Characterization of cytotoxic function of CMV-pp65-specific CD8+ T-lymphocytes identified by HLA tetramers in recipients and donors of stem-cell transplants

Background. Human cytomegalovirus (CMV) is a ubiquitous herpesvirus that is an important compli cation of bone marrow and allogeneic stem-eel transplant (HSCT). CD8(+) T-lymphocytes have an important role in immunity against CMV, but correlation between antigen-specific subpopulations of these cells and protection are still unclear. Methods. Flow analysis with fluorescently-conjugated human leukocyte antigen (HLA) class I tetramers (Tet) was used to investigate levels of CMV-specifi CD8(+) T-lymphocytes in peripheral blood monocyte cells (PBMC) samples from HSCT donors and recipients and their ability to produce interferon (IFN)-gamma or stimulation with either CMV antigenic peptide or non specific mitogenic stimulation. Chromium release as says were used to evaluate ex vivo CMV-specific cytotoxicity associated with the PBMC samples. Results. Use of Tet in conjunction with fluorescently conjugated anti-T-cell receptor (TCR) beta-chain variable (Vbeta) monoclonal antibodies indicated that the Vbeta repertoires associated with Tet(+) cells seen in two HSCT recipients were similar to the Vbeta repertoires of the Tet(+) cells in their HSCT donors. Significant ex vivo cytotoxicity against peptide-loaded targets was measured from several recipient samples after transplant However, PBMC from the HSCT donors, even when containing populations of CMV-specific Tet(+) cells capable of secreting IFN-gamma in response to peptide stimulation, possessed no ex vivo CMV-specific cytotoxicity. Conclusions. We hypothesize that in the setting of the reconstituting immune system of HSCT recipients, CMV reactivation may stimulate a functional change in CMV-specific CD8(+) T-lymphocytes, rendering them able to directly lyse target cells presenting CMV antigens without in vitro stimulation. These findings have important implications for development of vaccines designed to induce protective cellular immunity to CMV in transplant recipients.