Waters, R.; Martineau, A.; Laubscher, M.; Dunn, R. N.; Held, M.; Abrahams, M.-R.; Coussens, A. K.

The paucibacillary nature of spinal tuberculosis (STB) makes diagnosis challenging, particularly in people living with HIV-1 (PLWH). HIV-1 and Mycobacterium tuberculosis (Mtb) co-infection in tissues may favour reciprocal replication, infection and reservoir expansion. Yet, confirmation in diseased tissues is scant. In a prospective study of 25 adults (13 (52%) PLWH on antiretroviral treatment (ART)) undergoing spinal biopsy investigation for STB, 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. Mtb ddPCR sensitivity was validated against Xpert-Ultra and culture. Pathogen DNA abundance, co-detection, human cellularity, HIV status, and peripheral viral load (VL) relationships were evaluated. 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 TB history. 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), 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). 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 investigating the TB microenvironment for HIV-1 reservoir persistence and expansion in PLWH on ART.