Higher Infused CD34+ Cell Dose Improves Survival In Patients Undergoing In Vivo T-Cell Depleted, but Not T-Cell Replete Peripheral Blood Hematopoietic Cell Transplant

Allogeneic hematopoietic cell transplant (HCT) remains a potentially curative modality for various hematological disorders. The cellular composition of the infused allograft has important ramifications for transplantation outcomes, for example higher infused CD34+ cell doses have previously been shown to be is associated with early engraftment, improved survival and possibly increased acute graft-versus-host disease (GVHD) following HCT. The influence of cellular composition of infused allograft on transplant outcomes has been the subject of many previous studies. There is paucity of data on the impact of cellular composition of allograft on transplant outcomes of patients undergoing HCT with in vivo T-cell depletion (TCD) compared to patients receiving T-cell replete allografts. We report here a comparative analysis of the impact of CD34+, CD3+, CD4+ and CD8+ cell doses and survival outcomes of allogeneic, peripheral blood HCT patients receiving in vivo T-cell depletion with alemtuzumab or anti thymocyte globulin (TCD group) versus patients who underwent T-cell replete HCT (non-TCD group).

The study cohort includes 150 consecutive patients who underwent allogeneic HCT between January 2003 through December 2009. All patients received peripheral blood allografts from matched sibling or unrelated donors (URD). In vivo T-cell depletion consisted of alemtuzumab 40mg in two divided doses on days -4 and -1 (n=39) or Thymoglobulin at a total dose of 6 mg/kg for ablative and reduced intensity conditioning (RIC) transplants and 7.5 mg/kg total dose for non myeloablative allografts (n=51).

4 patients received Atgam at 30mg/kg on days -5, -4 and -3. Impact of CD34+, CD3+, CD4+ and CD8+ cell doses divided into two groups; >/= 50^th and < 50^th percentile on overall survival (OS), progression free survival (PFS) and non relapse mortality (NRM) was initially measured by univariate analysis. Multivariate logistic regression analysis was constructed for variables showing significance on univariate analysis (p<0.1). Cellular components of allografts was done by standard flow cytometric techniques.

Of the 150 patients, 94 (62.7%) were males. Median age was 49 (range 17–69). Baseline diagnosis included acute leukemia and myelodysplastic syndrome (n=88; 58.6%), chronic myeloid leukemia (n=19; 12.7%), non-Hodgkin lymphoma (n=27; 18%) and others (10.7%). There were 95 patients (63.3%) in the TCD group and 55 (36.7%) in the non-TCD group. The baseline characteristics of the TCD group and non-TCD group were well matched except that significantly more patients in the TCD group had high risk disease (86.3% vs. 61.8%, p = 0.0005) and received allografts from unrelated donors (62.1% vs. 29.1%, p < 0.001). Median doses of the infused cellular components in the allograft were; CD 34+ = 5.8 × 10⁶/Kg (range 1.2 – 16), CD3+ = 30.8 × 10⁷ (4.5 – 100.8), CD4+ = 18.6 × 10⁷ (1.9 – 63) and CD8+ = 11.3 × 10⁷ (0.8 – 52.4). Median follow-up time for surviving patients was 3 years.

In the TCD group, multivariate analysis showed that CD34+ cell doses >/= 5.8 × 10⁶ was associated with improved OS (p=0.0085; CI 0.28–0.83), PFS (p=0.03; CI 0.31–0.93) and NRM (p=0.02; CI 0.21–0.89). Multivariate analysis also showed that CD3+ cell dose >/= 30.8×10⁷ improved OS (p=0.03; CI 0.25–0.92), but not PFS (p=0.14; CI 0.16–1.31) and NRM (p=0.15; CI 0.23–1.26). No association was noted between CD4+ and CD8+ cell doses and OS, PFS and NRM (p>0.05), in the TCD group.

In the non-TCD group, univariate analysis of CD34+, CD3+, CD4+ and CD8+ cell doses failed to show any statistical significance for NRM, OS and PFS (p>0.1).

Our limited, retrospective analysis of 150 peripheral blood allogeneic HCT shows improved OS, PFS and NRM in patients receiving CD34+ cell dose >/= 5.8×10⁶/Kg and improved OS with CD3+ dose >/= 30.8×10⁷/Kg, limited only to the TCD group. No such association was seen in the non-TCD group. We hypothesize that higher CD34+ in TCD transplants probably improved survival by rapid engraftment and by robust immune reconstitution thereby reducing infectious complication otherwise associated with TCD.

Abraham:Genentech: Membership on an entity's Board of Directors or advisory committees. Hamadani:Celgene: Honoraria, Speakers Bureau; Otsuka: Research Funding, Speakers Bureau.