Prognostic value of CD20 antigen mediated immune checkpoint inhibition in patients with acute or chronic lymphocytic leukemia

Abstract Background: The addition of rituximab to standard chemotherapy has been shown to improve response rates in patients with acute or chronic lymphocytic leukemia. However, the prognostic factors associated with progression-free survival in rituximab treated patients with lymphocytic leukemias remains unclear. We will perform a comprehensive systematic review and meta-analysis on available data on prognostic factors associated with the clinical outcomes of patients with acute and chronic lymphocytic leukemia. Methods and analysis: This protocol for a systematic review and meta-analysis of prognostic factors has been prepared following the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) 2015 guidelines. Electronic databases will be searched using keywords related to the objectives of this review. This systematic review and meta-analysis will include published randomized clinical trials, observational, prospective, and retrospective comparative cohorts. Two reviewers (ZAM and SAM) will independently screen studies, with a third reviewer consulted in cases of disagreements using a defined inclusion and exclusion criteria. Data items will be extracted using a predefined data extraction sheet. Moreover, the risk of bias and the quality of evidence were independently assessed using the quality in prognostic studies tool (QUIPS). The I2 and chi squared statistical tests will be used to analyze statistical heterogeneity across studies. An I2 values of > 50% will be considered substantial. All data analysis will be performed using STATA 16.0 (StataCorp LP, TX, USA). The outcomes examined will be progression-free and overall survival. Ethics and dissemination: No ethical approval will be required and the findings of this meta-analysis will be published in a peer-reviewed journal. Systematic review registration: International prospective Register of Systematic Reviews (PROSERO) number: CRD42021218997.


Introduction
Chronic lymphocytic leukemia (CLL) is characterized by progressive proliferation and accumulation of functionally incompetent lymphocytes in the peripheral blood, bone marrow, lymph nodes, and spleen. [1,2] CLL is predominantly due to profound defects in B lymphocytes and is also characterized by T-cell exhaustion, [3] whereas acute lymphocytic leukemia (ALL) involves aggressive accumulation of blasts in the bone marrow and has been the primary cause of cancer-related mortalities in children and adolescents. [2,4] CLL is considerably more severe in adult patients over the age of 65 years [5] and men are disproportionally affected, with a higher incidence than women. [6][7][8][9] This can be attributed to gender-specific hormonal differences or the variance in IGVH gene usage and mutational status. [10] Several clinical and genetic-based prognostic markers have been established. In fact, the CLL international prognostic index (CLL-IPI) includes validated clinical, genetic, and laboratory features in the prognostication of patients with CLL. [11] The incidence of CLL varies widely across geographic locations, with a high distribution of chronic lymphocytic leukemia in most European and North American countries. [9] In comparison, ALL cases remain relatively high in North America, Northern and Western Europe, while lower rates are apparent in Asian and African populations [12] Notably, there is minimal data on the incidence or prevalence of lymphocytic leukemia in African countries. Based on currently available data on the prevalence of lymphocytic leukemia in multi-ethnic studies, CLL seems to affect Europeans more than Africans. The discrepancy in patient outcomes across racial and ethnic groups have been presented in some studies. [12][13][14][15][16][17][18][19] In studies including ethnic minorities, a poor overall survival rate was reported when compared with their white counterparts. Disparities could be partly attributed to demographic variables, varied biological responses, environmental and genetic factors as well as socioeconomic status between these racial groups. [20,21] Patient outcomes have improved remarkably over the years due to the adoption of risk-based therapy that is determined by patient characteristics and leukemia phenotype at diagnosis. [17] For several decades, high-dose standard chemotherapy has been the primary treatment, however, this regimen has no demonstrable improvement in overall survival. [22] Recently, a novel approach using monoclonal antibodies aimed at restoring the immune system by targeting immune checkpoints proteins has provided effective and complementary treatments. [23] The use of fludarabine, cyclophosphamide, and rituximab (FCR) therapy significantly improves the progressionfree and overall survival of patients with CLL. [24] To date, there are currently no published systematic review and meta-analysis providing cumulative evidence on the predictors of mortality or poor patient outcomes of patients with CLL on rituximab. This systematic review and meta-analysis will assess the available studies reporting on the prognostic factors and efficacy of combined chemoimmunotherapy containing rituximab. We will further synthesize the novel prognostic factors associated with poor clinical outcomes.

Research question
Does combining rituximab with standard chemotherapy improve progression-free survival of patients with CLL?
Which clinical and laboratory features are associated with poor prognosis and variable patient outcomes following rituximab therapy?

Methods
This protocol for a systematic review and meta-analysis has been prepared in accordance with Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols 2015 (PRISMA-P) guidelines. The protocol was registered with the online PROSPERO registry (CRD42021218997).

Study design
In this review, we will include randomized control trials, prospective and retrospective comparative cohorts.

Inclusion criteria.
Only primary studies assessing the prognosis (progression-free and overall survival) of patients with CLL on rituximab-based therapy will be included. The search will be restricted to full-text human studies written in English.

Exclusion criteria.
Cross-sectional and case-control studies will be excluded. In addition, review articles, letters, and editorials will be excluded.

Population
Patients with CLL on rituximab-based therapy, will be included.

Index prognostic factor
We will consider the predictive factors included in the widely used CLL International Prognostic Index (CLL-IPI). [25] We will also consider the predictive factors used in the German CLL Study Group (GCLLSG), [26] the MD Anderson Cancer Center (MDACC) nomogram [27] predictive models.

Comparators
The comparators will include patients receiving standard therapy or usual care.

Outcomes
The primary outcome will be the overall 5-year overall survival, and the secondary outcome will include 2-to 4-year progressionfree survival.

Timing and setting
The predictive information and measurements at diagnosis and initiation of treatment will be considered. Moreover, we will include studies reporting on inpatient and outpatient cohorts.
2.6.1. Search strategy and study selection. The search strategy will be developed using medical subject headings (MeSH) for MEDLINE, and this will be adapted to EBSCOhost search headings terms. We will search the databases from inception to February 28, 2021. The search strategy will consist of search terms that include chronic lymphocytic leukemia, acute lymphoblastic leukemia, rituximab (Supplementary file 1, http:// links.lww.com/MD/G614). will develop a structured data extraction form that will be used in the data extraction process. Mendeley referencing manager will be used in this systematic review. The screening of the articles will be independently assessed by 2 reviewers (ZAM and SAM).

Data items.
The 2 reviewers (ZAM and SAM) will extract data items using the data items defined in the checklist for critical appraisal and data extraction for systematic reviews of prediction modelling studies for prognostic factors (CHARMS-PF). [28] This will include the following information: source of data, participant description, the study dates, sample size, predicted outcome including outcome measures (hazards, odds ratio), candidate predictors, handling of missing data, modeling method, and model performance.

Data simplification.
Studies will be grouped according to the type of lymphocytic leukemia (CLL or ALL). In addition, studies will be grouped based on the, gender ratio, age of participants and chemotherapy regimen used (e.g., fludarabine, cyclophosphamide, ibrutinib), duration of intervention and follow-up.

Risk of bias in individual studies.
To assess the potential risk of bias in the included studies the quality in prognostic studies (QUIPS) tool will be used. [29] Two authors (ZAM and SAM) will independently assess the included studies based on the 6 domains of the tool. In a case of disagreements, a third reviewer (BBN) will be consulted for arbitration.

Data synthesis
A summary of findings table (SoF) will be used to provide a synthesis of the main outcomes of included studies. Furthermore, if the included studies are homogeneous in terms of the type of lymphocytic leukemia treated, therapy used, and participant characteristics, data will be analyzed using a fixed-effects model. All data analysis will be performed using R statistical software (The R foundation for statistical computing, Vienna, Austria). The I 2 and chi-squared statistical tests will be used to analyze statistical heterogeneity between studies. [30,31] An I 2 value of >50% will be considered substantial heterogeneity. [32]

Subgroup analysis
To explore the sources of heterogeneity within the included studies, we will perform a subgroup analysis based on the studylevel characteristics, including the risk of bias of the included studies, geographic location, intervention type (rituximab plus chemotherapy [R-Chemo] and chemotherapy regimens). Lastly, the reported measure of progression-free and overall survival will also be considered in the subgroup analysis.

Confirmation of predictive factors
The prognostic factors will be confirmed based on the consistency of the overall direction of the effect across the included studies. In addition, adjusted effect sizes that remain statistically significant (P < .05) after adjusting for covariates and multivariate analysis will be considered as confirmed.
2.10.1. Quality assessment of the cumulative evidence. The quality and strength of the evidence of the confirmed prognostic factors will be evaluated by 2 independent reviewers (ZAM, SAM) using the Grading of Recommendations Assessment Development and Evaluation approach (GRADE). [33]

Patient and public involvement
There is no patient or public involvement in the process of conducting this study.

Discussion
Rituximab-based therapy has demonstrated therapeutic benefits in the treatment of patients with lymphocytic leukemia. This systematic review and meta-analysis of prognostic factors will provide a comprehensive synthesis of studies reporting on progression-free survival in patients with CLL on a rituximabbased regimen compared with standard chemotherapy. Moreover, this review will provide a synthesis of traditional and novel cell-based prognostic factors. To our knowledge, this will be the first meta-analysis to evaluate the efficacy of R-chemo and predictive factors associated with progression-free survival in patients with ALL and CLL compared with chemotherapy alone. Findings from this study will provide insight into the prognostic factors in patients with CLL following R-chemo and will assist in the patient management and prognostication. Nkambule.