IgG2a-formatted 4-1BB agonism combined with S100A9 inhibition enhances T cell activation and tumor control in a preclinical model of multiple myeloma.

backgroundImmunotherapy has emerged as a promising strategy for multiple myeloma (MM), yet relapse remains frequent due to the immunosuppressive bone marrow (BM) microenvironment, characterized by T cell dysfunction and accumulation of immunosuppressive myeloid cells. The co-stimulatory receptor 4-1BB (CD137, TNFRSF9) can enhance T and NK cell effector functions, but its therapeutic utility in MM is not well established. Tasquinimod (TQ), a clinical-stage S100A9 inhibitor, offers a complementary approach by limiting the recruitment and activity of suppressive myeloid cells.

methods4-1BB expression was assessed during disease progression in MM mice and in newly diagnosed MM patients using single-cell RNA sequencing and flow cytometry. Therapeutic potential was evaluated in 5TGM1 tumor-bearing mice treated with two 4-1BB agonists, LOB12.3 (IgG1κ) and 3H3 (IgG2a), using isotype controls. The lead agonist was subsequently combined with TQ to investigate dual targeting of the immunosuppressive tumor microenvironment. Tumor burden was quantified via BM and spleen plasmacytosis and serum M-protein levels. Immune modulation was analyzed using multi-parameter flow cytometry. Statistical significance was determined using the Mann-Whitney U test or one-way ANOVA (p < 0.05).

results4-1BB expression progressively increased on T and NK cells during tumor development in mice. In primary MM patient BM samples, ex vivo 4-1BB stimulation with urelumab enhanced effector responses, increasing IFN-γ

conclusionsThese findings establish the isotype-specific efficacy of 4-1BB agonists and support 4-1BB stimulation combined with TQ as a promising strategy to enhance durable immunotherapeutic responses in MM.