Balancing access to BPaLM regimens and risk of resistance

Therapeutic developments for tuberculosis and nontuberculous mycobacterial lung disease

Tuberculosis (TB) drug discovery and development has undergone nothing short of a revolution over the past 20 years. Successful public-private partnerships and sustained funding have delivered a much-improved understanding of mycobacterial disease biology and pharmacology and a healthy pipeline that can tolerate inevitable attrition. Preclinical and clinical development has evolved from decade-old concepts to adaptive designs that permit rapid evaluation of regimens that might greatly shorten treatment duration over the next decade. But the past 20 years also saw the rise of a fatal and difficult-to-cure lung disease caused by nontuberculous mycobacteria (NTM), for which the drug development pipeline is nearly empty. Here, we discuss the similarities and differences between TB and NTM lung diseases, compare the preclinical and clinical advances, and identify major knowledge gaps and areas of cross-fertilization. We argue that applying paradigms and networks that have proved successful for TB, from basic research to clinical trials, will help to populate the pipeline and accelerate curative regimen development for NTM disease.

Molecular determinants of multidrug-resistant tuberculosis in Sierra Leone

Multidrug-resistant tuberculosis (MDR-TB) management has become a serious global health challenge. Understanding its epidemic determinants on the regional level is crucial for developing effective control measures. We used whole genome sequencing data of 238 of Mycobacterium tuberculosis complex (MTBC) strains to determine drug resistance profiles, phylogeny, and transmission dynamics of MDR/rifampicin-resistant (RR) MTBC strains from Sierra Leone. Forty-two strains were classified as RR, 196 as MDR, 5 were resistant to bedaquiline (BDQ) and clofazimine (CFZ), but none was found to be resistant to fluoroquinolones. Sixty-one (26%) strains were resistant to all first-line drugs, three of which had additional resistance to BDQ/CFZ. The strains were classified into six major MTBC lineages (L), with strains of L4 being the most prevalent, 62% (n = 147), followed by L6 (Mycobacterium africanum) strains, (21%, n = 50). The overall clustering rate (using ≤d12 single-nucleotide polymorphism threshold) was 44%, stratified into 31 clusters ranging from 2 to 16 strains. The largest cluster (n = 16) was formed by sublineage 2.2.1 Beijing Ancestral 3 strains, which developed MDR several times. Meanwhile, 10 of the L6 strains had a primary MDR transmission. We observed a high diversity of drug resistance mutations, including borderline resistance mutations to isoniazid and rifampicin, and mutations were not detected by commercial assays. In conclusion, one in five strains investigated was resistant to all first-line drugs, three of which had evidence of BDQ/CFZ resistance. Implementation of interventions such as rapid diagnostics that prevent further resistance development and stop MDR-TB transmission chains in the country is urgently needed.

IMPORTANCE

A substantial proportion of MDR-TB strains in Sierra Leone were resistant against all first line drugs; however this makes the all-oral-six-month BPaLM regimen or other 6-9 months all oral regimens still viable, mainly because there was no FQ resistance.Resistance to BDQ was detected, as well as RR, due to mutations outside of the hotspot region. While the prevalence of those resistances was low, it is still cause for concern and needs to be closely monitored.

Emergence of bedaquiline-resistant tuberculosis and of multidrug-resistant and extensively drug-resistant Mycobacterium tuberculosis strains with rpoB Ile491Phe mutation not detected by Xpert MTB/RIF in Mozambique: a retrospective observational study

BACKGROUND

In 2021, an estimated 4800 people developed rifampicin-resistant tuberculosis in Mozambique, 75% of which went undiagnosed. Detailed molecular data on rifampicin-resistant and multidrug-resistant (MDR) tuberculosis are not available. Here, we aimed at gaining precise data on the determinants of rifampicin-resistant and MDR tuberculosis in Mozambique.

METHODS

In this retrospective observational study, we performed whole-genome sequencing of 704 rifampicin-resistant Mycobacterium tuberculosis complex (Mtbc) strains submitted to the National Tuberculosis Reference Laboratory (NTRL) in Maputo, Mozambique, between 2015 and 2021. Phylogenetic strain classification, genomic resistance prediction, and cluster analysis were performed.

FINDINGS

Between Jan 1, 2015, and July 31, 2021, 2606 Mtbc isolates with an isoniazid or rifampicin resistance were identified in the NTRL biobank, of which, 1483 (56·9%) were from men, 1114 (42·7%) from women, and nine (0·4%) were unknown. Genome-based drug-resistant prediction classified 704 Mtbc strains as rifampicin resistant. 628 (89%) of the 704 Mtbc strains were classified MDR; of those, 146 (23%) were pre-extensively drug resistant (pre-XDR; additional fluoroquinolone resistance), and 24 (4%) extensively drug resistant (XDR; combined fluoroquinolone and bedaquiline resistance). Overall, 61 (9%) of 704 strains revealed resistance to bedaquiline: five (7%) of 76 rifampicin resistant plus bedaquiline resistant, 32 (7%) of 458 MDR plus bedaquiline resistant, and 24 (100%) of 24 XDR. Prevalence of bedaquiline resistance increased from 3% in 2016 to 14% in 2021. The cluster rate (12 single-nucleotide polymorphism threshold) was 42% for rifampicin-resistant strains, 78% for MDR strains, 94% for pre-XDR strains, and 96% for XDR Mtbc strains. 31 (4%) of 704 Mtbc strains, belonging to a diagnostic escape outbreak strain previously described in Eswatini (group_56), had an rpoB Ile491Phe mutation which is not detected by Xpert MTB/RIF (no other rpoB mutation). Of these, 23 (74%) showed additional resistance to bedaquiline, 13 (42%) had bedaquiline and fluoroquinolone resistance, and two (6%) were bedaquiline, fluoroquinolone, and delamanid resistant.

INTERPRETATION

Pre-XDR resistance is highly prevalent among MDR Mtbc strains in Mozambique and so is bedaquiline resistance; and the frequency of bedaquiline resistance quadrupled over time and was found even in Mtbc strains without fluoroquinolone resistance. Importantly, strains with Ile491Phe mutation were frequent, accounting for 31% (n=10) of MDR plus bedaquiline-resistant strains and 54% (n=13) of XDR Mtbc strains. Given the current diagnostic algorithms and treatment regimens, both the emergence of rifampicin resistance due to Ile491Phe and bedaquiline resistance might jeopardise MDR tuberculosis prevention and care unless sequencing-based technology is rolled out. The potential cross border spread of diagnostic escape strains needs further investigation.

FUNDING

The German Ministry of Health through the Seq_MDRTB-Net project, the Deutsche Forschungsgemeinschaft under Germany's Excellence Strategy Precision Medicine in Inflammation and the Research Training Group 2501 TransEvo, the Leibniz Science Campus Evolutionary Medicine of the Lung, and the German Ministry of Education and Research via the German Center for Infection Research.

Genotype-Phenotype Characterization of Serial Mycobacterium tuberculosis Isolates in Bedaquiline-Resistant Tuberculosis

BACKGROUND

Emerging resistance to bedaquiline (BDQ) threatens to undermine advances in the treatment of drug-resistant tuberculosis (DRTB). Characterizing serial Mycobacterium tuberculosis (Mtb) isolates collected during BDQ-based treatment can provide insights into the etiologies of BDQ resistance in this important group of DRTB patients.

METHODS

We measured mycobacteria growth indicator tube (MGIT)-based BDQ minimum inhibitory concentrations (MICs) of Mtb isolates collected from 195 individuals with no prior BDQ exposure who were receiving BDQ-based treatment for DRTB. We conducted whole-genome sequencing on serial Mtb isolates from all participants who had any isolate with a BDQ MIC >1 collected before or after starting treatment (95 total Mtb isolates from 24 participants).

RESULTS

Sixteen of 24 participants had BDQ-resistant TB (MGIT MIC ≥4 µg/mL) and 8 had BDQ-intermediate infections (MGIT MIC = 2 µg/mL). Participants with pre-existing resistance outnumbered those with resistance acquired during treatment, and 8 of 24 participants had polyclonal infections. BDQ resistance was observed across multiple Mtb strain types and involved a diverse catalog of mmpR5 (Rv0678) mutations, but no mutations in atpE or pepQ. Nine pairs of participants shared genetically similar isolates separated by <5 single nucleotide polymorphisms, concerning for potential transmitted BDQ resistance.

CONCLUSIONS

BDQ-resistant TB can arise via multiple, overlapping processes, including transmission of strains with pre-existing resistance. Capturing the within-host diversity of these infections could potentially improve clinical diagnosis, population-level surveillance, and molecular diagnostic test development.

Treatment-shortening regimens for tuberculosis: updates and future priorities

In the past 2 years, remarkable advances have been made in shortening tuberculosis (TB) treatment. In particular, four clinical trials (Study 31/A5349, Nix-TB, ZeNix and TB-PRACTECAL) have provided evidence of the efficacy of regimens based on new and repurposed drugs: the 4-month regimen for drug-susceptible TB, and the 6-month bedaquiline-pretomanid-linezolid regimen with or without moxifloxacin for multidrug-resistant/rifampicin-resistant TB. Even if the evidence at the basis of these new regimens is compelling, several questions remain open, particularly concerning linezolid dose finding, the upsurging threat of bedaquiline-resistant Mycobacterium tuberculosis and the feasibility of applying these results to the paediatric population. Several ongoing trials may fill the remaining gaps and produce further reliable evidence to address the outstanding questions in TB treatment shortening.

Update on the diagnosis of tuberculosis

BACKGROUND

Tuberculosis (TB) remains a global public health threat, and the development of rapid and precise diagnostic tools is the key to enabling the early start of treatment, monitoring response to treatment, and preventing the spread of the disease.

OBJECTIVES

An overview of recent progress in host- and pathogen-based TB diagnostics.

SOURCES

We conducted a PubMed search of recent relevant articles and guidelines on TB screening and diagnosis.

CONTENT

An overview of currently used methods and perspectives in the following areas of TB diagnostics is provided: immune-based diagnostics, X-ray, clinical symptoms and scores, cough detection, culture of Mycobacterium tuberculosis and identifying its resistance profile using phenotypic and genotypic methods, including next-generation sequencing, sputum- and non-sputum-based molecular diagnosis of TB and monitoring of response to treatment.

IMPLICATIONS

A brief overview of the most relevant advances and changes in international guidelines regarding screening and diagnosing TB is provided in this review. It aims at reviewing all relevant areas of diagnostics, including both pathogen- and host-based methods.

Rolling out new anti-tuberculosis drugs without diagnostic capacity

Deaths from tuberculosis (TB) reached over 1.6 million in 2021 with 10.6 million people becoming ill. Multidrug-resistant TB, defined as the Mycobacterium tuberculosis organism having resistance to at least isoniazid and rifampicin, represented 3.9% of new TB cases and 18% of previously treated cases. While new drug regimens continue to be developed and introduced to improve treatment of drug-resistant forms of TB, diagnostic capability to identify drug resistance lags woefully behind. While significant mortality benefits exist for these newer drug regimens, implementing them without proper drug resistance diagnostic capacity could lead to development of more drug resistances and exhaust these new therapeutic tools. Moving forward, the roll-out of new TB drugs and regimens must be paired with implementation of diagnostics to ensure judicious use of resources and the best chance for improving TB worldwide.

The relative transmission fitness of multidrug-resistant Mycobacterium tuberculosis in a drug resistance hotspot

Multidrug-resistant tuberculosis (MDR-TB) is among the most frequent causes of death due to antimicrobial resistance. Although only 3% of global TB cases are MDR, geographical hotspots with up to 40% of MDR-TB have been observed in countries of the former Soviet Union. While the quality of TB control and patient-related factors are known contributors to such hotspots, the role of the pathogen remains unclear. Here we show that in the country of Georgia, a known hotspot of MDR-TB, MDR Mycobacterium tuberculosis strains of lineage 4 (L4) transmit less than their drug-susceptible counterparts, whereas most MDR strains of L2 suffer no such defect. Our findings further indicate that the high transmission fitness of these L2 strains results from epistatic interactions between the rifampicin resistance-conferring mutation RpoB S450L, compensatory mutations in the RNA polymerase, and other pre-existing genetic features of L2/Beijing clones that circulate in Georgia. We conclude that the transmission fitness of MDR M. tuberculosis strains is heterogeneous, but can be as high as drug-susceptible forms, and that such highly drug-resistant and transmissible strains contribute to the emergence and maintenance of hotspots of MDR-TB. As these strains successfully overcome the metabolic burden of drug resistance, and given the ongoing rollout of new treatment regimens against MDR-TB, proper surveillance should be implemented to prevent these strains from acquiring resistance to the additional drugs.