Chimeric acceleration by donor CD4+CD25+T-reg depleted fraction in splenocyte transplantation

Abstract

Background: We have established a splenocytic chimera model that can induce donor-specific tolerance and reconstitute the recipient immune system by donor splenocytes.

Aim: To accelerate such reconstitution, we investigated the role of donor-derived CD4(+)CD25(+) regulatory T-cells (T-reg).

Methods: We established C3H/B6D2F1 mixed bone marrow chimeras in lethally irradiated C3H mice. We transplanted skin grafts from C57BL/6 mice 30 d later. After an additional 30 d, we transplanted the following types of splenocytes from B6C3F1 mice: total splenocytes (group A), CD4(+)CD25(+) T-reg depleted splenocytes (group B), CD8(+)-depleted splenocytes (group C), and CD4(+)-depleted splenocytes (group D). We assessed class I major histocompatibility complex, percentage of chimeric cells in peripheral blood, and survival of skin grafts in each group.

Results: Group A and B mice switched to splenocytic chimeras, permitting the long-term survival of skin grafts. The proportions of H-2K(b+)H-2K(k-) cells in group B were significantly lower than those in group A on day 14 (0.47% ± 0.68% versus 9.49% ± 8.30%; P = .01) and day 21 (0.16% ± 0.25% versus 3.35% ± 2.78%; P = .01). The initial increase in the proportion of H-2K(b+)H-2K(k+) double-positive cells in group B was faster than that in group A (from 0.33% ± 0.10% versus. 0.39% ± 0.14% before splenocyte injection to 39.03% ± 30.50% versus 10.73% ± 11.54% on day 7; P = .02). The initial increase in the proportion of CD8(+) T-cells was faster in group B than in group A (from 2.72% ± 0.52% versus 2.49% ± 1.07% before splenocyte injection to 29.61% ± 26.72% versus 4.92% ± 1.56% on day 7; P = .04).

Conclusions: The depletion of CD4(+)CD25(+) T-reg fraction in donor splenocytes can accelerate switching to splenocytic chimera.