No Influence of Peripheral Blood CD34+ and CD3+ Graft Cell Counts on Outcomes after Reduced-Intensity Conditioning Transplantation Using Post-Transplant Cyclophosphamide

Introduction

Although associated with a higher incidence of acute GVHD, peripheral blood stem cells (PBSC) are increasingly used for haploidentical allogeneic transplantation with post-transplant cyclophosphamide (PTCY). Data reporting whether or not the composition of the PBSC graft impacts outcomes of patients receiving PTCY are still scarce.

Materials and Methods

This retrospective study included all adults allografted in our department who received a PBSC allotransplant after reduced-intensity conditioning (RIC) with PTCY. Grafts originated from a matched or haploidentical donor and recipients received a Baltimore-based or a Clo-Baltimore (where fludarabine is replaced by clofarabine)-based RIC regimen. All patients received cyclosporine + mycophenolate mofetyl and PTCY as GVHD prophylaxis. CD34+ and CD3+ graft cell contents were considered to study their potential impact on the following outcomes: OS, DFS, GRFS, acute grade 2-4 and 3-4 GHVD and chronic GVHD, early immune reconstitution (IR, lymphocytes and monocytes counts at days+30 and +100 post-transplant, CD4+, CD8+, NK and B cells at day+100 post-transplant).

Results

Between November 2013 and May 2017, 77 patients met the inclusion criteria. There were 48 males and 29 females with a median age of 58 years (range: 22-71) and a median follow-up for alive patients of 29.2 months (range: 8.4-53.2). Initial diagnoses were mainly acute myeloid (n=21) or lymphoid (n=6) leukemia, lymphoma (n=13), myelodysplastic syndrome (SMD, n=12), myelofibrosis (n=9). Thirty-eight patients were in complete remission at time of transplant (CR1 n=23; CR2 n=12, CR3 n=3) while 22 had active disease and 17 were in partial remission. Donors were sibling in 6 cases, matched unrelated (MUD) in 14, 9/10 mismatched unrelated in 1 and haploidentical in 56. Forty patients received a Baltimore RIC regimen and 37 a Clo-Baltimore RIC regimen. Analyses were performed in July 2018.

Median infused CD34+ and CD3+ graft cell counts, based on recipients' weight, were 7.8 10⁶/Kg (range: 1.45-14.24) and 22.23 10⁷/kg (range: 1.95-66.75), respectively. All patients but three engrafted, the latter being 1 patient transplanted with a haplodonor, 1 with a MUD and 1 who died of infection during induction. Two-year OS, DFS and GRFS were 62.6% (52-74), 51.5% (40-63) and 36.6% (27-49), respectively. The incidences of grade 2-4 and 3-4 acute GVHD were 46.7% and 14.2%, respectively, while the incidence of moderate + severe chronic GVHD was 14%. Relapse occurred in 26 patients and non-relapse mortality (NRM) was 15.5%.

Baltimore vs Clo-Baltimore patients shared similar median infused CD34+ and CD3+ graft cell counts and outcomes. The same was observed for patients allografted with a haplodonor or not, except for the incidence of grade 2-4 acute GVHD which was significantly higher for the haplo group at 57.1% vs 19% (p=0.006). This difference was first attributed to the higher CD3+ cell content infused in this group (median: 24.05 vs 18.85 10⁷/kg, p=0.04). However, using the median of CD3+ cell graft content as threshold, the incidence of acute grade 2-4 GVHD was not different between low vs high groups when considering haplo patients. This suggests that it was rather the type of donor that did influence acute GVHD occurrence and that PTCY is of particular interest for GVHD prophylaxis when using matched donors.

Partitioning the patients according to the median level of CD34+ cells, there was no difference in terms of 2-year OS (57.1% vs 60.7%, p=0.53), DFS (44.5% vs 55.6%, p=0.47) , GRFS (31.7% vs 44.3%, p=0.32), acute grade 2-4 (59% vs 39%, p=0.13) and 3-4 GVHD (17% vs 6.4%, p=0.29), and moderate + severe chronic GVHD (19.5% vs 20%, p=0.57). Similarly, partitioning patients according to median graft CD3+ cell content, outcomes were similar for 2-year OS (64.8% vs 55.8%,p=0.45), DFS (46.3% vs 55.8%, p=0.62), GRFS (36.3% vs 40.4%, p=0.63), acute grade 2-4 (44.7% vs 56.4%, p=0.42) and 3-4 GVHD (10.5% vs 15.3%, p=0.76), and moderate + severe chronic GVHD (14% vs 17.6%, p=0.91). Finally, early IR was not influenced by CD34+ and CD3+ graft cell contents.

Conclusion: PBSC CD34+ and CD3+ graft cell contents have no impact on survivals, GVHD incidence nor early IR after a RIC allotransplant using PTCY as GVHD prophylaxis. As a consequence, there is no need to manipulate the graft nor cap the stem cells dose to be infused. These data have to be confirmed prospectively on a larger cohort of patients.