Abstract 6744: Activating anti-MDS immunity with polarized dendritic cell vaccines

Abstract Less than 50% of patients with higher-risk myelodysplastic syndromes (MDS) show clinical response to standard-of-care hypomethylating (HMA) therapy. Significant enthusiasm existed for immunotherapy/HMA combinations for these patients, but studies have failed to deliver on the initial promise. We have demonstrated that patients with MDS have a deficiency in antigen-presenting cells, called CD141Hi dendritic cells (DC). DC-deficient MDS patients have reduced response to HMAs, worse overall survival, and show less response to cancer vaccination. We hypothesized that restoration of this population using a novel DC vaccination approach - alpha-type-1 polarized dendritic cells (αDC1) - might compensate for this deficiency and restore immunity. To generate αDC1s, we collected monocytes from MDS patients and healthy donors (HD) and cultured them for 6 days in vitro in the presence of recombinant human GM-CSF and IL-4 followed by an additional 18-24 hours in the presence of αDC1 maturation factors (poly-I:C/IFNα/IFNγ/TNFα/IL-1β). Overall, we attempted to generate αDC1s from 15 MDS samples; 13/15 exhibited intermediate to very high-risk disease and 10/15 are currently receiving HMA therapy. We successfully cultured cells from 8/15 samples (53%). Of the 8 MDS samples, 5 were collected from patients receiving HMA therapy (62.5%). We were unable to successfully culture αDC1s from the other 5 patients receiving HMA therapy, and thus the effect of HMA therapy on aDC1 generation remains unclear. To test the function of MDS αDC1s, we focused on two signals necessary to activate immune responses: 1) the expression of co-stimulatory molecules and 2) the production of IL-12p70. Flow cytometric analysis on αDC1s and immature DCs from MDS samples revealed intra-patient variation in the fold-change surface expression of CD40/80/83/86 and HLA-DR proteins. Additionally, there was a trend towards decreased up-regulation of CD80 and CD86 in MDS specimens compared to HD. To assess production of IL-12p70, we stimulated immature DCs and αDC1s with CD40L and performed ELISA analysis on the media supernatant. We found that 3 out of 4 samples could produce IL-12p70 (range 27 - 5,480 pg/ml). To date, our results suggest that generation of MDS patient-derived αDC1 cells is feasible and additional work is being performed to fully characterize their ability to activate anti-MDS immune responses. Since αDC1s have an established safety profile in patients with solid tumors, we anticipate that we will be able to rapidly translate our results to the clinic. Citation Format: Daniel Alvarado, Jennifer Peresie, Adam Brinkman, Cheryl Allen, Weijian Jiang, Pawel Kalinski, Tiffany Tanaka, Elizabeth Griffiths, Michael Nemeth. Activating anti-MDS immunity with polarized dendritic cell vaccines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6744.