Biology subjects

Tam, Y. K.

Publications and source records attributed to Tam, Y. K..

11 recordsLinked to original sources

bioRxiv2026

Clonal dynamics of germinal center refueling by secondary immunization

Many vaccine regimens involve delivery of multiple doses to the same anatomical site, such that booster doses frequently encounter germinal centers (GCs) still active from prior immunization. The consequences of this "GC refueling" to B cell clonality have not been systematically investigated. Using mouse models of mRNA-LNP vaccination combined with multicolor fate-mapping, longitudinal GC imaging, and immunoglobulin sequencing, we show that refueling triggers clonal burst-type expansion of GC-resident B cells, rather than recruiting local memory, resulting in marked focusing of GCs on the descendants of individual B cells. Refueling with a drifted antigen led to limited but detectable retraining of primary-cohort clones, although most variant-specific responses in this setting arose from newly recruited naive B cells. These findings identify GC refueling as a distinct mode of vaccine response with implications for sequential immunization strategies against rapidly evolving pathogens.

immunology↗

bioRxiv2025

mRNA-LNP vaccines against Hepatitis B virus induce protective immune responses in preventive and chronic mouse challenge models

Over 300 million people worldwide suffer from chronic hepatitis B virus infections that can cause serious liver damage and hepatocellular carcinoma. Ineffective innate and adaptive immune responses characterize these chronic infections, making the development of a therapeutic vaccine an urgent medical need. While current vaccines can prevent HBV infections, they are ineffective in treating chronic disease. This study investigated lipid nanoparticle (LNP)-formulated nucleoside-modified mRNA vaccines encoding Hepatitis B surface antigen (HBsAg) for prophylactic and therapeutic applications. We found that HBsAg mRNA-LNP vaccines induced robust humoral and cellular immune responses, outperforming the protein-based vaccine approved for human use. The incorporation of an MHC class I signal peptide further enhanced Th1-biased responses preventing HBV infections in a mouse model. Importantly, mRNA-LNP vaccination led to seroconversion, HBsAg clearance, and strong T cell responses in a chronically infected mouse model. These findings highlight the potential of mRNA-LNP as an alternative and effective vaccine modality for HBV prophylaxis and therapeutic use in treating chronic infections.

immunology↗

bioRxiv2024

Computationally designed mRNA-launched protein nanoparticle vaccines

Both protein nanoparticle and mRNA vaccines were clinically de-risked during the COVID-19 pandemic1-6. These vaccine modalities have complementary strengths: antigen display on protein nanoparticles can enhance the magnitude, quality, and durability of antibody responses7-10, while mRNA vaccines can be rapidly manufactured11 and elicit antigen-specific CD4 and CD8 T cells12,13. Here we leverage a computationally designed icosahedral protein nanoparticle that was redesigned for optimal secretion from eukaryotic cells14 to develop an mRNA-launched nanoparticle vaccine for SARS-CoV-2. The nanoparticle, which displays 60 copies of a stabilized variant of the Wuhan-Hu-1 Spike receptor binding domain (RBD)15, formed monodisperse, antigenically intact assemblies upon secretion from transfected cells. An mRNA vaccine encoding the secreted RBD nanoparticle elicited 5- to 28-fold higher levels of neutralizing antibodies than an mRNA vaccine encoding membrane-anchored Spike, induced higher levels of CD8 T cells than the same immunogen when delivered as an adjuvanted protein nanoparticle, and protected mice from vaccine-matched and -mismatched SARS-CoV-2 challenge. Our data establish that delivering protein nanoparticle immunogens via mRNA vaccines can combine the benefits of each modality and, more broadly, highlight the utility of computational protein design in genetic immunization strategies.

immunology↗

bioRxiv2024

Treatment of a genetic liver disease in mice through transient prime editor expression

Prime editing is a versatile genome editing technology that does not rely on DNA double-strand break formation and homology-directed repair (HDR). This makes it a promising tool for correcting pathogenic mutations in tissues consisting predominantly of postmitotic cells, such as the liver. While recent studies have already demonstrated proof-of-concept for in vivo prime editing, the use of viral delivery vectors resulted in prolonged prime editor (PE) expression, posing challenges for clinical application. Here, we developed an in vivo prime editing approach where we delivered the pegRNA using self-complementary adeno-associated viral (scAAV) vectors and the prime editor using nucleoside-modified mRNA encapsulated in lipid nanoparticles (LNPs). This methodology led to transient expression of the PE for 48h and 26% editing at the Dnmt1 locus using AAV doses of 2.5x1013 vector genomes (vg)/kg and a single dose of 3mg/kg mRNA-LNP. When targeting the pathogenic mutation in the Pahenu2 mouse model of phenylketonuria (PKU), we achieved 4.3% gene correction using an AAV dose of 2.5x1013 vg/kg and three doses of 2 mg/kg mRNA-LNP. Editing was specific to the liver and the intended locus, and was sufficient to reduce blood L-phenylalanine (Phe) levels from over 1500 {micro}mol/l to below the therapeutic threshold of 600 {micro}mol/l. Our study demonstrates the feasibility of in vivo gene correction in the liver with transient PE expression, bringing prime editing closer to clinical application.

bioengineering↗

bioRxiv2023

Targeting lipid nanoparticles to the blood brain barrier to ameliorate acute ischemic stroke

After more than 100 failed drug trials for acute ischemic stroke (AIS), one of the most commonly cited reasons for the failure has been that drugs achieve very low concentrations in the at-risk penumbra. To address this problem, here we employ nanotechnology to significantly enhance drug concentration in the penumbras blood-brain barrier (BBB), whose increased permeability in AIS has long been hypothesized to kill neurons by exposing them to toxic plasma proteins. To devise drug-loaded nanocarriers targeted to the BBB, we conjugated them with antibodies that bind to various cell adhesion molecules on the BBB endothelium. In the transient middle cerebral artery occlusion (tMCAO) mouse model, nanocarriers targeted with VCAM antibodies achieved the highest level of brain delivery, nearly 2 orders of magnitude higher than untargeted ones. VCAM-targeted lipid nanoparticles loaded with either a small molecule drug (dexamethasone) or mRNA (encoding IL-10) reduced cerebral infarct volume by 35% or 73%, respectively, and both significantly lowered mortality rates. In contrast, the drugs delivered without the nanocarriers had no effect on AIS outcomes. Thus, VCAM-targeted lipid nanoparticles represent a new platform for strongly concentrating drugs within the compromised BBB of penumbra, thereby ameliorating AIS. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=198 SRC="FIGDIR/small/544645v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@86762dorg.highwire.dtl.DTLVardef@1b89a2aorg.highwire.dtl.DTLVardef@916d85org.highwire.dtl.DTLVardef@1ad4670_HPS_FORMAT_FIGEXP M_FIG C_FIG Acute ischemic stroke induces upregulation of VCAM. We specifically targeted upregulated VCAM in the injured region of the brain with drug- or mRNA-loaded targeted nanocarriers. Nanocarriers targeted with VCAM antibodies achieved the highest brain delivery, nearly orders of magnitude higher than untargeted ones. VCAM-targeted nanocarriers loaded with dexamethasone and mRNA encoding IL-10 reduced infarct volume by 35% and 73%, respectively, and improved survival rates.

pharmacology and toxicology↗

bioRxiv2023

The Regulation of Nucleic Acid Vaccine Responses by the Microbiome

SummaryNucleic acid vaccines, including both RNA and DNA platforms, are key technologies that have considerable promise in combating both infectious disease and cancer. However, little is known about the extrinsic factors that regulate nucleic acid vaccine responses and which may determine their effectiveness. The microbiome is recognized as a significant regulator of immune development and response, whose role in regulating some traditional vaccine platforms has recently been discovered. Using germ-free and specific-pathogen-free mouse models in combination with different protein, DNA, and mRNA vaccine regimens, we demonstrate that the microbiome is a significant regulator of nucleic acid vaccine immunogenicity. While the presence of the microbiome enhances CD8+ T cell responses to mRNA lipid nanoparticle (LNP) immunization, the microbiome suppresses immunoglobulin and CD4+ T cell responses to DNA-prime, DNA-protein-boost immunization, indicating contrasting roles for the microbiome in the regulation of these different nucleic acid vaccine platforms. In the case of mRNA-LNP vaccination, germ-free mice display reduced dendritic cell/macrophage activation that may underlie the deficient vaccine response. Our study identifies the microbiome as a relevant determinant of nucleic acid vaccine response with implications for their continued therapeutic development and deployment.

immunology↗

bioRxiv2022

A pan-variant mRNA-LNP T cell vaccine protects HLA transgenic mice from mortality after infection with SARS-CoV-2 Beta

Clinically licensed COVID-19 vaccines ameliorate viral infection by inducing vaccinee production of neutralizing antibodies that bind to the SARS-CoV-2 Spike protein to inhibit viral cellular entry (Walsh et al., 2020; Baden et al., 2021), however the clinical effectiveness of these vaccines is transitory as viral variants arise that escape antibody neutralization (Tregoning et al., 2021; Willett et al., 2022). Vaccines that solely rely upon a T cell response to combat viral infection could be transformational because they can be based on highly conserved short peptide epitopes that hold the potential for pan-variant immunity, but a mRNA-LNP T cell vaccine has not been shown to be sufficient for effective antiviral prophylaxis. Here we show that a mRNA-LNP vaccine based on highly conserved short peptide epitopes activates a CD8+ and CD4+ T cell response that prevents mortality in HLA-A*02:01 transgenic mice infected with the SARS-CoV-2 Beta variant of concern (B.1.351). In mice vaccinated with the T cell vaccine, 24% of the nucleated cells in lung were CD8+ T cells on day 7 post infection. This was 5.5 times more CD8+ T cell infiltration of the lungs in response to infection compared to the Pfizer-BioNTech Comirnaty(R) vaccine. Between days 2 and 7 post infection, the number of CD8+ T cells in the lung increased in mice vaccinated with the T cell vaccine and decreased in mice vaccinated with Comirnaty(R). The T cell vaccine did not produce neutralizing antibodies, and thus our results demonstrate that SARS-CoV-2 viral infection can be controlled by a T cell response alone. Our results suggest that further study is merited for pan-variant T cell vaccines, and that T cell vaccines may be relevant for individuals that cannot produce neutralizing antibodies or to help mitigate Long COVID.

immunology↗

bioRxiv2022

Molecular fate-mapping of serum antibodies reveals the effects of antigenic imprinting on repeated immunization

The ability of serum antibody to protect against pathogens arises from the interplay of antigen-specific B cell clones of different affinities and fine specificities. These cellular dynamics are ultimately responsible for serum-level phenomena such as antibody imprinting or "Original Antigenic Sin" (OAS), a proposed propensity of the immune system to rely repeatedly on the first cohort of B cells that responded to a stimulus upon exposure to related antigens. Imprinting/OAS is thought to pose a barrier to vaccination against rapidly evolving viruses such as influenza and SARS-CoV-2. Precise measurement of the extent to which imprinting/OAS inhibits the recruitment of new B cell clones by boosting is challenging because cellular and temporal origins cannot readily be assigned to antibodies in circulation. Thus, the extent to which imprinting/OAS impacts the induction of new responses in various settings remains unclear. To address this, we developed a "molecular fate-mapping" approach in which serum antibodies derived from specific cohorts of B cells can be differentially detected. We show that, upon sequential homologous boosting, the serum antibody response strongly favors reuse of the first cohort of B cell clones over the recruitment of new, naIve-derived B cells. This "primary addiction" decreases as a function of antigenic distance, allowing secondary immunization with divergent influenza virus or SARS-CoV-2 glycoproteins to overcome imprinting/OAS by targeting novel epitopes absent from the priming variant. Our findings have implications for the understanding of imprinting/OAS, and for the design and testing of vaccines aimed at eliciting antibodies to evolving antigens.

immunology↗

bioRxiv2022

Lipid nanoparticles delivering constitutively active STING mRNA as a novel anti-cancer therapeutic approach

Treating immunosuppressive tumors represents a major challenge in cancer therapies. Activation of STING signaling has shown remarkable potential to invigorate the immunologically cold tumor microenvironment (TME). However, we and others have shown that STING is silenced in many cancers, including pancreatic ductal adenocarcinoma (PDAC) and Merkel cell carcinoma (MCC), both of which are associated with an immune-dampened TME. In this study, we applied mRNA lipid nanoparticles (LNP) to deliver a permanently active gain-of-function STINGR284S mutant into PDAC and MCC cells. Expression of STINGR284S induces cytokines and chemokines crucial for promoting intratumoral infiltration of CD8+ T cells and, importantly, also leads to robust cancer cell death while avoiding T cell entry and toxicity. Our studies demonstrated that mRNA-LNP delivery of STINGR284S could be explored as a novel therapeutic tool to reactivate antitumor response in an array of STING-deficient cancers while overcoming the toxicity and limitations of conventional STING agonists.

bioengineering↗

bioRxiv2020

Modular lipid nanoparticle platform technology for siRNA and lipophilic prodrug delivery

Successfully employing therapeutic nucleic acids, such as small interfering RNA (siRNA), requires chemical modifications or the use of nanocarrier technology to prevent their degradation in the circulation and to facilitate intracellular delivery. Lipid nanoparticles (LNP) are among the most advanced nanocarriers culminating in the first siRNA therapeutics clinical translation and approval. At the same time, their applicability as modular platform technology due to the interchangeable building blocks and siRNA payload hallmarks one of LNPs major advantages. In addition, drug derivatization approaches to synthesize lipophilic small molecule prodrugs enable stable incorporation in LNPs. This provides ample opportunities to develop combination therapies by co-encapsulating multiple therapeutic agents in a single formulation. Here, we describe how the modular LNP platform can be applied for combined gene silencing and chemotherapy to induce additive anti-cancer effects. We show that various lipophilic taxane prodrug derivatives and siRNA against the androgen receptor, a prostate cancer driver, can be efficiently and stably co-encapsulated in LNPs. In addition, we demonstrate that prodrug incorporation does not affect LNPs gene silencing ability and that the combination therapy induces additive therapeutic effects in vitro. Using a double-radiolabeling approach, we quantitively determined the LNPs and prodrugs pharmacokinetic properties and biodistribution following systemic administration in tumor-bearing mice. Our results indicate that co-encapsulation of siRNA and lipophilic prodrugs into LNPs is an attractive and straightforward approach for combination therapy development. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=159 SRC="FIGDIR/small/907394v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@b61be4org.highwire.dtl.DTLVardef@1e130c5org.highwire.dtl.DTLVardef@148e5dcorg.highwire.dtl.DTLVardef@eb0cb9_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2019

Expression kinetics and innate immune response after electroporation and lipid nanoparticle mediated delivery of a self-amplifying mRNA in the skin of mice

In this work we studied the expression kinetics and innate immune response of a self-amplifying mRNA (sa-RNA) after electroporation and lipid nanoparticle (LNP) mediated delivery in the skin of mice. Intradermal electroporation of the sa-RNA resulted in a plateau-shaped expression with the plateau between day 3 and 10. The overall protein expression of sa-RNA was significant higher than that obtained after electroporation of pDNA or non-replication mRNAs. Moreover, intradermal electroporation of sa-RNA induced a short-lived innate immune response that did not affect the expression of the sa-RNA. A complete different expression profile and innate immune response was observed when LNPs were used. The expression peaked 24h after intradermal injection of sa-RNA-LNPs and subsequently showed a sharp drop. This drop can be explained by the strong innate immune response elicited by the sa-RNA-LNPs 4h after injection. Interestingly, sa-RNA-LNPs were able to transfection the draining lymph nodes after intradermal injection. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=59 SRC="FIGDIR/small/528612v1_ufig1.gif" ALT="Figure 1"> View larger version (16K): org.highwire.dtl.DTLVardef@fcbbb9org.highwire.dtl.DTLVardef@889a46org.highwire.dtl.DTLVardef@48784corg.highwire.dtl.DTLVardef@1d1ecb4_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗