BYSL and Burkitt lymphoma: ELISA with recombinant BYSL and SUMOylated BYSL or HSP40, and acetylated HSP40 expressed with a C‐terminal FLAG‐tag in HEK293, confirmed SUMOylated BYSL and acetylated HSP40 as target antigens of BL‐derived Fabs (Figure 1) and antibodies from sera of patients with BL.