Abstract: Patients with newly diagnosed multiple myeloma (NDMM) ineligible for autologous stem cell transplantation (ASCT) have lower survival rates and may benefit from frontline regimens that include novel agents. This Phase 1b study (NCT02513186) evaluated preliminary efficacy, safety, and pharmacokinetics (PK) of isatuximab, an anti-CD38 monoclonal antibody, combined with bortezomib-lenalidomide-dexamethasone (Isa-VRd) in patients with NDMM ineligible for/with no intent for immediate ASCT. Overall, 73 patients received four 6-week induction cycles of Isa-VRd, then maintenance with Isa-Rd in 4-week cycles. In the efficacy population ( n  = 71), the overall response rate was 98.6%, with 56.3% achieving a complete response or better (sCR/CR), and 36/71 (50.7%) patients reaching minimal residual disease negativity (10 −5 sensitivity). Grade ≥3 treatment-emergent adverse events (TEAEs) occurred in 79.5% (58/73) of patients but TEAEs leading to permanent study treatment discontinuation were reported in 14 (19.2%) patients. Isatuximab PK parameters were within the previously reported range, suggesting that VRd does not alter the PK of isatuximab. These data support additional studies of isatuximab in NDMM, such as the Phase 3 IMROZ study (Isa-VRd vs VRd).

Abstract: Allogeneic HCT is curative in myelofibrosis (MF) with a survival (OS) advantage compared to non-JAK-inhibitor treatments in patients (pts) with Int-2/high-risk DIPSS (Kroeger et al, Blood 2015). On the other hand, data demonstrate a OS benefit of the JAK1/JAK2 inhibitor ruxolitinib (RUX) in intermediate (Int)-2/high-risk IPSS (Cervantes et al, Blood 2013; Verstovsek et al, Haematologica 2015). Yet, comparative data to the impact of RUX and HCT on OS are lacking. This was pursued retrospectively at the University of Leipzig in light of clinical-, cytogenetic-, phenotype-driver-, and somatic mutations-based prognostic variables. Patient and Methods: RUX became available in November, 2009. MF pts (n=137; median age 58y) seen afterwards were included with the exception of MPL + pts (small number). Characteristics are shown in table 1. RUX was given for spleenomegaly and/or constitutional symptoms [n=76 (55%)]. Irrespective of RUX, a donor search was initiated in int-2 and high-risk IPSS pts 〈 70 y and HCT performed if a suitable donor identified. Based on this biologic randomization, 50 (37%) received HCT, 58 (42%) continued with RUX (median exposure 19 months), and 29 (21%) pts had other options. The RUX- and HCT-groups were balanced in terms of IPSS, platelets, cytogenetic-, and epigenetic molecular-risks. Treatment was initiated within the first year (median 10 months), thus probability of OS 5 years after diagnosis was calculated (SPSS20 software). Cytogenetic-risk was conducted according to Caramazza et al. Leukemia 2011. Somatic mutations detected by NGS were used to calculate molecular-risk (Vannucchi et al. Leukemia 2013). Results: Median OS time was 6.8 y. The RUX-group was older (median age 64 y) with profound spleenomegaly and a higher JAK2 V617F allele burden compared to the HCT group (median age 55 y) (p 〈 0.0005). The 56% OS at 5 years in the RUX group was comparable to that after HCT (60%; p=0.5). In the transplant setting, prior RUX-treatment (n=21; OS 65%) had no negative impact compared to up-front HCT (n=29; OS 55%) (p=0.9). Whilst IPSS low-/int-1-risk retained its survival impact (p=0.04), OS at 5 years was comparable for int-2 and high-risk. OS in the HCT and RUX groups for int-2 was 59% and 62% respectively (p=0.4) and for high-risk IPSS 54% and 50% respectively (p=0.2). Advanced age was associated with an inferior OS (p=0.002) and correlated with higher IPSS, transfusion-dependency and thrombocytopenia. In the HCT group, OS in pts 〈 50 y was 91% vs. 49% in pts 〉 50 y (p=0.001). In the RUX group, age 〈 60 and not 〈 50 y was OS-relevant [79% in pts 〈 60y vs. 43% in those 〉 60 y (p=0.02)]. No prognostic implication of anemia, WBC, peripheral blasts, and constitutional symptoms could be detected with both treatments. OS in JAK2 + pts was similar to CALR + pts in both therapy cohorts (p=0.3). Triple negativity retained its detrimental influence (p 〈 0.0001) even after HCT, with frequent AML-typical mutations (transcription and/or signaling genes) and a leukemic transformation (LT) rate of 35%. Although spliceosome mutations were associated with anemia (p=0.004)/transfusion-dependency (p=0.006) and mutations in chromatin modifiers (ASXL1, EZH2) with splenomegaly(p=0.02),high-molecular epigenetic risk had no impact on OS or LT in the treatment groups. Unfavourable cytogenetics were associated with LT (p=0.04) but not OS in the two groups. Of the 24 pts with a LT, 15 (62%) received no RUX and no HCT. Conclusions: Our data imply that, besides allogeneic HCT, a prolonged JAK1/JAK2 inhibition could, at least partly, attenuate most of the prognostic detrimental parameters. Pre-treatment with ruxolitinib prior to HCT does not seem to have a negative impact on survival. It is the first time where outcome with a non-transplant procedure is shown to be comparable to that after HCT in MF, even in high-risk disease. This needs to be verified in prospective randomized trials to define the role of allogeneic HCT in the era of JAK1/JAK2 inhibition. Table 1. Patients characteristics ( n = 137 ) Variable Impact on OS Impact on LT Median age (years) 58 0.002 0.6 JAK2+/CALR+/Double negative (%) 63 / 20 / 17 〈 0.0005 0.04 Median number of MF-related mutations (range) 1 (0-5) 0.4 0.07 High-molecular risk profile (%)(ASXL1, EZH2, SRSF2, IDH1/2) 33.6 0.8 0.7 Mutations in transcription/signaling genes (%) 28 0.3 0.008 Unfavorable cytogenetics (%) 30 0.1 0.04 IPSS (Int-2 / high-risk) (%) 34 / 41 0.04 0.2 Disclosures Roskos: Novartis: Honoraria. Al-Ali:Celgene: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding.

Abstract: Abstract 4461 Introduction: We have previously identified Nm23-H2 as a tumor antigen in a case of chronic myeloid leukemia. In the following project we investigated the molecular background for the increased expression of Nm23-H2 in CML cells from a large number of patients. Material and Methods: Clinical samples from 30 patients with CML in chronic phase at diagnosis [Bcr-Abl/Abl transcript levels from 69.5 to 93% IS (international scale)], in addition to patients with molecular response to imatinib [n=10; median 2 (range 0.1–11) % IS Bcr-Abl/Abl transcript level] and to imatinib resistant patients [n=10; median 66 (range 37–100) % IS Bcr-Abl/Abl transcript level] were investigated. Subpopulations were isolated from the blood (CD3+, CD14+) or bone marrow (CD34+) by FACS sorting. AML samples were obtained from 12 patients with de novo AML and 3 patients with secondary AML at diagnosis. Ba/F3 cells expressing either wild-type Bcr-Abl (Bcr-Ablwt Ba/F3), the T315I mutant of Bcr-Abl (Bcr-AblT315I Ba/F3) or the E255K mutant of Bcr-Abl (Bcr-AblE255K Ba/F3) were used in the cell line model. Messenger RNA levels of Nm23-H2 were measured using the QuantiTect Primer Assay (Qiagen). Results were normalized to mRNA for the ribosomal protein RPLP0. Western blotting for Nm23-H2 was performed by standard techniques using chemiluminescence and immunocytochemistry was performed using Nm23-H2 and ß-Actin antibodies. Mean fluorescence intensity was determined using the LSM Image Browser software. Results: Nm23-H2 protein is over-expressed in the cytoplasm of mononuclear cells from 30/30 CML patients at diagnosis and 10/10 patients with resistance to imatinib. In contrast, patients responding to Imatinib had markedly reduced levels of Nm23-H2 protein. Over-expression is limited to Bcr-Abl+ progenitor and myeloid populations and is absent from (Bcr-Abl-) T lymphoid cells, normal donors and 14/15 acute myeloid leukemia samples. The increase in Nm23-H2 protein is due to post-transcriptional regulation, with no detectable increase in mRNA levels. The increase in Nm23-H2 can be reversed by imatinib or nilotinib treatment of Ba/F3 cells expressing wild-type Bcr-Abl, but not of cells expressing the respective resistant Bcr-Abl mutants. Conclusions: The post-transcriptional up-regulation of Nm23-H2 is therefore a common and specific property of CML closely associated with Bcr-Abl activity, making Nm23-H2 a potential target for the development of novel immunotherapeutic or pharmaceutical therapies for CML. Disclosures: Al-Ali: Novartis: Consultancy, Honoraria. Niederwieser:Bristol-Myers Squibb: Speakers Bureau; Novartis: Speakers Bureau.

Abstract: The prognosis of AML in patients (pts) 〉 60 years (y) is poor and there is no universally accepted standard approach. After induction chemotherapy (IC), a complete remission (CR+CRi) rate of 56.4% and a mortality of 21% at day (d) 90 are expected (Niederwieser et al, ASH 2012). Azacitidine (AZA) yields a one-year survival (OS) rate of 46.5% in pts 〉 65 y and 〉 30% marrow (BM) blasts (Dombret et al, Blood 2015). Yet, AZA and IC are not mutually exclusive. First results of the interim analysis of the DRKS00004519 (RAS-AZIC) study which evaluates priming with AZA followed by AZA or IC in pts 〉 60 y with AML are presented. Patients and methods: Major inclusion criteria are newly diagnosed AML with marrow blasts 〉 20% by aspiration or biopsy irrespective of WBC count, age 〉 60 y, and eligibility for IC. Secondary AML from an antecedent hematologic disorder and therapy-related AML are not excluded. In the phase I part of the trial, safety of priming with AZA (75 mg/m2/day s.c) for 7 d followed by IC (Mitoxantrone 10 mg/ m2/day d 1-3 and cytarabine 1 g/m2/BID d 1, 3, 5, 7) on d 17 was established through a 3+3 design. In the multicenter phase II part (figure), priming was sequentially followed by AZA or IC based on d 15 BM blasts and d 56 response which were identified as early predictors for long-term response to AZA in AML (Al-Ali et al., Leuk Lymph 2012). The primary objective is overall response (OR) which includes CR, CRi, and PR at d 90 according to the International Working Group criteria (Cheson et al, J Clin Oncol 2003). Safety, OS, and mortality were secondary end points. According to the optimal two-stage design (Simon, Control Clin Trials 1989), an expected OR of 61% at the end of trial was estimated. Thus in a first stage analysis, 〈 19 of consecutive 40 (47.5%) pts not achieving the primary objective would be considered an indication for inferiority of the protocol treatment compared to standard IC. Hence, an interim analysis of the first stage was planned per protocol while accrual continues to include the first 40 pts who received the maximal tolerated priming dose of AZA. The trial is supervised by an independent Data Monitoring Committee. Adverse events (AEs) are reported according to the NCI CTCAE 4.03. All pts gave written informed consent. Results: Patient characteristics are shown in table 1. Median age is 69 y and median blast count 39%. All pts received priming with AZA. Median BM blasts at d 15 was 27% (range 2.4-88%). To date, data on subsequent therapies are captured in 33 (82.5%) pts. Except for one (withdrew consent on d 27), all pts received protocol assigned treatment based on BM blasts on d 15 [17/32 (53%) continued with AZA, 15/32 (47%) received IC]. Likewise, 26/32 (81%) pts ([2x data not yet available, 2x death (d 34; d 53), and 2x physician's choice] received response-adapted treatment on d 56 [12/26 (46%) started AZA maintenance and 14/26 (55%) received IC]. OR at d 90 for the 26 as yet evaluable pts is 80.7% [CR (61.5%, n=16); CRi (11.5%, n=3); PR (7.7%, n=2). No additional mortality till d 90 was reported. For the entire cohort, 85% of pts are alive after a median follow-up of 6 months. AEs were consistent with the known safety profile of AZA and IC. AEs 〉 grade 3 were reported 83x in 20 (50%) pts being mainly infectious and respiratory complications (60%). As expected, the majority (57%) were reported under IC, followed by 19% and 17% under priming and the 2. AZA cycle respectively. AEs led to postponement of the planned therapy in 6 pts (3x IC on d 17, 2x 2. AZA, 1x IC on d 56). The final assessment of the interim analysis is set in the near future. Conclusions: These data imply that in a heterogeneous disease like AML, integrating epigenetic therapy with chemotherapy in elderly pts in an individualized response-based approach is feasible, induces responses at least comparable to those seen after IC, and is associated with a remarkable low mortality. The definitive response rate and the impact of such an approach on survival will be answered at the end of the trial. Table 1. Patient characteristics (n=40) Median age, range (years) 69 ( 61 - 82) Male/Female (%) 55 / 45 Baseline ECOG (%)0/1/2 21 / 63 / 16 Type of AMLDo novo/secondary (%) 61 /39 Median WBC (range) x 109/L 6.7 (0.7 - 81.8 ) Median bone marrow blasts (aspiration) (range) (%) 39 (13 - 90) Cytogenetics (n=35)Normal/intermediate/unfavourable (%) 54 /23 / 23 FLT3+ (n=34) (%) 9 NPM1 + (n=34) (%) 9 Figure 1. Figure 1. Disclosures Al-Ali: Novartis: Consultancy, Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Off Label Use: Azacitidine is not approved for the use in patients with AML and blasts 〉 30% outside clinical trials.

Abstract: Background Rapid induction of remission is a favorable factor in pts with Hodgkin's disease and DLBCL. In MM, only few data are available on the impact of response kinetics on outcome in newly diagnosed transplant ineligible MM pts. Recently, (Abstract EP971, EHA 2021) we described a significant correlation between time to response and progression-free survival (PFS) and overall survival in this patient population. Response and time to response depend on several factors such as the biology of the underlying myeloma clone(s), the activity of the treatment regimen, and on the composition of the bone marrow immune environment. Here, we evaluated possible interconnections between the bone marrow immune environment at baseline and the time to response to therapy in a series of pts randomized to either 9 cycles KRd or KTd induction therapy followed by a second randomization to carfilzomib maintenance or observation. Patients and Methods Composition of the immune environment at baseline was analyzed in 55 pts with newly diagnosed transplant ineligible MM enrolled in a randomized phase II trial (AGMT_MM 02). Median age: 74 years (range: 58-84 years), ISS I: 21.8%, ISS II: 41.8%, and ISS III: 36.4%, cytogenetics: 30.9% high risk, 40% standard risk, 29.1% unknown, ECOG Status 0: 54.5%, 1: 45.6%. Treatment: Carfilzomib : Cycle 1 day 1+2: 20mg/m 2, days 8+9 and 15+16: 27 mg/m 2 ; Cycle 2 day 1,2,8,9,15 + 16: 27 mg/m 2 Cycle 3-9: 56mg/m 2 on days 1, 8 and 15. Lenalidomide: 25mg p.o. on days 1-21/cycle or thalidomide: 100 mg p.o. on days 1-28; in pts ≥75 years of age 50mg p.o. on days 1-28, dexamethasone: 40 mg p.o. on days 1, 8, 15, 22 (± 1 day), in pts ≥ 75 years of age 20 mg p.o. this treatment was administered for nine cycles. Thereafter, pts were randomized to carfilzomib maintenance at last tolerated dose on days 1+15 or to observation for 12 cycles. BM samples were stained with 3 different antibody combinations for the analysis of T, B and NK cells (T cells: CD45RA, CD127, CD8, TCRgd, CD25, CD197, CD4, CD3, B/NK cells: CD57, CCR7, CD314, CD85j, CD62L, CD3, CD16, CD56, CD335, HLADR, CD337). We used a semi-automated pipeline to unveil full cellular diversity based on unbiased clustering. The median and range of each cellular subgroup was calculated and compared between pts with short or longer time to response ( & lt; or ≥119 days (median)). Statistical significance of these comparisons was calculated using the Wilcoxon test. Results Median FU was 20.5 months. Twenty of the 55 pts achieved a CR (36.7%) and 16 (57.1%) of the 28 who had MRD testing were shown to be MRD negative at a sensitivity of 10 -6. Twenty-three pts achieved a VGPR (41.8%), while only 12 pts achieved a PR (21.8%). Pts were subdivided into two groups according to time to best response. Group A (n=26), median time 56 (26-112) days, group B (n=29), 265 (119-675) days. PFS was significantly longer in group B (19.1 months vs not reached, p=0.007), while for OS only a trend for better survival was noted for group B pts (median survival not reached, p=0.129). High numbers of total CD3 + cells (p=0.033) and CD4 T cells with a CD 197 loCD45RA -CD127 + phenotype (p=0.022) were associated with longer time to best response and longer PFS. An opposite result was noted for the following T cell subsets, which correlated with a shorter time to best response and shorter PFS: CD56 + T cells with (p=0.01) or without (p=0.024) HLADR and CD8 Naïve CD127 + T cells (p=0.041). Diverse results were noted when the NK cell compartment was analyzed. Higher levels of circulatory CD314 - (p & lt;0.0001) and circulatory CD314 + (p=0.049) NK cells correlated with longer time to best response and longer PFS. By contrast, lower levels of cytotoxic HLADR + NK cells (p=0.044) were associated with better outcome. Conclusion Our data show significant correlations between the composition of bone marrow immune cells at start of therapy with time to best response and PFS in newly diagnosed transplant ineligible MM pts uniformly treated with carfilzomib-based therapy. High numbers of total lymphocytes CD3 and CD4 Tcells with a CD197 loCD45RA -CD127 + phenotype correlated with significantly longer PFS and longer time to response. Furthermore, higher numbers of specific NK subsets such as those with a circulatory phenotype, correlated with better outcome. These results highlight the prognostic potential of immune monitoring and the interconnection between specific subsets of the immune environment with the course of the disease. Figure 1 Figure 1. Disclosures Greil: Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; AstraZeneca: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses; MSD: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Gilead: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Daiichi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Sankyo: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses, Research Funding; Sanofi: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Sandoz: Honoraria, Research Funding. Podar: Amgen Inc.: Consultancy, Honoraria; Janssen Pharmaceuticals: Consultancy, Honoraria; Roche Pharmaceuticals: Research Funding; Celgene: Consultancy, Honoraria. Petzer: Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kite-Gilead: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sandoz: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene-BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Saegen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Zojer: Celgene-BMS, Amgen, Takeda, Sanofi, Janssen: Consultancy, Speakers Bureau. Schreder: BMS-Celgene, Amgen: Consultancy. Melchardt: Abbvie, Celgene, Novartis: Honoraria. Knop: BMS/Celgene: Consultancy, Honoraria, Research Funding; Amgen: Research Funding; Janssen: Consultancy; Oncopeptides: Consultancy; Pfizer: Consultancy; Sanofi: Consultancy. Paiva: Bristol-Myers Squibb-Celgene, Janssen, and Sanofi: Consultancy; Adaptive, Amgen, Bristol-Myers Squibb-Celgene, Janssen, Kite Pharma, Sanofi and Takeda: Honoraria; Celgene, EngMab, Roche, Sanofi, Takeda: Research Funding. Ludwig: Janssen, Celgene-BMS, Sanofi, Seattle Genetics: Consultancy, Speakers Bureau; Amgen, Takeda: Consultancy, Research Funding, Speakers Bureau. OffLabel Disclosure: Carfilzomib in first-line therapy

Abstract: Introduction: Up to 30% of patients (pts) undergoing stem cell mobilization with granulocyte colony-stimulating factor (G-CSF) with or without prior chemotherapy mobilize poorly. Plerixafor is a potent CXCR4 receptor antagonist that is licensed for stem cell mobilization in autologous stem cell donors with multiple myeloma (MM) or lymphoma, who show poor mobilization after stimulation with recombinant G-CSF (r-metHuG-CSF, Filgastrim). Here we present our experience with plerixafor in poorly mobilizing autologous donors. Patients and Methods: We performed 35 stem cell collections between January 2011 and December 2014 in 28 poorly mobilizing autologous donors with MM (n=14), non-Hodgkin lymphoma (NHL, n=11), Hodgkin lymphoma (n=1) or both MM & NHL (n=2), adding plerixafor to the stimulation regimen with recombinant G-CSF. Known risk factors for poor mobilization included: diagnosis of lymphoma (50%); older age (61% 〉 60y at apheresis); 〉 1 chemotherapy lines (86%) & pretreatment with melphalan (18%). Median age of patients (pts) was 61 years (y, range 37-72y) at stem cell collection and 15 of the 28 pts were females. All pts received previous treatment with G-CSF (2x5µg/kg body weight [BW]) followed by a large volume leukapheresis (maximal 4 x total blood volume). All pts received 0.24 mg/kg BW plerixafor following insufficient mobilization of CD34+ cells into the peripheral blood (PB, 〈 10/µl CD34+ cells) - either after peripheral reconstitution of white blood cells (WBC, 〉 1 Gpt/l) following chemotherapy (n=22, 79%) or after 5 days of stimulation with G-CSF in steady state (n=6, 21%). Six pts treated with chemotherapy prior to mobilization received a second dose of plerixafor in response to insufficient CD34+ cell harvesting on the first collection day. As a control cohort, we evaluated the data of 151 collections from MM, NHL or Hodgkin lymphoma pts (106 males, 45 females, median age 56y, range 22-74y) with efficient mobilization in response to G-CSF treatment over the same time period. Results: The median concentration of CD34+ cells in PB before & after the first application of plerixafor was 8.4/µl (range 2.9-20.5 /µl) & 23.1/µl (range 10.2-54.1 /µl) respectively, corresponding to a median 3.3-fold increase (range 1.4-5.3-fold, P 〈 0.001, Figure 1). In comparison, pts in the control group had a median concentration of 101.9/µl (range 13-1190/µl) CD34+ cells in PB on the day of stem cell collection (Figure 1). The median CD34+ cell yield for pts receiving plerixafor was 3.7x10^6/kg BW (range 1.6-12.8x10^6/kg BW) compared to 10.5x10^6/kg BW (range 2.1-38.8x10^6/kg BW) in the control cohort (Figure 2). As expected, the WBC count in the product was higher in the plerixafor group (median 899.9x10^8, range 446-2214x10^8) compared to the efficiently mobilizing control cohort (median 470.2x10^8, range 99.9 -1537.1x10^8, P 〈 0.001). The vitality of the cells after thawing was tested with methan blue staining & was comparable in both groups: median 85.3% (range 73.3-92.8%) in the plerixafor group & 84.4% (range 50.6-96.8%) in the control cohort (P=0.242). Furthermore, all harvests were tested for their proliferation capacity by quantifying colony forming units (CFU). Pts receiving plerixafor had a median CFU number of 22.5 (range 1-199), which did not differ from the control cohort with a median of 200.2 CFUs (range 1-1341, P=0.568). To date, 22 (78.6%) of the poorly mobilizing pts have received an autologous stem cell transplantation. All showed good peripheral WBC (median day 11, range 10-15) & platelet (median day 16, range 11-46) recovery. Discussion: Our data shows that addition of plerixafor can increase the efficacy of stem cell harvesting in poor mobilizers. The collected stem cells fulfilled the appropriate quality control criteria including vitality after thawing ( 〉 50%) & proliferation capacity. We identified a median 3.3-fold increase in CD34+ cell concentration in PB & a median CD34+ cell yield of 3.7x10^6/kg BW after the application of plerixafor in poor mobilizers. Despite the fact that the CD34+ cell yield in pts receiving plerixafor remained significantly lower than the control cohort, we were able to harvest 〉 2x10^6/kg BW CD34+ cells in 93% (n=26) of poor mobilizers. Thus, the mobilization outcome of pts receiving plerixafor is acceptable and within the expected range. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures Franke: BMS: Honoraria; MSD: Other: Travel Costs; Novartis: Other: Travel Costs. Niederwieser:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.