Hematology · Medical Literature
Dual epitope anti-LILRB4 synthetic T-cell receptor and antigen receptor (STAR)-T-cell therapy for relapsed/refractory acute myeloid leukemia.
Abstract
Acute myeloid leukemia (AML) is a rapidly progressive malignancy with poor prognosis. To date, chimeric antigen receptor (CAR) T-cell therapy in AML has been limited by the lack of antigens with high specificity for AML cells. Here, we developed a synthetic T-cell receptor and antigen receptor-T (STAR-T) cell therapy targeting LILRB4, an immunosuppressive receptor highly expressed on monocytic AML blasts but not on hematopoietic stem cells. Two nanobodies with the highest affinity for LILRB4 were identified through phage display library screening and used to construct nanobody-based dual epitope anti-LILRB4 STAR-T cells, which exhibit more potent tumor inhibition in vitro and in vivo than single epitope anti-LILRB4 STAR-T cells or dual epitope anti-LILRB4 CAR-T cells do. We subsequently conducted the first human clinical trial (NCT05548088) involving 9 patients with LILRB4-positive relapsed and refractory (R/R) AML. Six patients completed the safety and efficacy evaluation (median follow-up, 10.7 months). No immune effector cell-associated neurotoxicity (ICANS) or grade ≥3 cytokine release syndrome (CRS) was observed. Three patients died due to laboratory-confirmed infections. The best overall response rate (ORR) was 50.0% (3/6) in the efficacy assessable set and 33.3% in the full analysis set. The number of LILRB4-positive STAR-T cells significantly increased, and the number of LILRB4-positive target cells decreased. Single-cell RNA sequencing revealed that monocyte-mediated suppression of autologous T-cell function may be a primary mechanism underlying the failure of STAR-T therapy in nonresponders. In conclusion, this first-in-human trial demonstrates the therapeutic potential of targeting LILRB4 with STAR-T-cell therapy in AML and warrants further investigation.
Clinical relevance
In adults with LILRB4-positive relapsed/refractory AML, is nanobody-based dual-epitope anti-LILRB4 STAR-T cell therapy safe and efficacious, and does it outperform single-epitope STAR-T or dual-epitope CAR-T approaches preclinically? __SNAPSHOT__ {"studyDesign":"Combined preclinical study (in vitro and xenograft models) with an embedded first-in-human, single-arm, open-label, phase I dose-escalation clinical trial (BOIN design)","setting":"Single center; Peking University People's Hospital, China (Ethics Approval No. 2022PHD007); registered at ClinicalTrials.gov (NCT05548088)","sampleSize":"Clinical cohort: n=9 enrolled; n=6 completed 28-day dose-limiting toxicity (DLT) assessment and were evaluable for safety and efficacy","population":"Adults aged 18–70 years with LILRB4-positive (by flow cytometry) relapsed/refractory AML; median age 36 years (range 25–60); 77.8% (7/9) had relapsed post-allogeneic hematopoietic stem cell transplantation (allo-HSCT); median bone marrow blast percentage 60% (range 12–81%); median LILRB4 expression on blasts 77% (range 42–97%); ECOG performance status 0–2","intervention":"Lymphodepletion with cyclophosphamide and fludarabine (days −5 to −3) followed by a single infusion of autologous nanobody-based dual-epitope (biparatopic) anti-LILRB4 STAR-T cells at escalating doses: 1×10⁶/kg (n=1), 3×10⁶/kg (n=3), 6×10⁶/kg (n=4), and 1×10⁷/kg (n=1). The STAR construct incorporates nanobodies fused to the N-termini of modified TCR-Cα and TCR-Cβ chains with an OX40 co-stimulatory domain.","comparator":"No concurrent clinical comparator arm. Preclinical comparators: single-epitope anti-LILRB4 STAR-T cells and dual-epitope anti-LILRB4 CAR-T cells (in vitro and xenograft models only)","primaryOutcome":"Safety: incidence of dose-limiting toxicity (DLT), adverse events (AE), serious adverse events (SAE), cytokine release syndrome (CRS), and immune effector cell-associated neurotoxicity (ICANS)","followUp":"Median follow-up 10.7 months in the published article (per abstract); an earlier ASH 2024 abstract reported a median follow-up of 5 months (range 0.5–13.5 months)","fundingSource":"Investigator-initiated trial; specific external funding sources not reported in the abstract"}
Key findings
PRECLINICAL: In vitro and in xenograft models, dual-epitope (biparatopic) anti-LILRB4 STAR-T cells demonstrated significantly enhanced cytotoxicity, broader antigen recognition, superior cytokine production, greater proliferative capacity, more durable tumor control, and reduced antigen escape compared with single-epitope STAR-T cells or dual-epitope CAR-T cells. Formal comparative statistics (p-values, confidence intervals, effect sizes) for these preclinical comparisons are not reported in the available abstract. CLINICAL (n=6 evaluable): No ICANS was observed and no grade ≥3 CRS occurred. Grade 1–2 CRS was observed in 83.3% (5/6) of evaluable patients. Three of 9 enrolled patients died from laboratory-confirmed infection (specific timing relative to DLT window not fully detailed in the abstract; earlier data noted 2 deaths prior to day 28 DLT assessment). STAR-T cell expansion peaked in peripheral blood at a median of day 7 (range day 5–10) by qPCR. Peripheral blood LILRB4-positive AML cell burden was inversely correlated with circulating STAR-T cell levels (correlation coefficient not reported). In responding patients, bone marrow LILRB4-positive AML cells were significantly reduced or undetectable. Best overall response rate (ORR) among 6 evaluable patients: 50.0% (3/6), comprising 1 complete remission (CR), 1 morphologic leukemia-free state (MLFS), and 1 partial remission (PR). Two of the 3 responders subsequently underwent a second or third allo-HSCT and remained MRD-negative at follow-up. Estimated 1-year overall survival (OS): 62.2% (95% CI: 35.5%–100%). No maximum tolerated dose (MTD) was identified in the published abstract. NNT is not calculable given the absence of a concurrent control arm.
Practice implications
This study provides early, first-in-human safety and activity data for a novel STAR-T cell platform targeting LILRB4, a target with favorable tumor selectivity (high expression on monocytic AML blasts, absent on hematopoietic stem cells). The preclinical data mechanistically support the dual-epitope STAR architecture's superiority over single-epitope and CAR-T alternatives; however, head-to-head clinical comparisons have not been performed. Clinically, the absence of grade ≥3 CRS and any ICANS in 6 evaluable patients is an encouraging safety signal in a population with extremely high-risk, heavily pretreated disease (>75% post-allo-HSCT relapse). The 50% ORR and the ability of 2 responders to proceed to allo-HSCT and achieve MRD negativity are clinically meaningful signals. However, the findings must be interpreted with significant caution: only 6 of 9 enrolled patients were evaluable, the 3 infection-related deaths represent a critical and potentially therapy-related safety signal that is incompletely characterized in the abstract, and all estimates derive from a very small sample with wide confidence intervals (e.g., 1-year OS 95% CI: 35.5%–100%). The population studied — predominantly young adults with relapsed post-allo-HSCT AML — may not be representative of the broader R/R AML population, including older adults or non-monocytic subtypes. LILRB4 expression is predominantly restricted to FAB M4/M5 (monocytic) AML, limiting applicability to non-monocytic subtypes. This study does not establish optimal dosing, durability of response, or superiority over existing salvage regimens. Only an abstract and the journal publication abstract were available for full critical appraisal; complete methods, patient-level data, and toxicity tables were not reviewed. __LIMITATIONS__ Extremely small clinical sample (n=9 enrolled; n=6 evaluable), precluding reliable safety or efficacy conclusions.,Single-arm design with no concurrent control; efficacy claims cannot be attributed to therapy over natural disease course or lymphodepletion alone.,Three of 9 patients (33%) died of infection; the causal relationship to therapy (lymphodepletion, STAR-T cell-induced immunosuppression, or underlying disease) is not established in the available abstract — this is a major unresolved safety question.,Short and variable follow-up (median ~10.7 months; 95% CI for 1-year OS spans nearly the full range 35.5%–100%), making survival estimates unreliable.,Heavily pre-treated, post-allo-HSCT population limits generalizability to other R/R AML patients and introduces confounding (graft effects, prior immunosuppression).,LILRB4 target expression restricts applicability to monocytic AML subtypes (FAB M4/M5); non-monocytic AML was not represented.,Preclinical superiority data over CAR-T cells and single-epitope STAR-T cells have not been validated in any clinical comparator arm.,Dose-escalation design based on the BOIN method; optimal biological or therapeutic dose has not been identified.,Investigator-initiated design introduces potential for performance bias; external validation in an independent cohort is absent.,Full peer-reviewed publication data (complete methods, all toxicity grades, pharmacokinetics, and MRD data) were not available for review — analysis based on abstract only. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ Dual-epitope anti-LILRB4 STAR-T cell therapy demonstrated a manageable early safety profile with no grade ≥3 CRS or ICANS, and a 50% ORR in 6 evaluable patients with heavily pretreated, predominantly post-allo-HSCT R/R monocytic AML. However, three infection-related deaths among 9 enrolled patients represent an important unresolved safety signal, and the extreme sample size limitation and single-arm design preclude definitive safety or efficacy conclusions. This therapy is not ready for clinical application outside of a clinical trial; confirmation in larger, multi-center, controlled studies is required before any practice implications can be drawn.