Research involving human specimens from unilateral upper extremity breast cancer-related lymphedema demonstrated that the number of CD4+ T cells was associated with the severity of lymphedema, and even a small number of these cells were sufficient to induce lymphedema (Zampell et al., 2012b; Avraham et al., 2013; Ly et al., 2019). The gene discussed is CD4; the disease is lymphedema.