Targeting METTL3/m6A/SOCS3 axis reprograms tumor-associated macrophage polarization to potentiate the efficacy of anti-PD-1 therapy in multiple myeloma.

Abstract

Background: This study investigated the immunomodulatory roles of suppressor of cytokine signaling 3 (SOCS3) in macrophage polarization and cytotoxic T-cell activation within the tumor microenvironment (TME) of multiple myeloma (MM).

Methods: SOCS3 expression was evaluated in clinical MM specimens and healthy controls. Gain- and loss-of-function assays and a MM cell-macrophage co-culture system were designed to elucidate the effects of SOCS3 on MM cell malignant progression and macrophage polarization. Mechanistic investigations focused on methyltransferase-like 3 (METTL3)-mediated N⁶-methyladenosine (m6A) modulation of SOCS3 and regulation of the Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway. Additionally, the antitumor efficacy of combined SOCS3 overexpression and anti-programmed cell death protein 1 (anti-PD-1) therapy was evaluated in a syngeneic subcutaneous tumor mouse model.

Results: SOCS3 was downregulated in clinical MM samples and cell lines, a silencing mechanism driven by METTL3-mediated m6A modification. SOCS3 overexpression inhibited MM cell proliferation and migration while inducing apoptosis. Co-culture with SOCS3-overexpressing MM cells promoted M1-like macrophage polarization, accompanied by suppression of the JAK2/STAT3 signaling pathway. Conversely, SOCS3 silencing promoted malignant behaviors in MM cells and inhibited the M1-like macrophage phenotype. Furthermore, METTL3 silencing exerted tumor-suppressive and immunomodulatory effects similar to those of SOCS3 overexpression, which were reversed by SOCS3 knockdown. In vivo, SOCS3 overexpression potentiated the antitumor efficacy of anti-PD-1 therapy by driving M1-like macrophage polarization and CD8⁺ T-cell activation.

Conclusion: SOCS3 exerts dual antitumor efficacy in MM by suppressing malignant tumor progression and reprogramming the TME toward M1-like macrophage polarization and CD8⁺ T-cell activation. Combining SOCS3 restoration with anti-PD-1 therapy provides a preclinical proof-of-concept for potential combinatorial strategies to enhance immune responses in MM.