Graft-versus-host disease is associated with skewed γδ T-cell clonality after umbilical cord blood transplantation in children with nonmalignant diseases.

BACKGROUND AIMS: The γδ T-cells (GDT) are a subpopulation of lymphocytes expressing a distinct T-cell receptor coded by the TRG and TRD genes. GDTs may have immunoregulatory function after stem cell transplantation (SCT), but the relationship between GDT clonality and acute graft-versus-host disease (aGVHD) is not known. METHODS: We prospectively studied spectratype complex complexity of TCR Vγ (γ) and TCR Vδ (δ) pre-SCT and at approximately day 100 and day 180 post-SCT in a cohort of immunocompetent children receiving allogeneic umbilical cord blood SCT for nonmalignant diseases, with identical reduced-intensity conditioning and aGVHD prophylaxis. RESULTS: We studied 13 children undergoing SCT at a median age of 0.9 years (total range 0.4-16.6). In those with grade 0-1 aGVHD (N = 10), the spectratype complexity of most γ and δ genes was not significantly different from baseline at day 100 or day 180 post-SCT, and there was balanced expression of genes at the γ and δ loci. In those with grade 3 aGVHD (N = 3), spectratype complexity was significantly below baseline at day 100 and day 180, and there was relative overexpression of δ2. CD3+ cell counts were also lower in participants with grade 3 aGVHD. CONCLUSIONS: Recovery of a polyclonal GDT repertoire is an early part of immunological recovery after SCT. γ and δ gene expression is balanced in young children before and after SCT. Severe aGVHD is associated with GDT oligoclonality post-SCT and with skewed expression of δ2, which has not been previously reported. This association may reflect aGVHD therapy or aGVHD-associated immune dysregulation. Further studies of GDT clonality during the early post-SCT period may establish whether abnormal GDT spectratype precedes the clinical manifestations of aGVHD.

Comparison of hematopoietic cell transplant conditioning regimens for hemophagocytic lymphohistiocytosis disorders.

BACKGROUND: Allogeneic hematopoietic cell transplantation for hemophagocytic lymphohistiocytosis (HLH) disorders is associated with substantial morbidity and mortality. OBJECTIVE: The effect of conditioning regimen groups of varying intensity on outcomes after transplantation was examined to identify an optimal regimen or regimens for HLH disorders. METHODS: We studied 261 patients with HLH disorders transplanted between 2005 and 2018. Risk factors for transplantation outcomes by conditioning regimen groups were studied by Cox regression models. RESULTS: Four regimen groups were studied: (1) fludarabine (Flu) and melphalan (Mel) in 123 subjects; (2) Flu, Mel, and thiotepa (TT) in 28 subjects; (3) Flu and busulfan (Bu) in 14 subjects; and (4) Bu and cyclophosphamide (Cy) in 96 subjects. The day 100 incidence of veno-occlusive disease was lower with Flu/Mel (4%) and Flu/Mel/TT (0%) compared to Flu/Bu (14%) and Bu/Cy (22%) (P < .001). The 6-month incidence of viral infections was highest after Flu/Mel (72%) and Flu/Mel/TT (64%) compared to Flu/Bu (39%) and Bu/Cy (38%) (P < .001). Five-year event-free survival (alive and engrafted without additional cell product administration) was lower with Flu/Mel (44%) compared to Flu/Mel/TT (70%), Flu/Bu (79%), and Bu/Cy (61%) (P = .002). The corresponding 5-year overall survival values were 68%, 75%, 86%, and 64%, and did not differ by conditioning regimen (P = .19). Low event-free survival with Flu/Mel is attributed to high graft failure (42%) compared to Flu/Mel/TT (15%), Flu/Bu (7%), and Bu/Cy (18%) (P < .001). CONCLUSIONS: Given the high rate of graft failure with Flu/Mel and the high rate of veno-occlusive disease with Bu/Cy and Flu/Bu, Flu/Mel/TT may be preferred for HLH disorders. Prospective studies are warranted.

A Germline Mutation in the C2 Domain of PLCγ2 Associated with Gain-of-Function Expands the Phenotype for PLCG2-Related Diseases.

We report three new cases of a germline heterozygous gain-of-function missense (p.(Met1141Lys)) mutation in the C2 domain of phospholipase C gamma 2 (PLCG2) associated with symptoms consistent with previously described auto-inflammation and phospholipase Cγ2 (PLCγ2)-associated antibody deficiency and immune dysregulation (APLAID) syndrome and pediatric common variable immunodeficiency (CVID). Functional evaluation showed platelet hyper-reactivity, increased B cell receptor-triggered calcium influx and ERK phosphorylation. Expression of the altered p.(Met1141Lys) variant in a PLCγ2-knockout DT40 cell line showed clearly enhanced BCR-triggered influx of external calcium when compared to control-transfected cells. Our results further expand the molecular basis of pediatric CVID and phenotypic spectrum of PLCγ2-related defects.