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Morita M, Okuyama M, Akutsu T, Ohdaira H, Suzuki Y, Urashima M. Vitamin D supplementation regulates postoperative serum levels of PD-L1 in patients with digestive tract cancer and improves survivals in the highest quintile of PD-L1: a post hoc analysis of the AMATERASU randomized controlled trial. Nutrients. 2021;13(6):1987.
To examine whether vitamin D supplementation regulates serum programmed cell death ligand 1 (PD-L1) and, thus, could alter survival time of gastrointestinal (GI) cancer patients
A post hoc analysis of the AMATERASU trial in Japan, which was a randomized, double-blind, placebo-controlled trial conducted at a single university hospital
The study recruited patients aged 30 to 90 years with stage I to III cancers of the digestive tract from the esophagus to the rectum, who were surgical candidates. Of the 439 eligible patients, 15 declined and 7 were excluded after surgery. The investigators included all 417 randomized patients (mean age 66 years; male 66%; esophageal cancer 10%; gastric cancer 42%; colorectal cancer 48%) in the analysis to compare the effects of vitamin D3 supplements (2,000 IU/day) and placebo on relapse and/or death, at an allocation ratio of 3:2, between January 2010 and February 2018.
The trial included patients with stage I (44% of participants), II (26%), or III (30%) digestive tract cancers who underwent curative surgery with complete tumor resection. Only those not taking vitamin D supplements already were included.
Investigators randomized patients to receive oral supplemental capsules of vitamin D (2,000 IU/d; n=251) or placebo (n=166) from the first postoperative outpatient visit until the end of the trial. Placebo contained sesame oil, gelatin (swine-derived), and glycerin, and the active supplement contained the same constituents plus vitamin D3 as 25-hydroxycholecalciferol, 25(OH)D.
Study Parameters Assessed
Investigators measured postoperative serum PD-L1 levels using ELISA and divided them into quintiles (Q1–Q5). Serum samples were available for 396 (95.0%) of the original trial participants. Investigators collected serum samples for PD-L1 measurements after the surgery (23 days, interquartile range (IQR): 13–43.5 days) and just before the start of vitamin D/placebo supplementation. They also measured serum PD-L1 levels 1 year after starting vitamin D/placebo supplements.
Subgroups analyzed had baseline serum 25(OH)D levels of 0 to less than 20 ng/mL, 20 to 40 ng/mL, and greater than 40 ng/mL. Because of small sample size for the highest-baseline-level group, investigators tested interactions between only the low- and middle-baseline-level serum 25(OH)D groups.
Primary Outcome Measures
The primary outcome was relapse-free survival, time to relapse, or death. The outcome of relapse or death was confirmed by regular outpatient follow-up. The elapsed time to relapse or death was calculated from the time of randomization (ie, time from starting the study supplements).
Vitamin D supplementation significantly (P=0.0008) increased serum PD-L1 levels in the lowest quintile of PD-L1 (Q1; ie, those patients who started out with the lowest levels of PD-L1), whereas it significantly (P=0.0001) decreased PD-L1 levels in the highest quintile of serum PD-L1 levels (Q5), and it neither increased nor decreased PD-L1 levels in the middle quintiles of PD-L1 (Q2–Q4).
Significant effects of vitamin D supplementation compared with placebo on death (HR, 0.34; 95% CI, 0.12–0.92) and relapse/death (HR, 0.37; 95% CI, 0.15–0.89) were observed in the highest quintile (Q5) of serum PD-L1, whereas significant effects were not observed in other quintiles (Pinteraction=0.02 for death, Pinteraction=0.04 for relapse/death).
Vitamin D supplementation significantly reduced the risk of relapse and/or death by approximately two-thirds in the highest quintile of serum PD-L1.
Cancer immunotherapy has been a rapidly progressing field of research over the last decade, with the first checkpoint inhibitor, ipilimumab, approved by the Food and Drug Administration (FDA) for the treatment of melanoma in 2011.1 Meanwhile, researchers were investigating the first PD-1 inhibitor, pembrolizumab, which was approved in 2014 for patients with advanced or unresectable melanoma.2 As of 2021, checkpoint inhibitors are likely the most well-known, and perhaps the most successful, immunomodulators developed so far, and have revolutionized oncology by improving outcomes and survival for many cancer patients.3 The mechanism of action and wide applicability of the checkpoint inhibitors have broadened our understanding of the complexity of immune function, particularly in relationship to cancer cells. Our immune system’s inhibitory checkpoint pathways are critical for ensuring we maintain self-tolerance (and prevent autoimmunity). However, we now know that tumors utilize immune checkpoint pathways to evade immune detection.4
It seems prudent in the interim to continue to test 25(OH)D serum levels in all cancer patients and replete those who are deficient into a healthy range.
During a healthy immune response, programmed cell death protein 1 (PD-1) serves to inhibit immune responses and promote self-tolerance via regulating the activity of T-cells. Likewise, programmed cell death ligand 1 (PD-L1) is a transmembrane protein that is a coinhibitory factor of the immune response and responsible for reducing the activity of PD-1 positive cells and inducing apoptosis.
We now know that the PD-1/PD-L1 pathway controls the initiation and maintenance of immune tolerance within the tumor microenvironment.5 In addition to activated immune cells, PD-1 is also highly expressed on tumor-specific T cells.6 PD-L1 is usually expressed by macrophages, some activated T cells and B cells, dendritic cells, and some epithelial cells, particularly under inflammatory conditions.7 In addition, PD-L1 is expressed by tumor cells as an “adaptive immune mechanism” to escape antitumor responses as well as activating proliferative and survival signaling pathways.8 PD-L1 is also implicated in subsequent tumor progression.9
A recent meta-analysis, including a total of 21 studies, demonstrated that elevated serum PD-L1 levels were associated with worse survival of patients with cancer.10 In particular, higher postoperative, but not preoperative, plasma total PD-L1, in addition to exosomal PD-L1, was shown to be associated with poor survival in patients with gastric cancer.11 It is theorized that in addition to checkpoint inhibitors, reducing serum PD-L1 levels after surgery may be a strategy to improve survival in patients with cancer.
Vitamin D signaling has been increasingly investigated for its role in stimulation of innate immunity and suppression of inflammatory responses. Hormonal 1,25-dihydroxyvitamin D (1,25D) is a direct transcriptional inducer of the human genes encoding PD-L1 and PD-L2 through the vitamin D receptor (VDR).12 In this clinical study, vitamin D supplementation increased serum PD-L1 levels in the lowest quintile (Q1; those patients with lowest baseline PD-L1 levels). In contrast, vitamin D supplementation decreased serum PD-L1 levels in the highest quintile (Q5). Thus, vitamin D appears to be serving as a biological response modifier, functioning to increase serum PD-L1 when the serum PD-L1 levels are low and to decrease serum PD-L1 when the serum PD-L1 levels are high.13
In this study, vitamin D supplementation, compared with placebo, significantly reduced the risk of all-cause death, as well as relapse or death, to approximately one-third in the highest quintile (Q5) of serum PD-L1, but not in other quintiles (ie, Q1–Q4 of PD-L1 levels). The authors noted that vitamin D supplementation mainly reduces the risk of total death and hypothesized that this was at least in part by enhancing anticancer immunity and perhaps keeping cancer tissue dormant by downregulating serum PD-L1 levels.13
The association of vitamin D and cancer has been studied for many years, and the data have at times been positive, at times conflicting, and at times shown no association.14 From the results of this study and others, it is apparent that a significant amount of interplay exists between vitamin D and genetic expression of PD-L1, and that further research is needed to explore the exact parameters of this relationship before specific clinical strategies can be created. However, it seems prudent in the interim to continue to test 25(OH)D serum levels in all cancer patients and replete those who are deficient into a healthy range.
As a note of caution, the results of this study may or may not be applicable to other patient populations. There are several limitations of this study: The study was conducted in Japan, and all the patients were of Asian descent; the esophageal carcinomas were squamous cell in origin; and the incidence of gastric cancer is relatively high, as compared to other patient populations.