We observed an overall irAE incidence of 27.0% across all cancer types considered. This irAE frequency is similar to that of a recent study based on 16 RCT studies in which the incidence of irAEs of all grades and for grade ≥ 3 was estimated to affect 35.6 and 7.3% of patients, respectively, for lung cancer treated with ICIs .
Occurrence of irAEs was especially common among patients who received anti-CTLA therapy, and multivariate analysis identified the use of the combination of anti-PD-1 and anti-CTL-4 antibodies as an independent risk factor for the incidence of immune-related liver injury with grade ≥ 2. The combination of anti-PD-1 and anti-CTL-4 therapy accounted for 77.8% of irAEs of any grade and 50.0% of irAEs with grade ≥ 3, respectively. These results are similar to previous reports that showed an increased incidence of irAEs in the case of ICI combination therapies [10,11,12]. Based on previous reports, immune-related liver injury is estimated to affect 1–4% and 4–9% of patients treated with anti-PD-1/PD-L1 and CTLA-4 antibody alone, respectively, and 18% of patients treated with the combination of anti-PD-1 and anti-CTLA-4 antibody [13,14,15]. Moreover, in a study of combination therapy with anti-PD-1 and anti-CTLA-4 for metastatic melanoma, 37% of patients developed irAE liver injury of any grade, and 16% reported grade ≥ 3 . Because the anti-tumor effects of anti-PD1/PD-L1 and anti-CTLA-4 employ different mechanisms, the combination of these ICIs promises higher potency against various malignancies but also increases the risk of irAEs.
Because the mechanisms of irAEs differ by organ, we focused on analyzing the characteristics and risk factors for liver injury, which was the most common irAE. Among the 28 patients with grade ≥ 2 immune-related liver injury in this study, 16 (57.1%) developed hepatocellular-type liver injury, 10 (35.7%) developed cholestatic-type liver injury, and the remaining 2 patients (7.1%) developed mixed-type liver injury, as assessed by CTCAE. The distribution of ICI-induced liver injury is similar to a previous report that analyzed 56 patients with ICI-induced liver injury . The current recommendation for Grade 2 liver injury is discontinuation of ICIs and switching to corticosteroid therapy at a dose of 0.5–1.0 mg/kg/day. When patients develop Grade 3–4 liver injury, corticosteroid therapy at a dose of 1.0–2.0 mg/kg/day is used. If liver injury fails to respond to corticosteroid therapy, addition of MMF is a fallback treatment option . In the present study, among the 18 patients who received PSL therapy for ICI-induced liver injury, 3 patients were also treated with MMF, but two patients died.
We performed histopathological analysis of liver biopsy on 7 patients with immune-related liver injury of grade ≥ 3. Immunostaining revealed predominantly CD8-positive T cell infiltration into the liver, and, to a lesser extent, CD4-positive and CD20-positive T cells in all patients (Fig. S1). Pathological findings are diagnostic in immune-related liver injury. The most common patterns are acute hepatitis with spotty or confluent lobular inflammation and centrilobular necrosis [19, 20]. In a previous report, immunostaining revealed that the majority of lymphocytes involved in both periportal and lobular inflammatory infiltration were CD8-positive lymphocytes [20, 21]. Zen et al. compared the histological features of patients with drug-induced liver injury, autoimmune hepatitis, and ICI-induced immune-mediated liver injury and found that immunostaining revealed the presence of large numbers of CD8-positive T cells, whereas CD20-positive B cells and CD4-positive T cells were fewer in ICI-induced liver injury than in drug-induced liver injury or autoimmune hepatitis or drug-induced liver injury . In fact, the present study also showed that infiltration of lymphocytes in the liver is mainly CD8-positive T cells. The relationship between the proportion of infiltrating lymphocytes and the pathological conditions in immune-related liver injury is unclear. Only seven patients underwent liver biopsy examination in this study, but it would be interesting to analyze the correlation between the proportions of CD4+, CD8+, CD20, or FOXP3-positive T cells and pathological conditions such as the diagnosis, severity and treatment response of irAEs using a larger number of histological examinations in the future.
The present study showed that a higher baseline white blood cell count including lymphocytes and eosinophils and a baseline eosinophilic count ≥130/μL were independent risk factors for the incidence of immune-related liver injury of grade ≥ 2. Several host factors have been reported to be associated with the occurrence of irAEs including female sex, baseline absolute lymphocyte and eosinophil numbers, presence of autoantibodies, sarcopenia, fever within 24 hrs of initial ICI administration, composition of the gut microbiome, and elevated BMI [22,23,24,25,26,27]. Diehi et al. demonstrated that higher baseline absolute lymphocyte number was an independent risk factor for irAEs of grade ≥ 2 for anti-PD-1 antibody-treated patients with solid tumors . Chu et al. reported that a higher baseline absolute eosinophil count was associated with the occurrence of ICI-induced pneumonia , and Nakamura et al. reported that a higher baseline absolute eosinophil count was associated with the occurrence of endocrine irAEs . Eosinophils play a role in regulating multiple immune functions, such as activation of T cells by antigen presentation and attraction of tumor-specific CD8-positive T cells . Both lymphocytes and eosinophils are important for immunity; therefore, the number of white blood cells might correlate with the occurrence of irAEs. These mechanisms of immune response may be involved in the development of irAEs. Although the specific predictive factors for ICI-induced liver injury are unclear, the results of this study may be useful for identifying early-onset irAEs, considering the availability of blood cell count data prior to the initiation of ICI treatment.
The present study showed a higher response rate to ICI therapy and an increased overall survival rate in patients who developed irAEs. The relationship between occurrence of irAEs and treatment response to ICIs remains controversial. Some studies have shown clinical benefits such as better treatment response or prognosis [4,5,6,7,8, 28, 29], but other large retrospective studies of ipilimumab have shown similar treatment outcomes between patients whether or not they experienced irAEs . ICIs target not only tumor-specific T cells but also other T cells and may cause the unintended activation of non-tumor-specific T cells, resulting in irAEs in a variety of organs. Recent studies suggest another possible mechanism underlying irAEs. T cells that target antigens common to both tumors and healthy tissue are activated by ICIs, leading both to higher antitumor efficacy as well as a higher incidence of irAEs . This mode of T cell activation might lead to irAEs in various organs while at the same time enhancing the anti-tumor effect.
This study has several limitations due to its retrospective nature. First, no clear diagnostic criteria for irAEs could be used; irAEs were diagnosed based on symptoms or laboratory tests temporally associated with the use of ICIs. Although irAEs were diagnosed by the attending physician and carefully evaluated retrospectively by us based on medical records, some irAEs, especially mild non-hematological irAEs, such as colitis or cholangitis, might have been overlooked; however, we believe that most severe irAEs were detected. We determined irAE grade ≥ 2 as significant in this study. Second, a variety of malignancies and treatment regimens were analyzed together in this study even though the number of patients with some malignancies was small. The pathological finding of irAEs might vary by cancer type. It may be necessary to identify the specific predictive factors associated with occurrence of specific irAEs and clarify the influence of irAE development on prognosis with respect to malignancy and treatment regimen. Third, several important pieces of clinical information were lacking, including details on concomitant medications that could induce adverse events. Although we confirmed based on the medical records that there was no significant change in concomitant medications used during the course of ICI therapy, it is possible that some adverse events observed in this study were caused by concomitant medications rather than as a direct result of ICI therapy. Lastly, the present study showed that the development of irAEs was associated with a higher response rate to ICI therapy and an increased survival rate. Although the median number of cycles of ICI therapy that were received was not different between patients with and without irAEs, it is not possible to exclude the possibility that longer treatment periods increased the chance of irAE development. To reduce this bias, the relationship between irAEs and survival was analyzed by Cox proportional hazards regression model, and the model showed that the presence of irAEs was significantly associated with survival after controlling for factors such as age, cancer type, and performance status. This result seems to support the conjecture that the presence of irAEs is associated with improved survival, but further analysis is needed to clarify the predictive factors for occurrence of irAEs and the relationship between the incidence of irAEs, treatment response to ICI therapy, and survival for each type of therapy in a prospective multicenter study.
In conclusion, we conducted a retrospective study on patients with malignancies who received ICI therapies such as anti-PD-1, PD-L1, and CTLA-4 antibodies. Patients who received anti-CTLA4 therapy were more likely to develop irAEs compared to those who received anti-PD-1 or anti-PD-L1 monotherapy. Use of ICI combination therapies, such as anti-PD-1 and anti-CTLA-4 antibodies, and baseline absolute eosinophil count might be predictive factors for the occurrence of immune-related liver injury, the most common irAE. The occurrence of irAEs seems to be associated with a higher efficacy of ICI therapy as well as longer survival.