Intracellular Antibody Research Articles

Abstract 05: Renal Resident Tissue Macrophages Contribute to Salt-Dependent Increases in IL-6

Salt-Sensitive hypertension is associated with an increase in pro-inflammatory cytokines and immune cells. We previously showed an acute increase in systolic blood pressure following IL-6 + high salt (HS) after 3 days, coupled with an immediate (1 day) reduction in sodium excretion. Renal resident tissue macrophages (rRTMs) form an intricate network within the kidney and function to both maintain homeostasis and secrete pro-inflammatory cytokines. We hypothesize that rRTMs are primary contributors to the immediate increases in IL-6 following high salt. To test this hypothesis, male wild-type mice lacking a functional CX 3 CR 1 chemokine receptor (CX 3 CR 1 - EGFP+/+ ) or wild-type (Wt, C57Bl6) were used. CX 3 CR 1 is required for RTM localization to the kidney; thus, these mice are rRTM-depleted. Mice were fed HS (1% saline or 4% HS chow) or normal chow (NC) for 6 days and kidneys harvested. Kidneys were digested and FACS analysis performed on total immune cell populations or used for RT-PCR (n=4-5 Wt & rRTM-depleted). Cells were gated on: Live + CD45 + + MHCII + Lyc6C - + B220 - + CD64 + + F4/F80 hi + CD11b lo. Or Lyc6C hi . Lyc6C hi and rRTMs were pre-stimulated (LPS, 1mg/mL, 3hrs) before staining with intracellular IL-6 antibody. FACS data were analyzed as a percent increase (mean fluorescence intensity, MFI) of IL-6 over control. RT-PCR data were analyzed as DCt/housekeeping. Our data show that rRTMs are the most abundant immune cell in the kidney (23.4% of total CD45 + ) and predominantly reside in the cortex and outer medulla (>99%). HS feeding (4%) significantly increased whole kidney IL-6 mRNA (12.0 ± 0.5 vs . 15.3 ± 0.6 DCt Wt NC, **p<0.01). This increase was completely prevented in rRTM-depleted mice. While intracellular IL-6 levels were generally increased in LPS-stimulated Lyc6C hi inflammatory monocytes, the rRTMs showed a preferential increase in intracellular IL-6 with both hyperosmolar saline (1%, >13% increase) and HS chow (4%, >50%). Here, we show that rRTM-depletion prevents the HS-induced increase in kidney IL-6. We additionally show that rRTMs are preferentially increasing intracellular levels of IL-6 following an acute HS load of hyperosmolar saline (1%) or HS chow (4%). We previously demonstrated that IL-6 contributes to increased blood pressure and sodium retention, and these data suggest that rRTMs preferentially contribute to the increased IL-6.

Selection and characterization of human scFvs targeting the SARS-CoV-2 nucleocapsid protein isolated from antibody libraries of COVID-19 patients

In 2019, the novel SARS-CoV-2 coronavirus emerged in China, causing the pneumonia named COVID-19. At the beginning, all research efforts were focused on the spike (S) glycoprotein. However, it became evident that the nucleocapsid (N) protein is pivotal in viral replication, genome packaging and evasion of the immune system, is highly immunogenic, which makes it another compelling target for antibody development alongside the spike protein. This study focused on the construction of single chain fragments variable (scFvs) libraries from SARS-CoV-2-infected patients to establish a valuable, immortalized and extensive antibodies source. We used the Intracellular Antibody Capture Technology to select a panel of scFvs against the SARS-CoV-2 N protein. The whole panel of scFv was expressed and characterized both as intrabodies and recombinant proteins. ScFvs were then divided into 2 subgroups: those that exhibited high binding activity to N protein when expressed in yeast or in mammalian cells as intrabodies, and those purified as recombinant proteins, displaying affinity for recombinant N protein in the nanomolar range. This panel of scFvs against the N protein represents a novel platform for research and potential diagnostic applications.

Nasal tau immunotherapy clears intracellular tau pathology and improves cognitive functions in aged tauopathy mice.

Pathological tau aggregates cause cognitive decline in neurodegenerative tauopathies, including Alzheimer's disease (AD). These aggregates are prevalent within intracellular compartments. Current tau immunotherapies have shown limited efficacy in clearing intracellular tau aggregates and improving cognition in clinical trials. In this study, we developed toxic tau conformation-specific monoclonal antibody-2 (TTCM2), which selectively recognized pathological tau aggregates in brain tissues from patients with AD, dementia with Lewy bodies (DLB), and progressive supranuclear palsy (PSP). TTCM2 potently inhibited tau-seeding activity, an essential mechanism underlying tauopathy progression. To effectively target intracellular tau aggregates and ensure rapid delivery to the brain, TTCM2 was loaded in micelles (TTCM2-ms) and administered through the intranasal route. We found that intranasally administered TTCM2-ms efficiently entered the brain in hTau-tauopathy mice, targeting pathological tau in intracellular compartments. Moreover, a single intranasal dose of TTCM2-ms effectively cleared pathological tau, elevated synaptic proteins, and improved cognitive functions in aged tauopathy mice. Mechanistic studies revealed that TTCM2-ms cleared intracellular, synaptic, and seed-competent tau aggregates through tripartite motif-containing 21 (TRIM21), an intracellular antibody receptor and E3 ubiquitin ligase known to facilitate proteasomal degradation of cytosolic antibody-bound proteins. TRIM21 was found to be essential for TTCM2-ms-mediated clearance of tau pathology. Our study collectively provides evidence of the effectiveness of nasal tau immunotherapy in targeting and clearing intracellular tau pathology through TRIM21 and enhancing cognition in aged tauopathy mice. This study could be valuable in designing effective tau immunotherapies for AD and other tauopathies.

Sar1A overexpression in Chinese hamster ovary cells and its effects on antibody productivity and secretion

Chinese hamster ovary (CHO) cells are the most widely used for therapeutic antibody production. In cell line development, engineering secretion processes such as folding-related protein upregulation is an effective way of constructing cell lines with high recombinant protein productivity. However, there have been few studies on the transport of recombinant proteins between the endoplasmic reticulum (ER) and the Golgi apparatus. In this study, Sar1A, a protein involved in COPII vesicle formation, was focused on to improve antibody productivity by enhancing COPII vesicle-mediated antibody transport from the ER to the Golgi apparatus, and to clarify its effect on the secretion process. The constructed Sar1A-overexpressing CHO cell lines were batch-cultured, in which they showed an increased specific antibody production rate. The intracellular antibody accumulation and the specific localization of the intracellular antibodies were investigated by chase assay using a translation inhibitor and observed by immunofluorescence-based imaging analysis. The results showed that Sar1A overexpression reduced intracellular antibody accumulation, especially in the ER. The effects of the engineered antibody transport on the antibody's glycosylation profile and the unfolded protein response (UPR) pathway were analyzed by liquid chromatography-mass spectrometry and UPR-related gene expression evaluation, respectively. Sar1A overexpression lowered glycan galactosylation and induced a stronger UPR at the end of the batch culture. Sar1A overexpression enhanced the antibody productivity of CHO cells by modifying their secretion process. This approach could also contribute to the production of not only monoclonal antibodies but also other therapeutic proteins that require transport by COPII vesicles.

Visualizing histone H4K20me1 in knock-in mice expressing the mCherry-tagged modification-specific intracellular antibody

During development and differentiation, histone modifications dynamically change locally and globally, associated with transcriptional regulation, DNA replication and repair, and chromosome condensation. The level of histone H4 Lys20 monomethylation (H4K20me1) increases during the G2 to M phases of the cell cycle and is enriched in facultative heterochromatin, such as inactive X chromosomes in cycling cells. To track the dynamic changes of H4K20me1 in living cells, we have developed a genetically encoded modification-specific intracellular antibody (mintbody) probe that specifically binds to the modification. Here, we report the generation of knock-in mice in which the coding sequence of the mCherry-tagged version of the H4K20me1-mintbody is inserted into the Rosa26 locus. The knock-in mice, which ubiquitously expressed the H4K20me1-mintbody, developed normally and were fertile, indicating that the expression of the probe does not disturb the cell growth, development, or differentiation. Various tissues isolated from the knock-in mice exhibited nuclear fluorescence without the need for fixation. The H4K20me1-mintbody was enriched in inactive X chromosomes in developing embryos and in XY bodies during spermatogenesis. The knock-in mice will be useful for the histochemical analysis of H4K20me1 in any cell types.

Characterization of cells expressing lipocalin-2 (LCN2) as a reporter.

Lipocalin-2 (LCN2), an effector molecule of the innate immune system that is small enough to be tagged as a reporter molecule, can be coupled with the ferric ion through a siderophore such as enterobactin (Ent). Mintbody (modification-specific intracellular antibody) can track a posttranslational protein modification in epigenetics. We constructed plasmids expressing the LCN2 hybrid of mintbody to examine the potential of LCN2 as a novel reporter for magnetic resonance imaging (MRI). Cells expressing the LCN2 hybrid of mintbody showed proper expression and localization of the hybrid and responded reasonably to Ent, suggesting their potential for in vivo study by MRI.

Abstract LB291: High-plexy intracellular and surface CITE-Seq offers multiomic insights into cell function

Abstract CITE-Seq allows researchers to combine high-plex protein information with whole transcriptome sequencing to gain insights about individual cell states. Due to the harsh fixation and permeabilization required for intracellular (IC) antibody staining, only a few studies have recovered mRNA expression profiles alongside IC protein detection. This experiment utilized a novel IC CITE-Seq assay that enables robust profiling of multiple IC protein targets in combination with mRNA and high-plex surface proteins. In this study, we stimulated human peripheral blood mononuclear cells (PBMCs) alongside a resting control. After stimulation, we stained the surface proteins with a 40-plex BD® AbSeq Panel, including the Immune Discovery Panel and human Single-Cell Multiplexing Kit (SMK). Resting and stimulated cells were pooled, and a portion of the sample pool immediately underwent cell capture as a live control using a BD Rhapsody™ single-cell microwell system. The other portion of the pool was stored in BD® OMICS-Guard Sample Preservation Buffer for either 5 minutes or 24 hours followed by permeabilization, IC staining with a 10-plex IC AbSeq Panel (50-plex total, surface and IC), and cells captured on the the same system. We show IC protein detection for the expected positive targets, including pH2AX, actCaspase-3, and cPARP in the stimulated population, as well as T-Bet, Granzyme B and Helios in the resting lymphocytes. Analysis shows excellent correspondence between IC CITE-Seq protein and transcriptome for T-Bet, Granzyme B and Helios. The gene expression correlation for surface antigen and mRNA between the IC and live control each had R2 values > 0.9. The mRNA sensitivity for the IC sample compared to live control was within whole transcriptome analysis (WTA) assay variation at 86–89% and 95–97% median molecules and genes per cell. Our data showed that the new IC CITE-Seq assay can provide rich single-cell multiomics information including mRNA and surface and intracellular proteins. For Research Use Only. Not for use in diagnostic or therapeutic procedures.BD, the BD Logo and BD Rhapsody are trademarks of Becton, Dickinson and Company or itsaffiliates. © 2023 BD. All rights reserved. NPM-2532 (v1.0) 1023 Citation Format: Tracy L. Campbell, Adam Wright, Ying Wah Lee, Anne Tran, Yan Chen, Joe Olives, Hye-Won Song, Larry Wang. High-plexy intracellular and surface CITE-Seq offers multiomic insights into cell function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB291.

P086 Identification of a Novel Immunometabolic Target and Agonist for PLXDC2 for Amelioration of DSS Colitis Model in Mice

Abstract Background PLXDC2 is expressed on the cell surface of macrophage, dendritic and specific mesenchymal and epithelial cells whose activation shifts cellular metabolism and reduces oxidative stress to rebalance the immune response and decrease inflammation. It’s role in IBD pathogenesis is unknown. PLXDC2 activation improves disease severity in rheumatoid arthritis models1, while loss of PLXDC2 exacerbates the severity of disease in DSS colitis2. PX-04 is a novel, first-in-class, orally active PLXDC2 agonist. Here, we report on the consequences of activating PLXDC2 using PX-04 in an acute DSS colitis model. Methods Mice were given DSS in drinking water for seven days to induce disruption of the epithelial layer. At project initiation, mice were 8 weeks of age and began once daily dosing with 20mg/kg of PX-04 24 hours after being placed on DSS. Mice were weighed and scored daily for 15 symptoms of disease (weight loss, diarrhea, rectal bleeding, rectal inflammation, pain, & overall behavior). Colons were collected and digested, and the resultant cellular suspensions were filtered to produce single cell suspensions. Colonic Lamina Propria Immune cells were isolated by Percoll gradient centrifugation. Cells were labeled with mixtures of extracellular (CD45, CD3, CD4, CD8, CD19, NK1.1, CD25, F4/80, CD11b, Gr1, CX3CR1, CD64) and intracellular (Tbet, RORγT, FOXP3, IFNγ, IL17, IL10, TNFα) antibodies in a sequential live staining in 96-well plates. Data was acquired using a FACS Celesta flow cytometer with FACSDiva software. Results Oral PX-04 treatment decreased the cumulative disease activity of mice challenged with DSS (FIG 1A). Immunologically, PX-04 affected both the adaptive and innate immune responses. First, PX-04 greatly decreased Th17 cells in the colon, while providing a slight increase to regulatory CD4+ T cells (FIG. 1C). A lower proportion of Natural Killer (NK) cells (FIG. 7D) produced IFNγ. Meanwhile, the proportion of TNF producing dendritic cells was decreased by PX-04 treatment. Conclusion Conclusion: PLXDC2 is expressed in cells relevant to IBD pathogenesis. PX-04, which binds to and activates PLXDC2, effectively decreases levels of effector T cells and myeloid cells, as well as overall disease severity in acute DSS colitis, warranting further investigation. 1Tubau-Juni et al. J Immunol 206(Supp) 2Tubau-Juni et al. Sci Rep 10(1)

Alcohol-containing protein transduction domain mimics

The application and design of protein transduction domains (PTDs) and protein transduction domain mimics (PTDMs) have revolutionized the field of biomacromolecule delivery. Our group has previously synthesized block copolymer PTDMs with well-defined hydrophobic and cationic blocks via ring-opening metathesis polymerization (ROMP). We have optimized the balance of hydrophobicity and cationic density to intracellularly deliver model proteins, active proteins, and antibodies. Despite the presence of serine, threonine, and tyrosine in naturally occurring PTDs, synthetic analogs have yet to be studied in PTDMs. In our present work, we introduce different alcohol groups to our PTDM structures as a new design parameter. A library of nine novel PTDMs were synthesized to incorporate alcohol groups of varying structures and evaluated based on their ability to intracellularly deliver fluorescently labeled antibodies. One PTDM in this novel library, named PTDM4, incorporates alcohol groups in both the hydrophobic and cationic blocks and was found to be the best performing PTDM with almost twice the median fluorescence intensity of the delivered antibody and half the cationic density compared to our positive control, a PTDM thoroughly studied by our group. PTDM4 was further studied by intracellularly delivering the active enzyme, TAT-Cre Recombinase. The activity of TAT-Cre Recombinase delivered by PTDM4 was comparable to that of the positive control, again with half the cationic density. This study is one of the first to examine the effects of alcohol groups on intracellular antibody and active enzyme delivery.

Epileptic manifestations of autoimmune encephalitis

The development of autoimmune encephalitis (AIE) is due to the formation of intracellular and extracellular neuronal antibodies to various structures of the brain tissue. Their prevalence and morbidity are comparable to infectious ones, and the detection rate has recently been increasing. Acute symptomatic seizures are an important component of the clinical core of AIE and are associated with a heterogeneous group of autoantibodies, which along with the features of the lesion topic causes a signi fi cant clinical variety of seizures. The EEG has ictal and interictal features, and the development of electrographic subclinical seizures is also possible. The basis of the treatment of AIE with epileptic seizures is immunotherapy along with the use of antiepileptic drugs with sodium channel blocking properties.

A Specific Mini-Intrabody Mediates Lysosome Degradation of Mutant Huntingtin.

Accumulation of misfolded proteins leads to many neurodegenerative diseases that can be treated by lowering or removing mutant proteins. Huntington's disease (HD) is characterized by the intracellular accumulation of mutant huntingtin (mHTT) that can be soluble and aggregated in the central nervous system and causes neuronal damage and death. Here, an intracellular antibody (intrabody) fragment is generated that can specifically bind mHTT and link to the lysosome for degradation. It is found that delivery of this peptide by either brain injection or intravenous administration can efficiently clear the soluble and aggregated mHTT by activating the lysosomal degradation pathway, resulting in amelioration of gliosis and dyskinesia in HD knock-in (KI-140Q) mice. These findings suggest that the small intrabody peptide linked to lysosomes can effectively lower mutant proteins and provide a new approach for treating neurodegenerative diseases that are caused by the accumulation of mutant proteins.

Utility of Protein Microarrays for Detection of Classified and Novel Antibodies in Autoimmune Neurologic Disease.

Neural antibodies are detected by tissue-based indirect immunofluorescence assay (IFA) in Mayo Clinic's Neuroimmunology Laboratory practice, but the process of characterizing and validating novel antibodies is lengthy. We report our assessment of human protein arrays. Assessment of arrays (81% human proteome coverage) was undertaken using diverse known positive samples (17 serum and 14 CSF). Samples from patients with novel neural antibodies were reflexed from IFA to arrays. Confirmatory assays were cell-based (CBA) or line blot. Epitope mapping was undertaken using phage display immunoprecipitation sequencing (PhiPSeq). Control positive samples known to be reactive with linear epitopes of intracellular antigens (e.g., ANNA-1 [anti-Hu]) were readily identified by arrays in 20 of 21 samples. By contrast, 10 positive controls known to be enriched with antibodies against cell surface protein conformational epitopes (e.g., GluN1 subunit of NMDA-R) were indistinguishable from background signal. Three antibodies, previously characterized by other investigators (but unclassified in our laboratory), were unmasked in 4 patients using arrays (July-December 2022): Neurexin-3α, 1 patient; regulator of gene protein signaling (RGS)8, 1 patient; and seizure-related homolog like 2 (SEZ6L2), 2 patients. All were accompanied by previously reported phenotypes (encephalitis, 1; cerebellar ataxia, 3). Patient 1 had subacute onset of seizures and encephalopathy. Neurexin-3α ranked high in CSF (second ranked neural protein) but low in serum (660th overall). Neurexin-3α CBA was positive in both samples. Patient 2 presented with rapidly progressive cerebellar ataxia. RGS8 ranked the highest neural protein in available CSF sample by array (third overall). RGS8-specific line blot was positive. Patients 3 and 4 had rapidly progressive cerebellar ataxia. SEZ6L2 was the highest ranked neural antigen by arrays in all samples (CSF, 1, serum, 2; Patient 3, ranked 9th overall in CSF, 11th in serum; Patient 4, 6th overall in serum]). By PhIPSeq, diverse neurexin-3α epitopes (including cell surface) were detected in CSF from patient 1, but no SEZ6L2 peptides were detected for serum or CSF samples from Patient 3. Individualized autoimmune neurologic diagnoses may be accelerated using protein arrays. They are optimal for detection of intracellular antigen-reactive antibodies, though certain cell surface-directed antibodies (neurexin-3α and SEZ6L2) may also be detected.

Aptamer-conjugated gold nanoparticles platform as the intracellular delivery of antibodies for cancer therapy

Antibodies are being increasingly used for therapeutic purposes due to their remarkable target specificity and affinity. However, currently available antibody therapies are restricted to target proteins in the outer cell membrane or in the extracellular fluids because of the lack of technologies for effective intracellular delivery of antibodies. Here, we report an efficient and versatile intracellular antibody delivery system. This system is based on gold nanoparticles (AuNPs) conjugated with DNA aptamers (Apt) against the Fc region of IgG (AuNP-AptIgG), allowing to load any antibodies onto the AuNP-AptIgG by simple mixing. This AuNP-AptIgG-Ab platform was effective for cytosolic delivery of antibodies to clinically important mutant proteins via scavenger receptors and caveolae-mediated endocytosis. Specifically, cancer cells expressing BRAFV600E, a variant of BRAF identified in numerous types of cancers, exhibited reduced cell viability by 70% when BRAFV600E antibodies were intracellularly delivered using the AuNP-AptIgG (AuNP-AptIgG-αBRAFV600E). In addition, subcutaneous injection of AuNP-AptIgG-αBRAFV600E into in vivo xenografted melanoma tumors expressing BRAFV600E resulted in both inhibition of proliferation and induction of apoptosis, leading to tumor regression in mice. Thus, our findings indicate that the AuNP-AptIgG-Ab system can serve as a promising platform for effective intracellular delivery of antibodies for therapeutic purposes.

Frequency and Referral Patterns of Neural Antibody Studies During the COVID-19 Pandemic: Experience From an Autoimmune Neurology Center.

To determine whether the frequency of paraneoplastic or autoimmune encephalitis antibodies examined in a referral center changed during the COVID-19 pandemic. The number of patients who tested positive for neuronal or glial (neural) antibodies during pre-COVID-19 (2017-2019) and COVID-19 (2020-2021) periods was compared. The techniques used for antibody testing did not change during these periods and included a comprehensive evaluation of cell-surface and intracellular neural antibodies. The chi-square test, Spearman correlation, and Python programming language v3 were used for statistical analysis. Serum or CSF from 15,390 patients with suspected autoimmune or paraneoplastic encephalitis was examined. The overall positivity rate for antibodies against neural-surface antigens was similar in the prepandemic and pandemic periods (neuronal 3.2% vs 3.5%; glial 6.1 vs 5.2) with a mild single-disease increase in the pandemic period (anti-NMDAR encephalitis). By contrast, the positivity rate for antibodies against intracellular antigens was significantly increased during the pandemic period (2.8% vs 3.9%, p = 0.01), particularly Hu and GFAP. Our findings do not support that the COVID-19 pandemic led to a substantial increase of known or novel encephalitis mediated by antibodies against neural-surface antigens. The increase in Hu and GFAP antibodies likely reflects the progressive increased recognition of the corresponding disorders.

P.028 Is there utility in duplicating antibody testing for autoimmune encephalitis? A comparison of results obtained from Mayo and Mitogen Dx

Background: Autoantibody testing for suspected autoimmune encephalitis (AIE) in Alberta is commonly performed by Mitogen Dx (MDx) using cell-based assays (CBAs) for cell surface antibodies and line immunoassay (LA) for intracellular antibodies without confirmatory tissue immunofluorescence/immunohistochemistry (TIFF/IHC). Duplicate testing is often sent to Mayo Clinic (MC) verify, resulting in increased costs. Methods: Antibody panel results were obtained for all patients who had testing sent to both MC and MDx from adult hospitals in Calgary between 2018 and 2020. Positive antibodies were evaluated to be pathogenic/non-pathogenic by chart review and expert consensus. Results: Thirty-four individuals had antibody panels completed at both labs. Overall agreement (positive/negative panel) was fair (κ = 0.24, p =.08), even after excluding low-titre GAD65 antibodies through MC (n=9, 26.5%). MDx reported more non-pathogenic serum results, including: anti-SOX1 (n=3), anti-NMDAR (n=2) and anti-GABA(B)R (n=1). All pathogenic antibodies (n=3) were positive in both laboratories. Conclusions: No new pathogenic antibodies were identified by sending duplicate testing to MC; however, a larger number of non-pathogenic antibodies were reported by MDx, likely due to lack of confirmatory TIFF/IHC. Antibody testing for AIE should be done in labs performing confirmatory TIFF/IHC on all CBA/LA results to avoid unnecessary investigations and/or treatments.

Trim-Away ubiquitinates and degrades lysine-less and N-terminally acetylated substrates

TRIM proteins are the largest family of E3 ligases in mammals. They include the intracellular antibody receptor TRIM21, which is responsible for mediating targeted protein degradation during Trim-Away. Despite their importance, the ubiquitination mechanism of TRIM ligases has remained elusive. Here we show that while Trim-Away activation results in ubiquitination of both ligase and substrate, ligase ubiquitination is not required for substrate degradation. N-terminal TRIM21 RING ubiquitination by the E2 Ube2W can be inhibited by N-terminal acetylation, but this doesn’t prevent substrate ubiquitination nor degradation. Instead, uncoupling ligase and substrate degradation prevents ligase recycling and extends functional persistence in cells. Further, Trim-Away degrades substrates irrespective of whether they contain lysines or are N-terminally acetylated, which may explain the ability of TRIM21 to counteract fast-evolving pathogens and degrade diverse substrates.

KRAS-specific antibody binds to KRAS protein inside colorectal adenocarcinoma cells and inhibits its localization to the plasma membrane.

Colorectal cancer (CRC) is the third highest incidence cancer and a leading cause of cancer mortality worldwide. To date, chemotherapeutic treatment of advanced CRC that has metastasized has a dismayed success rate of less than 30%. Further, most (80%) sporadic CRCs are microsatellite-stable and are refractory to immune checkpoint blockade therapy. KRAS is a gatekeeper gene in colorectal tumorigenesis. Nevertheless, KRAS is 'undruggable' due to its structure. Thus, focus has been diverted to develop small molecule inhibitors for its downstream effector such as ERK/MAPK. Despite intense research efforts for the past few decades, no small molecule inhibitor has been in clinical use for CRC. Antibody targeting KRAS itself is an attractive alternative. We developed a transient ex vivo patient-derived matched mucosa-tumor primary culture to assess whether anti-KRAS antibody can be internalized to bind and inactivate KRAS. We showed that anti-KRAS antibody can enter live mucosa-tumor cells and specifically aggregate KRAS in the cytoplasm, thus hindering its translocation to the inner plasma membrane. The mis-localization of KRAS reduces KRAS dwelling time at the site where it tethers to activate downstream effectors. We previously showed that expression of SOX9 was KRAS-mutation-dependent and possibly a better effector than ERK in CRC. Herein, we showed that anti-KRAS antibody treated tumor cells have less intense SOX9 cytoplasmic and nuclear staining compared to untreated cells. Our results demonstrated that internalized anti-KRAS antibody inhibits KRAS function in tumor. With an efficient intracellular antibody delivery system, this can be further developed as combinatorial therapeutics for CRC and other KRAS-driven cancers.

Intracellular Antibodies for Drug Discovery and as Drugs of the Future.

The application of antibodies in cells was first shown in the early 1990s, and subsequently, the field of intracellular antibodies has expanded to encompass antibody fragments and their use in target validation and as engineered molecules that can be fused to moieties (referred to as warheads) to replace the Fc effector region of a whole immunoglobulin to elicit intracellular responses, such as cell death pathways or protein degradation. These various forms of intracellular antibodies have largely been used as research tools to investigate function within cells by perturbing protein activity. New applications of such molecules are on the horizon, namely their use as drugs per se and as templates for small-molecule drug discovery. The former is a potential new pharmacology that could harness the power and flexibility of molecular biology to generate new classes of drugs (herein referred to as macrodrugs when used in the context of disease control). Delivery of engineered intracellular antibodies, and other antigen-binding macromolecules formats, into cells to produce a therapeutic effect could be applied to any therapeutic area where regulation, degradation or other kinds of manipulation of target proteins can produce a therapeutic effect. Further, employing single-domain antibody fragments as competitors in small-molecule screening has been shown to enable identification of drug hits from diverse chemical libraries. Compounds selected in this way can mimic the effects of the intracellular antibodies that have been used for target validation. The capability of intracellular antibodies to discriminate between closely related proteins lends a new dimension to drug screening and drug development.

Adenovirus vector-mediated single chain variable fragments target the nucleocapsid protein of porcine epidemic diarrhea virus and protect against viral infection in piglets.

Porcine epidemic diarrhea virus (PEDV) mainly infects the intestinal epithelial cells of pigs, causing porcine epidemic diarrhea (PED). In particular, the virus causes severe diarrhea, dehydration, and death in neonatal piglets. Maternal immunity effectively protects neonatal piglets from PEDV infection; however, maternal antibodies can only prevent PEDV attachment and entry into target cells, but have no effects on intracellular viruses. Intracellular antibodies targeting virus-encoded proteins are effective in preventing viral infection. We previously identified four single chain variable fragments (scFvs), ZW1-16, ZW3-21, ZW1-41, and ZW4-16, which specifically targeted the PEDV N protein and significantly inhibited PEDV replication and up-regulated interferon-λ1 (IFN-λ1) expression in host cells. In our current study, the four scFvs were subcloned into replication-defective adenovirus vectors to generate recombinant adenoviruses rAdV-ZW1-16, rAdV-ZW3-21, rAdV-ZW1-41, and rAdV-ZW4-16. ScFvs were successfully expressed in Human Embryonic Kidney 293 (HEK293) cells and intestinal porcine epithelial cell line J2 (IPEC-J2) and were biosafe for piglets as indicated by body temperature and weight, scFv excretion in feces, IFN-γ and interleukin-4 (IL-4) expression in jejunum, and pathological changes in porcine tissue after oral administration. Western blotting, immunofluorescence, and immunohistochemical analyses showed that scFvs were expressed in porcine jejunum. The prophylactic effects of rAdV-ZW, a cocktail of the four rAdV-scFvs, on piglet diarrhea caused by PEDV was investigated. Clinical symptoms in piglets orally challenged with PEDV, following a two-time treatment with rAdV-ZW, were significantly reduced when compared with PEDV-infected piglets treated with phosphate buffered saline (PBS) or rAdV-wild-type. Also, no death and jejunal lesions were observed. ScFv co-localization with the PEDV N protein in vivo was also observed. Next, the expression of pro-inflammatory serum cytokines such as tumor necrosis factor-α (TNF-α), IL-6, IL-8, IL-12, and IFN-λ was assessed by enzyme-linked immunosorbent assay (ELISA), which showed that scFvs significantly suppressed PEDV-induced pro-inflammatory cytokine expression and restored PEDV-inhibited IFN-λ expression. Therefore, our study supported a promising role for intracellular scFvs targeting the PEDV N protein to prevent and treat diarrhea in PEDV-infected piglets.

Evolution of nanobodies specific for BCL11A

Transcription factors (TFs) control numerous genes that are directly relevant to many human disorders. However, developing specific reagents targeting TFs within intact cells is challenging due to the presence of highly disordered regions within these proteins. Intracellular antibodies offer opportunities to probe protein function and validate therapeutic targets. Here, we describe the optimization of nanobodies specific for BCL11A, a validated target for the treatment of hemoglobin disorders. We obtained first-generation nanobodies directed to a region of BCL11A comprising zinc fingers 4 to 6 (ZF456) from a synthetic yeast surface display library, and employed error-prone mutagenesis, structural determination, and molecular modeling to enhance binding affinity. Engineered nanobodies recognized ZF6 and mediated targeted protein degradation (TPD) of BCL11A protein in erythroid cells, leading to the anticipated reactivation of fetal hemoglobin (HbF) expression. Evolved nanobodies distinguished BCL11A from its close paralog BCL11B, which shares an identical DNA-binding specificity. Given the ease of manipulation of nanobodies and their exquisite specificity, nanobody-mediated TPD of TFs should be suitable for dissecting regulatory relationships of TFs and gene targets and validating therapeutic potential of proteins of interest.