Chiara Gentilini

Mesenchymal stem cells remain host-derived independent of the source of the stem-cell graft and conditioning regimen used.

Background. Human bone marrow contains hematopoietic stem cells and stroma cells known as mesenchymal stem cells (MSC). MSC are cells with the morphological features of fibroblasts, which, in addition to their nursing function for hematopoietic stem cells, retain the ability to differentiate into cartilage, bone, fat, muscle, and tendon and have an important immunmodulatory function. To understand in more detail hematopoietic engraftment and immune modulation after hematopoietic cell transplantation, we investigated the ability of donor MSC to engraft after hematopoietic cell transplantation in dependency to the conditioning regimen (myeloablative vs. reduced intensity) and source of the graft (bone marrow vs. peripheral blood). Methods. Bone marrow MSC of 12 patients were analyzed, a median of 23.4 (range 0.9–137.8) months after human leukocyte antigen matched but gender mismatched bone marrow transplantation after myeloablative conditioning (n=4) or peripheral blood cell transplantation after myeloablative (n=4) or reduced intensity conditioning (n=4). MSC were characterized by morphology, positivity for CD 105+, CD73+, CD 44+, and CD 90+, and by their capacity to differentiate into adipocytic and osteogenic cells. Recipient and donor origins were determined by fluorescent in situ hybridization for sex chromosomes. Results. While overall blood and bone marrow chimerism was 100% donor type, MSC remained in all patients of recipient origin (>96%). There was no difference between patients receiving bone marrow and peripheral blood grafts, nor was any difference observed between patients receiving full intensity in comparison with reduced intensity conditioning. Conclusions. We conclude that MSC remain of host type irrespective of the conditioning regimen and graft source.

Allogeneic hematopoietic cell transplantation following conditioning with 90Y-ibritumomab-tiuxetan

Radioimmunotherapy (RIT) of relapsed lymphoma is gaining increasing importance. Especially the commercially available anti-CD20 antibody 90Y-ibritumomab tiuxetan is currently under investigation in various trials including dose escalation and autologous hematopoietic progenitor cell support. It is not clear, however, whether the implementation of this radiolabeled antibody into another treatment option for relapsed or poor risk lymphoma patients—allogeneic hematopoietic cell transplantation—interferes with or delays successful engraftment. This study reports encouraging results with 2 relapsed lymphoma patients (1 transformed marginal zone lymphoma and 1 mantle cell lymphoma) who underwent allogeneic hematopoietic cell transplantation from HLA-matched donors. The conditioning regimen consisted of Rituximab 250 mg m−2 on days −21 and −14, 0.4 mCi kg−1 body weight 90Y-ibritumomab tiuxetan on day −14 and fludarabine (30 mg m−2) plus cyclophosphamide (500 mg m−2) on days −7 to −3. The data demonstrate that engraftment is fast and reliable with leukocytes >1 × 109 L−1 on day 12 and platelets >50 × 109 L−1 on day 10. Thus, the incorporation of radioimmunotherapy into allogeneic transplant protocols combines established modalities with proven anti-lymphoma activity and, hence, offers an attractive new therapeutic option for relapsed lymphoma patients.

Tracking in vivo dynamics of NK cells transferred in patients undergoing stem cell transplantation

Haploidentical stem cell transplantation (haploSCT) offers an alternative treatment option for advanced leukemia patients lacking a HLA‐compatible donor. Transfer of NK cells represents a promising therapeutic option in combination with SCT, as NK cells can promote graft versus leukemia with low risk of GVH disease. In this study, we show results from a phase I/II trial in which 24 acute myeloid leukemia patients underwent haploSCT in combination with early transfer of unmodified NK cells and observed a promising 2‐year overall survival rate of 37%. By performing immunomonitoring and subsequent principal component analysis, we tracked donor NK‐cell dynamics in the patients and distinguished between NK cells reconstituting from CD34+ precursors, giving rise over time to a continuum of multiple differentiation stages, and adoptively transferred NK cells. Transferred NK cells displayed a mature phenotype and proliferated in vivo during the early days after haploSCT even in the absence of exogenous IL‐2 administration. Moreover, we identified the NK‐cell phenotype associated with in vivo expansion. Thus, our study indicates a promising path for adoptive transfer of unmodified NK cells in the treatment of high‐risk acute myeloid leukemia.

A novel method to quantify and characterize leukemia-reactive natural killer cells in patients undergoing allogeneic hematopoietic stem cell transplantation following conventional or reduced-dose conditioning

The antitumor activity of natural killer (NK) cells has recently been shown to be assessable at a single-cell level via flow cytometric detection of CD107a. We used this novel method to prospectively quantify and characterize tumor-reactive NK cells in patients undergoing myeloablative or nonmyeloablative conditioning and allogeneic hematopoietic stem cell transplantation (HSCT). Degranulation of NK cells in the peripheral blood of 34 patients after HSCT (day +30, day +90) was determined by evaluating CD107a expression after coincubation of the cells with tumor targets. The percentage of degranulating NK cells was higher after nonmyeloablative conditioning than after myeloablative conditioning (P < .001), indicating a higher activation state and increased antitumor activity of NK cells after nonmyeloablative conditioning. We were able to analyze NK cell subsets separately and found that CD56bright NK cells following HSCT are functionally different from CD56bright NK cells in healthy donors, as indicated by a high percentage of degranulating NK cells in response to tumor targets in patients after HSCT. The CD107a assay is a new and feasible method to quantify and characterize tumor-reactive NK cells after HSCT. Using this method, we found that NK cells had high antitumor cytotoxic activity after nonmyeloablative conditioning, which may contribute to the effectiveness of nonmyeloablative conditioning.