Harnessing T cells to target brain metastasis.

Brain metastases (BrM) are an unmet clinical need with poor prognosis. Melanoma is the third most common cause of BrM and up to 60% of melanoma patients will develop metastases in the brain during the course of their disease. Until recently, treatment options have been restricted to radiotherapy and surgery, and the median overall survival after combination of these therapies is below 1 year1, 2. Patients with BrM are frequently excluded from clinical trials1. Consequently, BrM are strongly understudied at the clinical and preclinical level, and the treatment options for BrM are commonly lagging behind. PD-1 and CTLA-4 are immune-inhibitory receptors (immune checkpoints) expressed mainly on T cells and their inhibition with function-blocking antibodies has been shown to enhance anti-tumour T cell responses. Antibodies targeting CTLA-4 (Ipilimumab) and PD-1 (Nivolumab, Pembrolizumab) have shown a great promise for the treatment of different cancers, including melanoma. The combination of CTLA-4 and PD-1 blockade in melanoma proved more effective than either treatment alone and has been approved by NICE in June 2016 (http://www.bbc.co.uk/news/health-36549674). Notably, considerable lymphocyte infiltration and expression of markers predictive of sensitivity to PD-1 blockade has been observed in metastatic brain tumours originating from melanoma and there is evidence for the efficacy of both anti-CTLA-4 and anti-PD-1 therapy against melanoma BrM; a handful of retrospective and prospective clinical studies indicated activity of ipilimumab in melanoma BrM with 16-25% intracranial response rate, but also suggested that only a subgroup of patients is likely to benefit. Pembrolizumab and nivolumab also showed efficacy in melanoma BrM with a ~21% response rate in the brain. Two very recent clinical trials in drug-treatment naïve patients with melanoma BrM (ABC trial and CheckMate 204 trial) reported a 50% and 55% intracranial response rate following combined anti-PD-1 plus anti-CTLA-4 therapy, and suggested a superior intracranial activity of combined PD-1/CTLA-4 blockade in melanoma BrM as compared to the respective monotherapies .Notably, therapeutic responses to ICI are variable and sustainable only in a proportion of patients with the combination therapy reaching objective response rates of 57% and a complete response in only 11.5% of the patients. It is currently unknown why the therapy is failing in a high proportion of patients and which approaches could be used to enhance the therapeutic efficacy. Using preclinical models, we have recently identified chemokine receptor (CR)-dependent trafficking of CD8+ T cells to brain metastases (BrM) as one of the key factors required for the intracranial activity of combined anti-PD-1 plus anti-CTLA-4 therapy. We are currently in a process of pinpointing functionally involved CRs expressed on T cells, which forms a part of our MRC-funded work. We hypothesize that stable overexpression of the key CRs in T cells prior to their adoptive transfer can potentiate their homing to BrM, and thereby enhance the intracranial efficacy of PD-1/CTLA-4 blockade.

Objectives:
(1) To determine whether the over-expression of key CR(s) in murine CD8+ T cells enhances T cell migration towards corresponding chemokines in vitro and their trafficking to BrM in vivo;
(2) To determine whether PD-1/CTLA-4 blockade enhances the migration of human blood-derived CD8+ T cells towards chemokines of interest, and whether there is a patient-to-patient variability in CR expression
(3) To test the efficacy of adoptive T cell therapy using CR-overexpressing T cells in combination with PD-1/CTLA-4 blockade;

Experimental approach:
CR(s) of interest will be over-expressed in murine T cells by stable retroviral transduction. The functionality of CRs will be confirmed in vitro, by demonstrating enhanced migration of CR-overexpressing T cells towards cognate chemokines as compared to control-transduced T cells. Hu