P1415: cellular dynamics in responders and non-responders after the treatment of patients with aggressive b-zell lymphomas with chimeric antigen receptor (car) t cells

Topic: 25. Gene therapy, cellular immunotherapy and vaccination - Clinical Background: Anti-CD19 Chimeric Antigen Receptor (CAR) T cells have revolutionized the treatment of patients (pts) with refractory or relapsed (r/r) aggressive B-cell lymphoma. Unfortunately, more than 50% of pts experience a relapse, most of them within the first four weeks after treatment. Aims: To assess changes of the cellular immune system after CAR therapy and the impact on the outcome in pts with CD19+ lymphomas. Methods: We performed flow-cytometric analysis (14 cellular surface markers) of peripheral blood immune cells of 12 pts (9 male, 3 female) with median age 62.5 years (18-73) before CAR T cell reinfusion and on day 7 and 14 post reinfusion (tisa-cel, n=9, axi-cel, n=3). Moreover, we incubated isolated (CAR) T cells from pts with CD19+ Raji cells in vitro to assess the cytotoxicity of pts’ CAR T cells. Pts with complete metabolic response (CMR) in combined FDG-Positron Emission Tomography/Computer Tomography one month after reinfusion were stratified as responders, the other pts as non-responders. Results: The median progression-free-survival of responders (n=7) and non-responders (n=5) were 434 and 14 days, respectively (p<0.01). The median overall-survival of responders (763 days) was higher than in non-responders (140 days, p=0.15). CD3+ CAR T cells in blood samples of all pts peaked on day 7, with a median of 87.4 x106/L (4.1-358.1). Regulatory T cells (Tregs) showed a significant increase (p<0.01) from a median of 2.05x106/L prior to reinfusion to 15.9x106/L 14 days post reinfusion with a trend for increased naive Tregs from 0.2x106/L to 0.9x106/L (p=0.07). Moreover, memory Tregs increased significantly between day 7 (median of 1.4x106/L) and day 14 (median of 11.2x106/L) after reinfusion (p=0.01). Prior to reinfusion, responders had a significantly lower number of CD3+/CD8+ effector memory cells (1x106/L) than non-responder (16.7x106/L, p=0.05). Furthermore, responders showed trends for lower CD3+/CD8+ cells (3.5x106/L) as well as for activated CD3+/CD8+ cells (0.76x106/L) than non-responder (28.0x106/L (p=0.09) and 27.5x106/L (p=0.08)). Analyses 14 days after reinfusion showed a trend (p=0.07) for higher total CD3+ counts with a median of 724x106/L in responders compared to 182x106/L in non-responders, count of CD3+ CAR cells with 105x106/L and 14x106/L (p=0.07) as well as CD3+/CD4+ cells with 291x106/L and 70x106/L, respectively, (p=0.10). (Figure 1) On day 7 after reinfusion axi-cel cohort showed significantly lower numbers of CD4+ CAR cells with 11.7x106/L compared to tisa-cel with 60.0x106/L (p=0.05) and activated CD4+ CAR cells with 9.29x106/L and 53.4x106/L (p=0.05), respectively. 14 days after reinfusion the axi-cel pts showed significantly lower numbers of activated CD4+ CAR cells with 9.29x106/L compared to 53.9x106/L (p=0.04). 9/11 pts confirmed the cytotoxicity in vitro. Interestingly, the cytotoxicity assay in non-responders was also successful, indicating the functional activity of CAR T cells. Summary/Conclusion: Despite a small patient cohort and morphological parameters only, we identified an association of low CD3+/CD8+ effector memory cells count with response to treatment with CAR T cells and a significant increase of Tregs during the therapy. Further studies are warranted to further elucidate cellular and genetic factors influencing response to treatment.Keywords: CAR-T, Flow cytometry, Cellular immunity