Tumour infiltrating lymphocyte (TIL) therapy extracts CD8+ and CD4+ T cells from a tumour mass, expands and re-infuses them back into the patient. TIL therapy can lead to substantial complete, durable responses, particularly in refractory melanoma. TIL therapy is more effective if more T cells are infused, if they are less differentiated and if they target tumour antigen. Radiotherapy (RT) prior to TIL extraction may have immunostimulatory effects and so increase T cell infiltration into tumours, alter the T cell phenotype or increase number of tumour specific T cells in the expanded TIL.
Two murine melanoma models (B16 and 4434) were grown in CD57Bl/6 mice. Treated tumours were irradiated with single dose (8 Gray) local radiotherapy, harvested 72 hours later and TIL were enriched. TIL were expanded for 9-10 days ex vivo using the allosensitised allogeneic lymphocyte expansion protocol (AEP), which uses soluble growth factors and allogeneic feeder cells to stimulate T cell growth. Live expanded TIL were counted using a haemocytometer, phenotyped using fluorescence-activated cell sorting and assayed for tumour reactivity by interferon gamma production.
CD8 + (≤ 61 fold) and CD4 + (≤ 16 fold) murine T cells expanded using the AEP in both murine tumour lines. 4434-derived and B16-derived TIL expanded to similar numbers with (n = 4) and without (n = 4) prior RT to tumour mass. When B16-derived TIL were analysed further, there were no changes in differentiation status or in the tumour reactivity (p = 0.48) of TIL from RT treated tumours. However, B16-derived TIL expanded from RT treated tumours had significantly greater expression of PD1 (as measured by percentage positive cells (p = 0.020) and geometric mean fluorescence intensity (p = 0.030)).
This is the first study to expand murine or human TIL treated with prior RT. The AEP expanded tumour reactive murine melanoma TIL to numbers (1-5 x 106 cells) which might effectively treat in vivo murine models. Increased PD1 expression on TIL from RT-treated tumours might predict increased in vivo effectiveness, particularly if combined with PD1 inhibitors. The effect of different RT regimens on TIL expansion and effectiveness could be investigated with this approach.
The University of Manchester.
The University of Manchester.
All authors have declared no conflicts of interest.