30 jan. 2026
Lichterman et al. (BioRxiv)
Keywords
Circadian rhythm
Chronobiology
Cancer
Checkpoint Inhibition Therapy
Main Findings
The circadian clock governs many immunological processes including cell tracking, cell differentiation and function. Anecdotally, several epidemiological studies have found that the time-of-day may have an impact on the efficacy of immune checkpoint inhibition (ICI) therapy. Yet, the possible underlying mechanism to this circadian phenomenon remain poorly understood.
In this preprint, Lichterman et al. investigate the role of cell-intrinsic clocks in immune cells for ICI therapy efficacy. Initially, the authors demonstrate that ICI therapy during the onset of the light cycle (zeitgeber (ZT) 2) showed a pronounced anti-tumour efficiency against a two different cancer models (MC38 adenocarcinoma and B16-F10 melanoma), while treatment at the onset of the dark cycle (ZT18) showed barely any improvement. In this approach, the initial dose was particularly important in mediating the anti-tumour effects. Trying to identify a possible reason for this, the authors found that during ZT2 myeloid and T cell interactions in the tumor are closer than at ZT18. Additional scRNAseq revealed that during ZT2 there is a higher contribution of CD8+ T cells in the tumour as well as dendritic cells.
Trying to identify which cell requires its circadian rhythm to mediate the anti-tumour effects, the authors knocked out Bmal, a key circadian regulator in either DCs (using a CD11c-Cre) or CD8+ T cells (using a CD8-Cre). Deleting Bmal from DCs completely prevented the anti-tumor effects upon ICI therapy and reduced tumor-inflitrating T cell numbers. Interestingly, equally the deletion of Bmal from CD8+ T cells reduced anti-tumor effects upon ICI therapy. The data collectively suggested that circadian rhythm in both cell types are crucial for efficient ICI therapy outcomes.
Lastly, the authors wanted to address the type of interaction between DCs and T cells that may be circadian regulated. Using RNA sequencing, the authors found that expression of Cx3cl1 in DCs in a circadian manner, may drive the recruitment of CX3CR1+ CD8+ T cells in the tumour, thereby promoting anti-tumoral effects.
Limitations & Suggestions
A major caveat of the study is that the authors did not include the tumor-draining lymph nodes in their study. This would have been of particular interest considering that the main proliferative burst of T cells upon ICI therapy occurs in the lymph node.
Additionally, the authors should further dissect how migration is affected by circadian patterns (in and out of tissues and the lymphatics). These normal circadian patterns may have a striking impact on the outcomes upon ICI therapy. How does it contrast differences in migration patterns into other tissue sites beside the tumor?
The authors should more clearly discuss in their paper their contrasting findings in comparison to Wang et al. (PMID: 38723627), which showed the strongest efficacy of ICI therapy at ZT13 (during the onset of the night cycle).
Throughout the paper, the authors could have added for consistency reasons a couple of readouts to improve the study findings. This can include the consistent measurement of T cell phenotypes, numbers and infiltration in their different genetic perturbations and experimental setups. This may also include using the DC-specific Bmal knockout mouse to confirm data from their ChIP-PCR.
If the phenotype were so dependent on the DC-T cell interaction at the tumor site, it remains unclear why the authors also found such a strong influence of the time-of-day for the initial ICI therapy. How does an anti-PD1 antibody mediate this increased efficacy in a circadian dependent manner. The authors should at least make this clearer in their discussion, if not aiming to address this question experimentally.
From a clinical perspective, it would have been interesting to see if chronotypic interventions could ameliorate ICI therapy in these contexts, but this may be beyond the scope of this study.
Significance/Novelty
The study adds to a mounting body of evidence suggesting that circadian rhythms in immunotherapy may hold an interesting potential to maximise treatment efficiency. The authors additionally identify that circadian rhythm in both DCs as well as CD8+ T cells are required for the beneficial effects of ICI therapy at ZT2 in their model. Having identified the CX3CL1-CX3CR1 axis as a circadian dependent interaction may allow for additional studies into ameliorating ICI therapy.
Credit
Reviewed by Joel Wong and Felix Richter as part of a cross-institutional journal club between the Max-Delbrück Center Berlin, the Ragon Institute Boston (Mass General, MIT, Harvard), the University of Virginia, the Medical University of Vienna and other life science institutes in Vienna.
The author declares no conflict of interests in relation to their involvement in the review.