Safety and Efficacy of Letetresgene Autoleucel (lete-cel; GSK3377794) Alone or in Combination with Pembrolizumab in Relapsed and Refractory Multiple Myeloma

Background: Outcomes remain poor for patients with relapsed and refractory multiple myeloma (RRMM) progressing on conventional therapy (proteasome inhibitors, IMiDs, anti-CD38 antibodies, BCMA targeting agents, corticosteroids). Lete-cel, an autologous T-cell therapy, targets NY-ESO-1/LAGE-1a+ tumors using a genetically modified, high-affinity T-cell receptor. NY-ESO-1 and LAGE-1a are immunogenic cancer/testis antigens frequently overexpressed in MM and are linked to poor clinical outcomes. Additionally, PD-1 expression, which may limit adaptive immune response, has been observed previously in RRMM patients following treatment with lete-cel (Stadtmauer et al. Blood Adv, 2019; 3: 2022-2034). This open-label, pilot study evaluated the safety and efficacy of lete-cel +/- pembrolizumab (pembro) in patients with RRMM. Study design and methods: Key eligibility criteria include: age ≥18 yr; HLA-A*02:01; A*02:05, and/or A*02:06; NY-ESO-1+ and/or LAGE-1a+; protocol-required prior regimens; specified washouts from prior therapy; no active/chronic/intercurrent illness. Following lymphodepletion (LD), patients received lete-cel (Arm 1) or lete-cel + pembro (Arm 2). Planned pembro dosing was 200 mg/dose Q3 weeks (wks) starting at Wk 3. Primary endpoint was safety and tolerability. Key efficacy endpoint was investigator-assessed overall response rate (ORR) by International Myeloma Working Group uniform response criteria for MM (2016); response was assessed Q3 wks from Wk 3 to Wk 24, then Q6 wks to Wk 72, then every 3 months (mo) to disease progression/death/withdrawal. NY-ESO-1/LAGE-1a expression was assessed by qRT-PCR on myeloma cells. Transduced cell kinetics were assessed by qPCR of transgene vector copies in DNA from peripheral blood mononuclear cells. Results: Six patients (all male; median age 63 yr) were enrolled; 3 per arm. All had prior systemic anti-cancer therapy; 3 patients had received ≥5 prior regimens. Five of 6 patients received systemic anti-cancer therapy between leukapheresis and LD. All received reduced LD due to age and, in some patients, renal impairment. Patients in each arm received similar numbers of transduced T cells. Each of the 3 patients in Arm 2 received a median of 3 pembro doses (range: 3-4 doses). Start of pembro dosing was delayed to Wk 6 in 2 patients due to ongoing toxicities. There were no Grade 5 AEs. Grade 3/4 T-cell related AEs were reported in 3 patients, and all patients had Grade 3/4 LD-related AEs. Hematopoietic cytopenias were the most common treatment-emergent and treatment-related Grade 3/4 AE, occurring in all patients. All cytopenias were reported to have resolved for 4 patients or to have improved to Grade 1 at final patient follow-up for 2 patients. Three patients had cytokine release syndrome (Arm 1: 1 patient, Grade 2; Arm 2: 2 patients; 1 Grade 1 and 1 Grade 2); all patients recovered. There was 1 event of graft vs host disease (GvHD skin; Grade 1) and, in a separate patient, 1 event of Immune Effector Cell-Associated Neurotoxicity Syndrome (ICANS) (Grade 1). Both events resolved. All patients had reduction in tumor burden. Arm 1 (lete-cel alone) had an ORR of 33.3% (1 CR, 2 SD) and median progression-free survival (PFS) of 2.79 mo, while Arm 2 (combination) had an ORR of 66.7% (1 VGPR, 1 PR, 1 SD) and median PFS of 2.78 mo. Time to response for all responders was 3 weeks. Pembro dosing for the 2 Arm 2 responders began at Wk 6. Duration of response in each responder was 2.1 mo. Overall survival data are not mature. Two of 3 responders exhibited clearance of antigen positive myeloma cells in the bone marrow for up to 6 weeks after lete-cel infusion. T cell kinetics trended toward higher peak expansion (Cmax) and area under the curve (AUC) over the first 28 days post-dose (AUC0-28d) in responders vs. non-responders. Serum cytokine profiles in relation to response and CRS will be discussed. Conclusions: A single lete-cel infusion was associated with antitumor activity in 6/6 heavily pretreated RRMM patients, including 1 CR, 1 VGPR, 1PR. Both responses in Arm 2 occurred prior to pembro initiation. The associated safety profile was manageable and consistent with that seen in other lete-cel studies. Responders showed a trend toward higher Cmax and AUC0-28d as compared to non-responders. The study was closed in November 2020 due to protracted enrollment. This study (208470; NCT03168438) was funded by GlaxoSmithKline. Submission support was provided by Fishawack Health. Disclosures Nishihori: Novartis: Research Funding; Karyopharm: Research Funding. Kaufman: Janssen: Honoraria; Heidelberg Pharma: Research Funding; Fortis Therapeutics: Research Funding; Tecnofarma SAS, AbbVie: Honoraria; Amgen: Research Funding; BMS: Consultancy, Research Funding; Incyte, celgene: Consultancy; Incyte, TG Therapeutics: Membership on an entity's Board of Directors or advisory committees; Genentech, AbbVie, Janssen: Consultancy, Research Funding; Novartis: Research Funding; Roche/Genetech, Tecnopharma: Consultancy, Honoraria; Sutro, Takeda: Research Funding. Huff: GSK: Current Employment, Current equity holder in publicly-traded company. Snape: Veramed: Current Employment. Jain: Butterfly Network: Current equity holder in publicly-traded company; Marker Therapeutics: Current equity holder in publicly-traded company; 23 and Me: Current equity holder in publicly-traded company; Sema4 Holdings: Current equity holder in publicly-traded company; GSK: Current Employment, Current equity holder in publicly-traded company. Kapoor: GSK: Current equity holder in publicly-traded company. Zajic: GSK: Current Employment, Current equity holder in publicly-traded company. Suchindran: GSK: Current Employment, Current equity holder in publicly-traded company. Chisamore: Merck & Co. Inc: Current Employment, Current equity holder in publicly-traded company. Rapoport: GSK: Other: Support received as site principal investigator for this study.

391 Biomarker correlates of response in patients with advanced myxoid/round cell liposarcoma (MRCLS) treated with NY-ESO-1 TCR T cells (Letetresgene autoleucel)

BackgroundThis is an open label pilot study (NCT02992743) on letetresgene autoleucel (lete-cel; GSK3377794), an NY-ESO-1-specific autologous CD4+ and CD8+ T cells expressing a high affinity T-cell receptor which recognizes the NY-ESO-1 antigen epitope in complex with specific HLA- alleles A*02, which exhibited anti-tumor activity and manageable safety profiles in patients with advanced MRCLS based on interim analysis (IA) data.1 Lymphodepletion has been shown to enhance the expansion, persistence, and homing of therapeutically infused T-cells, thereby potentiating therapeutic efficacy against malignant diseases.2 Initial T-cell kinetics data from this study demonstrated that lymphodepletion regimen (LDR)-B robustly depleted lymphocytes at infusion and was trended with higher peak cell expansion (Cmax) vs. LDR-A. The peak expansion was significantly associated with weight-normalized transduced cell dose and trended with response.1 Here, we will be discussing additional cell kinetics data and other exploratory biomarker correlates of response.MethodsPatients with advanced MRCLS were enrolled to 2 cohorts and received either planned A (N=10) or B (N=10) LDRs prior to lete-cel infusion (table 1). Response was assessed per RECIST v1.1. Transduced cell kinetics were measured by quantitative PCR of transgene vector copies in DNA from peripheral blood mononuclear cells (PBMCs). Serum cytokines (Meso Scale Discovery immunoassay) as pharmacodynamic (PD) markers of response and their association with T cell kinetics will be discussed. Phenotypic characterization of the cell product (pre- and post- infusion) via Flow cytometry using Cytek Aurora (23 color panel), to help understand correlation of response with engineered cell product attributes, will be presented. Potential biomarker correlates of clinical response were tested using generalized linear models.ResultsFive out of 6 responders with available lab data exhibited robust lymphocyte depletion at infusion (0–25 cell/µL) and high Cmax (>50,000 vector copies/µg gDNA) with LDR. Only 6/14 non-responders exhibited low lymphocytes counts at infusion and high Cmax. LDR-B also induced strong depletion of monocytes at infusion (p=0.03) vs. LDR-A, but depletion of monocytes did not show association with response. Higher Cmax was correlated with exposure (AUC0–28d) (Adj. R2=0.606). AUC0–28d was a better predictor of response in patients receiving LDR-B (p=0.0182), with AUC0–28d trending towards predicting response in the LDR-A cohort. AUC0–28d was associated with tumor volume reduction (p=0.0569).Abstract 391 Table 1ConclusionsExposure–response analysis of this study reveals that efficacy appears to be driven by weight-normalized transduced cell dose and LDR via AUC0–28d. Higher AUC0–28d was correlated with Cmax and maximum tumor volume reduction.AcknowledgementsThis study (208469; NCT02992743) was funded by GlaxoSmithKline.Trial RegistrationNCT02992743ReferencesD’Angelo SP, et al. J Clin Oncol 2021;39:15_suppl:11521.Bechman, Maher. Expert Opin Biol Ther 2021;21(5):627–637.Ethics ApprovalThis study was approved by institutional review boards (IRB) at the six participating sites.

Transamniotic Stem Cell Therapy for Experimental Congenital Diaphragmatic Hernia: Structural, Transcriptional, and Cell Kinetics Analyses in the Nitrofen Model

<b><i>Purpose:</i></b> We examined select pulmonary effects and donor cell kinetics after transamniotic stem cell therapy (TRASCET) in a model of congenital diaphragmatic hernia (CDH). <b><i>Methods:</i></b> Pregnant dams (<i>n</i> = 58) received nitrofen on gestational day 9.5 (E9) to induce fetal CDH. Fetuses (<i>n</i> = 681) were divided into 4 groups: untreated (<i>n</i> = 99) and 3 groups receiving volume-matched intra-amniotic injections on E17 of either saline (<i>n</i> = 142), luciferase-labeled amniotic fluid-derived mesenchymal stem cells (afMSCs; <i>n</i> = 299), or acellular recombinant luciferase (<i>n</i> = 141). Pulmonary morphometry, quantitative gene expression of pulmonary vascular tone mediators, or screening for labeled afMSCs were performed at term (E22). Statistical comparisons were by Mann-Whitney U-test, nested ANOVA, and Wald test. <b><i>Results:</i></b> TRASCET led to significant downregulation of endothelial nitric oxide synthase and endothelin receptor-A expressions compared to both untreated and saline groups (both <i>p</i> &#x3c; 0.001). TRASCET also led to a significant decrease in arteriole wall thickness compared to the untreated group (<i>p</i> &#x3c; 0.001) but not the saline group (<i>p</i> = 0.180). Donor afMSCs were identified in the bone marrow and umbilical cord (<i>p</i> = 0.035 and 0.015, respectively, vs. plain luciferase controls). <b><i>Conclusions:</i></b> The effects of TRASCET in experimental CDH appear to be centered on the pulmonary vasculature and to derive from circulating donor cells.

Comparison of the effects of C-KIT, MMP-2, Ki-67, Bcl-2 and metallothionein expression on prognostic factors in skin and non-skin malignant melanomas

Objectives: We aimed the relationship between with selected prognostic factors of MM, 1) C-KIT (CD117), which related to MM pathogenesis, 2) Ki-67, which is the determinant of cell kinetics, 3) MMP-2, which degradation of the basement membrane and extracellular matrix required for cell migration, invasion and metastasis in melanogenesis, 4) bcl-2, which reduces the apoptotic response to cytotoxic chemotherapy and 5) MT’s whose overexpression shows resistance to anticancer drugs and radiotherapy and thus poor prognosis.Material and Methods: In this study, 30 skin and 15 non-skin MMM cases diagnosed between January 01, 2000 and June 01, 2011 in SCU-TF Medical Pathology Department were examined. C-Kit, MMP-2, Ki-67, bcl-2 and MT markers were applied to these cases.Results: When comparing the skin and non-skin groups, the difference between Ki-67 and MMP-2 expressions was found to be statistically significant, but no significant difference was found in staining with c-Kit, MT and bcl-2. It was thought that high MMP-2, C-KIT, bcl-2 expressions and high Ki-67 index as well as loss of MT expression might be associated with poor prognosis. Despite the high level of KIT immunostaining in melanomas, this parameter does not appear to be a good predictor of the presence of molecular mutations. Mutations that activate KIT should be considered a rare event in this tumor.