Silicone-oil-based subvisible particles: their detection, interactions, and regulation in prefilled container closure systems for biopharmaceuticals.

Recent increased regulatory scrutiny concerning subvisible particulates (SbVPs) in parenteral formulations of biologics has led to the publication of numerous articles about the sources, characteristics, implications, and approaches to monitoring and detecting SbVPs. Despite varying opinions on the level of associated risks and method of regulation, nearly all industry scientists and regulators agree on the need for monitoring and reporting visible and subvisible particles. As prefillable drug delivery systems have become a prominent packaging option, silicone oil, a common primary packaging lubricant, may play a role in the appearance of particles. The goal of this article is to complement the current SbVP knowledge base with new insights into the evolution of silicone-oil-related particulates and their interactions with components in prefillable systems. We propose a "toolbox" for improved silicone-oil-related particulate detection and enumeration, and discuss the benefits and limitations of approaches for lowering and controlling silicone oil release in parenterals. Finally, we present surface cross-linking of silicone as the recommended solution for achieving significant SbVP reduction without negatively affecting functional performance.

HTLV-1 uses HSPG and neuropilin-1 for entry by molecular mimicry of VEGF165.

Human T-cell lymphotropic virus type 1 (HTLV-1) entry involves the interaction between the surface (SU) subunit of the Env proteins and cellular receptor(s). Previously, our laboratories demonstrated that heparan sulfate proteoglycans (HSPGs) and neuropilin-1 (NRP-1), a receptor of VEGF(165), are essential for HTLV-1 entry. Here we investigated whether, as when binding VEGF(165), HSPGs and NRP-1 work in concert during HTLV-1 entry. VEGF(165) binds to the b domain of NRP-1 through both HSPG-dependent and -independent interactions, the latter involving its exon 8. We show that VEGF(165) is a selective competitor of HTLV-1 entry and that HTLV-1 mimics VEGF(165) to recruit HSPGs and NRP-1: (1) the NRP-1 b domain is required for HTLV-1 binding; (2) SU binding to target cells is blocked by the HSPG-binding domain of VEGF(165); (3) the formation of Env/NRP-1 complexes is enhanced by HSPGs; and (4) the HTLV SU contains a motif homologous to VEGF(165) exon 8. This motif directly binds to NRP-1 and is essential for HTLV-1 binding to, internalization into, and infection of CD4(+) T cells and dendritic cells. These findings demonstrate that HSPGs and NRP-1 function as HTLV-1 receptors in a cooperative manner and reveal an unexpected mimicry mechanism that may have major implications in vivo.

Neuropilin-1 is involved in human T-cell lymphotropic virus type 1 entry.

Human T-cell lymphotropic virus type 1 (HTLV-1) is transmitted through a viral synapse and enters target cells via interaction with the glucose transporter GLUT1. Here, we show that Neuropilin-1 (NRP1), the receptor for semaphorin-3A and VEGF-A165 and a member of the immune synapse, is also a physical and functional partner of HTLV-1 envelope (Env) proteins. HTLV-1 Env and NRP1 complexes are formed in cotransfected cells, and endogenous NRP1 contributes to the binding of HTLV-1 Env to target cells. NRP1 overexpression increases HTLV-1 Env-dependent syncytium formation. Moreover, overexpression of NRP1 increases both HTLV-1 and HTLV-2 Env-dependent infection, whereas down-regulation of endogenous NRP1 has the opposite effect. Finally, overexpressed GLUT1, NRP1, and Env form ternary complexes in transfected cells, and endogenous NRP1 and GLUT1 colocalize in membrane junctions formed between uninfected and HTLV-1-infected T cells. These data show that NRP1 is involved in HTLV-1 and HTLV-2 entry, suggesting that the HTLV receptor has a multicomponent nature.