<i>EO2463 Peptide Immunotherapy in Patients with Indolent NHL: A Phase 1 Exploration of a Response Biomarker for EO2463 Monotherapy and EO2463 in Combination with Lenalidomide/Rituximab</i>

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 &amp; wait” setting, EO2463 plus rituximab for 1st line FL/MZL, and EO2463/lenalidomide +/- rituximab in relapsed FL/MZL.