1. ¹Department of Hematology and Oncology, Nagoya University Graduate School of Medicine, Nagoya, Japan
2. ²Department of Hematology, Fujita Health University Hospital, Toyoake, Japan
3. ³Division of Hematology and Oncology, JA Aichi Showa Hospital, Konan, Japan
4. ⁴Department of Hematology, Japanese Red Cross Nagoya First Hospital, Nagoya, Japan
5. ⁵Department of Hematology, Nagoya Daini Red Cross Hospital, Nagoya, Japan

Correspondence: H Narimatsu, E-mail: narimt54@med.nagoya-u.ac.jp

Preparative regimens for cord blood transplantation (CBT) that use a reduced-intensity preparative regimen (RI-CBT) can consist of fludarabine, alkylating agents and 2–4 Gy total body irradiation (TBI); low-dose TBI is frequently added to overcome a human leucocyte antigen (HLA) barrier.¹ However, TBI can increase regimen-related toxicity (RRT), which can cause life-threatening infection and/or organ dysfunction.²

To ameliorate RRT of RI-CBT, conditioning using a non-TBI regimen is being studied.³ We previously reported the safety and feasibility of a preparative regimen consisting of fludarabine 125 mg/m² and melphalan 180 mg/m² for unrelated bone marrow transplantation in elderly patients.⁴ Since 2005, we have been using this non-TBI regimen for RI-CBT. In the present paper, the results of this RI-CBT procedure are reviewed.

Between December 2005 and March 2007, 10 patients underwent RI-CBT at 5 collaborating hospitals in the Nagoya Blood and Marrow Transplantation Group (Table 1). Elderly patients (age 50 years) with hematologic diseases that were incurable with conventional treatments and were considered inappropriate for conventional allogeneic stem cell transplantations due to the lack of an HLA-identical sibling or a suitable unrelated donor were enrolled. All patients provided written informed consent to undergo RI-CBT. Patients 6 and 7 have been described in previous case reports.^{5, 6}

Table 1 - Patients' characteristics.

Full table

The preparative regimen included fludarabine 25 mg/m² on days - 6 to - 2 and melphalan 90 mg/m² on days - 3 to - 2. graft-versus-host disease (GVHD) prophylaxis consisted of a continuous infusion of tacrolimus 0.02 mg/kg from day - 1 until the patients could tolerate oral administration and short-term methotrexate (MTX) (10 mg/m² on day 1, 7 mg/m² on day 3 and 7 mg/m² on day 6). The patients received trimethoprim/sulfamethoxazole for prophylaxis against Pneumocystis jiroveci. They were also given fluoroquinolone and fluconazole for prophylaxis against bacterial and fungal infections, respectively, as well as acyclovir for prophylaxis against herpesvirus infection. Granulocyte colony-stimulating factor was administered intravenously from day 1 until neutrophil engraftment. Minor modifications of doses or schedules were permitted at physicians' discretion. Engraftment and graft failure were defined as described previously.⁷ Post transplant immune reactions were classified into three subgroups (Table 2).⁸

Table 2 - Patients' clinical courses.

Full table

The patients' characteristics and clinical courses are shown in Tables 1 and 2, respectively. The median number of infused total nucleated cells was 2.5 10⁷/kg (range, 2.1–5.3 10⁷/kg). The HLA match was 6/6 (n=1), 5/6 (n=6) and 4/6 (n=3) antigens. One patient (patient 9) had received a prior stem cell transplantation. Of the 10 patients, 5 achieved primary neutrophil engraftment at a median of day 20 (range, 17–33). One patient died before engraftment. Four patients were diagnosed with graft failure without recovery of autologous hematopoiesis; they received a second RI-CBT, but three of them died before engraftment. The infused total cell dose, CD34 cell dose and HLA match were not significantly associated with engraftment (data not shown). Five patients developed post-CBT immune reactions that were successfully treated without additional prednisolone. Five of the 10 patients died before day 100 due to multiorgan failure (n=3) or sepsis (n=2).

This study suggests that there is a significant concern with the non-TBI preparative regimen consisting of fludarabine and melphalan, as the rate of graft failure (40% ) was higher than in previous studies (7–15% ).^{1, 3, 7} One possible reason is that the infused cell dose, which is a major determinant of engraftment, might have affected the engraftment. However, this is unlikely, as the infused cell doses used in this study were almost comparable to those used in previous studies.^{1, 3, 7} Except in one patient, the CD34 cell doses in patients with graft failure exceeded 0.1 10⁶/kg. Alternatively, it is possible that this regimen might not have enough intensity to achieve stable engraftment in CBT. In contrast with the present study, a previous small study demonstrated successful engraftment following a non-TBI regimen.³ However, a high rate of graft failure was reported by Barker et al.¹ even when low-dose TBI was incorporated into the preparative regimen. Given these contradictory results, the role of low-dose TBI in engraftment continues to be controversial; further studies are warranted.

The high rate of early bloodstream infections (BSI) onset was another significant problem. It should be noted that all four patients with early BSI onset during neutropenic periods developed graft failure or died before engraftment. BSI following RI-CBT induces serious organ damage and is frequently fatal.² Although the basic mechanisms are unknown, BSI per se and/or adverse effects of the agents used to deal with BSI might unfavorably affect the mechanism of engraftment.

Recently, we reported that short-term MTX could be a good regimen for reducing immune reactions without affecting engraftment in CBT.⁸ On the basis of this finding, we used tacrolimus and MTX for GVHD prophylaxis. However, this intensive regimen may suppress donor T cells and the proliferative capacity of hematopoietic cells, thereby increasing the risk of graft failure. A previous study⁹ demonstrated that the dose of infused donor T cells could be associated with engraftment. In the present study, infused T-cell doses were not investigated because this information is not routinely provided by the cord blood banks. Thus, the infused T-cell dose should be investigated in future studies.

Preparative regimens for RI-CBT require further improvements. First, the optimal dose of melphalan should be investigated. In the present study, the dose of melphalan did not affect the engraftment. However, owing to the small sample size, no definite conclusion can be reached; larger studies are required. Second, less mucosal toxic, immunosuppressive conditioning regimens, such as cyclophosphamide, busulfan and antithymocyte globulin (ATG), have to be studied. ATG is commonly used as a reduced-intensity preparative regimen. However, it strongly suppresses host immunity as well as donor immune cells in the graft, and remains in the recipient circulation due to its long half-life. Thus, ATG in RI-CBT may increase the risk of graft failure. Given these considerations, ATG was avoided, and we selected agents with short half-lives, such as fludarabine and melphalan. On the other hand, a high rate of engraftment has been reported in CBT using ATG.¹⁰ Thus, further studies on ATG as a preparative regimen are warranted.