(239f) Multiplex, Longitudinal Immune Cellular Functional Proteomic Analyses Correlated with the Clinical Outcome of a Melanoma ACT Immunotherapy Trial

Background: Adoptive cell transfer (ACT) of transgenic T lymphocytes expressing tumor antigen specific T cell receptor (TCR) can mediate objective responses in 30%-50% of metastatic melanoma patients and result in long term tumor regression. However, little is known about the fate of engineered T cells once transferred and the dynamics of host immunity, which is important for understanding the biological mechanism of the therapy and differing long term efficacy between patients.

Methods: Utilizing newly developed, highly multiplexed clinical immune diagnostics methods (Ma, C. et al. Nature Medicine 17, 738-743 (2011)), we designed a comprehensive study that monitored the engineered and acquired immune response in 8 metastatic melanoma patients over 8-10 time points in the context of an ACT therapy with transgenic TCR T cells. (1) By integrating a clinical microchip platform with florescent activated cell sorting, we quantified 19 functional proteins secreted from single cells to evaluate the functional proteomics of 6 phenotypically defined T cell subsets; (2) We enumerated the abundance of 35 melanoma antigen specific T cell subsets using a peptide/MHC tetramer microarray; (3) We measured a panel of 37 blood proteins that incorporates melanoma associated markers, cytokines and chemokines by an ELISA-like assay. These assays yielded millions of high dimensional and highly informative readouts and we developed high dimensional machine learning algorithm to analyze the data.

Results: In all patients, there was an initial clinical antitumor response followed by disease progression. The change of blood marker abundance reflected this general process, starting from lymphodepletion pre-conditioning, immune system recovery, immune response, to tumor regression. This clinical course correlated with changes observed in T cell functional proteomics. The transgenic MART-1 T cells expanded rapidly after infusion, producing multiple cytotoxic and antitumor cytokines. However, their abundance and polyfunctionality diminished within 2-3 weeks. At around 30 days post infusion, a multi-clonal expansion of melanoma specific CTLs emerged in patients with regressing metastatic lesions. This wave of acquired endogenous cellular immunity exhibited antitumor functions initially, but gained inhibitory and non-specific functions and diminished when tumor started to progress. The patient with the most endogenous melanoma specific T cell populations emerged and with the strongest functions in the in vivo acquired immune response showed the most effective long term tumor control; weaker second wave response was associated with weaker therapeutic efficacy.

Conclusions: The melanoma-specific T cells within the ACT went through a process of in vivo functional changes that correlated with clinical antitumor activity. The appearance and the persistence of the in vivo acquired immune response featured by engineered and newly appeared endogenous antitumor cellular immunity provided indications of long term therapeutic efficacy. Therefore, the study points to the need to develop combinatorial therapeutic approaches that could maintain T cell functionality to improve the efficacy of ACT therapy.