We thus next sought to investigate the potential impact of the SP response driven by polyclonal naïve CD4+ T cell compartment on the typical slow rate of lymphopenia-induced homeostatic proliferation (LIP)—a response that is antigen-independent but IL-7-dependent—of naïve CD8+ T cells co-transferred into SPF RAG−/− hosts. The gene discussed is CD4; the disease is lymphopenia.