Vaccine 21 (2003) 3101–3109 Efficacy of commercial and field-strain Mycobacterium paratuberculosis vaccinations with recombinant IL-12 in a bovine experimental infection model Jude E. Uzonna a , Paula Chilton a,1 , Robert H. Whitlock a , Perry L. Habecker b , Phillip Scott b , Raymond W. Sweeney a,∗ a Department of Clinical Studies, University of Pennsylvania School of Veterinary Medicine, New Bolton Center, 382 West Street Road, Kennett Square, PA 19348, USA b Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104, USA Received 30 January 2003; accepted 26 March 2003 Abstract The efficacy of commercial (Strain 18) and field-isolate paratuberculosis vaccine preparations was investigated. The effect of prior exposure to Mycobacterium paratuberculosis and the adjuvant effect of rIL-12 on vaccine efficacy were also tested. Both Strain 18 and field-isolate vaccines induced strong local, systemic and enteric IFN- responses. A significant reduction in mycobacterial colonization was observed when calves were vaccinated with the field-isolate prior to challenge, but not following vaccination with Strain 18 vaccine. Vaccination with rIL-12 prevented infection in some calves but its overall effect on IFN- response and total mycobacterial load was not statistically significant. Efficacy of paratuberculosis vaccines may be enhanced if calves are vaccinated prior to M. paratuberculosis exposure with field-isolate vaccine instead of Strain 18 vaccine currently in use. © 2003 Elsevier Science Ltd. All rights reserved. Keywords: Mycobacterium paratuberculosis; Vaccine; rIL-12 1. Introduction Paratuberculosis (Johne’s disease) is an important chronic, infectious enteric disease of cattle. The causative or- ganism, Mycobacterium avium sub-sp. paratuberculosis (but here in after referred to by its traditional name, M. paratu- berculosis) is shed in the feces of infected adult cattle [1]. Vaccination is available on a limited basis in the United States. The vaccine currently approved for use is an oil sus- pension of killed Strain 18 organisms, originally thought to be a laboratory-adapted strain of M. paratuberculosis, but now known to be a closely related strain of M. avium (not sub-sp. paratuberculosis) [2,3]. The efficacy of vaccination has been questioned, and reported results of vaccine trials are varied [1,4]. Results range from no reduction in infec- tion rate [5,6], to 50–90% reduction [7–11]. In one field trial, vaccinated animals actually had higher intestinal load ∗ Corresponding author. Tel.: +1-610-444-5800x2132; fax: +1-610-925-8100. E-mail address: rsweeney@vet.upenn.edu (R.W. Sweeney). 1 Present address: Institute for Cellular Therapeutics, University of Louisville, Louisville, KY, USA. of M. paratuberculosis organisms than unvaccinated con- trols [8]. Other studies report prevalence of clinical disease in vaccinates approximately 10–50% that of unvaccinated herdmates [4,9]. The current consensus is that vaccination may reduce the incidence of clinical disease, and to a lesser extent the prevalence of infection, but vaccinates are not fully protected from infection. Why does vaccination fail? Vaccination induced a persis- tent serologic response in 90% of animals within 6 months [12], but as with other intracellular pathogens, humoral im- munity is probably not protective. One might speculate that the poor success of vaccination might be related to the in- ability of the vaccine to induce protective Th1 response, which is thought to mediate resistance against the disease [1,13,14]. However, vaccination of cattle appeared to induce cell-mediated immunity as measured by intradermal testing, lymphocyte proliferation and cytokine assays [11,15,16]. The usual portal of entry of M. paratuberculosis is the intestinal mucosa. The relationship between measured systemic immune responses induced by subcutaneous vac- cination (humoral or cellular) and mucosal immunity has not been determined in bovine paratuberculosis. Use of BCG to vaccinate against tuberculosis is thought to induce 0264-410X/03/$ – see front matter © 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0264-410X(03)00261-5