Immunization with chaperone-peptide complex induces low-avidity cytotoxic T lymphocytes providing transient protection against herpes simplex virus infection

Abstract

Heat shock proteins loaded with viral peptides were shown to induce a CD8+ T cell response and confer protective immunity against challenge with herpes simplex virus (HSV). The delivery system consisted of recombinant human hsp70 coupled to the peptide SSIEFARL, which is the immunodominant peptide epitope, recognized by HSV specific T cells in C57BL/6 mice. Immunization resulted in CD8+ T-cell responses, measured by peptide-specific tetramers and peptide-induced intracellular gamma interferon expression and cytotoxicity, similar to responses resulting from immunization with a recombinant vaccinia virus that expressed SSIEFARL as a minigene (VvgB) and UV-inactivated HSV. However, the durability of the hsp70-SSIEFARL response was less than that resulting from VvgB and HSV immunization and in addition the CD8+ T-cell responses in the memory phase were functionally less effective. Mice challenged soon after immunization showed excellent immunity, but by 90 days postimmunization this had waned to be significantly less than the level of immunity in both VvgB- and HSV-immunized mice.

FIG. 1.

Dose-response studies for optimization. C57BL/6 mice were immunized i.p. (after experimentation with inoculation by the intramuscular and subcutaneous routes) with various doses of hsp70-peptide preparation ranging from 0.1 to 10 γg/ml to arrive at an optimum dose to be used in the subsequent analysis of its efficacy. BSA-SSIEFARL and SSIEFARL alone were included as controls. The splenocytes were harvested from these mice and analyzed for the frequency of SSIEFARL-specific CD8⁺ T cells by peptide-stimulated intracellular IFN-γ assay. Based on the results shown, we chose 2.5 γg/ml as the optimum dose for administration.

FIG. 2.

hsp70-SSIEFARL immunization induces HSVgB _498-505 (SSIEFARL)-specific CD8⁺ T-cell proliferative response in B6 mice. C57BL/6 mice were immunized with rhsp70-SSIEFARL, SSIEFARL, VvgB (10⁶ PFU), HSV-1 KOS (10⁶ PFU), or buffer alone i.p. on days 0 and 21. One week later the splenocytes were harvested, and nylon wool-nonadherent T cells were assessed for in vitro proliferative response to SSIEFARL peptide-pulsed or HSV-infected syngeneic APCs. The controls included and not shown are anti-CD3- and concanavalin A-stimulated responders, stimulators alone, and responders with irrelevant peptide-pulsed APCs.