company. Walther-Jallow: XNK Therapeutics: Other: Shareholder in the company. Liwing: XNK Therapeutics AB: Current Employment. Gahrton: XNK Therapeutics AB: Current holder of individual stocks in a privately-held company; Fujimoto Pharmaceutical Corporation Japan: Membership on an entity's Board of Directors or advisory committees. Ljungman: Takeda: Consultancy, Other: Endpoint committee, speaker; OctaPharma: Other: DSMB; Enanta: Other: DSMB; Merck: Other: Investigator, speaker; AiCuris: Consultancy; Janssen: Other: Investigator. Ljunggren: XNK Therapeutics AB: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees. Alici: XNK Therapeutics AB: Current holder of individual stocks in a privately-held company.

Background Allogeneic hematopoietic stem cell transplantation (AlloSCT) for treatment of multiple myeloma (MM) is controversial mainly due to high non-relapse mortality (NRM) with myeloablative conditioning. However, AlloSCT is probably the only treatment that result in cure of a small fraction of patients. Treosulfan is a prodrug of a bifunctional alkylating agent which has both myelotoxic and immunosuppressive properties. Conditioning regimes with treosulfan have been tried in various hematologic neoplasia such as AML and MDS indicating low NRM and increased progression free survival (PFS). Previous studies on use of treosulfan condition in AlloSCT for MM indicated feasibility, stable engraftment and low NRM. In the present study we have analysed the results of low and high dose treosulfan respectively on OS, RFS, relapse incidence and NRM as well as results of Treosulfan conditioning compared to non-Treosulfan reduced intensity conditioning (RIC) and non-Treosulfan myeloablative conditioning (MAC). Patients and Methods We conducted a retrospective analysis of 4544 patients with MM undergoing AlloSCT 2008-2016 reported to the EBMT data registry. Out of 537 patients receiving Treosulfan based conditioning the impact of dose could be analysed in 441. Three hundred and twenty-seven patients received a total dose of >36g/m2 and 114 Results The 5-year OS in upfront Treosulfan conditioned patients was 62%, which was significantly superior to both non-Treo RIC and MAC patients respectively, apparently due to a tendency for lower NRM (10%) albeit a higher relapse rate (Table 2). Patients in later lines of conditioning had either low NRM (3rd line) or no significant difference (2nd line) (Table 2). Heterogeneity in the material makes it difficult to interpret results in the patients transplanted late in the course of the disease. A higher total treosulfan dose, >36g/m2, showed a tendency for improved OS and RFS compared to the lower dose treosulfan as well as RIC and MAC (table 2) respectively. In multivariate analysis of upfront transplanted patients, with a model adjusted for ISS score at diagnosis, age, Karnofsky score, response at AlloSCT, interval between diagnosis and transplant, donor type and donor - patient sex match, treosulfan and RIC retained significance for OS, HR 0.57 (P=0.006) and RFS, HR 0.65 (P= In multivariate analysis of treosulfan based conditioning regimes, upfront line of conditioning was superior for OS, PFS and relapse as expected (Table 3). Notably was an increased hazard ratio for donor-patient sex match other than female to male in OS, PFS as well as relapse, HR 1.64 (P=0.02), HR 1.66 (P=0.004) and HR 1.83 (P=0.003) respectively (Table 3). Conclusions Conditioning upfront with Treosulfan containing regimens for AlloSCT in multiple myeloma, is associated with a superior overall survival and a low NRM, however with a slightly higher relapse rate compared to other regimens. A higher dose > 36g/m2 tends to further improve OS, RFS and relapse rate without increasing NRM. The better results of Treo conditioning in female to male transplants as compared to other sex combinations and in contrast to MAC transplants may be due to the overall lower NRM with treosulfan, thus utilizing the GVM more effectively as indicated by the trend for lower relapse rate. In conclusion, Treosulfan containing regimens appear to be of value in upfront AlloSCT. Prospective studies on Treosulfan conditioning are warranted to further define the best dosing in MM AlloSCT. Disclosures Niederwieser: Miltenyi: Speakers Bureau; Novartis: Research Funding. Beelen:Medac: Consultancy, Other: Travel Support. Stelljes:Pfizer: Consultancy, Honoraria, Research Funding; MSD: Consultancy; JAZZ: Honoraria; Amgen: Honoraria; Novartis: Honoraria. Finke:Novartis: Consultancy, Honoraria, Other: travel grants, Research Funding; Medac: Consultancy, Honoraria, Other: travel grants, Research Funding; Neovii: Consultancy, Honoraria, Other: travel grants, Research Funding; Riemser: Consultancy, Honoraria, Research Funding. Garderet:Amgen: Consultancy; Celgene: Consultancy; Takeda: Consultancy. Kroeger:Celgene: Honoraria, Research Funding; Riemser: Honoraria, Research Funding; JAZZ: Honoraria; Novartis: Honoraria, Research Funding; Sanofi: Honoraria; Neovii: Honoraria, Research Funding.