FCRL5 and Miyoshi myopathy: To validate the binding affinity of FCRL5 for MM cells, we conjugated an FCRL5-specific single-chain variable fragment (scFv; patent US10913796B2) with human fragment crystallizable Fc domain (hFc) to generate an FCRL5–hFC construct (Fig. 2a), which was subsequently expressed in HEK-293T cells.