DNA vaccination with glutamic acid decarboxylase (GAD) generates a strong humoral immune response in BALB/c, C57BL/6, and in diabetes-prone NOD mice.

Abstract

The technique of DNA-based vaccination was used to generate a T-cell-dependent antibody response to glutamic acid decarboxylase (GAD) in BALB/c, C57BL/6, and non-obese diabetic (NOD) mice. Plasmids were constructed in which the expression of the rat GAD65 (rGAD65) or the rat GAD67 (rGAD67) gene was driven by the immediate early region promoter of the human cytomegalovirus (pCMV). This "naked" plasmid DNA was then injected into the regenerating muscles of the studied mice. In the vaccinated animals, antibody responses to GAD65 or to GAD67 were induced. Epitope recognition of GAD was studied by protein footprinting, a technique which makes use of a limited proteolysis of antibody-bound antigen. Different epitope recognition patterns were found, corresponding to strain-specific patterns. Mild trypsin treatment generated 50 kD, 46 kD, 40 kD, 30 kD, and 21 kD proteolytic fragments. In NOD mice, 50, 46 and 40 kD bands were the most prominent signals. In non-diabetes prone BALB/c mice, a faint 40 kD band appeared suggesting a rather weak protection of GAD from tryptic lysis. The pattern observed in C57BL/6 mice was more comparable to the NOD mice pattern with prominent 40 kD and 30 kD signals and a faint 21 kD fragment. Diabetes incidence was unchanged in NOD mice, and no diabetes was observed in C57BL/6 and BALB/c mice, respectively. The data demonstrate that genetic immunization is a suitable novel tool to stimulate and to manipulate an immune response against the diabetes-associated protein glutamic acid decarboxylase. Interestingly, our results indicate that, by genetic vaccination, distinct B-cell epitopes were generated in the various studied mouse strains.