Villasboas, José C.

7049 Background: Odronextamab, an investigational off-the-shelf CD20×CD3 bispecific antibody, demonstrated compelling efficacy and a generally manageable safety profile in heavily pretreated pts with R/R FL in the primary analysis of the Phase 2 ELM-2 study (NCT03888105; Kim TM, et al. Ann Oncol 2024). We present updated efficacy and safety data for odronextamab in pts with R/R FL from ELM-2 after >2 yrs follow-up. Methods: Odronextamab was administered intravenously until disease progression/unacceptable toxicity, with Cycle (C) 1 step-up dosing to help mitigate cytokine release syndrome (CRS) risk, as reported previously. Pts with a complete response (CR) for ≥9 months (mo) switched from maintenance dosing Q2W to Q4W. Primary endpoint: objective response rate (ORR) per Lugano criteria by independent central review (ICR); secondary endpoints: CR rate, duration of response (DOR), progression-free survival (PFS), overall survival (OS). Results: At the updated data cutoff (Aug 15, 2024), 157 pts with centrally confirmed R/R FL Grade (Gr) 1–3a were enrolled. Median no. of treatment cycles: 19.0 (range 0.1–117.3); 96.2% (n = 151) and 82.8% (n = 130) of pts completed C1 and C4, respectively. The global cohort comprised 128 pts evaluable for efficacy. At a median efficacy follow-up of 28.3 mo, ORR was 80.5% (n = 103) by ICR and CR rate was 74.2% (n = 95); 92.2% of responders achieved CR. Responses were durable (median DOR, 26.0 mo; median duration of CR, 32.2 mo). ORR was consistent across high-risk subgroups (Follicular Lymphoma International Prognostic Index score 3–5, 78.4%; progression of disease within 2 yrs of frontline therapy, 81.0%). Median PFS was 23.0 mo (estimated 36-mo PFS rate, 37.5%), and median OS was 54.2 mo (estimated 36-mo OS rate, 62.6%). Median PFS was longer in pts who were minimal residual disease (MRD) negative (42.4 mo) versus MRD positive (21.6 mo) at Week 12. Of 47/128 pts who switched to Q4W dosing, 32 remained in CR. The odronextamab long-term safety profile was consistent with the primary analysis. All 157 pts had TEAEs (Gr ≥3, 86.0%), and 15.3% discontinued treatment due to TEAEs (most common: COVID-19 infection, 2.5%). With 0.7/4/20 mg step-up dosing (n = 89), CRS events were mostly low grade (Gr 1, 46.1%; Gr 2, 13.5%; Gr 3, n = 1; Gr ≥4, n = 0), occurred mostly in C1, and resolved in a median of 8.4 hrs. Immune effector cell-associated neurotoxicity syndrome was reported in one pt (Gr 2). Infections were reported in 79.0% of pts (124/157; Gr ≥3, 42.0%). COVID-19-related infections were reported in 38.2% of pts (Gr 5, 5.7%). Conclusions: With longer follow-up, odronextamab demonstrated durable responses in heavily pretreated pts with R/R FL from ELM-2, with robust efficacy in those with high-risk features, and a generally manageable safety profile. Overall, these compelling results support odronextamab as a potential off-the-shelf treatment option for pts with R/R FL. Clinical trial information: NCT03888105 .

7032 Background: The impact of immune cell counts pre LD and during immune reconstitution on CAR T therapy outcomes is poorly understood. We investigated the association between CD4, CD8 and NK cell counts and CAR T therapy outcomes in patients with LBCL. Methods: Retrospective study of R/R LBCL patients who received CAR T cells between 2016-24 at Mayo Clinic, Rochester, were included in this analysis. Peripheral blood CD4, CD8 and NK counts were measured pre LD and at M1 post CAR T infusion. The receiver operating characteristic (ROC) curve was used to determine the optimal cutoff for pre LD and M1 immune cells to predict patients who were alive and in remission at 6 months (M6) post CAR T infusion. Patients who progressed or were lost to follow up prior to day 30 were excluded from M1 ROC analysis. Results: Of 140 patients, 81 were alive and in remission at M6 (Group A), while 59 had relapse or death (Group B). Axicabtagene ciloleucel was the CAR T product given in 81% of patients (114/140). Median pre LD CD4 counts were significantly lower in Group B compared to group A (143 vs 280 cells/µL, p = 0.001). No significant difference was observed in median pre LD CD8 counts (205 vs 221 cells/µL, p = 0.8). ROC analysis identified an optimal pre LD CD4 count of 124.5 cells/µL for M6 alive+remission. Lower pre LD CD4 counts (<124.5) predicted worse progression free survival (PFS) in univariate (HR = 3.02, 95% confidence interval [CI]: 1.73–5.27, p< 0.01) and multivariable analysis (MVA) adjusted for IPI and the number of prior lines (aHR = 2.54, 95% CI: 1.39–4.62, p< 0.01).Lower pre LD CD4 counts also predicted inferior overall survival (OS) in MVA (aHR = 2.27, 95% CI: 1.08–4.77, p = 0.03). (Table 1) On day 30 landmark analysis, ROC identified M1 optimal CD4 count of ≥ 99.5 cells/µL to be associated with a trend toward superior PFS (P=0.09), but not OS (p=0.90) in MVA. Median pre LD NK cell counts were significantly lower in Group B (73 vs 98 cells/µL, p = 0.04). ROC analysis identified an optimal pre LD NK count of 151 cells/µL for M6 alive + remission. Lower pre LD NK counts (<151) predicted worse PFS, both on univariate (HR = 4.17, 95% CI: 1.29–13.47, p = 0.02) and MVA (aHR = 4.64, p< 0.01). The lower pre LD NK cell count group had worse OS in MVA (aHR = 5.69, 95% CI: 1.16–28.1, p = 0.01). (Table 1) On D30 landmark analysis, M1 NK cell count of ≥ 128.5 cells/µL was associated with a trend toward superior PFS (P=0.08), but not OS (p=0.30) in MVA. Conclusions: Pre LD CD4 and NK cell counts are significantly associated with PFS and OS post CAR T therapy in patients with R/R LBCL. Pre-treatment immune subset levels may identify patients at higher risk of relapse or death after CAR-T therapy. Groups Median PFS 2 Year PFS Median OS 2 Year OS CD4 ≥124.5 cells/µL (N=75) NR 58% 3.31 years 67% CD4 <124.5 cells/µL (N=30) 2.2 months 22% 1.59 years 45% NK ≥151 cells/µL (N=17) NR 77% NR 84% NK <151 cells/µL (N=82) 10.6 months 44% 3.31 years 62%

7014 Background: Mosun is a CD20xCD3 bispecific antibody that can be administered in the outpatient setting for a fixed duration. Intravenous Mosun is approved for the treatment of relapsed/refractory FL after ≥2 prior lines of therapy. Mosun SC achieved high response rates with manageable safety in patients with 3L+ FL in a pivotal Phase II study (Bartlett et al. ASH 2024). We report the efficacy and safety of Mosun SC in patients with previously untreated high-tumor burden FL in the Phase II MorningSun study (NCT05207670). Methods: Patients with previously untreated high-tumor burden FL, per GELF criteria, were enrolled into this cohort. Mosun SC was administered with step-up dosing in Cycle (C)1 (Day [D]1, 5mg; D8, 45mg; D15, 45mg) then 45mg on D1 for up to 17 cycles (1 year; 21-day cycles). Patients with a partial or complete metabolic response (CMR) after C17 could receive additional Mosun maintenance therapy (45mg every 8 weeks for up to 1 year). Corticosteroid prophylaxis to reduce the risk of cytokine release syndrome (CRS) was mandatory in C1–2 and optional thereafter. The primary endpoint was progression-free survival (PFS) rate at 24 months. Key secondary endpoints included objective response rate (ORR), time to response (TTR), and safety. Results: As of May 29, 2024, 102 patients were enrolled; 55 patients had completed initial treatment (17 cycles), 31 had discontinued (most commonly due to progressive disease [n=19] and adverse events [AEs; n=4]), and 16 were ongoing initial treatment. Forty-two patients received maintenance treatment, and this was ongoing in 38 patients. Median age was 65 years (range: 24–86); 52.0% of patients were female. Most patients had Ann Arbor stage III/IV (91.2%) and a FLIPI score ≥2 (78.4%). Median duration of follow-up was 13.9 months. The 12-month PFS rate was 82.8% (95% confidence interval [CI]: 73.0–89.3). ORR was 87.3%; 60.8% of patients had a CMR. Among the 89 patients with a response, the median TTR was 2.7 months (range: 1.2–5.8). The most common AEs (≥30%) were injection-site reaction (57.8%), fatigue (42.2%), CRS (34.3%), headache (31.4%), and nausea (30.4%). Grade ≥3 AEs and serious AEs (SAEs) were reported in 44.1% and 29.4% of patients, respectively. CRS events were all Grade 1/2 and SAE of CRS occurred in 10.8% of patients (Table); all events resolved. Conclusions: Mosun SC demonstrated promising efficacy in patients with previously untreated high-tumor burden FL. The manageable safety profile, including rate of CRS, supports the administration of fixed duration Mosun SC in an outpatient setting. Additional data, including cytokine profiling and T/B/NK dynamics, will be presented. Clinical trial information: NCT05207670 . CRS events, n (%) PatientsN=102 Any grade 35 (34.3) Grade12 30 (29.4)5 (4.9) SAE 11 (10.8) ManagementSteroidsTocilizumabSteroids + tocilizumabFluidsICU admission 8 (7.8)6 (5.9)3 (2.9)3 (2.9)2 (2.0)

e19008 Background: Cytokine release syndrome (CRS) is typically reversible in CAR-T therapy, while hyperinflammatory syndromes like macrophage activation-like syndrome (MAS-L) and high-grade immune effector cell-associated hemophagocytic syndrome (IEC-HS) are associated with significant morbidity and mortality. Early interventions are critical for improving outcomes. We aim to analyze clinical cytokine assays and cellular phenotypes early in hyperinflammatory syndromes to identify profiles for severe cases to inform management decisions. Methods: This study included 113 CAR-T patients (pt) (September 2019-March 2024) with cytokine profiles (CP) performed at the second tocilizumab dose or with suspected hyperinflammatory states (CP1), followed by assessments at 24 hours (CP24) and 48 hours (CP48). 52 pts consented to blood (PB) and bone marrow (BM) cell immune phenotyping at pre-treatment (pre-LD) and day 1 for PB. Results: Among the 113 pts, CRS pts (N=74), when compared to MAS-L(N=19) & IEC-HS (N=20) at CP1, had lower levels of TNF (median in pg/mL; 31, 62.9, 47.7) , IL-18 (794, 1353, 2011), and MCP-1 (689, 2722, 2485.5). While MAS-L and IEC-HS had similar CP1 profiles, CP24 and CP48 differed between them: TNF & MCP-1 levels decreased in MAS-L but remained elevated or increased in IEC-HS. IL-18 was stable in MAS-L but increased steadily daily in IEC-HS. Infections were more frequent in IEC-HS (CRS: 43%; MAS-L: 58%; IEC-HS: 85%; p=0.002). Notably, patients who died with persistent E. faecium bacteremia had higher IL-18 in CP48. In the 52 pts with cell phenotypes available by flow, 33 had CRS, 18 MAS-L and 8 IEC-HS. The correlation between cell phenotypes and cytokine levels showed that elevated TNF at CP1 correlated with increased non-classical monocytes in pre-LD BM and higher NK and NK-T cells in pre-LD PB. Similarly, elevated IL-18 CP48 levels correlated with increased CD8 T-cells, NK-T cells, and intermediate monocytes in pre-LD PB, as well as increased NK cells at both pre-LD and day 1 (Table). Conclusions: We report distinct cytokine profiles in IEC-HS early in the inflammatory course post-CAR-T therapy. These elevated cytokines correlate with specific immune cell subsets, including BM-resident monocytes, intermediate monocytes with heightened cytokine trafficking and inflammatory capacity. This study demonstrates the feasibility for identifying potential biomarkers for early risk stratification and targeted interventions. Cytokine Sample source Immune cells R P value TNF CP1 BM pre-LD Non-classical monocytes (CD14loCD16+) 0.38 0.025 PB pre-LD Monocytes (All) 0.47 0.022 NK cells (CD56+CD16+) 0.34 0.024 NK-T cells (CD3+CD56+CD16-) 0.29 0.04 IL-18 CP48 PB pre-LD CD8+ T-cells 0.59 0.0093 NK-T cells (CD3+CD56+CD16-) 0.53 0.023 Intermediate monocytes (CD14+CD16+) 0.58 0.012 PB pre-LD NK cells (CD56+CD16+) 0.56 0.49 0.015 0.024

Background: Mosunetuzumab (Mosun), a CD20xCD3 bispecific antibody, received accelerated approval for the intravenous treatment of patients (pts) with relapsed/refractory (R/R) follicular lymphoma (FL) who have received ≥2 prior lines of systemic therapy. Mosun can be administered in the outpatient setting with a fixed treatment duration. In an ongoing Phase I/II study, Mosun administered subcutaneously (SC) induced durable responses with a manageable safety profile in pts with previously untreated low-tumor burden FL (LTB; Flinn et al. ASH 2023). Efficacy, safety and pharmacodynamic profiles of Mosun SC are being evaluated in an open-label, multicenter, Phase II study (MorningSun; NCT05207670) in pts with B-cell non-Hodgkin lymphomas, including previously untreated FL. Here we present &gt;8-month follow-up efficacy, safety and biomarker data for Mosun SC in first-line, LTB FL. Methods: Pts had untreated Grade (Gr) 1 or 2 FL, LTB by Groupe d'Etude des Lymphomes Folliculaires criteria, Ann Arbor stage III/IV disease, and Eastern Cooperative Oncology Group performance status (ECOG PS) of 0-2. Mosun SC injection was administered with step-up dosing in Cycle (C) 1 (Day [D] 1, 5mg; D8, 45mg; D15, 45mg), then 45mg on D1 of each 21-day cycle. Hospitalization was not mandatory. Pts with a complete metabolic response (CMR) after C8 could complete therapy. Pts with a partial metabolic response (PMR) or stable disease continued treatment for up to 17 cycles. Dexamethasone premedication was mandatory in C1 and C2 and optional thereafter. The primary endpoint was progression-free survival at 24 months. Exploratory analyses assessed cytokine levels in pts with versus without cytokine release syndrome (CRS) and pharmacodynamic changes in T and B cells in a subgroup of pts. Results: As of February 7, 2024, 65 pts were enrolled in US community (n=41) and academic (n=24) centers. At baseline, median age was 63 years (range: 34-82). Most pts had an ECOG PS of 0 (83.1%) or 1 (15.4%); 29 pts (44.6%) had extranodal involvement and 3 pts (4.6%) had B symptoms. Median duration of follow-up was 8.6 months (95% confidence interval [CI]: 5.7-10.9). Median number of cycles was 8 (range: 1-17). Among 60 pts with ≥1 post-baseline tumor assessment, the objective response rate was 95.0% (95% CI: 86.1-99.0; n=57) and CMR was 83.3% (95% CI: 71.5-91.7; n=50). Median time to response was 2.8 months (range: 2.3-8.3). At data cut-off, responses were ongoing in 48 pts with a CMR and in 5 pts with a PMR. In 64 safety-evaluable pts, the most common adverse event (AE) was injection-site reaction (70.3%; Gr 1, 65.6%; Gr 2, 4.7%). CRS by ASTCT occurred in 30 pts (46.9%; Gr 1, 39.1%; Gr 2, 7.8%); CRS events presented early in C1 (53.1%; Gr1, 45.3%; Gr2, 7.8%) and C2 (Gr1, 1.6%). Nineteen pts received CRS treatment (tocilizumab, 7.8%; steroids, 7.8%; tocilizumab + steroids, 4.7%; fluids, 3.1%; low-flow oxygen, 1.6%); 8 pts had a serious AE and were hospitalized. All CRS events resolved. Other common AEs included headache (45.3%; Gr 1, 29.7%; Gr 2, 15.6%), fatigue (45.3%; Gr 1, 35.9%; Gr 2, 9.4%), maculo-papular rash (31.3%; Gr 1, 14.1%; Gr 2, 15.6%; Gr 3, 1.6%), and increased alanine aminotransferase (28.1%; Gr 1, 21.9%; Gr 2, 4.7%; Gr 3, 1.6%). Gr 3/4 AEs in ≥5% of pts were neutropenia without fever (12.5%; Gr 3, 4.7%; Gr 4, 7.8%) and lymphopenia (7.8%; Gr 3, 1.6%; Gr 4, 6.3%). Suspected immune effector cell-associated neurotoxicity syndrome occurred in 2 pts (confusional state, Gr 1, n=1; Gr 2, n=1); all events resolved. Infections occurred in 30 pts (46.9%; Gr 1, 7.8%; Gr 2, 31.3%; Gr 3, 7.8%) with the most common (≥10%) being COVID-19 (17.2%; Gr 1, 7.8%; Gr 2, 7.8%; Gr 3, 1.6%) and upper respiratory tract infections (12.5%; Gr 1, 3.1%; Gr 2, 9.4%). One pt had a Gr 5 (fatal) AE 13.7 months after treatment was completed (reported as unrelated to Mosun; cause unknown). After the first Mosun dose, cytokine levels significantly increased on C1D2 (interleukin-6, n=44, p≤0.001; interferon-γ and tumor necrosis factor-α, n=41, p≤0.001). This spike in cytokine levels did not differ in pts with (n=19) versus without (n=25) CRS events in C1. Conclusions: Mosun SC monotherapy shows encouraging high efficacy as a fixed-duration treatment in first-line LTB FL. A manageable safety profile was reported, supporting ease of access for patients with drug administration in outpatient settings. Longer follow-up is needed to confirm long-term durability of response and safety.

Background: Chimeric antigen receptor T-cell (CAR-T) therapy has shown substantial promise in treatment of hematological malignancies, including non-Hodgkin Lymphoma (NHL). A subset of patients develop prolonged cytopenia, comprising quality of life, increasing healthcare utilization, and imparting considerable morbidity and mortality. Therapy-related myeloid neoplasms (t-MN), typically seen in patients who receive DNA-damaging agents such as radiotherapy and alkylators, have also been observed in CAR-T recipients. CAR-Hematotox score predicts the development of hematotoxicity in CAR-T recipients using laboratory parameters obtained at lymphodepleting (LD) chemotherapy, a timepoint when the patient has already gone through leukapheresis thus committed to the CAR-T process. Therefore, it is critical to identify patients at the highest risk of prolonged cytopenia and/or t-MN prior to apheresis, making it possible for a better triage of those who will proceed with CAR-T and those who might benefit from other strategies. Methods: A retrospective analysis was conducted in NHL patients who received commercial CAR-T products between January 2018 and March 2024 at Mayo Clinic Rochester, Arizona and Florida. Clinical and laboratory data including age, hemoglobin (Hb), absolute neutrophil count (ANC), platelet (PLT), ferritin, and LDH, obtained at the initial CAR-T evaluation, typically within 1 week of leukapheresis, were used for analysis. Prior lines of therapies including autologous stem cell transplant (ASCT) were collected. Prolonged cytopenias were defined as Hb &lt; 8 g/dL, ANC &lt; 0.5 x 109/L, and/or PLT &lt; 50 x 109/L at 3 months after CAR-T. t-MN was diagnosed per WHO 2016. For prolonged cytopenia, the optimal cutoff points for continuous variables were determined by maximizing the sum of sensitivity and specificity. Logistic regression was then used to determine the factors associated with cytopenia at 3 months post-CAR-T. For t-MN, maximally selected log-rank statistics was used to determine the optimal cutoffs. We used competing risk analysis to determine the factors associated with development of t-MN. Death without t-MN was considered a competing risk. For both analyses, the factors with P &lt; 0.1 in univariate analysis (UVA) were included in multivariate analysis (MVA). Results: Among the 387 NHL patients, with a median follow-up of 11 months (95% CI 8.7 - 12.2 months), 56 (14.4%) developed (41, 10.5% with 1 cytopenia; 14, 3.6% with 2 and 1, 0.2% with cytopenia in all 3 lineages), 20 (5.2%) developed and 315 (81.2%) did not have either. Factors associated with prolonged cytopenia: were age &gt;, PLT ≤ 150, ferritin ≥ 600, and LDH ≥ 250. Univariate analysis identified baseline Hb, ANC, PLT and ferritin to be significantly associated with prolonged cytopenia. MVA identified Hb ≤ 11 (HR = 1.98; 95% CI 1.03-3.85, P = 0.042) and PLT ≤ (HR = 2.56; 95% CI 1.39-4.78; P = 0.003) to be associated with the development of prolonged cytopenia. Factors associated with t-MN:were age &gt; 65 years, Hb ≤ 9 g/dl, ANC &lt; 3.8, PLT ≤ 80, Univariate analysis identified age, Hb, ANC, PLT, ferritin, and ≥ 3 prior lines of treatment to be significantly associated with t-MN. On MVA, age ≥ 65 (HR = 3.91; 95% CI 1.52-10.03; P = 0.004), Hb ≤ 9 (HR = 3.49; 95% CI 1.38-8.85; P = 0.008), ferritin ≥ 300 (HR = 3.06 ; 95% CI 1.08-8.67; P = 0.035) and ≥ 3 prior lines of therapy (HR = 3.25; 95% CI 1.33-7.94 ; P = 0.010) were associated with t-MN development. Association of prolonged cytopenia with t-MN development: Prolonged cytopenia was noted in 45% of patients who developed t-MN and 15% of those who did not (P = 0.002). Cumulative incidence of t-MN at 1 year was 3.3% and the presence of prolonged cytopenia was associated with a higher 1of t-MN (HR 8.93, 95% CI 2.15 - 37.1, P = 0.003). Conclusions: Readily accessible clinical and lab data such as blood count and inflammatory markers at the time of CAR-T evaluation were associated with the development of prolonged cytopenias. Similarly, advanced age, anemia, high ferritin levels and history of ≥3 lines of therapy were associated with the development of t-MN. These findings, when validated in larger dataset, can be used for patient counseling and therapy selection by identifying patients at high-risk of developing hematotoxicity and/or t-MN development.

Background Follicular lymphoma (FL) is a generally indolent disease where a watch and wait strategy is standard in asymptomatic patients (pts) with a low tumor-burden. Harnessing antitumor immunity through an anti-tumor immunization strategy at this stage may delay or avoid the subsequent need for more toxic and complex therapies. EO2463 is a therapeutic vaccine designed from non-self protein sequences, derived from gut bacteria, including 4 HLA-A2 synthetically produced 9-mer CD8 cytotoxic T cell epitopes, exhibiting molecular mimicry with specific epitopes on the B cell markers CD20, CD22, CD37, and CD268 (BAFF-receptor). Additionally, EO2463 contains a CD4 helper epitope UCP2 derived from hTERT. The compound expands pre-existing memory CD8 T cells recognizing the non-self protein sequences from gut bacteria which can then cross-react with the selected B cell antigens on tumor cells. EO2463 is being used to drive anti-tumor immunity against B cell malignancies, and has demonstrated long-lasting, specific CD8-memory T cell responses and clinical activity in relapsed/refractory FL and marginal zone lymphoma (MZL) [J Clinical Oncol 2024, 42 (S16), 7058]. Furthermore, CD8 T cells expanded from samples of patients treated with EO2463 can kill HLA-A2 expressing lymphoblastoid cell lines presenting the B cell targets [Hematological Oncol 2023, 41 (S2), 581-582]. Methods The current report describes Cohort 2 of trial EONHL1-20/SIDNEY (NCT04669171) and includes pts with newly diagnosed, previously untreated FL, grade 1-3A, HLA-A2, and not in need of treatment. Pts receive EO2463 (300μg/peptide) SC with adjuvant Montanide ISA 51 VG, q2 weeks (w) x 4, then q4w, for a total of 12 doses (39w; PET-CTs at w6, w19, and w42). Planned accrual for this cohort is 25 pts. Immune responses were assayed on thawed pt peripheral blood mononuclear cells by flow cytometry and EO2463 peptide specific tetramers or by IFN-γ ELISPOT (assaying responses against 9-mer peptides from CD20, CD22, CD37, and CD268; and from peptides of EO2463) without any proceeding in vitro stimulation (ex vivo). Results As of June 2024, 15 pts had started study treatment. Median age was 62 (range 55-66) year, 7 male and 6 female, 2 pts Ann Arbor stage I/II, 5 stage III, and 8 stage IV. Ten of 15 pts were still on treatment; median treatment duration was 18.4 weeks (range 5-39 w) for all pts. Among 13 evaluable pts, best responses by PET-CT using Lugano criteria were 1 pt CR, 5 pts PR (46% objective responses (OR)), 3 pts SD, and 4 pts PD. Of those with PD per Lugano, 2 had isolated increases in FDG-uptake without increase in lesion size/number at w6 and both remain on treatment (per protocol based on LYRIC criteria). OR was first noted w6 in 3 pts and w19 in 3 pts; duration of response is not evaluable at this time due to short follow-up. The pt with CR had isolated increases in FDG-uptake at w6, PR at w19, and CR at w35. Anti-EO2463 immune responses were observed in 4 of 5 tested pts at the 1st testing timepoint (w5) and onwards (currently longest tested up until w31). In an exploratory analysis, the percentage of EO2463 peptide specific CD8 T cells measured by tetramers seemed linked to clinical response (OR 3 pts vs non-OR 2 pts; 2-sided T-test, p=0.02; range of percentages in pts with OR 0.85%-1.39% of all CD8 T cells in peripheral blood, range in pts with non-OR 0.17%-0.27%). Functionality and cross-reactivity of responses were shown by IFN-γ ELISPOT using 9-mer peptides corresponding to the B cell targets in 4 tested pts. Expanded antigen-specific CD8 T cells displayed a memory phenotype; effector/memory (TEM), and terminally differentiated effector memory CD8 T cells (TEMRA). The most common related AEs were grade 1 (7 pts) and grade 2 (5 pts) local administration site reactions (mainly erythema, pruritus, and induration). Other related AEs in &gt; 1 pt were grade 1 headache (2 pts) and grade 1-3 fatigue/asthenia (3 pts). Asthenia lasting 2 days was the only related grade 3 adverse event (AE). Conclusions EO2463 monotherapy is associated with a very manageable safety profile and appears to demonstrate meaningful single-agent efficacy in FL. Consistent with the preclinical hypothesis, expansion of specific CD8 memory T cells may be associated with response. Results will be expanded at the meeting. Study EONHL1-20/SIDNEY also includes cohorts, not covered in this abstract, exploring EO2463 plus rituximab for 1st line FL/MZL, and EO2463 plus lenalidomide/rituximab in relapsed FL/MZL.

Introduction The tumor ecosystem in multiple myeloma (MM) involves complex interactions among various cell types, including clonal plasma cells (PCs) and immune cells. Previous research has indicated that the bone marrow (BM) microenvironment's metabolite and lipid profiles differ between MM patients and those with precursor conditions. This study aims to explore if differences in cell composition, metabolic phenotype of clonal PCs, and the spatial organization of various cell types are linked to the early versus late progression of high-risk smoldering MM (SMM) to MM. Methods We identified high-risk SMM patients using the IMWG 20-2-20 criteria, focusing on early progressors (EP), who progressed to MM within one year, and later progressors (LP), who progressed after more than four years. Using a high-dimensional single-cell spatial imaging platform, CODEX (CO-Detection by indEXing), we identified clonal PCs and immune cell types as well as their metabolic phenotypes at the single-cell level, in paired FFPE BM samples at SMM diagnosis and at the time of progression to MM. Our validated panel included markers such as CD3e, CD4, CD8, CD14, CD20, CD31, CD38, CD45, CD66a, CD68, CD138, HLA-DR, ASCT2, pNRF2, GLUT1, LDHA, ATPA5, CPT1A, and Citrate synthase. We employed single-cell segmentation, artifact cleanup, signal thresholding, and spatial analysis. Repeated measure models accommodated multiple regions of interest (ROIs) per patient and accounted for potential intrapatient correlation, while Poisson models estimated incidence rate ratios (RR) of cell types. Spatial statistical models evaluated cell type segregation and integration at the time of SMM diagnosis. Results Single cell events were acquired from 6 unique SMM patients who had paired FFPE BM samples from the time of their SMM diagnosis and at the time of their progression to MM. There were 3 EP SMM patients (Time to Progression (TTP):8, 8, 10 mos) and 3 LP SMM patients (TTP: 51, 58, 117 mos). The median number of single cell events identified per patient slide sample was 104,390 (Range: 24,357 - 314,877). We identified 8 main cell types: PCs, CD4+ T-cells, CD8+ T-cells, B-cells, granulocytes, Monocyte/Macrophages and two groups of other immune cells. The PCs and the remainder of the non-PCs were further classified based on the expression of the following metabolic markers: ASCT2 (Glutamine importer), CPT1A (Fatty acid metabolism), GLUT1 (Glucose importer), LDHA (Glycolysis), Citrate synthase and ATPA5 (Oxidative Phosphorylation). There was a higher RR of granulocytes (RR 2.1, CI 1.6-2.8, p&lt;0.001) in EP compared to LP samples at the time of SMM diagnosis, but a lower RR of CD4 T cells (RR 0.40, CI 0.3-0.6, p&lt; 0.001). Focusing on metabolic phenotypes of the PCs, we observed higher incidence RR of most metabolic markers: ASCT2 (RR=1.77; p=0.032), ATPA5 (RR=1.25; p&lt;0.001), CPT1a (RR=2.42; p=0.015), and LDHA (RR 2.13; p&lt;0.001) in EP compared to LP samples at the time of SMM diagnosis. However, GLUT1 had a lower incidence RR in EP patients (RR=0.79; p&lt;0.001). The same modeling for non-PCs at the time of SMM diagnosis yielded higher expression of LDHA (RR=1.98; p&lt;0.001) and ASCT2 (RR=3.3; p=0.002). Using the x and y coordinates and the corresponding phenotype classifications, we performed spatial statistical modeling based on spatial point processes to generate aggregated measures of how different types of cells of interest interacted. CD4 T cells were more isolated in LPs compared to EPs (p =0.046). Segregation indices for PCs and CD4 T cells indicated that they were more integrated/collocated in EPs. Granulocytes were more isolated in EPs although the difference was not as pronounced (p= 0.07). PCs were more integrated with granulocytes (p=0.06) and B cells (p=0.07) in LP patients. Further analyses of paired samples at the time of progression to MM will be reported at the time of the presentation. Conclusion This study is the first to provide whole-slide, single-cell, spatial proteomic characterization of clonal PCs and immune cells in the FFPE BMs of high-risk SMM patients with varying progression times to MM. Distinct metabolic pathway markers in clonal PCs and their spatial relationships with immune cell subsets are closely associated with the risk of progression to MM. These findings illuminate the complex interactions between the metabolic states of clonal PCs and their spatial orientation relative to immune cells in the pathogenesis of MM.

Background Follicular and marginal zone B cell lymphoma (FL; MZL) demonstrate an indolent course with heterogeneous outcomes and a potential for spontaneous remissions indicating immune system intervention. T cell-based therapeutic approaches are therefore an attractive proposition in FL and MZL. EO2463 peptide immunotherapy expands pre-existing memory CD8 T cells recognizing non-self-protein sequences from gut bacteria which cross-react with B cell antigens. The compound includes 4 HLA-A2 synthetically produced epitopes which exhibit molecular mimicry with the B cell markers CD20, CD22, CD37, and CD268 (BAFF-receptor), as well as a the CD4 helper-epitope UCP2 derived from hTERT. EO2463 is being used to drive anti-tumor immunity against B cell malignancies, and has demonstrated long-lasting, specific CD8-memory T cell responses and clinical activity in relapsed/refractory FL and MZL [J Clinical Oncol 2024, 42 (S16), 7058]. Furthermore, CD8 T cells expanded from samples of patients (pts) treated with EO2463 can kill HLA-A2 expressing lymphoblastoid cell lines presenting the B cell targets [Hematological Oncol 2023, 41 (S2), 581-582]. Methods The current report describes testing of a possible biomarker in the phase 1 portion of the ongoing EONHL1-20/SIDNEY trial (NCT04669171).This part of the trial (“Cohort 1”) included pts (n=9) with relapsed (at least 1, no limit, prior treatments) FL and MZL, stage 1-3A, confirmed to be positive for HLA-A2. Pts received EO2463 (150 [n=3] or 300μg/peptide [n=6]) SC with adjuvant Montanide ISA 51 VG q2 weeks (w) x 4, then q4w, for a max of 12 months; at w7 lenalidomide (20 mg/day for 21/28 days up to 12 cycles) was added (EL), and if no complete remission (CR) at w19, rituximab (375 mg/m IV, q1w x 4, then q4w x 4) was also added (ER2). Immune responses and clinical outcomes of Cohort 1 were previously reported [J Clinical Oncol 2024, 42 (S16), 7058]. To assess a possible biomarker, tetramers were used to specifically detect CD8 T cells recognizing the 4 epitopes in the EO2463 compound (derived from gut bacterial proteins exhibiting molecular mimicry with the B cell markers CD20, CD22, CD37, and CD268). The tetramers were all marked with phycoerythrin. Thawed samples of peripheral blood mononuclear cells taken at start of w5 (after 2 administrations of EO2463 monotherapy, each followed by 2w observation) were stained ex vivo (without any in vitro stimulation) with the tetramers and assayed by flow cytometry. Results are presented as percentage of EO2463 specific CD8 T cells among all CD8 T cells in the peripheral blood of the pt. Results Among the 9 treated pts, PET-CT at w6 (after 3 administrations of EO2463 monotherapy) suggested possible clinical activity in 4/9 pts (1 PR, 1 pt size reduction 15%, 1 pt 20% reduced tracer uptake, 1 pt 5/6 target lesions reduced metabolic activity). By PET-CT at w42 (after 12 administrations of EO2463 monotherapy, 11 cycles of lenalidomide, and rituximab treatment) the Lugano response assessment was complete response in 6/9 pts. A positive biomarker response was assessed in 5/9 pts (percentage of specific CD8 T cells ranged from 0.2-2.1%). EO2463 monotherapy PET-CT activity at w6 (n=4/9 pts): 4 of 4 pts with clinical activity were biomarker positive and 1/5 of the other pts was also positive; this pt had an isolated increase in FDG-uptake at w6, followed by a CR at w19. Four further other pts were biomarker negative. In this limited sample, the biomarker had sensitivity 100% and specificity 80%. EO2463 in combination with lenalidomide/rituximab PET-CT CR at w42 (n=6/9): 5 of 6 pts with CR were biomarker positive and 1 pt with CR was negative; the pt with a negative test had no objective tumor response until after rituximab. In this limited sample, the biomarker showed sensitivity 83% and specificity 100%. Conclusions The current preliminary assessment indicates that direct ex vivo tetramer staining for specific CD8 T cells after short term (5 w) treatment with EO2463 monotherapy could be a possible biomarker for clinical response, both for EO2463 monotherapy response, and for response to EO2463 in combination with lenalidomide/rituximab. We plan to validate these findings in the ongoing study cohorts of the trial; expansion phase 2 cohorts, exploring EO2463 monotherapy in the “watch & wait” setting, EO2463 plus rituximab for 1st line FL/MZL, and EO2463/lenalidomide +/- rituximab in relapsed FL/MZL.

Introduction Patients (pts) with relapsed/refractory (R/R) follicular lymphoma (FL) experience progressively worse outcomes with each successive line of therapy; complete response (CR) rates are 44% with third-line (3L), 27% with 4L, and 22% with 5L+ therapies (Ghione P et al. Haematologica 2023). CR duration is particularly important considering the rapid disease progression observed with 3L+ therapies in pts with FL, with especially poor outcomes in those with high-risk features (Liu J et al. Front Oncol 2023; Philips T et al. ASH 2023). In ELM-2 (NCT03888105), odronextamab (an investigational CD20×CD3 bispecific antibody) demonstrated deep and durable responses and generally manageable safety in pts with R/R FL who had received ≥2 prior lines of systemic therapy. Median progression-free survival (PFS) and overall survival (OS) in pts with CR were 28 months (95% CI 23.0-not evaluable [NE]) and not reached (95% CI 40.4-NE), respectively. Grade ≥3 treatment-emergent adverse events (TEAEs) occurred in 86% of pts (Taszner M et al. EHA 2024). For the current analysis, we present details on the efficacy and safety of 3L+ odronextamab treatment in pts with R/R FL who attained CR in ELM-2, including those with high-risk features. Methods ELM-2 is an ongoing, open-label, multicenter, Phase 2 trial of odronextamab in pts with R/R B-cell non-Hodgkin lymphoma, including a cohort with FL Grade 1-3a. Intravenous odronextamab was administered in step-up doses with steroid prophylaxis during Cycle (C) 1, followed by 80 mg on Days 1, 8, and 15 of C2-4. After C4, dosing continued at 160 mg once every 2 weeks (Q2W); pts switched to Q4W dosing if they had a durable CR for ≥9 months. The primary endpoint was objective response rate (ORR) according to Lugano classification, by independent central review (ICR). Secondary endpoints included CR rate, PFS, OS, duration of response, and safety. Results Primary results in pts evaluable for efficacy and safety (N=128) using the Oct 20, 2023, data cutoff have been reported. Median duration of efficacy follow-up was 20.1 months (95% CI 17.3-27.8). The ORR was 80.5% (103/128 pts; 95% CI 72.5-86.9), and CR rate was 73.4% (94/128; 95% CI 64.9-80.9). Median duration of CR (DOCR) was 25.1 months (95% CI 20.5-NE), and median time to CR was 2.7 months (range 2.3-7.9). Baseline characteristics of pts with CR (n=94) were similar to those of the overall population, and median duration of treatment exposure was 13.8 months (range 1.8-45.0). In total, 88 pts (93.6%) had CR at the first response assessment (~Week 12) and 6 (6.4%) reached CR later, including 3 pts who had stable disease initially. Twenty-eight pts (29.8%) were still receiving treatment at data cutoff, and 66 (70.2%) had discontinued treatment. Of those who discontinued, 42 still had CR at the last response assessment. Primary reasons for treatment discontinuation were disease progression (n=17), TEAEs (n=16 [including 6 pts with COVID-19]), physician decision (n=12), withdrawal by subject (n=11), and death (n=8). All 8 deaths resulted from TEAEs, including COVID-19 in 5 pts. Eighty-five pts (90.4%) with CR had high-risk features (POD24, 48.9%; FLIPI score 3-5, 55.3%; refractory to last treatment, 70.2%); median DOCR and median time to CR in these pts were similar to those in all pts (23.7 months [95% CI 18.2-NE] and 2.7 months [range 2.3-7.9], respectively). At the time of the current analysis, 44 pts with CR by ICR (46.8%) had switched to Q4W dosing, with a median duration of exposure of 17.7 months (range 13.1-45.0). Among these pts, 22 had discontinued treatment at data cutoff due to adverse events (n=7 [including 1 with COVID-19]), physician decision (n=6), death (n=3), withdrawal by subject (n=3), progressive disease (n=2), and an “other” reason (n=1). Conclusions Pts with R/R FL and CR to 3L+ odronextamab treatment in ELM-2 had a median DOCR of 25.1 months that was prolonged beyond the median duration of treatment exposure (13.8 months). Almost half (46.8%) of pts proceeded to monthly odronextamab administration, with a median duration of treatment exposure of 17.7 months. These data show the sustainability of CR in pts with FL treated with 3L+ odronextamab, including in those with high-risk features. The safety profile of odronextamab was generally manageable in the overall population, including in pts with CR, despite their prolonged drug exposure. These findings support the potential of odronextamab as a treatment for R/R FL.