Lack of protection in mice and necrotizing bronchointerstitial pneumonia with bronchiolitis in guinea pigs immunized with vaccines directed against the hsp60 molecule of Mycobacterium tuberculosis

Abstract

In this study, the hsp60 and hsp70 heat shock protein antigens of Mycobacterium tuberculosis were tested as potential vaccine candidates, using purified recombinant protein antigens or antigens encoded in the form of a DNA plasmid vaccine. Guinea pigs vaccinated with a mixture of the two proteins showed no evidence of resistance to low-dose aerosol challenge infection and quickly developed severe lung damage characterized by necrotizing bronchointerstitial pneumonia and bronchiolitis. As a result, we turned instead to a DNA vaccination approach using a plasmid encoding the hsp60 antigen of M. tuberculosis. Although immunogenic in mice, vaccination with plasmid DNA encoding hsp60 was not protective in that model or in the guinea pig model and again gave rise to similar severe lung damage. This study seriously questions the safety of vaccines against tuberculosis that target highly conserved heat shock proteins.

FIG. 1

Vaccination of guinea pigs with an hsp60-hsp70 protein vaccine mixture. (A) Bacterial load in lungs 30 days after aerosol challenge. (B) Mean survival. Note that none of the BCG-vaccinated animals had died when the experiment was stopped at 27 weeks. (C) Mean weight gain. For panels A to C, n = 4 and error bars indicate standard errors of the means. (D) Weight loss of individual animals. Open squares, adjuvant controls; closed squares, hsp60-hsp70-vaccinated animals.

FIG. 2

Representative photomicrographs of a lung from a guinea pig vaccinated with the hsp60-hsp70 protein mixture. (A) Terminal bronchiole surrounded by granulomatous-lymphocytic inflammation. The lumen is filled with mucus, sloughed epithelium, and necrosuppurative cellular debris. Magnification, ×160. (B) Terminal bronchiole with focal epithelial ulceration (arrowhead) and focal epithelial hyperplasia (arrow). The lumen is again filled with mucus, sloughed epithelium, and necrosuppurative cellular debris. Magnification, ×320. Hematoxylin and eosin staining was used.

FIG. 3

Lung pathology after DNA vaccination and aerosol challenge. (A) Plasmid vector control. Severe extensive granulomatous interstitial pneumonia with centralized area of necrosis (arrow) is seen. Magnification, ×160. (B) Guinea pig vaccinated with hsp60 plasmid DNA. Severe extensive granulomatous bronchointerstitial pneumonia with polymorphonuclear leukocytes, mucus, sloughed epithelium, and necrotic cellular debris filling the airway lumen is shown. Magnification, ×160. (C) High magnification of airway in panel B. Note transepithelial migration of polymorphonuclear cells and epithelial erosion (arrowhead) and epithelial hyperplasia (arrow). Magnification, ×310. Hematoxylin and eosin staining was used.