By choosing a long-lived central memory T cell population as the carrier, for example, specific for a DNA virus such as cytomegalovirus (CMV), it may be possible to achieve a sustained T cell control of AML.
An alternative approach in early clinical trials in ALL is the insertion of a chimeric antigen receptor (CAR) into the host T cell [100]. The external portion of the CAR is an antibody site binding to a leukaemia-restricted surface molecule, while the intracellular portion triggers T cell activation pathways leading to a cytotoxic T cell response after the T cell binds to the leukaemia. However, despite the identification of leukaemia-specific T cells in patients with AML [17–19], there are many hurdles to overcome before
Fostamatinib Talazoparib molecular weight adoptive autologous leukaemia-specific T cell transfer becomes a clinical possibility [101]. While current experience with antigen specific and cell-based vaccines supports the potential of such immunotherapy to control AML, response rates rarely surpass 20% and complete responses are uncommon and seldom sustained. To improve upon these results will require a combined approach to enhance all the components of the immune response to the leukaemia. We can now identify points in the pathway to AML cell destruction that could be enhanced to improve the therapeutic effect. It is now clear that lymphodepletion after immunosuppressive chemotherapy produces profound changes in the cytokine milieu favourable to both T cell and NK cell expansion and function, particularly in response to a rise in IL-15 [62,95]. The immune milieu after induction chemotherapy or after conditioning
for SCT may thus be favourable to lymphocyte expansion and enhance the response to vaccination. Clinical trials giving vaccines early after immunodepleting therapy are therefore worth exploring. Alternatively, vaccines or lymphocyte transfer might be enhanced by administrating lymphocyte growth factors such as IL-15, which may soon become available for clinical use. While regulatory T cells (Treg) perform a useful function in curtailing side effects from overaggressive T cell responses to infection, they limit the efficacy of vaccines. Rebamipide Animal studies confirm the improved anti-leukaemic effect of a DC vaccine given after Treg have been depleted [102]. In man Treg depletion can be achieved using Denileukin difitox (Ontacc), an IL-2-like molecule conjugated to diphtheria toxin which binds to the alpha chain of the IL-2 receptor and which is up-regulated on Treg cells, killing the cell when the receptor is internalized. Given just before vaccination or T cell infusion (to avoid killing activated T cells) this agent can increase immune responses to vaccines in an animal model and is currently being explored in clinical vaccine trials [103].