Importance of Interleukin-7 in the Development of Experimental Graft-Versus-Host Disease

Treatment with IL-7 increased GVHD-related mortality in B6.IL-7^-/- recipient animals after allogeneic LN BMT. The B6 or B6.IL-7^-/- recipients that had received 1300 cGy TBI received either 1 × 10⁶ TCD BM and 4 × 10⁶ LN cells from BALB/c donor mice, or similar cell numbers of LN and BM cells from congenic B6.SJL donors (CD45.1), and were then treated with recombinant human IL-7 (500 ng twice a day via subcutaneous injection) for 60 days. Survival over the 150 days after BMT is shown. Survival of all wild-type allogeneic B6 recipients was significantly lower than that of the congenic recipients (^∗P < .002). Survival of the PBS-treated B6.IL-7^-/- allogeneic recipients was significantly lower than that of congenic B6.IL-7^-/- recipients (^∗P < .03). The difference between the IL-7– and PBS-treated allogeneic B6.IL-7^-/- recipients is significant (^∗P < .002).

Treatment with IL-7 increased GVHD-related morbidity after allogeneic BMT. The severity of GVHD was determined by GVHD clinical grading system with scoring for 5 clinical criteria: percentage of weight loss, skin integrity, posture, mobility, and fur texture [31]. Clinical signs were graded on a scale of 0 to 2, (0, absent; 1, moderate; 2, severe), and the individual signs were summed. Shown are GVHD clinical index scores at 4 and 6 weeks for B6 recipients (A) and B6.IL-7^-/- recipients (B). Differences between the IL-7–treated and PBS-treated allogeneic recipients are P < .05 in both B6 recipients and B6.IL-7^-/- recipients (^∗).

Histological evidence of an increase in GVHD as a result of IL-7 administration. Skin and small intestine tissues from the recipients were analyzed at day 30 after BMT. Representative tissue samples from each group of mice were stained with hematoxylin and eosin. The tissue sections of skin and small intestine from the PBS-treated and IL-7–treated congenic BMT plus LN recipients and the PBS-treated allogeneic IL-7^-/- recipients demonstrated normal histology. The tissue sections from allogeneic wild-type B6 recipients treated with PBS or IL-7 and allogeneic B6.IL-7^-/- recipients treated with IL-7 showed evidence of GVHD, with lymphocytic infiltration and inflammation in the gut sections. Shown are hematoxylin and eosin staining of skin or gut sections from B6 (A) and B6.IL-7^-/- (B) recipients of either allogeneic or congenic LN and TCD BM.

Administration of IL-7 resulted in increased number of donor CD4 and CD8 T cells in blood, LNs, and spleen after allogeneic BMT. Donor-derived peripheral lymphocyte numbers in B6 and B6.IL-7^-/- recipients sacrificed 10 or 30 days after allogeneic transplantation with BALB/c LN and TCD BM cells were analyzed. Shown are numbers of donor CD4 and CD8 T cells in peripheral blood (A and B), LN (C and D), and spleen (E and F) of B6 and B6.IL-7^-/- recipients at days 10 and 30. ^∗Significant differences (P < .05) between the PBS- and IL-7–treated groups.

Administration of IL-7 resulted in increased number of donor CD4 and CD8 T cells in blood, LNs, and spleen after allogeneic BMT. Donor-derived peripheral lymphocyte numbers in B6 and B6.IL-7^-/- recipients sacrificed 10 or 30 days after allogeneic transplantation with BALB/c LN and TCD BM cells were analyzed. Shown are numbers of donor CD4 and CD8 T cells in peripheral blood (A and B), LN (C and D), and spleen (E and F) of B6 and B6.IL-7^-/- recipients at days 10 and 30. ^∗Significant differences (P < .05) between the PBS- and IL-7–treated groups.

Progressive disappearance of donor-derived allogeneic T lymphocytes in the absence of IL-7. After allogeneic transplantation with BALB/c LN and TCD BM cells, donor T cells from the peripheral blood of B6.IL-7^-/- recipient mice treated with IL-7 or PBS were gated and stained for CD4 and CD8 at days 10 and 30.

IL-7 is required for IL-7 administration to maintain activated donor T cells in the LN during allogeneic proliferation at day 10. 1 ×10⁶ TCD BM and 4 × 10⁶ CFSE-labeled LN cells from either congenic or allogeneic donors were transplanted into either lethally irradiated B6 or B6.IL-7^-/- recipients. At day 10, most of the proliferating CFSE-labeled congenic (CD45.1⁺) donor CD4 (A) and CD8 (B) T cells in lymph nodes of the B6 recipients did not express the CD69 activation marker, whereas the allogeneic (H2K^d) donor cells were predominantly CD69⁺. The frequency of donor-derived CD4 or CD8 T cells in the lymph nodes that expressed CD69 after allogeneic transplantation was not significantly changed by the IL-7 treatment of either B6 (C) or B6.IL-7^-/- (D) recipients. (E) IL-7 treatment of the B6.IL-7^-/- allogeneic recipients increased the absolute number of activated (CD69⁺) donor-derived CD4 and CD8 T lymphocytes (^∗P < .02 for PBS vs IL-7).