P1230: t cell cd62l expression following nivolumab therapy is associated with long term response to rituximab-nivolumab in treatment naïve follicular lymphoma: results from the 1st flor study

Topic: 20. Lymphoma Biology & Translational Research Background: Inter-tumoral T cell dysfunction and efficacy of immune checkpoint inhibitors (ICI) in follicular lymphoma (FL) has been well described. However, few studies have examined peripheral blood immunity at diagnosis or the impact of frontline ICI on circulating immunity in FL. Aims: We hypothesised that immune dysregulation in peripheral blood would be present in treatment naïve FL and would correlate to response to frontline ICI.. Methods: PBMC samples from 34 untreated FL patients receiving rituxibab (R) and nivolumab (nivo) in the 1st FLOR trial (Hawkes JCO 2021) were collected at baseline, after 4 cycles of nivo (PET-CT2) and after 6 months of nivo±R (PET-CT4) as part of a pre-planned translational analysis. Immune profile was assessed using a single-tube 29 antibody FACS panel on an Aurora spectral flow cytometer and compared to the immune profile of 12 age matched healthy donors. Results were correlated with centrally determined PET response (Lugano criteria). Results: Compared to healthy donors, FL patients had increased proportions of TRegs (P<0.0001) with decreased HLA-DR+ (P<0.01) and increased PD-1+ (P<0.01) populations. NK cells were increased (P<0.05) with a 2-fold increase in TIM3 expression (P<0.01). While total T cells were unchanged, expression of PD-1, TIM3, HLA-DR and 4-1BB were significantly increased in both CD4 and CD8 T cells from FL patients. B cell and monocyte populations were unchanged. Treatment with nivo significantly increased the populations of TRegs expressing 41BB, LAG-3, TIM3 or PD-L2 (P<0.05) with a decreased PD-L1 positive population at PET-CT2. Expression of immune checkpoints on T cells was unchanged by therapy and remained high compared to healthy donors. To assess biomarkers of response, patients were stratified into sustained CR (CR achieved by PET-CT4 and maintained for 6 months without evidence of relapse, n=15) vs PR/PD (n=21) and changes in immune profile assessed. At baseline, sustained CR was associated with a trend for increased proportions of Naïve CD4 and CD8 T cells and decreased TRegs and PD-L2 expressing TRegs. Baseline proportions of PD-1 expressing T and NK cells did not correlate with sustained response. Most strikingly, expression of CD62L was significantly downregulated across total CD4 and CD8 T cells and memory subsets and TRegs at PET-CT2 in PR/PD patients (P<0.05) and maintained at baseline levels in those patients who eventually achieved a sustained CR. At this early timepoint final patient responses had not been established with most patients having either progressive or stable disease, suggesting that dysfunctional downregulation of CD62L in response to nivo may reflect the inability of patient’s T cells to activate and/or migrate to the tumour site and facilitate tumour clearance and long-term treatment responses. Summary/Conclusion: Grade 1-3A treatment naïve FL is associated with significant dysregulation of peripheral blood T and NK cells prior to therapy including increased expression of multiple immune checkpoints. Early downregulation of CD62L on T cells of patients treated with nivo was associated with the inability to achieve long term complete responses and may indicate aberrant T cell activation and/or function which impacts on long term response to therapy. Keywords: T cell activation, Immunotherapy, Follicular lymphoma