Mechanistic Insights into Immune Related Toxicities in Subjects with Relapsed/ Refractory Follicular Lymphoma Treated with Zandelisib

Use of phosphatidylinositol 3 kinase (PI3K) delta inhibitors has been associated with potentially severe autoimmune toxicity. Recent studies have identified altered T cell function as a major contributor to immune related toxicities with idelalisib and duvelisib (Leukemia PMID:34743191, BJH PMID: 35170759). Zandelisib is a novel, oral next generation selective PI3Kδ inhibitor which is in registration trials in B cell malignancies. To mitigate the immune related toxicity of zandelisib, an intermittent dosing strategy of 7 days on and 21 days off was developed and successfully reduced autoimmune toxicities from 30% of patients to 10% of patients in the phase 1b study (Lancet Oncol PMID: 35835137). The TIDAL trial is an international phase 2 clinical trial that evaluated the efficacy of two months continuous zandelisib lead-in followed by intermittent dosing in patients with relapsed refractory follicular and marginal zone lymphoma. Results were recently reported at ASCO 2022, and demonstrated a promising 70% ORR and 35% CR rate, with less than 10% discontinuation for autoimmune toxicity (J Clin Oncol,suppl 16; abstr. 7511). Here we report the T cell changes observed in TIDAL in relation to the development of autoimmune toxicities.

To determine the difference in T-cell subsets between pre-and on-treatment PBMC samples, a total of 112 serial samples from 18 patients who did or did not develop any grade immune-related adverse events (irAEs: colitis, transaminitis, rash, mucositis) during daily and intermittent dosing were analyzed. We used two flow cytometry panels: a 15-antibody panel for Tregs, Th17 and Th2 subsets and a 14-antibody panel for Th1, Naive, Memory, and Activated/Effector T cell subsets. The FCS files were analyzed using the OMIQ platform (www.omiq.ai). In this analysis, Tregs were defined as CD4+ CD25hi CD127lo FoxP3+ Helios+, and Th17 cells as CD4+ CCR6+, CD161+ RORgT+. For manual gating of Treg and Th17 cells, the following criteria were used: after gating on CD4+ cells, Tregs were defined as CD127lo CD25hi and Th17s were defined as RORgT+.

Unsupervised analysis of the flow cytometry staining data on all samples from all patients identified 30 clusters each in the 15-color and 14-color panels. Comparing patients with and without irAEs across all timepoints, we identified several clusters significantly different in the OMIQ analysis, including clusters for Tregs (C_2), Th17 (C_28), Th2 (C_6), and activated CD8 with Granzyme B expression (C_7 & C_8). The counts for the Treg cluster C_2 were significantly lower in samples with irAEs compared to samples without irAEs. In addition, baseline levels of C_2 were significantly lower in the samples from patients who later developed irAEs compared to those who didn't. Clusters C_28 and C_6 representing Th17 and Th2 phenotypes, respectively, were significantly increased in the samples with irAEs as compared to the samples without irAEs. Both these Th17 and Th2 clusters also tend to increase over time in all samples compared to screen, and baseline levels of these clusters were higher in the samples from patients with irAEs compared to those without. An activated CD8 cluster (C_26) with Th17 marker CCR6 was also significantly increased in the samples with irAEs, and the baseline levels of this cluster were also higher in patients who later developed irAEs compared to those who didn't. Metacluster analysis in the 14-color panel also showed several significantly altered clusters, with an activated CD8 phenotype cluster (C_23) significantly higher in samples with irAEs compared to samples without irAEs. However, no significant difference was seen in naïve CD8 clusters between samples with and without irAEs. Interestingly when all CD8 T cells are analyzed together by manual gating, we see a trend to an increase in the samples with irAEs, leading to a lower CD4:CD8 ratio in samples with irAEs.

In summary, patients with irAEs have evidence of an activated CD8 T-cell population together with Th17 and Th2 differentiation over time and an associated decrease in Tregs. No significant T cell changes were seen among patients who did not develop irAEs by OMIQ analysis. Initial data suggests that low levels of Tregs, and high levels of Th17, Th2 and CD8 Th17 at baseline predispose patients to develop irAEs.

Phillips:Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Epizyme: Consultancy; ADCT: Consultancy; Eli Lilly: Consultancy; Curis: Consultancy; TG Therapeutics: Consultancy; Beigene: Consultancy; BMS: Consultancy, Research Funding; Pharmacyclics/Janssen: Honoraria; Bayer: Consultancy, Research Funding; Celgene: Consultancy; Seattle Genetics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Xencor: Consultancy; Genmab: Consultancy; Lymphoma & Myeloma Connect: Honoraria; Kite/Gilead: Consultancy; Incyte: Consultancy; Abbvie: Consultancy, Research Funding. Zelenetz:Gilead/Kite Pharma: Consultancy, Honoraria; Pharmacyclics/Abbvie: Consultancy, Honoraria; Beigene: Consultancy, Honoraria, Research Funding; MBS: Consultancy, Honoraria; Genentech/Roche: Consultancy, Honoraria, Research Funding; Juno Pharmaceuticals: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria. Brown:Abbvie, Acerta/Astra-Zeneca, BeiGene, Bristol-Myers Squibb/Juno/Celgene, Catapult, Eli Lilly, Genentech/Roche, Hutchmed, iOnctura, Janssen, MEI Pharma, Pharmacyclics: Consultancy; BeiGene, Gilead, Loxo/Lilly, MEI Pharma, SecuraBio, Sun, TG Therapeutics: Research Funding.