T Cell Monitoring of Chemotherapy in Experimental Rat Tuberculosis

Abstract

Mycobacterium tuberculosis is the causative agent of a pulmonary epidemic that is estimated to infect one-third of the world's population and that has an increased incidence of multidrug resistance. The evaluation of new chemical entities against M. tuberculosis is hampered by the lack of biological tools to help predict efficacy, from early drug development to clinical trials. As the rat is the animal species of choice in the pharmaceutical industry, we have developed a rat model of acute and chronic phases of M. tuberculosis infection for drug efficacy testing. In this model, we have evaluated the impact of tuberculosis drugs on T cell response using the enzyme-linked immunospot assay methodology. Infected rats treated with isoniazid (INH) or rifampin (RIF) responded to therapy, the potency of which was comparable to that seen in the mouse. Peripheral blood mononuclear cells from infected rats produced gamma interferon (IFN-␥) in response to RD-1 antigens, such as the 6-kDa early secretory antigen target (ESAT-6) and the 10-kDa culture filtrate protein (CFP-10). A decrease in IFN-␥ spot-forming cells (SFCs) was consistently observed in response to drug treatment. In both the acute-and chronic-phase models, the T cell response was more sensitive to ESAT-6 than to CFP-10. The SFC count in response to ESAT-6 appears to be an indicator of bacterial killing in the rat. Collectively, our data suggest that the ESAT-6 response could be used as a potential surrogate of drug efficacy in the rat and that such a readout could help shorten drug testing during preclinical development.Mycobacterium tuberculosis infection is among the world's leading infectious diseases, causing about 2 million deaths annually. The emergence of multidrug-resistant M. tuberculosis strains along with the increase of HIV coinfected cases worsens the situation (42). In countries with a high incidence of tuberculosis (TB), TB control programs rely on a diagnostic methods and drugs that have been developed decades ago and that are inadequate to effectively control the epidemic. The urgent need to develop new diagnostic tools as well as new therapeutic interventions is hampered by long clinical trials, where markers of infection and drug response are lacking (38).For decades, the tuberculin skin test (TST) has been used to diagnose TB (18). The TST measures cell-mediated immunity in the form of a delayed-type hypersensitivity response to the purified protein derivative (PPD), a crude mixture of antigens shared among M. tuberculosis, Mycobacterium bovis BCG, and several nontuberculous mycobacteria (NTM). As a result, the TST has lower specificity in populations with high BCG coverage and NTM exposure and shows poor sensitivity in immunocompromised individuals (30). The gamma interferon (IFN-␥) enzyme-linked immunospot (ELISpot) assay has emerged as an alternative to the TST. The assay consists of in vitro stimulation of peripheral blood mononuclear cells (PBMCs) using RD-1 antigens, the 6-kDa early secretory antigen target (ESAT-6) and the 10-kDa cul...

A Subset of Circulating Blood Mycobacteria-Specific CD4 T Cells Can Predict the Time to Mycobacterium tuberculosis Sputum Culture Conversion

“…In particular, the decline in IFNγ + IL2 − TNFα + CD4 T cells coincident with an increased population of IFNγ + IL2 + TNFα + CD4 T cells is in agreement with Day et al [27] , who investigated changes in relation to bacillary load, as defined by sputum smear acid-fast bacilli (AFB), during treatment. These results may indicate that higher mycobacterial load is associated with impaired IL2 production, which recovers with treatment and bacillary clearance [29] . This hypothesis is supported by several cross-sectional studies showing a higher proportion of mycobacteria-specific IFN + IL2 − TNF + or IFNg + IL2 − CD4 T cells or lower IL2 + CD4 T cells in patients with active TB than in patients after successful treatment [24] , [30] – [32] .…”

Animal models for COVID-19 and tuberculosis

“…Rats are generally susceptible to Mtb ( 132 ), and they have been used to distinguish bacteriostatic or bactericidal properties of investigational compounds ( 133 ). In the rat model, the decrease of T-cell reactivity to ESAT-6 has been proposed as a correlate of therapeutic efficacy ( 134 ) which principally sheds light on the maintenance of high-level T effector cell populations. Various rat models, including American cotton rats, Lewis rats, Wistar rats, and Sprague-Dawley rats, develop granulomatous lesions which do not liquefy ( 132 , 135 , 136 ), and thus human TB pathology is not fully mirrored.…”

One Size Fits All? Not in In Vivo Modeling of Tuberculosis Chemotherapeutics

“…In the search for an ideal TB model, investigators continue to test other animal species as models for TB and TB chemotherapy including various rats, the minipig, and the Chinese tree shrew among others ( Sugawara et al., 2004 ; Elwood et al., 2007 ; Gaonkar et al., 2010 ; Gil et al., 2010 ; Zhan et al., 2014 ). Of these, the Wistar rat is perhaps the most well characterized, because it is a common species used for PK/PD characterization and toxicity assessment of potential therapeutics, and it would be more economical to be able to use the same species for drug efficacy studies ( Gaonkar et al., 2010 ; Singhal et al., 2011 ; Foo et al., 2011 ; Ramani et al., 2012 ; Kondreddi et al., 2013 ; Kumar et al., 2014 ). The Wistar rat and Lewis rats lacked lesions with central necrosis when infected with the Mtb strains chosen by the investigators, but the two species of Cotton rat developed necrotic lesions and higher bacterial loads despite being exposed to a low dose of Mtb H37Rv ( Sugawara et al., 2004 ; Swaim et al., 2006 ; Elwood et al., 2007 ; Singhal et al., 2011 ).…”