Work

NaïVe T Cells From Cord Blood and CMV-Seronegative Donors Recognize Atypical Epitopes of Cmvpp65 and Can Be Used for Adoptive Immunotherapy

Year: 2011

Type: article

Abstract: Adoptive transfer of virus-specific T cells can effectively restore antiviral immunity after stem cell transplantation. However, protocols for eliciting virus-specific T cells from existing memory T cells of CMV-seropositive adult (CMVpos) donors have been ineffective when applied to naïve cord blood (CB) transplant (CBT) recipients due to absence of antigen-specific memory cells in these grafts. We previously demonstrated that CMVpp65-specific T cells could be generated from CB using a modified protocol and that 15/15 CB T cell lines recognized atypical epitopes of pp65. To test if naïve T cells from CMV-seronegative donors (CMVnegs) also recognize atypical epitopes, we again optimized our previous method. CD45RA+ naïve T cells were selected from peripheral blood and stimulated with pp65-pepmix-pulsed DC with IL7, IL12, and IL15. For subsequent stimulations T cells were stimulated with pp65-pepmix-pulsed EBV-LCL and IL15 or IL2. CMVpp65-specific T cells (CMV-CTL) expanded from 8 of 11 CMVnegs and were primarily CD8+ T cells (mean 71%). These T cells secreted markedly more IFN-γ in response to pp65 peptides (mean 224; range: 38-611 SFC/1x105 cells) than to irrelevant peptides (mean 12;Range 3-37) as measured in Elispot assays. These T cells lysed pp65-pulsed target cells (mean:48;Range:15-70%) but not negative controls (mean 22;Range 4-40%) in cytotoxicity assays. As with CB, CMVneg CMV-CTL were derived from naïve T cells and recognized only atypical pp65 epitopes. These findings raised the concern that the viral epitopes presented by endothelial cells infected with CMV in patients might not present the atypical peptides recognized by our CMV-CTL. We hypothesized that the epitopes presented to T cells by endothelial cells or other APCs after CMV infection are different to those presented in our in vitro system. We tested if different epitopes would dominate the naïve T cell response to CMV AD169-infected fibroblasts and CMV VR1814-infected DC. The responding naïve T cells were again specific for atypical epitopes showing that these epitopes were indeed presented by cells naturally infected with CMV. This reassured us that despite their unusual repertoire, T cells derived from CB or CMVnegs should control CMV infections. We are now evaluating their clinical efficacy in recipients of CBT and soon Hematopoietic Stem Cell Transplantation. These studies should determine if naïve T cells primed in vitro are able to persist and establish memory in vivo.

Source: Transplantation and Cellular Therapy

DOI: 10.1016/j.bbmt.2010.12.185