Schizophrenia is a devastating psychiatric disorder impacting 24 million people worldwide. Approximately one-third of people with schizophrenia do not respond to first-line antipsychotics and are prescribed clozapine. Despite its superior efficacy, the widespread use of clozapine is limited by concern for serious adverse effects including clozapine-induced neutropenia, which occurs in ~1% of treated patients and increases the risk of life-threatening infections. The mechanism by which clozapine causes neutropenia in a small subset of individuals is, however, poorly understood. This study aimed to elucidate the cellular mechanisms underlying clozapine-induced neutropenia by charactering cell type-specific gene expression changes associated with this adverse trait.
We recruited six individuals with treatment-resistant schizophrenia who had received clozapine, including three who ceased due to clozapine-induced neutropenia and three who stopped for unrelated reasons. Peripheral blood mononuclear cells (PBMCs) were collected and cultured in vitro for 72 hours under three conditions: untreated, clozapine treated, and clozapine plus its two major metabolites (i.e., N-desmethyl clozapine and clozapine-N-oxide). We then generated high quality single nucleus RNA-seq data on 58,000 cells using the 10x Genomics Flex platform, from which we identified 25 distinct clusters. After adjusting for age, sex and smoking status, differential gene expression analysis revealed a set of CD4- and CD8 T cell-specific genes and associated functional pathways that were significantly altered (Bonferroni-adjusted) in individuals who developed clozapine-induced neutropenia, but not in those taking clozapine without neutropenia. Additionally, limited evidence was found for the effect of clozapine-related metabolites on clozapine-induced neutropenia.
Our findings provide novel insights into immune cell-specific molecular signatures associated with clozapine-induced neutropenia, which may contribute to the future development of predictive biomarkers and safer therapeutic strategies for treatment-resistant schizophrenia.