Pregnancy dedifferentiates memory CD8+ T cells into hypofunctional cells with exhaustion-enriched programs.

Alloreactive memory, unlike naive, CD8+ T cells resist transplantation tolerance protocols and are a critical barrier to long-term graft acceptance in the clinic. We here show that semiallogeneic pregnancy successfully reprogrammed memory fetus/graft-specific CD8+ T cells (TFGS) toward hypofunction. Female C57BL/6 mice harboring memory CD8+ T cells generated by the rejection of BALB/c skin grafts and then mated with BALB/c males achieved rates of pregnancy comparable with naive controls. Postpartum CD8+ TFGS from skin-sensitized dams upregulated expression of T cell exhaustion (TEX) markers (Tox, Eomes, PD-1, TIGIT, and Lag3). Transcriptional analysis corroborated an enrichment of canonical TEX genes in postpartum memory TFGS and revealed a downregulation of a subset of memory-associated transcripts. Strikingly, pregnancy induced extensive epigenetic modifications of exhaustion- and memory-associated genes in memory TFGS, whereas minimal epigenetic modifications were observed in naive TFGS. Finally, postpartum memory TFGS durably expressed the exhaustion-enriched phenotype, and their susceptibility to transplantation tolerance was significantly restored compared with memory TFGS. These findings advance the concept of pregnancy as an epigenetic modulator inducing hypofunction in memory CD8+ T cells that has relevance not only for pregnancy and transplantation tolerance, but also for tumor immunity and chronic infections.

BRWD1 establishes epigenetic states for germinal center initiation, maintenance, and function.

Germinal center (GC) B cells segregate into three subsets that compartmentalize the antagonistic molecular programs of selection, proliferation, and somatic hypermutation. In bone marrow, the epigenetic reader BRWD1 orchestrates and insulates the sequential stages of cell proliferation and Igk recombination. We hypothesized BRWD1 might play similar insulative roles in the periphery. In Brwd1 -/- follicular B cells, GC initiation and class switch recombination following immunization were inhibited. In contrast, in Brwd1 -/- GC B cells there was admixing of chromatin accessibility across GC subsets and transcriptional dysregulation including induction of inflammatory pathways. This global molecular GC dysregulation was associated with specific defects in proliferation, affinity maturation, and tolerance. These data suggest that GC subset identity is required for some but not all GC-attributed functions. Furthermore, these data demonstrate a central role for BRWD1 in orchestrating epigenetic transitions at multiple steps along B cell developmental and activation pathways.