Granulocyte/macrophage-colony stimulating factor produced by recombinant avian poxviruses enriches the regional lymph nodes with antigen-presenting cells and acts as an immunoadjuvant

Recombinant avian poxviruses [fowlpox and canarypox (ALVAC)], restricted fo r replication in nonarian cell substrates and expressing granulocyte/macrop hage-colony stimulating factor (avipox-GM-CSF), were evaluated for their ab ility to enrich an immunization site with antigen-presenting cells (APCs) a nd, in turn, function as biological vaccine adjuvants. Avipox-GM-CSF admini stered as a single s.c. injection significantly enhanced the percentage and absolute number of APCs in the regional lymph nodes that drain the injecti on site. Both the magnitude and duration of the cellular and phenotypic inc reases within the lymph nodes induced by the avipox-GM-CSF viruses were sig nificantly (P < 0.05) greater than those measured in mice treated with four daily injections of recombinant GM-CSF protein. Temporal studies revealed that the APC enrichment of regional lymph nodes was sustained for 21-28 day s after injection of the recombinant avipox virus expressing GM-CSF and, mo reover, three injections of the recombinant virus could be given without an y appreciable loss of in vivo bioactivity. Mice expressing human carcinoemb ryonic antigen (CEA) as a transgene (CEA.Tg) developed CEA-specific humoral and cell-mediated immunity after being immunized with avipox-CEA. The coad ministration of recombinant avipox viruses expressing CEA and GM-CSF signif icantly enhanced CEA-specific host immunity with an accompanying immunother apeutic response in tumor-bearing CEA.Tg mice. The optimal use of avipox-GM -CSF, in terms of dose and dose schedule, especially when used with differe nt immunogens, remains to be determined. Nonetheless, the present findings demonstrate: (a) the effective delivery of GM-CSF to an immunization site u sing a recombinant avian poxvirus; (b) the compatibility of delivering an a ntigen and GMCSF in replication-defective viruses to enhance antigen-specif ic immunity; and (c) the combined use of recombinant avipox viruses express ing CEA and GM-CSF to generate antitumor immunity directed at a self tumor antigen.