T-Cell Receptor Vbeta Repertoire after Myeloablative and Reduced Intensity Conditioning Allogeneic Haematopoietic Stem Cell Transplantation

IL-7 Is the Limiting Homeostatic Factor that Constrains Homeostatic Proliferation of CD8+ T Cells after Allogeneic Stem Cell Transplantation and Graft-versus-Host Disease

Immune reconstitution after allogeneic hematopoietic stem cell transplantation relies primarily on homeostatic proliferation (HP) of mature T lymphocytes, but this process is typically impaired during graft-versus-host disease (GVHD). We previously showed that low IL-7 levels combined with lack of dendritic cell (DC) regeneration constrain CD4⁺ T cell HP during GVHD. However, it is not clear whether these alterations to the peripheral CD4⁺ T cell niche also contribute to impair CD8⁺ T cell regeneration during GVHD. We found that IL-7 therapy was sufficient for restoring CD8⁺ T cell HP in GVHD hosts while forcing DC regeneration with Flt3-L had only a modest effect on CD8⁺ T cell HP in IL-7 treated mice. Using bone marrow chimeras, we showed that HP of naïve CD8⁺ T cells is primarily regulated by MHC class I on radio-resistant stromal cells, yet optimal recovery of CD8⁺ T cell counts still requires expression of MHC class I on both radio-resistant and radio-sensitive hematopoietic cells. Thus, IL-7 level is the primary limiting factor that constrains naïve CD8⁺ T cell HP during GVHD, and accessibility of MHC class I on stromal cells explains how IL-7 therapy, as a single agent, can induce robust CD8 ⁺ T cell HP in the absence of DCs.

Thymic Activity and T Cell Repertoire Recovery after Autologous Hematopoietic Stem Cell Transplantation Preceded by Myeloablative Radiotherapy or Chemotherapy

It was previously postulated that pretransplant myeloablative treatment may impair thymopoiesis, contributing in this way to delayed reconstitution of T cells after hematopoietic stem cell transplantation (HSCT). On the other hand, de novo generation of T cells after HSCT requires a competent thymus. Various myeloablative conditioning regimens (total body irradiation [TBI] or high-dose chemotherapy) routinely used in clinical practice may have potentially different impacts on the thymus. However, no comparative study on thymic output and T cell repertoire in autologous (auto)HSCT model has been presented so far. Here we evaluated thymic output and TCR diversity in 45 lymphoma patients submitted to autoHSCT differing in respect to conditioning regimen: high-dose chemotherapy as monotherapy (BEAM, n = 22) or combination of total body irradiation with cyclophosphamide chemotherapy: Cy/TBI (n = 23). Thymic output was assessed before and on days +100, +180, and +365 after autoHSCT by flow cytometric counts of recent thymic emigrant (RTE) cells (CD31(+) CD62L(+) CD45RA(+) CD4(+)) and quantification of signal joint TCR receptor excision circles (sjTRECs) by quantitative PCR. T cell repertoire diversity was analyzed on day +365 after autoHSCT by spectra-typing of the CDR3 region in the TCRVβ chain. The BEAM group, in contrast to the Cy/TBI group, manifested significantly higher proportions of RTE cells and sjTREC copy numbers on days +100 and +180. Analysis of TCRVβ spectra-types on day +365 revealed more restricted (monoclonal or oligoclonal) T cell repertoires in the Cy/TBI versus BEAM group (48.8% versus 18.2%, P = .0002). In conclusion, the conditioning scheme based on BEAM chemotherapy may be performed with lower risk of thymic destruction and T cell repertoire distortion than Cy/TBI scheme. This finding may help to potentially improve conditioning schemes to efficiently perform myeloablation and maintain active thymopoiesis.

T-cell receptor repertoire usage in hematologic malignancies

Over the last few years several studies have addressed the possible influence of different immune mechanisms on the evolution of hematologic malignancies. More specifically, a fundamental role of reactive T-cells has now been demonstrated in the pathogenesis of many of these disorders as well as in the typical immunological milieu observed after stem cell transplantation in patients affected by these malignancies. In this context the study of the T-cell receptor (TCR) repertoire performed by different techniques, such as for instance flow cytometry and spectratyping, has undoubtedly provided a fundamental contribution. More recently, these seminal observations have even opened new potential therapeutic avenues based on the employment of adoptive T-cells somehow engineered toward potential neoplastic targets. This review will run through the most relevant studies which have tried to dissect the TCR repertoire usage in patients with different hematologic malignancies, especially focusing on the possible pathogenetic and therapeutic implications.

Impact of lymphocyte and monocyte recovery on the outcomes of allogeneic hematopoietic SCT with fludarabine and melphalan conditioning

We have recently shown that lymphocyte and monocyte recovery by day +100 are associated with survival post myeloablative allogeneic hematopoietic transplant for acute leukemia. We hypothesized that lymphocyte and monocyte recovery would have a similar impact on survival in the reduced intensity setting. To test this hypothesis, we analyzed clinical data from 118 consecutive fludarabine/melphalan-conditioned patients by correlating peripheral blood absolute lymphocyte counts and monocyte counts (ALC and AMC, respectively) at days +15, +30, +60 and +100 with the outcomes. Multivariate analysis revealed that day +100 AMC (risk ratio (RR) 0.22, 95% confidence interval (CI) 0.07-0.73, P=0.01) and mild chronic GVHD (RR 0.09, 95% CI 0.005-0.43, P=0.008) were independently associated with survival. To explore whether the patterns of lymphocyte and monocyte recovery had a prognostic value, we performed unsupervised hierarchical clustering on the studied hematopoietic parameters and identified three patient clusters, A-C. Patient clusters A and B both had improved OS compared with cluster C (77.8 months vs not reached vs 22.3 months, respectively, P<0.001). No patient in cluster C had a day +100 AMC >300. Both severe acute GVHD and relapse occurred more frequently in cluster C. Our data suggest that patients with low AMC by day +100 post fludarabine/melphalan-conditioned allogeneic hematopoietic SCT may be at risk for poor outcomes.

A potential role for B cells in suppressed immune responses in cord blood transplant recipients

We evaluated immune reconstitution in 58 adults who received hematopoietic stem cell transplants from allogeneic siblings (allosib), matched unrelated donors (MUD), or cord blood (CB) at 90-day intervals for one year post-transplant. CB recipients had a higher incidence of infections in the first 100 days compared to allosib and MUD recipients. The number of circulating T cells was lower in CB recipients compared to MUD recipients at 90 days and compared to allosib recipients at 180 days. Spectratype analysis of the TCR Vβ complementarity determining region 3 (CDR3) of patient lymphocytes revealed that the TCR repertoire remained poorly diversified even at 360 days in nearly all patients. In contrast, the number of circulating B cells was significantly elevated in CB recipients compared to allosib recipients throughout the first year post-transplant and compared to MUD recipients at 9-12 months. Spectratype analysis of the B cell receptor V_H CDR3 showed that the B cell repertoire was diversified in most patients by 90 days. CD5^pos B cells from assayed CB recipients expressed intracellular IL-10 early post-transplant. Our data suggest that B cells, in addition to T cells, may play a role in impaired immune responses in CB transplant patients.

Clinical expansion of cord blood-derived T cells for use as donor lymphocyte infusion after cord blood transplantation

Allogeneic stem cell transplantation (SCT) from cord blood (CB) as a stem cell source is a promising alternative when no human leukocyte antigen-matched donor is found. Donor lymphocyte infusion (DLI) is a possible treatment modality for threatening graft failure or relapse of an underlying malignancy after transplantation. Ethical and logistical reasons limit the possibility of DLI in the setting of CB SCT. To remedy this restriction, we performed expansion of donor T cells in vitro from CB grafts in a clinical setting for use as future DLI and characterized the expanded cells in comparison to T cells from CB acquired ex vivo and adult peripheral blood. T cells were expanded from grafts used for transplantation, upon CD3/CD28 crosslinking and culture in interleukin-2. Phenotype and function of T cells were assessed by flow cytometry and mixed lymphocyte culture assays. T-cell receptor repertoire distribution was evaluated with polymerase chain reaction-based spectratyping. We were able to amplify T cells to sufficient amounts for DLI in 13 out of 13 initiated expansions. Expanded T cells presented with an activated phenotype and could be induced to produce cytokines by a nonspecific stimulus. When exposed to allogeneic targets, expanded CB T cells proliferated at comparable levels to their ex vivo and adult blood counterparts. In summary, clinical expansion of CB T cells for DLI is feasible and may be a future modality for treatment of graft failure or relapse after SCT.

The immunopathology of thymic GVHD

The clinical success of allogeneic hematopoietic stem cell transplantation (HSCT) depends on the appropriate reconstitution of the host's immune system. While recovery of T-cell immunity may occur in transplant recipients via both thymus-dependent and thymus-independent pathways, the regeneration of a population of phenotypically naive T cells with a broad receptor repertoire relies entirely on the de novo generation of T-cells in the thymus. Preclinical models and clinical studies of allogeneic HSCT have identified the thymus as a target of graft-versus-host disease (GVHD), thus limiting T-cell regeneration. The present review focuses on recent insight into how GVHD affects thymic structure and function and how this knowledge may aid in the design of new strategies to improve T-cell reconstitution following allogeneic HSCT.

Chimerism and T-cell receptor repertoire analysis after unrelated cord blood transplantation with a reduced-intensity conditioning regimen following autologous stem cell transplantation for multiple myeloma

A 65-year-old Japanese male was diagnosed as multiple myeloma with Bence Jones kappa type, clinical stage IIIA. His disease status reached partial remission after chemotherapy. Thereafter, he received tandem transplantation, consisting of high-dose chemotherapy with autologous stem cell transplantation (ASCT), followed by unrelated cord blood transplantation (U-CBT). U-CBT with a reduced-intensity conditioning regimen (RI-CBT) was performed in August 2003. HLA mismatch between the patient and the CBT donor was present at two serological loci (B and DR). A total nucleated CBT cell dose of 2.45 x 10(7)/kg body weight was infused on day 0. Graft-vs.-host disease (GVHD) prophylaxis consisted of cyclosporine A and short-term methotrexate. Neutrophil engraftment (>0.5 x 10(9)/l) was obtained on day 46. He developed positive cytomegalovirus antigenemia, grade II acute GVHD involving skin and liver, varicella-zoster virus infection, septic shock, hemorrhagic cystitis caused by adenovirus and acute hepatitis B virus infection after U-CBT. We retrospectively analyzed T-cell receptor (TCR) repertoire diversity and found that TCR repertoire diversity decreased continuously after U-CBT. Therefore, low-TCR repertoire diversity in this patient appears to be associated with various infections caused by immunodeficiency.

TCR spectratyping revealed T lymphocytes associated with graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Clonal expansion of T cells after allogeneic hematopoietic stem cell transplantation (allo-HSCT) has been observed, but their characteristics remain to be fully elucidated. We report here that CD8(+) T cells were the dominant T lymphocytes seen and T-cell repertoire diversity decreased dramatically during the first 3 months after allo-HSCT. Patients with GVHD grade II - IV had significantly lower T-cell repertoire diversity compared with non-GVHD patients. TCR beta variable gene (TCRBV) subfamily 8, 5.1, 5.2, 4, and 13 were the five most frequently expanded subfamilies among these patients. Among the 49 over-expanded clones identified, clonotype "TCR3-5" and "TCR18-5" were isolated from four patients with HLA-A2 allele and skin GVHD. Their frequencies correlated well with skin symptoms (i.e. rash). Moreover, they were detected in donors but not detected in recipients before transplantation. Lastly, three common TCRBV CDR3 motifs shared by T cells related with GVHD were discovered: TGDS, GLAG, and GGG. These findings suggest that TCR spectratyping is helpful for revealing GVHD-related T cells and may have utility in early diagnosis.