Lentiviral Vector Production Titer Is Not Limited in HEK293T by Induced Intracellular Innate Immunity

Most gene therapy lentiviral vector (LV) production platforms employ HEK293T cells expressing the oncogenic SV40 large T-antigen (TAg) that is thought to promote plasmid-mediated gene expression. Studies on other viral oncogenes suggest that TAg may also inhibit the intracellular autonomous innate immune system that triggers defensive antiviral responses upon detection of viral components by cytosolic sensors. Here we show that an innate response can be generated after HIV-1-derived LV transfection in HEK293T cells, particularly by the transgene, yet, remarkably, this had no effect on LV titer. Further, overexpression of DNA sensing pathway components led to expression of inflammatory cytokine and interferon (IFN) stimulated genes but did not result in detectable IFN or CXCL10 and had no impact on LV titer. Exogenous IFN-β also did not affect LV production or transduction efficiency in primary T cells. Additionally, manipulation of TAg did not affect innate antiviral responses, but stable expression of TAg boosted vector production in HEK293 cells. Our findings demonstrate a measure of innate immune competence in HEK293T cells but, crucially, show that activation of inflammatory signaling is uncoupled from cytokine secretion in these cells. This provides new mechanistic insight into the unique suitability of HEK293T cells for LV manufacture.

Nonhuman TRIM5 Variants Enhance Recognition of HIV-1-Infected Cells by CD8+ T Cells

Tripartite motif-containing protein 5 (TRIM5) restricts human immunodeficiency virus type 1 (HIV-1) in a species-specific manner by uncoating viral particles while activating early innate responses. Although the contribution of TRIM5 proteins to cellular immunity has not yet been studied, their interactions with the incoming viral capsid and the cellular proteasome led us to hypothesize a role for them. Here, we investigate whether the expression of two nonhuman TRIM5 orthologs, rhesus TRIM5α (RhT5) and TRIM-cyclophilin A (TCyp), both of which are potent restrictors of HIV-1, could enhance immune recognition of infected cells by CD8(+) T cells. We illustrate how TRIM5 restriction improves CD8(+) T-cell-mediated HIV-1 inhibition. Moreover, when TRIM5 activity was blocked by the nonimmunosuppressive analog of cyclosporine (CsA), sarcosine-3(4-methylbenzoate)-CsA (SmBz-CsA), we found a significant reduction in CD107a/MIP-1β expression in HIV-1-specific CD8(+) T cells. This finding underscores the direct link between TRIM5 restriction and activation of CD8(+) T-cell responses. Interestingly, cells expressing RhT5 induced stronger CD8(+) T-cell responses through the specific recognition of the HIV-1 capsid by the immune system. The underlying mechanism of this process may involve TRIM5-specific capsid recruitment to cellular proteasomes and increase peptide availability for loading and presentation of HLA class I antigens. In summary, we identified a novel function for nonhuman TRIM5 variants in cellular immunity. We hypothesize that TRIM5 can couple innate viral sensing and CD8(+) T-cell activation to increase species barriers against retrovirus infection.

IMPORTANCE

New therapeutics to tackle HIV-1 infection should aim to combine rapid innate viral sensing and cellular immune recognition. Such strategies could prevent seeding of the viral reservoir and the immune damage that occurs during acute infection. The nonhuman TRIM5 variants, rhesus TRIM5α (RhT5) and TRIM-cyclophilin A (TCyp), are attractive candidates owing to their potency in sensing HIV-1 and blocking its activity. Here, we show that expression of RhT5 and TCyp in HIV-1-infected cells improves CD8(+) T-cell-mediated inhibition through the direct activation of HIV-1-specific CD8(+) T-cell responses. We found that the potency in CD8(+) activation was stronger for RhT5 variants and capsid-specific CD8(+) T cells in a mechanism that relies on TRIM5-dependent particle recruitment to cellular proteasomes. This novel mechanism couples innate viral sensing with cellular immunity in a single protein and could be exploited to develop innovative therapeutics for control of HIV-1 infection.

The infectious synapse formed between mature dendritic cells and CD4(+) T cells is independent of the presence of the HIV-1 envelope glycoprotein

BACKGROUND

Since cell-mediated infection of human immunodeficiency virus type 1 (HIV-1) is more efficient than cell-free infection, cell-to-cell propagation plays a crucial role in the pathogenesis of HIV-1 infection. Transmission of HIV-1 is enabled by two types of cellular contacts, namely, virological synapses between productively infected cells and uninfected target cells and infectious synapses between uninfected dendritic cells (DC) harboring HIV-1 and uninfected target cells. While virological synapses are driven by expression of the viral envelope glycoprotein on the cell surface, little is known about the role of envelope glycoprotein during contact between DC and T cells. We explored the contribution of HIV-1 envelope glycoprotein, adhesion molecules, and antigen recognition in the formation of conjugates comprising mature DC (mDC) and CD4(+) T cells in order to further evaluate their role in mDC-mediated HIV-1 transmission at the immunological synapse.

RESULTS

Unlike virological synapse, HIV-1 did not modulate the formation of cell conjugates comprising mDC harboring HIV-1 and non-activated primary CD4(+) T cells. Disruption of interactions between ICAM-1 and LFA-1, however, resulted in a 60% decrease in mDC-CD4(+) T-cell conjugate formation and, consequently, in a significant reduction of mDC-mediated HIV-1 transmission to non-activated primary CD4(+) T cells (p < 0.05). Antigen recognition or sustained MHC-TcR interaction did not enhance conjugate formation, but significantly boosted productive mDC-mediated transmission of HIV-1 (p < 0.05) by increasing T-cell activation and proliferation.

CONCLUSIONS

Formation of the infectious synapse is independent of the presence of the HIV-1 envelope glycoprotein, although it does require an interaction between ICAM-1 and LFA-1. This interaction is the main driving force behind the formation of mDC-CD4(+) T-cell conjugates and enables transmission of HIV-1 to CD4(+) T cells. Moreover, antigen recognition boosts HIV-1 replication without affecting the frequency of cellular conjugates. Our results suggest a determinant role for immune activation driven by mDC-CD4(+) T-cell contacts in viral dissemination and that this activation likely contributes to the pathogenesis of HIV-1 infection.

Siglec-1 is a novel dendritic cell receptor that mediates HIV-1 trans-infection through recognition of viral membrane gangliosides

The novel dendritic cell receptor Siglec-1 binds sialyllactose moieties on HIV-1 membrane gangliosides, thereby enhancing HIV-1 transinfection.

Dendritic cells (DCs) are essential antigen-presenting cells for the induction of immunity against pathogens. However, HIV-1 spread is strongly enhanced in clusters of DCs and CD4⁺ T cells. Uninfected DCs capture HIV-1 and mediate viral transfer to bystander CD4⁺ T cells through a process termed trans-infection. Initial studies identified the C-type lectin DC-SIGN as the HIV-1 binding factor on DCs, which interacts with the viral envelope glycoproteins. Upon DC maturation, however, DC-SIGN is down-regulated, while HIV-1 capture and trans-infection is strongly enhanced via a glycoprotein-independent capture pathway that recognizes sialyllactose-containing membrane gangliosides. Here we show that the sialic acid-binding Ig-like lectin 1 (Siglec-1, CD169), which is highly expressed on mature DCs, specifically binds HIV-1 and vesicles carrying sialyllactose. Furthermore, Siglec-1 is essential for trans-infection by mature DCs. These findings identify Siglec-1 as a key factor for HIV-1 spread via infectious DC/T-cell synapses, highlighting a novel mechanism that mediates HIV-1 dissemination in activated tissues.

Mature dendritic cells (mDCs) capture and store infectious HIV-1 and subsequently infect neighboring CD4⁺ T cells in lymphoid organs. This process, known as trans-infection, is a key contributor to HIV pathogenesis, but the precise mechanism and the identity of the receptor on the mDC surface that recognizes viral particles remain controversial. Although the interaction of HIV-1 envelope glycoproteins with the C-type lectin DC-SIGN has been suggested to mediate HIV-1 capture and trans-infection, later studies revealed an envelope glycoprotein-independent virus capture mechanism in mDCs. Here, we identify Siglec-1 as the surface receptor on mDCs that boosts their uptake of HIV-1 and their capacity to trans-infect CD4⁺ cells, leading in turn to HIV-1 disease progression. Siglec-1 captures the virus by interacting with sialyllactose-containing gangliosides exposed on viral membranes. This indicates that Siglec-1 functions as a general binding molecule for any vesicle carrying sialyllactose in its membrane, including exosomes and other viruses. We suggest that this natural pathway through mDC, which would normally lead to antigen processing and presentation, has been subverted by HIV-1 for its own storage and transmission.

HIV-1 capture and antigen presentation by dendritic cells: enhanced viral capture does not correlate with better T cell activation

During HIV-1 infection, dendritic cells (DC) facilitate dissemination of HIV-1 while trying to trigger adaptive antiviral immune responses. We examined whether increased HIV-1 capture in DC matured with LPS results in more efficient Ag presentation to HIV-1-specific CD4(+) and CD8(+) T cells. To block the DC-mediated trans-infection of HIV-1 and maximize Ag loading, we also evaluated a noninfectious integrase-deficient HIV-1 isolate, HIV(NL4-3ΔIN). We showed that higher viral capture of DC did not guarantee better Ag presentation or T cell activation. Greater HIV(NL4-3) uptake by fully LPS-matured DC resulted in higher viral transmission to target cells but poorer stimulation of HIV-1-specific CD4(+) and CD8(+) T cells. Conversely, maturation of DC with LPS during, but not before, viral loading enhanced both HLA-I and HLA-II HIV-1-derived Ag presentation. In contrast, DC maturation with the clinical-grade mixture consisting of IL-1β, TNF-α, IL-6, and PGE(2) during viral uptake only stimulated HIV-1-specific CD8(+) T cells. Hence, DC maturation state, activation stimulus, and time lag between DC maturation and Ag loading impact HIV-1 capture and virus Ag presentation. Our results demonstrate a dissociation between the capacity to capture HIV-1 and to present viral Ags. Integrase-deficient HIV(NL4-3ΔIN) was also efficiently captured and presented by DC through the HLA-I and HLA-II pathways but in the absence of viral dissemination. HIV(NL4-3ΔIN) seems to be an attractive candidate to be explored. These results provide new insights into DC biology and have implications in the optimization of DC-based immunotherapy against HIV-1 infection.

Sialyllactose in viral membrane gangliosides is a novel molecular recognition pattern for mature dendritic cell capture of HIV-1

HIV-1 is internalized into mature dendritic cells (mDCs) via an as yet undefined mechanism with subsequent transfer of stored, infectious virus to CD4+ T lymphocytes. Thus, HIV-1 subverts a DC antigen capture mechanism to promote viral spread. Here, we show that gangliosides in the HIV-1 membrane are the key molecules for mDC uptake. HIV-1 virus-like particles and liposomes mimicking the HIV-1 lipid composition were shown to use a common internalization pathway and the same trafficking route within mDCs. Hence, these results demonstrate that gangliosides can act as viral attachment factors, in addition to their well known function as cellular receptors for certain viruses. Furthermore, the sialyllactose molecule present in specific gangliosides was identified as the determinant moiety for mDC HIV-1 uptake. Thus, sialyllactose represents a novel molecular recognition pattern for mDC capture, and may be crucial both for antigen presentation leading to immunity against pathogens and for succumbing to subversion by HIV-1.

Polymerase chain reaction for diagnosis and serogrouping of meningococcal disease in children

A prospective study was performed including all children younger than 18 years with the clinical diagnosis of invasive meningococcal disease (IMD) hospitalized at the University Hospital Sant Joan de Déu in Barcelona, Spain, from January 2001 to December 2006. During the study period, 168 meningococcal disease cases were reported. Microbiologic confirmation was obtained in 118 cases. Forty-six (38.9%) of 118 cases were only detected by polymerase chain reaction (PCR); 6 patients were culture positive and PCR negative (5%). Serogroup B predominated in the 6-year period with 83.1% of the strains. A significant decrease in serogroup C was observed in the last 3 years of the study (P=0.029), and less common serogroups, such as serogroup A and W135, emerged. Serogroup distribution of patient diagnoses only by real-time PCR showed a similar distribution: serogroup B, 85.7%; serogroup C, 7.1%; and nontypeable serogroups, 7.1%. In conclusion, real-time PCR is more rapid and sensitive than culture for diagnosis and serogrouping of IMD.