Use of Third Party Ancillary Cells for Enhancement of Full Donor Chimerism and Immunomodulation in Cord Blood Transplants.
Authors: Fernandez Manuel N. , Cabrera Jose R. , Regidor Carmen , Bautista Guiomar , Ojeda Emilio , Fores Rafael , Sanjuan Isabel , Ruiz Elena , Gil Santiago , Gonzalo Rosa , Millan Isabel , Krsnik Isabel , Navarro Belen , Garcia-Marco Jose A. 
Published: October 2019

We have pioneered co-infusion of a low number of T-cell highly depleted mobilized hematopoietic stem cells (MHSC) from a third party donor (TPD) as a tool to increase rates of cord blood transplant (CBT) engraftment and full chimerism in adults with high risk hematologic malignancies (“dual transplant”, Haematologica2006; 9:640–8). The conditioning regimes used have been myeloablative although of reduced extra-hematological toxicity. After achieving very favourable results regarding both engraftment and full chimerism, we have started using this approach to evaluate the addition of other TPD cells to the purpose of optimizing CBT immune reconstitution. Results on CBT engraftment, chimerism and survival are available for analysis at this time on 53 patients (M/F 33/20, median age 35 years, range 16–60) who received units with a total cell count (TCC) of 1.1 to 4.3 x 107/Kg (median 2.3) and 0–3/6 HLA disparities, who have received TPD MHSC: 38 from an haploidentical donor, 15 from a related or unrelated donor not sharing an HLA haplotype. Days to ANC>500/uL ranged 9–36 (P50: 11; P90: 20). Initially most of the ANC was predominantly from the TPD with increasing proportions of granulocytes of CB source. Days to full CB chimerisms ranged from 11 to 97 (P50: 37; P90: 93). With a median follow up of 15 months, 3 year OS and DFS of these 53 patients are 60% and 53%. OS for patients older and younger than 40 years are 50% and 64% respectively (p= 0,37). Five patients relapsed, 2 of them achieved new complete remission maintaining full CB chimerism. Acute GVHD occurred in 19 patients, most of them grade I-II with favorable response to treatment. Four cases were grade III-IV, causing death to 3 patients. Other were toxic (VOD 2, MOF 3 and cerebral hemorrhage 1) or infections (all but one CMV). These have been the main cause of morbidity after post-transplant neutropenia and were favoured by a slow recovery of the protective immunity. Reconstitution of lymphocyte subpopulations (detailed data available for 31) is similar to what has been described for single unit CBT: prompt recovery of NK cells (1 month), followed by recovery of B cells (3 months) and slower recovery of T cells subpopulations: T8 in about one year, T4 and T-regs within the second year. No adverse effects due to the co-infusion of the TPD MHSC have been observed. Ex-vivo expanded MSC from the same TPD have been co-infused to 8 patients in addition to the MHSC. The number of co-infused MSC has ranged 1.16–3.24 x 106 cells/kg (median 1.38) without adverse effects observed so far: ANC has occurred as in the other patients and only one had signs of aGVHD, who did nor achieve stable response to antivirals for CMV, achieving continued control of both after the infusion of a new dose of 1.12 x106 cells/kg.

Conclusion: These results consolidate our previous description of the “dual transplant” strategy as an approach that may allow high rates of engraftment, full chimerisms and survival of HLA mismatch CBT of relatively low cell content for adults of a wide age range with haematological malignancies, with the possibility of adding other subpopulations of the same TPD as cell therapy tools.