Investigating the Relationship between CD34+and CD3+ Cell Doses, One-Year Graft-Versus-Relapse-Free-Survival, Graft-Versus-Host Disease, and Overall Survival in Haploidentical Hematopoietic Stem Cell Transplantation: A Single Center Experience

Abstract

Background: Haploidentical hematopoietic cell transplantation (haplo-HCT) has emerged as a popular alternative to traditional HLA-matched hematopoietic cell transplant. As the number of haplo-HCT's rises, investigating the factors that may affect outcomes is necessary in order to improve overall survival and reduce transplant-related mortality. The optimal dose of CD34+ cells used during haplo-HCT to ensure favorable outcomes using PTCy has not yet been reported though a range of 2 to 5.00x106 cells/kg is commonly used.Furthermore, the optimal dose of CD3+ cells is unknown however recent data has suggested less than 3.00x108 cells/kg may prevent the development of acute GVHD. The importance of studying the impact of CD34+/CD3+ cell dosing may help to improve outcomes in this setting. Methods: We retrospectively analyzed adult patients at USC Norris Cancer Hospital (age ≥ 21) who received haplo-HCT from 2014 to 2019. The primary end-point assessed was 1-year GVHD-free/relapse-free survival (GRFS) defined as grade 3-4 acute GVHD, systemic therapy-requiring chronic GVHD, relapse, or death in the first post-HCT year. Secondary end-points included 1-, 2-, and 3-year relapse-related mortality (RRM) and overall survival (OS) in addition to 1-year transplant related mortality (TRM) and incidence of both acute and chronic GVHD. Results: A total of 67 adult haplo-HCT recipients were reviewed. Of the patients evaluated, approximately 50% (n = 33) were male and 49% (n = 32) were female. The age range was 21-71 years old (median = 44), and the most common underlying hematologic disorders included AML (40%), ALL (38%), aplastic anemia (7.7%), and others (MDS, lymphoma, myelofibrosis, and HLH) (13.8%). 67% of patients received myeloablative conditioning regimens while 33% received reduced intensity regimens. 70% (n = 47) of patients received peripheral blood as a stem cell source with 30% (n = 20) receiving bone marrow. The mean CD34+ dose infused was 6.07x106 cells/kg and the mean CD3+ dose was 2.94x108 cells/kg. The mean time to recovery of platelets, neutrophils, and lymphocytes was 25, 18, and 37 days respectively. CD34+ stem cells ≥5.00x106 cells/kg was significantly associated with shorter time to lymphocyte recovery (p = 0.0265) though recovery less than 30 days was not significantly associated with OS (p = 0.5268). Incidence of 1-year GRFS was 71% (n= 46) and 1-, 2-, and 3-year RRM were 4.6%, 6%, and 7.7% respectively. 1-year TRM was 15.3% with 50% of deaths from acute GVHD. 1-, 2-, and 3-year OS were 80%, 78%, and 77% respectively. Factors significantly associated with increased mortality included use of RIC regimen (p = 0.004) and disease status at time of transplant (p = 0.04). Cumulative incidence of GVHD was 63% (n = 42) with 33% (n = 22) and 30% of patients (n = 20) with acute and chronic GVHD respectively. Lack of mild chronic GVHD was associated with increased mortality (p = 0.0029) and use of a myeloablative regimen (p = 0.0029) was significantly associated with GVHD. Subgroup analysis of those who received CD34+ dose ≥7.00x106 cells/kg (n = 24) and ≥10x106 cells/kg (n = 7) were found to have 1-year OS of 87.5% and 85.7% compared with 77% and 80% in those that received lower doses (p= 0.2229 and p = 1.00) respectively however this was not found to be significantly associated with increased incidence of GVHD, relapse, or mortality. Discussion: Our results demonstrate improved outcomes specifically 71% survived 1 year without experiencing at least 1 GRFS event compared with 24-35% reported by CIBMTR, Holtan et al 2015, and Solh et al 2016 with 3-year OS of 77% when compared with a previously reported 48%. The mean CD34+ cell dose of our population is higher than the standard range which may account for the improved outcomes however the dosing of CD34+/CD3+ cells were not significantly associated with our primary and secondary end-points. It was significantly associated, however, with shorter time to lymphocyte recovery, a factor that has been reported to be associated with decreased RRM and therefore improved OS. Furthermore, subgroup analysis of higher CD34+ dose did show a better 1-year OS though this was not statistically significant. Limitations of this study include small sample size and short follow-up period. Further research with a prospective study identifying the optimal CD34+/CD3+ cell dose in addition to comprehensive evaluation of immune recovery is warranted in order to improve haplo-HCT outcomes. Figure Disclosures Yaghmour: Jazz Pharmaceutical company: Consultancy, Speakers Bureau; Astella company: Speakers Bureau; Takeda: Speakers Bureau.

Mechanisms of Leukemia Immune Evasion and Their Role in Relapse After Haploidentical Hematopoietic Cell Transplantation

“…In this new scenario, it will be of utmost relevance to also associate to the analysis of clinical endpoints a detailed study on how changing the recipe of allo-HCT influences its immunobiology. For instance, understanding the relative contribution of each immune cell subset transferred as part of the graft in the induction of GvHD and protection against relapse will be fundamental to guide further improvements in "tailoring" graft composition and posttransplantation cell therapies, as convincingly suggested by a number of recent studies (218)(219)(220). It is now evident that the success or failure of transplantation is linked to our ability to take full advantage of the many features endowed in the immune system and to combine them with targeted therapies to hit as many tumor targets as possible, reducing the chances of selection of escape variants.…”