Antibody-Mediated Targeting of the Orai1 Calcium Channel Inhibits T Cell Function

Abstract

Despite the attractiveness of ion channels as therapeutic targets, there are no examples of monoclonal antibodies directed against ion channels in clinical development. Antibody-mediated inhibition of ion channels could offer a directed, specific therapeutic approach. To investigate the potential of inhibiting ion channel function with an antibody, we focused on Orai1, the pore subunit of the calcium channel responsible for store-operated calcium entry (SOCE) in T cells. Effector T cells are key drivers of autoimmune disease pathogenesis and calcium signaling is essential for T cell activation, proliferation, and cytokine production. We show here the generation of a specific anti-human Orai1 monoclonal antibody (mAb) against an extracellular loop of the plasma membrane-spanning protein. The anti-Orai1 mAb binds native Orai1 on lymphocytes and leads to cellular internalization of the channel. As a result, T cell proliferation, and cytokine production is inhibited in vitro. In vivo, anti-Orai1 mAb is efficacious in a human T cell-mediated graft-versus host disease (GvHD) mouse model. This study demonstrates the feasibility of antibody-mediated inhibition of Orai1 function and, more broadly, reveals the possibility of targeting ion channels with biologics for the treatment of autoimmunity and other diseases.

Ion Channels in Innate and Adaptive Immunity

“…Two independently developed monoclonal antibodies selectively bound ORAI1 (but not ORAI2 and ORAI3), inhibited CRAC currents and SOCE in lymphocytes and suppressed the proliferation and cytokine production of human PBMCs and synovial fluid cells from rheumatoid arthritis patients in vitro (358, 359). In vivo treatment with anti-ORAI1 antibodies ameliorated the severity of xenogeneic T cell–mediated GvHD in mice (358) and reduced the production of IL-2, IL-4, and IL-17 by ex vivo–stimulated T cells isolated from cynomolgus monkeys (360). Collectively, these data suggest that CRAC channel inhibition may be useful for the treatment of autoimmune diseases, transplant rejection, and allergic diseases.…”

Targeting calcium signaling in cancer therapy

“…Taking a similar approach, another specific anti-Orai1 mAb targeting the second extracellular loop, inhibits the proliferation of T cells and cytokine production both in vitro and in vivo . Further mechanistic studies suggested that mAb-targeted Orai1 proteins are internalized, which resulting in loss of functional SOCE activity 211 . Although the anti-Orai1 mAbs-based potential therapy is limited in immune diseases, it raises high hope of similar application for cancer treatment.…”

Screening Strategies for the Discovery of Ion Channel Monoclonal Antibodies

“…Due to the structural and functional diversity of ion channels, different strategies need to be considered for generation of antigen formats of the ion channel or antigens derived from the channel (Wilkinson, Gardener, & Williams, ). While peptides derived from the ion channel can be used as antigens (Cox et al., ), it is usual to use a conformationally relevant form of the channel as the antigen (Bednenko et al., ). Ion channels are normally expressed in low abundance in vivo and the heterologous expression of the proteins needed to achieve high expression levels requires considerable experimentation to optimize the host expression system, particularly as heterologous overexpression can be toxic (Vu, Bautos, Hong, & Gelli, ).…”