AFM26 - Targeting B Cell Maturation Antigen (BCMA) for NK Cell-Mediated Immunotherapy of Multiple Myeloma

Significant progress in multiple myeloma (MM) treatment has been made in recent years and achieving sustained minimal residual disease (MRD) negativity now constitutes a major goal of treatment. High dose melphalan combined with autologous stem cell transplantation (ASCT) is currently regarded the standard of care in 1^st line treatment of MM in eligible patients, but fails to eradicate MRD in the majority of patients ultimately leading to disease relapse. Consequently, additional therapies are needed to target residual disease to delay or potentially prevent relapse.

The cell surface antigen B cell maturation antigen (BCMA, CD269) constitutes a highly attractive target antigen for immunotherapy because of its restricted expression in non-malignant tissue but almost universal expression on MM cells.

AFM26 is a BCMA-targeted tetravalent bispecific antibody that selectively engages natural killer (NK) cells to induce myeloma cell lysis. Through its high-affinity bivalent binding to CD16A (FcγRIIIa), AFM26 possesses prolonged cell retention times, and has been shown to be less prone to interference by high levels of circulating IgG than antibody Fc-domains. Thus, AFM26 can be used to "arm" NK cells for effective killing of tumor cells. AFM26 also induces markedly lower levels of pro-inflammatory cytokines in peripheral blood mononuclear cell (PBMC) cultures in the presence of target cells compared to BCMA-directed T cell activating approaches. In contrast to other monoclonal antibodies (mAbs) such as daratumumab and elotuzumab, AFM26 does not confer target-independent NK cell activation or NK cell depletion.

NK cells are promising effectors to target MRD. Due to their early reconstitution following ASCT and their ability to rapidly destroy malignant cells through direct cytotoxicity. Redirecting NK cells through AFM26 may therefore offer an effective treatment of MM patients early after ASCT.

Employing a wide range of functional assays, we demonstrate here that AFM26 exhibits potent cytotoxic activity against primary myeloma cells using patient (autologous) and donor-derived (allogeneic) NK cells as well as against a panel of high and low BCMA expressing cell lines. In particular, we show that AFM26 induces NK cell cytotoxicity towards cells expressing almost undetectable surface levels of BCMA, suggesting the potential for broad and deep anti-MM activity. In summary, AFM26 is well-differentiated from other mAbs and a promising therapeutic candidate to address the unmet medical need of MRD positivity in MM.