Embodiments relate to peptide antagonists of ƴc-farnily cytokines, which is associated with important human diseases, such as leukemia, autoimmune diseases, collagen diseases, diabetes mellitus, skin diseases, degenerative neuronal diseases and graft-versus-host disease (GvHD). Thus, inhibitors of ƴc-cytokine activity are valuable therapeutic and cosmetic agents as well as research tools. Traditional approaches to inhibiting yc-cytokine activity involve raising neutralizing antibodies against each individual ƴc-cytokine family member/' receptor subunit. However, success has been limited and often multiple ƴc-cytokine family members co-operate to cause the disease state. Combinatorial use of neutralizing antibodies raised against each factor is impractical and poses an increased risk of adverse immune reactions. The present embodiments overcome these shortcomings by utilizing peptide antagonists based on the consensus ƴc-subunit binding site to inhibit ƴc-cytokine activity. Such approach allows for flexibility in antagonist design. In several embodiments, peptides exhibit Simul -Block activity, inhibiting the activity of multiple ƴc-cytokine family members.Des modes de réalisation concernent des antagonistes peptidiques de cytokines de la famille ƴc, qui est associée à des maladies humaines importantes, telles que la leucémie, les maladies auto-immunes, les maladies du collagène, le diabète sucré, les maladies de la peau, les maladies neuronales dégénératives et la réaction de greffe contre hôte (GvHD) Ainsi, les inhibiteurs de l'activité des cytokines γc sont des agents thérapeutiques et cosmétiques de valeur ainsi que des outils de recherche. Des approches traditionnelles de l'inhibition de l'activité des cytokines γc consistent à dresser des anticorps neutralisants contre chaque sous-unité membre de la famille de cytokines γc/récepteur. Toutefois, le succès a été limité et souvent de multiples membres de la famille de cytokines γc coopèrent pour provoquer l'état p
