Bacillus Calmette-Guerin (BCG) induces superior anti-tumour responses by Vδ2+ T cells compared with the aminobisphosphonate drug zoledronic acid

Vδ2+ T cells can recognize malignantly transformed cells as well as those infected with mycobacteria. This cross-reactivity supports the idea of using mycobacteria to manipulate Vδ2+ T cells in cancer immunotherapy. To date, therapeutic interventions using Vδ2+ T cells in cancer have involved expanding these cells in or ex vivo using zoledronic acid (ZA). Here, we show that the mycobacterium Bacillus Calmette–Guérin (BCG) also causes Vδ2+ T-cell expansion in vitro and that resulting Vδ2+ cell populations are cytotoxic toward tumour cell lines. We show that both ZA and BCG-expanded Vδ2+ cells effectively killed both Daudi and THP-1 cells. THP-1 cell killing by both ZA and BCG-expanded Vδ2+ cells was enhanced by treatment of targets cells with ZA. Although no difference in cytotoxic activity between ZA- and BCG-expanded Vδ2+ cells was observed, BCG-expanded cells degranulated more and produced a more diverse range of cytokines upon tumour cell recognition compared to ZA-expanded cells. ZA-expanded Vδ2+ cells were shown to upregulate exhaustion marker CD57 to a greater extent than BCG-expanded Vδ2+ cells. Furthermore, ZA expansion was associated with upregulation of inhibitory markers PD-1 and TIM3 in a dose-dependent manner whereas PD-1 expression was not increased following expansion using BCG. Intradermal BCG vaccination of rhesus macaques caused in vivo expansion of Vδ2+ cells. In combination with the aforementioned in vitro data, this finding suggests that BCG treatment could induce expansion of Vδ2+ T cells with enhanced anti-tumour potential compared to ZA treatment and that either ZA or BCG could be used intratumourally as a means to potentiate stronger anti-tumour Vδ2+ T-cell responses.