(PA-468) Nanobody-based Multifunctional Killer Engagers for Next-Gen BCMA-Directed Myeloma Therapy

Developing innovative therapies for multiple myeloma (MM) is both timely and crucial, given the persistent challenge of relapses in this incurable malignancy originating from plasma cells. Targeting B-cell maturation antigen (BCMA) with antibody-based therapies is a well-established strategy due to its selective and elevated expression on MM cells. Among recent advances, immunotherapy leveraging natural killer (NK) cells is emerging as a promising approach due to their lack of MHC restriction and lower immunogenicity. NK cells express a variety of activating receptors that can be targeted to activate cell-mediated cytotoxicity, such as CD16, NKp30, NKp44, or NKp46

Methods:

We developed a novel class of nanobody-based therapeutic molecules called Bi- and Tri-specific Killer Engagers (BiKEs and TriKEs) to harness NK cell activity against MM. Llamas were immunized with human BCMA, NKp-family cytotoxicity receptors, and human serum albumin (HSA) to generate high-affinity nanobody binders. We generated dual-nanobody BCMA-NKp30 nanobodies, and also explored triple-nanobody molecules integrating HSA-binding or IgG-like BiKE fused to a human Fc fragment (BiKE hFc), designed to enhance serum stability and effector function. Candidates were screened for antigen binding, NK cell activation, and cytotoxicity in vitro; followed by in vivo xenograft studies for anti-MM efficacy and pharmacokinetics.

Results:

All BiKE formats tested showed similar strong binding to BCMA and NK cell receptors, antigen-specific NK cell activation, and efficient tumor cell killing in vitro. In contrast, in vivo analysis revealed that molecular format significantly influenced therapeutic performance, with BiKE hFc showing much greater anti-MM effect compared to TriKE and non-Fc BiKE formats. Pharmacokinetic analysis indicated significantly higher plasma antibody concentration—approximately 200-fold greater than TriKE in mice—providing a potential mechanistic explanation of this greatly improved efficacy.

Conclusions:

This work provides strong proof of concept that BiKE hFc, among other nanobody-based formats, holds significant therapeutic potential for NK cell–based immunotherapy in MM. We are now exploring similar molecules which target alternative MM surface antigens such as TACI, FCRL5, and CD38. Future directions include manufacturing scale-up, preclinical safety/specificity evaluations, and progression toward clinical trials of BiKE hFc for the treatment of multiple myeloma.