Reduced memory B-cell populations in boys with B-cell dysfunction after bone marrow transplantation for X-linked severe combined immunodeficiency

IL-21 is the primary common γ chain-binding cytokine required for human B-cell differentiation in vivo

SCID resulting from mutations in IL2RG or JAK3 is characterized by lack of T and natural killer cells; B cells are present in normal number, but antibody responses are defective. Hematopoietic cell transplantation (HCT) is curative for SCID. However, B-cell dysfunction persists in a substantial proportion of patients. We hypothesized that impaired B-cell responses after HCT in IL2RG/JAK3 deficiency results from poor donor B-cell engraftment and defective γc-dependent cytokine signaling in host B cells. To test this, and to identify which γc cytokine(s) is critical for humoral immunity, we studied 28 transplanted patients with IL2RG/JAK3 deficiency. Lack of donor B-cell engraftment associated with persistent humoral dysfunction and significantly reduced memory B cells. B-cell proliferation induced by CD40L alone or together with CpG, anti-Ig, IL-4, IL-10, or IL-13 was comparable in healthy controls and in post-HCT SCID patients, irrespective of their chimerism status. However, in vitro stimulation with CD40L/IL-21 induced B-cell proliferation, plasmablast differentiation, and antibody secretion in patients with donor B cells, but not in patients with autologous B cells. These data imply that IL-21-mediated signaling is critical for long-lived humoral immunity and to restore antibody responses in IL2RG/JAK3-deficient patients after HCT. Furthermore, in vitro stimulation with CD40L/IL-21 can predict in vivo B-cell immunity in IL2RG/JAK3 SCID after transplantation.

Role of the spleen in peripheral memory B-cell homeostasis in patients with autoimmune thrombocytopenia purpura

The effect of splenectomy on circulating memory B cells in autoimmune thrombocytopenia purpura (AITP) patients has not yet been addressed. We therefore analyzed the distribution and phenotypic characteristics of B-cell subsets in non-splenectomized and splenectomized AITP patients and controls, as well as CD95 expression after B cell activation. Decreased frequencies of memory B cells in splenectomized individuals were observed, with a rapid decline of CD27+IgD+ and a slower decrease of CD27+IgD- and CD27-/IgD- cells. Similar results were noted following splenectomy in healthy donors (HD). CD95+ B cells were substantially increased in all subsets in patients with active AITP, indicating their enhanced activation status. After splenectomy, the percentage of CD95+ B cells were further increased in the CD27+IgD- post-switch memory population in AITP, but not in HD. CD95+CD27+ memory B cells largely reside in the region in the human spleen analogous to the murine marginal zone. Thus, the spleen plays a fundamental role in controlling peripheral memory B cell homeostasis in both AITP and HD and regulates activated CD95+ B cells in patients with AITP.

Long-term immune reconstitution after anti-CD52-treated or anti-CD34-treated hematopoietic stem cell transplantation for severe T-lymphocyte immunodeficiency

BACKGROUND

Results of treatment of severe T-lymphocyte immunodeficiencies by means of hematopoietic stem cell (HSC) transplantation have improved. T cell-depleted haploidentical transplantations are successful if there is no HLA-identical donor. Methods to remove T lymphocytes include addition of anti-CD52 antibodies and CD34(+) HSC selection.

OBJECTIVE

Assessment of long-term immune function is important after these treatments. We looked at immune reconstitution in 36 survivors for more than 2 years after HSC transplantation for severe T-lymphocyte immunodeficiencies and compared engraftment quality between the 2 T-lymphocyte depletion methods.

METHODS

Chimerism, T- and B-lymphocyte subsets, immunoglobulin levels, and specific antibody production at last follow-up were examined. The chi(2) (Fisher exact test) and Wilcoxon rank sum analyses were used to compare the groups.

RESULTS

Nineteen patients received anti-CD52-treated and 19 anti-CD34-treated HSCs. More anti-CD52-treated patients had full donor myeloid chimerism (P = .025). All patients had full donor T-lymphocyte chimerism. There was no difference in donor B-lymphocyte chimerism, but significantly more anti-CD52-treated patients had class-switched memory B lymphocytes (P = .024), normal IgG levels, and normal responses to tetanus and Haemophilus influenzae type B vaccination. More anti-CD52-treated patients with common gamma chain or Janus-associated kinase 3 severe combined immunodeficiency had donor B lymphocytes.

CONCLUSION

Long-term T-lymphocyte function is good with either treatment method, with a low incidence of graft-versus-host disease. The results imply more incomplete donor chimerism in anti-CD34-treated patients with less B-lymphocyte function.

T cell repertoire development in XSCID dogs following nonconditioned allogeneic bone marrow transplantation

Dogs with X-linked severe combined immunodeficiency (XSCID) can be successfully treated by bone marrow transplants (BMT) resulting in full immunologic reconstitution and engraftment of both donor B and T cells without the need for pretransplant conditioning. In this study, we evaluated the T cell diversity in XSCID dogs 4 months to 10.5 years following BMT. At 4 months posttransplantation, when the number of CD45RA+ (naïve) T cells had peaked and plateaued, the T cells in the transplanted dogs showed the same complex, diverse repertoire as those of normal young adult dogs. A decline in T cell diversity became evident approximately 3.5 years posttransplant, but the proportion of Vbeta families showing a polyclonal Gaussian spectratype still predominated up to 7.5 years posttransplant. In 2 dogs evaluated at 7.5 and 10.5 years posttransplant, >75% of the Vbeta families consisted of a skewed or oligoclonal spectratype that was associated with a CD4/CD8 ratio of <0.5. The decline in the complexity of T cell diversity in the transplanted XSCID dogs is similar to that reported for XSCID patients following BMT. However, in contrast to transplanted XSCID boys who show a significant decline in their T cell diversity by 10 to 12 years following BMT, transplanted XSCID dogs maintain a polyclonal, diverse T cell repertoire through midlife.

Severe papillomavirus infection progressing to metastatic squamous cell carcinoma in bone marrow-transplanted X-linked SCID dogs

Canine X-linked severe combined immunodeficiency (XSCID) is due to mutations in the common gamma chain (gammac) gene and is identical clinically and immunologically to human XSCID, making it a true homologue of the human disease. Bone marrow-transplanted (BMT) XSCID dogs not only engraft donor T cells and reconstitute normal T-cell function but, in contrast to the majority of transplanted human XSCID patients, also engraft donor B cells and reconstitute normal humoral immune function. Shortly after our initial report of successful BMT of XSCID dogs, it soon became evident that transplanted XSCID dogs developed late-onset severe chronic cutaneous infections containing a newly described canine papillomavirus. This is analogous to the late-onset cutaneous papillomavirus infection recently described for human XSCID patients following BMT. Of 24 transplanted XSCID dogs followed for at least 1 year post-BMT, 71% developed chronic canine papillomavirus infection. Six of the transplanted dogs that developed cutaneous papillomas were maintained for >3 1/2 years post-BMT for use as breeders. Four of these six dogs (67%) developed invasive squamous cell carcinoma (SCC), with three of the dogs (75%) eventually developing metastatic SCC, an extremely rare consequence of SCC in the dog. This finding raises the question of whether SCC will develop in transplanted human XSCID patients later in life. Canine XSCID therefore provides an ideal animal model with which to study the role of the gammac-dependent signaling pathway in the response to papillomavirus infections and the progression of these viral infections to metastatic SCC.

Immune deficiencies due to defects in cytokine signaling

Severe combined immunodeficiency (SCID) represents a syndrome comprising the most severe forms of inherited immunodeficiencies. Defects in cytokine signaling pathways can result in impaired development of lymphoid cells and/or defective functioning of these cells, and most cases of SCID result from defective signaling through the common cytokine receptor g chain (g(c)) or associated molecules and signaling pathways. Studies of these patients and the analysis of gene-targeted mice provide insight into the underlying signaling defects in inherited immunodeficiencies. The identification of the genetic defects in humans with SCID provides the basis for future therapies for these patients. More subtle deficiencies in cytokine signaling have also been found as causes of other forms of immunodeficiency, and the knowledge learned could lead to novel approaches to antimicrobial therapy.

Abnormal T cell-dependent B-cell responses in SCID mice receiving allogeneic bone marrow in utero. Severe combined immune deficiency

In allogeneic hematopoietic stem cell transplant recipients, restoration of humoral immunity is delayed and can remain impaired for years. In many severe combined immune deficiency (SCID) patients given haploidentical bone marrow (BM), lesions in humoral immunity are exacerbated by poor engraftment of donor B cells. The nature of these defects is important to understand as they render patients susceptible to infection. Previous work in mice suggested that in utero transplantation (IUT) of allogeneic BM might offer several advantages for the correction of primary immune deficiencies. In SCID mice given fully allogeneic BM in utero, the lymphoid compartment was restored with minimal evidence of graft-versus-host disease (GVHD). The present report examines B-cell reconstitution and function in mice that have received allogeneic IUT. Results are compared with those of adult mice given total body irradiation (TBI) followed by transplantation with allogeneic BM. In addition to enumerating the various B-cell subsets present in BM, spleen, and peritoneal cavity (PC), B-cell competence was assessed by challenging mice with T cell-independent (TI) and T cell-dependent (TD) antigens. The results demonstrated that all B-cell subsets in the BM and periphery were restored in allogeneic IUT and TBI mice, as were antibody responses after TI challenge. Upon immunization with TD antigens, however, IUT and TBI mice exhibited suboptimal responses as measured by the capacity to isotype switch and generate germinal center (GC) B cells. Thus, although allogeneic BM transplantation results in complete recovery of the B-cell compartment, certain elements of the humoral response remain defective.

Nonmyeloablative hematopoietic cell transplant for treatment of immune deficiency

Hematopoietic stem cell transplantation (HCT) may offer the only curative therapy for certain life-threatening immune deficiency disorders. Conventional HCT poses a risk to patients for severe morbidity, mortality, and late sequelae resulting from myeloablative preparative regimens. This review summarizes the development of nonmyeloablative regimens that have the potential to reduce both short-and long-term risks of HCT. Results of NM-HCT in a small number of patients indicate that this procedure may play an important role in treating life-threatening immune deficiencies.