Gene polymorphisms in the cyclophosphamide metabolism pathway correlate with complications after haplo-HSCT

Haploidentical hematopoietic stem cell transplantation (haplo-HSCT) is used as curative treatment for patients with hematologic malignancies who do not have a full-matched donor. Posttransplant cyclophosphamide is used as a prophylactic treatment to prevent graft-versus-host disease (GvHD) after haplo-HSCT. Cyclophosphamide is an inactive prodrug that is metabolized by polymorphic enzymes in the liver to produce phosphoramide mustard, a DNA alkylating agent with antineoplastic and immunosuppressive activities.¹

During the 47th Annual Meeting of the European Society for Blood and Marrow Transplantation (EBMT), Paula Muñiz, Gregorio Marañón General University Hospital, Madrid, ES, presented a retrospective study aimed at identifying polymorphisms in genes of the cyclophosphamide metabolism pathway that correlate with post-HSCT complications, including GvHD, transplant-related mortality (TRM), sinusoidal obstruction syndrome (SOS), and hemorrhagic cystitis (HC).¹

Study design and patient characteristics

182 consecutive patients that had received a haplo-HSCT with posttransplant cyclophosphamide (50mg/kg on Days 3 and 4) at the Gregorio Marañón General University Hospital between 2007–2019 were included in the analysis. Treatment schema for this patient population can be seen in Figure 1. Patients received either myeloablative conditioning or reduced intensity conditioning prior to haplo-HSCT.

Figure 1. Treatment schema*

GvHD, graft-versus-host disease; Haplo-HSCT, haploidentical hematopoietic stem cell transplantation; IV, intravenous; MMF, mycophenolate mofetil.

*Adapted from Paula Muñiz et al., 2021¹

 A custom panel of 11 genes relating to cyclophosphamide metabolism were analyzed by genotyping in a MiSeq platform.

• Variations located in the coding and splicing sites were analyzed.
• Polymorphisms that corresponded to a read depth ≥30X in the canonical isoform with an allele frequency greater than 40%, and represented in at least 5% of the cohort, were selected.

Patient characteristics can be seen in Table 1.

• Approximately half of the patients had acute myeloid leukemia or non-Hodgkin lymphoma, and in total, 57% were in complete remission pretransplant.
• Posttransplant complications were: 41% of patients developed Grade II-IV acute GvHD (aGvHD), 35% developed global chronic GvHD (cGvHD), 9% developed SOS, and 25% developed HC.

Table 1. Patient characteristics*

Results¹

In total, 35 polymorphisms across nine genes were found. The 19 single nucleotide polymorphisms (SNPs) that demonstrated a correlation with post-haplo-HSCT complications by univariate analysis are shown in Table 2.

• SNPs associated with a decrease in activity of cyclophosphamide activation enzymes (cytochrome P450) were associated with a higher incidence of GvHD, TRM, and SOS.
• SNPs associated with a decrease in activity of detoxification enzymes (glutathione S-transferases) were associated with a higher incidence of severe GvHD, TRM, and SOS.

Table 2. Univariate analysis of SNPs associated with posttransplant complications^*

Multivariate analysis revealed that eight polymorphisms in five genes were associated with posttransplant complications (Table 3).

• SNPs associated with a decrease in activity of activation enzymes, were associated with a higher incidence of GvHD.
• SNPs that were associated with a decrease in activity of detoxification enzymes were associated with a higher incidence of severe GvHD, TRM, and SOS.

Table 3. Multivariate analysis of SNPs associated with posttransplant complications^*

Conclusions

Genetic variation in genes involved in the cyclophosphamide metabolism pathway correlated with several post-haplo-HSCT complications, most notably GvHD, but also TRM, and SOS. Only one SNP correlated with HC in the univariate analysis. Therefore, the analysis of these variants before haplo-HSCT transplant could facilitate personalized risk approaches and clinical management of patients with hematologic malignancies. However, these results need to be validated in other patient cohorts.