Transfected Leishmania expressing biologically active IFN-gamma

Area of Science:

• Immunology
• Parasitology
• Molecular Biology

Background:

• Susceptible BALB/c mice infected with Leishmania major exhibit progressive disease due to impaired Th1 CD4+ T cell responses and insufficient interferon-gamma (IFN-γ) production.
• IFN-γ is a critical cytokine for controlling Leishmania infection.

Purpose of the Study:

• To investigate whether introducing the murine IFN-γ gene into Leishmania major could enhance the immune response and control disease progression in infected mice.

Main Methods:

• Engineered Leishmania major parasites to express the murine IFN-γ gene using a drug-selectable plasmid.
• Confirmed IFN-γ gene expression, RNA splicing, and secretion of biologically active IFN-γ by engineered parasites in vitro.
• Infected nude mice and susceptible BALB/c mice with engineered or control parasites and monitored disease progression and immune cell responses.

Main Results:

• Engineered Leishmania major secreted biologically active IFN-γ, which slowed disease progression in nude mice.
• In susceptible BALB/c mice, IFN-γ delivery did not prevent Th2 cell expansion or disease progression, despite increased IFN-γ transcription in vivo.
• Macrophages and CD4+ lymphocytes in BALB/c mice did not show expected IFN-γ-induced activation markers in vivo.
• Engineered parasites remained stable and continued secreting IFN-γ in infected tissues.

Conclusions:

• While targeted IFN-γ delivery can slow disease in some models, it is insufficient to overcome the Th2-biased immune response in genetically susceptible mice.
• IFN-γ alone is not enough to impede Th2 cell activation and maturation in the context of Leishmania major infection in susceptible BALB/c mice.