Rapid Immune Reconstitution Following Unmanipulated Haploidentical BMT with Post-Transplant High Dose Cyclophosphamide
Authors: Dominietto Alida , Raiola Anna Maria , Bruno Barbara , van Lint Maria Teresa , Frassoni Francesco , Grazia Carmen Di , Gualandi Francesca , Bregante Stefania , Varaldo Riccardo , Ghiso Anna , Bacigalupo Andrea 
Published: October 2019

Abstract
Abstract 3050

Background.
Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for the majority of hematological malignancies. Early and successful immunologic reconstitution after HSCT reduces morbidity and mortality due to infection complications and improves survival. Aim of the study. We analyzed immune recovery after HSCT in 444 patients according to donor source. Patients and Methods. From January 2005 to June 2011 176 patients were grafted from HLA identical siblings (MSD), 125 from alternative donors (1 antigen mismatched family or unrelated donors) (ALT), 103 from unrelated cord blood grafted intra bone (CBIB) and 40 from haplo-identical mismatched family donors (HAPLO). All patients received unmanipulated bone marrow: 283 after a myeloablative (MA) conditioning regimen (CY-TBI or BU-CY) and 161 after a fludarabine based reduced intensity regimen (RIC). Graft versus host disease (GvHD) prophylaxis was cyclosporin methotrexate (CyA+MTX) for all patients except for CBIB (CyA and mycophenolate, MMF) and for HAPLO transplants which consisted of CyA+MMF and post-transplant high dose cyclophosphamide (HDCY) according to the Baltimore protocol (Lutznik et al BBMT 2008). Anti-thymocyte globulin (ATG) was used only for ALT transplants. Results. We compared immune reconstitution in MA and RIC transplants according to donor type at different time points post BMT. CD3+ absolute median counts/μl in MA conditioning on day+30, +90, +180 were respectively in MSD 477, 565, 700; in ALT donors were 146, 404, 470; in CBIB were 30, 57, 196; for HAPLO transplants they were 195, 182, 499. CD3+ absolute median counts/μl in RIC conditioning on day+30, +90, +180 were respectively in MSD 301, 660, 700; in ALT donors were 506, 186, 721; in CBIB 234, 399, 522; in HAPLO were 178, 276, 1300. CD4+ absolute median counts/μl in MA conditioning on day+30, +90, +180 were respectively in MSD 166, 170, 198; in ALT donors were 36, 86, 111; in CBIB 7, 36, 106; for HAPLO transplants they were 45, 127, 211. CD4+ absolute median counts/μl in RIC conditioning on day+30, +90, +180 were respectively in MSD 89, 189, 274; in ALT donors were 131, 210, 220; in CBIB 52, 110, 130; for HAPLO transplants they were 41, 205, 385. CD8+ absolute median counts/μl in MA conditioning on day+30, +90, +180 were respectively in MSD 280, 389, 500; in ALT donors were 102, 278, 413; in CBIB 42, 16, 51; in HAPLO transplants were 73, 424, 408. CD8+ absolute median counts/μl in RIC conditioning on day+30, +90, +180 were respectively in MSD 196, 432, 300; in ALT donors were 366, 65, 494; in CBIB 71, 167, 199; for HAPLO transplants they were 137, 129, 900. CD3, CD8, and CD4 counts in HAPLO transplants were not statistically different from MSD with the only exception of day +30, both for MA and RIC conditioning. Platelet median counts/μl on day+30, +90, +180 in MA conditioning were in MSD 142, 129, 180, in ALT 75, 101, 147, in CBIB were 19, 77, 128 and for HAPLO transplants were 67, 126, 128; in RIC conditioning platelets counts were in MSD 137, 156, 168, in ALT 33, 134, 142, in HAPLO were 77, 95, 188. Acute GvHD II-IV developed in 29% (MSD) 38% (ALT) 16% (CBIB) and 12% (HAPLO) (p=0.004) in MA conditioning and 40% (MSD) 18% (ALT) 25% (CBIB) and 10% (HAPLO) (p=0.07). Overall Cumulative Incidence of Non-Relapse Mortality (CI-NRM) was respectively 18% (MSD), 35% (ALT), 34% (CBIB), 22% (HAPLO) (p=0.02) in MA conditioning (p=0.02) and was 30% (MSD), 33% (ALT), 45% (CBIB), 0% (HAPLO) (p=0.02) in RIC conditioning (p=0.02). Day+100 CI-NRM was respectively 10% (MSD), 21% (ALT), 19% (CBIB), 12% (HAPLO) in MA conditioning (p=0.01) and 11% (MSD), 19% (ALT), 26% (CBIB), 0% (HAPLO) in RIC conditioning (p=0.02). Death due to infections were respectively 6% (MSD), 26% (ALT), 30% (IBCB), 17% (HAPLO) in MA conditioning and for RIC were 15 (MSD), 36% (ALT), 32% (IBCB), 0% (HAPLO). Conclusions. HAPLO transplant with HDCY post transplant as proposed by the Baltimore group, is associated with (1) rapid immunologic (CD3, CD4, CD8) recovery (2) low infectious death rate, (3) low overall and Day+100 CI-NRM, (4) rapid hematologic recovery. These results are comparable with those achieved with MSD and warrant further studies with HDCY post transplant as a GvHD prophylaxis. Figure: absolute CD4+ counts/μl on day+30, +90, +180, according to donor type in MA conditioning regimen.

Disclosures:
No relevant conflicts of interest to declare.