Second-Generation Relative Donor for T-Replete Haplo-Identical Allogeneic Stem Cell Transplantation with High-Dose Post-Transplant Cyclophosphamide: Towards Disappearance of the HLA Barrier

Introduction: Allogeneic stem cell transplantations (allo-SCT) using alternative donors are increasingly used in patients lacking suitable matched sibling or unrelated donor. Recently, the use of post-transplant cyclophosphamide (CY) has allowed to re-consider first-generation relatives (brother, sister, father, mother, son or daughter) as haplo-identical donors for allo-SCT. Indeed, the incidence of severe acute GVHD is lowered by post-transplant administration of CY, due to the early destruction of putative alloreactive T cells. Still, some patients may not have a suitable relative donor for various reasons such as older age of the parents, no siblings nor children, no cord blood available, or because use of a graft from a first-generation haplo-identical relatives is contra-indicated. The probability of having a haplo-identical donor among siblings is 50% while it is almost 100% when considering both biological parents and offspring. When considering as a potential donor the child of a matched or haplo-identical sibling, the probabilities for the donor to be haplo-identical with the recipient remain 50% and 25%, respectively. Thus, second-generation relative donor (i.e. nephew or niece) may be finally considered as a source of stem cell graft.

Methods: Here we report the case of a 61-year old man who received a T-replete haplo-identical allo-SCT with high-dose post-transplant CY from his second-generation relative nephew. In 2010, the patient was diagnosed with ALK- CD30+ anaplastic T-cell lymphoma and received 8 cycles of CHOD allowing to obtain morphologic and metabolic partial response. The patient received an allo-SCT from a sibling matched donor (brother) on November 2010 after an FB2A2 reduced-intensity conditioning regimen but secondary graft failure was rapidly documented in spite of donor lymphocyte infusions. Relapse occurred in September 2014 and brentuximab vedotin was administered each 21 days for seven cycles allowing to obtain a complete morphologic and metabolic response. It was decided to perform a second allograft using a different donor. The patient was childless and no unrelated donor or cord blood units were available. It was thus chosen to ask for donor the son of the matched brother, who was haplo-identical and had no antibodies directed against the patient's HLA specificities. This nephew had a O- blood group and negative CMV serology while the recipient was O+ and CMV+.

Results: The second allograft was performed on April 2^nd 2015 using the Baltimore (Luznik, BBMT 2008) conditioning regimen with 2 days of post-transplant CY. A megadose of peripheral blood stem cell was administered (14.16x10⁶ CD34⁺ cells/Kg) at day 0. Neutrophils and platelets recovery (>50 Giga/L) were achieved as early as days +18 and +33, respectively, with full donor whole blood chimerism (99.8%) at day +30, persisting on day +60 and +100 (both whole blood 99.9%, CD3+ T cells: 99.9%).Grade 2 acute cutaneous GVHD occurred at day +21. The evolution was favorable after initiating corticosteroids at 2 mg/kg/day with tapering thereafter. Not surprisingly, CMV reactivation was documented at day+22, controlled by ganciclovir treatment. Immune reconstitution evaluated at days +30, +60 and +100 showed normal monocyte counts while B lymphocytes were undetectable. NK cells increased from 42/mm³ at day+30 to 453/mm³ at day +60 and 665/mm³ at day +100. Interestingly, after profound lymphopenia within the first 100 days post-transplant, CD8+ T large granular lymphocytes expansion was documented at day + 110. At four months post-transplant, the patient is alive in persistent metabolic remission with no active acute or chronic GVHD nor active infection. His outcomes will be updated for the meeting.

Conclusion: T-replete haplo-identical allo-SCT with high-dose post-transplant CY using a second-generation relative donor was feasible allowing for full engraftment and moderate acute GVHD in our patient. This result expands the possibility to find a donor for a selected patient, meanwhile paving the way for using unrelated haplo-identical donor, which could be of interest when considering solid transplantation. Indeed, combining solid organ transplantation and allo-SCT from the same haplo-identical donor may open the door to withdraw immunosuppression in this particular setting, because stable tolerance may be induced, as it has been already reported for kidney transplant (Kawai, NEJM 2013).