Reconstitution rate of absolute CD8+ T lymphocyte counts affects overall survival after pediatric allogeneic hematopoietic stem cell transplantation

Multivariate Analysis of Immune Reconstitution and Relapse Risk Scoring in Children Receiving Allogeneic Stem Cell Transplantation for Acute Leukemias

A timely and effective immune reconstitution after hematopoietic stem cell transplantation (HSCT) is of crucial importance to enhance graft-versus-leukemia reaction in hematological malignancies. Several factors can influence the yield of this process, and new mathematical models are needed to describe this complex phenomenon.

Comparison of reference values for immune recovery between event-free patients receiving haploidentical allografts and those receiving human leukocyte antigen-matched sibling donor allografts

To establish optimal reference values for recovered immune cell subsets, we prospectively investigated post-transplant immune reconstitution (IR) in 144 patients who received allogeneic stem cell transplantation (allo- SCT) and without showing any of the following events: poor graft function, grades II‒IV acute graft-versus-host disease (GVHD), serious chronic GVHD, serious bacterial infection, invasive fungal infection, or relapse or death in the first year after transplantation. IR was rapid in monocytes, intermediate in lymphocytes, CD3⁺ Tcells, CD8⁺ T cells, and CD19⁺ B cells, and very slow in CD4⁺ T cells in the entire patient cohort. Immune recovery was generally faster under HLA-matched sibling donor transplantation than under haploidentical transplantation. Results suggest that patients with an IR comparable to the reference values display superior survival, and the levels of recovery in immune cells need not reach those in healthy donor in the first year after transplantation.We suggest that data from this recipient cohort should be used as reference values for post-transplant immune cell counts in patients receiving HSCT.

Predicting CD4 T-Cell Reconstitution Following Pediatric Hematopoietic Stem Cell Transplantation

Hematopoietic stem cell transplantation (HSCT) is an increasingly common treatment for children with a range of hematological disorders. Conditioning with cytotoxic chemotherapy and total body irradiation leaves patients severely immunocompromised. T-cell reconstitution can take several years due to delayed restoration of thymic output. Understanding T-cell reconstitution in children is complicated by normal immune system maturation, heterogeneous diagnoses, and sparse uneven sampling due to the long time spans involved. We describe here a mechanistic mathematical model for CD4 T-cell immune reconstitution following pediatric transplantation. Including relevant biology and using mixed-effects modeling allowed the factors affecting reconstitution to be identified. Bayesian predictions for the long-term reconstitution trajectories of individual children were then obtained using early post-transplant data. The model was developed using data from 288 children; its predictive ability validated on data from a further 75 children, with long-term reconstitution predicted accurately in 81% of the patients.

Impact of very early CD4(+) /CD8(+) T cell counts on the occurrence of acute graft-versus-host disease and NK cell counts on outcome after pediatric allogeneic hematopoietic stem cell transplantation

BACKGROUND

Increasing evidence suggests that early and rapid lymphocyte recovery following allogeneic hematopoietic stem cell transplantation (HSCT) is associated with better survival.

PROCEDURE

We retrospectively analyzed very early lymphocyte subset counts following transplantation from our 5-year pediatric allogeneic HSCT material to find clinically relevant associations with post transplant outcome, and the major complication of HSCT, acute graft-versus-host disease (aGVHD). We analyzed HSCTs performed due to acute leukemias and lymphomas from matched unrelated donors (MUD, n = 33), unrelated cord blood (UCB, n = 9) and matched sibling donors (MSD, n = 17).

RESULTS

Patients with grafts from MUDs and grade II-IV aGVHD) had higher (median 2.1 compared to 0.3, P<0.0001) and earlier (at day +18 post transplant vs. day +25, P = 0.004) first measurable CD4(+) /CD8(+) T cell ratio, compared to patients with no or grade I aGVHD, respectively. At day +32 after HSCT patients with MUDs and significant aGVHD had higher levels of both CD4(+) and CD8(+) T cell subsets. Low (below median 120/µL) versus high natural killer (NK) cell counts at day +32 were associated with 3-year event-free survival of 27.4 +/- 9.0% versus 82.4 +/- 6.4% (P < 0.0001), cumulative transplant-related mortality of 44.7 +/- 12.2% versus 3.0 +/- 3.0% (P < 0.001) and cumulative relapse incidence of 50.4 +/- 12.2% versus 15.0 +/- 6.2% (P = 0.019), respectively.

CONCLUSIONS

We conclude that early lymphocyte subset counts following allogeneic HSCT have an association with aGVHD and post transplant outcome.

Stem cell transplantation as a dynamical system: are clinical outcomes deterministic?

Outcomes in stem cell transplantation (SCT) are modeled using probability theory. However, the clinical course following SCT appears to demonstrate many characteristics of dynamical systems, especially when outcomes are considered in the context of immune reconstitution. Dynamical systems tend to evolve over time according to mathematically determined rules. Characteristically, the future states of the system are predicated on the states preceding them, and there is sensitivity to initial conditions. In SCT, the interaction between donor T cells and the recipient may be considered as such a system in which, graft source, conditioning, and early immunosuppression profoundly influence immune reconstitution over time. This eventually determines clinical outcomes, either the emergence of tolerance or the development of graft versus host disease. In this paper, parallels between SCT and dynamical systems are explored and a conceptual framework for developing mathematical models to understand disparate transplant outcomes is proposed.

Pharmacokinetic/pharmacodynamic modelling approaches in paediatric infectious diseases and immunology

Pharmacokinetic/pharmacodynamic (PKPD) modelling is used to describe and quantify dose-concentration-effect relationships. Within paediatric studies in infectious diseases and immunology these methods are often applied to developing guidance on appropriate dosing. In this paper, an introduction to the field of PKPD modelling is given, followed by a review of the PKPD studies that have been undertaken in paediatric infectious diseases and immunology. The main focus is on identifying the methodological approaches used to define the PKPD relationship in these studies. The major findings were that most studies of infectious diseases have developed a PK model and then used simulations to define a dose recommendation based on a pre-defined PD target, which may have been defined in adults or in vitro. For immunological studies much of the modelling has focused on either PK or PD, and since multiple drugs are usually used, delineating the relative contributions of each is challenging. The use of dynamical modelling of in vitro antibacterial studies, and paediatric HIV mechanistic PD models linked with the PK of all drugs, are emerging methods that should enhance PKPD-based recommendations in the future.

Lower TGFß serum levels and higher frequency of IFNγ-producing T cells during early immune reconstitution in surviving children after allogeneic stem cell transplantation

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (SCT) is increasingly used as a salvage therapy for patients with high-risk malignancies as well as life-threatening non-malignant diseases. However, only limited data about the association between outcome and functional parameters of recovering lymphocytes are available so far.

PROCEDURES

In this prospective study of 19 pediatric SCT recipients, we serially evaluated immune parameters quantitatively and qualitatively before and throughout allogeneic SCT. These data were analyzed with respect to survival.

RESULTS

Age, gender, GvHD, and type of graft were not different between surviving and non-surviving patients. Notably, in our cohort there was no case of transplant-related or infectious mortality. However, with the exception of two patients with advanced MDS, all patients not in complete remission (CR) relapsed in addition to three patients in higher CR (n = 7). All seven patients relapsing after allogeneic SCT later succumbed to their disease recurrence. Uni- and multivariate analysis showed that relapsing patients had higher TGFß serum levels as well as lower percentages of IFNγ-producing T cells before and early after transplantation. Furthermore, relapsing patients had a further decline in their thymic function between day 60 and 120 whereas non-relapsing patients already showed increasing TREC values during this time interval.

CONCLUSIONS

Collectively, patients who later relapse show a different pattern of immune reconstitution before and at early time points post-transplantation.