|T cells team up with DC in anti-PD-1-mediated
tumour cell killing
|Immune checkpoint inhibitors, such as anti-CLTA4 and anti-PD-1 antibodies, have demonstrated effectiveness in a variety of cancers. In order to overcome resistance to immune checkpoint inhibitor therapy, which occurs in a majority of cancer patients, it is important to understand the mechanisms of anti-PD-1-mediated anti-tumour immunity.
Dr. Pittet and colleagues published their findings in a recent issue of Immunity (here), which allows us to better understand the mechanisms. By using intravital microscopy and anti-PD-1 treatment-sensitive MC38 murine colon cancer, the team traced IFNgamma-producing and IL12p40-secreting cells. One day after anti-PD-1 administration, more IFNgamma-producing cells were observed in the tumour microenvironment through 3 days after injection, which were further confirmed to be CD8+ T cells. Also, anti-PD-1 injection increased IL12p40-secreting cells through day 1 to 5 after treatment. These IL12p40-secreting cells were further confirmed to be dendritic cells (DC). Single-cell RNA sequencing on CD45+ tumour-infiltrating leukocytes from treated and untreated confirmed the expansion of Il12b (encoding IL12p40)-expressing DC after anti-PD-1 treatment. Depletion of DC resulted in a failure of rejecting tumour after anti-PD-1 treatment. Similarly, blocking IL12 by anti-IL12 neutralizing antibodies also abolished anti-PD-1-mediated tumour killing, indicating DC and IL12p40 secreted by DC are indispensable in anti-PD-1-mediated tumour immunity. As IL-12p40-secreting DC did not express PD-1 and intravital imaging showed anti-PD-1 antibodies accumulated with tumour-associated macrophages rather than DC 24 h after anti-PD-1 treatment, it seemed that anti-PD-1 might indirectly activate DC.
It has been reported that anti-PD-1 antibodies bind to CD8+ T cells, therefore the authors proposed that antibodies could activate DC through binding to CD8+ T cells. Depletion of CD8+ T cells or neutralization of INFgamma abrogated IL12 production in the tumour microenvironment, resulting from less IL12 produced by DC and fewer IL12-producing DC. Depletion IFNgamma receptor 1 in DC resulted inimpairment in IL12 production and failure in tumour rejection. Intratumoural injection of IL12 increased the abundance of IFNgamma-producing cells and promoted antitumor effects. Moreover, tumour-infiltrating CD8+ T stimulated by IL12 in vitro produced increased levels of IFNgamma.
As IL12-producing DC expressed more CD40 than IL12-negative DC and tumour-associated macrophages, agonist CD40 antibody was deployed. Intravital imaging indicated CD40 antibodies contacted with IL12-producing tumour-infiltrating cells (which were confirmed as DC), and increased the abundance of these cells. Similarly, activation of noncanonical NF-kappaB signalling by AZD5582 increased the proportion of IL12-producing cells in the tumour. Both agonist CD40 antibodies and AZD5582 had a tumour-killing effect, which was IL12-dependent, as neutralization of IL12 abolished the anti-tumour effect. More importantly, the combination of anti-PD-1 and agonist CD40 antibodies showed a complete, durable response in a majority of animals.
This study well established a role of T cells to interact with anti-PD-1 antibodies and subsequently produce IFNgamma, which is sensed by DC to produce IL12. The anti-cancer effect of anti-PD-1 antibodies can be amplified by co-administration of agonist CD40 antibodies that enhance IL12 production by DC.