Drug treatment combined with BCG vaccination reduces disease reactivation in guinea pigs infected with Mycobacterium tuberculosis

Abstract

Bacillus-Calmette-Guerin (BCG), the only human tuberculosis vaccine, primes a partially protective immune response against M. tuberculosis infection in humans and animals. In guinea pigs, BCG vaccination slows the progression of disease and reduces the severity of necrotic granulomas, which harbor a population of drug-tolerant bacilli. The objective of this study was to determine if reducing disease severity by BCG vaccination of guinea pigs prior to M. tuberculosis challenge enhanced the efficacy of combination drug therapy. At 20 days of infection, treatment of vaccinated and non-vaccinated animals with rifampin, isoniazid, and pyrizinamide (RHZ) was initiated for 4 or 8 weeks. On days 50, 80 and 190 of infection (10 weeks after drug were withdrawn), treatment efficacy was evaluated by quantifying clinical condition, bacterial loads, lesion severity, and dynamic changes in peripheral blood and lung leukocyte numbers by flow cytometry. In a separate, long-term survival study, treatment efficacy was evaluated by determining disease reactivation frequency post-mortem. BCG vaccination alone delayed pulmonary and extra-pulmonary disease progression, but failed to prevent dissemination of bacilli and the formation of necrotic granulomas. Drug therapy either alone or in combination with BCG, was more effective at lessening clinical disease and lesion severity compared to control animals or those receiving BCG alone. Fewer residual lesions in BCG vaccinated and drug treated animals, equated to a reduced frequency of reactivation disease and improvement in survival even out to 500 days of infection. The combining of BCG vaccination and drug therapy was more effective at resolving granulomas such that fewer animals had evidence of residual infection and thus less reactivation disease.

Establishment of Early Endpoints in Mouse Total-Body Irradiation Model

“…[ 29 ] Bio Medic Data System implantable microchips have also been reported being used in ferrets[ 5 , 30 , 31 ] and guinea pigs. [ 32 ] Respiratory rate was not evaluated in this study as part of MISS 2 but can be helpful. This measure was one of the ones used when evaluating mice which were equivocal (a mouse of cumulative score 7 as per MISS 2) and was helpful in determining how soon the increased monitoring was needed.…”

A new unifying theory of the pathogenesis of tuberculosis

“…Reactivation occurs from the vicinity of the residual primary lesions, 13 and we know that even if this residual necrosis is minimal it can still harbor live bacilli capable of retriggering disease. 45 In the putative model shown here [Fig.4] as the primary lesions heal and calcify, the residual necrosis containing the surviving NECs become highly compressed by the calcification process and these get pushed towards the edge of the lesion. This gradually brings them close to open intact airspaces [Fig.4B] and, obviously, a steep rise in oxygen tension.…”

Whole genome response in guinea pigs infected with the high virulence strain Mycobacterium tuberculosis TT372

“…As for cytokine receptors, several were up-regulated in the INF group, including receptors associated with the TH17 axis [IL-17R, IL-23R], with the expansion of CD8 memory [IL-15R], and support of the effector response [IL-21R]. Both neutrophil and regulatory T cell influx are characteristics of the response in non-vaccinated guinea pigs which are delayed or reduced in BCG vaccinated animals [22, 33], and this may explain depression of the genes for IL-17R and IL-27R in the V/INF group.…”