A rare monoclonal antibody discovery based on indirect competitive screening of a single hapten-specific rabbit antibody secreting cell

Rational hapten design, antibody preparation, and immunoassay development for rapid screening xylazine in biological samples

Xylazine (XYL) is an illicit adulterant in opioids and an approved veterinary sedative drug, which has been abused, misused, and residued in food samples, endangering people health, causing drug-facilitated crimes and even death. Immunoassay used antibody as core biomaterial could to achieve highly sensitive and rapid detection screening purpose for XYL in situ. Here, we rationally designed four novel XYL haptens with different spacer arms to produce antibodies with high affinity and specificity. Ten monoclonal antibodies (mAbs) were obtained and mAb 7H5 showed a high affinity with IC50 of 0.23 ng mL-1 and ignorable cross-reactivity for the other eight analogs. One highly sensitive indirect competitive ELISA (icELISA) and lateral flow immunoassay (LFIA) were established based on heterologous haptens for XYL detection in a series of human urine and food samples. The limit of detections (LODs) of the icELISA were 0.10-2.24 μg L-1 with recovery of 83.5 % to 128.6 % and CV below 15.8 % in different samples, while, the visual limits of detection (vLOD) of LFIA were 0.10-1.80 μg L-1 with the cut-off value of 0.60-4.80 μg L-1. In addition, the molecular recognition mechanism of mAbs was explored. The study provides powerful tools for rapid screening of XYL in human urine and food samples for the first time.

Antibody Recognition Profile-Aided Hapten Design to Modulate Antibody Generation with Anticipated Performance for Immunoassay Development

The hapten design to chemical compound currently considered only structural aspects of targets may suffer from the failure of antibody generation with anticipated performances, especially for broad-specific antibodies. To address the problem, this study proposed a novel strategy, named antibody recognition profile-aided hapten design (ARPHD), based on clues from both reported antibodies, haptens, and targets after uncovering antibody recognition profiles using fluorfenicol (FF) and fluorfenicol amine (FFA) as model analytes in this work. Specifically, we confirmed that the fluorine atom promoted the generation of antibodies to FFA, while the -COCHCl2 moiety was unfavorable for inducing broad-specific antibodies to FF and FFA. Based on the structural information from ARPHD, four novel haptens without -COCHCl2 and containing a fluorine atom are intentionally designed, then identified by computational chemistry and animal immunization, successfully inducing antibodies to FF and FFA with uniform IC50 values of 3.09 and 3.75 ng mL-1. The explanation of molecular mechanisms from the obtained antibodies has supported the scientific base behind ARPHD, and we also found that the light chain of the antibody contributed an important role in differential recognition of the antibody. Finally, an indirect competitive ELISA (icELISA) was developed for the simultaneous detection of FF and FFA in river water and animal-derived food with a LOD of 2.24-14.6 μg kg-1, which has never been achieved before. The study demonstrated that the ARPHD we proposed could rationally guide the design of haptens that modulate the generation of antibodies with appreciated performances and easily be extended to other chemical compounds as a versatile platform.

Highly selective and sensitive immunoassays for flurogestone acetate analysis in goat milk: From rational hapten design and antibody production to assay development

The preparation of high specificity and affinity antibodies is challenging due to limited information on characteristic groups of haptens in traditional design strategy. In this study, we first predicted characteristic groups of flurogestone acetate (FGA) using quantitative analysis of molecular surface combined with atomic charge distribution. Subsequently, FGA haptens were rationally designed to expose these identified characteristic groups fully. As a result, seven monoclonal antibodies were obtained with satisfactory performance, exhibiting IC50 values from 0.17 to 0.45 μg/L and negligible cross-reactivities below 1% to other 18 hormones. The antibody recognition mechanism further confirmed hydrogen bonds and hydrophobic interactions involving predicted FGA characteristic groups and specific amino acids in the antibodies contributed to their high specificity and affinity. Finally, one selective and sensitive ic-ELISA was developed for FGA determination with a detection limit as low as 0.12 μg/L, providing an efficient tool for timely monitoring of FGA in goat milk samples.

Response to Comments on "Monoclonal Antibody Discovery Based on Precise Selection of Single Transgenic Hybridomas with an On-Cell-Surface and Antigen-Specific Anchor"

Listek et al. described some technical concerns for the single transgenic hybridoma selection method (STHSM) that we developed. In this work, we developed the STHSM to screen hapten-specific hybridoma cells based on a streptavidin-labeled antigen originally proposed by Listek et al. that was used for the selection of OVA-specific hybridoma. Due to the obvious differences between hapten with a single epitope and protein with multiple epitopes, we significantly innovated the specific procedures in the STHSM that could answer the questions raised by Listek's group.

Significantly improved detection performances of immunoassay for ractopamine in urine based on highly urea-tolerant rabbit monoclonal antibody

Highly sensitive and accurate screening of ractopamine (RAC) residue in animal urine is greatly needed to ensure food security. The detection performance of immunoassay for RAC was always seriously harmed by the antibody inactivation derived from urea. Here, we first discovered one rabbit monoclonal antibody (RmAb) to RAC with a high affinity of 0.007 ng mL^-1 and a surprising urea tolerance of 3 M urea, which is beneficial for developing robustly developed immunoassay in urine without sample pretreatment. The limits of detection of developed indirect competitive enzyme-linked immunosorbent assay based on RmAb1 for RAC were 0.0042-0.014 μg L^-1 with the coefficient of variation below 11.7% in swine, sheep, and cow urine, significantly improved 10-100-fold in sensitivity. Moreover, the urea-tolerant mechanism of RmAb1 showed that more non-polar amino acids, more hydrogen bond donors on the surface, and preponderant Pi interaction of antibody-RAC all contributed to the stability of the RmAb1 in a high concentration of urea.