Granzyme B is known to be a serine protease contained in granules of cytotoxic T 
cells. We have previously reported an influence of granzyme B expression in T 
regulatory cells (Tregs) on the risk of acute graft versus host disease (GVHD) 
onset. However, it is still unknown if conventional T cells (Tcon) use the 
granzyme B pathway as a mechanism of alloimmunity. We hypothesized that granzyme 
B in Tcon may affect recurrence within the first 6 months after allogeneic 
transplantation (allo-HSCT). A total of 65 patients with different hematological 
malignancies were included in this study. Blood samples were collected on day 
+30 after allo-HSCT. The percentage of granzyme B positive conventional T cells 
in patients who developed relapse in the first 6 months after allo-HSCT was 11.3 
(4.5-35.3) compared to the others in continuous complete remission-1.3 
(3.65-9.7), р = 0.011. The risk of relapse after allo-HSCT was in 3.9 times 
higher in patients with an increased percentage of granzyme B positive 
conventional T cells. The findings demonstrated that the percentage of granzyme 
B positive conventional T cells on day +30 after allo-HSCT could be a 
predictable marker of relapse within the first 6 months after allo-HSCT.