Mother Donors Improve Outcomes after HLA Haploidentical Hematopoietic Transplantation: A Retrospective Study By the Cell Therapy and Immunobiology Working Party of the EBMT

Introduction

Trans-placental trafficking of maternal and fetal cells during pregnancy establishes long-term, reciprocal micro-chimerism in both mother and child (Maloney et al., J Clin Invest, 104:41, 1999). As a consequence, the immune system of the mother may become sensitized to paternal histocompatibility antigens. In fact, antibodies directed against paternal HLA-antigens (van Rood JJ et al., Nature 181:1735, 1958) and T lymphocytes directed against paternal major and minor histocompatibility antigens (van Kampen CA et al., Hum Immunol 62:201, 2001; Verdijk RM et al., Blood 103:1961, 2004) were detected in multiparous women. More recently, it was hypothesized that mother's "exposure" to paternal HLA haplotype antigens during pregnancy may affect transplantation outcomes when the mother acts as donor for the child. Indeed, survival after T cell-depleted HLA haploidentical haematopoietic transplantation was improved using the mother as donor (vs all other family members) (Stern et al., Blood 112:2990, 2008; Kruchen et al., BMT 50:1367 2015). However, maternal donors were associated with increased incidence of GvHD and decreased survival after un-manipulated HLA haploidentical blood and marrow grafts (Wang Y et al., Blood 124:843, 2014).

Patients and Methods

A retrospective EBMT registry-based study was performed in a combined series of adult (n=333) and pediatric (n=105) patients with acute leukemia (AML=268, ALL=160, Mixed phenotype=10) who received transplant from one MHC mismatched family donor. Forty-four percent (233) of patients were in I or II complete remission (CR) at the time of transplant, 193 were in chemo-resistant relapse or in CR > 2. Median age was 32.7 (range: 0.67-70). Seventy-one percent of patients received ex-vivo T cell depleted transplants. Twenty-two patients were given bone marrow and peripheral blood stem cells, the others were given peripheral blood cells only. The mother was used as donor in 98 patients.

Results

Eighty patients developed acute GvHD ≥ grade II. At a median follow up of 58.7 months, 130 patients are alive without disease, 146 relapsed and 152 died of non-relapse mortality (NRM). Univariate analyses of factors influencing relapse-free survival (RFS) showed age, disease status at transplant, Karnofsky score and ex-vivo T cell depletion impacted significantly. As transplantation outcomes from family members other than mothers did not differ from one another, such transplants were combined for analyses. When compared with transplantation from all other family members (n=330), transplantation from mother donors (n=98) was associated with lower relapse incidence (RI) (28% vs 39%, P=0.06) and non-relapse mortality (NRM) (30% vs 40%, P=0.09) and, consequently, better relapse-free survival (RFS) (43% vs 21%, P < 0.001). Multivariate analyses showed transplantation from mother donors was an independent factor predicting better RFS (other donors vs mothers: HR: 1.42; CI: 1.01-2.00; P=0.04) and lower RI (other donors vs mothers: HR: 1.93; CI: 1.16-3.22; P = 0.01). In addition, transplantation in relapse (vs remission) predicted worse RFS (HR: 2.33, CI: 1.80-3.00, P < 0.001) such as ≥18 (vs < 18) adversely impacted on RFS (HR: 1.40, CI: 1.00-1.96, P=0.04).

Discussion

Our retrospective analyses in 438 HLA haploidentical hematopoietic transplants for acute leukemia patients (pediatric and adult) show that transplantation from mother donors, when compared with transplantation from any other family member, is an independent factor predicting better outcomes, i.e., better RFS and lower RI. Mothers should therefore be preferred when selecting an HLA haploidentical family donor. Further clinical and preclinical studies are needed to unveil the mysteries underlying mother-to-child immune interaction during pregnancy and its bearing on the reproductive success of the human species.