Apart from the insight this offers for future TB vaccination strategies, we feel that these data support the use of PPD, which as a rich antigen mixture, generates higher frequency responses than RD-1 encoded antigens and therefore is likely to be beneficial in the investigation of a condition associated with immune suppression and CD4 lymphopenia in HIV-infected and HIV-uninfected individuals [26], [27], [14]. The gene discussed is PDE6B; the disease is lymphopenia.