CCL19-IgG Prevents Allograft Rejection by Impairment of Immune Cell Trafficking

Abstract

R apid initiation of a primary antigen-specific T cell immune response depends on the coordinated and efficient interaction between antigen-presenting dendritic cells (DC) and naive T cells. The chemokine receptor CCR7 and its homeostatic ligands CCL19 and CCL21 are pivotal for recirculation of both cell types into secondary lymphoid organs (SLO) (1). In particular, homing of CCR7-positive antigen-loaded mature DC into secondary lymphoid tissues occurs along a chemoattractant gradient of CCL19 or CCL21. DC that migrate within secondary lymphoid tissues spontaneously express CCL19 itself (2). Both chemokines also attract CCR7-positive naive and central memory T cells that support their colocalization with DC. Co-localized T cells encounter DC that are searching for a stimulating antigen within this specific microenvironment, the first step to initiate an immune response. In CCR7 genedeficient mice (CCR7 Ϫ/Ϫ ) or in the ligand-deficient mice (plt Ϫ/Ϫ ), the ability to initiate and generate a T H 1/T H 2 immune response, memory, or tolerance is severely limited (3-6). Targeting CCL19 or CCL21 might modulate immune responses in a clinically useful manner (7-9). To extend the in vivo half-life of the chemokine, we fused CCL19 to the Fc part of IgG1 and tested whether this CCL19-IgG is applicable as a therapeutic tool to interfere with CCR7-mediated recirculation. We detected an immunosuppressive effect mediated by CCL19-IgG in different murine models, including delayed-type hypersensitivity (DTH) and two different models of allograft transplantation.In this study we show, that in contrast to only limited prolongation of graft survival in transplantation models that were performed in CCR7-deficient mice (10,11), application of CCL19-IgG was able to provide a marked prolongation of both kidney and heart graft survival. The mechanisms involved include disturbed homing of T cells and DC into SLO as well as disturbed co-localization and consequently an impaired response of T cell priming, so the alterations of immune cell trafficking that are induced by CCL19-IgG are similar to the effects described for CCR7 deficiency. However, the discrepancy between our approach and knockout models show that, when interfering with CCR7 in an intact environment, there might be additive effects to those induced by the genetic knockout. To our knowledge, this is the first study to demonstrate a clinically applicable tool to target CCR7-mediated cell trafficking for immunosuppression after solid-organ transplantation.

CCR7 Signaling Inhibits T Cell Proliferation

“…We have previously shown that the CCL19-IgG fusion protein is able to suppress an alloimmune response in vivo (15). This effect can be partially explained by an impairment of T cell and APC accumulation in secondary lymphoid organs, reducing T cell Ag priming.…”

“…The CCL19-IgG fusion protein was generated as described previously (15). The CCL21-IgG construct was generated by exchanging the CCL19 domain with the CCL21 domain, which was obtained by PCR amplification of murine lymph node cDNA.…”

“…In our previous work (15), systemic application of pharmacological doses of CCL19-IgG in mice was used to disturb this particular chemokine/chemokine-receptor system. We were able to show that recirculation and colocalization of T cells and DCs in secondary lymphoid organs were impaired, which prompted us to test CCL19-IgG in different models of solid organ transplantation.…”

Complement 5a Receptor Inhibition Improves Renal Allograft Survival

“…54 Briefly, mice were anesthetized with isoflurane, the left donor kidney was attached to a cuff of the aorta and the renal vein with a small caval cuff, and the ureters were removed en block. After left nephrectomy of the recipient, the vascular cuffs were anastomosed to the recipient abdominal aorta and vena cava, respectively, below the level of the native renal vessels.…”

Dendritic Cells in the Kidney

“…9 -12,19 Resident rDC probe their immediate environment (which may include the lumen of the nephron) 19 and capture self and nonself molecules, whether derived from within or outside the kidney, via phagocytosis, pinocytosis, and receptormediated endocytosis. 12,19 In response to the same "danger" signals that invoke innate immune responses, rDC also upregulate the expression of co-stimulatory molecules and CCR7 (the CCR for ligands, CCL19, and CCL21, expressed by stromal cells in T lymphocyte-rich areas of lymph nodes 86,87 ) and migrate to secondary lymphoid tissues bearing any molecules captured within the kidney (or generated within rDC) for processing and presentation to adaptive immune cells. 9,10,12,53 These mature rDC potently stimulate T lymphocyte proliferation 9 -12 and, depending on the nature of maturing stimuli, 61,62,88 presumably secrete cytokines that promote the differentiation of naive T lymphocytes toward specific T helper (Th) effectors such as Th1, Th2, or Th17 lymphocytes 89 (this has yet to be formally reported).…”