Pregnancy is a state where high and stage-dependent plasticity of the maternal immune system is necessary in order to equilibrate between immunosuppression of harmful responses towards the fetus and ability to fight infections. TCR γδ cells have been implicated in the responses in infectious diseases, in the regulation of immune responses, and in tissue homeostasis and repair. The variety of functions makes γδ T cells a particularly interesting population during pregnancy. In this study, we investigated the proportion, phenotype and TCR γ and δ repertoires of γδ T cells at the maternal–fetal interface and in the blood of pregnant women using FACS, immunohistochemistry and spectratyping. We found an enrichment of activated and terminally differentiated pro-inflammatory γδ T-cell effectors with specific location in the human decidua during early pregnancy, while no significant changes in their counterparts in the blood of pregnant women were observed. Our spectratyping data revealed polyclonal CDR3 repertoires of the δ1, δ2 and δ3 chains and γ2, γ3, γ4 and γ5 chains and oligoclonal and highly restricted CDR3γ9 repertoire of γδ T cells in the decidua and blood of pregnant women. Early pregnancy induces recruitment of differentiated pro-inflammatory γδ T-cell effectors with diverse TCR repertoires at the maternal–fetal interface.

The ability of bacteria to exist as a population of self-replicating forms with defective or entirely missing cell wall (L-forms) is an adaptive mechanism for their survival and reproduction under unfavorable conditions. Bacterial mother-to-fetus transfer is a universal phenomenon in the animal kingdom. However, data about vertical transfer of L bacterial forms are extremely scarce. Bacille Calmette-Guérin is an attenuated strain of M. bovis and the only licensed vaccine used for tuberculosis prevention. We already have shown that filterable L-forms of BCG exist freely in the vaccine and are able to reproduce and to form colonies. The present study was focused on the placental microbiome in the context of mother’s BCG vaccination. Here we report an isolation of filterable mycobacterial L-form cultures from gestational tissues and blood of healthy newborns delivered by healthy BCG-vaccinated mothers after normal pregnancy. Of note, vertically transmitted mycobacterial L-forms as a part of placentobiome of the pregnant women didn’t influence the number of resident pathogen-reactive Vδ2 cells. Placenta colonization with mycobacterial L-forms occurs by maternal blood-to-decidua transfer very early in gestation. Together, these data showed that BCG L-forms have the capacity to pass trans-placental barrier and that maternal BCG vaccination affects the placentobiome.

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