Granzyme B–Mediated Damage of CD8+ T Cells Impairs Graft-versus-Tumor Effect

Abstract

Allogeneic hematopoietic cell transplantation is an established treatment for hematologic and other malignancies. Donor-derived immune cells can identify and attack host tumor cells, producing a graft-versus-tumor (GVT) effect that is crucial to the treatment. Using multiple tumor models and diverse donor–host combinations, we have studied the role of granzyme B (GzmB) in GVT effect. We first confirmed previous findings that GzmB deficiency diminished the ability of a high dose of CD8+ T cells to cause lethal graft-versus-host disease. However, when GVT studies were performed using a moderate cell dose that the hosts could tolerate, GzmB−/− CD8+ T cells demonstrated a significantly enhanced GVT effect. GzmB-mediated, activation-induced cell death in wild-type CD8+ T cells was found responsible for their reduced GVT activity. Conversely, GzmB−/− CD8+ T cells exhibited enhanced expansion, skewed toward an effector or effector memory phenotype, and produced higher amounts of IFN-γ and Fas ligand that might contribute to GzmB-independent tumor control. These findings demonstrate for the first time, to our knowledge, that GzmB-mediated damage of CD8+ T cells impairs the desired GVT effect. This study suggests that inhibiting donor-derived GzmB function may represent a promising strategy to improve GVT effect without exacerbating graft-versus-host disease.

Cytokines in Graft-versus-Host Disease

“…First, cognate T cell-MHC interactions are required for effector, usually CD8, T cells that are able to evoke cytolytic machinery, including perforins and granzymes that induce target cell death via apoptosis (5,6,28). Interestingly, granzyme B-deficient donor T cells mediate less severe GVHD but may still generate GVL (29), via reduced activation-induced death of CD8 T cells (30). In a complementary pathway in which cognate T cell-MHC interactions are not required, myeloid cells, in addition to lymphoid cells, are primed during aGVHD to release cytopathic quantities of inflammatory cytokines (e.g., TNF, IL-6) that directly invoke apoptosis (31).…”

Granzyme B–Mediated Activation-Induced Death of CD4+ T Cells Inhibits Murine Acute Graft-versus-Host Disease

“…GzmB was shown to be critical for CD8 + T cells to cause severe GVHD (10–12), but was not required for CD4 + CD25 + Treg cell-mediated suppression of GVHD (20). In addition, GzmB did not seem to impact GVHD mediated by CD4 + CD25 − T cells (12).…”

“…GzmB was shown to be critical for CD8 + T cells to cause severe GVHD (10–12), but was not required for CD4 + CD25 + Treg cell-mediated suppression of GVHD (20). In addition, GzmB did not seem to impact GVHD mediated by CD4 + CD25 − T cells (12). However, the previous studies used lethal doses of (1–10×10 5 ) CD4 + T cells in MHC-mismatched HCT that caused rapid and uniform lethality to both groups of mice receiving WT and GzmB −/− T cells within 2 weeks.…”

“…As a key cytotoxic molecule, granzyme B (GzmB) deficiency was shown to alleviate CD8 + T cell-mediated GVHD but did not alter CD4 + T cell-mediated GVHD (10, 11). However, while our recent study confirmed that GzmB is an essential molecule used by CD8 + T cells to cause severe GVHD, it also raised a question about the contribution of GzmB in CD4 + T cell-mediated GVHD (12). The major issue may lie in the significantly higher GVH activity of CD4 + T cells as opposed to CD8 + T cells in the MHC-mismatched models preciously used.…”

“…The major issue may lie in the significantly higher GVH activity of CD4 + T cells as opposed to CD8 + T cells in the MHC-mismatched models preciously used. For example, while 1.5×10 6 CD8 + T cells were required to cause lethal GVHD in 4 weeks after allo-HCT, 1×10 5 CD4 + T cells caused rapid and lethal GVHD within 2 weeks after allo-HCT (12). Therefore, we suspected that the hyperacute GVHD caused by lethal doses of CD4 + T cells may have concealed a role of GzmB in previous studies.…”