Circadian variation of the response of T cells to antigen

Impact of time-of-day atezolizumab plus bevacizumab combination therapy infusion for unresectable hepatocellular carcinoma: A retrospective multicenter study

AIM

This study aimed to evaluate the impact of infusion timing of time-of-day on clinical outcomes in patients with unresectable hepatocellular carcinoma (HCC) treated with atezolizumab plus bevacizumab combination therapy.

METHODS

A retrospective analysis was conducted using data from 751 unresectable HCC patients treated with atezolizumab plus bevacizumab between September 2020 and April 2024. Patients were categorized into morning (AM; n = 351) and afternoon (PM; n = 400) groups based on infusion timing of time-of-day. Outcomes, including progression-free survival (PFS), overall survival, objective response rate, and disease control rate, were assessed using Kaplan-Meier survival analysis and Cox regression analysis.

RESULTS

The PFS was significantly longer in the AM group (8.6 months, 95% CI 7.6-10.5) compared with the PM group (6.0 months, 95% CI 5.4-7.0; p = 0.006). In contrast, overall survival was similar between the groups (AM: 24.7 months vs. PM: 21.4 months; p = 0.99). Cox regression analysis revealed that morning infusion was an independent favorable predictor of PFS (HR 1.23, 95% CI 1.04-1.45). Additionally, the AM group demonstrated superior objective response rate and disease control rate compared with the PM group, suggesting better tumor control.

CONCLUSION

Morning infusion of atezolizumab plus bevacizumab is associated with improved PFS and response rates in unresectable HCC patients, highlighting the potential for optimizing treatment outcomes through circadian timing.

Circadian Rhythm Disruption Exacerbates Autoimmune Uveitis: The Essential Role of PER1 in Treg Cell Metabolic Support for Stability and Function

Circadian rhythm plays a critical role in the progression of autoimmune diseases. While our previous study demonstrated the therapeutic effects of melatonin in experimental autoimmune uveitis, the involvement of circadian rhythm remained unclear. Using a light-induced circadian rhythm disruption model, we showed that disrupted circadian rhythms exacerbate autoimmune uveitis by impairing the stability and function of Treg cells. Mechanistically, we identified the core clock gene Per1, which is significantly reduced under circadian disruption, is essential for Treg cell metabolism and immunoregulatory function. This study underscores the pivotal role of circadian rhythm-related Treg cells in autoimmune disease progression.

Investigating the circadian rhythm signaling pathway in HTLV-1 pathogenesis using Boolean analysis

The Human T-cell lymphotropic virus type 1 (HTLV-1), an oncogenic virus belonging to the Deltaretrovirus genus, expresses various proteins, including Tax and HBZ, which can affect many cellular pathways. In this study, we have investigated the role of the circadian rhythm signaling pathway, a key regulator of human health, in the pathogenesis of HTLV-1 using Boolean Network analysis and laboratory methods. After an extensive search of the circadian rhythm pathway, we analyzed the relationships between the genes of this pathway using the R programming language and the BoolNet package. Subsequently, we examined the impact of viral proteins on the cellular clock rhythm genes. Finally, we identified three genes, PER2, CRY1, and DEC1, as the main checkpoints from the attractors obtained. These three genes and two viral genes, Tax and HBZ, were quantitatively assessed on two groups of individuals, including ten asymptomatic carriers infected with HTLV-1 and ten healthy individuals using the qRT-PCR method. Our results showed that the expression level of PER2 and DEC1 genes was significantly higher in the asymptomatic carriers compared to the healthy control group. Also, we recorded positive correlations between PER2 and DEC1, CRY1 and DEC1, and negative correlations between HBZ and CRY1 and DEC1. In this study, we suggested that in asymptomatic carriers, the virus might try to induce a chronic infection by escaping from the immune system due to an alteration in circadian rhythm pathways. We also detected three promising genes in this pathway that could have therapeutic or diagnostic value in these individuals. However, this possibility requires further research in different periods, different groups (e.g., ATLL and HAM/TSP), and examining a more significant number of circadian rhythm genes.

Complex gene-dependent and-independent mechanisms control daily rhythms of hematopoietic cells

The abundance and behaviour of all hematopoietic components display daily oscillations, supporting the involvement of circadian clock mechanisms. The daily variations of immune cell functions, such as trafficking between blood and tissues, differentiation, proliferation, and effector capabilities are regulated by complex intrinsic (cell-based) and extrinsic (neuro-hormonal, organism-based) mechanisms. While the role of the transcriptional/translational molecular machinery, driven by a set of well-conserved genes (Clock genes), in nucleated immune cells is increasingly recognized and understood, the presence of non-transcriptional mechanisms remains almost entirely unexplored. Studies on anucleate hematopoietic components, such as red blood cells and platelets, have shown that auto-sustained redox reaction cycles persist and operate in mammals. This opens to the possibility that transcriptional and non-transcriptional circadian mechanisms might coexist in nucleated immune cell populations, potentially complementing each other. It is becoming increasingly clear that disruption of the circadian rhythm at the central level (core clock) is strongly implicated in a plethora of diseases that are associated with maladaptive immune responses. On the other hand, several evidence imply that dysregulated immune activity (e.g. excessive inflammation) may alter/disrupt the proper functioning of peripheral clocks. This knowledge paves the way to the exploitation of chronobiological concepts in clinical practice. A better comprehension of various transcriptional/translational and biochemical mechanisms that maintain rhythmicity in immune system activities, as well as the many factors (host-derived, microbiota-derived, environment) that can alter or disrupt these processes, will facilitate the development of novel chrono-immunotherapeutic approaches.

Basic helix-loop-helix ARNT like 1 regulates the function of immune cells and participates in the development of immune-related diseases

The circadian clock is an internal timekeeper system that regulates biological processes through a central circadian clock and peripheral clocks controlling various genes. Basic helix-loop-helix ARNT-like 1 (BMAL1), also known as aryl hydrocarbon receptor nuclear translocator-like protein 1 (ARNTL1), is a key component of the circadian clock. The deletion of BMAL1 alone can abolish the circadian rhythms of the human body. BMAL1 plays a critical role in immune cell function. Dysregulation of BMAL1 is linked to immune-related diseases such as autoimmune diseases, infectious diseases, and cancer, and vice versa. This review highlights the significant role of BMAL1 in governing immune cells, including their development, differentiation, migration, homing, metabolism, and effector functions. This study also explores how dysregulation of BMAL1 can have far-reaching implications and potentially contribute to the onset of immune-related diseases such as autoimmune diseases, infectious diseases, cancer, sepsis, and trauma. Furthermore, this review discusses treatments for immune-related diseases that target BMAL1 disorders. Understanding the impact of BMAL1 on immune function can provide insights into the pathogenesis of immune-related diseases and help in the development of more effective treatment strategies. Targeting BMAL1 has been demonstrated to achieve good efficacy in immune-related diseases, indicating its promising potential as a targetable therapeutic target in these diseases.

Immune checkpoint inhibitor infusion times and clinical outcomes in patients with melanoma

BACKGROUND

Circadian rhythms impact immune function; a previous study demonstrated that immunotherapy treatment times taking place later in the day correlated with poorer outcomes in patients with melanoma. However, this finding has not been replicated, and other infusion timing schemas are unexplored. The objective of this retrospective, cohort study was to determine if the time of immunotherapy infusion affects outcomes.

MATERIALS AND METHODS

Five hundred and sixteen participants age ≥18 years diagnosed with cutaneous, acral, mucosal, or unknown primary melanoma treated with >1 infusion of nivolumab, pembrolizumab, or combination ipilimumab/PD-1 inhibitors were included. Response rate, toxicity rate, overall survival (OS), and progression-free survival (PFS) were determined based on infusion timing.

RESULTS

Patients with ≥1 late infusion (after 4 pm) among their first 4 infusions had slightly poorer objective response rate compared with only pre-4 pm infusions (39.7% vs 44.5%), but no significant associations with late infusions and PFS and OS (P = .23, .93, respectively). Multivariable analyses showed no statistically significant association with outcomes for patients with any post-4 pm infusion among the first 4; median infusion time was also not associated with outcomes. However, considering all infusion times, we found inferior PFS (median 10.6 vs 38.9 months, P < .0001), and numerically inferior OS (median 54.6 vs 81.2 months, P = .19) in patients with ≥20% late infusions. Multivariable models had similarly inferior response and PFS for patients with ≥20% late infusions, and later median infusion times were associated with inferior response, PFS, and OS.

CONCLUSIONS

Late immunotherapy infusion times were associated with inferior outcomes when considering all infusions, but not when considering initial (first 4) infusions.

Human sleep and immunity: The role of circadian patterns

It is well established that sleep promotes health and welfare. Literature data suggests that sleep is a recurrent resting state that performs multiple biological functions, such as memory consolidation and regulation of glucose, lipid metabolism, energy metabolism, eating behavior, and blood pressure, besides, regulating the immune system. These immunological functions depend on regular sleep and circadian rhythms, as both impact the magnitude of immune responses. Circadian rhythm is the 24-h internal clock in our brain that regulates cycles of alertness and sleepiness by responding to light changes in our environment. It encompasses physical and behavioral daily oscillations. Sleep deprivation and circadian misalignment affect immunity, and both have been related to adverse health effects and chronic diseases. Studies have shown that individuals with regular and consistent sleep patterns have a more effective immune response. Thus, understanding how sleep disturbance will affect the immune response is vital in developing interventions to prevent the health burden of irregular sleep patterns and circadian misalignment, favoring a homeostatic immune defense to microbial or inflammatory insults. Therefore, the scope of this chapter is to explore evidence that regular circadian rhythms and sleep patterns are needed for optimal resistance to infectious challenges.

Circadian clock component PER2 negatively regulates CD4+ T cell IFN-γ production in ulcerative colitis

Period circadian clock 2 (PER2) is involved in the pathogenesis of various inflammatory and autoimmune diseases. However, there are gaps in our understanding of the role of PER2 in regulating CD4+ T cells beyond its time-keeping function in ulcerative colitis (UC) pathogenesis. Our findings revealed PER2 was predominantly expressed in CD4+ T cells, while it was significantly decreased in the inflamed mucosa and peripheral blood CD4+ T cells of UC patients compared with that in Crohn's disease (CD) patients and healthy controls (HC). Notably, PER2 expression was significantly recovered in UC patients in remission (R-UC) compared to that in active UC patients (A-UC) but not in CD patients. It was negatively correlated with the Ulcerative Colitis Endoscopic Index of Severity (UCEIS), Crohn's Disease Activity Index (CDAI), Simple Endoscopic Score for Crohn's disease (SES-CD), and C-reactive protein (CRP), respectively. Overexpression of PER2 markedly inhibited IFN-γ production in UC CD4+ T cells. RNA-seq analysis showed that overexpression of PER2 could repress the expression of a disintegrin and metalloproteinase 12 (ADAM12), a costimulatory molecule that determines Th1 cell fate. Mechanistically, cleavage under targets and tagmentation (CUT&Tag) analysis revealed that PER2 down-regulated ADAM12 expression by reducing its binding activity, thereby suppressing IFN-γ production in UC CD4+ T cells. Additionally, our data further demonstrated that ADAM12 was upregulated in CD4+ T cells and inflamed mucosa of A-UC patients compared to HC. Our study reveals a critical role of PER2 in regulating CD4+ T cell differentiation and highlights its potential as a therapeutic target for UC treatment.

Circadian rhythms of macrophages are altered by the acidic tumor microenvironment

Tumor-associated macrophages (TAMs) are prime therapeutic targets due to their pro-tumorigenic functions, but varying efficacy of macrophage-targeting therapies highlights our incomplete understanding of how macrophages are regulated within the tumor microenvironment (TME). The circadian clock is a key regulator of macrophage function, but how circadian rhythms of macrophages are influenced by the TME remains unknown. Here, we show that conditions associated with the TME such as polarizing stimuli, acidic pH, and lactate can alter circadian rhythms in macrophages. While cyclic AMP (cAMP) has been reported to play a role in macrophage response to acidic pH, our results indicate pH-driven changes in circadian rhythms are not mediated solely by cAMP signaling. Remarkably, circadian disorder of TAMs was revealed by clock correlation distance analysis. Our data suggest that heterogeneity in circadian rhythms within the TAM population level may underlie this circadian disorder. Finally, we report that circadian regulation of macrophages suppresses tumor growth in a murine model of pancreatic cancer. Our work demonstrates a novel mechanism by which the TME influences macrophage biology through modulation of circadian rhythms.

How does geographical diversity shape vaccine efficacy?

Vaccination is a cornerstone of public health, saving millions of lives each year by preventing a variety of infectious diseases. Yet, despite global vaccination efforts, emerging research highlights significant geographical disparities in vaccine efficacy and immunogenicity. These variations underscore the critical interplay between immunological factors and environmental, genetic, and nutritional elements across different populations. Our review article aimed to explore the multifactorial reasons behind geographical variations in vaccine efficacy. Also, this study has shown how important host factors like age, obesity, gender, and genetic diversity, especially within the major histocompatibility complex, are in determining how well a vaccine works. Nutritional status, namely deficiencies in micronutrients such as vitamins and zinc, and lifestyle factors including stress, sleep, alcohol consumption, and physical activity are also shown to have profound effects on vaccine-induced immunity. Importantly, our paper also brought to light the influence of microbial and ecological factors, such as the gut microbiome and environmental pollutants, on the immune system's response to vaccination. The findings emphasize the importance of tailoring vaccination strategies to accommodate the unique immunological landscapes shaped by geographical and societal factors. This tailored approach could enhance vaccine efficacy, reduce disparities in vaccine response, and ultimately contribute to the global fight against infectious diseases.

A New Frontier in Cystic Fibrosis Pathophysiology: How and When Clock Genes Can Affect the Inflammatory/Immune Response in a Genetic Disease Model

Cystic fibrosis (CF) is a monogenic syndrome caused by variants in the CF Transmembrane Conductance Regulator (CFTR) gene, affecting various organ and systems, in particular the lung, pancreas, sweat glands, liver, gastrointestinal tract, vas deferens, and vascular system. While for some organs, e.g., the pancreas, a strict genotype-phenotype occurs, others, such as the lung, display a different pathophysiologic outcome in the presence of the same mutational asset, arguing for genetic and environmental modifiers influencing severity and clinical trajectory. CFTR variants trigger a pathophysiological cascade of events responsible for chronic inflammatory responses, many aspects of which, especially related to immunity, are not ascertained yet. Although clock genes expression and function are known modulators of the innate and adaptive immunity, their involvement in CF has been only observed in relation to sleep abnormalities. The aim of this review is to present current evidence on the clock genes role in immune-inflammatory responses at the lung level. While information on this topic is known in other chronic airway diseases (chronic obstructive pulmonary disease and asthma), CF lung disease (CFLD) is lacking in this knowledge. We will present the bidirectional effect between clock genes and inflammatory factors that could possibly be implicated in the CFLD. It must be stressed that besides sleep disturbance and its mechanisms, there are not studies directly addressing the exact nature of clock genes' involvement in inflammation and immunity in CF, pointing out the directions of new and deepened studies in this monogenic affection. Importantly, clock genes have been found to be druggable by means of genetic tools or pharmacological agents, and this could have therapeutic implications in CFLD.

Identification of circadian clock-related immunological prognostic index and molecular subtypes in prostate cancer

BACKGROUND

Evidence suggests that the circadian clock (CIC) is among the important factors for tumorigenesis. We aimed to provide new insights into CIC-mediated molecular subtypes and gene prognostic indexes for prostate cancer (PCa) patients undergoing radical prostatectomy (RP) or radical radiotherapy (RT).

METHODS

PCa data from TCGA was analyzed to identify differentially expressed genes (DEGs) with significant fold changes and p-values. A prognostic index called CIC-related gene prognostic index (CICGPI) was developed through clustering methods and survival analysis and validated on multiple data sets. The diagnostic accuracy of CICGPI for resistance to chemotherapy and radiotherapy was confirmed. Additionally, the interaction between tumor immune environment and CICGPI score was explored, along with their correlation with prognosis.

RESULTS

TOP2A, APOE, and ALDH2 were used to classify the PCa patients into two subtypes. Cluster 2 had a higher risk of biochemical recurrence (BCR) than cluster 1 for PCa patients undergoing RP or RT. A CIC-related gene prognostic index (CICGPI) was constructed using the above three genes for PCa patents in the TCGA database. The CICGPI score showed good prognostic value in the TCGA database and was externally confirmed by PCa patients in GSE116918, MSKCC2010 and GSE46602. In addition, the CICGPI score had a certain and high diagnostic accuracy for tumor chemoresistance (AUC: 0.781) and radioresistance (AUC: 0.988). For gene set variation analysis, we observed that both beta alanine metabolism and limonene and pinene degradation were upregulated in cluster 1 for PCa patients undergoing RP or RT. For PCa patients undergoing RP, cell cycle, homologous recombination, mismatch repair, and DNA replication were upregulated in cluster 2. A strongly positive relationship between cancer-related fibroblasts and CICGPI score was observed in PCa patients undergoing RP or RT. Moreover, a high density of CAFs was highly closely associated with poorer BCR-free survival of PCa patients.

CONCLUSIONS

In this study, we established CIC-related immunological prognostic index and molecular subtypes, which might be useful for the clinical practice.

Diurnal rhythms in varicella vaccine effectiveness

BACKGROUNDImmune processes are influenced by circadian rhythms. We evaluate the association between varicella vaccine administration time of day and vaccine effectiveness.METHODSA national cohort, children younger than 6 years, were enrolled between January 2002 and December 2023. We compared children vaccinated during morning (7:00-10:59), late morning to afternoon (11:00-15:59), or evening hours (16:00-19:59). A Cox proportional hazards regression model was used to adjust for ethnicity, sex, and comorbidities. The first varicella infection occurring at least 14 days after vaccination and a second dose administration were treated as terminal events.RESULTSOf 251,141 vaccinated children, 4,501 (1.8%) experienced breakthrough infections. Infection rates differed based on vaccination time, with the lowest rates associated with late morning to afternoon (11:00-15:59), HR 0.88, 95% CI 0.82-0.95, P < 0.001, and the highest rates with evening vaccination (16:00-19:59), HR 1.41, 95% CI 1.32-1.52, P < 0.001. Vaccination timing remained significant after adjustment for ethnicity, sex, and comorbidities. The association between immunization time and infection risk followed a sinusoidal pattern, consistent with a diurnal rhythm in vaccine effectiveness.CONCLUSIONWe report a significant association between the time of varicella vaccination and its clinical effectiveness. Similar association was observed with the COVID-19 vaccine, providing proof of concept consistent with a diurnal rhythm in vaccine effectiveness.

Why does circadian timing of administration matter for immune checkpoint inhibitors' efficacy?

BACKGROUND

Tolerability and antitumour efficacy of chemotherapy and radiation therapy can vary largely according to their time of administration along the 24-h time scale, due to the moderation of their molecular and cellular mechanisms by circadian rhythms. Recent clinical data have highlighted a striking role of dosing time for cancer immunotherapy, thus calling for a critical evaluation.

METHODS

Here, we review the clinical data and we analyse the mechanisms through which circadian rhythms can influence outcomes on ICI therapies. We examine how circadian rhythm disorders can affect tumour immune microenvironment, as a main mechanism linking the circadian clock to the 24-h cycles in ICIs antitumour efficacy.

RESULTS

Real-life data from 18 retrospective studies have revealed that early time-of-day (ToD) infusion of immune checkpoint inhibitors (ICIs) could enhance progression-free and/or overall survival up to fourfold compared to late ToD dosing. The studies involved a total of 3250 patients with metastatic melanoma, lung, kidney, bladder, oesophageal, stomach or liver cancer from 9 countries. Such large and consistent differences in ToD effects on outcomes could only result from a previously ignored robust chronobiological mechanism. The circadian timing system coordinates cellular, tissue and whole-body physiology along the 24-h timescale. Circadian rhythms are generated at the cellular level by a molecular clock system that involves 15 specific clock genes. The disruption of circadian rhythms can trigger or accelerate carcinogenesis, and contribute to cancer treatment failure, possibly through tumour immune evasion resulting from immunosuppressive tumour microenvironment.

CONCLUSIONS AND PERSPECTIVE

Such emerging understanding of circadian rhythms regulation of antitumour immunity now calls for randomised clinical trials of ICIs timing to establish recommendations for personalised chrono-immunotherapies with current and forthcoming drugs.

The influence of circadian rhythms on CD8+ T cell activation upon vaccination: A mathematical modeling perspective

Circadian rhythms have been implicated in the modulation of many physiological processes, including those associated with the immune system. For example, these rhythms influence CD8+ T cell responses within the adaptive immune system. The mechanism underlying this immune-circadian interaction, however, remains unclear, particularly in the context of vaccination. Here, we devise a molecularly-explicit gene regulatory network model of early signaling in the naïve CD8+ T cell activation pathway, comprised of three axes (or subsystems) labeled ZAP70, LAT and CD28, to elucidate the molecular details of this immune-circadian mechanism and its relation to vaccination. This is done by coupling the model to a periodic forcing function to identify the molecular players targeted by circadian rhythms, and analyzing how these rhythms subsequently affect CD8+ T cell activation under differing levels of T cell receptor (TCR) phosphorylation, which we designate as vaccine load. By performing both bifurcation and parameter sensitivity analyses on the model at the single cell and ensemble levels, we find that applying periodic forcing on molecular targets within the ZAP70 axis is sufficient to create a day-night discrepancy in CD8+ T cell activation in a manner that is dependent on the bistable switch inherent in CD8+ T cell early signaling. We also demonstrate that the resulting CD8+ T cell activation is dependent on the strength of the periodic coupling as well as on the level of TCR phosphorylation. Our results show that this day-night discrepancy is not transmitted to certain downstream molecules within the LAT subsystem, such as mTORC1, suggesting a secondary, independent circadian regulation on that protein complex. We also corroborate experimental results by showing that the circadian regulation of CD8+ T cell primarily acts at a baseline, pre-vaccination state, playing a facilitating role in priming CD8+ T cells to vaccine inputs according to the time of day. By applying an ensemble level analysis using bifurcation theory and by including several hypothesized molecular targets of this circadian rhythm, we further demonstrate an increased variability between CD8+ T cells (due to heterogeneity) induced by its circadian regulation, which may allow an ensemble of CD8+ T cells to activate at a lower vaccine load, improving its sensitivity. This modeling study thus provides insights into the immune targets of the circadian clock, and proposes an interaction between vaccine load and the influence of circadian rhythms on CD8+ T cell activation.

Circadian rhythms of macrophages are altered by the acidic pH of the tumor microenvironment

Macrophages are prime therapeutic targets due to their pro-tumorigenic and immunosuppressive functions in tumors, but the varying efficacy of therapeutic approaches targeting macrophages highlights our incomplete understanding of how the tumor microenvironment (TME) can influence regulation of macrophages. The circadian clock is a key internal regulator of macrophage function, but how circadian rhythms of macrophages may be influenced by the tumor microenvironment remains unknown. We found that conditions associated with the TME such as polarizing stimuli, acidic pH, and elevated lactate concentrations can each alter circadian rhythms in macrophages. Circadian rhythms were enhanced in pro-resolution macrophages but suppressed in pro-inflammatory macrophages, and acidic pH had divergent effects on circadian rhythms depending on macrophage phenotype. While cyclic AMP (cAMP) has been reported to play a role in macrophage response to acidic pH, our results indicate that pH-driven changes in circadian rhythms are not mediated solely by the cAMP signaling pathway. Remarkably, clock correlation distance analysis of tumor-associated macrophages (TAMs) revealed evidence of circadian disorder in TAMs. This is the first report providing evidence that circadian rhythms of macrophages are altered within the TME. Our data further suggest that heterogeneity in circadian rhythms at the population level may underlie this circadian disorder. Finally, we sought to determine how circadian regulation of macrophages impacts tumorigenesis, and found that tumor growth was suppressed when macrophages had a functional circadian clock. Our work demonstrates a novel mechanism by which the tumor microenvironment can influence macrophage biology through altering circadian rhythms, and the contribution of circadian rhythms in macrophages to suppressing tumor growth.

Circadian Variation in the Response to Vaccination: A Systematic Review and Evidence Appraisal

Molecular timing mechanisms known as circadian clocks drive endogenous 24-h rhythmicity in most physiological functions, including innate and adaptive immunity. Consequently, the response to immune challenge such as vaccination might depend on the time of day of exposure. This study assessed whether the time of day of vaccination (TODV) is associated with the subsequent immune and clinical response by conducting a systematic review of previous studies. The Cochrane Library, PubMed, Google, Medline, and Embase were searched for studies that reported TODV and immune and clinical outcomes, yielding 3114 studies, 23 of which met the inclusion criteria. The global severe acute respiratory syndrome coronavirus 2 vaccination program facilitated investigation of TODV and almost half of the studies included reported data collected during the COVID-19 pandemic. There was considerable heterogeneity in the demography of participants and type of vaccine, and most studies were biased by failure to account for immune status prior to vaccination, self-selection of vaccination time, or confounding factors such as sleep, chronotype, and shiftwork. The optimum TODV was concluded to be afternoon (5 studies), morning (5 studies), morning and afternoon (1 study), midday (1 study), and morning or late afternoon (1 study), with the remaining 10 studies reporting no effect. Further research is required to understand the relationship between TODV and subsequent immune outcome and whether any clinical benefit outweighs the potential effect of this intervention on vaccine uptake.

Circadian rhythms in solid organ transplantation

Circadian rhythms are daily cycles in physiology that can affect medical interventions. This review considers how these rhythms may relate to solid organ transplantation. It begins by summarizing the mechanism for circadian rhythm generation known as the molecular clock, and basic research connecting the clock to biological activities germane to organ acceptance. Next follows a review of clinical evidence relating time of day to adverse transplantation outcomes. The concluding section discusses knowledge gaps and practical areas where applying circadian biology might improve transplantation success.

The temporal expression pattern of classical MHC class I in sleep-restricted mice: Generalizations and broader implications

The intricate relationship between sleep and leukocyte trafficking has garnered intense attention, particularly their homing dynamics to secondary lymphoid organs under normal and restricted sleep (SR). Considering the scarcity of information regarding circadian rhythms in major histocompatibility class I (MHC-I) expression in SR, we designed a study that assessed the temporal expression of MHC-I in murine lymph nodes and spleen and the subsequent effects of sleep recovery. Male C57BL/6, housed in 12:12 light/dark cycle, were grouped into control (C) and SR. SR was carried for one week before lymphoid tissues were sampled at selected time points and assessed for leukocyte number and MHC-I expression. SR resulted in 21% decrease in granulocyte and 24% increase in agranulocyte numbers. In C, MHC-I expression pattern in lymph nodes was bimodal and relatively higher than splenocytes during the animal's active phase (110.2 ± 1.8 vs 81.9 ± 3.8, respectively; p = 0.002). Splenocytes; however, showed a bimodal pattern upon SR, with higher protein levels during the rest than the activity period (154.6 + 36.2 vs 99.5 + 15.9, respectively; p = 0.002), suggesting preparedness for a potential infection. Furthermore, SR caused a significant drop in MHC-I expression at the onset of rest with 57% and 30% reduction in lymph nodes and splenocytes, respectively. However, the overall protein expression collectively taken from both lymphoid tissues remained stable, emphasizing its indispensable role in immunological homeostasis. This stability coincided with the restoration of protein levels to baseline after a short sleep recovery period, resembling a reset for MHC-I antigen presentation following a week of SR. Understanding the interplay between MHC-I expression and contextual factors could enhance treatment protocols, refining the efficacy and time precision of glucocorticoid-based therapies in immune modulation.

Circadian rhythm regulates the function of immune cells and participates in the development of tumors

Circadian rhythms are present in almost all cells and play a crucial role in regulating various biological processes. Maintaining a stable circadian rhythm is essential for overall health. Disruption of this rhythm can alter the expression of clock genes and cancer-related genes, and affect many metabolic pathways and factors, thereby affecting the function of the immune system and contributing to the occurrence and progression of tumors. This paper aims to elucidate the regulatory effects of BMAL1, clock and other clock genes on immune cells, and reveal the molecular mechanism of circadian rhythm's involvement in tumor and its microenvironment regulation. A deeper understanding of circadian rhythms has the potential to provide new strategies for the treatment of cancer and other immune-related diseases.

Circadian Effects on Vascular Immunopathologies

Circadian rhythms exert a profound impact on most aspects of mammalian physiology, including the immune and cardiovascular systems. Leukocytes engage in time-of-day-dependent interactions with the vasculature, facilitating the emigration to and the immune surveillance of tissues. This review provides an overview of circadian control of immune-vascular interactions in both the steady state and cardiovascular diseases such as atherosclerosis and infarction. Circadian rhythms impact both the immune and vascular facets of these interactions, primarily through the regulation of chemoattractant and adhesion molecules on immune and endothelial cells. Misaligned light conditions disrupt this rhythm, generally exacerbating atherosclerosis and infarction. In cardiovascular diseases, distinct circadian clock genes, while functioning as part of an integrated circadian system, can have proinflammatory or anti-inflammatory effects on these immune-vascular interactions. Here, we discuss the mechanisms and relevance of circadian rhythms in vascular immunopathologies.

The β2-adrenergic receptor (ADRB2) entrains circadian gene oscillation and diurnal responses to virus infection in CD8 + T cells

Adaptive immune cells are regulated by circadian rhythms (CR) under both steady state conditions and during responses to infection. Cytolytic CD8 + T cells display variable responses to infection depending upon the time of day of exposure. However, the neuronal signals that entrain these cyclic behaviors remain unknown. Immune cells express a variety of neurotransmitter receptors including nicotinic, glucocorticoid, and adrenergic receptors. Here, we demonstrate that the β2-adrenergic receptor (ADRB2) regulates the periodic oscillation of select core clock genes, such as Per2 and Bmal1 , and selective loss of the Adrb2 gene dramatically perturbs the normal diurnal oscillation of clock gene expression in CD8 + T cells. Consequently, their circadian-regulated anti-viral response is dysregulated, and the diurnal development of CD8 + T cells into variegated populations of cytolytic T cell (CTL) effectors is dramatically altered in the absence of ADRB2 signaling. Thus, the Adrb2 directly entrains core clock gene oscillation and regulates CR-dependent T cell responses to virus infection as a function of time-of-day of pathogen exposure.

One Sentence Summary

The β2-adrenergic receptor regulates circadian gene oscillation and downstream daily timing of cytolytic T cell responses to virus infection.

Readily available drugs and other interventions to potentially improve the efficacy of immune checkpoint blockade in cancer

To improve the efficacy of immune checkpoint inhibitors (ICIs) for cancer treatment, various strategies, including combination therapies with repurposed drugs, are being explored. Several readily available interventions with potential to enhance programmed death 1 (PD-1) blockade have been identified. However, these interventions often remain overlooked due to the lack of financial incentives for their development, making them financial orphans. This review summarizes current knowledge regarding off-label drugs, supplements, and other readily available interventions that could improve the efficacy of PD-1 blockade. The summary of each intervention includes the proposed mechanism of action for combination with checkpoint inhibitors and data from animal and human studies. Additionally, we include summaries of common interventions to be avoided by patients on PD-1 blockade. Finally, we present approaches for conducting further studies in patients, with the aim of expediting the clinical development of these interventions. We strive to increase awareness of readily available combination therapies that may advance cancer immunotherapy and help patients today.

Chronic Inflammation Disrupts Circadian Rhythms in Splenic CD4+ and CD8+ T Cells in Mice

Internal circadian clocks coordinate 24 h rhythms in behavior and physiology. Many immune functions show daily oscillations, and cellular circadian clocks can impact immune functions and disease outcome. Inflammation may disrupt circadian clocks in peripheral tissues and innate immune cells. However, it remains elusive if chronic inflammation impacts adaptive immune cell clock, e.g., in CD4+ and CD8+ T lymphocytes. We studied this in the experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis, as an established experimental paradigm for chronic inflammation. We analyzed splenic T cell circadian clock and immune gene expression rhythms in mice with late-stage EAE, CFA/PTx-treated, and untreated mice. In both treatment groups, clock gene expression rhythms were altered with differential effects for baseline expression and peak phase compared with control mice. Most immune cell marker genes tested in this study did not show circadian oscillations in either of the three groups, but time-of-day- independent alterations were observed in EAE and CFA/PTx compared to control mice. Notably, T cell effects were likely independent of central clock function as circadian behavioral rhythms in EAE mice remained intact. Together, chronic inflammation induced by CFA/PTx treatment and EAE immunization has lasting effects on circadian rhythms in peripheral immune cells.

Chikungunya Virus, Metabolism, and Circadian Rhythmicity Interplay in Phagocytic Cells

Chikungunya virus (CHIKV) is transmitted to humans by mosquitoes of the genus Aedes, causing the chikungunya fever disease, associated with inflammation and severe articular incapacitating pain. There has been a worldwide reemergence of chikungunya and the number of cases increased to 271,006 in 2022 in the Americas alone. The replication of CHIKV takes place in several cell types, including phagocytic cells. Monocytes and macrophages are susceptible to infection by CHIKV; at the same time, they provide protection as components of the innate immune system. However, in host-pathogen interactions, CHIKV might have the ability to alter the function of immune cells, partly by rewiring the tricarboxylic acid cycle. Some viral evasion mechanisms depend on the metabolic reprogramming of immune cells, and the cell metabolism is intertwined with circadian rhythmicity; thus, a circadian immunovirometabolism axis may influence viral pathogenicity. Therefore, analyzing the interplay between viral infection, circadian rhythmicity, and cellular metabolic reprogramming in human macrophages could shed some light on the new field of immunovirometabolism and eventually contribute to the development of novel drugs and therapeutic approaches based on circadian rhythmicity and metabolic reprogramming.

The Impact of Vaccination Time on the Antibody Response to an Inactivated Vaccine against SARS-CoV-2 (IMPROVE-2): A Randomized Controlled Trial

There is still controversy about whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination at different times of day will induce a stronger immune response. Therefore, a randomized controlled trial (ChiCTR2100045109) is conducted to investigate the impact of vaccination time on the antibody response to the inactivated vaccine against SARS-CoV-2 from April 15 to 28, 2021. Participants are randomly assigned in a 1:1 ratio to receive inactivated SARS-CoV-2 vaccine in the morning or afternoon. The primary endpoint is the change of neutralizing antibody between baseline and 28 days after the second dose. In total, 503 participants are randomized, and 469 participants (238 in the morning group and 231 in the afternoon group) complete the follow-up. There is no significant difference in the change of neutralizing antibody between baseline and 28 days after the second dose between the morning and afternoon groups (22.2 [13.2, 45.0] AU mL-1  vs 22.0 [14.4, 40.7] AU mL-1 , P = 0.873). In prespecified age and sex subgroup analyses, there is also no significant difference in the morning and afternoon group (all P > 0.05). This study demonstrates that the vaccination time does not affect the antibody response of two doses of inactivated SARS-CoV-2 vaccine.

Potential effects of shift work on skin autoimmune diseases

Shift work is associated with systemic chronic inflammation, impaired host and tumor defense and dysregulated immune responses to harmless antigens such as allergens or auto-antigens. Thus, shift workers are at higher risk to develop a systemic autoimmune disease and circadian disruption with sleep impairment seem to be the key underlying mechanisms. Presumably, disturbances of the sleep-wake cycle also drive skin-specific autoimmune diseases, but epidemiological and experimental evidence so far is scarce. This review summarizes the effects of shift work, circadian misalignment, poor sleep, and the effect of potential hormonal mediators such as stress mediators or melatonin on skin barrier functions and on innate and adaptive skin immunity. Human studies as well as animal models were considered. We will also address advantages and potential pitfalls in animal models of shift work, and possible confounders that could drive skin autoimmune diseases in shift workers such as adverse lifestyle habits and psychosocial influences. Finally, we will outline feasible countermeasures that may reduce the risk of systemic and skin autoimmunity in shift workers, as well as treatment options and highlight outstanding questions that should be addressed in future studies.

Dendritic cells direct circadian anti-tumour immune responses

The process of cancer immunosurveillance is a mechanism of tumour suppression that can protect the host from cancer development throughout its lifetime1,2. However, it is unknown whether the effectiveness of cancer immunosurveillance fluctuates over a single day. Here we demonstrate that the initial time of day of tumour engraftment dictates the ensuing tumour size across mouse cancer models. Using immunodeficient mice as well as mice lacking lineage-specific circadian functions, we show that dendritic cells (DCs) and CD8+ T cells exert circadian anti-tumour functions that control melanoma volume. Specifically, we find that rhythmic trafficking of DCs to the tumour draining lymph node governs a circadian response of tumour-antigen-specific CD8+ T cells that is dependent on the circadian expression of the co-stimulatory molecule CD80. As a consequence, cancer immunotherapy is more effective when synchronized with DC functions, shows circadian outcomes in mice and suggests similar effects in humans. These data demonstrate that the circadian rhythms of anti-tumour immune components are not only critical for controlling tumour size but can also be of therapeutic relevance.

Influence of circadian clocks on adaptive immunity and vaccination responses

The adaptive immune response is under circadian control, yet, why adaptive immune reactions continue to exhibit circadian changes over long periods of time is unknown. Using a combination of experimental and mathematical modeling approaches, we show here that dendritic cells migrate from the skin to the draining lymph node in a time-of-day-dependent manner, which provides an enhanced likelihood for functional interactions with T cells. Rhythmic expression of TNF in the draining lymph node enhances BMAL1-controlled ICAM-1 expression in high endothelial venules, resulting in lymphocyte infiltration and lymph node expansion. Lymph node cellularity continues to be different for weeks after the initial time-of-day-dependent challenge, which governs the immune response to vaccinations directed against Hepatitis A virus as well as SARS-CoV-2. In this work, we present a mechanistic understanding of the time-of-day dependent development and maintenance of an adaptive immune response, providing a strategy for using time-of-day to optimize vaccination regimes.

Regulation of Cytotoxic CD8+ T Cells by the Circadian Clock

Most aspects of physiology, including immunity, present 24-h variations called circadian rhythms. In this review, we examine the literature on the circadian regulation of CD8+ T cells, which are important to fight intracellular infections and tumors. CD8+ T cells express circadian clock genes, and ∼6% of their transcriptome presents circadian oscillations. CD8+ T cell counts present 24-h rhythms in the blood and in secondary lymphoid organs, which depend on the clock in these cells as well as on hormonal rhythms. Moreover, the strength of the response of these cells to Ag presentation varies according to time of day, a rhythm dependent on the CD8+ T cell clock. The relevance of CD8+ T cell circadian rhythms is shown by the daily variations in the fight of intracellular infections. Such a circadian regulation also has implications for cancer, as well as the optimization of vaccination and immunotherapy.

The circadian clock influences T cell responses to vaccination by regulating dendritic cell antigen processing

Dendritic cells play a key role in processing and presenting antigens to naïve T cells to prime adaptive immunity. Circadian rhythms are known to regulate many aspects of immunity; however, the role of circadian rhythms in dendritic cell function is still unclear. Here, we show greater T cell responses when mice are immunised in the middle of their rest versus their active phase. We find a circadian rhythm in antigen processing that correlates with rhythms in both mitochondrial morphology and metabolism, dependent on the molecular clock gene, Bmal1. Using Mdivi-1, a compound that promotes mitochondrial fusion, we are able to rescue the circadian deficit in antigen processing and mechanistically link mitochondrial morphology and antigen processing. Furthermore, we find that circadian changes in mitochondrial Ca²⁺ are central to the circadian regulation of antigen processing. Our results indicate that rhythmic changes in mitochondrial calcium, which are associated with changes in mitochondrial morphology, regulate antigen processing.

Acircadian rhythm-related gene signature for predicting survival and drug response in HNSC

Head and neck squamous cell carcinoma (HNSC) represents one of the most common malignant carcinomas worldwide. Because the 5-year survival rate of patients with HNSC is poor, it is necessary to develop an effective signature for predicting the risk of HNSC. To identify a circadian rhythm (CR)-related predictive signature, we analyzed the RNA-seq data of patients with HNSC from The Cancer Genome Atlas and Gene Expression Omnibus cohorts. Nine CR-related genes (PER2, PER3, GHRL, CSF2, HDAC3, KLF10, PRKAA2, PTGDS, and RORB) were identified to develop a CR-related signature. The area under the curve values for 5-year overall survival were 0.681, 0.700, and 0.729 in the training set, validation set, and an external independent test set (GSE41613), respectively. The Kaplan‒Meier curve analysis showed that the high-risk group had a reduced relapse-free survival compared with the low-risk group in the training set, validation set, and test set (P < 0.05). Finally, we observed that the CR-related gene signature was associated with the tumor immune microenvironment, somatic nucleotide variation, and drug response in HNSC. In conclusion, we developed a circadian rhythm-related gene signature for predicting overall survival in HNSC.

When the clock ticks wrong with COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a member of the coronavirus family that causes the novel coronavirus disease first diagnosed in 2019 (COVID-19). Although many studies have been carried out in recent months to determine why the disease clinical presentations and outcomes can vary significantly from asymptomatic to severe or lethal, the underlying mechanisms are not fully understood. It is likely that unique individual characteristics can strongly influence the broad disease variability; thus, tailored diagnostic and therapeutic approaches are needed to improve clinical outcomes. The circadian clock is a critical regulatory mechanism orchestrating major physiological and pathological processes. It is generally accepted that more than half of the cell-specific genes in any given organ are under circadian control. Although it is known that a specific role of the circadian clock is to coordinate the immune system's steady-state function and response to infectious threats, the links between the circadian clock and SARS-CoV-2 infection are only now emerging. How inter-individual variability of the circadian profile and its dysregulation may play a role in the differences noted in the COVID-19-related disease presentations, and outcome remains largely underinvestigated. This review summarizes the current evidence on the potential links between circadian clock dysregulation and SARS-CoV-2 infection susceptibility, disease presentation and progression, and clinical outcomes. Further research in this area may contribute towards novel circadian-centred prognostic, diagnostic and therapeutic approaches for COVID-19 in the era of precision health.

The Association of Time of Day of ChAdOx1 nCoV-19 Vaccine Administration With SARS-CoV-2 Anti-Spike IgG Antibody Levels: An Exploratory Observational Study

Data from human and animal studies are highly suggestive of an influence of time of day of vaccine administration on host immune responses. In this population-based study, we aimed to investigate the effect of time of day of administration of a COVID-19 vector vaccine, ChAdOx1 nCoV-19 (AstraZeneca), on SARS-CoV-2 anti-spike S1 immunoglobulin (IgG) levels. Participants were 803 university employees who received their first vaccine dose in March 2021, had serology data at baseline and at 3 weeks, and were seronegative at baseline. Antibody levels were determined in binding antibody units (BAU/mL) using enzyme-linked immunosorbent assay (ELISA). Generalized additive models (GAM) and linear regression were used to evaluate the association of time of day of vaccination continuously and in hourly bins with antibody levels at 3 weeks. Participants had a mean age of 42 years (SD: 12; range: 21-74) and 60% were female. Time of day of vaccination was associated non-linearly ("reverse J-shape") with antibody levels. Morning vaccination was associated with the highest (9:00-10:00 h: mean 292.1 BAU/mL; SD: 262.1), early afternoon vaccination with the lowest (12:00-13:00 h: mean 217.3 BAU/mL; SD: 153.6), and late afternoon vaccination with intermediate (14:00-15:00 h: mean 280.7 BAU/mL; SD: 262.4) antibody levels. Antibody levels induced by 12:00-13:00 h vaccination (but not other time intervals) were significantly lower compared to 9:00-10:00 h vaccination after adjusting for potential confounders (beta coefficient = -75.8, 95% confidence interval [CI] = -131.3, -20.4). Our findings show that time of day of vaccination against SARS-CoV-2 has an impact on the magnitude of IgG antibody levels at 3 weeks. Whether this difference persists after booster vaccine doses and whether it influences the level of protection against COVID-19 needs further evaluation.

Circadian rhythms in psoriasis and the potential of chronotherapy in psoriasis management

The physiology and pathology of the skin are influenced by daily oscillations driven by a master clock located in the brain, and peripheral clocks in individual cells. The pathogenesis of psoriasis is circadian-rhythmic, with flares of disease and symptoms such as itch typically being worse in the evening/night-time. Patients with psoriasis have changes in circadian oscillations of blood pressure and heart rate, supporting wider circadian disruption. In addition, shift work, a circadian misalignment challenge, is associated with psoriasis. These features may be due to underlying circadian control of key effector elements known to be relevant in psoriasis such as cell cycle, proliferation, apoptosis and inflammation. Indeed, peripheral clock pathology may lead to hyperproliferation of keratinocytes in the basal layers, insufficient apoptosis of differentiating keratinocytes in psoriatic epidermis, dysregulation of skin-resident and migratory immune cells and modulation of angiogenesis through circadian oscillation of vascular endothelial growth factor A (VEGF-A) in epidermal keratinocytes. Chronotherapeutic effects of topical steroids and topical vitamin D analogues have been reported, suggesting that knowledge of circadian phase may improve the efficacy, and therapeutic index of treatments for psoriasis. In this viewpoint essay, we review the current literature on circadian disruption in psoriasis. We explore the hypothesis that psoriasis is circadian-driven. We also suggest that investigation of the circadian components specific to psoriasis and that the in vitro investigation of circadian regulation of psoriasis will contribute to the development of a novel chronotherapeutic treatment strategy for personalised psoriasis management. We also propose that circadian oscillations of VEGF-A offer an opportunity to enhance the efficacy and tolerability of a novel anti-VEGF-A therapeutic approach, through the timed delivery of anti-VEGF-A drugs.

The impact of circadian rhythms on the immune response to influenza vaccination in middle-aged and older adults (IMPROVE): a randomised controlled trial

BACKGROUND

Vaccination is important in influenza prevention but the immune response wanes with age. The circadian nature of the immune system suggests that adjusting the time of vaccination may provide an opportunity to improve immunogenicity. Our previous cluster trial in Birmingham suggested differences between morning and afternoon vaccination for some strains in the influenza vaccine in older adults. Whether this effect is also seen in a younger age group with less likelihood of compromised immunity is unknown. We therefore conducted an individual-based randomized controlled trial in Guangzhou to test the hypothesis that influenza vaccination in the morning induces a stronger immune response in older adults than afternoon vaccination. We included adults in middle age to determine if the effect was also seen in younger age groups.

RESULTS

Of the 418 participants randomised, 389 (93.1%, 191 middle-aged adults aged 50-60 years and 198 older adults aged 65-75 years) were followed up. Overall, there was no significant difference between the antibody titers (geometric mean /95% CI) after morning vs afternoon vaccination (A/H1N1: 39.9 (32.4, 49.1) vs. 33.0 (26.7, 40.7), p = 0.178; A/H3N2: 92.2 (82.8, 102.7) vs. 82.0 (73.8, 91.2), p = 0.091; B: 15.8 (13.9, 17.9) vs. 14.4 (12.8, 16.3), p = 0.092), respectively. However, in pre-specified subgroup analyses, post-vaccination titers for morning versus afternoon vaccination in the 65-75 years subgroup were (A/H1N1): 49.5 (36.7, 66.6) vs. 32.9 (24.7, 43.9), p = 0.050; (A/H3N2): 93.5 (80.6, 108.5) vs. 73.1 (62.9, 84.9), p = 0.021; (B): 16.6 (13.8, 20.1) vs. 14.4 (12.3, 17.0), p = 0.095, respectively. Among females, antibody titers for morning versus afternoon vaccination were (A/H1N1): 46.9 (35.6, 61.8) vs. 31.1 (23.8, 40.7), p = 0.030; (A/H3N2): 96.0 (83.5, 110.3) vs. 84.7 (74.4, 96.5), p = 0.176; (B): 14.8 (12.7, 17.3) vs. 13.0 (11.3, 14.9), p = 0.061, respectively. In the 50-60 years old subgroup and males, there were no significant differences between morning and afternoon vaccination.

CONCLUSIONS

Morning vaccination may enhance the immunogenicity to influenza vaccine in adults aged over 65 and women. An intervention to modify vaccination programs to vaccinate older individuals in the morning is simple, cost free and feasible in most health systems.

Tregs in visceral adipose tissue up-regulate circadian-clock expression to promote fitness and enforce a diurnal rhythm of lipolysis

Regulatory T cells (Tregs) in nonlymphoid organs provide critical brakes on inflammation and regulate tissue homeostasis. Although so-called "tissue Tregs" are phenotypically and functionally diverse, serving to optimize their performance and survival, up-regulation of pathways related to circadian rhythms is a feature they share. Yet the diurnal regulation of Tregs and its consequences are controversial and poorly understood. Here, we profiled diurnal variations in visceral adipose tissue (VAT) and splenic Tregs in the presence and absence of core-clock genes. VAT, but not splenic, Tregs up-regulated their cell-intrinsic circadian program and exhibited diurnal variations in their activation and metabolic state. BMAL1 deficiency specifically in Tregs led to constitutive activation and poor oxidative metabolism in VAT, but not splenic, Tregs. Disruption of core-clock components resulted in loss of fitness: BMAL1-deficient VAT Tregs were preferentially lost during competitive transfers and in heterozygous TregBmal1Δ females. After 16 weeks of high-fat diet feeding, VAT inflammation was increased in mice harboring BMAL1-deficient Tregs, and the remaining cells lost the transcriptomic signature of bona fide VAT Tregs. Unexpectedly, VAT Tregs suppressed adipocyte lipolysis, and BMAL1 deficiency specifically in Tregs abrogated the characteristic diurnal variation in adipose tissue lipolysis, resulting in enhanced suppression of lipolysis throughout the day. These findings argue for the importance of the cell-intrinsic clock program in optimizing VAT Treg function and fitness.

Time of day as a critical variable in biology

BACKGROUND

Circadian rhythms are important for all aspects of biology; virtually every aspect of biological function varies according to time of day. Although this is well known, variation across the day is also often ignored in the design and reporting of research. For this review, we analyzed the top 50 cited papers across 10 major domains of the biological sciences in the calendar year 2015. We repeated this analysis for the year 2019, hypothesizing that the awarding of a Nobel Prize in 2017 for achievements in the field of circadian biology would highlight the importance of circadian rhythms for scientists across many disciplines, and improve time-of-day reporting.

RESULTS

Our analyses of these 1000 empirical papers, however, revealed that most failed to include sufficient temporal details when describing experimental methods and that few systematic differences in time-of-day reporting existed between 2015 and 2019. Overall, only 6.1% of reports included time-of-day information about experimental measures and manipulations sufficient to permit replication.

CONCLUSIONS

Circadian rhythms are a defining feature of biological systems, and knowing when in the circadian day these systems are evaluated is fundamentally important information. Failing to account for time of day hampers reproducibility across laboratories, complicates interpretation of results, and reduces the value of data based predominantly on nocturnal animals when extrapolating to diurnal humans.

The circadian immune system

The immune system is highly time-of-day dependent. Pioneering studies in the 1960s were the first to identify immune responses to be under a circadian control. Only in the last decade, however, have the molecular factors governing circadian immune rhythms been identified. These studies have revealed a highly complex picture of the interconnectivity of rhythmicity within immune cells with that of their environment. Here, we provide a global overview of the circadian immune system, focusing on recent advances in the rapidly expanding field of circadian immunology.

Sleep and vaccine administration time as factors influencing vaccine immunogenicity

The immunogenicity of vaccines is affected by host, external, environmental, and vaccine factors; in addition, sleep or circadian rhythms may also have effects. With the use of vaccines to mitigate the coronavirus disease 2019 (COVID-19) pandemic, research is underway to clarify what time of the day is optimal for COVID-19 vaccination and how disturbances of circadian rhythms will affect the immunogenicity of the vaccine in shift workers. Studies on the relationship between sleep time and the immunogenicity of vaccines for influenza and hepatitis have demonstrated that less sleep time and sleep deprivation tended to adversely affect immunogenicity. In some studies, there were even sex differences in these effects. When comparing shift workers with disturbances in their circadian rhythms and those who only worked during the day, one study found less antibody formation in shift workers; however, further studies on the relationship between shift work and the immunogenicity of vaccines are needed. Studies on the relationship between vaccine administration time and immunogenicity have shown different results according to age and sex. Therefore, future studies on vaccine administration time and immunogenicity may require an individualized approach for each vaccine and each population to be vaccinated. There is accumulating evidence on the effects of sleep and vaccine administration time on the immunogenicity of vaccines. However, further studies are needed to determine whether the association between immunogenicity and circadian rhythms and vaccine administration time can be used as a basis to increase the immunogenicity for individual vaccines.

The Influence of Time of Day of Vaccination with BNT162b2 on the Adverse Drug Reactions and Efficacy of Humoral Response against SARS-CoV-2 in an Observational Study of Young Adults

An increasing body of evidence from both academic and clinical studies shows that time-of-day exposure to antigens might significantly alter and modulate the development of adaptive immune responses. Considering the immense impact of the COVID-19 pandemic on global health and the diminished efficacy of vaccination in selected populations, such as older and immunocompromised patients, it is critical to search for the most optimal conditions for mounting immune responses against SARS-CoV-2. Hence, we conducted an observational study on 435 healthy young adults vaccinated with two doses of BNT162b2 (Pfizer-BioNTech) vaccine to determine whether time-of-day of vaccination influences either the magnitude of humoral response or number of adverse drug reactions (ADR) being reported. We found no significant differences between morning and afternoon vaccination in terms of both titers of anti-Spike antibodies and frequency of ADR in the studied population. In addition, our analysis of data on the occurrence of ADR in 1324 subjects demonstrated that the second administration of vaccine in those with previous SARS-CoV-2 infection was associated with lower incidence of ADR. In aggregate, vaccination against COVID-19 with two doses of BNT162b2 mRNA vaccine is presumed to generate an equally efficient anti-Spike humoral response.

Metabolic programs tailor T cell immunity in viral infection, cancer, and aging

Productive T cell responses to infection and cancer rely on coordinated metabolic reprogramming and epigenetic remodeling among the immune cells. In particular, T cell effector and memory differentiation, exhaustion, and senescence/aging are tightly regulated by the metabolism-epigenetics axis. In this review, we summarize recent advances of how metabolic circuits combined with epigenetic changes dictate T cell fate decisions and shape their functional states. We also discuss how the metabolic-epigenetic axis orchestrates T cell exhaustion and explore how physiological factors, such as diet, gut microbiota, and the circadian clock, are integrated in shaping T cell epigenetic modifications and functionality. Furthermore, we summarize key features of the senescent/aged T cells and discuss how to ameliorate vaccination- and COVID-induced T cell dysfunctions by metabolic modulations. An in-depth understanding of the unexplored links between cellular metabolism and epigenetic modifications in various physiological or pathological contexts has the potential to uncover novel therapeutic strategies for fine-tuning T cell immunity.

Time-Dependent Efficacy of Checkpoint Inhibitor Nivolumab: Results from a Pilot Study in Patients with Metastatic Non-Small-Cell Lung Cancer

HYPOTHESIS

Prior experimental and human studies have demonstrated the circadian organization of immune cells' proliferation, trafficking, and antigen recognition and destruction. Nivolumab targets T(CD8) cells, the functions, and trafficking of which are regulated by circadian clocks, hence suggesting possible daily changes in nivolumab's efficacy. Worse progression-free survival (PFS), and overall survival (OS) were reported for malignant melanoma patients receiving more than 20% of their immune checkpoint inhibitor infusions after 16:30 as compared to earlier in the day.

METHODS

Consecutive metastatic non-small-cell cancer (NSCLC) patients received nivolumab (240 mg iv q 2 weeks) at a daily time that was 'randomly' allocated for each course on a logistical basis by the day-hospital coordinators. The median time of all nivolumab administrations was computed for each patient. The study population was split into two timing groups based upon the median value of the median treatment times of all patients. CTCAE-toxicity rates, iRECIST-tumor responses, PFS and OS were computed according to nivolumab timing. PFS and OS curves were compared and hazard ratios (HR) were computed for all major categories of characteristics. Multivariable and sensitivity analyses were also performed.

RESULTS

The study accrued 95 stage-IV NSCLC patients (PS 0-1, 96%), aged 41-83 years. The majority of nivolumab administrations occurred between 9:27 and 12:54 for 48 patients ('morning' group) and between 12:55 and 17:14 for the other 47 ('afternoon' group). Median PFS (95% CL) was 11.3 months (5.5-17.1) for the 'morning' group and 3.1 months (1.5-4.6) for the 'afternoon' one (p < 0.001). Median OS was 34.2 months (15.1-53.3) and 9.6 months (4.9-14.4) for the 'morning' group and the 'afternoon' one, respectively (p < 0.001). Multivariable analyses identified 'morning' timing as a significant predictor of longer PFS and OS, with respective HR values of 0.26 (0.11-0.58) and 0.17 (0.08-0.37). The timing effect was consistent across all patient subgroups tested.

CONCLUSIONS

Nivolumab was nearly four times as effective following 'morning' as compared to 'afternoon' dosing in this cohort of NSCLC patients. Prospective timing-studies are needed to minimize the risk of resistance and to maximize the benefits from immune checkpoint inhibitors.

The involvement of host circadian clocks in the regulation of the immune response to parasitic infections in mammals

Circadian rhythms are recurring variations of physiology with a period of ~24 hours, generated by circadian clocks located throughout the body. Studies have shown a circadian regulation of many aspects of immunity. Immune cells have intrinsic clock mechanisms, and innate and adaptive immune responses - such as leukocyte migration, magnitude of inflammation, cytokine production and cell differentiation - are under circadian control. This circadian regulation has consequences for infections including parasitic infections. In the context of Leishmania infection, the circadian clock within host immune cells modulates the magnitude of the infection and the inflammatory response triggered by the parasite. As for malaria, rhythms within the immune system were shown to impact the developmental cycles of Plasmodium parasites within red blood cells. Further, host circadian rhythms impact infections by multicellular parasites; for example, infection with helminth Trichuris muris shows different kinetics of worm expulsion depending on time of day of infection, a variation that depends on the dendritic cell clock. Although the research on the circadian control of immunity in the context of parasitic infections is in its infancy, the research reviewed here suggests a crucial involvement of host circadian rhythms in immunity on the development and progression of parasitic infections.

Circadian rhythms in adaptive immunity and vaccination

Adaptive immunity allows an organism to respond in a specific manner to pathogens and other non-self-agents. Also, cells of the adaptive immune system, such as T and B lymphocytes, can mediate a memory of an encounter with a pathogen, allowing a more efficient response to a future infection. As for other aspects of physiology and of the immune system, the adaptive immune system is regulated by circadian clocks. Consequently, the development, differentiation, and trafficking between tissues of adaptive immune cells have been shown to display daily rhythms. Also, the response of T cells to stimuli (e.g., antigen presentation to T cells by dendritic cells) varies according to a circadian rhythm, due to T cell-intrinsic mechanisms as well as cues from other tissues. The circadian control of adaptive immune response has implications for our understanding of the fight against pathogens as well as auto-immune diseases, but also for vaccination, a preventive measure based on the development of immune memory.

Effect of immunotherapy time-of-day infusion on overall survival among patients with advanced melanoma in the USA (MEMOIR): a propensity score-matched analysis of a single-centre, longitudinal study

BACKGROUND

The dependence of the adaptive immune system on circadian rhythm is an emerging field of study with potential therapeutic implications. We aimed to determine whether specific time-of-day patterns of immune checkpoint inhibitor infusions might alter melanoma treatment efficacy.

METHODS

Melanoma Outcomes Following Immunotherapy (MEMOIR) is a longitudinal study of all patients with melanoma who received ipilimumab, nivolumab, or pembrolizumab, or a combination of these at a single tertiary cancer centre (Winship Cancer Institute of Emory University, Atlanta, GA, USA). For this analysis, we collected deidentified participant-level data from the MEMOIR database for adults (age ≥18 years) diagnosed with stage IV melanoma between 2012 and 2020. Those who received fewer than four infusions were excluded. Standard of care doses were used, with modifications at the treating physicians' discretion. The primary outcome was overall survival, defined as death from any cause and indexed from date of first infusion of immune checkpoint inhibitor. We calculated the association between overall survival and proportion of infusions of immune checkpoint inhibitors received after 1630 h (a composite time cutoff derived from seminal studies of the immune-circadian rhythm to represent onset of evening) using Cox regression and propensity score-matching on age, Eastern Cooperative Oncology Group performance status, serum lactate dehydrogenase concentration, and receipt of corticosteroids and radiotherapy. Treatment-related adverse events that led to change or discontinuation of immune checkpoint inhibitors were also assessed.

FINDINGS

Between Jan 1, 2012, and Dec 31, 2020, 481 patients with melanoma received treatment with immune checkpoint inhibitors at the study centre, of whom 299 had stage IV disease and were included in this study; median follow-up was 27 months (IQR 14 to 47). In the complete unmatched sample, 102 (34%) patients were female and 197 (66%) were male, with a median age of 61 years (IQR 51 to 72). Every additional 20% of infusions of immune checkpoint inhibitors received after 1630 h (among all infusions received by a patient) conferred an overall survival hazard ratio (HR) of 1·31 (95% CI 1·00 to 1·71; p=0·046). A propensity score-matched analysis of patients who did (n=73) and did not (n=73) receive at least 20% of their infusions of immune checkpoint inhibitors after 1630 h (54 [37%] of 146 patients were women and 92 [63%] were men, with a median age of 58 years [IQR 48 to 68]) showed that having at least 20% of infusions in the evening was associated with shorter overall survival (median 4·8 years [95% CI 3·9 to not estimable] vs not reached; HR 2·04 [1·04 to 4·00; p=0·038]). This result remained robust to multivariable proportional hazards adjustment with (HR 1·80 [1·08 to 2·98; p=0·023]) and without (2·16 [1·10 to 4·25; p=0·025]) inclusion of the complete unmatched study sample. The most common adverse events were colitis (54 [18%] of 299 patients), hepatitis (27 [9%]), and hypophysitis (15 [5%]), and there were no treatment-related deaths.

INTERPRETATION

Our findings are in line with an increasing body of evidence that adaptive immune responses are less robust when initially stimulated in the evening than if stimulated in the daytime. Although prospective studies of the timing of immune checkpoint inhibitor infusions are warranted, efforts towards scheduling infusions before mid-afternoon could be considered in the multidisciplinary management of advanced melanoma.

FUNDING

National Institutes of Health, American Society for Radiation Oncology and Melanoma Research Alliance, and Winship Cancer Institute.

Cell-associated HIV RNA has a Circadian Cycle in Males Living with HIV on Antiretroviral Therapy

BACKGROUND

Circadian transcription factors that regulate cell-autonomous circadian clocks can also increase HIV transcription in vitro. We aimed to determine if circadian variation in HIV transcription exists in people living with HIV (PLHIV) on antiretroviral therapy (ART).

METHODS

We performed a prospective observational study of male PLHIV on ART, sampling blood every four hours for 24 hours. Using qPCR, we quantified expression of circadian associated genes, HIV DNA and cell-associated unspliced (CA-US) RNA in peripheral blood CD4+ T-cells. Plasma sex hormones were quantified alongside plasma and salivary cortisol. The primary outcome was to identify temporal variations in CA-US HIV RNA using a linear mixed effect regression framework and maximum likelihood estimation.

RESULTS

Salivary and plasma cortisol, and circadian genes including Clock, Bmal1, and Per3 varied with a circadian rhythm. CA-US HIV RNA and the ratio of CA-US HIV RNA-to-DNA in CD4+ T-cells also demonstrated circadian variations, with no variation in HIV DNA. Circulating oestradiol was highly predictive of CA-US HIV RNA variation in vivo.

CONCLUSION

CA-US HIV RNA in PLHIV on ART varies temporally with a circadian rhythm. These findings have implications for the design of clinical trials and biomarkers to assess HIV cure interventions.

Circadian disruption and human health

Circadian disruption is pervasive and can occur at multiple organizational levels, contributing to poor health outcomes at individual and population levels. Evidence points to a bidirectional relationship, in that circadian disruption increases disease severity and many diseases can disrupt circadian rhythms. Importantly, circadian disruption can increase the risk for the expression and development of neurologic, psychiatric, cardiometabolic, and immune disorders. Thus, harnessing the rich findings from preclinical and translational research in circadian biology to enhance health via circadian-based approaches represents a unique opportunity for personalized/precision medicine and overall societal well-being. In this Review, we discuss the implications of circadian disruption for human health using a bench-to-bedside approach. Evidence from preclinical and translational science is applied to a clinical and population-based approach. Given the broad implications of circadian regulation for human health, this Review focuses its discussion on selected examples in neurologic, psychiatric, metabolic, cardiovascular, allergic, and immunologic disorders that highlight the interrelatedness between circadian disruption and human disease and the potential of circadian-based interventions, such as bright light therapy and exogenous melatonin, as well as chronotherapy to improve and/or modify disease outcomes.