Reconstitution of the immune system after hematopoietic stem cell transplantation in humans. Semin Immunopathol. 2008;30:425-437. [PMID: 18949477 DOI: 10.1007/s00281-008-0132-5]

Unbalanced recovery of regulatory and effector T cells after allogeneic stem cell transplantation contributes to chronic GVHD

The development and maintenance of immune tolerance after allogeneic hematopoietic stem cell transplantation (HSCT) requires the balanced reconstitution of donor-derived CD4 regulatory T cells (CD4Tregs) as well as effector CD4 (conventional CD4 T cells [CD4Tcons]) and CD8 T cells. To characterize the complex mechanisms that lead to unbalanced recovery of these distinct T-cell populations, we studied 107 adult patients who received T-replete stem cell grafts after reduced-intensity conditioning. Immune reconstitution of CD4Treg, CD4Tcon, and CD8 T cells was monitored for a 2-year period. CD3 T-cell counts gradually recovered to normal levels during this period but CD8 T cells recovered more rapidly than either CD4Tregs or CD4Tcons. Reconstituting CD4Tregs and CD4Tcons were predominantly central memory (CM) and effector memory (EM) cells and CD8 T cells were predominantly terminal EM cells. Thymic generation of naive CD4Tcon and CD8 T cells was maintained but thymic production of CD4Tregs was markedly decreased with little recovery during the 2-year study. T-cell proliferation was skewed in favor of CM and EM CD4Tcon and CD8 T cells, especially 6 to 12 months after HSCT. Intracellular expression of BCL2 was increased in CD4Tcon and CD8 T cells in the first 3 to 6 months after HSCT. Early recovery of naive and CM fractions within each T-cell population 3 months after transplant was also strongly correlated with the subsequent development of chronic graft-versus-host disease (GVHD). These dynamic imbalances favor the production, expansion, and persistence of effector T cells over CD4Tregs and were associated with the development of chronic GVHD.

Optimal Threshold and Time of Absolute Lymphocyte Count Assessment for Outcome Prediction after Bone Marrow Transplantation

The recovery pace of absolute lymphocyte count (ALC) is prognostic after hematopoietic stem cell transplantation. Previous studies have evaluated a wide range of ALC cutoffs and time points for predicting outcomes. We aimed to determine the optimal ALC value for outcome prediction after bone marrow transplantation (BMT). A total of 518 patients who underwent BMT for acute leukemia or myelodysplastic syndrome between 1999 and 2010 were divided into a training set and a test set to assess the prognostic value of ALC on days 30, 60, 90, 120, 180, as well as the first post-transplantation day of an ALC of 100, 200, 300, 400, 500, and 1000/μL. In the training set, the best predictor of overall survival (OS), relapse-free survival (RFS), and nonrelapse mortality (NRM) was ALC on day 60. In the entire patient cohort, multivariable analyses demonstrated significantly better OS, RFS, and NRM and lower incidence of graft-versus-host disease (GVHD) in patients with an ALC >300/μL on day 60 post-BMT, both including and excluding patients who developed GVHD before day 60. Among the patient-, disease-, and transplant-related factors assessed, only busulfan-based conditioning was significantly associated with higher ALC values on day 60 in both cohorts. The optimal ALC cutoff for predicting outcomes after BMT is 300/μL on day 60 post-transplantation.

NK Cell Functional Impairment after Allogeneic Hematopoietic Stem Cell Transplantation Is Associated with Reduced Levels of T-bet and Eomesodermin

NK cells play a major role in protection against tumor recurrence and infection after allogeneic hematopoietic stem cell transplantation (HSCT). It has been shown that NK cell function after HSCT is impaired, but underlying molecular mechanisms are not well-known. In this report we show that the level of T-bet and Eomesodermin (Eomes), two T-box transcription factors regulating lymphocyte effector functions, is strongly reduced in NK cells from HSCT recipients compared with healthy control subjects. Reduction of T-bet and Eomes expression appeared early and persisted for years after HSCT, affecting all peripheral blood NK cells independently of their differentiation status. Reduced T-bet levels in NK cells from allogeneic HSCT recipients significantly correlated with reduced perforin expression. Acute, but not chronic, graft-versus-host disease, as well as CMV reactivation, was associated with further downregulation of T-bet expression in NK cells. Lower levels of T-bet expression in NK cells were associated with less favorable outcome after HSCT as a result of increased nonrelapse mortality. Collectively, our results provide a possible molecular explanation for the previously reported functional exhaustion of NK cells after allogeneic HSCT and suggest an impact of the NK transcriptional machinery status on HSCT outcome.

Apoptosis Susceptibility Prolongs the Lack of Memory B Cells in Acute Leukemic Patients After Allogeneic Hematopoietic Stem Cell Transplantation

Long-term survival after allogeneic hematopoietic stem cell transplantation requires intact immunosurveillance, which is hampered by lymphoid organ damage associated with conditioning therapy, graft-versus-host disease, and immunosuppression. Our study aimed to identify the mechanisms contributing to sustained low memory B cell numbers after transplantation. Peripheral B and T cell subset recovery and functional marker expression were investigated in 35 acute leukemic patients up to 1 year after transplantation. Apoptosis of B cells after CD40/TLR-9, CD40/BCR, and CD40/BCR/TLR-9-dependent stimulation and drug efflux capacity were analyzed. One half of the patients suffered from infections after day 180. All patients had strongly diminished CD27(+) memory B cells despite already normalized total B cell numbers and fully recovered CD27(-)IgD(-) memory B cells, putatively of extra-follicular origin. Circulating memory follicular helper T cells were reduced in the majority of patients as well. Naïve B cells exhibited a decreased expression of CXCR5, which mediates follicular B cell entry. Additionally, a lower HLA-DR expression was found on naïve B cells, impairing antigen presentation. Upon CD40/TLR-9-dependent activation, B cells underwent significantly increased apoptosis paralleled by an aberrant up-regulation of Fas-L on activated T cells and Fas on resting B cells. Significantly increased B cell apoptosis was also observed after CD40/BCR and CD40/BCR/TLR-9-dependent activation. Drug efflux capacity of naïve B cells was diminished in cyclosporin A-treated patients, additionally contributing to an apoptosis-prone phenotype. We conclude that B cell survival and migration and T cell communication defects are contributing candidates for an impaired germinal center formation of memory B cells after allogeneic hematopoietic stem cell transplantation. Follow-up studies should evaluate effectiveness of revaccinations on the cellular level and should address the long-term sequelae of B cell defects after transplantation.

Immunology of hematopoietic stem cell transplant

Hematopoietic stem cell transplantation (HSCT) is a procedure in which infusion of hematopoietic stem cells is used to reestablish hematopoietic function in patients with damaged or defective bone marrow or immune systems. Early and late complications following allogeneic HSCT include acute and chronic graft-versus-host disease (GVHD), donor rejection, graft failure, relapse of primary malignancy, conditioning-related toxicity, immunodeficiency and infections. Immunology has a central role in allogeneic hematopoietic cell transplantation. Any appreciation of the immunological mechanism involved in engraftment, GVHD, the development of tolerance, immune reconstitution, and the control of malignancy requires some understanding of the immunologic basis for immune reactions provoked by grafting tissue from one individual to another. In the future it should be possible to learn what gene(s) must be activated and which must be repressed to force stem cells into division without maturation; to engineer a mechanism into the cells that stops proliferation and sets the stage for amplification; to search if there could be a universal donor cell line, neatly packaged and stabilized in sealed vials and distributed by the pharmaceutical industry; to modify the transplanted cells in such a way that they have a proliferative advantage over those of the host and to deliver the lethal blow against the neoplasm, perhaps the cells that are infused will be engineered in such a way as to be able to distinguish between normal host cells and tumor.

Clinical Relevance of Apheretic Graft Composition in Patients With Acute Myeloblastic Leukemia Who Received a Busulfan-Fludarabine-Antithymocyte Globulin Conditioning Regimen for Allogeneic Transplant

OBJECTIVES

Sparse data are available about the effects of apheretic graft composition on the clinical transplant outcome in allotransplanted patients who have hematologic malignant disease. Major obstacles in recent studies have included heterogeneity of patient populations and differences in the conditioning regimens used.

MATERIALS AND METHODS

This prospective study included 50 patients who had acute myeloblastic leukemia and received busulfan-fludarabine-antithymocyte globulin-based conditioning for peripheral allogeneic stem cell transplant. The concentration of CD34+ cells, T-cell subsets, B cells, and natural killer cells in the graft were analyzed by flow cytometry in the donors who were matched for human leukocyte antigen.

RESULTS

In univariate analysis, infusion with a higher dose of natural killer cells (> 1.55 × 106/kg) was associated with improved survival (P = .007 for disease-free survival; P = .024 for overall survival) in patients with acute myeloblastic leukemia. Cox regression models revealed that increased concentration of natural killer cells and CD34+ cells positively affected the clinical outcome of allotransplanted patients (P = .005 for both cell types). According to univariate analysis, these findings were dependent on minimal residual disease and acute graft-versus-host disease. Graft-versus-host disease (acute and chronic forms) was not affected by graft composition.

CONCLUSIONS

Our results suggest that increased concentration of natural killer cells and CD34+ cells in the apheretic product may predict better survival. In contrast, busulfan-fludarabine-antithymocyte globulin-based conditioning eliminates the disadvantages that resulted from the high content of T-cell subsets and B cells, and the course of the transplant and clinical parameters were not affected by the amount of T and B cells.

Effect of ATG-F on B-cell reconstitution after hematopoietic stem cell transplantation

Antithymocyte globulin Fresenius (ATG-F) is used before hematopoietic stem cell transplantation to prevent graft rejection and graft-versus-host disease in patients with HLA-matched unrelated donors or mismatched volunteers. However, little is known about the effect of ATG-F on the reconstitution of B-cell subsets. Sixty-seven patients were longitudinally studied at day 15, day 30, and then monthly after hematopoietic stem cell transplantation. Conditioning regimes included ATG-F, which was infused at days 3, 2 and 1 at a dosage of 10 mg/kg/d. Twenty-seven patients received conditioning regimes without ATG. ATG-treated patients showed a significant delay of CD19+ B cells in the early recovery period. The absolute numbers of circulating CD19+ B cells were significantly lower (P < 0.05) up to 5 months post-transplantation compared to non-ATG patients. The recovery of the memory compartment was delayed in both groups and did not reach normal values 1-year post-transplantation. ATG-treated patient showed significantly lower absolute numbers of circulating CD27+ memory B cells in the first-month after transplantation compared to non-ATG patients. In conclusion, treatment with ATG in the conditioning regime of patients undergoing allogeneic hematopoietic stem cell transplantation leads to a significant delay of CD19+ B cells. Thus, ATG seems also to negatively influence B-cell immune reconstitution.

The immunology of Epstein-Barr virus-induced disease

Epstein-Barr virus (EBV) is usually acquired silently early in life and carried thereafter as an asymptomatic infection of the B lymphoid system. However, many circumstances disturb the delicate EBV-host balance and cause the virus to display its pathogenic potential. Thus, primary infection in adolescence can manifest as infectious mononucleosis (IM), as a fatal illness that magnifies the immunopathology of IM in boys with the X-linked lymphoproliferative disease trait, and as a chronic active disease leading to life-threatening hemophagocytosis in rare cases of T or natural killer (NK) cell infection. Patients with primary immunodeficiencies affecting the NK and/or T cell systems, as well as immunosuppressed transplant recipients, handle EBV infections poorly, and many are at increased risk of virus-driven B-lymphoproliferative disease. By contrast, a range of other EBV-positive malignancies of lymphoid or epithelial origin arise in individuals with seemingly intact immune systems through mechanisms that remain to be understood.

CD4+ T cell counts reflect the immunosuppressive state of CD4 helper cells in patients after allogeneic stem cell transplantation

The recovery of the host immune system after allogeneic hematopoietic stem cell transplantation is pivotal to prevent infections, relapse, and secondary malignancies. In particular, numerical CD4+ T cells reconstitution is delayed and CD4 helper cell function is considered impaired as a consequence of the transplant procedure and concomitant immunosuppressive medication. From HIV/AIDS patients, it is known that numerical and functional CD4 defects increase the risk of opportunistic infections. However, and in contrast to patients with HIV, anti-infective prophylaxis after allogeneic transplantation is usually given for 6 months depending on immunosuppressive medication and existing graft-versus-host disease but independently of absolute CD4+ T cells counts. We hypothesized that a qualitative T cell defect is existing after allogeneic transplantation, especially in patients with delayed immune-reconstitution. Applying transcriptional as well as functional approaches, we show that CD4+ T cells with delayed recovery have a distinct transcriptional profile and cluster differently from T cells originated from patients with completed immune recovery. Moreover, inhibitory signatures are substantially enriched within the transcriptional profile of these T cells translating to functional defects and impaired interleukin 2 production. In addition to time after transplant, CD4+ T cells numbers should be considered for the decision to stop or maintain antimicrobial prophylaxis in patients after allogeneic stem cell transplantation.

Comparison of different rabbit ATG preparation effects on early lymphocyte subset recovery after allogeneic HSCT and its association with EBV-mediated PTLD

PURPOSE

Rabbit antithymocyte globulin (ATG) is commonly used before allogeneic hematopoietic stem cell transplantation (allo-HSCT) to prevent graft-versus-host disease. Studies comparing the effect of different ATG preparations and dosages on immune reconstitution and risk for Epstein-Barr virus (EBV)-mediated post-transplant lymphoproliferative disorder (PTLD) are rare.

METHODS

In this retrospective study, we determined T and B cell subsets by flow cytometry after allo-HSCT in children, who received ATG-Genzyme (ATG-G, n = 15), ATG-Fresenius (ATG-F, n = 25) or no-ATG treatment (n = 19). Additionally, PCR-quantified EBV-genome copy counts were correlated with incidence of PTLD.

RESULTS

We could confirm a dose-dependent impairment of CD8(+) and CD4(+) T cell regeneration by ATG-G, including naïve and memory CD4(+) T cells. No differences were seen between the currently applied dosages of 5-10 mg/kg ATG-G and 20-60 mg/kg ATG-F. Significantly delayed T cell subset reconstitution was determined only at high dosages of 20-60 mg/kg ATG-G compared to ATG-F. B cell reconstitution was comparably impaired in ATG-G- and ATG-F-treated patients. Although the incidence of EBV reactivation was similar in both ATG groups, EBV copy counts of >10(4) copies/10(5) peripheral blood mononuclear cells and the occurrence of PTLD were only found in ATG-G-treated patients.

CONCLUSIONS

We conclude that high, but importantly not currently applied low dosages of ATG-G, impair thymic T cell regeneration and memory T cell immunity to a greater extent than ATG-F in pediatric patients. In addition, our results suggest an increased risk for EBV-PTLD when treated with ATG-G. Prospective studies are warranted to compare different ATG preparations with regard to the immune reconstitution and EBV-PTLD.

Infectious complications of stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is an accepted treatment for a variety of hematologic malignancies. The profound immunosuppression these patients experience adversely affects their risk of infection. This risk is much higher than in the general population and requires aggressive diagnostic and therapeutic interventions. The chapter will outline the major infections after HSCT.

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.

New proposed guidelines for early identification of successful myeloid and erythroid engraftment in hematopoietic stem cell transplantation

BACKGROUND

After hematopoietic stem cell transplantation (HSCT), early detection of engraftment would be of critical value for clinicians. The aim of this study was to identify faster parameters for engraftment.

METHODS

We evaluated blood cell parameters including complete blood count (CBC), differential counts, and various reticulocyte parameters in 115 patients who received HSCT (allogeneic, n = 93; autologous, n = 22) in the purpose of identifying possible improved laboratory guidelines for engraftment prediction.

RESULTS AND CONCLUSION

Days to white blood cell (WBC) count over 100 cells/μl with more than two-fold increase from nadir after transplantation (proposed new WBC guideline) preceded absolute neutrophil count (ANC) >500 cells/μl by 1.7 days. Among erythroid parameters, the earliest marker for erythroid engraftment was high light scattering reticulocytes (HLR) >0.1 (proposed new red blood cell guideline), which preceded reticulocyte counts (RET) >1% and immature reticulocyte fraction >0.5 by 3.9 and 1.6 days, respectively. Among the clinical parameters compared, those with statistically significant influence on myeloid engraftment were donor type (P = 0.009) and conditioning intensity (P = 0.009). As for erythroid recovery, ABO incompatibility was the only significant factor. In conclusion, the new guidelines may ensure engraftment several days earlier than the conventional parameters, which may help clinicians for decision-making on rescue therapy earlier.

Evolution of peripheral blood T lymphocyte subsets after allogenic or autologous hematopoietic stem cell transplantation

With the aim to search for differences in T cell reconstitution after allogenic or autologous hematopoietic stem cell transplantation (HSCT), we characterized peripheral blood T-cell subsets by means of flow cytometry, in adult patients who had undergone either allogenic (n=23) or autologous (n=29) HSCT for the treatment of hematological malignancies. The patients were followed every 3 months for 21 months after HSCT. Compared to healthy controls (n=20 blood donors), the two transplanted groups displayed (i) a CD4 lymphopenia, (ii) a low percentage of naive T cells, (iii) high percentages of memory T cells and of activated T cells (HLA-DR+, CD25+) and high percentages of CD4 T cells with a high expression of CD25. The levels of TRECs (TCR rearrangement excision circles) were not significantly different between the two groups. In total, the differences of the nature and the speed of T lymphocyte reconstitution observed between the two patient groups were minor. This leads us to conclude that in allografted patients, lymphocyte activation as well as many other disturbances of subpopulations of peripheral blood lymphocytes are probably not related to the allogenicity of the graft, but are due to the expansion of T cells transfused with HSC and slow differentiation of T lymphocytes in the thymus progressively colonized by bone marrow-derived T-cell precursors.

Novel markers of early neutrophilic and monocytic engraftment after hematopoietic stem cell transplantation

BACKGROUND

Numerous studies tried to find new markers that after hematopoietic stem cell transplantation predict engraftment earlier than the conventional marker, absolute neutrophil count (ANC >500/µL). Early engraftment prediction can be achieved by a marker that reflects the release of neutrophils and monocytes into the leukopenic peripheral blood.

METHODS

We analyzed blood cell parameters, including cell population data such as volume, conductivity, and light scatter in 77 patients who underwent HSCT (allogeneic, n=63; autologous, n=11) to detect possible markers.

RESULTS

We identified 2 early engraftment markers of neutrophils (NEUTRO) and monocytes (MONO); a pair of mean-volume-neutrophils (MNV) and mean-conductivity-neutrophils (MNC) for NEUTRO; and a pair of mean-volume-monocytes (MMV) and mean-conductivity-monocytes (MMC) for MONO. The new markers showed distinct patterns for early engraftment wherein 1) on the engraftment day, MNV peaked as MNC notched simultaneously for every case, and 2) MMV peaked as MMC notched simultaneously in most cases. Engraftment was predicted 3.8±2.7 days earlier than by ANC in 74 successful engraftment cases by using NEUTRO and/or MONO: 1) 72 cases (97.3%), in which NEUTRO and/or MONO predicted earlier engraftment than ANC, 2) 1 case, in which the 3 markers predicted engraftment on the same day, and 3) 1 case, in which NEUTRO predicted engraftment on the same day as ANC and MONO failed to predict engraftment.

CONCLUSIONS

By analyzing the data from daily complete blood counts, engraftment can be predicted approximately 4 days earlier than ANC >500/µL using NEUTRO as a base marker and MONO as a supplementary marker.

Human proT-cells generated in vitro facilitate hematopoietic stem cell-derived T-lymphopoiesis in vivo and restore thymic architecture

Hematopoietic stem cell transplantation (HSCT) is followed by a period of immune deficiency due to a paucity in T-cell reconstitution. Underlying causes are a severely dysfunctional thymus and an impaired production of thymus-seeding progenitors in the host. Here, we addressed whether in vitro-derived human progenitor T (proT)-cells could not only represent a source of thymus-seeding progenitors, but also able to influence the recovery of the thymic microenvironment. We examined whether co-transplantation of in vitro-derived human proT-cells with hematopoietic stem cells (HSCs) was able to facilitate HSC-derived T-lymphopoiesis posttransplant. A competitive transfer approach was used to define the optimal proT subset capable of reconstituting immunodeficient mice. Although the 2 subsets tested (proT1, CD34(+)CD7(+)CD5(-); proT2, CD34(+)CD7(+)CD5(+)) showed thymus engrafting function, proT2-cells exhibited superior engrafting capacity. Based on this, when proT2-cells were coinjected with HSCs, a significantly improved and accelerated HSC-derived T-lymphopoiesis was observed. Furthermore, we uncovered a potential mechanism by which receptor activator of nuclear factor κb (RANK) ligand-expressing proT2-cells induce changes in both the function and architecture of the thymus microenvironment, which favors the recruitment of bone marrow-derived lymphoid progenitors. Our findings provide further support for the use of Notch-expanded progenitors in cell-based therapies to aid in the recovery of T-cells in patients undergoing HSCT.

A glycosylation-dependent CD45RB epitope defines previously unacknowledged CD27⁻IgM(high) B cell subpopulations enriched in young children and after hematopoietic stem cell transplantation

The immune system is dysfunctional for years after hematopoietic stem cell transplantation (HSCT). A potential cause is an intrinsic B cell deficiency. In a cohort of pediatric HSCT patients few CD27(+) B cells formed after transplantation with the number of CD27(+)IgM(high) cells more affected than class-switched ones. A previously unacknowledged population of CD27(-)IgM(high) cells made up the majority of B cells and this population was also enlarged in healthy children compared to adults. Only a minority of these CD27(-)IgM(high) B cells expressed markers typical for transitional B cells, and the non-transitional CD27(-)IgM(high) cells could be further divided into subpopulations based on their ability to extrude the dye Rhodamine 123 and their expression of CD45RB(MEM55), a glycosylation-dependent epitope. Thus, we define several novel human CD27(-)IgM(high) B cell subpopulations in blood, all of which are present in higher frequencies and numbers in young children and after HSCT than in adults.

An anti-human thymocyte globulin-based reduced-intensity conditioning regimen is associated with a higher quality of life and lower organ toxicity without affecting lymphocyte reconstitution

Reduced-intensity (RIT) conditioning regimens are gaining increased attention as a result of their advantages and efficacy. However, no data are available regarding whether these regimens improve patient quality of life (QoL). In our study, health-related QoL (HRQoL) was retrospectively assessed in 111 patients with hematological malignancies. Analysis of the Quality of Life Questionnaire indicated that 35 of the RIT patients were able to perform their normal work and returned to their baseline levels of function 2 to 3 months after transplantation. In the myeloablative (MA) group, only 24 patients were able to resume work, and these patients returned to their baseline levels of function 6 to 8 months after transplantation (68.6% vs. 40.0%, P = 0.004). Grade III–IV organ toxicity occurred in 20% of the RIT patients and in 52% of the MA patients (P = 0.001), and the cumulative incidences of grades III–IV acute graft-versus-host disease (GVHD) were 13.7% and 35.0% in RIT and MA patients, respectively (P = 0.015). In conclusion, the RIT conditioning regimens were well tolerated by the patients, with a low incidence of transplant-related mortality (TRM) and serious acute GVHD. In addition, these regimens minimized procedure-related toxicity, improved QoL and did not influence lymphocyte reconstitution; however, OS was similar for both regimens because the relapse rate was relatively increased in the RIT groups.

Utilization of TREC and KREC quantification for the monitoring of early T- and B-cell neogenesis in adult patients after allogeneic hematopoietic stem cell transplantation

BACKGROUND

After hematopoietic stem cell transplantation (HSCT) T- and B-cell reconstitution from primary lymphoid organs are a prerequisite for an effective early lymphocyte reconstitution and a long-term survival for adult patients suffering from acute leukemia. Here, we asked whether quantification of T cell receptor excision circle, (TREC) and kappa-deleting recombination excision circle (KREC) before and within six month after allogeneic HSCT could be used to measure the thymic and bone marrow outputs in such patients.

METHODS

We used a duplex real time PCR assay to quantify the absolute copy counts of TREC and KREC, and correlated the data with absolute cell counts of CD3+CD4+ T-cell and CD19+ B-cell subsets determined by flow cytometry, respectively.

RESULTS

By comparing two recently proposed naïve T cell subsets, CD31+ naive and CD31- naive T cells, we found a better correlation for the CD31+ subset with TREC level post alloHSCT, in line with the assumption that it contained T cells recently derived from the thymus, indicating that TREC levels reflected real thymic de novo production. Transitional as well as naïve B cells highly correlated with KREC levels, which suggested an association of KREC levels with ongoing bone marrow B cell output. CD45RO+ memory T cells and CD27+ memory B cells were significantly less correlated with TREC and KREC recovery, respectively.

CONCLUSION

We conclude that simultaneous TREC/ KREC quantification is as a suitable and practicable method to monitor thymic and bone marrow output post alloHSCT in adult patients diagnosed with acute leukemia.

Changes in the number of CD8⁺ T lymphocytes in the peripheral blood of patients with various autoimmune diseases after autologous hematopoietic stem cell transplantations and their relations to the survival times

The changes in the number of CD8⁺ T lymphocytes were studied before (0 day) and then 30 days after the autologous hematopoietic stem cell transplantations (AHSCT) in 14 therapy refractory patients with autoimmune diseases. The years of survival and the clinical states were also evaluated. The number of CD8⁺ T cells was determined by an hematologic automat and by flow cytometry. Longer than 5-year survival times were found in 6 cases, whereas there was no progression (improvement) in 2 cases, and 4 patients were lost. The increase in the number of CD8⁺ cytotoxic T cells was gradual in the first 2 months and reached the significantly highest values among all subtypes of lymphocytes. It was of a special interest that in all the 4 patients who died, the numbers of CD8⁺ T cells were less than 150/μl on the 30th day after AHSCT, whereas all the 10 patients with a higher cell number survived. These results suggest that the early monitoring of the number (not only the ratio) of regenerating CD8⁺ T cells in the peripheral blood can be a useful and quantitative laboratory measurement after AHSCT, and it has a significant relation also to the survival times of transplanted patients.

Murine NK-cell licensing is reflective of donor MHC-I following allogeneic hematopoietic stem cell transplantation in murine cytomegalovirus responses

Natural killer (NK) cells express inhibitory receptors with varied binding affinities to specific major histocompatibility complex class I (MHC-I) haplotypes. NK cells can be classified as licensed or unlicensed based on their ability or inability to bind MHC-I, respectively. The role of donor vs host MHC on their development after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is not known. Following reciprocal MHC-disparate allogeneic transplants and during de novo NK-cell recovery, depletion of the licensed and not unlicensed population of NK cells as determined by the licensing patterns of donor MHC-I haplotypes, resulted in significantly increased susceptibility to murine cytomegalovirus (MCMV) infection. A corresponding expansion of the licensed Ly49H(+) NK cells occurred with greater interferon γ production by these cells than unlicensed NK cells in the context of donor MHC-I. Thus, NK licensing behavior to MCMV corresponds to the donor, and not recipient, MHC haplotype after allo-HSCT in mice.

Advances in critical care of the pediatric hematopoietic stem cell transplant patient

Hematopoietic stem cell transplant (SCT) remains a curative option for a variety of malignant and non-malignant disorders in children. Following transplant a proportion of SCT recipients become critically ill and need intensive care. Critical illness may occur in the setting of transplant complications such as graft versus host disease (GVHD), idiopathic pneumonia syndrome (IPS), veno-occlusive disease (VOD) and transplant associated thrombotic microangiopathy (TA-TMA). Hence, familiarity with recent advances in the transplant process and complications is crucial for the intensivist. This article will highlight common complications encountered in the critically ill SCT recipient.

Murine natural killer cell licensing and regulation by T regulatory cells in viral responses

Natural killer (NK) cells show differential functionality based on their capability of binding to self-MHC consistent with licensing. Here we show in vivo confirmation of the physiologic effects of licensing with differential effects of NK subsets on anti-murine cytomegalovirus (anti-MCMV) responses after syngeneic hematopoietic stem cell transplantation (HSCT) or regulatory T-cell (Treg) depletion. After HSCT, depletion of licensed NK cells led to far greater viral loads in target organs early after infection compared with nondepleted and unlicensed depleted mice. There was a preferential expansion of licensed, C-type lectin-like activating receptor Ly49H+ NK cells with increased IFNγ production after infection in nondepleted mice post-HSCT and after Treg depletion. Adoptive transfer of licensed NK subsets into immunodeficient hosts provided significantly greater MCMV resistance compared with transfer of total NK populations or unlicensed subsets. In non-HSCT mice, only concurrent depletion of Tregs or TGF-β neutralization resulted in detection of NK licensing effects. This suggests that licensed NK cells are the initial and rapidly responding population of NK cells to MCMV infection, but are highly regulated by Tregs and TGF-β.

Human T-lymphoid progenitors generated in a feeder-cell-free Delta-like-4 culture system promote T-cell reconstitution in NOD/SCID/γc(-/-) mice

Slow T-cell reconstitution is a major clinical concern after transplantation of cord blood (CB)-derived hematopoietic stem cells. Adoptive transfer of in vitro-generated T-cell progenitors has emerged as a promising strategy for promoting de novo thymopoiesis and thus accelerating T-cell reconstitution. Here, we describe the development of a new culture system based on the immobilized Notch ligand Delta-like-4 (DL-4). Culture of human CD34⁺ CB cells in this new DL-4 system enabled the in vitro generation of large amounts of T-cell progenitor cells that (a) displayed the phenotypic and molecular signatures of early thymic progenitors and (b) had high T lymphopoietic potential. When transferred into NOD/SCID/γc^−/− (NSG) mice, DL-4 primed T-cell progenitors migrated to the thymus and developed into functional, mature, polyclonal αβ T cells that subsequently left the thymus and accelerated T-cell reconstitution. T-cell reconstitution was even faster and more robust when ex vivo-manipulated and nonmanipulated CB samples were simultaneously injected into NSG mice (i.e., a situation reminiscent of the double CB transplant setting). This work provides further evidence of the ability of in vitro-generated human T-cell progenitors to accelerate T-cell reconstitution and also introduces a feeder-cell-free culture technique with the potential for rapid, safe transfer to a clinical setting.

Quantitative assessment of T cell repertoire recovery after hematopoietic stem cell transplantation

Delayed T-cell recovery and restricted T-cell receptor (TCR) diversity after allogeneic hematopoietic stem cell transplantation (allo-HSCT) are associated with increased risks of infection and cancer relapse. Technical challenges have limited faithful measurement of TCR diversity following allo-HSCT. Here we combined 5′-RACE PCR with deep sequencing, to quantify TCR diversity in 28 allo-HSCT recipients using a single oligonucleotide pair. Analysis of duplicate blood samples confirmed that the frequency of individual TCRs was accurately determined. After 6 months, cord blood graft recipients approximated the TCR diversity of healthy individuals, whereas recipients of T-cell-depleted peripheral blood stem cell grafts had a 28-fold and 14-fold lower CD4⁺ and CD8⁺ T-cell diversity, respectively. After 12 months, these deficiencies had improved for the CD4⁺, but not the CD8⁺ T-cell compartment. Overall, this method provides unprecedented views of T-cell repertoire recovery after allo-HSCT and may identify patients at high risk of infection or relapse.

MicroRNA regulation of natural killer cells

Natural killer (NK) cells are innate immune lymphocytes critical for host defense against viral infection and surveillance against malignant transformation. MicroRNAs (miRNAs) are a family of small, non-coding RNAs that regulate a wide variety of cellular processes. Recent advances have highlighted the importance of miRNA-mediated post-transcriptional regulation in NK cell development, maturation, and function. This review focuses on several facets of this regulatory mechanism in NK cells: (1) the expressed NK cell miRNA transcriptome; (2) the impact of total miRNA deficiency on NK cells; (3) the role of specific miRNAs regulating NK cell development, survival, and maturation; (4) the intrinsic role of miRNAs regulating NK cell function, including cytokine production, proliferation, and cytotoxicity; and (5) the role of NK cell miRNAs in disease. Currently our knowledge of how miRNAs regulate NK cell biology is limited, and thus we also explore key open questions in the field, as well as approaches and techniques to ascertain the role of individual miRNAs as important molecular regulators.

Immune reconstitution and graft-versus-host reactions in rat models of allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) extends the lives of thousands of patients who would otherwise succumb to hematopoietic malignancies such as leukemias and lymphomas, aplastic anemia, and disorders of the immune system. In alloHCT, different immune cell types mediate beneficial graft-versus-tumor (GvT) effects, regulate detrimental graft-versus-host disease (GvHD), and are required for protection against infections. Today, the “good” (GvT effector cells and memory cells conferring protection) cannot be easily separated from the “bad” (GvHD-causing cells), and alloHCT remains a hazardous medical modality. The transplantation of hematopoietic stem cells into an immunosuppressed patient creates a delicate environment for the reconstitution of donor blood and immune cells in co-existence with host cells. Immunological reconstitution determines to a large extent the immune status of the allo-transplanted host against infections and the recurrence of cancer, and is critical for long-term protection and survival after clinical alloHCT. Animal models continue to be extremely valuable experimental tools that widen our understanding of, for example, the dynamics of post-transplant hematopoiesis and the complexity of immune reconstitution with multiple ways of interaction between host and donor cells. In this review, we discuss the rat as an experimental model of HCT between allogeneic individuals. We summarize our findings on lymphocyte reconstitution in transplanted rats and illustrate the disease pathology of this particular model. We also introduce the rat skin explant assay, a feasible alternative to in vivo transplantation studies. The skin explant assay can be used to elucidate the biology of graft-versus-host reactions, which are known to have a major impact on immune reconstitution, and to perform genome-wide gene expression studies using controlled combinations of minor and major histocompatibility between the donor and the recipient.

Restoration of immune system function is accelerated in immunocompromised mice by the B-cell-tropic isoxazole R-11

BACKGROUND

Restoration of impaired immune response in immunocompromised patients is a crucial problem. In this study we evaluated the efficacy of isoxazole R-11 in reconstitution of the immune response in immunosuppressed mice.

METHODS

Mice were given a sublethal dose (250 mg/kg b.w.) of cyclophosphamide (CP). The cellular immune response to ovalbumin (OVA) and the humoral immune response to sheep erythrocytes (SRBC) were generated. R-11 was administered at repetitive, intraperitoneal doses (20 μg/mouse) until determination of the immune responses: 7 and 15 doses on alternate days for cellular and humoral immune response, respectively. For phenotypic studies R-11 was given per os, at a single dose of 20 μg/mouse. The ability of R-11 to affect interleukin- 6 (IL-6) production was determined in the whole human blood cell culture.

RESULTS

R-11 increased the content of CD19+ cells in the spleens and lymph nodes with a concomitant decrease of CD3+ and CD4+ cells. The compound significantly accelerated restoration of both cellular and humoral immune responses, elevated the numbers of circulating leukocytes and splenocytes and normalized the blood cell picture. Supplementary experiments showed that R-11 was not toxic with regard to human peripheral blood mononuclear cells (PBMC) and that it upregulated IL-6 production in blood cell culture stimulated with lipopolysaccharide (LPS).

CONCLUSIONS

We demonstrated that R-11 is likely a B-cell tropic agent which can restore both cellular and humoral immune responses in immunocompromised mice and may have a potential to be applied in therapy of immunocompromised patients.

Treatment with low doses of polyclonal immunoglobulin improves B cell function during immune reconstitution in a murine model

PURPOSE

[corrected] After autologous stem cell transplantation (ASCT) the immunological B cell compartment recovers slowly. Delays on the recovery of B cell function after autologous stem cell transplantation are due to the low lymphocytes count and to their intrinsic dysfunction.

METHODS

We studied the in vivo B cell reconstitution after ASCT examining the independent effect of polyclonal IgG (PolyIg), Fab or Fc fragments infusions in a murine animal model during a period of 12 weeks. These molecules were used in low doses, mimicking the recommended use of IVIg in the case of hypogammaglobulinemia in humans. Flow cytometry analysis and ELISA tests were conducted to monitor the reconstitution of B cells and serum immunoglobulin production. Panama blot and PCA factor 1 analysis were used to study the kinetics of immunoglobulin repertoires reconstitution. Mechanistic studies were also performed using in vitro cell culture.

RESULTS

During follow-up after ASCT, peripheral B cells expand independently of treatment, correcting the immediate increase in sBAFF (soluble B cell activating factor) induced by previous intense myeloablation. Treatments with Fab and Fc fragments infusions promote significant IgM and IgG production comparing to control. Although the complete recovery of antibody repertoire is only achieved at the end of follow-up after ASCT, there is an earlier and significantly stronger recovery in the treated mice, which is evident at 9 weeks after ASCT. At 30 weeks after ASCT, normal values of antibody repertoire were detected in all individuals. Mechanistic studies show that Fab and Fc fragments promote IgG1 production by indirect pathways.

CONCLUSIONS

The results presented here demonstrate that polyclonal immunoglobulin indirectly improves the function of the reconstituted B cells and their IgG production by means of Fc-mediated effects on bystander cells. These results further stimulate the discussion about the advantages of IVIg therapy during immune reconstitution after human ASCT.

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.

Co-transplantation of pure blood stem cells with antigen-specific but not bulk T cells augments functional immunity

Impaired immunity is a fundamental obstacle to successful allogeneic hematopoietic cell transplantation. Mature graft T cells are thought to provide protection from infections early after transplantation, but can cause life-threatening graft-vs.-host disease. Human CMV is a major pathogen after transplantation. We studied reactivity against the mouse homologue, murine CMV (MCMV), in lethally irradiated mice given allogeneic purified hematopoietic stem cells (HSCs) or HSCs supplemented with T cells or T-cell subsets. Unexpectedly, recipients of purified HSCs mounted superior antiviral responses compared with recipients of HSC plus unselected bulk T cells. Furthermore, supplementation of purified HSC grafts with CD8(+) memory or MCMV-specific T cells resulted in enhanced antiviral reactivity. Posttransplantation lymphopenia promoted massive expansion of MCMV-specific T cells when no competing donor T cells were present. In recipients of pure HSCs, naive and memory T cells and innate lymphoid cell populations developed. In contrast, the lymphoid pool in recipients of bulk T cells was dominated by effector memory cells. These studies show that pure HSC transplantations allow superior protective immunity against a viral pathogen compared with unselected mature T cells. This reductionist transplant model reveals the impact of graft composition on regeneration of host, newly generated, and mature transferred T cells, and underscores the deleterious effects of bulk donor T cells. Our findings lead us to conclude that grafts composed of purified HSCs provide an optimal platform for in vivo expansion of selected antigen-specific cells while allowing the reconstitution of a naive T-cell pool.

Rapid thymic reconstitution following bone marrow transplantation in neonatal mice is VEGF-dependent

Age-related differences in thymic function influence the rapidity of T cell reconstitution following hematopoietic stem cell transplantation (HSCT). In adults, thymic reconstitution is delayed until after marrow engraftment is established, and is significantly improved by approaches that increase marrow chimerism, such as pretransplantation irradiation. In contrast, we show that neonatal mice undergo more rapid and efficient thymic reconstitution than adults, even when bone marrow (BM) engraftment is minimal and in the absence of pretransplantation radiation. We have previously shown that the neonatal thymus produces high levels of vascular endothelial growth factor (VEGF) that drives angiogenesis locally. In this report, we show that inhibition of VEGF prior to HSCT prevents rapid thymic reconstitution in neonates, but has no effect on thymic reconstitution in adults. These data suggest that the early radiation-independent thymic reconstitution unique to the neonatal host is mediated through VEGF, and reveals a novel pathway that might be targeted to improve immune reconstitution post-HSCT.

Translational Mini-Review Series on B cell subsets in disease. Reconstitution after haematopoietic stem cell transplantation - revelation of B cell developmental pathways and lineage phenotypes

Haematopoietic stem cell transplantation (HSCT) is an immunological treatment that has been used for more than 40 years to cure a variety of diseases. The procedure is associated with serious side effects, due to the severe impairment of the immune system induced by the treatment. After a conditioning regimen with high-dose chemotherapy, sometimes in combination with total body irradiation, haematopoietic stem cells are transferred from a donor, allowing a donor-derived blood system to form. Here, we discuss the current knowledge of humoral problems and B cell development after HSCT, and relate these to the current understanding of human peripheral B cell development. We describe how these studies have aided the identification of subsets of transitional B cells and also a robust memory B cell phenotype.

Immunological reconstitution after autologous stem cell transplantation in patients with refractory systemic autoimmune diseases

OBJECTIVE

High-dose chemotherapy followed by autologous haematopoietic stem cell transplantation (AHSCT) can be a salvage therapy for patients with severe, refractory systemic autoimmune diseases. The function of the newly rebuilt immune system is important, but little is known about immune reconstitution after AHSCT in autoimmune disorders. Our aim was to investigate the repopulation of different lymphocyte subsets in patients with systemic autoimmune diseases after AHSCT.

METHODS

Twelve patients with severe refractory, autoimmune diseases were enrolled in the study: four with rheumatoid arthritis (RA), four with systemic sclerosis (SSc), three with systemic lupus erythematosus (SLE), and one with autoimmune overlap syndrome (myositis and RA). After stem-cell mobilization, CD34+ apheresis was carried out, followed by conditioning and AHSCT. After transplantation, peripheral lymphocyte subsets were regularly assessed by flow cytometry.

RESULTS

The follow-up time was 24 months. The overall transplantation-related mortality (TRM) was 16.7% and the transplant-related toxicity was 33% 2 years after AHSCT. Regarding the immune reconstitution, CD56+ natural killer (NK) cells appeared in the earliest phase after transplantation, followed by CD8+ T cells. B cells and CD4+ T cells became normal within 150 days. The ratio of naive cells was low 30 days after AHSCT; however, naive B cells regenerated within 2 months whereas the repopulation of naive T cells took longer. After a short increase, the ratio of memory cells decreased 2 months after transplantation. Regulatory T (Treg) cells did not change significantly in the peritransplant period. Altogether approximately 5-6 months were required for the reconstitution of the peripheral immune network.

CONCLUSIONS

AHSCT can be a salvage therapeutic modality in autoimmune patients who are refractory to other conventional therapies.

Hydrodynamic delivery of human IL-15 cDNA increases murine natural killer cell recovery after syngeneic bone marrow transplantation

Immune deficiency immediately following bone marrow transplantation (BMT) increases susceptibility to opportunistic infections as well as tumor relapse. Natural Killer (NK) cells play important roles in the resistance to virally infected and transformed cells. Interleukin (IL)-15 has been shown to be essential for NK cell development and survival. We administered human (h) IL-15 cDNA (pIL-15) via hydrodynamic delivery to murine recipients undergoing congenic BMT to determine its effects on NK cell reconstitution. Hydrodynamic pIL-15 delivery resulted in high levels of hIL-15 protein in the serum that lasted for several days and then quickly declined. The appearance of hIL-15 was followed by a significant increase of mature donor-derived NK cells within the bone marrow, spleens, and livers of the treated recipients. No accumulation of immature NK cell progenitors was observed. The NK cells from IL-15-treated recipients displayed an activated phenotype and were lytically active toward tumor targets in vitro to a similar degree as did those cells from recipients treated with control plasmid. This suggests that the predominant effect of IL-15 was a quantitative increase in total NK cell numbers and not qualitative changes in NK cell functions. No toxicities or adverse effects were observed. Studies performed in transplanted mice bearing renal carcinoma tumors demonstrated that this mode of hIL-15 gene delivery resulted in increased antitumor responses. These results support the use of cytokine gene transfer-based regimens as a platform to augment NK cell recovery after BMT.