Session Information
Session Type: Abstract Submissions (ACR)
Background/Purpose
Epratuzumab is a humanized monoclonal antibody targeting the B cell-specific protein CD22 and is in Phase 3 clinical trials in patients with systemic lupus erythematosus (SLE). Epratuzumab does not deplete B cells, rather, the mechanism of action centers on CD22 regulatory activity of B cell receptor (BCR) modulation, via inhibition of specific BCR-driven phosphorylation events (Syk, PLCγ2) and Ca2+ flux.1 The aim of this study was to assess the effects of epratuzumab on receptor activation and BCR signaling across multiple B cell subsets in peripheral blood mononuclear cells (PBMC) from a large cohort of healthy donors.
Methods
Single Cell Network Profiling (SCNP) is a multiparametric, flow cytometry-based technology that enables simultaneous analysis of signaling networks in multiple immune cell subsets.2 BCR modulated signaling (anti-IgG/anti-IgM) was profiled by SCNP in PBMC from 60 healthy donors (HD) across naïve (CD27-/IgD+), switched memory (CD27+/IgD-) and unswitched memory (CD27+/IgD+) B cell subsets. Surface receptor (CD22, CD19), proximal (Syk, Slp76, BTK, PLCγ2) and distal (Akt, Erk, S6, p38, IkBa, NFκB-p105) signaling was interrogated 5 or 15 minutes post modulation in the presence and absence of epratuzumab (10mg/ml), which had been pre-incubated with cells for 1 hour.
Results
On-target epratuzumab activity in B cells was identified as induction of pCD22 Tyr807, most pronounced in naïve B cells (p<0.001). Broad inhibition of all examined BCR-proximal signaling (p<0.0001) was observed in the whole B cell population with the most pronounced effects observed in the switched memory population. Strong inhibition of BCR modulated pCD19 (p<0.001) was also seen in this population, which may contribute to inhibition of BCR activation events. Inhibition of distal signals was demonstrated specifically in the switched memory B cell population whilst conversely, in the naïve B cell subset, evidence for activation of distal signaling (p<0.0001) was observed. Interestingly, weak activation of pAkt was observed in both naïve and switched memory B cells.
Conclusion
Broad analysis of functional immune signaling across B cell subsets identified epratuzumab inhibition of BCR-proximal signaling, supporting an inhibitory role in BCR activation. Opposing effects on distal signaling were identified in the naïve and memory populations. In switched memory B cells inhibition of pCD19 and downstream signals was demonstrated. In contrast, in naïve B cells activation of distal signals was observed. These data have implications for understanding the functional consequences of epratuzumab treatment on B cell pathologic activity in patients with autoimmune diseases such as SLE.
References
1. Sieger N. Arthritis Rheum 2013;65:770
2. Cesano A. Cytometry Part B 2012;82B:158
Disclosure:
A. Maloney,
UCB Pharma,
3;
D. Hotson,
Nodality Inc.,
3;
S. Rapecki,
UCB Pharma,
3;
G. Fossati,
UCB Pharma,
3;
S. Lumb,
UCB Pharma,
3;
D. Rosen,
Nodality Inc.,
3;
S. Putta,
Nodality Inc.,
3;
N. Wale,
Nodality Inc,
3;
D. Spellmeyer,
Nodality Inc.,
3,
Nodality Inc.,
1;
A. Cesano,
Nodality Inc.,
3;
R. Hawtin,
Nodality Inc.,
3;
A. Shock,
UCB Pharma,
3.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/epratuzumab-induces-broad-inhibition-of-b-cell-receptor-proximal-signaling-but-has-opposing-effects-on-distal-signaling-in-b-cell-subsets-a-profile-of-effects-on-functional-immune-signaling-by-single/