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Purpose:Venetoclax-based therapy is a standard-of-care option in first-line and relapsed/refractory chronic lymphocytic leukemia (CLL). Patient management following venetoclax discontinuation remains nonstandard and poorly understood.Experimental Design:To address this, we conducted a large international study to identify a cohort of 326 patients who discontinued venetoclax and have been subsequently treated. Coprimary endpoints were overall response rate (ORR) and progression-free survival for the post-venetoclax treatments stratified by treatment type [Bruton's tyrosine kinase inhibitor (BTKi), PI3K inhibitor (PI3Ki), and cellular therapies].Results:We identified patients with CLL who discontinued venetoclax in the first-line (4%) and relapsed/refractory settings (96%). Patients received a median of three therapies prior to venetoclax; 40% were BTKi naïve (n = 130), and 81% were idelalisib naïve (n = 263). ORR to BTKi was 84% (n = 44) in BTKi-naïve patients versus 54% (n = 30) in BTKi-exposed patients. We demonstrate therapy selection following venetoclax requires prior novel agent exposure consideration and discontinuation reasons.Conclusions:For BTKi-naïve patients, selection of covalently binding BTKis results in high ORR and durable remissions. For BTKi-exposed patients, covalent BTK inhibition is not effective in the setting of BTKi resistance. PI3Kis following venetoclax do not appear to result in durable remissions. We conclude that BTKi in naïve or previously responsive patients and cellular therapies following venetoclax may be the most effective strategies.See related commentary by Rogers, p. 3501

Supplemental Figure 2: Progression free survival of patients without prior BTKi exposure who had progressed on venetoclax and were then treated with BTKi.

Supplemental Figure 1: Overall survival of entire cohort from initiation of venetoclax.

Herein, we present the long-term follow-up of the randomized E1912 trial comparing the long-term efficacy of ibrutinib–rituximab (IR) therapy to fludarabine, cyclophosphamide, and rituximab (FCR) and describe the tolerability of continuous ibrutinib. The E1912 trial enrolled 529 treatment-naïve patients aged ≤70 years with chronic lymphocytic leukemia (CLL). Patients were randomly assigned (2:1 ratio) to receive IR or 6 cycles of FCR. With a median follow-up of 5.8 years, median progression-free survival (PFS) is superior for IR (hazard ratio [HR], 0.37; P < .001). IR improved PFS relative to FCR in patients with both immunoglobulin heavy chain variable region (IGHV) gene mutated CLL (HR: 0.27; P < .001) and IGHV unmutated CLL (HR: 0.27; P < .001). Among the 354 patients randomized to IR, 214 (60.5%) currently remain on ibrutinib. Among the 138 IR-treated patients who discontinued treatment, 37 (10.5% of patients who started IR) discontinued therapy due to disease progression or death, 77 (21.9% of patients who started IR) discontinued therapy for adverse events (AEs)/complications, and 24 (6.8% of patients who started IR) withdrew for other reasons. Progression was uncommon among patients able to remain on ibrutinib. The median time from ibrutinib discontinuation to disease progression or death among those who discontinued treatment for a reason other than progression was 25 months. Sustained improvement in overall survival (OS) was observed for patients in the IR arm (HR, 0.47; P = .018). In conclusion, IR therapy offers superior PFS relative to FCR in patients with IGHV mutated or unmutated CLL, as well as superior OS. Continuous ibrutinib therapy is tolerated beyond 5 years in the majority of CLL patients. This trial was registered at www.clinicaltrials.gov as #NCT02048813.

Inhibitors of Bruton’s Tyrosine Kinase (BTKi) and phosphoinositide 3-kinase (PI3Ki) have significantly improved therapy of chronic lymphocytic leukemia (CLL). However, the emergence of resistance to BTKi has introduced an unmet therapeutic need. Here we demonstrate in vitro and in vivo the essential roles of PI3K-δ for CLL B-cell survival and migration and of PI3K-γ in T-cell migration and macrophage polarization; and more efficacious inhibition in CLL-cell burden by dual inhibition of PI3K-δ,γ. We also report an ibrutinib-resistant CLL case, whose clone exhibited BTK and PLCγ2 mutations, responded immediately to single agent duvelisib with a redistribution lymphocytosis followed by a partial clinical remission associated with subsequent modulation of T and myeloid cells. CLL samples from patients progressed on ibrutinib were also responsive to duvelisib in patient-derived xenografts irrespective of BTK mutations. Our data support dual inhibition of PI3K-δ,γ as a valuable approach for therapeutic interventions, including patients refractory to BTKi.

Clonal expansion of B cell chronic lymphocytic leukemia (B-CLL) is linked to mutagenesis and occurs within lymphoid tissues. CpG DNA (ODN-2006) and IL-15, a cytokine found within stromal cells of B-CLL-infiltrated tissues, manifest striking synergy in promoting in vitro growth of B-CLL cells (J Immunol 195:901–923, 2015). Synergy is in part explained by an ODN-induced, NF-kB (p65)-dependent elevation of IL-15Rα and IL-2/15Rβ (CD122) mRNA and protein (J Immunol 201:1570–1585, 2018). Most recently, we examined the downstream consequences of IL-15 signaling through experiments involving intracellular immunofluorescence staining, pharmacologic inhibitors, RT-PCR, and western blotting. Levels of activated pAKTSer473 and pSTAT5Tyr694 were significantly elevated soon after IL-15 exposure to ODN-primed B-CLL cells; furthermore, STAT5 remained activated throughout cycling. Pharmacologic inhibitors of PI-3K or STAT5 blocked IL-15-driven growth, indicating the functional relevance of these pathways. RT-PCR experiments +/− these inhibitors show that IL-15 signaling in B-CLL is characterized by PI-3K & STAT5-dependent rise in cyclin-D2 and repression of two important DNA damage response (DDR) mediators, ATM and TP53BP1, known to dampen growth and facilitate DNA repair. Repression of the latter two proteins was confirmed by western blotting and immunofluorescence studies. We conclude that IL-15 signaling in TLR9-primed B-CLL can provoke a rapid burst in growth via mechanisms resembling those recently described in CD8 T cells. Nonetheless, because dividing B-CLL cells additionally upregulate the mutagenic enzyme, AICDA (Blood 120: 4802–4811, 2012), these simultaneous events may augment B-CLL mutagenesis.

B-cell chronic lymphocytic leukemia (B-CLL) clones express BCR specific for microbes and/or apoptotic cells and elevated TLR-9. In patients, B-CLL clonal expansion occurs within lymphoid tissues. We recently reported that CpG DNA (ODN-2006) and IL-15, found within stromal cells of CLL-infiltrated lymphoid tissues, manifest synergy in promoting in vitro B-CLL growth (J. Immunol 195:901–923, 2015). This study explores the mechanism responsible by using purified B-CLL from peripheral blood to assess the temporal requirements for IL-15; effect of ODN on expression of IL-15 receptors (IL-15Rα and CD122 (IL-2/15Rβ)); and IL-15-induced activation of AKT and STAT5. Experiments with CFSE-labeled B-CLL show that IL-15 is critical during a 20–36 h window after ODN priming. Neutralizing mAbs to IL-15 or CD122 fully abrogate IL-15-driven growth when added during this interval. RT-PCR/immunofluorescence studies show that ODN triggers rapid increases in mRNA/protein for IL-15Rα and CD122 that are blocked by IkBα inhibitor. Furthermore, ODN-primed B-CLL exposed to IL-15 manifest elevated pAKT(Ser473) and pSTAT5(Tyr694) levels. Both PI-3K/AKT and STAT5 pathways are functionally relevant, as indicated by growth abrogation by pharmacologic inhibitors, LY294002, pimozide or STAT5 Inh II. Importantly, activated STAT5 levels are high in cycling CFSE-labeled B-CLL; furthermore, extended divisions were blocked by delayed (day 4) administration of STAT5 inhibitors or neutralizing mAbs to IL-15/CD122. Together, findings show that ODN + IL-15-driven growth represents coordinated early functions of TLR-9 and CD122 as well as later CD122 signaling during clonal expansion. This synergy may help drive in vivo growth of B-CLL clones in patients.