CCR7 as a potential therapeutic target for GvHD – results from preclinical models

Acute graft-versus-host disease (aGvHD) is a major complication following hematopoietic stem cell transplant (HSCT) that contributes to high non-relapse mortality. The disease process is initiated by the migration of donor T cells to the host secondary lymphoid organs and their activation by allo-antigens on host antigen-presenting cells (APC).¹ CCR7, a chemokine receptor, and its ligands CCL19 and CCL21 expressed by donor T cells is critically important for lymph node specific homing and activation of T cells by APCs.²

Previous reports demonstrated that a high proportion of CCR7⁺ donor T-cell subsets in the graft was an independent risk factors for aGvHD and correlated with poorer outcome.³

A study published by Carlos Cuesta-Mateos and colleagues explored whether apheresis with a low proportion of CCR7⁺ cells or blocking the function of CCR7 with an anti-human CCR7 monoclonal antibody (mAb) could prevent or treat aGvHD in preclinical models.⁴

Methods

• Apheresis samples were stained with a panel of antibodies including anti-CD45RA, anti-CD62L, anti-CD3, anti-CD4 to identify the following T cell subsets:
  • T cells considered as primary mediators of aGVHD
    • CCR7⁺ naïve T cells (T_N)
    • central memory T cells (T_CM)
  • T cells associated with responses against infections and graft-versus-leukemia (GvL) effect
    • CCR7^- effector memory T cells (T_EM)
    • CCR7^- CD45RA⁺ T_EM cells (T_EMRA)
• Migration and complement-dependent cytotoxicity (CDC) assays were performed on peripheral blood mononuclear cells (PBMC) from apheresis samples
• Xenogeneic models of aGvHD were induced by engrafting human (h) PBMC in sub-lethally irradiated NSG mice

Main findings

In total, 103 donor–recipient pairs who underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) were analyzed. Transplant characteristics are presented in Table 1.

Table 1. Selected transplant characteristics

Correlating rate of transfused CCR7⁺ cells with induction of GvHD in humans and mice

In patients, apheresis with < 3.6% of CD4⁺ CCR7⁺ cells showed low risk of developing aGvHD, with 87.88% (75.23–100%) of patients not developing the complication. The cut off for CD8⁺ CCR7⁺ was < 2.2% cells in the apheresis, with 88.57% (76.60–100%) of patients free from chronic (c)GvHD.

In contrast, xenograft models of GvHD demonstrated that lowering the proportion of CCR7⁺ cells used for apheresis failed to prevent or delay GvHD. The median overall survival (OS) was 14 days for animals engrafted with apheresis products containing ≤3% of CD4⁺ CCR7⁺ (n = 6) vs 13 days for mice with apheresis around 20% of CCR7⁺ cells.

Using anti-CCR7 mAb impairs CCR7⁺ T_N and T_CM cells chemotaxis and induces CDC

The addition of anti-CCR7 mAb to PBMC reduced the migration of CCR7⁺ T_N and T_CM cells stimulated with CCL19 or CCL21. CCR7 ligands and anti-CCR7 mAb did not induce responses in T_EM and T_EMRA cells which were CCR7^-. Moreover, in vitro assays using anti-CCR7 mAb with fresh hPBMC from apheresis demonstrated strong depletion of CCR7⁺ but not CCR7^- human T_N and T_CM cells via CDC.

CCR7⁺ T-cells are not involved in CMV reactivation and GvL effect

In patients, the levels of donor CCR7⁺ T cells in the apheresis did not correlate with cytomegalovirus (CMV) reactivation within the first six months after transplantation or with a relapse of the underlying disease.

Anti-hCCR7 mAb prevents aGvHD in xenograft models

In xenogenic models of aGvHD induced by engrafting of hPBMC, early administration of anti-CCR7 mAb, after hPBMC inoculation, prevented the development of aGvHD. Animals treated later than on Day 5 after engraftment had infiltration of human T cells in all tissues, which was, however, lower than in control mice.

• In animals that started treatment two hours before engraftment and had additional four doses given every three days, there was an increased median OS with the anti-hCCR7 mAb vs control (30 days vs 12 days; p = 0.0025)
• In animals that started treatment on Day 5 after engraftment and had additional four doses administered, anti-hCCR7 mAb was able to reverse first clinical signs of aGvHD and provide survival benefit compared to control treatment (median OS of 33 days vs 18 days; p = 0.0211)
• In animals that started treatment on Day 3, Day 7, or Day 10 after engraftment and had additional four doses given every three days, best responses were seen at Day 3 (median OS of 26 days with anti-hCCR7 mAb vs 12 days with control; p = 0.0026) compared to Day 7 (median OS 18 days vs 12 days, respectively; p = 0.0742) and Day 10 (median OS 17 days vs 12 days, respectively; p = 0.0181)

Conclusions

The authors of the article demonstrated that selective targeting of CCR7 with antibodies is a feasible and promising way to prevent donor T-cell migration to secondary lymphoid organs and to reduce the severity of aGVHD. Importantly, CCR7⁺ T cells seem not to be involved in the GvL effect or CMV reactivation. Other than in humans, xenograft models suggest that even small amounts of CCR7⁺ T cells can induce GvHD. The most profound anti-aGvHD effect was observed in transplanted mice, when an anti-hCCR7 mAb was administrated within the first five days after transplantation. This novel prophylactic approach could offer a benefit to patients in haploidentical settings, who have a particularly large unmet need for safe and effective therapies preventing GvHD.