The present invention provides methods and compositions for treating and/or preventing a cytomegalovirus infection in a subject, comprising administering to the subject an effective amount of a cytomegalovirus interleukin-10 (IL-10) protein modified to have reduced functional activity while retaining immunogenicity. The present invention further provides nucleic acid molecules encoding a cytomegalovirus IL-10 protein or fragment thereof of this invention as well as vectors comprising such nucleic acids. Also provided herein are neutralizing antibodies that specifically bind cmvIL-10.