PF4 and cancer: GARP can enrich and activate latent TGF-β in the tumor microenvironment to promote FOXP3+ regulatory T cell activity, leading to immune tolerance and enhanced cancer progression.[65] However, platelets and PMPs have also been found to suppress the activation of T-helper cell 17 via PF4, promoting cancer proliferation but also boosting IFN-γ production and killing effect on cancer cells.[66]