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Enhancing adoptive T cell transfer therapies: Novel treatments through IL-12 CD8 T cell priming and adjunctive use of a histone deacetylase inhibitor


Adoptive cell transfer (ACT) immunotherapy is the infusion of a large number of autologous tumor specific immune cells that have the ability to proliferate, traffic and mediate tumor eradication. Tumor specific cells are obtained by expansion of endogenous tumor specific lymphocytes ex vivo, or by the in vitro redirection of lymphocyte specificity through genetic engineering. The addition of a preparative lymphodepletion prior to ACT has dramatically improved the efficacy and responsiveness of adoptively transferred cells through increased access to homeostatic cytokines and elimination of suppressive T regulatory cell populations. Although associated with serious toxicities, administration of high doses of the T cell growth factor, IL-2, has further expanded the ability of adoptively transferred cells to proliferate and persist in vivo. However, despite the initial proliferation and effector function of these tumor specific T cells, a majority of patients fail to achieve complete remission. This can occur as a result of multiple mechanisms including immunoediting of the tumor, the initial differentiation state of transferred cells, or an eventual induction of T cell tolerance.

This thesis describes the utilization of two different strategies in order to prolong the proliferative and functional anti-tumor activity of adoptively transferred tumor specific T cells. The first strategy addresses whether the in vitro expansion and priming of tumor specific T cells with the pro-inflammatory cytokine IL-12 could enhance ACT in an in vivo melanoma model. Previous research in our group indicated that administration of a Toll like receptor (TLR)-7 agonist, imiquimod, enhanced dendritic cell priming of tumor specific T cells. We hypothesized that pro-inflammatory cytokine signals as a result of TLR7 administration, such as IL-12, could have a direct effect on adoptively transferred T cells without the systemic toxicities seen by imiquimod administration. We were able to demonstrate that in vitro IL-12 priming and expansion of tumor specific T cells prior to adoptive transfer dramatically improved polyfunctional cytokine secretion and anti-tumor activity without severe systemic toxicities in comparison to priming with only IL-2. Furthermore, we were able to show that this increased anti-tumor activity relied upon enhanced IL-2 signaling, and abrogated the need for high doses of systemically administered IL-2.

The second strategy we employed utilized the administration of a histone deacetylase (HDAC) inhibitor, LBH589, in combination with ACT. HDAC inhibitors have been shown to increase the expression of TNF superfamily associated death receptors, MHC molecules and costimulatory ligands in multiple cell lines. The ability to pharmacologically immunomodulate a tumor with LBH589 provided a strong rationale for its adjunctive use with adoptively transferred tumor specific T cells. In an in vivo subcutaneous melanoma model, we were able to demonstrate that LBH589 mediated enhanced tumor regression. However, we were surprised to learn that LBH589 was modulating T cell function, even in the absence of tumor. LBH589 treated groups had significantly decreased T regulatory cell populations and significantly increased the proliferation and polyfunctional phenotype of tumor specific T cells over time. Furthermore, the potent effector phenotype of these T cells was characterized by an enhanced expression of the IL-2 receptor, CD25, and the TNF superfamily co-stimulatory ligand, OX-40.

In conclusion, this thesis demonstrates two distinct strategies to enhance adoptive cell transfer in a pre-clinical model. These strategies clearly highlight the necessity of highly functional and proliferative T cells with an ability to continuously traffic and secrete multiple effector cytokines. Our findings also reinforce that responsiveness to the growth factor IL-2 through continued and enhanced expression of the IL-2 receptor, CD25, provides a critical determinant of antitumor activity. Both strategies enhanced ACT by two distinct mechanisms and highlights the need to further investigate the molecular basis of HDAC activity in activated effector T cells during an antitumor response and whether this is compatible with pro-inflammatory signals such as IL-12.

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