Schade, Henning

Abstract Increased absolute lymphocyte count (ALC) may predict risk of treatment-related mortality and atypical neurologic events among patients receiving chimeric antigen receptor (CAR) T-cell therapies for relapsed/refractory multiple myeloma. In this study, we analyzed the clinical outcomes of patients receiving ciltacabtagene autoleucel (cilta-cel) at the Colorado Blood Cancer Institute, from September 2023 to January 2025. Baseline data were collected pre/post-CAR T-cell therapy. Patients were stratified into preintervention (treated September 2023 to July 2024) and intervention (treated August 2024 to January 2025; those with ALC >5 × 103/μL received 3 days of dexamethasone prophylaxis on first identification of elevated ALC). In the preintervention group, 9 of 30 patients had peak ALC >5 × 103/μL; 5 of 9 (55.6%) experienced atypical neurologic events and all 5 died (cilta-cel therapy-related complications). In the intervention group, 7 of 23 patients had peak ALC >5 × 103/μL and received dexamethasone; 1 of 7 had an atypical neurologic event; and 1 death occured (infectious complication, 9 months posttreatment). Dexamethasone prophylaxis in patients with ALC of >5 × 103/μL resulted in rapid ALC reduction. Overall survival (OS) was significantly lower in preintervention patients with ALC of >5 × 103/μL vs intervention patients with ALC of >5 × 103/μL and patients with ALC of ≤5 × 103/μL (P = .0013). ALC >5 × 103/μL (vs ALC ≤ 5 × 103/μL) was significantly associated with atypical neurologic events (odds ratio, 6.8; P = .0157) and lower OS (hazard ratio, 6.2; P = .0106). In conclusion, ALC >5 × 103/μL after cilta-cel treatment predicted severe early neurologic events and high mortality risk. Dexamethasone prophylaxis demonstrated promise for risk mitigation.

Background HPN217 is a B Cell Maturation Antigen (BCMA)-targeting tri-specific T cell engager (TCE). HPN217 contains three binding domains including anti-BCMA for MM cell binding, anti-albumin for half-life extension, and anti-CD3 for T cell engagement and activation. HPN217 is a small (~50 kDa) globular protein, designed to increase the therapeutic window by minimizing off-target toxicities and cytokine release syndrome (CRS). HPN217 is under investigation in patients (pts) with heavily pretreated relapsed/refractory MM (RRMM). Methods This study is designed to assess the safety, pharmacology and early clinical activity of HPN217 using fixed and step-dose (prime dose followed by target doses) regimens in dose escalation cohorts along with expansion of selected regimens for further evaluation. Pts with RRMM who have received at least 3 prior therapies including a proteasome inhibitor, an immunomodulatory drug, and CD38-targeted therapy are eligible. Prior exposure to a BCMA-targeting agent is permitted. Primary objectives include evaluation of safety, tolerability, pharmacokinetics (PK), and determination of the Recommended Phase 2 Dose(s) (RP2D). Secondary objectives include preliminary efficacy. HPN217 is administered IV once weekly or once every 2 weeks. Adverse events (AEs) are graded by CTCAE 5.0, and ASTCT for cytokine release syndrome (CRS) and ICANS. Clinical activity is assessed per IMWG Response Criteria. Results Dose escalation has been completed. 97 pts were enrolled across 15 dose escalation cohorts and expansion of 3 regimens with the highest target dose levels from dose escalation (12mg weekly; 24mg every 2 weeks; 24mg weekly for 1 cycle followed by 24mg every 2 weeks). As of 26 June 2023, across all cohorts, 94 pts were treated and had received a median (range) of 6 (2-19) prior lines of treatment (62% penta-exposed, 17% BCMA-targeted therapy, 68% prior transplantation). Median age was 70 (38-85) years. 36 pts (38%) remain on treatment. The most common (≥25%) treatment-emergent adverse events (TEAEs) across all cohorts and in the 12mg and 24mg cohorts are summarized in Table 1. Dose limiting toxicities (DLTs) of reversible transaminitis (Gr 3, n=1; Gr 4, n=1) in 2 pts at 2.86 mg fixed dose during dose escalation informed the choice of 2.15 mg as priming dose in the highest step dose cohorts; a maximum tolerated dose (MTD) has not been reached in step dose cohorts. All CRS events were grade 1-2 except one event of grade 3 CRS at 24 mg. Grade 1 ICANS was reported in 2 pts. Responses were observed at doses ≥ 2.15 mg. Among the 12mg and 24mg cohorts, 55% (22/40) of efficacy-evaluable pts currently have had a confirmed response (PR or better) including 2 pts with prior BCMA directed CAR-T cell therapy; disease assessments for recently enrolled patients are pending. Among pts with a response, 73% (16/22) have had a confirmed response of VGPR or better. Across all dose levels, the median time on treatment for pts with a confirmed response was 40 weeks (range 8.3-114 weeks), including 9 patients on treatment for over 12 months, with data maturing to include longer follow-up on patients recently enrolled. HPN217 exhibited linear and dose proportional PK across all dose groups with a median half-life of 68 hours (range 26-197 hours). Transient cytokine increases were higher with the initial/priming dose compared to subsequent/target doses. Conclusions Dose escalation of HPN217, a novel half-life extended BCMA-targeting T-cell engager, has been completed; the MTD was not reached in step dose cohorts. The 12mg and 24mg target doses are well tolerated with manageable adverse event profiles similar to those at lower dose levels and are associated with robust and durable clinical responses. Additional follow up of recently enrolled pts in 12 mg and 24 mg cohorts will inform the choice of the RP2D(s), and complete data on all pts enrolled will be presented. NCT04184050