CD138-targeted bispecific protein engager-armed T cells exhibit potent and selective cytotoxicity against multiple myeloma cells

Multiple myeloma (MM) is a hematologic malignancy that remains incurable, with most patients eventually relapsing or developing resistance to available therapies. Bispecific T cell engagers (BiTEs) have shown promise by redirecting T cells to target and kill tumor cells; however, their clinical application is hindered by a short in vivo half-life, the need for high dosing, and treatment-related toxicities. To address these limitations, bispecific protein engager-armed T cells (BATs) have been developed as a novel cell-based immunotherapy platform that enhances antigen specificity and in vivo persistence. In this study, we evaluated the antitumor efficacy of BATs targeting CD138, a heparan sulfate proteoglycan highly expressed on MM cells and associated with disease progression. BATs were generated by arming T cells with an anti-CD138 × anti-CD3 bispecific protein engager (BiPE), and their antitumor activity was assessed through counting bead technique and flow cytometry. CD138-specific BATs exhibited potent cytotoxicity against CD138-positive MM.1R cells, achieving up to 89.62 ± 2.22% cell lysis after 48 h of co-culture, significantly surpassing the activity of unarmed T cells (33.04 ± 6.57% lysis). Additionally, BATs induced robust expression of interleukin-2 (IL-2) cytokine and cytolytic mediators, including perforin, granzyme A/B, soluble Fas ligand (sFasL), and TNF-α, indicating effective antigen-specific activation. Importantly, pro-inflammatory cytokines such as IL-6, IL-10, and IFN-γ remained at low levels, suggesting a favorable safety profile. These findings support the therapeutic potential of CD138-targeted BATs as a promising and potentially safer cellular immunotherapy for the treatment of MM.