CCL4 and chlamydia trachomatis infectious disease: The individuals included in our study are healthy young men (6) and it is unlikely that would have experienced inflammatory conditions leading to upregulation of CCL4 and other chemokines following PrEP administration; in this context, STI screens carried out at enrolment only identified 6 cases of chlamydia and the outcome of our analyses did not change if these subjects were excluded (results not shown).