SYnAbs therapeutic anti-CD2  - LO-CD2b

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.

Specificity to CD2 transmembrane receptor

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.

LO-CD2 inhibition of mitogenic stimulation

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.

Inhibition of allogeneic one-way MLR

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).