Assessing Vaccine Efficacy in Different Animal Models
Testing efficacy of any new vaccine requires a disease model and gold standard controls to act as quantitative markers. The slow progression of MAP pathogenesis, the lack of reliable correlates of protection and the inability of current vaccines to effectively stop transmission make delivering these a logistical challenge.
Ruminant models are certainly required for the final testing of vaccines but are very expensive. As discussed above, cheaper mouse models have been used for initial screening but have shown poor predictability for protection in larger animals. The problem of how to screen new LAV candidates quickly and effectively has been compoundedTable 23.4. Summary of live vector subunit and other vaccine candidates tested in animals.
| Vaccine target and delivery type | Other name(s) | Size (kDa) | Function | Tested species | Challenge strain | Dose and route of infection | Comments |
| Bull eta/., 2007, 2014 | |||||||
| Fusion construct of non- | AphC MAP- | 95 | Alkyl hydroperoxidase | C57BI√6 mice | Low-passage isolate | 1?10,j CFU ip. | Immunized sc. with Ad5 prime. |
| transmembrane regions from | RS08085 | of MAP (K37) from | 2 weeks after | Boost after 2 weeks. One- | |||
| four MAP genes MAP1589c, | gsd MAP_ RS06265 | GPL fucosyl transferase | cow with JD | (prophylactic) or | log decrease in spleen and | ||
| MAPI234, MAP2444c, | 3 weeks before | liver in both therapeutic and | |||||
| MAPI235 inserted as an | (therapeutic) | prophylactic administration 6 | |||||
| expression construct into | vaccination | weeks (prophylactic) and 12 weeks | |||||
| modified Adenovirus 5 and | (therapeutic) post-challenge | ||||||
| Vaccinia Ankara delivery vectors | p12 MAP | Antisense protein to | 3-week-old | Low-passage isolate | 1 ? 10’ CFU total | Immunized id. with adenoviral | |
| RS12460 | IS900 transferase | calves | of MAP (R0808) from | orally in two doses | prime (11 weeks prior to challenge) | ||
| mρa MAP_ RS22605 | GPL acetyl transferase | cow with JD | 5 weeks after MVA boost vaccination | and vaccinia boost (5 weeks prior to challenge). Significant two log decrease in gut mucosal load. No faecal shedding in vaccinated group at 36 weeks post-challenge | |||
| Chandra et al., 2012 | |||||||
| Fusion constructs of partial | Ag85A (202-347) | 34.5 | Secretable fragments | 180 C57BL∕6 | MAP strain 66115- | 1 ? 10’ CFU | Immunized ip. with 5 ? 108 CFU |
| proteins from MAP0216, MAPI609c, MAP3527, | Ag85B (173-330) | 33.3 | of mycolyl- transferases involved | mice | 98 | in PBS ip. 6 weeks after last | in PBS or 10 μg of each purified antigen in MPLadjuvant. Boosted |
| MAPI519 and MAP0187c | in cell wall synthesis | immunization | at 3 weeks. Both purified Ag and | ||||
| expressing in attenuated Salmonella species. Also purified fusion partial protein | MAP74F (1-148 & 669-786) | 40.7 | Secretable serine protease & PPE gene fragments | Salmonella delivery induced three- log reduction in spleen and liver CFU at 16 weeks post-challenge. | |||
| mix | Some decrease in histopathological | ||||||
| SOD (1-72) | 19.5 | Secretable fragments of superoxide dismutase | and granuloma scores | ||||
| Faisal et al., 2013b | |||||||
| MAP0216 | Ag85A | 32 | Secretable fragments | Goats | MAP strain 66115- | Seven doses | Immunized sc. 5 ? 108 CFU/ |
| of mycolyl- | 98 | 5 ? 108 oral 3 | animal. Boosted at 3 weeks | ||||
| transferases involved | weeks after last | ||||||
| in cell wall synthesis | immunization | ||||||
| MAPI 609c | Ag85B | 30 | |||||
Table 23.4. Continued
| Vaccine target and delivery type | Other name(s) | Size (kDa) | Function | Tested species | Challenge strain | Dose and route of infection | Comments |
| MAP0187c | SOD | 23 | superoxide dismutase Jolly et al., 2013 | ||||
| Lipoarabinomannan (LAM) produced by phenol/ methanol extraction of MAP culture | LAM | 20 | Glycolipid | 106-month- old Aberdeen Angus calves | Local MAP strain from JD cow | 1 ? 109 CFUoraI 10 days after last immunization | Immunized and boosted at 6, 12 and 24 weeks with 2 mg of LAM extract dissolved in 1 ml of PBS and emulsified in 1 ml of Freund’s Incomplete Adjuvant. No faecal shedding in two out of two cattle in vaccine group |
CFU1 colony-forming units; MAP, Mycobacterium avium subsp. paratuberculosis; sc., subcutaneous; ip., intraperitoneal; id., intradermal; PBS, phosphate buffered saline; MPL, monophosphoryl lipid A; JD, Johne’s disease.
398 T. Bull
by the apparent failure of in vitro macrophage assays.
Protective efficacy of a prophylaxic vaccine is generally demonstrated by comparing challenge loads present in naive vs vaccinated animals after a designated immune clearance period. It is unlikely that any vaccine directed against pathogenic mycobacteria however will have sterilizing capacity; thus, comparisons against current ‘gold standard' vaccine efficacy are also essential. Replication in liver and spleen is usually monitored by CFU plating and when testing LAV commonly includes a selection marker to monitor immunogen persistence. Examples include kanamycin or hygromycin but could also include luminometry using constructs expressing luciferase or GFP (Rosseels et al., 2006b; Park et al., 2011). Standardized protocols for certain animal models have been proposed (Hines et al., 2007a) but not validated as authoritative. If new vaccines are to be brought to the market place, a significant improvement in the manner in which trials are performed is required. New tests are needed to detect the direct presence of MAP and the host's specific responses to challenge by live MAP and many of its individual components; models require rigorous standardizing and a realistic achievable output measure of efficacy related to faecal shedding is needed.
23.5