Ding, Li

Abstract Multiple myeloma is a malignancy of clonally expanded plasma cells shaped by complex interactions with the immune microenvironment (IME). To investigate immune correlates of treatment response and disease progression, we conducted multi-omics profiling including CD138neg single-cell RNA sequencing of 243 bone marrow samples from 102 patients (631,226 cells) and CD138pos bulk RNA and whole-genome sequencing from 209 samples. In longitudinal analyses, interferon-γ signaling associated with markers of impaired T-cell memory after autologous stem cell transplant, whereas naïve B-cell abundance and immunoglobulin diversity correlated with improved progression-free survival (HR = 0.48; P = 2.3e−4). At disease progression, multiple myeloma cells upregulated cancer–testis antigens (CTAg) and immune effector genes, with concurrent B-cell depletion, enrichment of myeloid-derived suppressor cell expression, and phenotypic T-cell exhaustion. These findings highlight dynamic immune–tumor interactions, identifying naïve B-cell reconstitution as a biomarker of durable response and CTAgs as potential targets for high-risk disease at progression. Significance: Longitudinal profiling of multiple myeloma and the IME revealed dynamic immune–tumor interactions across the disease course. Altered expression in CD8+ T cells limited memory phenotype after transplant, whereas naïve B-cell recovery associated with sustained treatment response. At progression, CTAg expression associated with immunosuppression, revealing novel mechanisms of immune dysregulation.

As part of the Multiple Myeloma Research Foundation (MMRF) immune atlas pilot project, we compared immune cells of multiple myeloma bone marrow samples from 18 patients assessed by single-cell RNA sequencing (scRNA-seq), mass cytometry (CyTOF), and cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) to understand the concordance of measurements among single-cell techniques. Cell type abundances are relatively consistent across the three approaches, while variations are observed in T cells, macrophages, and monocytes. Concordance and correlation analysis of cell type marker gene expression across different modalities highlighted the importance of choosing cell type marker genes best suited to particular modalities. By integrating data from these three assays, we found International Staging System stage 3 patients exhibited decreased CD4+ T/CD8+ T cells ratio. Moreover, we observed upregulation of RAC2 and PSMB9, in natural killer cells of fast progressors compared with those of nonprogressors, as revealed by both scRNA-seq and CITE-seq RNA measurement. This detailed examination of the immune microenvironment in multiple myeloma using multiple single-cell technologies revealed markers associated with multiple myeloma rapid progression which will be further characterized by the full-scale immune atlas project. Significance: scRNA-seq, CyTOF, and CITE-seq are increasingly used for evaluating cellular heterogeneity. Understanding their concordances is of great interest. To date, this study is the most comprehensive examination of the measurement of the immune microenvironment in multiple myeloma using the three techniques. Moreover, we identified markers predicted to be significantly associated with multiple myeloma rapid progression.

e20626 Background: It is important to increase our understanding of recruitment barriers in the elderly population to improve their participation in clinical trials. The primary objective of this study was to describe the demographics, treatment, toxicity, and overall survival (OS) of all patients ≥ 65 years who presented to the Phase I clinical trials service at KCI between 1995–2005. Methods: Patient demographics, co-morbidities, tumor type, reason not enrolled on a Phase 1 clinical trial, toxicities, and OS were obtained by retrospective chart reviews. The patients were divided into 3 mutually exclusive groups: patients considered but not enrolled (PC), enrolled but not treated (PE), and treated (PT). OS was compared across these three groups. Results: 216 patients met the study criteria. Of these, there were 114 PC, 7 PE, and 95 PT. Lack of enrollment was due to ineligibility (30%), loss to follow-up (12%), refusal (8%), or no trial available (2%). Median age was 71 years, 63% were males and 87% were Caucasian. 59% had performance status (PS) 1; 16% had PS 2. 66% of patients had a history of cardiovascular disease but renal, liver, hematological diseases were found in less than 7% of patients at baseline. Colorectal (27%), lung (15%) and prostate (8%) were the 3 most common cancers. 54% received a cytotoxic agent, 62% a biologic agent, and 17% combination therapy. The 3 most common Grade 3–4 toxicities were: 15% leucopenia, 11% electrolyte abnormalities, and 4% anemia. The median OS for PC, PE, and PT was 3.9 mos, 2.2 mos, and 8.4 mos, respectively (p < 0.001 between any pair). However, PS 0–1 patients comprised 47%, 75%, and 73% of those 3 patient subgroups, respectively. Conclusions: More than half of the elderly patients initially considered for Phase 1 clinical trials at KCI were not enrolled due to ineligibility, refusal, or lost to follow up. Phase I chemotherapy appears feasible in patients age ≥ 65 years old. OS was significantly longer for patients treated on Phase I trials compared to those who were not, although that may be confounded by PS differences. More detailed OS comparisons will be presented. No significant financial relationships to disclose.