Our suspicion was confirmed by the results of another trial of palifermin, published during the course of this study, which demonstrated that up to 3 doses of 60 μg/kg palifermin increased neither CD4+ T cell counts nor thymic function (assessed by measuring naive CD4+ cells, RTEs, and thymic size on CT scan) in HIV-infected patients with persistent CD4+ T cell lymphopenia despite virologically effective antiretroviral treatment (26); suboptimal dosing was postulated as a cause for the negative result. This evidence concerns the gene CD4 and lymphopenia.