Abstract:
Extrapulmonary tuberculosis (TB) is a significant public health challenge in South Africa and worldwide,
largely fuelled by the HIV epidemic. In spinal TB, Mycobacteria infect the spinal column without dissemination
to the spinal cord. The immune microenvironment, target cell characteristics, and other evolutionary
forces within granulomas during HIV/TB coinfection are poorly characterized. We investigated whether spinal
TB granulomas represent a sequestered anatomical site where independent HIV evolution occurs, and assessed
the role of macrophages as a target cell for both HIV and mycobacteria. RNA was extracted from plasma and
granulomatous tissue from six antiretroviral-naive HIV-1/spinal TB-coinfected patients, RT-PCR amplified,
and the C2-V5 env segment was cloned and sequenced. Analysis of genetic diversity, phylogeny and coalescence
patterns was performed on clonal sequences. To investigate their role in HIV sequestration, macrophages
and the HIV-1 p24 protein were immune localized and ultrastructural features were studied. Intercompartment
diversity measurements and phylogenetic reconstruction revealed anatomically distinct monophyletic HIV-1
clusters in four of six patients. Genotypic CCR5-tropic variants were predominant (98.9%) with conservation of
putative N-linked glycosylation sites in both compartments. CD68+ reactivity was associated with higher tissue
viral load (r = 1.0; p < 0.01) but not greater intrapatient diversity (r = 0.60; p > 0.05). Ultrastructural imaging
revealed the presence of bacterial and virus-like particles within membrane-bound intracellular compartments
of macrophages. Spinal tuberculosis granulomas may form anatomically discreet sites of divergent viral evolution.
Macrophages in these granulomas harbored both pathogens, suggesting that they may facilitate the
process of viral sequestration within this compartment.
