Antibody-dependent Cellular Phagocytosis Research Articles

Phase I Study of the T-Cell Receptor-like Antibody, Hu8F4 in Patients with Relapsed and Refractory Myeloid Malignancies

Background: Relapse after conventional chemotherapy for newly diagnosed AML is responsible for the majority of treatment failure. Relapsed (R/R) disease is frequently refractory to salvage attempts with further chemotherapy. The effectiveness of stem cell transplant and associated graft vs. leukemia effect implies an important role for immune-based therapy in producing long lasting remissions. Existing approaches using immunotherapy have failed to establish a suitable surface target or treatment paradigm that is effective in myeloid malignancies. Hu8F4 is a humanized T-cell receptor-like monoclonal antibody that binds to the conformational epitope of PR1 bound to HLA-A2, which is highly, differentially expressed on the surface of AML compared to normal progenitors. Methods: This is a first-in-human, Phase I dose escalation trial of Hu8F4 in patients (pts) with myeloid malignancies. Pts with R/R AML, MDS, CMML, and myeloid blast phase of CML with adequate organ function and PS ≤ 2 were eligible. Pts were treated on 7 escalating dose levels, ranging from 0.01 mg/kg to 10 mg/kg IV on D1 & 15. Initial dose levels required 1 pt per dose (0.01, 0.03, 0.1, 0.3, 1), followed by 3 pts per dose (3, 10). Results: Fifteen pts with R/R AML have been enrolled, with a median age of 62 years (range, 23-77 years), including 7 females (47%). Pts had received a median of 4 prior therapies; 5 pts (33%) had a PS of 2. At enrollment, the median WBC was 2 (0.1 - 18.4), median BM blasts were 21% (0 - 76); 9 pts (60%) had complex karyotype and 4 (27%) had a TP53 mutation. All pts had > 98% surface expression of PR1 on the myeloid blasts. Hu8F4 C max ranged up to 160,000 ng/mL with t 1/2 of 48 hours and clearance of 2.61 hr*ng/mL at the highest dose. Weak anti-drug antibodies were observed after week 4 in 2 of 3 pts treated at 3 mg/kg. With a median follow up of 5 months (1.1 - 9.9), pts have received a median of 1 (1-4) cycle of therapy. No DLTs were observed at the 3 mg/kg cohort.; 4 additional pts who were on concomitant tacrolimus were enrolled at this level to assess safety with concurrent use, and no DLTs were observed. Three pts were enrolled at the 10 mg/kg level, and 1 experienced dose limiting thrombocytopenia, triggering expansion to 6 pts. Two pts had a decline in BM blasts and 4 had stable disease. There was rapid decline in peripheral blasts immediately after infusion of Hu8F4 on D1 and 15 with associated elevation in serum LDH in some pts and a rise in normal granulocytes, consistent with drug-mediated anti-leukemia effects. The pharmacokinetic parameters and transient blast reduction indicated a possible sink effect mediated by high levels of circulating blasts. SAEs documented on study were mostly disease-related and included infections, cytopenias, hemoptysis, pneumonia, and GI bleeding. Treatment related AEs were temporally related to the drug infusion, including hypotension (Grade 2: N=2), and rigors (Grade 2: N=10; Grade 1: N=1). Infusion reactions were observed at all dose levels, more common at 3 and 10 mg/kg, but were transient, and managed with steroids and antihistamines. All pts proceeded with their next dose without further issues. Neither cytokine release syndrome nor neurologic toxicities were observed. Correlative studies support antibody dependent cellular cytotoxicity and phagocytosis as important mechanisms of anti-AML activity, which was more effective at lower dose levels. Conclusion: Hu8F4, a first-in-class TCR mimic antibody, was well tolerated with expansion planned at more frequent dose intervals. On-target peripheral blast reduction temporally related to infusion suggests biological activity. Real-time pharmacokinetic data indicate a possible sink effect that may be overcome by a more frequent dosing strategy that is planned.

Immunotherapy targeting isoDGR‐protein damage extends lifespan in a mouse model of protein deamidation

Aging results from the accumulation of molecular damage that impairs normal biochemical processes. We previously reported that age‐linked damage to amino acid sequence NGR (Asn‐Gly‐Arg) results in “gain‐of‐function” conformational switching to isoDGR (isoAsp‐Gly‐Arg). This integrin‐binding motif activates leukocytes and promotes chronic inflammation, which are characteristic features of age‐linked cardiovascular disorders. We now report that anti‐isoDGR immunotherapy mitigates lifespan reduction of Pcmt1−/− mouse. We observed extensive accumulation of isoDGR and inflammatory cytokine expression in multiple tissues from Pcmt1−/− and naturally aged WT animals, which could also be induced via injection of isoDGR‐modified plasma proteins or synthetic peptides into young WT animals. However, weekly injection of anti‐isoDGR mAb (1 mg/kg) was sufficient to significantly reduce isoDGR‐protein levels in body tissues, decreased pro‐inflammatory cytokine concentrations in blood plasma, improved cognition/coordination metrics, and extended the average lifespan of Pcmt1−/− mice. Mechanistically, isoDGR‐mAb mediated immune clearance of damaged isoDGR‐proteins via antibody‐dependent cellular phagocytosis (ADCP). These results indicate that immunotherapy targeting age‐linked protein damage may represent an effective intervention strategy in a range of human degenerative disorders.

Low Dose Rituximab Efficiently Clears Circulating CLL Cells and Maintains Sensitivity to Antibody Dependent Cellular Phagocytosis (ADCP)

Introduction: We have recently shown that high frequency (2 x week) low dose (50 mg)(HFLD) rituximab (RTX) and acalabrutinib is highly effective initial therapy for patients (n=38) with progressive CLL (ClinicalTrials.gov NCT03788291, PMID:36689726). The first dose of 50 mg of IV rituximab administered at 25 mg/h decreased the median circulating CLL cell count by 84% from pre-treatment baseline at 1h with no further decrease in the count during the remainder of the infusion (PMID:37003030). During the first hour of infusion, median CLL cell membrane CD20 levels decreased to 65% of baseline and were 41% of baseline at the end of the infusion. Median serum rituximab concentration was 2 mcg/ml at 1h and 10 mcg/ml at the end of the infusion. Median complement (CH50) concentration decreased to 91% of baseline at 1 h and to 81% of baseline at the end of the infusion. The cessation of clearance of CLL cells from the circulation within 1h of starting rituximab therapy is thus unlikely to be caused by low rituximab levels, decreased CLL cell CD20 expression or low serum complement levels. We and others have previously shown that ADCP is the primary mechanism of clearance of anti-CD20 mAb opsonized B cells in both humans and mice. We hypothesized that clearance of circulating CLL cells decreases because residual circulating CLL cells are resistant to mAb induced ADCP. To test this hypothesis, we measured in vitro ADCP sensitivity of CLL cells sampled from patients before and after rituximab treatment. Methods: Blood specimens were collected from 13 patients prior to starting therapy (C1D1_pre), 1h after start of IV rituximab infusion (C1D1_1h), at end of rituximab infusion (C1D1_post), and 48 h after initiation of therapy (C1D3_pre). Sensitivity of circulating CLL cells to in vitro ADCP was measured using live cell time-lapse high-content microscopy imaging of phagocytosis of CLL cells by human monocyte derived macrophages (hMDM) as previously described (PMID:32005699). Phagocytosis was quantified using a void index and sensitivity of samples was compared using the area under the curve of the 2h void index plot (AUC). Experiments were done in triplicate with co-cultures of hMDM and CLL cells without mAb as controls. Rituximab (10 mcg/ml) was used to test CD20 mAb mediated ADCP and alemtuzumab (10 mcg/ml) to test non-CD20 mediated ADCP. Results: Figure (median and 95% confidence intervals) shows that neither rituximab nor alemtuzumab induced ex-vivo ADCP as measured by median void index AUC was significantly altered by prior in vivo exposure of CLL cells to rituximab (Wilcoxon Match-Paired Sign test; all p>0.05). Discussion: The rapid decrease in circulating CLL cells induced by IV rituximab occurred only within the first hour after initiation of mAb infusion. Our measurements show that serum rituximab and complement concentrations and CLL cell membrane CD20 levels should be adequate to support additional CLL cell clearance after 1h. We now demonstrate that residual circulating CLL cells remain sensitive to in vitro ADCP by both rituximab and alemtuzumab. This suggests that despite reduced levels of surface antigen, circulating cells remain sensitive to mAb mediated clearance. Alternative explanations for the limited clearance of circulating CLL cells include: 1. Saturation of the limited cytotoxic capacity of the innate immune effector cells (Kupffer cells and splenic macrophages) compatible with our previously reported data on finite macrophage ADCP capacity (PMID:32556153); 2. Mobilization of CLL cells from lymphoid tissue; and 3. Temporary sequestration of rituximab opsonized CLL cells in tissue (e.g. spleen or lungs), which is unlikely given the observed decrease in lymph node size following initiation of therapy. Ongoing research is testing these hypotheses.

CD47 Blockade Enhances Phagocytic Activity of the TCR-Mimic Antibody Hu8F4 Against HLA-A2+ AML

Hu8F4, a humanized monoclonal antibody that recognizes PR1/HLA-A2 complex, is a first-in-class T cell receptor (TCR) - mimic antibody is currently being tested in a phase 1 trial for AML. We previously reported that activity of Hu8F4 primarily depends on its binding to Fcγ receptors (FcγR) on effector cells. Additionally, we identified antibody-dependent cellular phagocytosis (ADCP) as a principal mechanism of Hu8F4 anti-AML activity in vivo. Leukemia cells overexpress the “don't eat me” membrane protein CD47. CD47 on AML binds SIRPα on macrophages and neutrophils to inhibit phagocytosis. Blocking this interaction can allow antibodies to exert powerful phagocytic activity. Importantly, the role CD47 may play in the anti-tumor activity of TCR-mimic antibodies has not yet been investigated. To examine the relationship between CD47 and Hu8F4 activity, we used both in vitro ADCP assays and in vivo NSG mouse models. CD47 blockade was studied as a potential strategy to enhance Hu8F4 activity. To characterize the in vitro phagocytosis, we used an HLA-A2 transfected leukemia cell line, U937 (U937-A2), and an endogenously expressing HLA-A2 cell line THP1, as targets. NSG mouse bone marrow derived macrophages (BMDM) were used as effectors. At an initial E:T=1, Hu8F4 alone (10 mg/ml) was insufficient to prevent growth of U937-A2 and THP1. However, addition of neutralizing anti-CD47 F(ab') 2 antibody significantly slowed leukemia growth and eliminated both target cells by day 5. To further confirm the critical role of CD47 in Hu8F4-mediated ADCP, we created CRISPR/Cas9 CD47 KO U937-A2 and THP1 cells lines. Complete phagocytosis of both CD47KO cell lines was only observed in the presence, but not the absence of Hu8F4. To test if CD47 blockade plays a role in Hu8F4 anti-AML activity in vivo, we injected NGS mice with U937-A2 (5x10^3). Mice were treated with Hu8F4 +/- anti-CD47 F(ab') 2 antibody at 1mg/kg (three times per week for a total of 10 doses starting on day 5, n=5 per group). Control mice, treated with PBS, succumbed to leukemia by day 28. Both Hu8F4 and anti-CD47 F(ab') 2 single-agent treatment slowed leukemia growth, while the combination of Hu8F4 and anti-CD47 F(ab') 2 completely prevented outgrowth of the aggressive U937-A2 cells ( Figure 1), indicating that blocking CD47 significantly increased the activity of Hu8F4 in vivo. Interestingly, CD47 KO U937-A2 did not engraft in NSG mice as expected, (n=5), confirming that CD47 expression is critically important for cell line engraftment in NSG. HuCD47 is known to bind to NSG mouse SIRPα with high affinity providing protection to the human cells from phagocytosis by mouse macrophages. Growth of CD47 KO THP1 in NSG mice was delayed compared to parental THP1, median survival of untreated mice increased from 58 days for THP1 to 99 days for CD47 KO THP1 (p=0.0017, n=5). To facilitate THP1 cell growth in vivo, we used NSGS mice which allows for faster growth of human myeloid cells. Treatment with Hu8F4 for 7 weeks (1 mg/kg three times per week; started on day 2), significantly reduced THP1 leukemia growth and fully eliminated CD47 KO THP1 cells, confirming the role of CD47 in the activity of Hu8F4 ( Figure 2). Finally, to test whether CD47 is also important in Hu8F4-mediated phagocytosis by human effector cells, we generated human macrophages (Mφ) from CD14+ monocytes from healthy donors. We incubated fluorescently labeled human Mφ with CFSE-labelled target cells (U937-A2 or THP1), that had been pre-treated with Hu8F4 or isotype control antibody (Herceptin), at E:T=10, with or without anti-CD47 F(ab') 2. After 3 hours, Hu8F4-mediated phagocytosis, defined as the mean percentage of double-positive target cells, increased from mean 9.7% to 12.3% (n=4, p=0.199) for U937-A2, and from 12.25% to 17.58% (n=4, p=0.005) for THP1 when anti-CD47 F(ab') 2 blocking antibody was added. Anti-CD47 F(ab') 2 alone and in the presence of control Herceptin did not induce phagocytosis. Our data shows that the presence of CD47 on leukemia cells can significantly limit the activity of Hu8F4 both in vitro and in vivo. Importantly, combining Hu8F4 with CD47 blockade significantly increased the Hu8F4 activity and together eliminated AML. The role of other phagocytosis checkpoints, such as SIRPα and LILRB-1 also warrant further investigation.

CYT-338 NK Cell Engager Mutispecific Antibody Engagement of NKp46 Activation Receptor Overcomes Anti-CD38 Mab Mediated Fratricide of NK Cells and Accords Enhanced Cancer Immunotherapy

Background and Significance: Despite the clinical success of the first anti-CD38 targeted monoclonal antibody, daratumumab, approved for the treatment of multiple myeloma (MM), significant challenges remain such as CD38 antigen loss/internalization and/or natural killer (NK) cell fratricide resulting in resistance to treatment over time. Study Design and Methods: To overcome the above-mentioned challenges, Cytovia has utilized its proprietary multifunctional tetravalent Flex Engager TM bispecific antibody IgG scaffold platform that contains a flexible linker for simultaneous engagement of effector immune cells and tumors targets. Through this, we generated CYT-338, an NK cell engager mutispecific antibody that targets CD38 on MM tumors and NKp46 and CD16 activation receptors on NK cells to mediate potent NK cell redirected killing of MM tumor cells more efficaciously than daratumumab. In serial killing assays against MM tumors, CYT-338 reversed dysfunctional NK cells to its original activation state and prevented exhaustion of killing activity of NK cells over time. In addition, we have also previously reported that CYT-338 has a higher potency over daratumumab for antibody dependent cellular phagocytosis (ADCP) of MM tumors. Preclinically,CYT-338 shows significantly reduced NK cell fratricide compared to daratumumab but the reason for this was unknown. We hypothesized that CYT-338 could overcome anti-CD38 mAb mediated fratricide of NK cells by engaging NKp46 activation receptor. To this end we incubated peripheral blood NK cells (PBNK) with either anti-CD38 mAb, daratumumab, CYT-338 or human IgG1 isotype control either in the presence or absence of blocking anti-NKp46 mAb (IgG1) for 24 hrs at 37 oC and stained with Annexin V apoptosis and Zombie NIR viability dye and analyzed NK fratricide by flow cytometry. We also evaluated the ability of anti-NKp46 mAb to inhibit daratumumab-mediated fratricide of NK cells under the same conditions. Current Status: Through functional preclinical investigations, we have been able to deconvolute the novel molecular mechanisms whereby NKp46 and CD16 co-engagement signals by CYT-338 on NK cells are able to overcome the CD38 apoptotic fratricide signals induced by the single anti-CD38 mAb. Specifically, we have found that blockade of CYT-338 binding to NKp46 by anti-NKp46 IgG1 antibody reversed the fratricide protection provided by CYT-338, indicating that the fratricide protection was mediated by NKp46 activation signals. In addition, the single anti-NKp46 mAb was able to inhibit daratumumab-mediated NK cell fratricide providing direct evidence that daratumumabmediated fratricide can also be reversed by engagement of NKp46 activation receptor. Conclusions: The unique NKp46 activation mechanism provided by CYT-338 for reducing NK cell fratricide and maintaining NK cell levels together with the enhanced potency including reversal of NK cell dysfunction makes it an attractive best-in-class anti-CD38 therapeutic against MM compared to daratumumab. These results support the development of CYT-338 in both monotherapy and combination with other complementary immunotherapy agents being developed or approved for MM. A first-in-human Phase 1 study targeting patients with relapsed/refractory MM is in development in the U.S.

A Novel Fc-Optimized Antibody Drug Conjugate Targeting CD7 As a Therapeutic Strategy in T-Cell Acute Lymphoblastic Leukemia

Despite progress in improving treatment regimens for patients with T-cell acute lymphoblastic leukemia (T-ALL), the therapeutic options are still limited, and especially antibody-based immunotherapy is not established. The CD7 antigen represents a promising target structure in T-ALL since it is strongly expressed in different T-ALL subtypes including early T-cell precursor (ETP)-ALL. Therefore, different approaches are currently pursued for targeting CD7, including CAR-T cell therapy. Due to its high internalization capacity CD7 also represents an ideal target structure for antibody drug conjugates (ADC). Here, a novel antibody engineering approach for CD7-targeting was evaluated in vitro and in xenograft mouse models of T-ALL. A CD7 antibody was optimized for its ability to trigger antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) by introducing two amino acid substitutions (S239D/I332E; DE-variant) in the Fc-domain. In addition, the Fc-engineered antibody was conjugated to the microtubule-disrupting agent monomethyl auristatin E (MMAE) via an enzymatic-cleavable linker (mc-vc-PABC). The Fc-optimized ADC, CD7-DE-vcMMAE, as well as the unconjugated antibody, CD7-DE, showed improved binding to activating Fcγ receptors (FcγRIIa, FcγRIIIa) compared to a CD7 antibody lacking the DE-modification. This resulted in potent ADCC- and ADCP-activity against different T-ALL cell lines mediated by NK-cells or macrophages as effector cells (EC 50 ADCC, 1-7 pM). In contrast to the CD7-DE antibody, CD7-DE-vcMMAE showed strong cytotoxic effects independently of immune effector cell engagement by releasing its cytotoxic compound into T-ALL cells in an antigen-restricted manner, thereby inducing G2/M cell cycle arrest and apoptosis. CD7-DE-vcMMAE was active at subnanomolar concentrations demonstrating dose-dependent cytotoxic effects in six T-ALL cell lines (IC 50 0.2 - 1 nM). The extent of maximum growth inhibition ranged between 54-98 % and correlated with CD7 antigen density. Yet, although CD7-DE-vcMMAE did not kill CD7-negative cells directly, the linker design facilitated bystander killing activity. Thus, in co-culture experiments using CEM cells and CEM-CD7-knockout cells mimicking CD7-antigen escape, the ADC demonstrated significant killing of neighbouring CD7-negative cells, thereby extending its mode of action. The antitumor activity of the CD7-ADC was further investigated in xenograft mouse models of T-ALL. In a first model, CEM cells were injected subcutaneously into NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice and CD7-DE-vcMMAE treatment was evaluated in comparison to the unconjugated antibody CD7-DE. Treatment with CD7-DE-vcMMAE led to a significantly reduced tumor growth in comparison to CD7-DE or untreated animals (p<0.05; see panel A). A preclinical phase II-like patient-derived xenograft (PDX) study employing eight randomly selected T-ALL-PDX samples from pediatric and adult patients was conducted. PDX-cells were injected intravenously into NSG mice and treatment was started when the leukemia load reached 1 % human blasts in the peripheral blood, reflecting an overt leukemia situation. Animals receiving therapy with CD7-DE-vcMMAE showed significant prolongation of median survival in comparison to animals treated with a similarly designed control ADC targeting an irrelevant antigen (control-DE-vcMMAE) or which were left untreated (median survival time; CD7-DE-vc-MMAE: 82 days; untreated/control-DE-vcMMAE: 60 days; p<0.05; see panel B). Importantly, no leukemic blasts were found in the peripheral blood, spleen or bone marrow in animals treated with CD7-DE-vcMMAE and surviving the experimental period of 150 days. Together, the novel ADC CD7-DE-vcMMAE showed a unique set of Fc effector functions, potent direct growth inhibitory effects, bystander killing activity and efficacy in xenograft models of T-ALL. These results exhibit CD7-DE-vcMMAE as a promising therapeutic strategy and form the basis for new approaches in the treatment of T-ALL.

Initial Dose Escalation of ISB 1442, a Novel CD38 Biparatopic x CD47 Bispecific Antibody, in Patients with Relapsed / Refractory Multiple Myeloma (RRMM)

Introduction: ISB 1442 is a fully human bispecific, biparatopic antibody that targets CD38 and CD47, generated using Ichnos' Bispecific Engagement by Antibodies based on the T cell receptor (BEAT ®) platform. ISB 1442 is designed to kill CD38-expressing tumor cells through multiple mechanisms of action including blocking CD47-signal regulatory protein alpha (SIRPα) axis to increase several antibody effector functions: antibody-dependent cellular phagocytosis (ADCP), antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) through optimized architecture, affinity to targets, and Fc engineering. ISB 1442 has 2 Fab domains binding to distinct CD38 epitopes that do not compete functionally with daratumumab. ISB 1442 is expected to have optimized tolerability with low potential for adverse effects on red blood cells (RBC) such as hemagglutination, platelet aggregation and RBC depletion (Sammicheli at al., ASH 2021, Blood (2021) 138 (Supplement 1): 73). We report here initial findings from the early dose-escalation portion of an ongoing, multi-center, open-label, single-agent phase 1/2 study (NCT05427812) of ISB 1442 in patients with RRMM. Methods: Adult patients with relapsed refractory multiple myeloma (RRMM) to prior therapies, including a proteasome inhibitors (PIs), an immunomodulatory drugs (IMiDs), and an anti-CD38 antibodies received subcutaneous (SC) doses of ISB 1442 weekly (QW) in 28-day cycles. Patients had measurable disease per the International Myeloma Working Group (IMWG) criteria (2016). Dose escalation began at 6 mg dose with single patient accelerated titration phase for the first 3 cohorts, followed by a standard titration phase with a “3 + 3” design. The primary study objective for phase 1 is to assess the safety and tolerability to determine the maximum tolerated dose (MTD) and select the recommended phase 2 dose (RP2D) of ISB 1442. For phase 2 the primary study objective is to evaluate efficacy of ISB 1442. Secondary objectives include evaluation of pharmacokinetics (PK) and immunogenicity of ISB 1442. Exploratory objectives include assessment of minimal residual disease (MRD), assessment of cellular biomarkers in blood and bone marrow, and soluble factors in blood, and their correlation with efficacy, safety and other clinical endpoints of interest. Results: As of July 18, 2023, based on preliminary data from ongoing clinical database, 10 subjects had received once weekly SC injections of ISB 1442 in 4 dose-escalation groups from 6 mg to 150 mg. The majority were male (60%) and white (90%). The median age was 67 years (range 57-79). The median number of prior anti-myeloma lines of therapy was 6 (range 3-7); 70% were exposed to 5 drugs (2PIs, 2IMiDs, and CD38). The median number of ISB 1442 cycles was 1(range 1-2). Eight subjects (80%) experienced treatment-related adverse events (TRAEs), all were grade 1 or 2: cytokine release syndrome (CRS) (50%), injection site reactions (injection site erythema 20%, injection site bruising 10%), anemia (10%, 1 subject, grade 2) (Table 1). No grade 5 TRAE was observed. Following QW SC injection, ISB 1442 was slowly absorbed into the systemic circulation with T max generally occurring on day 2 of dosing. The ISB 1442 serum concentrations generally remained quantifiable over the entire dosing duration from 20 mg and above. The available PK data suggest an approximately dose-linear increase in serum concentration up to DL 3 (60 mg), followed by a supra-proportional increase in serum levels in subjects treated at DL 4 (150 mg). To date, 5 subjects treated at DL4 (150 mg) have experienced clinical symptoms of CRS (Grade 1-2) following the first dose of ISB 1442. Assessment of a panel of 63 soluble factors (including multiple cytokines, chemokines and growth factors) in the peripheral blood revealed that several subjects at DL3-4 exhibited transient increases (>10-fold) in macrophage inflammatory protein-1b (MIP-1b/CCL4) within 24h after treatment with ISB 1442, consistent with a macrophage-associated mechanism of action. Conclusions: Treatment with ISB 1442 was well tolerated at the dose levels evaluated. The observed clinical CRS events were moderate and potentially related to macrophage activation following ISB 1442 administration. Updated clinical, biomarker and PK data will be presented for this ongoing study.

GB261, an Fc-Function Enabled and CD3 Affinity De-Tuned CD20/CD3 Bispecific Antibody, Demonstrated a Highly Advantageous Safety/Efficacy Balance in an Ongoing First-in-Human Dose-Escalation Study in Patients with Relapsed/Refractory Non-Hodgkin Lymphoma

Introduction: GB261 is a novel and highly differentiated CD20/CD3 bispecific T cell engager antibody computationally designed to maintain Fc effector function, i.e., antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC) to broaden the mechanisms of action (MOA) for tumor cell killing. Furthermore, the “imbalanced” design of GB261 integrates de-tuned CD3 binding to reduce CRS incidence and improve safety features of the Fc effector function. Extensive pre-clinical studies have shown that GB261 has a highly advantageous safety/efficacy balance.Here, we present the preliminary clinical safety and efficacy results of an ongoing phase I/II study for GB261 (NCT04923048). Methods: This is an open-label, multicenter (China and Australia), dose-escalation/expansion phase 1/2 study of GB261 to evaluate the safety, tolerability and efficacy in patients with Relapsed or Refractory B-Cell Non-Hodgkin Lymphoma(B-NHL) and Chronic Lymphocytic Leukemia (CLL). Adult patients were eligible when they have CD20+ r/r B-NHL or CLL with no available standard of care treatments, adequate organ function, and no CNS involvement or other CNS disease, infections or other active/serious medical issues that may affect compliance or interpretation of results. GB261 was administered in 21-day cycles, weekly (QW) for the first 6 doses followed by every 3 weeks (Q3W) until disease progression, or other situation defined in protocol. Response assessment was based on Lugano 2014 and LYRIC 2016 criteria. Results: As of June 17, 2023, 47 r/r B-NHL patients (DLBCL:76.6%; FL:23.4%) were enrolled at flat or step-up doses of GB261 ranging from 1mg to 300 mg. Median age was 60.0 years (range: 28, 81), 55.3% of patients were male. Median prior lines of therapy were 3 (range: 1, 10). 78.7% of patients were refractory to any anti-CD20 therapy, 70.2% refractory to their last systemic therapy. Median time since last prior therapy to first study treatment was 1.9 months. In efficacy evaluable patients (n=22) from 3mg to 100mg, with at least 75% dose exposure before the first radiographic assessment, the median duration of study follow-up was 4.5 months (95%CI: 4.0, 7.4). The overall response rate (ORR) was 73% (16/22), and complete response rate (CRR) was 45.5% (10/22). ORR and CRR were 100% and 100% in 3mg, 56% and 22% in 10mg, 67% and 33% in 30mg. At 100mg dose, there were 5 evaluable patients, with ORR 100% (5/5), CRR 80% (4/5) and PR (20%, 1/5; mosunetuzumab-refractory rrDLBCL patient). Median time to response (TTR) was 1.3 months (95%CI: 1.2, 1.5), the same as median time to CR. Median duration of response (DOR) was not reached. In safety evaluable patients (n=47), the median duration of study follow-up was 4.1 months (95%CI: 2.9, 5.3). Treatment-emergent adverse events (TEAEs) were 95.7%, treatment-related adverse events were 85.1%. The most common TEAEs were COVID-19 infection (40.4%; grade 1 or 2: 27.6%; grade >=3: 12.8%) and neutropenia (31.9%; grade 1or 2: 14.9%; grade >=3: 17.0%). AE related treatment discontinuation and death were reported in 2 patients, which were all due to COVID-19 pneumonia. CRS occurred in 12.8% (6/47) patients, was mild and transient. CRS in 100mg were 14.3% (2/14). All cases of CRS were grade 1 (8.5%, 4/47) or 2 (4.3%, 2/47), no grade 3 (Lee et al., ASTCT criteria), no interruptions of treatment, and no administration of Tocilizumab. The median duration of CRS was 7 hours. No ICANS were reported. The PK profile of GB261 appeared to be linear across dose ranges tested (1mg-100mg). Effective half-life appeared to be 2-3 weeks which supports every 3-4 weeks dosing. Conclusion: GB261, a novel and highly differentiated CD20/CD3 bispecific antibody, is the first clinical stage Fc+ CD20/CD3 T cell engager. In heavily pretreated B-NHL patients, GB261 showed a highly advantageous safety/efficacy balance, consistent with the MOA. The safety profile is excellent especially for the CRS which is very mild, transient and less frequent compare with other CD20/CD3 bispecific antibodies. The response after GB261 treatment was early, deep and durable. At the 100mg dose level, 80% of patients achieved CR and with favorable safety. Additionally, clinical benefit seen in other CD20/CD3 bispecific antibody failed patients provides clinical support to the unique and differentiated MOA of GB261.

Preliminary Results of a Phase 2 Study of IMM01 Combined with Azacitidine (AZA) As the First-Line Treatment in Adult Patients with Chronic Myelomonocytic Leukemia (CMML)

Background: Patients with Chronic Myelomonocytic Leukemia (CMML) have poor prognosis and an inherent risk for transformation to acute myeloid leukemia. IMM01 is a recombinant signal regulatory protein α (SIRPα) IgG1 fusion protein that exerts anti-tumor activity via blocking “Don't eat me” signal and activating the “Eat me” signal to induce strong antibody-dependent cellular phagocytosis (ADCP). Furthermore, IMM01 activated macrophages could process and present tumor antigen to T cells and elicit long-last tumor-specific T cell immune response. Methods : This is an open-label, multi-center, phase 2 study (NCT05140811) that evaluated safety and efficacy of IMM01 in combination with AZA as the first-line treatment in patients with newly diagnosed CMML. We enrolled patients aged 18 years or older with the diagnosis of CMML, including subtypes CMML-1 and 2, not eligible for stem cell transplant. Patients with treatment-naive CMML were administered intravenous IMM01 at a dosage of 2.0mg/kg/week and subcutaneous AZA at a dosage of 75 mg/m 2 on D1-7 per 28-day cycle. Safety was assessed by CTCAE V5.0 and efficacy by IWG 2006 (MDS) criteria. Results : Between August 4, 2022 and July 7, 2023, 24 patients were enrolled: median age was 62 years, 15 (62.5%) males, 18(75.0%) ECOG≥1. Additionally, 1(4.2%), 7(29.2%) and 16(66.7%) patients were intermediate risk(IR)-1, IR-2 and high risk(HR) by CPSS-mol classification, respectively. According to World Health Organization (WHO) classification of CMML, patients enrolled included CMML-1(50.0%) and CMML-2(50.0%). Majority of patients had poor baseline hematologic conditions with a median Hb of 69.5 (32, 132) g/L and a median PLT of 73.5 (5, 667)×10 9/L. By the data cut-off date of July 7, 2023, the median follow-up for the study was 4 months (95%CI:3.3-4.8). Among the 16 efficacy evaluable patients who received initial treatment ≥3 months, overall response rate (ORR) was 87.5% (14/16), including 25.0% (4/16) complete response (CR), 18.8% (3/16) marrow CR (mCR) with hematologic improvement (HI), 6.3% (1/16) HI and 37.5% (6/16) mCR alone. Among the 9 efficacy evaluable patients who received initial treatment ≥4 months, ORR was 88.9% (8/9), including 44.4% (4/9) CR, 11.1% (1/9) mCR with HI and 33.3% (3/9) mCR alone. The CR rate of IMM01 combined with AZA is increasing with longer treatment duration. The median duration of response (DoR) was not reached. NGS analysis of bone marrow collected from responders were included in this study. The most frequent treatment related adverse events (TRAEs) (≥20%) were lymphopenia (70.8%), leukopenia (70.8%), neutropenia (70.8%), thrombocytopenia (58.3%), infusion related reaction (33.3%), anemia (25.0%), pyrexia (25.0%), pneumonia (25.0%), constipation (20.8%), nausea (20.8%), vomiting (20.8%) and leukocytosis (20.8%). The most common ≥Grade 3 TRAEs (≥10%) included lymphopenia (66.7%), neutropenia (54.2%), leukopenia (54.2%), thrombocytopenia (54.2%), anemia (20.8%) and pneumonia (16.7%), all of which were commonly reported in AZA monotherapy studies for treatment naive MDS/CMML patients in China. The study is ongoing. Conclusions: Preliminary data showed that IMM01 (without a low-dose priming) combined with AZA were well tolerated. The combo, when compared to the historical data of AZA alone, showed exciting efficacy result for patients with treatment-naive CMML1-2.

Preliminary Results of a Phase 2 Study of IMM01 Combined with Azacitidine (AZA) As the First-Line Treatment in Adult Patients with Higher Risk Myelodysplastic Syndromes (MDS)

Background: Patients diagnosed with higher-risk myelodysplastic syndrome (MDS) have poor prognosis. IMM01 is a recombinant signal regulatory protein α (SIRPα) IgG1 fusion protein that exerts anti-tumor activities via blocking “Don't eat me” signal and activating the “Eat me” signal to induce strong antibody-dependent cellular phagocytosis (ADCP). Furthermore, IMM01 activated macrophages could process and present tumor antigen to T cells and elicit long-last tumor-specific T cell immune response. Methods: This is an open-label, multi-center, phase 2 study (NCT05140811) that evaluated safety and efficacy of IMM01 in combination with AZA as the first-line treatment for patients with untreated higher-risk MDS. Enrolled patients were aged ≥18 years with intermediate to very high risk MDS (IPSS-R >3.5) who were not eligible for stem cell transplant or intensive chemotherapy. Patients with treatment-naive MDS were administered intravenous IMM01 at a dosage of 2.0mg/kg/week and subcutaneous AZA at a dosage of 75 mg/m 2 on D1-7 per 28-day cycle. Adverse events (AEs) were reported according to CTCAE v5.0. Efficacy was assessed by IWG 2006 (MDS) criteria. Results: A total of 54 patients were enrolled from June 29, 2022 to June 11, 2023. The median age was 64 (30-83) years, with 39 (72.2%) being male, and 52 (96.3%) having an ECOG of ≥1. Based on risk classification per IPSS-R, 13 patients (24.1%) were intermediate risk (IR), 25 (46.3%) high risk (HR), and 16 (29.6%) very high risk (vHR). At baseline, the median levels of blood counts were 69 (35-95)g/L for hemoglobin, 39.5 (2-409)×10 9/L for platelets and 0.8 (0.1-8.6)×10 9/L for neutrophils. By the data cut of June 11th, 2023, the median duration of follow-up was 5.6 months (95%CI:3.6-7.9). Among the 22 efficacy evaluable patients who received initial treatment of ≥4 months, overall response rate (ORR) was 81.8% (18/22), including 36.4%(8/22) complete response (CR) rate, 22.7%(5/22) marrow CR (mCR) with hematologic improvement (HI), 9.1% (2/22) HI and 13.6% (3/22) mCR alone. Among the 17 efficacy evaluable patients who received initial treatment of ≥6 months, ORR was 88.2%(15/17), including 41.2% (7/17) CR, 29.4% (5/17) mCR with HI, 5.9% (1/17) HI and 11.8% (2/17) mCR alone. The median duration of response (DoR) was not reached. Biomarker data showed mutation burdens of several markers, including TP53, DNMT3A, ASXL1, U2AF1, were dramatically reduced on study treatment. The most frequent treatment related adverse events (TRAEs) (≥20%) were leukopenia (85.2%), thrombocytopenia (72.2%), neutropenia (66.7%), lymphopenia (57.4%), anemia (44.4%), vomiting (44.4%), pyrexia (33.3%), infusion related reaction (33.3%), constipation (29.6%), nausea (25.9%), hypoalbuminemia (22.2%) and infection (20.4%). The most common ≥G3 TRAEs (≥10%) included leukopenia (81.5%), thrombocytopenia (68.5%), neutropenia (66.7%), lymphopenia (57.4%), anemia (44.4%) and infection(16.7%). These AEs were consistent with the AE profile of the AZA monotherapy in treatment-naive MDS as commonly reported in China. Without using of a low priming dose, no Grade ≥3 hemolysis occurred. The study is ongoing. Conclusions: Preliminary data from IMM01 (without low-dose priming) combined with AZA were well tolerated and showed exciting efficacy results in patients with treatment-naive higher-risk MDS.

A CD38/CD28xCD3 Trispecific T-Cell Engager (TCE) As a Potentially Active Agent for the Treatment of Older Patients with Acute Myeloid Leukemia (AML)

Background: Refractory disease is common and the outcome of elderly AML patients unable to receive intensive chemotherapy with acceptable side effects remains dismal. Thus, the identification of effective and safer drugs in AML is warranted. Immunotherapeutic strategies have shown extraordinary efficacy for the treatment of hematological malignancies, such as anti-CD38 monoclonal antibodies (mAbs) in multiple myeloma. Indeed, CD38 could represent a potential therapeutic target for AML too, not only because it is expressed in AML blasts, but also because AML patients with heterogeneous or low CD38 expression could benefit from T-cell based immunotherapies that are less dependent of the density of the targeted antigen. Aims: To evaluate CD38 as a potential therapeutic target in AML, and to determine the mode of action and preclinical efficacy of isatuximab (an IgG1 anti-CD38 mAb) and SAR442257, which is a new CD38/CD28xCD3 trispecific TCE. Results: We evaluated CD38 expression in bone marrow blasts from 241 newly diagnosed elderly AML patients by flow cytometry. Overall, 99.2% of AML patients expressed CD38, 55.6% with homogeneous pattern and 44.6% with heterogeneous pattern. CD38 expression had no impact in the overall survival of AML patients. Interestingly, CD38 expression increased 2-fold in MRD positive leukemic blasts compared with patient-matched blasts at diagnosis (n=10). At 24h and up to 96h, isatuximab (70 nM) decreased CD38 surface level in 3 AML cell lines expressing low (KG-1), intermediate (MOLM-13) and high or similar (OCI-AML3) basal CD38 density as compared to AML patients. Isatuximab (70 nM) did not induce complement-dependent cytotoxicity; by contrast, we observed a trend to an increased antibody-dependent cellular phagocytosis and significant antibody-dependent cellular cytotoxicity (ADCC) only in OCI-AML3 cells in the presence of purified NK cells. In 17 primary samples from AML patients with homogeneous vs heterogeneous CD38 expression, isatuximab (70 nM) showed a median of 19% and 4.5% tumor-cell death, respectively. Altogether, these findings indicated an association between CD38 density and the mode of action triggered by isatuximab and its efficacy. As such, AML patients with heterogeneous CD38 expression are less likely to respond to isatuximab, but might benefit from TCE that are less dependent of the density of the targeted antigen. Contrary to isatuximab, the CD38/CD28xCD3 TCE did not induce a dose- and time-dependent decrease in CD38 surface levels in any AML cell line measured with a non-competing anti-CD38 antibody, regardless of the CD38 antigen density. When we cultured PBMCs from healthy adults (n=6) with MOLM-13 cells (E:T ratio of 10:1) in the presence of isatuximab or the CD38/CD28xCD3 TCE (700 pM), we observed a significantly higher tumor cell lysis at 48h induced by the latter. The same effect of the CD38/CD28xCD3 TCE was observed with purified T-, but not NK-cells from healthy adults (n=3). To identify the immune cells involved in tumor cell lysis, we confirmed that isatuximab only induced NK-cell activation, whereas the CD38/CD28xCD3 TCE induced both T- and NK-cell activation, measured as percentage of CD69+ cells. Co-culture of purified NK- or T-cells with MOLM-13 cells in the presence of the CD38/CD28xCD3 TCE demonstrated a T-cell dependent bystander activation of NK cells. Furthermore, isatuximab downregulated CD38 in a dose-dependent manner, especially in NK cells, while the CD38/CD28xCD3 TCE did not. Surprisingly, the CD38/CD28xCD3 TCE induced CD38 upregulation on T cells, indicating again T-cell activation. The efficacy of isatuximab and the CD38/CD28xCD3 TCE was analyzed in primary AML samples (n=8) and blast lysis was observed in two and three samples, respectively. Notably, two of the three CD38/CD28xCD3 TCE-responders were resistant to isatuximab. CD38/CD28xCD3 TCE-mediated lysis was independent of CD38 expression and induced no significant off-target toxicity. Conclusions: CD38 is widely present in blasts from older AML patients but nearly half show heterogeneous expression. While isatuximab-driven ADCC in AML cell lines and primary samples is dependent on CD38 density in tumor cells, the CD38/CD28xCD3 TCE exerted its anti-tumor efficacy regardless of CD38 density. Thus, AML patients expressing both high and low/heterogenous levels of CD38 could benefit from T cell based immunotherapeutic strategies targeting CD38.

Stromal cell inhibition of anti-CD20 antibody mediated killing of B-cell malignancies.

Introduction: The glycoengineered type II anti-CD20 monoclonal antibody obinutuzumab has been licensed for treatment in follicular non-Hodgkin lymphoma and B-CLL following clinical trials demonstrating superior outcomes to standard of care treatment. However, ultimately many patients still relapse, highlighting the need to understand the mechanisms behind treatment failure to improve patient care. Resistance to chemotherapy is often caused by the ability of malignant B-cells to migrate to the bone marrow and home into the stromal layer. Therefore, this study aimed to investigate whether stromal cells were also able to inhibit type II anti-CD20 antibody mechanisms of action, contributing to resistance to therapy. Methods: A stromal-tumor co-culture was established in vitro between Raji or Daudi B-cell tumor cells and M210B4 stromal cells in 24 well plates. Results: Contact with stromal cells was able to protect tumor cells from obinutuzumab mediated programmed cell death (PCD), antibody dependent cellular phagocytosis and antibody dependent cellular cytotoxicity. Furthermore, such protection required direct contact between stroma and tumor cells. Stromal cells appeared to interfere with obinutuzumab mediated B-cell homotypic adhesion through inhibiting and reversing actin remodelling, potentially as a result of stromal-tumor cell contact leading to downregulation of CD20 on the surface of tumor cells. Further evidence for the potential role of CD20 downregulation comes through the reduction in surface CD20 expression and inhibition of obinutuzumab mediated PCD when tumor cells are treated with Ibrutinib in the presence of stromal cells. The proteomic analysis of tumor cells after contact with stromal cells led to the identification of a number of altered pathways including those involved in cell adhesion and the actin cytoskeleton and remodeling. Discussion: This work demonstrates that contact between tumor cells and stromal cells leads to inhibition of Obinutuzumab effector functions and has important implications for future therapies to improve outcomes to anti-CD20 antibodies. A deeper understanding of how anti-CD20 antibodies interact with stromal cells could prove a useful tool to define better strategies to target the micro-environment and ultimately improve patient outcomes in B-cell malignancies.

T cell-Dependent Bispecific Therapy Enhances Innate Immune Activation and Antibody-Mediated Killing.

T cell-retargeting therapies have transformed the therapeutic landscape for hematologic diseases. T cell-dependent bispecific antibodies (TDB) function as conditional agonists that induce a polyclonal T-cell response, resulting in target cell destruction and cytokine release. The relationship between this response and its effects on surrounding innate immune populations has not been fully explored. Here we show that treatment with mosunetuzumab in patients results in natural killer (NK) cell activation in the peripheral blood. We modeled this phenomenon in vitro and found that TDB-mediated killing activated NK cells, increasing NK function and antibody-dependent cellular cytotoxicity (ADCC), and enhanced the capability of macrophages to perform antibody-dependent cellular phagocytosis (ADCP). This enhancement was triggered by cytokines released through TDB treatment, with IL2 and IFNγ being major drivers for increased ADCC and ADCP, respectively. Surprisingly, cytolytic ability could be further augmented through neutralization of IL10 for NK cells and TNFα for macrophages. Finally, we showed that TDB treatment enhanced the efficacy of Fc-driven killing to an orthogonal solid tumor target in vivo. These results provide rationale for novel antibody therapy combinations that take advantage of both adaptive and innate immune responses.

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.

CD38 x ICAM-1 Bispecific Antibody Is a Novel Approach for Treating Multiple Myeloma and Lymphoma.

The cluster of differentiation 38 (CD38) is a well-validated target for treating multiple myeloma. Although anti-CD38 mAbs have demonstrated outstanding initial responses in patients with multiple myeloma, nearly all patients eventually develop resistance and relapse. In addition, currently approved CD38 targeting therapies have failed to show monotherapy efficacy in lymphomas, where CD38 expression is present but at lower levels. To effectively target CD38 on tumor cells, we generated an antibody-dependent cellular cytotoxicity (ADCC) enhanced bispecific CD38 x intercellular cell adhesion molecule 1 (ICAM-1) antibody, VP301. This bispecific antibody targets unique epitopes on CD38 and ICAM-1 on tumor cells with reduced red blood cell binding compared with the benchmark CD38 antibody daratumumab. VP301 demonstrated potent ADCC and antibody-dependent cellular phagocytosis activities on a selected set of myeloma and lymphoma cell lines even those with low CD38 expression. In an ex vivo drug sensitivity assay, we observed responses to VP301 in multiple myeloma primary samples from relapsed/refractory patients. Moreover, VP301 demonstrated potent tumor inhibition activities in in vivo myeloma and lymphoma models. Interestingly, combination of VP301 with the immunomodulatory drug, lenalidomide, led to synergistic antitumor growth activity in an in vivo efficacy study. In conclusion, the CD38 x ICAM-1 bispecific antibody VP301 demonstrated promising efficacy and specificity toward CD38+ and ICAM-1+ tumor cells and represents a novel approach for treating multiple myeloma and lymphoma.

Macrophage N-glycan processing inhibits antibody-dependent cellular phagocytosis.

Factors regulating macrophage effector function represent potential targets to optimize the efficacy of antibody-mediated therapies. Macrophages are myeloid cells capable of engulfing and destroying diseased or damaged target cells. Antibodies binding to the target cell surface can engage macrophage Fc gamma receptors (FcγRs) to elicit antibody-dependent cellular phagocytosis (ADCP), a process that contributes to treatments mediated by anti-tumor antibodies. Conversely, macrophage ADCP of apoptotic T cells is also linked to tolerance in the tumor environment. Here we evaluated the role of asparagine(N)-linked glycans in the function of macrophages derived from primary human monocytes. Macrophages treated with kifunensine, an inhibitor of N-glycan processing, exhibited greater target binding and ADCP of antibody-coated target cells. Kifunensine treatment increased ADCP of both rituximab-coated Raji B cells and trastuzumab-coated SKBR3 cells. ADCP required FcγRs; inhibiting CD64 / FcγRI led to the greatest reduction, followed by CD32 / FcγRII and then CD16 / FcγRIII in most donors. Kifunensine treatment also increased the antibody-binding affinity of CD16. Differences in the abundance of phosphorylated immune receptors, including Siglec-9, CD32a, and LAIR-1 correlated with the increased ADCP. These results demonstrate that N-glycan processing regulates macrophage effector function.

Priming with Japanese encephalitis virus or yellow fever virus vaccination led to the recognition of multiple flaviviruses without boosting antibody responses induced by an inactivated Zika virus vaccine

Complex patterns of cross-reactivity exist between flaviviruses, yet there is no precise understanding of how sequential exposures due to flavivirus infections or vaccinations impact subsequent antibody responses. We investigated whether B cell priming from Japanese encephalitis virus (JEV) or yellow fever virus (YFV) vaccination impacted binding and functional antibody responses to flaviviruses following vaccination with a Zika virus (ZIKV) purified inactivated virus (ZPIV) vaccine. Binding antibody responses and Fc gamma receptor engagement against 23 flavivirus antigens were characterized along with neutralization titres and Fc effector responses in 75 participants at six time points. We found no evidence that priming with JEV or YFV vaccines improved the magnitude of ZPIV induced antibody responses to ZIKV. Binding antibodies and Fc gamma receptor engagement to ZIKV antigens did not differ significantly across groups, while antibody-dependent cellular phagocytosis (ADCP) and neutralizing responses were higher in the naïve group than in the JEV and YFV primed groups following the second ZPIV immunization (p≤0.02). After a third dose of ZPIV, ADCP responses remained higher in the naïve group than in the primed groups. However, priming affected the quality of the response following ZPIV vaccination, as primed individuals recognized a broader array of flavivirus antigens than individuals in the naïve group. While a priming vaccination to either JEV or YFV did not boost ZIKV-specific responses upon ZIKV vaccination, the qualitatively different responses elicited in the primed groups highlight the complexity in the cross-reactive antibody responses to flaviviruses. This work was supported by a cooperative agreement between The Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc., and the U.S. Department of the Army [W81XWH-18-2-0040]. The work was also funded in part by the National Institute of Allergy and Infectious Diseases (NIAID) R01AI155983 to SJK and KM.

SGN-B7H4V, an investigational vedotin ADC directed to the immune checkpoint ligand B7-H4, shows promising activity in preclinical models

BackgroundSGN-B7H4V is a novel investigational vedotin antibody–drug conjugate (ADC) comprising a B7-H4-directed human monoclonal antibody conjugated to the cytotoxic payload monomethyl auristatin E (MMAE) via a protease-cleavable maleimidocaproyl valine citrulline...

Application of Computational Techniques in Antibody Fc-Fused Molecule Design for Therapeutics.

Since the advent of hybridoma technology in the year 1975, it took a decade to witness the first approved monoclonal antibody Orthoclone OKT39 (muromonab-CD3) in the year 1986. Since then, continuous strides have been made to engineer antibodies for specific desired effects. The engineering efforts were not confined to only the variable domains of the antibody but also included the fragment crystallizable (Fc) region that influences the immune response and serum half-life. Engineering of the Fc fragment would have a profound effect on the therapeutic dose, antibody-dependent cell-mediated cytotoxicity as well as antibody-dependent cellular phagocytosis. The integration of computational techniques into antibody engineering designs has allowed for the generation of testable hypotheses and guided the rational antibody design framework prior to further experimental evaluations. In this article, we discuss the recent works in the Fc-fused molecule design that involves computational techniques. We also summarize the usefulness of in silico techniques to aid Fc-fused molecule design and analysis for the therapeutics application.

Function-structure approach reveals novel insights on the interplay of Immunoglobulin G 1 proteoforms and Fc gamma receptor IIa allotypes.

Human Fc gamma receptor IIa (FcγRIIa) or CD32a has two major allotypes with a single amino acid difference at position 131 (histidine or arginine). Differences in FcγRIIa allotypes are known to impact immunological responses such as the clinical outcome of therapeutic monoclonal antibodies (mAbs). FcγRIIa is involved in antibody-dependent cellular phagocytosis (ADCP), which is an important contributor to the mechanism-of-action of mAbs by driving phagocytic clearance of cancer cells. Hence, understanding the impact of individual mAb proteoforms on the binding to FcγRIIa, and its different allotypes, is crucial for defining meaningful critical quality attributes (CQAs). Here, we report a function-structure based approach guided by novel FcγRIIa affinity chromatography-mass spectrometry (AC-MS) assays to assess individual IgG1 proteoforms. This allowed to unravel allotype-specific differences of IgG1 proteoforms on FcγRIIa binding. FcγRIIa AC-MS confirmed and refined structure-function relationships of IgG1 glycoform interactions. For example, the positive impact of afucosylation was higher than galactosylation for FcγRIIa Arg compared to FcγRIIa His. Moreover, we observed FcγRIIa allotype-opposing and IgG1 proteoform integrity-dependent differences in the binding response of stress-induced IgG1 proteoforms comprising asparagine 325 deamidation. The FcγRIIa-allotype dependent binding differences resolved by AC-MS were in line with functional ADCP-surrogate bioassay models. The molecular basis of the observed allotype specificity and proteoform selectivity upon asparagine 325 deamidation was elucidated using molecular dynamics. The observed differences were attributed to the contributions of an inter-molecular salt bridge between IgG1 and FcγRIIa Arg and the contribution of an intra-molecular hydrophobic pocket in IgG1. Our work highlights the unprecedented structural and functional resolution of AC-MS approaches along with predictive biological significance of observed affinity differences within relevant cell-based methods. This makes FcγRIIa AC-MS an invaluable tool to streamline the CQA assessment of therapeutic mAbs.