Down Regulation of CXC Chemokine Receptor 3 Impedes the Ability of Anti-CXCR3 Antibody To Block Graft-Versus-Host Disease.

Graft versus host disease (GVHD) is caused by infused donor T cells that primarily target specific organs, such as skin, liver and intestine. While it has been demonstrated that chemokines are critical to directing in vivo trafficking of host-reactive donor T cells into GVHD target organs, blocking GVHD using antagonist antibody (Ab) against chemokine receptors remains an elusive goal. We found that in vivo administration of anti-CXCR3 Ab for 1 week (named short-term treatment) only partially prevented acute GVHD in B6/SJL mice receiving donor C3H.SW naïve CD8⁺ T cells, with 45% of them dying from the disease. Flow cytometry analysis showed that CXCR3⁺ CD8⁺ T cells occurred in the spleens and livers of these GVHD B6/SJL mice by day 3 and peaked by day 7 after transplantation, and persisted throughout the disease course. When donor CXCR3⁺ CD8⁺ T cells were recovered from these GVHD B6/SJL recipients at day 14 after transplantation (named day-14 CXCR3⁺ CD8⁺ T cells) and adoptively transferred into secondary B6/SJL mice, they caused severe GVHD in these secondary recipients with 90% mortality. Interestingly, short-term treatment using anti-CXCR3 Ab protected 78% of B6/SJL mice receiving these donor day-14 CXCR3⁺ CD8⁺ T cells. Thus, besides CXCR3⁺ T cells, some other pathogenic T cells have developed during GVH reactions. We found that a substantial population of CXCR3⁻ CD8⁺ T cells occurred by day 14 (termed day-14 CXCR3⁻ CD8⁺ T cells) after transplantation in the spleens (71.1%) and livers (81.6%) of B6/SJL recipients with ongoing GVHD. As compared to donor day-14 CXCR3⁺ CD8⁺ T cells, donor day-14 CXCR3⁻ CD8⁺ T cells expressed lower levels of CCR2, CCR3, CCR5, CD127, granzyme B and FasL, and produced less IFN-g and TNF-a. Furthermore, adoptive transfer of donor day-14 CXCR3⁻ CD8⁺ T cells caused delayed onset of GVHD as compared to those recipients of day-14 CXCR3⁺ CD8⁺ T cells, with 55% of them dying from the diseases. Prolonged treatment of B6 mice receiving day-14 CXCR3⁻ CD8⁺ T cells with anti-CXCR3 Ab up to 3 weeks (named long-term treatment) significantly inhibited the development of GVHD. More than 70% of these recipients survived without clinical signs of GVHD. In vivo experiments showed that 23% of day-14 CXCR3⁻ CD8⁺ T cells were converted into CXCR3⁺ by 12 hours after adoptive transfer into B6/SJL recipients, and up to 60% by 24 hours. Interestingly, about 25% of CXCR3⁺ CD8⁺ T cells were also converted into CXCR3⁻ by 24 hours after their transfer. We found in ex vivo cultures that both dendritic cells and interleukin-2 accounted for this conversion between CXCR3⁺ and CXCR3⁻ subsets, which was inhibited by addition of Ab specific to MHC-I or CTLA-4 Ig. Taken together, these results suggest that alloantigen-induced repression of chemokine receptor(s) may present a major barrier to the success of GVHD prevention and treatment when using antagonists against chemokines or chemokine receptors.