To the Editor: Autoimmune liver disease is a chronic immune-mediated liver disease. The term “overlap syndrome” (OS) is used to describe the conditions in which patients simultaneously or consecutively present with features of primary biliary cholangitis (PBC) or primary sclerosing cholangitis and autoimmune hepatitis (AIH). PBC-AIH OS is described most frequently, with a prevalence of approximately 8% to 20% in adult patients with either pure PBC or AIH.
A recent study revealed that the inpatient outcomes and survival of PBC-AIH OS patients were significantly worse and shorter than those of patients with either pure PBC or AIH, respectively. At present, there is no consensus regarding which specific risk factors can predict poor response in PBC-AIH OS. To identify the baseline clinical characteristics and immunological markers for predicting non-response in PBC-AIH OS, we evaluated the survival and factors that were significantly associated with response and systematically assessed cytokine perturbations in the periphery and liver in 134 PBC-AIH OS patients at West China Hospital of Sichuan University from October 2013 to January 2021. The study protocol was approved by the Ethics Committee of West China Hospital of Sichuan University (No. 2013-221). Informed consent was obtained from each patient. PBC patients were diagnosed with PBC-AIH OS according to the Paris criteria and/or PBC patients with distinct AIH features, which included sustained high levels of serum transaminase >3-fold above the upper limit of normal (ULN) for at least 3 months and/or serum immunoglobulin G (IgG) level >1.3-fold above the ULN and/or histological features of moderate to severe interface hepatitis. When patients met two or more of these diagnostic criteria, PBC-AIH OS was conservatively diagnosed. Patients were treated with ursodeoxycholic acid (UDCA) plus methylprednisolone alone or in combination with azathioprine or other immunosuppressants according to the guidelines.
The criteria to evaluate the response were complete biochemical response (CBR) or partial biochemical response (PBR) within 6 months after immunosuppression therapy. CBR was defined as normal serum transaminase and IgG levels, while PBR was referred to as alanine aminotransferase (ALT) or aspartate aminotransferase (AST) ≤ 2 × ULN. Anything less than a CBR and PBR was considered a non-responder. Kaplan–Meier survival curves were used to compare the prognosis between the two groups. Eleven cytokines were detected in serum from some patients (27 responders and 35 non-responders) in the two groups by Luminex assays (AliveX Biotech, Shanghai, China). Liver tissues were collected from six random patients in the two groups, and real-time quantitative polymerase chain reaction (qPCR) was conducted to determine the mRNA levels of those cytokines in liver tissues.
Supplementary Table 1, https://links.lww.com/CM9/B120 summarizes the baseline demographic data of all enrolled patients. The histopathological features of PBC-AIH OS were presented in Supplementary Figure 1, https://links.lww.com/CM9/B120. A total of 48.5% of patients did not respond to treatment [Supplementary Figure 2A, https://links.lww.com/CM9/B120]. CBR was achieved in only 41 (30.6%) patients, while 28 (20.9%) patients obtained PBR. The median follow-ups were 30.0 and 24.0 months for the responders and non-responders, respectively. Kaplan–Meier analysis revealed that responders had a significantly higher liver-related adverse event-free survival rate than non-responders (log-rank: P < 0.001) [Supplementary Figure 2B, https://links.lww.com/CM9/B120].
Non-responders were more prone to jaundice than responders (P = 0.038) [Supplementary Table 2, https://links.lww.com/CM9/B120]. Univariate analysis revealed that total bilirubin, alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (GGT), and cholesterol (CHOL) levels were higher in non-responders than in responders (all P < 0.05), and the frequency of anti-mitochondrial antibody (AMA) positivity was higher in non-responders than in responders (P = 0.007). In addition, the frequency of cirrhosis was higher in the non-responders than in the responders (P = 0.001) [Supplementary Table 3, https://links.lww.com/CM9/B120]. There was no difference between the hallmarks of AIH histology that were recorded, but it is important to note that ductopenia, as a typical change in PBC, was seen more often in non-responders than in responders (P < 0.001). No significant differences were observed for the fibrosis stage and activity grade between the two groups [Supplementary Table 4, https://links.lww.com/CM9/B120]. In the final stepwise multivariate logistic regression analysis model, high CHOL levels, ductopenia, and the presence of cirrhosis were identified as risk factors for a poor response (all P < 0.01) [Supplementary Table 5, https://links.lww.com/CM9/B120].
Serum interleukin-33 (IL-33), interferon-γ (IFN-γ), and IL-21 levels in the non-response group were higher than those in the responders (all P < 0.05) [Supplementary Figure 2C, https://links.lww.com/CM9/B120]. Similar to the difference in serum, we observed a small but significant elevation in IL-33 and IFN-γ levels in the liver in the non-responders (both P < 0.05) [Supplementary Figure 2D, https://links.lww.com/CM9/B120].
Studies have already linked hypercholesterolemia to poor prognosis in patients with cholestasis, and in the present study, higher baseline serum CHOL levels were found to be associated with non-response. As CHOL-lowering medications are recommended on a case-by-case basis in a subgroup of PBC patients with metabolic syndrome, our finding is encouraging for the potency of CHOL-lowering therapy in PBC-AIH OS patients with poor response, such as pravastatin, which is metabolized in a two-channel fashion, which may be efficient and safe in this setting.
The present study shows that baseline ductopenia was more common in the poor response group. Ductopenia refers to evident bile duct destruction, which is not a typical feature of AIH and then signs the consideration of PBC or variant syndrome, implying that a histologically predominant PBC feature may help predict a poor response to immunosuppressive therapy. In our study, cirrhosis was prevalent and was significantly associated with a poor response, which was consistent with those of Ozaslan et al, as they found that the presence of advanced fibrosis was associated with an incomplete response to the combination of UDCA and immunosuppressants.
Our findings showed that the baseline levels of serum IL-33, IL-21, and IFN-γ at baseline were elevated in the poor-response group, and the mRNA levels of IL-33 and IFN-γ at diagnosis were also upregulated in their liver tissues, indicating that cytokine-based therapies may be a new therapeutic target in this group of patients.
This study describes the largest cohort of patients with PBC-AIH OS to date and describes the treatment response and outcomes. A limitation of this study is that it was conducted in a large single-center and was a retrospective analysis of prospectively documented data; however, prospective interventional therapeutic trials may not be expected in the foreseeable future due to the low prevalence of this condition.
In conclusion, the current results suggest that nearly half of patients with PBC-AIH OS had a poor response to immunosuppressive therapy, with a worse prognosis than responders. Features of high CHOL level, ductopenia, and the presence of cirrhosis at baseline appear to predict a poor response to immunosuppressive therapy. Additionally, higher baseline IL-33 and IFN-γ levels in serum may help identify patients who need timely intervention and second-line immunosuppressive agents.
We would like to thank the patients who enrolled in the study and the staff and postgraduate students.
This study was supported by grants from the National Natural Science Foundation of China (No. 82100552), the Science and Technology Department of Sichuan Province of China (No. 2021YJ0468), and the PostDoctor Research Project, West China Hospital, Sichuan University (No. 2020HXBH085).
Conflicts of interest
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