Analysis of the immune effects of two heat-killed whole cell mycobacterial preparations

Heat killed (HK) whole-cell preparations of the rapidly-growing mycobacteria, Mycobacterium vaccae and M. obuense, have been shown to possess immunomodulatory properties and hence a promising therapeutic potential. However, the outcome of interaction between both HK mycobacterial preparations and primary human innate immune cells remains largely undefined. The aim of this study was to investigate the regulation of surface expression of different categories of receptors on human neutrophils, monocytes, myeloid (m), and plasmacytiod (p) dendritic cells (DCs) following their in vitro stimulation with HK M. vaccae or M. obuense. Moreover, the pattern of cytokine and chemokine production in whole blood cultures and by purified total blood DCs in response to mycobacterial stimulation was examined. The current study also examined the phenotypic, functional, and transcriptomic profiles of non-activated and LPS/IFNy- activated human monocyte derived macrophages (MDM) differentiated with HK M. obuense (Mob-MDM), M-CSF (M-MDM), and GM-CSF (GM-MDM). Both HK mycobacterial preparations were found, first, to regulate the surface expression of adhesion, antigen-presenting, costimulatory, pattern recognition, cytokine/chemokine, complement, and Fe receptors on whole blood monocytes and neutrophils and, second, to induce mainly the production of pro-inflammatory cytokines/chemokines (CCL3, CCL5, CXCL8, IL-6, IL-12/23p40 and TNF-a) in whole blood cultures. Additionally, HK M. obuense was shown to primarily upregulate the surface expression of DCs and to augment the release of pro-inflammatory cytokines/chemokines (IL-6, IL12/23p40, TNF-a, CCL4, CCL5 and CXL8) by purified total blood DCs. Toll-like receptor (TLR-1) and TLR-2 were also identified to be engaged in mediating the HK M. obuense-induced up-regulation of CD11c and MHC class II surface expression on whole blood monocytes and mDCs. Of note, HK M. obeunse demonstrated an ability to trigger human monocyte-to-macrophange differentiation. Integrative phenotypic and genome-wide transcriptomic analysis revealed cytokine/chemokine secretion patterns, gene expression profiles and gene-gene networks in non-activated and LPS/IFNy-activated Mob-MDM that were quite distinct from those observed in non-activated and LPS/IFNy-activated M-MDM and GM-MDM. Overall, data from this study suggested that HK M. obuense exhibit potent immunomodulatory effects on primary human innate immune cells. Moreover, these results, together with previous clinical studies, point to a potential implication of HK M.obuense in the immunotherapy of cancer