Antibody-dependent Cellular Phagocytosis Activity Research Articles

A genetically engineered mouse/human chimeric antibody targeting CD99 enhances antibody-dependent cellular phagocytosis against human mantle cell lymphoma Z138 cells

Background: Mantle cell lymphoma (MCL) is an aggressive form of B-cell nonHodgkin lymphoma. The elimination of MCL cells via phagocytosis is essential for cancer eradication. Therefore, discovering novel targeted antibodies that can induce phagocytosis is needed. We have demonstrated that our in-houseproduced mouse anti-CD99 mAb clone MT99/3 could induce potent anticancer activities against MCL cell lines in both in vitro and in vivo mouse xenograft models. Nevertheless, for use in humans, the mouse mAb needs to be transformed into a mouse/human chimeric mAb that contains a human Fc region to activate human immune effector functions, especially macrophage-mediated phagocytosis. Antibody-dependent cellular phagocytosis (ADCP) mediated by mouse/human chimeric mAb MT99/3 against MCL has not been previously reported. Objective: This study aimed to genetically engineer a mouse/human chimeric antibody against human CD99 derived from mouse mAb MT99/3 and to evaluate its effect in mediating the ADCP mechanism for eradicating MCL cells in vitro using monocyte-derived macrophages. Materials and methods: The expression plasmid to produce chimeric anti-CD99 antibody, ChAbMT99/3, was constructed by fusing the variable domains of mouse mAb MT99/3 with the constant domains of human IgG1 and the constant domains of kappa light chain. ChAbMT99/3 was expressed in the stable human expression system based on HEK293T cells. ChAbMT99/3 was purified from the culture supernatant of ChAbMT99/3-expressing HEK293T cells using Protein G chromatography. The purity and structure of ChAbMT99/3 were verified by SDS-PAGE and western blotting. The binding specificity and activity were determined by staining with cells expressing recombinant and native human CD99. The anticancer activity of ChAbMT99/3 in mediating the ADCP mechanism against MCL cell line Z138 using human monocytederived macrophages was evaluated. Results: We successfully constructed the plasmid to produce ChAbMT99/3. Human HEK293T cells stably expressing ChAbMT99/3 were established. The ChAbMT99/3- expressing HEK293T cells could secrete ChAbMT99/3 into the culture supernatant. The high purity and complete IgG structure of ChAbMT99/3 were obtained from the purification process. Crucially, this chimeric antibody retained its binding reactivity to recombinant and native human CD99. In addition, the produced ChAbMT99/3, upon binding to MCL cells, significantly enhanced ADCP against MCL cell line Z138 in a dose-dependent manner. Conclusion: The production of a mouse/human chimeric antibody against human CD99 derived from mouse mAb MT99/3 was successful. The engineered antibody could mediate ADCP activity against MCL cells. The produced ChAbMT99/3 might be a promising therapeutic candidate for MCL treatment.

Blockade of the CD47/SIRPα checkpoint axis potentiates the macrophage-mediated anti-tumor efficacy of tafasitamab.

Macrophages are one of the key mediators of the therapeutic effects exerted by monoclonal antibodies, such as the anti-CD19 antibody tafasitamab, approved in combination with lenalidomide for the treatment of relapsed or refractory (r/r) diffuse large B cell lymphoma (DLBCL). However, antibody-dependent cellular phagocytosis (ADCP) in the tumor microenvironment can be counteracted by increased expression of the inhibitory receptor SIRPα on macrophages and its ligand, the immune checkpoint molecule CD47 on tumor cells. The aim of this study was to investigate the impact of the CD47-SIRPα axis on tafasitamabmediated phagocytosis and explore the potential of anti-CD47 blockade to enhance its antitumor activity. Elevated expression of both SIRPα and CD47 was observed in DLBCL patient-derived lymph node biopsies compared to healthy controls. CRISPR-mediated CD47 overexpression impacted tafasitamab-mediated ADCP in vitro and increased expression of SIRPα on macrophages correlated with decreased ADCP activity of tafasitamab against DLBCL cell lines. Combination of tafasitamab and an anti-CD47 blocking antibody enhanced ADCP activity of in vitro generated macrophages. Importantly, tafasitamab-mediated phagocytosis was elevated in combination with CD47 blockade using primary DLBCL cells and patient-derived lymphoma-associated macrophages (LAMs) in an autologous setting. Furthermore, lymphoma cells with low CD19 expression were efficiently eliminated by the combination treatment. Finally, combined treatment of tafasitamab and an anti-CD47 antibody resulted in enhanced tumor volume reduction and survival benefit in lymphoma xenograft mouse models. These findings provide evidence that CD47 blockade can enhance the phagocytic potential of tumor targeting immunotherapies such as tafasitamab and suggest there is value in exploring the combination in the clinic.

Hemagglutinin stalk-specific Fc-mediated functions are associated with protection against influenza-illness after seasonal influenza vaccination in pregnant women.

Several influenza vaccine candidates aim to elicit antibodies against the conserved hemagglutinin stalk domain. Understanding the protective mechanism of these antibodies, which mediate broad neutralization and Fc-mediated functions, following seasonal vaccination is critical. Plasma samples were obtained from a subset of pregnant women living with or without HIV-1 enrolled in a randomised trial (138 trivalent inactivated vaccine [TIV] and 145 placebo recipients). Twenty-three influenza-illness cases were confirmed within 6 months postpartum. We measured H1 stalk-specific antibody-dependent cellular phagocytosis (ADCP), complement deposition (ADCD) and cellular cytotoxicity (ADCC) at enrolment and 1-month post-vaccination. The association between these Fc-mediated functions and protection against influenza-illness following vaccination was examined using multiple logistic regression analysis and risk reduction thresholds were defined by the score associated with the lowest odds of influenza-illness. Amongst TIV and placebo recipients, lower H1 stalk-specific ADCP and ADCD activity was detected for participants with confirmed influenza compared with individuals without confirmed influenza-illness 1-month post-vaccination. Pre-existing ADCP scores ≥250 reduced the odds of A/H1N1 infection (odds ratio 0.11; p=0.01) with an 83% likelihood of risk reduction. Following TIV, ADCD scores of ≥25 and ≥15 significantly reduced the odds against A/H1N1 (0.10; p=0.01) and non-group 1 (0.06; p=0.0004) influenza virus infections, respectively. These ADCD scores were associated with >84% likelihood of risk reduction. H1 stalk-specific ADCC potential was not associated with protection against influenza-illness. H1 stalk-specific ADCD correlates with protection against influenza-illness following influenza vaccination during pregnancy. These findings provide insight into the protective mechanisms of HA stalk antibodies.

Druggability properties of a L309K mutation in the antibody CH2 domain.

In the early stages of antibody drug development, it is imperative to conduct a comprehensive assessment and enhancement of the druggability attributes of potential molecules by considering their fundamental physicochemical properties. This study specifically concentrates on the surface-exposed hydrophobic region of the candidate antibody aPDL1-WT and explores the effectiveness of the L309K mutation strategy. The resulting aPDL1-LK variant demonstrates a notable enhancement over the original antibody in addressing the issue of aggregation and formation of large molecular impurities under accelerated high-temperature conditions. The mutated molecule, aPDL1-LK, exhibits excellent physicochemical properties such as hydrophilicity, conformational stability, charge variant stability, post-translational modifications, and serum stability. In terms of biological function, aPDL1-LK maintains the same glycosylation pattern as the original antibody and shows no significant difference in affinity for antigen hPDL1 protein, CD16a-F158, CD64, CD32a-H131, and complement C1q, compared to aPDL1-WT. The L309K mutation results in an approximately twofold reduction in its affinity for CD16a-V158 and CD32a-R131. In vitro biological assays, including antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC), reveal that the L309K mutation may decrease CD16a-V158-mediated ADCC activity due to the mutation-induced decrease in ligand affinity, while not affect CD32a-R131-mediated ADCP activity. In conclusion, the L309K mutation offers a promising strategy to enhance the druggability properties of candidate antibodies.

Fc-mediated functions of nirsevimab complement direct respiratory syncytial virus neutralization but are not required for optimal prophylactic protection.

Nirsevimab is an extended half-life (M252Y/S254T/T256E [YTE]-modified) monoclonal antibody to the pre-fusion conformation of the respiratory syncytial virus (RSV) Fusion protein, with established efficacy in preventing RSV-associated lower respiratory tract infection in infants for the duration of a typical RSV season. Previous studies suggest that nirsevimab confers protection via direct virus neutralization. Here we use preclinical models to explore whether fragment crystallizable (Fc)-mediated effector functions contribute to nirsevimab-mediated protection. Nirsevimab, MEDI8897* (i.e., nirsevimab without the YTE modification), and MEDI8897*-TM (i.e., MEDI8897* without Fc effector functions) binding to Fc γ receptors (FcγRs) was evaluated using surface plasmon resonance. Antibody-dependent neutrophil phagocytosis (ADNP), antibody-dependent cellular phagocytosis (ADCP), antibody-dependent complement deposition (ADCD), and antibody-dependent cellular cytotoxicity (ADCC) were assessed through in vitro and ex vivo serological analyses. A cotton rat challenge study was performed with MEDI8897* and MEDI8897*-TM to explore whether Fc effector functions contribute to protection from RSV. Nirsevimab and MEDI8897* exhibited binding to a range of FcγRs, with expected reductions in FcγR binding affinities observed for MEDI8897*-TM. Nirsevimab exhibited in vitro ADNP, ADCP, ADCD, and ADCC activity above background levels, and similar ADNP, ADCP, and ADCD activity to palivizumab. Nirsevimab administration increased ex vivo ADNP, ADCP, and ADCD activity in participant serum from the MELODY study (NCT03979313). However, ADCC levels remained similar between nirsevimab and placebo. MEDI8897* and MEDI8897*-TM exhibited similar dose-dependent reduction in lung and nasal turbinate RSV titers in the cotton rat model. Nirsevimab possesses Fc effector activity comparable with the current standard of care, palivizumab. However, despite possessing the capacity for Fc effector activity, data from RSV challenge experiments illustrate that nirsevimab-mediated protection is primarily dependent on direct virus neutralization.

Development of a quantitative systems pharmacology (QSP) model to support dose optimization of DS-1103a (anti SIRPa antibody) in combination with trastuzumab deruxtecan in patients with cancer.

e14509 Background: DS-1103a, an anti-human signal regulatory protein α (SIRPα) monoclonal antibody (mAb), is designed to block the SIRPα-CD47 axis “Don’t Eat Me” signal and trigger phagocytosis of tumor cells when combined with an Fc-active antitumor mAb. DS-1103a is being developed as a combination therapy with trastuzumab deruxtecan (T-DXd; DS-8201a) as the antibody-dependent cellular phagocytosis (ADCP) enabling antibody. We developed a QSP model to support the first in human (FIH) intravenous dosing (IV) based on predicted intratumoral receptor occupancy (RO) within immunological synapses (the intercellular contact zone between macrophages and cancer cells) and corresponding ADCP activity. Methods: The QSP model mechanistically integrated DS-1103a plasma pharmacokinetics (PK), tumor distribution and binding of receptors to both antibodies and their ligands to simulate RO in the tumor microenvironment (TME). A proximal pharmacodynamics pathway model was first developed to estimate the intratumoral RO required to induce desired levels of ADCP for DS-1103a+T-DXd combination therapy. A human model was then developed to integrate DS-1103a PK with derived intratumormal RO in patients considering key human pathophysiological parameters, including SIRPα expression, tumor lesion permeability, SIRPα+ cell fractions in TME, tumor capillary radius, SIRPα internalization, CD47 expression and tumor lesion size. Virtual patient simulations were conducted in various cancer types to facilitate FIH dose selection. Results: The proximal pharmacodynamics pathway model quantitatively recapitulated the dose dependent in vitro ADCP activities for DS-1103a+T-DXd combination therapy. The intratumoral RO (within synapses) required to induce desired levels of ADCP activity were also derived. The human model predicted similar dose dependent intratumoral RO in various cancer types. Virtual patient simulations indicated that a flat dose of 100 mg Q3W IV DS-1103a could achieve steady-state intratumoral RO sufficient to reach half of the maximal ADCP activity and would be a suitable FIH starting dose. The predicted steady-state intratumoral RO after a flat dose of ≥1000 mg Q3W IV DS-1103a is well above the predicted intratumoral RO threshold to achieve maximum ADCP activity. Conclusions: The QSP model mechanistically characterized DS-1103a mechanism of action and linked PK to intratumoral RO and corresponding ADCP activity in both in vitro and in vivo setting. The model was used to derive the FIH starting dose and potentially clinically effective doses for DS-1103a in combination with T-DXd. This QSP model will be integrated into a large-scale disease platform to support dose expansion and further dose optimization as new clinical data emerge.

Quantifying in vitrocomplement-dependent cytotoxicity (CDC) using advanced flow cytometry

Abstract Complement dependent cytotoxicity (CDC) is a key Fc mediated function of monoclonal antibody (mAb) therapeutics. mAb binding to antigen triggers a complex molecular cascade with sequential recruitment of serum proteins, eventuating in target cell lysis. Here we demonstrate CDC quantification in a streamlined, in vitro, advanced flow cytometry assay. Anti-CD20 mAbs were incubated with target cell lines in 96- or 384-well plates. Human serum (15%) was then added to induce CDC. Cells were labeled with iQue® Cell Membrane Integrity (R/Red) Dye to enable assessment of cell death using the iQue® Advanced Flow Cytometry Platform. Induction of CDC by anti-CD20 mAbs correlated with target cell CD20 expression, with most cell death observed with high-CD20 expressing Ramos cells. Maximal Ramos cell death induced by Rituximab and Truxima® was 68% and 70%, respectively. Comparatively, cell death of mid-CD20 expressing Raji cells was lower at 34% and 24%. No CDC was induced with CD20 negative Jurkat cells. Another anti-CD20-IgG1 mAb was compared against two isotype mutants: IgG1fut (non-fucosylated) and IgG1NQ (non-glycosylated). Their activity was profiled towards three previously described effector functions: antibody-dependent cellular cytotoxicity (ADCC); antibody-dependent cellular phagocytosis (ADCP) and CDC. CDC induction was comparable between the three mAbs, however their ADCC and ADCP activity differed. The IgG1NQ did not exert ADCP or ADCC activity, whilst the IgG1fut showed more ADCC and less ADCP than the native. These data exemplify the use of advanced flow cytometry to quantify Fc function of mAbs towards a range of effector mechanisms, highlighting the potential to profile libraries of novel therapeutics in minimal time.

Abstract 6341: Preclinical development of a monoclonal antibody targeting CD70 as cancer immunotherapy

Abstract CD70 is a novel immune checkpoint highly expressed on cancers of kidney, blood and lymphoid tissues, mesothelium and gastrointestinal system. High expression of CD70 is a prognostic marker for poor survival in patients with ovarian carcinoma, pancreatic cancer and mesothelioma, etc. Several CD70 antibodies are under early stages of clinical trials for oncology indications. We have developed IMM40H, a humanized IgG1 antibody that differentially induces phagocytosis and cytotoxicity in CD70-expressing cancer cells. Results of in vitro study have demonstrated that, in comparison with cusatuzumab, IMM40H possesses better CD70 binding (kD= 3.22E-11M) and functional inhibition ability, as well as more potent activities of ADCC (antibody-dependent cellular cytotoxicity, EC50 = 0.5 -2.0ng/ml) and CDC (complement-dependent cytotoxicity, EC50 = 170 ng/mL) against certain cancer cells. IMM40H also induces strong ADCP (antibody-dependent cellular phagocytosis) activity (EC50 = 0.02nM). At doses between 0.3 mg/kg to 10mg/kg, IMM40H significantly reduced tumor volume in mouse models of multiple myeloma, lymphoma and kidney cancer. Notably, in a U266 multiple myeloma model, IMM40H, at the dose of 0.3 mg/kg, completely inhibited tumor growth in a way that therapeutic effects appeared significantly earlier than that of cusatuzumab at a higher dose of 1 mg/kg. Therapeutic effects of IMM40H at the dose of 3 mg/kg also appeared earlier than that of bortezomib at the dose of 0.5 mg/kg. Interestingly, combination of IMM40H and IMM01 (a SIRPα-IgG1 Fc fusion protein targeting CD47) generated significant therapeutic synergy in models of A498 kidney cancer and Raji lymphoma. Importantly, maximum tolerated dose of IMM40H exceeds 100 mg/kg (IV, single dose) in cynomolgus monkeys and no significant adverse reaction was observed at a dose range of 3 to 30 mg/kg (IV, QW, 5 times) in monkeys. Taken together, our data show that targeting CD70 on tumor cells using IMM40H antibody may serve as a potent immunotherapy for multiple cancer indications. IND of IMM40H has been approved in China and US. This antibody is now in a phase 1 study in patients with advanced malignancies expressing CD70. Citation Format: Wenzhi Tian, Song Li, Dianze Chen, Dandan Liu, Huiqin Guo, Chunmei Yang, Li Zhang, Wei Zhang, Xiaoping Tu, Liang Peng, Gui Zhao, Ruliang Zhang, Fan Zhang, Frank X. Gan. Preclinical development of a monoclonal antibody targeting CD70 as cancer immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6341.

Abstract 4139: Functional human myeloid cells in BRGSF-HIS humanized mice enables myeloid-directed therapy assessment

Abstract Translational preclinical assessment of myeloid-targeting therapies is considered challenging due to the reduced availability of humanized mouse models expressing both lymphoid and myeloid compartments. Most of the humanized models harboring myeloid compartment overexpress human cytokines, leading to body weight loss, anemia and a short life span. Recent report described the BRGSF-HIS as an alternative model displaying all major human hematopoietic cell subsets, such as B, T, natural killer (NK), dendritic cells (DCs), plasmacytoid cells (pDCs) and monocytes/macrophages. Human myeloid cells developed in the BRGSF-HIS mice without side effects and human immune system engraftment is stable for over a year (Labarthe et al., 2019), favoring long terms studies with agents requiring a wide therapeutic window. Here we report that myeloid compartment developed in BRGSF-HIS mice is recruited in the tumor microenvironment of tumor bearing mice, and are also capable of triggering effector mechanisms such as ADCP and ADCC. Myeloid cells developed in the BRGSF-HIS mice are functional as, ex vivo stimulation with TLR and STING agonists induce CD83 expression and pro-inflammatory cytokine secretion (TNF-α, IL-1β, CCL2, ⋯) by monocytes and bone marrow derived macrophages (BMDM). In vivo, myeloid cells are activated through LPS challenge, leading to increased CD83-expressing cDCs frequency and CD83 and CD86 expression levels. Furthermore, BMDM are efficiently skewed toward M1 and M2-like profiles in response to LPS and IL-4, respectively. Analyses of TME from MDA-MB-231, show the recruitment of human immune cells, including T cells, NK cells, cDC and activated M2 macrophages (expressing both CD86 and CD206). Expression of FcγR, essential for antibody dependent cellular cytotoxicity (ADCC) and antibody dependent cellular phagocytosis (ADCP) activities, is found on human peritoneal macrophages and BMDM from BRGSF-HIS. ADCP activity mediated by macrophages was established as tumor cells are specifically phagocyted ex vivo in presence of a bispecific antibody (anti-human CD47 x tumor-associated antigen). Such findings were corroborated by B cell depletion in vivo induced by Rituximab (anti-CD20 mAb - hIgG1), which has been described to trigger CDC, ADCC and ADCP via FcγR (Teige et al., 2019). Finally, OKT3 induces cytokine release syndrome in these mice, evidenced by cytokine release, body weight and temperature drop. Treatment with Infliximab reduced these symptoms, suggesting that BRGSF-HIS mice enable assessment of safety and its clinical management. In summary, BRGSF-HIS mice develop myeloid cells without side effects and has a wide therapeutic window, enabling the assessment of effector mechanisms such as ADCP and ADCC, triggered by of myeloid-targeted therapies. Citation Format: Florence Renart-Depontieu, Gaëlle Martin, Valery Moine, Coline Burnet-Merlin, Florent Creusat, Alexis Gonon, Perrine Martin-Jeantet, Fabiane Sônego, Lise Nouveau, Yacine Cherifi, Kader Thiam. Functional human myeloid cells in BRGSF-HIS humanized mice enables myeloid-directed therapy assessment. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4139.

Trial in progress: A phase II study (with safety run-in) of evorpacept (ALX148), cetuximab, and pembrolizumab in patients with refractory microsatellite-stable metastatic colorectal cancer (AGICC-ALX148 21CRC01).

TPS257 Background: Refractory microsatellite stable colorectal cancer (MSS CRC) is immunologically cold and single-agent anti-PD-1/PD-L1 drugs are ineffective; novel immune-based approaches are needed. Evorpacept (E, ALX148) is an engineered protein (high-affinity CD47-blocker fused to an inactive IgG Fc region), which blocks the CD47/SIRPα innate immune inhibitory phagocytosis checkpoint expressed on CRC and phagocytes, respectively. The Fc region of E does not bind to Fcγ receptors, thereby limiting hematologic toxicity, and is intended to be given in combination. In CT26 CRC syngeneic models, E ± anti-PD-1 monoclonal antibody decreases tumor growth, reduces myeloid immunosuppression, increases dendritic cell activation, and increases T cell activation (Kauder, 2018); E enhances the antibody-dependent cellular phagocytosis activity of cetuximab (C) in vitro (Kauder, 2018); and E + pembrolizumab (P) was well-tolerated in the first-in-human trial (Lakhani, 2021). Methods: AGICC-ALX148 21CRC01 (NCT05167409) is a phase 2, single-arm, multicenter, investigator-initiated trial of E (15 mg/kg weekly), C (400 mg/m2 then 250 mg/m2 weekly), and P (200 mg every 3 weeks) in 21-day cycles for patients with unresectable MSS/proficient mismatch repair CRC refractory to oxaliplatin, irinotecan, and a fluoropyrimidine, regardless of tumor sidedness and RAS/BRAF status. Additional key eligibility criteria include ECOG performance status 0-1, evaluable disease per RECIST v1.1, adequate hematologic and end organ function, absence of prior checkpoint inhibitor use, and absence of significant autoimmune disease. Six patients will be enrolled in Stage 1 (safety run-in) and treated with ECP. The study will proceed to Stage 2 (dose expansion, N = 42, and all treated with ECP) if less than 33% of patients in Stage 1 experience a dose-limiting toxicity. Otherwise, additional patients will be enrolled in Stage 1 at lower dose level(s). The co-primary objectives are to determine 1) the recommended dose of E with CP, and 2) objective response rate by RECIST v1.1 (by one-sided exact test with α = 0.05, H0 p ≤ 3% [historical controls], HA p ≥ 15%; power is 87%). The study will close for futility if there are no responses (partial or complete) in the first 24 evaluable patients (by MinMax design with α = 0.025 [1-sided]; power is 87%). Secondary and exploratory aims include determination of progression-free survival, overall survival, safety, response assessment by iRECIST, and blood- and tumor-based immune modulation and baseline tumor expression (PD-L1, EGFR, and CD47) for association with tumor response. The study is open through the Academic GI Cancer Consortium and 5 patients have been enrolled at time of submission. Clinical trial information: NCT05167409 .

Blocking the CD47-Sirpa Axis Enhances Tafasitamab-Mediated Phagocytosis

Introduction Around 40% of diffuse large B cell lymphoma (DLBCL) patients have refractory disease or experience relapse, thus highlighting the need for novel, more effective therapies (Coiffier et al). The immunotherapy Tafasitamab (MOR208) is an Fc-modified, humanized, monoclonal anti-CD19 antibody approved in combination with lenalidomide as a second line of therapy for R/R DLBCL. Tafasitamab mediates its therapeutic effect directly or via antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Macrophages represent a key component of the DLBCL microenvironment and are critical effectors of antibody therapies (Uchida et al). However, ADCP is reportedly counteracted by increased expression of the immune checkpoint molecule CD47 on lymphoma targets (Chao et al). In addition, the inhibitory receptor of CD47, signal regulatory protein alpha (SIRPα) is increased on macrophages from patients with follicular lymphoma who relapse or progress after frontline lenalidomide and rituximab (Marques-Piubelli et al). Aim of the study The current study investigates the impact of the CD47-SIRPα axis on tafasitamab-mediated phagocytosis and the potential of concomitant treatment with an anti-CD47 blocking antibody to improve its efficacy. Results We show that both, CD47 and its inhibitory receptor SIRPa were elevated in lymph node biopsies from DLBCL patients. CD47 expression was evaluated in 6 DLBCL patients and 5 healthy controls and SIRPα was evaluated in 9 patients and 7 controls. In fact, increased expression of SIRPa on macrophages correlated with decreased ADCP activity of tafasitamab, and CRISPR-mediated CD47 overexpression on lymphoma targets impaired tafasitamab-mediated phagocytosis, in vitro. Combination of tafasitamab and an anti-CD47 blocking antibody enhanced ADCP activity of in vitro generated macrophages. Furthermore, lymphoma cells with low CD19 expression were efficiently eliminated by the combination therapy. Importantly, the combination enhanced tafasitamab-mediated phagocytosis of primary DLBCL cells using primary, patient-derived lymphoma-associated macrophages (LAMs) as effectors, in an autologous setting. Conclusion Our results show increased expression of CD47-SIRPa axis in primary DLBCL samples and indicate that CD47 blockade can enhance the phagocytic potential of tumor-targeting immunotherapies such as tafasitamab. Our findings suggest that there is merit in exploring the clinical utility of combining tafasitamab with an anti-CD47 blocking antibody in lymphoma. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Humanized T Cell Receptor-like Antibody Hu8F4 Reduces Leukemia By Fc-Mediated Mechanism

8F4, a T cell receptor (TCR) - like antibody which targets the leukemia-associated antigen PR1 (VLQELNVTV) when presented in the context of MHC class I (HLA-A2:01), is a mouse IgG2a monoclonal antibody (mAb) which mediates both complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) in vitro and eliminates AML in PDX (patient derived xenograft) mouse models. Recognizing the potential therapeutic value of 8F4, we produced a humanized IgG1 (Hu8F4) as a first-in-class mAb for preclinical development and clinical use. Characterization of Hu8F4 by ELISA and surface plasmon resonance showed high affinity (KD=6.5 nM) and specificity of Hu8F4 binding to PR1/HLA-A2 monomer. Staining of peptide-pulsed T2 cells confirmed Hu8F4 specificity to PR1, but not to control peptide MART1. To study anti-leukemia activity of Hu8F4 we used HLA-A2-transfected leukemia cell lines U937 (U937-A2) and MV411 (MV411-A2), as well as THP1 (endogenous HLA-A2+) as targets. In contrast to mouse 8F4, Hu8F4 did not induce CDC in vitro. Rather, Hu8F4 mediated both potent antibody-dependent cellular phagocytosis (ADCP) and ADCC of U937-A2 and THP1 cells in NFAT reporter assays, using FcgRI- (EC50 = 0.002 µg/ml), FcgRII- (EC50 = 1.49 µg/ml), and FcgRIII- (EC50 = 0.04 µg/ml) transfected Jurkat cells, as well as pooled human PBMC (EC50 = 0.95 µg/ml) and donor-derived macrophages (EC50 = 1.1 µg/ml), as effectors. Based on the ADCP activity of Hu8F4, we sought to examine the potential synergy of anti-CD47 antibody, a macrophage checkpoint inhibitor, with Hu8F4. Treatment of U937-A2 and THP1 target cells with anti-CD47 F(ab')2 neutralizing antibody made cells susceptible to Hu8F4-mediated phagocytosis by NSG mouse bone marrow derived macrophages (BMDM) in vitro. To confirm the critical role of CD47 in Hu8F4-mediated ADCP we created CD47 KO U937-A2 and THP1 AML lines. Within 96 hours of treatment with Hu8F4 both CD47 KO cell lines were completely phagocytosed by NSG BMDM, thus confirming the role of phagocytosis as a mechanism. To test Hu8F4 activity in vivo, we established xenografts using luciferase-transfected U937-A2 and MV411-A2 cell lines in NSG mice. Hu8F4 was then administered starting on either day 3 (U937-A2) or day 7 (MV411-A2). Treatment with Hu8F4 resulted in elimination of leukemia as measured by FACS and BLI and increased median survival (from 33 days to >85 days for U937-A2, p=0.0075; and from 125 days to >225 days for MV411-A2, p=0.0033). To further test Hu8F4 efficacy, we established PDX in NSG mice using cells from HLA-A2+ refractory/relapsed AML patients. Hu8F4 treatment reduced leukemia by 90.3% to 99.9% when assessed by FACS in four out of five PDX and resulted in increased median survival of the mice (from 41 days to 49 days, p=0.0002) in one PDX tested. To study the mechanism of action of Hu8F4, we produced a 3 aa mutant (Hu8F4 PG LALA), which completely abrogated binding to Fcg receptors. Hu8F4 PG LALA, as well as Hu8F4 F(ab')2, showed no in vivo activity against U937-A2 or MV411-A2 xenografts, confirming that the anti-leukemia activity of Hu8F4 is dependent on its ability to bind Fc receptors. Because FcgR may be expressed on AML we tested fratricide as a possible in vivo mechanism of Hu8F4. We utilized the CRISPR /Cas9 system to edit out both FcgRI and II in the U937-A2 cell line that is naturally deficient in FcgRIII (DKO U937-A2). We then used a retroviral system to stably express FcgRI or FcgRII in U937-A2 to create FcgRI-U937-A2 and FcgRII-U937-A2, respectively, and tested their susceptibility to Hu8F4 in the xenograft model. Compared to FcR-expressing wild-type U937-A2, Hu8F4 showed similar anti-leukemia activity in all three xenografts. There was no significant difference noted in the anti-leukemia potency of Hu8F4 between DKO U937-A2 or single FcR-expressing xenografts compared with FcgRI/FcgRII expressing wild-type U937-A2 xenografts, suggesting that fratricide is an unlikely mechanism in this model. Here we demonstrate high specificity, affinity, and remarkable anti-AML activity of Hu8F4, a first-in-class humanized TCR mimic monoclonal antibody that is currently being tested in a phase I clinical trial for HLA-A2+ refractory/relapsed AML and MDS. This study provides evidence for the importance of FcgR-mediated mechanisms (ADCC and ADCP) in the activity of Hu8F4. In addition, our results support future combination trials with treatments that promote phagocytosis.

Characterization of Plasma Immunoglobulin G Responses in Elite Neutralizers of Human Cytomegalovirus.

Human cytomegalovirus (HCMV) is the most common infectious complication of organ transplantation and cause of birth defects worldwide. There are limited therapeutic options and no licensed vaccine to prevent HCMV infection or disease. To inform development of HCMV antibody-based interventions, a previous study identified individuals with potent and broad plasma HCMV-neutralizing activity, termed elite neutralizers (ENs), from a cohort of HCMV-seropositive (SP) blood donors. However, the specificities and functions of plasma antibodies associated with EN status remained undefined. We sought to determine the plasma antibody specificities, breadth, and Fc-mediated antibody effector functions associated with the most potent HCMV-neutralizing responses in plasma from ENs (n = 25) relative to that from SP donors (n = 19). We measured antibody binding against various HCMV strains and glycoprotein targets and evaluated Fc-mediated effector functions, antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP). We demonstrate that ENs have elevated immunoglobulin G binding responses against multiple viral glycoproteins, relative to SP donors. Our study also revealed potent HCMV-specific antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis activity of plasma from ENs. We conclude that antibody responses against multiple glycoprotein specificities may be needed to achieve potent plasma neutralization and that potently HCMV elite-neutralizing plasma antibodies can also mediate polyfunctional responses.

Impact of adjuvants on the biophysical and functional characteristics of HIV vaccine-elicited antibodies in humans

Adjuvants can alter the magnitude, characteristics, and persistence of the humoral response to protein vaccination. HIV vaccination might benefit from tailored adjuvant choice as raising a durable and protective response to vaccination has been exceptionally challenging. Analysis of trials of partially effective HIV vaccines have identified features of the immune response that correlate with decreased risk, including high titers of V1V2-binding IgG and IgG3 responses with low titers of V1V2-binding IgA responses and enhanced Fc effector functions, notably antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). However, there has been limited opportunity to compare the effect of different adjuvants on these activities in humans. Here, samples from the AVEG015 study, a phase 1 trial in which participants (n = 112) were immunized with gp120SF-2 and one of six different adjuvants or combinations thereof were assessed for antibody titer, biophysical features, and diverse effector functions. Three adjuvants, MF59 + MTP-PE, SAF/2, and SAF/2 + MDP, increased the peak magnitude and durability of antigen-specific IgG3, IgA, FcγR-binding responses and ADCP activity, as compared to alum. While multiple adjuvants increased the titer of IgG, IgG3, and IgA responses, none consistently altered the balance of IgG to IgA or IgG3 to IgA. Linear regression analysis identified biophysical features including gp120-specific IgG and FcγR-binding responses that could predict functional activity, and network analysis identified coordinated aspects of the humoral response. These analyses reveal the ability of adjuvants to drive the character and function of the humoral response despite limitations of small sample size and immune variability in this human clinical trial.

Method for Measurement of Antibody-Dependent Cellular Phagocytosis.

Antibody-based therapeutics are powerful tools to treat disease. While their mechanism of action (MOA) always involves binding to a specific target via the antibody-binding fragment (Fab) region of the antibody, the induction of immune-mediated effector functions through the fragment crystallizable (Fc) region is a vital aspect of antibody therapeutics targeting tumor cells. Cross-linking of the Fc gamma receptors (FcγRs) via cell-bound antibodies activate immune effector cells, leading to antibody-dependent cellular cytotoxicity via natural killer (NK) cells. Linking of FcγRs on macrophages triggers the process of antibody-dependent cellular phagocytosis (ADCP), where antibody-opsonized target cells are internalized in phagosomes and degraded through the process of phagosome maturation and acidification. ADCP activity can be challenging to measure accurately due to the difficulty in differentiating target cells that are bound to a macrophage versus those that are internalized within phagosomes. In this chapter, we describe a protocol that measures ADCP activity by labeling target cells with a pH-sensitive dye that fluoresces brightly in mature phagosomes. The ADCP activity of therapeutics is then measured via flow cytometry. This assay is capable of detecting glycosylation differences arising from manufacturing processes and is suitable for evaluation of ADCP activity of monoclonal antibodies (mAb) to support in vitro biological characterization of drug candidates and lead candidate selection for desirable effector functions.

The path to find an HIV vaccine.

The path to find an HIV vaccine.

A Novel CD138-Targeting Monoclonal Antibody Induces Potent Myeloma Killing and Further Synergizes with IMiDs or Bortezomib in in Vitro and In Vivo Preclinical Models of Human Multiple Myeloma

Immunotherapeutically targeting CD138 has not been successfully translated into substantial clinical benefit in multiple myeloma (MM) patients. We here developed and determined in preclinical models of human MM the efficacy of VIS832, a novel humanized monoclonal antibody (MoAb) with differentiated CD138 target binding to the anti-CD138 MoAb BB4 within indatuximab ravtansine (BT082). Compared with BB4, VIS832 has significantly improved binding (P<.005, up to 1-log increases) to all MM cell lines (n>8). In the reporter-based antibody-dependent cellular cytotoxicity (ADCC) bioassay, EC50 of VIS832 was approximately 99.31 ng/ml (0.66 nM), whereas the BB4 possessing an isotype matched human IgG1 minimally induced ADCC against U266 MM cells. Evaluation of VIS832-induced ADCC in NK-MM cell co-cultures determined its EC50 values ranged from 2.22 + 0.37 to 15.3 + 2.71 ng/ml, with % maximal lysis of 37.06 + 1.45 % to 97.3 + 3.34 %, across tested MM cell lines (n=12), both sensitive or resistant to current therapies including dexamethasone, IMiDs, and bortezomib. While VIS832 effectively induced ADCC against parental cells with high and low CD138 levels, no lysis was detected in paired CD138-knockout MM cells. In the presence of BM stromal cells or osteoclasts, two key MM-supporting accessory cells in the BM milieu, VIS832-induced MM cytolysis was minimally affected. Importantly, VIS832 eliminated autologous MM cells of bone marrow (BM) samples from relapsed/refractory (RRMM) patients, with > 60% maximal lysis and > 90% killing in 4 out of 7 patient BM samples. EC50 values of VIS832 were 8.58-86.04 ng/ml in this patient cohort, comparable to those (17.28-179.3 ng/ml) of its non-humanized predecessor mAb 2810 against another RRMM patient cohort (n=6). In contrast to its potent autologous CD138+ patient cell lysis, VIS832 did not affect CD138-negative patient BM cells. VIS832 induced higher maximal lysis (~3-fold) of all target MM cell lines than CD38-targeting daratumumab (dara), regardless of resistance to lenalidomide and pomalidomide. These results also confirmed significantly higher CD138 vs CD38 levels in all MM cell lines and patient MM cells (P<.0001). Specifically, VIS832 remained active against MM cells resistant to dara, either via loss of CD38 or acquired drug resistance following extended dara treatment in exvivo co-cultures. Unlike dara, VIS832 selectively induced MM cell lysis via NK activation, without inducing NK cell apoptosis due to CD38 expression. When combined with lenalidomide, either pretreatment or added concomitantly, VIS832-induced MM cell lysis was significantly enhanced, with combination index (CI) of < 1 indicating synergism. Furthermore, antibody-dependent cellular phagocytosis (ADCP) represented another effector-mediated killing of VIS832 against MM cells, with phagocytosis dependent on both VIS832 and the E:T ratio. The ADCP activity of VIS832 was significantly higher than that observed for dara (P<.05) against MM cell lines sensitive or resistant to IMiDs and dara, and VIS832 induced significant ADCP against dara-resistant MM cells. Finally, in a disseminated MM1S xenograft model of human MM in CB-17 SCID mice, VIS832 alone reduced median tumor burden and improved overall survival from 30 to >60 days (P<.0001). This efficacy was sustained after discontinuation of treatment 3 weeks prior to study termination. Combined treatment of tumor-bearing mice with both VIS832 and bortezomib at sub-optimal doses rapidly eradicated tumors, resulting in 100% survival of all tumor-free animals to the end of study at day 73. The superior efficacy of combined VIS832 and bortezomib when compared to either agent alone suggests synergistic invivo activity, consistent with synergistically enhanced invitro cytotoxicity of this combination (CI < 1). Taken together, the significant invivo efficacy of VIS832, coupled with its mechanisms of action and potent in vitro MM cytotoxicity, strongly support clinical development of VIS832, as monotherapy and in combination, to overcome multidrug resistance and improve patient outcome in MM. Once its efficacy is established in RRMM, its favorable therapeutic index should allow for moving rapidly to earlier stages of disease, newly diagnosed MM and smoldering MM. Disclosures Chaganty: Visterra Inc: Current Employment. Ramakrishnan:Visterra Inc: Current Employment. Wollacott:Visterra Inc: Current Employment. Viswanathan:Visterra Inc: Current Employment. Adari:Visterra Inc: Current Employment. Munshi:Karyopharm: Consultancy; Amgen: Consultancy; Legend: Consultancy; Adaptive: Consultancy; Janssen: Consultancy; C4: Current equity holder in private company; OncoPep: Consultancy, Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties; BMS: Consultancy; Takeda: Consultancy; AbbVie: Consultancy. Babcock:Visterra Inc: Current Employment. Shriver:Visterra Inc: Current Employment. Myette:Visterra Inc: Current Employment. Anderson:Celgene: Membership on an entity's Board of Directors or advisory committees; Millenium-Takeda: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Oncopep and C4 Therapeutics.: Other: Scientific Founder of Oncopep and C4 Therapeutics.; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Sanofi-Aventis: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees.

The Combination of Tafasitamab and Rituximab Increases Cytotoxicity Against Lymphoma Cells In Vitro

Introduction Tafasitamab (MOR208) is a CD19-targeting, Fc effector function-enhanced antibody that has shown promising clinical activity in patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL). For patients newly-diagnosed with DLBCL, R-CHOP regimens combining the anti-CD20 antibody, rituximab (RTX) with chemotherapy is the standard of care; however, 30-40% of patients experience relapse with a high mortality rate. CD20 is not as broadly expressed as CD19 on B-cell lymphomas, and CD19 expression is preserved on CD20-negative tumor sub-populations and following CD20-targeting therapy (Horna, et al. EHA 2020). These findings support the evaluation of immunotherapies combining anti-CD19 and anti-CD20 antibodies to target all malignant lymphoma cells. To further explore the rationale for adding tafasitamab to a RTX-containing regimen, we analyzed the effect of this combination on antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and tumor B-cell viability in vitro. Additionally, protein expression of the oncogenic transcription factor c-Myc was investigated to gain deeper insight into the molecular effects mediated by RTX and tafasitamab. Methods A comprehensive panel of 11 aggressive lymphoma cell lines was analyzed (9 DLBCL and 2 Burkitt's lymphoma). For the ADCC assays, tumor cells were incubated with tafasitamab and/or RTX at saturating concentrations in the presence of natural killer cells from healthy human donors at effector-to-target (E:T) ratios of 0.5:1 to 3:1 for 2 hours. Cytotoxicity was assessed by quantification of DAPI-positive, CFSE-labeled target cells. For the ADCP assays, lymphoma cells were incubated with tafasitamab and/or RTX at saturating concentrations in the presence of in vitro differentiated macrophages derived from healthy human donors at an E:T ratio of 2:1 for 3 hours. Phagocytosis was assessed by quantification of double-positive events (CFSE-labeled macrophages and CellTrace Violet-stained target cells). C-Myc protein levels were measured following the treatment of tumor cells with tafasitamab and/or RTX for 17-48 hours. CD19/CD20 surface expression, ADCC and ADCP rates, as well as intracellular c-Myc protein levels were analyzed by flow cytometry. Direct effects of antibody treatment on cell viability were assessed by the determination of ATP levels upon incubation of lymphoma cells for 24-96 hours. Results Increased ADCC activity for the combination of tafasitamab and RTX compared with the respective monotherapies was observed in 4/11 cell lines. For the remaining cell lines, the combination activity was similar to the most active monotherapy (tafasitamab: 5/11, RTX: 2/11). Furthermore, in 5/11 cell lines, the combination of tafasitamab and RTX resulted in enhanced ADCP activity compared with the monotherapies. Similar to ADCC, the combination activity in the other cell lines was comparable to the most active monotherapy (tafasitamab: 2/11, RTX: 4/11). Interestingly, a slight correlation between ADCC/ADCP activity and CD19/CD20 surface expression levels was observed. Treatment of tumor cells with the respective antibodies without effector cells showed a beneficial combinatorial effect of tafasitamab with RTX on the reduction of cell viability in 3/8 cell lines, whereas 2 cell lines were primarily sensitive to tafasitamab and 3 were sensitive to RTX. This observed difference in the activity profile of tafasitamab versus RTX suggests different mechanisms for induction of direct cytotoxicity (Figure 1). To further elucidate the molecular basis of the observed direct effects on cell proliferation, expression levels of c-Myc were assessed. A correlation between decreased cell viability and reduction of c-Myc expression was demonstrated. This finding is in line with the role of c-Myc in the regulation of cellular processes, such as proliferation and apoptosis. Conclusions The co-treatment of tafasitamab with RTX demonstrated superiority compared with the respective monotherapies for at least one and up to all three of the modes of action tested (ADCC, ADCP, or direct impact on cell viability) in 9/11 lymphoma cell lines. These data demonstrate that the combination of tafasitamab and RTX mediates increased tumor cell death in vitro via different mechanisms of action and support the clinical evaluation of this antibody combination in patients with DLBqCL. Disclosures Patra: MorphoSys AG: Current Employment. Augsberger:MorphoSys AG: Current Employment. Ginzel:MorphoSys AG: Current Employment. Polzer:MorphoSys AG: Current Employment. Landgraf:MorphoSys AG: Current Employment. Bartel:MorphoSys AG: Current Employment. Ness:MorphoSys AG: Current Employment. Steidl:MorphoSys AG: Current Employment. Heitmüller:MorphoSys AG: Current Employment. Schanzer:MorphoSys AG: Current Employment. Endell:Morphosys: Current Employment.

A cross-reactive mouse monoclonal antibody against rhinovirus mediates phagocytosis in vitro

Rhinoviruses (RVs) are the main cause of the common cold worldwide. To date, more than 160 types of the virus have been recognized, categorized into three major species - A, B, and C. There are currently no approved vaccines available to prevent infection with RVs. To elicit antibodies against conserved regions located on capsid proteins of RV A viruses, mice were sequentially vaccinated with DNA plasmids encoding capsid proteins of different RV A types. After a final boost with whole virus, antibody-expressing hybridomas were generated. After isotyping, 11 monoclonal antibodies (mAbs) expressing an IgG subtype Fc-domain were selected for further expansion and purification. Three mAbs showed cross-reactivity against multiple strains of RV A viruses by ELISA, including strains A1A, A1B, A15, A16 and A49. Other mAbs had strain-specific binding patterns, with the majority of mAbs showing reactivity to RV-A15, the strain used for the final vaccination. We found that the RV-A15-specific mAbs, but not the cross-reactive mAbs, had neutralizing activity against RV-A15. An antibody dependent cellular phagocytosis (ADCP) assay revealed substantial ADCP activity for one of the cross-reactive mAbs. Epitope mapping of the neutralizing mAbs via escape mutant virus generation revealed a shared binding epitope on VP1 of RV-A15 for several neutralizing mAbs. The epitope of the ADCP-active, non-neutralizing mAb was determined by microarray analysis of peptides generated from the VP1 capsid protein. VP1-specific, cross-reactive antibodies, especially those with ADCP activity, could contribute to protection against RV infections.

Differential influence on antibody dependent cellular phagocytosis by different glycoforms on therapeutic Monoclonal antibodies

Therapeutic monoclonal antibodies (mAbs), particularly of the IgG1 subclass, are capable of effector function activities that may be important for their mechanism of action. One such effector function activity is Antibody Dependent Cellular Phagocytosis (ADCP), which has been shown to be mediated primarily through the activating FcγR, FcγRIIa, on macrophages and neutrophils. The critical quality attributes that are the most impactful and predictive of ADCP activity, and therefore most suitable to monitor during IgG1 antibody manufacturing, are not well established. Primary cell assays for ADCP are often laborious and subject to donor to donor variability, making such assays less desirable for product characterization. By developing and employing an ADCP reporter gene assay, we have been able to determine with high sensitivity the glycan structures that can impact FcγRIIa mediated ADCP across multiple different IgG1 antibodies. Interestingly we observed that some IgG1 antibodies are very potent mediators of ADCP while others do not mediate ADCP even though they possess other effector function activities (ADCC and CDC). Additionally, we find that ADCP by different IgG1 antibodies has markedly different sensitivity to glycan species, with one antibody demonstrating a surprisingly strong influence of β-galactosylation and high mannose levels.