S35 Human mesenchymal stromal cells modulate cytokine expression and enhance intracellular clearance of Mycobacterium avium in primary macrophages

• Published in: Thorax Vol. 76; no. Suppl 1; pp. A24 - A25
• Main Authors: Shaw, TD, Krasnodembskaya, AD, Schroeder, GN, O’Kane, CM
• Format: Journal Article
• Language: English
• Published: London BMJ Publishing Group LTD 01.02.2021
• Subjects: Biopsy; Cancer therapies; Cytokines; Disease; Hospitals; Infections; Lung cancer; Mortality; Patients; Pneumonectomy; Thoracic surgery; Thorax
• ISSN: 0040-6376; 1468-3296
• DOI: 10.1136/thorax-2020-BTSabstracts.40

Introduction and ObjectivesThere is clear unmet need to develop more efficacious therapies for Mycobacterium (M. avium) pulmonary disease, particularly to disrupt their intracellular niche in lung macrophages. Mesenchymal Stromal Cells (MSCs) are multipotent adult cells with antimicrobial and immunomodulatory properties, currently being trialled for treating infection and chronic lung diseases, but their effect on M. avium is not known. This study aims to determine whether human MSCs can directly kill M. avium and modulate primary macrophages to enhance intracellular clearance.MethodsPrimary human monocyte-derived macrophages (MDM) from healthy volunteers were infected with M. avium (Chester reference laboratory strain) at multiplicity of infection (MOI) 1 for 4 hours, before washing. Infected MDMs were cultured with human bone marrow-derived MSCs, either in direct co-culture or with MSCs in transwells (0.4µm pore diameter). After 72 hours supernatant was collected, and cells lysed in 0.2% saponin, to determine extracellular and cell-associated colony counts. Supernatant cytokines and lipid mediators were quantified by ELISA. Statistical analysis was performed using the Kruskal-Wallis test.ResultsMSCs restricted intracellular growth of M. avium in MDMs in direct co-culture (median 19%, IQR 9–52%, p<0.05) and transwell (median 40%, IQR 25–50%, p<0.05) conditions compared to infected MDMs alone (figure 1A). Supernatant bacterial count was unaffected by presence of MSCs. Combining cell-associated and supernatant counts MSC treatment resulted in total growth reduction of 25% (direct co-culture) and 30% (transwell) over 72 hours (data not shown, p<0.05). Similar results were found for clinical isolates from patients with NTM-PD.MSCs infected alone with M. avium did not restrict bacterial growth, suggesting their anti-mycobacterial effect is mediated through activation of macrophages.Co-culture of MSCs and infected MDMs led to significantly increased concentrations of IL-6, IL-8 and PGE2 (figure 1B-1D).Abstract S35 Figure 1ConclusionsMSCs have no direct bactericidal activity against M. avium but enhance MDMs’ ability to restrict intracellular growth. MSCs co-cultured with infected MDM leads to increased secretion of IL-6, IL-8 and PGE2 which could contribute to more efficient growth restriction by macrophages. Further investigation will determine the role of these mediators and uncover the mechanisms underlying MSC ability to enhance the antimycobacterial capacity of MDMs.