Sub-Cutaneous Administration of Rituximab Triggers a Pro-Phagocytic Phenotype of Monocytic Compartment in Low-Tumor Burden Follicular Lymphoma Patients Included in the Flirt Clinical Trial, a Lysa Study

Introduction FLIRT (NCT02303119) is a phase III randomized clinical trial designed to evaluate whether Rituximab (R) induction by one IV infusion followed by 3 sub-cutaneous (SC) infusions and short maintenance using SC route (SC-arm) could improve PFS compared to 4-weekly IV R infusions without maintenance (IV-arm) in first line/low tumor burden (GELF criteria) Follicular Lymphoma (FL) patients (202 patients). This study met its primary endpoint and demonstrated that the SC-arm improves PFS of patients with low-tumor burden (#EHA 2022, #ASCO 2022). R is known to exert its anti-tumor activity through complement activation, antibody-dependent cell cytotoxicity, and antibody-dependent cell phagocytosis (ADCP). An ancillary study of the FLIRT trial planned to explore the differential impacts on immune response in the 2 arms and to identify predictive biomarkers.

Methods Peripheral blood cells were analyzed in 39 patients from the SC-arm and 43 patients from the IV-arm before treatment (D1) and at M3, i.e. after 4 R infusions in both arms, by multicolor flow cytometry to evaluate circulating T, B, NK, dendritic, and monocyte subset counts and activation status.

Results The 82 patients studied display the same clinical features than the whole cohort and the PFS was significantly longer in the SC-arm than in the IV-arm in this limited cohort (P=0.0059). When focusing only on the differences between the 2 arms, monocytes were differentially affected, with an upregulation at M3 of the Fcγ receptors CD32 and CD64 on the 3 main circulating monocyte subsets (CD14^hiCD16^lo classical, CD14^loCD16^hi non classical, and intermediate) exclusively in the SC-arm (P<0.05), whereas the SIRPα phagocytosis inhibitory receptor was significantly upregulated on these 3 monocyte subsets exclusively in the IV-arm (P<0.05). In addition, the percentage of CD25^hiFoxp3^pos Treg among CD4^pos T cells was decreased only in the SC-arm (P<0.01), together with an increase of naïve (CD45RA^posCCR7^pos) and effector memory (CD45RA^negCCR7^neg) CD4^pos T cells (P<0.05), and naïve CD8^pos T cells (P<0.05). Interestingly, CD32 and CD64 expression on M3 monocytes in the SC-arm was correlated with T-cell activation, as evaluated by the expression of HLA-DR on CD8^pos T cells and PD-1 on CD4^pos T cells (Spearman, P<0.05). Conversely, no modification of T cell subsets was found exclusively in the IV-arm. Additional studies are ongoing to establish whether this differential impact on monocyte phenotype translate to transcriptomic and functional differences.

Conclusions Treatment of low-tumor burden FL with R only using SC route is associated with a specific pro-phagocytic activation profile of the monocytic compartment that is not found when R is administrated exclusively by the IV route that favors conversely an anti-phagocytic polarization. This SC-specific monocyte reprogramming is associated with a T-cell activation phenotype, opening the way for additional studies on the impact of R route of administration on ADCP and anti-tumor immune response activation.

Menard:Bristol-Myers Squibb: Honoraria. Bachy:Amgen, BMS: Research Funding; Kite, Gilead, Novartis, Roche, Incyte, Miltenyi Biotech, Takeda, Sanofi: Honoraria; Roche, Gilead, ADC Therapeutics, Takeda, Novartis, Incyte: Membership on an entity's Board of Directors or advisory committees; Hospices Civils de Lyon: Current Employment. Morschhauser:Novartis: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Genmab: Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Epizyme: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; F. Hoffmann-La Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy; Genentech: Consultancy; Miltenyi: Membership on an entity's Board of Directors or advisory committees; Allogene therapeutics: Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Cartron:MabQi, Ownards Therapeutics, Abbvie, Roche, Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Gilead, Novartis, Mylteni, Sanofi, Abbvie, Takeda, Roche, Janssen, Celgene, Novartis, Bristol Myers Squibb: Honoraria. Tarte:Roche: Research Funding.