In a Phase 2 renal transplant study, the anti-ΑΒ TCR antibody TOL101 inhibited T cell function in transplant patients at a range of doses. When administered in a daily escalating dosing regimen (escalating doses from 14 to 42mg/day) to renal transplant patients, TOL101, in addition to inhibiting effector T cell function, also promoted Treg expansion. Expansion of CD4+CD25+FOXP3+CD127lo Tregs in response to escalating amounts of TOL101 was also shown in vitro. It was hypothesized that TOL101 binds to the ΑΒTCR in a novel fashion that generates a unique signaling cascade that inactivates effector T cells and promotes Tregs.
In vitro, TOL101 was originally shown to be highly effective at inhibiting the mixed lymphocyte reaction. It is non-mitogenic when in soluble or immobilized form, inducing IL10 production in vitro in both cases. The signaling cascades triggered by TOL101 in fresh PBMC were compared to those induced by mitogenic CD3 (OKT3). As expected, OKT3 caused significant calcium flux, ZAP70 and STAT1 phosphorylation, and proinflammatory cytokine (TNF, IL6, Type II Interferon) production. In contrast, in TOL101 treated PBMC, proinflammatory cytokines were at low levels, and only a small percentage of CD4 T cells exhibited calcium flux. However, TOL101 did induce an increase in phosphorylated STAT5 as well as AKT and ERK. Furthermore, when TOL101 was added to T cells undergoing anti-CD3 proliferation T cells, it terminated further proliferation, resulting in inhibition of ZAP70 phosphorylation and reduction in proinflammatory cytokine production.
CD3 is required for TCR signaling downstream from the ΑΒTCR. The data suggest a potentially novel TCR mediated, CD3 independent signaling cascade. Furthermore, TOL101-induced phosphorylation of AKT and ERK, adaptor molecules mostly associated with co-stimulatory molecules, suggests that this novel pathway may promote T cell survival, which may explain the ability for TOL101 to promote Treg expansion when given in an escalating dosage regimen.
To cite this abstract in AMA style:Getts D, Chastain E, Terry R, Brown S, Thompson J, Flechner S, Wiseman A, Miller S. TOL101 Signaling Pathways, a Novel CD3 Independent T Cell Inactivation & Treg Induction Cascade [abstract]. Am J Transplant. 2013; 13 (suppl 5). http://atcmeetingabstracts.com/abstract/tol101-signaling-pathways-a-novel-cd3-independent-t-cell-inactivation-treg-induction-cascade/. Accessed January 17, 2018.
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