CD4 and rheumatoid arthritis: Polymeric microneedle-mediated transdermal delivery of MEL inhibited the progression of RA in arthritis rat and mouse models, suppressed the levels of IL-17 and TNF-α, and raised the percentage of regulatory CD4 T cells, which suggested that polymeric microneedle-mediated MEL transdermal delivery could be used as a new treatment for RA and other autoimmune diseases (Du et al., 2021).