Cells from a vanished twin as a source of microchimerism 40 years later in a male with a scleroderma-like condition.

Transmaternal cell flow leads to antigen-experienced cord blood

“…We hypothesize that male microchimeric cells of other sources than an older brother may be capable of inducing anti-HY responses, for instance, older brothers of the mother, known or unknown miscarriages of male fetuses, or microchimerism from an unknown vanished twin brother of the UCB sample. 29,30 Also paternal leukocytes or semen-derived peptides might enter the maternal and fetal circulation through uptake in the vaginal mucosa or via the decidua. [31][32][33] Note that one of the mothers of the UCB sample without older brothers had an elective abortion after 6 weeks of pregnancy (Table 1, UCB 18), while the other mothers within this group had a blank obstetric history or only gave birth to a girl.…”

Donor parity no longer a barrier for female-to-male hematopoietic stem cell transplantation

“…13 It is however questionable if simply labeling a donor as being parous or nulliparous correctly reflects a sufficient difference in alloimmunization status. There is increasing evidence that women may already be exposed to HY antigens in early childhood, for instance through transmaternal flow of cells derived from an older male sibling 23 or from a twin brother who vanished in utero 24 ; both can lead to persistence of low levels of tissue-resident or circulating male sibling cells carrying HY antigens. 1 How the putatively lifelong presence of male microchimeric cells, in combination with mucosal exposure to male proteins in sexually active women, affects the adult female immune system had never been addressed.…”

Naturally acquired microchimerism

“…86 Interestingly, male chimerism is not necessarily restricted to women with male offspring, given that trans-maternal flow of male cells derived from a former pregnancy or from a twin sibling who died in utero can be transferred during a next pregnancy. 47,55,87 Consequently, female cord blood units may comprise functional T cells directed against alloantigens, which are not expressed by the mother but which have been encountered through trans-maternal cell flow of chimeric cells. 55 Likewise, the alloimmune T cell repertoire of multiparous women may contain considerable precursor frequencies of cells directed against the various mismatched HLA alleles expressed by either the maternal grandmother or by her offspring, or against mismatched minor histocompatibility antigens presented by shared HLA antigens.…”