Characteristics of study patients and transplantation
The characteristics of the patients have been summarized in Table 1. A total of seven patients with T-B+NK- SCID received HSCT from 2002–2018. All patients were male, and the median age at transplantation was 4.7 months (range, 2.3–7.0). All seven patients were diagnosed with T-B+NK- SCID using immunological tests. Interleukin-2 receptor γ chain deficiency was genetically confirmed in four patients. Genetic testing was not performed in two patients (M1, S2). One patient (S3) underwent next-generation sequencing analysis; however, we could not find disease-causative genetic abnormalities.
Four patients received MD HSC, while three patients received SD HSC. Among the former, three received HSCT from an MSD, while one patient (M3) received the transplantation from a familial mismatched donor (FMMD). Transplantation was performed without conditioning and GVHD prophylaxis in the MD group. Three patients in this group received 5 mL of BM aspirate, while the remaining patient received 2 mL of BM aspirate. The median TNC, CD34+ cells, and CD3+ cell doses were 0.49 (range, 0.32–0.84) × 108/kg, 0.62 (range, 0.38–0.84) × 106/kg, and 0.44 (range, 0.11–1.14) × 107/kg, respectively.
Among the three patients receiving SD HSCT, two received peripheral blood stem cell transplantation from FMMD that was manipulated using the ex vivo CD3+ T-cell receptor (TCR) αβ+ depletion technique without conditioning or GVHD prophylaxis, and the other patient (S3) received mismatched, unrelated CBT with reduced-intensity conditioning. Patient S3, the younger brother of patient S2 and born as a dizygotic twin, received CBT at three months after birth without a Bacillus Calmette-Guérin (BCG) vaccination.
Excluding patient S3, who received transplantation closest to the time of birth, the other six patients all experienced severe infections prior to transplantation. Four patients (M2, M3, M4, and S2) suffered from disseminated BCG infection prior to HSCT. Patient M1 received transplantation while under ventilator care for severe pneumonia at the intensive care unit. Ventilation was discontinued six days after HSCT. Patient M3 suffered rotavirus viremia after vaccination for rotavirus. Patients M4 and S2 developed Pneumocystis jirovecii pneumonia. Patient M4 also experienced recurrent diarrhea. Patient S1 frequently suffered from upper respiratory tract infections and otitis media. Patient S2 had cytomegalovirus (CMV) disease of the lung and central nervous system at the time of SCID diagnosis.
Donor chimerism and survival outcome
All patients who received MD HSCT showed donor-derived cells that ranged from 7.3%–26.4% at 28 days after HSCT. This range decreased to 1.4–8.7% 100 days after HSCT before gradually increasing to 10.12%–100% at the final evaluation. Although patient M3 showed 2.7% donor chimerism 100 days after HSCT, complete donor chimerism was obtained following a stem cell boost with 1 mL of BM aspirate from the same donor 119 days after the first HSCT for uncontrolled, disseminated BCG infection. The serial STR results of the MD group have been presented in Figure 1. All patients were alive without infections related to disease recurrence at a median of 127 months (range, 21–203 months) after HSCT.
In the SD group, patient S2 experienced primary graft failure and received a second HSCT from the same FMMD 34 days after the first HSCT, albeit unsuccessfully. A third transplantation was performed using unrelated cord blood after busulfan-based conditioning, and complete donor chimerism was accomplished. However, this patient ultimately died of disseminated CMV disease 68 days after the third HSCT, which was refractory to treatment with ganciclovir (Roche Korea), foscarnet (Fresenius Kabi), and CMV immunoglobulin (Biotest pharm). Patient S1 and S3 achieved donor chimerism of 48.11% and 88.72% at 3 years and 1year after HSCT, respectively.
Graft-versus-host disease
The patient outcomes after HSCT have been summarized in Table 2. Three of four patients in the MD group experienced grade II acute GVHD. One case was resolved without specific treatment, while the other two patients underwent GVHD treatment with corticosteroids and cyclosporine. Patient M3 developed extensive chronic GVHD, involving the lungs, skin, and mouth, after received FMMD transplantation and boost infusion. He was treated with corticosteroid and rituximab but became free from immunosuppressive agents 63 months after HSCT.
Two of the three SD HSCT recipients experienced acute GVHD of grades II and III, respectively. The grade III patient recovered following corticosteroid treatment.
Immune reconstitution after HSCT
Changes in the numbers of various immune cells and serum immunoglobulin levels of each patient after HSCT have been presented in Figure 2 and Supplementary Table S1. Patient M3, who underwent immunosuppressive treatments for extensive chronic GVHD, had a reduced T cell count 1 year after HSCT. The B cell count decreased to < 200 cells/mm3 in patients M1 and M3 during the first 3 months after HSCT; however, the patients recovered after 6 months and 1 year, respectively. IVIg supplementation was discontinued in all MD patients at a median of 4 months (range, 1–37 months) following HSCT.
In the SD group, both the T cell and B-cell counts recovered in patient S1 6 months after HSCT; however, IgG, IgA, and IgM did not reach the normal range. This patient is on IVIg supplementation at 41 months after HSCT. Patient S3, who underwent CBT after conditioning, achieved B cell and T cell recovery at 3 and 6 months, respectively.