Construction of Nanobody Library in Mammalian Cells by Linear-double-stranded DNA Based AND Gate Genetic Circuit
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ABSTRACT: Nanobody is one special type of single-domain antibody fragment with multiple advantages over traditional antibody. Our previous work established linear-double-stranded DNA (ldsDNA, or PCR amplicon) as novel biological parts for building AND gate genetic circuits in mammalian cells. During this AND-gate circuit formation process, the co-transfected up- and down-stream ldsDNAs could be linked together to form intact gene expression cassette. Here, we employed this ldsDNA-based AND-gate (LBAG) strategy to construct nanobody library in mammalian cells. The sequence complexity of complementary determining regions (CDRs) was introduced into ldsDNA by PCR amplification. After being co-transfected into mammalian cells, the up- and down- stream ldsDNAs undergo AND gate linkage and form full nanobody coding regions, containing CDR1-3. High throughput sequencing identified 22,173 unique oligonucleotide sequences in total generated by this strategy. Thus, we developed a novel method to construct nanobody library, which is a start point for building high content nanobody library in mammalian cells.
Project description:Display technologies, e.g., phage, ribosome, mRNA, bacterial, and yeast-display, combine high content peptide libraries with appropriate screening strategies to identify functional peptide sequences. Construction of large peptide library and display-screen system in intact mammalian cells will facilitate the development of peptide therapeutics targeting transmembrane proteins. Our previous work established linear-double-stranded DNAs (ldsDNAs) as innovative biological parts to implement AND gate genetic circuits in mammalian cell line. In the current study, we employ ldsDNA with terminal NNK degenerate codons as AND gate input to build highly diverse peptide library in mammalian cells. Only PCR reaction and cell transfection experiments are needed to construct the library. High-throughput sequencing (HTS) results reveal that our new strategy could generate peptide library with both amino acid sequence and peptide length diversities. Our work establishes ldsDNA as biological parts for building highly diverse peptide library in mammalian cells, which shows great application potential in developing therapeutic peptides targeting transmembrane proteins.
Project description:A nanobody is an antibody fragment consisting of a single monomeric variable antigen-binding domain. Mammalian cells are ideal platforms for identifying nanobodies targeting hard-to-display transmembrane proteins and nanobodies that function as modulators of cellular phenotypes. However, the introduction of a high-diversity nanobody library into mammalian cells is challenging. We have developed two novel methods for constructing a nanobody library in mammalian cells. Complementarity-determining region (CDR) random sequences were first incorporated into upstream and downstream dsDNAs by PCR. In the first method, named dsDNA-HR, upstream and downstream dsDNAs containing an identical overlapping sequence were co-transfected into cultured mammalian cells for intracellular homologous recombination that resulted in the formation of an intact nanobody library expression cassette. In the second method, named in vitro ligation, we generated full-length nanobody expression dsDNAs via ligation of restriction digested upstream and downstream dsDNAs. The obtained full-length dsDNAs were transfected into mammalian cells for nanobody library expression. Using both methods, we generated over a million unique nanobody sequences, as revealed by high-throughput sequencing. Single-cell sequencing was employed to resolve the diversity of the dsDNA-HR nanobody library. We also identified a small molecule, Nocodazole, which could enhance the efficacy of dsDNA-HR.
Project description:Anti-CD19 CAR T cells can induce remissions in some patients with B-cell malignancies. However, new immunotherapeutic targets are urgently needed for the many who relapse. We recently described CD72 as a promising target in B-cell leukemia and lymphoma, developing fully synthetic nanobody-based CAR-T cells (nanoCARs) against this antigen. Toward clinical translation, here we humanize our previous nanobody framework regions, derived from llama, and surprisingly discover a clone ("H24") with enhanced potency against B-cell tumors both in vitro and in vivo. In vitro, H24 nanoCARs showed improved cytokine secretion and favorable immunophenotypic properties. RNA sequencing before and after tumor exposure reveals humanized H24 CD72 nanoCARs have unique transcriptional programs compared to CD19 CAR T cells. We further find that H24 nanoCARs lead to sustained CD72 downregulation on tumors treated in vivo. Underpinning this improved potency, H24 had higher binding affinity to CD72 compared to a fully llama framework. Further affinity maturation moderately increased cytotoxicity versus antigen-low tumors. This work supports clinical translation of H24 CD72 nanoCARs, reveals potential mechanisms of resistance to this cellular therapy, and unexpectedly demonstrates that nanoCAR potency can be improved by framework alterations alone, without any change to the complementarity determining regions (CDRs) of the nanobody sequence.
Project description:We designed an oligonucleotide libraries containing a potential frameshifting site, cloned the library variants into a dedicated reporter construct, transfected and integrated these constructs in the genome of K562 cells, and performed FACSseq (as well as targeted RNA sequencing) to determine if and to what extent frameshifting occurs.
Project description:Subunit proteins BAF250a and Brd9 are specific to mammalian SWI/SNF subfamilies BAF and ncBAF respectively. We have performed RNA-seq analysis for C2C12 myoblasts stably knocked down for each subunits using specific shRNA constructs. C2C12 cells stably transfected with non-targeting scrambled shRNA construct were used as controls.
Project description:In this project, we conducted an evaluation of mass spectrometry methods using mouse heart and HCT116 cell samples. The results demonstrated that the data-independent acquisition (DIA) approach outperformed data-dependent acquisition (DDA) in the identification of Altprot and canonical proteins. Subsequently, we assessed several different DIA library building methods, including traditional DDA-based library building, gas-phase fractionation(GPF) library building, and machine learning-based prediction library building. Notably, the traditional DDA library building method exhibited a higher likelihood of false positive identifications. Furthermore, we applied the aforementioned mass spectrometry methods to investigate the process of mouse heart development. Through this analysis, we identified a subset of Altprots, including ASDURF, which may potentially play crucial roles in heart development. These findings serve as a fundamental basis for future exploration and investigation of Altprot in this context.
Project description:Antibodies and derivative drugs targeting immune checkpoints have been approved for the treatment of several malignancies, but there are fewer responses in patients with pancreatic cancer. Here, we designed a nanobody molecule with bi-targeting on PD-L1 and CXCR4, as both targets are overexpressed in many cancer cells and play important roles in tumorigenesis. The nanobody sequences targeting PD-L1 and CXCR4 were linked by the (G4S)3 flexible peptide to construct the anti-PD-L1/CXCR4 bispecific nanobody. The bispecific nanobody was expressed in E. coli cells and purified by affinity chromatography. The purified nanobody was biochemically characterized by mass spectrometry, Western blotting and flow cytometry to confirm the molecule and its association with both PD-L1 and CXCR4. The biological function of the nanobody and its anti-tumour effects were examined.