After the original description of CD19low and CD19high BMPC7, came studies showing that CD19low BMPC are refractory to B-cell depletion by rituximab28, secrete antibodies against unique childhood experiences like measles and mumps, and are resistant to CD19-specific CAR T cells48, defining CD19low BMPC as long-lived49. The gene discussed is CD19; the disease is mumps infectious disease.