The maintenance of effective immunity over time is dependent on the capacity of hematopoietic stem cells (HSCs) to sustain the pool of immunocompetent mature cells. Decline of immune competence with old age may stem from HSC defects, including reduced self-renewal potential and impaired lymphopoiesis, as suggested in murine models. To obtain further insights into aging-related alteration of hematopoiesis, we performed a comprehensive study of blood hematopoietic progenitor cells (HPCs) from older humans. In the elderly, HPCs present active oxidative phosphorylation and are pressed to enter cell cycling. However, p53-p21 and p15 cell senescence pathways, associated with telomerase activity deficiency, strong telomere attrition, and oxidative stress, are engaged, thus limiting cell cycling. Moreover, survival of old HPCs is impacted by pyroptosis, an inflammatory form of programmed cell death. Lastly, telomerase activity deficiency and telomere length attrition of old HPCs may be passed on to progeny cells such as naive T lymphocytes, further highlighting the poor hematopoietic potential of the elderly. This pre-senescent profile is characteristic of the multiple intrinsic and extrinsic factors affecting HPCs in elderly individuals and represents a major obstacle in terms of immune reconstitution and efficacy with advanced age.

The tegument protein pp65 of human cytomegalovirus (HCMV) is abundant in lytically infected human foreskin fibroblasts (HFF), as well as in virions and subviral dense bodies (DB). Despite this, we showed previously that pp65 is dispensable for growth in HFF. In the process of refining a DB-based vaccine candidate, different HCMV mutants were generated, expressing a dominant HLA-A2-presented peptide of the IE1 protein fused to pp65. One of the mutant viruses (RV-VM1) surprisingly showed marked impairment in virus release from HFF. We hypothesized that analysis of the phenotypic alterations of RV-VM1 would provide insight into the functions of pp65, poorly defined thus far. RV-VM1 infection resulted in nuclear retention of the fusion protein and reorganization of nuclear inclusion bodies. Coimmunoprecipitation experiments suggested that wild-type (wt) pp65 and pp65-VM1 were substrates of the viral pUL97 kinase in vitro and formed a complex with the viral RNA-export protein pUL69 and with pUL97 in lysates of infected cells. No evidence for an impairment of pUL97 within this complex was found. However, RV-VM1 replication in infected cells was resistant to a pUL97 inhibitor, and pUL97 inhibitors mimicked the mutant in terms of pp65 being retained in the nucleus. The results suggest that the life cycle of RV-VM1 was impeded at the stages of early-late transcription, RNA export or capsid maturation. wt-pp65 may play a role at these stages of infection, and complex formation with pUL69 and pUL97 may be important for that function. INTRODUCTIONHuman cytomegalovirus (HCMV) is a ubiquitous pathogen that severely affects individuals with impaired or immature immune-defence functions (Griffiths et al., 2009;Mocarski et al., 2007). The components of the HCMV tegument have recently attracted considerable attention, as these proteins carry functions important for various stages of the virus replication cycle (reviewed by Kalejta, 2008). The phosphoprotein pp65 (ppUL83) has long been known as an abundant tegument constituent (Roby & Gibson, 1986), yet it is dispensable for HCMV growth in human foreskin fibroblast (HFF) cell cultures (Schmolke et al., 1995b).pp65 is an important target antigen of cellular and humoral immune responses (Beninga et al., 1995; McLaughlinTaylor et al., 1994; Plachter et al., 1990;Wills et al., 1996). It would thus be reasonable to assume that modification or deletion of the protein would be favourable for the virus. However, the sequence of pp65 is highly conserved in laboratory strains and clinical isolates (Dolan et al., 2004;Pande et al., 1991) and lack of pp65 expression in such strains has never been reported. Indeed, detection of pp65 has been used as a reliable diagnostic marker for acute HCMV infection in transplant recipients for over 15 years (Grefte et al., 1992a, b Initial studies described an association of pp65 with serine/ threonine kinase activity (Britt & Auger, 1986;Somogyi et al., 1990). Subsequent analyses identified the cellular Polo-like kinase 1 (Gallina et al., 1999) and the vi...

Thymopoiesis is deeply impacted from the first days of SIV infection. Reduced thymocyte proliferation - a time-consuming process - together with modified chemokine networks is consistent with thymocyte differentiation speed-up. This may transiently enhance thymic output, thus increasing naive T-cell counts and diversity and the immune competence of the host. Nonetheless, long-lasting modification of thymic physiology may lead to thymic exhaustion, as observed in late primary HIV infection.