Fig. S16. Effect of anti-HLA antibody on the generation of apoptotic MM cells after treatment with HDCA6 inhibitors and co-culture with autologous T-cells. MM patient CD138+ cells (20,000/ sample) were treated with each HDAC6 inhibitor (1 uM) for 24 h followed by incubated with 0.5 ug/mL mouse anti-HLA ABC antibody W6/32 (catalog number 14-9983-82, Fisher Scientific, Pittsburgh, PA) followed by co-culture with T-cells (E:T 2:1). The percent of apoptotic cells was quantitated by flow cytometry. Values represent the average of triplicate measurements. Error bars represent the SD of the mean.
ARTICLE ABSTRACT
Proteasomes degrade intracellular proteins to generate antigenic peptides that are recognized by the adaptive immune system and promote anticancer immunity. However, tumors subvert the antigen presentation machinery to escape immunosurveillance. We hypothesized that proteasome activation could concomitantly increase antigen abundance and diversity in multiple myeloma cells. High-throughput screens revealed that histone deacetylase 6 (HDAC6) inhibitors activated proteasomes to unmask neoantigens and amplify the tumor-specific antigenic landscape. Treatment of patient CD138+ cells with HDAC6 inhibitors significantly promoted the antimyeloma activity of autologous CD8+ T cells. Pharmacologic blockade and genetic ablation of the HDAC6 ubiquitin-binding domain released HR23B, which shuttles ubiquitinylated cargo to proteasomes, while silencing HDAC6 or HR23B in multiple myeloma cells abolished the effect of HDAC6 inhibitors on proteasomes, antigen presentation, and T-cell cytotoxicity. Taken together, our results demonstrate the paradigm-shifting translational impact of proteasome activators to expand the myeloma immunopeptidome and have revealed novel, actionable antigenic targets for T cell–directed immunotherapy.
The elimination of therapy-resistant tumor cells remains a major challenge in the treatment of multiple myeloma. Our study identifies and functionally validates agents that amplify MHC class I–presented antigens and pave the way for the development of proteasome activators as immune adjuvants to enhance immunotherapeutic responses in patients with multiple myeloma.
