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Vaccines
Volume 13
Issue 7
10.3390/vaccines13070697
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Article

A Novel, Safe, Non-Adjuvanted Alphavirus Replicon-Based Vaccine Expressing the Feline Leukemia Virus Envelope Protein Protects Against Virulent FeLV Challenge

by
Kari Carritt
1,
Randall Davis
1,*,
Ken Stachura
1,
Paige Crumley
1,
Mark Mogler
2,
Madeleine Stahl
3,
Lijuan Deng
4,
Zach Xu
1 and
Ian Tarpey
5
1
Research and Development Department, Merck Animal Health, Elkhorn, NE 68022, USA
2
Research and Development Department, Merck Animal Health, Ames, IA 50010, USA
3
Veterinary Insights and Medical Affairs, Merck Animal Health, Rahway, NJ 07065, USA
4
Global Statistics and Data Management, Merck Animal Health, Elkhorn, NE 68022, USA
5
Research and Development Department, MSD Animal Health, 5831 AN Boxmeer, The Netherlands
*
Author to whom correspondence should be addressed.
Vaccines 2025, 13(7), 697; https://doi.org/10.3390/vaccines13070697 (registering DOI)
Submission received: 15 May 2025 / Revised: 18 June 2025 / Accepted: 24 June 2025 / Published: 27 June 2025
(This article belongs to the Section Veterinary Vaccines)
Versions Notes

Abstract

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.
Keywords: feline leukemia virus; RNA particle; envelope protein; vaccine; efficacy; safety feline leukemia virus; RNA particle; envelope protein; vaccine; efficacy; safety

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MDPI and ACS Style

Carritt, K.; Davis, R.; Stachura, K.; Crumley, P.; Mogler, M.; Stahl, M.; Deng, L.; Xu, Z.; Tarpey, I. A Novel, Safe, Non-Adjuvanted Alphavirus Replicon-Based Vaccine Expressing the Feline Leukemia Virus Envelope Protein Protects Against Virulent FeLV Challenge. Vaccines 2025, 13, 697. https://doi.org/10.3390/vaccines13070697

AMA Style

Carritt K, Davis R, Stachura K, Crumley P, Mogler M, Stahl M, Deng L, Xu Z, Tarpey I. A Novel, Safe, Non-Adjuvanted Alphavirus Replicon-Based Vaccine Expressing the Feline Leukemia Virus Envelope Protein Protects Against Virulent FeLV Challenge. Vaccines. 2025; 13(7):697. https://doi.org/10.3390/vaccines13070697

Chicago/Turabian Style

Carritt, Kari, Randall Davis, Ken Stachura, Paige Crumley, Mark Mogler, Madeleine Stahl, Lijuan Deng, Zach Xu, and Ian Tarpey. 2025. "A Novel, Safe, Non-Adjuvanted Alphavirus Replicon-Based Vaccine Expressing the Feline Leukemia Virus Envelope Protein Protects Against Virulent FeLV Challenge" Vaccines 13, no. 7: 697. https://doi.org/10.3390/vaccines13070697

APA Style

Carritt, K., Davis, R., Stachura, K., Crumley, P., Mogler, M., Stahl, M., Deng, L., Xu, Z., & Tarpey, I. (2025). A Novel, Safe, Non-Adjuvanted Alphavirus Replicon-Based Vaccine Expressing the Feline Leukemia Virus Envelope Protein Protects Against Virulent FeLV Challenge. Vaccines, 13(7), 697. https://doi.org/10.3390/vaccines13070697

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