T-Cell Depleted Haematopoietic Stem Cells (HSC) Transplantation with Add Back of CD45RA Negative DLI: About 2 Cases
Authors: Dal-Cortivo Liliane Liliane , Creidy Rita , Gabrion Aurélie , Héritier Sébastien , Cros Guilhem , Brignier Anne , Luby Jean-Marc , Picard Capucine , Cambouris Christophe , Hacein-Bey Salima , Fischer Alain , Cavazzana-Calvo Marina 
Published: October 2019

Abstract
Abstract 4350

Introduction:
Transplantation of T cell depleted (TCD) HSC transplantation has been associated with:1) an increased risk of infectious complications due to a very late immune reconstitution, 2) a non negligible risk of Graft Versus Host Disease (GVHD) requiring immunosuppressive therapy, and 3) an increased risk of graft rejection. It has been demonstrated that GVHD in murine models is mostly mediated by naïve T cells. Memory T cells have a reduced capacity to induce GVHD while preserving the anti-infectious capacity (Anderson BE et al., 2003). Removing CD45RA cells from donor lymphocytes could reduce infectious complications without induction of GVHD. This procedure was evaluated in two patients presenting multiple infections and treated with mismatch HSC transplantation.

Methods:
Post transplant immune reconstitution has been compared between two groups. Group 1: 7 patients (1 ostepetrosis, 1 Fanconi anemia and 5 Severe Combined Immuno Deficiency) transplanted with TCD HSC (age: 3 months-11 years, sex ratio F/M: 4/3). Group 2: 2 patients (1 ORAI1 deficiency and 1 MHC class II deficiency) transplanted with TCD HSC and CD45RA depleted cells of the CD34 negative fraction (age: 8 and 23 months, 1 female and 1 male).
All patients had myeloablative conditioning regimen.
CD34+ cell selection and CD45RA cell depletion procedures were performed using the Clini Macs system (Miltenyi Biotec).
Group 1 received a median of 15.3 × 106CD34+ cells/kg with less than 5000 T lymphocytes/kg.
Group 2 received respectively 8.8 and 12.3×106 CD34+ cells/kg with less than 5000 T lymphocytes/kg in HSC transplant and 0.9 and 9.2×106/kg CD45RO+ T cells.
The thresholds of 100 CD4+ T lymphocytes and 50 CD8+ T lymphocytes per microliter at three months post transplantation, shown to allow sufficient protection against infectious complications (Hakki et al. 2003), were used in our analysis.

Results:
No significant difference in GVHD incidence was shown between the two groups since only 2/7 patients presented moderate GVHD in group 1 and no GHVD in group 2. Engrafment for both kind of pathology in group 2 was also remarkable
Immune reconstitution of CD4+ and CD8+ T lymphocytes was earlier in group 2 as at one month we detected CD4+ T lymphocytes (430 and 24/μl) and CD8+ T lymphocytes (520 and 40/μl) respectively for patient 1 and 2. Whereas in group 1 no T lymphocytes were detected before two months post transplant.
The number of CD4+ and CD8+ T lymphocytes at three months post transplantation was considerably increased in group 2 (CD4+: 609 and 190/μl; CD8+: 2088 and 95/μl) versus group 1 (CD4+: 14/μl; CD8+: 0.4/μl).
Patient 1 in group 2 presented CMV reactivation at day 10 post transplant (87650 copies/ml, threshold 500) and was able to clear this infection at day 37 concomitantly to an increased CMV tetramer positive cells percentage (Tetramers at day 37/tetramers at day 10: 433 fold increase).

Conclusion:
The two patients treated with T-cell depleted haematopoietic stem cells (HSC) transplantation and add back of CD45RA negative DLI showed good engraftment, earlier and enhanced immune reconstitution without GVHD. Moreover, one patient developed specific and efficient anti-CMV response probably due to an expansion of the injected CD45RO T cells.
These interesting preliminary results should be confirmed by a clinical trial.

Disclosures:
No relevant conflicts of interest to declare.