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Blood, Vol. 95 No. 11 (June 1), 2000:
pp. 3323-3327
CLINICAL OBSERVATIONS, INTERVENTIONS, AND THERAPEUTIC TRIALS
From the International Bone Marrow Transplant Registry, Health
Policy Institute, Medical College of Wisconsin, Milwaukee, WI;
Hematology Branch, National Heart, Lung and Blood Institute, National
Institutes of Health, Bethesda, MD; Department of
Transplantation Surgery, Huddinge University Hospital, Huddinge,
Sweden; Department of Hematology/Oncology, University of California,
San Diego, CA; Service d'Hematologie, Hôpital Minjoz, France;
Department of Pediatrics, Georgetown University Medical Center,
Washington, DC; Center for Advanced Studies in Leukemia, Los Angeles,
CA; Department of Hematology, Kantonsspital, Basel, Switzerland;
University of Pavia, Pavia, Italy; Servicio de Hematologia Clinica,
Hospital de Sant Pau, Barcelona, Spain; Department of Pediatrics,
University of British Columbia, Vancouver, BC, Canada; and Cell and
Gene Therapy Unit, Etablissement de Transfusion Sanguine de
Franche-Comte, Bescancon, France. A complete list of the members of
the GVHD/GVL Working Committee of the International Bone Marrow
Transplant Registry appears at the end of this article.
The impact of cell dose (number of nucleated donor cells per
kilogram recipient weight) on transplantation outcome is controversial and may differ for allogeneic and identical twin (syngeneic) bone marrow transplants. We studied the association between cell dose and
outcome in 100 unmanipulated identical twin bone marrow
transplantations for leukemia, reported to the International Bone
Marrow Transplant Registry between 1985 and 1994, using Cox
proportional hazards regression for multivariate analyses. Cell doses
ranged from 0.3 to 7.4 × 108 nucleated cells/kg
(median, 3.0 × 108cells/kg). Median follow-up was 75 months. Five-year cumulative incidences of transplant-related mortality
with high (more than 3 × 108 cells/kg) versus low (less
than or equal to 3 × 108 cells/kg) cell doses were
2% (95% confidence interval [CI], 0% to 8%) versus 10%
(95% CI, 4% to 20%), respectively. Five-year probabilities of
leukemia-free survival were 53% (95% CI, 39% to 67%) and 37% (95%
CI, 23% to 52%), respectively. In multivariate analysis, among
patients surviving in remission at least 9 months after
transplantation, those receiving high cell doses were at significantly
lower risk for treatment failure (relapse or death) than those
receiving low cell doses (RR, 0.27; 95% CI, 0.12 to 0.6;
P = .001). Lower treatment failure resulted from fewer
relapses in the high cell dose group (RR for relapse, 0.28; 95% CI,
1.2 to 0.66; P = .003). These findings suggest that
outcomes after syngeneic bone marrow transplantation could be improved
by transplanting more than 3 × 108 nucleated cells per
kilogram. The benefit of high cell dose on relapse may represent a
delayed graft-versus-leukemia effect.
(Blood. 2000;95:3323-3327)
Bone marrow transplantations for leukemia using
identical twin donors have low transplant-related mortality rates and
negligible graft-versus-host disease (GVHD) but higher risks for
leukemia relapse than allografts.1,2 Factors determining
outcome after identical twin bone marrow transplantation may differ
significantly from those determining allograft outcome because there
are no allogeneic effects. They may also differ from autotransplants because the graft was not previously exposed to cytotoxic agents and is
not at risk for leukemia contamination. In related3-5 and
unrelated6 donor allogeneic bone marrow transplantation, low nucleated graft cell doses are associated with higher
transplant-related mortality rates, with variable impacts on incidence
and severity of acute GVHD. Because proportions of cell types in grafts
vary, it is not possible to determine whether lymphocytes, stem cells, or both are responsible for these cell dose effects.7,8
However, in a study of T-cell-depleted allografts, low CD34+ cell
doses (less than 106/kg) resulted in higher early
transplant-related deaths.3
In syngeneic bone marrow transplantation, cell dose is one of the few
variables (other than the preparative regimen) that can be controlled.
It is therefore important to determine its impact on transplantation
outcome. We studied this effect in 100 syngeneic transplantations
reported to the International Bone Marrow Transplant Registry (IBMTR).
Patient selection
Outcomes
International Bone Marrow Transplant Registry The IBMTR is a voluntary working group of more than 350 transplant teams worldwide who contribute detailed data on their allogeneic and syngeneic blood and bone marrow transplantations to the Statistical Center at the Medical College of Wisconsin. Participants are required to report all consecutive transplantations; compliance is monitored by on-site audits. Approximately 60% of all active transplant centers report their data to the IBMTR. The IBMTR database includes 40% to 45% of all recipients of allogeneic and syngeneic transplants since 1970. Patients are followed up longitudinally. Computerized error checks, physician review of submitted data, and on-site audits of participating centers ensure data quality.Statistical methods Using treatment failure as the outcome, we first examined cut points of cell dose ranging from 2.5 to 3.5 × 108 nucleated cells/kg to determine the value that best discriminated between high and low cell doses. Cell dose was subsequently treated as a dichotomous variable in all analyses greater
than versus equal to or less than the cut point. Characteristics of
patients receiving high versus low nucleated cell doses were compared
using the chi-square statistic and the Wilcoxon rank sum
test for categorical and continuous variables,
respectively. Cumulative incidence rates of transplant-related
mortality, leukemia relapse, and Kaplan-Meier estimates of LFS were
compared using the log-rank test.9 Cox proportional hazards
regression was used to examine the effect of cell dose on
transplant-related mortality rate, relapse rate, and treatment failure
in multivariate analyses adjusting for other significant
covariates.10 Because cell dose was the main variable of
interest, all models contained the dichotomous cell dose covariate (high versus low). Other factors considered in multivariate model building were disease type (AML versus ALL versus CML); disease stage
(advanced [refractory or relapsed acute leukemia, blastic-phase CML]
versus intermediate [acute leukemia in second or higher remission, accelerated-phase CML] versus early [acute leukemia in first
remission, chronic-phase CML]); recipient and donor sex (female versus
male); year of transplantation (1989-1994 versus 1985-1988);
conditioning regimen (CyTBI versus BuCy); white blood cell (WBC) count
at diagnosis (greater than or equal to 25 versus less than
25 × 109/L); Karnofsky score (greater than or equal
to 90% versus less than or equal to 80%) and age at transplant (older
than 25 versus 25 years or younger). The assumption of proportional
hazards over time was tested for all explanatory covariates using a
time-dependent covariate. The tests indicated that high versus low cell
dose (more than 3.0 versus less than or equal to
3.0 × 108 nucleated cells/kg) had a
time-varying effect on relapse and treatment failure. Various cut
points were tested for the early versus late effect; the cut point
giving the greatest discrimination between early and late effects was
selected for regression analysis. At the optimum cut points,
proportionality assumptions were again tested to validate
proportionality between the high and low cell dose groups. A forward
stepwise model was used to identify the factors significantly
associated with outcomes. Within each model one additional significant
factor was added at each step, and the remaining factors were
reexamined. When all covariates significant at P = .05 were
entered, model building was stopped. First-order interactions between
each significant covariate and the main effect of cell dose were also
examined. Adjusted probabilities of LFS were generated from the final
Cox model stratified on cell dose and weighted averages of covariates
using the sample proportion as the weight function. Adjusted
probabilities represent predicted outcomes for similar groups of
patients receiving each treatment.
Patient characteristics and overall outcome Patient characteristics are shown in Table 1. In the higher cell dose group, there was a significantly greater number of transplants between female twins (P = .01) and a trend toward more advanced disease (P = .07). Body weights were somewhat lower in the high cell dose group (59 vs 67 kg; P = .05). Otherwise the 2 groups were similar.
Comparison of high and low cell doses Hematologic recovery. There was a nonsignificant trend toward slower recovery of neutrophils (P = .32) and platelets (P = .15) in the low cell dose group (Table 1). GVHD. A clinical syndrome consistent with acute GVHD developed in 10 patients. The median onset was 16 days (range, 7-31 days) after transplantation. In 7 patients (biopsy taken in 5), GVHD affected only skin, and its severity was stage I or II. All patients received topical or systemic steroids, and GVHD resolved in a median of 16 days (range, 10 to 45 days). Three patients had clinical features (no biopsies) of more extensive GVHD that affected skin, gut, and liver (overall grades II, II, and III). After treatment with systemic steroids with or without other agents, GVHD resolved in 1 patient after 25 days; in 2 patients it progressed to limited chronic GVHD. Median nucleated cell dose in these 10 patients was 3.3 (range, 1.1 to 4.7) × 108/kg; 4 patients received fewer than 3 × 108 nucleated cells/kg. De novo chronic GVHD did not develop in any patient. Transplant-related mortality.
Five-year cumulative incidence rates of transplant-related mortality
with high versus low cell doses were 2% (0% to 8%) versus 10% (3%
to 20%), respectively (univariate log rank test, P = .04) (Figure 1). In multivariate analysis, the
relative risk of transplant-related mortality with high versus low cell
doses was 0.16 (95% CI, 0.02 to 1.29; P = .08) (Table
2). The only other factor significantly associated with transplant-related mortality in multivariate analysis was advanced disease versus early or intermediate stage disease (RR,
5.97; 95% CI, 1.14 to 31.31; P = .03). Table
3 compares treatment-related mortality
rates in high and low cell dose groups according to disease and
treatment characteristics. Treatment-related mortality rates were
higher in the low cell dose group in all categories.
Relapse.
Five-year cumulative incidence rates of relapse with high
versus low cell doses were 45% (31% to 59%) versus 53% (38% to
67%), respectively (P = .19) (Figure
2). In multivariate analysis, cell dose had
a time-varying effect on relapse (Table 2). The maximum likelihood
method indicated that the relative hazard for relapse changed at
approximately 9 months after transplantation. In the first 9 months
after transplantation, the risk for relapse was similar in the high and
low cell dose groups. Among patients surviving in remission 9 months
after transplantation, the relative risk for subsequent relapse in the
high versus low cell dose groups was 0.28 (95% CI, 0.12 to 0.66;
P = .003). Other factors associated with increased relapse
risk were advanced disease, high WBC count at diagnosis, and use of
BuCY rather than CyTBI for pretransplant conditioning. Table 3 compares
relapse in high and low cell dose groups according to disease and
treatment characteristics. For all subcategories, patients receiving
low cell doses had higher relapse frequencies than those receiving high
cell doses, except for patients with advanced disease. However, only 4 patients with advanced disease received low cell doses, and 2 of them
died of treatment-related causes.
Treatment failure.
Cell dose also had a time-varying effect on treatment failure
(relapse or death) in multivariate analysis (Table 2). In the first 9 months after transplantation, the risk for treatment failure was
similar in the high and low cell dose groups. Among patients surviving
in remission 9 months after transplantation, the relative risk for
subsequent treatment failure in the high versus low cell dose groups
was 0.27 (95% CI, 0.12 to 0.6; P < .01). Other factors associated with higher risks for treatment failure were advanced disease, high WBC count at diagnosis, BuCY rather than CyTBI for pretransplant conditioning, and Karnofsky score less than 90% before
transplantation. These significant factors were considered in
calculating adjusted probabilities of LFS. Such adjusted probabilities represent predicted probabilities of LFS for similar groups of patients
receiving high or low cell doses. After adjusting for these prognostic
factors, 5-year probabilities of LFS were 55% (43% to 67%) and 36%
(24% to 49%) for the high versus low cell dose groups, respectively
(P = .05) (Figure 3). There were
no significant interactions between other prognostic variables and the
cell dose effect. The lower risk for treatment failure with higher cell
doses was significant for the following subgroups: early and
intermediate or advanced leukemia; age older than 25 years; male or
female sex; presenting WBC count more than or less than
25 × 109/L; and BuCY or CyTBI conditioning
regimens.
In this series of patients receiving identical twin bone
marrow transplants for leukemia, we found almost a log variation in
nucleated bone marrow cell doses given. High-nucleated cell doses were
associated with significantly lower late relapse rates and superior
LFS. A statistically nonsignificant reduction in transplant-related
mortality might also have contributed to the higher LFS.
Other authors, members of the GVHD/GVL Working Committee of
the International Bone Marrow Transplant Registry, are as follows:
Jennifer Bird, Southmead Hospital, University of Bristol, Bristol, UK;
Gerald J. Elfenbein, University of South Florida, Tampa, FL; Joseph W. Fay, Baylor University Medical Center, Dallas, TX; P. Jean
Henslee-Downey, Richland Memorial Hospital, University of South
Carolina, Columbia, SC; Mary M. Horowitz, International Bone Marrow
Transplant Registry, Health Policy Institute, Medical College of
Wisconsin, Milwaukee, WI; Mark R. Litzow, Mayo Clinic, Rochester,
MN; Philip L. McCarthy, Roswell Park Cancer Institute, Buffalo, NY;
Hakumei Oh, INOUE Memorial Hospital, Chiba, Japan; Anibal J. Robinson,
Navy Hospital Pedro Mallo, Buenos Aires, Argentina; James A. Russell,
Tom Baker Cancer Centre, Calgary, Alberta, Canada; and Gérard
Socié, Hôpital Saint Louis, Paris, France.
Submitted September 13, 1999; accepted January 27, 2000.
Supported by Public Health Service grants P01-CA40053 and
U24-CA76518 from the National Cancer Institute, the National Institute of Allergy and Infectious Diseases, and the National Heart, Lung and
Blood Institute of the U.S. Department of Health and Human Services;
and by grants from Alpha Therapeutic Corp; Amgen, Inc; Anonymous;
Baxter Fenwal; Berlex Laboratories; BioWhittaker, Inc; Blue Cross and
Blue Shield Association; Lynde and Harry Bradley Foundation;
Bristol-Myers Squibb Co; Cell Therapeutics, Inc; Centeon; Center for
Advanced Studies in Leukemia; Chimeric Therapies, Inc; Chiron
Therapeutics; Charles E. Culpeper Foundation; Eleanor Naylor Dana
Charitable Trust; Eppley Foundation for Research; Genentech, Inc; Human
Genome Sciences; Immunex Corporation; The Kettering Family Foundation;
Kirin Brewery Co; Robert J. Kleberg, Jr and Helen C. Kleberg
Foundation; Herbert H. Kohl Charities, Inc; Nada and Herbert P. Mahler
Charities; Milstein Family Foundation; Milwaukee Foundation/Elsa
Schoeneich Research Fund; NeXstar Pharmaceuticals, Inc; Samuel Roberts
Noble Foundation; Novartis Pharmaceuticals; Orphan Medical; Ortho
Biotech, Inc; John Oster Family Foundation; Jane and Lloyd Pettit
Foundation; Alirio Pfiffer Bone Marrow Transplant Support Association;
Pfizer, Inc; RGK Foundation; Roche Laboratories; Rockwell Automation
Allen Bradley Co; SangStat Medical Corp; Schering AG; Schering-Plough
Oncology; Searle; SEQUUS Pharmaceuticals; SmithKline Beecham
Pharmaceutical; Stackner Family Foundation; Starr Foundation; Joan and
Jack Stein Foundation; SyStemix; United Resource Networks; and
Wyeth-Ayerst Laboratories.
Reprints: Mary M. Horowitz, International Bone Marrow
Transplant Registry, Medical College of Wisconsin, 8701 Watertown Plank
Rd, Milwaukee, WI 53226; e-mail: marymh{at}mcw.edu.
The publication costs of this
article were defrayed in part by
page charge payment. Therefore,
and solely to indicate this fact,
this article is hereby marked
"advertisement"
in accordance with 18 U.S.C.
section 1734.
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