Quantification and detection of Mycobacterium tuberculosis, HIV-1 co-localization, and reciprocal expansion in spinal...

The paucibacillary nature of spinal tuberculosis (STB) challenges diagnosis. Tissue sites of Mycobacterium tuberculosis (Mtb) and HIV-1 co-infection are suggested to favor reciprocal replication, and reservoir expansion, including in people living with HIV-1 (PLWH) on antiretroviral treatment (ART); however, evidence is scant. This study aimed to evaluate the utility of droplet digital polymerase chain reaction (ddPCR) to detect and quantify Mtb DNA in spinal biopsy tissue, with sensitivity validated against culture and Xpert Mtb/rifampicin (MTB/RIF) Ultra, and determine whether Mtb, and reciprocally HIV-1, DNA abundance is increased in sites of spinal co-infection.

Overall, 93 spinal biopsy segments from adults (≥18 years; n = 25, 52% PLWH on ART) with presumptive STB in South Africa had DNA extracted and ddPCR quantified copies of Mtb complex (MTBC) (rpoB, IS6110), HIV-1 (pol, gag) and Human (RPP30) genes.

ddPCR detected MTBC DNA in biopsies from 10/10 (100%) culture-confirmed STB, 5/6 (83%) Xpert Ultra-confirmed STB and 4/9 (44%) culture and Xpert MTB/RIF Ultra negative patients (all four had previous pulmonary TB). Detected MTBC ranged from 8-59144 rpoB copies/biopsy. RpoB copies/10⁶ human cells were higher in biopsies from PLWH (P = 0.0096) and positively correlated with matched biopsy segment HIV-1 pol copies/10⁶ cells (r = 0.40; P = 0.0003), and not peripheral viral load. HIV-1 pol copies/10⁶ cells were higher in segments with MTBC DNA co-detected (P = 0.011) and also correlated with viral load (r = 0.91; P = 0.0003).

DdPCR has high sensitivity for STB diagnosis. Confirming reciprocal relationships exists between Mtb and HIV-1 abundance in spinal tissue in PLWH on ART, supports characterizing the immune microenvironment in co-infected tissue sites to elucidate factors that impact HIV-1/Mtb reservoir persistence and/or expansion.