Abstract: Provided are chimeric cytokine modified antibodies containing an ultralong CDR3, such as based on a bovine antibody sequence or a humanized sequence thereof, in which a portion of the CDR3 of the heavy chain is replaced by an interleukin (IL-15) or IL-2, and related antibodies. Among provided antibodies are chimeric IL-15 cytokine modified antibody molecules that are further linked or complexed with an extracellular portion of the IL15R?, such as the IL15R? sushi domain. Also provided are methods of making and using the chimeric cytokine modified antibodies.