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Reconstitution of cellular immunity by 3 months after hematopoietic stem cell transplantation (HSCT) is a critical determinant of the long-term success of the transplantation. We analyzed the factors affecting recovery of cytomegalovirus (CMV)-specific CD4 ؉ and CD8 ؉ function at 3 months after HSCT by univariate and multivariable analyses including source of stem cells (bone marrow vs peripheral blood stem cells [PBSCs]), age, sex, graftversus-host disease (GVHD), steroid use, conditioning regimens, ganciclovir use, HLA matching, circulating CMV antigenemia, absolute CD4 ؉ and CD8 ؉ counts, and donor CMV serology. High-dose steroids and CD4 ؉ count less than 100 ؋ 10 9 /L were significant predictors of impaired CD4 ؉ functional recovery in the multivariable analysis. High-dose steroids, bone marrow as a source of stem cells, and CD8 ؉ count less than 50 ؋ 10 9 /L were associated with impaired CD8 ؉ function in the multivariable analysis. Steroids were found to impair both CD4 ؉ and CD8 ؉ function in a dose-dependent manner. In the absence of high-dose steroids, low-level subclinical CMV antigenemia was found to stimulate both CD4 ؉ and CD8 ؉ functional recovery in recipients of ganciclovir prophylaxis. There was no difference in immune reconstitution between those who received prophylactic ganciclovir versus antigenemia-guided pre-emptive therapy. Thus, absolute CD4 ؉ and CD8 ؉ counts less than 100 ؋ 10 9 /L and 50 ؋ 10 9 /L, respectively; bone marrow as the source of stem cells; and high-dose steroid use all predict delayed recovery of functional T-cell immunity at 3 months after transplantation. Subclinical CMV reactivation while on ganciclovir appears to be a potent stimulator of T-cell function. These findings have implications for vaccination and adoptive-immunotherapy strategies in this population.

During infection with human cytomegalovirus (HCMV), cellular protein synthesis continues even as viral proteins are being synthesized in abundance. Thus, HCMV may have a mechanism for counteracting host cell antiviral pathways that act by shutting off translation. Consistent with this view, HCMV infection of human fibroblasts rescues the replication of a vaccinia virus mutant lacking the double-stranded RNA-binding protein gene E3L (VV⌬E3L). HCMV also prevents the phosphorylation of the eukaryotic translation initiation factor eIF-2␣, the activation of RNase L, and the shutoff of viral and cellular protein synthesis that otherwise result from VV⌬E3L infection. To identify the HCMV gene(s) responsible for these effects, we prepared a library of VV⌬E3L recombinants containing HCMV genomic fragments. By infecting nonpermissive cells with this library and screening for VV gene expression and replication, we isolated a virus containing a 2.8-kb HCMV fragment that rescues replication of VV⌬E3L. The fragment comprises the 3 end of the J1S open reading frame through the entire TRS1 gene. Analyses of additional VV⌬E3L recombinants revealed that the protein encoded by TRS1, pTRS1, as well as the closely related IRS1 gene, rescues VV⌬E3L replication and prevent the shutoff of protein synthesis, the phosphorylation of eIF-2␣, and activation of RNase L. These results demonstrate that TRS1 and IRS1 are able to counteract critical host cell antiviral response pathways.Among the cellular responses to viral infections are at least two interferon-induced, double-stranded RNA (dsRNA)-activated pathways that are designed to shut off protein synthesis and thereby limit viral replication (reviewed in references 30 and 35). Activation of the protein kinase R (PKR) results in phosphorylation of the eukaryotic translation initiation factor eIF-2␣, which in turn inhibits translation initiation. Oligoadenylate synthetases (OAS) activate RNase L, resulting in degradation of rRNA and mRNAs and thereby limiting the synthesis of both viral and cellular proteins.Because viral replication requires protein synthesis, many viruses contain genes that counteract these pathways. Some of these genes encode inhibitory RNAs, such as VA1 RNA of adenovirus, while others encode proteins that interfere with various steps in the PKR and OAS/RNase L pathways (30,35). Several viruses contain two or more genes that prevent the shutoff of protein synthesis. For example, vaccinia virus (VV) produces a dsRNA-binding protein, pE3L, as well as a PKR pseudosubstrate, pK3L (19). Herpes simplex virus type 1 (HSV-1) contains U S 11, which encodes a dsRNA-binding protein as well as ␥34.5, the product of which stimulates the dephosphorylation of eIF-2␣ phosphate (18,27).Preventing activation of these antiviral response pathways is critical for viral pathogenesis. VV lacking E3L (VV⌬E3L) exhibits markedly reduced virulence compared to that of wildtype (WT) VV in animal models (5, 39). An HSV-1 mutant lacking the ␥34.5 gene exhibits reduced virulence in WT mice, but it is ...