PRS-343, engaging 4-1BB-specific Anticalin proteins to a modified variant of trastuzumab with a mutation modified IgG4 isotype to avoid the risk of ADCC and non–tumor-target activation of 4-1BB-positive lymphocytes, facilitates HER2+ tumor-localized co-stimulation of T cells with reduced peripheral toxicity (84). The gene discussed is ERBB2; the disease is neoplasm.