CCR5 and coinfection: Further analysis of study methodologies and participants’ baseline characteristics revealed several potential sources of heterogeneity, including a higher co-infection rate of cytomegalovirus [35], the use of older-generation immunosuppressants [37, 53], differences in antiretroviral therapies (e.g., CCR5 antagonists) [27], the use of national transplant registry data as a comparison cohort [30], and an imbalanced distribution of recipient ethnicity [28, 30, 35, 37, 53, 57].