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

Abstract

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.

Conflict of interest statement

Conflict-of-interest disclosure: The authors declare no competing financial interests.

Figures

Graphical abstract

Figure 1.

TFHdevelopment in healthy children and adults and in patients post-HSCT. Percentage of TFH (the percentage of CD4+ T cells that are CD45RA− and CXCR5+) was measured in (A) umbilical cord blood (UCB), healthy children of the ages shown, and healthy adults; (B) patients with IL2RG/JAK3 SCID at varying times post-HSCT; and patients with IL2RG/JAK3 SCID analyzed according to (C) conditioning, (D) donor B-cell chimerism, (E) Ig replacement status, and (F) response to tetanus vaccine. Medians and interquartile ranges are shown.

Figure 2.

Switched memory B cells and in vitro plasmablast generation in patients post-HSCT. Percentage of switched memory B cells (the percentage of CD19+ B cells that are IgD− and CD27+) and percentage of plasmablasts (the percentage of CD19+ B cells that are CD27high and CD38high) after in vitro stimulation with CD40L and IL-21-Fc were measured in patients with IL2RG/JAK3 SCID analyzed according to conditioning (A-B), donor B-cell chimerism (C-D), Ig replacement status (E-F), and response to tetanus vaccine (G-H). Control patients were combined from healthy adults and children. Medians and interquartile ranges are shown. Brackets depict comparisons with significant P values: *P < .05; **P < .01; ***P < .001; ****P < .0001.

Figure 3.

Secreted IgM and IgG in response to CD40L and IL-21-Fc. Percentage of plasmablasts after in vitro stimulation with CD40L and IL-21-Fc correlates with secretion of (A) IgM and (B) IgG in the supernatant. IgM and IgG secretion from patients post-HSCT were analyzed according to conditioning (C-D), donor B-cell chimerism (E-F), Ig replacement status (G-H), and response to tetanus vaccine (I-J). Control patients were combined from healthy adults and children. Medians and interquartile ranges are indicated. Brackets depict comparisons with significant P values: *P < .05; **P < .01; ***P < .001; and **** P < .0001.

Figure 3.

Secreted IgM and IgG in response to CD40L and IL-21-Fc. Percentage of plasmablasts after in vitro stimulation with CD40L and IL-21-Fc correlates with secretion of (A) IgM and (B) IgG in the supernatant. IgM and IgG secretion from patients post-HSCT were analyzed according to conditioning (C-D), donor B-cell chimerism (E-F), Ig replacement status (G-H), and response to tetanus vaccine (I-J). Control patients were combined from healthy adults and children. Medians and interquartile ranges are indicated. Brackets depict comparisons with significant P values: *P < .05; **P < .01; ***P < .001; and **** P < .0001.

Figure 4.

Correlation of patient serum IgM with in vitro response to IL-21. IL-21-induced in vitro plasmablast percentage (A), secreted IgM (B), and secreted IgG (C) are shown for healthy control patients, patients receiving Ig who had either normal or low serum IgM for age, or patients off Ig. Medians and interquartile ranges are indicated. Brackets depict comparisons with significant P values: *P < .05; **P < .01; ***P < .001; and ****P < .0001.

Figure 5.

Biomarkers of B-cell function correlate with clinical humoral immunity. Receiver operating curves measuring the sensitivity and specificity of the indicated parameters to predict Ig replacement status (A) and vaccine response (B) are shown.