Vaccine-Induced Subcutaneous Granulomas in Goats Reflect Differences in Host–Mycobacterium Interactions between BCG- and Recombinant BCG-Derivative Vaccines

Abstract

Tuberculous granulomas are highly dynamic structures reflecting the complex host–mycobacterium interactions. The objective of this study was to compare granuloma development at the site of vaccination with BCG and its recombinant derivatives in goats. To characterize the host response, epithelioid cells, multinucleated giant cells (MNGC), T cell subsets, B cells, plasma cells, dendritic cells and mycobacterial antigen were labelled by immunohistochemistry, and lipids and acid-fast bacteria (AFB) were labelled by specific staining. Granulomas with central caseous necrosis developed at the injection site of most goats though lesion size and extent of necrosis differed between vaccine strains. CD4+ T and B cells were more scarce and CD8+ cells were more numerous in granulomas induced by recombinant derivatives compared to their parental BCG strain. Further, the numbers of MNGCs and cells with lipid bodies were markedly lower in groups administered with recombinant BCG strains. Microscopic detection of AFB and mycobacterial antigen was rather frequent in the area of central necrosis, however, the isolation of bacteria in culture was rarely successful. In summary, BCG and its recombinant derivatives induced reproducibly subcutaneous caseous granulomas in goats that can be easily monitored and surgically removed for further studies. The granulomas reflected the genetic modifications of the recombinant BCG-derivatives and are therefore suitable models to compare reactions to different mycobacteria or TB vaccines.

Safety and Immunogenicity of Recombinant Bacille Calmette-Guérin Strain VPM1002 and Its Derivatives in a Goat Model

“…Acid-fast bacteria (AFB) were detected in all granulomas from BCG- and VPM1002-vaccinated goats and in four of the six goats vaccinated with PDX and NUOG, respectively. Details about morphological characteristics and cellular composition of these granulomas were recently reported [ 31 ]. Viable bacteria were recovered from the vaccination sites of three animals of the BCG group, two animals of the VPM1002 group, and one animal of the NUOG group ( Table 2 ).…”

“…At necropsy (16 weeks post vaccination (pv)), lesions were confirmed to be circumscribed vaccine granulomas, with central necrosis in the subcutis, and the re-isolation of viable vaccine strains was successful in some goats of all vaccinated groups, except for the PDX group. A detailed histological characterization of these vaccination granulomas has recently been published [ 31 ]. Vaccine granulomas have been reported as sequelae of subcutaneous vaccination with BCG, both in adult goats and in goat kids [ 36 ].…”

“…The data presented by our group in a prior publication [ 31 ] and the current manuscript are based on samples obtained from the same cohort of animals. We consider this an important implementation of the 3R principles (replacement, reduction, and refinement) for the use of experimental animals.…”

“…Granulomas were classified according the classification scheme for tuberculous granulomas in ruminants by Wangoo et al [ 63 ]. Samples from the injections sites of the animals were also used for a detailed morphological investigations of vaccine granulomas [ 31 ].…”

Adjuvants influence the immune cell populations present at the injection site granuloma induced by whole-cell inactivated paratuberculosis vaccines in sheep

“…Therefore, the characterization of the cell populations present at the vaccine inoculation site is crucial to understanding the development of the granulomas at the injection site ( 18 ) and the establishment of the immune response after vaccination ( 19 ). Macrophages are the main component of any granulomatous lesion ( 20 ), and their role as APC is essential in the development of the immune response ( 21 , 22 ).…”