CD4(+) T cells induced by a DNA vaccine: immunological consequences of epitope-specific lysosomal targeting

J Virol. 2001 Nov;75(21):10421-30. doi: 10.1128/JVI.75.21.10421-10430.2001.

Abstract

Our previous studies have shown that targeting DNA vaccine-encoded major histocompatibility complex class I epitopes to the proteasome enhanced CD8(+) T-cell induction and protection against lymphocytic choriomeningitis virus (LCMV) challenge. Here, we expand these studies to evaluate CD4(+) T-cell responses induced by DNA immunization and describe a system for targeting proteins and minigenes to lysosomes. Full-length proteins can be targeted to the lysosomal compartment by covalent attachment to the 20-amino-acid C-terminal tail of lysosomal integral membrane protein-II (LIMP-II). Using minigenes encoding defined T-helper epitopes from lymphocytic choriomeningitis virus, we show that the CD4(+) T-cell response induced by the NP(309-328) epitope of LCMV was greatly enhanced by addition of the LIMP-II tail. However, the immunological consequence of lysosomal targeting is not invariably positive; the CD4(+) T-cell response induced by the GP(61-80) epitope was almost abolished when attached to the LIMP-II tail. We identify the mechanism which underlies this marked difference in outcome. The GP(61-80) epitope is highly susceptible to cleavage by cathepsin D, an aspartic endopeptidase found almost exclusively in lysosomes. We show, using mass spectrometry, that the GP(61-80) peptide is cleaved between residues F(74) and K(75) and that this destroys its ability to stimulate virus-specific CD4(+) T cells. Thus, the immunological result of lysosomal targeting varies, depending upon the primary sequence of the encoded antigen. We analyze the effects of CD4(+) T-cell priming on the virus-specific antibody and CD8(+) T-cell responses which are mounted after virus infection and show that neither response appears to be accelerated or enhanced. Finally, we evaluate the protective benefits of CD4(+) T-cell vaccination in the LCMV model system; in contrast to DNA vaccine-induced CD8(+) T cells, which can confer solid protection against LCMV challenge, DNA vaccine-mediated priming of CD4(+) T cells does not appear to enhance the vaccinee's ability to combat viral challenge.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antibodies, Viral / blood
  • CD36 Antigens / physiology
  • CD4-Positive T-Lymphocytes / immunology*
  • Cathepsin D / metabolism
  • Cell Line
  • Epitopes
  • Lymphocytic choriomeningitis virus / immunology*
  • Lysosome-Associated Membrane Glycoproteins
  • Lysosomes / metabolism*
  • Membrane Glycoproteins*
  • Mice
  • Mice, Inbred C57BL
  • Molecular Sequence Data
  • Peptide Fragments / immunology
  • Vaccines, DNA / immunology*
  • Viral Vaccines / immunology*

Substances

  • Antibodies, Viral
  • CD36 Antigens
  • Epitopes
  • Lysosome-Associated Membrane Glycoproteins
  • Membrane Glycoproteins
  • Peptide Fragments
  • Scarb2 protein, mouse
  • Vaccines, DNA
  • Viral Vaccines
  • Cathepsin D