The Perennial Use of the Green Fluorescent Protein Marker in a Live Vaccinia Virus Ankara Recombinant Platform Shows No Acute Adverse Effects in Mice.

Recombinant virus vectors represent a promising strategy for vaccine research. Among available viral vectors, members of the Poxviridae family-especially the modified Vaccinia virus Ankara (MVA)-stand out as immunogenic and safe vaccine platforms. Because MVA usually does not produce plaques in cell culture, visible selection markers such as the green fluorescent protein (GFP) are frequently incorporated into the constructions in order to facilitate the recognition of recombinants. However, these genetic markers have to be removed before any clinical trial. Here, we evaluated the acute responses generated in mice immunized with a MVA vector in which the GFP marker was not removed. We observed no differences in neutrophil, monocyte, or total leucocyte recruitment among animals inoculated with MVA or MVA-GFP. Likewise, there were no differences in neutrophil activation between mice groups. Hepatic functions were not altered in either MVA or MVA-GFP-inoculated mice, and we observed no histopathological alterations in different tissues from virus-inoculated animals. In conclusion, the presence of GFP is innocuous to immunized animals and do not alter acute physiopathological responses to the MVA vector. We suggest that keeping the GFP marker may be a good strategy for vaccine development, production, and evaluation.