Session: 641. Chronic Lymphocytic Leukemias: Basic and Translational: Poster III
Hematology Disease Topics & Pathways:
Research, Lymphoid Leukemias, CLL, Translational Research, Diseases, Lymphoid Malignancies
Longitudinal analysis of the PF under IBR in 31 CLL cases, enrolled in the IOSI-EMA-001 with sequential blood samplings (156 samples, median 6 samples/case) showed a depletion of the PF over time, from 17.7% at pre-treatment to 4.75, 0.4, 1.5, 0.6, 1.5% at later timepoints (0.5, 6, 12, 18, 24 months; p < 0.001, U test), along with loss of proliferative potential by Ki67 expression.
We then retrospectively analyzed the PF in 100 IBR-treated CLL cases from the real world, referred for routine immunophenotyping (296 samples, median 3 samples/case). Median PF of pre-IBR samples was 12.0% (range 0.7-50), with a significant drop to 2.7% within one year of treatment and to 1.0% in the second year (p<0.001, U test). 77 cases discontinued IBR due to: toxicity (n=13), progression (n=51), other/death (n=13). Mutations of BTK/PLCG2 were detected in 30 cases, 28 of which discontinued IBR due to progression and 2 for other/death.
To correlate reappearance of the PF with cause of discontinuation, we focused on 64 cases collected within 12 months before/after IBR discontinuation due to toxicity (n=10), progression (n=47) or other/death (n=7), and compared with 22 samples still on treatment for the next 12 months after testing (Panel A). ROC analysis of the PF suggested a criterion of PF>3% as the most discriminating to predict IBR discontinuation due to progression, with a sensitivity of 86.7% and a specificity of 71.1%. This cut-off could separate patients with a longer time-to-progression (median 56 vs. 45 months, p=0.031). 26/47 progressing cases bore BTK/PLCG2 mutations, with a PF higher than wild-type cases discontinuing for toxicity (8.4% vs. 2.2%; p<0.001) or still on treatment (1.8%, p<0.001). Notably, the 21 BTK/PLCG2- wild-type progressing cases also showed higher PF compared to cases discontinuing for toxicity (6.9% vs. 2.2%; p<0.001) or still on treatment (1.8%; p<0.001). Notably, PF levels showed no significant correlation with white blood cell counts. Sequential dosages of plasmatic B2M in progressing cases (n=5) revealed steady levels below the 3.5 ug/mL threshold, despite the PF increase (median PF 18%).
Cell sorting of the PF/RF fractions from 10 cases showing PF reappearance after prolonged IBR treatment (median 50.7 months) revealed a mean of 1.7 BTK mutations per sample (27 total, range 1-4), a median VAF higher in the PF (23.0%, 0.3-92.3) on average 2.8 times larger than in the RF (5.2%, 0.1-84.8; p=0.003, paired rank test). A similar skewing was present for PLCG2 mutations (median PF VAF: 2.0%, 0.1-6.2; RF VAF: 1.35%, 0.4-2.8; p=0.014).
Finally, mRNA-seq was performed in 20 cases, on matching PF/RF fractions both at pre-IBR and progression (9 cases with BTK mutations). Differential expression signature of pre-IBR PF vs. RF, concordant with published gene sets, drove co-clustering of post-IBR PF/RF with their respective counterparts, indicating that PF at progression functionally resembles its pre-treatment counterpart. A strong enrichment of multiple proliferation-related signatures, present in pre-treatment samples, was significantly up-regulated also at progression, independently from BTK mutations (Panel B).
In summary, here we report that CLL progression under IBR associates with reappearance of the CD5bright/CXCR4dim PF which precedes clinical progression, increase of serum B2M and WBC counts. Transcriptomic/genetic profiling of the post-IBR PF suggests presence of clonal selection dynamics and active bypass signaling pathways, bona fide taking place within the lymph node microenvironment, including BTK/PLCG2 mutations. Clinically, longitudinal monitoring of the CXCR4/CD5 fractions by flow cytometry may provide a simple tool helping to intercept CLL progression under IBR therapy.
Disclosures: Zaja: Sobi: Honoraria, Research Funding; Grifols: Consultancy, Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Rossi: AbbVie, AstraZeneca, Gilead, BeiGene, BMS, Janssen, Lilly, Kyte: Honoraria, Research Funding.
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