MS4A3 promotes differentiation in chronic myeloid leukemia by enhancing common ß-chain cytokine receptor endocytosis.

The chronic phase of chronic myeloid leukemia (CP-CML) is characterized by the excessive production of maturating myeloid cells. As CML stem/progenitor cells (LSPCs) are poised to cycle and differentiate, LSPCs must balance conservation and differentiation to avoid exhaustion, similar to normal hematopoiesis under stress. Since BCR-ABL1 tyrosine kinase inhibitors (TKIs) eliminate differentiating cells but spare BCR-ABL1-independent LSPCs, understanding the mechanisms that regulate LSPC differentiation may inform strategies to eliminate LSPCs. Upon performing a meta-analysis of published CML transcriptomes, we discovered that low expression of the MS4A3 transmembrane protein is a universal characteristic of LSPC quiescence, BCR-ABL1 independence, and transformation to blast phase (BP). Several mechanisms are involved in suppressing MS4A3, including aberrant methylation and a MECOM-C/EBPε axis. Contrary to previous reports, we find that MS4A3 does not function as a G1/S phase inhibitor but promotes endocytosis of common ß-chain (ßc) cytokine receptors upon GM-CSF/IL-3 stimulation, enhancing downstream signaling and cellular differentiation. This suggests that LSPCs downregulate MS4A3 to evade ßc cytokine-induced differentiation and maintain a more primitive, TKI-insensitive state. Accordingly, knockdown (KD) or deletion of MS4A3/Ms4a3 promotes TKI resistance and survival of CML cells ex vivo and enhances leukemogenesis in vivo, while targeted delivery of exogenous MS4A3 protein promotes differentiation. These data support a model in which MS4A3 governs response to differentiating myeloid cytokines, providing a unifying mechanism for the differentiation block characteristic of CML quiescence and BP-CML. Promoting MS4A3 reexpression or delivery of ectopic MS4A3 may help eliminate LSPCs in vivo.

Assessment of Outcomes After Stopping Tyrosine Kinase Inhibitors Among Patients With Chronic Myeloid Leukemia: A Nonrandomized Clinical Trial.

IMPORTANCE: Tyrosine kinase inhibitors (TKIs) have been associated with improved survival of patients with chronic myeloid leukemia (CML) but are also associated with adverse effects, especially fatigue and diarrhea. Discontinuation of TKIs is safe and is associated with the successful achievement of treatment-free remission (TFR) for some patients. OBJECTIVE: To evaluate molecular recurrence (MRec) and patient-reported outcomes (PROs) after TKI discontinuation for US patients with CML. DESIGN, SETTING, AND PARTICIPANTS: The Life After Stopping TKIs (LAST) study was a prospective single-group nonrandomized clinical trial that enrolled 172 patients from 14 US academic medical centers from December 18, 2014, to December 12, 2016, with a minimum follow-up of 3 years. Participants were adults with chronic-phase CML whose disease was well controlled with imatinib, dasatinib, nilotinib, or bosutinib. Statistical analysis was performed from August 13, 2019, to March 23, 2020. INTERVENTION: Discontinuation of TKIs. MAIN OUTCOMES AND MEASURES: Molecular recurrence, defined as loss of major molecular response (BCR-ABL1 International Scale ratio >0.1%) by central laboratory testing, and PROs (Patient-Reported Outcomes Measurement Information System computerized adaptive tests) were monitored. Droplet digital polymerase chain reaction (ddPCR) was performed on samples with undetectable BCR-ABL1 by standard real-time quantitative polymerase chain reaction (RQ-PCR). RESULTS: Of 172 patients, 89 were women (51.7%), and the median age was 60 years (range, 21-86 years). Of 171 patients evaluable for molecular analysis, 112 (65.5%) stayed in major molecular response, and 104 (60.8%) achieved TFR. Undetectable BCR-ABL1 by either ddPCR or RQ-PCR at the time of TKI discontinuation (hazard ratio, 3.60; 95% CI, 1.99-6.50; P < .001) and at 3 months (hazard ratio, 5.86; 95% CI, 3.07-11.1; P < .001) was independently associated with MRec. Molecular recurrence for patients with detectable BCR-ABL1 by RQ-PCR was 50.0% (14 of 28), undetectable BCR-ABL1 by RQ-PCR but detectable by ddPCR was 64.3% (36 of 56), and undetectable BCR-ABL1 by both ddPCR and RQ-PCR was 10.3% (9 of 87) (P ≤ .001). Of the 112 patients in TFR at 12 months, 90 (80.4%) had a clinically meaningful improvement in fatigue, 39 (34.8%) had a clinically meaningful improvement in depression, 98 (87.5%) had a clinically meaningful improvement in diarrhea, 24 (21.4%) had a clinically meaningful improvement in sleep disturbance, and 5 (4.5%) had a clinically meaningful improvement in pain interference. Restarting a TKI resulted in worsening of PROs. CONCLUSIONS AND RELEVANCE: In this study, TKI discontinuation was safe, and 60.8% of patients remained in TFR. Discontinuation of TKIs was associated with improvements in PROs. These findings should assist patients and physicians in their decision-making regarding discontinuation of TKIs. Detectable BCR-ABL1 by RQ-PCR or ddPCR at the time of TKI discontinuation was associated with higher risk of MRec; clinical application of this finding should be confirmed in other studies. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02269267.

Rates of deep molecular response by digital and conventional PCR with frontline nilotinib in newly diagnosed chronic myeloid leukemia: a landmark analysis.

ENESTnext (NCT01227577) was a single-arm, multicenter trial evaluating the rate of deep molecular response by 2 years in patients with newly diagnosed (within 6 months) chronic myeloid leukemia in chronic phase (CML-CP) treated with nilotinib 300 mg twice daily. Among 128 enrolled patients, 94 (73%) achieved major molecular response (MMR; BCR-ABL1 ≤ 0.1% on the International Scale [BCR-ABL1IS]) and 34 (27%) achieved confirmed MR4.5 (BCR-ABL1IS ≤0.0032% detectable or undetectable; primary endpoint) by 2 years. Three-month BCR-ABL1 levels were predictive of later responses. In exploratory analyses, digital polymerase chain reaction (PCR) detected BCR-ABL1 in 39.4% of samples from patients with confirmed MR4.5 and identified further decreases in BCR-ABL1 with continued nilotinib. Safety results, including cardiovascular events, were consistent with those in other nilotinib trials. These results further substantiate the molecular response rates associated with frontline nilotinib therapy and demonstrate the feasibility of monitoring very low BCR-ABL1 transcript levels using digital PCR.

Development of an integrated assay for detection of BCR-ABL RNA.

BACKGROUND: Current practice guidelines for managing patients with chronic myelogenous leukemia (CML) call for monitoring BCR-ABL transcript concentrations with a quantitative reverse transcription-PCR (qRT-PCR) assay. Because the available laboratory-developed assays lack consensus on the appropriate design, reporting of results, and reference intervals, we developed and evaluated an integrated BCR-ABL assay that yields standardized results for any laboratory and can be performed by technicians with no specialized training. METHODS: We used the Cepheid Xpert BCR-ABL Monitor assay to measure both BCR-ABL and ABL (endogenous control) transcripts in blood samples from CML patients and healthy individuals. The assay involves 8 manual pipetting steps, fully automated nucleic acid purification, a nested qRT-PCR step, and data analysis. RESULTS: The BCR-ABL assay requires approximately 2 h 20 min and covers a 5-log concentration range with a lower detection limit for the BCR-ABL:ABL ratio of approximately 0.005%. Assay results were negative for 100% of the 56 known CML-negative samples (12 patients with other hematologic disorders and 44 healthy blood donors). Testing of CML-positive patients undergoing disease monitoring showed 85% agreement with negative results (17 of 20) and 100% agreement with positive results (26 of 26). An imprecision/portability study revealed no differences in performance between sites, days, instruments, and operators. CONCLUSIONS: The Xpert BCR-ABL Monitor assay provides a robust and reproducible alternative to laboratory-developed assays. Its ease of use may allow more laboratories to offer BCR-ABL testing for patients, and the short assay time enables same-day results for treating physicians.