Vaccinal Efficacy of Recombinant Marek's Disease Vaccine 301B/1 Expressing Chicken Interleukin-15

Marek's disease (MD) vaccine does not provide sterilizing immunity that prevents subsequent MD virus (MDV) replication and shedding in vaccinated birds. It is hypothesized that cell-mediated immunity is critical to control the virus replication in chickens because MDV exists in cell-associated forms in the host. To improve the MD vaccine efficacy, particularly cell-mediated immunity, we constructed recombinant v301B/1-IL-15, an MDV serotype 2 vaccine strain 301B/1 expressing chicken interleukin-15 (IL-15), a cytokine which promotes T-cell proliferation and enhances T-cell responses. We examined the vaccine efficacy of v301B/1-IL-15 given as a bivalent MD vaccine in combination with turkey herpesvirus (HVT) against a very virulent MDV challenge. The expression of IL-15 did not interfere with virus stability and the growth of recombinant v301B/1-IL-15. However, the protective efficacy of v301B/1-IL-15 was not significantly different from that of v301B/1, the parental virus used to construct v301B/1-IL-15. Shedding of challenge virus was slightly reduced at Day 21 (16 days postchallenge) in the v301B/1-IL-15 plus HVT vaccinated group, with no statistically significant difference to that of the v301B/1 plus HVT vaccinated group, and thymus atrophy was observed to be less severe in the v301B/1-IL-15 plus HVT vaccinated group. Overall, the protection of v301B/1-IL-15 was not differentiable from v301B/1 against very virulent MDV challenge, but there is no interference with bivalent MD vaccine efficacy.

Automated summary

The study constructed a recombinant vaccine strain expressing chicken interleukin-15 (IL-15) to enhance the efficacy of Marek's disease (MD) vaccine. Although the expression of IL-15 did not interfere with the virus stability and growth, the protective efficacy of the recombinant vaccine was not significantly different from the parental virus. When used in combination with turkey herpesvirus (HVT), the recombinant vaccine slightly reduced viral shedding and mitigated thymus atrophy.