Veterinary sources of nonrodent monoclonal antibodies: interspecific and intraspecific hybridomas

Specific anti-SARS-CoV-2 S1 IgY-scFv is a promising tool for recognition of the virus

As severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread globally, a series of vaccines, antibodies and drugs have been developed to combat coronavirus disease 2019 (COVID-19). High specific antibodies are powerful tool for the development of immunoassay and providing passive immunotherapy against SARS-CoV-2 and expected with large scale production. SARS-CoV-2 S1 protein was expressed in E. coli BL21 and purified by immobilized metal affinity chromatography, as antigen used to immunize hens, the specific IgY antibodies were extracted form egg yolk by PEG-6000 precipitation, and the titer of anti-S1 IgY antibody reached 1:10,000. IgY single chain variable fragment antibody (IgY-scFv) was generated by using phage display technology and the IgY-scFv showed high binding sensitivity and capacity to S1 protein of SARS-CoV-2, and the minimum detectable antigen S1 protein concentration was 6 ng/µL. The docking study showed that the multiple epitopes on the IgY-scFv interacted with multiple residues on SARS-CoV-2 S1 RBD to form hydrogen bonds. This preliminary study suggests that IgY and IgY-scFv are suitable candidates for the development of immunoassay and passive immunotherapy for COVID-19 to humans and animals.

Generation of avian-derived anti-B7-H4 antibodies exerts a blockade effect on the immunosuppressive response

For highly conserved mammalian protein, chicken is a suitable immune host to generate antibodies. Monoclonal antibodies have been successfully targeted with immunity checkpoint proteins as a means of cancer treatment; this treatment enhances tumor-specific immunity responses through immunoregulation. Studies have identified the importance of B7-H4 in immunoregulation and its use as a potential target for cancer treatment. High levels of B7-H4 expression are found in tumor tissues and are associated with adverse clinical and pathological characteristics. Using the phage display technique, this study isolated specific single-chain antibody fragments (scFvs) against B7-H4 from chickens. Our experiment proved that B7-H4 clearly induced the inhibition of T-cell activation. Therefore, use of anti-B7-H4 scFvs can effectively block the exhaustion of immunity cells and also stimulate and activate T-cells in peripheral blood mononuclear cells. Sequence analysis revealed that two isolated scFv S2 and S4 have the same VH complementarity-determining regions (CDRs) sequence. Molecule docking was employed to simulate the complex structures of scFv with B7-H4 to analyze the interaction. Our findings revealed that both scFvs employed CDR-H1 and CDR-H3 as main driving forces and had strong binding effects with the B7-H4. The affinity of scFv S2 was better because the CDR-L2 loop of the scFv S2 had three more hydrogen bond interactions with B7-H4. The results of this experiment suggest the usefulness of B7-H4 as a target for immunity checkpoints; the isolated B7-H4-specific chicken antibodies have the potential for use in future cancer immunotherapy applications.

An approach towards development of monoclonal IgY antibodies against SARS CoV-2 spike protein (S) using phage display method: A review

The present state of diagnostic and therapeutic developmental race for vaccines against the SARS CoV-2 (nCOVID-19) focuses on prevention and control of this global pandemic which also represents a critical challenge to the global health community. Although development of novel vaccines can prevent the SARS CoV-2 infections, it is still impeded by several other factors and therefore novel approaches towards treatment and management of this disease is the urgent need. Passive immunotherapy plays a vital role as a possible alternative to meet this challenge and among various antibody sources, chicken egg yolk antibodies (IgY) can be used as an alternative to mammalian antibodies which have been previously studied against SARS CoV outbreak in China. In this review, we discuss the strategies for the use of chicken egg yolk (IgY) antibodies in the development of rapid diagnosis and immunotherapy against SARS CoV-2. Also, IgY antibodies have previously been used against various respiratory bacterial and viral infections in humans and animals. Compared to mammalian antibodies (IgG), chicken egg yolk antibodies (IgY) have greater binding affinity to specific antigens, ease of extraction and lower production costs, hence possessing remarkable pathogen-neutralizing activity of pathogens in respiratory and lungs. We provide an overall importance for the use of monoclonal chicken egg yolk antibodies (IgY) using phage display method describing their potential passive immunotherapeutic application for the treatment and prevention of SARS CoV-2 infection which is simple, fast and safe way of approach for treating patients effectively.

Hybridoma technology a versatile method for isolation of monoclonal antibodies, its applicability across species, limitations, advancement and future perspectives

The advancements in technology and manufacturing processes have allowed the development of new derivatives, biosimilar or advanced improved versions for approved antibodies each year for treatment regimen. There are more than 700 antibody-based molecules that are in different stages of phase I/II/ III clinical trials targeting new unique targets. To date, approximately more than 80 monoclonal antibodies (mAbs) have been approved. A total of 7 novel antibody therapeutics had been granted the first approval either in the United States or European Union in the year 2019, representing approximately 20% of the total number of approved drugs. Most of these licenced mAbs or their derivatives are either of hybridoma origin or their improvised engineered versions. Even with the recent development of high throughput mAb generation technologies, hybridoma is the most favoured method due to its indigenous nature to preserve natural cognate antibody pairing information and preserves innate functions of immune cells. The recent advent of antibody engineering technology has superseded the species level barriers and has shown success in isolation of hybridoma across phylogenetically distinct species. This has led to the isolation of monoclonal antibodies against human targets that are conserved and non-immunogenic in the rodent. In this review, we have discussed in detail about hybridoma technology, its expansion towards different animal species, the importance of antibodies isolated from different animal sources that are useful in biological applications, advantages, and limitations. This review also summarizes the challenges and recent progress associated with hybridoma development, and how it has been overcome in these years to provide new insights for the isolation of mAbs.

Generation and characterization of avian-derived anti-human CD19 single chain fragment antibodies

The human cluster of differentiation 19 (CD19) is highly expressed in most leukemia, rendering is a promising therapeutic target. In this study, we generated anti-CD19 single-chain variable fragments (scFv) from immunized chickens by phage display technology. After constructing a scFv antibody library with 2.5 × 10⁸ compositional diversity for panning, one representative scFv clone S2 which can specifically recognize to the CD19 protein was isolated and characterized. The binding reactivity of the scFv S2 to the endogenous CD19 protein of the ARH-77 leukemia cancer cell was verified through flow cytometry and the binding affinity of scFv S2 is 6.9 × 10^-8 M determined by the surface plasmon resonance system. Compared with the chicken germline, hyper mutation in the complementarity-determining regions (CDRs) suggested that scFv S2 could be generated through an antigen-driven humoral response. By molecular modeling, the possible CDR configurations of scFv S2 were constructed rationally. Furthermore, the characteristics of chicken antibodies of a protein database were investigated. The findings in this study contribute to antibody development and engineering because they reveal the geometric structures and properties of the CDRs in chicken antibodies.

Transgenic rabbits that overexpress the neonatal Fc receptor (FcRn) generate higher quantities and improved qualities of anti-thymocyte globulin (ATG)

Immune suppression with rabbit anti-thymocyte globulin (rATG) is a well-established therapeutic concept for preventing host rejection of transplanted organs and graft versus host disease. Increasing the efficiency of rATG production by reducing the number of animals would be highly beneficial to lower cost and to improve quality standards. We have developed transgenic (Tg) mice and rabbits that overexpress the neonatal Fc receptor (FcRn) and have shown an augmented humoral immune response in these animals. To test whether our FcRn Tg rabbits produced rATG more efficiently, we immunized them and their New Zealand White controls with live Jurkat cells. By day 21 after immunization, Tg animals produced significantly, 1.5 times higher amount of total IgG compared to their wt littermates. Also, the binding efficiency of Tg sera to Jurkat cells and their complement-mediated cytotoxicity was significantly higher. The purified Tg IgG preparation contained 2.6 the amount of Jurkat specific IgG as the wt preparation analyzed by complement-mediated lysis, suggesting greater antigen-specific B cell activation in the Tg rabbits. To test this hypothesis, immunization with ovalbumin and human α₁-antitrypsin was performed, resulting in significantly greater numbers of antigen-specific B-cells in the FcRn Tg rabbits as compared with wt controls. The shift towards significantly larger populations of antigen-specific B cells relative to the non-specific B cell pool is further corroborated by our previous findings in FcRn Tg mice. Consequently, our FcRn Tg rabbits have the potential to offer substantial qualitative and quantitative improvements for the production of rATG and other polyclonal or monoclonal antibodies.

When tissue antigens and antibodies get along: revisiting the technical aspects of immunohistochemistry--the red, brown, and blue technique

Once focused mainly on the characterization of neoplasms, immunohistochemistry (IHC) today is used in the investigation of a broad range of disease processes with applications in diagnosis, prognostication, therapeutic decisions to tailor treatment to an individual patient, and investigations into the pathogenesis of disease. This review addresses the technical aspects of immunohistochemistry (and, to a lesser extent, immunocytochemistry) with attention to the antigen-antibody reaction, optimal fixation techniques, tissue processing considerations, antigen retrieval methods, detection systems, selection and use of an autostainer, standardization and validation of IHC tests, preparation of proper tissue and reagent controls, tissue microarrays and other high-throughput systems, quality assurance/quality control measures, interpretation of the IHC reaction, and reporting of results. It is now more important than ever, with these sophisticated applications, to standardize the entire IHC process from tissue collection through interpretation and reporting to minimize variability among laboratories and to facilitate quantification and interlaboratory comparison of IHC results.

Characterization of the rabbit neonatal Fc receptor (FcRn) and analyzing the immunophenotype of the transgenic rabbits that overexpresses FcRn

The neonatal Fc receptor (FcRn) regulates IgG and albumin homeostasis, mediates maternal IgG transport, takes an active role in phagocytosis, and delivers antigen for presentation. We have previously shown that overexpression of FcRn in transgenic mice significantly improves the humoral immune response. Because rabbits are an important source of polyclonal and monoclonal antibodies, adaptation of our FcRn overexpression technology in this species would bring significant advantages. We cloned the full length cDNA of the rabbit FcRn alpha-chain and found that it is similar to its orthologous analyzed so far. The rabbit FcRn - IgG contact residues are highly conserved, and based on this we predicted pH dependent interaction, which we confirmed by analyzing the pH dependent binding of FcRn to rabbit IgG using yolk sac lysates of rabbit fetuses by Western blot. Using immunohistochemistry, we detected strong FcRn staining in the endodermal cells of the rabbit yolk sac membrane, while the placental trophoblast cells and amnion showed no FcRn staining. Then, using BAC transgenesis we generated transgenic rabbits carrying and overexpressing a 110 kb rabbit genomic fragment encoding the FcRn. These transgenic rabbits--having one extra copy of the FcRn when hemizygous and two extra copies when homozygous--showed improved IgG protection and an augmented humoral immune response when immunized with a variety of different antigens. Our results in these transgenic rabbits demonstrate an increased immune response, similar to what we described in mice, indicating that FcRn overexpression brings significant advantages for the production of polyclonal and monoclonal antibodies.

Identification of Eps15 as antigen recognized by the monoclonal antibodies aa2 and ab52 of the Wuerzburg Hybridoma Library against Drosophila brain

The Wuerzburg Hybridoma Library against the Drosophila brain represents a collection of around 200 monoclonal antibodies that bind to specific structures in the Drosophila brain. Here we describe the immunohistochemical staining patterns, the Western blot signals of one- and two-dimensional electrophoretic separation, and the mass spectrometric characterization of the target protein candidates recognized by the monoclonal antibodies aa2 and ab52 from the library. Analysis of a mutant of a candidate gene identified the Drosophila homolog of the Epidermal growth factor receptor Pathway Substrate clone 15 (Eps15) as the antigen for these two antibodies.

Efficient immunoglobulin gene disruption and targeted replacement in rabbit using zinc finger nucleases

Rabbits are widely used in biomedical research, yet techniques for their precise genetic modification are lacking. We demonstrate that zinc finger nucleases (ZFNs) introduced into fertilized oocytes can inactivate a chosen gene by mutagenesis and also mediate precise homologous recombination with a DNA gene-targeting vector to achieve the first gene knockout and targeted sequence replacement in rabbits. Two ZFN pairs were designed that target the rabbit immunoglobulin M (IgM) locus within exons 1 and 2. ZFN mRNAs were microinjected into pronuclear stage fertilized oocytes. Founder animals carrying distinct mutated IgM alleles were identified and bred to produce offspring. Functional knockout of the immunoglobulin heavy chain locus was confirmed by serum IgM and IgG deficiency and lack of IgM(+) and IgG(+) B lymphocytes. We then tested whether ZFN expression would enable efficient targeted sequence replacement in rabbit oocytes. ZFN mRNA was co-injected with a linear DNA vector designed to replace exon 1 of the IgM locus with ∼1.9 kb of novel sequence. Double strand break induced targeted replacement occurred in up to 17% of embryos and in 18% of fetuses analyzed. Two major goals have been achieved. First, inactivation of the endogenous IgM locus, which is an essential step for the production of therapeutic human polyclonal antibodies in the rabbit. Second, establishing efficient targeted gene manipulation and homologous recombination in a refractory animal species. ZFN mediated genetic engineering in the rabbit and other mammals opens new avenues of experimentation in immunology and many other research fields.

Generation and characterization of anti-alpha-enolase single-chain antibodies in chicken

It was previously reported that up-regulation of α-enolase protein was detected in 65% of patients with non-small cell lung cancers (NSCLC). Moreover, a high titer of anti-α-enolase antibodies was developed in a smaller proportion (7.4%) of these patients than in non-tumor-associated patients and healthy subjects. In the present study, we characterized polyclonal and single-chain variable fragment (scFv) anti-α-enolase antibodies from immunized chickens. The E. coli-derived recombinant α-enolase protein was purified to its high homogenicity as verified by SDS-PAGE. After the 4th immunization, a high titer of specific polyclonal anti-α-enolase antibodies was elicited in immunized chickens and specifically recognized the purified human α-enolase antigen as determined by Western blot and ELISA. The expressed heavy and light chain variable genes (VH and VL) were isolated from spleen B cells and amplified to construct phage antibody libraries containing scFv molecules. After four rounds of panning selection, the scFv antibodies of randomly chosen clones were expressed and their binding specificity to α-enolase protein was verified using competitive ELISA, flow cytometry and immunofluorescence staining. Nucleotide sequence analysis from 10 α-enolase binding clones showed that 3 (30%) clones used identical heavy and light genes for scFv antibody expression, as represented by EnL5. Notably, amino acid changes in complementarity-determining regions (CDRs) were more frequently observed than those in framework regions (FRs) in all clones, indicating a strong affinity selection through mutations. All together, it is believed that these polyclonal and scFv IgY antibodies may be helpful in the development of molecular diagnostic and therapeutic agents for lung cancers in the future.

A humanized anti-VEGF rabbit monoclonal antibody inhibits angiogenesis and blocks tumor growth in xenograft models

Rabbit antibodies have been widely used in research and diagnostics due to their high antigen specificity and affinity. Though these properties are also highly desirable for therapeutic applications, rabbit antibodies have remained untapped for human disease therapy. To evaluate the therapeutic potential of rabbit monoclonal antibodies (RabMAbs), we generated a panel of neutralizing RabMAbs against human vascular endothelial growth factor-A (VEGF). These neutralizing RabMAbs are specific to VEGF and do not cross-react to other members of the VEGF protein family. Guided by sequence and lineage analysis of a panel of neutralizing RabMAbs, we humanized the lead candidate by substituting non-critical residues with human residues within both the frameworks and the CDR regions. We showed that the humanized RabMAb retained its parental biological properties and showed potent inhibition of the growth of H460 lung carcinoma and A673 rhabdomyosarcoma xenografts in mice. These studies provide proof of principle for the feasibility of developing humanized RabMAbs as therapeutics.

Efficient serum clearance of botulinum neurotoxin achieved using a pool of small antitoxin binding agents

Antitoxins for botulinum neurotoxins (BoNTs) and other toxins are needed that can be produced economically with improved safety and shelf-life properties compared to conventional therapeutics with large-animal antisera. Here we show that protection from BoNT lethality and rapid BoNT clearance through the liver can be elicited in mice by administration of a pool of epitope-tagged small protein binding agents together with a single anti-tag monoclonal antibody (MAb). The protein binding agents used in this study were single-chain Fv domains (scFvs) with high affinity for BoNT serotype A (BoNT/A). The addition of increasing numbers of differently tagged scFvs synergistically increased the level of protection against BoNT/A. It was not necessary that any of the BoNT/A binding agents possess toxin-neutralizing activity. Mice were protected from a dose equivalent to 1,000 to 10,000 50% lethal doses (LD(50)) of BoNT/A when given three or four different anti-BoNT scFvs, each fused to an E-tag peptide, and an anti-E-tag IgG1 MAb. Toxin protection was enhanced when an scFv contained two copies of the E tag. Pharmacokinetic studies demonstrated that BoNT/A was rapidly cleared from the sera of mice given a pool of anti-BoNT/A scFvs and an anti-tag MAb but not from the sera of mice given scFvs alone or anti-tag MAb alone. The scFv pool and anti-tag MAb protected mice from lethality when administered up to 2 h following exposure of mice to a dose equivalent to 10 LD(50) of BoNT/A. These results suggest that it will be possible to rapidly and economically develop and produce therapeutic antitoxins consisting of pools of tagged binding agents that are administered with a single, stockpiled anti-tag MAb.

Chicken single-chain variable fragments against the SARS-CoV spike protein

The major concern for severe acute respiratory syndrome (SARS), caused by the SARS-associated coronavirus (SARS-CoV), is the lack of diagnostic and therapeutic agents. Using a phage display technology in a chicken system, high-affinity monoclonal antibody fragments against the SARS-CoV spike protein were characterized. Ten truncated spike protein gene fragments were expressed in Escherichia coli cells. Following the immunization of chickens with these recombinant spike proteins, two single-chain variable fragment (scFv) antibody libraries were established with short or long linkers to contain 5x10(7) and 9x10(6) transformants, respectively. After four rounds of panning selection, the scFv antibodies of randomly chosen clones were demonstrated by Coomassie blue staining, and verified by western blot analysis. In a comparison of nucleotide sequences with the chicken germline gene, we found that all clones varied in the complementarity-determining regions, that two scFv antibodies reacted significantly with SARS-CoV-infected Vero cells, and that those two specific scFv antibodies recognized the same region of the spike protein spanning amino acid residues 750-1000. In conclusion, the results suggest that the chicken scFv phage display system can be a potential model for mass production of high-affinity antibodies against the SARS-CoV spike protein.

Generation of high-affinity chicken single-chain Fv antibody fragments for measurement of the Pseudonitzschia pungens toxin domoic acid

Antibody-based assay systems are now accepted by regulatory authorities for detection of the toxins produced by phytoplankton that accumulate in shellfish tissues. However, the generation of suitable antibodies for sensitive assay development remains a major challenge. We have examined the potential of using the chicken immune system to generate high-affinity, high-specificity recombinant antibody fragments against phytotoxins. Following immunization of the chicken with domoic acid-bovine serum albumin, a single-chain antibody variable region (scFv) gene library was generated from single V(H) and V(L) genes isolated from the immune cells in the spleen and bone marrow. scFvs reacting with domoic acid were isolated by phage display and affinity matured by light chain shuffling, resulting in an approximate 10-fold increase in sensitivity. The isolated scFvs were effectively expressed in Escherichia coli and readily purified by affinity chromatography. They were then used to develop a convenient and sensitive indirect competitive enzyme-linked immunosorbent assay for domoic acid, with a 50% effective dose of 156 ng/ml, which could be used reliably with shellfish extracts. This study demonstrates that chickens provide a valuable model system for the simplified, rapid generation of high-affinity recombinant antibody fragments with specificity for small toxin molecules.

Bispecific and human disease-related anti-keratin rabbit monoclonal antibodies

Rabbit antibodies may have favorable properties compared to mouse antibodies, including high affinities and better antigen recognition. We used a biochemical and reverse immunologic approach to generate and characterize rabbit anti-phospho-keratin and anti-keratin monoclonal antibodies (MAb). Human keratins 8 and 18 (K8/K18) were used as immunogens after isolation from cells pretreated with okadaic acid or pervanadate to promote Ser/Thr or Tyr hyperphosphorylation, respectively. Selected rabbit MAb were tested by immunofluorescence staining, immunoprecipitation, and 2-dimensional gels. Keratin phospho and non-phospho-mutants were used for detailed characterization of two unique antibodies. One antibody recognizes a K8 G61-containing epitope, an important epitope given that K8 G61C is a frequent mutation in human liver diseases. This antibody binds K8 that is not phosphorylated on S73, but its binding is ablated by G61 but not S73 mutation. The second antibody is bispecific in that it simultaneously recognizes two epitopes: one phospho (K8 pS431) conformation-independent and one non-phospho conformation-dependent, with both epitopes residing in the K8 tail domain. Therefore, a reverse immunologic and biochemical approach is a viable tool for generating versatile rabbit MAb for a variety of cell biologic applications including the potential identification of physiologic phosphorylation sites.

Technical aspects of immunohistochemistry

Immunohistochemistry is an integral technique in many veterinary laboratories for diagnostic and research purposes. In the last decade, the ability to detect antigens (Ags) in tissue sections has improved dramatically, mainly by countering the deleterious effects of formaldehyde with antigen retrieval (AR) and increasing sensitivity of the detection systems. In this review, I address these topics and provide an overview of technical aspects of immunohistochemistry, including those related to antibodies (Abs) and Ags, fixation, AR, detection methods, background, and troubleshooting. Microarray technology and the use of rabbit monoclonal Abs in immunohistochemistry are also discussed.

Rational monoclonal antibody development to emerging pathogens, biothreat agents and agents of foreign animal disease: The antigen scale

Many factors influence the choice of methods used to develop antibody to infectious agents. In this paper, we review the current status of the main technologies used to produce monoclonal antibodies (mAbs) from the B cells of antigen-sensitized animals. While companies are adopting advanced high-throughput methods, the major technologies used by veterinary and medical research laboratories are classical hybridoma fusion and recombinant library selection techniques. These methods have inherent advantages and limitations but have many common aspects when using immunized rodents. Laboratories with expertise in both methods of antibody development have a distinct advantage in their ability to advance mAb technology. New and re-emerging infectious threats in today's world emphasize the need for quality immunoreagents and the need to maintain expertise in mAb development. We provide examples of some common applications for mAb reagents used to identify pathogens such as the SARS-coronavirus (SARS-CoV), Bacillus anthracis, and foot-and-mouth disease (FMD) virus. We also outline a framework for investigators to make rational decisions concerning which method to use to develop mAbs based upon characteristics of the pathogen under study and the intended downstream application. Lastly, we provide parameters for the immunisation of mice and a classification system which describes the expected outcome for mAb development strategies when using classes of immunogens to generate mAbs with desired activities.

Consistent immunostaining for cyclin D1 can be achieved on a routine basis using a newly available rabbit monoclonal antibody

Rabbit monoclonal antibody (MAb), which has become available only recently, theoretically combines the advantage of the high affinity attributable to its rabbit origin and the high specificity due to its monoclonal nature. Since immunohistochemical demonstration of cyclin D1 is notoriously difficult, this study aims to assess whether a newly available rabbit MAb against cyclin D1 (SP4) can improve the consistency of immunostaining, especially for the diagnosis of mantle cell lymphoma (MCL). A total of 150 cases of lymphoproliferative lesions, including 30 cases of MCL, histologic mimickers of MCL, and various types of lymphomas and leukemias, were studied. Immunostaining was performed on formalin-fixed, paraffin-embedded tissue sections using a labeled streptavidin-biotin peroxidase system in an automated immunostainer. All cases of MCL expressed cyclin D1, with a higher median staining score (8 out of a maximum of 12) compared with mouse MAb DCS-6 (score 4). In addition, 2 of 15 cases of B-cell chronic lymphocytic leukemia (B-CLL), 3 of 12 cases of multiple myeloma, and 2 of 5 cases of hairy cell leukemia were also positive. Comparable staining results could also be achieved by an optimized manual staining protocol. This study thus confirms the superior performance of the rabbit MAb SP4, which should permit consistent immunostaining for cyclin D1 to be readily achieved. The value of cyclin D1 immunohistochemistry in the differential diagnosis of MCL from other low-grade B-cell lymphomas is also affirmed, but with the caveat that rare cases of B-CLL can also be cyclin D1 positive.

Estimation of hormone receptor status in fine-needle aspirates and paraffin-embedded sections from breast cancer using the novel rabbit monoclonal antibodies SP1 and SP2

We describe a method of immunocytochemical assessment of estrogen receptor (ER) status on alcohol-fixed smears obtained by fine-needle aspiration (FNA) from breast cancer patients, using a commercially available rabbit monoclonal antibody anti-ER (SP1) without any antigen retrieval. A series of 40 aspirates were analyzed and the results of ER status were compared with the respective formalin-fixed tissue using the same procedure and with assessment by the classical method using the mouse monoclonal antibody 6F11 (anti-ER) with antigen retrieval on paraffin sections. Twenty-four out of the 40 cases examined were positive at least by two methods and 16 were negative for all three determinations. The results obtained in the ER immunocytochemical assay on aspirates and paraffin sections using the antibody SP1 and those obtained on paraffin sections using the antibody 6F11 were quite similar. In one case the material was insufficient to interpret the reaction in the cytological specimen and only one case, with focal positivity reaction on paraffin sections, was negative in the cytological specimen. The intensity of nuclei staining in cytological smears of breast cancer cells was stronger than that observed by traditional methods. We also assessed progesterone receptor (PR) status on 40 paraffin-sections from breast cancer patients, using a commercially available rabbit monoclonal antibody anti-PR (SP2), with the same characteristics described for anti-ER (SP1). The results were compared with assessment by the classic method with mouse monoclonal antibody 1A6 (PR) on paraffin sections and total agreement was observed. Of the 40 cases examined, 18 were positive and 22 were negative for the two determinations. We conclude that the application of the ER method on alcohol-fixed smears/paraffin sections with the rabbit monoclonal antibody SP1, and the PR method on paraffin sections with the rabbit monoclonal antibody SP2, provide several advantages, such as high sensitivity and specificity of the reaction, stronger immunostaining, shorter procedures times, and avoidance of antigenic retrieval methods.

Bacterial expression and purification of recombinant bovine Fab fragments

We have previously described a recombinant phagemid expression vector, pComBov, designed for the production of native sequence bovine monoclonal antibodies (mAb) generated by antibody phage display. Bovine mAb Fab fragments isolated from libraries constructed using pComBov in Escherichia coli strain XL1-Blue, which is routinely used for antibodies expressed on the surface of phage, were expressed at very low yields. Therefore, a study was undertaken to determine optimal growth conditions for maximal expression of bovine Fab fragments in E. coli. By varying the E. coli strain, and the temperature and length of the culture growth, we were able to substantially increase the yield of soluble Fab fragments. A high yield of Fab fragments was found in the culture growth medium, which enabled us to devise a rapid and simple single-step method for the purification of native (nondenatured) Fabs based on immobilized metal affinity chromatography against a six-histidine amino acid carboxyl-terminal extension of the heavy-chain constant region. Using these methods we were able to express and purify antigen-specific bovine Fab fragments from E. coli.