Identification of Novel Immune Cell Populations in Lenalidomide Refractory Relapsed Multiple Myeloma Patients Treated with Pomalidomide and Low Dose Dexamethasone

The ALLG MM14 trial evaluated the impact of low dose dexamethasone (LoDEX) withdrawal in lenalidomide (LEN) refractory and relapsed (RR) multiple myeloma (MM) patients achieving initial disease control with pomalidomide (POM) and LoDEX re-induction. As previously reported, patients continuing with POM LoDEX had superior progression free survival (PFS) compared to maintenance with POM alone, however, this early PFS benefit was lost and by 18m was reversed to favour POM only. In patients who received post-progression therapy, more durable responses (second PFS: 12.7m vs 4.6m, p=0.034) and superior survival (OS: 19.4m vs 12.5m, p=0.092) were seen in those previously treated with POM alone. Here we present findings from the preliminary correlative immune studies of this trial. Aims To undertake mass cytometry (CyTOF) based immune profiling in patients with advanced MM receiving treatment with POM LoDEX. Methods MM14 was a multicentre, open-label, randomised phase 2 study of LEN refractory RRMM patients who had received ≥ 2 prior lines of therapy. Patients were treated with POM 4mg d1-21 (28d cycle) and LoDEX (40mg weekly). After 4 cycles (induction), patients with stable disease or better (≥SD) were randomised to receive maintenance with ongoing POM-LoDEX or POM alone. Therapy continued until toxicity/progression. PBMCs were collected at baseline and sequentially while on treatment. Cells were barcoded using the Cell-ID 20-Plex Pd barcoding kit (Fluidigm) followed by staining with sub-set/function defining antibodies (targeting myeloid, B, T and NK cells: CD16, CD24, CD11c, CD45RO, CD314, CD38, CD336, HLA-DR, CD14, CD56, CD158a, CD27, CD28, CD159a, CD8, CD19, CD45RA, CD11b, CD4, IgD, CD335, FOXP3, CD25, CD66b, CD3, CD337, CD20, CD158b, CD127 CD57, CD197, CD194, CD304 and CD279). Samples were acquired on the Helios instrument. Data were clustered in the VORTEX package. Significant differences in cluster frequency were assessed by Mann-Whitney test for statistical significance. Cluster phenotypes were determined and validated via multiple visualisation approaches. CD3-CD19-CD56+ NK cells were pre-gated from patient datasets. We then performed Boolean gating using seven NK cell activation/inhibitory markers - CD158a, CD158b, CD159a, CD314, CD335, CD336 and CD337. Boolean populations that comprised 3% or greater of the total NK cell population (median) were then compared. A Mann-Whitney test was used to determine statistical significance. Results 154 patients from 11 Australian sites were enrolled. The median number of prior treatment lines was 4.5, 82.5% were double refractory. 78 patients who achieved ≥SD were randomised to maintenance: POM n = 40, Pom LoDEX n = 38. CD336+CD20+ cells ("NK-B-cells") were identified in the pre-induction samples of all patients and were significantly more frequent in responders (median 2% of total cells) than in non-responders (0.8% of total cells, p Conclusion Utilising CyToF, we have identified a novel "NK B cell" population in RRMM patients, with a higher baseline frequency of these cells being associated with a greater likelihood of response to POM LoDEX. Importantly, we have also confirmed the presence of these cells in an independent MM cohort. Moreover, subsequent to POM LoDEX exposure we have demonstrated the enrichment of heterogeneous neutrophil populations as well as an increase in activated NK cells and commensurate decrease in inhibited NK cells. These novel observations may provide new insights into the mechanisms of action of pomalidomide in MM. Disclosures Kalff: Amgen: Honoraria; Celgene: Honoraria; pfizer: Honoraria. Khong:Novartis Oncology: Research Funding. Reynolds:Alfred Health: Employment, Other: Biostatistician for trials funded by the Australian government and Abbvie, Amgen, Celgene, GSK, Janssen-Cilag, Merck, Novartis, Takeda, but sponsored by Alfred Health.; AUSTRALASIAN LEUKAEMIA & LYMPHOMA GROUP (ALLG): Consultancy; Novartis AG: Equity Ownership; Novartis Australia: Honoraria. Quach:GSK: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees. Ho:Novartis: Other: Trial Investigator meeting travel costs; La Jolla: Other: Trial Investigator meeting travel costs; Celgene: Other: Trial Investigator meeting travel costs; Janssen: Other: Trial Investigator meeting travel costs. Mollee:Janssen: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Amgen: Consultancy, Honoraria. Spencer:Takeda: Other: Consulting/advisory role, Research Funding; Janssen Oncology: Other: Consulting/advisory role, Research Funding, Speakers Bureau; Amgen: Other: Consulting/advisory role, Research Funding; AbbVie: Other: Consulting/advisory role, Research Funding; Servier: Other: Consulting/advisory role; Secura Bio: Other: Consulting/advisory role; Haemalogix: Other: Consulting/advisory role; Celgene: Other: Consulting/advisory role, Research Funding, Speakers Bureau; Sanofi: Other: Consulting/advisory role; Specialised Therapeutics Australia: Consultancy, Honoraria.