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Oral vaccination via virus-like particles encapsulated in Lactococcus lactis.

  • 2026-02
  • Fish & shellfish immunology 169

Study Design

Type
Clinical Trial
Population
Asian seabass (Lates calcarifer) fingerlings
Methods
NNV capsid protein was expressed in Lactococcus lactis and evaluated as a vaccine candidate; intraperitoneal injection of purified VLPs and oral vaccination with VLPs encapsulated in live, heat-inactivated, or sodium hypochlorite-inactivated L. lactis cells
  • Animal Study
Nervous necrosis virus (NNV) causes severe disease in marine fish, leading to high mortality and significant economic losses in aquaculture. Effective oral vaccines are urgently needed for large-scale, labour-efficient immunization of farmed fish. In this study, NNV capsid protein was successfully expressed in Lactococcus lactis (L. lactis) and evaluated as a vaccine candidate in Asian seabass (Lates calcarifer) fingerlings. The capsid protein assembled into virus-like particles (VLPs), structurally similar to those produced in E. coli. Intraperitoneal injection of purified VLPs elicited strong humoral immunity, with NNV-specific IgM titers four-fold higher than oral delivery, despite a tenfold lower antigen dose. However, encapsulation of VLPs in live or heat-inactivated L. lactis cells failed to induce protective immunity through oral delivery, likely due to poor antigen release. In contrast, sodium hypochlorite-inactivated L. lactis preserved VLP encapsulation, solubility and structural integrity, and oral vaccination with these cells induced approximately two-fold higher antibody and neutralizing titers than the purified VLPs. Challenge studies demonstrated a significant ∼2.5-log reduction in brain viral load 7 days post-challenge. Overall, these findings highlight hypochlorite-inactivated L. lactis as a promising oral vaccine platform, offering a sustainable strategy for aquaculture immunization against NNV.

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