The use of PTCy for GvHD prophylaxis in adults post-HSCT: Data from a phase II trial

Currently, there is no optimal graft-versus-host disease (GvHD) prophylaxis that is used in combination with reduced-intensity conditioning (RIC) regimen for patients who receive allogeneic hematopoietic stem cell transplantation (HSCT) from fully matched donors.¹ Antithymocyte globulin (ATG) and posttransplant cyclophosphamide (PTCy) are widely used in patients who receive allogeneic HSCT from matched unrelated donors for the prevention of GvHD. However, the effectiveness of using PTCy for GvHD prophylaxis, in patients who receive peripheral blood stem cell (PBSC) transplantation from fully matched donors remains unclear.¹

Here, we summarize an article by Brissot et al.¹ published in Blood Cancer Journal evaluating PTCy vs ATG after RIC allogeneic PBSC transplantation in recipients of fully matched donors (NCT02876679).

Study design¹

• This was a randomized, open-label, phase II trial comparing PTCy and ATC in adult patients who received a RIC regimen (fludarabine and 2 days of busulfan) before HSCT from matched sibling donors or 10/10 human leukocyte antigen matched unrelated donors.
• Patients were randomized 1:1 to receive ATG 5 mg/kg plus standard GvHD prophylaxis or PTCy 50 mg/kg/d at Days +3 and +4 plus standard GvHD prophylaxis (Table 1).

Table 1. Treatment regimens*

	Drug (administrated)	Dosage	Day/s from HSCT
Control group	ATG (IV)	2.5 mg/kg/day	-2, -1
CsA† (IV)	3 mg/kg/day continuously	Starting at -3
MMF‡ (oral)	2 g/day continuously	Starting at -3
Experimental group	PTCy	50 mg/kg/day	+3, +4
CsA† (IV)	3 mg/kg/day continuously	Starting at +5
MMF‡ (oral)	2 g/day continuously	Starting at +5
ATG, antithymocyte globulin; CsA, cyclosporine A; HSCT, hematopoietic stem cell transplantation; IV, intravenous; MMF, mycophenolate mofetil. *Data from Brissot et al.1 †Dose adjusted to maintain a trough level of 200–400 ng/mL. CsA was tapered over 4 weeks from Day +62, if clinically possible. ‡Tapered over 4 weeks starting from Day +35, if clinically possible.

• Outcomes included:
  • GvHD-free relapse-free survival at 12 months after HSCT (primary endpoint).
  • Acute GvHD (aGvHD), chronic GvHD (cGvHD), non-relapse mortality, relapse incidence, disease-free survival, overall survival, cGvHD-free relapse-free survival, and adverse events.
• Health-related quality of life was assessed using the European Organization for Research and Treatment of Cancer Quality of Life Core Questionnaire and the Functional Assessment of Cancer Therapy-Bone Marrow Transplant.

Key findings¹

• In total, 80 patients were randomized to receive PTCy (n = 44) or ATG (n = 45), and 44 and 37 patients in each arm underwent HSCT, respectively
  • Overall, the median age was 64 years and baseline demographics were well-balanced between the two study arms.
• The primary endpoint of difference in 1-year GvHD-free relapse-free survival between the two arms was not met (Figure 1).
• There were no significant differences observed between the PTCy group compared with the ATG group for DFS or OS (Figure 1).

 ATG, antithymocyte globulin; DFS, disease-free survival; GRFS, graft-versus-host disease-free, relapse-free survival; OS, overall survival; PTCy, posttransplant cyclophosphamide.
*Data from Brissot et al.¹

• The median time to neutrophil and platelet count recovery was longer in the PTCy group compared with the ATG group (Table 2).

Table 2. Neutrophil and platelet count recovery posttransplant, with PTCy and ATG*

	ATG group	PTCy group	p-value
Median time to reach an absolute neutrophil count of ≥0.5 × 109/L	19 days	21 days	p = 0.01
Median time to achieve platelet count of ≥20 × 109/L	11 days	20 days	< 0.0001
ATG, antithymocyte globulin; PTCy; posttransplant cyclophosphamide. *Data from Brissot, et al.1

• At 5 years, there was no difference observed in relapse incidence (p = 0.52), cumulative incidence of non-relapse mortality (p = 0.57), and cGvHD-free relapse-free survival (p = 0.37) between the PTCy and ATG groups.
• At 6 months, the cumulative incidence of Grade 2─4 aGvHD in the PTCy group was 36.4% compared with 24.3% in the ATG group (p = 0.35). In total, 6.8% of patients went on to develop Grade 3─4 aGvHD in the PTCy group compared with 5.4% of patients in the ATG group (p = 0.81).
• There was no difference in the cumulative incidence of cGVHD at 1 -year in the PTCy group (32.5%) and ATG group (36.1%), and there was no difference in the number of patients requiring systemic treatment between the two groups (p = 0.58).
• The cumulative incidence of cardiac events at 1 year did not differ between the two groups (p = 0.69).
• Within the first month of the study, 72.7% of patients in the PTCy group and 59.5% of patients in the ATG group experienced an infection (p = 0.21).
• Day +30 European Organization for Research and Treatment of Cancer Quality of Life Core Questionnaire scores were lower in the PTCy group vs the ATG group (p = 0.01) with a non-significant trend towards a lower Functional Assessment of Cancer Therapy-Bone Marrow Transplant score in the PTCy group (p = 0.051). The scores did not differ significantly at any other time points measured.

Key learnings

In this study, the effectiveness and safety of PTCy vs ATG for GvHD prophylaxis were comparable in patients receiving fludarabine and 2 days of busulfan conditioning with a PBSC graft from a fully matched donor. While ATG has been recognized as the standard-of-care for GvHD prophylaxis in human leukocyte antigen-matched donor HSCT, PTCy could be an appropriate option for prophylaxis in this setting.