Preservation of memory CD4(+) T lymphocytes in breast milk of lactating rhesus monkeys during acute simian immunodeficiency virus infection

Refinement of a protocol for the induction of lactation in nonpregnant nonhuman primates by using exogenous hormone treatment

Obtaining sufficient quantities of milk from NHP is necessary for pharmacologic and immunologic studies required for the development and safety assessment of drugs and vaccines to be used in the maternal-infant setting. We previously induced lactation in nonpregnant female rhesus macaques (RM, Macaca mulatta) and African green monkeys (AGM, Chlorocebus sabaeus) for studies of immune responses in milk, but the volume collected was variable. To improve lactation induction protocols for nonbreeding nonhuman primates, we investigated serum hormone levels and collection protocols in AGM and RM. Here, we correlated milk volume with serum levels of endogenous and administered hormones: estradiol, prolactin, progesterone, and medroxyprogesterone in RM and AGM. We also investigated whether age, parity or the timing of milk collections were associated with the volume of milk collected from the AGM and RM in which lactation was induced by using exogenous hormones. We found an inverse correlation with serum estradiol and milk volume in the RM but no significant correlation between milk volumes and the remaining serum hormone levels in the induced RM or AGM. In addition, HIL AGM had higher peak estradiol levels than did naturally lactating AGM. A revised estradiol-sparing protocol increased milk volumes in the AGM. In addition, milk volume in RM was greater in the morning than the afternoon. In conclusion, we have refined a lactation induction protocol in nonpregnant primates, which is a needed alternative to using nursing primates for the assessment of drug levels and immune responses in milk.

Mucosal immunization of lactating female rhesus monkeys with a transmitted/founder HIV-1 envelope induces strong Env-specific IgA antibody responses in breast milk

We previously demonstrated that vaccination of lactating rhesus monkeys with a DNA prime/vector boost strategy induces strong T-cell responses but limited envelope (Env)-specific humoral responses in breast milk. To improve vaccine-elicited antibody responses in milk, hormone-induced lactating rhesus monkeys were vaccinated with a transmitted/founder (T/F) HIV Env immunogen in a prime-boost strategy modeled after the moderately protective RV144 HIV vaccine. Lactating rhesus monkeys were intramuscularly primed with either recombinant DNA (n = 4) or modified vaccinia virus Ankara (MVA) poxvirus vector (n = 4) expressing the T/F HIV Env C.1086 and then boosted twice intramuscularly with C.1086 gp120 and the adjuvant MF59. The vaccines induced Env-binding IgG and IgA as well as neutralizing and antibody-dependent cellular cytotoxicity (ADCC) responses in plasma and milk of most vaccinated animals. Importantly, plasma neutralization titers against clade C HIV variants MW965 (P = 0.03) and CAP45 (P = 0.04) were significantly higher in MVA-primed than in DNA-primed animals. The superior systemic prime-boost regimen was then compared to a mucosal-boost regimen, in which animals were boosted twice intranasally with C.1086 gp120 and the TLR 7/8 agonist R848 following the same systemic prime. While the systemic and mucosal vaccine regimens elicited comparable levels of Env-binding IgG antibodies, mucosal immunization induced significantly stronger Env-binding IgA responses in milk (P = 0.03). However, the mucosal regimen was not as potent at inducing functional IgG responses. This study shows that systemic MVA prime followed by either intranasal or systemic protein boosts can elicit strong humoral responses in breast milk and may be a useful strategy to interrupt postnatal HIV-1 transmission.

High cell-free virus load and robust autologous humoral immune responses in breast milk of simian immunodeficiency virus-infected african green monkeys

The design of immunologic interventions to prevent postnatal transmission of human immunodeficiency virus (HIV) will require identification of protective immune responses in this setting. Simian immunodeficiency virus (SIV)-infected rhesus monkeys (RMs), a species that develops an AIDS-like illness following experimental infection, transmit the virus at a high rate during breastfeeding. In contrast, postnatal transmission of SIV occurs rarely or not at all in natural, asymptomatic primate hosts of SIV. These contrasting transmission patterns provide a unique opportunity to study mechanisms that evolved to protect suckling infants from SIV infection. We compared the virologic and immunologic properties of milk of SIV-infected and uninfected natural hosts of SIV, African green monkeys (AGMs), to that of RMs. Interestingly, despite a low number of milk CD4(+) T lymphocytes in uninfected AGMs, milk virus RNA load in SIV-infected AGMs was comparable to that of SIV-infected RMs and that in AGM plasma. This observation is in contrast to the relatively low virus load in milk compared to that in plasma of SIV-infected RMs and HIV-infected women. Milk of SIV-infected AGMs also displayed robust virus-specific cellular immune responses. Importantly, an autologous challenge virus-specific neutralization response was detected in milk of five of six SIV-infected AGMs that was comparable in magnitude to that in plasma. In contrast, autologous challenge virus neutralization was not detectable in milk of SIV-infected RMs. The autologous virus-specific adaptive immune responses in breast milk of AGMs may contribute to impedance of virus transmission in the infant oral/gastrointestinal tract and the rarity of postnatal virus transmission in natural hosts of SIV.