Fig 2: SBT115301 preferentially depletes CD2hi-expressing T cells in vitro(A) Median fluorescence intensity (MFI) of CD2 expression on NK cells (CD3−CD56+) and CD3+CD4+ Treg (CD25hiFOXP3+ Tn (CD45RA+CCR7+), Tcm (CD45RA−CCR7+), and Tem (CD45RA−CCR7-) cell subsets (n = 30). Boxes represent the interquartile range (25th to 75th percentile). Individual data points are shown.(B) Activation of the high affinity (V158; each condition in triplicate, 5 experiments) and low affinity (F158; each condition in triplicate, 4 experiments) CD16a variants by SBT115301 as measured by mean ± SD relative light units (RLU) in a Jurkat ADCC reporter assay.(C) Representative histogram demonstrating the difference in CD2 expression of a PBMC sample incubated for 20 h with 100 nM SBT115301 or control (left). PBMC were incubated with increasing concentrations of SBT115301 or control in triplicate and mean ± SD cell numbers were quantified at the end of the assay (right).(D) Mean ± SD cell counts normalized to no test or control added of naive (CD45RA+) and proliferating (Prolif) and non-proliferating (Non-prolif) memory (CD45RO+) CD4+ T cells following incubation of CMV-reactive PBMC with CMV antigen and SBT115301 for 6 days. Each condition run in triplicate. Wilcoxon rank-sum ∗∗∗∗p ≤ 0.001 by Wilcoxon rank-sum test (A).

Fig 3: Pharmacodynamics of a single dose of SBT115301 in healthy participants(A) Mean ± SD numbers of circulating CD4+ Tem (CD45RA−CCR7-), Tcm (CD45RA−CCR7+), and Tn (CD45RA+CCR7+) subsets reported as % change of pre-treatment values over time.(B and C) Maximum reduction of (B) CD4+ Tem and (C) Treg (CD4+CD127loCD25hiFOXP3+) in each cohort reported in % change from baseline as measured by the net area under the effect curve from Day 3 to Day 8 using % change from baseline based on cell counts divided by duration of time (Eavg(3-8)). Boxes represent the interquartile range (25th to 75th percentile). One-way analysis of variance and Dunnett’s test were used to compare between treated groups and placebo groups. Statistical significance (compared to placebo) was set at ns, p > 0.05; ∗, p < 0.05; ∗∗, p < 0.01.(D) Mean ± SD ratio of Treg to Tem cells reported as a % change of pre-treatment values following dosing in the 10 and 30 mg IM cohorts compared to participants who received placebo.(E) Durability of the CD4+ Tem PD response at timepoints after 32 days compared to the initial PD response measured by Eavg(3-8).(F) Correlation of baseline CD2 median fluorescence intensity on all cell subsets tested (CD4+ and CD8+ T cell subsets) with the PD responses of each subset as measured by Eavg(3-36). Linear regressions were used to depict relations between Eavg(3-36) and baseline CD2 median fluorescence intensity within each dose. Fitted regression lines (solid lines) with 95% confidence bands (dotted lines) are displayed. Colored dots represent estimated Eavg(3-36) for each cell subset at the average CD2 level and vertical edges represent 95% confidence intervals. ∗p < 0.05, ∗∗p < 0.01, ns (not significant) by one-way analysis of variance and Dunnett’s test (B and C).

Fig 4: SBT115301 depletes T cell subsets with higher CD2 expression in an NHP model(A) Comparison of ADCC activity of SBT115301 in human versus non-human primate (NHP) in a primary PBMC in vitro assay. Boxes represent the interquartile range (25th to 75th percentile). Individual data points are shown.(B and C) Mean ± SD numbers of (B) circulating total (CD3+) T cells, CD4+ T cells, and CD8+ T cells, (C) CD4+ Tem (CD45RA−CCR7-), Tcm (CD45RA−CCR7+), Tn (CD45RA+CCR7+), and Treg (CD4+CD25hiFOXP3+) expressed as % of baseline (pre-dose) cell counts after a single dose of SBT115301.(D) Mean ± SD numbers of circulating (CD3+) T cells in combined male and female NHP in a multi-dose (weekly) study. Data were collected pre-treatment (pre-Tx; Day 1) and up to 168 h post-Dose 1 (n = 5 animals/sex/group), pre-Dose 5 (Day 29) and up to 168 h post-Dose 5 (n = 5 animals/sex/group), and at the end of the study (Day 92; n = 2 animals/sex/group).(E) Mean ± SD anti-drug antibody (ADA) titers in NHP receiving multiple doses of SBT115301.

Fig 5: Sequence alignment of the engineered CD2 binding domain of SBT115301 with human WT LFA-3Yellow boxes denote amino acids identified as being involved in binding to CD2, with white, gray, and black dots showing the effects of single amino acid mutagenesis on binding of human LFA-3 to human CD2.27 Red arrows and boxes identify residues that were altered in SBT115301.