Preclinical models to optimize treatment of tuberculous meningitis - A systematic review

Advancing the chemotherapy of tuberculous meningitis: a consensus view

Tuberculous meningitis causes death or disability in approximately 50% of affected individuals and kills approximately 78 200 adults every year. Antimicrobial treatment is based on regimens used for pulmonary tuberculosis, which overlooks important differences between lung and brain drug distributions. Tuberculous meningitis has a profound inflammatory component, yet only adjunctive corticosteroids have shown clear benefit. There is an active pipeline of new antitubercular drugs, and the advent of biological agents targeted at specific inflammatory pathways promises a new era of improved tuberculous meningitis treatment and outcomes. Yet, to date, tuberculous meningitis trials have been small, underpowered, heterogeneous, poorly generalisable, and have had little effect on policy and practice. Progress is slow, and a new approach is required. In this Personal View, a global consortium of tuberculous meningitis researchers articulate a coordinated, definitive way ahead via globally conducted clinical trials of novel drugs and regimens to advance treatment and improve outcomes for this life-threatening infection.

Investigating the Diagnostic and Therapeutic Potential of a T Cell Receptor (TCR)-like single Domain Antibody (sDAb)-Human IgG1 Antibody against Heat Shock Protein (HSP) 16KDa/HLA-A2 for Latent Tuberculosis

Heat shock protein 16-kDa (HSP 16-kDa) is essential for the survival of Mycobacterium tuberculosis (M. tuberculosis) during the latent period; hence, a peptide-MHC presentation of HSP 16-kDa could be a potential diagnostic and therapeutic target for latent tuberculosis (LTB). This study aimed to generate a TCR-like single-domain antibody (sDAb)-human IgG1 antibody and subsequently investigate its diagnostic and therapeutic potential in LTB, utilizing a model cell presenting the target peptide. A previously generated TCR-like sDAB that can bind to HSP 16-kDa was first fused to a human IgG1 Fc-receptor via a linker. The fusion product, sDAb-IgG1, was expressed with HEK293-F and was subsequently purified. Its diagnostic potential was investigated via cell-based ELISA utilizing MCF-7 cells peptide-pulsed with HSP 16-kDa peptides. Investigation into the antibody-dependent cell-mediated cytotoxicity (ADCC) of MCF-7 cells was also conducted to investigate its therapeutic potential. Finally, TCR-like sDAb-IgG1 was successfully produced transiently with HEK-293F and was purified using protein A chromatography. The generated antibody was tested using cell-based ELISA, which demonstrated the effective binding of the TCR-like sDAb-IgG1 to the 16-kDa peptide-MHC on the cell surface. The ADCC assay also showed that the antibody effectively mediated the ADCC of MCF-7 cells with the help of 16-kDa peptide-MHC. This allows us to hypothesize the possible utility of the said antibody for both diagnostics and therapeutics of latent tuberculosis after more investigations with clinical samples.

A preclinical model of TB meningitis to determine drug penetration and activity at the sites of disease

Tuberculosis meningitis (TBM) is essentially treated with the first-line regimen used against pulmonary tuberculosis, with a prolonged continuation phase. However, clinical outcomes are poor in comparison, for reasons that are only partially understood, highlighting the need for improved preclinical tools to measure drug distribution and activity at the site of disease. A predictive animal model of TBM would also be of great value to prioritize promising drug regimens to be tested in clinical trials, given the healthy state of the development pipeline for the first time in decades. Here, we report the optimization of a rabbit model of TBM disease induced via inoculation of Mycobacterium tuberculosis into the cisterna magna, recapitulating features typical of clinical TBM: neurological deterioration within months post-infection, acid-fast bacilli in necrotic lesions in the brain and spinal cord, and elevated lactate levels in cerebrospinal fluid (CSF). None of the infected rabbits recovered or controlled the disease. We used young adult rabbits, the size of which allows for spatial drug quantitation in critical compartments of the central nervous system that cannot be collected in clinical studies. To illustrate the translational value of the model, we report the penetration of linezolid from plasma into the CSF, meninges, anatomically distinct brain areas, cervical spine, and lumbar spine. Across animals, we measured the bacterial burden concomitant with neurological deterioration, offering a useful readout for drug efficacy studies. The model thus forms the basis for building a preclinical platform to identify improved regimens and inform clinical trial design.

Cerebrospinal fluid concentrations of fluoroquinolones and carbapenems in tuberculosis meningitis

Background: Tuberculosis meningitis (TBM) is the most lethal form of TB. It is difficult to treat in part due to poor or uncertain drug penetration into the central nervous system (CNS). To help fill this knowledge gap, we evaluated the cerebrospinal fluid (CSF) concentrations of fluoroquinolones and carbapenems in patients being treated for TBM. Methods: Serial serum and CSF samples were collected from hospitalized patients being treated for TBM. CSF was collected from routine lumbar punctures between alternating timepoints of 2 and 6 h after drug administration to capture early and late CSF penetration. Rich serum sampling was collected after drug administration on day 28 for non-compartmental analysis. Results: Among 22 patients treated for TBM (8 with confirmed disease), there was high use of fluoroquinolones (levofloxacin, 21; moxifloxacin, 10; ofloxacin, 6) and carbapenems (imipenem, 11; meropenem, 6). Median CSF total concentrations of levofloxacin at 2 and 6 h were 1.34 mg/L and 3.36 mg/L with adjusted CSF/serum ratios of 0.41 and 0.63, respectively. For moxifloxacin, the median CSF total concentrations at 2 and 6 h were 0.78 mg/L and 1.02 mg/L with adjusted CSF/serum ratios of 0.44 and 0.62. Serum and CSF concentrations of moxifloxacin were not affected by rifampin use. Among the 76 CSF samples measured for carbapenem concentrations, 79% were undetectable or below the limit of detection. Conclusion: Fluoroquinolones demonstrated high CSF penetration indicating their potential usefulness for the treatment of TBM. Carbapenems had lower than expected CSF concentrations.

Advancing our understanding of HIV co-infections and neurological disease using the humanized mouse

Humanized mice have become an important workhorse model for HIV research. Advances that enabled development of a human immune system in immune deficient mouse strains have aided new basic research in HIV pathogenesis and immune dysfunction. The small animal features facilitate development of clinical interventions that are difficult to study in clinical cohorts, and avoid the high cost and regulatory burdens of using non-human primates. The model also overcomes the host restriction of HIV for human immune cells which limits discovery and translational research related to important co-infections of people living with HIV. In this review we emphasize recent advances in modeling bacterial and viral co-infections in the setting of HIV in humanized mice, especially neurological disease, and Mycobacterium tuberculosis and HIV co-infections. Applications of current and future co-infection models to address important clinical and research questions are further discussed.