Efficacy and Safety of Immunotherapy and Standard of Care in High-Grade Gliomas: A Systematic Review and Meta-analysis

BACKGROUND: Immunotherapy combined with standard of care (SOC) is often used for high-grade glioma (HGG). There are few comparisons about immunotherapy with or without SOC treatment (IMT) versus SOC. It is important to understand what interventions exist and their relative effectiveness. METHODS: The Cochrane Library, Embase, Medline, and the Web of Science Core Collection were systematically searched by two librarians. Retrieved hits were screened for inclusion. Subgroup analysis was used to examine main factors associated with overall survival (OS). Progression-free survival (PFS), objective response rate (ORR), and occurrence rate of adverse events (AE) as primary endpoints were used to assess the efficacy and safety of IMT . This study was registered with PROSPERO, number CRD42019112356. RESULTS: The search yielded 2315 results of which 11 met eligibility criteria. We identified 11 publications. Compared to SOC alone, IMT improved OS (HR = 0.62, 95% CI 0.48-0.81; p = 0.0003), PFS (HR = 0.59, 95% CI 0.39-0.89; p = 0.0117), ORR (RR = 3.12, 95% CI 1.09-8.95; p = 0.034). But it increased the occurrence rate of AE (RR = 1.56; p < 0.0001). CONCLUSIONS: It suggests that IMT compared to SOC has a certain effectiveness. Our findings support the use of immunotherapy in brain tumor to improve HGG outcomes.

society. The median overall survival (OS) times of SOC (TMZ combined with radiotherapy) were 14.6 months for newly diagnosed GBM(WHO grade IV) [4], 7.4 months for recurrent Grade IV gliomas, and 11.4 months for recurrent Grade III gliomas [5].
Despite remarkable advances in neurosurgery, radiotherapy and chemotherapy, HGG patients still face a poor prognosis. Standard of care for HGG usually entails surgery followed by maximal surgical resection, followed by radiotherapy plus concomitant and adjuvant temozolomide (TMZ) chemotherapy, sometimes including carmustine and PCV (Procarbazine+CCNU+Vincristine) scheme as alternative chemotherapy or bevacizumab as targeted-therapy. Influenced by O-6-methylguanine-DNA methyltransferase (MGMT) promoter, about 55% GBM patients could't benefit from TMZ [6]. Microsatellite instability (MSI) arise in GBM during TMZ therapy and mediate TMZ resistance [7]. Resistance to chemotherapy of HGG appears to another concerning issue. The possible susceptibility of HGGs to IMT has been explored.
The concept of cancer immunotherapy can be tracked back to William Coley who first use bacteria to cure cancer in 1891 [8]. It means that the immune system can recognize and control tumor growth. In recent years, immunotherapies are gaining much research attention and exceedingly more evidences show that high grade gliomas can get certain benefits from it [9]. Six meta-analysis respectively published in 2014 and 2018 indicated improved OS and PFS were obtained applying immunotherapy in HGG patients [10][11][12][13][14][15]. As far as we known, our context is first meta -analysis to do such detailed subgroup-analyses.
Nonetheless, we also use some more stringent criteria to decrease the possible difference from clinical background.
The interventions of current systematic review included immunotherapy categorized as follows: 1.

Immunopotentiator: TGF-b 2 inhibitor, Cpg-ODN
In order to verify and quantify the efficacy and safety of the combination of immunotherapy and SOC, current meta-analysis was started by utilizing survival data of published papers. We also hope to inform clinicians which kind of IMT is more effective than SOC for HGG patients.

Search strategy and selection criteria
For this systematic meta-analysis, we searched for randomized controlled trials (RCTs) published from the date of database start to December 1,2018, comparing immunotherapy combined SOC treatment (IMT) and standard of care (SOC) in adults (age ≥18), with a diagnosis of HGG according to standardized diagnostic criteria.
Two authors (S.N. Zhang and X.D. Hu) searched online using thematic and free words as a strategy through the Cochrane Library/Embase/Pubmed/Web of science four libraries for relevant articles published up to December 1, 2018. Search terms included "glioma", " astrocytoma", "glioblastoma", "immunity", "immunotherapy", "viruses", "humans" and "randomized". An English language restriction was pronounced. Clinical trials registered on the website (http://ClinicalTrials. gov) were also explored.
The following inclusion criteria have been adopted: therapy intervention restricted in IMT, adults with HGG, two arms with IMT and SOC. SOC entails surgery, radiotherapy, or chemotherapy. All included studies are English.
The following exclusion criteria have been adopted: lack of relevant outcome data, trials with non-standard of care control arm, phase I trials, phase II single arm trials, animal or cell trials. Abstracts and presentations from all major conference proceedings were excluded.

Data extraction and quality assessment
Two investigators (X.Y. Peng and X.M. Liu) extracted relevant information from the included articles. The HR described as a more suitable measure for analyzing time-toevent outcomes than odds ratio (OR) or relative risk (RR) was extracted [16,17]. When report of HR and 95 % CI was not available, estimated value was derived indirectly from Kaplan-Meier curves according to the methodology described by Jayne F Tierney [16].

Statistical analysis
Details of our statistical analyses were performed by R (version 3.6.1 for Windows; https://www.r-project.org/). Specific methods of operation could be found [18].
The primary end point was overall survival (OS), progression-free survival (PFS), objective response rate (ORR), and occurrence rate of adverse events (AE); secondary end points were subgroup analysis, meta regression, heterogeneity exploration and cumulative metaanalysis.
Hazard ratio and 95% confidence intervals (CIs) were calculated for OS and PFS. Risk ratios and 95% CIs were calculated for ORR and AE. A random-effects model was used for data synthesis in the presence of significant heterogeneity, while a fixed-effects model was used when there was no significant heterogeneity. Heterogeneity across trials was assessed with I 2 test, and I 2 > 50%, p < 0.1 suggested there was significant heterogeneity.
Subgroup analysis was conducted. Heterogeneity across entire study were examined by galbraith radial plot.
Sensitivity analysis was performed to explore the impact of an individual study by deleting 1 study each time. Publication bias was examined by funnel plots.

Trial selection
Overall, 2,315 citations were identified by the researchers and 66 potentially eligible articles were retrieved in full text. We excluded 55 reports, but included 4 additional studies from other sources, resulting in 11 publications describing 10 RCTs published and 6 historical-matched control trials (HMCTs) between 2004 and 2018 ( Figure 1).

Main Characteristics of studies
1,288 participants who are conformed HGG by clinical, radiological or MRI evidence were including in this study. 67 participants were diagnosed AA/AO/Others (WHO grade Ⅲ ).
In viral therapy studies, five were without TMZ as a kind of SOC and six were with TMZ.
Totally 931 participants were recruiting in viral therapy studies (393 patients in experimental arm and 538 patients in control arm). Three studies reported PFS and eleven studies reported OS . Details could be found in Table 1. As for DC therapy, there were three studies in DC therapy. And all studies used TMZ in SOC. 90 participants were recruiting in DC therapy (43 patients in experimental arm and 47 patients in control arm) ( Table 2). Immunopotentiator(IP) was used in two studies with TMZ as one of SOC as experimental arm (88 patients in experimental arm and 179 patients in control arm (Table   1).

PFS
With respect to PFS, we used random-effect to assess efficacy of immunotherapy through HR of it. We pooled six trials, a total of 316 participants (113 patients treated with IMT, 203 patients treated with SOC). It shows that IMT could decrease the risk of recurrence by 41% compared with SOC (HR = 0.59, 95% CI 0.39-0.89; p = 0.012). Significant heterogeneity was found (tau 2 = 0.166, p = 0.018; I 2 =62.9%) ( Figure 1A). Besides, two subgroups were divided according to intervention type (IMT with SOC or IMT alone), which decrease heterogeneity significantly ( Figure 1B Figure   1D). It reveals that immunotherapy existed a certain potential safety problem.

Secondary endpoints
Considering substantial heterogeneity within studies, we explore the source in several ways. We dedicated to decrease the heterogeneity and make our context homogeneity.
Thereof, Ji(1)(2) and cho2012 carried out in China, Westphal2013 and Rainov2000 was in a background that TMZ has not been widely applied. It hinted that recruiting area and TMZ applying may have some effect in heterogeneity between studies. ( Figure 1E)

Main factors influencing efficacy
Besides exploring the source of heterogeneity, we also try to find out factors influencing efficacy of IMT. (Table 4) As mentioned above, subgroups divided according to IMT type manifested a statistically difference among viral therapy, DC vaccine and immunopotentiator (p < 0.05).
In addition, we divided all studies reported OS in terms of recruiting area(Europe/China/USA) and deleting two multi-area studies [19,20], which significantly decreased heterogeneity. What's more, it also suggested that recruiting area may be a main factor for efficacy of IMT (p < 0.05; Figure 2A). Forest plot before deleting two studies can be found in Supplementary Fig. 4.
Besides, subgroup analysis in accordance with TMZ applying was done(TMZ/Not TMZ/Not TMZ partly) as galbraith radial plot indicating. After subgroups divided, heterogeneity was decreased respectively. And pooled HR effective value was statistically different among subgroups (p < 0.05).
Furthermore, IMT was defined as immunotherapy with or without SOC treatment. The former means IMT was used as an adjuvant, while the latter means IMT was used as a new therapy. We also found no matter as an adjuvant or as a new therapy, immnunotherapy has a certain effect to prolong the OS of HGGs. But when it was used alone, the confidence interval is larger.
At last but not least, whether studies are randomized-controlled or double-bind trials doesn't have statistically significance to effective value (p > 0.05). Gliomas whether recurrent or not, and whether Grade III or IV are does not have statistically significance to effective value, too(p > 0.05) ( Figure 2B).

Sensitivity analysis
Sensitivity analysis was done to assess which study contributes to influence our current results. We didn't find any study which have a potential impact on results, and the results did not materially change by deleting any study at a time ( Figure 4C).

Publication bias
Publication bias was explored with an inverted funnel plot, which showed a significant asymmetry around 95% CI and Begg's test showed a significance of bias (p < 0.001). We We did a systematic review of the efficacy and safety of IMT and SOC in adult HGG Moreover, a meta-analysis about it also suggests that immunotherapy has a tail-dragging effect so that use it early could have better results [26]. In the future, we hope more trials about it could emerge out of, and then we will update our reviews aiming at it.

Ethics approval and consent to participate
This study is a systematic review and meta-analysis that provides secondary research evidence. The ethics is not applicable. Also, the consent is unable to be obtained because the patients are not traceable. However, all the information is sufficiently anonymized.
Details have been removed from the case descriptions to ensure anonymity. The editors and reviewers have reviewed the available details and are satisfied that the information supports the authors' conclusions.
data is available from PROSPERO, number CRD42019112356.

Ethical approval
This article does not contain any studies with human participants or animals performed by any of the authors.

Consent for publish
Not applicable.