Anti-CD45 Pretargeted Radioimmunotherapy Prior to Bone Marrow Transplantation without Total Body Irradiation Facilitates Engraftment From Haploidentical Donors and Prolongs Survival in a Disseminated Murine Leukemia Model

s / Biol Blood Marrow Transplant 19 (2013) S211eS232 S228 chemotherapy was HIDAC (1-3 grams/m2 for 6-8 doses)/ Etoposide(15-40mg/kg) in 16 patients and growth factor alone in one patient. Median time from diagnosis to ASCT was 4.2 (range 3.6-7) months. Preparative regimen for ASCT was Busulfan (3.2mg/kg x 4)/Etoposide (60 mg/kg) in 12 patients and high dose melphalan in 5 patients. The median CD34 cells infused was 4.9 x 10e6/kg (range 2.8 to 15.9).All patients engrafted with a median time to neutrophil engraftment of 11 (range10-12) days. The median time to platelet engraftment was 20 (range15-40) days. The median length of inpatient stay during the ASCT admission was 14 (range 10-25) days. One patient died of progressive disease 14 months post ASCT. Two patients died in remission on day 53 (sepsis) and day 836 (unknown cause) post ASCT. Fourteen patients (82%) are currently alive in complete remission. at a median follow-up of 20 (range 140) months post ASCT. Conclusion: Consolidation of good risk AML patients with ASCT following induction of complete remission is safe and effective in preventing relapse in good risk AML patients

Humoral Immune Response Recognizes a Complex Set of Epitopes on Human Papillomavirus Type 6 L1 Capsomers

Although epitope mapping has identified residues on the human papillomavirus (HPV) major capsid protein (L1) that are important for binding mouse monoclonal antibodies, epitopes recognized by human antibodies are not known. To map epitopes on HPV type 6 (HPV6) L1, surface-exposed loops were mutated to the corresponding sequence of HPV11 L1. HPV6 L1 capsomers had one to six regions mutated, including the BC, DE, EF, FG, and HI loops and the 139 C-terminal residues. After verifying proper conformation, hybrid capsomers were used in enzyme-linked immunosorbent assays with 36 HPV6-seropositive sera from women enrolled in a study of incident HPV infection. Twelve sera were HPV6 specific, while the remainder reacted with both HPV6 and HPV11 L1. By preadsorption studies, 6/11 of these sera were shown to be cross-reactive. Among the HPV6-specific sera there was no immunodominant epitope recognized by all sera. Six of the 12 sera recognized epitopes that contained residues from combinations of the BC, DE, and FG loops, one serum recognized an epitope that consisted partially of the C-terminal arm, and three sera recognized complex epitopes to which reactivity was eliminated by switching all five loops. Reactivity in two sera was not eliminated even with all six regions swapped. The patterns of epitope recognition did not change over time in women whose sera were examined 9 years after their first-seropositive visit

Radioimmunotherapy with 90Y-DOTA-BC8 (anti-CD45 Antibody): Effect of Spleen Size and Uptake on Bone Marrow Absorbed Dose

1018 Objectives 90Y-DOTA-BC8 (anti-CD45 antibody) is being investigated as a treatment for hematologic malignancies in several ongoing clinical trials at the Fred Hutchinson Cancer Research Center. We analyzed the effect of spleen size and relative splenic uptake (%ID/g) of radiolabeled antibody on the absorbed dose to bone marrow. Methods: We reviewed biokinetic data on 39 patients who received radiotracer infusions of (129.5 to 406 MBq) 111In-DOTA-BC8 (0.5 or 0.75 mg/kg) followed by serial gamma camera imaging. Iliac crest bone marrow biopsies were obtained approximately 24 hours after antibody infusion to calculate the percent of administered activity (% ID/g) in marrow and to normalize the marrow time-activity curves from direct counting for dosimetry. Patient-specific organ absorbed doses were calculated with correction for organ volumes obtained from CT scans. We compared the calculated red marrow dose with spleen size and splenic uptake to ascertain whether the spleen acts as a sink for radiolabeled antibody and reduces the dose to the marrow. Results: Spleen size ranged from 62 to 758 cm3 (321.692 ± 144.33); initial antibody uptake in the spleen ranged from 0.054 to 0.317 % ID/g (0.184 ± 0.069). Calculated marrow doses ranged from 1.98 to 26.8 cGy/mCi (12.39 ± 7.70). Increasing spleen size reduced the marrow dose, but measurement uncertainties associated with biopsy specimen marrow content may have reduced the correlation coefficient (r = 0.25). The spleen acts as a natural sink for radiolabeled antibody which reduces uptake and retention of radiolabeled antibody in red marrow. Conclusions: Radioimmunotherapy with 90Y-DOTA-BC8-antibody has the ability to deliver substantial radiation doses to hematopoietic tissues in patients treated for hematologic malignancies. Spleen size weakly correlated with both red marrow clearance half-time (r = 0.19) and marrow dose (r = 0.25). (Research was supported by NCI P01CA044991, K08CA151682, and the David and Patricia Giuliani Family Foundation.

Prediction of Progression-Free Survival with Brentuximab Vedotin Therapy for Relapsed Hodgkin Lymphoma: A Retrospective Analysis

Introduction: The role of brentuximab vedotin (BV) in Hodgkin Lymphoma (HL) is expanding, but factors predicting progression-free survival (PFS) after BV therapy are poorly defined. Age, tumor bulk, presence of extranodal disease, neutrophil:lymphocyte ratio (ANC/ALC), and lymphocyte:monocyte ratio (ALC/AMC) predict outcome in HL patients (pts) treated with chemotherapy, but their impact on PFS after BV has not been well-studied. Also, among pts with relapsed/refractory HL (rel/ref HL) who progress after BV, efficacy of additional chemotherapy is undefined. To inform patient selection and future clinical trial design with BV, we undertook a retrospective study to identify factors predicting PFS with BV therapy in rel/ref HL, and explore chemotherapy efficacy as salvage after BV failure. Methods: Pts receiving BV since 2009 were identified through pharmacy and research records and studied with IRB approval. Those with rel/ref HL receiving BV before or after transplant without intervening therapy were excluded. Age ≥40 at time, sex, pre-BV PET findings (SUV max, extranodal [EN] involvement, bulk > 5cm), prior therapy (# lines of therapy> median; prior transplant, platinum-containing, radiotherapy), and lab findings (AMC/ALC³4.3, ALC/AMC ratio³1) at time of start of BV were examined for an impact on PFS and OS via log-rank testing of Kaplan-meier projections(JMP 11.0 software). PFS was defined as time from first BV dose to radiographic or clinical progression, initiation of post-BV salvage, or death from any cause. OS was measured from date of first BV dose to death from any cause. Efficacy of salvage therapy for those failing BV was recorded. Results: Of 90 patient receiving BV, 43 met above criteria. Median age was 34 yrs (range 17-80), median # of pre-BV therapies was 3 (range 1-7). 31 (73%) had failed autologous transplant, 10 (23%) had undergone allogeneic transplant, and 20 (46%) received radiotherapy prior to BV. Pre-BV PET staging data was available in 26 pts; post-BV PET was not analyzed in this dataset as response criteria were nonstandardized. BV was administered for a median 6 cycles (range 2-20). Median PFS after BV was 6 mo. (Figure 1) with 4 pts having PFS >4 yrs. At 31 mo. median follow-up, 71% of pts were alive with no plateau in the survival curve. On univariate analysis, age 40 or older at time of BV predicted inferior PFS (p=.03) and inferior OS though 95% confidence intervals were wide (OS by age: Figure 2, p=.02). HR for death for pts age 40 or older was 4 (98% CI .03-2.3, p=.05). No other factor predicted PFS or OS. Among 29 pts who failed BV, OS was 3.4 yrs. 40 chemotherapy regimens were given with 11 responses. Five of 11 pts responded to bendamustine, but median time to progression was 4 mo. Two of 4 responded to gemcitabine as did 3/8 receiving platinum chemotherapy. Conclusions: In this cohort of rel/ref HL pts treated with BV, PFS was 6 mo. overall and inferior among pts 40 yrs or older. OS was also worse in this group, although confidence intervals were wide in both univariate analyses. We confirm and expand upon prior data showing features predicting outcomes in HL after chemotherapy do not clearly apply after BV; and that most pts progress Disclosures Off Label Use: Brentuximab is approved in HL after failure of autologous stem cell transplant; in this series, some patients received Brentuximab before or when ineligible for an autologous stem cell transplant.. Gopal:Seattle Genetics: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Honoraria, Research Funding, Speakers Bureau; Janssen: Research Funding; Pfizer: Consultancy, Research Funding; BMS: Research Funding; Gilead: Research Funding; Spectrum: Research Funding; Teva: Research Funding. Shustov:Seattle Genetics, Inc.: Research Funding

Development of Astatine-211 ( 211 At)-Based Anti-CD123 Radioimmunotherapy for Acute Leukemias and Other CD123+ Hematologic Malignancies

Abstract Background: Radioimmunotherapy (RIT) has long been pursued to improve outcomes in acute leukemia. Of current interest are alpha-particle emitting radionuclides as they deliver a very large amount of radiation over just a few cell diameters, enabling efficient and selective target cell kill. So far, alpha-emitters including astatine-211 (211At) have been primarily explored with monoclonal antibodies (mAbs) targeting CD45 or CD33 but their broad display on non-malignant target-expressing cells can lead to marked "on-target, off tumor cell" toxicities. To overcome this limitation, we developed a novel form of 211At-based RIT targeting CD123. CD123 is displayed widely on acute leukemia cells, including underlying leukemic stem cells, but is expressed only on a discrete subset of normal hematopoietic cells and is virtually absent on non-blood cells. Methods: We immunized BALB/c mice with peptides consisting of the extracellular domain of human CD123 to generate anti-CD123 mAbs. Flow cytometry-based assays with human acute leukemia cell lines were used to characterize binding of hybridoma supernatants and mAbs to CD123. mAbs were conjugated with isothiocyantophenethyl-ureido-closo-decaborate(2-) (B10), a boron cage molecule for subsequent astatination, and were then labeled with 211At. In vivo leukemia cell targeting ("biodistribution") and efficacy studies were conducted in immunodeficient NOD-Rag1 null IL2rɣ null/J (NRG) mice xenografted with MOLM-13 cells, a CD123+ human acute myeloid leukemia cell line. Results: Based on initial hybridoma screening studies, we selected 4 mAbs (10C4, 5G4, 11F11, and 1H8) for further characterization. Phenotyping studies with CD123+ and CD123- human acute leukemia cell lines (including CD123+ cell lines in which CD123 was deleted via CRISPR/Cas9) confirmed specific binding of all mAbs to human CD123 (binding intensity: 10C4&gt;5G4=11F11=1H8), with 10C4 yielding a higher median fluorescence intensity than the widely used commercial anti-CD123 mAb clones, 7G3 and 6H6 (Figure 1). In vitro internalization with a panel of human acute leukemia cell lines studies demonstrated uptake of all mAbs by CD123+ target cells with a kinetic slower than that for anti-CD33 antibodies (typically, 30-50% of the anti-CD123 mAb internalized over 2-4 hours). All 4 anti-CD123 mAbs could be conjugated to B10 and subsequently labeled with 211At. Unlike a non-binding 211At-labeled control mAb, 211At-labeled anti-CD123 mAbs showed uptake at MOLM-13 flank tumors in NRG mice carrying MOLM-13 xenografts. After additional leukemia cell targeting studies to optimize the dosing of 10C4, we conducted proof-of-concept efficacy studies in NRG mice injected intravenously with luciferase-transduced MOLM-13 cells (disseminated leukemia model). Animals were either untreated or treated with 10 µCi, 20 µCi, or 40 µCi of 211At-labeled 10C4-B10 mAb (9-11 animals/group). This was followed by the infusion of bone marrow cells from donor mice as stem cell support 3 days later. As shown in Figure 2 and Figure 3, 211At-10C4-B10 led to a dose dependent decrease in tumor burden. Further, the treatment significantly prolonged survival compared to untreated animals (median survival: 49 days [40 µCi of 211At] vs. 31 days [10 µCi of 211At] vs. 21 days [Ctrl]; P&lt;0.0001 for Ctrl vs. 10 µCi, P&lt;0.004 for 10 µCi vs. 40 µCi), demonstrating potent in vivo anti-leukemia efficacy of a single dose of 211At-CD123 RIT. Conclusion: Our data support the further development of 211At-CD123 RIT for the treatment of patients with acute leukemia and other CD123+ hematologic malignancies. Figure 1 Figure 1. Disclosures Green: Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Cellectar Biosciences: Research Funding; GSK: Membership on an entity's Board of Directors or advisory committees; JANSSEN Biotech: Membership on an entity's Board of Directors or advisory committees, Research Funding; Juno Therapeutics: Patents & Royalties, Research Funding; Legend Biotech: Consultancy; Neoleukin Therapeutics: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; SpringWorks Therapeutics: Research Funding. Walter: Kite: Consultancy; Janssen: Consultancy; Genentech: Consultancy; BMS: Consultancy; Astellas: Consultancy; Agios: Consultancy; Amphivena: Consultancy, Other: ownership interests; Selvita: Research Funding; Pfizer: Consultancy, Research Funding; Jazz: Research Funding; Macrogenics: Consultancy, Research Funding; Immunogen: Research Funding; Celgene: Consultancy, Research Funding; Aptevo: Consultancy, Research Funding; Amgen: Research Funding. </jats:sec

Anti-CD45 radioimmunotherapy with 90Y but not 177Lu is effective treatment in a syngeneic murine leukemia model.

Radioimmunotherapy (RIT) for treatment of hematologic malignancies has primarily employed monoclonal antibodies (Ab) labeled with 131I or 90Y which have limitations, and alternative radionuclides are needed to facilitate wider adoption of RIT. We therefore compared the relative therapeutic efficacy and toxicity of anti-CD45 RIT employing 90Y and 177Lu in a syngeneic, disseminated murine myeloid leukemia (B6SJLF1/J) model. Biodistribution studies showed that both 90Y- and 177Lu-anti-murine CD45 Ab conjugates (DOTA-30F11) targeted hematologic tissues, as at 24 hours 48.8 ± 21.2 and 156 ± 14.6% injected dose per gram of tissue (% ID/g) of 90Y-DOTA-30F11 and 54.2 ± 9.5 and 199 ± 11.7% ID/g of 177Lu-DOTA-30F11 accumulated in bone marrow (BM) and spleen, respectively. However, 90Y-DOTA-30F11 RIT demonstrated a dose-dependent survival benefit: 60% of mice treated with 300 µCi 90Y-DOTA-30F11 lived over 180 days after therapy, and mice treated with 100 µCi 90Y-DOTA-30F11 had a median survival 66 days. 90Y-anti-CD45 RIT was associated with transient, mild myelotoxicity without hepatic or renal toxicity. Conversely, 177Lu- anti-CD45 RIT yielded no long-term survivors. Thus, 90Y was more effective than 177Lu for anti-CD45 RIT of AML in this murine leukemia model

Biokinetics of Radiolabeled Monoclonal Antibody BC8: Differences in Biodistribution and Dosimetry among Hematologic Malignancies.

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