CD19 and plasma cell myeloma: Focusing on multiple myeloma (MM) patients, infections, in general, and COVID-19, in particular, pose a major threat due to plasma-cell-dysfunction-related immunodeficiency, based on suppression of CD19+ B lymphocytes, lower levels of polyclonal immunoglobulins, and both quantitative and functional T-cell abnormalities [7,8,9,10,11].