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Mycobacterial interactions promote Vγ9Vδ2 T cells to target and kill cancer cells

I C Schiavi(1) M Bodman-Smith(1) L Ridgley(2) T Bull(1)

1:St. George's University of London; 2:AstraZeneca

Inoculation of live BCG into melanoma or bladder cancer sites promotes host Vγ9Vδ2 (Vδ2) T cell infiltration and disease regression. Efficacy can be enhanced by priming with bisphosphonates, such as zoledronic acid (ZA), suggesting engagement of phosphoantigens and BTN3A1-Vδ2TCR receptors. Unfortunately, repeated dosing with BCG can be detrimental, resulting in granulomas and is contraindicated in immunosuppressed individuals. Additionally, ZA is rapidly sequestered in the bone. Defining components driving these phenomena could offer focussed, practical and safer application of this form of cancer immunotherapy. We aim to derive capacity of mycobacterial lipid fractions to activate human Vδ2 T cell populations driving cancer cell killing. 

Lipids from diverging morphological phenotypic cultures of Mycobacterium vaccae and BCG were fractionated using chloroform, methanol, and water. Vδ2 T cells were exposed to live mycobacterial cultures or corresponding extracted lipids, expanded for 13 days then co-cultured with tumour cell lines or ZA-primed tumour cell lines. The degree of Vδ2 T cell directed cytotoxicity was determined using live/dead staining and FACS. 

Live mycobacteria exhibited a diverse interactivity with Vδ2 T cells related to morphotype, allowing them to expand, target and kill cancer cells. Killing was enhanced by ZA-priming of target cell populations. Lipids extracted from the same morphotypes similarly activated and expanded Vδ2 T cell populations but generated a significantly greater cancer cell killing efficiency than stimulation by live bacteria alone. Additionally, this effect was independent of ZA-priming of target cells. Interaction of mycobacterial lipid fractions with Vδ2 T cells promotes their ability to kill cancer cells.

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