Roberta E. Parrott

Transplantation Outcomes for Severe Combined Immunodeficiency, 2000–2009

BACKGROUND The Primary Immune Deficiency Treatment Consortium was formed to analyze the results of hematopoietic-cell transplantation in children with severe combined immunodeficiency (SCID) and other primary immunodeficiencies. Factors associated with a good transplantation outcome need to be identified in order to design safer and more effective curative therapy, particularly for children with SCID diagnosed at birth. METHODS We collected data retrospectively from 240 infants with SCID who had received transplants at 25 centers during a 10-year period (2000 through 2009). RESULTS Survival at 5 years, freedom from immunoglobulin substitution, and CD3+ T-cell and IgA recovery were more likely among recipients of grafts from matched sibling donors than among recipients of grafts from alternative donors. However, the survival rate was high regardless of donor type among infants who received transplants at 3.5 months of age or younger (94%) and among older infants without prior infection (90%) or with infection that had resolved (82%). Among actively infected infants without a matched sibling donor, survival was best among recipients of haploidentical T-cell-depleted transplants in the absence of any pretransplantation conditioning. Among survivors, reduced-intensity or myeloablative pretransplantation conditioning was associated with an increased likelihood of a CD3+ T-cell count of more than 1000 per cubic millimeter, freedom from immunoglobulin substitution, and IgA recovery but did not significantly affect CD4+ T-cell recovery or recovery of phytohemagglutinin-induced T-cell proliferation. The genetic subtype of SCID affected the quality of CD3+ T-cell recovery but not survival. CONCLUSIONS Transplants from donors other than matched siblings were associated with excellent survival among infants with SCID identified before the onset of infection. All available graft sources are expected to lead to excellent survival among asymptomatic infants. (Funded by the National Institute of Allergy and Infectious Diseases and others.).

Thymic function after hematopoietic stem-cell transplantation for the treatment of severe combined immunodeficiency.

BACKGROUND Immune function can be restored in infants with severe combined immunodeficiency by transplantation of unfractionated bone marrow from HLA-identical donors or T-cell-depleted marrow stem cells from haploidentical donors, with whom there is a single haplotype mismatch, without the need for chemotherapy before transplantation or prophylaxis against graft-versus-host disease. The role of the thymus in this process is unknown. METHODS We analyzed the phenotypes of circulating T cells and the proliferative responses of peripheral-blood mononuclear cells to phytohemagglutinin in 83 patients with severe combined immunodeficiency who received allogeneic marrow transplants without T-cell ablation from related donors over an 18-year period. We also tested for the presence of episomes of T-cell antigen receptors (extrachromosomal DNA circles formed during intrathymic T-cell development) to assess thymus-dependent T-cell reconstitution. RESULTS Before and early after transplantation, the numbers of circulating T cells were low, with a predominance of mature CD45RO+ T cells (primarily resulting from the transplacental transfer of maternal cells); T-cell antigen-receptor episomes were undetectable in peripheral-blood mononuclear cells. In 73 of the infants, thymus-derived T cells expressing CD45RA and T-cell antigen-receptor episomes were detected within three to six weeks after transplantation. The mean (+/-SD) value for thymus-dependent T-cell antigen-receptor episomes peaked (at 7311+/-8652 per microgram of peripheral-blood mononuclear-cell DNA) 1 to 2 years after transplantation and declined to low levels (less than 100 episomes per microgram of DNA) within 14 years, as compared with a gradual decline from birth to the age of about 80 years in normal subjects. CONCLUSIONS The vestigial thymus in infants with severe combined immunodeficiency is functional and can produce enough T cells after bone marrow transplantation to provide normal immune function.

T Cell Repertoire Development in Humans with SCID After Nonablative Allogeneic Marrow Transplantation

Transplantation of HLA-identical or haploidentical T cell-depleted allogeneic bone marrow (BM) into SCID infants results in thymus-dependent T cell development in the recipients. Immunoscope analysis of the TCR Vβ repertoire was performed on 15 SCID patients given BM transplants. Before and within the first 100 days after bone marrow transplantation (BMT), patients’ PBMC displayed an oligoclonal or skewed T cell repertoire, low TCR excision circles (TREC) values, and a predominance of CD45RO+ T cells. In contrast, the presence of high numbers of CD45RA+ cells in the circulation of SCID patients >100 days post-BMT correlated with active T cell output by the thymus as revealed by high TREC values and a polyclonal T cell repertoire demonstrated by a Gaussian distribution of Vβ-specific peaks. Ten years after BMT, we observed a decrease of the normal polyclonal T cell repertoire and an increase of a more skewed T cell repertoire. A decline of TREC levels and a decrease in the number of CD45RA+ cells beyond 10 years after BMT was concomitant with the detection of oligoclonal CD3+CD8+CD45RO+ cells. The switch from a polyclonal to a more skewed repertoire, observed in the CD3+CD8+CD45RO+ T cell subset, is a phenomenon that occurs normally with decreased thymic output during aging, but not as rapidly as in this patient population. We conclude that a normal T cell repertoire develops in SCID patients as a result of thymic output and the repertoire remains highly diverse for the first 10 years after BMT. The TCR diversity positively correlates in these patients with TREC levels.

Thymic output, T-cell diversity, and T-cell function in long-term human SCID chimeras

Severe combined immunodeficiency (SCID) is a syndrome of diverse genetic cause characterized by profound deficiencies of T, B, and sometimes NK-cell function. Nonablative human leukocyte antigen-identical or rigorously T cell-depleted haploidentical parental bone marrow transplantation (BMT) results in thymus-dependent genetically donor T-cell development in the recipients, leading to long-term survival. We reported previously that normal T-cell numbers, function, and repertoire developed by 3 to 4 months after transplantation in SCID patients, and the repertoire remained highly diverse for the first 10 years after BMT. The T-cell receptor diversity positively correlated with T-cell receptor excision circle levels, a reflection of thymic output. However, the fate of thymic function in SCID patients beyond 10 to 12 years after BMT remained to be determined. In this greater than 25-year follow-up study of 128 patients with 11 different molecular types of SCID after nonconditioned BMT, we provide evidence that T-cell function, thymic output, and T-cell clonal diversity are maintained long-term.

Post-Transplantation B Cell Function in Different Molecular Types of SCID

PurposeSevere combined immunodeficiency (SCID) is a syndrome of diverse genetic cause characterized by profound deficiencies of T, B and sometimes NK cell function. Non-ablative HLA-identical or rigorously T cell-depleted haploidentical parental bone marrow transplantation (BMT) results in thymus-dependent genetically donor T cell development in the recipients, leading to a high rate of long-term survival. However, the development of B cell function has been more problematic. We report here results of analyses of B cell function in 125 SCID recipients prior to and long-term after non-ablative BMT, according to their molecular type.MethodsStudies included blood immunoglobulin measurements; antibody titers to standard vaccines, blood group antigens and bacteriophage Φ X 174; flow cytometry to examine for markers of immaturity, memory, switched memory B cells and BAFF receptor expression; B cell chimerism; B cell spectratyping; and B cell proliferation.ResultsThe results showed that B cell chimerism was not required for normal B cell function in IL7Rα-Def, ADA-Def and CD3-Def SCIDs. In X-linked-SCID, Jak3-Def SCID and those with V-D-J recombination defects, donor B cell chimerism was necessary for B cell function to develop.ConclusionThe most important factor determining whether B cell function develops in SCID T cell chimeras is the underlying molecular defect. In some types, host B cells function normally. In those molecular types where host B cell function did not develop, donor B cell chimerism was necessary to achieve B cell function. 236 words

Long-term outcome of non-ablative booster BMT in patients with SCID.

SCID is a fatal syndrome caused by mutations in at least 13 different genes. It is characterized by the absence of T cells. Immune reconstitution can be achieved through nonablative related donor BMT. However, the first transplant may not provide sufficient immunity. In these cases, booster transplants may be helpful. A prospective/retrospective study was conducted of 49 SCID patients (28.7% of 171 SCIDs transplanted over 30 years) who had received booster transplants to define the long-term outcome, factors contributing to a need for a booster and factors that predicted success. Of the 49 patients, 31 (63%) are alive for up to 28 years. Age at initial transplantation was found to have a significant effect on outcome (mean of 194 days old for patients currently alive, versus a mean of 273 days old for those now deceased, P=0.0401). Persistent viral infection was present in most deceased booster patients. In several patients, the use of two parents as sequential donors resulted in striking T-and B-cell immune reconstitution. A majority of the patients alive today have normal or adequate T-cell function and are healthy. Nonablative booster BMT can be lifesaving for SCID.SCID is a fatal syndrome caused by mutations in at least 13 different genes. It is characterized by the absence of T cells. Immune reconstitution can be achieved through nonablative related donor BMT. However, the first transplant may not provide sufficient immunity. In these cases, booster transplants may be helpful. A prospective/retrospective study was conducted of 49 SCID patients (28.7% of 171 SCIDs transplanted over 30 years) who had received booster transplants to define the long-term outcome, factors contributing to a need for a booster and factors that predicted success. Of the 49 patients, 31 (63%) are alive for up to 28 years. Age at initial transplantation was found to have a significant effect on outcome (mean of 194 days old for patients currently alive, versus a mean of 273 days old for those now deceased, P=0.0401). Persistent viral infection was present in most deceased booster patients. In several patients, the use of two parents as sequential donors resulted in striking T-and B-cell immune reconstitution. A majority of the patients alive today have normal or adequate T-cell function and are healthy. Nonablative booster BMT can be lifesaving for SCID.

SCID genotype and 6-month posttransplant CD4 count predict survival and immune recovery

The Primary Immune Deficiency Treatment Consortium (PIDTC) performed a retrospective analysis of 662 patients with severe combined immunodeficiency (SCID) who received a hematopoietic cell transplantation (HCT) as first-line treatment between 1982 and 2012 in 33 North American institutions. Overall survival was higher after HCT from matched-sibling donors (MSDs). Among recipients of non-MSD HCT, multivariate analysis showed that the SCID genotype strongly influenced survival and immune reconstitution. Overall survival was similar for patients with RAG, IL2RG, or JAK3 defects and was significantly better compared with patients with ADA or DCLRE1C mutations. Patients with RAG or DCLRE1C mutations had poorer immune reconstitution than other genotypes. Although survival did not correlate with the type of conditioning regimen, recipients of reduced-intensity or myeloablative conditioning had a lower incidence of treatment failure and better T- and B-cell reconstitution, but a higher risk for graft-versus-host disease, compared with those receiving no conditioning or immunosuppression only. Infection-free status and younger age at HCT were associated with improved survival. Typical SCID, leaky SCID, and Omenn syndrome had similar outcomes. Landmark analysis identified CD4+ and CD4+CD45RA+ cell counts at 6 and 12 months post-HCT as biomarkers predictive of overall survival and long-term T-cell reconstitution. Our data emphasize the need for patient-tailored treatment strategies depending upon the underlying SCID genotype. The prognostic significance of CD4+ cell counts as early as 6 months after HCT emphasizes the importance of close follow-up of immune reconstitution to identify patients who may need additional intervention to prevent poor long-term outcome.

B cell differentiation and IL-21 response in IL2RG/JAK3 SCID patients after hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplant (HSCT) typically results in donor T-cell engraftment and function in patients with severe combined immunodeficiency (SCID), but humoral immunity, particularly when using donors other than matched siblings, is variable. B-cell function after HSCT for SCID depends on the genetic cause, the use of pre-HSCT conditioning, and whether donor B-cell chimerism is achieved. Patients with defects in IL2RG or JAK3 undergoing HSCT without conditioning often have poor B-cell function post-HSCT, perhaps as a result of impairment of IL-21 signaling in host-derived B cells. To investigate the effect of pre-HSCT conditioning on B-cell function, and the relationship of in vitro B-cell function to clinical humoral immune status, we analyzed 48 patients with IL2RG/JAK3 SCID who were older than 2 years after HSCT with donors other than matched siblings. T follicular helper cells (TFH) developed in these patients with kinetics similar to healthy young children; thus, poor B-cell function could not be attributed to a failure of TFH development. In vitro differentiation of B cells into plasmablasts and immunoglobulin secretion in response to IL-21 strongly correlated with the use of conditioning, donor B-cell engraftment, freedom from immunoglobulin replacement, and response to tetanus vaccine. Patients receiving immunoglobulin replacement who had normal serum immunoglobulin M showed poor response to IL-21 in vitro, similar to those with low serum IgM. In vitro response of B cells to IL-21 may predict clinically relevant humoral immune function in patients with IL2RG/JAK3 SCID after HSCT.