Outcomes of Cord Blood Transplantation Using
Reduced-Intensity Conditioning for Chronic Lymphocytic
Leukemia: A Study on Behalf of Eurocord and Cord Blood
Committee of Cellular Therapy and Immunobiology Working
Party, Chronic Malignancies Working Party of the European
Society for Blood and Marrow Transplantation, and the Societé
Française de Greffe de Moelle et Therapie Cellulaire
Erick Xavier
1,*, Jérôme Cornillon
2, Annalisa Ruggeri
1,3, Patrice Chevallier
4, Jan J. Cornelissen
5,
Niels S. Andersen
6, Natacha Maillard
7, Stephanie Nguyen
8, Didier Blaise
9, Eric Deconinck
10,
Hendrik Veelken
11, Noel Milpied
12, Michel Van Gelder
13, Regis Peffault de Latour
14,
Eliane Gluckman
1, Nicolaus Kröger
15, Johannes Schetelig
16, Vanderson Rocha
171Eurocord International Registry, Hôpital Saint-Louis, Paris, France
2Department of Hematology, Cancer Institute Lucien Neuwirth, Saint Etienne, France 3Service d’hématologie et de Thérapie Cellulaire, Hôpital Saint-Antoine, Paris, France 4Department of Hematology, Nantes University Hospital, Nantes, France
5Department of Hematology, Erasmus MC/Daniel Den Hoed, Rotterdam, Netherlands 6Department of Hematology, Rigshospitalet, Copenhagen, Denmark
7Service Oncologie Hématologique et Thérapie Cellulaire, CHU de Poitiers, Poitiers, France 8Department of Hematology, Pitie-Salpetriere Hospital, Paris, France
9Department of Hematology, Paoli Calmettes Hospital, Marseille, France 10Department of Hematology, Jean Minjoz Hospital, Besançon, France
11Department of Hematology, Leiden University Medical Center, Leiden, Netherlands
12Hematology and Cell Therapy Department, University Hospital and University of Bordeaux, Bordeaux, France 13Department Internal Medicine/Hematology, Maastricht University Medical Center, Maastricht, Netherlands 14Blood and Marrow Transplantation Unit, Saint Louis Hospital, Paris, France
15Department of Stem Cell Transplantation, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
16University Hospital Carl Gustav Carus, Medical Department & DKMS German Bone Marrow Donor Center, Dresden, Germany 17Department of Clinical Haematology, Bone Marrow Transplantation Unit, Oxford University Hospitals NHS Trust, United Kingdom
Article history:
Received 19 February 2015 Accepted 29 April 2015 Key Words:
Umbilical cord blood transplantation
Chronic lymphocytic leukemia Reduced-intensity conditioning regimen
a b s t r a c t
Outcomes after umbilical cord blood transplantation (UCBT) for chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) are unknown. We analyzed outcomes of 68 patients with poor-risk CLL/SLL who underwent reduced-intensity (RIC) UCBT from 2004 to 2012. The median age was 57 years and median follow-up 36 months; 17 patients had del 17p/p53mutation, 19 patients hadfludarabine-refractory disease, 11 relapsed after autologous stem cell transplantation, 8 had diagnosis of prolymphocytic leu-kemia, 4 had Richter syndrome, and 8 underwent transplantation with progressive or refractory disease. The most common RIC used was cyclophosphamide,fludarabine, and total body irradiation (TBI) in 82%; 15 patients received antithymocyte globulin. Most of the cord blood grafts were HLA mismatched and 76% received a double UCBT. Median total nucleated cells collected was 4.7 107/kg. The cumulative
in-cidences (CI) of neutrophil and platelet engraftment were 84% and 72% at 60 and 180 days respectively; day 100 graft-versus-host disease (GVHD) (grade II to IV) was 43% and 3-year chronic GVHD was 32%. The CI of relapse, nonrelapse mortality, overall survival, and progression-free survival (PFS) at 3 years were
Financial disclosure: See Acknowledgments on page 1521.
* Correspondence and reprint requests: Erick Xavier, MD, Eurocord Of-fice, Hôpital Saint Louis, 1, Av Claude Vellefaux 75010, Paris, France.
E-mail address:erick_menezes@yahoo.com(E. Xavier).
http://dx.doi.org/10.1016/j.bbmt.2015.04.026
1083-8791/Ó 2015 American Society for Blood and Marrow Transplantation.
Biology of Blood and
Marrow Transplantation
16%, 39%, 54%, and 45%, respectively. Fludarabine-sensitive disease at transplantation and use of low-dose TBI regimens were associated with acceptable PFS. In conclusion, use of RIC-UCBT seems to be feasible in patients with poor-risk CLL/SLL and improved outcomes were observed in patients with fludarabine-sensitive disease who received low-dose TBI regimens.
Ó 2015 American Society for Blood and Marrow Transplantation.
INTRODUCTION
Chronic lymphocytic leukemia (CLL) is a heterogeneous disease with a variable clinical course and survival can range from months to decades, according to different biological features[1,2]. Poor-risk disease is characterized by mutations or deletions of the TP53 gene [3-7], nonresponse or early relapse after purine analogue treatment (within 12 months), or relapse (less than 24 months) after purine analogue combination therapy[8].
Until now, allogeneic stem cell transplantation (allo-HSCT) has been accepted as standard of care infit patients with poor-risk CLL[8-10]. Two drugs inhibiting downstream signaling of the B cell receptor, ibrutinib and idelalisib, have recently been approved. These drugs expose a very favorable risk benefit profile for patients with refractory CLL/small lymphocytic lymphoma (SLL) [11]. Longer follow-up is needed to better assess the safety and efficacy of these drugs but clearly they do not have the potential to eradicate the disease. Comparative studies with allo-HSCT are lacking and this therapeutic tool is still the only therapy to evoke the graft-versus-leukemia (GVL) effect that is highly active in achieving and maintaining disease control, even in advanced stages of CLL/SLL[12,13]. Although the role of allo-HSCT in the therapeutic algorithm may have to be redefined, allo-HSCT will maintain its place in the treatment of patients with refractory stages of CLL/SLL.
In recent years, the use of reduced-intensity conditioning (RIC) regimens in the allo-HSCT setting has become standard treatment, even in poor-risk CLL, and it may lead to cure [14,15]. Almost exclusively, outcomes on matched related or unrelated donor transplantation have been published and data on alternative stem cell donors are lacking. Generally, clinical experience with umbilical cord blood transplantation (UCBT) in poor-risk malignancies has increased in recent years, especially with the use of double UCBT, which allows adult patients to proceed to allo-HSCT[16]. Nevertheless, to our knowledge, no studies have yet addressed directly the role of UCBT specifically for CLL/SLL. Therefore, we analyzed results of unrelated UCBT in CLL/SLL patients and identified risk factors associated with outcomes.
METHODS
Study Design: Patients and Definitions
The primary objective of this study was to describe progression-free survival (PFS) after UCBT and to identify risk factors in a retrospective reg-istry analysis. We analyzed adult patients with CLL/SLL, prolymphocytic leukemia (PLL), or Richter syndrome (RS) who underwent afirst unrelated and unmanipulated allogeneic UCBT after RIC. Sixty-eight patients meeting the study criteria were registered with the Eurocord/European Society for Blood and Marrow Transplantation (EBMT) databases from 2004 to 2012. All patients or legal guardians provided informed consent for the UCBT, ac-cording to the Declaration of Helsinki.
The primary endpoint was PFS, defined as the time from UCBT to relapse, disease progression, or death. Secondary endpoints were probability of overall survival (OS), defined as the probability of survival regardless of disease state at any point in time; incidence of neutrophil recovery, defined as first of 3 consecutive days with a neutrophil count of at least .5 109/L; acute
graft-versus-host disease (GVHD) at day 100 and chronic GVHD, which were diagnosed and graded according to published criteria[17,18]; relapse or
progression, as defined by the centers; and nonrelapse mortality (NRM), defined as deaths without previous relapse or progression. Full donor chimerism was defined as the presence of more than 95% of the cells of donor origin, mixed chimerism as more than 5% but less than 95% donor cells, and autologous recovery as less than 5% of donor cells. Data on the method of chimerism detection were not collected.
Statistical Analysis
Median values and ranges are reported for continuous variables and percentages for categorical variables. The probabilities of OS and PFS were calculated using the Kaplan-Meier method and the log-rank test for uni-variate comparisons[19]. The cumulative incidence (CI) function using death as a competing event was used to estimate neutrophil and platelet engraftment, acute and chronic GVHD, and relapse.
The following variables were tested in the univariate analyses: age at UCBT, year of UCBT, gender, patient cytomegalovirus (CMV) serology before transplantation, hematopoietic stem cell transplantation comorbidity index (HCT-CI), Binet staging at diagnosis, intervals between diagnosis and UCBT, graft source (single/double), CLL/SLL cytogenetic risk, disease status at transplantation (complete remission versus no complete remission), con-ditioning regimen (low-dose total body irradiation [TBI] versus others), antithymocyte globulin (ATG), GVHD prophylaxis (cyclosporine and myco-phenolate mofetil versus others), number of courses of chemotherapy lines (CTL) before UCBT, previous autologous stem cell transplantation (ASCT), total nucleated cells per kilogram of recipient’s weight, and number of HLA disparities. Multivariate analysis was performed using Cox proportional hazards regression model for PFS[20]. Variables that reached a P value of .15 in the univariate analysis were included in the initial multivariate model and eliminated 1 at a time in a stepwise fashion to only keep variables that reached a P value of .05 in the final model. P values were 2 sided. Statistical analyses were performed with SPSS version 19 (Inc., Chicago, IL) and Splus (MathSoft, Inc., Seattle, WA).
RESULTS
Patients and Disease Characteristics
Patients and transplantation characteristics are summa-rized in Table 1. Sixteen patients received single and 52 received double UCBT. Seventeen patients had del 17p/ p53mutation, 19 patients had fludarabine-refractory dis-ease, 11 relapsed after ASCT, 8 had diagnosis of PLL, and 4 had RS. Median age at UCBT was 57 years (range, 26 to 68), median year of UCBT was 2009, and median follow-up was 36 months (range, 3 to 98). Comorbidities were assessed according to the HCT-CI[21]and scoring was as follows: 40 patients had no comorbidity, 9 had score of 1, 7 had a score of 2, 9 had a score of 3, and 1 had a score of 4. Information on fludarabine exposure were retrieved from 67 of 68 pa-tients. Fludarabine-refractory disease was classified as dis-ease that failed to respond tofludarabine-based treatment or that progressed within 12 months after fludarabine-based combination regimen. Fifty-three patients were treated withfludarabine combination regimens. The other 14 patients were treated with alemtuzumab-based regi-mens as first-line treatment and were not considered fludarabine resistant.
Transplantation Outcomes Neutrophil and platelet engraftment
The CI of neutrophil and platelet engraftment were 84% 5% and 72% 6%, with a median time for engraftment of 22 (range, 5 to 67) and 44 days (range, 6 to 189), respectively. Patients who received previous ASCT had a higher incidence
of neutrophil engraftment (100% versus 82%, P¼ .03). Eleven patients did not engraft. Of these patients, 8 died (5 died of
early NRM without marrow reconstitution and 3 of relapse after autologous reconstitution). Three patients are alive with autologous reconstitution (2 of them relapsed and are on rescue treatment and 1 is alive 13 months after trans-plantation without signs or symptoms of relapse). For the remaining 57 patients with neutrophil engraftment, 36 had complete donor chimerism, 16 had mixed chimerism, and 5 were unknown.
GVHD
The CI of acute GVHD at 100 days was 42% 5% for grade II to IV and 19% 5% for grades III and IV with a median time of onset of 26 days (range, 9 to 95). The use of ATG was associated with a lower risk of grade II to IV acute GVHD (14% versus 45%, P¼ .02). Three-year CI of chronic GVHD was 32% 6% with a median time of onset of 138 days (range, 90 to 393). Positive CMV serology before UCBT (50% versus 22%, P¼ .05) was associated with higher chronic GVHD incidence (Table 2).
NRM
Twenty-five patients died of transplantation-related causes (10 infections, 4 post-transplantation lymphoproli-ferative disease, 3 acute GVHD, 3 toxicity, 1 secondary lung cancer, and 4 other causes). The cumulative incidence of NRM was 39% 6% at 3 years. Factors associated with lower NRM were use of low-dose TBI (2 to 4 Gy) conditioning regimen (34% versus 62%, P< .001), 2 different CTL before UCBT (18% versus 49%, P ¼ .02), and fludarabine-sensitive disease at UCBT (30% versus 61%, P¼ .009) (Figure 1). Relapse or progression
The cumulative incidence of relapse or progression was 16% 5% at 3 years. Median time to relapse or progression was 19 months (range, 2 to 89 months) and fludarabine-sensitive disease (13% versus 45%, P¼ .04) was the only factor associated with lower incidence of relapse. No relapse outcome differences were observed from del 17p and non-17p patients (Figure 2). We analyzed the impact of acute (P¼ .66) and chronic GVHD (P ¼ .67) on relapse (in a time-dependent fashion), but we could not find any statistical impact, probably because of low relapse rate.
Twenty-three patients underwent transplantation in complete remission. Of these patients 15 were alive at last follow-up and 8 died (1 of relapse after 36 months of transplantation and 7 died of NRM causes, mainly infection). Of the 15 patients alive, 3 relapsed with a median time to relapse of 11 months. Thirty-seven patients were in partial remission, 18 patients died (4 of relapse with a median time to relapse of 19 months, 14 of NRM causes with a median survival of 3 months), and 19 patients are alive (16 without relapse with a median follow-up of 45 months and 3 patients relapsed with a median time to relapse of 77 months). Eight patients had relapse-progressive disease before UCBT; 6 of them died (2 of relapse with a median time to relapse of 7 months and 4 died of NRM with a median time to death of 2 months) and 2 are alive without relapse with a median follow-up of 26 months.
Overall, 13 patients relapsed or progressed after UCBT. Eight of these 13 patients underwent transplantation in partial remission or had refractory disease at transplantation. Of these 13 patients, 6 are alive (1 received treatment with R-bendamustine, 1 received an unknown treatment, and 4 of them did not receive further treatment after relapse), and 7 died (2 after relapse following a second stem cell
Table 1
Patients and Transplantation Characteristics
Characteristic Value (N¼ 68)
Age, median (range) yrs 57 (27-68) Diagnosis CLL/SLL 56 (82%) PLL 8 (12%) RS 4 (6%) Sex Male 50 (74%) Female 18 (26%)
Year of UCBT, median (range) 2009 (2004-2012) Time from diagnosis to UCBT,
median (range), mo
58 (3-360) Binet staging at diagnosis (n¼ 54)
Stage A 18 Stage B 28 Stage C 09 Cytogenetics Normal 13 Abnormal 35 Del 17p/p53 mutation 17 Del 13q 8 Del 11q 4 Trisomy 12 2 Complex 2 Others 2 Failed/not done 20 Previous ASCT No 57 (84%) Yes 11 (16%) Single UCBT 16 (18%) Double UCBT 52 (82%) Conditioning regimen Cy-Flu-TBI (2-4 Gy) 57 (84%) Flu-TBI (2-4 Gy) 3 (4%) Cy-Flu 2 (3%) Cy-Flu-Thio 1 (2%) Cy-Bu-Flu 2 (3%) Bu-Flu-Thio 3 (4%) GVHD prophylaxis CsAþMMF 61 (89%) CsAþprednisone 5 (7%) CsAþMMFþMTX 1 (2%) TacroþMMF 1 (2%) ATG No 53 (78%) Yes 15 (22%) HLA compatibility (n¼ 64) 0-1 HLA MM 19 (30%) 2 HLA MM 45 (70%) Fludarabine refractoriness (n¼ 67) Fludarabine-refractory disease 19 (28%) Fludarabine-sensitive disease 48 (72%) HCT-CI (n¼ 66) 0-2 (56) >2 (10) TNC collected, median, 108TNC/kg (n¼ 64) sUCBT 3.70 dUCBT 5.04 No. of previous CTL (n¼ 65) 1-2 23 (35%) 3 42 (65%)
Disease status at transplantation
First CR 17 (25%)
Second CR 4 (6%)
Third or higher CR 2 (3%)
Partial remission 37 (54%)
Refractory/resistant 8 (12%)
Cy indicates cyclophosphamide; Flu, fludarabine; Thio, thiotepa; Bu, busulfan; CsA, cyclosporine; MMF, mycophenolate mofetil; MTX, metho-trexate; Tacro, tacrolimus; MM, mismatch; TNC, total nucleated cells; sUCBT, single umbilical cord blood transplantation; dUCBT, double umbilical cord blood transplantation; CR, complete remission.
transplantation, 1 received clorambucil but progressed, and 4 patients did not receive any further treatment).
OS and PFS
The probability of OS and PFS were 54% 6% and 45% 7% at 3 years. Negative CMV serology (70% versus 45%, P¼.03), use of low-dose TBI (58% versus 35%, P< .001), 2 different CTL before UCBT (59% versus 18%, P ¼ .01), and fludarabine-sensitive disease at UCBT (70% versus 21%, P < .001) were associated with increased OS (Table 2). The use of low-dose TBI (49% versus 14%, P¼ .02), 2 different CTL before UCBT (66% versus 37%, P¼.04), fludarabine-sensitive disease at UCBT (53% versus 21%, P¼ .001), and HCT-CI 2 (51% versus 25%, P ¼ .04) were associated with improved PFS (Figure 3). Patients with fludarabine-resistant disease at UCBT frequently had 3 different CTL and advanced stage disease before UCBT. Thus, these 3 variables were intrinsically linked in this study. The collinearity was assessed through Fisher’s exact test that demonstrated the association betweenfludarabine sensitivity with number of prior lines of chemotherapy (P¼ .019) and disease status at transplantation (P¼ .044).
Overall, 38 patients died or relapsed. In a multivariate model for PFS, the use of low-dose TBI (hazard ratio [HR], 4.16 [95% confidence interval, 1.33 to 12.5]; P ¼ .014), HCT-CI score 2 (HR, 2.29 [95% confidence interval, 1.0 to 5.2]; P ¼ .05), and fludarabine-sensitive disease at UCBT (HR, 3.07 [95% confidence interval, 1.51 to 6.25]; P ¼ .002) were asso-ciated with improved PFS (Table 3).
Concerning the 4 patients diagnosed with RS, 3 patients died (2 of NRM causes and 1 of relapse 8 months after transplantation; rescue with chlorambucil was initiated, but eventually disease progressed and the patient died 18 months after UCBT). Only 1 patient is alive after 27 months of follow-up, without evidence of disease and with full donor chimerism. Of the 8 PLL patients, 4 are alive (3 without relapse and with full donor chimerism, with a median follow-up of 13 months after transplantation; 1 patient had autologous reconstitution and relapsed 1 year after transplantation; no further treatment was offered). Four patients died (3 of NRM and 1 relapsed within 16 months of a second stem cell transplantation), with a median time to death of 3.8 months after UCBT.
Table 2
Outcomes in Univariate Analysis
Variable % P Value
Neutrophil engraftment at 60 d
sUCBT versus dUCBT 84% versus 86% .71
TNC 4.7 versus > 4.7 84% versus 78% .55
HLA MM 2 versus < 2 82% versus 86% .17
Low-dose TBI versus no TBI 84% versus 83% .11
Previous ASCT versus no ASCT 100% versus 82% .03
Grade II-IV acute GVHD at 100 d
HLA MM 2 versus < 2 47% versus 35% .47
sUCBT versus dUCBT 44% versus 38% .43
TNC 4.7 versus > 4.7 34% versus 48% .22
CR versus not in CR 24% versus 49% .08
Use of ATG versus no ATG 14% versus 45% .02
Chronic GVHD at 3 yr
HLA MM 2 versus < 2 24% versus 37% .74
CR versus not in CR 37% versus 33% .68
sUCBT versus dUCBT 41% versus 32% .45
Use of ATG versus no ATG 24% versus 41% .30
TNC 4.7 versus > 4.7 37% versus 27% .24
CMV-positive versus CMV-negative serostatus 50% versus 22% .05
NRM at 3 yr
TNC 4.7 versus > 4.7 34% versus 49% .19
sUCBT versus dUCBT 46% versus 38% .21
HCT-CI 2 versus > 2 36% versus 57% .07
Age 57 yr versus > 57 yr 26% versus 52% .07
CMV-positive versus CMV-negative serostatus 46% versus 27% .09
No. CTL before UCBT 2 versus > 2 18% versus 49% .02
Fludarabine-sensitive versus fludarabine-refractory disease
30% versus 61% .009
Low-dose TBI versus no TBI 34% versus 62% <.001
Relapse incidence at 3 yr
sUCBT versus dUCBT 9% versus 14% .24
CMV-positive versus CMV-negative serostatus 14% versus 13% .51
CR versus not in CR 17% versus 11% .23
Use of ATG versus no ATG 24% versus 10% .18
TNC 4.7 versus > 4.7 14% versus 13% .40
HLA MM 2 versus < 2 9% versus 16% .90
No. CTL before UCBT 2 versus > 2 15% versus 30% .70
Fludarabine-sensitive versusfludarabine-refractory disease 13% versus 45% .04 OS at 3 yr
Age 57 yr versus > 57 yr 64% versus 42% .07
sUCBT versus dUCBT 43% versus 55% .22
HLA MM 2 versus < 2 58% versus 42% .13
HCT-CI 2 versus > 2 58% versus 36% .07
CMV-positive versus CMV-negative serostatus 45% versus 70% .03
No. CTL before UCBT 2 versus > 2 59% versus 18% .01
Low-dose TBI versus no TBI 58% versus 35% <.001
DISCUSSION
This study aimed to analyze the impact of UCBT in CLL/SLL patients. Since the validation of double UCBT in 2005 by the Minnesota group, UCBT has been extended as an alternative stem cells source to different malignant and nonmalignant disorders in patients lacking suitable HLA donors[16,22-24]. Approximately 15% to 20% of patients lack HLA-identical siblings or HLA-compatible unrelated donors[25], and only a handful of cases evaluating alternative stem cell trans-plantation in CLL/SLL have been published so far. Bashey et al. reported 7 CLL/SLL patients who underwent haploidentical transplantation with 2-year OS ranging from 44% to 55%[26]. Dodero et al. also reported 5 cases of CLL/SLL receiving T celledepleted haploidentical transplantation[27]. Rodri-gues et al. reported 14 CLL/SLL patients who underwent transplantation using UCBT with encouraging results, even for patients not in complete remission[28]. More recently, the Eurocord-EBMT group reported comparable outcomes of UCBT and matched unrelated donors for mature lymphoid malignancies, including 22 CLL/SLL patients [29], and the
Chinese group reported outcomes of a large group of patients who underwent haploidentical T cellereplete transplantation [30]. Despite the increasing number of publications over the last years, stem cell transplantation using alternative donors such as UCBT in CLL/SLL is scarce in the literature.
This is thefirst study to date to directly evaluate outcomes and risk factors of UCBT for CLL/SLL. As expected in our study, most patients underwent transplantation with double UCBT, which historically, in adults, has been associated with higher PFS compared with single UCBT. However, recent data have suggested similar outcomes if a reasonable number of nucleated cells (>2.5 108total nucleated cells/kg) would have been used in single UCBT [31,32]. In our study, the majority of recipients received an adequate cell dose (>2.5) and we could notfind outcome differences, mainly because of the low number of patients receiving single UCBT.
Because of the small sample size, univariate analysis was used to identify risk factors associated with engraftment, GVHD, NRM, relapse, and OS. Although we expected lower engraftment rates in patients with advanced disease and, consequently, extensive marrow infiltration, rates of engraftment did not changed based on disease status or conditioning regimen, and engraftment rate in CLL/SLL was as previously reported for other hematological malignancies [16,33,34]. Of the 11 patients who did not engraft, only 2 patients had available HLA antibodies analysis, which were both negative. Since thefirst publication of the impact of donor-specific antibodies in UCBT in 2010, other publications have addressed the role of donor-specific antibodies in UCBT [35-37]. Most transplantation centers are performing anti-HLA antibodies before selecting the cord blood units, but this became common, especially after 2010, and in our series most patients received UCBT before 2010 (48 patients). Unfortunately, we did not have data on the presence of anti-HLA antibodies to be able to understand the incidence of graft failure in this series.
The use of low-dose TBI did not influence engraftment. Improved engraftment was observed in patients who had undergone previous ASCT, probably because of higher degree of immune suppression before allogeneic transplantation. This observation has been previously reported in UCBT[38]. Most ASCT were performed before 2009, when data on prospective studies analyzing the impact of ASCT in OS were not yet available.
Regarding acute and chronic GVHD, the incidences were quite high when compared with other hematological
Figure 1. (A) NRM according to fludarabine sensitivity (straight line represents fludarabine-refractory CLL/SLL and dotted line represents fludarabine-sensitive CLL/ SLL). (B) NRM according to the number of previous lines of chemotherapy (straight line represents patients who received3 lines of chemotherapy and dotted represents2 lines of chemotherapy before UCBT).
malignancies [28,33,39], which could be explained by the infrequent use of ATG, common use of double UCBT, and high-risk disease status at transplantation[40-42].
Used as an alternative stem cell source, umbilical cord blood has been indicated in patients usually in a very advanced/refractory stage of disease. In our study, approxi-mately two thirds of our patients underwent transplantation for poor-risk disease (del 17p/p53mutation, fludarabine-refractory disease, or diagnosis of PLL or RS), and higher tumor burden before RIC-UCBT has been associated with worst outcomes [43]. Importantly, the median age of our patients was 57 years, most of patients received 3 or more chemotherapy regimens before transplantation, and 15% of patients had an HCT-CI 3, reflecting this poor-risk popula-tion and the burden of comorbidities, which could, in part, explain the NRM reported. Higher comorbidity scores and type of conditioning regimen have long been associated with increased NRM and reduced PFS in CLL[14,44]. Myeloablative conditioning has been associated with increased NRM when compared with RIC transplantations [14,45]. Despite analyzing only patients undergoing RIC, an unexpectedly high rate of NRM was observed (39%). This could be also because of delayed engraftment and immune reconstitution and a higher risk of infection associated with UCBT[43,46,47-49].
We found 3 factors associated with improved PFS in multivariate analysis: use of low-dose TBI, lower HCT-CI scores, andfludarabine-sensitive disease at UCBT. Patients who received low-dose TBI had better PFS compared with patients who did not receive radiation, which was previously noticed by an analysis of the EBMT group [28]. Although, there has never been a prospective randomized comparison between TBI versus non-TBI regimens in the RIC setting, excellent long-term outcomes have been reported in patients who underwent a reduced-intensity TBI-based regimen in matched related donor or matched unrelated donor trans-plantation[12,50]. Low-dose TBI and low HCT-CI scores were
associated with superior PFS because of lower NRM; these variables did not influence relapse. On the other hand, fludarabine-sensitive disease was associated with lower NRM and lower relapse incidence.
Purine analogueeresistant disease had poor PFS (re-fractory CLL/SLL had a 3-year PFS of 21%) mainly because of the higher number of CTL and more advanced disease at UCBT, which could explain the higher associated NRM in this group of patients. Moreover, bacterial infections were the main cause of NRM and strategies to prevent it should be investigated in future studies on RIC-UCBT in CLL/SLL. Improvement in supportive therapy and infectious prophy-laxis are currently ongoing for those patients who are highly immunosuppressed [51]. Because of delayed engraftment and higher risk of graft failure in UCBT, strategies to improve engraftment are in the spotlight of many clinical trials. Ex vivo expansion of the cord blood unit is becoming an interestingfield of research in different countries, mainly in the United States. Different techniques of ex vivo expansion (Notch, CXCR4 cell pathway, or cytokines stimulations) are under research, but no preferable technique has come forth as the standard[52,53]. With earlier engraftment and higher engraftment rates, the incidences of bacterial and fungal infections are decreased.
Fludarabine-refractory disease was also associated with higher incidence of relapse. As NRM is a competitive risk for disease relapse and knowing that NRM was high in patients withfludarabine-refractory disease, the actual relapse rate in this group of patients is, indeed, underestimated (it is possible that patients with fludarabine-refractory disease who died of early NRM may have experienced relapse if they remained alive). Despite the poor-risk patient population in this study, relapse incidence was relatively low, which could be because of the GVL effect that can be active, even in high-risk cytogenetic categories. Analyzing only patients with available cytogenetics, no relapse outcome differences were
Figure 3. (A) Overall PFS from the entire cohort of patients. (B) PFS according to fludarabine sensitivity.
Table 3
Univariate and Multivariate Analysis for PFS at Three Years
Variable Univariate Analysis Multivariate Analysis
HCT-CI 2 versus > 2 51% versus 25%, P¼ .04 HR, .45 (95% confidence interval, .20-1.00); P ¼ .05 Low-dose TBI versus no TBI 49% versus 14%, P¼ .02 HR, .25 (95% confidence interval, .08-.78); P ¼ .017 Fludarabine-sensitive disease versusfludarabine-refractory disease 57% versus 21%, P¼ .001 HR, .32 (95% confidence interval, .16-.66); P ¼ .002 Age 57 yr versus > 57 yr 54% versus 34%, P¼ .17 HR, .68 (95% confidence interval, .35-1.33); P ¼ .26
observed from del 17p and non-17p patients. This observa-tion has been previously reported, thus reinforcing the GVL effect, even in high-risk cytogenetic patients[54]. The role of minimal residual disease (MRD) before transplantation in the setting of allo-HSCT for CLL has yet to be clearly defined. Because of different monitoring techniques and thresholds, multicenter studies are difficult, and no cut-off values have been accepted worldwide[55]. Few studies have addressed the role of MRD before transplantation in CLL, and these studies are limited with small sample cohorts[56]. Instead of MRD, a post-transplantation tool associated with relapse is chimerism status, which can influence post-transplantation MRD as rapid T cell engraftment is associated with lower MRD and relapse rate[57]. In our study, the CI of relapse in patients who achieved full donor chimerism before day 100 after UCBT was only 5%, whereas in patients with mixed chimerism before day 100, the incidence of relapse was 36%. The immunologic reaction of the graft against the leukemic cells has been reported to decrease incidence of relapse [58-61]. Even with the impossibility of donor lymphocyte infusion after UCBT, several studies reported a strong GVL effect using UCBT without an increased incidence of chronic GVHD[62,63]. Another risk factor that has an impact in the relapse rate in CLL is the presence of bulky disease before transplantation[58,64]. Unfortunately, the characteristic of size masses was not reported by the participating centers; therefore, we could not assess the impact of bulky disease in this study.
Different strategies to overcome the poor prognosis of refractory CLL have been tried and with the advent of new therapeutic options (Bcl-2 antagonists, Bruton’s kinase in-hibitors, new monoclonal antibodies) that are effective and with lower toxicity, even in chemo-resistant CLL/SLL, selec-tion of patients for allo-HSCT is becoming more difficult because of high NRM, even in RIC setting[2,11,65,66]. How-ever, longer follow-up is needed to evaluate long-term out-comes of these drugs and resistance to Bruton’s kinase inhibitors has already been reported[67]. Still, better long-term disease control after allo-HSCT may lead to better overall results long term. Although no potential cure has been described with novel therapy tools, pretransplantation cytoreduction could have an impact on post-transplantation outcomes and maintenance strategies after transplantation could be of a great value in reducing relapse rate, at least until the GVL effect exerts its immunologic reaction on leukemic cells.
One could argue that our series of patients is biased as many studies have described a higher frequency of fludarabine-refractory disease before HSCT (this is 1 of the main indications for allogeneic stem cell transplantation in CLL) [8]. In fact, in our series, only 19 patients had fludarabine-refractory disease, but of the 48 patients without fludarabine-resistant disease, 3 had diagnosis of Richter transformation, 8 had PLL, 12 had del 17 p, and 3 had del 11 q, which are high-risk features of disease.
Although there are intrinsic limitations of interpreting the results of a small sampleesized study, this retrospective multicenter analysis shows favorable PFS in this poor-risk CLL/SLL population. Overall, outcomes after UCBT seem to approach those of identical HLA-matched transplantation [14,15,64,68]. Despite the small number of patients, the good results support the use of low-dose TBI (mainly cyclophos-phamide,fludarabine, and TBI) as a RIC regimen in UCBT. This approach has previously been associated with good out-comes[69,70]. In conclusion, RIC-UCBT using low-dose TBI
appears to be a valid option of allo-HSCT for CLL/SLL patients lacking an HLA-matched donor. Strategies to enhance engraftment, optimization of infection prophylaxis, and trials comparing different conditioning approaches are need to improve future outcomes.
ACKNOWLEDGMENTS
The authors thank the following physicians for contrib-uting to this study: Anne Corby, Angers University Hospital, Angers, France; Anna Huynh, Purpan Hospital, Toulouse, France; Marta Sonia Gonzalez Perez, Hospital Clinico Uni-versitario, Santiago de Compostela, Spain; Jan Yves Cahn A. Michallon Hospital, Grenoble, France; Mohamad Mohty, Saint-Antoine Hospital, Paris, France; Mauricette Michallet, Edouard Herriot Hospital, Lyon, France; Jean Henri Bourhis, Institut Gustave Roussy, Villejuif, France; Thierry de Revel, Percy Hospital, Clamart, France; Christian Berthou, Morvan Hospital, Brest, France; Patrice Ceballos, Lapeyronie Hospital, Montpellier, France; Pascale Turlure, CHU Dupuytren, Limoges, France; Irene Donnini, Ospedale di Careggi, Firenze, Italy; Simona Sica, Universita Cattolica S. Cuore, Rome, Italy. They also thank all European Group for Blood and Marrow Transplantation (EBMT) centers and national registries for contributing patients to the study and data managers for their work. A special thanks to Chantal Kenzey and Fernanda Volt for helping in the development of this paper.
Financial disclosure statement: The authors have no financial disclosures to declare.
Conflict of interest statement: There are no conflicts of in-terest to report.
Authorship statement: V.R. and A.R. designed the study. E.X. and J.C. collected data. E.X. and A.R. performed statistical analysis. E.X, V.R., A.R., E.G., M.V.G., J.S., and N. K. wrote the article. P.C., J.J.C., N.S.A., N.M., S.N., D.B., E.D., H.V, N.M., and R.P.L. contributed patient information. All authors edited and approved manuscript. J.S and V.R. share the last authorship. REFERENCES
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