Digital PCR detection of Mycobacterium tuberculosis and HIV-1 co-localization in spinal tuberculosis biopsies

BackgroundMycobacterium tuberculosis (Mtb) and HIV-1 co-infection in tissues is suggested to favour reciprocal replication, infection and reservoir expansion. Yet, confirmation of this detrimental synergism in diseased tissues is limited. MethodsIn this prospective study of 25 adults investigated for spinal tuberculosis (STB) in South Africa (13 (52%) people living with HIV-1 (PLWH), on antiretroviral treatment) 25 open surgery or CT-guided biopsies were collected and portioned into 93 segments. Extracted DNA was analysed by droplet digital PCR (ddPCR) to detect and quantify Mtb complex (MTBC) (rpoB, IS6110), HIV-1 (pol, gag) and Human (RPP30) gene copies. ddPCR sensitivity for Mtb was validated against Xpert-Ultra and culture. Total biopsy and intra-biopsy variation in pathogen DNA abundance, co-detection, and relationships to human cellularity, HIV status, and peripheral viral load (VL) evaluated. ResultsddPCR detected MTBC DNA in biopsies from 10/10 (100%) culture-confirmed STB, 5/6 (83%) Xpert Ultra-confirmed STB and 4/9 (44%) diagnosed Not STB (all 4 with previous pulmonary TB). Detected MTBC ranged from 8-59,144 rpoB copies/biopsy. RpoB copies/million human cells were higher in biopsies from PLWH (p=0.0096) and positively correlated with matched-segment HIV-1 pol copies/million cells (r=0.40; p=0.0003), but not VL. HIV-1 DNA was detected in all PLWH biopsies, four with undetectable VL. HIV-1 pol copies/million cells were higher in segments with MTBC DNA co-detected (p=0.011) and also correlated with VL (r=0.91; p=0.0003). ConclusionsReciprocal relationships exists between Mtb and HIV-1 abundance in spinal tissue. Findings support investigating TB-HIV co-infected tissue segments to characterise how the immune microenvironment impacts HIV-1/Mtb reservoir persistence and/or expansion.