Single-cell RNA sequencing informs enhanced antitumor immunity after brentuximab vedotin and combination strategy in mycosis fungoide

Summary: Abstract Body: Mycosis fungoides with large-cell transformation (MF-LCT) has a poor prognosis and lacks effective therapies. Brentuximab vedotin (BV), an antigen-drug conjugate targeting CD30+ cells, is approved for CD30+ MF after prior systemic therapy. However, many patients suffer progression and resistance. We applied single-cell RNA and TCR sequencing on 13 paired samples from BV-treated MF-LCT patients to uncover the underlying mechanism. Post BV, tumor improved remarkably while the CD30+ cell fractions remained invariable, confirming its bystander effect on CD30- cells. Notably, BV might have similar yet different impacts on CD30+ and CD30- cells. Genes related to mTOR signaling and inflammatory response were enriched in CD30+ tumor cells after BV, mainly driven by autocrine IL4 and IL13. The alterations in CD30- tumor cells were chiefly ascribed to IFNγ and IFNα ligands. Beyond its toxicity, BV exerted a multifaceted boost on the antitumor immunity. The antigen-presenting mediated by MHC-II molecules in tumor cells and by dendritic cells (DCs), especially mregDC derived from classic DCs, was enhanced. This led to a stronger recruitment of NK and CD8+ T cells, which were less exhausted. Moreover, the inhibitory signals from Tregs (e.g. CTLA4) to effector cells were reversed, and the dominant phenotype of macrophages shifted towards M1 type. Additionally, three non-responsive lesions were included. They showed higher malignant signature of tumor cells, sparse immune cell infiltration, and impaired response to comparable IFNγ level. Their resistance to BV might stem from defective clathrin-mediated endocytosis caused by decreased AP2 subunits, increased drug efflux mediated by MDR1, and anti-apoptosis effect due to increased BCL2. Combining BV with BCL2 inhibitor, venetoclax, showed promising synergistic effect in CD30+ cutaneous T cell lymphoma cell lines. These findings highlight the comprehensively enhanced antitumor immunity after BV beyond its cytotoxicity and inspires potential combination with venetoclax to overcome the drug resistance. Yi Jiang¹, Mingjia Li¹, Yang Wang¹ 1. Dermatology and Venereology, Peking University First Hospital, Beijing, China. Bioinformatics, Computational Biology, and Imaging