In a model of herpes simplex virus-2 (HSV-2) infection, where thymidine-kinase defective (TK−) HSV-2 was used to avoid neurovirulence (29), CD4 T cells infiltrated the female genital mucosa during infection and provided help for mobilizing cytotoxic effector CD8 T cells that cleared the infection (30). The gene discussed is CD4; the disease is infection.