Rapid immune reconstitution after a reduced‐intensity conditioning regimen and a CD3‐depleted haploidentical stem cell graft for paediatric refractory haematological malignancies

Abstract

Summary The main obstacles to successful haploidentical haematopoietic stem cell transplantation from a mismatched family member donor are delayed immune reconstitution, vulnerability to infections and severe graft‐versus‐host disease (GvHD). We designed a reduced‐intensity conditioning regimen that excluded total body irradiation and anti‐thymocyte globulin in order to expedite immune reconstitution after a CD3‐depleted haploidentical stem cell transplant. This protocol was used to treat 22 paediatric patients with refractory haematological malignancies. After transplantation, 91% of the patients achieved full donor chimaerism. They also showed rapid recovery of CD3+ T‐cells, T‐cell receptor (TCR) excision circle counts, TCRβ repertoire diversity and natural killer (NK)‐cells during the first 4 months post‐transplantation, compared with those results from a group of patients treated with a myeloablative conditioning regimen. The incidence and extent of viremia were limited and no lethal infection was seen. Only 9% of patients had grade 3 acute GvHD, while 27% patients had grade 1 and another 27% had grade 2 acute GvHD. This well‐tolerated regimen appears to accelerate immune recovery and shorten the duration of early post‐transplant immunodeficiency, thereby reducing susceptibility to viral infections. Rapid T‐cell reconstitution, retention of NK‐cells in the graft and induction of low grade GvHD may also enhance the potential anti‐cancer immune effect.

Haploidentical SCT in children: an update and future perspectives

“…In our experience, primary engraftment was observed in 83% of patients who received CD34 þ selected grafts after BU or TBI-based myeloablative regimens. Preliminary results of ongoing studies with melphalan-based reduced-intensity conditioning regimens and T/B cell-depleted grafts show similar or even better engraftment rates (85-91%), 7,14,15 probably because of graft facilitating effects of co-transfused alloreactive NK cells. Final and sustained engraftment was achieved after reconditioning and second stem cell donation in 98% of our patients.…”

“…The rates ranged between 0-24% (acute GVHDXgrade II) and between 0-19% (chronic) 5,9,11,13,35,40 after CD34 or CD133 positive selection and between 36 and 27% (acute GVHDXgrade II) after CD3 depletion and CD20 or CD19 depletion. 7,14 In contrast to those studies, Chinese and Japanese groups investigated the use of G-CSF primed BM/PBSC without any in vitro T cell depletion on the basis of antithymocyte globulin and post-transplant immunosuppression with 3-4 agents. 41,42 Considering the large number of infused T-cells, a surprisingly low rate of GVHD was observed (cumulative incidences of 57% (acute GVHD II-IV) and 56% (chronic GVHD)).…”

“…5,9,11,13,18 However, new stem cell markers, targeting CD34 negative progenitors, have questioned whether positive selection procedures will be sufficient to identify early and pluripotent progenitor cells. 7 Further, other immune components such as natural killer (NK) cells, DCs and monocytes are lost during the separation procedure and cannot be used to generate antitumor, antiviral or graft-facilitating effects. 19 Nowadays, new methods for direct depletion of T and B cells on the basis of CD3/CD19 coated magnetic microbeads are available, resulting in depletion factors comparable with positive selection 20 and allowing co-transfusion of high numbers of vital NK cells.…”

“…Mean numbers of 4.9 Â 10 4 -7 Â 10 4 /kg residual T cells and 137 Â 10 6 /kg NK cells have been infused in ongoing studies. 7,8,14,15 Accurate enumeration of residual T cells after depletion with CD3 reagent is crucial and requires a special multi-gating strategy because of the high number of nucleated cells and low frequency of T cells for flow-cytometric analysis. 20 Another interesting approach is the use of CD6 þ -depleted PBSC together with unmanipulated BM, which has been already utilized in a limited number of pediatric patients.…”

“…(1) direct depletion of T cells with soybean lectin agglutination in vitro 2 or with MoAb in vitro and in vivo, 3 (2) positive selection of CD34 þ or CD133 þ progenitor cells with immunomagnetic microbeads in vitro, which includes indirect depletion of all other cell types, 4-6 (3) direct depletion of T cells with antiCD3 coated microbeads, 7 in combination with Ab mediated (antiCD20, rituximab) depletion of B cells in vivo or with CD19 coated microbeads 8 ( Table 1).…”