Abstract: Replication-defective recombinant poxvirus encoding granulocyte-macrophage colony-stimulating factor (GM-CSF) are disclosed for use in enriching an immunization site with antigen-presenting cells (APC), for enhancing an immunological response to antigen or immunological epitopes by functioning as a biological adjuvant, for prevention or treatment of neutropenia, and for the treatment of myeloidysplastic syndromes. Compositions comprising a replication-defective recombinant virus encoding GM-CSF alone or in combination with a recombinant virus encoding an antigen and optionally encoding an immunostimulatory molecule are disclosed for enhancing antigen-specific immunological responses, in particular enhancing tumor antigen responses for anti-tumor therapy. Methods for enriching an immunization site with APC and for enhancing immunological responses to an antigen or immunological epitope using replication-defective recombinant poxvirus encoding GM-CSF are disclosed.