Abstract: The present disclosure provides variant major histocompatibility complex class II (MHCII) beta chains, as well as heterodimers and multimers including MHCII alpha chains and the variant MHCII beta chains. Also provided by the present disclosure are nucleic acids, expression cassettes, and expression vectors encoding the MHCII beta chains. The heterodimers and multimers of the present disclosure have a higher affinity for CD4 co-receptors than comparable reagents including wild type MHCII beta chains, and therefore are advantageous for use in methods of phenotyping or activating CD4+ T cells.