Modulating human alloresponses with lenalidomide to improve the outcome of allogeneic haematopoietic stem cell transplantation

Each year thousands of people undergo allogeneic stem cell transplantation (AHSCT) to try to cure them of blood cancers. For many it is the only chance of cure, as treatment with chemotherapy has been ineffective. AHSCT involves transplanting healthy bone marrow-derived stem cells from a donor into a patient. It was initially thought that this approach cured cancer by allowing higher doses of toxic chemotherapy and radiotherapy to be given which killed cancer cells more effectively. However, it is now known that AHSCT cures cancer by a process called alloreactivity. This occurs when donor immune cells present within the stem cell transplant recognise patient cells as foreign and damage or kill them. These donor immune cells are called alloreactive cells. The most important alloreactive immune cells are T cells. When donor alloreactive T cells target cancerous patient tissue this results in the benefical graft-versus-tumour (GvT) effect which prevents the cancer coming back. Unfortunately, as well as killing tumour cells, alloreactive donor T cells can also recognise and damage healthy patient tissues which results in harmful graft-versus-host disease (GvHD). It is unlikely that GvT effects and GvHD can be completely separated as they are closely interelated. However, many doctors are trying to develop ways to strengthen GvT effects without increasing GvHD, to improve the outcome of patients undergoing AHSCT. For this reason it is important to look at ways of enhancing alloreactivity that can selectively promote GvT effects. One way to do this may be to use drugs that promote activation of donor alloreactive immune cells and develop new ways to use such drugs after allogeneic stem cell transplantation.

Lenalidomide is a new drug that has been shown in the laboratory to increase activation of T cells when they are artifically stimulated. In addition, lenalidomide can improve recognition of tumour cells by the patients own immune cells. Thus this drug has great potential for use to increase GvT effects by stimulating alloreactivity after allogeneic stem cell transplantation. However, early clinical experience giving lenalidomide maintenence therapy to patients after AHSCT has resulted in an increase in GvHD which limits the current approach. Very little is known about how lenalidomide affects human immune alloreactivity and a better understanding of this will help us used more safely and effectively to improve GvT effects after AHSCT.

We have already shown for the first time in our laboratory that lenalidomide exposure increases human alloreactivity by selectively increasing growth of a subset of donor T cells called CD8+ cells, and that these cells have a unique pattern of the genes they express. Thus we have already identified the donor alloreactive cell subset potentiated by lenalidomide and several cellular pathways likely to mediate this effect. This project now seeks to build on these important findings with a series of laboratory experiments aimed at identifying the best way to use lenalidomide to maximize beneficial GvT without causing too much harmful GvHD. We will use cells from volunteer donors to further characterize the alloreactive CD8+ cells in both tissue-mismatched and -matched settings. We will use models to represent different ways lenalidomide could be given to pateints (e.g before, during or after the transplant) and use donor immune cells from different sources that are used clinically in AHSCT e.g adult or umbilical cord blood cells. Finally we will measure the effect of lenalidomide on several immune pathways that can selectively potentiate GvT but not GvHD.

These studies will define the optimal way to use lenalidomide to potentiate alloreactive responses to strengthen GvT without excessive GvHD after AHSCT. Once defined, thes strategies could be directly translated to early phase clinical trials to try and improve the outcome of AHSCT for pateints with blood cancers.

A major toxicity after allogeneic haematopoieteic stem cell transplant (AHSCT) is Graft-versus-Host-Disease (GvHD), mediated by alloreactive donor T cells that damage healthy recipient tissues. Donor T cells also kill malignant cells via the Graft-versus-Tumour (GvT) effect. Treatment failure after AHSCT results from either too little alloreactivity (no GvT, disease relapse) or too much (severe GvHD). Lenalidomide is a new drug with immunostimulatory capacity and therefore potential to strengthen GvT effects after AHSCT. However, early clinical experience of lenalidomide maintenence after AHSCT has resulted in increased GvHD limiting this approach. Little is known about how lenalidomide affects human alloreactivity and a better mechanistic understanding is needed for the drug to be used more effectively post-transplant. We have already shown in the laboratory that lenalidomide selectively increases proliferation of alloreactive CD8+ T cells, and that these cells have a unique gene expression pattern. Thus we have already identified the donor alloreactive cell subset potentiated by lenalidomide and several candidate cellular pathways likely to mediate this effect. This project now seeks to build on these important findings with a series of labaratory experiments aimed at identifying the best way to use lenalidomide to maximize GvT without causing excess GvHD. Using T cells from both adult volunteer donors and umbilical cord blood we will phenotypically and functionally characterize the potentiated alloreactive CD8+ cells in HLA-mismatched and -matched settings. We will use models of different ways to give lenalidomide (e.g before, during or after the transplant) Finally we will measure the effect of lenalidomide on several immune parameters that can potentiate GvT but not GvHD (tissue-restricted minor antigen-specific responses, alloreactive NK reposnses). These studies have direct clinical and translational potential to reduce treatment failure after AHSCT

The impact of the research to be performed as part of this project can be divided up into anticipated impact upon different broad non-academic groups.

Firstly, the project may lead to potential clinical impact that may directly benefit patients with haematologic cancers. The project is a pre-clinical and laboratory series of studies but is translational in both design and eventual goal. If successful, the expectation is that further funding will be sought to develop the strategy to a clinical scale and test the strategy in a novel Phase 1 pilot study of adults undergoing allogeneic haematopoietic stem cell transplantation.

Secondly, the research has profound potential public and societal impact. Public impact will be educational, maximized through the plans for dissemination and engagement in science already described. This public impact would be expected to have a knock-on impact on charities central to the field (which include Cancer Research UK, Leukaemia Lymphoma Research and the Kay Kendall Leukaemia Fund) though raising awareness.

Finally,there is also potential long-term positive impact upon public health and economic issues. Allogeneic haematopoietic stem cell transplantation (AHSCT) remains an expensive treatment, and a considerable component of the cost is prevention and treatment of graft-versus-host disease (GvHD) and the resulting immunosuppression and infection that occurs. New technologies and strategies to reduce GvHD but potentiate Graft-versus-Tumour (GvT) effects are currently mainly based around adoptive cellular immunotherapy approaches. These cell engineering strategies are expensive and slow to bring to clinical trials. In contrast more effective use of pharmacological agents such as lenalidomide, or other IMiDs would be a less expesnive way to augment GvT after AHSCT with the resultant potential economic benefits.