Huipin Yuan

Multiple myeloma (MM) is a plasma cell malignancy that disrupts bone homeostasis by suppressing osteogenesis and promoting osteoclast activity. While most therapeutic interventions to date have focused on targeting tumor cells and reducing osteolysis, we investigate whether osteoinductive strategies can restore bone formation and counteract disease progression. Using a human bone marrow-like scaffold model that enables direct in vivo evaluation of tumor–stroma interactions and human bone formation, we demonstrate that MM-derived mesenchymal stromal cells (MSCs) retain osteogenic potential but are functionally suppressed by MM cells. Transcriptomic profiling of MM-primed MSCs revealed the downregulation of small leucine-rich proteoglycans (SLRPs), ASPN, OGN, and OMD, key mediators of bone morphogenetic protein (BMP) signaling, which governs osteoblast differentiation. Among the BMPs analyzed, BMP6 emerged as a potent inducer of osteogenesis and regulator of the expression of these SLRPs. Notably, BMP6 selectively promoted bone formation without enhancing osteoclastogenesis and attenuated inflammatory and tumor-supportive MSC phenotypes. BMP6 also directly inhibited MM cell proliferation and suppressed IL6-induced growth. These findings highlight BMP6 as a distinct multifunctional regulator warranting further investigation as a potential therapeutic approach, while establishing the humanized model as a valuable platform for dissecting tumor–bone interactions in MM.

Supplementary Table containing nucleotide sequences used in CAR designs

Osteoclastogenesis in vitro and ectopic bone formation reflect regenerative potential in maxillary sinus lift, serving as predictive indicators of biomaterials for clinical bone regeneration.

Supplementary Table containing nucleotide sequences used in CAR designs

Purpose: The success of BCMA-specific chimeric antigen receptor (CAR) T-cells illustrates the potential of this novel therapy for multiple myeloma (MM). Nonetheless, broadening CAR T-cell therapy beyond BCMA requires inventive strategies as there are only a few MM- or plasma cell-specific target antigens. We investigated the feasibility of achieving MM specificity by dual-split CD38/CD138 CAR targeting, whereby the stimulatory and costimulatory signals for T-cell activation are split into two separate stimulatory (sCAR) and costimulatory CARs (cCAR). Experimental Design: Using various combinations of CD38 and CD138 sCARs and cCARs with different affinities, we generated several dual-split CAR T-cells and analyzed them for MM-specific effector functions in vitro. The best-functioning CAR T-cells were tested in vivo in a murine xenograft model. Results: We found optimal designs of both CD38sCAR/CD138cCAR and CD138sCAR/CD38cCAR combinations, that effectively lysed MM cells, but spared single CD38 or CD138 positive healthy hematopoietic cells. While the CD38sCAR/CD138cCAR T-cells achieved MM-specific activity solely due to the low affinity of the CD38sCARs, the MM-specific cytotoxicity, cytokine release, and proliferation of CD138sCAR/CD38cCAR T‑cells were established through a true combinatorial stimulatory and costimulatory effect. The most optimal combination comprised a low affinity CD138sCAR combined with a high affinity CD38cCAR. These CD138sCAR/CD38cCAR T-cells also showed dual-antigen specific anti-MM effects in vivo. Importantly, they were also effective against MM cells from daratumumab pre-treated patients with decreased CD38 expression levels. Conclusions: We demonstrate the possibility to specifically target MM cells, even after CD38 targeted therapy, with carefully-designed dual-split CARs directed against CD38 and CD138.

Supplementary Table containing nucleotide sequences used in CAR designs