The means of how phagocytes handle apoptotic cells has a great impact on the outcome of immune responses. Here, we show that phagocytosis of allogeneic, apoptotic neutrophils by human monocyte-derived DCs is slow and less efficient than that of macrophages, and CD1a^– DCs are more active in the engulfment of apoptotic neutrophils than CD1a⁺ DCs. Blocking DC-SIGN function partially interferes with the uptake of apoptotic cells, and long-term interaction of apoptotic neutrophils with DCs makes them prone to proinflammatory cytokine responses. Engulfment of apoptotic cells sensitizes CD1a^– DCs for high IL-8, TNF-α, IL-6, and CD1a⁺ cells for IL-12 and IL-10 cytokine secretion elicited by additional inflammatory stimuli, which also result in the polarization of autologous T lymphocytes to Th1 effector cells. Ligand-induced activation of PPARγ by RSG results in enhanced phagocytosis, but the proinflammatory response and the capacity to trigger Th1 cell activation of CD1a^– DCs are not enhanced. These results demonstrate that DCs are able to respond to allogeneic, apoptotic neutrophils with inflammatory cytokines and T cell responses in a subtype-specific manner that is modulated by the anti-inflammatory effects of PPARγ.

Maraviroc is a chemokine receptor 5 (CCR5) inhibitor used in the treatment of HIV that also shows therapeutic potential for several autoimmune, cancer and inflammatory diseases that can afflict pregnant women. However, only limited information exists on the mechanisms underlying the transplacental transfer of the drug. We aimed to expand the current knowledge base on how maraviroc interacts with several placental ABC efflux transporters that have a recognized role in the protection of a developing fetus, i.e. ABCB1, ABCG2 and ABCC2. We found that maraviroc does not inhibit any of the three studied ABC transporters, and that its permeability is not affected by ABCG2 or ABCC2. However, our in vitro results revealed that maraviroc shows affinity for human ABCB1 and the endogenous canine Abcb1 expressed in MDCKII cells. Perfusion of rat term placenta showed accelerated transport of maraviroc in the feto-maternal direction, which suggests that ABCB1/Abcb1 facilitate in situ maraviroc transport. This transplacental transport was saturable and significantly diminished following the addition of the ABCB1/Abcb1 inhibitors elacridar, zosuquidar, and ritonavir. Our results indicate that neither ABCG2 nor ABCC2 influence maraviroc pharmacokinetic, but that ABCB1/Abcb1 may be partly responsible for the decreased transplacental permeability of maraviroc to the fetus. The strong affinity of maraviroc to Abcb1 found in our animal models necessitates studies in human tissue so that maraviroc pharmacokinetics in pregnant women can be fully understood. SIGNIFICANCE STATEMENT Antiretroviral drug maraviroc shows low toxicity potential and therefore it is a good candidate for prevention of mother-to-child transmission of HIV when failure of recommended therapy occurs. Although previous studies suggested interactions of maraviroc with ABCB1 transporter and its limited transfer across the placenta, this interaction has never been tested functionally in placental tissue. Using in vitro cell-based experiments and in situ method of dually perfused rat term placenta, here we examined maraviroc interactions with the three most important placental ABC drug transporters, ABCB1, ABCG2 and ABCC2. We demonstrate for the first time that placental ABCB1 significantly decreases mother-to-fetus transport of maraviroc. We conclude that ABCB1 may be responsible for the low cord blood/maternal blood ratio observed in humans.

Orally administered small molecules may have important therapeutic potential in treating COVID-19 disease. The recently developed antiviral agents, Molnupiravir and Nirmatrelvir, have been reported to be efficient treatments, with only moderate side effects, especially when applied in the early phases of this disease. However, drug–drug and drug–transporter interactions have already been noted by the drug development companies and in the application notes. In the present work, we have studied some of the key human transporters interacting with these agents. The nucleoside analog Molnupiravir (EIDD-2801) and its main metabolite (EIDD-1931) were found to inhibit CNT1,2 in addition to the ENT1,2 nucleoside transporters; however, it did not significantly influence the relevant OATP transporters or the ABCC4 nucleoside efflux transporter. The active component of Paxlovid (PF-07321332, Nirmatrelvir) inhibited the function of several OATPs and of ABCB1 but did not affect ABCG2. However, significant inhibition was observed only at high concentrations of Nirmatrelvir and probably did not occur in vivo. Paxlovid, as used in the clinic, is a combination of Nirmatrelvir (viral protease inhibitor) and Ritonavir (a “booster” inhibitor of Nirmatrelvir metabolism). Ritonavir is known to inhibit several drug transporters; therefore, we have examined these compounds together, in relevant concentrations and ratios. No additional inhibitory effect of Nirmatrelvir was observed compared to the strong transporter inhibition caused by Ritonavir. Our current in vitro results should help to estimate the potential drug–drug interactions of these newly developed agents during COVID-19 treatment.