Genomic Characterization of a Pediatric Cohort with Non-Malignant Lymphoproliferative Disorders

Introduction: Pediatric non-malignant lymphoproliferative disorders (LPDs) are a clinically and genetically heterogeneous. While transient lymphadenopathy is extremely common and rarely dangerous, long-standing immune dysregulation and lymphoproliferation in children may be life-threatening. Data to guide evaluation and treatment of children with benign LPD are lacking. The primary objective of this study was to define the genomic spectrum and clinical characteristics of a cohort of children with nonmalignant LPD. Identification of the underlying pathogenic mechanisms may facilitate timely interventions and potentially guide optimal therapeutic strategies.

Methods: Patients at Texas Children's Hospital and collaborating referral centers who met criteria for non-malignant LPD were offered participation in this study, approved by the Baylor College of Medicine Institutional Review Board. LPD was defined as persistent lymphadenopathy, lymph organ involvement, or lymphocytic infiltration for more than 3 months, with or without chronic or significant EBV infection. Chronic or significant EBV infection was defined as recurrent or persistent EBV viremia more than 3 months, invasive EBV disease, or EBV PCR copies >100,000. All subjects and/or family members provided written informed consent to have their clinical and genetic information published. Genetic testing was performed clinically or through research-based whole-exome sequencing (WES).

Results: Fifty-one subjects from 47 different families with non-malignant LPD were identified. Median age at disease presentation was 3.3 years (range 3.9 weeks - 21 years) with nearly equal proportions of males (n = 26) and females (n = 25). Almost half of subjects were Hispanic (49%), and 29% were non-Hispanic white. Fifteen subjects (29%) met HLH-2004 diagnostic criteria for HLH. Twenty-one patients had EBV-associated lymphoproliferative disorders (EBV-LPD) and 6 of the 51 ultimately developed malignancy. Clinical genetic testing was performed in 29 patients, and research-based WES was performed in 44 patients. Potential disease-causing genetic defects were identified in 62% of families. Of these pathogenic variants, targeted therapies may be effective for treatment in at least 10 of the conditions (17 subjects, 33%). Furthermore, genetic results supported potential for curative HSCT in 35% of the patients. Mechanistically, all of the LPD-associated genes could be placed into 1 of 3 categories: 1) defective control of lymphocyte activity; 2) impaired lymphocyte activation, cytoskeletal organization, and apoptosis; and 3) dysregulated inflammation. Ten-year survival for the entire cohort was 72.4% with a median 5.6 years of follow-up (range 0.10 - 26.6). Patients without evidence of a genetic explanation had a lower ten-year survival compared to those patients for whom a genetic explanation was identified (48% versus 82%, respectively, p=0.03). When both EBV-LPD and genetic explanation were considered, the ten-year survival estimate for those with EBV-associated disease and no genetic explanation was significantly worse than those with EBV-associated disease and a genetic explanation (17% vs. 90%; p =0.002). Patients without EBV-associated disease were at lower risk of death than those with EBV-LPD. Evaluating outcomes associated with maximum treatment received, ten-year survival was lowest (25% survival) among those who underwent HSCT.

Conclusions: Pediatric non-malignant LPD represents a group of conditions with high risk of death. WES identified actionable mutations in the majority of LPD cases in this cohort. Early identification of these mutations can guide therapy by confirming diagnosis, revealing molecular targets and/or supporting definitive therapy with stem cell transplant.