Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) represents a valuable alternative for children with nonmalignant disease and ex vivo negative selection of TCR-αβ⁺ cells is an emerging graft manipulation option that carries several potential advantages in terms of reduced risk of graft-versus-host disease (GvHD) and improved immune reconstitution. We report all consecutive patients with a diagnosis of nonmalignant disease who received a TCR-αβ⁺ and CD19⁺depleted haplo-HSCT at "IRCCS Istituto Giannina Gaslini" from 2013 to 2019; the conditioning regimen was myeloablative or non-myeloablative, depending on underlying disease; all patients received antithymocyte globulin and rituximab. No post-transplantation GvHD prophylaxis was given in presence of a TCR-αβ⁺ cell dose in the graft lower than the threshold of 1 × 10⁵/kg of the recipient's weight. Among 20 HSCTs, engraftment occurred in 17 (85%) after a median of 14 and 12 days from graft infusion for neutrophils and platelets, respectively. Primary graft failure was diagnosed in 3 (15%) patients, and 2 (10%) experienced secondary rejection; all of these patients underwent a second HSCT. The cumulative incidence of a-GvHD and c-GvHD was 15% (2 = grade 1, 1 = grade 4) at 90 days and 5% (1 = grade 1) at 7 months, respectively. Cytomegalovirus reactivation requiring pre-emptive treatment was observed in 9 patients (45%). One patient developed a JC virus-related progressive multifocal leukoencephalopathy, successfully managed with donor-derived virus-specific T-cell infusions. A complete immunological recovery was reached in most patients within 6 months. After a median follow-up of 4 years, 18 patients are alive, with a cumulative survival probability of 90%. Haplo-HSCT after ex vivo TCR-αβ⁺/CD19⁺ negative selection may be considered a good option for children with nonmalignant diseases because it ensures a high engraftment rate with an acceptable risk of graft failure, very low incidence of significant GvHD, and good immune reconstitution with low frequency of severe virus-related disease. However, the control of viral infection/reactivation should be kept high to promptly provide pre-emptive treatments and approaches of antiviral adoptive immunotherapy.

HLA-mismatched transplants with either in vitro depletion of CD3+ T-cell receptor (TCR)αβ/CD19 (TCRαβ) cells or in vivo T-cell depletion using posttransplant cyclophosphamide (PTCY) have been increasingly used for patients with inborn errors of immunity (IEIs). We performed a retrospective multicenter study via the EBMT registry on 306 children with IEIs undergoing their first transplant between 2010 and 2019 from an HLA-mismatched donor using TCRαβ (n = 167) or PTCY (n = 139). The median age for hematopoietic stem cell transplantation (HSCT) was 1.2 years (range, 0.03-19.6 years). The 3-year overall survival (OS) was 78% (95% confidence interval (CI), 71-84) after TCRαβ and 66% (57-74) after PTCY (P = .013). Pre-HSCT morbidity score (hazard ratio [HR], 2.27; 1.07-4.80, P = .032) and non-busulfan/treosulfan conditioning (HR, 3.12; 1.98-4.92, P < .001) were the only independent predictors of unfavorable OS. The 3-year event-free survival (EFS) was 58% (50%-66%) after TCRαβ and 57% (48%-66%) after PTCY (P = .804). The cumulative incidence of severe acute graft-versus-host disease (GvHD) was higher after PTCY (15%, 9%-21%) than TCRαβ (6%, 2%-9%, P = .007), with no difference in chronic GvHD (PTCY, 11%, 6%-17%; TCRαβ, 7%, 3%-11%, P = .173). The 3-year GvHD-free EFS was 53% (44%-61%) after TCRαβ and 41% (32%-50%) after PTCY (P = .080). PTCY had significantly higher rates of veno-occlusive disease (14.4% vs TCRαβ 4.9%, P = .009), acute kidney injury (12.7% vs 4.6%, P = .032), and pulmonary complications (38.2% vs 24.1%, P = .017). Adenoviremia (18.3% vs PTCY 8.0%, P = .015), primary graft failure (10% vs 5%, P = .048), and second HSCT (17.4% vs 7.9%, P = .023) were significantly higher in TCRαβ. In conclusion, this study demonstrates that both approaches are suitable options in patients with IEIs, although they are characterized by different advantages and outcomes.

Mevalonate kinase deficiency (MKD) is a rare autosomal recessive inborn error of metabolism with an autoinflammatory phenotype that may be expressed as a spectrum of disease phenotypes, from those with prevailing autoinflammatory syndrome and variable response to anti-inflammatory therapies, to mevalonic aciduria, which is associated with dysmorphic features, severe neurologic involvement, and the worst prognosis. We describe a boy, aged 2 years, 10 months, with severe phenotype of mevalonate kinase deficiency who underwent allogeneic hematopoietic stem cell transplantation (HSCT) from HLA-identical unrelated cord blood because his condition had failed to improve with antiinflammatory treatment as first-line therapy and an anticytokine drug as second-line therapy. The child had a sustained remission of febrile attacks and inflammation after transplant, and during a 5-year follow-up period, psychomotor and neurologic development were normal, without signs of underlying disease or late transplant-related effects. This case confirms that allogeneic HSCT is a safe and effective cure for patients affected by MKD in whom anticytokine drugs alone are insufficient for the management of autoinflammatory syndrome and for the unfavorable outcome of the disease.

Haploidentical stem cell transplantation (haplo‐SCT) represents the main alternative for children with inherited bone marrow failure syndrome (I‐BMF) lacking a matched donor. This retrospective study, conducted on behalf of the EBMT SAAWP and PDWP, aims to report the current outcomes of haplo‐SCT in I‐BMFs, comparing the different in vivo and ex vivo T‐cell depletion approaches. One hundred and sixty‐two I‐BMF patients who underwent haplo‐SCT (median age 7.4 years) have been registered. Fanconi Anemia was the most represented diagnosis (70.1%). Based on different T‐cell depletion (TCD) approaches, four categories were identified: (1) TCRαβ⁺/CD19⁺‐depletion (43.8%); (2) T‐repleted with post‐transplant Cyclophosphamide (PTCy, 34.0%); (3) In‐vivo T‐depletion with ATG/alemtuzumab (14.8%); (4) CD34⁺ positive selection (7.4%). The cumulative incidences (CI) of neutrophil and platelet engraftment were 84% and 76% respectively, while that of primary and secondary graft failure was 10% and 8% respectively. The 100‐day CI of acute GvHD grade III‐IV(95% CI) was 13%, while the 24‐month CI of extensive chronic GvHD was 4%. After a median follow‐up of 43.4 months, the 2‐year overall survival(OS) and GvHD/Rejection‐free Survival (GRFS) probabilities are 67% and 53%, respectively. The TCR CD3⁺αβ⁺/CD19⁺ depletion group showed a significantly lower incidence of both acute and chronic GvHD and higher OS (79%; p0.013) and GRFS (71%; p < .001), while no significant differences in outcomes have been observed by different diagnosis and conditioning regimens. This large retrospective study supports the safety and feasibility of haplo‐SCT in I‐BMF patients. TCRαβ⁺/CD19⁺ depletion offers higher chances of patients' survival, with a significantly lower risk of severe a‐ and c‐GvHD in I‐BMFs compared to other platforms.