RESUMO
Recent advances are described for the isolation and affinity maturation of antibodies that couple in vitro somatic hypermutation (SHM) with mammalian cell display, replicating key aspects of the adaptive immune system. SHM is dependent on the action of the B cell specific enzyme, activation-induced cytidine deaminase (AID). AID-directed SHM in vitro in non-B cells, combined with mammalian display of a library of human antibodies, initially naïve to SHM, can be used to isolate and affinity mature antibodies via iterative cycles of fluorescence-activated cell sorting (FACS) under increasingly stringent sort conditions. SHM observed in vitro closely resembles SHM observed in human antibodies in vivo in both mutation type and positioning in the antibody variable region. In addition, existing antibodies originating from mouse immunization, in vivo based libraries, or alternative display technologies such as phage can also be affinity matured in a similar manner. The display system has been developed to enable simultaneous high-level cell surface expression and secretion of the same protein through alternate splicing, where the displayed protein phenotype remains linked to genotype, allowing soluble secreted antibody to be simultaneously characterized in biophysical and cell-based functional assays. This approach overcomes many of the previous limitations of mammalian cell display, enabling direct selection and maturation of antibodies as full-length, glycosylated IgGs.
Assuntos
Anticorpos Monoclonais/genética , Animais , Anticorpos Monoclonais/isolamento & purificação , Anticorpos Monoclonais/metabolismo , Afinidade de Anticorpos , Antígenos/imunologia , Sequência de Bases , Separação Celular , Primers do DNA/genética , Evolução Molecular Direcionada , Descoberta de Drogas , Citometria de Fluxo , Biblioteca Gênica , Células HEK293 , Humanos , Dados de Sequência Molecular , Ligação Proteica , Engenharia de ProteínasRESUMO
A mammalian expression system has been developed that permits simultaneous cell surface display and secretion of the same protein through alternate splicing of pre-mRNA. This enables a flexible system for in vitro protein evolution in mammalian cells where the displayed protein phenotype remains linked to genotype, but with the advantage of soluble protein also being produced without the requirement for any further recloning to allow a wide range of assays, including biophysical and cell-based functional assays, to be used during the selection process. This system has been used for the simultaneous surface presentation and secretion of IgG during antibody discovery and maturation. Presentation and secretion of monomeric Fab can also be achieved to minimize avidity effects. Manipulation of the splice donor site sequence enables control of the relative amounts of cell surface and secreted antibody. Multi-domain proteins may be presented and secreted in different formats to enable flexibility in experimental design, and secreted proteins may be produced with epitope tags to facilitate high-throughput testing. This system is particularly useful in the context of in situ mutagenesis, as in the case of in vitro somatic hypermutation.
Assuntos
Processamento Alternativo , Anticorpos Monoclonais/biossíntese , Afinidade de Anticorpos/genética , Evolução Molecular Direcionada , Expressão Gênica , Imunoglobulina G/biossíntese , Anticorpos Monoclonais/genética , Células HEK293 , Humanos , Imunoglobulina G/genética , Precursores de RNA/biossíntese , Precursores de RNA/genéticaRESUMO
A method for simultaneous humanization and affinity maturation of monoclonal antibodies has been developed using heavy chain complementarity-determining region (CDR) 3 grafting combined with somatic hypermutation in vitro. To minimize the amount of murine antibody-derived antibody sequence used during humanization, only the CDR3 region from a murine antibody that recognizes the cytokine hßNGF was grafted into a nonhomologous human germ line V region. The resulting CDR3-grafted HC was paired with a CDR-grafted light chain, displayed on the surface of HEK293 cells, and matured using in vitro somatic hypermutation. A high affinity humanized antibody was derived that was considerably more potent than the parental antibody, possessed a low pm dissociation constant, and demonstrated potent inhibition of hßNGF activity in vitro. The resulting antibody contained half the heavy chain murine donor sequence compared with the same antibody humanized using traditional methods.
Assuntos
Anticorpos/química , Regiões Determinantes de Complementaridade/metabolismo , Mutação , Animais , Anticorpos Monoclonais/química , Antígenos/química , Sequência de Bases , Ligação Competitiva , Separação Celular , Códon , Citocinas/metabolismo , Citometria de Fluxo , Células HEK293 , Humanos , Técnicas In Vitro , Camundongos , Modelos Genéticos , Dados de Sequência Molecular , Engenharia de Proteínas/métodos , Transdução de SinaisRESUMO
Directed evolution technologies were used to selectively improve the stability of an enzyme without compromising its catalytic activity. In particular, this article describes the tandem use of two evolution strategies to evolve a xylanase, rendering it tolerant to temperatures in excess of 90 degrees C. A library of all possible 19 amino acid substitutions at each residue position was generated and screened for activity after a temperature challenge. Nine single amino acid residue changes were identified that enhanced thermostability. All 512 possible combinatorial variants of the nine mutations were then generated and screened for improved thermal tolerance under stringent conditions. The screen yielded eleven variants with substantially improved thermal tolerance. Denaturation temperature transition midpoints were increased from 61 degrees C to as high as 96 degrees C. The use of two evolution strategies in combination enabled the rapid discovery of the enzyme variant with the highest degree of fitness (greater thermal tolerance and activity relative to the wild-type parent).
