ALBERT

Description: Background and rationale In chronic myeloid leukemia (CML) about half of patients (pts) achieving a deep and stable molecular response (MR) with tyrosine kinase inhibitors (TKIs) may discontinue TKI treatment without disease recurrence. As such, treatment free remission (TFR) has become an ambitious goal of treatment. Given the evidence that deepness and duration of molecular response are necessary but not sufficient requisites for a successful TFR, additional biological criteria to possibly identify more and better CML patients suitable for an efficacious discontinuation are today focus of research in CML. Leukemia stem cells (LSCs) are supposed to be the reservoir of disease. We first showed in a cross-sectional study including 112 pts in TFR for a median of 31 months (mos) that residual circulating CD34+/CD38-/CD26+ CML-specific LSCs were still detectable in the majority of CML pts despite stable and deep molecular response. This evidence suggested that the level of BCR-ABL transcript only may not reflect the actual residual CML LSCs burden and that there could be a "threshold" of LSCs predicting a successful TFR. Aims To further study the behavior of residual LSCs during TKI discontinuation we designed a prospective multicentered study (AIRC IG 20133 study) in which we monitored circulating CD26+ LSCs in CML pts from the time of TKI discontinuation until molecular relapse. Methods CML pts meeting the current molecular criteria for TKI withdrawal entered this multicenter study. At TKI stop (baseline) and at +1, +2, +3, +6, + 12 mos after discontinuation and at any time if molecular relapse, CML pts were evaluated for peripheral blood number of CD34+/CD38-/CD26+ LSCs by centralized flow-cytometry analysis and for BCR-ABL transcript level by standard (IS) quantitative RT-PCR assay. Results 49 consecutive CML pts were enrolled in the study so far. Pts characteristics at diagnosis, type of TKI, disease response and treatment duration before discontinuation are shown in Tab. 1. After a median time of 7 mos since TKI stop (range 1-24), 13/49 (26.5%) pts lost their molecular response and restarted TKI treatment. Median time to relapse after discontinuation was 4 mos (range 2-7). 36/49 (73.4%) pts are still in TFR after a median time of 7.5 mos (range 1-24). If considering a cut-off of 6 mos from discontinuation as the period with higher risk of relapse, 14/36 pts actually in TFR have discontinued treatment for ≤ 6 mos (range 1-6) while 22/36 pts are in TFR for a median of 10 mos (range 7-24). Regarding residual CML LSCs evaluation, at baseline 23/49 (46%) pts had still measurable circulating CD26+LSCs with a median number of 0.0204µ/L (range 0.0077-0.1197), while 26/49 (54%) had no detectable CD26+ LCSs. Considering the small number of molecular relapses no statistical difference in number of residual CD26+ LSCs at time of discontinuation was shown between pts losing vs maintaining TFR (13 pts median CD26+ LSC 0.0237/µ/L, range 0-0.1197 and 36 pts median CD26+ LSCs 0.0204/µ/L, range 0-0.1039, respectively). However, the number of pts with undetectable CD26+ LSCs at baseline was 6/13 (45%) and 20/36 (55%) in the two subgroups, respectively. Considering subsequent time points, the 13 relapsed pts showed a small yet progressive increase of residual CD26+ LSCs number until molecular relapse, while the 36 pts in TFR showed a fluctuation of CD26+ cells number. However, Kendall rank correlation coefficient, Mood test and bi-linear relation model of the whole cohort showed no correlation between BCR-ABL/ABLIS ratio and number of residual CD26+ LSCs either at baseline or at each time points after discontinuation, thus confirming our previous observations. Conclusions Yet very preliminary our results showed that CD26+ LSCs are detectable at time of TKI discontinuation and during TFR. Moreover, at least for the observation median time of the study (7.5 mos) the persistence of "fluctuating" values of residual CD26+ LSCs do not hamper the possibility to maintain a stable TFR. Due to the short follow up and the small number of molecular relapsed pts we could not find a threshold of CD26+ LSCs predictive of TFR loss. Our data may suggest other factors then LSCs "burden" to play an active role in controlling disease recurrence. Additional studies evaluating CD26+ LSCs ability to modulate the immune system through a variable expression of immune response inhibitory molecules and through their interactions with effectors cells are ongoing. Table Disclosures Bocchia: Novartis: Honoraria; Incyte: Honoraria; BMS: Honoraria. Pregno:Bristol Myers Squibb: Honoraria; Incyte: Consultancy, Honoraria; Novartis: Honoraria; Pfizer: Honoraria. Abruzzese:Incyte: Consultancy; Novartis: Consultancy; Pfizer: Consultancy; BMS: Consultancy. Crugnola:Novartis: Honoraria; Incyte: Honoraria. Iurlo:Pfizer: Honoraria; BMS: Honoraria; Incyte: Honoraria; Novartis: Honoraria. Galimberti:Roche: Speakers Bureau; Celgene: Speakers Bureau; Novartis: Speakers Bureau. Liberati:Bristol & Mayer: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria; Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy; Amgen: Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria.

Description: Background. A Deep Molecular Response (DMR), defined as BCR-ABL1 p210 transcript at levels

Description: Background We already showed that in CML pts peripheral blood CD34+/CD38-/CD26+ cell population represent a "CML specific" leukemia stem cell (LSC) circulating compartment. Indeed, we demonstrated that CD26+LSCs are measurable by flow-cytometry in 100% of CML pts at diagnosis the latter representing an alternative and rapid diagnostic tool. In addition, in a cross-sectional study we were able to spot peripheral blood CD26+LSCs also in about 65% of CML during TKI treatment regardless of type and length of TKI treatment and degree of molecular response. However, no prospective data are available regarding the behavior of PB CD26+LSCs in terms of rate and timing of reduction during TKI therapy and the correlation, if any, with the attainment of response according to ELN guidelines. Interestingly, even CML patients in stable TFR may harbor circulating CD26+LSCs thus suggesting a probable active role of the immune system in the control of residual disease. One hypothesis could reside in the presence or absence on the LSCs of molecules (such as PD-L1) able to hamper an anti-leukemic T cell response. From Jan 2018 we conducted a prospective multicenter Italian study including CML pts at diagnosis treated and managed by each of 15 participating center according to ELN guidelines. We here present the first interim analysis after a median time of treatment of 12 mos. Aims The main goals of this study were to prospectively monitoring PB CD26+LScs in CML pts during TKI treatment and to correlate the behavior of LSCs with molecular response. In a proportion of pts PD-L1 expression on CD26+ LSCs at diagnosis was also evaluated. Methods At diagnosis and during TKI treatment, pts have been centrally evaluated in Siena lab for flow-cytometry PB CD26+ LSCs (+3, +6, +12, +18, +24 mos) and PD-L1 expression (at diagnosis). At each time point molecular BCR-ABL/ABLIS ratio was monitored locally in each center. Results 176 consecutive CML pts (IMA 92; NILO 61; DASA 23) were enrolled in the study so far (table 1). PB CD26+LSCs were measured at time 0 (baseline) in all 176 CML pts and in 165/176 (94%), 142/176 (81%) and 112/176 (71%) at +3, +6, +12 mos of TKI treatment, respectively. Median CD26+LSCs absolute number/µL at baseline was 6.96/µL (range 0.0126-64429), at +3 mos 0.0137/µL (range 0-6,49), at +6 mos 0.0056/µL (range 0-1.188), and at +12 mos 0.0112/µL (range 0-0.1824). No significant correlation between number of CD26+LSC, degree of response and BCR-ABL copies was found (Table 2). Interestingly, median CD26+LSCs at diagnosis was found significantly higher in NILO and DASA treated pts (12, 48/µL and 17,48/µL, respectively) than in IMA pts (4,58/µL). So far, 20/176 (11.4%) pts switched to different TKIs, due to failure/suboptimal response: of note, median CD26+ LSCs of this cohort at diagnosis was the highest (23.12/µL). Starting from Jun 2019, 44/176 (25%) CML pts have been evaluated also for PD-L1 expression at diagnosis: of these, 23/44 (52%) resulted PD-L1 positive and 21/44 (48%) resulted negative with a median of CD26+LSCs of 15.39/µL (range 1.28-635.5) and 4.45/µL (range 0.234-113.9), respectively. Conclusions After a sensible drop observed at 3 mos of any TKI treatment, CD26+LSCs are fluctuating and measurable at low level in most of pts (〉 65%) even at 18 and 24 mos. We confirmed no correlation between the absolute number of persisting CD26+LSCs and BCR-ABL copies. However, pts with failure or suboptimal response showed the highest level of CD26+ at diagnosis. CD26+LSCs were found PD-L1+ in about half of 44 pts tested. At diagnosis higher CD26+LSCs number, PD-L1 positivity or both may correlate with a lower probability to achieve an optimal response; interim data of this first report will be presented; enrolment and follow up are ongoing. Disclosures Bocchia: Incyte: Honoraria; CELGENE: Honoraria. Abruzzese:Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bms: Honoraria. Galimberti:Novartis: Speakers Bureau; Incyte: Honoraria. Pregno:Incyte-Italy,: Membership on an entity's Board of Directors or advisory committees, Other: conference reports; Novartis-Italy: Membership on an entity's Board of Directors or advisory committees, Other: conference reports; Pfizer-Italy: Membership on an entity's Board of Directors or advisory committees, Other: conference reports. Crugnola:BMS: Honoraria; Janssen: Honoraria; Celgene: Honoraria; Novartis: Honoraria. Liberati:MORPHOSYS: Honoraria, Research Funding; ONCONOVA: Honoraria, Research Funding; INCYTE: Honoraria; VERASTEM: Honoraria, Research Funding; ROCHE: Honoraria, Research Funding; PFIZER: Honoraria, Research Funding; ONCOPEPTIDES AB: Honoraria, Research Funding; TAKEDA: Honoraria, Research Funding; FIBROGEN: Honoraria; BIOPHARMA: Honoraria; ARCHIGEN: Honoraria; BEIGENE: Honoraria; BMS: Honoraria; AMGEN: Honoraria; CELGENE: Honoraria; JANSSEN: Honoraria; ABBVIE: Honoraria, Research Funding; NOVARTIS: Honoraria, Research Funding; KARYOPHARM: Honoraria, Research Funding.

Description: Background. New drugs with or without autologous stem cell transplantation (ASCT) can induce deep CR responses. MRD can be now considered in the response evaluation by the IMWG and many studies propose it as surrogate for survivals. Multiparametric flow cytometric assays have now been replaced by advanced assays that permit to assess simultaneously more than 8 markers in a single tube. In particular, Euro-flow consortium has developed NGF, a novel high sensitive and standardized approach for MM MRD evaluation that is based on the use of 2 single 8-color tubes, containing all the markers needed to distinguish normal vs MM PCs. However, it is necessary to work on fresh samples and to acquire 107 cell/sample, so to have the possibility to evaluate the Limit Of Quantification (LOQ) and the Limit Of Detection (LOD). The LOQ is calculated as 50 clonal plasmacells among 107 nucleated cells; the LOD as 20 clonal plasmacells among 107 nucleated cells. Aim. DART4MM is a single arm, multicenter, prospective study that evaluate Daratumumab effect on MM patients who already achieved VGPR/CR but MRD positive by NGF after a first line therapy (ASCT, VMP) (Gozzetti et al. IMW 2019). The purpose was to analyze 10.000.000 cells for MRD evaluation and reach at least 10-6 level. Patients and Methods. Next generation flow (NGF) is centralized and measured at Siena University Hospital with two 8 colors tubes panel developed by the EuroFlow Consortium (BD OneFLOW Tm PCSTe BD OneFLOW Tm PCD. BD BioSciences) with detection of MRD with a sensitivity (≥ 1 in 105 /10-6). Daratumumab 16 mg/kg administered at weekly intervals for 8 weeks, then every 2 weeks for an additional 8 weeks, will be given to 50 MM patients who achieved a VGPR or more defined as per IMWG criteria and MRD-positivity (by NGF). Daratumumab starts at least 12 weeks from ASCT and at least 4 weeks after VMP. Free light chain (FLC) and CT/PET are evaluated at time 0 and every 6 months. NGF is done on marrow aspirate at time 0, at 2 months and every 6 months for 2 years. Primary endpoint is achievement of MRD negativity at 6 months: if patients are MRD negative after 6 months of therapy, treatment is stopped. Otherwise treatment will continue every 4 weeks up to 2 years. Rapid infusion was allowed from the third dose (cycle 1, day 15) if no serious IRR was seen in the previous infusion (second). The infusion rate was calculated to deliver 20% of the dose over 30 min (200 mL/hr), and then the rate was increased to deliver the remaining 80% over 60 min (450 mL/hr). This resulted in a 90 min estimated infusion time (total volume 550 mL). Results. Recruitment started at the end of December 2018. 70 patients were screened until July 2020 at 5 centers in Italy. At least 10 million cells were analyzed for sensitivity at flow for each sample. 31/70 (44%) resulted MRD positive and eligible. M/F =15/16, median age was 61 (range 48-68).Three patients were excluded from the protocol because of consent withdraw. Previous therapy were single ASCT (21 patients), double ASCT 3 patient, VMP (3 patients), KRD (1 patient). ISS stage was I in 8 patients, II in 9 patients, and III in the other 6 patients. Cytogenetics/FISH analysis at diagnosis was done in 25/28 patients : it was negative for 17p deletion, t(14q) and 1q amplification in 16 patients, 2 had t(4;14) , 5 had t(11;14), 2 had del 17p, 1 del 13q, +11 in 2. Grade 2 reaction (moderate infusion-related reactions) during first daratumumab infusion was seen in 10/28 (35%) patients and promptly resolved with corticosteroids administration and temporary infusion interrumption. More than 200 rapid infusions were given to 16 patients. No serious adverse event was registered. 22/28 (79%) patients completed 8 weeks of treatment (2 months) and evaluated MRD. 17/28 (60%) completed 6 months of therapy. MRD negativity was reached at 6 months in 9/17patients (53%). Interestingly 9/13 (62%) patients treated previously with ASCT were MRD negative (10-6) after 6 months of Dara and stopped treatment. 12 patients reached 12 months of follow up: 2/12 patients are still MRD negative at 10-7 (6 lost MRD negativity). Conclusions. Follow up will continue with marrow evaluation for MRD every 6 months until 2 years. Having at disposition high quality BM samples for MRD evaluation can ameliorate our assays, even to 10-6 or 10-7 and it is crucial to have a good coordination between clinicians and laboratories so to improve the accuracy, sensitivity, and specificity of MM MRD detection in MM patients. Disclosures Gozzetti: Janssen: Honoraria, Research Funding; Amgen: Honoraria; Takeda: Honoraria. Liberati:INCYTE: Honoraria; VERASTEM: Honoraria, Research Funding; ROCHE: Honoraria, Research Funding; PFIZER: Honoraria, Research Funding; ONCOPEPTIDES AB: Honoraria, Research Funding; TAKEDA: Honoraria, Research Funding; MORPHOSYS: Honoraria, Research Funding; ONCONOVA: Honoraria, Research Funding; ABBVIE: Honoraria, Research Funding; NOVARTIS: Honoraria, Research Funding; KARYOPHARM: Honoraria, Research Funding; FIBROGEN: Honoraria; BIOPHARMA: Honoraria; ARCHIGEN: Honoraria; BEIGENE: Honoraria; BMS: Honoraria; AMGEN: Honoraria; CELGENE: Honoraria; JANSSEN: Honoraria. Galieni:Celgene: Honoraria; Takeda: Honoraria; AbbVie: Honoraria; Janssen: Honoraria. Bocchia:CELGENE: Honoraria; Incyte: Honoraria.