Early and Favourable Immune Reconstitution After Unmanipulated Haploidentical Stem Cell Transplantation With High Dose Post-Transplant Cyclophosphamide Regardless Intensity Of Conditioning Regimen
Authors: Gonzalez-Gascon y Marin Isabel , Pérez-Corral Ana María , Gayoso Jorge , Anguita Javier , Franco Ana Carolina , Pascual Cristina , Kwon Mi , Serrano David , Balsalobre Pascual , Buno Ismael , Martínez-Laperche Carolina , Sarmiento Elisabeth , Diez-Martin Jose Luis 
Published: October 2019

Introduction
Favourable immune reconstitution (IR) has been reported after reduced intensity conditioning (RIC) Unmanipulated Haploidentical Stem cell transplantation (Haplo SCT) with high dose post-transplant cyclophosphamide, and it has been suggested as a relevant factor for the good clinical outcomes observed. Due to the encouraging results in our centre the intensity of conditioning regimen has been increased in some patients with high risk of relapse. The aim of this study is to analyze whether the increase in intensity of conditioning influences immune reconstitution after Haplo-SCT.

Methods and patients
22 patients (pts) with high risk hematologic malignancies treated in our centre with Haplo-SCT from 2007 to 2013 were included in the analysis. 8 pts received myeloablative(MA) conditioning regimen(fludarabine 30 mg/m2 IV (day -6 to -3) and busulfan 3.2 mg/kg IV (day -6 to -3) or fludarabine 30 mg/m2 IV (day -6 to -2), cyclophosphamide 14.5 mg/kg (day -6 to -5), and busulfan 3.2 mg/kg IV (day -4 to -2)). 14 pts received RIC conditioning regimen (fludarabine 30 mg/m2 (day -6 to -2), cyclophosphamide 14.5 mg/kg (day -6 and -5), and busulfan 3.2mg/kg IV (day -3 or day -4 to -3)). GVHD prophylaxis was high dose cyclophosphamide on days +3 and +4, cyclosporine A and mycophenolate mofetil for all patients. Median age was 43 years (26-65) and underlying diseases included: AML (8); ALL (1); MDS (2); MM (2); Hodgkin´s disease (7); mantle cell lymphoma (1); accelerated myelofibrosis (1). Median follow-up was 16 m (5-53). 13 pts were alive and disease-free at last follow-up and 4 pts died (3 relapse, 1 progressive multifocal leukoencephalopaty). We evaluated lymphocyte subsets (absolute numbers of CD3, CD4, CD8, CD19, NK, NKbright, and CD19) by flow cytometry (FC500 Beckman Coulter® cytometer) at 1, 3, 6, 9 and 12 months (m) post Haplo-SCT in the two groups (MA and RIC conditioning regimen). Immunoglobin serum levels were recorded at the same time points. For comparison Mann–Whitney U-test was used.

Results
In the 22 pts, NK cells were the first lymphocyte subset to recover with a median of 84/μl (5-480) and 145/μl (12-562) by m1 and m3 respectively. A high proportion of NKbright cells was observed at m1 post-transplant. This NKbright population decreased from a median of 83% (15-95) at m1 to 32% (9-95%) at m3, and 30% (9-57%) at m6. CD3+ T-lymphocytes (TL) reached normal levels at m3 after haplo-SCT (median 1109/μl (40-3187), and remained at normal range throughout the study period. CD4+ reached levels > 200/μl at m3 with a median of 247/μl (1-570), and also remained above this threshold during the follow up. Reconstitution of CD19+ B lymphocytes was adequate, with a median of 2/μl (0-76); 91/μl (0-556); 139/μl (3-600); 238 (105-575) and 236/μl (12-1098) on m1, 3, 6, 9 and 12 respectively. No difference was observed between RIC and MA conditioning for NK, NKbright; CD3+, CD4+, CD8+ T-lymphocyte and CD19+ B-lymphocyte count recovery. IgM was the first immunoglobulin to recover, reaching normal levels by m3 (61 mg/dL (10-264)), followed by IgG (normal levels at m12 (692 mg/dL (242-1530)). IgA reconstitution was delayed and did not reach normal levels by m12, as described before. No difference was found between RIC and MA conditioning for immunoglobulin recovery. Table 1 shows IR after haplo-SCT.

Conclusions
Rapid and favourable immunologic recovery was observed after haplo-SCT as reported before. Intensity of conditioning did not have any significant impact on the kinetics of immune recovery.
Acknowledgments
This work has been partially supported by Project “Evaluación de la reconstitución inmune después del trasplante haploidéntico de progenitores hemopoyéticos sin depleción T” from Fundación Mutua Madrileña.

Disclosures:
No relevant conflicts of interest to declare.