BackgroundHIV-1 integration is prone to a high rate of failure, resulting in the accumulation of unintegrated viral genomes (uDNA) in vivo and in vitro. uDNA can be transcriptionally active, and circularized uDNA genomes are biochemically stable in non-proliferating cells. Resting, non-proliferating CD4 T cells are prime targets of HIV-1 infection and latently infected resting CD4 T cells are the major barrier to HIV cure. Our prior studies demonstrated that uDNA generates infectious virions when T cell activation follows rather than precedes infection.ResultsHere, we characterize in primary resting CD4 T cells the dynamics of integrated and unintegrated virus expression, genome persistence and sensitivity to latency reversing agents. Unintegrated HIV-1 was abundant in directly infected resting CD4 T cells. Maximal gene expression from uDNA was delayed compared with integrated HIV-1 and was less toxic, resulting in uDNA enrichment over time relative to integrated proviruses. Inhibiting integration with raltegravir shunted the generation of durable latency from integrated to unintegrated genomes. Latent uDNA was activated to de novo virus production by latency reversing agents that also activated latent integrated proviruses, including PKC activators, histone deacetylase inhibitors and P-TEFb agonists. However, uDNA responses displayed a wider dynamic range, indicating differential regulation of expression relative to integrated proviruses. Similar to what has recently been demonstrated for latent integrated proviruses, one or two applications of latency reversing agents failed to activate all latent unintegrated genomes. Unlike integrated proviruses, uDNA gene expression did not down modulate expression of HLA Class I on resting CD4 T cells. uDNA did, however, efficiently prime infected cells for killing by HIV-1-specific cytotoxic T cells.ConclusionsThese studies demonstrate that contributions by unintegrated genomes to HIV-1 gene expression, virus production, latency and immune responses are inherent properties of the direct infection of resting CD4 T cells. Experimental models of HIV-1 latency employing directly infected resting CD4 T cells should calibrate the contribution of unintegrated HIV-1.Electronic supplementary materialThe online version of this article (doi:10.1186/s12977-015-0234-9) contains supplementary material, which is available to authorized users.

Unraveling the long-term kinetics of antibodies to SARS-CoV-2 and the individual characteristics influencing it, including the impact of pre-existing antibodies to human coronaviruses causing common cold (HCoVs), is essential to understand protective immunity to COVID-19 and devise effective surveillance strategies. IgM, IgA and IgG levels against six SARS-CoV-2 antigens and the nucleocapsid antigen of the four HCoV (229E, NL63, OC43 and HKU1) were quantified by Luminex, and antibody neutralization capacity was assessed by flow cytometry, in a cohort of health care workers followed up to 7 months (N = 578). Seroprevalence increases over time from 13.5% (month 0) and 15.6% (month 1) to 16.4% (month 6). Levels of antibodies, including those with neutralizing capacity, are stable over time, except IgG to nucleocapsid antigen and IgM levels that wane. After the peak response, anti-spike antibody levels increase from ~150 days post-symptom onset in all individuals (73% for IgG), in the absence of any evidence of re-exposure. IgG and IgA to HCoV are significantly higher in asymptomatic than symptomatic seropositive individuals. Thus, pre-existing cross-reactive HCoVs antibodies could have a protective effect against SARS-CoV-2 infection and COVID-19 disease.

Recent studies suggest that particular dendritic cells (DC) subpopulations may be tolerogenic. To test the capacity of different DC subpopulations to modulate allograft rejection, we generated two distinct populations of rat bone marrow-derived DCs (BMDC) with low doses of GM-CSF and IL-4. The non-adherent population (nBMDC), which are the 'classical' DCs was able to stimulate naïve allogeneic T cells and could be induced to completely mature using various stimuli. In contrast, the adherent population (aBMDC), which displayed an immature phenotype, was unable to stimulate T cells and was more resistant to maturation. We found that syngeneic aBMDCs, injected one day before transplantation, induced significant prolongation of heart allograft survival and decreased anti-donor humoral and cellular responses. Similarly, syngeneic aBMDCs inhibited T-cell responses to KLH in the spleen but not in lymph node in a KLH immunization model without graft. This effect was not antigen specific and could be reversed using an inhibitor of inducible nitric oxide synthase. This compartmentalized inhibition could be in part explained by the fact that the majority of syngeneic adherent cells administered intravenously were found in the spleen with some of them reaching the T-cell areas. These data suggest that syngeneic aBMDCs can modulate immune responses.