Natacha Merindol

HIV-1 Genetic Diversity in Antenatal Cohort, Canada

Non-B HIV-1 was consistent with patients’ area of origin.

Post-transcriptional down-regulation of Toll-like receptor signaling pathway in umbilical cord blood plasmacytoid dendritic cells.

Plasmacytoid dendritic cells (PDCs) from human umbilical cord blood (UCB) produce lower amounts of IFN-α upon TLR stimulation compared with adult counterparts. This difference may play a role in the low graft-versus-host disease rate after UCB transplantation and in the impaired immune response of the neonate to pathogens. Comparing UCB PDC to their adults counterparts, we found that they exhibited a mature surface phenotype and a normal antigen uptake. They upregulated costimulatory molecules upon activation, although with delayed kinetics. Protein, but not ARN, levels of TLR-9, MyD88, IRAK1 and IRF-7, involved in the TLR-9 signaling pathway were reduced. The expression levels of miR-146a and miR-155, known to be involved in the post-transcriptional down-regulation of immune responses, were higher. These data point out a post-transcriptional down-regulation of the TLR-9/IRF-7 signaling pathway in UCB PDC.

Complementary and contrasting roles of NK cells and T cells in pediatric umbilical cord blood transplantation

UCBT has been used for almost 25 years to treat a variety of malignant and nonmalignant childhood diseases. The biological properties of NK cells and T cells and their implication in engraftment, immune reconstitution, OIs, leukemic relapse, and GvHD have been explored in the context of UCBT. These studies have established that lymphocytes have a major impact on the outcome of UCBT and that NK cells and T cells play complementary and contrasting roles in immune reconstitution and the GvL effect. Therefore, novel strategies to improve the outcome of UCBT recipients, including immunotherapeutic regimens, should be based on key immunologic features of UCB T lymphocytes and NK cells.

CD8+ T-cell reconstitution in recipients of umbilical cord blood transplantation and characteristics associated with leukemic relapse

Recipients of umbilical cord blood (UCB) transplantation (UCBT) face a high risk of morbidity and mortality related to opportunistic infections (OI) and leukemic relapse. To understand the molecular basis of these UCBT-related complications, the characteristics of UCB-derived antigen-specific CD8(+) T cells were examined in a group of pediatric UCBT recipients. Compared with the UCB graft inoculum and the late post-UCBT period (12-36 months), declining clonal diversity of UCB-derived CD8(+) T cells specific for the Melan-A(26-35) A27L peptide and high frequencies of PD-1-expressing CD8(+) T cells were observed in the first 3 months after UCBT, a period during which OIs are most frequent. The CD8(+) T-cell compartment predominantly comprised CD45RA(+) CCR7(-) terminally differentiated effector-memory T cells until 6 months after UCBT, at which time the polyfunctionality of antigen-specific CD8(+) T cells was reestablished. Finally, the frequency of PD-1(+) CD8(+) T cells was significantly higher in subjects who subsequently experienced leukemic relapse. This study informs the biologic properties of UCB-derived CD8(+) T cells and provides a rationale for the characteristics of UCBT in terms of immune reconstitution and OI. These results also suggest that the elevated frequency of PD-1(+) CD8(+) T cells could be associated with leukemic relapse in pediatric UCBT recipients.

Umbilical Cord Blood T Cells Respond against the Melan-A/MART-1 Tumor Antigen and Exhibit Reduced Alloreactivity as Compared with Adult Blood-Derived T Cells

Umbilical cord blood (UCB) is increasingly used as a source of hematopoietic progenitor cells to treat a variety of disorders. UCB transplant is associated with comparatively reduced incidence of graft-versus-host disease, robust graft versus leukemia effect, and relatively high incidence of opportunistic infections, three processes in which donor-derived T lymphocytes are known to be predominantly involved. To examine the differential functionality of UCB T cells, CD8+ T cells specific for the melanoma-associated HLA-A2–restricted Melan-A26–35 A27L peptide were isolated from HLA-A2+ and HLA-A2− UCB samples and HLA-A2+ and HLA-A2− adult peripheral blood using A2/Melan-A tetramers. In UCB samples, A2/Melan-A+ CD8+ T cells were detected at a frequency of 0.04%, were more frequent in HLA-A2+ UCB, and were polyclonal and mostly naive. Consistent with Ag-driven expansion, the frequency of A2/Melan-A+ CD8+ T cells was increased following stimulation with cognate peptide or polyclonal activation, they acquired cell-surface markers reflective of effector/memory differentiation, their TCR repertoire became oligoclonal, and they expressed cytolytic activity and produced IFN-γ. Although functional properties of A2/Melan-A+ CD8+ T cells derived from HLA-A2+ UCB resembled those of HLA-A2+ adult peripheral blood, they were more likely to reach terminal differentiation following polyclonal stimulation and produced less IFN-γ in response to cognate peptide. A2/Melan-A+ CD8+ T cells from HLA-A2− UCB were poorly cytolytic, produced little IFN-γ, and were predominantly monofunctional or nonfunctional. These properties of UCB-derived CD8+ T cells could contribute to the reduced incidence of graft-versus-host disease and heightened incidence of opportunistic infections observed following UCB transplant.

Reconstitution of Protective Immune Responses against Cytomegalovirus and Varicella Zoster Virus Does Not Require Disease Development in Pediatric Recipients of Umbilical Cord Blood Transplantation

CMV and varicella zoster virus (VZV) are significant causes of morbidity and mortality following umbilical cord blood transplantation (UCBT). However, the kinetics of reconstitution and protective potential of antiviral cell-mediated immune responses following UCBT remain poorly characterized. In this study, the reconstitution of CMV- and VZV-specific T cell responses was assessed using IFN-γ ELISPOT in 28 children who underwent UCBT to treat hematological or inherited disorders. Barely detectable in the first 3 mo posttransplantation, CMV- and VZV-specific T cell responses were observed in 30.4% and 40.3% of study subjects after 36 mo of follow-up. Four of five CMV-seropositive subjects developed detectable levels of circulating CMV DNA (DNAemia), and 5 of 17 VZV-seropositive patients experienced herpes zoster during the posttransplant period. Four CMV-seronegative subjects developed IFN-γ responses against CMV, and four subjects developed a VZV-specific IFN-γ response without clinical signs of infection. No CMV- or VZV-related events were observed in study subjects following the development of CMV- or VZV-specific responses > 150 spot-forming units/106 PBMCs, consistent with T cell-mediated protection. Finally, famciclovir prophylaxis did not strictly prevent the reconstitution of the VZV-specific T cell repertoire, because the frequency of T cells producing IFN-γ in response to VZV Ags reached levels consistent with protection in two nonzoster subjects. Monitoring of CMV- and VZV-specific cell-mediated immunity could inform immunocompetence and guide the initiation and cessation of antiherpetic prophylaxis in UCBT recipients.

Novel HIV-1 recombinant forms in antenatal cohort, Montreal, Quebec, Canada.

Near full-length genomes of 4 unclassified HIV-1 variants infecting patients enrolled in an antenatal cohort in Canada were obtained by sequencing. All 4 variants showed original recombination profiles, including A1/A2/J, A1/D, and A1/G/J/CRF11_cpx structures. Identification of these variants highlights the growing prevalence of unique recombinant forms of HIV-1 in North America.