Heat-killed Mycobacterium tuberculosis-induced trained immunity elicits antitumor activity in PBMCs from colon cancer patients with unresponsiveness to anti-PD-1 in vitro

Introduction:

Trained immunity (TI) is a form of innate immune memory characterized by boosted innate immune responses to secondary heterologous challenges following an initial stimulus. Several inducers, including fungal β-glucan and the Bacillus Calmette–Guérin (BCG) vaccine, induce TI in human peripheral blood mononuclear cells (PBMCs). Although the potential of TI in colon cancer has been explored in murine models, its relevance in patients remains poorly understood.

Methods:

Building on our previous demonstration that heat-killed Mycobacterium tuberculosis (HKMtb) induces TI, we applied a standardised training protocol to PBMCs from colon cancer patients (CC patients) and healthy volunteers (HV). Cytokine responses to heterologous stimulation were assessed using multiplex assays. To evaluate functional antitumour relevance, we performed in vitro tumour-killing assays against the SW480 colon cancer cell line, in the presence or absence of anti-PD-1 treatment, and characterised the associated cytokine milieu.

Results:

HKMtb-trained PBMCs from CC patients exhibited a partially preserved TI phenotype against secondary heterologous challenges, with increased TNF and IFN-γ and reduced IL-10, comparable to HV. By contrast, IL-6 and IL-1β production were not enhanced. Notably, HKMtb-induced training significantly increased the tumour-killing capacity of PBMCs from both CC patients and HV. In CC patients, this effect was accompanied by a specific heightened production of IL-12p70 and IP-10. Furthermore, whereas the anti-PD-1 treatment alone failed to induce a significant antitumour response in PBMCs from CC patients compared with HV, HKMtb-induced TI overcame this lack of response. Of note, this was again associated with an enhanced IL-12p70 and IP-10 profile.

Conclusion:

These findings provide proof of concept that HKMtb-induced TI enhances the antitumour activity of PBMCs from CC patients that are unresponsive to PD-1 blockade in vitro, supporting its potential as a promising immunomodulatory strategy in non-responsive CC patients.