Full dose MTX + Tac vs mini-MTX + Tac/MMF for GvHD prophylaxis

Combination therapy comprising tacrolimus (Tac), a calcineurin inhibitor, and methotrexate (MTX) is the current standard-of-care treatment for graft-versus-host disease (GvHD) prevention after allogeneic hematopoietic cell transplantation.¹ However, methotrexate has been associated with toxicities, which can require dose limitations and lead to reductions in efficacy.¹ Several other treatments investigated for GvHD prophylaxis have failed to improve outcomes in patients post-HSCT¹; however, a study by Mizumoto et al. suggested that a combination of Tac, mycophenolate mofetil (MMF), and reduced dose MTX (mini-MTX) can be used safely and effectively as GvHD prophylaxis.²

This trial is the first to compare the safety and efficacy of Tac/full-dose MTX (full-MTX) and Tac/mini-MTX/mycophenolate mofetil (MMF).¹

Study design¹

This phase III randomized single-center trial enrolled 101 patients, with 96 included in the final analysis. Of these, 47 patients received the mini-MTX regimen and 49 received the full-MTX regimen. The study design and key inclusion/exclusion criteria is shown in Figure 1.

The primary endpoints of this study were incidence of acute GvHD (aGvHD) by Day 100 (including incidence and severity of Grade 2–4 and Grade 3–4  aGVHD), incidence and severity of mucositis by Day 28, and incidence of neutrophil/platelet engraftment by Day 28. Key secondary endpoints included chronic GvHD, organ toxicity, infection, relapse, non-relapse mortality, and overall survival.

GvHD, graft-versus-host disease; HLA, human leukocyte antigen; MMF, mycophenolate mofetil; MTX, methotrexate.
*Data from Hamilton, et al.^1
†Day 1 dose was 15 mg/m² which was reduced to 10 mg/m² for following doses. Reductions or dose holds occurred per institutional guidelines for renal/liver toxicities and per physician for mucositis.
^‡Dose was 5 mg/m² for all doses. Reductions or dose holds occurred per institutional guidelines for renal/liver toxicities, and per physician for mucositis.

Results¹

Key patient characteristics are shown in Table 1. The majority of patients were white, apart from one black patient in the full-MTX group. Average follow-up time was 19.9 months.

Table 1. Baseline patient characteristics*

Bu, busulfan; Cy, cyclophosphamide; MMF, mycophenolate mofetil; MTX, methotrexate; Tac, tacrolimus; tac, tacrolimus; TBI, total body irradiation; VP, etoposide. *Adapted from Hamilton, et al.1 †Tac/full-dose MTX ‡Tac/mini-MTX/MMF
Characteristic, % (unless otherwise stated)	Full-MTX† (N = 49)	Mini-MTX‡ (N = 47)	p value
Sex			0.04
Male	42.9	63.8
Female	57.1	36.2
Median age at transplant (range), years	47 (5–59)	45 (2–62)	0.47
Donor			0.56
Matched                unrelated	77.6	72.3
Matched                sibling	22.4	27.7
Conditioning			0.54
Bu/Cy	81.6	83.0
TBI/VP	18.4	14.9
Cy/TBI	0	2.1
MTX doses			<0.001
2	2.0	0
3	26.5	100.0
4	71.4	0

Efficacy

There were no significant differences in GvHD outcomes between the groups. GvHD outcomes at Day 100 (incidence of Grade 2–4 aGvHD and Grade 3/4 aGvHD) and Month 12 (incidence of moderate/severe chronic GvHD) are shown in Figure 2.

aGvHD, acute graft-versus-host disease; cGvHD, chronic GvHD; MTX, methotrexate.
*Adapted from Hamilton, et al.¹ 

Although relapse rates differed between groups, these differences were not significant; the study was not powered to detect statistical differences in survival outcomes. The most common cause of death in both groups was relapse (full-MTX, 50%; mini MTX, 67%). Survival and relapse outcomes are shown in Figure 3.

GvHD, graft-versus-host disease; MTX, methotrexate.
*Adapted from Hamilton, et al.¹

Engraftment failure occurred in one patient who received full-MTX. Neutrophil and platelet engraftment was significantly faster in patients who received mini-MTX compared with full-MTX (15 days vs 17 days and 23 days vs 28 days, respectively); therefore, patients who received mini-MTX had a significantly shorter duration of hospitalization than those who received full-MTX (27 days vs 31 days).

Safety

Key safety results for full-MTX vs mini-MTX treated patients included:

• significantly higher World Health Organization (WHO) Grade 3–4 mucositis (82% vs 57%; p = 0.01);
• significantly higher median duration of mucositis (18 days vs 11 days; p < 0.001);
• no significant difference in use of patient-controlled analgesia; and
• no significant difference in the rate of infections.

Conclusion 

This study demonstrated that mini-MTX can result in significantly less mucositis and significantly faster neutrophil and platelet engraftment compared to full-MTX.¹ However, the primary endpoint of aGvHD incidence at Day 100 was not significantly different between the two groups.¹

The study was not powered to detect statistical differences in survival outcomes; however, non-relapse mortality was lower in patients who received mini-MTX.¹ Although his study suggests that mini-MTX can be safe and effective in patients undergoing transplant, additional studies in larger and more varied patient cohorts are needed. Tac/MTX was used in the majority of human leukocyte antigen matched-related (63%) and unrelated (64%) transplants between 2018 and 2020, it will likely remain the standard-of-care GvHD prophylaxis.¹