Inflammatory bowel diseases (IBD) with the main entities of Crohn’s disease (CD) and ulcerative colitis (UC) arise from a complex pathogenesis that crucially involves pro-inflammatory T cells (1–3). Most available therapies including the monoclonal anti-α4β7 integrin antibody vedolizumab prominently target these T cells and mediate their beneficial effect on chronic intestinal inflammation by controlling numbers and function of intestinal T cells (4).

While this in some cases includes the promotion of T cell apoptosis (5) or inhibition of pro-inflammatory differentiation (6), vedolizumab is thought to reduce replenishment of intestinal T cells by impeding α4β7 integrin-dependent gut homing (7, 8). Gut homing is a multistep-process facilitating the access of effector and effector memory T cells that have been primed in the gut-associated lymphoid tissue in the presence of retinoid acid to the intestinal lamina propria (9, 10). This process crucially depends on tight adhesion of T cell-expressed α4β7 integrin to endothelial mucosal vascular addressin cell adhesion molecule (MAdCAM)-1 and, consistently, recent in vitro and in vivo data have shown that vedolizumab mechanistically blocks adhesion of α4β7-expressing T lymphocytes to endothelial MAdCAM-1 (11–13). This is thought to lead to reduced infiltration of pro-inflammatory T cells to the gut with subsequent decrease in inflammation (14).

While vedolizumab has developed to a new mainstay in the therapy of IBD and is successfully used throughout the world (15–17), deeper insights into the immunological effects of α4β7 blockade are still scarce. In particular, the reasons why some patients show no clinical response are still unclear and the factors influencing mucosal healing in vedolizumab-treated patients are largely unknown. Moreover, several pieces of evidence suggest that the efficacy in CD and UC might be different (7, 8, 18), and only partial explanations for these observations are available.

In the present study, we reasoned that different degrees of clinical response to vedolizumab therapy might reflect in different changes in the expression of α4β7 integrin and related T cell surface markers. Accordingly, we sequentially analyzed integrin expression profiles in CD and UC patients receiving clinical vedolizumab therapy and show that several clinical features of disease activity are correlated with specific changes in integrin expression in UC but not CD, which might even serve for prediction of therapeutic response.

The approval of vedolizumab for clinical therapy of both UC and CD has substantially increased the therapeutic armamentarium in IBD (7, 8). Meanwhile, efficacy and safety have not only been documented in randomized clinical trials but also in real-world settings (15–17). This has been accompanied by mechanistic investigations elucidating in vivo effects of vedolizumab on T cell homing (13, 23). However, a number of questions regarding the immunological effects of vedolizumab remain. For instance, it remains elusive why vedolizumab lacks effect in a portion of patients and why this portion seems to be larger in CD compared with UC (7, 8, 18). Moreover, this also includes questions addressing the immunological sequelae of α4β7-dependent homing disruption, e.g., regarding the expression and functionality of other homing molecules in view of their effects on the equilibrium of peripheral blood and intestinal T cell populations (14).

Our present study was conducted with the aim to bring some light into these uncertainties and, therefore, we systematically analyzed associations of changes in α4β7 and related integrins (24) as well as in chemokine receptors with changes in clinical parameters over the course of vedolizumab therapy. For the first time, our data show that several parameters of patient-reported and physician-documented response to vedolizumab treatment are associated with specific changes in the expression of integrins but not chemokine receptors in UC providing new insights into the mechanisms of vedolizumab therapy and fueling hopes for their use in prediction of response to therapy.

While several significant correlations between integrin expression changes and clinical parameter changes were identified in UC, none could be identified in CD. On a molecular level, this further substantiates the empirical clinical observation that differences in the efficacy of vedolizumab treatment seem to exist between UC and CD (18). The only correlation that was approaching significance was that of changes in α4β1 expression with changes in HBI score, suggesting that decrease of the former might go along with increase of the latter parameter. This is in line with earlier observations in an in vivo mouse model showing that compensatory homing via the α4β1/vascular cell adhesion molecule (VCAM)-1 pathway might bypass α4β7 blockade in CD (23) and matching to rodent data that propose considerable redundancy in different homing pathways (25, 26) and VCAM-1-dependent homing as an important pathway in CD-like experimental colitis (27). Accordingly, decreasing α4β1⁺ CD4 T cells in the peripheral blood might reflect increased gut homing of such cells triggering increased intestinal inflammation.

In UC, increase in α4β7 seemed to be associated with favorable clinical development, while increase of α4β1 or αEβ7 expression were correlated with worsening of several clinical parameters. The specificity of these findings for integrins was supported by the fact that changes in CCR2 and CCR6 expression, which are primarily unrelated to α4β7, did not correlate with any of the parameters analyzed.

While these observations are undoubtedly interesting, they are raising new questions regarding the underlying mechanisms. A possible explanation of our findings could be that patients in which α4β7 blockade by vedolizumab sufficiently works have both more peripheral blood T cells expressing α4β7 and amelioration of clinical symptoms due to preclusion of α4β7⁺ T cells from the gut tissue. On the other hand, upregulation of α4β1 and αEβ7 might be a sign of upregulation of rescue pathways, which has also been proposed to be responsible for extraintestinal side effects observed under vedolizumab therapy (28). In particular, cells might upregulate the expression of alternative integrins in an attempt to ensure access to or positioning in the lamina propria via alternative pathways beyond the blocked α4β7–MAdCAM-1 axis, which could subsequently lead to severer or maintained inflammation. However, especially since the coherence of α4β1 expression changes with changes in clinical parameters seems to be different in CD und UC, this remains speculative and underscores that additional translational research is necessary to better understand the alterations in integrin-expressing cell subsets at the interface of the peripheral blood and the intestine. Yet, in light of the above remarks, such differences between CD and UC must not be surprising but should be interpreted as another cue illustrating differences in therapeutic interference with homing in CD and UC. It has also to be taken into account that our cohort mainly consisted of patients previously exposed to anti-tumor necrosis factor (TNF)-α antibodies, and results might not show such a difference in anti-TNF naïve CD and UC collectives.

No comparable data for the use of anti-adhesion antibodies have been reported so far. However, one study sequentially assessed the peripheral blood of IBD patients under therapy with the anti-TNF-α antibody infliximab for expression of regulatory T cell (Treg) markers. The authors showed that infliximab responders and non-responders had differential development in peripheral Treg profiles (29). Thus, although infliximab is believed to mediate its effect predominantly by inhibition of increased TNF-α signaling in the lamina propria, associated changes could be noted in the blood. Since vedolizumab blocks α4β7 integrin on T cells in the peripheral blood, such analyses even assess the changes of immunological markers at the point of action vedolizumab.

The findings reported for αEβ7 match with a recent report from our group suggesting that a subset of αEβ7⁺ T cells does not express α4β7 (22), and αEβ7⁺ cells might accumulate in the gut via additional or alternative pathways. Of note, αEβ7 itself has been proposed to mediate gut homing independently of α4β7 via a so far unknown ligand (30). Moreover, it has to be mentioned that additional αEβ7⁺ T cells have been shown to be induced in the gut in response to epithelium-released transforming growth factor-β (31), and the only known ligand for αEβ7 is E-cadherin expressed on the intestinal epithelium (32–34). Thus, it seems possible that cells deprived of α4β7 compensatorily upregulate αEβ7 on their surface in search of another homing pathway to reach the gut or—more general—in search of possibilities to ensure positioning in the lamina propria (whether by homing or by epithelial retention). As we show, many αEβ7-bearing cells can be found in close contact with E-cadherin-expressing epithelium. Thus, it is very likely that αEβ7⁺ T cells communicate with the epithelium. Independent reports have recently shown that αEβ7 is enriched in pro-inflammatory T cell subsets (22, 35) and that αEβ7⁺ T cells express higher levels of granzyme A than αEβ7⁻ T cells (36). In vivo, this might result in deleterious effects of such αEβ7-expressing on epithelial cells, which is supported by some of our data showing correlations of changes in αEβ7 integrin with changes in clinical parameters that are indicative of intestinal epithelial barrier function.

Taken together, these correlation analyses indicate so far unknown associations between clinical and immunological parameters, while the exact mutual dependencies need to be clarified in further research. Though, from a clinical perspective the questions whether such associations or initial expression levels might be exploited for monitoring or even prediction of therapeutic response to vedolizumab obtrudes and, thus, we performed respective analyses as detailed above. Unexpectedly, we observed that IBD patients with a clinical response after 16 weeks had lower initial levels of α4β7-expressing CD4⁺ T cells than non-responders. This is intriguing since one could have assumed that higher α4β7 expression is a sign of higher importance of α4β7-dependent homing, and it might thus be more promising to block α4β7 in patients with higher expression. Yet, the explanation for our finding could be that even low numbers of α4β7-expressing T cells are crucial for disease pathogenesis and low initial expression might raise the odds of completely preventing these T lymphocytes from homing to the gut. It will be an important task of future studies to prospectively validate this preliminary observation. Moreover and most interestingly, we also found a surprisingly clear association of changes in α4β1 expression on CD4⁺ T cells after 6 weeks with clinical response after 16 weeks. While these pilot data—like the whole study—are limited by the rather small patient number and retrospective collection of clinical data, thus requiring confirmation in larger multicenter studies, it is nevertheless an observation that disserves further investigation and raises hopes that 2 months of ineffective treatment could be saved in some patients by measurement of the α4β1 expression profile at baseline and after 6 weeks of treatment. Although this would not be a prediction marker that can be assessed before beginning therapy like it was conceptually shown for membrane-bound TNF-α receptor in therapy with anti-TNF-α antibodies (37) or intestinal αE expression in therapy with the experimental anti-β7 integrin antibody etrolizumab (38), it could yet accelerate the assessment of individual response to vedolizumab.

In conclusion, our results suggest that individual response to vedolizumab treatment in UC might be reflected by specific changes in integrin profiles in the peripheral blood. Further studies are required to confirm the translational potential of these observations for the prediction of response to therapy.

All subjects gave written informed consent in accordance with the Declaration of Helsinki. The protocol was approved by the Ethics Committee of the University Hospital Erlangen.

FF, DS, and SZ performed the experiments; RA, SH, SF, CN, IA, MN, and SZ provided clinical samples, protocols, reagents, or designed experiments; FF, DS, CN, IA, MN, and SZ analyzed and interpreted the data; SZ drafted the manuscript; all authors critically revised the manuscript for important intellectual content.

MN has served as an advisor for Pentax, Giuliani, MSD, Abbvie, Janssen, Takeda, and Boehringer. SZ and MN received research support from Takeda and Hoffmann-La Roche. All other authors declare no conflict of interest.