ABSTRACT
Varicella zoster virus (VZV) is a significant cause of morbidity and mortality following umbilical cord blood transplantation (UCBT). For this reason, antiherpetic prophylaxis is administrated systematically to pediatric UCBT recipients to prevent complications associated with VZV infection, but there is no strong, evidence based consensus that defines its optimal duration. Because T cell mediated immunity is responsible for the control of VZV infection, assessing the reconstitution of VZV specific T cell responses following UCBT could provide indications as to whether prophylaxis should be maintained or can be discontinued. To this end, a VZV specific gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) assay was developed to characterize IFN-γ production by T lymphocytes in response to in vitro stimulation with irradiated live attenuated VZV vaccine. This assay provides a rapid, reproducible and sensitive measurement of VZV specific cell mediated immunity suitable for monitoring the reconstitution of VZV specific immunity in a clinical setting and assessing immune responsiveness to VZV antigens.
Subject(s)
Cord Blood Stem Cell Transplantation/adverse effects , Enzyme-Linked Immunosorbent Assay/methods , Herpesvirus 3, Human/immunology , Interferon-gamma/biosynthesis , T-Lymphocytes/immunology , Antigens, Viral/immunology , Chickenpox Vaccine/immunology , Chickenpox Vaccine/pharmacology , Cord Blood Stem Cell Transplantation/methods , Humans , Immunity, Cellular , Interferon-gamma/analysis , Interferon-gamma/immunology , Leukocytes, Mononuclear/drug effects , Leukocytes, Mononuclear/immunology , T-Lymphocytes/drug effects , Transplantation Immunology , Vaccines, Attenuated/immunology , Vaccines, Attenuated/pharmacologyABSTRACT
In a context where injection of antigen (Ag)-specific T cells probably represents the future of leukemia immunotherapy, identification of optimal target Ags is crucial. We therefore sought to discover a reliable marker for selection of the most potent Ags. To this end, (1) we immunized mice against 8 individual Ags: 4 minor histocompatibility Ags (miHAs) and 4 leukemia-associated Ags (LAAs) that were overexpressed on leukemic relative to normal thymocytes; (2) we assessed their ability to reject EL4 leukemic cells; and (3) we correlated the properties of our Ags (and their cognate T cells) with their ability to induce protective antileukemic responses. Overall, individual miHAs instigated more potent antileukemic responses than LAAs. Three features had no influence on the ability of primed T cells to reject leukemic cells: (1) MHC-peptide affinity; (2) the stability of MHC-peptide complexes; and (3) epitope density at the surface of leukemic cells, as assessed using mass spectrometry. The cardinal feature of successful Ags is that they were recognized by high-avidity CD8 T cells that proliferated extensively in vivo. Our work suggests that in vitro evaluation of functional avidity represents the best criterion for selection of Ags, which should be prioritized in clinical trials of leukemia immunotherapy.
Subject(s)
Antigens, Neoplasm/immunology , CD8-Positive T-Lymphocytes/immunology , Immunotherapy, Adoptive , Minor Histocompatibility Antigens/immunology , Peptides/immunology , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/prevention & control , Animals , Antigens, Neoplasm/genetics , CD8-Positive T-Lymphocytes/cytology , CD8-Positive T-Lymphocytes/transplantation , Cell Proliferation , Dendritic Cells/drug effects , Dendritic Cells/immunology , Dendritic Cells/pathology , Epitopes, T-Lymphocyte/genetics , Epitopes, T-Lymphocyte/immunology , Female , Gene Expression , Immunization , Major Histocompatibility Complex/genetics , Male , Mice , Mice, Transgenic , Minor Histocompatibility Antigens/genetics , Peptides/administration & dosage , Peptides/genetics , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/genetics , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/immunology , Precursor T-Cell Lymphoblastic Leukemia-Lymphoma/pathology , Thymocytes/drug effects , Thymocytes/immunology , Thymocytes/pathologyABSTRACT
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/10(6) 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.
