Vaccinal efficacy of recombinant Marek’s disease vaccine 301B/1 expressing chicken interleukin-15

Authors: Kim, Taejoong; Hearn, Cari

Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2022
Publication Date: 3/1/2022
Citation: Kim, T.N., Hearn, C.J. 2022. Vaccinal efficacy of recombinant Marek’s disease vaccine 301B/1 expressing chicken interleukin-15. Avian Diseases. 66(1):79-84. https://doi.org/10.1637/21-00089.
DOI: https://doi.org/10.1637/21-00089

Interpretive Summary: Marek’s disease (MD) is an important poultry disease causing mortality, immunosuppression, and poor performance. The avian alphaherpes virus, Marek’s disease virus (MDV) is the etiological agent of the disease and is ubiquitous in poultry farms, allowing it to establish infection at the day of hatch. MD vaccine does not completely prevent MDV replication and shedding in the vaccinated birds, because MDV exists in cell-associated forms in the host. To improve the MD vaccine efficacy, we constructed recombinant MD vaccine strain 301B/1 that expresses interleukin-15 (IL-15), a cytokine which promotes T cell proliferation and enhance 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 very virulent MDV challenge. The expression of IL-15 did not interfere with virus stability or 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 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 no side effects were observed from the expression of IL-15 on vaccine efficacy.

Technical Abstract: 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.