Multidimensional Single Cell Analysis Shows Increased T/NK Cell Subsets in Both Blood and Bone Marrow of Iberdomide (CC-220) Treated Relapsed/Refractory Multiple Myeloma Patients

Background: Iberdomide (IBER), a novel cereblon (CRBN) E3 ligase modulatory compound (CELMoD), is being evaluated in a phase 1/2 clinical trial for treatment (tx) of RRMM, as a monotherapy, in combination with low-dose dexamethasone (DEX), or in combination with DEX and daratumumab, bortezomib, or carfilzomib (CC-220-MM-001; NCT02773030). IBER modulates the CRBN E3 ligase, inducing ubiquitination and proteasome-dependent degradation of Ikaros, Aiolos, and ZFP91, resulting in inhibition of myeloma-cell growth and immunomodulation.

Methods: As of June 28, 2019, 95 patients (pts) had received IBER as monotherapy or in combination with DEX at doses ranging from 0.3 to 1.3 mg taken once daily (QD) on Days 1-21 of 28-day cycles (21/28). Longitudinal immune profiling by peripheral blood (PB) flow cytometry was completed at Cycle (C) 1 Day (D) 1 and C2D15 in 90 pts dosed up to 1.3 mg. T cell and NK cell proliferation was assessed by Ki67 staining and T cell activation was assessed by HLA-DR expression. T cell differentiation was assessed using markers for CD45RA, CD45RO, and CCR7. To assess immune changes in the bone marrow (BM) microenvironment, viably frozen CD138- cells from BM aspirates were obtained from pts at screening and C2D15 (10 and 6 samples available respectively; dosed from 0.3 - 0.9 mg). Samples were analyzed using both single-cell RNA sequencing (scRNA-seq) and mass cytometry by time-of-flight (CyTOF) with a novel panel designed to identify B cells, T and NK cell (sub)populations, monocytes, dendritic cells, MDSCs and Tregs. An R based workflow using the CATALYST (Crowell et al. 2019) and Seurat package (Stuart et al. Cell 2019) was used to analyze CyTOF and scRNA-seq data, respectively.

Results: PB immune profiling of pts showed increases in total and proliferating NK cells following IBER tx across all doses (median increase = 35.5% and 74.2%, respectively). A dose-dependent increase in proliferating, activated and effector memory CD4+ (median increase = 92.3%, 45.5%, 51.7%, respectively, across all doses) and CD8+ (median increase = 116.0%, 13.9%, 45.8%, respectively, across all doses) T cells was also observed. To understand if these changes were concurrent with changes in the tumor microenvironment, a novel CyTOF panel was produced to analyze BM samples. Analogous to the PB findings, total BM NK cells increased (6.05% cells at screening vs. 9.91% at C2D15). CD16+ NK cells, known for their cytolytic activity, increased most prominently (35.9% of NK cells to 42.4%) vs. CD16- NK cells (64.1% of NK cells to 57.6%). Higher median CD16, CD56 and HLA-DR surface expression at C2D15 was also observed vs screening, demonstrating increased abundance and differentiation of NK cells. Similar to observations in the T cell compartment of PB, decreases in naïve CD4+ (24.4% to 9.09% of CD4+ cells) and CD8+ (6.42% to 2.14% of CD8+ cells) T cells and increases in effector memory CD4+ (35.8% to 40.1%) and CD8+ (26.7% to 39.5%) T cells were observed in BM. Transcriptomic data in BM showed increased expression of genes associated with cytolytic/cytotoxic activity (NKG7, GZMB, CCL3/4) and the interferon response pathway (IFNG, TNF, IFIT2/3) in CD8+ T cells, further supporting a shift towards activation in BM T cells with IBER tx. Conversely, we observed decreased expression of genes associated with a resting state (KLF2, ITGB7, CD52, S100A4) on CD4+ T cells in BM. Consistent with data from PB and of other immunomodulatory drugs, we also observed an increase in CD4+ regulatory T cells upon tx (0.72% to 5.06% of CD4+ T cells) in BM, however, the consequence of this observation in terms of response remains unclear.

Conclusions: Pharmacodynamic profiling of immune subsets in PB and BM of RRMM pts receiving IBER showed consistent changes in NK cells and T cell subsets, suggesting increased proliferation and a more activated phenotype. Ongoing analyses will address whether such patterns of immune cell responses are more pronounced at higher doses of IBER and how they may correlate with clinical outcome.

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