High prevalence of CD3, NK, and NKT cells in the graft predicts adverse outcome after matched-related and unrelated transplantations with post transplantation cyclophosphamide

Graft-versus-tumor effect of post-transplant cyclophosphamide-based allogeneic hematopoietic cell transplantation

Post-transplant cyclophosphamide (PTCy) is becoming the standard prophylaxis for graft-versus-host disease (GVHD) in HLA-haploidentical allogeneic hematopoietic cell transplantation (allo-HCT) and in HLA-matched allo-HCT. Immune reconstitution in the post-transplant setting may influence the graft-versus-tumor (GVT) effect because PTCy has a profound effect on T cell and natural killer cell functions and their reconstitution after allo-HCT. However, many recent studies have shown that the incidence of relapse after allo-HCT with PTCy is comparable to that after conventional allo-HCT. To further improve the outcomes, it is critical to establish a strategy to maintain or effectively induce the GVT effect when using PTCy as a platform for GVHD prophylaxis. However, there is a paucity of studies focusing on the GVT effect in allo-HCT with PTCy. Therefore, focusing on this issue may lead to the establishment of more appropriate strategies to improve transplantation outcomes without exacerbating GVHD, including novel therapies involving cell modification.

Outcomes of Human Leukocyte Antigen-Matched Related Donor and Haploidentical Allogeneic Hematopoietic Cell Transplantation Recipients by Immune Profiles of Recipients and Donors

Haploidentical (Haplo) allogeneic HCTs (alloHCT) have been used more frequently over the last decade as survival is similar to HLA-matched related donor (MRD) alloHCTs. We aimed to identify donor and recipient immune signatures before alloHCT that are associated with clinically meaningful outcomes in MRD vs Haplo alloHCT recipients. This retrospective cohort study of 165 MRD (n = 132) and Haplo (n = 33) alloHCT recipients and their related donors between 2007-2019 with paired peripheral blood samples immunophenotyped for T-cell, B-cell, NK cell and dendritic cell (DC) subsets. Immune cells were quantified before alloHCT in donors and recipients; calculations of immune cell ratios were classified as high, intermediate, and low and analyzed with alloHCT outcomes. Haplo donors were younger than MRD donors (median: 35 vs 51 years), whereas Haplo recipients were older than MRD recipients (median: 68 vs 54 years), were more likely to have a Karnofsky Performance Score ≤ 70 (76% vs 57%), 3+ comorbidities (54% vs 47%), and were in complete remission prior to alloHCT (58% vs 42%). In MRD alloHCT, a lower ratio of CD4+ to CD8+ effector memory cells in the donor was associated with lower 4-yr overall survival (OS; 25% vs 61%; P = .009), lower 4-yr progression free survival (PFS; 25% vs 58%; P = .014) and higher incidence of 1-yr transplant-related mortality (TRM; 39% vs 7%; P = .009) in recipients. A higher ratio of CD8+ effector memory to total NK cells measured in MRD recipients was associated with a higher incidence of grade II-IV aGvHD (63% vs 37%; P = .004) but was not statistically significant for III-IV aGvHD (23% vs 12%). In Haplo alloHCT, a lower ratio of total T-regulatory to CD4+ central memory cells in the donor was associated with lower 4-yr PFS (22% vs 60%; P = .0091). A higher ratio of CD4+ effector memory to CD8+ effector memory cells measured in Haplo recipients pre-alloHCT was associated with lower 4-yr OS (25% vs 88%; P = .0039). In both MRD and Haplo recipients, a higher ratio of CD4+ naïve to CD4+ central memory cells was associated with a higher incidence of grade II-IV aGvHD (64% vs 38%; P = .04). Evaluation of pre-alloHCT immune signatures of the donor and recipient may influence clinically meaningful patient outcomes in both MRD and Haplo transplants.

Variable impact of graft CD3+ cell content on graft versus host disease in hematopoietic stem cell transplant recipients: Is the role of donor CD3+ cells overestimated?

Graft cellular composition is considered as a significant determinant of transplant outcome. Donor CD3⁺ cells were shown to have a significant association with the development of graft vs host disease (GvHD). The aim of this study was to investigate the impact of graft CD3⁺ cell content on transplant outcome, particularly in terms of GvHD and relapse. We retrospectively analysed the records of 515 allo-HCT recipients [median age: 37(15-71) years; male/female: 323/192]. The optimal threshold of infused CD3⁺ cell count for acute GvHD development was estimated to be 197.5 × 10⁶/kg (AUC: 0.572; 95 % CI: 0.513-0.631; p = 0.018) and 198.5 × 10⁶/kg (AUC: 0.6; 95 % CI: 0.520-0.679; p = 0.019) for the general population and reduced-intensity conditioning (RIC) subgroup, respectively. Acute GvHD was more frequent in low-CD3⁺ group in the whole study population, particularly in RIC transplants. The incidence of cytomegalovirus reactivation was higher in low-CD3⁺ group and neutrophil engraftment occured earlier in the same group of patients. Overall survival and non-relapse mortality were comparable between high and low-CD3⁺ groups. Age, ECOG performance status, hypogammaglobulinemia, chronic GvHD and post-transplant relapse were found to predict prognosis in multivariate analysis. By focusing mainly on donor T cells, the potential role of host immune cells in the early post-transplant milieu may have been underestimated. Drawing a more detailed profile of graft and host immune cells in the joint microenvironment may elucidate our way to a better understanding of GvHD pathogenesis. By this way a comprehensive pre-transplant risk assessment could be improved to generate more personalized approaches.

Immune reconstitution after T-cell replete HLA haploidentical hematopoietic stem cell transplantation using high-dose post-transplant cyclophosphamide

As HLA haploidentical related donors are quickly available, HLA haploidentical hematopoietic stem cell transplantation (haploHSCT) using high-dose post-transplant cyclophosphamide (PTCy) is now widely used. Recent basic and clinical studies revealed the details of immune reconstitution after T-cell replete haploHSCT using PTCy. T cells and NK cells in the graft proliferate abundantly at day 3 post-haploHSCT, and the PTCy eliminates these proliferating cells. After ablation of proliferating mature cells, donor-derived NK cell reconstitution occurs after the second week; however, recovering NK cells remain functionally impaired for at least several months after haploHSCT. PTCy depletes proliferating cells, resulting in the preferential accumulation of Treg and CD4+ T cells, especially the memory stem T cell (T_^SCM) phenotype. T_^SCM capable of both self-renewal and differentiation into effector T cells may play an important role in the first month of immune reconstitution. Subsequently, de novo T cells progressively recover but their levels remain well below those of donor CD4+ T cells at the first year after haploHSCT. The phenotype of recovering T cells after HSCT is predominantly effector memory, whereas B cells are predominantly phenotypically naive throughout the first year after haploHSCT. B cell recovery depends on de novo generation and they are not detected until week 4 after haploHSCT. At week 5, recovering B cells mostly exhibit an unconventional transitional cell phenotype and the cell subset undergoes maturation. Recent advances in immune reconstitution have improved our understanding of the relationship between haploHSCT with PTCy and the clinical outcome.