Thanks to its unique platform, SYnAbs has been able to generate a new anti-IL-2R monoclonal antibody (LO-Tact-1), produced in the LOU/C rat species, available for clinical use with T depletion strategy. This asset, with the same MoA as SiplizumAb (LO-CD2a, MEDI-507) previously developed by SYnAbs, shows cross-reactivity to human and cynomolgus CD2. LO-CD2b IgG2bκ rat-LOU monoclonal antibody has been tested into several in-vitro, ex-vivo and in-vivo studies as described below.
Dehoux JP, Talpe S, Dewolf N, Otsuka M, Oike F, Jamar F, de la Parra B, Latinne D, Bazin H, Gianello P. Effects on human and nonhuman primate immune response of a new rat anti-CD2 monoclonal antibody. Transplantation. 2000 Jun 27;69(12):2622-33. doi: 10.1097/00007890-200006270-00024. PMID: 10910286.
1. Competitive assay: Serial dilutions of LO-CD2b were incubated with baboon PBMCs and then with rhodamine-labeled T11, Leu5b (anti-CD2) mAbs. The percentage of rhodamine-labeled cells was assessed by FC, thereby demonstrating a specific competition for the CD2 molecule.
2. E-rosetting: LO-CD2b blocked E-rosetting at an average of 91±2% for LO-CD2b-coated cells (data not shown)
3. Western blot: 125I anti-rat sheep Ig binding to (A) IgG2b rat mAb as a positive control; (B) IgG1b mouse Ig and (C) no reagent as negative controls; (D) supernatant of lysed PBMC+LO-CD2b. LO-CD2b is reactive with a lysed PBMC supernatant of a molecular weight of 52 kDa.
When LO-CD2b was added at day 0, the phytohemagglutinin (PHA) stimulation of baboon PBMCs was inhibited at 72.8±12.1%, and the concanavalin (ConA) stimulation at 71.0±8.4%.
LO-CD2b was still able to partially inhibit a mitogenic stimulation after the culture initiation: the addition of LO-CD2b at 1 or 2 days after culture initiation inhibited the PHA stimulation at 56±8.5% and 38.5±9.8%, respectively, and inhibited the ConA stimulation at 29.3±7.5% and 15.7±11.5%, respectively.
LO-CD2b had a similar inhibitor effect on PHA-stimulated human PBMCs. In the presence of human PBMCs, the inhibition after PHA stimulation was 62.1% at day 0, 48% at day 1, and 18% at day 2.
When added at the day of initiation of culture, a LO-CD2b concentration more than 156 ng/ml almost completely (96.4±1.1%) inhibited a baboon allogeneic MLR. Low doses such as 4.8 and 9.7 ng/ml inhibited 50% of the proliferative response, and 1.2 ng/ml of LO-CD2b inhibited the MLR up to 22.9±14.1%.
The same effect was observed in allogeneic human MLR but with a (10–20%) lower degree of inhibition. In comparison, no inhibition was obtained with a rat IgG2b isotype control (data not shown).
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