CD4 and lymphopenia: Recently, three studies have demonstrated that CD4+ T-cell lymphopenia or a lower total lymphocyte count are also risk factors for PCP in transplant recipients [27,29,86], although with some differences in threshold levels (750/μL and 500/μL in Iriart et al.’s and De Castro et al.’s studies, respectively [27,86]) and the decay kinetics of lymphocytes.