{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,17]],"date-time":"2026-07-17T13:23:20Z","timestamp":1784294600657,"version":"3.55.0"},"reference-count":42,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2025,6,27]],"date-time":"2025-06-27T00:00:00Z","timestamp":1750982400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vaccines"],"abstract":"<jats:p>Background\/Objectives: A number of different vaccines against feline leukemia virus (FeLV) are available; however, there is continuous debate regarding the efficacy advantages of adjuvanted vaccines versus the potential safety advantages of non-adjuvanted vaccines. Methods: For this reason, we developed a non-adjuvanted vaccine based on a replicon RNA particle (RP) expressing the FeLV gp85 envelope protein, which possesses the safety of a non-adjuvanted vaccine while consistently providing high efficacy. Results: In two efficacy studies, a high-level of protection against virulent FeLV challenge was demonstrated with two doses given 3 weeks apart based on the prevention of FeLV p27 antigenemia. Furthermore, in both studies, we compared this novel vaccine against a non-adjuvanted, canarypox-vectored FeLV vaccine, demonstrating that none of the cats that received two doses of the RP-FeLV vaccine developed persistent antigenemia post-challenge. In comparison, of cats receiving the canarypox-vectored FeLV vaccine, three of seven (43%) became persistently antigenemic in one study, and three of ten (30%) became persistently antigenemic in the other study. In a field safety study using two commercial serials, safety of the RP-FeLV vaccine was demonstrated in over 800 cats receiving two doses of the vaccine. Conclusions: These data suggest that the RP-FeLV vaccine offers advantages over some current FeLV vaccines by combining the safety profile of a non-adjuvanted vaccine with the induction of a robust immune response demonstrated by some adjuvanted vaccines.<\/jats:p>","DOI":"10.3390\/vaccines13070697","type":"journal-article","created":{"date-parts":[[2025,7,1]],"date-time":"2025-07-01T07:42:06Z","timestamp":1751355726000},"page":"697","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["A Novel, Safe, Non-Adjuvanted Alphavirus Replicon-Based Vaccine Expressing the Feline Leukemia Virus Envelope Protein Protects Against Virulent FeLV Challenge"],"prefix":"10.3390","volume":"13","author":[{"given":"Kari","family":"Carritt","sequence":"first","affiliation":[{"name":"Research and Development Department, Merck Animal Health, Elkhorn, NE 68022, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Randall","family":"Davis","sequence":"additional","affiliation":[{"name":"Research and Development Department, Merck Animal Health, Elkhorn, NE 68022, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ken","family":"Stachura","sequence":"additional","affiliation":[{"name":"Research and Development Department, Merck Animal Health, Elkhorn, NE 68022, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Paige","family":"Crumley","sequence":"additional","affiliation":[{"name":"Research and Development Department, Merck Animal Health, Elkhorn, NE 68022, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mark","family":"Mogler","sequence":"additional","affiliation":[{"name":"Research and Development Department, Merck Animal Health, Ames, IA 50010, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Madeleine","family":"Stahl","sequence":"additional","affiliation":[{"name":"Veterinary Insights and Medical Affairs, Merck Animal Health, Rahway, NJ 07065, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lijuan","family":"Deng","sequence":"additional","affiliation":[{"name":"Global Statistics and Data Management, Merck Animal Health, Elkhorn, NE 68022, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zach","family":"Xu","sequence":"additional","affiliation":[{"name":"Research and Development Department, Merck Animal Health, Elkhorn, NE 68022, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ian","family":"Tarpey","sequence":"additional","affiliation":[{"name":"Research and Development Department, MSD Animal Health, 5831 AN Boxmeer, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,6,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"136","DOI":"10.1016\/j.tvjl.2010.04.025","article-title":"Feline Injection-Site Sarcoma: Past, Present and Future Perspectives","volume":"188","author":"Martano","year":"2011","journal-title":"Vet. 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