Efficacy and safety of chimeric antigen receptor T-cells treatment in central nervous system lymphoma: a PRISMA-compliant single-arm meta-analysis

Abstract

Background

Chimeric antigen receptor (CAR) T cells are used to treat refractory and recurrent B-cell lymphoma. When administered intravenously, CAR T cells can be detected in cerebrospinal fluid, and thus represent a promising method for the treatment of central nervous system lymphoma (CNSL). This meta-analysis aimed to clarify the effectiveness and safety of CAR T-cell therapy in the treatment of CNSL.

Methods

Studies involving patients with CNSL who received CAR T-cell therapy that reported overall response (OR), complete response (CR), and partial response (PR) were included. A random-effects or fixed-effects model with double arcsine transformation was used for the pooled analysis and 95% confidence intervals (CI) were determined for all outcomes.

Results

Eight studies, comprising 63 patients, were identified and were included in the meta-analysis. The pooled OR and CR rates after treatment with CAR T cells were 69% (95% CI, 56–81%) and 51% (95% CI, 37–64%), respectively. The pooled rate of progressive disease after remission was 38% (95% CI, 21–55%). The pooled rate for neurotoxicity grade 3 or above was 12% (95% CI, 3–24%, I² = 0.00%, p = 0.53). No treatment-related deaths were reported.

Conclusions

CAR T-cell therapy is a promising option for the treatment of CNSL owing to a high short-term remission rate and controllable side effects. However, the high recurrence rate after remission must be addressed. Long-term follow-up data with large sample sizes are also needed to better assess the effectiveness and safety of CAR T-cell therapy.

Registration

This meta-analysis was registered in the international prospective register of systematic reviews (PROSPERO) (CRD42022301332).

Supplementary Information

The online version contains supplementary material available at 10.1007/s00262-022-03246-w.

Introduction

Central nervous system lymphoma (CNSL) can be primary or secondary. Primary CNSL (PCNSL) is a rare and aggressive form of extranodal non-Hodgkin lymphoma (NHL) that primarily affects the brain, spinal cord, meninges, and eyes [1]. The vast majority of PCNSL pathology is represented by diffuse large B-cell lymphoma (DLBCL) [2]. Secondary CNSL (SCNSL) refers to secondary involvement of the central nervous system, at presentation or relapse, in patients with systemic lymphoma [3]. Regardless of whether the patient is diagnosed with PCNSL or SCNSL, treatment is greatly complicated by the presence of the blood–brain barrier (BBB). This makes the treatment of CNSL more difficult, and exploring new and effective therapeutic options is very important to improve the prognosis.

The advent of chimeric antigen receptor (CAR) T cells has revolutionized the treatment of refractory and recurrent (r/r) NHL. The complete response (CR) rate of CD19 CAR T cell-treated patients with r/r DLBCL is greater than 50% [4]. However, in 12–32% of cases, CD19 CAR T-cell therapy is associated with mild to severe neurotoxicity, including delirium, cognitive dysfunction, and seizures [5]. Consequently, early clinical trials of CAR T cells excluded patients with CNSL. Intravenously administered CAR T cells can be detected in the cerebrospinal fluid (CSF) of patients [6, 7], indicating that they can migrate to the central nervous system and exert anti-lymphoma effects. Nevertheless, the efficacy and safety of CAR T-cell therapy in the treatment of CNSL remains uncertain. The purpose of this meta-analysis was to address this knowledge gap to help guide the clinical treatment of this malignancy.

Materials and methods

Data sources and literature search

This study was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [8, 9]. Three investigators independently searched for studies published before February 6, 2022, in the Cochrane Library, PubMed, Embase, China National Knowledge Infrastructure Databases, Chinese BioMedical Literature database, and Wanfang Data Knowledge Service Platform. The search terms were “central nervous system lymphoma” and “chimeric antigen receptor”; the search strategy for each database is shown in Supplementary Table 1. The search was not restricted by region, race, or payment method. In addition, references in reviews and original studies were reviewed to avoid omission of relevant studies. The results of the database searches were imported into EndNote (X8 version) to consolidate the results and exclude duplicate articles.

Selection criteria

The inclusion criteria were as follows: (1) The research subjects were adults (≥ 18 years of age) diagnosed with CNSL; (2) the intervention was CAR T-cell therapy, regardless of the dose, combination treatment regimen, or previous treatment; (3) complete data for the main outcomes.

The exclusion criteria were as follows: (1) Outcomes reported for multiple populations or disease cohorts; (2) articles were reviews, comments, case reports, or referred to cellular or animal studies.

Two researchers independently reviewed the title and abstract of each study and submitted eligible studies for full-text analysis to confirm whether they should be included in the meta-analysis. Any inconsistency was discussed with a third researcher until a consensus was reached.

Quality assessment

Prospective studies were assessed using a methodological index for non-randomized studies (MINORS) [10]. Retrospective studies were assessed using the JBI Critical Appraisal Checklist for Case Series [11].

Data extraction

Two researchers independently conducted data extraction and any difference in opinion was discussed with the third researcher until a consensus was reached.

The main outcomes included overall response (OR), CR, and partial response (PR) according to the criteria of the International Primary CNS Lymphoma Collaborative Group [12]. If available, the following data were also extracted: progression-free survival (PFS), overall survival (OS), and adverse events (AEs). PFS was defined as the time from CAR T-cell treatment to disease progression, death from any cause, or last follow-up. OS was defined as the time from initiation of CAR T-cell treatment to death from any cause or last follow-up. AEs were classified by the criteria of Lee et al. [13] or the Common Terminology Criteria for Adverse Events version 4.

Statistical analysis

All data were analyzed using STATA SE14.0 (StataCorp LLC, College Station, TX, USA). The pooled rates adopt the random-effect model or fixed-effect model after double arcsine conversion. The effect size of all combined results was represented by the 95% confidence intervals (CI) (with upper and lower limits). Heterogeneity between studies was assessed using I² statistics. The fixed-effect model was selected for the pooled results of low heterogeneity (I² ≤ 50%); on the contrary, the random-effect model was used for analysis. For highly heterogeneous pooled results, sensitivity analysis was performed by excluding each study from the results one by one. Potential publication bias was examined using the Begg’s and Egger’s tests.

Results

Study selection and characteristics

A total of 388 relevant articles were identified in the initial search (340 in English and 48 in Chinese). The literature review and identification processes are shown in Fig. 1. The 8 remaining studies—5 prospective clinical trials [14–18] and 3 retrospective studies [19–21]—fulfilled the eligibility criteria and were included in the meta-analysis. The meta-analysis evaluated the efficacy and toxicity of the CAR T-cell regimen for a total of 63 patients with CNSL across eight cohort studies [14–21]. The ages of the patients ranged from 18 to 81 years. The baseline clinical characteristics of these patients are summarized in Table 1.

Fig. 1.

Flow diagram of the study selection

Table 1.

Baseline clinical characteristics of the included studies

Study	Country	Design	Study period	Median follow-up time, months (range)	Disease status	Sample size	Median age, years (range)	KPS or ECOG score	Median number of cycles of prior therapies (range)	Intervention
Wu 2021	China	Open-label clinical trial (ChiCTR-OPN-16009847)	01/2019–02/2021	14.2(1.37–24.17)	PCNSL r/r B-cell NHL with SCNSL	13	42 (23–65)	NR	NR	CD19 and CD22 CAR T cells after auto-HSCT; median cell number: CD19: 4.3 (2.0–9.2) × 106/kg CD22: 4.1 (2.6–8.4) × 106/kg
Siddiqi 2021	USA	Ongoing phase 1 clinical trial (NCT02153580)	As of 10/2020	NR	r/r PCNSL	5	49 (42–53)	KPS 70–90	5 (2–12)	CD19 CAR T cells DL1 = 200 million CAR+ cells (n = 3) DL2 = 600 million CAR+ cells (n = 2)
Ghafouri 2021	USA	Retrospective	10/2017–01/2020	5.17 (2.87–6.93)	r/r B-cell NHL with SCNSL	5	58.5 (28.3–76.4)	NR	2.4 (1–4)	Axicabtagene ciloleucel
Li 2020	China	Clinical trial (ChiCTR-OPN-16008526)	NR	(6–16)	r/r PCNSL (n = 1) r/r B-cell NHL with SCNSL (n = 4)	5	39 (18–60)	KPS 20–50	7 (5–15)	CD19 and CD22 CAR T cells CD19: 2.23–7.06 × 106/kg CD22: 3.1–7.0 × 106/kg
Frigault 2019	USA	Retrospective	08/2018–03/2019	NR	r/r B-cell NHL with SCNSL	8	50 (17–79)	ECOG 0–2	5 (3–6)	Tisagenlecleucel
Alcantara 2022	France	Retrospective	05/2020–03/2021	8.5	r/r PCNSL	9	67 (48–75)	ECOG 0–4	3 (2–5)	Tisagenlecleucel (n = 7) Axicabtagene ciloleucel (n = 2)
Abramson 2019	USA	Phase 1 TRANSCEND NHL 001 study	NR	NR	r/r B-cell NHL with SCNSL	9	60 (47–73)	NR	3 (2–7)	liso-cel (JCAR017) DL1 = 50 × 106 CAR T cells (n = 4) DL2 = 100 × 106 CAR T cells (n = 5)
Frigault 2021	USA	Clinical trial (NCT04134117)	As of 04/2021	7.43	r/r PCNSL	9	67 (34–81)	NR	4	Tisagenlecleucel

r/r relapsed/refractory; PCNSL primary central nervous system lymphoma; SCNSL secondary central nervous system lymphoma; NHL non-Hodgkin lymphoma; KPS Karnofsky Performance Status; ECOG Eastern Cooperative Oncology Group; auto-HSCT autologous hematopoietic stem cell transplantation; NR not reported

Quality assessment

The quality assessment results of all included articles are acceptable for the present meta-analysis (Table 2).

Table 2.

Quality assessment of the included studies

a. Methodological index for included non-randomized studies
Study	I	II	III	IV	V	VI	VII	VIII	Total
Wu 2021	2	2	2	2	2	1	2	0	13
Siddiqi 2021	2	2	2	2	2	1	1	2	14
Li 2020	2	2	2	2	2	1	2	0	13
Abramson 2019	2	2	2	2	2	1	2	2	15
Frigault 2021	2	2	2	2	2	1	2	0	13

b. JBI critical appraisal checklist for case series for included retrospective studies
Study	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Q10	Overall appraisal
Ghafouri 2021	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No	Yes	Include
Frigault 2019	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No	Yes	Include
Alcantara 2022	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	No	Yes	Include

Numbers I–VIII in the heading refer to I, a clearly stated aim; II, inclusion of consecutive patients; III, prospective data collection; IV, endpoints appropriate for the aim of the study; V, unbiased assessment of the study endpoint; VI, follow-up period appropriate for the aim of the study; VII, loss of follow-up less than 5%; VIII, prospective calculation of the study size

Questions Q1–Q10 in the heading refer to Q1, were there clear criteria for inclusion in the case series? Q2, was the condition measured in a standard, reliable way for all participants included in the case series? Q3, were valid methods used for identification of the condition for all participants included in the case series? Q4, did the case series have consecutive inclusion of participants? Q5, did the case series have complete inclusion of participants? Q6, was there clear reporting of the demographics of the participants in the study? Q7, was there clear reporting of clinical information of the participants? Q8, were the outcomes or follow-up results of cases clearly reported? Q9, was there clear reporting of the presenting site(s)/clinic(s) demographic information? Q10, was the statistical analysis appropriate?

Efficacy

Tumor response

The eight included studies [14–21] reported OR, CR, and PR as clinical outcomes. The pooled OR rate after CAR T-cell therapy was 69% (95% CI, 56–81%, I² = 12.99%, p = 0.33) while the pooled CR and PR rates were 51% (95% CI, 37–64%, I² = 0.00%, p = 0.99) and 12% (95% CI, 4–24%, I² = 32.68%, p = 0.17), respectively (Fig. 2). Seven studies [14–20] reported progressive disease (PD) after remission, for which the pooled rate was 38% (95% CI, 21–55%, I² = 6.45%, p = 0.38) (Fig. 2).

Fig. 2.

Pooled response rate for central nervous system lymphoma. a Overall response; b complete response; c partial response; d progressive disease after remission

For 28 PCNSL patients in five studies, [14–17, 20, 21] the pooled OR rate was 79% (95% CI, 57–96%, I² = 0.00%, p = 0.72) while the pooled CR and PR rates for these patients were 56% (95% CI, 32%–78%, I² = 0.00%, p = 0.86) and 12% (95% CI, 0–33%, I² = 24.49%, p = 0.26), respectively (Figs. 3 and 4). For 35 SCNSL patients enrolled in five studies, [14, 16, 18–20] the pooled OR rate after treatment with CAR T cells was 64% (95% CI, 45–81%, I² = 26.34%, p = 0.25) while the pooled CR and PR rates were 47% (95% CI, 29–65%, I² = 0.00%, p = 0.96) and 10% (95% CI, 1%–25%, I² = 37.91%, p = 0.17), respectively (Figs. 3 and 4).

Fig. 3.

Subgroup analysis of response rates. a, b Overall response (a) and complete response (b) of primary central nervous system lymphoma. c, d Overall response (c) and complete response (d) of secondary central nervous system lymphoma

Fig. 4.

Subgroup analysis of partial response rates. a Partial response of primary central nervous system lymphoma. b Partial response of secondary central nervous system lymphoma

Survival

Four studies [14, 16, 19, 21] reported 1-year survival after CAR T-cell treatment. The 12-month pooled PFS rate for CNSL patients treated with CAR T cells was 58% (95% CI, 34–80%, I² = 42.63%, p = 0.17) (Fig. 5) and the 12-month pooled OS rate was 75% (95% CI, 42–98%, I² = 64.29%, p = 0.04) (Fig. 5).

Fig. 5.

Survival for patients with central nervous system lymphoma. a 12-month overall survival. b 12-month progression-free survival

Toxicity

The main AEs associated with CAR T-cell treatment were cytokine-release syndrome (CRS) and neurotoxicity. The pooled rate of grade 1–2 CRS was 72% (95% CI, 48–92%, I² = 70.46%, p = 0.00) (Fig. 6). Only one study [21] reported severe (≥ grade 3) CRS (one patient, 11.1%). The pooled rate of grade 1–2 neurotoxicity was 29% (95% CI, 16–43%, I² = 42.26%, p = 0.11) while the pooled rate for neurotoxicity grade 3 and above was 12% (95% CI, 3–24%, I² = 0.00%, p = 0.53) (Fig. 7). None of the included studies reported residual neurological impairment or treatment-related deaths.

Fig. 6.

Pooled results for grade 1–2 cytokine-release syndrome

Fig. 7.

Pooled results for neurotoxicity. a Grade 1–2 neurotoxicity. b Neurotoxicity above grade 3 or above

Sensitivity analysis

After excluding each study from the results one by one, the pooled results of OS and CRS did not change significantly, indicating that our comprehensive results were reliable (Fig. 8).

Fig. 8.

Sensitivity analysis. a 12-month overall survival. b Grade 1–2 cytokine-release syndrome

Publication bias

Assessment of the pooled OR did not identify significant publication bias among the included studies (p = 0.905 for the Egger test and p = 0.896 for Begg’s test). Similarly, Egger’s test (p = 0.139) and Begg’s test (p = 0.347) for AEs (≥ grade 3) did not identify any publication bias for safety outcomes.

Discussion

CAR T cells are genetically engineered T cells expressing CARs [22]. CARs are engineered synthetic receptors that redirect T cells to recognize and eliminate cells expressing specific target antigens [22]. CARs bind to target antigens expressed on the surface of cells in a major histocompatibility complex (MHC)-independent manner and provoke strong T-cell activation and anti-tumor responses [23]. CD19-directed CAR T cells are considered to be revolutionary immunotherapy for the treatment of r/r B-cell malignancies. However, owing to the risk of severe neurotoxicity, almost all early clinical trials excluded patients with central nervous system involvement. A 68-year-old female with DLBCL and central nervous system involvement who participated in the TRANSCEND-NHL-001 phase 1 trial (NCT02631044) and received CD19-CAR T-cell therapy achieved complete remission of brain lesions [24]. This case report confirmed for the first time that CAR T cells can cross the BBB and exert anti-tumor effects in the central nervous system, suggesting that CAR T cell therapy could potentially be used for the treatment of CNSL.

A meta-analysis of patients with r/r DLBCL who were treated with CAR T cells reported a total CR rate of 46.8% (95% CI: 0.408–0.533) [25], which was in line with our results. This shows that CAR T cells are also effective in the treatment of CNSL. Our previous meta-analysis of ibrutinib found OR and CR rates of 66% and 42%, respectively, for patients with r/r CNSL who were treated with ibrutinib [26]. In this study, patients receiving CAR T-cell therapy achieved a higher remission rate, and CAR T cells may even have an advantage over other novel therapies, such as ibrutinib. However, studies that directly compare CAR T-cell therapy and Bruton tyrosine kinase (BTK) inhibitors or other new therapeutic drugs are currently lacking, and thus definite conclusions cannot be drawn. Furthermore, in four of the eight included studies [14–17], CAR T-cell expansion was detected in both the CSF and peripheral blood, independently of active systemic lymphoma. This further demonstrates that CAR T cells can enter brain lymphoma through the BBB and exert their anti-tumor effects. However, the distribution and duration of CAR T cells in brain lymphoma requires further research.

A review of data for several important clinical trials involving PCNSL indicated that the OR rate for first-line application of high-dose methotrexate (HD-MTX)-based combined chemotherapy in the treatment of newly diagnosed PCNSL patients was 60–86%, while the CR rate was approximately 40% [27, 28]. The results of subgroup analysis in our study showed that CAR T-cell therapy can result in a high remission rate in patients with PCNSL, especially those with r/r PCNSL, which can even be close to the remission rate for initial treatment. The OR and CR rates for patients with SCNSL treated with HD-MTX-based combination chemotherapy were 68.4 and 57.9%, respectively [29]. In another multicenter phase II study, SCNSL patients were given chemotherapy combined with autologous stem cell transplantation (ASCT), resulting in OR and CR rates of 71 and 63%, respectively [30]. Compared with chemotherapy or ASCT, CAR T-cell therapy does not seem to be superior; however, all SCNSL cases included in this study were r/r patients. Thus, CAR T cells remain an alternative treatment option for SCNSL, especially r/r SCNSL.

Although CAR T-cell therapy has brought a high remission rate for patients with CNSL, we found a high rate of relapse or progression. Moreover, all instances of PD occurred within 1 year, and most within half a year. Disease recurrence or progression after CAR T-cell therapy can be either antigen-positive or antigen-negative [31]. The main causes of antigen-positive recurrence were CAR T-cell exhaustion or an immune-suppressive tumor microenvironment [31]. Antigen-negative recurrence mainly occurs under the strong selective pressure applied by CAR T-cell therapy [31]. Following antigen loss, CAR T cells cannot continue to exert targeted cytotoxicity [31]. Possible methods to address the high recurrence rate after CAR T-cell therapy include optimizing CAR structure, CAR T-cell therapy in combination with an immune checkpoint inhibitor or a BTK inhibitor, and multi-target CAR T-cell therapy. Notably, in an included study, CAR T-cell therapy was performed after ASCT in CNSL patients [14]. And only one patient (11.1%) achieved PD after remission [14]. This suggests that CAR T-cell therapy combined with ASCT may be of greater benefit to CNSL patients than CAR T-cell therapy alone. Some of the included studies also reported that patients received additional treatment subsequent to CAR T-cell therapy, including lenalidomide [15], allogeneic hematopoietic stem cell transplantation [19], radiotherapy, or anti-PD1 antibody therapy [16]. None of these patients achieved PD during the follow-up period. However, the best combination scheme for use with CAR T cells is currently the subject of intense research.

Compared with that for peripheral systemic lymphoma, CAR T-cell therapy for CNSL is also restricted by the ability of CAR T cells to infiltrate the tumor owing to permeability limitations imposed by the BBB. One strategy to improve this limitation is to change the mode of administration from intravenous to intracerebral injection [32]. In a CNSL mouse model, after intracerebral injection, CD19 CAR T cells were shown to reach deeper into the tumor when compared with intravenous injection. This is more conducive to controlling tumor growth and inducing tumor regression, thereby prolonging survival time [33]. A mechanistic study in a mouse model demonstrated that compared with intravenous infusion, CAR T cells administered by intraventricular infusion had superior anti-lymphoma activity and memory function through exposure to CSF [34]. Another strategy to improve the entry of CAR T cells into brain lymphoma is to express chemokine receptors on CAR T cells, which are conducive to their migration to the tumor site [35]. However, neither of these strategies have been reported for patients with CNSL, and their safety and effectiveness remain unclear.

Despite the high short-term recurrence rate after CAR T-cell treatment, patients still benefit in terms of survival. Notably, however, only four studies contained 1-year survival data, and the follow-up time of the other studies was relatively short. Long-term follow-up data are needed to better assess the effectiveness of CAR T-cell therapy in terms of survival.

We also noted that some patients who did not achieve a treatment response showed rapid progression in the early stage of CAR T-cell therapy and died within 1–2 months [14, 20]. This suggests that patient selection and bridging therapy are critical for improving the efficacy of CAR T-cell treatment. A reasonable patient selection mechanism is conducive to patients receiving CAR T-cell therapy at the right time [31] while bridging therapy can help patients gain more treatment time [36]. Studies have shown that patient age, tumor burden, IL-7, and circulating tumor DNA are correlated with the efficacy of CAR T-cell therapy [31]. In our analysis, two studies reported a patient older than 75 years [19, 20]. Both patients achieved CR after CAR T-cell therapy. In addition, although there were differences in the performance status of patients among the studies, the CR rate reached 40% after CAR T-cell therapy, even among patients whose Karnofsky performance Status score ranged from 20 to 50 [16]. However, owing to the small number of cases and the lack of controls, the factors that influence the efficacy of CAR T-cell therapy against CNSL are not clear. We look forward to developing patient selection criteria for CAR T-cell therapy.

Regarding safety, as for other systemic lymphomas, the main AEs among CNSL patients treated with CAR T cells were CRS and neurotoxicity. CRS is a severe systemic inflammatory response after CAR T-cell infusion driven by a cytokine surge and bystander immune cell cascade-like recruitment during CAR effector cell expansion [37]. The mechanism underlying the pathology of central nervous system injury induced by CAR T cells remains unclear. Potential pathophysiological mechanisms include endothelial cell activation and the disruption of BBB integrity [38]. In this study, despite the high incidence of CRS and neurotoxicity, no treatment-related deaths were reported. And all the patients recovered after symptomatic treatment such as corticosteroid, tocilizumab, or supportive therapy. Our analysis indicated that CRS and neurotoxicity were controllable in patients with CNSL who were administered CAR T cells by intravenous injection.

The results of this study indicate that CAR T cells are safe and effective in the treatment of CNSL. Nevertheless, this meta-analysis had several limitations, including (1) the currently available clinical studies are single-arm studies with small sample sizes; (2) owing to the small number of relevant studies and cases, this meta-analysis included the ongoing clinical trials and conference abstracts; (3) the follow-up time was short; (4) CAR T cells have primarily been used in patients with NHL involving the central nervous system, and there are few clinical studies on PCNSL; (5) owing to language limitations, this analysis only included studies in English and Chinese.

Conclusions

In our meta-analysis, we found that CAR T-cell therapy is a promising treatment option for CNSL, and can produce high remission rates. Although CAR T-cell treatment resulted in a higher incidence of CRS and neurotoxicity in patients with CNSL, the adverse reactions were reversible after treatment. Meanwhile, we also identified several limitations, such as the high short-term recurrence rate after CAR T-cell treatment and the lack of patient selection criteria and bridging therapy options. Additionally, whether CAR T-cell therapy has advantages over ASCT and small-molecule targeted drugs remains unknown. These observations highlight the need for a greater optimizing the structure of CAR T cells and understanding of the mechanism of action of CAR T cells, while the best method of infusion and the optimal combination therapy for CAR T cells remains to be determined. Moreover, more prospective randomized controlled trials with large cohorts are needed to verify the available data. We hope to obtain more optimized application schemes and more comprehensive data to help clinicians improve the application of CAR T cells as CNSL treatment options.

Supplementary Information

Below is the link to the electronic supplementary material.

Authors' Contributions

LL conceived the research design; LL, YW, and HS conducted the literature search and data extraction. LL, ZD, HH, and RL performed the statistical analysis and contributed to writing of the report. XS and YL reviewed and edited the manuscript in detail. All authors contributed to the article and approved the submitted version.

Funding

This work was supported by Capital’s Funds for Health Improvement and Research, NO.2020–2-2049.

Data Availability

All data were extracted from already published research and can be accessed by everyone; all publicly available data is cited. The datasets supporting the conclusions of this article are included within the article (and its additional files).

Declarations

Conflict of interest

The authors declare that they have no competing interests.

Ethics approval

Not applicable.

Consent to participate

Not applicable.

Consent to publish

Not applicable.