Immune cell dynamics following rituximab and epcoritamab as first-line therapy for patients with high-tumor burden follicular lymphoma

Abstract Introduction: Epcoritamab (epco) is a CD3xCD20 bispecific antibody that achieves high objective response rates as a single agent and is approved for patients with relapsed or refractory follicular lymphoma (FL) who have received 2 or more prior systemic therapies. Our institution is leading an investigator-sponsored, phase II multicenter trial (NCT05783609) testing time-limited treatment with rituximab and epco for patients with previously untreated, high-tumor burden FL, offering the opportunity to investigate immune dynamics without the biological effects of prior or concurrent cytotoxic chemotherapy. Patients receive debulking treatment with 4 weekly doses of rituximab (R) (Day -14, -7, 1, 8) followed by 9 four-week cycles of epco, including epco step-up dosing (SUD) during cycle 1. Preliminary results of the trial are promising with a best complete metabolic response (CMR) rate of 91% and lower than expected rates of grade 2 or higher cytokine release syndrome (CRS). We conducted a preliminary analysis of peripheral blood from patients with and without high-grade CRS to assess treatment-associated changes in T-cell and B-cell dynamics following R+epco therapy. Methods: Spectral flow cytometry was performed on 18- and 16-color panels to distinguish T-cell and B-cell populations, respectively. Five of the initial patients were selected based on CRS grade and initial response to therapy. Samples from 4 timepoints were analyzed: screening (C1D-14), C1D1 (after 2 doses of R and before epco), C1D8 (after first epco SUD), and C1D15 (after 2 epco SUDs). Due to limited specimen availability, some C1D1 (n=2) and C1D15 (n=2) timepoints were excluded from the analysis. In addition, a progression timepoint sample was analyzed for one patient with progressive disease. Results: According to our preliminary analyses, we saw an overall decrease in CD8+ T cells after two weeks of R pre-treatment at C1D1 from 30.9% to 22.6%, followed by a steady increase at C1D8 (28.7%) and C1D15 (27.6%). This observation is consistent with previous studies (Falchi et al., MedRxiv 2024 and Hutchings et al., The Lancet 2021), supporting our experimental analyses. We also observed several changes within the CD8+ T cell subpopulation. Naïve T cells increased from screening to C1D1 for patients who experienced grades 0-1 CRS from 29.6% to 37.6%. However, naïve T cells remained low (6.1-7.3%) while effector T cells were higher for a patient who experienced grade 2 CRS during R+epco (71.8-75.5% vs 9.8-35.3% across the grade 0-1 patients). Additionally, the percentage of PD1+ among CD8+ T cells showed a downward trend from screening (35.3%) to C1D1 (31.5%), C1D8 (27.9%), and C1D15 (27.9%) for patients who experienced complete response (CR). A similar trend occurs for Granzyme B+ for patients who experienced CR. In contrast, for a patient during progression, PD1+, Granzyme B+, and TIM3+ increased compared to screening and C1D8, from 41.9%, 34.3% and 10.2% to 45.6%, 39.2% and 42.4% respectively. Within the CD4+ T cell subpopulation, PD1+ and TIM3+ generally decreased from screening (47.8% and 7.1%), reached a minimum on C1D1 (37.3% and 3.6%) to C1D8 (42.9% and 5.4%), and increased on C1D15 (44.8% and 5.7%). PD1+ and TIM3+ had the highest expression during progression in one patient (52.5% and 16.5%). T follicular helper cells (CD4+ CXCR5+) and regulatory T cells (CD4+ FoxP3+ CD127+) also seem to increase during R from 3.2% to 8%, and decrease during R+epco from 9.8% to 5.9%, respectively. Analyses of the B cell compartment showed that the majority of CD19+ CD20+ B cells were depleted by C1D1, highlighting the potency of R pretreatment in eradicating circulating B cells. Kappa light chain (51%) was also highly favored in B cells compared to lambda light chain (11.1%), and IgM was highly present across naïve (93%), unswitched (94.8%), and switched memory (29.3%) B cell compartments with minimal IgG. Conclusion: Our preliminary analyses suggest several changes within the T-cell and B-cell populations throughout R+epco therapy in patients with FL. We found that exhaustion markers are overexpressed during treatment, especially at progression. While these results are preliminary and a larger sample size is needed, there are favorable changes in both T-cell and B-cell populations between screening and C1D1, supporting pretreatment with monoclonal antibody. Analyses of the complete trial cohorts will be presented at the meeting.