Reconstitution of cytomegalovirus (CMV)-specific CD8 ؉ T cells is essential to the control of CMV infection in CMV-

It has been shown that activating killer Ig-like receptor (aKIR) genes are important for control of CMV reactivation after hematopoietic cell transplantation (HCT). To date, using the broad classification of KIR haplotypes A and B, the precise role of individual KIR genes in control of infection cannot be discerned. To address this, a consecutive case series of 211 non T-cell depleted HCT patients all at risk for CMV, were monitored bi-weekly for CMV DNA in plasma by Q-PCR and at intervals for CMV-specific T cell immunity. Comparing patients with CMV reactivation (n=152) to those with no reactivation (n=59), the presence of specific aKIR haplotypes in the donor, but not in the recipient, were associated with protection from CMV reactivation and control of peak plasma CMV DNA (p< 0.001). A donor aKIR profile, predictive for low risk of CMV reactivation, contained either aKIR2DS2 and aKIR2DS4 or had ≥ 5 aKIR genes. Neither donor nor recipient iKIR played a role in a protective effect. CD4+- and CD8+-specific CMV immunity did not explain reduced CMV infection. The initial control of CMV infection after HCT is managed by aKIR functions, and donor aKIR haplotypes deserve further evaluation in donor selection for optimized HCT outcome.

The functional status of cytotoxic T lymphocyte (CTL) populations recognizing cytomegalovirus intermediate-early antigen (IE1) and pp65 polypeptides was investigated in peripheral blood mononuclear cells from hematopoietic stem-cell transplant (HSCT) and solid organ transplant recipients. Combined flow-based CD107a/b degranulation/mobilization and intracellular cytokine (ICC) assays using peptide libraries as antigens indicated that a significantly higher proportion of pp65-specific CTLs were in a more mature functional state, compared with IE1-specific CTLs. Degranulation/multiple cytokine ICC assays also indicated that a significantly higher proportion of pp65-specific than IE1-specific CTLs secreted both interferon- gamma and tumor necrosis factor- alpha and possessed greater cytotoxic potential. These results support our earlier findings of functional differences between CTLs recognizing individual epitopes within the IE1 and pp65 antigens in healthy donors and HSCT recipients and extend them to a broader array of human leukocyte antigen-restricted responses to those antigens. We also provide evidence of a relationship between cytotoxic function and the ability of cytomegalovirus-specific CTLs to secrete multiple cytokines.

The important role of activating Killer Immunoglobulin-like Receptors (aKIR) in protecting against cytomegalovirus (CMV) reactivation has been described previously in hematopoietic cell transplantation (HCT). More specifically, the presence of multiple aKIR and the presence of at least KIR2DS2 and KIR2DS4 in the donor genotype identified a group of HCT patients that were at low risk for CMV reactivation. However, CMV infection still occurs in patients with KIR protective genotype and the question was raised as to whether this was due to the lack of KIR expression. In this report, the expression of KIR2DS2 and 2DS4 gene, as measured by mRNA-based Q-PCR both in the donor cells and in the HCT recipient cells was studied relative to CMV reactivation. In the control samples from healthy HCT donors, the median range of for KIR2DS2 and KIR2DS4 expression was low with 35% considered null-expressers. Interestingly, KIR2DS2 and KIR2DS4 expression was elevated after HCT when compared to donor expression prior to transplant, and significantly elevated in the CMV viremic (V) compared to non-viremic (NV) HCT recipients. CMV seropositivity of donors was not associated with aKIR expression, and donor null-expression in those with KIR2DS2 or KIR2DS4 genotype did not predict for CMV reactivation in the recipient. After controlling for other transplant factors that included donor type (sibling or unrelated), transplant source -bone marrow (BM) or peripheral blood stem cells (PB) and acute GVHD grade, the result of the regression analysis of elevated KIR gene expression was found to be associated for both KIR2DS2 and KIR2DS4, with seven fold increase in risk for CMV reactivation. We speculate that the elevated aKIR expression in CMV viremic HCT recipients is either coincidental with factors that activate CMV or is initiated by CMV or cellular processes responsive to such CMV infection reactivation.

A panel of 7 human cytomegalovirus (CMV) epitope peptides and corresponding major histocompatibility class 1 tetramers was used to evaluate cellular immunity in healthy seropositive donors and in hematopoietic stem-cell transplant recipients. Broad CMV-specific T cell responses to epitopes were found within several CMV polypeptides and were restricted by multiple human leukocyte antigen alleles. Their cytotoxic functionality was evaluated by use of an assay that measures transient surface levels of lysosomal membrane proteins LAMP-1 (CD107a) and LAMP-2 (CD107b) after peptide stimulation. This assay can be combined with tetramer staining of antigen-specific CD8(+) T lymphocytes and has potential as a surrogate marker for cytotoxic function. CD8(+) T lymphocytes specific for epitopes within the pp65 or pp50 gene products exhibited significantly higher functionality, compared with populations recognizing CMV major immediate early-1 epitopes. These functional differences between T lymphocyte populations within the same individual may have implications for protection against CMV.