Abstract 1894: Immunophenotypic and functional characterization of higher-risk MDS patient moDCs
Authors: Tsai Randy G. , Fields Hannah F. , Zhang Xinlian , Ferrari Valentina , Park Soo J. , Bejar Rafael , Tanaka Tiffany N. 
Published: July 2021

Abstract
Background: Myelodysplastic syndromes (MDS) are the most common acquired cause of bone marrow failure. Baseline immunity among MDS patients varies significantly with limited ability to mount a clinically significant immune response, affecting treatment and survival outcomes. Dendritic cells (DCs) can be derived from the malignant MDS clones and have compromised immune function. Here we examine the immunophenotypes and endocytic capacity of monocyte-derived DCs (moDCs) from higher-risk MDS patients.
Methods: Purified CD14+ cells were magnetically isolated from peripheral blood mononuclear cells from patients with IPSS-R Intermediate/High/Very High-risk MDS (collectively referred as higher-risk MDS) and age-matched healthy donors (n=8 and n=3, respectively). CD14+ cells were cultured in complete medium with IL-4 and GM-CSF for 6 days. Immature moDCs were then incubated with Ovalbumin-Alexa Fluor 488 conjugate (OVA), and cells from higher-risk MDS patients were also incubated with autologous tumor cell lines (TCLs) stained with a pH-sensitive red fluorescent dye (TCL-pHrodo). Phenotypic analysis was performed prior to transformation, pre- and post-incubation with OVA. Phenotypic parameters and endocytosis assays were measured by flow cytometry.
Results: Comparing CD14-CD209+ immature moDCs from higher-risk MDS patients to healthy donors, there was no significant difference in CD86 (p=0.476) and CD80 expression (p=0.190), but significantly lower CCR7 expression (p=0.010). Higher-risk MDS moDCs post-incubation with OVA also had significantly lower CCR7 expression (p=0.013) compared to donor moDCs post-incubation. Uptake of OVA was comparable in higher-risk MDS and healthy donor immature moDCs (p=0.322). However, higher-risk MDS immature moDCs had significantly decreased internalization when incubated with TCL-pHrodo compared to OVA (p&lt;0.001). TCL-pHrodo uptake varied significantly across patients (range 5-34%). When TCL-pHrodo uptake was correlated with marker expression, CD80, CD209, and CCR7 were largely uncorrelated (r&lt;0.300), and CD86 was moderately correlated (r=0.579). Multiple correlation analysis found that two-marker combinations of CD80 with CD86 and CD86 with CCR7 correlated moderately well with TCL-pHrodo uptake (r=0.698 and r=0.592, respectively).
Conclusions: Lower CCR7 expression among higher-risk MDS immature moDCs and post-incubation with OVA suggests dysfunction in the chemotactic ability of moDCs. Endocytic capacity of the autologous TCLs varies widely across MDS patients and is significantly lower than endocytic capacity for OVA, suggesting that DC and tumor micro-interactions are more complex than with an ovalbumin bead. Further studies, including whole exome and transcriptome sequencing of moDCs, may help elucidate mechanisms underlying differential endocytic capacity across MDS patients that could predict tumor sensitivity to immunotherapy.
Citation Format: Randy G. Tsai, Hannah F. Fields, Xinlian Zhang, Valentina Ferrari, Soo J. Park, Rafael Bejar, Tiffany N. Tanaka. Immunophenotypic and functional characterization of higher-risk MDS patient moDCs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1894.