scholarly journals Inhibition of C3 with APL-2 Results in Normalisation of Markers of Intravascular and Extravascular Hemolysis in Patients with Autoimmune Hemolytic Anemia (AIHA)

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 3623-3623 ◽  
Author(s):  
Federico Grossi ◽  
Merrill Kingman Shum ◽  
Morie A. Gertz ◽  
Eloy Roman ◽  
Pascal Deschatelets ◽  
...  
Keyword(s):  
Cell Surface ◽  
Hemolytic Anemia ◽  
Autoimmune Hemolytic Anemia ◽  
Complement C3 ◽  
Complement Cascade ◽  
Employment Equity ◽  
Indirect Bilirubin ◽  
Antiglobulin Test ◽  
Equity Ownership ◽  
Positive Direct

Abstract Background: Autoimmune hemolytic anemia (AIHA) is a rare autoimmune disease characterized by hemolysis mediated by autoantibodies directed against red blood cells (RBC). AIHA is classified as either warm (60-70%), or cold agglutinin disease (CAD, 20-25%), depending upon the temperature at which the autoantibodies show maximum binding. Warm AIHA is mediated by warm reactive autoantibodies, which are usually of the immunoglobulin G class (IgG). Almost 90% of CAD is medicated by monoclonal antibodies of IgM class. The diagnosis of wAIHA or CAD is based on the presence of hemolytic anemia, signs of hemolysis, and a positive direct antiglobulin test (DAT) for IgG or IgM, and/or complement C3. Complement plays an important role in warm antibody AIHA. When erythrocytes are heavily coated with immunoglobulin, the amount of antigen-antibody complex can be sufficient for binding complement protein complex C1, thereby activating the classical complement pathway. CAD is almost entirely a complement-dependent disorder. Cold antibodies (IgM) temporarily bind to the RBC membrane, activate complement, and deposit complement factor C3 on the cell surface. These C3-coated RBCs are cleared slowly by the macrophages of the liver through extravascular hemolysis. Less frequently, the complete complement cascade is activated on the cell surface, resulting in the insertion of membrane attack complex C5b to C9 and intravascular hemolysis. Therefore, treatment with inhibitors of complement cascade may halt or at least attenuate acute complement mediated hemolysis in AIHA patients and improve recovery of RBC destruction. Aims: This Phase 2, open-label study is being conducted in the US and Italy to assess the safety, tolerability, efficacy, and PK of multiple subcutaneous (SC) doses of APL-2 administered daily in subjects with wAIHA or CAD. Methods: Patients with primary AIHA are eligible. Patients are required to have hemoglobin (Hb) levels <11 g/L, signs and symptoms of hemolysis, and a positive direct antiglobulin test (DAT) for IgG or IgM, and/or complement C3. The study will recruit 12 subjects with wAIHA and 12 subjects with CAD. APL-2 270 mg/d or 360 mg/d will be administered for 48 weeks. Efficacy is assessed by change from baseline in Hb, transfusion requirements, reticulocytes, lactate dehydrogenase (LDH), haptoglobin, bilirubin, and FACIT fatigue score. Endpoints will be assessed at Weeks 8, 12, 44, and 48. Results: 2 subjects with CAD (Subject 1: 270 mg/d; Subject 2: 360 mg/d) have been treated for at least 8 weeks and up to 12 weeks; 2 subjects with wAIHA (Subject 3: 270 mg/d; Subject 4: 360 mg/d) have been treated for at least 4 weeks. Subject 1 screened with Hb (NR 13.5 g/dL-17.5g/dL) of 10.0 g/dL and reported an increase to 13.0 g/dL at Week 12, with reticulocyte (NR 30-100 10^9/L) reduction from 99.6 10^9/L at Week 2 to 56.34 10^9/L at Week 8 (screening/baseline values not available). Subject 2 had baseline Hb of 7.9 g/dL and reported an increase to 13.6 g/dL at Week 8, with reticulocyte reduction from 154.34 10^9/L at baseline to 67 10^9/L at Week 8. Subject 3 had baseline Hb of 8.0 g/dL and reported an increase to 11.2 g/dL at Week 4, with reticulocyte reduction from 223.44 10^9/L at baseline to 27.12 10^9/L at Week 4. Subject 4 did not show signs of haematological improvement by Week 4, and the principal investigator decided to discontinue the subject at Day 42. Subject 1 had LDH levels within the normal range (100-200 I/U) at screening and remained normal through the study. Subjects 2 reported a baseline LDH of 339 I/U with a reduction to within NR to 107 I/U at Week 8. Subject 3 reported a baseline LDH of 235 I/U, which was also reduced to within NR at Week 4 to 123 I/U. Subject 1 had consistent indirect bilirubin (NR 0.2-0.7 mg/dL) through the study with a baseline value of 1.5 mg/dL and a Week 12 value of 1.4 mg/dL. Subject 2 had a reduction in indirect bilirubin with a baseline value of 1.3 mg/dL and a Week 8 value of 0.5 mg/dL.To date, APL-2 has generally been well-tolerated. No significant infections have been observed. Summary/Conclusions: Interim results demonstrate that systemic inhibition of C3 with APL-2 has demonstrated positive trends in haematological parameters in patients with wAIHA and CAD as early as Week 4. To date, APL-2 has been safe and well tolerated. The study is ongoing and will enroll up to 12 subjects with wAIHA and 12 subjects with CAD. Disclosures Grossi: Apellis Pharmaceuticals: Employment, Equity Ownership. Gertz:spectrum: Consultancy, Honoraria; Medscape: Consultancy; Amgen: Consultancy; Physicians Education Resource: Consultancy; Apellis: Consultancy; Teva: Consultancy; Alnylam: Honoraria; Prothena: Honoraria; janssen: Consultancy; Ionis: Honoraria; Research to Practice: Consultancy; celgene: Consultancy; Abbvie: Consultancy; annexon: Consultancy. Deschatelets:Apellis Pharmaceuticals: Employment, Equity Ownership. Hamdani:Apellis Pharmaceuticals: Employment, Equity Ownership. Stout:Apellis Pharmaceuticals: Employment, Equity Ownership. Francois:Apellis Pharmaceuticals: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

scholarly journals Autoimmune Hemolytic Anemia During Pregnancy With Hemolytic Disease in the Newborn

Blood ◽  
1973 ◽  
Vol 41 (2) ◽  
pp. 293-297 ◽  
Author(s):  
Rolf Baumann ◽  
Harry Rubin
Keyword(s):  
Young Woman ◽  
Hemolytic Anemia ◽  
Steroid Therapy ◽  
Autoimmune Hemolytic Anemia ◽  
Mild Form ◽  
Hemolytic Disease ◽  
Indirect Bilirubin ◽  
Antiglobulin Test ◽  
Anemia During Pregnancy ◽  
Positive Direct

Abstract A young woman had idiopathic autoimmune hemolytic anemia occurring in the last weeks of pregnancy. The hemolytic process was quite severe in the mother but responded to steroid therapy and transfusions. The baby was born with a mild form of hemolytic disease with elevated indirect bilirubin levels, increased normoblasts and reticulocytes, and a positive direct antiglobulin test. The child did not require any exchange transfusions, and although the hemoglobin fell to a low of 9.7 g/100 ml 1 mo after delivery, it continued to rise to normal levels after that. The child is developing normally. The antibody was an IgG globulin, presumably 7S, and crossed the placenta to react with the fetal red cells. The antibody showed no specificity when tested with a panel of cells, including Rh null cells.

scholarly journals Clinical Patterns and Hematological Spectrum in Autoimmune Hemolytic Anemia

2010 ◽  
Vol 2 (01) ◽  
pp. 017-020 ◽  
Author(s):  
Vanamala Alwar ◽  
Shanthala Devi A M. ◽  
Sitalakshmi S. ◽  
Karuna R K.
Keyword(s):  
Connective Tissue ◽  
Hemolytic Anemia ◽  
Autoimmune Hemolytic Anemia ◽  
Severe Anemia ◽  
Red Cell ◽  
Connective Tissue Disorders ◽  
Red Cell Membrane ◽  
Antiglobulin Test ◽  
Circulating Autoantibodies ◽  
Positive Direct

ABSTRACT Background: Autoimmune hemolytic anemia (AIHA) results from red cell destruction due to circulating autoantibodies against red cell membrane antigens. They are classified etiologically into primary and secondary AIHAs. A positive direct antiglobulin test (DAT) is the hallmark of diagnosis for AIHA. Methods and Results: One hundred and seventy-five AIHA cases diagnosed based on positive DAT were included in the study. The cases showed a female predilection (M: F = 1:2.2) and a peak incidence in the third decade. Forty cases were found to be due to primary AIHA, while a majority (n = 135) had AIHA secondary to other causes. The primary AIHA cases had severe anemia at presentation (65%) and more often showed a blood picture indicative of hemolysis (48%). Forty-five percent of primary AIHAs showed positivity for both DAT and indirect antiglobulin test (IAT). Connective tissue disorders were the most common associated etiology in secondary AIHA (n = 63). Conclusion: AIHAs have a female predilection and commonly present with symptoms of anemia. AIHA secondary to other diseases (especially connective tissue disorders) is more common. Primary AIHAs presented with severe anemia and laboratory evidence of marked hemolysis.

scholarly journals Warm Autoimmune Hemolytic Anemia with a Direct Antiglobulin Test Positive for C3 and Negative for IgG: A Case Study and Analytical Literature Review of Incidence and Severity

2013 ◽  
Vol 6 ◽  
pp. CCRep.S11469 ◽  
Author(s):  
Amruth R. Palla ◽  
Farhad Khimani ◽  
Michael D. Craig
Keyword(s):  
Literature Review ◽  
Hemolytic Anemia ◽  
Autoimmune Hemolytic Anemia ◽  
Interesting Case ◽  
Clinical Entity ◽  
Direct Antiglobulin Test ◽  
Complement C3 ◽  
Igg Antibodies ◽  
Antiglobulin Test

Polygenic IgG autoantibodies are implicated in majority of the cases of warm autoimmune hemolytic anemia (WAIHA). In some of these cases, complement (C3) proteins accompany the IgG antibodies. WAIHA mediated by C3 alone is relatively rare. We present an interesting case of WAIHA with a direct antiglobulin test (DAT) positive for C3 but negative for IgG in a 79-year-old woman and perform an analytical literature review of the incidence and severity of this clinical entity.

scholarly journals Cold Agglutinin Disease Transfusion Practices in the United States: An Electronic Medical Record-Based Analysis

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 3690-3690
Author(s):  
Jun Su ◽  
Rajeshwari Punekar ◽  
Jaime Morales Arias ◽  
Nisha Jain
Keyword(s):  
Medical Record ◽  
Hemolytic Anemia ◽  
Autoimmune Hemolytic Anemia ◽  
Index Date ◽  
Cold Agglutinin ◽  
Cold Agglutinin Disease ◽  
Employment Equity ◽  
Medical Activity ◽  
Equity Ownership ◽  
Rbc Transfusion

Introduction Cold agglutinin disease (CAD) is a rare autoimmune hemolytic anemia (AIHA) accounting for 20% of all cases, with no approved therapies and limited management options for patients. CAD is characterized by immunoglobulin M-mediated erythrocyte agglutination, which triggers activation of the classical complement pathway leading to hemolysis and subsequent anemia. Red blood cell (RBC) transfusions are used as a supportive treatment in CAD to temporarily alleviate anemia, although the transfusion practices are variable among providers treating patients with CAD. Recent RBC transfusion guidelines from the AABB (formerly the American Association of Blood Banks) recommend that transfusions be administered with a restrictive threshold in most clinical scenarios (ie, transfusion is not indicated until hemoglobin [Hb] reaches 7-8 g/dL and/or patients exhibit anemia-related symptoms) to avoid associated complications such as acute reactions, alloantibody development, and hemochromatosis (Carson et al, JAMA, 2016; Carson et al, N Engl J Med, 2017). Because of the dearth of information available regarding trends in RBC transfusion practices among US hematologists, the objective of this longitudinal, retrospective, observational assessment of an electronic medical record database was to evaluate transfusion practices applied to patients with CAD in the US. Methods Patients were retrospectively identified from Optum® de-identified Electronic Health Record (EHR) dataset. Adult patients with ≥1 AIHA-related medical encounter between January 2007 and September 2018 (study period) and ≥3 mentions of CAD-related terms from physician notes ("cold agglutinin disease," "cold autoimmune hemolytic anemia," or "cold agglutinin hemoglobinuria") were included (Broome et al, Blood, 2017). The index date for each patient was the date of first mention of CAD during the study period. The baseline period was defined as the interval from the start of medical activity in the EHR database or study period (whichever occurred later) to the index date, and the follow-up period was defined as the interval from the index date to the end of the study period, end of medical activity, or death (whichever occurred earlier). The study sample was categorized into 2 study groups, the transfusion group (patients with CAD with ≥1 RBC transfusion after the index date) and the non-transfusion group (patients with CAD without any transfusions during the study period). Patients were further grouped based on the following Hb levels (g/dL): &lt;8, ≥8 to ≤10, and &gt;10 to ≤12. The closest Hb level prior to the most recent transfusion (within the prior 15 days and the lowest level) was used for the transfusion group and the lowest Hb level during the study period was used for the non-transfusion group. Descriptive statistics included mean, standard deviation, and median values for continuous variables and frequency (n and percent) for categorical variables. No adjustment was made for this descriptive analysis. Results A total of 903 patients with CAD were identified from the Optum EHR database; most patients were white (n=760 [84%]) and female (n=560 [62%]). Baseline demographics and clinical characteristics of each group can be found in the Table. Of the patients with CAD, 548 (61%) did not receive transfusions and 355 (39%) received ≥1 RBC transfusion. Among patients with CAD who received transfusions, 84% (n=297) had ≥2 RBC transfusions. Out of the 903 patients with CAD, 864 had Hb levels reported and 752 had Hb levels ≤12 g/dL. Forty-four percent (n=329/752) of those CAD patients received ≥1 RBC transfusion. When separated by Hb levels, 18% of patients with Hb &gt;10 to ≤12 g/dL (n=19/108); 41% (n=88/216) of patients with Hb ≥8 to ≤10 g/dL; and 52% (n=222/428) of patients with Hb &lt;8 g/dL received ≥1 RBC transfusion. Of the 423 (56%) patients with CAD and Hb levels ≤12 g/dL who did not receive RBC transfusions, 21% (n=89/423) had Hb levels &gt;10 to ≤12 g/dL; 30% (n=128/423) had Hb levels ≥8 to ≤10 g/dL; and 49% (n=206/423) had Hb levels &lt;8 g/dL. Conclusions Overall, patients with CAD are not a heavily transfused population. Even in those with a significantly decreased Hb (&lt;8 g/dL), approximately half of them (49%) did not receive RBC transfusions. This suggests that the use of transfusions in patients with CAD may not reflect disease severity. Further prospective studies are needed to fully understand the impact of transfusions on patients with CAD. Disclosures Su: Sanofi Genzyme: Employment, Equity Ownership. Punekar:Sanofi: Employment, Equity Ownership. Morales Arias:Sanofi: Employment, Equity Ownership. Jain:Sanofi Genzyme: Employment, Equity Ownership.

scholarly journals Warm antibody autoimmune hemolytic anemia in pregnancy: A case report

2020 ◽  
Vol 73 (7-8) ◽  
pp. 235-238
Author(s):  
Nevenka Bujandric ◽  
Jasmina Grujic ◽  
Zorana Budakov-Obradovic
Keyword(s):  
Case Report ◽  
Red Blood Cells ◽  
Hemolytic Anemia ◽  
Immunoglobulin G ◽  
Autoimmune Hemolytic Anemia ◽  
Blood Cells ◽  
Direct Antiglobulin Test ◽  
Indirect Antiglobulin Test ◽  
Antiglobulin Test ◽  
Positive Direct

Introduction. Warm autoimmune hemolytic anemia is the presence of warm autoantibodies against red blood cell with or without complement activation. The presence of warm autoantibodies on the red blood cells is detected by direct antiglobulin test with polyspecific and immunoglobulin G reagents. Antibodies removed from the red blood cells tested by indirect antiglobulin test show panagglutination with a panel of red blood cells. Case Report. We report a rare case of idiopathic warm autoimmune hemolytic anemia in a 26-year-old woman in the early pregnancy. Warm autoimmune hemolytic anemia was mild, so during monitoring the risk to the fetus was assessed as low. The fetal status was assessed every four weeks. The noninvasive Doppler examination of the fetal middle cerebral artery revealed no fetal anemia. The last control before childbirth was done in the 38 week of pregnancy and the fetal direct antiglobulin test was 4+ and indirect antiglobulin test was 2+. The newborn presented with warm autoantibody immunoglobulin G, and positive direct antiglobulin test (3+). The infant was breastfed for nine months after birth. The direct antiglobulin tests were positive (3+) in both mother and child over the following 12 months. Conclusion. In case of warm autoimmune hemolytic anemia, the main purpose is to stop hemolysis and correct anemia in pregnant women, but it is also necessary to monitor the fetal condition in order to detect fetal hemolytic anemia as early as possible.

Direct antiglobulin test reactive with complement only in warm type autoimmune hemolytic anemia

2007 ◽  
Vol 0 (0) ◽  
pp. 071003000343002-???
Author(s):  
L. SHVIDEL ◽  
M. SHTALRID ◽  
A. DUEK ◽  
M. HARAN ◽  
A. BERREBI ◽  
...  
Keyword(s):  
Hemolytic Anemia ◽  
Autoimmune Hemolytic Anemia ◽  
Direct Antiglobulin Test ◽  
Antiglobulin Test

TT30, a Novel Human Protein Therapeutic, Selectively Modulates the Complement Alternative Pathway by Targeted Supplementation of Local Factor H Activity.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3021-3021 ◽  
Author(s):  
V. Michael Holers ◽  
Istvan Mazsaroff ◽  
Hillary Akana ◽  
Christopher G. Smith ◽  
J. Woodruff Emlen ◽  
...  
Keyword(s):  
Cell Surface ◽  
Potent Inhibitor ◽  
Ex Vivo ◽  
Alternative Pathway ◽  
Factor H ◽  
Employment Equity ◽  
Complement Alternative Pathway ◽  
Equity Ownership ◽  
The Complement System

Abstract Abstract 3021 Poster Board II-997 The complement system is activated through three pathways: classical, lectin/mannose and alternative. Polymorphisms and mutations that promote Complement Alternative Pathway (CAP) activity are associated with human diseases including atypical hemolytic uremic syndrome (aHUS) and age-related macular degeneration (AMD). The complement system is also centrally involved in many hemolytic disorders, including paroxysmal nocturnal hemoglobinuria (PNH) where the CAP initiates complement activation resulting in intravascular hemolysis (IVH) after engagement of C5 and formation of the membrane attack complex (MAC). Systemic neutralization of C5 with the anti-C5 monoclonal antibody, eculizumab, abrogates IVH when plasma concentrations are maintained above the minimal efficacious concentration (Cmin = 35 μg/mL). However, because eculizumab does not inhibit CAP activity prior to C5, C3 fragments (C3frag) continue to covalently bind to and accumulate on PNH red blood cells (RBCs). Clearance by the reticuloendothelial system of PNH RBCs that are C3frag-coated is a putative cause of extravascular hemolysis (EVH) in eculizumab-treated patients. In order to selectively modulate CAP activity, we developed TT30, a novel therapeutic 65kD fusion protein linking the first four short consensus repeat (SCR) domains of human complement receptor type 2 (CR2/CD21) with the first five SCR of human factor H (fH). CR2 SCR1-4 encompasses the antigen-fixed C3frag (iC3b, C3dg and C3d) binding domain. Factor H is the primary soluble phase, negative regulator of CAP activity functioning via the SCR1-5 domains. The unique mechanism of TT30 utilizes CR2 SCR1-4 to recognize and bind to C3frag on cells in which complement activation is occurring, thus delivering cell surface-targeted inhibition of CAP activity via fH SCR 1-5. TT30 both prevents CAP-dependent hemolysis of rabbit RBCs in human serum and blocks accumulation of C3frag on the RBC surface. By design, TT30 should also be a potent inhibitor of the CAP, but with minimal inhibition of the complement classical (CCP) and mannose (lectin; CMP) pathways. To test this hypothesis, we utilized sensitive pharmacodynamic assays that allow in vitro or ex vivo assessment in an ELISA format of individual complement pathway activity present in human serum. In this format, TT30 is a potent and selective inhibitor of CAP activity in normal human complement-preserved serum, with EC50 and EC100 values of ∼0.1 and 1 μg/mL serum. As predicted by the use of fH in its construction, TT30 is a much less potent inhibitor of the CCP and CMP, with EC100 values of ∼65 μg/mL. By contrast, in these assays a monoclonal and polyclonal anti-C5 antibody each demonstrate non-selective inhibition of CAP and CCP activity at all effective concentrations. TT30 activity is dependent upon CR2 binding to C3frag, as an anti-CR2 monoclonal antibody reverses the surface inhibition of CAP activity. This surface-targeting approach to delivering fH SCR1-5 results in a molecule with a 10-fold potency gain in CAP inhibition relative to added purified fH and an ∼30-fold potency gain relative to the total fH present in the serum used in the assay. TT30 administered as a single IV injection at 20 mg/kg to rats, rabbits and monkeys results in Cmax values of ∼400, 500 and 300 μg/mL and concentration-dependent inhibition of CAP activity. At serum concentrations of TT30 that induced maximal (100%) inhibition of systemic CAP activity for up to 12 hours, CCP activity is modestly (∼35-60%) inhibited for only 2 hours. CAP activity returns to baseline levels in a predictable fashion. Pharmacokinetic analysis indicates no gender-related differences and the expected scaling of parameters across species. TT30 is pharmacologically active in monkeys, rabbits and mice. TT30 administered as a single subcutaneous injection at 20 mg/kg to monkeys results in Cmax values of ∼25 μg/mL, and EC100 values identical to those observed with IV administration, but with a 3-fold prolongation of the maximal pharmacodynamic effect. The novel therapeutic TT30 has been shown in vitro and ex vivo to deliver cell surface-targeted control of CAP activation with minimal CCP and CMP inhibition and effective blockade of C3frag accumulation and MAC formation. As a result, TT30 has potential utility for the treatment of complement-mediated diseases such as PNH, AMD and aHUS, in which cell surface-targeted control of CAP activation may be clinically beneficial. Disclosures Holers: Taligen Therapeutics: Employment, Equity Ownership, Patents & Royalties, Research Funding. Mazsaroff:Taligen Therapeutics: Employment. Akana:Taligen Therapeutics: Employment. Smith:Taligen Therapeutics: Employment. Emlen:Taligen Therapeutics: Employment, Equity Ownership. Marians:Taligen Therapeutics: Employment. Horvath:Taligen Therapeutics: Employment.

Mechanistic and Pharmacodynamic Studies of Adct-301, a Pyrrolobenzodiazepine (PBD) Dimer-Containing Antibody Drug Conjugate (ADC) Targeting CD25-Expressing Hematological Malignancies

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 1559-1559 ◽  
Author(s):  
Michael J. Flynn ◽  
Patrick H. van Berkel ◽  
Francesca Zammarchi ◽  
Peter C. Tyrer ◽  
Ayse U. Akarca ◽  
...  
Keyword(s):  
Cell Surface ◽  
Clinical Development ◽  
Cross Linking ◽  
Cross Link ◽  
Employment Equity ◽  
Interstrand Cross Links ◽  
Cross Links ◽  
Equity Ownership ◽  
Dose Dependent ◽  
Link Formation

Abstract ADCT-301, currently in Phase I clinical trial, is an ADC composed of a recombinant human IgG1, HuMax®-TAC against human IL-2R-α (CD25) conjugated through a cleavable linker to a PBD dimer warhead with a drug-antibody ratio of 2.3. In vitro and ex vivo, ADCT-301 binds human CD25 with picomolar affinity. ADCT-301 has highly potent and targeted cytotoxicity against a panel of human lymphoma cell lines. On release, PBD dimers bind in the DNA minor groove and exert their cytotoxic action via the formation of DNA interstrand cross-links. In vivo, ADCT-301 demonstrates dose-dependent antitumor activity against subcutaneous and disseminated lymphoma models. For example, in the Karpas 299 xenograft model, 10/10 tumor-free survivors are observed following a single dose of 0.5 mg/kg, whereas Adcetris® gives only a modest delay in mean tumor growth at 0.5 mg/kg, despite this tumor expressing three-fold higher target antigen levels for this drug. The current study aimed to further define the mechanism of action of ADCT-301 and validate pharmacodynamic assays for clinical development. In Karpas 299 cells, evidence for internalization of ADCT-301 was shown by a reduction of CD25 molecules on the cell surface over the first three hours post-treatment followed by a return to pre-treatment levels by 16 hours. This is consistent with the documented rapid recycling of CD25 to the membrane after exposure to IL-2 (Hemar et al Journal of Cell Biology 1995). Furthermore, ADCT-301 on the cell surface declined by >70% over four hours. Following a two-hour exposure to ADCT-301, DNA interstrand cross-linking, measured using a modification of the single cell gel electrophoresis (comet) assay, reached a peak between 4 and 8 hours after which cross-links persisted up to 36 hours. In contrast, the peak of cross-link formation for an equimolar concentration of warhead was immediately following drug exposure and a non-targeted PBD-containing ADC did not produce crosslinks in these cells. A strong correlation (r = 0.97) between loss of viability and DNA cross-link formation provides support for this DNA damage being the critical initiating mechanism of cytotoxicity of ADCT-301. We have previously shown that PBD-induced DNA interstrand cross-links elicit a robust, but delayed γ-H2AX response (Wu et al Clinical Cancer Research 2013). In Karpas 299 cells phosphorylation of H2AX was observed 24 hours after a two-hour exposure to sub-GI50 concentrations of ADCT-301. In these cells continuous exposure to ADCT-301 resulted in a dose-dependent G2/M arrest, peaking at 48 hours, later than for the naked warhead. The peak of the early apoptosis marker annexin-V on the cell surface of Karpas 299 cells was observed between 60 and 72 hours and maximal loss of viability was at 96 hours. Significant bystander killing of CD25-negative human Burkitt's lymphoma-derived Ramos cells was demonstrated for ADCT-301 both by co-culture experiments with CD25-positive Karpas 299 cells, and by media transfer from Karpas 299 cells treated with ADCT-301. This is important as many lymphomas are heterogeneous in their CD25 expression profile (Strauchen et al American Journal of Pathology 1987). In SCID mice with Karpas 299 subcutaneous tumors a single dose of ADCT-301 was administered at 0.2 or 0.6 mg/kg. 24 hours after treatment, excised tumors showed a dose proportional increase in intensity of membrane and cytoplasmic staining by an anti-PBD payload antibody. Cross-linking was determined as 23% (0.2 mg/kg) vs 49% (0.6 mg/kg) (p ≤ 0.01) reduction in Tail Moment using the comet assay and dose-dependent γ-H2AX formation measured by immunohistochemistry was observed. No cross-linking was observed in matched lymphocyte samples. These data confirm the mechanism of cell killing of ADCT-301 and provide relevant pharmacodynamic assays for use in the clinical development of PBD-based ADCs. Disclosures Flynn: Spirogen/Medimmune: Employment. van Berkel:ADC Therapeutics: Employment, Equity Ownership, Patents & Royalties. Zammarchi:ADC Therapeutics: Employment. Tyrer:Spirogen/Medimmune: Employment. Williams:Spirogen/Medimmune: Employment. Howard:ADCT Spirogen/Medimmune: Employment, Equity Ownership, Patents & Royalties. Hartley:ADCT Spirogen/Medimmune: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

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