Key Points Ibrutinib is the first clinically viable irreversible ITK inhibitor. Ibrutinib inhibits the formation of Th2 but not Th1 immunity.

B-cell receptor (BCR) signaling is aberrantly activated in chronic lymphocytic leukemia (CLL). Bruton tyrosine kinase (BTK) is essential to BCR signaling and in IntroductionChronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia with an immunophenotype expressing the T-cell marker CD5 together with CD19, CD20, CD23, and dim-surface immunoglobulin. 1 Although immunophenotypically similar to the normal B1 lymphocytes, CLL cells have a distinct mRNA gene expression profile that most approximates a postgerminal memory B cell. 2 For many years CLL has been viewed as a nonproliferating leukemia based on the nonproliferating blood compartment; however, as with normal B cells, it has come to be recognized that CLL cell proliferation probably occurs in sites where microenvironmental stimulation occurs such as the lymph nodes and spleen. In such sites, proliferation centers are observed with a high proportion of dividing CLL cells expressing survivin that are often surrounded by either T cells or accessory stromal cells capable of providing cytokine costimulation. 3,4 Studies administering heavy water allow accurate measurement of all body compartments of CLL and assess the birth rate of CLL tumor cells in vivo. 5 These studies have demonstrated a broad range of proliferation of CLL cells that varies based on disease state and also immunoglobulin heavy chain variable (IVGH) mutational status. 5,6 In particular, a higher tumor birth rate is noted in CLL patients with IVGH unmutated disease and ZAP-70 expression. Multiple studies have documented evidence of enhanced B-cell receptor (BCR) signaling in patients with IVGH unmutated disease or those with increased ZAP-70 expression. [7][8][9] Thus, accessory cytokines, cell-cell contact in the microenvironment, and also BCR-signaling coupled to B-cell proliferation appear sentinel to CLL progression and pathogenesis.While understanding of CLL biology has improved dramatically, until very recently integration of these findings to treatment interventions has been lacking. Specifically, treatment has included alkylators, nucleoside analogs, and their combination where small advances in improved response and progression-free survival (PFS) have been noted. 10,11 However, these therapies have had very little impact on overall survival of CLL. The addition of the chimeric CD20 antibody, rituximab, perhaps represents the most significant advance in CLL therapy. Rituximab single agent activity 12 and phase 2 studies combining it with fludarabine (FR) or fludarabine and cyclophosphamide (FCR) have demonstrated improved overall survival (OS) over historical controls. 13,14 A randomized trial of FCR versus fludarabine or cyclophosphamide alone 15 demonstrated significant improvement in response; PFS and OS. While the presumptive mechanism of rituximab in CLL has been assumed to be immunologic (reviewed in Jaglowski and Byrd 16 ), a recent study demonstrated a direct effect on BCR-signaling in both normal and malignant B cells via perturbation of membrane rafts by CD20 anti...

Importance The Bruton’s Tyrosine Kinase inhibitor ibrutinib is effective in patients with chronic lymphocytic leukemia (CLL). Reasons for discontinuation from this drug and outcomes following discontinuation have not been evaluated outside of clinical trials with relatively short follow-up. Objective To determine features associated with discontinuation of ibrutinib and outcomes. Design 308 patients participating in four sequential trials of ibrutinib were included. These trials accrued patients included in this analysis from May 2010 until April 2014, and data were locked in June 2014. Setting The Ohio State University Comprehensive Cancer Center Participants Patients with CLL enrolled on 4 sequential clinical trials. Main Outcome Measure Patients were evaluated for time to discontinuation, reasons for discontinuation, and survival following discontinuation. For patients who discontinued due to progression, targeted deep sequencing was performed in samples at baseline and relapse. Results With a median follow-up of 20 months, 232 patients remain on therapy, 31 have discontinued because of progression, and 45 have discontinued for other reasons. Disease progression includes Richter’s transformation or progressive CLL. Richter’s appeared to occur early and CLL progressions later (cumulative incidence at 12 months: 4.5% (95% CI: 2.0% to 7.0%) and 0.3% (95% CI: 0% to 1.0%), respectively). Median survival following Richter’s transformation was 3.5 months (95% CI: 0.3–6.0), and 17.6 months (95% CI: 4.7-not reached) following CLL progression. Sequencing on peripheral blood from 8 patients with Richter’s transformation revealed 2 with mutations in BTK, and a lymph node sample showed no mutations in BTK or PLCγ2. Deep sequencing on 11 patients with CLL progression revealed BTK or PLCγ2 mutations in all. These mutations were not identified pre-treatment in any patient. Conclusions and Relevance This single institution experience with ibrutinib confirms it to be an effective therapy and identifies, for the first time, baseline factors associated with ibrutinib discontinuation. Outcomes data show poor prognosis after discontinuation, especially for those patients with Richter’s transformation. Finally, sequencing data confirm initial reports associating mutations in BTK and PLCγ2 with progression and clearly show that CLL progressions are associated with these mutations, while Richter’s transformation is likely not.

IntroductionChronic lymphocytic leukemia (CLL) is the most common type of adult leukemia in the United States, with approximately 15 000 new cases and approximately 4500 deaths per year. 1 CLL is characterized by a B1 monoclonal lymphocyte immunophenotype with expression of the surface antigens CD19, CD5, CD20, CD23, and dim surface immunoglobulin G. The cell of origin of CLL is uncertain, but a gene expression pattern most similar to a mature memory B cell has been hypothesized. 2 In addition, CLL cells display disrupted apoptosis that is caused by both primary tumor features and codependent stromal elements. 3 Although many patients are asymptomatic at diagnosis, CLL is a progressive disease that in most patients eventually will require treatment. Once they become symptomatic, patients have a relatively short overall survival, ranging from 18 months to 6 years, with a 22.5% 10-year survival expectation. 4 Common treatments for CLL include alkylating chemotherapeutic drugs (such as chlorambucil and cyclophosphamide), purine analogs (such as fludarabine), and rituximab (used in combination with fludarabine, fludarabine and cyclophosphamide, or pentostatin and cyclophosphamide). Newer studies with either single-agent bendamustine or alemtuzumab have been shown to have improved response and progression-free survival over alkylator-based therapy. However, no current treatment option results in curative therapy, and all patients eventually relapse. This provides strong justification for developing additional types of therapies for CLL. Of particular interest are therapies that target signal transduction pathways essential to CLL cell survival mechanisms that are known to be aberrantly activated.One such pathway is the phosphoinositide 3-kinase (PI3K) pathway. The PI3K pathway is acknowledged as a key component of cell survival in many cancers, including CLL. It is activated by receptors, or the small guanosine triphosphatase Ras, and is made up of various classes of PI3K isoforms. 5 There are 3 classes of PI3K isoforms; however, only the class I isoforms phosphorylate inositol lipids to form second messenger phosphoinositides. Specifically, class I PI3K enzymes convert PtdIns(3,4)P 2 into PtdIns(3,4,5)P 3 , in the cell membrane that recruit, via binding to the amino-terminal pleckstrin homology domain, downstream signaling proteins such as Tec kinases, phosphatidylinositol-dependent kinase, Akt, integrin-linked kinase, and Rac guanine exchange factor. Class I isoforms are made up of 2 subsets (IA and IB). Class IA encompasses p110␣, p110␤, and p110␦ (catalytic domains), bound by p85, p50, or p55 (regulatory domains). Class IB is made up solely of the p110␥ (catalytic domain) bound by the regulatory domain p101. The p110␣ and p110␤ isoforms are ubiquitously expressed, and knock-out mice for both are embryonic lethal. 6 It is thought that this widespread functionality of PI3K signaling is at An Inside Blood analysis of this article appears at the front of this issue.The publication costs of this article were defrayed ...

Therapeutic targeting of Bruton tyrosine kinase (BTK) with ibrutinib in chronic lymphocytic leukemia has led to a paradigm shift in therapy, and relapse has been uncommon with current follow-up. Acquired mutations in BTK and PLCG2 can cause relapse, but data regarding the prevalence and natural history of these mutations are limited. Patients and MethodsPatients accrued to four sequential studies of ibrutinib were included in these analyses. Deep sequencing for BTK and PLCG2 was performed retrospectively on patients who experienced relapse and prospectively on a screening population. ResultsWith a median follow-up time of 3.4 years, the estimated cumulative incidence of progression at 4 years is 19% (95% CI, 14% to 24%). Baseline karyotypic complexity, presence of del(17)(p13.1), and age less than 65 years were risk factors for progression. Among patients who experienced relapse, acquired mutations of BTK or PLCG2 were found in 85% (95% CI, 71% to 94%), and these mutations were detected an estimated median of 9.3 months (95% CI, 7.6 to 11.7 months) before relapse. Of a group of 112 patients examined prospectively, eight patients have experienced relapse, and all of these patients had acquired resistance mutations before relapse. A resistance mutation was detected in an additional eight patients who have not yet met criteria for clinical relapse. ConclusionRelapse of chronic lymphocytic leukemia after ibrutinib is an issue of increasing clinical significance. We show that mutations in BTK and PLCG2 appear early and have the potential to be used as a biomarker for future relapse, suggesting an opportunity for intervention.