The Role of Proteinase Inhibitor 9 (PI-9) and Granzyme B in Peripheral Leukocytes for GVL and GVHD After Allogeneic Hematopoietic Stem Cell Transplantation

Abstract 1984

The serpin proteinase inhibitor 9 (PI-9) protects cells from serine protease granzyme B (GrB)- and perforin (PFR)-induced cytotoxicity and apoptosis by specifically inhibiting GrB. Graft-versus-leukemia (GVL) effect and graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (HSCT) are the reciprocal aspects of the established immunotherapeutic approach in hematopoietic malignancies, and are thought to be caused at least in part through GrB and PFR produced by donor-derived cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. However, GrB and PFR expressions with respect to a GVL effect, and the role of PI-9 in both GVHD and GVL, are unknown. In this study we analyzed the expression of GrB, PFR and PI-9 in acute leukemia patients to whom allogeneic HSCT was performed during remission. This study was performed under the approval of the ethical committee of Kobe University Graduate Schools of Medicine and Health Sciences, and all human samples were obtained from whom a written informed consent was obtained. We first investigated the age- and gender-related differences of expressions of PI-9 and GrB mRNA by quantitative RT-PCR in mononuclear and polymorphonuclear cells from healthy volunteers. GrB and PFR mRNAs were expressed almost exclusively in mononuclear cells that included CTLs and NK cells, while PI-9 was expressed both in mononuclear and polymorphonuclear cells. GrB and PFR expression levels were comparable among all age and gender groups. Intriguingly, however, the expression of PI-9 mRNA in lymphocytes gradually increased with age, and the PI-9 expression in the volunteer group aged 60 years old or older was significantly higher than the one in the group aged 20 to 39 years old (p=0.002). Meanwhile, the PI-9 expression in polymorphonuclear cells was comparable among all age groups, and there was no gender difference in PI-9 expression levels. Next, we analyzed the expressions of PI-9, GrB and PFR mRNAs in mononuclear and polymorphonuclear cells of 3 patients (male 2, female 1) with acute GVHD and 11 patients without acute GVHD (male 6, female 5). The GrB, PFR and PI-9 expression levels were comparable between patient groups with and without acute GVHD, both before transplantation and a week after engraftment. However, the GrB and PFR expressions prominently augmented when acute GVHD became overt in all 3 patients, while PI-9 expression level increased mildly. As a result, the ratio of GrB (or PFR) and PI-9 expressions was stable in patients with and without acute GVHD. Among them, 4 cohort patients eventually relapsed and 10 cohorts remained in remission. The GrB mRNA expression in lymphocytes one week after engraftment was 3-fold higher in 10 patients without relapse of primary disease than in 4 patients who eventually relapsed (P=0.044). This might suggest that GrB plays a role in eliciting a GVL effect as well as acute GVHD. On the other hand, PFR and PI-9 mRNA expressions were then relatively stable among patients both with and without later relapse (P=0.667; P=0.103), and the ratio of GrB (or PRF) and PI-9 expressions did not change. The expressions of GrB and PFR mRNAs in polymorphonuclear cells of all patients were under the detectable level throughout the course. Finally, we analyzed the expressions of GrB, PFR and PI-9 in leukocytes 6 months after HSCT, to see if these expressions might change in patients with chronic GVHD. Among 14 patients with chronic GVHD, the GrB expression increased (up to 6.2-fold) in 10 patients, but the PFR expression did not change. In contrast, the expression of PI-9 decreased profoundly in all of the cases both with and without chronic GVHD, relative to healthy volunteers (P=0.028). Importantly, the ratio of GrB and PI-9 expressions was significantly higher in patients with chronic GVHD than in those without GVHD (P = 0.035). In conclusion, (1) high PI-9 expression in elderly people might explain a mechanism of escape from tumor immunity in them, where PI-9 might inhibit functions of cytotoxic T cells and NK cells; (2) a high expression of GrB shortly after engraftment may be a novel biomarker for a GVL effect; and (3) a low level of PI-9 expression or an increased ratio of GrB/PI-9 later after allogeneic HSCT might be an important biomarker for cGVHD. Monitoring of both GrB and PI-9 mRNAs in peripheral blood after allogeneic HSCT could be useful for predicting the GVL effect, as well as for monitoring both acute and chronic GVHD.