Intensified Conditioning for Children Undergoing BMT for First Bone Marrow Relapse of Acute Lymphoblastic Leukaemia.
Authors: Moppett John , Hancock Jerry , Knechtli Christopher J.C. , Oakhill Anthony , Goulden Nicholas J. 
Published: April 2020

BMT remains the treatment of choice for early BM relapse of childhood ALL. We reasoned that further intensification of cytoreductive therapy pre-BMT may further improve survival amongst those with the highest risk of treatment failure, early BM relapse (BFM groups S3/4) and high level MRD pre-BMT. A cohort of 32 patients transplanted at a single institution (1996–1999) provided an historical control. 8 high risk patients transplanted 1999–2000 received additional fludarabine cytoreduction therapy at the time of transplant (FLA group). MRD analysis and time to relapse were used in a subsequent cohort of 22 patients (BMT 2000–2002) to allocate those at highest risk of treatment failure to receive a further cytoreductive block, FLX, pre-BMT.

Method. All patients were conditioned with cyclophosphamide (60mg/m2 x2) and TBI (14.4 Gy). UD and haplo-BMT were T-cell depleted with Campth-1M in vitro and Campath-1G day -9 to -5 (Control and FLA group), and by Miltenyi CD34+ cell depletion (FLX group). GvHD prophylaxis - CSA + MTX for matched related, CSA for Campath treated grafts and none for Miltenyi grafts. The FLA group received fludarabine 25mg/m2 from d −12 to d −10. Patients with on treatment relapse (S4) or high level MRD pre-BMT (MRD++) in the FLX group received DaunoXome 100mg/m2, fludarabine 30mg/m2 x 5d and cytosine 2g/m2 x 5d 3 weeks prior to BMT.

Patients and donors. Control group: 28 precursor-B ALL 4 T-ALL; donors - 7 matched related, 13 matched unrelated (MUD) and 12 mismatched unrelated (MMUD); 14 S2, 18 S3/4. FLA group: 5 presursor-B ALL and 3 T-ALL; donors - 2 SIB, 4 MUD, 1 MMUD and 2 haplo; all S4. FLX group: 21 precursor-B and 1 T-ALL; donors - 6 SIB, 7 MUD, 5 MMUD and 4 haplo;13 S2, 9 S4. 7 patients received FLX intensified conditioning (6 S4, 5 high level MRD ++). 3 high risk patients violated protocol and did not receive FLX (1 age &lt;1yr on treatment relapse, 2 S2 MRD ++).

Results. Considering those in the high-risk S3/4 group, there was no significant difference in OS between the 3 groups.

Survival by study and risk group

Study S2 S3/4 Overall Control 10/14 (71%) 3/18 (17%) 13/32 (41%) FLA 2/8 (25%) 2/8 (25%) FLX 11/13 (85%) 3/9 (33%) 14/22 (64%)

No excess cardiac events were seen. The TRM is higher in the FLX group than in the control.

Outcome data

Study TRM Relapse Alive Total Control 3 16 13 32 S2 2 2 10 14 S3/4 1 14 3 18 FLA 3 3 6 12 S2 - - - - S3/4 3 3 3 9 FLX 6 2 14 22 S2 2 0 11 13 S3/4 4 2 3 9 Total 12 21 33 66

2 of 7 patients treated with FLX are in CCR, 2 relapsed and 3 died of TRM. The 3 high risk patients in the FLX study, but who did not receive FLX, are also in CCR. Survival in those in the S2 group (late BM relapse) has been good throughout the study period.

Conclusion. In this study the addition of intensive pre-BMT conditioning has not improved survival amongst high risk (S3/4 or MRD ++ pre-BMT) relapses. The number of post-BMT relapses has fallen but this is not clearly related to the use of FLX. The use of more haploidentical donors, more immunosupressive BMT regimes and additional cytoreductive chemotherapy may have contributed to the increased TRM seen. Time and site of relapse remain the clearest predictor of outcome. Further novel strategies are required to improve survival for the S4 risk group. The good OS for children receiving BMT in the S2 group should be noted.