Because BCMA is a secreted protein that has been detected in the serum of multiple myeloma patients at a median level of 17.8 ng/mL10, we assessed whether solubilized BCMA could either block FHVH CAR recognition of BCMA+ target cells or cause nonspecific activation of CAR T cells. The gene discussed is TNFRSF17; the disease is plasma cell myeloma.