ALBERT

Description: Ofatumumab is a unique monoclonal antibody that targets a distinct small loop epitope on the CD20 molecule. Preclinical data show that ofatumumab is active against B-cell lymphoma/chronic lymphocytic leukemia cells with low CD20-antigen density and high expression of complement inhibitory molecules. In a phase 1/2 trial evaluating safety and efficacy of ofatumumab in relapsed or refractory follicular non-Hodgkin lymphoma (FL) grade 1 or 2, 4 dose groups of 10 patients received 4 weekly infusions of 300, 500, 700, or 1000 mg. Patients had a median of 2 prior FL therapies and 13% had elevated lactate dehydrogenase. No safety concerns or maximum tolerated dose was identified. A total of 274 adverse events were reported; 190 were judged related to ofatumumab, most occurring on the first infusion day with Common Terminology Criteria grade 1 or 2. Eight related events were grade 3. Treatment caused immediate and profound B-cell depletion, and 65% of patients reverted to negative BCL2 status. Clinical response rates ranged from 20% to 63%. Median time to progression for all patients/responders was 8.8/32.6 months, and median duration of response was 29.9 months at a median/maximum follow-up of 9.2/38.6 months. Ofatumumab is currently being evaluated in patients with rituximab-refractory FL. This trial was registered at www.clinicaltrials.gov as #NCT00092274.

Description: Abstract 3955 Background: Patients (pts) with relapsed diffuse large B-cell lymphoma (DLBCL) ineligible for autologous stem cell transplant (ASCT) or relapsing after ASCT have a poor prognosis and limited therapeutic options. New treatment options are needed for these pts. Ofatumumab is a human monoclonal antibody that targets a membrane-proximal epitope comprising both the large loop and small loop of CD20, and has shown effective lysis of chemotherapy-refractory DLBCL cells in vitro (Teeling et al. Blood 2004; Cillessen et al. Blood 2007; abstract 2346). We report the first results from an open-label, single-arm, international Phase II trial that evaluated ofatumumab monotherapy in relapsed or progressive DLBCL. Methods: Pts (age ≥18 years) with relapsed or progressive CD20+ DLBCL ineligible for ASCT or with relapsed or progressive disease after ASCT were enrolled between December 2007 and August 2009 (N=81). Relapsed or progressive disease was defined as relapse after a complete remission (CR) or disease progression after partial remission (PR). Pts received 8 weekly infusions of ofatumumab (dose 1, 300 mg; doses 2–8, 1000 mg). The primary endpoint was overall response rate (ORR) evaluated during the 6 months from the start of treatment, as assessed by an Independent Endpoint Review Committee according to the revised response criteria (Cheson et al. J Clin Oncol 2007). Secondary endpoints included duration of response, progression-free survival (PFS), overall survival (OS) and safety. Results: Baseline characteristics are shown in the Table. Pts were heavily pretreated (median 3 prior systemic therapies), and 32% of pts did not respond to their last prior therapy. Nearly all pts (96%) had received prior rituximab-containing treatment; 54% had received 2 or more courses of prior rituximab therapy (Table). Overall, 58% of pts completed all 8 infusions of ofatumumab, 65% received at least 6 infusions, and 81% received at least 4 infusions. The primary reason for treatment discontinuation was disease progression. The ORR (95% CI) was 11% (4–18%), including 3 CRs (4%) and 6 PRs (7%). Of these 9 responding pts, 8 had responded to their last systemic therapy. The median duration of response (95% CI) was 6.9 months (5.3–6.9) and median PFS (95% CI) was 2.5 months (2.3–2.9). Infusion-related events occurred in 59% of pts, primarily occurred during infusion 1 (40% of pts) and infusion 2 (22%), and subsided during subsequent infusions; these events were predominantly grade 1–2 in severity (96% of pts). The most common (〉10% of pts) adverse events (AEs; any grade) were diarrhea (17%), fatigue (15%), peripheral edema (15%), neutropenia (14%), abdominal pain (12%), constipation (12%), nausea (12%), pyrexia (11%), anemia (11%) and leukopenia (11%). Of these, ≥ grade 3 events included neutropenia (10%), leukopenia (6%), anemia (5%) and fatigue (1%). Grade 3 or greater thrombocytopenia and febrile neutropenia were reported in 6% and 4% of pts, respectively. The most common infectious events were upper respiratory tract infections (7% of pts), all of which were grade 1–2 events. In total, 13 pts died during the study; 3 pts died during the treatment period and 10 pts died during post-treatment follow up (until 24 months from study start). Deaths were due to disease progression (n=10), sepsis (n=1), circulatory collapse (no further details; n=1) and multi-organ failure (n=1). Conclusions: Single-agent ofatumumab was well tolerated with an ORR of 11% in heavily pretreated pts with relapsed or progressive DLBCL, nearly all of whom had received prior rituximab therapy. Response to last systemic treatment appeared to influence response to ofatumumab in this pt population. Further studies of ofatumumab in combination with chemotherapy in relapsed DLBCL are currently underway. Disclosures: Off Label Use: Ofatumumab is an investigational anti-CD20 monoclonal antibody, currently under development for the treatment of B-cell malignancies (chronic lymphocytic leukemia, diffuse large B-cell lymphoma, Waldenstroms macroglobulinemia and follicular lymphoma) as well as autoimmune diseases (rheumatoid arthritis and multiple sclerosis). Davies:GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees. Padmanabhan:GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Gupta:GlaxoSmithKline: Employment. Lin:GlaxoSmithKline: Consultancy, Employment. Davis:GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees. Losic:Genmab A/S: Employment, Equity Ownership. Lisby:Genmab A/S: Employment. Radford:GlaxoSmithKline: Equity Ownership; Genmab: Consultancy, Honoraria.

Description: Introduction: Daratumumab is a first-in-class human anti-CD38 IgG1 monoclonal antibody in clinical development across the multiple myeloma (MM) disease spectrum. A population pharmacokinetics (PK) analysis was conducted (1) to characterize the target-mediated drug disposition (TMDD) and the variability associated with daratumumab disposition, (2) to evaluate the effects of individual demographic characteristics and other factors (e.g., laboratory tests and baseline disease status) on the disposition of daratumumab, (3) to understand daratumumab exposure in special populations (e.g., patients with renal or hepatic impairment and elderly patients), and (4) to predict target saturation and its relationship with daratumumab exposure. Methods: A total of 2,572 daratumumab concentration measurements from 223 patients enrolled in a Phase 1/2 study (GEN501 [NCT00574288]) and a Phase 2 study (MMY2002 [NCT01985126]) were included in the population PK modeling. Daratumumab doses ranged from 0.1 to 24 mg/kg, and 150 of these patients received 16 mg/kg. A mixed-effects 2-compartment pharmacokinetic model based on Michaelis-Menten approximation TMDD was developed. Model-based covariate analyses and simulations were conducted to evaluate the influence of individual characteristics/factors on exposure to daratumumab. Results: The population PK model suggested that the disposition of daratumumab was concentration- and dose-dependent, i.e., lower clearance at higher daratumumab concentrations. The model further revealed that the nonlinear concentration-dependent clearance decreased over time, which could be described as a first-order process. The concentration- and time-dependency of daratumumab clearance suggested that the dynamics of target/tumor burden significantly influenced daratumumab disposition in MM patients. The estimated target binding affinity (ie, concentration at 50% target saturation) was 2.38 µg/mL. The population PK model predicted that a concentration of 21.4 µg/mL and 236 µg/mL would be needed to achieve 90% and 99% target saturation, respectively. The estimated linear clearance (0.17 L/day) was very close to the clearance of non-specific endogenous IgG described in the literature and the volume of distribution of central compartment (V1) approached plasma volume, confirming the robustness of the model. The clearance and V1 of daratumumab significantly increased with increasing body weight. Consequently, exposure to daratumumab was relatively consistent across the range of body weights of MM patients after administration on a mg/kg basis. Age, race, renal impairment, and mild hepatic impairment had neither statistically significant nor clinically relevant effects on exposure to daratumumab. In addition, exposure was consistent across the different subgroups for performance status (ECOG), refractory status, and number of prior lines of therapy. Although baseline albumin levels, type of myeloma (IgG vs non-IgG), sex, and drug products had a statistically significant effect on daratumumab pharmacokinetics, further analyses demonstrated that these covariates had no clinically relevant impact on efficacy or safety profiles. Conclusion: The population PK model revealed a concentration- and time-dependent clearance of daratumumab, suggesting the presence of TMDD. A serum daratumumab concentration of 236 μg/mL was predicted to yield 99% target (CD38) saturation. This analysis suggests that body weight-based dosing is a feasible strategy for MM patients. No clinically relevant demographic or clinical characteristics were identified. Therefore, no dose adjustment based on these factors is recommended. Disclosures Yan: Janssen: Employment. Clemens:Janssen: Employment. Puchalski:Janssen: Employment. Lonial:Novartis: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Millennium: Consultancy, Research Funding; Onyx: Consultancy, Research Funding; Janssen: Consultancy, Research Funding. Lokhorst:Genmab: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Amgen: Honoraria. Orlowski:Millennium Pharaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Onyx Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Acetylon Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Array Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Spectrum: Research Funding; Biotheryx: Membership on an entity's Board of Directors or advisory committees; Forma Therapeutics: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees. Losic:Genmab A/S: Employment. Khan:Janssen: Employment. Jansson:Janssen: Employment. Ahmadi:Janssen: Employment. Lantz:Janssen: Employment. Perez Ruixo:Janssen: Employment. Zhou:Janssen: Employment. Xu:Janssen: Employment.

Description: Abstract 921 Background: Patients with chronic lymphocytic leukemia (CLL) refractory to fludarabine and alemtuzumab (FA-ref) or refractory to fludarabine with bulky (〉5 cm) lymphadenopathy (BF-ref) have poor prognosis with salvage regimens (Tam et al. Leuk Lymphoma 2007). Ofatumumab, a human CD20 monoclonal antibody, was recently approved by the US FDA and EMEA for treatment of CLL refractory to fludarabine and alemtuzumab based on the interim analysis of the pivotal international clinical trial, which included data from 138 patients with FA-ref and BF-ref CLL. At the interim analysis, the overall response rate (ORR; primary endpoint) with single-agent ofatumumab was 58% (99% CI: 40, 74) in the FA-ref group and 47% (99% CI: 32, 62) in the BF-ref group (Wierda et al. J Clin Oncol 2010). Here, we report the final result for the primary endpoint in 206 patients with FA-ref or BF-ref CLL enrolled in this study. Methods: Patients with FA-ref or BF-ref CLL received 8 weekly doses of ofatumumab followed by 4 monthly doses (dose 1, 300 mg; doses 2–12, 2000 mg). Premedication included acetaminophen, antihistamine and glucocorticoid. The primary endpoint (ORR, 1996 NCI-WG criteria) was evaluated over the 24-week treatment period by an Independent Endpoint Review Committee (IRC). Secondary endpoints included duration of response, progression-free survival (PFS), overall survival (OS) and safety. Results: Baseline characteristics are summarized in the Table; 89% and 50% of patients completed 8 and 12 ofatumumab doses, respectively. The ORR (95% CI) by IRC evaluation was 51% (40, 61) for the FA-ref group and 44% (35, 64) for the BF-ref group. Two patients in the BF-ref group achieved complete remission (Table). Results for time-to-event analyses are shown in the Table. Infusion-related AEs occurred in 63% of patients, which primarily occurred during doses 1 and 2, and diminished with subsequent doses. Infusion-related reactions were grade 1–2 events in 95% of patients; no fatal reactions were reported. The most common (≥5% of all patients) grade ≥3 adverse events (AEs) that occurred from start of treatment until 30 days after the last infusion were infections (24%), neutropenia (12%) and anemia (5%). The most common grade ≥3 infection was pneumonia (8% of patients). Fatal infections occurred in 8% of patients (13% in FA-ref; 5% in BF-ref groups). Grade 3–4 thrombocytopenia occurred in 8 patients (4%), febrile neutropenia in 4 patients (2%) and autoimmune hemolytic anemia in 2 patients (1%). Early death (within 8 weeks from start of treatment) occurred in 5 patients (5%) in the FA-ref group (infections, n=5) and 4 patients (4%) in the BF-ref group (infections, n=2; myocardial infarction, n=1; pulmonary edema, n=1). Conclusions: These final results from the pivotal trial clearly demonstrate the efficacy and safety of ofatumumab monotherapy in this heavily pretreated patient population with FA-ref and BF-ref CLL. Additional data analyses are ongoing, and efficacy outcomes for patient subgroups will be presented. Disclosures: Wierda: GlaxoSmithKline: Honoraria, Research Funding. Kipps:GlaxoSmithKline: Research Funding. Mayer:GlaxoSmithKline: Consultancy, Research Funding. Robak:GlaxoSmithKline: Consultancy, Honoraria, Research Funding; Genmab: Consultancy, Research Funding; Roche: Consultancy, Honoraria, Research Funding. Furman:GlaxoSmithKline: Consultancy, Speakers Bureau; Genentech: Consultancy, Speakers Bureau; Cephalon, Inc.: Speakers Bureau; Celegene: Consultancy; Calistoga: Consultancy. Stilgenbauer:Amgen: Research Funding; Bayer: Consultancy, Honoraria, Research Funding; Boehringer-Ingelheim: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Genzyme: Consultancy, Honoraria, Research Funding; GSK: Consultancy, Honoraria, Research Funding; Mundipharma: Consultancy, Honoraria, Research Funding; Roche: Consultancy, Honoraria, Research Funding; Sanofi Aventis: Research Funding. Cartron:GlaxoSmithKline: Honoraria; Roche: Honoraria. Padmanabhan:GlaxoSmithKline: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Chan:GlaxoSmithKline: Employment. Gupta:GlaxoSmithKline: Employment. Gorczyca:GlaxoSmithKline: Employment. Davis:GlaxoSmithKline: Employment. Losic:Genmab A/S: Employment, Equity Ownership. Lisby:Genmab A/S: Employment. Österborg:GlaxoSmithKline: Consultancy, Honoraria, Research Funding; Genzyme: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Merck KGaA: Research Funding.

Description: Background: The prognosis for patients with CLL refractory to fludarabine and alemtuzumab (double-refractory, DR) or refractory to fludarabine with bulky (〉5cm) lymphadenopathy (bulky fludarabine-refractory, BFR) is poor. The overall response rate (ORR) to salvage therapy for such patients is approximately 20% with a median survival of 9 mo (Tam et al, Leuk Lym, 2007). New effective treatments are needed for these patients. Ofatumumab (HuMax-CD20) is a human monoclonal antibody that targets a unique small-loop epitope on CD20 and elicits potent in vitro complement-dependent cytotoxicity, even in malignant B cells with low CD20 expression levels. We report on a planned interim analysis of an international, multicenter, pivotal study of ofatumumab in patients with DR and BFR CLL. Methods: Patients with DR or BFR CLL received 8 weekly infusions of ofatumumab followed by 4 monthly infusions (Dose 1, 300 mg; Doses 2–12, 2000 mg). Patients were premedicated with paracetamol, antihistamine and glucocorticoid. The primary end point was ORR (1996 NCI-WG response criteria) assessed by an Independent end points Review Committee (IRC) over a 24 wk period. Overall survival (OS) and safety were also evaluated. Results: This interim analysis included all 138 treated patients (DR, n=59; BFR, n=79: Table); 54% received all 12 infusions and 90% received □8 infusions. The ORR (99% CI) based upon IRC assessment was 51% (34, 68%) for the DR group and 44% (30, 59%) for the BFR group; 1 patient had CR. Additionally, a considerable number of patients had stable disease (Table). Median time to next CLL therapy was 9 mo for the DR group and 8 mo for the BFR group (Table); clinical progression was typically due to worsening lymphadenopathy. The median OS was about 14 mo for the DR group and 15 mo for the BFR group (Table); based upon a landmark analysis at wk 12, response was significantly correlated with longer survival for both groups. Updated efficacy results will be presented at the meeting. Ofatumumab was associated with infusion-related adverse events on the first infusion day in 46% of patients in the DR group and 38% in the BFR group, which were grade 3 (no grade 4) in 7% and 3%, respectively (only 1 grade 3 event was considered a serious adverse event). These events generally subsided with subsequent infusions. The most common grade 3 or 4 toxicities were infections (25% in DR; 27% in BFR group) and hematologic events including neutropenia (12% in DR; 10% in BFR group) and anemia (8% in DR; 4% in BFR group). Early death (within 8 wks from start of treatment) occurred in 2 patients (3%) in the DR group (sepsis, n=1; fungal pneumonia, n=1) and 3 patients (4%) in the BFR group (PD, n=1; sepsis, n=1; myocardial infarction, n=1). No patient tested developed antibodies to ofatumumab. Conclusions: These results demonstrate the effectiveness of ofatumumab in patients with double-refractory CLL or bulky fludarabine-refractory disease. Ofatumumab was well tolerated with no unexpected toxicities. This monoclonal antibody potentially represents an active treatment option with clinical benefit for patients with very poor prognosis who have exhausted standard treatment options. The encouraging single-agent activity in patients with refractory CLL warrants further investigation of ofatumumab in earlier disease settings, in combination with other agents, as maintenance, and in other B-cell malignancies. Table DR (n=59) BFR (n=79) CI=confidence interval; NR=not reached Characteristic Median(range) Age, yrs 64 (41–86) 62 (43–84) No. of prior treatments 5 (1–14) 4 (1–16) % of patients Rai Stage III/IV 54 70 Binet Stage C 51 65 ECOG performance status 0 44 30 1–2 53 67 Lymph node or CT lesion 〉5cm 93 100 Prior rituximab-containing regimen 59 54 ORR (%) (99% CI) 51 (34, 68) 44 (30, 59) Complete response 0 1 Partial response 51 43 Stable disease 39 43 Progressive disease 3 10 Median (95% CI) Time to next CLL therapy, mo 9.0 (7.3, 10.7) 7.9 (7.1, 9.3) Overall survival, mo 13.7 (9.4, NR) 15.4 (10.2, 20.2)

Description: DuoBody®-CD3xCD20 (GEN3013) is a bispecific antibody (bsAb), recognizing the T-cell antigen CD3 and the B-cell antigen CD20, that triggers potent T-cell-mediated lysis of CD20-expressing cells. DuoBody-CD3xCD20 is a full-length bispecific IgG1 generated by controlled Fab-arm exchange (cFAE) [1, 2] and contains an effector function-silenced Fc region. In vitro, DuoBody-CD3xCD20 induced potent activation, proliferation and cytotoxic activity of both CD4+ and CD8+ T cells in the presence of CD20-expressing cells, as measured by flow cytometry and bromodeoxyuridine (BrdU) incorporation assays. DuoBody-CD3xCD20 induced T-cell-mediated cytotoxicity towards a diverse panel of cell lines derived from various B-cell malignancies and endogenous B cells, with EC50 values in the low picomolar range (EC50: 0.2-5.0 pM). The CD20-specific antibody 7D8 [3-5] forms the basis for the CD20-specific Fab arm of DuoBody-CD3xCD20. To study the contribution of this specific Fab arm to the observed potency of DuoBody-CD3xCD20, we compared the target binding characteristics and the capacity to induce T-cell-mediated cytotoxicity of a CD3 bsAb based on 7D8, with CD3 bsAbs using B-cell targeting arms derived from alternative CD20 antibodies or from antibodies against other well-known B-cell membrane molecules CD22, CD24, CD37, CD70, CD79b, CD138 and HLA-DR. In addition, target expression levels of the B-cell targets were assessed in a panel of B-cell lines. Using a classic chromium release assay, the 7D8-based CD3 bsAb displayed cytotoxic activity superior to all other B-cell-targeting CD3 bsAbs tested, including alternative CD20-targeting CD3 bsAbs. This unique cytotoxic activity could not be explained by expression levels of the target antigen, nor by the binding affinity or epitope of the B-cell specific Fab arm. This illustrates the complexity of factors that determine the potency of CD3 bsAbs. The anti-tumor activity of DuoBody-CD3xCD20 was confirmed in vivo in humanized mouse models using three different B-cell lymphoma xenograft models, in prophylactic and therapeutic settings. Non-clinical safety studies with DuoBody-CD3xCD20 in cynomolgus monkeys demonstrated profound and long-lasting B-cell depletion (at least 70 days, at dose levels 〉 0.1 mg/kg) from both peripheral blood and lymphoid organs. B-cell depletion was reversible, with time to B-cell recovery correlating with the treatment dose. Notably, at the same dose level, B-cell depletion was comparable between subcutaneous and intravenous administration. Pharmacokinetic (PK) analysis demonstrated comparable bioavailability for the two administration routes, although peak plasma levels were lower and delayed after subcutaneous administration. Moreover, lower plasma cytokine levels were observed after subcutaneous administration. Based on these data, Genmab has initiated a First-in-Human clinical trial to evaluate the safety and preliminary efficacy of DuoBody-CD3xCD20 by subcutaneous administration in patients with B-cell malignancies. The study is currently enrolling (EudraCT No: 2017-001748-36). References Labrijn, A.F., et al., Efficient generation of stable bispecific IgG1 by controlled Fab-arm exchange. Proc Natl Acad Sci U S A, 2013. 110(13): p. 5145-50. Labrijn, A.F., et al., Controlled Fab-arm exchange for the generation of stable bispecific IgG1. Nat Protoc, 2014. 9(10): p. 2450-63. Teeling, J.L., et al., Characterization of new human CD20 monoclonal antibodies with potent cytolytic activity against non-Hodgkin lymphomas. Blood, 2004. 104(6): p. 1793-800. Teeling, J.L., et al., The Biological Activity of Human CD20 Monoclonal Antibodies Is Linked to Unique Epitopes on CD20. Journal of Immunology, 2006. 177(1): p. 362-71. van Meerten, T., et al., HuMab-7D8, a monoclonal antibody directed against the membrane-proximal small loop epitope of CD20 can effectively eliminate CD20 low expressing tumor cells that resist rituximab-mediated lysis. Haematologica, 2010. 95(12): p. 2063-71. Disclosures Hiemstra: Genmab: Employment, Other: Warrants. Engelberts:Genmab: Employment, Other: Warrants. de Jong:Genmab: Employment, Other: Warrants. Schuurhuis:Genmab: Employment, Other: Warrants. Salcedo:Genmab: Employment, Other: Warrants. Verploegen:Genmab: Employment, Equity Ownership. van der Zee:Genmab: Employment, Other: Warrants. Gerritsen:Genmab: Employment, Other: Warrants. Losic:Genmab: Employment, Other: Warrants. Horbach:Genmab: Employment, Other: Warrants. Oliveri:Genmab: Employment, Other: Warrants. Lammerts van Bueren:Genmab: Employment, Other: Warrants. Autzen Usher:Genmab: Employment, Other: Warrants. Schuurman:Genmab: Employment, Other: Warrants. Parren:Genmab: Equity Ownership; Lava Therapeutics: Employment. Breij:Genmab: Employment, Equity Ownership.

Description: Abstract 3433 Poster Board III-321 Introduction Monoclonal antibody (mAb) therapies represent an important clinical advance for patients (pts) with CLL, yet little is known about the pharmacokinetics (PK) and pharmacodynamics of mAb therapy in these pts. Ofatumumab is a human mAb targeting a membrane-proximal small-loop epitope on CD20 and mediates efficient complement-dependent cytotoxicity in vitro. Ofatumumab is being evaluated in a pivotal trial for pts with fludarabine-refractory CLL also refractory to alemtuzumab (FA-ref; n=59) or less suitable for alemtuzumab due to bulky (〉5 cm) lymphadenopathy (BF-ref; n=79). Overall response rate (ORR; primary endpoint) was 58% in FA-ref and 47% in BF-ref pts at an interim analysis; median progression-free survival (PFS) was 5.7 and 5.9 months, respectively. We evaluated relationships between baseline factors and ofatumumab PK and between PK parameters and treatment outcomes from the pivotal trial. Patients and Methods Pts received 8 weekly infusions of ofatumumab followed by 4 monthly infusions (Dose 1, 300 mg; Doses 2-12, 2000 mg). Response (1996 NCI-WG criteria) was assessed by an Independent Review Committee over 24 weeks of therapy. Blood samples for PK analysis were collected at Dose 1, Dose 8 (last weekly dose), and Dose 12 (last monthly dose). A population PK model was employed that included data from a previous study (Coiffier et al, Blood 2008;111:1094). For Dose 1, Cmax was determined; for Doses 8 and 12, Cmax, Cmin, AUC, clearance (CL), volume of distribution (Vss) and t½ were determined. The relationships between baseline pt characteristics and disease factors and PK parameters were evaluated by multivariate regression analysis. Associations between PK and ORR or PFS were explored using univariate and multivariate logistic regression or Cox regression analyses. Results 90% of the 154 pts received 8 weekly infusions of ofatumumab and 55% received all 12 infusions. PK parameters were similar between FA-ref and BF-ref pts. In multivariate analysis, higher Cmax at Dose 1 was significantly associated with lower % of bone marrow infiltration (p