Abstract: Monoclonal antibodies have entered the therapy of multiple myeloma (MM) and are currently being evaluated in phase I-III trials. PAT-SM6 is a fully human IgM antibody that specifically binds to a cancer-specific cell surface variant of the chaperone molecule glucose regulated protein 78 (GRP78). Finding a GRP78 cancer-specific form on the surface of cancer cells, but not normal cells in vivo, presents an opportunity for cancer-specific targeting. This antibody is able to specifically target primary myeloma cells without showing cross-reactivity to healthy tissues (including plasma cells from healthy donors). Moreover, antibody treatment in vitro led to apoptosis in primary myeloma cells (Rasche L; PLOS One 2013). In vitro,PAT-SM6 was combined with Lenalidomide and/or Bortezomib and Dexamethasone in double and triple combinations on myeloma cell lines. Synergistic and additive cytotoxic effects were analyzed using the Chou-Talalay method. All double and triple combinations showed synergistic effect with a combination index (CI) 〈 1. In all double combinations, low doses of agents appear more effective than high doses. In triple, PAT-SM6 + Dexamethasone + Lenalidomide seem to be the most efficient combination (CI from 0.005 to 0.011). In vitro data is further supported by positive in vivodata using PAT-SM6 in a 5T33 multiple myeloma mouse model. Upon injection of 5T33 cells mice developed multiple myeloma disease with clinical, biological and genetic characteristics similar to those of the human disease. A total of 6 doses PAT-SM6 were given i.p. followed by the collection of serum and bone marrow samples. Doses 〉 10mg/kg resulted in a significant reduction of plasma cells in the bone marrow (up to 54%) and a reduction of blood levels (up to 48%) of M protein. No cytotoxicity was observed. Based on these results we performed a Phase I clinical trial to examine the tolerability and safety of the PAT-SM6 antibody in patients with relapsed / refractory multiple myeloma. A pilot Phase I dose-escalating study was initiated (NCT01727778). Relapsed myeloma patients according to IMWG criteria were treated in different dose cohorts (0.3, 1,3 and 6mg/kg/dose) with at least four doses of PAT-SM6 as single agent in a two week cycle. A serological staging was performed on day 36. At the date of the abstract submission 9/12 subjects were treated. PAT-SM6 therapy was very well tolerated. No dose limiting toxicity (DLT), no related SAE and no related adverse events greater than grade 3 were observed. Mild leucopenia seemed to be a specific side effect. At date of submission 8 patients are evaluable for response. Two out of 8 patients showed stable disease according to IMWG criteria. In summary, PAT-SM6 provides a very promising approach for the immune therapy of patients with relapsed and refractory multiple myeloma. Disclosures: Braendlein: Patrys Ltd: Consultancy. Dubljevic:Patrys Ltd: Employment. Einsele:Celgene GmbH: Consultancy, Honoraria, Research Funding. Topp:Patrys Ltd: Honoraria.

Abstract: Introduction: Customized gene panel sequencing is an attractive approach to genomic tumor characterization in clinical care. Based on published MM exome data we developed a MM Mutation Panel (M3 P) that includes the most commonly mutated genes, actionable drug targets, genes targeted by current standard of care (SOC) therapies and which allows tracking of clonal evolution, copy number and sample purity. Methods and Material: M3 P (v3.0) covers 88 genes (1327 amplicons, 181kb). MM samples from 504 patients (pts) have been analyzed (corresponding germline in 81%) through collaborations between Mayo Clinic and Hospital-12-de-Octubre (Madrid, Spain), the DSMM and GMMG (Würzburg, Ulm, Freiburg and Heidelberg, Germany) and the HOVON trial groups (Rotterdam, The Netherlands). The investigated cohort includes 410 untreated pts (81%), which includes a high risk cohort of 72 pts with del17p, 25 paired samples with later follow up from the same cohort, and 94 relapsed patients, of which 50 were relapsed and refractory. Results: Overall coverage per mutation averaged 〉 500x depth. We identified 945 variants (1.9 per pt) and in 83% of the pts a mutation was found. Clonal heterogeneity was assessed with mutations ranging from 3%-100% variant reads suggesting the presence of a significant number of subclones (e.g. 21% of mutations were in 〈 10% of reads). The mutation incidence was compared with and closely resembles the most recent MM comprehensive genomic data from the MMRF CoMMpass study: We compare here all pts sequenced by M3 P, untreated pts sequenced by M3 P and CoMMpass: KRAS (24%/23%/24%), NRAS (20%/20%/18%), DIS3 (13%/14%/10%), BRAF (9%/7%/6%), FAM46C (6%/6%/8%) and TRAF3 (6%/6%/7%). TP53 mutation incidence, however, was significantly increased in our cohort (14%/12%/4.2%), a difference explained by the inclusion of del17p (untreated) and relapsed refractory MM in panel sequenced pts, cohorts with elevated incidences of TP53 mutations (32% / 26% respectively). Potentially actionable targets include BRAF mutationsin 43 patients (9%), with druggable p.V600E in 19 or 5%, 8 pts (2%) with FGFR3 (p.R248C and p.G375C one patient each), p.R132 mutation in 4 out of 5 IDH1 (1%) and p.R172K IDH2 mutation in 1 of 3 (1%) pts. Mutations in the MAPK pathway (NRAS, KRAS, BRAF) were detected in 59% of pts, ranging from 36% untreated MM to 72% in refractory MM. Similarly, the CRBN/CUL4B/IKZF1/IKZF3/IRF4 pathway, important for IMiD function, harbored a significant enrichment of mutations in advanced disease (6% untreated vs 17% relapsed), including CRBN mutations (0.5% vs 7%). Nine of 17 IRF4 mutations were located at the p.K123R hotspot, with minor difference between early or late disease (1% vs 3%). Notably, in 8 of 9 pts with CRBN mutation and clinical information, all were unresponsive to IMiD therapy, supporting association of these mutations with resistance to IMiDs. Conversely, M3 P genes related to other SOC therapies, including NR3C1 (targeted by steroids) and 5 proteasome subunit genes (proteasome inhibitors), were rarely mutated across the cohorts not exceeding 1% mutation incidence for each gene. Significant differences in DIS3 and FAM46C mutation incidences were observed across cohorts: DIS3 mutations are more common in untreated pts with a 1.7 fold increased predominance (14% untreated and 8% treated). FAM46C has an expected incidence of 8% but was rarely mutated in untreated del17p high risk disease with only one of 100 patients harboring both mutations. The significance of this finding needs to be determined but implies a possible overlap in function. Finally we assessed impact on survival of the mutation variants identified in 142 untreated Mayo patients and found STAT3 mutations negatively impacting PFS (p=0.034) and OS (p=0.001). This gene is rarely mutated in MM (2% of the total cohort) thus the sample size was small and this finding needs further validation. Conclusion: We here describe 504 MM patients sequenced using the M3 P gene panel, which identified mutations in 〉 80% of investigated patients, overlaps well with published whole exome sequence data and provides clinically relevant information. New findings were the high frequency of minor clones, the relative lack of overlap of del17 and FAM46C mutation, a higher frequency of DIS3 mutation at diagnosis compared to relapse, the prognostic significance of STAT3 mutation and the frequent presence of CRBN pathway mutation in drug resistant relapsed patients. Disclosures Sonneveld: Janssen-Cilag, Celgene, Onyx, Karyopharm: Honoraria, Research Funding; novartis: Honoraria. Mai:Janssen-Cilag: Other: Travel Grant; Onyx: Other: Travel Grant; Mundipharma: Other: Travel Grant; Celgene: Other: Travel Grant. Goldschmidt:Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Onyx: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Millenium: Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Chugai: Honoraria, Research Funding, Speakers Bureau; Janssen-Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Knop:Celgene Corporation: Consultancy. Kull:Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Martinez-Lopez:Novartis: Honoraria, Research Funding; Bristol-Meyer Squibb: Honoraria; Celgene: Honoraria; Janssen: Honoraria. Einsele:Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Amgen/Onyx: Consultancy, Honoraria, Speakers Bureau. Raab:Novartis: Research Funding. Stewart:Oncospire Inc.: Equity Ownership; Celgene: Consultancy; Novartis: Consultancy; BMS: Membership on an entity's Board of Directors or advisory committees.

Abstract: Background Allogeneic stem cell transplantion (allo SCT) for multiple myeloma (MM) takes advantage of a tumor cell-free graft along with potential immunosurveillance of residual malignant plasma cells. However, multiple factors such as treatment-related mortality (TRM) and morbidity and post-allo disease progression question the more widespread use of allo SCT. The induction of an early complete donor chimerism (DC) is thought to be associated with a low incidence of relapse and improved survival. Interestingly, data on chimerism analysis are relatively scarce for allo SCT in MM. Therefore, we retrospectively evaluated longitudinal DC results by short tandem repeat (STR)-based techniques from a single lab. Data were correlated with a set of baseline and outcome variables. In addition, disease- and treatment related factors like extramedullary disease (EMD), acute and chronic graft-versus-host disease (GvHD) and post-transplant consolidation were analyzed for impact on outcome. Patients and methods We identified 118 MM patients (pts) receiving non-myeloablative allo SCT at two German centers between 01/2006 and 12/2014. 90% of pts underwent allo SCT at relapse. Median follow-up was 42 months (mos), median overall survival (OS) 25 mos (range, 1-106) and TRM was 15%. Two-thirds of pts had received treosulfan/fludarabine as conditioning regimen. Median interval between MM diagnosis and allo SCT was 40.5 mos (range, 7-175) and median number of prior treatment lines was 3 (range, 1-10). 24 pts received allografts from matched related donors, 61 from matched-unrelated donors, and 33 pts from mismatched donors. Chimerism analysis was performed by STR-PCR on whole blood and T cell subsets using a validated multiplex STR-assay with a documented sensitivity of 1%. Response assessment was performed according the international myeloma working group guidelines. Results 1398chimerism samples (mean: 12/patient, 119 marrow, 1279 blood)) were analyzed. Median interval from allo SCT to first assessment was 15 (range, 3-62) days. Median duration of chimerism sampling was 24 mos. No graft rejections occurred. Full DC ( 〉 99%) was achieved in 117/118 pts. Pts who lost full DC had a significantly shorter progression free survival (PFS) than those with sustained DC (HR 0.2; p 〈 .0001). OS, however, was not different. In patients who developed disease progression, loss of DC versus sustained DC was not predictive for outcome. In spite of relapse, a full DC was found in peripheral blood in 82% and in 45% in bone marrow samples of pts, respectively. With respect to clinical predictors of outcome, the occurrence of acute GvHD had no impact on PFS nor OS. In contrast, induction of chronic GvHD was associated with prolonged PFS (HR 0.50; p=.0088) and OS (HR 0.39; p 〈 .001). Despite the induction of full DC in the blood, 13/118 (11%) of pts not in complete response received preemptive donor lymphocyte infusions (DLI). DLI without any concomitant signs of graft rejection or disease progression was associated with favourable OS (HR 0.43; p=.0067). When analysing relapse patterns after allo SCT, a 35% rate of EMD was observed. Interestingly, OS was not different when compared to intramedullary relapses. However, when allo SCT was performed as part of a consolidation therapy for prior EMD or plasma cell leukemia, OS was significantly shorter than compared to patients without EMD history (median OS 6 vs. 41 mos, p=.0035) Nevertheless, 25% of these EMD patients showed long-lasting remissions beyond 4 years. High risk cytogenetics (del17p, t(4;14) and +1q21), CMV reactivation or use of ATG had no impact on outcome. Conclusions To the best of our knowledge, this is the largest study of serial DC analysis in a cohort of clinically well characterized MM pts. The robust engraftment in almost all patients as well as the lack of graft rejections indicate the severe immunosuppression in MM due to pre-treatment and underlying disease. On the other hand, the most important predictors for PFS and OS was the occurrence of cGvHD. Preemptive DLI may further improve tumour control. The frequent spread of myeloma to extramedullary sites can be interpreted as an escape to more immuno-privileged regions as compared to the bone marrow. This pattern clearly limits the potential of prolonged serial DC analysis as the only tool for relapse detection. Our observations underscore the need to prospectively evaluate complementary strategies in this setting. Disclosures Einsele: Amgen/Onyx: Consultancy, Honoraria, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau. Thiede:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AgenDix GmBH: Equity Ownership. Knop:Celgene Corporation: Consultancy.