Digital PCR detection of Mycobacterium tuberculosis and HIV-1 co-localization in spinal tuberculosis biopsies
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Background.
The paucibacillary nature of spinal tuberculosis (STB) makes diagnosis challenging, particularly in people living with HIV-1 (PLWH). It is suggested that HIV-1 and Mycobacterium tuberculosis ( Mtb ) co-infection in tissues favours reciprocal replication, infection and reservoir expansion. Yet, confirmation of this detrimental synergism in diseased tissues is scant.
Methods
In a prospective study of 25 adults (13 (52%) people living with HIV-1 (PLWH) on antiretroviral treatment (ART)) undergoing spinal biopsy investigation for STB in South Africa, droplet digital PCR (ddPCR) was used to detect and quantify Mtb complex (MTBC) DNA ( rpoB and IS6110 ) in 93 biopsy segments, and HIV-1 DNA ( pol and gag ) in 41 segments from PLWH. ddPCR sensitivity for Mtb was validated against Xpert-Ultra and culture. Relationships between pathogen DNA abundance, co-detection, human cellularity, HIV status, and peripheral viral load (VL) were evaluated.
Findings
ddPCR detected MTBC DNA in 19/25 (76%) patients (range: 8- 59,144 rpoB copies/biopsy), with increased detection in those with confirmed STB and a history of TB. MTBC rpoB copies/million cells were higher in biopsies from PLWH (p=0.0096) and positively correlated with matched biopsy segment HIV-1 pol copies/million cells (r=0.40; p=0.0003), but not peripheral VL. HIV-1 DNA was detected in all biopsies from PLWH, four with undetectable VL. HIV-1 pol copies/million cells were higher in biopsy segments with MTBC DNA co-detected (p=0.011) and strongly correlated with VL (r=0.91; p=0.0003).
Interpretation
ddPCR has high sensitivity for Mtb and HIV-1 DNA quantification in STB biopsies. Mtb tissue abundance correlated with localised but not systemic HIV-1 abundance. Increased HIV-1 DNA detection at sites co-localised with Mtb supports further investigating the TB microenvironment as a site for HIV-1 reservoir persistence and expansion in PLWH on ART.
Funding
Wellcome (203135Z/16/Z); Academy of Science of SA (ASSAf); ORU, UCT; UCT Merit Award.
Contacts
Anna Coussens, Walter and Eliza Hall Institute of Medical Research (WEHI), 1G Royal Parade, Parkville, 3052, Australia; Tel: +61 3 39452699; Email: coussens.a@wehi.edu.au Robyn Waters, Division of Orthopaedic Surgery, University of Cape Town, Anzio Rd, Observatory, 7925, South Africa; Email: robyn.waters@uct.ac.za
