Daniela Montagna

Human Bone Marrow–Derived Mesenchymal Stem Cells Do Not Undergo Transformation after Long-term In vitro Culture and Do Not Exhibit Telomere Maintenance Mechanisms

Significant improvement in the understanding of mesenchymal stem cell (MSC) biology has opened the way to their clinical use. However, concerns regarding the possibility that MSCs undergo malignant transformation have been raised. We investigated the susceptibility to transformation of human bone marrow (BM)-derived MSCs at different in vitro culture time points. MSCs were isolated from BM of 10 healthy donors and propagated in vitro until reaching either senescence or passage (P) 25. MSCs in the senescence phase were closely monitored for 8 to 12 weeks before interrupting the cultures. The genetic characterization of MSCs was investigated through array-comparative genomic hybridization (array-CGH), conventional karyotyping, and subtelomeric fluorescent in situ hybridization analysis both before and after prolonged culture. MSCs were tested for the expression of telomerase activity, human telomerase reverse transcriptase (hTERT) transcripts, and alternative lengthening of telomere (ALT) mechanism at different passages. A huge variability in terms of proliferative capacity and MSCs life span was noted between donors. In eight of 10 donors, MSCs displayed a progressive decrease in proliferative capacity until reaching senescence. In the remaining two MSC samples, the cultures were interrupted at P25 to pursue data analysis. Array-CGH and cytogenetic analyses showed that MSCs expanded in vitro did not show chromosomal abnormalities. Telomerase activity and hTERT transcripts were not expressed in any of the examined cultures and telomeres shortened during the culture period. ALT was not evidenced in the MSCs tested. BM-derived MSCs can be safely expanded in vitro and are not susceptible to malignant transformation, thus rendering these cells suitable for cell therapy approaches.

Anti-leukemia activity of alloreactive NK cells in KIR ligand-mismatched haploidentical HSCT for pediatric patients: evaluation of the functional role of activating KIR and redefinition of inhibitory KIR specificity

We analyzed 21 children with leukemia receiving haploidentical hematopoietic stem cell transplantation (haplo-HSCT) from killer immunoglobulin (Ig)-like receptors (KIR) ligand-mismatched donors. We showed that, in most transplantation patients, variable proportions of donor-derived alloreactive natural killer (NK) cells displaying anti-leukemia activity were generated and maintained even late after transplantation. This was assessed through analysis of donor KIR genotype, as well as through phenotypic and functional analyses of NK cells, both at the polyclonal and clonal level. Donor-derived KIR2DL1(+) NK cells isolated from the recipient displayed the expected capability of selectively killing C1/C1 target cells, including patient leukemia blasts. Differently, KIR2DL2/3(+) NK cells displayed poor alloreactivity against leukemia cells carrying human leukocyte antigen (HLA) alleles belonging to C2 group. Unexpectedly, this was due to recognition of C2 by KIR2DL2/3, as revealed by receptor blocking experiments and by binding assays of soluble KIR to HLA-C transfectants. Remarkably, however, C2/C2 leukemia blasts were killed by KIR2DL2/3(+) (or by NKG2A(+)) NK cells that coexpressed KIR2DS1. This could be explained by the ability of KIR2DS1 to directly recognize C2 on leukemia cells. A role of the KIR2DS2 activating receptor in leukemia cell lysis could not be demonstrated. Altogether, these results may have important clinical implications for the selection of optimal donors for haplo-HSCT.

Analysis of immune reconstitution in children undergoing cord blood transplantation

OBJECTIVE The aim of this study was to investigate and compare immune reconstitution in allogeneic cord blood transplantation (CBT) and bone marrow transplantation (BMT) recipients. MATERIALS AND METHODS Twenty-three children underwent CBT from either human leukocyte antigen-identical siblings (11 cases) or unrelated donors (12 cases) were enrolled in the study, together with 23 matched children receiving BMT. Patients were analyzed 2-3 and 12-15 months after transplant. Recovery of T-, B-, and NK-lymphocyte subsets, proliferative in vitro response to mitogens, as well as cytotoxic activities, were investigated. RESULTS CBT recipients showed a marked increase in the number of B lymphocytes as compared with patients who underwent BMT (p < 0.001). The absolute number of CD3(+) and CD8(+) T cells, as well as the proliferative response to T-cell mitogens, recovered with time after transplantation, irrespective of the source of stem cells used. Recipients of unrelated CBT had a better recovery of CD4(+) T lymphocytes (p < 0.01). Among patients experiencing acute graft-versus-host disease (GVHD), children given CBT had a much greater production of CD4(+) CD45RA(+) T cells than BMT recipients (p < 0.005). Recovery of NK cell number and innate cytotoxic activities was fast, irrespective of the source of stem cells used. CONCLUSIONS Despite the much lower number of lymphocytes transferred with the graft, recovery of lymphocyte number and function toward normal in CBT recipients was rapid and comparable to that observed after transplantation of bone marrow progenitors. This prompt immune recovery possibly was favored by the reduced incidence and severity of GVHD observed in children who underwent CBT.

Neonatal invariant Vα24+ NKT lymphocytes are activated memory cells

NKT cells are a small subset of T lymphocytes which express an invariant Vα24JαQ TCR and recognize glycolipids presented by CD1d. In adults, NKT cells have a memory phenotype, frequently associated with oligoclonal expansion, express NK cell markers, and produce T0 cytokines upon primary stimulation. Because of these features, NKT cells are regarded as lymphocytes of innate immunity. We investigated NKT cells from cord blood to see how these cells appear in the absence of exogenous stimuli. We found that NKT cells are present at comparable frequencies in cord blood and adult peripheral blood mononuclear cells and in both cases display a memory (CD45RO+CD62L–) phenotype. However, neonatal NKT cells differ from their adult counterparts by the following characteristics: (1) they express markers of activation, such as CD25; (2) they are polyclonal; (3) they do not produce cytokines in response to primary stimulation. Together, our data show that human NKT cells arise in the newborn with an activated memory phenotype, probably due to recognition of an endogenous ligand(s). The absence of oligoclonal expansion and primary effector functions also suggest that neonatal NKT cells, despite their activated memory phenotype, require a further priming / differentiation event to behave as fully functional cells of innate immunity.

Marked and sustained improvement two years after autologous stem cell transplantation in a girl with systemic sclerosis

Autologous transplantation of hematopoietic stem cells has recently been proposed as a possible treatment for autoimmune diseases that are associated with a very severe prognosis. A 12-year-old girl who, since 4 years of age, had systemic sclerosis with progressive pulmonary involvement underwent autologous peripheral blood-derived stem cell transplantation (aPBSCT) using CD34+ selection, cyclophosphamide, and the infusion of the monoclonal antibody CAMPATH-1G. Following transplantation, in the absence of any treatment other than symptomatic therapy, the patients exertional dyspnea and alveolitis disappeared and she experienced a marked improvement in skin score, height velocity, and general well-being that has persisted 2 years after the transplantation procedure. Autologous PBSCT associated with the infusion of the monoclonal antibody CAMPATH-1G appears to be a useful therapy for otherwise intractable forms of progressive systemic sclerosis.

Donor/recipient mixed chimerism does not predict graft failure in children with β-thalassemia given an allogeneic cord blood transplant from an HLA-identical sibling

This study indicates that mixed chimerism is a frequent event and does not predict the occurrence of graft failure in children with thalassemia major given a cord blood transplant from an HLA-identical sibling. See related perspective article on page 1780. Background Donor/recipient mixed chimerism has been reported to be associated with an increased risk of graft failure in patients with β-thalassemia given a bone marrow transplant. We investigated the relationship between the degree of mixed chimerism over time and clinical outcome of children undergoing cord blood transplantation for β-thalassemia. Design and Methods Twenty-seven consecutive children given a cord blood transplant from a related donor were analyzed by short tandem repeat polymerase chain reaction and their chimerism results were compared with those of 79 consecutive patients who received a bone marrow transplant from either a relative (RD-BMT, n=42) or an unrelated donor (UD-BMT, n=37). Cord blood and bone marrow recipients received comparable preparative regimens. Results All cord blood recipients engrafted and displayed mixed chimerism early after transplantation; 13/27 converted to full donor chimerism over time, while 14 maintained stable mixed chimerism; all patients are alive and transfusion-independent. Twenty-four of the 79 bone marrow-recipients (12 UD- and 12 RD-BMT) exhibited full donor chimerism at all time points examined, 4/79 (2 UD- and 2 RD-BMT) did not engraft and 51/79 (23 UD- and 28 RD-BMT) displayed mixed chimerism at the time of hematologic reconstitution. Forty of 51 bone marrow recipients with mixed chimerism converted to full donor chimerism (17 UD- and 23 RD-BMT), 3/51 maintained stable mixed chimerism (1 UD- and 2 RD-BMT), while 8/51 (5 UD- and 3 RD-BMT) progressively lost the graft, and became transfusion-dependent again. Conclusions Mixed chimerism is a frequent event and does not predict the occurrence of graft failure in children with β-thalassemia given a cord blood transplant from a relative.

An improved PCR-heteroduplex method permits high-sensitivity detection of clonal expansions in complex T cell populations

We have modified the PCR-heteroduplex technique to render it more suitable for the study of the clonal make up of complex T cell populations. This technique is based on separate PCR amplifications of all the TCR V beta genes expressed by a polyclonal T cell sample, followed by a heteroduplex reaction of the PCR products and a gel separation. Our modification involves performing each heteroduplex reaction in the presence of excess carrier DNA, which is the PCR product of a cloned TCR V beta cDNA having the same variable and constant region of the amplified V beta family, but a different N region. In this way, every clonotypic V beta chain that is amplified in the polyclonal mixture forms a unique and reproducible pair of heteroduplex bands with the carrier DNA. This molecular footprint permits the identification of a given T cell clone over time, or in different anatomical sites. The specificity and sensitivity of the detection of T cell clones can be further increased by hybridising the blotted heteroduplex gel with oligonucleotides specific for either a TCR V beta N region or the carrier DNA. In conclusion, we have developed a simple and reproducible technique that permits the simultaneous detection of the expanded T cell clones present in heterogeneous T cell populations in a very specific and sensitive manner.

Invariant NKT cell reconstitution in pediatric leukemia patients given HLA-haploidentical stem cell transplantation defines distinct CD4+ and CD4- subset dynamics and correlates with remission state.

Immune reconstitution plays a crucial role on the outcome of patients given T cell-depleted HLA-haploidentical hematopoietic stem cell transplantation (hHSCT) for hematological malignancies. CD1d-restricted invariant NKT (iNKT) cells are innate-like, lipid-reactive T lymphocytes controlling infections, cancer, and autoimmunity. Adult mature iNKT cells are divided in two functionally distinct CD4+ and CD4− subsets that express the NK receptor CD161 and derive from thymic CD4+CD161− precursors. We investigated iNKT cell reconstitution dynamics in 33 pediatric patients given hHSCT for hematological malignancies, with a follow-up reaching 6 y posttransplantation, and correlated their emergence with disease relapse. iNKT cells fully reconstitute and rapidly convert into IFN-γ–expressing effectors in the 25 patients maintaining remission. CD4+ cells emerge earlier than the CD4− ones, both displaying CD161− immature phenotypes. CD4− cells expand more slowly than CD4+ cells, though they mature with significantly faster kinetics, reaching full maturation by 18 mo post-hHSCT. Between 4 and 6 y post-hHSCT, mature CD4− iNKT cells undergo a substantial expansion burst, resulting in a CD4+<CD4− NKT cell ratio similar to that found in healthy adults. In contrast with patients maintaining remission, iNKT cells failed to reconstitute in all eight patients experiencing disease relapse. These findings define the peripheral dynamics of human iNKT cells and suggest a contribution of these cells to maintain remission, possibly via early IFN-γ provision. Adoptive transfer of donor-derived iNKT cells into HLA-haploidentical patients failing to reconstitute these cells might represent a novel therapeutic option to prevent leukemia recurrence.

Characterisation of CTL directed towards non-inherited maternal alloantigens in human cord blood

Allogeneic cord blood transplantation (CBT), especially from unrelated donors, is being increasingly used for treating paediatric patients with both malignant and non-malignant disorders. Recent clinical and experimental evidence suggests that human cord blood mononuclear cells (CBMC) may acquire in utero a state of tolerance towards non-inherited maternal antigens (NIMA). In order to better define this phenomenon, we measured, by means of a limiting dilution assay (LDA), the frequency of NIMA-specific CTL precursors (CTLp) in cord blood samples obtained from 13 healthy neonates. The immunophenotype of the effector cells recovered from LDA was also analysed. Data concerning both CTLp frequency and phenotype of effector cells were compared with those obtained stimulating CBMC with cells of paternal origin (NIPA) and adult PBMC with allogeneic targets. Results showed that cytotoxic cells directed towards cells of maternal origin could be detected in all cord blood samples tested. Phenotype analysis demonstrated that NIPA elicit the expansion of CD3+/CD8bright T cells, a phenotype associated with alloreactive CTL. By contrast, NIMA preferentially stimulated the expansion of CD3−/CD8dim+ cells, a phenotype associated with NK cells, which are known to be able, in certain clinical conditions, to kill allogeneic haematopoietic cells without causing GVHD. Thus, our results indicate that, when evaluated in a limiting dilution condition, NIMA-reactive cord blood cells are detectable and a preferential expansion of NK cells is observed.

A novel self-lipid antigen targets human T cells against CD1c(+) leukemias.

CD1c self-reactive T cells recognize a novel class of self-lipids that are accumulated on leukemia cells.