Association of Donor T Cell Repertoire in Host Lymphoid and Target Organs and Gvhd Development

The diversity and composition of T cell receptor (TCR) repertoire, which is the result of V, D and J gene recombination in TCR gene locus, has been found to impact immune responses in autoimmune and infectious diseases. The correlation of T-cell repertoire with the pathogenesis and outcome of graft-versus-host disease (GVHD) remain undefined. Here, by utilizing high-throughput sequencing of the gene encoding the TCRβ-chain, we comprehensively analyzed the profile of T-cell repertoire in host lymphoid and GVHD target organs after bone marrow transplantation (BMT).

To understand whether T-cell repertoire is affected by different strength of alloantigen stimulation, we transferred same donor T cells derived from C57BL/6 (B6) mice into irradiated BALB/c (MHC-fully mismatched), B6D2F1 (MHC-haploidentical), BALB.b (MHC-matched ) and B6 recipients (syngeneic). Fourteen days later, T cells were isolated from recipient peripheral blood, spleen, peripheral lymphoid nodes (pLN), mesenteric lymphoid nodes (mLN), liver, lung, gut and skin for TCR sequencing. Clonality of donor T cells, which is inversely associated with TCR diversity, was significantly increased in either syngeneic or allogeneic recipients when compared with naïve donor T-cells, consistent with the concept that TCR diversity is reduced after T-cell activation and expansion. Increased TCR clonality was observed in lymphoid organs of allogeneic compared with syngeneic recipients, confirming that donor T cells were further activated in allogeneic recipients. However, decreased TCR clonality was observed in GVHD target organs of allogeneic compared with syngeneic recipients, suggesting that only limited donor T-cell clones were able to migrate in target organs in syngeneic compared to allogeneic recipients. The frequency of top clones in total productive rearrangements was increased in GVHD target organs especially liver of allogenic than syngeneic receipts. Interestingly, the frequency of top clones was positively associated with MHC disparity between donor and host, ranging from low to high in syngeneic, MHC-matched, haploidentical, and fully-mismatched recipients, respectively.

To understand the extent to which TCR rearrangement is shared among different organs after BMT, we analyzed the overlap of TCR clones across different organs in the same recipients. T-cell clones were highly overlapping across organs, especially among GVHD target organs, in the same recipients after allogeneic BMT, although much lower overlapping in recipients after syngeneic BMT. The results suggest that alloantigen stimulation selectively activate certain T-cell clones and enrich antigen specific clones. On the other hand, much fewer shared clones were found among different recipients within the same group, regardless of MHC-disparity between donor and host. These results suggest that specific T-cell clones activated and expanded by alloantigens stimulation were highly different in individual recipients even with the same MHC-disparity between donor and host. Interestingly, the levels of clone overlapping were different in distinct organs among individual recipients. The level of T-cell clone overlapping was found high in liver of individual recipients regardless of the strength of alloantigen stimulation. The level of T cell clone overlapping was relatively high in pLNs and skin of the recipients after haploidentical BMT; whereas the level of T cell clone overlapping was relatively high in mLNs and gut of the recipients after MHC-matched BMT. These results suggest that skin may be a dominant target in haploidentical BMT and gut as a dominant target in MHC-matched BMT; whereas liver is a common target organ regardless.

In conclusion, the current study establishes the association between MHC disparity, T-cell activation, and GVHD development in the level of donor T-cell repertoire. While TCR repertoire of donor T cells in peripheral blood or lymph nodes likely is representative in any individual recipient/patient, it is nearly impossible to identify T-cell clones that are pathogenic and shared among groups of recipients/patients even with the same MHC-disparity between donor and host.