To further test the functional attributes of Fab specific for the two-domain RTL1000, we utilized an Fab specific for RTL1000 that was also cross-reactive with a similar Selleckchem PLX4032 antigenic determinant on RTL342m (α1β1 domains of DR2 linked to mMOG-35-55 peptide). DR2 Tg

mice were immunized with mMOG-35-55 peptide/CFA/pertussis toxin (Ptx) to induce EAE and were treated with pre-formed complexes of 2E4 Fab:RTL342m, the control D2 Fab:RTL342m (specific for RTL2010 that comprised DR4–GAD-555-567 described in Fig. 8C) or TRIS buffer (Fig. 5). As shown in Fig. 5, mice receiving RTL342m plus TRIS buffer were effectively treated, whereas a 2:1 ratio of 2E4 Fab:RTL342m almost completely neutralized the RTL therapeutic effect on EAE. In contrast, a 1:1 ratio of Fab:RTL342m had less neutralizing activity as assessed by daily EAE scores (Fig. 5A) and by the entire experimental effect on EAE for each group as assessed by the cumulative disease index (CDI) (Fig.

5B). Importantly, D2 Fab (also used at a 2:1 ratio) did not neutralize the therapeutic effect of RTL342m on EAE, indicating specificity of the 2E4 Fab for the two-domain RTL342m. In a recent phase I safety study in DR2+ MS subjects 34 to be treated with Fulvestrant clinical trial RTL1000 or placebo, we observed detectable baseline plasma levels of two-domain RTL-like structures in 4 of 13 donors (31%). This observation suggested the natural occurrence of two-domain Thymidylate synthase structures that could be derived from four-domain intermediates possibly shed from MHC-II expressing APC upon immunization. Using the power of our conformationally sensitive Fabs, we evaluated the appearance and persistence of naturally occurring two-domain MHC-II structures in human MS subjects. Fab 1B11 is specific for the two-domain HLA-DR conformation. It was found to bind to all HLA-DR-derived RTLs (with no peptide specificity), but not to other human and murine allele-derived RTLs or four-domain HLA-DR molecules (Fig. 6A). Serum or plasma samples were diluted 1:10 and adsorbed onto plastic wells pre-coated with the TU39 mAb (that detects all forms of MHC), washed and reacted with 1B11 Fab specific

for HLA-DR-derived RTLs, followed by the addition of enzyme-labeled anti-Fab and substrate for ELISA detection. As shown in Fig. 6B, the 1B11 Fab detected RTL-like material in serum or plasma from the healthy control pool as well as all six MS subjects tested at baseline, with detected levels of protein ranging from 13 to 1100 ng/mL. These results indicate for the first time the existence of soluble serum MHC-II structures with a distinct RTL-like conformation that differs from the classical membrane-bound MHC conformation. Increased signal for two-domain MHC-II was also observed in subject ♯42 after 30 min of infusion of 200 mg RTL1000 and in subject ♯44 after 2 h of infusion of 100 mg RTL1000, consistent with increased levels of injected RTL1000.