Introduction

Relapse after allogeneic hematopoietic cell transplantation (HCT) portends a poor prognosis.^{1, 2} Therapeutic options include withdrawal of immunosuppression, colony-stimulating factors, immunotherapy with -interferon, donor lymphocyte infusion (DLI), and chemotherapy with or without second HCT. The optimal strategy for post-HCT relapse, particularly in acute leukemia, remains poorly defined. Second HCT is the best-studied intervention, resulting in prolonged disease-free survival in a minority of patients, but is typically associated with high treatment-related mortality (TRM).^{3, 4, 5} Longer remission duration after first HCT, lower disease burden at second HCT⁶ and achievement of complete remission prior to second HCT⁷ are associated with improved outcomes. The magnitude of benefit provided by second HCT remains undefined since only a fraction of those relapsing after an initial HCT undergo a second HCT.

Reduced intensity conditioning (RIC) regimens have become more common, partly because they are associated with decreased acute toxicity, which may permit allografting in older and sicker patients.^{8, 9, 10} We hypothesized that patients relapsing after RIC might be more likely to receive and tolerate salvage therapy.

Here we report the treatment course, outcomes and prognostic factors for survival in a cohort of patients with acute myelogenous leukemia (AML) or myelodysplastic syndrome (MDS) who relapsed after RIC transplantation.

Materials and methods

Between February 2002 and October 2005, 70 consecutive patients with high-risk AML or MDS were enrolled in a prospective trial using a reduced intensity in vivo T-cell depleted transplantation.¹¹ The University of Chicago Institutional Review Board approved the protocol and all patients provided written informed consent. Twenty-five patients developed relapse or progression of disease and were included in this analysis.

Treatment regimen and supportive care for initial HCT

Details regarding the conditioning regimen and supportive care have previously been published.¹¹ Briefly, conditioning consisted of fludarabine 30 mg/m²/day intravenous (150 mg/m² total) and alemtuzumab 20 mg/day intravenous (100 mg total) for 5 consecutive days (day -7 through day -3), followed by melphalan 140 mg/m² intravenous on day -2. Post transplantation immunosuppression consisted of tacrolimus from day -2 until day 100, targeting a trough level of 5–15 ng/ml. A 2-week tapering period began after day 100 unless patients had developed significant GVHD. Neither post transplantation therapy nor DLI was administered, except in cases of relapse.

Donors

Recipients and donors were typed for HLA-A, HLA-B, HLA-C and HLA-DRB1. Related or unrelated donors with no more than one antigen or allelic mismatch were used. G-CSF mobilized peripheral blood stem cells were preferred, although bone marrow harvests were accepted at the preference of the donor or collection center. Because of ready availability of donor cells, second HCT was always performed with the same donor used for the first transplantation.

Definition of relapse

Relapse was defined as morphological evidence of disease recurrence or progression. Detection of minimal residual disease by flow cytometry or falling donor chimerism did not constitute evidence of recurrence in the absence of morphological abnormalities.

Chimerism

Unsorted bone marrow chimerism was assessed at relapse using a PCR-based variable number of tandem repeats method. Occasionally for sex-mismatched donor/recipient pairs, fluorescence in situ hybridization for X and Y chromosomes was used.^{12, 13} No lineage-specific engraftment analysis (e.g. T-cell chimerism) was available.

Cytogenetics

Cytogenetic analysis was performed from the bone marrow and occasionally peripheral blood using a trypsin-Giesma banding technique on at least 20 metaphase cells. To determine karyotypic evolution, we compared baseline karyotype with the karyotype at relapse. Baseline karyotype was defined as the most complex karyotype at any time between diagnosis and initial HCT.

Treatment after relapse following initial HCT

The patient and treating physician determined the treatment course at relapse or progression after initial HCT. All patients receiving immunosuppression at relapse had it withdrawn. Additional therapies were categorized as: DLI (at a dose of 2 10⁷ CD3 cells/kg), chemotherapy with or without biological agents, and/or second HCT.

Response after salvage therapy

A complete response (CR) required having less than 5% blasts in the bone marrow, less than 1% blasts in the peripheral blood and an absolute neutrophil count >1000 cells/l. It did not require platelet recovery above 100 000/l.

Statistical analysis

Survival analysis after relapse from initial HCT used the day of relapse or progression as day 0. Overall survival (OS) probabilities were estimated using the method of Kaplan and Meier. Cox proportional hazard models were used to estimate hazard ratios with 95% confidence interval and P-values for prognostic factors. A Cox model adding a time-varying covariate to remove the bias of elapsed time prior to further therapy was used to estimate the benefit of treatment at relapse. TRM was defined as any death which occurred in the absence of progression or relapse. The censor date was 15 June 2006. Statistical analysis was carried out using Stata Version 9.2.¹⁴

Results

Study characteristics

Table 1 summarizes baseline characteristics before initial HCT and at the time of relapse. Among the 70 patients, 25 (36%) relapsed or progressed. Most relapses occurred early, with a median duration from initial HCT to relapse of only 120 days (range 28–434). Twenty-one (84%) had active disease at the time of initial HCT. Seventeen out of 25 (68%) achieved or maintained a CR after initial HCT and subsequently relapsed, while 8/25 (32%) never achieved a CR after initial HCT. Twenty-one of the 25 relapsing patients had AML, three had MDS and one had mast cell leukemia. Median age was 52 years (range 20–67). Median bone marrow blast count at relapse was 24% (range 0–99%) and median unsorted donor chimerism at relapse was 73% (range 0–99%). There was no significant correlation between the blast percentage and the percentage of donor chimerism at relapse (R=0.14, P=0.57).

Table 1 - Patient characteristics.

Full table

Cytogenetic patterns at relapse

Twenty patients had cytogenetic data at baseline and at relapse. Three cytogenetic patterns emerged. In four patients (Table 2; Group A) an abnormal karyotype prior to initial HCT reverted to normal at relapse. Of note, one patient had a loss of Y chromosome in 30% of cells at the time of relapse, likely attributable to the normal loss of Y chromosomes in older men, rather than a new clonal abnormality.¹⁵ In eight patients (Table 2; Group B) the karyotype did not change; again, the loss of Y chromosome in one patient both at baseline and at relapse was not considered to be a clonal abnormality; the 45,X,-Y clone was also observed in a pre-HCT remission sample. In 8/20 (40%) (Table 2; Group C), karyotypic evolution occurred.

Table 2 - Cytogenetics at diagnosis and at relapse.

Full table

Salvage therapy for relapse after initial HCT

Figure 1 depicts salvage therapies after relapse following initial HCT. All patients receiving immunosuppression had it withdrawn initially, without any responses. Table 3 lists specific treatment regimens and responses for each individual. Aside from withdrawal of immunosuppression, three received no further intervention. Patients 7 and 18 were deemed unlikely to benefit from further treatment, and patient 13 opted to not be treated. All died of disease progression, 126, 29 and 37 days after relapse, respectively. Patient 25 received only G-CSF for disease control¹⁶ and failed to respond. Subsequent treatment was limited to intermittent steroids for an idiopathic thrombocytopenic purpura (ITP)-like syndrome. He remains alive with adequate blood counts, a dysplastic marrow and less than 5% bone marrow blasts 397 days after relapse, despite having less than 10% residual donor hematopoiesis.

Figure 1.

Treatment strategy and outcomes.

Full figure and legend (78K)

Table 3 - Treatment and outcome.

Full table

Chemotherapy and biological agents

Fourteen patients received chemotherapy as their initial salvage treatment; regimens varied and are shown in Table 3. In four of these 14 patients, salvage chemotherapy was administered as induction, followed within 2 weeks by conditioning for a second HCT, preventing formal response evaluations. Among the remaining 10 patients evaluable for responses, the three who received high-dose cytarabine combinations, obtained a CR and converted to 100% donor cells. One patient (patient 3) eventually died of TRM while in CR, whereas the other two were consolidated with a second HCT (patients 10 and 15). Among the 10 evaluable patients receiving induction, seven did not respond. An additional patient (patient 22) only received chemotherapy after disease progression developed following the initial salvage therapy employing DLI. The high-dose cytarabine regimen resulted in a CR that has persisted for 196 days and led to 95% donor chimerism.

Second HCT

Thirteen patients underwent second HCT, typically using alemtuzumab-based GVHD-prophylaxis; as stated above, eight patients first received induction chemotherapy. After second HCT, two patients maintained CR, eight achieved a CR and three failed to respond. Two patients died of complications and nine died of disease progression. Two patients (patients 9 and 14) remain alive in remission 939 and 504 days after second HCT, respectively.

Donor lymphocyte infusion

Three patients received DLIs. Patient 2 achieved a durable CR lasting more than 3 years, but has extensive chronic GVHD of the skin. Patient 22 developed GVHD and failed to respond, but subsequently achieved a durable CR after chemotherapy. Patient 8 received a DLI upon relapse after second HCT but failed to respond.

Survival

Five out of 25 patients remain alive with a median follow-up of 25.7 months (range 12.9–38.4 months) (Figure 2). Four of the five are in remission; two after transplantation, one after DLI and one after a chemotherapy-induced remission. The median OS was 6 months (95% confidence interval=2.7–9.9 months). Twenty patients died, either of disease progression (n=17) or of TRM (n=3).

Figure 2.

Overall survival.

Full figure and legend (46K)

In an unadjusted analysis, the receipt of cellular therapy (DLI and/or second HCT) appeared to result in a benefit in OS (hazard ratio=0.28; 95% confidence interval=0.11–0.71; P=0.008). However, after adjustment for the time elapsed prior to the cellular therapy no survival benefit was found (hazard ratio=0.88; 95% confidence interval=0.30–2.56; P=0.82).

Prognostic factors: univariate survival analysis

At relapse, older age, a higher percentage of bone marrow blasts, shorter time to relapse, a lower percentage of donor chimerism and the presence of a new cytogenetic abnormality all showed trends toward decreased survival. However, none of these associations reached statistical significance, possibly due to the small number of patients in the study.

Discussion

We describe the management and prognosis of patients who relapsed after allogeneic transplantation after conditioning with fludarabine, melphalan and alemtuzumab. This conditioning regimen has been used with excellent success rates by several groups.^{11, 17} Almost all relapsing patients received salvage therapy for relapse, but DLI alone was rarely used, because of its limited activity in AML and MDS. Over half of the patients underwent second HCT; many achieved or maintained a CR, and only two of them died of TRM after second HCT. The excellent tolerance to reinduction and particularly the low TRM rate for second transplant compare favorably to reported results for second HCT despite the short median time from first HCT to relapse and the relatively older recipient age.^{18, 19, 20, 21} For example, in a study by Radich et al.²⁰ of myeloablative conditioning for allogeneic HCT after relapse following autologous transplantation, approximately 70% of adult patients died of complications. Several factors may have contributed to the improved tolerance to salvage therapy in our series. These include the relative lack of toxicity and low incidence of GVHD after prior conditioning with fludarabine, melphalan and alemtuzumab,²² allowing patients who recur after this conditioning regimen to better tolerate further treatments. In addition, the majority of patients undergoing second HCT received another RIC regimen that may have enhanced tolerance relative to a myeloablative regimen. Lastly, advances in supportive care may improve tolerance to therapy and obviate historical results.²³

The overall CR rate of 61% (13/21) in this series is highly encouraging, especially since almost all patients, rather than a select subset, underwent treatment. The median survival of 6 months, reasonable CR rate, low TRM and the observation that four patients achieved persistent disease-free survival indicate that for many of these patients, further treatment provided meaningful benefit. However, 17 out of 25 patients (68%) ultimately died of disease progression, a finding consistent with outcomes for relapse after myeloablative regimens^{1, 3, 24} or other studies of relapse after RIC regimens.^{19, 25}

In contrast to prior studies, we did not find a strong association between remission duration after initial HCT and OS after relapse.^{3, 6, 7, 25} The small sample size precludes a precise determination of the prognostic value of this and other factors.

Considerable donor chimerism was detected at relapse (median 73%, range 0–99%), indicating persistent donor hematopoiesis. We hypothesize that persistent donor chimerism may favorably impact upon the effects of salvage chemotherapy. For example, patient 22 did not undergo second HCT because of GVHD from a prior ineffective DLI. The patient obtained reversal to full donor chimerism after one course of high-dose cytarabine with a durable remission, in contrast to the short remission that resulted from high-dose cytarabine given prior to the first HCT.

Karyotypic abnormalities at relapse after HCT have been rarely reported. Frassoni et al.,² in a study of acute leukemia, found that 10 out of 117 patients developed a new karyotypic abnormality at relapse. We found new karyotypic abnormalities at relapse in 8 of 20 evaluable subjects. Interestingly, four patients also had a reversal to normal karyotype at relapse, suggesting that certain highly proliferative clones might be preferentially eradicated by allogeneic transplantation. Larger studies are necessary to determine whether a specific cytogenetic pattern at relapse compared to baseline holds prognostic value.

In conclusion, the median survival in AML and MDS patients who relapsed after allogeneic HCT using a RIC preparative regimen was 6 months. The high CR rate and relatively low TRM despite aggressive interventions in almost all patients suggest that therapy for AML and MDS relapsing after HCT is beneficial in many patients. Optimal management remains to be defined, but chemotherapy-based treatment or T cell-depleted transplantation can occasionally induce durable remissions without overt GVHD. Residual donor chimerism was usually present at the time of disease progression. Clonal evolution was common, although a minority had reversal to a normal karyotype. Future studies testing interventional strategies are both feasible and warranted.

References

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