Association of Gene Polymorphisms in Cyclophosphamide Metabolism Pathway with Complications after Haploidentical Hematopoietic Stem Cell Transplantation
Authors: Muñiz Sevilla Paula , Andres Cristina , Carbonell Diego , Chicano Lavilla María , Bailen Rebeca , Oarbeascoa Gillen , Suárez González Julia , Anguita Javier , Kwon Mi , Diez-Martin Jose L. , Martínez-Laperche Carolina , Buño Ismael 
Published: February 2021

INTRODUCTION
Allogeneic hematopoietic stem cell transplantation (alloHSCT) has been established as a powerful treatment modality for patients with hematological malignancies. The graft-versus-leukemia effect, however, is strongly associated with the occurrence of graft-versus-host disease (GVHD) and subsequent transplant-related mortality (TRM). Several strategies are applied in order to prevent GVHD, the post-transplant cyclophosphamide (PT-Cy) is one of the most used in Haploidentical HSCT (Haplo-HSCT). Cyclophosphamide (CY) is an alkylating agent with antineoplastic and immunosuppressive activities. CY is metabolized by highly polymorphic enzymes to produce phosphoramide mustard which is a bifunctional DNA alkylating agent, is the therapeutically active metabolite. Thus, the aim of our study is to identity polymorphisms in the genes of the CY metabolism and correlated with complications post-HSCT (GVHD, TRM, veno-occlusive disease (VOD) or hemorrhagic cystitis (HC)).
METHODS
We selected 182 consecutive patients who received an Haplo-HSCT from 2007 to 2019. Eleven genes related to CY metabolism were analyzed (Table 1).
The genotyping was performed in peripheral blood samples for recipient using an enrichment-capture custom gene panels (IDT probes) in a MiSeq platform (Illumina, USA). The bioinformatic analysis was carried out with BaseSpace software (Illumina, USA).
Variants located in coding region and splicing sites were analyzed. We selected polymorphisms corresponding to read depth ≥30X in the canonical isoform with an allele frequency ≥0.4 and represented in at least 5% in our cohort.
The collected clinical variables were age/gender recipient and donor, pathology, pretransplant status, conditioning regimen, total body irradiation, basal ferritin and CMV reactivation. Fisher test was used to compare the differences among groups.
Statistical Package for the Social Sciences (SPSS, Chicago, USA) was used for statistical test.
RESULTS
The cumulative incidence rates for aGVHD of II-IV and III-IV grades at 100 days was 39% and 12% respectively. The cumulative incidence rates for cGVHD, moderate or severe cGVHD and TRM at 1000 days were 37%, 19% and 29%, respectively. Among the cases analyzed, 9% developed VOD and 25% HC.
Patients who received ablative conditioning regimen presented a higher incidence of TRM (p=0.005). No other clinical data was associated with complications post HSCT.
Forty polymorphisms were detected in 9 genes by bioinformatic analysis. The variants that presents some correlation (p&lt;0.05) with complications post HSCT are shown in Table 1.
Overall, polymorphisms related with decrease activity of enzymes that active cyclophosphamide (level lor active metabolite) were correlated with higher aGVHD, cGVHD, TRM and VOD (Table 1). On the other hand, polymorphisms associated with low activity in detoxification enzymes were correlated with higher toxicity (TRM). As described in bibliography, GSTM1 null allele were correlated with higher probability of developing VOD.
CONCLUSIONS
Genetic analysis of CY metabolism genes correlated with several post HSCT complications. The analyses of this variants before transplant could facilitate personalized risk and clinical management of patients undergoing Haplo HSCT. Results must validated in others cohorts of patients.

Disclosures
Kwon: Gilead: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria; Jazz: Consultancy, Honoraria.