Safety of pre-emptive donor lymphocyte infusions (DLI) based on mixed chimerism (MC) in peripheral blood or bone marrow subsets in children undergoing hematopoietic stem cell transplant (HSCT) for hematologic malignancies

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Approximately 30–40% of children with acute leukemia relapse after hematopoietic stem cell transplant (HSCT).1 These patients often succumb to disease progression. Infusion of donor lymphocytes (DLI) is a mode of immunotherapy (IT) effective in patients with CML2 and low disease burden.3 However, efficacy of DLI is limited in pediatric acute leukemia. Fewer than 20–30% of patients with relapsed acute leukemia following HSCT achieve remission after DLI.4

Persistent mixed chimerism (MC) is a known predictor of relapse potential. It implies a state of donor tolerance to host Ags.1 Pre-emptive immunotherapy (IT) with fast withdrawal of immunosuppression (FWI) and/or DLI based on MC are strategies to mitigate risk of leukemia relapse. However, it also increases the incidence of GvHD.5, 6, 7 In GvHD, donor T cells mediate an immunogenic response against host cells, causing significant organ damage with consequent host morbidity and mortality.

We describe a cohort of pediatric patients with acute leukemia receiving chimerism-based pre-emptive IT, including DLI after unmodified peripheral blood (PB) or bone marrow (BM) HSCT. Our center implements an aggressive mode of pre-emptive DLI administration, defined by DLI given in light of negative disease based on detection of 1% or more host chimerism in unfractionated (whole) peripheral blood (PB) or any of the PB or BM subsets. This contrasts conventional administration of DLI based on detection of MC in whole PB.5, 6, 7 In this report, we evaluate the safety of our aggressive DLI approach looking at incidence of GvHD and event-free survival.

Presented patients belonged to a larger cohort of patients with hematologic malignancies receiving unmodified PB or BM transplants between 2005 and 2015 at UCSF Benioff Children’s Hospital. These patients were treated using chimerism-based IT, consisting of FWI or FWI+DLI. Chimerism was measured using semi-quantitative PCR of short tandem repeats in whole PB, BM and cellular subsets (CD3+, CD14/15+, CD19+ from PB/BM; CD33+, CD34+ from BM). MC requiring DLI intervention was defined as 1% of donor cells in any of the tested PB or BM subsets identified after withdrawal of all immunosuppression, as previously described.8, 9 If the purity of the tested subset was <85%, repeat testing was done and DLI initiated, if MC persisted on at least two tests. The starting DLI dose was 1 × 105 CD3+ cells/kg for unrelated/one-Ag-mismatched related donor transplants and 1 × 106 CD3+ cells/kg in matched related transplants. Subsequent doses were increased by 2–5-fold and continued until achieving either 100% donor chimerism in subsets or development of GvHD. In patients requiring multiple administrations, DLI was given with a median interval of 42 days (range 15–144). DLI was withheld in patients with active infection and those with a history of GVHD requiring systemic therapy. DLI were derived from frozen BM, GCSF-mobilized HSCT product or newly collected unmobilized PB.

We present a detailed analysis of 35 patients with acute leukemia who received pre-emptive DLI. Sixteen (46%) patients in current series were presented in our previous publications, which did not include GvHD analysis or long-term follow-up.8, 9 All patients/legal guardians were consented for HSCT and IT. UCSF Committee on Human Research approved our retrospective review.

The data were analyzed using statistical software SPSS v23 (IBM Corp. Armonk, NY, USA). We used descriptive statistics, two-tailed Fisher’s Exact test for categorical variables and Mann–Whitney U test for comparison of medians between groups with similarly shaped distributions. Probability of event-free survival (EFS) was estimated by Kaplan–Meier and log-rank test. Significance was set at P=0.05.

Thirty-eight patients treated between 2005 and 2015 had persistent MC following FWI and 35 received pre-emptive DLI. Three patients had relapse at time of DLI and were excluded from this analysis of pre-emptive DLI. Characteristics of the 35 patients who received pre-emptive DLI and DLI details are described in Table 1. The median follow-up of living patients is 41 months (range 9.7–129 months).

Table 1 Patient characteristics and DLI description

Eight of 35 (22%) patients developed either acute GvHD (n=1), chronic GvHD (n=5) or mixed acute and chronic GvHD (n=2) after DLI. Median time from last DLI dose to newly diagnosed GvHD (acute and/or chronic) was 64 days (range 30–84). Grades of aGvHD were 2 (n=1) and 3 (n=2). cGvHD was moderate grade in five patients and severe in two patients. GvHD resolved in two patients, four patients continued to have active GvHD and two patients died (one from GvHD and multi-organ failure; the second one from microangiopathy).

DLI was administered in light of high degree of donor chimerism. Median percent of donor cells in whole PB was 98% (range 55–100%) and 99% (range 62–100%) prior to first and last DLI, respectively. The majority (28 out of 35) of patients received their first DLI based on MC in whole PB. Twenty-two patients (22 out of 35) received their last DLI based on MC in whole PB, while 13 patients (13 out of 35) received their last DLI based on MC in subsets despite 100% donor chimerism in whole PB. Of interest, there was no difference in prevalence of GvHD in the patients who received their last DLI for MC in subsets (3 out of 13, 23%), compared with patients who received their last DLI for ≤99% donor chimerism in whole PB (5 out of 22, 23%).

Earlier administration of DLI post transplant was related to an increased risk of GvHD. Median time to first DLI was 100 days (range 86–145) in patients with GvHD vs 123 days (range: 79–351) in patients without GvHD (Mann–Whitney U test P=0.013). Additionally, risk of GvHD appeared lower for DLI given later after transplant. Administration of DLI after 7.5 months post transplant was associated with a 6% (1 out of 17) GvHD risk vs 39% (7 out of 18) in patients who received their last DLI prior to this period (two-tailed Fisher Exact P=0.04).

On examining EFS, 25 (71.4%) of 35 patients were alive and well, 6 (17%) developed relapse, 2 (6%) developed myelodysplastic syndrome (secondary malignancy), 1 (2.8%) died from multi-organ failure exacerbated by GvHD, and 1 (2.8%) died from transplant-related microangiopathy with concurrent GvHD. In patients with GvHD (n=8), incidence of transplant-related mortality (TRM) was 25% (2 of 8) vs 0% (0 of 27) in those without GvHD (two-tailed Fisher Exact P=0.04). Although GvHD appeared protective of relapse and secondary hematologic malignancy since no patients with GvHD (0 of 8) experienced either outcome compared with a 29% (8 of 27) incidence in patients without GvHD, this was not statistically significant (Fisher Exact P=0.15). Figure 1 describes similar EFS in patients with and without GvHD (log-rank P=1); however, the causes of deaths/events were treatment-related mortality in the group with GvHD and relapse/secondary malignancy in the group without GvHD.

Figure 1
figure1

Event-free survival (EFS) in patients who developed GvHD (63%, 95%CI: 42–84) after pre-emptive DLI was no different than in patients who did not develop GvHD (66%, 95%CI: 25–100) (P=1, log-rank test).

Literature on pre-emptive DLI and GvHD outcomes in pediatric patients is limited. We observed a lower incidence of any GvHD (22%) following pre-emptive DLI compared to rates previously described. Bader et al.5 reported that 16 out of 31 (51%) pediatric ALL patients receiving pre-emptive DLI based on increasing MC developed aGvHD. In a similar study, GvHD was reported in 6 of 8 (75%) patients with myeloid malignancies treated with pre-emptive DLI.6 Our results are however comparable to those of Rujkijyanont et al.,7 who described 10 of 38 patients (26%) developing GvHD after escalating doses of pre-emptive (n=31) or therapeutic (n=7) DLI.

We report an equal incidence of GvHD (23%) in patients receiving pre-emptive DLI for MC in PB or BM subsets and in those with MC in whole PB. This implies that our aggressive DLI administration based on subset MC results does not increase GvHD risk above conventional DLI use for MC found in whole PB. However, we recognize the important caveat that our small series may have limited the power of detection.

Our findings demonstrate that the incidence of TRM is higher in GvHD patients, which is offset by protection from relapse and second hematologic malignancy following GvHD, as previously reported.10 We consequently see no adverse effect on cumulative EFS after developing GvHD. However, GvHD remains a determinant of morbidity, and more effective GvHD therapies will be needed to minimize GvHD-related morbidity and mortality. As previously described,1 we observe a low GvHD risk for administering DLI in the late post-transplant period. Our data indicate that after 7.5 months from HSCT, continuing DLIs to achieve 100% donor chimerism is safe with minimal GvHD risk.

In summary, pre-emptive DLI may be safely implemented without increasing GvHD incidence even when whole-blood chimerism is 100% and only minimal residual host cells persist in cellular subsets. We additionally demonstrate that when balancing rates of TRM vs relapse/secondary hematologic malignancy, DLI-induced GvHD does not negatively affect EFS. Furthermore, continuing doses of DLI 7.5 months post transplant is associated with a very low GvHD risk (6%).

The data that support the findings of this study are available on request from the corresponding author (AL). The data are not publically available due to inclusion of information that could compromise patient privacy.

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Correspondence to A Liou.

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Liou, A., Wahlstrom, J., Dvorak, C. et al. Safety of pre-emptive donor lymphocyte infusions (DLI) based on mixed chimerism (MC) in peripheral blood or bone marrow subsets in children undergoing hematopoietic stem cell transplant (HSCT) for hematologic malignancies. Bone Marrow Transplant 52, 1057–1059 (2017) doi:10.1038/bmt.2017.45

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