Repertoire selection of AQP4-specific T cells that cause CNS autoimmune disease in mice

When modeling neuromyelitis optica (NMO), it has been observed that only AQP4-reactive Th17 cells from AQP4-deficient (AQP4-/-), but not wild-type (WT) mice, cause CNS autoimmunity in recipient WT mice, indicating that a tightly regulated mechanism normally ensures tolerance to AQP4. If loss of thymic negative selection in AQP4-/- mice permits expansion of pathogenic AQP4-specific T cells, one might predict that TCRs selected by AQP4-reactive T cells in AQP4-/- and WT mice would differ. AQP4-/- and WT mice were primed with the pathogenic epitope AQP4 p133-149, and T cells from draining lymph nodes were tested for binding to MHC II (I-Ab):AQP4 133-149 tetramers. Analysis of primary lymph node CD4+ T cells from AQP4 peptide-immunized WT and AQP4-deficient mice identified a ten-fold higher frequency of proliferative tetramer-positive (tet+) T cells in AQP4-deficient mice. To analyze whether this difference in Tetramer binding indicated a difference in T cell repertoire, rearranged TCR alpha/beta genes within individual AQP4-reactive T cells from AQP4 p133-149-primed AQP4-deficient and WT mice by scTCR-Seq using the 10X Genomics platform. Only a small fraction (0.3%) of AQP4-specific TCR alpha/beta clonotypes examined were shared between WT and AQP4-/- mice. AQP4-specific tet+ T cells from AQP4-/- mice had minimal overlap between WT and AQP4-deficient T cells. The tet+ T cells from AQP4-/- mice contained many expanded TCR clonotypes that were shared amongst multiple AQP4-/- mice (public). In contrast, the AQP4-reactive tet- T cells contained very few public TCR sequences, where overlap was primarily with WT T cells. Although this sampling represents a small proportion of the entire TCR repertoire, our results indicate that thymic negative selection is one mechanism that restricts development of pathogenic AQP4-reactive T cells in WT mice.