Mapping Colorectal Distribution of Cell-free and Cell-associated HIV Surrogates Following Simulated Anal Intercourse to Aid Rectal Microbicide Development.

BACKGROUND: Anal sex remains the greatest HIV transmission risk for men who have sex with men and carries substantial population attributable risk among women. Despite a growing array of HIV pre-exposure prophylaxis (PrEP) options, rectal microbicides remain desirable as on demand, non-systemic PrEP. Rectal microbicide product development for PrEP requires understanding the spatiotemporal distribution of HIV infectious elements in the rectosigmoid to optimize formulation development.

SETTING: Outpatient setting with healthy research participants.

METHODS: Six healthy men underwent simulated receptive anal sex with an artificial phallus fitted with a triple lumen catheter in the urethral position. To simulate ejaculation of HIV-infected semen, autologous seminal plasma laden with autologous blood lymphocytes from apheresis labeled with 111Indium-oxine (cell-associated) and 99mTechnetium-sulfur colloid (cell-free) as HIV surrogates were injected into the rectal lumen through the phallic urethra. Spatiotemporal distribution of each radioisotope was assessed using SPECT/CT over eight hours. Analysis of radiolabel distribution used a flexible principal curve algorithm to quantitatively estimate rectal lumen distribution.

RESULTS: Cell-free and cell-associated HIV surrogates distributed to a maximal distance of 15 and 16 cm, respectively, from the anorectal junction (∼19 and ∼20 cm from the anal verge), with a maximal signal intensity located 6 and 7 cm, respectively. There were no significant differences in any distribution parameters between cell-free and cell-associated HIV surrogate.

CONCLUSIONS: Cell-free and cell-associated HIV surrogate distribution in the rectosigmoid can be quantified with spatiotemporal pharmacokinetic methods. These results describe the ideal luminal target distribution to guide rectal microbicide development.