Vaccination of cattle with a CpG oligodeoxynucleotide-formulated mycobacterial protein vaccine and Mycobacterium bovis BCG induces levels of protection against bovine tuberculosis superior to those induced by vaccination with BCG alone

Abstract

The development of a subunit protein vaccine for bovine tuberculosis which could be used either in combination with Mycobacterium bovis BCG (to improve the efficacy of that vaccine) or alone would offer significant advantages over currently available strategies. A study was conducted with cattle to determine the protective efficacy of a strategy based on concurrent immunization with an M. bovis culture filtrate (CFP) vaccine and BCG compared to vaccination with either vaccine alone. One group of calves (10 animals per group) was vaccinated subcutaneously with CFP formulated with Emulsigen and combined with a CpG oligodeoxynucleotide (ODN). A second group was vaccinated with both the CFP vaccine and BCG injected at adjacent sites (CFP-BCG). One further group was vaccinated subcutaneously with BCG, while another group served as nonvaccinated control animals. Vaccination with CFP-BCG induced levels of antigen-specific gamma interferon (IFN-gamma) and interleukin-2 (IL-2) in whole-blood cultures that were higher than those induced by vaccination with BCG alone. The combination of CFP and BCG did not enhance the production of antibodies to M. bovis CFP compared to vaccination with CFP alone. Vaccination with CFP alone led to delayed antigen-specific IFN-gamma and IL-2 responses. Vaccination with CFP-BCG induced a high level of protection against an intratracheal challenge with virulent M. bovis, based on a significant enhancement of six pathological and microbiological parameters of protection compared with the nonvaccinated group. In contrast, vaccination with BCG alone induced a significant enhancement of protection in only one parameter, while CFP alone induced no protection. These results suggest that a combination of a CpG ODN-formulated protein vaccine and BCG offers better protection against bovine tuberculosis than does BCG alone.

FIG. 1.

Mean levels of IFN-γ (A) and IL-2 (B) released from bovine PPD-stimulated whole-blood cultures and serum antibody responses to M. bovis culture filtrate (C) for animals vaccinated with CFP (▴) (n = 10), BCG (▪) (n = 10), or CFP and BCG (×) (n = 9) and for nonvaccinated animals (⋄) (n = 10). IFN-γ levels are presented as mean concentrations in plasma (ng/ml), IL-2 levels are given as mean stimulation indexes (SI), and antibody levels are given as percentages of a positive control serum. The bars above the data points represent SEM. The arrows indicate vaccination times (0 for BCG and 0, 3, and 6 weeks for CFP).

FIG. 2.

Skin test responses to avian PPD (white bars) and bovine PPD (black bars) 17 weeks after vaccination (A) and 14 weeks after challenge (B). The data are expressed as mean (± SEM) increases in skin thickness (mm) between the time of inoculation and 72 h later. *, significantly higher than the mean of the nonvaccinated group (P < 0.05).