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COMPREHENSIVE ANALYSIS OF HUMAN CMV T CELL RESPONSE REVEALS EPITOPES COMMON TO BOTH HLA CLASS I AND CLASS II RESTRICTION.
Maria P. Bettinotti, Stefanie Slezak, Lorraine Caruccio and David Stroncek. Bethesda MD, USA, National Institutes of Health, 20892, DTM.

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Human cytomegalovirus (CMV) is a persistent virus which can cause severe disease in immuno compromised hosts, such as patients undergoing hematopoietic stem cell transplantation (HSCT). Immunotherapy is growing in importance as treatment, making the study of the immune response against CMV clinically relevant. T cell immunity is a main component and two proteins, pp65 and IE1, are immunodominant. We investigated the T cell response against CMV using flow cytometry (FACS) in 10 seropositive adults typed for HLA class I and class II at high resolution. Gamma interferon production was detected by intracellular FACS after PBMC stimulation with peptides. Staining with CD3, CD4, and CD8 antibodies discriminated between class I and class II restricted response. The peptides were 15-mers overlapping every 4 residues and spanning the pp65 (138 peptides) and IE1 (120 peptides) proteins. Two new class I epitopes: IE1 (81-103), (297-310), and 5 new class II epitopes: pp65 (221-235), (285-299), (365-388), (488-503), (495-503) were found. In addition, IE1 (305-323) which we found as presented by HLA-B*07, has been previously described in the context of HLA-A*0201 and pp65 (422-431) presented by HLA-A*01 has been previously described in association with HLA-B*07. The class II epitope pp65 (488-503) overlaps with the immunodominant HLA-A*0201 epitope pp65 (495-503). In conclusion, the same or overlapping CMV epitopes are presented by different alleles, even sharing class I and class II presentation. We are continuing to study normal and patient populations to achieve a more complete view of the immune response against CMV; knowledge important for immunotherapy and monitoring of HSCT patients.