We evaluated the ability of an integrase (IN)-defective self-inactivating lentiviral vector (sinLV) for the delivery of human immunodeficiency virus-1 (HIV-1) envelope sequences in mice to elicit specific immune responses. BALB/c mice were immunized with a single intramuscular injection of the IN-defective sinLV expressing the codon optimized HIV-1(JR-FL) gp120 sequence, and results were compared with those for the IN-competent counterpart. The IN-defective sinLV elicited specific and long-lasting immune responses, as evaluated up to 90 days from the immunization by enzyme-linked immunosorbent spot (ELISPOT) and intracellular staining (ICS) for interferon-gamma (IFN-gamma) assays in both splenocytes and bone marrow (BM) cells, chromium release assay in splenocytes, and antibody detection in sera, without integration of the vector into the host genome. These data provide evidence that a single administration of an IN-defective sinLV elicits a significant immune response in the absence of vector integration and may be a safe and useful strategy for vaccine development.

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Use of Env in HIV vaccine development has been disappointing. Here we show that, in the presence of a biologically active Tat subunit vaccine, a trimeric Env protein prevents in monkeys virus spread from the portal of entry to regional lymph nodes. This appears to be due to specific interactions between Tat and Env spikes that form a novel virus entry complex favoring R5 or X4 virus entry and productive infection of dendritic cells (DCs) via an integrin-mediated pathway. These Tat effects do not require Tat-transactivation activity and are blocked by anti-integrin antibodies (Abs). Productive DC infection promoted by Tat is associated with a highly efficient virus transmission to T cells. In the Tat/Env complex the cysteine-rich region of Tat engages the Env V3 loop, whereas the Tat RGD sequence remains free and directs the virus to integrins present on DCs. V2 loop deletion, which unshields the CCR5 binding region of Env, increases Tat/Env complex stability. Of note, binding of Tat to Env abolishes neutralization of Env entry or infection of DCs by anti-HIV sera lacking anti-Tat Abs, which are seldom present in natural infection. This is reversed, and neutralization further enhanced, by HIV sera containing anti-Tat Abs such as those from asymptomatic or Tat-vaccinated patients, or by sera from the Tat/Env vaccinated monkeys. Thus, both anti-Tat and anti-Env Abs are required for efficient HIV neutralization. These data suggest that the Tat/Env interaction increases HIV acquisition and spreading, as a mechanism evolved by the virus to escape anti-Env neutralizing Abs. This may explain the low effectiveness of Env-based vaccines, which are also unlikely to elicit Abs against new Env epitopes exposed by the Tat/Env interaction. As Tat also binds Envs from different clades, new vaccine strategies should exploit the Tat/Env interaction for both preventative and therapeutic interventions.

Objectives A seroprevalence study of SARS-CoV-2 was conducted in a high-incidence area located in North-eastern Italy. Methods All citizens above ten years of age resident in 5 municipalities of the Autonomous Province of Trento, with the highest incidence of COVID-19 cases, were invited to participate in the study. Overall, among 6098 participants, 6075 sera and a standardized questionnaire administered face-to-face were collected between May 5 and 15, 2020 and examined. Symptomatic individuals and their family contacts were tested by RT-PCR. Anti-SARS-CoV-2 antibodies were detected using an Abbott SARS-CoV-2 IgG assay which was performed on the Abbott Architect i2000SR automated analyzer. Seroprevalence was calculated as the proportion of positive people on the total number of tested. A multivariable logistic regression model was performed to assess the relationship between seropositive versus seronegative individuals for a set of explanatory variables. Results A total of 1402 participants were positives for IgG antibodies against SARS-CoV-2, with a prevalence of 23.1% (1402/6075). The highest prevalence was found in the age class 40-49 years. Overall, 34.4% (2096/6098) of the participants reported at least 1 symptom. The ratio between reported cases identified by molecular test and those resulting seropositive was 1:3, with a maximum ratio of about 1:7 in the age group <20 years and a minimum around 1:1 in those >70 years old. The infection fatality rate was 2.5% (35/1402). Among the symptoms, anosmia and ageusia were strongly associated with seropositivity. Conclusions The estimated seroprevalence of 23% was 3-fold higher than the number of cases reported in the COVID-19 Integrated Surveillance data in the study area. This may be explained in part by a relatively high number of individuals presenting mild or no illness, especially of younger age, and/or who did not seek medical care or testing, but who may contribute to virus transmission in the community.

Integrase (IN) defective lentiviral vectors have a high safety profile and might prove useful as immunizing agents especially against HIV-1. However, IN defective SIV-based vectors must be developed in order to test their potential in the non human primate models (NHP) of AIDS. To this aim we tested a novel SIV-based IN defective lentiviral vector for its ability to induce sustained immune responses in mice. BALB/c mice were immunized once intramuscularly with a SIV-based IN defective lentiviral vector expressing the model antigen enhanced green fluorescence protein (eGFP). Immune responses were evaluated 90 days after the injection and compared with those elicited with the IN competent counterpart. The IN defective vector was able to efficiently elicit specific and long-lasting polyfunctional immune responses as evaluated by enzyme-linked immunospot (ELISPOT) assays for interferon-γ (IFN-γ) in spleens, bone marrow (BM) and draining lymph nodes, and by intracellular staining (ICS) for IFN-γ, Interleukin-2 (IL-2) and tumor necrosis factor (TNF-α) in both splenocytes and BM cells without integration of the vector into the host genome. This is the first demonstration that an IN defective SIV-based lentiviral vector provides effective immunization, thus paving the way for the construction of IN defective vectors expressing SIV antigen(s) and test their efficacy against a SIV virus challenge in the NHP model of AIDS.