Analysis of the Proliferative T Cell Response to Human Cytomegalovirus Major Immediate‐Early Protein (IEl): Phenotype, Frequeney and Variability*

Abstract

Cellular immune responses are important in the recovery from human cytomegalovirus (HCMV) infection. However, little is known about the CD4+ T cell response and the target antigens (Ag) recognized. In this paper, we have analysed the proliferative T cell response of healthy HCMV seropositive (HCMV+) blood donors to recombinant immediate-early proteins expressed in transfected astrocytoma cells and to total HCMV Ags expressed in infected astrocytoma cells. We found that CD4+ T cells were the major cell population that proliferated in the presence of IE or total HCMV Ags. Among healthy HCMV seropositive blood donors with anti-HCMV specific proliferative response, 33-44% also responded to IE Ags. Moreover, in high responders, the precursor frequencies of cells which proliferated in the presence of total HCMV, IE, or IE1 Ags were high (1/103 to 1/255, 1/2785 to 1/7744 and 1/5190 to 1/13531, respectively). In some donors, the anti-IE response was variable over time, whereas the anti-total HCMV Ags response remained constant, which suggests regulation of the anti-IE response in immunocompetent subjects. Our results suggest that the CD4+ anti-IE1 response represents a significant part of the anti-HCMV proliferative response, both at the population level, and within individual immune systems.

Human Cytomegalovirus pp65- and Immediate Early 1 Antigen-Specific HLA Class I-Restricted Cytotoxic T Cell Responses Induced by Cross-Presentation of Viral Antigens

“…Despite the numerous viral evasion strategies, HCMV-specific effector or memory CD8 ϩ and CD4 ϩ T cells are present in the peripheral blood of healthy seropositive carriers at relatively high frequencies, as demonstrated by limiting dilution analysis (15)(16)(17)(18), intracellular cytokine staining (19,20), and by peptide-HLA tetramer staining (21). To explain how this robust cellular immune response develops in the presence of viral interference with the HLA class I and class II Ag presentation pathways, we examined the possibility that cross-priming via dendritic cells (DCs) enables Ag presentation of epitopes that would otherwise be blocked in the virally infected cell.…”

Dynamics of T cell memory in human cytomegalovirus infection

“…pp65 and IE-speciWc T cells as well as other speciWcities have been demonstrated [43][44][45]. Individual epitopes have been identiWed in pp65, IE, gB and gH [43, 46,47] and others [6].…”

Ex Vivo Stimulation and Expansion of both CD4+and CD8+T Cells from Peripheral Blood Mononuclear Cells of Human Cytomegalovirus-Seropositive Blood Donors by Using a Soluble Recombinant Chimeric Protein, IE1-pp65

“…CD4 ϩ and CD8 ϩ T lymphocytes have been proposed to play a major role in the control of viral replication and in protection from disease. The contribution of anti-IE1-and anti-pp65-specific Tcell precursors to the total anti-HCMV immunity is now well established (7,8,15,19,34). IE1 is the major protein produced in the immediate-early phase of the HCMV replication cycle, and the matrix protein pp65 has been shown to be internalized immediately after the viral input without de novo synthesis and then to be available for presentation to specific CD8 ϩ cytotoxic T lymphocytes (CTL) (2,19).…”