IgE type multiple myeloma exhibits hypermutated phenotype and tumor reactive T cells.

Multiple myeloma (MM) is a hematological malignancy originating from malignant and clonally expanding plasma cells. MM can be molecularly stratified, and its clonal evolution deciphered based on the Ig heavy and light chains of the respective malignant plasma cell clone. Of all MM subtypes, IgE type MM accounts for only <0.1% of cases and is associated with an aggressive clinical course and consequentially dismal prognosis. In such malignancies, adoptive transfer of autologous lymphocytes specifically targeting presented (neo)epitopes encoded by either somatically mutated or specifically overexpressed genes has resulted in substantial objective clinical regressions even in relapsed/refractory disease. However, there are no data on the genetic and immunological characteristics of this rare and aggressive entity. Here, we comprehensively profiled IgE type kappa MM on a genomic and immune repertoire level by integrating DNA- and single-cell RNA sequencing and comparative profiling against non-IgE type MM samples. We demonstrate distinct pathophysiological mechanisms as well as novel opportunities for targeting IgE type MM. Our data further provides the rationale for patient-individualized neoepitope-targeting cell therapy in high tumor mutation burden MM.

Generation and Biological Evaluation of Fc Antigen Binding Fragment-Drug Conjugates as a Novel Antibody-Based Format for Targeted Drug Delivery.

Fragment crystallizable (Fc) antigen binding fragments (Fcabs) represent a novel antibody format comprising a homodimeric Fc region with an engineered antigen binding site. In contrast to their full-length antibody offspring, Fcabs combine Fc-domain-mediated and antigen binding functions at only one-third of the size. Their reduced size is accompanied by elevated tissue penetration capabilities, which is an attractive feature for the treatment of solid tumors. In the present study, we explored for the first time Fcabs as a novel scaffold for antibody-drug conjugates (ADCs). As model, various HER2-targeting Fcab variants coupled to a pH-sensitive dye were used in internalization experiments. A selective binding on HER2-expressing tumor cells and receptor-mediated endocytosis could be confirmed for selected variants, indicating that these Fcabs meet the basic prerequisite for an ADC approach. Subsequently, Fcabs were site-specifically coupled to cytotoxic monomethyl auristatin E yielding homogeneous conjugates. The conjugates retained HER2 and FcRn binding behavior of the parent Fcabs, showed a selective in vitro cell killing and conjugation site-dependent serum stability. Moreover, Fcab conjugates showed elevated penetration in a spheroid model, compared to their full-length antibody and Trastuzumab counterparts. Altogether, the presented results emphasize the potential of Fcabs as a novel scaffold for targeted drug delivery in solid cancers and pave the way for future in vivo translation.