Characterization of Clozapine-Responsive Human T Cells

Abstract

Use of the atypical antipsychotic clozapine is associated with life-threatening agranulocytosis. The delayed onset and the association with HLA variants are characteristic of an immunological mechanism. The objective of this study was to generate clozapine-specific T cell clones (TCC) and characterize pathways of T cell activation and cross-reactivity with clozapine metabolites and olanzapine. TCC were established and characterized by culturing PBMCs from healthy donors and patients with a history of clozapine-induced agranulocytosis. Modeling was used to explore the drug–HLA binding interaction. Global TCC protein changes were profiled by mass spectrometry. Six well-growing clozapine-responsive CD4+ and CD8+ TCC were used for experiments; activation of TCC required APC, with clozapine interacting directly at therapeutic concentrations with several HLA-DR molecules. TCC were also activated with N-desmethylclozapine and olanzapine at supratherapeutic concentrations. Marked changes in TCC protein expression profiles were observed when clozapine treatment was compared with olanzapine and the medium control. Docking of the compounds into the HLA-DRB1*15:01 and HLA-DRB1*04:01 binding clefts revealed that clozapine and olanzapine bind in a similar conformation to the P4–P6 peptide binding pockets, whereas clozapine N-oxide, which did not activate the TCC, bound in a different conformation. TCC secreted Th1, Th2, and Th22 cytokines and effector molecules and expressed TCR Vβ 5.1, 16, 20, and 22 as well as chemokine receptors CXCR3, CCR6, CCR4, and CCR9. Collectively, these data show that clozapine interacts at therapeutic concentrations with HLA-DR molecules and activates human CD4+ T cells. Olanzapine only activates TCC at supratherapeutic concentrations.

Clozapine Induces an Acute Proinflammatory Response That Is Attenuated by Inhibition of Inflammasome Signaling: Implications for Idiosyncratic Drug-Induced Agranulocytosis

“…IDIAG is believed to be an adaptive immune-mediated reaction associated with specific HLA haplotypes ( Chowdhury et al , 2011 ; Legge and Walters, 2019 ) and T cell receptors ( Ogese et al , 2020 ). However, induction of this adaptive response must be preceded by innate immune activation; an early response that does not appear to be idiosyncratic ( Sernoskie et al , 2021 ).…”

“…Thus, this innate response is likely another necessary but, alone, insufficient step in the progression to agranulocytosis, which is believed to be an adaptive immune-mediated reaction associated with specific human leukocyte antigen (HLA) haplotypes ( Chowdhury et al , 2011 ; Legge and Walters, 2019 ). Specifically, mechanistic studies have demonstrated that an adaptive immune response mediated by CD4 + T cells is generated in response to the interaction of clozapine with HLA-DR molecules ( Ogese et al , 2020 ); a response which must be preceded by innate immune activation.…”

Clozapine re-challenge and initiation following neutropenia: a review and case series of 14 patients in a high-secure forensic hospital

“…Many non-chemotherapy drugs can cause idiosyncratic drug-induced neutropenia (IDIN); while the individual mechanisms are not all elucidated, it is hypothesized that oxidized drug metabolites combine with human leukocyte antigens (HLAs) to act as haptens, inducing the production of antibodies mediated by T-helper cells; this has recently been demonstrated for clozapine. 18 …”

“…Many non-chemotherapy drugs can cause idiosyncratic drug-induced neutropenia (IDIN); while the individual mechanisms are not all elucidated, it is hypothesized that oxidized drug metabolites combine with human leukocyte antigens (HLAs) to act as haptens, inducing the production of antibodies mediated by T-helper cells; this has recently been demonstrated for clozapine. 18 Differentiating IDIN from other causes of neutropenia can be difficult as, although the majority of cases occur within weeks or months of drug initiation, some can occur after years of uneventful therapy. Whilst clozapine is one of the most commonly implicated drugs, many widely used drugs have significant effects; therefore, careful attention to the temporal relationships between drug initiation and side effects as well as scrutiny of concomitant medication is required.…”

Clozapine-specific proliferative response of peripheral blood-derived mononuclear cells in Japanese patients with clozapine-induced agranulocytosis

“…Attempts by a Canadian group to support this indication mechanistically in vitro by developing clozapine or clozapine metabolite-responsive T cells were unsuccessful (Guest et al, 1998), but a recent German study reported a significant increase in the proliferative response of peripheral blood-derived mononuclear cell (PBMC) cultures from patients with CIA (Regen et al, 2017). Very recently, clozapine- and clozapine metabolite-specific T cells were successfully developed in patients with CIA from the UK population, suggesting that the clozapine-specific memory T cells may mediate CIA (Ogese et al, 2020). The main purpose of this study is to support these recent developments—CIA is mediated by the adaptive immune systems—by investigating the responses of PBMCs to clozapine using blood from Japanese patients with a history of CIA or clozapine-tolerant control subjects on treatment with clozapine.…”