Unrelated Single Cord Blood Transplant Supported by Co-Infusion of a Low Number of Mobilized Peripheral Blood Highly Purified CD34+ Cells from a Third Party Donor after Low Toxicity Myeloablative Conditioning. a Strategy That Makes Cord Blood Transplant Feasible for Most Patients. (An “Allostem” Study).

We report results of single unit Cord Blood (CB) transplants and co-infusion of a low number of highly purified mobilized PB CD34+ (MPB) cells from a 3rd party donor in 22 consecutive adults with high risk leukemia, median age 29 (16–63) and weight 66 (53–85) Kg. Basic conditioning regimen was Fludarabine, TBI, CTX and ALG, with modifications in 6 patients because of circumstancial factors. The CB units had 2.3 (1.31–3.7) x10⁷ TNC/Kg and 0.1 (0.049–0.37) x10⁶ CD34+ cells/Kg and were 0–2 HLA mismatches to the recipient. The 3rd party donor was an HLA haploidentical relative for 18 (sibling 10; mother 4; father 2; son 1; nephew 1), a higher HLA mm relative for 3 and a fully HLA mm unrelated donor for 1; infused cells were 2.3 (1.05–2.54) x10⁶ CD34+/Kg and 0.23 (0.05–0.98) x10⁴ CD3+/Kg. Post-transplant all patients received CsA and low dose Prednisone for GVHD prophylaxis. G-CSF was started on day +1 in all but 1 on day +5 and continued as required for ANC>1.5x10⁹/L. For the 18 patients receiving MPB-SC from a non-maternal donor, median time to ANC>0.5x10⁹/L was 10 days (9–12 days for 16; 16 and 17 for the other 2, 1 with G-CSF started on day +5). Analysis of DNA polymorphisms showed initial predominance of the 3d party donor both in granulocytes and mononuclear cells and subsequent progressive replacement by CB cells. Final complete CB chimerism was achieved in 17 patients between days 23 and 96 (median 56); 1, transplanted with residual disease, died on day 56 because of CMV Pn with 95% CB cells. The 4 who received maternal cells had no significant engraftment of these, although 3 had exclusive CB chimerism, 2 of which reached full CB engraftment (days 20 and 36). This different behaviour was not related to the non-inherited maternal antigens. Current clinical data suggest that replacement of the 3rd party graft by the CB engraftment may be due to rejection by the CB derived immune system. Morbidity due to early bacterial or fungal infections was remarkably low. Severe GVHD (grade>II) occurred in 2 patients resulting in death (1 did not receive ALG); another 8 had less severe GVHD that responded to treatment. Third party donor cells were not detected in biopsy material of GVHD skin lesions. Deaths were toxic in 2 (1 had received “full intensity” TBI conditioning) and primarily due to opportunistic infections in 4 (2 CMV and 2 Toxoplasmosis, on days 64, 72, 96 and 241). Regression analyses show number of CB-CD34+ cells/Kg as the main factor influencing time to CB engraftment, with no significant effect of number of 3rd party donor CD34+ infused cells. Five years OS and DFS are 57 % for all patients and 80% for those under 40 receiving non-maternal 3rd party cells. No relapses have been observed.

Our data show that the strategy of single unit CB transplant supported by 3rd party donor highly purified MPB CD34+ cells results in a short period of post-transplant neutropenia (as a consequence of prompt and transient engraftment of the 3rd party donor cells), significant GVL effect and high rates of OS and DFS, which makes CB transplant a favorable option for almost any patient requiring a hematopoietic unrelated stem cell transplant.