Martin Gengenbacher

Bacille Calmette–Guérin (BCG) provides limited protection against tuberculosis relapse. We investigated whether adjunctive immunotherapy targeting B cells enhances BCG-mediated protection in a murine model of latent tuberculosis. While BCG alone had modest effects, adjunctive immunotherapy with recombinant A proliferation–inducing ligand significantly reduced relapse. Protection was associated with selective remodeling and activation of marginal-zone B-cell compartments, whereas effects on T-cell populations were comparatively modest. These findings support further investigation of B-cell–targeted immunomodulation to improve durable immune control and reduce tuberculosis relapse.

Treatment optimization through pharmacokinetic evaluation is needed to improve outcomes in tuberculous meningitis (TBM). Clinical assessment of drug penetration into the central nervous system (CNS) is limited to cerebrospinal fluid (CSF) sampling, which may not reflect drug exposures at the site-of-disease. We characterized the pharmacokinetics of antituberculosis drugs in CNS tissues using a rabbit model of TBM. Rabbits infected with Mycobacterium tuberculosis received human-equivalent doses of antituberculosis drugs after displaying signs of TBM. Blood was intensively sampled on day 1 and until euthanasia on day 3 when terminal plasma, CSF, and CNS tissues were collected. Total drug concentrations were quantified by LC–MS/MS and analyzed in NONMEM to estimate equilibration half-lives and CSF- and CNS tissue-to-plasma ratios. Across 5 experiments, 48 rabbits provided 600 plasma samples and 48 sets of terminal CSF/CNS tissue samples. Pyrazinamide and isoniazid showed high and consistent penetration, with CSF ratios of 0.98 and 0.85 and CNS tissue ratios ranging from 0.44 to 0.73 and 0.60–0.82, respectively. Linezolid demonstrated modest and uniform penetration (CSF ratio 0.39; CNS tissue ratios 0.15–0.44). Rifampicin showed the lowest overall penetration (CSF ratio 0.08; CNS tissue ratios 0.07–0.32). In contrast, the most lipophilic drugs, bedaquiline and rifabutin, showed low CSF ratios (0.01 and 0.42, respectively) compared with much higher CNS tissue ratios (1.11–6.34 and 1.23–6.78, respectively). CSF penetration in the rabbit TBM model closely mirrored reported human data, establishing its translational value. High relative CNS exposures of bedaquiline and rifabutin support their clinical evaluation for TBM treatment.

Alveolar macrophages are the first immune cells to encounter Mycobacterium tuberculosis (Mtb) in the lungs, but they frequently fail to eliminate this pathogen, allowing Mtb to persist and replicate. Interstitial macrophages (IMs) are enlisted to restrict bacterial growth and limit immune evasion. While IMs have been implicated in controlling acute Mtb infection, their role during latent tuberculosis infection (LTBI) remains unexplored. To address this, we utilized a previously established mouse model of paucibacillary Mtb infection that recapitulates key aspects of human LTBI to deplete IMs during the latent phase. Depletion of IMs and recruited macrophages (RMs) led to TB relapse in 26% of mice compared to 2% in controls. Mice that relapsed exhibited an increased proportion of pro-inflammatory IMs and elevated concentrations of G-CSF, GM-CSF, IL-3, IL-12, IL-13, IL-17A, and KC in the lung. These findings demonstrate that IMs and RMs play a critical role in controlling latent Mtb and preventing TB relapse.

Tuberculosis, a persistent public health challenge worldwide, is transmitted when exhaled Mycobacterium tuberculosis (Mtb) particles expelled from an infected individual are inhaled by a susceptible person. To study the adaptation of Mtb during transition between hosts, we developed a transmission simulation system (TSS) that combines controlled pathogen aerosolization and measurement of bioaerosol particle characteristics with in-flight sampling of Mtb and infection of mice by nose-only exposure. Using scattered-light spectrometry, we demonstrated that Mtb aerosol concentrations generated by the TSS better represented human cough than the aerosol concentrations produced by a full-body inhalation exposure system commonly used for Mtb infection of mice. Additionally, the TSS deposited clinically relevant low doses of Mtb into murine lungs with greater precision than the full-body inhalation exposure systems. The TSS revealed a linear correlation between Mtb inoculum concentration and pathogen deposition in murine lungs up to 200 colony-forming units. Higher inoculum concentrations led to a reduction in total particle number, which resulted in disproportionately lower pulmonary infection doses. Importantly, the particle size distributions of Mtb-laden aerosols produced by the TSS mirrored those of tuberculosis patient coughs, with 90% of culturable Mtb found in particles with aerodynamic diameters below 3.3 µm. In conclusion, the TSS represents a novel effective and precise translational platform enabling detailed biophysical and molecular studies of Mtb transmission. IMPORTANCE: Tuberculosis is transmitted when exhaled Mycobacterium tuberculosis (Mtb)-laden microdroplets of an infected individual are inhaled by a susceptible person. Historically, studies on Mtb transmission have focused mainly on epidemiology due to the technical challenges in replicating the transmission process effectively in a laboratory setting. In this study, we introduce a transmission simulation system (TSS) that integrates controlled Mtb aerosolization, biophysical aerosol particle measurements, in-flight Mtb sampling, and aerosol infection of mice. The TSS generated Mtb bioaerosol concentrations comparable to those produced by human coughs. These pathogen droplets were accurately deposited in mouse lungs at low Mtb doses relevant to human transmission. Notably, the distribution of Mtb among aerosol particles of various sizes closely mirrored that found in the coughs of tuberculosis patients. In summary, the TSS represents a novel tool for conducting molecular studies of Mtb transmission through the air.

Background: Cavitary tuberculosis is difficult to cure and constitutes a site of relapse. Bedaquiline has been a wonder drug in the treatment of multidrug-resistant tuberculosis, but emergence of resistance threatens the sustainability of its success. We designed site-of-disease pharmacokinetic studies to spatially resolve the penetration of bedaquiline, and 2 next-generation diarylquinolines, TBAJ876 and TBAJ587, in cavities. Methods: Rabbits with established cavitary tuberculosis received the study drugs. A laser-capture microdissections scheme was developed to measure drug concentrations as a function of distance from blood supply in caseum. To simulate drug coverage in patient cavities, the data were modeled, and parameter estimates were linked to clinical plasma pharmacokinetic models. Results: Pharmacokinetic-pharmacodynamic simulations in caseum revealed that bedaquiline reaches steady state and efficacious concentrations in deep caseum after several weeks to months and lingers at subtherapeutic concentrations up to 3 years after therapy ends. TBAJ876 and TBAJ587, achieve bactericidal concentrations in caseum layers more rapidly and shorten the window of suboptimal concentrations post treatment compared to bedaquiline. Conclusions: The slow kinetics of diffusion of bedaquiline into and out of caseum creates spatiotemporal windows of subtherapeutic concentrations. Site-of-disease simulations of TBAJ587 and TBAJ876 predict reduced opportunities for resistance development.

Introduction: Bacille Calmette-Guérin (BCG), the only tuberculosis vaccine currently in clinical use, provides inadequate long-term protection. Administered at birth, BCG induces broad immune responses against a large number of antigens shared with Mycobacterium tuberculosis (Mtb), but protection wanes over time. We have previously shown that unconventional B cell subsets play a role in tuberculosis control.Methods: High-dimensional flow cytometry and multiplex cytokine analysis were employed to investigate the effects of immunotherapy on BCG-vaccinated mice in an Mtb challenge model.Results: In this study, we investigate the potential of recombinant cytokines targeting B cells – B-cell activating factor (BAFF) and A proliferation-inducing ligand (APRIL) – to modulate BCG immunity and improve protection in mice. Both cytokines play overlapping roles in B cell development and peripheral survival. Following subcutaneous BCG vaccination, immunotherapy with BAFF or APRIL resulted in an increased frequency of unconventional B cells potentially transitioning into antibody-producing plasma cells. Concurrently, we observed an increased frequency of central memory T cells, a subset critical for protective immunity. Changes in cellular immune responses were accompanied by reduced pro-inflammatory cytokine profiles and a contraction of the leukocyte population in lungs. Importantly, mice receiving BCG vaccination followed by BAFF or APRIL immunotherapy exhibited superior long-term protection against pulmonary tuberculosis relative to controls that received only BCG.Conclusion: In summary, our findings demonstrate that combining BCG vaccination with B cell targeted immunomodulatory therapies can improve long-term protection against pulmonary tuberculosis, highlighting the continued relevance and underutilized potential of BCG as a vaccine platform.

TBI-223, a novel oxazolidinone for tuberculosis, is designed to provide improved efficacy and safety compared to linezolid in combination with bedaquiline and pretomanid (BPaL). We aim to optimize the dosing of TBI-223 within the BPaL regimen for enhanced therapeutic outcomes. TBI-223 is investigated in preclinical monotherapy, multidrug therapy, and lesion penetration experiments to describe its efficacy and safety versus linezolid. A translational platform incorporating linezolid and BPaL data from preclinical experiments and 4 clinical trials (NCT00396084, NCT02333799, NCT03086486, NCT00816426) is developed, enabling validation of the framework. TBI-223 preclinical and Phase 1 data (NCT03758612) are applied to the translational framework to predict clinical outcomes and optimize TBI-223 dosing in combination with bedaquiline and pretomanid. Results indicate that daily doses of 1200–2400 mg TBI-223 may achieve efficacy comparable to the BPaL regimen, with >90% of patients predicted to reach culture conversion by two months.

Tuberculous meningitis (TBM) has a high mortality, possibly due to suboptimal therapy. Drug exposure data of antituberculosis agents in the central nervous system (CNS) are required to develop more effective regimens. Rifabutin is a rifamycin equivalently potent to rifampin in human pulmonary tuberculosis. Here, we show that human-equivalent doses of rifabutin achieved potentially therapeutic exposure in relevant CNS tissues in a rabbit model of TBM, supporting further evaluation in clinical trials.

Conditions affecting the brain are the second leading cause of death globally. One of the main challenges for drugs targeting brain diseases is passing the blood-brain barrier (BBB). Here, the effectiveness of mesoporous silica nanostars (MSiNSs) with two different spike lengths to cross an in vitro BBB multicellular model was evaluated and compared to spherical nanoparticles (MSiNP). A modified sol-gel single-micelle epitaxial growth was used to produce MSiNS, which showed no cytotoxicity or immunogenicity at concentrations of up to 1 μg mL^-1 in peripheral blood mononuclear and neuronal cells. The nanostar MSiNS effectively penetrated the BBB model after 24 h, and MSiNS-1 with a shorter spike length (9 ± 2 nm) crossed the in vitro BBB model more rapidly than the MSiNS-2 with longer spikes (18 ± 4 nm) or spherical MSiNP at 96 h, which accumulated in the apical and basolateral sides, respectively. Molecular dynamic simulations illustrated an increase in configurational flexibility of the lipid bilayer during contact with the MSiNS, resulting in wrapping, whereas the MSiNP suppressed membrane fluctuations. This work advances an effective brain drug delivery system based on virus-like shaped MSiNS for the treatment of different brain diseases and a mechanism for their interaction with lipid bilayers.