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Some children with relapsed or high-risk acute leukaemia have an improved outcome if they have an allogeneic stem cell transplant, preferably from a sibling or well-matched unrelated donor. However, some children do not have these options or there is an urgent need to proceed to transplant because of disease status. We have investigated the role of haploidentical family members as donors in 34 patients with acute leukaemia (median age 11 years, range 1–16 years). Patients were conditioned with cyclophosphamide and total body irradiation (14·4 Gy in eight fractions) and received T-cell depleted peripheral blood stem cell grafts with a median CD34 cell dose of 13·8 × 106/kg (range 4·2–35·1) and 0·7 × 104 CD3-positive cells/kg. The actuarial survival at 2 years was 26% (13–41%, 95% CI). Eight patients have survived disease-free with a median follow up of 62 months. They have good performance status and a median lymphocyte count of 1·8 × 109/l. Relapse (14 patients) and adenoviral (six patients) or fungal infections (four patients) were the major causes of death. Haploidentical stem cell transplantation can produce medium term disease-free survival in a proportion of children with high-risk or relapsed acute leukaemia. None of the nine patients with acute myeloid leukaemia not in remission have survived.
Only a quarter to a third of children with acute leukaemia who are candidates for allogeneic stem cell transplantation (SCT) have a human leucocyte antigen (HLA)-identical sibling donor. Of the remaining patients, about 60–85% have a suitable unrelated donor, depending on the degree of mismatch that is accepted and the ethnic and racial background of the child. Search times for unrelated donors vary from 2 to 6 months and, sometimes, alternative stem cell sources are considered because of clinical urgency. Alternative sources of stem cells in this group are from unrelated cord blood donors and haplotype mismatched family members. Moreover, with the promising results obtained by the Perugia group in predominantly adult patients with acute myeloid leukaemia (AML) not in remission (Aversa et al, 1998, 2005), many centres have investigated haploidentical SCT in paediatric practice where there is unstable or refractory disease (Veys et al, 2003).
In Germany, of 63 paediatric patients (the majority of whom had leukaemia) transplanted with one to three antigen-mismatched grafts, sustained engraftment was seen in 98% (15% after ‘boosts’) and acute and chronic graft-versus-host disease (GVHD) occurred in 7% and 13% respectively (Lang et al, 2004). This group used CD34 or CD133 selected peripheral blood stem cells (at a median dose of nearly 20 × 106/kg) but with a similar T-cell dose to our series. The survival in patients with AML and chronic myeloid leukaemia (CML) was 18% and was 48% in patients with acute lymphoblastic leukaemia (ALL) or non-Hodgkin lymphoma (NHL). Overall, 18% experienced lethal viral infections but newer strategies reduced this incidence to 8%. Ortin et al (2002) reported excellent survival in 16 children with malignant conditions who received partially matched related donor allografts. With a follow up of 1·5 years, 13 had survived free of disease and the incidence of grade III–IV GVHD was low. This latter group used conventional full intensity chemoradiotherapy, post-transplant ciclosporin and higher T-cell doses in the graft.
The results of treatment for children with ALL and AML are improving but relapse is still a common event. The majority of these children achieve a second remission and, depending on the duration of the first remission, may be candidates for allogeneic SCT. Some of these second remissions are of short duration or are only obtained with multiple chemotherapy regimens. Other potential candidates for this approach are children who have such high-risk features at diagnosis that they are unlikely to be cured by chemotherapy alone, children whose leukaemia never achieves remission and those with refractory relapsed leukaemia.
We report here the clinical outcome and toxicities of 34 children with acute leukaemia or related diseases treated on Medical Research Council protocols who underwent haploidentical SCT. Our protocol differed from those above, in that Campath 1H was mainly used in pretransplant conditioning and the median dose of T cells was <1 × 104/kg. This study also reports the results in nine children with AML not in remission.
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The place of haploidentical donors for allogeneic SCT in the management of paediatric and adult patients with leukaemia is gaining credence. Following the results published by the Perugia group (Aversa et al, 1998) many units with a track record in alternative donor transplantation began to explore the use of haploidentical SCT in patients with no other allogeneic donor option or where there was a need to proceed to transplant urgently. Results in children from Germany and St Jude's are impressive (Lang et al, 2004). More recently there is renewed interest in single or double cord blood transplants, which offer a very different graft composition and toxicity profile (Laughlin et al, 2004; Barker et al, 2005). Comparisons of umbilical cord blood transplant and haemopoietic SCT are underway but registry-based studies will always have limitations and both types of transplants are constantly evolving.
Of the 34 patients with leukaemia who received conventional full intensity conditioning, megadoses of CD34-selected cells and a median of 0·7 × 104 CD3-positive cells/kg in the graft, about a quarter could become medium term disease-free survivors. The disease state at the time of SCT was the major determinant of outcome. Patients in remission can achieve an outcome similar to that with other donor stem cell sources (Green et al, 1999). Twenty-five of these children had diseases associated with a poor survival after other forms of SCT and only three have survived. Half died of relapse and half of infection. Their diseases included: Philadelphia-positive ALL, ALL in CR2 in BFM S4, AML not in CR after course 2, CR1 < 12 months or not in CR, CML in second chronic phase and AML/ALL in CR3 or greater.
There was no evidence for efficacy in nine patients with refractory AML, but there could be a number of reasons for this observation. The use of pre-transplant Campath antibodies in some of these patients may have reduced the effect of natural killer (NK) cells in the KIR-mismatched group. The ability of KIR-mismatched haploidentical allografts to cure patients with AML not in remission is being tested by a UK national study in adults using the Perugia protocol including ATG.
How might haploidentical transplants cure patients with resistant leukaemia? High-dose chemoradiotherapy and the provision of ‘clean’ marrow play a role but there is a clear evidence that a graft-versus-leukaemia effect is important in both AML and ALL (Passweg et al, 1998). These effects are generally insufficient for DLI to be effective in overt disease but may be extremely important in patients who have achieved a minimal residual disease status. Haploidentical SCT does result in some ‘conventional’ GVHD (both acute and chronic) but there may also be some effect via NK cell alloreactivity in AML. This effect may be sufficient to cure a minority of patients with relapsed refractory leukaemia although the initial results of the Perugia group (Aversa et al, 1998) have not been verified by other groups and are in relatively small numbers of patients.
The way we currently perform these transplants requires refinement. The effective near total elimination of the immune system by a profound T-cell depletion in order to achieve engraftment and prevent severe GVHD seems a high price to pay. It is possible that pretransplant Campath 1H delayed immune reconstitution and may have contributed to the high incidence of viral deaths. Much research is ongoing into engineering grafts so that patients can respond to viruses (Peggs, 2004) and specifically kill tumour cells, but this work is in the early stages.
Infection remains a major stumbling block. In the largest series of paediatric haploidentical transplants reported so far (63 children) 16% of patients succumbed to viral infection within the first 180 d. These deaths were due to disseminated adenoviral infection, CMV disease or herpes simplex virus (Feuchtinger et al, 2005), adenovirus being the most prevalent – a feature common to all series of haploidentical SCT.
Cellular immunotherapy approaches are being developed in an attempt to combat these problems. One approach involves in vitro removal of alloreactive cells that express activation markers, such as CD25, in allogeneic reactions. This allows administration of residual cells capable of responding to many different pathogens, accompanied by a lower risk of GVHD induction than would be expected with unselected DLI. One group have reported death from infection in only one of 15 patients treated and improvement in antiviral immunity from as few as 3 × 105/kg T cells (Amrolia et al, 2005).
An alternative approach is to clone cytotoxic lymphocytes against specific viral and fungal antigens, administering pools of those clones that appear free of alloreactivity in vitro. Such a system has shown promising early results in the haploidentical setting (Perruccio et al, 2005). Unfortunately, this technique requires very large-scale laboratory culture, is prolonged (taking approximately 1 month) and is difficult to perform to modern Good Manufacturing Practice standards.
In summary, the results reported in this series are modest but they are helpful in defining future directions. We found no evidence for these transplants in children with refractory AML or resistant ALL using our protocols but are aware that our conditioning may have reduced the effect of alloreactive NK cells. The results in children in remission do indicate that medium-term disease-free survival can be achieved and careful consideration of a haploidentical SCT in selected patients can be justified.