ALBERT

Description: Background : DLBCL is an aggressive non-Hodgkin lymphoma (NHL) with poor outcomes in the R/R setting; overall survival (OS) is 28% at 1 year and 20% at 2 years in refractory patients (Crump, Blood 2017). Outcomes are particularly poor for patients ineligible for stem cell transplant (SCT). Ibrutinib is the only once-daily inhibitor of Bruton's tyrosine kinase and is approved for the treatment of various B-cell malignancies. Based on preclinical models, ibrutinib and lenalidomide, an immunomodulator that downregulates the MYD88 pathway, may synergize when combined (Yang, Cancer Cell 2012). Rituximab, an anti-CD20 antibody, has shown activity combined with ibrutinib in NHL (Wang, Lancet Onc 2016). PCYC-1123 is a multicenter, open-label phase 1b/2 study (NCT02077166) evaluating the combination of ibrutinib, lenalidomide, and rituximab (iR2) in R/R DLBCL. Methods : Patients ≥18 years of age with R/R non-GCB DLBCL ineligible for SCT received lenalidomide 20 or 25 mg orally on Days 1-21 of each 28-day cycle plus ibrutinib 560 mg orally once daily and rituximab 375 mg/m2 IV on Day 1 of Cycle 1-6. Treatment was continued until progressive disease (PD) or unacceptable toxicity. Immunohistochemistry (IHC) was performed by central laboratory per the Hans algorithm. The primary endpoint was overall response rate (ORR); secondary endpoints were complete response (CR), duration of response (DOR), progression-free survival (PFS), OS, and safety. Response was determined by investigator assessment per Cheson (J Clin Oncol 2014) every 3 treatment cycles for the first 24 months (mos) and then every 6 cycles thereafter. Results: In total, 89 patients were enrolled and treated in phase 2 (n=55 and n=34 in the lenalidomide 20 mg and 25 mg cohorts, respectively). The median patient age was 64 years; 58% were male. At study entry, 53% of patients were refractory to their last therapy and 16% were primary refractory, 47% had relapsed, and 63% had stage IV disease. Median number of prior DLBCL therapies was 2 (range 1-5), with the most common being R-CHOP (73%), RICE (26%), and R-DHAP (13%). Twenty patients had prior SCT. All patients were non-GCB by IHC; for the 47 patients with tumor tissue available for nanostring testing by GEP, there was 84% concordance in non-GCB status (activated B-cell [ABC] or unclassified). The median time on study was 16 mos (range 30% of patients) were diarrhea (53%), fatigue (42%), neutropenia (40%), cough (34%), anemia (33%), peripheral edema (33%), and maculopapular rash (31%). The most common Grade 3/4 AEs were neutropenia (36%) and maculopapular rash (18%); Grade 3/4 atrial fibrillation occurred in 2% of patients. Grade 5 TEAEs occurred in 12 patients; of these, 7 were due to worsening of DLBCL, and 5 were not related to PD (pneumonia [n=3], sepsis [n=1], and cardiac arrest [n=1]). AEs led to discontinuation in 17% of patients (n=15) overall (those occurring in ≥2 patients were worsening of DLBCL [n=4], pneumonia [n=2], and thrombocytopenia [n=2]). Conclusions : The iR2 combination of ibrutinib, lenalidomide, and rituximab showed an ORR of 47% in patients with follow-up response assessment, with 28% CRs, including durable CRs of up to 22 mos. The safety profile was manageable in this phase 2 study of patients with R/R non-GCB DLBCL ineligible for SCT. Further evaluation of the iR2 regimen is ongoing. Disclosures Ramchandren: Seattle Genetics, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Sandoz-Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Merck: Research Funding; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech: Research Funding; Pharmacyclics LLC, an Abbvie company: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Research Funding. Johnson:Boehringer Ingelheim: Honoraria; Incyte: Honoraria; Epizyme: Honoraria, Research Funding; Takeda: Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Novartis: Honoraria; Bristol-Myers Squibb: Honoraria; Genmab: Honoraria; Celgene: Honoraria; Kite: Honoraria. Ghosh:Gilead: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Pharmacyclics LLC, an AbbVie Company: Consultancy, Honoraria, Research Funding, Speakers Bureau; SGN: Consultancy, Honoraria, Research Funding, Speakers Bureau; Genentech: Research Funding; Forty Seven Inc: Research Funding; Bristol-Myers Squibb: Honoraria, Speakers Bureau; AstraZeneca: Honoraria, Speakers Bureau; TG Therapeutics: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Research Funding. Ruan:Seattle Genetics: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria; Kite: Consultancy; Pharmacyclics LLC, an AbbVie company: Research Funding; Juno: Consultancy. Ardeshna:Celgene: Consultancy, Honoraria; Gilead: Consultancy, Honoraria. Johnson:Takeda: Other: Travel, accomodations, expenses; Roche: Consultancy, Honoraria, Speakers Bureau. Cunningham:Clovis: Research Funding; Eli Lilly: Research Funding; 4SC: Research Funding; Bayer: Research Funding; MedImmune: Research Funding; Celgene: Research Funding; AstraZeneca: Research Funding; Sanofi: Research Funding; Amgen: Research Funding; Janssen: Research Funding; Merck: Research Funding; Merrimack: Research Funding. de Vos:Portola Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Verastem: Consultancy; Bayer: Consultancy. Radford:Seattle Genetics: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Research Funding; ADC Therapeutics: Consultancy, Research Funding; GSK: Equity Ownership; Novartis: Consultancy, Honoraria; AstraZeneca: Equity Ownership, Research Funding; BMS: Consultancy, Honoraria. Morgan:Biogen: Equity Ownership; Eli Lilly: Equity Ownership; Gilead: Equity Ownership; Johnson and Johnson: Equity Ownership; Merck: Equity Ownership; Novo Nordisk: Equity Ownership; Pfizer: Equity Ownership; Vertex: Equity Ownership; Zoetis: Equity Ownership. Munoz:Celgene/Juno: Consultancy, Research Funding; Genentech: Consultancy, Research Funding, Speakers Bureau; Kite/Gilead: Consultancy, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy; Alexion: Consultancy; Pfizer: Consultancy; Fosunkite: Speakers Bureau; AstraZeneca: Speakers Bureau; Portola: Research Funding; Incyte: Research Funding; Kyowa: Consultancy, Honoraria, Speakers Bureau; Seattle Genetics: Consultancy, Honoraria, Research Funding, Speakers Bureau; Pharmacyclics /Janssen: Consultancy, Research Funding, Speakers Bureau; Bayer: Consultancy, Speakers Bureau; Merck: Consultancy. Ping:Pharmacyclics LLC, an AbbVie company: Employment; AbbVie: Equity Ownership. Kwei:Gilead: Equity Ownership; Pharmacyclics LLC, an AbbVie company: Employment; AbbVie: Equity Ownership. Eckert:AbbVie: Equity Ownership; Pharmacyclics LLC, an AbbVie Company: Employment, Other: Travel, Accommodations, Expenses. Neuenburg:Pharmacyclics LLC, an AbbVie company: Employment, Other: Travel, accomodations, expenses. Goy:University of Nebraska: Research Funding; Pharmacyclics/Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants outside of the submitted work, Research Funding; Acerta: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants outside of the submitted work, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Other: Grants outside of the submitted work, Research Funding; Hackensack University Medical Center, RCCA: Employment; Hakensackumc: Research Funding; COTA: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Other: leadership role for profit healthcare company; Takeda: Other: Grants outside of the submitted work; Kite, a Gilead Company: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Grants outside of the submitted work; Astrazenca: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. OffLabel Disclosure: Ibrutinib in combination with lenalidomide and rituximab is not approved by the FDA for treatment of diffuse large B-cell lymphoma (DLBCL)

Description: Design/methods: Rituximab added to 8 cycles of CVP (R-CVP) chemotherapy improves time to progression and duration of response in previously untreated patients with stage III/IV CD20 positive follicular NHL compared with CVP alone (Marcus et al Blood2005;105:1417–23). A protocol pre-planned analysis of this study with a median follow-up of 53 months has now been performed. Results: A total of 321 patients (median age 53 years) were recruited. Eighty-three percent of patients in both arms had intermediate to high-risk disease according to the Follicular Lymphoma International Prognostic Index (FLIPI, score 2–5). Median time to progression or death (TTP) in the R-CVP arm was 34 months compared with 15 months in the CVP arm, p

Description: To study transplanted unperturbed and mobilized long-term hematopoiesis after selection with an alkylating agent, bone marrow (BM) from 5 C57BL/6J mice was pooled, repeatedly transduced with retroviruses encoding the alkylating agent resistance protein O6-Methylguanine-DNA and enhanced green fluorescent protein (eGFP) as an easily traceable marker. Between 1 to 9x105 transfected BM cells were transplanted into 15 myeloablatively irradiated sex-mismatched C57BL/6J mice. Subsequently, 3 to 4 selection rounds with BCNU/O6-BG were carried out, enriching eGFP marked hematopoiesis in these mice up to 70–90%. Between 1 and 7x107BM cells of different mice were transplanted according to marrow location into groups of 5 sex-matched Bri44[1] mice. Two mice each received BM from the hind limbs, two from the pelvis and one received cells from the spleen, only, respectively. Altogether the study comprised 15 groups divided into 6 female and 9 male groups. Of these, 4 male and 3 female groups received 3 HSC-mobilization courses with G-CSF at intervals of 2 months starting 3 month after transplantation. Hematopoiesis in the other fraction remained unperturbed. During the observation period of 11–14 months in these tertiary recipients, repeated FACS analyses as well as linear amplification mediated (LAM) PCRs were carried out to track the clonal contributions. A decrease in the percentage of eGFP expressing marked hematopoiesis was observed in most cases. However, eGFP expression never disappeared altogether and could still be detected in the different hematopoietic lineages and successfully sorted for further analyses by MoFlo (Dako-Cytomation). Assessment of the clonal status of the Bri44 by LAM-PCR displayed interesting results. In some mice a decline in clone numbers was observed, whereas clone numbers remained stable in others. Tertiary transplantation with long-term follow-up indicates that this observation may be related to the transplantation of limited long-term repopulating clone numbers and progenitor cell exhaustion over time.

Description: Background : Patients with relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) typically have poor treatment outcomes, especially patients who are ineligible for stem cell transplantation (SCT). Ibrutinib, a first-in-class, once-daily inhibitor of Bruton's tyrosine kinase, is approved in the US for various B-cell malignancies. Preclinical data suggest potential synergy when combining ibrutinib with lenalidomide, a thalidomide analogue that disrupts signaling downstream of B-cell receptor and MYD88. An open-label, multicenter, phase 1b/2 study (NCT02077166) was initiated to evaluate the iR2 regimen of ibrutinib, lenalidomide, and rituximab in R/R DLBCL. Results from the ongoing phase 2 portion of the study evaluating the safety and activity of the iR2 regimen in SCT-ineligible adults aged ≥18 y with R/R non-germinal center B-cell-like (non-GCB) DLBCL per Hans method are presented here. Methods : The iR2 regimen was administered at the recommended phase 2 dose (RP2D) of once-daily 560 mg PO ibrutinib with 20 mg PO lenalidomide on Days 1-21 and 375 mg/m2 IV rituximab on Day 1 of Cycles 1-6 in 28-day cycles (additional 25-mg cohort ongoing). The primary phase 2 efficacy endpoint was ORR; the null hypothesis of an ORR of 40% will be tested against the alternative hypothesis of an ORR 〉60%. Secondary endpoints included complete response (CR) rate, duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Response was based on investigator assessments and performed using CT or MRI scans after every 3 treatment cycles for the first 24 mo and every 6 mo thereafter. For rash and neutropenia, if clinically indicated, study medication was withheld until resolution or improvement to grade 1, and treatment with oral corticosteroids and antihistamines (for rash) or hematopoietic growth factors (for neutropenia) was initiated. Results : A total of 55 patients were enrolled and treated at the RP2D with 20 mg PO lenalidomide in phase 2. The median age was 63 y; 58% were male; 64% had stage IV disease; 24% had primary refractory disease; 53% were refractory to the last therapy. Patients had received a median of 2 (range: 1-5) prior systemic therapies for DLBCL; the most common regimens were R-CHOP (71%), RICE (29%), and R-DHAP (16%). Among the 44 response-evaluable patients with follow-up imaging, the ORR was 55% (95% CI: 39%-70%; n=24) and included CR in 30% (n=13) and PR in 25% (n=11); 5 patients (11%) had stable disease. The median DOR was 9 mo for all responders and 10 mo for those who achieved a CR. The median maximum percent change from baseline in the size of the target lesion(s) was −61%. Among all 55 treated patients, the median duration of iR2 treatment was 4 mo (range: 0-13), and almost half (45%) of patients were still receiving iR2 treatment at the time of analysis (Figure 1A). Progressive disease was the most common reason for treatment discontinuation (45%). Median PFS was 5 mo (95% CI: 3-12; Figure 1B), with 6-mo and 12-mo PFS rates of 44% and 28%, respectively. Median OS was 17 mo (95% CI: 8-17), with 6-mo and 12-mo OS rates of 85% and 58%, respectively. For the 24 responders, median PFS was 12 mo (95% CI: 6-12), and median OS was 17 mo (95% CI: not evaluable). The majority (85%) of patients experienced a grade 3-4 TEAE; events reported in ≥5% of patients included neutropenia (33%), maculopapular rash (15%), anemia (11%), diarrhea, dyspnea, fatigue, and hypokalemia (5% each). Neutropenia, maculopapular rash, and anemia were the only grade 3-4 TEAEs in 〉2 patients considered related to either ibrutinib or lenalidomide. Of the 8 patients with grade 3/4 maculopapular rash, 7 received concomitant corticosteroids. Grade 5 TEAEs were experienced by 6 patients and included worsening of DLBCL (n=3), pneumonia (n=2), and sepsis (n=1). Doses of study treatment were temporarily interrupted or reduced due to TEAEs in 62% and 29% of patients, respectively. Discontinuation due to TEAEs occurred in 11% of patients (worsening of DLBCL [5%], pneumonia [4%], and sepsis [2%]). No cases of febrile neutropenia were reported. Conclusions : The iR2 combination regimen of 560 mg ibrutinib, 20 mg lenalidomide, and 375 mg/m2 rituximab demonstrated promising activity with a manageable safety profile in these difficult-to-treat R/R non-GCB DLBCL patients ineligible for SCT. Evaluation of the iR2 regimen using a dose of 25 mg lenalidomide and biomarker analyses, including GEP, are ongoing. Disclosures Ramchandren: Merck: Research Funding; Bristol-Myers Squibb: Consultancy; Seattle Genetics: Consultancy, Research Funding; Pharmacyclics LLC an AbbVie Company: Consultancy, Research Funding; Janssen: Consultancy, Research Funding. Johnson:Genmab: Consultancy; Novartis: Honoraria; Takeda: Honoraria, Travel, accommodations, expenses; Zenyaku Kogyo: Other: Travel, accommodations, expenses; Janssen: Consultancy, Research Funding; Kite: Consultancy; Incyte: Consultancy; Boeringher Ingelheim: Consultancy; Bristol-Myers Squibb: Honoraria; Epizyme: Consultancy, Honoraria, Research Funding; Celgene: Honoraria; Eisai: Research Funding. Ghosh:Forty seven Inc: Research Funding; SGN: Consultancy, Research Funding, Speakers Bureau; Juno: Consultancy, Research Funding; Celgene: Consultancy; Genentech: Research Funding; PCYC: Consultancy, Research Funding, Speakers Bureau; Pharmacyclics, an Abbvie Company: Consultancy, Research Funding, Speakers Bureau; Abbvie: Consultancy, Speakers Bureau; Gilead: Consultancy, Speakers Bureau; TG Therapeutics: Honoraria, Research Funding; Spectrum: Consultancy; F. Hoffman-La Roche Ltd: Research Funding. Ardeshna:ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; ADC Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations, Expenses. Johnson:Takeda Pharma: Other: Funded an educational place for me to attend the Lugano Lymphoma conference in June 2017. Cunningham:Roche pharmaceuticals: Research Funding. Kassam:AbbVie: Equity Ownership. Radford:Pfizer: Research Funding; BMS: Consultancy, Speakers Bureau; ADC Therapeutics: Consultancy, Research Funding; AstraZeneca: Equity Ownership; GlaxoSmithKline: Equity Ownership; Celgene: Research Funding; Novartis: Consultancy, Speakers Bureau; Takeda: Consultancy, Research Funding, Speakers Bureau; Seattle Genetics: Consultancy, Speakers Bureau. Bailly:Abbvie: Other: Travel, Accommodations, Expenses; Roche: Other: Travel, Accommodations, Expenses; Takeda: Other: Travel, Accommodations, Expenses. Munoz:Bayer: Consultancy, Speakers Bureau; Janssen: Consultancy; Kite Pharmaceuticals: Consultancy, Speakers Bureau; Juno: Consultancy; Bristol-Myers Squibb: Consultancy; Pfizer: Consultancy; Alexion: Consultancy; Pharmacyclics LLC, an ABBVIE Company: Consultancy. Ping:Pharmacyclics, an Abbvie company: Employment; Abbvie: Equity Ownership. Co:Abbvie: Employment, Equity Ownership, Other: Travel, Accommodations, Expenses. Neuenburg:Pharmacyclics, an Abbvie company: Employment.

Description: Pax5-deficient pre-B I–cell clones, transplanted into natural killer (NK)–cell–deficient RAG2−/−IL-2Rγ−/−hosts, populate the NK-cell compartment with functional NK cells. NK-cell generation fromPax5−/−pre-B I cells is also observed in NK-cell–proficient Balb/c RAG2−/− hosts. In the same Balb/c RAG2−/− hosts,Pax5−/− pre-B I–cell clones not only populate the pre-B I–cell compartment and fill the deficient T-cell–lineage compartment in the thymus and the periphery of all hosts, as shown before, they also generate CD8α− and CD8α+ dendritic cells (DCs), macrophages, and granulocytes in vivo in approximately half the hosts. In some recipients, practically all the mature myeloid cells are ofPax5−/− origin, indicating the effectiveness by which Pax5−/−pre-B I cells can compete with endogenous myeloid precursors. In a smaller percentage of hosts, the generation of Pax5−/−pre-B I–cell–derived erythrocytes is observed 4 to 6 months after transplantation. The results indicate that Pax5−/−pre-B I cells can develop in vivo in hosts that have undergone transplantation to erythroid, myeloid, and lymphoid cell lineages. Hence, the Pax5−/−mutation introduces an unusual instability of differentiation in pre-B I cells so that they appear to dedifferentiate as far back as the pluripotent hematopoietic stem cell.

Description: Self-renewal, pluripotency, and long-term reconstitution are defining characteristics of single hematopoietic stem cells.Pax5−/− precursor B cells apparently possess similar characteristics. Here, using serial transplantations, with in vitro recloning and growth of the bone marrow–homed donor cells occurring after all transplantations, we analyzed the extent of self-renewal and hematopoietic multipotency ofPax5−/− precursor B-cell clones. Moreover, telomere length and telomerase activity in these clones was analyzed at various time points. Thus far, 5 successive transplantations have been performed. Clones transplanted for the fifth time, which have proliferated for more than 150 cell divisions in vitro, still repopulate the bone marrow with precursor B cells and reconstitute these recipients with lymphoid and myeloid cells. During this extensive proliferation, Pax5−/− precursor B cells shorten their telomeres at 70 to 90 base pairs per division. Their telomerase activity remains at 3% of that of HEK293 cancer cells during all serial in vivo transplantations/in vitro expansions. Together, these data show thatPax5−/− precursor B-cell clones possess extensive in vivo self-renewal capacity, long-term reconstitution capacity, and hematopoietic multipotency, with their telomeres shortening at the normal rate.

Description: Background CD123 (IL-3 receptor alpha-chain) is a therapeutic target for hematological malignancies based on high expression levels in acute myeloid leukemia (AML), blastic plasmacytoid dendritic cell neoplasm (BPDCN), and other cancers. The anti-CD123 antibody-drug conjugate (ADC), IMGN632, comprises a humanized monoclonal antibody covalently linked to a DNA - alkylating cytotoxic payload which is currently in phase 1 evaluation for relapsed/refractory CD123-positive hematological malignancies (NCT03386513). Novel approaches to enhance the efficacy of ADCs are of significant therapeutic interest. Our laboratory has previously demonstrated that the Poly ADP Ribose (PARP) inhibitor, olaparib, synergistically enhances the activity of the CD33-targeted ADC, IMGN779, in preclinical AML models (Portwood S et al, ASH 2016). Based on the hypothesis that PARP inhibition will synergize with DNA damaging mechanism of IMGN632, we investigated the ability of olaparib and other PARP inhibitors (PARPi) in clinical development (talazoparib, niraparib, rucaparib, and veliparib) to enhance the therapeutic efficacy of IMGN632 across diverse human AML cell lines and primary relapsed/refractory AML samples. Materials and Methods CD123 expression on human AML cell lines (HEL, HL60, MV411, Molm13, EOL-1, THP-1, and Kasumi-1) was quantified by flow cytometry using QuantriBrite beads. AML cells were continuously cultured for 72-96 hours with varying doses of IMGN632 (range 100pM - 100nM) and specific PARP inhibitors (range 100pM -15μM) alone and in combination. Cell viability was measured using a WST-8 colorimetric assay. Primary clinically annotated CD123+ AML cells from patients with relapsed/refractory disease were obtained under IRB-approved protocols from the Roswell Park Hematologic Procurement Shared Resource and cultured short-term in the presence of multiple cytokines plus IMGN632 +/- PARP inhibitors. Apoptosis (Annexin V/PI), cell cycle, and DNA damage (H2AX) were evaluated by flow cytometry. Additive vs. synergistic effects were determined by combination indices using Compusyn software. PARP trapping was evaluated by Western blot analysis in nuclear lysates obtained from IMGN632 +/- PARP inhibitors treated AML cells. Results High expression levels of CD123 (range 937 - 2231 CD123 molecules/cell) were detected on multiple human AML cell lines (HEL-luc, MV411, Molm13, EOL-1, and THP-1) relative to unstained negative controls. Western blot analysis of nuclear lysates from AML cells demonstrated that all PARP inhibitors had varying degrees of PARP trapping on DNA. Continuous single agent 5-day treatment with all tested PARP inhibitors resulted in dose dependent in vitro inhibition of AML cell line growth with IC50 values ranging from 360 nM (talazoparib, most potent) to 78uM (veliparib, least potent). Combination therapy using PARP inhibitors (doses ranging from 300nM - 15uM) and IMGN632 (10nM) consistently resulted in enhanced anti-leukemic effects over monotherapy (Figure 1 for example). Synergistic anti-proliferative effects were obtained across all tested AML cell lines (n=5) with combination indexes ranging from 0.3-0.7 by Compusyn analysis. Combination therapy correlated with enhanced DNA damage, tumor cell apoptosis, and cell cycle arrest of AML cells. Moreover, IMGN632 and PARPi (olaparib or talazoparib) resulted in single agent activity against clinically annotated primary relapsed/refractory AML patient samples with evidence of synergistic effects when combined in vitro. Conclusions Addition of PARP inhibitors to IMGN632, a novel anti-CD123 antibody-drug conjugate, further enhances DNA damage effects and consistently results in synergistic in vitro anti-leukemic effects across multiple CD123+ AML cell lines and primary AML patient samples. Further studies investigating this novel combinatorial approach in specific molecular subtypes of AML with variable baseline sensitivities to PARPi are currently ongoing. Our results strongly support future investigation of PARPi as a novel class of agents with the potential to significantly enhance the efficacy of DNA-alkylating ADCs and/or cytotoxic chemotherapy for hematological malignancies. Figure. Figure. Disclosures Sloss: ImmunoGen: Employment. Watkins:ImmunoGen Inc.: Employment. Kovtun:ImmunoGen Inc.: Employment. Adams:ImmunoGen Inc.: Employment. Wang:Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Speakers Bureau; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Novartis: Speakers Bureau; Jazz: Speakers Bureau; Jazz: Speakers Bureau; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Description: Leukocyte extravasation depends on various adhesion receptors at endothelial cell contacts. Here we have analyzed how mouse CD99 and CD99L2 cooperate with PECAM-1. We found that antibodies against mouse CD99 and PECAM-1 trap neutrophils between endothelial cells in in vitro transmigration assays. A sequential function, as has been suggested for human PECAM-1 and CD99, could not be demonstrated. In contrast to these in vitro results, blocking CD99 or CD99L2 or gene disruption of PECAM-1 trapped neutrophils in vivo between endothelial cells and the underlying basement membrane as revealed by electron microscopy and by 3-dimensional confocal fluorescence microscopy in the inflamed cremaster tissue. Leukocyte extravasation was inhibited in interleukin-1β-inflamed peritoneum and in the cremaster by PECAM-1 gene disruption and was further attenuated by blocking antibodies against CD99 and CD99L2. In addition, CD99 and CD99L2 were required for leukocyte extravasation in the cremaster after stimulation with tumor necrosis factor-α, where the need for PECAM-1 is known to be bypassed. We conclude that CD99 and CD99L2 act independently of PECAM-1 in leukocyte extravasation and cooperate in an independent way to help neutrophils overcome the endothelial basement membrane.

Description: CTLA-4 is a critical inhibitory “checkpoint” molecule of immune activation. Several recent reports have described patients with immune dysregulation and lymphoproliferative disease resulting from 2 different genetic diseases that directly or indirectly cause CTLA-4 deficiency. Numerous articles have also been published describing CTLA-4 blockade in cancer immunotherapy and its side effects, which are ultimately the consequence of treatment-induced CTLA-4 deficiency. Here, we review these 2 diseases and CTLA-4 blockade therapy, emphasizing the crucial role of CTLA-4 in immune checkpoint regulation.