Updated Outcomes during the Pandemic: Relationship between CD34and CD3 Cell Doses, One-Year Graft-Versus-Relapse-Free-Survival, Graft-Versus-Host Disease, and Overall Survival in Haploidentical Hematopoietic Stem Cell Transplantation Using Post Transplant Cytoxan: A Single Center Experience
Authors: Martynova Anastasia , Chennapan Krithika , Rodman Jack , Hsiao Mindy , Ladha Abdullah , Tam Eric , Woan Karrune , Chaudhary Preet M. , Yaghmour George 
Published: November 2021

Abstract
Background:
Haploidentical hematopoietic cell transplantation (haplo-HCT) has emerged as a popular alternative to traditional HLA-matched hematopoietic cell transplant. The major advancement of haplo-HCT has increased donor availability to many patients in need, therefore investigating the factors that may affect outcomes is necessary to improve overall survival and reduce transplant-related mortality. Data regarding optimal dose of CD34 cells, CD3 cells and CD34/CD3 ratio used during haplo-HCT to ensure favorable outcomes with post-transplant cyclophosphamide (PTCy) is lacking. Previously we have reported improved outcomes using CD34 cells limited to 7x10^6 cells/kg or less. In this report we are presenting an updated analysis including outcomes related to CD34/CD3 ratio used during haplo-HCT.
Methods:
We retrospectively analyzed adult patients at USC Norris Cancer Hospital who received haplo-HCT from 2014 to 2020. The primary endpoint assessed was 1-year GVHD-free/relapse-free survival (GRFS). Secondary endpoints included overall survival (OS), 1-year transplant related mortality (TRM) and incidence of acute and chronic GVHD. Kaplan Meier survival curves and log-rank tests were used to evaluate 1-year GRFS and OS with CD34 cell dose ≥ 7x10^6 cells/kg and &lt; 7x10^6 cells/kg; CD3 cell dose &lt; 2.5x10^8 cells/kg and ≥ 2.5x10^8 cells/kg; and CD34/CD3 ratio &lt;2, 2-3, &gt;3-5 and &gt;5.
Results:
103 adult haplo-HCT recipients were reviewed with 55.3% male and 44.7% female. The age range was 21-71 years old (median = 51), and a majority of patients were Hispanic (62%). The most common underlying hematologic disorders included AML (40.8%), ALL (34.1%), and MDS/MPN (13.6 %). 41.7% patients with leukemia were in CR1, 55% were CR2/CR3 and 78% were MRD negative by flow cytometry prior to transplant. 73% received myeloablative conditioning and 83.5% received peripheral blood stem cells.
Median CD34 dose, CD3 dose and CD34/CD3 ratio were 6.1 x10^6cells/kg, 2.27 x10^8 cells/kg and 3.2 respectively. Median time to recovery of neutrophil, platelets, and lymphocyte was 17, 24, and 124 days respectively. Incidence of 1-year GRFS was 43.7%. 1-year TRM was 13.6% and rate of aGVHD and cGVHD was 42.7% (n = 44) and 35.9% (n = 37) respectively.
There was no difference in 1-year GRFS and OS when multiple dose levels of CD34 cells and CD3 cells were compared. Although when dichotomized, a CD34 cell dose of ≥ 7x10^6 cells/kg compared to &lt; 7x10^6 cells/kg showed higher dose had significant improvement in 1- year overall survival (p-value=0.01) but no statistical difference in 1 year GRFS (p value=0.24).
CD3 cell dose &lt; 2.5 x 10^8 cells/kg trended towards worse 1-Year GRFS compared to ≥ 2.5 x 10^8 cells/kg (43.9% compared to 58.6%; p-value 0.075), similarly CD3 dose of &lt; 2.5x10^8 cells/kg showed a lower 1-year OS compared to &gt; 2.5x10^8 cells/kg but was not statistically significant (78.7% compared to 89.4%; p-value 0.092). 1-year GRFS and OS did not show statistical difference at CD34:CD3 ratios of &lt; 2, 2-3, 3-5 and &gt; 5, although on cox regression analysis the HR for 1-year GRFS was 2.92 (95% CI 1.21-7.05) in patients with CD34:CD3 &gt; 5 as compared to reference of &lt; 2 (p-value 0.017). Multivariate regression also showed CD3 cell doses of 2-3x10^8 cells/kg and &gt;3 x 10^8 cells/kg were associated with worse 1-year GRFS with HR of 0.43 and 0.40 and p-value of 0.041 and 0.048 respectively when compared to reference of &lt; 1x10^8 CD3 cells/kg.
Discussion:
Our results demonstrate 43.7% survived 1 year compared with reports of 24-35%. The OS was significantly better in the CD34 dose &gt; 7x10^6 cells/kg. CD3 &lt;2.5x10^8 cells/kg showed a trend towards lower 1-year GRFS and OS, which was not statistically significant. On multivariate analysis CD3 dose of &gt; 2x10^8 cells/kg was associated with inferior 1-year GRFS. Conversely, higher CD34/CD3 ratio &gt;5 was associated with increased 1-year GRFS. Thus, our findings indicate that along with improvement in OS by using &gt;7x10^6 CD34 cells/kg, lower CD 3 cell dose &lt;2x10^8 cells/kg and higher CD34/CD3 ratio &gt; 5 can improve 1-year GRFS in patients receiving haplo-HCT.
Figure 1 Figure 1.

Disclosures
Chaudhary: Angeles Therapeutics: Current holder of individual stocks in a privately-held company, Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees, Other: Founder, Patents & Royalties: Cell therapy ; Athelas: Consultancy, Current holder of stock options in a privately-held company; Oncotartis: Consultancy; Pancella: Consultancy; Moderna: Current equity holder in publicly-traded company; Celldex: Current equity holder in publicly-traded company; TCR2: Current equity holder in publicly-traded company; Allogene: Current equity holder in publicly-traded company. Yaghmour: Jazz: Consultancy, Honoraria; Astellas: Consultancy; Takeda: Consultancy; Incyte: Consultancy.