The rescue by phage display of human Fabs to gp120 HIV-1 glycoprotein using EBV transformed lymphocytes

A novel strategy for efficient production of anti-V3 human scFvs against HIV-1 clade C

Background

Production of human monoclonal antibodies that exhibit broadly neutralizing activity is needed for preventing HIV-1 infection, however only a few such antibodies have been generated till date. Isolation of antibodies by the hybridoma technology is a cumbersome process with fewer yields. Further, the loss of unstable or slowly growing clones which may have unique binding specificities often occurs during cloning and propagation and the strongly positive clones are often lost. This has been avoided by the process described in this paper, wherein, by combining the strategy of EBV transformation and recombinant DNA technology, we constructed human single chain variable fragments (scFvs) against the third variable region (V3) of the clade C HIV-1 envelope.

Results

An antigen specific phage library of 7000 clones was constructed from the enriched V3- positive antibody secreting EBV transformed cells. By ligation of the digested scFv DNA into phagemid vector and bio panning against the HIV-1 consensus C and B V3 peptides followed by random selection of 40 clones, we identified 15 clones that showed V3 reactivity in phage ELISA. DNA fingerprinting analysis and sequencing showed that 13 out of the 15 clones were distinct. Expression of the positive clones was tested by SDS-PAGE and Western blot. All the 13 anti-V3 scFvs showed cross-reactivity against both the clade C and B V3 peptides and did not show any reactivity against other unrelated peptides in ELISA. Preliminary neutralization assays indicated varying degrees of neutralization of clade C and B viruses. EBV transformation, followed by antigen selection of lines to identify specific binders, enabled the selection of phage from un-cloned lines for scFv generation, thus avoiding the problems of hybridoma technology. Moreover, as the clones were pretested for antigen binding, a comparatively small library sufficed for the selection of a considerable number of unique antigen binding phage. After selection, the phage clones were propagated in a clonal manner.

Conclusions

This strategy can be efficiently used and is cost effective for the generation of diverse recombinant antibodies. This is the first study to generate anti-V3 scFvs against HIV-1 Clade C.

Identification using phage display of peptides promoting targeting and internalization into HPV-transformed cell lines

'High-risk' human papilloma viruses (HPVs) cause cervical tumours. In order to treat these tumours therapeutic approaches must be developed that efficiently target the tumour cells. Using phage display, we selected tumour-targeting peptides from a library of constrained nonamer peptides presented multivalently on pVIII of M13. Three different consensus peptide sequences were isolated by biopanning on HPV16-transformed SiHa cells. The corresponding phage-peptides targeted and were internalized in HPV16 transformed SiHa and CaSki cells as well as in HPV18-transformed HeLa cells, but failed to bind a panel of normal or transformed cell lines. Two of the three selected peptides targeted cells only when presented on phage particles in a constrained conformation. However, all three peptides retained their targeting capacity when presented on the reporter protein enhanced green fluorescent protein (EGFP) in a monovalent form. These peptides may be useful for the design of drug or gene delivery vectors for the treatment of cervical cancer.

Combining EL4-B5-based B-cell stimulation and phage display technology for the successful isolation of human anti-Scl-70 autoantibody fragments

Scl-70 is the major antigen recognised by autoantibodies in the sera of patients with systemic sclerosis (SSc). The autoantibodies that specifically react with Scl-70 are highly characteristic of the disease and represent valuable markers for the diagnosis of SSc. We describe a novel strategy for cloning autoantibody fragments starting with a small blood sample from an SSc patient. B cells isolated from the collected peripheral blood mononuclear cells (PBMCs) were cultured in vitro using the EL4-B5 system. Anti-Scl-70 IgG-producing cells were pooled for RNA preparation followed by the generation of phagemid libraries of approximately 10(7) independent single-chain Fvs (scFvs). The screening of these libraries by phage display allowed us to isolate four anti-Scl-70 scFvs following three rounds of biopanning. About 10 times more starting blood material was needed to generate scFv libraries of similar size from PBMCs of an SSc patient and only two anti-Scl-70 scFvs were isolated after three rounds of phage selection. Together, this work shows that functional autoantibody fragments can be advantageously cloned after in vitro expansion of B cells. The isolated anti-Scl-70 autoantibody fragments represent useful tools for calibrating SSc diagnostic assays.

Cell surface phenotyping and cytokine production of Epstein-Barr Virus (EBV)-transformed lymphoblastoid cell lines (LCLs)

Epstein-Barr Virus-transformed B lymphoblastoid cell lines (EBV-LCLs) are routinely used for the in vitro expansion of T cells. However, these cell lines are reported to produce the cytokine IL-10, which is inhibitory for T cells. We, therefore, characterized a panel of 37 EBV-LCLs for a variety of cell surface markers, for secretion of various cytokines including IL-10 and for immunoglobulin production. These cell lines were derived from normal donors or patients with nonsmall cell lung cancer, acute myelogenous leukemia, melanoma or colon cancer. Overall, 26 lines were positive for CD19 and CD20, and 11 were negative for both. All of the lines were strongly HLA-DR+, while CD40 expression was variable. Twenty-four (65%) were both CD23+ and secreted immunoglobulin, and 33 expressed kappa and/or lambda light chains. Additionally, all of the EBV-LCLs were negative for T cell (CD3), NK cell (CD16, CD56), monocyte (CD14) and granulocyte (CD66b) surface markers. Some level of IL-10, IL-6, IL-12p40 and TNF-alpha cytokine production was detected in 33, 18, 19 and 12 EBV-LCLs, respectively. Together, these data reflect the heterogeneity of EBV-LCLs, which cautions their use nondiscriminately in various immunologic assays.