Medication development for methamphetamine use disorder has historically focused on targeting neurotransmitter systems with limited success, and there are currently no FDA-approved treatments for methamphetamine use disorder. Emerging evidence demonstrates how immune factors can influence addictive behaviors and contribute to substance use disorders. We have shown that our MHC class II constructs bind to and downregulate the expression of CD74—the primary receptor for macrophage migration inhibitory factor (MIF), a key inflammatory mediator in a number of diseases, including methamphetamine use disorder. These constructs have therapeutic impact on cognitive function, drug- seeking behavior, and inflammation in animal disease models. The primary objective of this U18 proposal is to conduct preclinical and in vitro drug validation experiments that evaluate CD74 as a treatment target for methamphetamine use disorder. We hypothesize that blocking CD74 with our MHC class II construct DRQ will promote abstinent-like behavior, improve cognitive function, and reduce MIF/CD74 activation. Cd74 knockout mice and C57BL/6J control mice will be used to assess the effects of methamphetamine and DRQ on cognitive function (e.g., working memory, attention). Sprague Dawley rats will be used to test whether DRQ decreases operant methamphetamine self-administration, as recently demonstrated in Lewis rats, thereby assuring data robustness. Preclinical in vitro target assessment experiments will investigate the effects of methamphetamine and DRQ immunotherapy on CNS inflammation. Focusing on brain areas critical for cognitive function and known to be damaged by methamphetamine (i.e., striatum, hippocampus, and prefrontal cortex), we will evaluate whether DRQ immunotherapy and/or CD74 deficiency: 1) inhibits inflammatory cell infiltration into the brain in methamphetamine exposed animals, 2) alters the cell-surface expression of CD74 on peripheral and CNS infiltrating myeloid cells, 3) blocks the binding of MIF to CD74, and 4) reduces MIF-stimulated extracellular-signal-regulated kinase activation and the expression of inflammatory cytokines in the CD74 signaling cascade [e.g., monocyte chemoattractant protein-1 (MCP-1)]. In addition, we will use human in vitro experiments to determine whether CD74 is important for pathogenic mechanisms in methamphetamine addiction and to evaluate the feasibility of using CD74 (expression or function) as a future biomarker for assessing DRQ immunotherapy treatment response. We expect that following the completion of this one-year project, we will have definitive evidence to validate CD74 as a treatment target and to support continued development of DRQ as a medication for methamphetamine use disorder.