Sustained Donor Chimerism and Rapid Immune Cell Reconstitution Following Familial Haploidentical (FHI) CD34 Enriched Stem Cell Transplantation with Pbmnc Addback in Patients with High Risk Sickle Cell Disease (SCD) (IND 14359)
Authors: Chu Yaya , Talano Julie-An , Baxter-Lowe Lee Ann , Keever-Taylor Carolyn A. , Morris Erin , Mahanti Harshini , Ayello Janet , Weinberg Rona Singer , Shi Qiuhu , Moore Theodore B. , Fabricatore Sandra , Grossman Brenda J. , van de Ven Carmella , Shenoy Shalini , Cairo Mitchell S 
Published: November 2019

Background: Allogeneic stem cell transplantation (AlloSCT) from an HLA-matched sibling donor is the only known curative therapy in patients with high-risk SCD (Talano/Cairo, EJH, 2015). Unfortunately only about 15% of high risk patients with SCD have an HLA-matched unaffected sibling donor. T cell depletion has been employed to reduce AGVHD e.g., CD3/CD19 cell depletion (Barfiled RC, et al, Cytotherapy, 2004), αβ T-cell/CD19 cell depletion (Locatelli F, et al, Blood, 2017), CD34+ positive selection (Aversa F, et al, NEJM, 1998). MUD transplantation in high-risk SCD recipients has shown unexpectedly high rates of CGVHD (Shenoy et al, Blood, 2016). We reported a very low incidence of acute and chronic GVHD in pediatric recipients receiving CD34 enriched HPC products with PB MNC addback with 2 x 105 CD3/kg from MUD donors (Geyer/Cairo et al, BJH, 2012). Furthermore, rapid NK cell reconstitution after AlloSCT is associated with a significant improvement in 1yr OS (Pical-Izard, BBMT, 2015; Dunbar et al, Hematologica, 2008). Recently, we reported promising results for high-risk SCD patients at 1 year follow-up after FHI CD34 enriched/PBMNC with addback AlloSCT with the probability of 1-year overall survival (OS) n=17; 88.2% (CI95: 60.6-96.9) (Talano/Cairo, ASH, 2017), expanding the donor pool and hopefully improving outcomes for high-risk patients with SCD.
Objective: To investigate donor chimerism, immune cell reconstitution and NK cell function in high-risk patients with SCD following AlloSCT using FHI CD34 enrichment/PBMNC (2 x 105 CD3/kg) addback.
Methods: Twenty-one eligible SCD patients (2-<21 yrs) were enrolled. Nineteen patients received hydroxyurea, azathioprine, fludarabine, busulfan, thiotepa, cyclophosphamide, R-ATG, and TLI followed by FHI AlloSCT to date (Talano/Cairo, ASH, 2017). CD34 cells were enriched using the CliniMACS® system, kindly provided by Miltenyi Biotec, with a target dose of 10 x 106 CD34+ cells/kg with a PBMNC addback dose of 2x10*5 CD3/kg in the final product. Whole blood and RBC chimerism (estimated using CD71 to isolate an eythroid lineage-enriched fraction) were determined by STR. Immune cell and subset reconstitution was assessed by flow cytometry as previously described (Geyer/Cairo et al. BJH, 2012). NK function was determined by cytotoxic activity against K562 tumor targets at 10:1 E:T ratio by europium release assay and intracellular LAMP-1 (CD107a) and granzyme B expression by flow cytometry as previously described (Chu/Cairo et al, Can Imm Res, 2015).
Results:
There was 100% engraftment of neutrophils and platelets. The median day post-HISCT to neutrophil and platelet engraftment was +9 and +19, respectively.
Whole blood donor chimerism (mean±SEM) at 1-year, 2-year, and 3-year post-HISCT was 97±1%, 97±1%, 97±1%, respectively (Fig.1). Donor chimerism for CD71+ RBCs (mean±SEM) at 1-year, 2-year, 3-year post-HISCT was 97±2%, 98±1%, 98±1%, respectively (Fig.1).
Immune reconstitution of CD3, CD4, CD8, and CD19 was evaluated. The time to recovery of minimally normal levels post-HISCT of CD3 (800 cells/ul), CD4 (400 cells/ul), CD8 (200 cells/ul), and CD19 (200 cells/ul), was approximately 365, 365, 270, and 60 days post-HISCT (Fig.2), respectively. Probability of Grade II-IV AGVHD, CGVHD and 1 year EFS/OS was 6.2%, 6.7% and 90%, respectively.
NK reconstitution was rapid and peaked at d+30 (36±9%, 2710cells/ml). NK cytotoxicity against K562 at a E:T=10:1 peaked at d+30 (26±3%) and d+180 (28±3%) vs at pre-t (16±2%) (p<0.01) (Fig. 3A). Consistent with increased NK cytotoxicity, CD56dimCD3- subset was increased at d+30 vs pre- HISCT (p<0.05). The NK activation marker, CD107a peaked at d+30 (38±9%) and d+180 (41±6%) (Fig.3B). More over, reconstituted NK cells expressed higher level of activating receptors NKp46 (24±9%), NKG2D (32±9%) and KIR2DS (8±3%) and inhibitory receptors NKG2A (33±9%), CD94 (28±9%) and KIR2DL2/3 (11±2%) at d+30 compared to other time points.
Conclusion:
Despite a 5 log depletion of T cells, the PBMNC addback (fixed at 2 x 105 CD3/kg) facilitated rapid donor chimerism and immune reconstitution with a low probability of Grade II-IV AGVHD. The rapid NK reconstitution may have in part contributed to the excellent 1yr OS in the FHI study. (Supported by FDA R01FD004090 (MSC)).

Disclosures
Cairo: Jazz Pharmaceuticals: Other: Advisory Board, Research Funding, Speakers Bureau; Osuka: Research Funding; Miltenyi: Other: MTA.