Abstract LB558: Single cell profiling of PBMCs reveals correlates of clinical response to glofitamab
Authors: Nassiri Sina , Habegger Lucas , Gerber Petra , Tosevski Vinko , Hüsser Tamara , Yanguez Emilio , Herter Sylvia , Weisser Martin , Korfi Koorosh , Umana Pablo , Piccione Emily , Bröske Ann-Marie , Bacac Marina 
Published: June 2022

Abstract
Glofitamab is a novel CD20-targeted bispecific T cell-engaging antibody that has demonstrated significant clinical efficacy in aggressive forms of Non-Hodgkin Lymphoma (aNHL). Despite significant clinical efficacy in aNHL (Hutchings et al. JCO 2021), some patients only achieve a partial response or progress upon treatment. To investigate the cellular and molecular factors that correlate with clinical activity of glofitamab, we applied CyTOF, single cell RNA and TCR sequencing to study PBMCs collected at baseline and at cycle 2 of treatment from patients with aNHL. Our cohort included 9 patients with complete response (CR) and 9 patients with progressive disease (PD) status (response assessed at cycle 3) recruited during dose escalation of glofitamab in a Ph1 clinical trial (NP30179).
We identified a higher proportion of CD4 T cells and a lower proportion of monocytes in CR versus PD patients. Complementary to changes in cell proportions, we explored the covariation of genes across single cells to isolate co-regulated processes and identified several gene expression programs associated with the response status, of which some were shared between two or more cell types while others were cell type-specific. Focusing on the T cell compartment, we further identified subtypes of CD8 and CD4 T cells enriched in either CR or PD patients, and used topic modeling, a computational approach that excels in settings of continuous phenotypes, to contrast the transcriptional state of T cells in CR patients compared to PD patients at baseline and on treatment. Interestingly, we found CR patients to exhibit a less exhausted CD8 T cell population at baseline, confirming our previous observations using tumor bulk RNA sequencing data. Moreover, we observed that hyper-expanded clonotypes were generally enriched in the CD8 T cell compartment, and that the clonal cells had a stronger cytotoxic phenotype compared to non-clonal T cells. This observation was further corroborated when looking at TCR diversity. Indeed, we observed that distinct T cell populations exhibited differences in TCR diversity, with exhausted CD8 T cells showing decreased clonal diversity. Finally, to better understand the changes in CD8 T cells, we performed trajectory inference and observed that the position of individual cells along the pseudotime varied largely according to timepoint and response status. This analysis further allowed us to identify the expression dynamic of numerous markers of T cell exhaustion, as well as transcription factors associated with progenitor and self-renewing state.
Notwithstanding the limited sample size and patient heterogeneity, our analysis provides a deep characterization of the cellular and molecular features associated with response to glofitamab using peripheral biomarkers. As glofitamab is being evaluated in a number of clinical trials either as a single agent or in combination, our dataset and findings can help broaden the understanding of its mode of action, and might be relevant for patient enrichment and monitoring response.
Citation Format: Sina Nassiri, Lucas Habegger, Petra Gerber, Vinko Tosevski, Tamara Hüsser, Emilio Yanguez, Sylvia Herter, Martin Weisser, Koorosh Korfi, Pablo Umana, Emily Piccione, Ann-Marie Bröske, Marina Bacac. Single cell profiling of PBMCs reveals correlates of clinical response to glofitamab [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB558.