Long-term remission after fetal liver transplantation in acute leukemia: a 30-year follow-up report of two cases

Abstract

Fetal liver hematopoietic stem cells (HSCs) have the capacity to temporarily engraft, thereby facilitating the reconstitution of hematopoiesis without severe graft-versus-host disease (GVHD). In two cases of acute leukemia, the patients underwent fetal liver transplantation (FLT), receiving cells from multiple donors at doses ranging from 7.02 to 8.3 × 10^8 cells/kg, following an intensive conditioning regimen in 1983 and 1985. Remarkably, both individuals have since achieved sustained complete remission and hematopoietic recovery, and have maintained a normal life for over three decades. Although FLT is no longer a viable clinical option, the positive outcomes of these cases are noteworthy and are shared herein. Our findings underscore the potential of FLT to offer short-term hematopoietic support, contributing to the recovery of patients with acute leukemia and may inspire research into ideal HSCs that emulate the characteristics of fetal liver cells for future transplantation applications.

Background

The liver serves as the principal site of hematopoiesis during a certain phase of human fetal development. In 1980, a young Chinese technician suffered accidental exposure to 5.2-Gy gamma (γ) radiation. Given the absence of HLA-matched bone marrow, he underwent fetal liver transplantation (FLT), marking the first FLT case in China [1]. To evaluate the therapeutic efficacy of FLT, we initiated a clinical study in the 1980s. This article presents two cases of acute leukemia, each with over 30 years of follow-up since their respective FLTs in 1983 and 1985. To date, both patients have maintained complete remission (CR) for more than three decades and have led normal lives.

Case presentation

Patient characteristics and responses in the 1980s

Patient #1 (P1), a 12-year-old male, was diagnosed with acute lymphoblastic leukemia (ALL) in 1983; Patient #2 (P2), a 22-year-old male, received a diagnosis of acute myeloid leukemia (AML) in 1985. Both patients achieved complete remission (CR) following chemotherapy. For Patient #1 with acute lymphoblastic leukemia (ALL), before FLT, he underwent two cycles of POMP chemotherapy regimen. The specifics are as follows: Vincristine 2 mg on Day 2, Day 8, and Day 15. Methotrexate 20 mg on Day 3, Day 6, Day 17, and Day 20. 6-Mercaptopurine (6-MP) 50 mg on Day 1, Day 8, Day 15, and Day 22; 100 mg from Day 2 to Day 7, and from Day 16 to Day 21. Prednisone 15 mg on Day 1, Day 23 and 24, 45 mg from Days 2 to Day 21, and 30 mg on Day 22. For Patient #2 with acute myeloid leukemia (AML), before undergoing FLT, the patient received six cycles of chemotherapy with the HOCP regimen. The specific dosages were as follows: Vincristine 1 mg on Day 1, Cyclophosphamide 400 mg on Day 2, Homoharringtonine 4 mg from Day 3 to Day 7, Prednisone 30 mg from Day 1 to Day 11. The sixth cycle of chemotherapy was prematurely discontinued due to the patient’s intolerance. Subsequently, a reduced-dose HOCP regimen was administered, with the following specifics: Vincristine 2 mg on Day 1, Cyclophosphamide 200 mg on Day 2, Homoharringtonine 2 mg from Day 2 to Day 6, Prednisone 30 mg from Day 2 to Day 6.

Then the patients received a conditioning regimen comprising cyclophosphamide at a dosage of 40 mg/kg per day and total body irradiation (TBI) at 5 Gy (Gy). Prophylaxis against graft-versus-host disease (GVHD) was not administered. Subsequently, they underwent transfusion with fetal liver cells, sourced from multiple fresh fetuses aged between 3 and 6 months, at a dosage range of 7.02 to 8.3 × 10^8 cells per kilogram of body weight, administered successively within a three-day period (Table 1). The interval from the initial diagnosis to FLT was 2 months for P1 and 4 months for P2.

Table 1 Fetal characteristics

Following FLT, both patients’ WBC counts dropped to their lowest point on day 7 (0.3 × 10⁹/L of P1 and 0.022 × 10⁹/L of P2). Regarding platelet counts, P1 reached the lowest point on day 23 at 13 × 10⁹/L, and P2 on day22 at 5 × 10⁹/L. We defined sustained WBC counts above 1.0 × 10⁹/L and/or platelets counts above 20 × 10⁹/L as indicative of the initiation of hematopoietic reconstitution. P1’s WBC count began to recover on day 9, whereas P2’s recovery occurred on day 28, which was earlier than the recovery of platelet counts, observed on day 27 for P1 and day 32 for P2. In P1, 2% 46XX karyotype could be detected 10 days post-FLT, and 3.7% in P2 on the 11th day post-FLT, indicated successful engraftment of the fetal liver cells in both patients. Throughout their hospitalization, both maintained a 46XX karyotype. P2 developed atypical rashes on day 7 post-FLT, which were diagnosed as mild cutaneous acute graft-versus-host disease (aGVHD). No signs of GVHD were observed in P1.

After undergoing FLT, P1 received routine supportive care, including immunoglobulin injections and blood transfusions, and was discharged 60 days post-FLT. P2, however, exhibited 5.1% myeloblastic and promyelocytic leukemia cells in bone marrow on day 43 post-FLT. Consequently, P2 underwent an additional six cycles of chemotherapy. By five months post-FLT, P2 achieved complete remission (CR) in the bone marrow. Both patients were in CR status at the time of their hospital discharge.

Follow-up of the two patients in 2014

In 2014, we were surprised to find both patients still alive 30 years after FLT. Over the intervening years, neither patient had experienced a relapse and both had maintained continuous CR. STR-PCR showed no evidence of engraftment by the transplanted fetal liver cells. Karyotype analysis, conducted using the G-banding technique, revealed that both patients exhibited complex karyotypes, as detailed below:

P1:

46,XY, del(7)(q11.2q22) [2]/ 46,XY,+7,del(7)(q11.2q22),-16 [1]/ 46,XY, del(1)(p34),del(5)(q11.1q13),add(6)(q13),+7,del(7)(q11.2q22),add(14)(p11),-16,add(19)(q13.3) [1]/ 45,XY, der(13;15)(q10;q10) [2]/ 46,XY, del(3)(q21),add(15)(q24),add(15)(q26) [1]/ 46,XY, add(13)(q32) [1]/ 46,XY,-1,add(20)(q13.3),+mar [1]/ 46,XY [11].

P2:

46,XY, t(1;8)(p36.1;q22) [4]/ 46,XY, add(20)(p11) [1]/ 46,XY, t(3;6)(q21;p21),ins(15;?)(q22;?) [1]/ 46,XY [16].

Additionally, P2 exhibited cutaneous hypopigmentation (Fig. 1). However, due to the patient’s refusal of a skin biopsy, a definitive diagnosis of chronic graft-versus-host disease (cGVHD) or an alternative skin disease could not be established. P2 has regained fertility and fathered a healthy child. In contrast, P1 remains infertile, with biochemical analysis indicating elevated levels of follicle-stimulating hormone (FSH = 36.42 mIU/ml) and a marginally increased level of luteinising hormone (LH = 17.47mIU/ml) [2]. Aside from these findings, all other examination results were within normal limits.

Figure 1

Hypopigmentation in Patient #2

Discussion and conclusions

In this report, we present the long-term outcomes for two patients with ALL and AML who received chemotherapy, radiotherapy, and subsequent FLT in 1983 and 1985, respectively. Both patients achieved hematopoietic recovery and have maintained long-term CR, leading normal lives for over three decades.

Their complex karyotypes present certain pathogenic mutations, such as deletions of chromosomes 7 (del(7)) and 5 (del(5)), which are known to be unfavorable cytogenetic findings in AML [3]. Nonetheless, their bone marrow showed no signs of residual leukemia or engraftment of the transplanted fetal liver cells. It is reported that TBI can induce cytological abnormalities [4]. The lack of relapse or development of new malignancies in these patients may be attributed to the relatively low proportion of each abnormal karyotype, which was insufficient to cause disease. Unfortunately, we were unable to perform next-generation sequencing (NGS) for somatic mutations due to technical constraints, such as DNMT3A, TET2, and ASXL1 during follow-up, which are associated with clonal hematopoiesis of indeterminate potential (CHIP). This represents a limitation in our analysis.

Hematopoietic stem cells (HSCs) in fetal livers at 4–5 months exhibit the highest number and proliferative capacity [1]. Concurrently, the lymphocyte population during this period is sparse, with the majority not being post-thymic T cells [5]. In some respects, FLT is analogous to transplantation of T-cell-depleted bone marrow [6]. Our findings confirm previous reports indicating that HSCs derived from the fetal liver cannot engraft long-term. Bone marrow cells usually revert to the host genotype within six months post-FLT [7]. Regrettably, after the patients’ discharge from the hospital, we lost contact with them, and were unable to determine the duration of chimerism. The sustained engraftment may be hindered by genetic disparity between the donor and the host due to ontogenetic and histoincompatible barriers [8].

The patients’ long-term remission primarily depended on intensive chemotherapy and radiotherapy, which aimed to eliminate the maximum number of leukemia cells in vivo. Additionally, Zhu’s research reported the isolation and purification of two suppressors from the methanol extract of human fetal liver; these suppressors may potentially inhibit tumor cell growth [9, 10]. Furthermore, FLT could indeed assist in restoring immune function and promoting the patients’ own bone marrow hematopoietic recovery. The mechanism remains unclear, possibilities include: firstly, fetal liver HSCs can temporarily engraft in the recipient’s bone marrow, providing a supportive role. Secondly, hematopoietic growth factors present in the fetal liver cell suspension may have stimulated the recovery of autologous hematopoiesis [1, 11,12,13,14], and bone marrow proliferation might be attributed to fibroblastic cells derived from the fetal liver [15]. Moreover, the large number of allogeneic fetal liver cells could activate the recipient’s residual T-lymphocytes, enhancing graft-versus-leukemia (GVL) reactions and improving cellular immune function [1]. Lastly, since fetal liver HSCs do not engraft permanently, the use of immunosuppressive drugs is not required.

Over three decades have passed since these two patients with acute leukemia underwent FLT. During this period, they have not required any further medical treatment, such as chemotherapy or stem cell transplantation. Their growth and development remained unaffected, and there has been no recurrence of leukemia. We believe there are two significant favorable prognostic factors. The first is the age and timing of the transplantation; adolescents and children possess robust hematopoietic function. At the time of FLT, these patients were 12 and 22 years old, respectively, both in favorable age group [16]. The second factor is the intensive immunosuppression of the host and the administration of a substantial number of nuclear cells, at a dosage of 3.68 × 10⁸/kg of fetal cells. To a certain extent, the more rigorous the conditioning regimen, the more effectively residual leukemia cells are eradicated.

Our report provides valuable insights into the long-term outcomes of fetal liver transplantation (FLT) in two patients with acute leukemia. Our study, in conjunction with others [8, 17,18,19], suggests that FLT may facilitate the recovery of the patient’s own stem cells, with the risk of GVHD appearing to be low. Moreover, our cases illustrate that patients could survive with complex karyotypic abnormalities. For these reasons, we present the favorable outcomes of these two patients who underwent FLT in the 1980s. However, we acknowledge the limitations associated with the small sample size. The generalizability of our findings is indeed constrained, and we advise caution in interpreting these results as representative of the broader patient population. It is crucial to emphasize that our observations should not be considered definitive evidence of the long-term success of FLT. The unique characteristics of these two cases, such as their young age at the time of transplantation and the intensive conditioning regimen they underwent, may have contributed to the positive outcomes.

Today, FLT is no longer utilized in clinical therapy due to ethical concerns. Nonetheless, considering the advantages of fetal liver hematopoietic stem cell (HSC) transfusion—such as the absence of a need for HLA matching, a low risk of GVHD, a potent GVL effect, and no requirement for immunosuppressive drugs—our findings may inspire research into ideal HSCs that emulate the characteristics of fetal liver cells for future transplantation applications.