In vitro human embryonic stem cell hematopoiesis mimics MYB-independent yolk sac hematopoiesis

Although hematopoietic precursor activity can be generated in vitro from human embryonic stem cells, there is no solid evidence for the appearance of multipotent, self-renewing and transplantable hematopoietic stem cells. This could be due to short half-life of hematopoietic stem cells in culture or, alternatively, human embryonic stem cellinitiated hematopoiesis may be hematopoietic stem cell-independent, similar to yolk sac hematopoiesis, generating multipotent progenitors with limited expansion capacity. Since a MYB was reported to be an excellent marker for hematopoietic stem cell-dependent hematopoiesis, we generated a MYB-eGFP reporter human embryonic stem cell line to study formation of hematopoietic progenitor cells in vitro. We found CD34(+) hemogenic endothelial cells rounding up and developing into CD43(+) hematopoietic cells without expression of MYB-eGFP. MYB-eGFP+ cells appeared relatively late in embryoid body cultures as CD34(+) CD43(+) CD45(-/lo) cells. These MYB-eGFP(+) cells were CD33 positive, proliferated in IL-3 containing media and hematopoietic differentiation was restricted to the granulocytic lineage. In agreement with data obtained on murine Myb(-/-) embryonic stem cells, bright eGFP expression was observed in a subpopulation of cells, during directed myeloid differentiation, which again belonged to the granulocytic lineage. In contrast, CD14(+) macrophage cells were consistently eGFP-and were derived from eGFPprecursors only. In summary, no evidence was obtained for in vitro generation of MYB+ hematopoietic stem cells during embryoid body cultures. The observed MYB expression appeared late in culture and was confined to the granulocytic lineage

RHAMM/HMMR (CD168) is not an ideal target antigen for immunotherapy of acute myeloid leukemia

Background : Criteria for good candidate antigens for immunotherapy of acute myeloid leukemia are high expression on leukemic stem cells in the majority of patients with acute myeloid leukemia and low or no expression in vital tissues. It was shown in vaccination trials that Receptor for Hyaluronic Acid Mediated Motility (RHAMM/HMMR) generates cellular immune responses in patients with acute myeloid leukemia and that these responses correlate with clinical benefit. It is not clear however whether this response actually targets the leukemic stem cell, especially since it was reported that RHAMM is expressed maximally during the G2/M phase of the cell cycle. In addition, tumor specificity of RHAMM expression remains relatively unexplored. Design and Methods : Blood, leukapheresis and bone marrow samples were collected from both acute myeloid leukemia patients and healthy controls. RHAMM expression was assessed at protein and mRNA levels on various sorted populations, either fresh or after manipulation. Results : High levels of RHAMM were expressed by CD34+CD38+ and CD34- acute myeloid leukemia blasts. However, only baseline expression of RHAMM was measured in CD34+CD38- leukemic stem cells, and was not different from that in CD34+CD38- hematopoietic stem cells from healthy controls. RHAMM was significantly up-regulated in CD34+ cells from healthy donors during in vitro expansion and during in vivo engraftment. Finally, we demonstrated an explicit increase in the expression level of RHAMM after in vitro activation of T cells. Conclusions : RHAMM does not fulfill the criteria of an ideal target antigen for immunotherapy of acute myeloid leukemia. RHAMM expression in leukemic stem cells does not differ significantly from the expression in hematopoietic stem cells from healthy controls. RHAMM expression in proliferating CD34+ cells of healthy donors and activated T cells further compromises RHAMM-specific T-cell-mediated immunotherapy

Modelling traffic dependent lock capacity with combinatorial Benders' decomposition

Waterborne multimodal transportation is becoming an increasingly important part of the logistics chain given its comparatively low pollution levels when compared to other transportation methods. Analysis of the increased traffic flows on rivers and canals indicates, however, that locks will soon become a major bottleneck for inland waterway transportation. Inland waterway operators are thus facing the significant challenge of scheduling their waterway's series of locks in such a way that the transit time of ships traversing the waterway is minimized. The serial Lock Scheduling Problem (sLSP) is the combinatorial optimization problem corresponding to this increasingly difficult challenge for inland waterway operators. A combinatorial Benders' decomposition for the single-chamber serial lock scheduling problem is presented. This approach enables a straightforward transition from fixed/infinite capacity models to those with traffic-dependent lock capacity at little to no additional computational cost. The presented decomposition approach considers the original fixed/infinite capacity model as the Master Problem and evaluates the traffic dependent capacity constraints in a sub problem. By adding combinatorial Benders' cuts to the Master Problem before and during the solution process, it quickly converges to a feasible and optimal traffic dependent capacity sLSP solution. The method's performance is evaluated on a large set of small to medium sized instances, analysing the influence of traffic dependent lock capacities on both the ship waiting time and total computation time. The results demonstrate how the total required computation time of both models are within the same interval, thus highlighting the efficiency of the presented decomposition approach. For larger lock capacities, the decomposition approach is consistently faster than its fixed capacity counterpart. Furthermore, the results reveal significant differences in ship waiting times between fixed/infinite and traffic dependent models on the instances with real-life ship sizes. These results indicate that traffic dependent lock capacity is a prerequisite for an accurate prediction of ship waiting times in realistic scenarios where ships of different sizes are handled by the lock.status: publishe

A late acceptance algorithm for the lock scheduling problem

In this paper we present a number of (meta-)heuristics for tackling the lock scheduling problem. The lock scheduling problem is introduced as the problem of minimising both the water usage of the lock and the waiting time of all the ships. The performance of several local search heuristics with the best improving criterion and the late acceptance criterion is examined. First parameter values for the late acceptance list length are determined. With these values all heuristics and criteria are applied to a large test set. From these experiments we conclude that the performance of the heuristics is increased by the late acceptance criterion.edition: 1status: publishe

A Late Acceptance metaheuristic for the Lock Scheduling Problem

status: publishe

Late Acceptance Multiple Neighbourhood Search for Lock Planning

The lock planning problem aims at transferring a number of ships, which arrive within a certain time horizon, in the most efficient way. The problem requires a multi-objective approach: minimize the number of turnings of the lock by arranging different ships into the chambers and minimize the waiting time for each ship. This waiting time is the time between the arrival of a ship and the turning time of the ship. We applied a multiple neighbourhood search approach to the lock planning problem. In this approach the neighbourhoods are explored separately using the same starting solution. The best resulting solution from these searches is selected as the new starting solution for the multiple neighbourhood search. This process is repeated until none of the neighbourhoods generate improvements. When exploring the neighbourhoods, a candidate solution is accepted if it satisfies the Late Acceptance criterion. It depends on one parameter L only, which is the length of the acceptance list. A candidate solution will be compared to the solution that was ‘current’ L steps before. Increasing this parameter will allow more worsening moves, and thus help avoiding local optima. When several improving moves exist, the best of them will be selected to update the acceptance list. To validate this new approach, we generated several test instances for the lock planning problem. We carried out experiments with different heuristic optimisation methods: the multiple neighbourhood search with the late acceptance criterion, the multiple neighbourhood search with the best improving criterion and the late acceptance and the best improving criterion applied to all the neighbourhoods at the same time. The multiple neighbourhood search with the late acceptance criterion performs better than all the other methods, within a comparable amount of calculation time.status: publishe

Simulation and optimization for ship lock scheduling: a case study

This paper introduces a simulation and optimization tool for ship lock scheduling capable of simulating the effects of infrastructural changes upon traffic handling at a ship lock with parallel chambers. Simulation parameters are determined via an analysis of historical data. The tool’s accuracy is ascertained via a simulation of the current operations at the lock. The effect of infrastructural changes upon traffic handling may then be accurately assessed via new simulations. The downtimes of lock chambers due to canal drainage requirements, for example, represent a particularly interesting element of the simulation’s input. Optimization of traffic handling in the new infrastructural environment is consequently performed to increase the ship lock’s throughput and decrease passage times for ships. Results demonstrate the huge influence drainage policy has upon passage times, how optimizing the process results in greatly improved lock traffic handling and finally how it is in lock proprietors’ best interest to seriously consider alternatives for chamber drainage downtimes.status: publishe

Scheduling serial locks: a combinatorial Benders’ based approach

With the increasing share of waterbound multimodal transportation in the logistics chain, inland locks are becoming a major bottleneck whose unpredictable service times may limit the long term viability of inland waterway transport. The presentation focusses on scheduling locks in a serial configuration. We introduce a mathematical model for the single-chamber serial lock scheduling problem with traffic-dependent capacity constraints and apply a combinatorial Benders' decomposition approach. The results show promising performance on small to medium sized instances, while leaving an improvement gap for large and real-size instances.status: publishe

Scheduling Serial Locks: A Green Wave for Waterbound Logistics

The present chapter focuses on locks and their impact on (inland) waterbound logistics. Examples of lock systems are given, and the main characteristics of the serial lock scheduling problem discussed. Locks are often scheduled manually and, despite constituting a complex combinatorial problem, academia has given little attention to optimizing lock operations. Two measures can be suggested to considerably improve the competitiveness of inland waterway transportation within the supply chain: increasing the scheduling horizon of locks and treating series of locks as a single system, instead of operating them individually. A decision support system for the ship placement problem is introduced. The system is analysed both from the algorithmic and operational side, and some implementation difficulties are highlighted. Transferring ships through a series of locks based on their requested time of arrival at a destination, has potential to generate a green wave for waterbound logistics.status: publishe