B lymphocyte reconstitution after hematopoietic stem cell transplantation: functional immaturity and slow recovery of memory CD27+ B cells

Depletion of autoreactive immunologic memory followed by autologous hematopoietic stem cell transplantation in patients with refractory SLE induces long-term remission through de novo generation of a juvenile and tolerant immune system

Clinical trials have indicated that immunoablation followed by autologous hematopoietic stem cell transplantation (ASCT) has the potential to induce clinical remission in patients with refractory systemic lupus erythematosus (SLE), but the mechanisms have remained unclear. We now report the results of a single-center prospective study of long-term immune reconstitution after ASCT in 7 patients with SLE. The clinical remissions observed in these patients are accompanied by the depletion of autoreactive immunologic memory, reflected by the disappearance of pathogenic anti-double-stranded DNA (dsDNA) antibodies and protective antibodies in serum and a fundamental resetting of the adaptive immune system. The latter comprises recurrence of CD31(+)CD45RA(+)CD4(+) T cells (recent thymic emigrants) with a doubling in absolute numbers compared with age-matched healthy controls at the 3-year follow-up (P = .016), the regeneration of thymic-derived FoxP3(+) regulatory T cells, and normalization of peripheral T-cell receptor (TCR) repertoire usage. Likewise, responders exhibited normalization of the previously disturbed B-cell homeostasis with numeric recovery of the naive B-cell compartment within 1 year after ASCT. These data are the first to demonstrate that both depletion of the autoreactive immunologic memory and a profound resetting of the adaptive immune system are required to reestablish self-tolerance in SLE.

Response to pneumococcal (PNCRM7) and haemophilus influenzae conjugate vaccines (HIB) in pediatric and adult recipients of an allogeneic hematopoietic cell transplantation (alloHCT)

Young children and allogeneic hematopoietic cell transplantation (HCT) recipients respond poorly to polysaccharide antigens, rendering them susceptible to severe infections because of encapsulated bacteria. This study evaluated the responses of 127 HCT patients, median age 23.0 years, vaccinated with PNCRM7 and Haemophilus influenzae (HIB) conjugate, 2 conjugate vaccines highly immunogenic in healthy children. Median time to vaccination was 1.1 years after HCT. Sixty-two percent of patients responded to PNCRM7 (45 of 51 children, 34 of 76 adults, P < .001). Overall response to HIB was 86%, including 77% of PNCRM7 nonresponders. Although PNCRM7 response was adversely affected by older age (P < .001), individuals > or =50 years old responded significantly better if vaccinated following acquisition of specific minimal milestones of immune competence, CD4 >200/microL, IgG >500 mg/dL, PHA within 60% lower limit of normal (11 of 19 versus 0 of 8, P < .006). A similar trend was observed in patients with limited chronic graft-versus-host disease (cGVHD). In all patients, higher levels of circulating CD4(+)CD45RA cells correlated with improved PNCRM7 response. These data demonstrate that PNCRM7 is immunogenic in allogeneic HCT patients, including older adults, but suggest that vaccination at fixed intervals after HCT, irrespective of immune competence, may limit its effectiveness. Prospective, multicenter trials assessing the best strategy to administer this vaccine and its impact on pneumococcal infections following transplantation are warranted.

Anti-CD20 therapy in patients with rheumatoid arthritis: predictors of response and B cell subset regeneration after repeated treatment

OBJECTIVE

B cell depletion with the anti-CD20 antibody rituximab has proven efficacy in patients with rheumatoid arthritis (RA). The effects on B cell homeostasis after repeated treatments and the relationship of certain B cell subsets to clinical response or relapse are currently not known.

METHODS

In this open-label study, 17 patients with RA refractory to standard therapy were treated with 1 cycle of rituximab. Of these 17 patients, 11 received a second cycle of rituximab therapy. Immunophenotyping was performed before therapy and during B cell recovery.

RESULTS

Twelve of 17 patients showed a good European League Against Rheumatism response after receiving 1 cycle of rituximab therapy. At the time of B cell recovery, the IgD+,CD27+ memory B cell subset was significantly larger (P = 0.019) in the nonresponder group. Within the group of 12 responders, 6 patients, whose disease was characterized by a significantly higher proportion of overall CD27+ memory B cells before therapy, experienced an early relapse (weeks 24-40 posttreatment). Eleven patients were re-treated, again resulting in a good clinical response. B cell reconstitution followed a similar pattern after each cycle. The early reconstitution phase was characterized by immature CD38++,IgD+,CD10+ B cells, whereas the number of naive B cells increased continuously thereafter. The number of memory B cells was still reduced at the time of the second depletion but recovered to levels similar to those following the first cycle of therapy.

CONCLUSION

Data derived from repeated B lymphocyte depletion with rituximab in patients with RA suggest that analysis of certain memory B cell subsets provides information on efficacy, response, and late as well as early relapse, consistent with the conclusion that targeting memory B cells is a key to its mechanism of action.

Elevated numbers of immature/transitional CD21- B lymphocytes and deficiency of memory CD27+ B cells identify patients with active chronic graft-versus-host disease

Chronic graft-versus-host disease (cGVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (HSCT) and a leading cause of non-relapse mortality (NRM). Currently, biology-based markers are lacking both for diagnosis and for monitoring the activity of cGVHD. Seventy patients who received HSCT were enrolled in a pilot study, including 21 without cGVHD and 49 with active or resolved cGVHD. Evaluations were comprised of clinical parameters including cGVHD severity and infections. Peripheral blood cells were analyzed by multi-parameter flow cytometry. The CD19+ B cell compartment was further subdivided by staining for surface IgD, CD21 and CD27. No significant differences in absolute B, T, and natural killer (NK) cell numbers were observed between the groups with and without cGVHD. However, elevated numbers (>15% of B lymphocytes) of immature/transitional CD19+/CD21(-) B cells were associated with the occurrence of severe infections (P = .003). Most significantly, all patients with active cGVHD and elevated numbers of CD19+/CD21(-) B lymphocytes experienced severe infections (P = .00016). The numbers of both non-class-switched and class-switched memory B cells were significantly lower in patients with active cGVHD when compared to patients who never experienced cGVHD (P = .002 and P = .001). Perturbation of circulating B lymphocyte compartments may serve as a novel biomarker for monitoring cGVHD activity and its impact on the immune system. A prospective study on unselected patients assessed serially for B cell reconstitution after HSCT is warranted.

Delayed memory B cell recovery in peripheral blood and lymphoid tissue in systemic lupus erythematosus after B cell depletion therapy

OBJECTIVE

Recent data suggest that the reconstituting peripheral B cell compartment after B cell depletion therapy may be functionally immature, with a preponderance of transitional B cells and a paucity of memory B cells. This study was undertaken to determine the magnitude, duration, and cause of these defects in rituximab-treated systemic lupus erythematosus (SLE) patients.

METHODS

Fifteen patients with SLE previously treated with rituximab as part of a phase I/II dose-escalation study were evaluated during a long-term followup (mean followup period 41 months). B cells from peripheral blood and tonsils were assessed using multicolor flow cytometry, and their developmental pathway was classified based on the expression of defined surface markers.

RESULTS

Reconstitution of peripheral blood CD27+ memory B cells was delayed for several years after B cell depletion therapy in a subset of patients with prolonged clinical responses and autoantibody normalization. This delay correlated with the degree of expansion of B cells of a transitional phenotype during the B cell reconstitution phase (P = 0.005) and the absence of baseline autoantibodies directed against extractable nuclear antigens (RNP, Sm, Ro antigen, La antigen). Despite the paucity of peripheral blood memory cells and the prolonged expansion of functionally immature transitional B cells, tonsil biopsy tissues revealed active germinal center (GC) reactions, but with decreased Fc receptor homolog 4-positive memory B cells.

CONCLUSION

These results suggest heterogeneity in the B cell depletion and reconstitution process that impacts clinical and immunologic outcomes in SLE. The presence of GC reactions, but with altered memory B cell subpopulations in tonsils, suggests that peripheral blood memory cell reconstitution lags behind a slow secondary lymphoid tissue recovery, with important implications for immunologic competence and tolerance.

Kinetics of human B cell behavior and amplification of proliferative responses following stimulation with IL-21

Although recent studies indicated that IL-21 is an important regulator of human B cell activation, detailed comparison of the effects of IL-21 on distinct B cell subsets have not been performed. Our studies revealed that IL-21R is expressed by naive and germinal center B cells, but not memory or plasma cells. IL-21R was increased on naive and memory B cells following in vitro activation. Investigation into the kinetics and magnitude of responses of human B cells to IL-21 revealed that IL-21 potently augmented proliferation of CD40L-stimulated neonatal, splenic naive, and memory and tonsil germinal center B cells. This response exceeded that induced by IL-4, IL-10, and IL-13, cytokines that also induce B cell proliferation. Remarkably, CD40L/IL-21-stimulated naive B cells underwent the same number of divisions as memory cells and exhibited a greater enhancement in their response compared with CD40L alone than memory B cells. Therefore, IL-21 is a powerful growth factor for naive B cells. This may result from the higher expression of IL-21R on naive, compared with memory, B cells. Stimulation of human B cells with CD40L/IL-21 also induced IL-10 production and activation of STAT3. We propose that IL-21 may have therapeutic application in conditions of immunodeficiency where it could expand naive B cells, the predominant B cell subset in such patients. Conversely, because IL-21 is increased in murine models of lupus, dysregulated IL-21 production may contribute to perturbed B cell homeostasis observed in systemic lupus erythematosus. Thus, antagonizing IL-21 may be a novel strategy for treating Ab-mediated autoimmune diseases.

Low percentages of circulating CD8(+)/CD45RA(+) human T lymphocytes expressing beta7 integrin correlate with the occurrence of intestinal acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

OBJECTIVE

Effector phase of acute graft-versus-host disease (a-GVHD) is mainly mediated by donor-derived, anti-host cytotoxic T cells. T-cell homing into gut-associated lymphoid tissues is ascribed to the alpha4beta7 integrin. We reasoned that development of intestinal a-GVHD might be triggered by recruitment in the intestinal mucosa of circulating, alloreactive, alpha4beta7(+) donor T cells. Therefore, we evaluated the correlation existing between circulating beta7(+) T-lymphocyte subsets early after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and occurrence of a-GVHD.

PATIENTS AND METHODS

Surface expression of beta7 integrin on T cells was evaluated by means of direct immunofluorescence, in three-color analysis. Sixty-five patients given allo-HSCT were evaluated: 13 of them experienced intestinal a-GVHD, 14 developed a-GVHD without intestinal involvement, and 38 did not develop a-GVHD. Patients were studied early after initial signs of hematologic reconstitution and before occurrence of a-GVHD.

RESULTS

We found a significantly higher absolute number of CD8(+) and a significantly lower percentage of CD8(+)CD45RA(+)beta7(+) T cells in patients with intestinal a-GVHD than in patients with a-GVHD without intestinal involvement (p = 0.003 and p = 0.003, respectively) or not experiencing a-GVHD (p = 0.02 and p = 0.002, respectively). In particular, we found that intestinal a-GVHD occurred in over 70% of patients showing an absolute number of CD8(+) T cells > or = 60 x 10(6)/L and a percentage of circulating CD8(+)CD45RA(+)beta7(+) T cells < 35%.

CONCLUSION

Measuring the absolute number of CD8(+) T cells and percentage of CD8(+)CD45RA(+)beta7(+) T cells at time of hematologic reconstitution may help identify patients at risk of developing intestinal a-GVHD who could benefit from strategies aimed at hampering alloreactive T-cell homing to intestinal mucosa.

Immunogenicity of recombinant hepatitis B vaccine (rHBV) in recipients of unrelated or related allogeneic hematopoietic cell (HC) transplants

Current European and US guidelines for recombinant hepatitis B vaccine (rHBV) after hematopoietic-cell transplantation (HCT) vary. The European Group for Blood and Marrow Transplantation (EBMT) recommends rHBV starting 6 to 12 months after HCT. Immunization is optional in the Centers for Disease Control and Prevention (CDC) guidelines. Nevertheless, rHBV is required for re-entry to school and certain workplaces. To determine the immunogenicity of rHBV following HCT, the prevaccine and postvaccine titers of 292 allogeneic transplant recipients who were immunized with rHBV were analyzed. Immunization was initiated in patients off immunosuppression who achieved specific minimal milestones of immune competence. Overall, 64% of patients seroconverted. In multivariate analyses, response was adversely affected by age older than 18 years (P < .01) and history of prior chronic graft-versus-host disease (GVHD; P < .001) but not by donor type or by use of T-cell depletion, adoptive immunotherapy, or rituximab. By comparison, 89% of rHBV nonresponders mounted a 3-fold or greater rise in polio titers following 3 doses of inactivated poliovirus. These data demonstrate that the rate of seroconversion following rHBV is lower in allogeneic HC transplant recipients compared with age-matched healthy controls. The data emphasize the need to document prevaccine and postvaccine titers to ensure response and suggest that immunization guidelines based on time interval from HCT, irrespective of immune competence, may not ensure adequate protection against certain vaccine-preventable diseases.

B cell reconstitution after rituximab treatment of lymphoma recapitulates B cell ontogeny

The long-term immunologic effects of B cell depletion with rituximab and the characteristics of the reconstituting B cell pool in lymphoma patients are not well defined, despite the widespread usage of this therapy. Here we report that during the B cell reconstitution phase a majority of the peripheral blood B cells have an immature transitional phenotype (47.8%+/-25.2% vs. 4.4%+/-2.4% for normal controls, p<0.0001), similar to what has been described during the original ontogeny of the immune system and following bone marrow transplantation. Moreover, the recovery of the CD27+ memory B cell pool was delayed compared to normal B cell ontogeny, remaining below normal controls at 1 year post-rituximab (4.4%+/-3% vs. 31%+/-7%, p<0.0001). Expansion of functionally immature B cells and decreased memory B cells may contribute to an immunodeficient state in patients recovering from rituximab mediated B cell depletion, particularly with repeated treatment.

Antibody response to Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan in patients after solid-organ transplantation

Cryptococcosis is an important complication of solid-organ transplantation, but the risk factors for disease are poorly understood. The goal of this study was to investigate whether specific or nonspecific serum immunoglobulin levels determined in samples obtained before and after solid-organ transplantation differed in patients who did or did not develop cryptococcosis after transplantation. We analyzed pretransplantation sera from 25 subjects, 15 who subsequently developed cryptococcosis and 10 who did not, and posttransplantation sera from 24 subjects, 13 who developed cryptococcosis and 11 who did not. All subjects received a tacrolimus-based immunosuppressive regimen. Total immunoglobulin levels were measured by immunodiffusion, and Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM)-specific serum antibody levels were determined by enzyme-linked immunosorbent assays. The results showed that solid-organ transplantation had a significant effect on total immunoglobulin and GXM-reactive antibody levels. GXM-reactive antibody levels differed in subjects who did and did not develop cryptococcosis. In pretransplant serum samples, the levels of GXM-reactive immunoglobulin M (IgM) were significantly lower in subjects who developed cryptococcosis after transplantation than in those who did not. For posttransplant serum samples, the levels of GXM-reactive IgM and IgG were significantly higher among the subjects who developed cryptococcosis than among those who did not. These findings suggest that perturbations in the preexisting antibody or B-cell repertoire and/or related to treatment of rejection, transplantation, or immunosuppressive therapy could translate into an increased risk for transplant-associated cryptococcosis.

Expansion of Functionally Immature Transitional B Cells Is Associated with Human-Immunodeficient States Characterized by Impaired Humoral Immunity

X-linked lymphoproliferative disease (XLP) is a severe immunodeficiency associated with a marked reduction in circulating memory B cells. Our investigation of the B cell compartment of XLP patients revealed an increase in the frequency of a population of B cells distinct from those previously defined. This population displayed increased expression of CD10, CD24, and CD38, indicating that it could consist of circulating immature/transitional B cells. Supporting this possibility, CD10+CD24highCD38high B cells displayed other immature characteristics, including unmutated Ig V genes and elevated levels of surface IgM; they also lacked expression of Bcl-2 and a panel of activation molecules. The capacity of CD24highCD38high B cells to proliferate, secrete Ig, and migrate in vitro was greatly reduced compared with mature B cell populations. Moreover, CD24highCD38high B cells were increased in the peripheral blood of neonates, patients with common variable immunodeficiency, and patients recovering from hemopoietic stem cell transplant. Thus, an expansion of functionally immature B cells may contribute to the humoral immunodeficient state that is characteristic of neonates, as well as patients with XLP or common variable immunodeficiency, and those recovering from a stem cell transplant. Further investigation of transitional B cells will improve our understanding of human B cell development and how alterations to this process may precipitate immunodeficiency or autoimmunity.