High-affinity scFv Research Articles

Rapid and sensitive detection of SARS-CoV-2 based on a phage-displayed scFv antibody fusion with alkaline phosphatase and NanoLuc luciferase

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the subsequent pandemic have led to devastating public health and economic losses. The development of highly sensitive, rapid and inexpensive methods to detect and monitor coronaviruses is essential for family diagnosis, preventing infections, choosing treatments and programs and laying the technical groundwork for viral diagnosis. This study established one-step immunoassays for rapid and sensitive detection of SARS-CoV-2 by using a single-chain variable fragment (scFv) fused to alkaline phosphatase (AP) or NanoLuc (NLuc) luciferase. First, a high-affinity scFv antibody specific to the SARS-CoV-2 nucleocapsid (N) protein was screened from hybridoma cells-derived and phage-displayed library. Next, prokaryotic expression of the scFv-AP and scFv-NLuc fusion proteins were induced, leading to excellent antibody binding properties and enzyme catalytic activities. The scFv-AP fusion had a detection limit of 3 pmol per assay and was used to produce eye-readable biosensor readouts. Moreover, the scFv-NLuc protein was applied in a highly sensitive luminescence immunoassay, achieving a detection limit lower than 0.1 pmol per assay. Therefore, the scFv-AP and scFv-NLuc fusion proteins can be applied for the rapid and simple diagnosis of SARS-CoV-2 to safeguard human health and provide guidance for the detection of other pathogenic viruses.

A novel co-receptor with mutated TIGIT to enhance PSCA CAR-T therapy for bladder cancer.

e14574 Background: TIGIT plays a crucial role in immune regulation, particularly in tumor environments, by acting as an inhibitory receptor. Leveraging its interaction with ligands like CD155 on tumor cells, we developed an innovative CAR-T cell therapy using a mutated TIGIT co-receptor to overcome inhibitory effect induced by CD155, together with targeting Prostate Stem Cell Antigen (PSCA) CAR, chosen for its high expression in bladder and other cancers versus its minimal presence in normal tissues. Methods: We initiated our approach by inducing strategic mutations in TIGIT, selecting a variant with heightened affinity for CD155. Bio-Layer Interferometry (BLI) analysis confirmed the variant's high binding affinity (KD = 1.635 nM). This mutated TIGIT, combined with CD28's signaling components, was integrated as a co-receptor in our CAR construct. For PSCA targeting, we isolated a high-affinity ScFv against PSCA from a fully human phage display library. The specificity of this ScFv for PSCA was rigorously validated using Cell Membrane Protein Targeting Catcher (CMPTC) technology, covering over 6000 human cell membrane proteins. Results: In our comparative analyses, CAR-T cells featuring a mutated TIGIT co-receptor (T-PSCA-CAR-T) matched the cytotoxicity of traditional second-generation BBz-structured CAR-T cells (PSCA-CAR-T) against PSCA-expressing HT-1376 bladder cancer cells. However, T-PSCA-CAR-T cells distinguished themselves by producing significantly higher IFN-γ levels (3805.683±65.506 vs 1271.712±39.768 pg/mL). Our in vivo tumor model, utilizing luciferase-expressing HT-1376 cells, demonstrated T-PSCA-CAR-T's enhanced anti-tumor efficacy, as evidenced by a more significant reduction in bioluminescence signal intensity (average decreasing ratio: 0.02 for T-PSCA-CAR-T vs 0.35 for PSCA-CAR-T; p < 0.05). These results underscore the efficacy of the mutated TIGIT co-receptor in improving CAR-T cell therapy. Conclusions: Our study signifies a transformative advancement in CAR-T cell therapy by incorporating a mutated TIGIT co-receptor, markedly improving therapeutic outcomes in bladder cancer treatment. Utilizing PSCA as a model target not only validates the efficacy of this novel approach but also paves the way for its application in a broader range of cancers, representing a significant leap in the field of immunotherapy.

Isolation and characterization of a novel single-chain variable fragment (scFv) against Lymphocyte function-associated antigen-1 (LFA-1) using phage display method.

Lymphocyte function-associated antigene-1 (LFA-1) is a well-described integrin found on lymphocytes and other leukocytes, which is known to be overexpressed in leukemias and lymphomas. This receptor plays a significant role in immune responses such as T-cell activation, leukocyte cell-cell interactions, and trafficking of leukocyte populations. Subsequently, binders of LFA-1 emerge as potential candidates for cancer and autoimmune therapy. This study used the phage display technique to construct and characterize a high-affinity single-chain fragment variable (scFv) antibody against LFA-1. After expression, purification, dialysis, and concentration of the recombinant LFA-1 protein, four female BALB/c mice were immunized, splenocyte's mRNA was extracted, and cDNA was synthesized. A scFv library was constructed by linking the amplified VH/Vκ fragments through a 72-bp linker using SOEing PCR. Next, the scFv gene fragments were cloned into the pComb-3XSS phagemid vector; thus, the phage library was developed. The selection process involved three rounds of phage-bio-panning, polyclonal, and monoclonal phage ELISA. AF17 was chosen and characterized among the positive clones through SDS-PAGE, Western blotting, indirect ELISA, and in-silico analyses. The results of the study showed the successful construction of a high-affinity scFv library against LFA-1. The accuracy of the AF17 production and its ability to bind to the LFA-1 were confirmed through SDS-PAGE, Western blot, and ELISA. This study highlights the potential application of the high-affinity AF17 against LFA-1 for targeting T lymphocytes for therapeutic purposes.

Canine distemper virus (CDV)-neutralizing activities of an anti-CDV canine-derived single-chain variable antibody fragment 4-15 (scFv 4-15) screened by phage display technology

Canine distemper virus (CDV) is a highly contagious pathogen that causes severe diarrhea, fever and vomiting in domestic dogs, posing a serious threat to the dog breeding industry. Currently, there are no effective therapeutic agents for emergency treatment despite the availability of vaccines against CDV infection. Single-chain fragment variable (scFv) antibody has been demonstrated to effectively inhibit virus infections, suggesting a potential candidate as a therapeutic agent for canine distemper. In this study, a phage-displayed scFv library was constructed from the peripheral blood lymphocytes of dog immunized intramuscularly with live-attenuated CDV vaccine, and was subjected to four rounds of pannings against CDV. Subsequent indirect enzyme-linked immunosorbent assay screening revealed high-affinity scFv antibodies specific to CDV, and indirect immunofluorescence assay screening revealed CDV-neutralizing activity of scFv antibodies. Our results showed that a scFv antibody 4–15 (scFv 4–15) with high-affinity binding to CDV and neutralizing activity against CDV was obtained, which displayed effective therapeutic potential in vivo for dogs challenged with a lethal dose of CDV. Conclusively, the scFv 4–15 with high-affinity binding and neutralizing activity to CDV that was obtained by phage display technology provides a promising candidate for the therapeutic agents against CDV infection.

Developing a dual VEGF/PDL1 inhibitor based on high-affinity scFv heterodimers as an anti-cancer therapeutic strategy

Cancer progression is enhanced by the interaction of programmed death-ligand 1 (PDL1), which is associated with inhibition of the immune response against tumors, and vascular endothelial growth factor (VEGF), which inhibits immune cell activity while inducing angiogenesis and proliferation of cancer cells. Dual inhibition of PDL1 and VEGF may therefore confer a synergistic anti-cancer therapeutic effect. We present a novel strategy for developing a therapeutic that simultaneously binds and inhibits both PDL1 and VEGF. We generated a bi-specific protein, designated DuRan-Bis, comprising a single chain variable fragment (scFv)-based inhibitor of PDL1 fused to an scFv-based inhibitor of VEGF, with the latter being attached to an Fc fragment. We found that DuRan-Bis binds to both PDL1 and VEGF with high affinity. Compared to treatments with mono-specific proteins, alone or in combination, the DuRan-Bis chimera showed superior inhibition of the proliferation of glioblastoma cells. In comparison to treatment with immune cells alone, a combination of immune cells with DuRan-Bis decreased the viability of head and neck cancer cells. To the best of our knowledge, this study is the first to use a single polypeptide chain scFv-scFv-Fc scaffold for engineering a high-affinity bi-specific inhibitor of PDL1 and VEGF.

Human-murine chimeric autoantibodies with high affinity and specificity for systemic sclerosis.

Scleroderma 70 (Scl-70) is commonly used in the clinic for aiding systemic sclerosis (SSc) diagnosis due to its recognition as autoantibodies in the serum of SSc patients. However, obtaining sera positive for anti-Scl-70 antibody can be challenging; therefore, there is an urgent need to develop a specific, sensitive, and easily available reference for SSc diagnosis. In this study, murine-sourced scFv library were screened by phage display technology against human Scl-70, and the scFvs with high affinity were constructed into humanized antibodies for clinical application. Finally, ten high-affinity scFv fragments were obtained. Three fragments (2A, 2AB, and 2HD) were select for humanization. The physicochemical properties of the amino acid sequence, three-dimensional structural basis, and electrostatic potential distribution of the protein surface of different scFv fragments revealed differences in the electrostatic potential of their CDR regions determined their affinity for Scl-70 and expression. Notably, the specificity test showed the half-maximal effective concentration values of the three humanized antibodies were lower than that of positive patient serum. Moreover, these humanized antibodies showed high specificity for Scl-70 in diagnostic immunoassays for ANA. Among these three antibodies, 2A exhibited most positive electrostatic potential on the surface of the CDRs and highest affinity and specificity for Scl-70 but with least expression level; thus, it may provide new foundations for developing enhanced diagnostic strategies for SSc.

Dual CAR-T cells to treat cancers co-expressing NKG2D and PD1 ligands in xenograft models of peritoneal metastasis.

While the expression of either NKG2D ligands or PD-1 ligands has been reported in various types of cancers, the co-expression of the two sets of ligands in the same tumour tissues is still un-investigated. After examining 68 primary ovarian cancer samples, we observed around 80% of the co-expression in low grade serous and endometrioid ovarian cancer samples. We then constructed a dual CAR system that splits the conventional single-input of a 2nd generation CAR into two independent chimeric receptors, one composed of the NKG2D extracellular domain linked with DAP12 for T cell activation and another using the PD-1 extracellular domain linked with 4-1BB for costimulatory signal 2 input. Given the limitation of the low-affinity PD-1 receptor in recognizing cancer cells with low levels of PD-1 ligands, we also used a high-affinity scFv specific to PD-L1 in our combinatorial approach to expand the range of target cancer cells with different expression levels of PD-L1. The two types of dual CAR-T cells were generated through electroporation of non-viral piggyBac transposon plasmids and were effective in eliminating the target cancer cells. Especially, the dual CAR-T cells with anti-PD-L1 scFv were capable of eradicating established tumors in mouse models of peritoneal metastasis of colorectal cancer and ovarian cancer. Since both NKG2D ligands and PD-1 ligands have been marked as favourable cancer therapeutic targets, the new dual CAR-T cells developed in this study hold attractive application potential in treating metastatic peritoneal carcinoma.

Isolation and characterization of a novel GRP78-specific single-chain variable fragment (scFv) using ribosome display method.

Glucose-regulated protein 78 (GRP78) is a well-characterized endoplasmic reticulum (ER) chaperon frequently overexpressed at the surface of tumor cells and associated with tumor survival, metastasis, and chemoresistance. Hence, potential GRP78 binders emerge as promising candidates for cancer therapy and diagnosis. We applied ribosome display to isolate a single-chain variable domain (scFv) specific for the C-terminal domain of a recombinant human GRP78 (CGRP). Six female BALB/c mice were immunized and then splenocyte mRNA was extracted. An scFv-ribosome display library was established by joining the amplified VH/Vκ fragments through a 72-bp linker using overlap extension PCR. Then, selection was performed by applying two rounds of eukaryotic ribosome display panning with stepwise decreased amount of CGRP. Ultimately, the selected scFv was characterized using the indirect-ELISA assay, competitive-ELISA assay, Western blotting, Surface Plasmon Resonance (SPR), and in-silico analyses. The constructed library had a length of ~ 1100bp and the high-affinity scFvs were isolated using the outputs of the final panning round. Among 60 positive clones, GSF3 was selected and its expression, purification, and binding capacity was confirmed by SDS-PAGE and Western blotting. GSF3 exhibited an affinity of 13 × 107M-1 to CGRP as assessed by SPR. Moreover, the in-silico analyses indicated that GSF3 binds the C-terminal domain of GRP78 through key residues engaged in antibody-antigen interactions. We found that ribosome display is a swift and reliable technique for specific and high-affinity scFv isolation. Moreover, our results suggest that GSF3 might be applied as a potential cancer immunotherapeutic and diagnostic tool if this approach is carefully followed by successful preclinical and clinical evaluations to validate the findings for further confirmation.

Phage Display Screening of Bovine Antibodies to Foot-and-Mouth Disease Virus and Their Application in a Competitive ELISA for Serodiagnosis.

For serodiagnosis of foot-and-mouth disease virus (FMDV), monoclonal antibody (MAb)-based competitive ELISA (cELISA) is commonly used since it allows simple and reproducible detection of antibody response to FMDV. However, the use of mouse-origin MAb as a detection reagent is questionable, as antibody responses to FMDV in mice may differ in epitope structure and preference from those in natural hosts such as cattle and pigs. To take advantage of natural host-derived antibodies, a phage-displayed scFv library was constructed from FMDV-immune cattle and subjected to two separate pannings against inactivated FMDV type O and A. Subsequent ELISA screening revealed high-affinity scFv antibodies specific to a serotype (O or A) as well as those with pan-serotype specificity. When BvO17, an scFv antibody specific to FMDV type O, was tested as a detection reagent in cELISA, it successfully detected FMDV type O antibodies for both serum samples from vaccinated cattle and virus-challenged pigs with even higher sensitivity than a mouse MAb-based commercial FMDV type O antibody detection kit. These results demonstrate the feasibility of using natural host-derived antibodies such as bovine scFv instead of mouse MAb in cELISA for serological detection of antibody response to FMDV in the susceptible animals.

Enhancing the Antigen-Sensitivity of the CD22 CAR through Modulation of the Affinity and Linker-Length of the Single-Chain Fragment Variable

The advent of chimeric antigen receptor (CAR) T cell therapy has revolutionized the treatment of relapsed/refractory acute lymphoblastic leukemia (r/r ALL). CD19 directed CAR T cells have demonstrated the ability to induce complete remissions in up to 90% of r/r ALL patients. Despite this remarkable upfront success, relapse after CAR T cell therapy remains a major obstacle to long term remissions. A major mechanism for relapse after CD19-directed CAR T cell therapy is the recurrence of antigen-negative ALL cells. In recent years, CD22 CAR T cell therapy has emerged as an effective salvage therapy for patients with CD19-negative ALL. In a phase I clinical trial, CD22 CAR T cells were able to induce remission in up to 80% of patients with CD19-negative ALL. Patients achieving remission, who did not undergo a consolidative hematopoietic stem cell transplant, were found to be at high risk of relapse due to downregulation of the CD22 antigen below the threshold required for effective CD22 CAR T cell activity. Thus, strategies to increase the antigen-sensitivity of CD22 CAR T cells have the potential to enhance the induction and duration of remission in ALL patients. As the properties of a CAR that influence sensitivity to antigen are not well defined, we began by testing the impact of increasing the affinity of the single-chain fragment variable (scFv) for the CD22 antigen. T cells from healthy donors were activated and transduced with a second-generation, 4-1BB CAR containing either the standard affinity (SA)-m971 scFv used in the prior clinical trial, or a high affinity (HA) scFv generated by affinity maturation of the m971 scFv. SA- and HA-CD22 CAR T cells were evaluated in vitro and in vivo against clones of the pre-B ALL cell line, NALM6, which express CD22 at wild type levels (CD22WT), sub-physiologic levels (CD22Lo), supra-physiologic levels (CD22Hi) or in which CD22 was deleted (CD22Neg). We found that the amount of CD22 expressed on the leukemia cells resulted in dose-dependent expression of activation markers, such as CD69 and CD25 (p<0.05) on CD22 CAR T cells. Similarly, CAR T cell functions, such as the secretion of interferon-gamma (IFNg, p<0.0001) and interleukin-2 (IL-2, p<0.0001) as well as cytotoxic degranulation (p<0.0001) were all significantly impacted by the amount of CD22 on the surface of NALM6. A similar pattern of antigenic dose-response was seen in the signaling of CAR T cells, with phosphorylation of ERK reflecting the level of CD22 antigen (p<0.001) and correlating with the increased in vivo efficacy of the CAR T cells against CD22WT NALM6, relative to CD22Lo NALM6. Increasing the affinity of the CD22 CAR did not impact the in vivo efficacy against CD22WT NALM6 at either a therapeutic or subtherapeutic dose, however, HA-CD22 CAR T cells significantly prolonged the survival of NSG mice with CD22Lo NALM6, relative to SA-CD22 CAR T cells (p<0.01). The enhanced activity of HA-CD22 CAR T cells against CD22Lo leukemia did not correlate with improved in vitro functionality, as the HA-CD22 CAR T cells surprisingly demonstrated lower IL-2 secretion (p<0.01), lower proliferation (p<0.05) and diminished in vitro lysis of CD22Lo NALM6 (p<0.05), relative to SA-CD22 CAR T cells. ERK phosphorylation, however, was significantly increased in HA-CD22 CAR T cells (p<0.01) and was the only in vitro marker which correlated with the enhanced in vivo activity seen with the affinity-matured CAR. Previous clinical experience has demonstrated the importance of using a short linker (consisting of a single G4S sequence) between the heavy and light chains of the m971 scFv, therefore we next evaluated the impact of linker length on the activity of the HA-CD22 CAR. HA-CD22 CARs were generated with either a short- or long-linker (G4S x1 vs G4S x3, respectively) and evaluated in vitro and in vivo. While the short linker improved proliferation in vitro, there was no significant impact of linker length on cytokine production or lysis of CD22Lo NALM6. In a xenograft model, HA-CD22 CAR T cells with the long-linker demonstrated slower progression of CD22Lo leukemia and significantly prolonged survival of NSG mice with CD22WT leukemia relative to HA-CD22 CAR T cells with the short-linker (p<0.01). Taken together, these studies suggest that increasing the affinity of a scFv is a promising strategy for enhancing CAR sensitivity to low levels of target antigen, with the potential to decrease post-CAR T cell relapses due to antigen downregulation. Disclosures No relevant conflicts of interest to declare.

Development of a novel anti-HER2 scFv by ribosome display and in silico evaluation of its 3D structure and interaction with HER2, alone and after fusion to LAMP2B.

HER2 is a member of epidermal factor receptor (EGFR) family which is overexpressed in breast cancer, ovarian cancer and gastric cancer. Development of new binders for cancer cell surface receptors and expressing them at the surface of exosomes would be a great approach in targeted cancer therapy. We found a high affinity scFv against HER2 using ribosome display with the approach of applying it as a targeting moiety at the surface of exosomes by fusion to lysosomal associated membrane protein 2B (LAMP2B). We also provide some structural information about the ribosome display selected scFv (scFv HFS2) through modeling the 3D structure of scFv HFS2 using RosettaAntibody and docked it at the extracellular domain of HER2. We also evaluated the structure of scFv HFS2 and its binding to HER2 after fusion to LAMP2B. Our results showed no significant change in 3D structure of scFv HFS2 when fused to LAMP2B (RMSD 1.3) and interaction analysis represented that scFv HFS2 binds HER2 domain III before and after fusion to LAMP2B. Although binding domain of scFv HFS2 on HER2 was the same at both state, residues involved in their interactions showed significant differences as it was probably due to the spatial hindrance of scFv HFS2 when fused to LAMP2B through a short linker and it should be considered before proceeding to experiment.

High-Affinity Ligands Can Trigger T Cell Receptor Signaling Without CD45 Segregation.

How T cell receptors (TCRs) are triggered to start signaling is still not fully understood. It has been proposed that segregation of the large membrane tyrosine phosphatase CD45 from engaged TCRs initiates signaling by favoring phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) in the cytoplasmic domains of CD3 molecules. However, whether CD45 segregation is important to initiate triggering is still uncertain. We examined CD45 segregation from TCRs engaged to anti-CD3 scFv with high or low affinity and with defined molecular lengths on glass-supported lipid bilayers using total internal reflection microscopy. Both short and elongated high-affinity anti-CD3 scFv effectively induced similar calcium mobilization, Zap70 phosphorylation, and cytokine secretion in Jurkat T cells but CD45 segregated from activated TCR microclusters significantly less for elongated versus short anti-CD3 ligands. In addition, at early times, triggering cells with both high and low affinity elongated anti-CD3 scFv resulted in similar degrees of CD3 co-localization with CD45, but only the high-affinity scFv induced T cell activation. The lack of correlation between CD45 segregation and early markers of T cell activation suggests that segregation of CD45 from engaged TCRs is not mandatory for initial triggering of TCR signaling by elongated high-affinity ligands.

High-Affinity Internalizing Human scFv-Fc Antibody for Targeting FGFR1-Overexpressing Lung Cancer.

Targeted delivery of anticancer drugs using antibodies specific for tumor-associated antigens represents one of the most important approaches in current immuno-oncology research. Fibroblast growth factor receptor 1 (FGFR1) has been demonstrated to be a high-frequency targetable oncogene specific for smoking-associated lung cancers, present in over 20% of lung squamous cell carcinoma cases. This report describes the generation of a potent, fully human antibody fragment in scFv-Fc format efficiently targeting FGFR1. Antibody phage display was used to select high-affinity scFv antibody fragments against the extracellular domain of FGFR1(IIIc). Enzyme immunoassay (ELISA) and surface plasmon resonance (SPR) analysis were used for antibody screening and characterization. The best binder (named D2) was cloned to diabody and Fc fusion formats. All D2 antibodies demonstrated high affinity for FGFR1 with dissociation constants of 18 nmol/L (scFvD2), 0.82 nmol/L (scFvD2 diabody), and 0.59 nmol/L (scFvD2-Fc). scFvD2 was found to be exquisitely selective for FGFR1 versus other FGFR family members and bound FGFR1 even in the presence of its natural ligand FGF2, as shown by competitive analysis. Confocal microscopy revealed that scFvD2-Fc was specifically and rapidly internalized by a panel of cell lines overexpressing FGFR1. Finally, it was demonstrated that scFvD2-Fc mediated specific delivery of a cytotoxic payload into lung cancer cells harboring oncogenic FGFR1 gene amplifications.Implications: This study reports a highly specific internalizing antibody fragment that can serve as a therapeutic targeting agent for efficient delivery of cytotoxic drugs into FGFR1-positive lung cancer cells. Mol Cancer Res; 15(8); 1040-50. ©2017 AACR.

Prokaryotic expression of MLAA-34 and generation of a novel human ScFv against MLAA-34 by phage display technology.

MLAA-34 is a newly identified monocytic leukemia-associated antigen that is overexpressed in acute monocytic leukemia specifically, thus providing a novel target for the therapy of acute monocytic leukemia. In this study, we first expressed MLAA-34 protein in Escherichia coli (E.coli) BL21 (DE3) cells and purified it by nickel ion affinity chromatography with high purity (>90%). Then, MLAA-34 was used as antigen for biopanning anti-MLAA-34 single chain antibody fragment (ScFv) from a fully human ScFv library, and a high affinity ScFv named MA1 was selected by phage-ELISA. Finally, after expression of MA1, we found that MA1 can specifically bind with U937 MLAA-34 positive cells, and the binding affinity of MA1 was at the nanomolar level. Furthermore, inhibition of U937 cell proliferation indicated that the novel antibody MA1 has the potential to be used as a therapeutic agent for acute monocytic leukemia.

CAR T Cells Targeted with a High Affinity Scfv Against the HCMV Glycoprotein Gb As Adoptive T Cell Therapy after Hematopoietic Stem Cell Transplantation

Introduction: Reactivation of human cytomegalovirus (HCMV) in immune compromised patients after hematopoietic stem cell transplantation (HSCT) is associated with high morbidity and mortality, particularly after cord blood transplantation (CBT). Adoptive transfer of T cells expanded in vitro is currently used as therapy for drug-refractory HCMV disease. A major limitation of this approach is the requirement of HLA-restricted HCMV-specific memory T cells. An alternative approach exploring HLA-independent T cell recognition was sought. Because the HCMV envelope glycoprotein B (gB) is highly expressed during lytic infection and in latently infected cells, we hypothesized that T cells can be redirected to recognize and kill HCMV-specific cells by means of a gB-specific chimeric antigen receptor (CAR). We have synthesized and tested a gB-specific CAR derived from the SM5-1 monoclonal antibody which binds with high affinity (KD 5.7x1011) to a conserved antigenic and non-glycosylated domain of gB.Methods: We generated two codon-optimized SM5-derived scFvs (VH->VL and VL->VH) and fused with an existing CAR backbone containing an IgG Fc spacer and intracellular signaling domains. CARs containing either CD28.zeta or 4-1BB.zeta were synthesized and expressed in T cells following a standard retroviral transduction protocol yielding 80-90% transduction rate. Expression of the CARs on T cells was confirmed by flow cytometry using goat anti-human immunoglobulin reactive against the IgG Fc region. 293T cells co-expressing gB and dTomato were used for in vitro cytotoxicity assays.Results: T cells expressing gB-CAR/CD28.zeta were cytotoxic against gB+ target cells producing 90% killing of 293T/gB-dTom cells compared with control CD19 CAR/CD28.zeta cells at an effector-to-target ratio 3:1 for 48 h (parental 293T cells were not killed). The cytolytic activity correlated with expansion of CAR T cells and concomitant loss of gB-dTom expression in the remaining viable 293T cells. Sequential co-culture of these gB-CAR T cells with freshly seeded 293T/gB-dTom resulted into further elimination of target cells. We are currently evaluating the effects of different gB-CAR T cell designs in the killing of HCMV-infected cell lines and primary cells using HCMV laboratory strains expressing the GFP and Gaussia Luciferase reporter genes. Pilot experiments indicated that gB-CAR/CD28.zeta cells with the scFv in the VL->VH orientation resulted into more clustering and killing of HepG2 cells infected with HCMV-GFP after 24h of co-culture than a control CD19 CAR/CD28.zeta. Humanized mice transplanted with cord blood CD34+ stem cells and challenged with these HCMV laboratory strains will be used to evaluate the in vivo effectivity of cord blood-derived donor-matched gB-CAR-T cells to eliminate acute and latent HCMV infections.Conclusion: These studies explore a novel approach in preventing HCMV reactivation in immunosuppressed patients by redirecting T cells expressing a high-affinity gB-CAR to eliminate HCMV-infected cells in a TCR/MHC-independent manner. DisclosuresNo relevant conflicts of interest to declare.

A novel anti-PSMA human scFv has the potential to be used as a diagnostic tool in prostate cancer.

Prostate cancer (PCa) is the most commonly diagnosed malignancy and the second leading cause of cancer related death in men. The early diagnosis and treatment of PCa are still challenging due to the lack of efficient tumor targeting agents in traditional managements. Prostate specific membrane antigen (PSMA) is highly expressed in PCa, while only has limited expression in other organs, providing an ideal target for the diagnosis and therapy of PCa. The antibody library technique has opened the avenue for the discovery of novel antibodies to be used in the diagnosis and therapy of cancer. In this paper, by screening a large yeast display naive human single chain antibody fragment (scFv) library, we obtained a high affinity scFv targeting PSMA, called gy1. The gy1 scFv was expressed in E.coli and purified via a C terminal 6His tag. The binding affinity of gy1 was shown to be at the nanomolar level and gy1 can specifically bind with PSMA positive cancer cells, and binding triggers its rapid internalization through the endosome-lysosome pathway. The specific targeting of gy1 to PSMA positive tumor tissues was also evaluated in vivo. We showed that the IRDye800CW labeled gy1 can efficiently target and specifically distribute in PSMA positive tumor tissues after being injected into xenograft nude mice. This study indicated that the novel antibody gy1 could be used as a great tool for the development of PSMA targeted imaging and therapy agents for PCa.

Production of a soluble single-chain variable fragment antibody against okadaic acid and exploration of its specific binding

Okadaic acid is a lipophilic marine algal toxin commonly responsible for diarrhetic shellfish poisoning (DSP). Outbreaks of DSP have been increasing and are of worldwide public health concern; therefore, there is a growing demand for more rapid, reliable, and economical analytical methods for the detection of this toxin. In this study, anti-okadaic acid single-chain variable fragment (scFv) genes were prepared by cloning heavy and light chain genes from hybridoma cells, followed by fusion of the chains via a linker peptide. An scFv–pLIP6/GN recombinant plasmid was constructed and transformed into Escherichia coli for expression, and the target scFv was identified with IC–CLEIA (chemiluminescent enzyme immunoassay). The IC15 was 0.012 ± 0.02 μg/L, and the IC50 was 0.25 ± 0.03 μg/L. The three-dimensional structure of the scFv was simulated with computer modeling, and okadaic acid was docked to the scFv model to obtain a putative structure of the binding complex. Two predicted critical amino acids, Ser32 and Thr187, were then mutated to verify this theoretical model. Both mutants exhibited significant loss of binding activity. These results help us to understand this specific scFv–antigen binding mechanism and provide guidance for affinity maturation of the antibody in vitro. The high-affinity scFv developed here also has potential for okadaic acid toxin detection.

A Novel Small Animal Model to Test on-Target Off-Tumor Cytoxicity of Adoptive Immune Therapies

Chimeric antigen receptor (CAR) engineered T cells have been used clinically to improve outcomes in patients with hematopoietic malignancies owing to the ability of CAR T cells to recognize tumor antigens and kill malignant cells. CAR T cells possess the antigen recognizing capability of an antibody through the single chain variable fragment (scFv) and their cytotoxicity is enhanced through signaling via the intracellular domains of T cell receptors and co-activating receptors such as CD3zeta and 4-1BB, respectively. Thus, CAR expressing T cells are able to detect cancer cells through tumor antigens and can become activated to unleash their cytotoxic potentials in a non-MHC restricted manner. Therapeutic side-effects can occur when T-cell receptor targeting is misdirected to the incorrect tissue causing potentially serious on-target off-tumor cytotoxicity. Factors that influence CAR targeting include expression levels of tumor-associated antigen in normal tissue and the binding affinities of scFvs.Our first step in developing an in vivo, on target, off-tumor, CAR T cell toxicity model was to generate mice with tunable expression of a human tumor antigen in normal tissue. NSG mice were IV injected with recombinant adeno-associated virus serotype 8 (rAAV8) to deliver a truncated human ErbB2 (Her2/neu or CD340) gene and a Katushka fluorescent reporter that were driven by the liver-specific promoter, thyroxine binding globulin (TBG). AAV8 genomic copies (GCs) were injected at varying dilutions of 1.5 x 1012 GC/mouse, 7.25 x 1011 GC/mouseand 1.5x1010 GC/mouse to induce a range of expression of ErbB2 in the liver. Katushka expression was visualized in vivo using the IVIS small animal imager. ErbB2 gene expression was detected using reverse transcription polymerase chain reaction (qRT-PCR) and the ErbB2 protein was detected using western blots and immunohistochemistry (IHC). Our data has shown that expression levels of ErbB2 and the Katushka reporter positively correlated with the number of AAV8 GCs that were injected. This enabled us to obtain ErbB2 expression levels in the liver comparable to the levels seen in either ErbB2High tumors (eg. SK-OV3) or ErbB2Low tumors (eg. PC3 and HEK293T).To determine if affinity tuning of scFvs will allow CAR T cells to discriminate between high and low ErbB2 expression in the liver, T cells were engineered to co-express the click beetle red (CBR) reporter and either a high-affinity scFv, anti-ErbB2 CAR (4D5) or a low-affinity scFv, anti-ErbB2 CAR (4D5-5). These T cells were then IV injected into NSG mice that had either high or low ErbB2-expressing livers. Although these experiments were ongoing at the time of abstract submission, we will show our results on T cell trafficking in the liver, which will be visualized by IHC and by in vivo imaging using the IVIS small animal imager. Liver toxicity will be assessed by histological examination and by measuring liver function via standard enzymatic testing of blood.Furthermore, we aim to show whether affinity tuning of scFvs will allow CAR T cells to selectively recognize and target ErbB2High tumors while sparing ErbB2Low normal tissue. This will be performed by inoculating ErbB2high SK-OV3 tumor cells into mice with ErbB2Low livers followed by IV injection with either 4D5 or 4D5-5 CAR T cells. We expect that the low-affinity anti-ErbB2 CAR (4D5-5) T cells will target the ErbB2High SK-OV3 tumor cells and cause tumor regression while preserving function in the ErbB2Low liver. If so, then we will have shown that our pre-clinical mouse model can be used to identify on-target off-tumor CAR T cell toxicity, which will aid in improving the safety profile and clinical outcomes of future CAR T cell therapies. DisclosuresScholler:Novartis: Patents & Royalties. Zhao:Novartis: Patents & Royalties, Research Funding. June:Novartis: Patents & Royalties, Research Funding.

An affinity improved single-chain antibody from phage display of a library derived from monoclonal antibodies detects fumonisins by immunoassay

Fumonisin B analogs, particularly FB1, FB2, and FB3, are major mycotoxins found in cereals. Single-chain fragment variable (scFv) antibodies represent a promising alternative immunoassay system. A phage-displayed antibody library derived from four monoclonal antibodies (mAbs) generated against FB1 was used to screen high binding affinity scFv antibodies; the best candidate was designated H2. Surface plasmon resonance measurements confirmed that the H2 scFv displayed a 82-fold higher binding affinity than its parent mAb. Direct competitive enzyme-linked immunosorbent assay demonstrated that the H2 antibody could competitively bind to free FB1, FB2, and FB3, with an IC50 of 0.11, 0.04, and 0.10μM, respectively; it had no cross-reactivity to deoxynivalenol, nivalenol and aflatoxin. Validation assays with naturally contaminated samples revealed a linear relationship between the H2 antibody-based assay results and chemical analysis results, that could be expressed as y=1.7072x+5.5606 (R2=0.8883). Homology modeling of H2 revealed a favorable binding structure highly complementary to the three fumonisins. Molecular docking analyses suggested that the preferential binding of the H2 scFv to FB2 was due to the presence of a hydrogen radical in its R1 position, leading to a proper electrostatic matching and hydrophobic interaction. The H2 scFv antibody can be used for the rapid, accurate, and specific detection of fumonisin contamination in agricultural samples.

Excessively High-Affinity Single-Chain Fragment Variable Region in a Chimeric Antigen Receptor Can Counteract T-Cell Proliferation

Background: Single-chain fragment variable region (scFv) in a chimeric antigen receptor (CAR) is a key component that directly binds the target antigen and transmits an activating signal into the CAR-T cells, subsequently triggering its effector function against the target cell. Thus, the affinity of scFv is considered to be critically important for CAR-T-cell function. However, optimal scFv affinity to induce maximal CAR function remains unclear.Methods: In this study, we constructed anti-CD20 scFv based on the reported sequence of humanized anti-CD20 monoclonal antibody with five different affinities: 20-vv (Kd value=7.07 nM), -fv (7.21), -fa (10.09), -sv (12.56), and -sa (14.66). Each scFv was then fused to an IgG4 hinge, a CD3-zeta chain, a CD28 costimulatory domain, and a truncated version of the epidermal growth factor receptor (tEGFR) as a transduction and selection marker. CD8-positive T cells from a healthy donor were activated with anti-CD3/28 beads, transduced with the CARs on day 3, and enriched by selection with anti-EGFR mAb. CAR-T cells were expanded using anti-CD3/28 beads and used in the subsequent analysis.Results: To determine the lytic activity according to the scFv affinity, we tested cytotoxicity against CD20-transduced K562 cells (K562-CD20) by 51Cr releasing assay. CAR-T cells with the three highest-affinity scFv (20CAR-vv, -fv, -fa) effectively and equally lysed K562-CD20, while CAR-T cells with the two lowest-affinity scFv (20CAR-sv, -sa) failed to exhibit significant cytotoxicity (20CAR-vv, -fv, -fa, -sv, and -sa: 60.2±2.85%, 57.3±2.03%, 57.0±3.82%, 2.8±0.1%, and 2.0±0.64% at an E:T ratio = 10:1, respectively). To examine CAR-T-cell activation, cytokine secretion in the supernatant after 16 hours of culture with K562-CD20 was analyzed. Similarly to the cytotoxicity, 20CAR-vv, -fv, and -fa produced cytokine, but 20CAR-sv and -sa did not. The highest-affinity CAR-T (20CAR-vv) produced significantly higher IFN-g and IL-2 than the other CAR-T cells [IFN-g (pg/ml): 7644±326, 3380±179, 4718±315, 4.9±0.4, and 5.4±1.2; IL-2 (pg/ml): 4179±177, 1071±30, 1379±118, 0, and 0, respectively]. We next analyzed cell proliferation upon stimulation with K562-CD20 over 72 hours. 20CAR-vv resulted in rather poor absolute cell proliferation, while CAR-T cells with the second and third highest-affinity scFv (20CAR-fv, -fa) resulted in preferable proliferation (1.22±0.20-, 2.52±0.12-, 2.01±0.42-, 0.65±0.11-, and 1.15±0.13-fold expansion, respectively). To explore the possible reason for the difference of CAR-T proliferation, we evaluated activation-induced cell death (AICD) at 24 hours after the K562-CD20 stimulation (Annexin-V/PI staining). 20CAR-vv underwent significantly higher AICD than the other CAR-T cells (68.4±1.1, 39.6±0.7, 37.9±5.3, 25.9±11.2, and 16.1±1.2% cell death). Finally, we tested cell proliferation and AICD of the three highest-affinity scFv CAR-T cells (-vv, -fv, and -fa) upon CD20 high and low stimulation. In this experiment, we used CD20-transduced CEM cells, which are controlled to express high and low CD20: CEM-CD20 high (CD20 = 143,000 molecules/cell, the same level as other B-cell lines) and CEM-CD20 low (5,320 molecules/cell, the same level as the rituximab refractory cell line). The replacement of the stimulator from CD20-CEM high to low resulted in partial reduction of AICD to a level comparable to those of other 20CARs (-vv, 62.7%→33.0%, -fv, 56.0%→37.4%, –fa, 55.3%→27.7%), but the cell proliferation upon stimulation did not improve (-vv, 1.2-, -fv, 2.6-, -fa, 2.7-fold expansion after CD20-CEM low stim). These results suggest that the higher-affinity scFv was not necessarily associated with better CAR-T proliferation after ligation and may inhibit cell proliferation, possibly by multiple factors besides AICD.Conclusions: We observed that scFv with affinity above a certain level is needed to induce CAR-T function. Higher-affinity scFv induced more robust cytokine production; however, excessively high-affinity scFv in CAR can counteract T-cell proliferation, which may be partially associated with increased AICD. Optimization of scFv affinity is desirable for effective CAR-T production. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.