Low B-cell and monocyte counts on day 80 are associated with high infection rates between days 100 and 365 after allogeneic marrow transplantation

Immune Reconstitution of Patients Who Recovered From Steroid-Refractory Acute Graft-Versus-Host Disease After Basiliximab Treatment

We aimed to identify the characteristics of immune reconstitution (IR) in patients who recovered from steroid-refractory acute graft-versus-host disease (SR-aGVHD) after basiliximab treatment. A total of 179, 124, 80, and 92 patients were included in the analysis for IR at 3, 6, 9, and 12 months, respectively, after haploidentical donor hematopoietic stem cell transplantation (HID HSCT). We observed that IR was fastest for monocytes and CD8⁺ T cells, followed by lymphocytes, CD3⁺ T cells, and CD19⁺ B cells and slowest for CD4⁺ T cells. Almost all immune cell subsets recovered comparably between patients receiving <5 doses and ≥5 doses of basiliximab. Most immune cell subsets recovered comparably between SR-aGVHD patients who recovered after basiliximab treatment and event-free HID HSCT recipients. Patients who recovered from SR-aGVHD after basiliximab treatment experienced satisfactory IR, which suggested that basiliximab may not have prolonged the negative impact on IR in these patients.

Interleukin-21 promotes thymopoiesis recovery following hematopoietic stem cell transplantation

BACKGROUND

Impaired T cell reconstitution remains a major deterrent in the field of bone marrow (BM) transplantation (BMT) due to pre-conditioning-induced damages inflicted to the thymi of recipient hosts. Given the previously reported thymo-stimulatory property of interleukin (IL)-21, we reasoned that its use post-BMT could have a profound effect on de novo T cell development.

METHODS

To evaluate the effect of IL-21 on de novo T cell development in vivo, BM derived from RAG2p-GFP mice was transplanted into LP/J mice. Lymphocyte reconstitution was first assessed using a hematological analyzer and a flow cytometer on collected blood samples. Detailed flow cytometry analysis was then performed on the BM, thymus, and spleen of transplanted animals. Finally, the effect of human IL-21 on thymopoiesis was validated in humanized mice.

RESULTS

Using a major histocompatibility complex (MHC)-matched allogeneic BMT model, we found that IL-21 administration improves immune reconstitution by triggering the proliferation of BM Lin^-Sca1⁺c-kit⁺ (LSK) subsets. The pharmacological effect of IL-21 also culminates in the recovery of both hematopoietic (thymocytes) and non-hematopoietic (stromal) cells within the thymi of IL-21-treated recipient animals. Although T cells derived from all transplanted groups proliferate, secrete various cytokines, and express granzyme B similarly in response to T cell receptor (TCR) stimulation, full regeneration of peripheral naïve CD4⁺ and CD8⁺ T cells and normal TCRvβ distribution could only be detected in IL-21-treated recipient mice. Astonishingly, none of the recipient mice who underwent IL-21 treatment developed graft-versus-host disease (GVHD) in the MHC-matched allogeneic setting while the graft-versus-tumor (GVT) effect was strongly retained. Inhibition of GVHD onset could also be attributed to the enhanced generation of regulatory B cells (B10) observed in the IL-21, but not PBS, recipient mice. We also tested the thymopoiesis-stimulating property of human IL-21 in NSG mice transplanted with cord blood (CB) and found significant improvement in de novo human CD3⁺ T cell development.

CONCLUSIONS

In sum, our study indicates that IL-21 represents a new class of unforeseen thymopoietin capable of restoring thymic function following BMT.

National Institutes of Health Hematopoietic Cell Transplantation Late Effects Initiative: The Immune Dysregulation and Pathobiology Working Group Report

Immune reconstitution after hematopoietic stem cell transplantation (HCT) beyond 1 year is not completely understood. Many transplant recipients who are free of graft-versus-host disease (GVHD) and not receiving any immunosuppression more than 1 year after transplantation seem to be able to mount appropriate immune responses to common pathogens and respond adequately to immunizations. However, 2 large registry studies over the last 2 decades seem to indicate that infection is a significant cause of late mortality in some patients, even in the absence of concomitant GVHD. Research on this topic is particularly challenging for several reasons. First, there are not enough long-term follow-up clinics able to measure even basic immune parameters late after HCT. Second, the correlation between laboratory measurements of immune function and infections is not well known. Third, accurate documentation of infectious episodes is notoriously difficult. Finally, it is unclear what measures can be implemented to improve the immune response in a clinically relevant way. A combination of long-term multicenter prospective studies that collect detailed infectious data and store samples as well as a national or multinational registry of clinically significant infections (eg, vaccine-preventable severe infections, opportunistic infections) could begin to address our knowledge gaps. Obtaining samples for laboratory evaluation of the immune system should be both calendar and eventdriven. Attention to detail and standardization of practices regarding prophylaxis, diagnosis, and definitions of infections would be of paramount importance to obtain clean reliable data. Laboratory studies should specifically address the neogenesis, maturation, and exhaustion of the adaptive immune system and, in particular, how these are influenced by persistent alloreactivity, inflammation, and viral infection. Ideally, some of these long-term prospective studies would collect information on long-term changes in the gut microbiome and their influence on immunity. Regarding enhancement of immune function, prospective measurement of the response to vaccines late after HCT in a variety of clinical settings should be undertaken to better understand the benefits as well as the limitations of immunizations. The role of intravenous immunoglobulin is still not well defined, and studies to address it should be encouraged.

Hepatitis E virus: A potential threat for patients with liver disease and liver transplantation

Immunocompromised patients are at risk of acquiring acute hepatitis E virus infection (HEV), leading to chronicity. Chronic HEV infection is associated with persistent viraemia, raised transaminase activity, histological features associated with chronic hepatitis and evidence of rapid development of cirrhosis. Extrahepatic manifestations have been associated with HEV. Most frequently reported are neurological disorders with predominantly involvement of the peripheral nervous system. In patients using immunosuppressive drugs antibody production is often delayed and HEV RNA detection is superior to serology to detect infection. Therapeutic options for chronic HEV includes tapering immunosuppressive and secondly ribavirin, pegylated interferon alpha (PEG-IFN). Present recommendation is to treat chronic HEV patients for 3 months, asses serum HEV RNA and stool HEV RNA and stop therapy if both are undetectable. Studies are required to determine which other antiviral agents than ribavirin and (PEG-)IFN are of clinical utility in treating HEV in the minority of patients who do not respond to ribavirin.

Improved prognostic stratification power of CIBMTR risk score with the addition of absolute lymphocyte and eosinophil counts at the onset of chronic GVHD

The CIBMTR chronic graft-versus-host disease (cGVHD) risk score can be refined and improved for better prognostic stratification. Three hundred and seven consecutive patients diagnosed with cGVHD by the NIH consensus criteria were retrospectively reviewed and had the CIBMTR risk score applied and analyzed. The CIBMTR risk score was successfully validated in our cohort (n = 307). The 3-year overall survival (OS) rates in each risk group (RG) were 82.5 ± 11.3% (RG1), 79.4 ± 3.0% (RG2), 71.8 ± 6.3% (RG3), and 27.3 ± 13.4% (RG4). A significantly lower OS rate and higher non-relapse mortality (NRM) were noted in RG4 compared to the other RGs. However, there were no differences in OS or NRM among RG1 to 3. To improve prognostic stratification power of the CIBMTR risk score, we incorporated the absolute lymphocyte (ALC) and eosinophil count (EC) at time of cGVHD into the CIBMTR risk score. Lower ALC (<1.0 × 10⁹/L, HR 1.94, p = 0.014) and lower EC (<0.5 × 10⁹/L, HR 3.27, p = 0.014) were confirmed as adverse risk factors for OS. Patients were stratified into four revised risk groups (rRG). The 3-year OS rates were 93.3 ± 6.4% (rRG1, score 0-3), 84.9 ± 3.4% (rRG2, score 4-6), 70.9 ± 4.4% (rRG3, score 7-9), and 32.0 ± 1.1% (rRG4, score ≥ 10) (p < 0.001). The 3-year NRM rates were 0.0% (rRG1), 6.7 ± 0.4% (rRG2), 18.4 ± 0.7% (rRG3), and 57.7 ± 5.1% (rRG4) (p < 0.001). The revised CIBMTR risk score was superior to the original CIBMTR risk score for OS (p < 0.001). The revised CIBMTR risk score including ALC and EC at the onset of cGVHD improved the prognostic stratification power of the CIBMTR risk score for long-term outcomes.

Hepatitis E virus infection in hematopoietic stem cell transplant recipients

PURPOSE OF REVIEW

Recipients of allogeneic stem cell transplantations are at risk of acquiring acute hepatitis E virus (HEV) infection, leading to chronicity. We review the incidence, sequela, extrahepatic manifestations, and treatment of hepatitis due to HEV infection in allogeneic hematopoietic stem cell transplantation (alloHSCT) recipients.

RECENT FINDINGS

HEV infection and progression to chronic HEV in alloHSCT recipients are recently described. Misdiagnosis of HEV in alloHSCT recipients occurs, with liver enzyme abnormalities often attributed to hepatic graft-versus-host disease or drug-induced liver injury. HEV infection may occur in HSCT donors and emphasizes the need for HEV screening not only after HSCT, but also in donors presenting with liver function disturbances. The discussion about HEV screening of blood products will continue. Extrahepatic manifestations of hepatitis E are described.

SUMMARY

HEV RNA screening in alloHSCT recipients with elevated liver enzymes is advised. Intervention strategies should be considered in cases of acute or chronic HEV infection. The first-line approach includes reduction of immunosuppressive medication. Oral ribavirin is in experienced hands a reasonable well tolerated treatment option, although the optimal dose, duration, and quantitative goals of ribavirin treatment are still unknown. Further studies are needed to improve our understanding of HEV, including extrahepatic manifestations and evaluation of therapeutic options.

Low Counts of B Cells, Natural Killer Cells, Monocytes, Dendritic Cells, Basophils, and Eosinophils are Associated with Postengraftment Infections after Allogeneic Hematopoietic Cell Transplantation

Hematopoietic cell transplant (HCT) recipients are immunocompromised and thus predisposed to infections. We set out to determine the deficiency of which immune cell subset(s) may predispose to postengraftment infections. We determined day 28, 56, 84, and 180 blood counts of multiple immune cell subsets in 219 allogeneic transplant recipients conditioned with busulfan, fludarabine, and Thymoglobulin. Deficiency of a subset was considered to be associated with infections if the low subset count was significantly associated with subsequent high infection rate per multivariate analysis in both discovery and validation cohorts. Low counts of monocytes (total and inflammatory) and basophils, and low IgA levels were associated with viral infections. Low plasmacytoid dendritic cell (PDC) counts were associated with bacterial infections. Low inflammatory monocyte counts were associated with fungal infections. Low counts of total and naive B cells, total and CD56(high) natural killer (NK) cells, total and inflammatory monocytes, myeloid dendritic cells (MDCs), PDCs, basophils and eosinophils, and low levels of IgA were associated with any infections (due to any pathogen or presumed). In conclusion, deficiencies of B cells, NK cells, monocytes, MDCs, PDCs, basophils, eosinophils, and/or IgA plasma cells appear to predispose to postengraftment infections.

Impact of acute and chronic graft-versus-host disease on human B-cell generation and replication

Using B-cell rearrangement excision circle measurements, we analyzed B-cell reconstitution in a cohort of 243 patients who underwent allogeneic stem cell transplantation. Acute and chronic graft-versus-host disease (aGVHD and cGVHD, respectively) transiently increased B-cell replication but decreased overall B-cell neogenesis with a clear difference in terms of kinetics. Moreover, the impact of aGVHD in the absence of cGVHD was transient, recovering at month 6 similar values as in patients who did not suffer from GVHD. Conversely, impact of cGVHD at month 12 in multivariate analysis was independent of the previous aGVHD effect on B-cell output. Finally, we showed in patients affected with cGVHD a higher B-cell division rate that correlates with an elevated BAFF/CD19(+) B-cell ratio, supporting a B-cell hyperactivation state in vivo.

Mobilization of healthy donors with plerixafor affects the cellular composition of T-cell receptor (TCR)-αβ/CD19-depleted haploidentical stem cell grafts

BACKGROUND

HLA-haploidentical hematopoietic stem cell transplantation (HSCT) is suitable for patients lacking related or unrelated HLA-matched donors. Herein, we investigated whether plerixafor (MZ), as an adjunct to G-CSF, facilitated the collection of mega-doses of hematopoietic stem cells (HSC) for TCR-αβ/CD19-depleted haploidentical HSCT, and how this agent affects the cellular graft composition.

METHODS

Ninety healthy donors were evaluated. Single-dose MZ was given to 30 'poor mobilizers' (PM) failing to attain ≥40 CD34+ HSCs/μL after 4 daily G-CSF doses and/or with predicted apheresis yields ≤12.0x106 CD34+ cells/kg recipient's body weight.

RESULTS

MZ significantly increased CD34+ counts in PM. Naïve/memory T and B cells, as well as natural killer (NK) cells, myeloid/plasmacytoid dendritic cells (DCs), were unchanged compared with baseline. MZ did not further promote the G-CSF-induced mobilization of CD16+ monocytes and the down-regulation of IFN-γ production by T cells. HSC grafts harvested after G-CSF + MZ were enriched in myeloid and plasmacytoid DCs, but contained low numbers of pro-inflammatory 6-sulfo-LacNAc+ (Slan)-DCs. Finally, children transplanted with G-CSF + MZ-mobilized grafts received greater numbers of monocytes, myeloid and plasmacytoid DCs, but lower numbers of NK cells, NK-like T cells and Slan-DCs.

CONCLUSIONS

MZ facilitates the collection of mega-doses of CD34+ HSCs for haploidentical HSCT, while affecting graft composition.

Bone marrow T-cell infiltration during acute GVHD is associated with delayed B-cell recovery and function after HSCT

B-cell immune dysfunction contributes to the risk of severe infections after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Delayed B-cell regeneration is found in patients with systemic graft-versus-host disease (GVHD) and is often accompanied by bone marrow (BM) suppression. Little is known about human BM GVHD. We analyzed the reconstitution kinetics of B-cell subsets in adult leukemic patients within 6 months after allo-HSCT. B-cell deficiency already existed before transplant and was aggravated after transplant. Onset of B-cell reconstitution characterized by transitional B-cell recovery occurred either early (months 2-3) or late (from month 6 on) and correlated highly positively with reverse transcription-polymerase chain reaction quantified numbers of κ-deleting recombination excision circles (KRECs). Delayed recovery was associated with systemic acute GVHD and full-intensity conditioning therapy. Histological analysis of BM trephines revealed increased T-cell infiltration in late recovering patients, which was associated with reduced numbers of osteoblasts. Functionally, late recovering patients displayed less pneumococcal polysaccharide-specific immunoglobin M-producing B cells on ex vivo B-cell activation than early recovering patients. Our results provide evidence for acute BM GVHD in allo-HSCT patients with infiltrating donor T cells and osteoblast destruction. This is associated with delayed B-cell reconstitution and impaired antibody response. Herein, KREC appears suitable to monitor BM B-cell output after transplant.

Hepatitis e virus: current concepts and future perspectives

For many years, hepatitis E was considered a disease found only in certain developing countries. In these geographical settings, hepatitis E virus (HEV) causes a self-limiting hepatitis in young adults, except in pregnant females, in whom the mortality is 25 %. Our understanding of HEV has changed radically in the past decade. It is now evident that HEV is a threat to global health. This review article considers the current concepts and future perspectives of HEV and its effects on human health, with particular reference to developed countries.

Immune cell reconstitution after exposure to potentially lethal doses of radiation in the nonhuman primate

Delayed immune reconstitution remains a major cause of morbidity associated with myelosuppression induced by cytotoxic therapy or myeloablative conditioning for stem cell transplant, as well as potentially lethal doses of total- or partial-body irradiation. Restoration of a functional immune cell repertoire requires hematopoietic stem cell reconstitution for all immune cells and effective thymopoiesis for T cell recovery. There are no medical countermeasures available to mitigate damage consequent to high-dose, potentially lethal irradiation, and there are no well characterized large animal models of prolonged immunosuppression to assess efficacy of potential countermeasures. Herein, the authors describe a model of T and B cell reconstitution following lethal doses of partial-body irradiation with 5% bone marrow sparing that includes full exposure of the thymus. Rhesus macaques (n = 31 male, 5.5-11.3 kg body weight) were exposed to midline tissue doses of 9.0-12.0 Gy using 6 MV LINAC-derived photons at a dose rate of 0.80 Gy min, sparing approximately 5% of bone marrow (tibiae, ankles, and feet). All animals received medical management and were monitored for myeloid and lymphoid suppression and recovery through 180 d post-exposure. Myeloid recovery was assessed by neutrophil and platelet-related hematological parameters. Reconstitution of B and T cell subsets was assessed by flow cytometric immunophenotyping, and recent thymic emigrants were identified by RT-PCR of T cell receptor excision circles. Mortality was recorded through 180 d post-exposure. Acute myelo-suppression was characterized by severe neutropenia and thrombocytopenia, followed by recovery 30-60 d post-exposure. Total T (CD3+) and B (CD20+) cells were reduced significantly following exposure and exhibited differential recovery patterns post-exposure. Both CD4+ and CD8+ subsets of naïve T cells and total CD4+ T cell counts remained significantly lower than baseline through 180 d post-exposure. The failure of recent thymic emigrants and naïve T cell subsets to recover to normal baseline values reflects the severe radiation effects on the recovery of marrow-derived stem and early thymic progenitor cells, their mobilization and seeding of receptive thymic niches, and slow endogenous thymic regeneration.

Methods of detection of immune reconstitution and T regulatory cells by flow cytometry

Allogeneic hematopoietic stem cell therapy (HSCT) remains one of the few curative treatments for high-risk hematological malignancies (high-risk leukemia, myelodysplastic syndromes, advanced myeloproliferative disorders, high-risk lymphomas, and multiple myeloma) and is currently applied in more than 15,000 patients per year in Europe. Following HSCT, patients experience a period of reconstitution of the immune system, which seems to be highly dependent on conditioning, immunosuppression regimes, and the level of adverse events the patients experience. During this reconstitution period, the patient is immune compromised and susceptible to opportunistic infections and disease relapse. Consequently, a large number of clinical studies have been devoted to monitoring the recovery of the immune system following HSCT in the hopes of determining which cellular subsets are indicative of a favorable outcome. In this chapter we review the methods that have been employed to monitor the immune reconstitution and what clinical observations have been made. Of particular interest is the regulatory T cell (Treg) subset, which has been associated with tolerance and has been the subject of recent clinical trials as a possible cellular therapy for rejection reactions. Finally we will detail a proposed methodology for the flow cytometric assessment of cellular reconstitution post-HSCT.

Hepatitis E virus: an underestimated opportunistic pathogen in recipients of allogeneic hematopoietic stem cell transplantation

Hepatitis E virus (HEV) is increasingly acknowledged as a cause of hepatitis in healthy individuals as well as immunocompromised patients. Little is known of HEV infection in recipients of allogeneic hematopoietic stem cell transplantation (alloHSCT). Therefore, we set out to study the incidence and sequelae of HEV as a cause of hepatitis in a recent cohort of 328 alloHSCT recipients. HEV RNA was tested in episodes of liver enzyme abnormalities. In addition, HEV RNA and HEV serology were assessed pre- and post-alloHSCT. We found 8 cases (2.4%) of HEV infection, of which 5 had developed chronic HEV infection. Seroprevalence pre-alloHSCT was 13%. Four patients died with HEV viremia, with signs of ongoing hepatitis, having a median time of infection of 4.1 months. The 4 surviving patients cleared HEV after a median period of 6.3 months. One patient was diagnosed with HEV reactivation after a preceding infection prior to alloHSCT. Although the incidence of developing acute HEV post-alloHSCT is relatively low, the probability of developing chronic hepatitis in severely immunocompromised patients is high. Therefore, alloHSCT recipients should be screened pretransplantation by HEV serology and RNA. Furthermore, a differential diagnosis including hepatitis E is mandatory in all alloHSCT patients with severe liver enzyme abnormalities.

Immune reconstitution after hematopoietic cell transplantation

PURPOSE OF REVIEW

Successful immune reconstitution is important for decreasing posthematopoietic cell transplant (post-HCT) infections, relapse, and secondary malignancy, without increasing graft-versus-host disease (GVHD). Here we review how different parts of the immune system recover, and the relationship between recovery and clinical outcomes.

RECENT FINDINGS

Innate immunity (e.g., neutrophils, natural killer cells) recovers within weeks, whereas adaptive immunity (B and T cells) recovers within months to years. This has been known for years; however, more recently, the pattern of recovery of additional immune cell subsets has been described. The role of these subsets in transplant complications like infections, GVHD and relapse is becoming increasingly recognized, as gleaned from studies of the association between subset counts or function and complications/outcomes, and from studies depleting or adoptively transferring various subsets.

SUMMARY

Lessons learned from observational studies on immune reconstitution are leading to new strategies to prevent or treat posttransplant infections. Additional knowledge is needed to develop effective strategies to prevent or treat relapse, second malignancies and GVHD.

Clinical applications for biomarkers of acute and chronic graft-versus-host disease

Acute and chronic graft-versus-host disease (aGVHD, cGVHD) are serious complications of allogeneic hematopoietic cell transplantation. The complex pathophysiology of these disease processes is associated with immune system activation, the release of cytokines and chemokines, and alterations in cell populations. The blood levels of specific protein and cellular levels in patients with GVHD have correlated with the development, diagnosis, and prognosis of GVHD. Here, we review the most promising biomarkers for aGVHD and cGVHD with clinical relevance. The utility of GVHD biomarkers in clinical care of allogeneic hematopoietic cell transplantation recipients needs to be proven through clinical trials, and potential approaches to trial design are discussed.

Factors influencing lymphocyte reconstitution after allogeneic hematopoietic stem cell transplantation in children

Background

Immune reconstitution (IR) after hematopoietic stem cell transplantation (HSCT) reduces transplantation-related complications such as infection and improves HSCT outcomes.

Methods

We retrospectively analyzed IR of lymphocyte subpopulations in 38 pediatric patients for hematologic malignant diseases after allogeneic HSCT from April 2006 to July 2008. T-cell-, B-cell-, and natural killer (NK) cell-associated antigens were assayed in peripheral blood by flow cytometry analysis of 5 lymphocyte subsets, CD3+, CD3+/CD4+, CD4+/CD8+, CD16+/CD56+, and CD19+, before and 3 and 12 months after transplantation.

Results

Reconstitutions of CD16+/CD56+ and CD3+/CD8+ lymphocytes were achieved rapidly, whereas that of CD3+/CD19+ lymphocytes occurred later. Age was not related to reconstitution of any lymphocyte subset. Total body irradiation (TBI) and anti-thymocyte globulin (ATG) administration were related to delayed reconstitution of total lymphocytes and CD3+ lymphocytes, respectively. Reconstitutions of CD3+/CD4+ lymphocytes and CD3+/CD8+ lymphocytes were significantly delayed in patients who received umbilical cord blood stem cells. In patients with chronic graft-versus-host disease (cGVHD), recovery of the total lymphocyte count and CD19+ lymphocytes at 3 months post-transplant were significantly delayed. However, acute GVHD (aGVHD) and cytomegalovirus (CMV) reactivation did not influence the IR of any lymphocyte subset. Further, delayed reconstitution of lymphocyte subsets did not correspond to inferior survival outcomes in this study.

Conclusion

We observed that some lymphocyte reconstitutions after HSCT were influenced by the stem cell source and preparative regimens. However, delayed CD19+ lymphocyte reconstitution may be associated with cGVHD.

Bone marrow B cell precursor number after allogeneic stem cell transplantation and GVHD development

Patients without chronic graft-versus-host disease (cGVHD) have robust B cell reconstitution and are able to maintain B cell homeostasis after allogeneic hematopoietic stem cell transplantation (HSCT). To determine whether B lymphopoiesis differs before cGVHD develops, we examined bone marrow (BM) biopsies for terminal deoxynucleotidyl transferase (TdT) and PAX5 immunostaining early post-HSCT at day 30 when all patients have been shown to have high B cell activating factor (BAFF) levels. We found significantly greater numbers of BM B cell precursors in patients who did not develop cGVHD compared with those who developed cGVHD (median = 44 vs 2 cells/high powered field [hpf]; respectively; P < .001). Importantly, a significant increase in precursor B cells was maintained when patients receiving high-dose steroid therapy were excluded (median = 49 vs 20 cells/hpf; P = .017). Thus, we demonstrate the association of BM B cell production capacity in human GVHD development. Increased BM precursor B cell number may serve to predict good clinical outcome after HSCT.

The lack of memory B cells including T cell independent IgM+ IgD+ memory B cells in chronic graft-versus host disease is associated with susceptibility to infection

The chronic graft-versus host disease (cGVHD) is associated with a perturbed B cell homeostasis and an increased infection rate. Aiming to determine the impact of lymphocyte subsets on cGVHD, blood samples from 98 patients at least 100 days following allogeneic haematopoietic stem cell transplantation (median 1066 days) were analyzed, serum levels of immunoglobulins measured and the incidence of severe infections retrospectively documented. Absolute CD19(+) B cell counts, including counts of immature (CD10(+) CD38(++) CD20(+) IgM(++)) and transitional (CD10(-) CD38(++) CD20(+) IgM(++)) as well as class switched memory (CD19(+) CD27(+) IgM(-) IgD(-)) B cells in patients with active cGVHD (n = 52) were significantly decreased as compared to those with inactive (n = 18) or without cGVHD (n = 28). In addition, nonclass switched IgM(+) memory B cells (CD19(+) CD27(+) IgM(+) IgD(+)) were absent in patients with cGVHD, but not in patients with inactive (0.4 × 10(6) /l) or without (1.7 × 10(6) /l) cGVHD (both P < 0.001). In line with these results we found significantly decreased lgG levels in patients with cGVHD, which was associated with a significantly higher rate of severe infections in cGVHD patients. Our data underline the close association of diminished B cell counts with cGVHD and the onset of severe infections. The lack of IgM(+) memory B cells in patients with cGVHD may indicate functional asplenia.

The role of B cells in the pathogenesis of graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation is an established treatment modality for malignant and nonmalignant hematologic diseases. Acute and chronic graft-versus-host diseases (GVHDs) are a major cause of morbidity and mortality after allogeneic stem cell transplantation. T cells have been identified as key players in the graft-versus-host reaction and, therefore, most established drugs used against GVHD target T cells. Despite our knowledge on the pathogenesis of the GVH reaction, success of established therapies for prevention and treatment of GHVD is unsatisfactory. Recently, animal and human studies demonstrated that B cells are involved in the immunopathophysiology of acute and chronic GVHD. Early phase clinical trials of B-cell depletion with rituximab have shown beneficial effects on both acute and chronic GVHD. This review summarizes the current experimental and clinical evidence for the involvement of B cells in the pathogenesis of acute and chronic GVHD and discusses the clinical implications for the management of patients undergoing allogeneic stem cell transplantation.

Immune reconstitution and implications for immunotherapy following haematopoietic stem cell transplantation

Recovery of a fully functional immune system is a slow and often incomplete process following allogeneic stem cell transplantation. While innate immunity reconstitutes quickly, adaptive B- and especially T-cell lymphopoeisis may be compromised for years following transplantation. In large part, these immune system deficits are due to the decrease, or even absence, of thymopoiesis following transplantation. Thereby, T-cell reconstitution initially relies upon expansion of mature donor T cells; a proliferation driven by high cytokine levels and the presence of allo-reactive antigens. This peripheral mechanism of T-cell generation may have important clinical consequences. By expanding tumouricidal T cells, it may provide a venue to enhance T-cellular immunotherapy following transplantation. Alternatively, decreased thymic function may impair long-term anti-tumour immunity and increase the likelihood of graft-versus-host disease.

Post-transplant adoptive T-cell immunotherapy

Immune reconstitution following haematopoietic stem cell transplantation (SCT) is an often slow and incomplete process that leads to increased risk of infection and malignant disease. Immunization in SCT is frequently unsuccessful due to the prolonged lymphopenia, especially of CD4 T cells, seen following transplant. The transfusion of T cells, also called 'adoptive T-cell therapy', has the potential to enhance anti-tumour and overall immunity, and augment vaccine efficacy in the post-transplant setting. Recent advances in tissue culture, cellular immunology and tumour biology are guiding new approaches to adoptive T-cell therapy. This chapter will discuss the challenges that face the field before adoptive T-cell therapy can be translated into routine clinical practice.

Considerations in the approach to invasive fungal infection in patients with haematological malignancies

Invasive infections because of opportunistic yeasts and moulds have contributed significantly to the morbidity and mortality associated with potentially curative treatment for haematological malignancies. Many risk factors have been identified that permit the clinician to predict the likelihood of these infections. The diagnostic process involves maintaining a high index of suspicion based upon an understanding of the clinical circumstances under which invasive fungal infections occur, of the spectrum of fungal syndromes, and of the advantages and limitations of diagnostic testing strategies now available. Treatment strategies may be categorized as prophylactic, pre-emptive, empiric, or directed based upon the circumstances. The therapeutic options have increased in recent years but are not applicable to all clinical circumstances. These considerations are discussed.

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.

Immune reconstitution following hematopoietic stem-cell transplantation

Hematopoietic stem-cell transplantation is associated with a profound immune deficiency manifested as an increased propensity to develop infections and probably also malignancies. Innate immunity, including epithelial barriers and phagocytes, typically recovers within weeks after grafting, and B-cell counts and CD8 T-cell counts recover within months. CD4 T-cell counts are low for years, and their recovery is particularly slow in older patients with poor thymic function. Therapies to improve immune function include vaccinations, immunoglobulins for recurrent infections, cytokines, and antigen-specific donor lymphocyte infusions.

Lymphocyte reconstitution following allogeneic hematopoietic stem cell transplantation: a retrospective study including 148 patients

Here we investigated the influence of parameters known before hematopoietic stem cell transplantation (HSCT) as well as the relevance of graft-versus-host disease (GvHD) and cytomegalovirus (CMV) reactivation on post transplant lymphocyte reconstitution in 148 patients treated in our institution between 1996 and 2003. Median patient age was 42 (19-68) years, HSCT followed standard high dose (n=91) or reduced-intensity conditioning regimens (n=57) with bone marrow (BM, n=67) or peripheral blood stem cells (PBSC, n=81) from related (n=71) or unrelated (n=77) donors. In the first months, we observed a partially faster reconstitution of CD3+4+, CD3+8+ and CD4+45RA+ T cells in patients following peripheral blood stem cell transplantation when compared to bone marrow transplantation. Prolonged CD3+4+ and CD4+45RA+ lymphopenia was noted after unrelated donor HSCT and GvHD prophylaxis containing anti-T-lymphocyte globulin. Lymphocyte subset counts in patients older than the median age were comparable to those in patients transplanted at a younger age and not influenced by the conditioning regimen. CD3+8+ T cell reconstitution was strongly correlated with CMV reactivation, but not significantly affected by CMV serostatus before HSCT. Incidence or extent of GvHD did not significantly influence lymphocyte reconstitution. Therefore, the source of graft is the most predictive parameter in early lymphocyte reconstitution, but the differences in lymphocyte recovery completely resolved within the first year after HSCT.

Crucial role of FLT3 ligand in immune reconstitution after bone marrow transplantation and high-dose chemotherapy

Almost 5 decades after the first clinical transplantations, delayed immune reconstitution remains a considerable hurdle in bone marrow transplantation, and the mechanisms regulating immune reconstitution after transplantation remain to be established. Whereas adult fms-like tyrosine kinase 3 ligand-deficient (FL(-/-)) mice have reduced numbers of early B- and T-cell progenitors, they sustain close to normal levels of mature B and T cells. Herein, we demonstrate that adult bone marrow cells fail to reconstitute B-cell progenitors and conventional B cells in lethally irradiated FL(-/-) recipients, which also display delayed kinetics of T-cell reconstitution. Similarly, FL is essential for B-cell regeneration after chemotherapy-induced myeloablation. In contrast, fetal progenitors reconstitute B lymphopoiesis in FL(-/-) mice, albeit at reduced levels. A critical role of FL in adult B lymphopoiesis is further substantiated by an age-progressive decline in peripheral conventional B cells in FL(-/-) mice, whereas fetally and early postnatally derived B1 and marginal zone B cells are sustained in a FL-independent manner. Thus, FL plays a crucial role in sustaining conventional B lymphopoiesis in adult mice and, as a consequence, our findings implicate a critical role of FL in promoting immune reconstitution after myeloablation and bone marrow transplantation.

Severe infections after unrelated donor allogeneic hematopoietic stem cell transplantation in adults: comparison of cord blood transplantation with peripheral blood and bone marrow transplantation

We evaluated the occurrence of severe infections in 192 consecutive adult recipients of volunteer unrelated donor allogeneic hematopoietic stem cell transplants, with a detailed analysis of severe infections after receipt of cord blood transplants (CBTs; n = 48) or bone marrow transplants (BMTs)/peripheral blood stem cell transplants (PBSCTs; n = 144). At a 3-year median follow-up, CBT recipients had a higher risk of developing any severe infection (85% versus 69% in BMT/PBSCT recipients, P < .01). CBT recipients had a higher incidence of severe bacterial infections before day +100, but at 3 years the risks of these and other infections were similar in the CBT and BMT/PBSCT groups. In addition, the 100-day and 3-year incidences of infection-related mortality (IRM) did not differ between groups (P = .2 and .5, respectively). In multivariate analysis, the most significant risk factor for IRM in all 192 patients was monocytopenia (.2 x 10(9)/L). In CBT recipients, only neutropenia (.2 x 10(9)/L) on day +30 and low nucleated cell dose infusion (< 2 x 10(7)/kg) showed a trend for increased IRM (P = .05 in both cases). Stem cell source had no effect on day +100 or 3-year nonrelapse mortality (NRM), cytomegalovirus infection, cytomegalovirus disease (7% versus 6%), or overall survival (36% versus 39%, respectively). The number of mismatches in HLA (A, B, and DRB1) had no effect on any outcome in CBT recipients. In contrast, in the BMT/PBSCT group, the presence of any mismatch by low or high-resolution HLA typing (A, B, C, and DRB1) increased NRM and decreased overall survival (P < .01). IRM was the primary or secondary cause of death in 61% and 59% of CBT and BMT/PBSCT recipients who died, respectively. Our results confirm the relevance of severe infectious complications as source of severe morbidity and NRM after volunteer unrelated donor hematopoietic stem cell transplantation in adults, but suggest that CBT recipients have a similar risk of dying from an infection if an accurate selection of a cord blood unit is done.

Proliferation-based T-cell selection for immunotherapy and graft-versus-host-disease prophylaxis in the context of bone marrow transplantation

Graft-versus-host disease (GvHD) caused by alloreactive T cells within the graft is a major drawback of allogeneic BMT, but depletion of T cells leads to higher rates of relapse, opportunistic infections and graft failure. Therefore, selective removal of GvHD-inducing alloreactive T cells might be beneficial. We describe here the separation of alloresponsive T cells, based on carboxyfluorescein succimidyl ester labeling, in vitro allostimulation and FACS-sorting. In vivo effects of the separated cell populations were investigated in the context of allogeneic BMT in murine models: in vitro resting T cells were shown to survive in the allogeneic host and retain immunoreactivity against 'third-party' antigens. As demonstrated in two different transplantation models, elimination of proliferating cells significantly reduces GvHD but offers no advantages to using T-cell-depleted bone marrow alone concerning engraftment and tumor control. Transplanting T cells that proliferate in response to tumor antigens in vitro may narrow down the spectrum of antigens recognized by T cells and therefore reduce GvHD while maintaining graft-facilitating function and tumor control. Therefore, selecting tumor-reactive T cells on the basis of their proliferative response in vitro may be beneficial for the recipient, less time consuming than T-cell cloning and still reduce the extent of GvHD.

Immune reconstitution following hematopoietic progenitor cell transplantation: challenges for the future

Successful hematopoietic progenitor cell transplantation requires rapid and complete transfer of the donor hematopoietic and immune systems to the host. Whereas the uncontrolled transfer of a nontolerant donor immune system results in GVHD in many cases, strategies which diminish GVHD also diminish immune reconstitution. Thus, the reliable, rapid and safe transfer of immunity from donor to host remains a major challenge for the field. Advances in the understanding of the biology of immune reconstitution have elucidated that thymic-dependent immune reconstitution can restore global immunity, but is especially vulnerable to toxicities associated with transplant. Alternatively, homeostatic peripheral expansion can be exploited for targeted immunity toward pathogens and tumors, but is difficult to manipulate without exacerbating GVHD risk. New translatable strategies are needed to safely augment one or both of these pathways in the setting of allogeneic hematopoietic progenitor cell transplantation.

Numbers of -expressing CD4CD25 T cells do not correlate with the establishment of long-term tolerance after allogeneic stem cell transplantation

OBJECTIVE

Regulatory CD4 T cells that express high levels of CD25 play a vital role in the maintenance of tolerance to self antigens and are required for the induction of nonresponsiveness to alloantigens. The long-term CD4+CD25high T-cell reconstitution after allogeneic stem cell transplantation is unknown. Here, we evaluated whether recovery of this T-cell subset might be linked to the establishment of full donor/recipient tolerance.

METHODS

The frequency of CD4+CD25high T cells was determined by Fluorescence Activated Cell Sorter (FACS) analysis in 31 patients, with a mean follow-up of more than 31 months posttransplant. The expression levels of Foxp3 mRNA were assessed by quantitative real-time polymerase chain reaction (RT-PCR).

RESULTS

Patients with or without graft-versus-host disease (GvHD) had significant and persistent CD4 T-cell lymphopenia. The relative frequency of CD25high cells and the expression levels of FoxP3 mRNA within this subset were similar between all patients and healthy controls. No significant difference was found in the number of Foxp3-expressing CD4+CD25high T cells in patients with or without GvHD. Finally, younger age and absence of previous GvHD were significantly linked to CD4+CD25high T-cell recovery.

CONCLUSION

The low number of Foxp3-expressing CD4+CD25high T cells in grafted patients is not a specific default of this compartment but a consequence of global CD4 T-cell lymphopenia after allogeneic stem cell transplantation. Moreover, levels of Foxp3 mRNA in the CD25+ T-cell compartment do not allow predicting the development of GvHD in the long term.

Leukocyte phenotype and function predicts infection risk in renal transplant recipients

BACKGROUND

The degree to which transplant recipients are immunosuppressed influences their risks of rejection, infection and cancer. Current measures of immune suppression are crude (clinical events) or indirect (drug exposure). We assessed a direct measure of immune status, leukocyte phenotype and function (LPF, a composite measure of five aspects of peripheral blood leukocyte phenotype and function), as a predictor of infection.

METHODS

A double-blind, prospective, cohort study was conducted, to determine the burden of infection in stable renal transplant recipients with moderate-severe (Group I, n = 34) or minimal (Group II, n = 36) impairment of LPF, a composite score of: (i) CD4 count; (ii) lymphocyte proliferation in response to phytohaemagglutinin A (PHA); (iii) serum Ig concentrations; (iv) neutrophil phagocytic function; and (v) reactive oxygen species generation. Subjects completed a 6 month diary and each recorded infection was scored 1-4: 1, minor undefined infection (e.g. URTI); 2, minor, microbiologically defined infection (e.g. UTI); 3, major defined infection (requiring hospitalization); 4, opportunistic infection (e.g. Herpes zoster). Final infection score was the sum of all infective episodes. Subjects were then followed-up for 5 years for outcome measures.

RESULTS

Groups were well matched for age, sex, diabetes, serum creatinine, rejection and trough cyclosporin concentrations. Group I (moderate to severe impairment of LPF) recorded a higher infection score, 2.4+/-2.8 vs 1.2+/-1.2 for Group II, P = 0.02, due to a higher incidence of moderate to severe infection. This relationship was confirmed by multivariate analysis (OR 1.83, CI 1.08, 3.11, P = 0.03 per unit increase in infection score). During the 5 year follow-up period they had significantly more episodes of admission to hospital, and twice as many admissions due to infections, but no difference in malignancy, graft or patient outcome.

CONCLUSION

LPF testing prospectively identified a cohort who incurred a higher burden of infection. Further studies are required to determine the predictive value of LPF for acute rejection, infection and cancer, and to determine whether adjustments to therapy on the basis of LPF can lead to improved outcomes.

Assessment of cellular immunity to human cytomegalovirus in recipients of allogeneic stem cell transplants

Effective reconstitution of cellular immunity following hematopoietic stem cell transplantation (HCT) is thought to be important for protection from the morbidity caused by cytomegalovirus (CMV) reactivation and disease. This review critically discusses current methods for assessment of CMV-specific cellular immune responses, with emphasis on flow cytometry-based methodologies such as MHC-I and MHC-II tetramer staining and intracellular cytokine assays. The advantages and weaknesses of these assays are considered in comparison to traditional immunologic techniques. Application of these newer methodologies has provided insight into the dynamics of the levels of CMV-specific CD4(+) and CD8(+) T-lymphocytes following HCT, and into the sources and diversity of these cells. Data from preliminary clinical studies suggest that CMV-specific CD8(+) T-lymphocyte levels greater than 1 x 10(7)/L of peripheral blood may correlate with protection from CMV disease. Studies on the functional phenotypes of CMV-specific CD8(+) T-lymphocytes such as cytokine production, degranulation, and cytotoxicity have indicated that these cells are heterogeneous with regard to these properties. Future research will focus on establishing whether any of these immunologic assays will serve as a correlate of protection and inform as to which patients are at high risk for CMV reactivation and disease. Identification of an informative assay may allow its incorporation into standard clinical practice for monitoring HCT patients.

Long-term antifungal prophylaxis in high-risk hematopoietic stem cell transplant recipients

The risks for invasive fungal infections, particularly mould infections such as invasive aspergillosis, among hematopoietic stem cell transplant (HSCT) recipients are linked to the duration and severity of myelosuppression and immunosuppression. Strategies to prevent invasive fungal infections have focused primarily on the use of orally administered azole antifungal agents during the neutropenic period rather than on the more prolonged post-engraftment period. The major limitations of these studies included the heterogeneity among the subjects studied for fungal infection risk factors, the agents administered, the dosing, and duration of prophylaxis. More recent studies have attempted to examine the efficacy of antifungal prophylaxis strategies among allogeneic HSCT recipients to day 100 and beyond. It is clear that a variety of products have efficacy in preventing invasive candidiasis, including imidazole and triazole antifungals, low-dose amphotericin B, and the echinocandin, micafungin; however, only the extended spectrum azole, itraconazole, has been shown to impact the incidence of proven invasive aspergillosis. Other extended spectrum azole antifungal agents, voriconazole and posaconazole, are being studied as long-term prophylaxis in high-risk HSCT recipients. While clinical trials have suggested that a duration of prophylaxis against moulds of six months or more may be required, it remains unclear if this is required in all cases. The prophylactic efficacy over time may be linked to the degree of immunosuppression as measured by markers such as the numbers of circulating CD4 T lymphocytes. Concerns about selection for resistant moulds among long-term recipients of these drugs are emerging. The cumulative experience to date suggests that long-term antifungal chemoprophylaxis is feasible and effective when applied in defined circumstances. The concerns about treatment-related toxicities, resistance, and costs are valid.

Factors affecting reconstitution of the T cell compartment in allogeneic haematopoietic cell transplant recipients

The factors affecting T cell reconstitution post haematopoietic cell transplantation (HCT) are not well characterised. We carried out a longitudinal analysis of T cell reconstitution in 32 HCT recipients during the first 12 months post transplant. We analysed reconstitution of naïve, memory and effector T cells, their diversity and monitored thymic output using TCR rearrangement excision circles (TRECs). Thymic-independent pathways were responsible for the rapid reconstitution of memory and effector T cells less than 6 months post HCT. Thymic-dependent pathways were activated between 6 and 12 months in the majority of patients with naïve T cell numbers increasing in parallel with TREC levels. Increasing patient age, chronic GVHD and T cell depletion (with or without pretransplant Campath-1H) predicted low TREC levels and slow naïve T cell recovery. Furthermore, increasing patient age also predicted high memory and effector T cell numbers. The effects of post HCT immunosuppression, total body irradiation, donor leucocyte infusions, T cell dose and post HCT infections on T cell recovery were also analysed. However, no effects of these single variables across a variety of different age, GVHD and T cell depletion groups were apparent. This study suggests that future analysis of the factors affecting T cell reconstitution and studies aimed at reactivating the thymus through therapeutic intervention should be analysed in age-, GVHD- and TCD-matched patient groups.

Long-term outcome after bone marrow transplantation for severe aplastic anemia

From January 1978 to December 2001, 133 patients with severe aplastic anemia (SAA) underwent non-T cell-depleted allogeneic bone marrow transplantation from an HLA-identical sibling donor, at the Hospital Saint Louis using either the combination of cyclophosphamide (Cy) and thoracoabdominal irradiation (TAI; n = 100) or Cy and antithymocyte globulin (ATG; n = 33), as a conditioning regimen. With 13.6 years of follow-up, the 10-year survival estimate was 64%. Four factors were associated with lower survival: older age, use of Cy-TAI, any form of treatment prior to transplantation (either androgens or immunosuppressive therapy, [IST]), and grade II to IV acute graft-versus-host disease (GvHD). TAI was the sole factor associated with the occurrence of acute GvHD. The risk of cancers (15-year cumulative incidence, 10.9%) was associated with older age and with the use of cyclosporine as IST before transplantation. Cumulative incidences and risk factors of nonmalignant late effect including avascular osteonecrosis and late bacterial, viral, and fungal infection were also analyzed. Improved results using Cy-ATG as conditioning can lead to more than 90% chance of cure in patients with SAA. Even if, in our experience, the role of Cy-ATG versus that of Cy-TAI remained inextricably related to the year of transplantation, the major detrimental role of the GvHD disease in the long-term outcome and its relation to TAI supports avoidance of irradiation in the conditioning regimen. Furthermore, avoidance of any IST before transplantation in patients with a sibling donor is a prerequisite for attaining such excellent results.

Long-term outcome of hepatitis C infection after bone marrow transplantation

Chronic hepatitis C is often asymptomatic, at least during the first decade following hematopoietic stem cell transplantation. Progression to advanced liver disease or cirrhosis in patients surviving more than 10 years is currently thought to be rare. Among 1078 patients who underwent an allogeneic transplantation between January 1973 and January 1995, 96 patients infected by hepatitis C virus (HCV) during the transplantation period were studied. Cumulative incidence and analysis of risk factors for cirrhosis were analyzed, and the rate and risk of cirrhosis in transplant recipients were compared with those of 158 HCV-infected controls who did not receive transplants. At a median follow-up of 15.7 years, 15 patients developed biopsy-proven cirrhosis, leading to a cumulative incidence of cirrhosis of 11% and 24% at 15 and 20 years, respectively. By multivariate analysis, extrahepatic HCV manifestations and HCV genotype 3 were associated with risk of cirrhosis. The median time to cirrhosis in transplant recipients was 18 years as compared with 40 years in the control population. The risk of cirrhosis in transplant recipients relative to controls was significantly higher by multivariate analysis (P =.0008). Roughly a quarter of long-term HCV-infected survivors with transplants progressed to cirrhosis that is much more rapid than in patients without transplants. Systematic detection of HCV infection, liver biopsy, and therapeutic intervention are therefore warranted in long-term marrow transplant recipients.

Immunologic recovery after hematopoietic cell transplantation with nonmyeloablative conditioning

OBJECTIVE

We studied immune reconstitution in 51 recipients of HLA-identical hematopoietic cellular transplant (HCT) after nonmyeloablative conditioning compared to a reference group of 67 recipients after myeloablative conditioning.

METHODS

Nonmyeloablative conditioning consisted of 2 Gy total-body irradiation+/-fludarabine and postgrafting cyclosporine and mycophenolate mofetil. All patients received G-CSF-mobilized peripheral blood mononuclear cells. Patients were followed with serial assessments of lymphocyte subset counts, antibody levels, virus-induced lymphoproliferation, and limiting-dilution assays for cytomegalovirus (CMV) T helper (T(H)) cells. Rates of infections over the first year after transplant were calculated.

RESULTS

During the first 180 days, absolute lymphocyte subset counts were similar (except higher total and memory B cell counts on day 80 in nonmyeloablative patients). At 1 year, however, total and naïve CD4 counts, and naïve CD8 counts, were higher in myeloablative patients. The levels of antibodies were similar at all time points and after vaccinations. The function of CD4 cells assessed by virus-induced lymphoproliferation was similar. However, the absolute counts of CMV T(H) cells were higher at days 30 and 90 (p=0.002 and p=0.0003, respectively) after nonmyeloablative conditioning. The rates of definite infections were lower for nonmyeloablative patients during the first 90 days, but were higher later. The higher number of CMV-specific T cells days 30 and 90 after nonmyeloablative HCT coincided with a lower rate of CMV infections during that time.

CONCLUSION

The immunity of nonmyeloablative HCT recipients appears better than the immunity of conventional HCT recipients early, but not late, after HCT.

Memory B lymphocytes determine repertoire oligoclonality early after haematopoietic stem cell transplantation

The objective of this study was to investigate if oligoclonality of the Ig repertoire post-haematopoietic stem cell transplantation (HSCT) is restricted to memory B lymphocytes or if it is a general property among B lymphocytes. As a measure of B lymphocyte repertoire diversity, we have analysed size distribution of polymerase chain reaction (PCR) amplified Ig H complementarity determining region 3 (CDR3) in naive and memory B lymphocytes isolated from patients before HSCT and at 3, 6 and 12 months after HSCT as well as from healthy controls. We demonstrate a limited variation of the IgH CDR3 repertoire in the memory B lymphocyte population compared to the naive B cell population. This difference was significant at 3 and 6 months post-HSCT. Compared to healthy controls there is a significant restriction of the memory B lymphocyte repertoire at 3 months after HSCT, but not of the naive B lymphocyte repertoire. Twelve months after HSCT, the IgH CDR3 repertoire in both memory and naive B lymphocytes are as diverse as in healthy controls. Thus, our findings suggest a role for memory B cells in the restriction of the oligoclonal B cell repertoire observed early after HSCT, which may be of importance when considering reimmunization of transplanted patients.

Compromised recovery of natural interferon-alpha/beta-producing cells after allogeneic hematopoietic stem cell transplantation complicated by acute graft-versus-host disease and glucocorticoid administration

Delayed recovery of the immune system is a major cause of post-transplant infection. Natural interferon (IFN)-alpha/beta-producing cells (IPC) appear to play a critical role in inducing effective immune responses to a variety of microbial pathogens by producing an enormous amount of IFN-alpha/beta and thereafter by differentiating into dendritic cells. Here, we examined the recovery of IPC as well as other immune cells in 28 patients after allogeneic hematopoietic stem cell transplantation (HSCT) in order to investigate the role of IPC in post-transplant immune reconstitution. In uncomplicated cases, IPC frequency recovered to the lower range of normal values within 30 days after transplantation, resembling the prompt recovery of other cell types in innate immunity. In contrast, the recovery of IPC was profoundly suppressed in the cases with acute graft-versus-host disease (GVHD) and glucocorticoid administration. The patients with lower numbers of IPC were significantly more susceptible to viral infection. The prompt recovery of IPC in uncomplicated cases may contribute to establishing a first line of host defense at the early stage after allogeneic HSCT, whereas the marked suppression of IPC recovery accompanying acute GVHD and glucocorticoid administration may increase the risk of opportunistic infections.