ABSTRACT
PURPOSE: Newborn screening (NBS) quantifies T cell receptor excision circles (TREC) and identifies infants with T cell lymphopenia (TCL). This study elucidates the demographics, laboratory characteristics, genetics, and clinical outcomes following live viral vaccine administration of term infants with transient or persistent idiopathic TCL. METHODS: A single-center retrospective analysis was performed from September 2010 through June 2018. Laboratory variables were compared with Mann-Whitney tests. Correlations between initial TREC levels and T cell counts were determined by Spearman tests. RESULTS: Twenty-two transient and 21 persistent TCL infants were identified. Males comprised 68% of the transient and 52% of the persistent TCL cohorts. Whites comprised 23% of the transient and 29% of the persistent cohorts. Median initial TREC levels did not differ (66 vs. 60 TRECs/µL of blood, P = 0.58). The transient cohort had higher median initial CD3+ (2135 vs. 1169 cells/µL, P < 0.001), CD4+ (1460 vs. 866 cells/µL, P < 0.001), and CD8+ (538 vs. 277 cells/µL, P < 0.001) counts. The median age of resolution for the transient cohort was 38 days. Genetic testing revealed 2 genes of interest which warrant further study and several variants of uncertain significance in immunology-related genes in the persistent cohort. 19 transient and 14 persistent subjects received the initial rotavirus and/or MMRV immunization. No adverse reactions to live viral vaccines were reported in either cohort. CONCLUSION: Transient and persistent TCL infants differ by demographic, laboratory, and clinical characteristics. Select transient and persistent TCL patients may safely receive live attenuated viral vaccines, but larger confirmatory studies are needed.